1 /*
2 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.misc.JavaLangAccess;
29 import jdk.internal.misc.SharedSecrets;
30 import jdk.internal.module.IllegalAccessLogger;
31 import jdk.internal.org.objectweb.asm.ClassReader;
32 import jdk.internal.reflect.CallerSensitive;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.vm.annotation.ForceInline;
35 import sun.invoke.util.ValueConversions;
36 import sun.invoke.util.VerifyAccess;
37 import sun.invoke.util.Wrapper;
38 import sun.reflect.misc.ReflectUtil;
39 import sun.security.util.SecurityConstants;
40
41 import java.lang.invoke.LambdaForm.BasicType;
42 import java.lang.reflect.Constructor;
43 import java.lang.reflect.Field;
44 import java.lang.reflect.Member;
45 import java.lang.reflect.Method;
46 import java.lang.reflect.Modifier;
47 import java.lang.reflect.ReflectPermission;
48 import java.nio.ByteOrder;
49 import java.security.ProtectionDomain;
50 import java.util.ArrayList;
51 import java.util.Arrays;
52 import java.util.BitSet;
53 import java.util.Iterator;
54 import java.util.List;
55 import java.util.Objects;
56 import java.util.Set;
57 import java.util.WeakHashMap;
58 import java.util.concurrent.ConcurrentHashMap;
59 import java.util.stream.Collectors;
60 import java.util.stream.Stream;
61
62 import static java.lang.invoke.MethodHandles.Lookup.ClassProperty.*;
63 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
64 import static java.lang.invoke.MethodHandleNatives.Constants.*;
65 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
66 import static java.lang.invoke.MethodType.methodType;
67
68 /**
69 * This class consists exclusively of static methods that operate on or return
70 * method handles. They fall into several categories:
71 * <ul>
72 * <li>Lookup methods which help create method handles for methods and fields.
73 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
74 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
75 * </ul>
76 * A lookup, combinator, or factory method will fail and throw an
77 * {@code IllegalArgumentException} if the created method handle's type
78 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
79 *
80 * @author John Rose, JSR 292 EG
81 * @since 1.7
82 */
83 public class MethodHandles {
84
85 private MethodHandles() { } // do not instantiate
86
87 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
88
89 // See IMPL_LOOKUP below.
90
91 //// Method handle creation from ordinary methods.
92
93 /**
94 * Returns a {@link Lookup lookup object} with
95 * full capabilities to emulate all supported bytecode behaviors of the caller.
96 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
97 * Factory methods on the lookup object can create
98 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
99 * for any member that the caller has access to via bytecodes,
100 * including protected and private fields and methods.
101 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
102 * Do not store it in place where untrusted code can access it.
103 * <p>
104 * This method is caller sensitive, which means that it may return different
105 * values to different callers.
106 * @return a lookup object for the caller of this method, with private access
107 */
108 @CallerSensitive
109 @ForceInline // to ensure Reflection.getCallerClass optimization
110 public static Lookup lookup() {
111 return new Lookup(Reflection.getCallerClass());
112 }
113
114 /**
115 * This reflected$lookup method is the alternate implementation of
116 * the lookup method when being invoked by reflection.
117 */
118 @CallerSensitive
119 private static Lookup reflected$lookup() {
120 Class<?> caller = Reflection.getCallerClass();
121 if (caller.getClassLoader() == null) {
122 throw newIllegalArgumentException("illegal lookupClass: "+caller);
123 }
124 return new Lookup(caller);
125 }
126
127 /**
128 * Returns a {@link Lookup lookup object} which is trusted minimally.
129 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
130 * It can only be used to create method handles to public members of
131 * public classes in packages that are exported unconditionally.
132 * <p>
133 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
134 * of this lookup object will be {@link java.lang.Object}.
135 *
136 * @apiNote The use of Object is conventional, and because the lookup modes are
137 * limited, there is no special access provided to the internals of Object, its package
138 * or its module. Consequently, the lookup context of this lookup object will be the
139 * bootstrap class loader, which means it cannot find user classes.
140 *
141 * <p style="font-size:smaller;">
142 * <em>Discussion:</em>
143 * The lookup class can be changed to any other class {@code C} using an expression of the form
144 * {@link Lookup#in publicLookup().in(C.class)}.
145 * but may change the lookup context by virtue of changing the class loader.
146 * A public lookup object is always subject to
147 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
148 * Also, it cannot access
149 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
150 * @return a lookup object which is trusted minimally
151 *
152 * @revised 9
153 * @spec JPMS
154 */
155 public static Lookup publicLookup() {
156 return Lookup.PUBLIC_LOOKUP;
157 }
158
159 /**
160 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
161 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
162 * private access</a>, on a target class.
163 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
164 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
165 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
166 * the target class, then this check ensures that
167 * <ul>
168 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
169 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
170 * the target class to at least {@code m1}.</li>
171 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
172 * </ul>
173 * <p>
174 * If there is a security manager, its {@code checkPermission} method is called to
175 * check {@code ReflectPermission("suppressAccessChecks")}.
176 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
177 * was created by code in the caller module (or derived from a lookup object originally
178 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
179 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
180 * access to the caller.
181 * @param targetClass the target class
182 * @param lookup the caller lookup object
183 * @return a lookup object for the target class, with private access
184 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or array class
185 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
186 * @throws IllegalAccessException if the access check specified above fails
187 * @throws SecurityException if denied by the security manager
188 * @since 9
189 * @spec JPMS
190 * @see Lookup#dropLookupMode
191 */
192 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
193 if (lookup.allowedModes == Lookup.TRUSTED) {
194 return new Lookup(targetClass);
195 }
196
197 SecurityManager sm = System.getSecurityManager();
198 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
199 if (targetClass.isPrimitive())
200 throw new IllegalArgumentException(targetClass + " is a primitive class");
201 if (targetClass.isArray())
202 throw new IllegalArgumentException(targetClass + " is an array class");
203 Module targetModule = targetClass.getModule();
204 Module callerModule = lookup.lookupClass().getModule();
205 if (!callerModule.canRead(targetModule))
206 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
207 if (targetModule.isNamed()) {
208 String pn = targetClass.getPackageName();
209 assert pn.length() > 0 : "unnamed package cannot be in named module";
210 if (!targetModule.isOpen(pn, callerModule))
211 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
212 }
213 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
214 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
215 if (!callerModule.isNamed() && targetModule.isNamed()) {
216 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
217 if (logger != null) {
218 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
219 }
220 }
221 return new Lookup(targetClass);
222 }
223
224 /**
225 * Performs an unchecked "crack" of a
226 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
227 * The result is as if the user had obtained a lookup object capable enough
228 * to crack the target method handle, called
229 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
230 * on the target to obtain its symbolic reference, and then called
231 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
232 * to resolve the symbolic reference to a member.
233 * <p>
234 * If there is a security manager, its {@code checkPermission} method
235 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
236 * @param <T> the desired type of the result, either {@link Member} or a subtype
237 * @param target a direct method handle to crack into symbolic reference components
238 * @param expected a class object representing the desired result type {@code T}
239 * @return a reference to the method, constructor, or field object
240 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
241 * @exception NullPointerException if either argument is {@code null}
242 * @exception IllegalArgumentException if the target is not a direct method handle
243 * @exception ClassCastException if the member is not of the expected type
244 * @since 1.8
245 */
246 public static <T extends Member> T
247 reflectAs(Class<T> expected, MethodHandle target) {
248 SecurityManager smgr = System.getSecurityManager();
249 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
250 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
251 return lookup.revealDirect(target).reflectAs(expected, lookup);
252 }
253 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
254 private static final java.security.Permission ACCESS_PERMISSION =
255 new ReflectPermission("suppressAccessChecks");
256
257 /**
258 * A <em>lookup object</em> is a factory for creating method handles,
259 * when the creation requires access checking.
260 * Method handles do not perform
261 * access checks when they are called, but rather when they are created.
262 * Therefore, method handle access
263 * restrictions must be enforced when a method handle is created.
264 * The caller class against which those restrictions are enforced
265 * is known as the {@linkplain #lookupClass() lookup class}.
266 * <p>
267 * A lookup class which needs to create method handles will call
268 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
269 * When the {@code Lookup} factory object is created, the identity of the lookup class is
270 * determined, and securely stored in the {@code Lookup} object.
271 * The lookup class (or its delegates) may then use factory methods
272 * on the {@code Lookup} object to create method handles for access-checked members.
273 * This includes all methods, constructors, and fields which are allowed to the lookup class,
274 * even private ones.
275 *
276 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
277 * The factory methods on a {@code Lookup} object correspond to all major
278 * use cases for methods, constructors, and fields.
279 * Each method handle created by a factory method is the functional
280 * equivalent of a particular <em>bytecode behavior</em>.
281 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
282 * Here is a summary of the correspondence between these factory methods and
283 * the behavior of the resulting method handles:
284 * <table class="striped">
285 * <caption style="display:none">lookup method behaviors</caption>
286 * <thead>
287 * <tr>
288 * <th scope="col"><a id="equiv"></a>lookup expression</th>
289 * <th scope="col">member</th>
290 * <th scope="col">bytecode behavior</th>
291 * </tr>
292 * </thead>
293 * <tbody>
294 * <tr>
295 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
296 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
297 * </tr>
298 * <tr>
299 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
300 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
301 * </tr>
302 * <tr>
303 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
304 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
305 * </tr>
306 * <tr>
307 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
308 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
309 * </tr>
310 * <tr>
311 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
312 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
313 * </tr>
314 * <tr>
315 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
316 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
317 * </tr>
318 * <tr>
319 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
320 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
321 * </tr>
322 * <tr>
323 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
324 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
325 * </tr>
326 * <tr>
327 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
328 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
329 * </tr>
330 * <tr>
331 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
332 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
333 * </tr>
334 * <tr>
335 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
336 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
337 * </tr>
338 * <tr>
339 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
340 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
341 * </tr>
342 * <tr>
343 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
344 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
345 * </tr>
346 * <tr>
347 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
348 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
349 * </tr>
350 * </tbody>
351 * </table>
352 *
353 * Here, the type {@code C} is the class or interface being searched for a member,
354 * documented as a parameter named {@code refc} in the lookup methods.
355 * The method type {@code MT} is composed from the return type {@code T}
356 * and the sequence of argument types {@code A*}.
357 * The constructor also has a sequence of argument types {@code A*} and
358 * is deemed to return the newly-created object of type {@code C}.
359 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
360 * The formal parameter {@code this} stands for the self-reference of type {@code C};
361 * if it is present, it is always the leading argument to the method handle invocation.
362 * (In the case of some {@code protected} members, {@code this} may be
363 * restricted in type to the lookup class; see below.)
364 * The name {@code arg} stands for all the other method handle arguments.
365 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
366 * stands for a null reference if the accessed method or field is static,
367 * and {@code this} otherwise.
368 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
369 * for reflective objects corresponding to the given members.
370 * <p>
371 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
372 * as if by {@code ldc CONSTANT_Class}.
373 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
374 * <p>
375 * In cases where the given member is of variable arity (i.e., a method or constructor)
376 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
377 * In all other cases, the returned method handle will be of fixed arity.
378 * <p style="font-size:smaller;">
379 * <em>Discussion:</em>
380 * The equivalence between looked-up method handles and underlying
381 * class members and bytecode behaviors
382 * can break down in a few ways:
383 * <ul style="font-size:smaller;">
384 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
385 * the lookup can still succeed, even when there is no equivalent
386 * Java expression or bytecoded constant.
387 * <li>Likewise, if {@code T} or {@code MT}
388 * is not symbolically accessible from the lookup class's loader,
389 * the lookup can still succeed.
390 * For example, lookups for {@code MethodHandle.invokeExact} and
391 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
392 * <li>If there is a security manager installed, it can forbid the lookup
393 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
394 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
395 * constant is not subject to security manager checks.
396 * <li>If the looked-up method has a
397 * <a href="MethodHandle.html#maxarity">very large arity</a>,
398 * the method handle creation may fail with an
399 * {@code IllegalArgumentException}, due to the method handle type having
400 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
401 * </ul>
402 *
403 * <h1><a id="access"></a>Access checking</h1>
404 * Access checks are applied in the factory methods of {@code Lookup},
405 * when a method handle is created.
406 * This is a key difference from the Core Reflection API, since
407 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
408 * performs access checking against every caller, on every call.
409 * <p>
410 * All access checks start from a {@code Lookup} object, which
411 * compares its recorded lookup class against all requests to
412 * create method handles.
413 * A single {@code Lookup} object can be used to create any number
414 * of access-checked method handles, all checked against a single
415 * lookup class.
416 * <p>
417 * A {@code Lookup} object can be shared with other trusted code,
418 * such as a metaobject protocol.
419 * A shared {@code Lookup} object delegates the capability
420 * to create method handles on private members of the lookup class.
421 * Even if privileged code uses the {@code Lookup} object,
422 * the access checking is confined to the privileges of the
423 * original lookup class.
424 * <p>
425 * A lookup can fail, because
426 * the containing class is not accessible to the lookup class, or
427 * because the desired class member is missing, or because the
428 * desired class member is not accessible to the lookup class, or
429 * because the lookup object is not trusted enough to access the member.
430 * In any of these cases, a {@code ReflectiveOperationException} will be
431 * thrown from the attempted lookup. The exact class will be one of
432 * the following:
433 * <ul>
434 * <li>NoSuchMethodException — if a method is requested but does not exist
435 * <li>NoSuchFieldException — if a field is requested but does not exist
436 * <li>IllegalAccessException — if the member exists but an access check fails
437 * </ul>
438 * <p>
439 * In general, the conditions under which a method handle may be
440 * looked up for a method {@code M} are no more restrictive than the conditions
441 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
442 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
443 * a method handle lookup will generally raise a corresponding
444 * checked exception, such as {@code NoSuchMethodException}.
445 * And the effect of invoking the method handle resulting from the lookup
446 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
447 * to executing the compiled, verified, and resolved call to {@code M}.
448 * The same point is true of fields and constructors.
449 * <p style="font-size:smaller;">
450 * <em>Discussion:</em>
451 * Access checks only apply to named and reflected methods,
452 * constructors, and fields.
453 * Other method handle creation methods, such as
454 * {@link MethodHandle#asType MethodHandle.asType},
455 * do not require any access checks, and are used
456 * independently of any {@code Lookup} object.
457 * <p>
458 * If the desired member is {@code protected}, the usual JVM rules apply,
459 * including the requirement that the lookup class must either be in the
460 * same package as the desired member, or must inherit that member.
461 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
462 * In addition, if the desired member is a non-static field or method
463 * in a different package, the resulting method handle may only be applied
464 * to objects of the lookup class or one of its subclasses.
465 * This requirement is enforced by narrowing the type of the leading
466 * {@code this} parameter from {@code C}
467 * (which will necessarily be a superclass of the lookup class)
468 * to the lookup class itself.
469 * <p>
470 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
471 * that the receiver argument must match both the resolved method <em>and</em>
472 * the current class. Again, this requirement is enforced by narrowing the
473 * type of the leading parameter to the resulting method handle.
474 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
475 * <p>
476 * The JVM represents constructors and static initializer blocks as internal methods
477 * with special names ({@code "<init>"} and {@code "<clinit>"}).
478 * The internal syntax of invocation instructions allows them to refer to such internal
479 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
480 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
481 * <p>
482 * If the relationship between nested types is expressed directly through the
483 * {@code NestHost} and {@code NestMembers} attributes
484 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
485 * then the associated {@code Lookup} object provides direct access to
486 * the lookup class and all of its nestmates
487 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
488 * Otherwise, access between nested classes is obtained by the Java compiler creating
489 * a wrapper method to access a private method of another class in the same nest.
490 * For example, a nested class {@code C.D}
491 * can access private members within other related classes such as
492 * {@code C}, {@code C.D.E}, or {@code C.B},
493 * but the Java compiler may need to generate wrapper methods in
494 * those related classes. In such cases, a {@code Lookup} object on
495 * {@code C.E} would be unable to access those private members.
496 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
497 * which can transform a lookup on {@code C.E} into one on any of those other
498 * classes, without special elevation of privilege.
499 * <p>
500 * The accesses permitted to a given lookup object may be limited,
501 * according to its set of {@link #lookupModes lookupModes},
502 * to a subset of members normally accessible to the lookup class.
503 * For example, the {@link MethodHandles#publicLookup publicLookup}
504 * method produces a lookup object which is only allowed to access
505 * public members in public classes of exported packages.
506 * The caller sensitive method {@link MethodHandles#lookup lookup}
507 * produces a lookup object with full capabilities relative to
508 * its caller class, to emulate all supported bytecode behaviors.
509 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
510 * with fewer access modes than the original lookup object.
511 *
512 * <p style="font-size:smaller;">
513 * <a id="privacc"></a>
514 * <em>Discussion of private access:</em>
515 * We say that a lookup has <em>private access</em>
516 * if its {@linkplain #lookupModes lookup modes}
517 * include the possibility of accessing {@code private} members
518 * (which includes the private members of nestmates).
519 * As documented in the relevant methods elsewhere,
520 * only lookups with private access possess the following capabilities:
521 * <ul style="font-size:smaller;">
522 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
523 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
524 * such as {@code Class.forName}
525 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
526 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
527 * for classes accessible to the lookup class
528 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
529 * within the same package member
530 * </ul>
531 * <p style="font-size:smaller;">
532 * Each of these permissions is a consequence of the fact that a lookup object
533 * with private access can be securely traced back to an originating class,
534 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
535 * can be reliably determined and emulated by method handles.
536 *
537 * <h1><a id="secmgr"></a>Security manager interactions</h1>
538 * Although bytecode instructions can only refer to classes in
539 * a related class loader, this API can search for methods in any
540 * class, as long as a reference to its {@code Class} object is
541 * available. Such cross-loader references are also possible with the
542 * Core Reflection API, and are impossible to bytecode instructions
543 * such as {@code invokestatic} or {@code getfield}.
544 * There is a {@linkplain java.lang.SecurityManager security manager API}
545 * to allow applications to check such cross-loader references.
546 * These checks apply to both the {@code MethodHandles.Lookup} API
547 * and the Core Reflection API
548 * (as found on {@link java.lang.Class Class}).
549 * <p>
550 * If a security manager is present, member and class lookups are subject to
551 * additional checks.
552 * From one to three calls are made to the security manager.
553 * Any of these calls can refuse access by throwing a
554 * {@link java.lang.SecurityException SecurityException}.
555 * Define {@code smgr} as the security manager,
556 * {@code lookc} as the lookup class of the current lookup object,
557 * {@code refc} as the containing class in which the member
558 * is being sought, and {@code defc} as the class in which the
559 * member is actually defined.
560 * (If a class or other type is being accessed,
561 * the {@code refc} and {@code defc} values are the class itself.)
562 * The value {@code lookc} is defined as <em>not present</em>
563 * if the current lookup object does not have
564 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
565 * The calls are made according to the following rules:
566 * <ul>
567 * <li><b>Step 1:</b>
568 * If {@code lookc} is not present, or if its class loader is not
569 * the same as or an ancestor of the class loader of {@code refc},
570 * then {@link SecurityManager#checkPackageAccess
571 * smgr.checkPackageAccess(refcPkg)} is called,
572 * where {@code refcPkg} is the package of {@code refc}.
573 * <li><b>Step 2a:</b>
574 * If the retrieved member is not public and
575 * {@code lookc} is not present, then
576 * {@link SecurityManager#checkPermission smgr.checkPermission}
577 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
578 * <li><b>Step 2b:</b>
579 * If the retrieved class has a {@code null} class loader,
580 * and {@code lookc} is not present, then
581 * {@link SecurityManager#checkPermission smgr.checkPermission}
582 * with {@code RuntimePermission("getClassLoader")} is called.
583 * <li><b>Step 3:</b>
584 * If the retrieved member is not public,
585 * and if {@code lookc} is not present,
586 * and if {@code defc} and {@code refc} are different,
587 * then {@link SecurityManager#checkPackageAccess
588 * smgr.checkPackageAccess(defcPkg)} is called,
589 * where {@code defcPkg} is the package of {@code defc}.
590 * </ul>
591 * Security checks are performed after other access checks have passed.
592 * Therefore, the above rules presuppose a member or class that is public,
593 * or else that is being accessed from a lookup class that has
594 * rights to access the member or class.
595 *
596 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
597 * A small number of Java methods have a special property called caller sensitivity.
598 * A <em>caller-sensitive</em> method can behave differently depending on the
599 * identity of its immediate caller.
600 * <p>
601 * If a method handle for a caller-sensitive method is requested,
602 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
603 * but they take account of the lookup class in a special way.
604 * The resulting method handle behaves as if it were called
605 * from an instruction contained in the lookup class,
606 * so that the caller-sensitive method detects the lookup class.
607 * (By contrast, the invoker of the method handle is disregarded.)
608 * Thus, in the case of caller-sensitive methods,
609 * different lookup classes may give rise to
610 * differently behaving method handles.
611 * <p>
612 * In cases where the lookup object is
613 * {@link MethodHandles#publicLookup() publicLookup()},
614 * or some other lookup object without
615 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
616 * the lookup class is disregarded.
617 * In such cases, no caller-sensitive method handle can be created,
618 * access is forbidden, and the lookup fails with an
619 * {@code IllegalAccessException}.
620 * <p style="font-size:smaller;">
621 * <em>Discussion:</em>
622 * For example, the caller-sensitive method
623 * {@link java.lang.Class#forName(String) Class.forName(x)}
624 * can return varying classes or throw varying exceptions,
625 * depending on the class loader of the class that calls it.
626 * A public lookup of {@code Class.forName} will fail, because
627 * there is no reasonable way to determine its bytecode behavior.
628 * <p style="font-size:smaller;">
629 * If an application caches method handles for broad sharing,
630 * it should use {@code publicLookup()} to create them.
631 * If there is a lookup of {@code Class.forName}, it will fail,
632 * and the application must take appropriate action in that case.
633 * It may be that a later lookup, perhaps during the invocation of a
634 * bootstrap method, can incorporate the specific identity
635 * of the caller, making the method accessible.
636 * <p style="font-size:smaller;">
637 * The function {@code MethodHandles.lookup} is caller sensitive
638 * so that there can be a secure foundation for lookups.
639 * Nearly all other methods in the JSR 292 API rely on lookup
640 * objects to check access requests.
641 *
642 * @revised 9
643 */
644 public static final
645 class Lookup {
646 /** The class on behalf of whom the lookup is being performed. */
647 private final Class<?> lookupClass;
648
649 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
650 private final int allowedModes;
651
652 static {
653 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
654 }
655
656 /** A single-bit mask representing {@code public} access,
657 * which may contribute to the result of {@link #lookupModes lookupModes}.
658 * The value, {@code 0x01}, happens to be the same as the value of the
659 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
660 */
661 public static final int PUBLIC = Modifier.PUBLIC;
662
663 /** A single-bit mask representing {@code private} access,
664 * which may contribute to the result of {@link #lookupModes lookupModes}.
665 * The value, {@code 0x02}, happens to be the same as the value of the
666 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
667 */
668 public static final int PRIVATE = Modifier.PRIVATE;
669
670 /** A single-bit mask representing {@code protected} access,
671 * which may contribute to the result of {@link #lookupModes lookupModes}.
672 * The value, {@code 0x04}, happens to be the same as the value of the
673 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
674 */
675 public static final int PROTECTED = Modifier.PROTECTED;
676
677 /** A single-bit mask representing {@code package} access (default access),
678 * which may contribute to the result of {@link #lookupModes lookupModes}.
679 * The value is {@code 0x08}, which does not correspond meaningfully to
680 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
681 */
682 public static final int PACKAGE = Modifier.STATIC;
683
684 /** A single-bit mask representing {@code module} access (default access),
685 * which may contribute to the result of {@link #lookupModes lookupModes}.
686 * The value is {@code 0x10}, which does not correspond meaningfully to
687 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
688 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
689 * with this lookup mode can access all public types in the module of the
690 * lookup class and public types in packages exported by other modules
691 * to the module of the lookup class.
692 * @since 9
693 * @spec JPMS
694 */
695 public static final int MODULE = PACKAGE << 1;
696
697 /** A single-bit mask representing {@code unconditional} access
698 * which may contribute to the result of {@link #lookupModes lookupModes}.
699 * The value is {@code 0x20}, which does not correspond meaningfully to
700 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
701 * A {@code Lookup} with this lookup mode assumes {@linkplain
702 * java.lang.Module#canRead(java.lang.Module) readability}.
703 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
704 * with this lookup mode can access all public members of public types
705 * of all modules where the type is in a package that is {@link
706 * java.lang.Module#isExported(String) exported unconditionally}.
707 * @since 9
708 * @spec JPMS
709 * @see #publicLookup()
710 */
711 public static final int UNCONDITIONAL = PACKAGE << 2;
712
713 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
714 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
715 private static final int TRUSTED = -1;
716
717 private static int fixmods(int mods) {
718 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
719 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
720 }
721
722 /** Tells which class is performing the lookup. It is this class against
723 * which checks are performed for visibility and access permissions.
724 * <p>
725 * The class implies a maximum level of access permission,
726 * but the permissions may be additionally limited by the bitmask
727 * {@link #lookupModes lookupModes}, which controls whether non-public members
728 * can be accessed.
729 * @return the lookup class, on behalf of which this lookup object finds members
730 */
731 public Class<?> lookupClass() {
732 return lookupClass;
733 }
734
735 // This is just for calling out to MethodHandleImpl.
736 private Class<?> lookupClassOrNull() {
737 return (allowedModes == TRUSTED) ? null : lookupClass;
738 }
739
740 /** Tells which access-protection classes of members this lookup object can produce.
741 * The result is a bit-mask of the bits
742 * {@linkplain #PUBLIC PUBLIC (0x01)},
743 * {@linkplain #PRIVATE PRIVATE (0x02)},
744 * {@linkplain #PROTECTED PROTECTED (0x04)},
745 * {@linkplain #PACKAGE PACKAGE (0x08)},
746 * {@linkplain #MODULE MODULE (0x10)},
747 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
748 * <p>
749 * A freshly-created lookup object
750 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
751 * all possible bits set, except {@code UNCONDITIONAL}.
752 * A lookup object on a new lookup class
753 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
754 * may have some mode bits set to zero.
755 * Mode bits can also be
756 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
757 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
758 * The purpose of this is to restrict access via the new lookup object,
759 * so that it can access only names which can be reached by the original
760 * lookup object, and also by the new lookup class.
761 * @return the lookup modes, which limit the kinds of access performed by this lookup object
762 * @see #in
763 * @see #dropLookupMode
764 *
765 * @revised 9
766 * @spec JPMS
767 */
768 public int lookupModes() {
769 return allowedModes & ALL_MODES;
770 }
771
772 /** Embody the current class (the lookupClass) as a lookup class
773 * for method handle creation.
774 * Must be called by from a method in this package,
775 * which in turn is called by a method not in this package.
776 */
777 Lookup(Class<?> lookupClass) {
778 this(lookupClass, FULL_POWER_MODES);
779 }
780
781 private Lookup(Class<?> lookupClass, int allowedModes) {
782 this.lookupClass = lookupClass;
783 this.allowedModes = allowedModes;
784 assert !lookupClass.isPrimitive() && !lookupClass.isArray();
785 }
786
787 /**
788 * Creates a lookup on the specified new lookup class.
789 * The resulting object will report the specified
790 * class as its own {@link #lookupClass() lookupClass}.
791 * <p>
792 * However, the resulting {@code Lookup} object is guaranteed
793 * to have no more access capabilities than the original.
794 * In particular, access capabilities can be lost as follows:<ul>
795 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
796 * the new lookup class is in a different module {@code M}, then no members, not
797 * even public members in {@code M}'s exported packages, will be accessible.
798 * The exception to this is when this lookup is {@link #publicLookup()
799 * publicLookup}, in which case {@code PUBLIC} access is not lost.
800 * <li>If the old lookup class is in an unnamed module, and the new lookup class
801 * is a different module then {@link #MODULE MODULE} access is lost.
802 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
803 * <li>If the new lookup class is in a different package
804 * than the old one, protected and default (package) members will not be accessible.
805 * <li>If the new lookup class is not within the same package member
806 * as the old one, private members will not be accessible, and protected members
807 * will not be accessible by virtue of inheritance.
808 * (Protected members may continue to be accessible because of package sharing.)
809 * <li>If the new lookup class is not accessible to the old lookup class,
810 * then no members, not even public members, will be accessible.
811 * (In all other cases, public members will continue to be accessible.)
812 * </ul>
813 * <p>
814 * The resulting lookup's capabilities for loading classes
815 * (used during {@link #findClass} invocations)
816 * are determined by the lookup class' loader,
817 * which may change due to this operation.
818 *
819 * @param requestedLookupClass the desired lookup class for the new lookup object
820 * @return a lookup object which reports the desired lookup class, or the same object
821 * if there is no change
822 * @throws IllegalArgumentException if {@code requestedLookupClass} is
823 * a primitive type or array class
824 * @throws NullPointerException if the argument is null
825 *
826 * @revised 9
827 * @spec JPMS
828 */
829 public Lookup in(Class<?> requestedLookupClass) {
830 Objects.requireNonNull(requestedLookupClass);
831 if (requestedLookupClass.isPrimitive())
832 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
833 if (requestedLookupClass.isArray())
834 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
835
836 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
837 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
838 if (requestedLookupClass == this.lookupClass)
839 return this; // keep same capabilities
840 int newModes = (allowedModes & FULL_POWER_MODES);
841 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
842 // Need to drop all access when teleporting from a named module to another
843 // module. The exception is publicLookup where PUBLIC is not lost.
844 if (this.lookupClass.getModule().isNamed()
845 && (this.allowedModes & UNCONDITIONAL) == 0)
846 newModes = 0;
847 else
848 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
849 }
850 if ((newModes & PACKAGE) != 0
851 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
852 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
853 }
854 // Allow nestmate lookups to be created without special privilege:
855 if ((newModes & PRIVATE) != 0
856 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
857 newModes &= ~(PRIVATE|PROTECTED);
858 }
859 if ((newModes & PUBLIC) != 0
860 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
861 // The requested class it not accessible from the lookup class.
862 // No permissions.
863 newModes = 0;
864 }
865
866 checkUnprivilegedlookupClass(requestedLookupClass);
867 return new Lookup(requestedLookupClass, newModes);
868 }
869
870
871 /**
872 * Creates a lookup on the same lookup class which this lookup object
873 * finds members, but with a lookup mode that has lost the given lookup mode.
874 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
875 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
876 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
877 * dropped and so the resulting lookup mode will never have these access capabilities.
878 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
879 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
880 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
881 * is dropped then the resulting lookup has no access.
882 * @param modeToDrop the lookup mode to drop
883 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
884 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
885 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
886 * @see MethodHandles#privateLookupIn
887 * @since 9
888 */
889 public Lookup dropLookupMode(int modeToDrop) {
890 int oldModes = lookupModes();
891 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
892 switch (modeToDrop) {
893 case PUBLIC: newModes &= ~(ALL_MODES); break;
894 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
895 case PACKAGE: newModes &= ~(PRIVATE); break;
896 case PROTECTED:
897 case PRIVATE:
898 case UNCONDITIONAL: break;
899 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
900 }
901 if (newModes == oldModes) return this; // return self if no change
902 return new Lookup(lookupClass(), newModes);
903 }
904
905 /**
906 * Defines a class to the same class loader and in the same runtime package and
907 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
908 * {@linkplain #lookupClass() lookup class}.
909 *
910 * This method is equivalent to calling
911 * {@link #defineClass(byte[], ClassProperty[])
912 * defineClass(bytes, (ClassProperty[])null)}.
913 *
914 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
915 * {@link #PACKAGE PACKAGE} access as default (package) members will be
916 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
917 * that the lookup object was created by a caller in the runtime package (or derived
918 * from a lookup originally created by suitably privileged code to a target class in
919 * the runtime package). </p>
920 *
921 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
922 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
923 * same package as the lookup class. </p>
924 *
925 * <p> This method does not run the class initializer. The class initializer may
926 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
927 * Specification</em>. </p>
928 *
929 * <p> If there is a security manager, its {@code checkPermission} method is first called
930 * to check {@code RuntimePermission("defineClass")}. </p>
931 *
932 * @param bytes the class bytes
933 * @return the {@code Class} object for the class
934 * @throws IllegalArgumentException the bytes are for a class in a different package
935 * to the lookup class
936 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
937 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
938 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
939 * @throws SecurityException if denied by the security manager
940 * @throws NullPointerException if {@code bytes} is {@code null}
941 * @since 9
942 * @spec JPMS
943 * @see Lookup#privateLookupIn
944 * @see Lookup#dropLookupMode
945 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
946 */
947 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
948 return defineClass(bytes, (ClassProperty[])null);
949 }
950
951 /**
952 * Defines a class to the same class loader and in the same runtime package
953 * and {@linkplain java.security.ProtectionDomain protection domain} as
954 * this lookup's {@linkplain #lookupClass() lookup class}.
955 * The {@code props} parameter specifies the properties of the class.
956 *
957 * <p> A class can be defined with the following properties:
958 * <ul>
959 * <li>A {@linkplain ClassProperty#NESTMATE <em>nestmate</em>} of the lookup class,
960 * i.e. in the same {@linkplain Class#getNestHost nest}
961 * of the lookup class. The class will have access to the private members
962 * of all classes and interfaces in the same nest.
963 * </li>
964 * <li>A {@linkplain ClassProperty#HIDDEN <em>hidden</em>} class,
965 * i.e. a class cannot be referenced by other classes.
966 * A hidden class has the following properties:
967 * <ul>
968 * <li>Naming:
969 * The name of this class is derived from the name of
970 * the class in the class bytes so that the class name does not
971 * collide with other classes defined to the same class loader.
972 * <li>Class resolution:
973 * The Java virtual machine does not find a hidden class with
974 * its name. A hidden class can reference its members
975 * locally with the name of the class in the class bytes as if
976 * a non-hidden class. The name returned by {@link Class#getName()}
977 * is not known when the class bytes are generated.
978 * <li>Class retransformation:
979 * The class is not modifiable by Java agents or tool agents using
980 * the <a href="{@docRoot}/../specs/jvmti.html">JVM Tool Interface</a>.
981 * </ul>
982 * </li>
983 * <li>A {@linkplain ClassProperty#WEAK <em>weak</em>} class,
984 * i.e. a class may be unloaded even if its defining class loader is
985 * <a href="../ref/package.html#reachability">reachable</a>,
986 * as if the defining class loader would only hold a
987 * {@linkplain java.lang.ref.WeakReference weak reference} of
988 * the class.
989 * A weak class is hidden. If the {@code WEAK} property is set,
990 * then it implies that {@code HIDDEN} property is also set.</li>
991 * </ul>
992 *
993 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must
994 * include {@link #PACKAGE PACKAGE} access as default (package) members
995 * will be accessible to the class. The {@code PACKAGE} lookup mode serves
996 * to authenticate that the lookup object was created by a caller in
997 * the runtime package (or derived from a lookup originally created by
998 * suitably privileged code to a target class in the runtime package).
999 * If the class is defined as a {@linkplain ClassProperty#NESTMATE nestmate}
1000 * then the {@linkplain #lookupModes() lookup modes} for this lookup must
1001 * include {@link #PRIVATE PRIVATE} access. </p>
1002 *
1003 * <p> The {@code bytes} parameter is the class bytes of a valid class file
1004 * (as defined by the <em>The Java Virtual Machine Specification</em>)
1005 * with a class name in the same package as the lookup class.
1006 * The class bytes of a nestmate class must not contain
1007 * the {@code NestHost} attribute nor the {@code NestMembers} attribute. </p>
1008 *
1009 * <p> If there is a security manager, its {@code checkPermission} method is first called
1010 * to check {@code RuntimePermission("defineClass")}. </p>
1011 *
1012 * <p> This method does not run the class initializer. The class initializer
1013 * may run at a later time, as detailed in section 12.4 of the The Java Language Specification.
1014 *
1015 * <p> The class can obtain {@code classData} by calling
1016 * the {@link Lookup#classData()} method of its {@code Lookup} object.
1017 *
1018 * @apiNote An implementation of the Java Progamming Language may
1019 * unload classes as specified in section 12.7 of the Java Language Specification.
1020 * A class or interface may be unloaded if and only if
1021 * its defining class loader may be reclaimed by the garbage collector.
1022 * If the implementation supports class loading, a weak class
1023 * may become weakly reachable as if the defining class loader would
1024 * only hold a {@linkplain java.lang.ref.WeakReference weak reference}
1025 * of the class.
1026 *
1027 * @param bytes the class bytes
1028 * @param props {@linkplain ClassProperty class properties}
1029 * @return the {@code Class} object for the class
1030 *
1031 * @throws IllegalArgumentException the bytes are for a class in a different package
1032 * to the lookup class
1033 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access, or
1034 * if {@code properties} contains {@code NESTMATE} but this lookup
1035 * does not have {@code PRIVATE} access
1036 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1037 * verified ({@code VerifyError}), is already defined,
1038 * or another linkage error occurs
1039 * @throws SecurityException if denied by the security manager
1040 * @throws NullPointerException if {@code bytes} is {@code null}
1041 *
1042 * @since 12
1043 * @jls 12.7 Unloading of Classes and Interfaces
1044 * @see Lookup#privateLookupIn(Class, Lookup)
1045 * @see Lookup#dropLookupMode(int)
1046 */
1047 public Class<?> defineClass(byte[] bytes, ClassProperty... props) throws IllegalAccessException {
1048 Objects.requireNonNull(bytes);
1049
1050 // clone the properties before access
1051 Set<ClassProperty> properties;
1052 if (props == null || props.length == 0) {
1053 properties = EMPTY_PROPS;
1054 } else {
1055 properties = Set.of(props);
1056 }
1057
1058 // Is it ever possible to create Lookup for int.class or Object[].class?
1059 assert !lookupClass.isPrimitive() && !lookupClass.isArray();
1060
1061 if ((lookupModes() & PACKAGE) == 0){
1062 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1063 }
1064
1065 if (properties.contains(NESTMATE) && (lookupModes() & PRIVATE) == 0){
1066 throw new IllegalAccessException("Lookup does not have PRIVATE access");
1067 }
1068
1069 assert (lookupModes() & (MODULE | PUBLIC)) != 0;
1070
1071 SecurityManager sm = System.getSecurityManager();
1072 if (sm != null)
1073 sm.checkPermission(new RuntimePermission("defineClass"));
1074
1075 return defineClassWithNoCheck(bytes, classPropertiesToFlags(properties));
1076 }
1077
1078 /**
1079 * Defines a class to the same class loader and in the same runtime package
1080 * and {@linkplain java.security.ProtectionDomain protection domain} as
1081 * this lookup's {@linkplain #lookupClass() lookup class} with
1082 * the given class properties and {@code classData}.
1083 *
1084 * <p> This method defines a class as if calling
1085 * {@link #defineClass(byte[], ClassProperty...) defineClass(bytes, props)}
1086 * and then the class initializer with an injected the {@code classData}
1087 * as a pre-initialized static unnamed field.
1088 * The injected pre-initialized static unnamed field can be
1089 * obtained by calling the {@link Lookup#classData()} method of
1090 * its {@code Lookup} object.
1091 *
1092 * <p> If there is a security manager, its {@code checkPermission} method is first called
1093 * to check {@code RuntimePermission("defineClass")}. </p>
1094 *
1095 * @apiNote
1096 * This method initializes the class, as opposed to the {@link #defineClass(byte[], ClassProperty...)}
1097 * method which does not invoke {@code <clinit>}, because the returned {@code Class}
1098 * is as if it contains a private static unnamed field that is initialized to
1099 * the given {@code classData} along with other declared static fields
1100 * via {@code <clinit>}.
1101 *
1102 * @param bytes the class bytes
1103 * @param classData pre-initialized class data
1104 * @param props {@linkplain ClassProperty class properties}
1105 * @return the {@code Class} object for the class
1106 *
1107 * @throws IllegalArgumentException the bytes are for a class in a different package
1108 * to the lookup class
1109 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access, or
1110 * if {@code properties} contains {@code NESTMATE} but this lookup
1111 * does not have {@code PRIVATE} access
1112 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1113 * verified ({@code VerifyError}), is already defined,
1114 * or another linkage error occurs
1115 * @throws SecurityException if denied by the security manager
1116 * @throws NullPointerException if {@code bytes} or {@code classData} is {@code null}
1117 *
1118 * @since 12
1119 * @jls 12.7 Unloading of Classes and Interfaces
1120 * @see Lookup#privateLookupIn(Class, Lookup)
1121 * @see Lookup#dropLookupMode(int)
1122 */
1123 public Class<?> defineClassWithClassData(byte[] bytes, Object classData, ClassProperty... props)
1124 throws IllegalAccessException
1125 {
1126 Objects.requireNonNull(bytes);
1127 Objects.requireNonNull(classData);
1128
1129 // Is it ever possible to create Lookup for int.class or Object[].class?
1130 assert !lookupClass.isPrimitive() && !lookupClass.isArray();
1131
1132 if ((lookupModes() & PACKAGE) == 0){
1133 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1134 }
1135
1136 Set<ClassProperty> properties;
1137 if (props == null || props.length == 0) {
1138 properties = EMPTY_PROPS;
1139 } else {
1140 properties = Set.of(props);
1141 }
1142
1143 if (properties.contains(NESTMATE) && (lookupModes() & PRIVATE) == 0){
1144 throw new IllegalAccessException("Lookup does not have PRIVATE access");
1145 }
1146
1147 assert (lookupModes() & (MODULE | PUBLIC)) != 0;
1148
1149 SecurityManager sm = System.getSecurityManager();
1150 if (sm != null)
1151 sm.checkPermission(new RuntimePermission("defineClass"));
1152
1153 return defineClassWithNoCheck(bytes, classPropertiesToFlags(properties), classData);
1154 }
1155
1156 private static int classPropertiesToFlags(Set<ClassProperty> props) {
1157 if (props.isEmpty()) return 0;
1158
1159 int flags = 0;
1160 for (ClassProperty cp : props) {
1161 flags |= cp.flag;
1162 if (cp == WEAK) {
1163 // weak class property implies hidden
1164 flags |= HIDDEN.flag;
1165 }
1166 }
1167 return flags;
1168 }
1169
1170 /**
1171 * Returns the class data associated with this lookup class.
1172 * If this lookup class was defined via
1173 * {@link #defineClassWithClassData(byte[], Object, ClassProperty...)
1174 * defineClassWithClassData(bytes, classData, properties)}
1175 * then the supplied {@code classData} object is returned; otherwise,
1176 * {@code null}.
1177 *
1178 * <p> This method will invoke the static class initializer of
1179 * this lookup class if it has not been initialized.
1180 *
1181 * @apiNote
1182 * A class data can be considered as
1183 * private static unnamed field that has been pre-initialized
1184 * and supplied at define class time.
1185 *
1186 * <p> For example a class can pack one or more pre-initialized objects
1187 * in a {@code List} as the class data and at class initialization
1188 * time unpack them for subsequent access.
1189 * The class data is {@code List.of(o1, o2, o3....)}
1190 * passed to {@link #defineClassWithClassData(byte[], Object, ClassProperty...)} where
1191 * {@code <clinit>} of the class bytes does the following:
1192 *
1193 * <pre>{@code
1194 * private static final T t;
1195 * private static final R r;
1196 * static {
1197 * List<Object> data = (List<Object>) MethodHandles.lookup().classData();
1198 * t = (T)data.get(0);
1199 * r = (R)data.get(1);
1200 * }
1201 *}</pre>
1202 *
1203 * @return the class data if this lookup class was defined via
1204 * {@link #defineClassWithClassData(byte[], Object, ClassProperty...)}; otherwise {@code null}.
1205 *
1206 * @throws IllegalAccessException if this lookup does not have {@code PRIVATE} access
1207 * @since 12
1208 */
1209 public Object classData() throws IllegalAccessException {
1210 if ((lookupModes() & PRIVATE) == 0){
1211 throw new IllegalAccessException("Lookup does not have PRIVATE access");
1212 }
1213
1214 // should we allow clearing? getAndClearClassData
1215 return CLASS_DATA_MAP.get(lookupClass);
1216 }
1217
1218 // package-private
1219 static final int HIDDEN_NESTMATE = NESTMATE_CLASS|NONFINDABLE_CLASS|ACCESS_VM_ANNOTATIONS;
1220 static final int WEAK_HIDDEN_NESTMATE = WEAK_CLASS|NESTMATE_CLASS|NONFINDABLE_CLASS|ACCESS_VM_ANNOTATIONS;
1221 static final Set<ClassProperty> EMPTY_PROPS = Set.of();
1222
1223 Class<?> defineClassWithNoCheck(byte[] bytes, int flags) {
1224 return defineClassWithNoCheck(bytes, flags, null);
1225 }
1226
1227 Class<?> defineClassWithNoCheck(byte[] bytes, int flags, Object classData) {
1228 // Can't use lambda during bootstrapping
1229 // parse class bytes to get class name (in internal form)
1230 bytes = bytes.clone();
1231 String name;
1232 try {
1233 ClassReader reader = new ClassReader(bytes);
1234 name = reader.getClassName();
1235 } catch (RuntimeException e) {
1236 // ASM exceptions are poorly specified
1237 ClassFormatError cfe = new ClassFormatError();
1238 cfe.initCause(e);
1239 throw cfe;
1240 }
1241
1242 // get package and class name in binary form
1243 String cn, pn;
1244 int index = name.lastIndexOf('/');
1245 if (index == -1) {
1246 cn = name;
1247 pn = "";
1248 } else {
1249 cn = name.replace('/', '.');
1250 pn = cn.substring(0, index);
1251 }
1252 if (!pn.equals(lookupClass.getPackageName())) {
1253 throw new IllegalArgumentException(cn + " not in same package as lookup class: " + lookupClass.getName());
1254 }
1255
1256 Class<?> host = lookupClass;
1257 if ((flags & NESTMATE_CLASS) != 0) {
1258 // cached in the Class object
1259 host = lookupClass.getNestHost();
1260 }
1261
1262 if ((flags & NONFINDABLE_CLASS) != 0) {
1263 // assign a new name
1264 // cn = cn + "\\" + ++seq;
1265 cn = null;
1266 }
1267
1268 // invoke the class loader's defineClass method
1269 ClassLoader loader = lookupClass.getClassLoader();
1270 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
1271 Class<?> clazz = JLA.defineClass(loader, host, cn, bytes, pd, flags, classData);
1272 assert clazz.getClassLoader() == lookupClass.getClassLoader()
1273 && clazz.getPackageName().equals(lookupClass.getPackageName());
1274
1275 // ## TBD what if multiple threads defining this same class??
1276 // may need VM to inject the classData in a Class itself at define class time
1277 if (classData != null) {
1278 CLASS_DATA_MAP.putIfAbsent(clazz, classData);
1279 }
1280 return clazz;
1281 }
1282
1283 private static volatile int seq = 0;
1284
1285 private ProtectionDomain lookupClassProtectionDomain() {
1286 ProtectionDomain pd = cachedProtectionDomain;
1287 if (pd == null) {
1288 cachedProtectionDomain = pd = JLA.protectionDomain(lookupClass);
1289 }
1290 return pd;
1291 }
1292
1293 // cached protection domain
1294 private volatile ProtectionDomain cachedProtectionDomain;
1295
1296 // don't see the need to use ClassValue
1297 private static final WeakHashMap<Class<?>, Object> CLASS_DATA_MAP = new WeakHashMap<>();
1298
1299 // Make sure outer class is initialized first.
1300 static { IMPL_NAMES.getClass(); }
1301
1302 /** Package-private version of lookup which is trusted. */
1303 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
1304
1305 /** Version of lookup which is trusted minimally.
1306 * It can only be used to create method handles to publicly accessible
1307 * members in packages that are exported unconditionally.
1308 */
1309 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
1310
1311 static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
1312
1313 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1314 String name = lookupClass.getName();
1315 if (name.startsWith("java.lang.invoke."))
1316 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1317 }
1318
1319 /**
1320 * Displays the name of the class from which lookups are to be made.
1321 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1322 * If there are restrictions on the access permitted to this lookup,
1323 * this is indicated by adding a suffix to the class name, consisting
1324 * of a slash and a keyword. The keyword represents the strongest
1325 * allowed access, and is chosen as follows:
1326 * <ul>
1327 * <li>If no access is allowed, the suffix is "/noaccess".
1328 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1329 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1330 * <li>If only public and module access are allowed, the suffix is "/module".
1331 * <li>If only public, module and package access are allowed, the suffix is "/package".
1332 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1333 * </ul>
1334 * If none of the above cases apply, it is the case that full
1335 * access (public, module, package, private, and protected) is allowed.
1336 * In this case, no suffix is added.
1337 * This is true only of an object obtained originally from
1338 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1339 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1340 * always have restricted access, and will display a suffix.
1341 * <p>
1342 * (It may seem strange that protected access should be
1343 * stronger than private access. Viewed independently from
1344 * package access, protected access is the first to be lost,
1345 * because it requires a direct subclass relationship between
1346 * caller and callee.)
1347 * @see #in
1348 *
1349 * @revised 9
1350 * @spec JPMS
1351 */
1352 @Override
1353 public String toString() {
1354 String cname = lookupClass.getName();
1355 switch (allowedModes) {
1356 case 0: // no privileges
1357 return cname + "/noaccess";
1358 case PUBLIC:
1359 return cname + "/public";
1360 case PUBLIC|UNCONDITIONAL:
1361 return cname + "/publicLookup";
1362 case PUBLIC|MODULE:
1363 return cname + "/module";
1364 case PUBLIC|MODULE|PACKAGE:
1365 return cname + "/package";
1366 case FULL_POWER_MODES & ~PROTECTED:
1367 return cname + "/private";
1368 case FULL_POWER_MODES:
1369 return cname;
1370 case TRUSTED:
1371 return "/trusted"; // internal only; not exported
1372 default: // Should not happen, but it's a bitfield...
1373 cname = cname + "/" + Integer.toHexString(allowedModes);
1374 assert(false) : cname;
1375 return cname;
1376 }
1377 }
1378
1379 /**
1380 * Produces a method handle for a static method.
1381 * The type of the method handle will be that of the method.
1382 * (Since static methods do not take receivers, there is no
1383 * additional receiver argument inserted into the method handle type,
1384 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1385 * The method and all its argument types must be accessible to the lookup object.
1386 * <p>
1387 * The returned method handle will have
1388 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1389 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1390 * <p>
1391 * If the returned method handle is invoked, the method's class will
1392 * be initialized, if it has not already been initialized.
1393 * <p><b>Example:</b>
1394 * <blockquote><pre>{@code
1395 import static java.lang.invoke.MethodHandles.*;
1396 import static java.lang.invoke.MethodType.*;
1397 ...
1398 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1399 "asList", methodType(List.class, Object[].class));
1400 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1401 * }</pre></blockquote>
1402 * @param refc the class from which the method is accessed
1403 * @param name the name of the method
1404 * @param type the type of the method
1405 * @return the desired method handle
1406 * @throws NoSuchMethodException if the method does not exist
1407 * @throws IllegalAccessException if access checking fails,
1408 * or if the method is not {@code static},
1409 * or if the method's variable arity modifier bit
1410 * is set and {@code asVarargsCollector} fails
1411 * @exception SecurityException if a security manager is present and it
1412 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1413 * @throws NullPointerException if any argument is null
1414 */
1415 public
1416 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1417 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1418 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1419 }
1420
1421 /**
1422 * Produces a method handle for a virtual method.
1423 * The type of the method handle will be that of the method,
1424 * with the receiver type (usually {@code refc}) prepended.
1425 * The method and all its argument types must be accessible to the lookup object.
1426 * <p>
1427 * When called, the handle will treat the first argument as a receiver
1428 * and, for non-private methods, dispatch on the receiver's type to determine which method
1429 * implementation to enter.
1430 * For private methods the named method in {@code refc} will be invoked on the receiver.
1431 * (The dispatching action is identical with that performed by an
1432 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1433 * <p>
1434 * The first argument will be of type {@code refc} if the lookup
1435 * class has full privileges to access the member. Otherwise
1436 * the member must be {@code protected} and the first argument
1437 * will be restricted in type to the lookup class.
1438 * <p>
1439 * The returned method handle will have
1440 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1441 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1442 * <p>
1443 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1444 * instructions and method handles produced by {@code findVirtual},
1445 * if the class is {@code MethodHandle} and the name string is
1446 * {@code invokeExact} or {@code invoke}, the resulting
1447 * method handle is equivalent to one produced by
1448 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1449 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1450 * with the same {@code type} argument.
1451 * <p>
1452 * If the class is {@code VarHandle} and the name string corresponds to
1453 * the name of a signature-polymorphic access mode method, the resulting
1454 * method handle is equivalent to one produced by
1455 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1456 * the access mode corresponding to the name string and with the same
1457 * {@code type} arguments.
1458 * <p>
1459 * <b>Example:</b>
1460 * <blockquote><pre>{@code
1461 import static java.lang.invoke.MethodHandles.*;
1462 import static java.lang.invoke.MethodType.*;
1463 ...
1464 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1465 "concat", methodType(String.class, String.class));
1466 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1467 "hashCode", methodType(int.class));
1468 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1469 "hashCode", methodType(int.class));
1470 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1471 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1472 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1473 // interface method:
1474 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1475 "subSequence", methodType(CharSequence.class, int.class, int.class));
1476 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1477 // constructor "internal method" must be accessed differently:
1478 MethodType MT_newString = methodType(void.class); //()V for new String()
1479 try { assertEquals("impossible", lookup()
1480 .findVirtual(String.class, "<init>", MT_newString));
1481 } catch (NoSuchMethodException ex) { } // OK
1482 MethodHandle MH_newString = publicLookup()
1483 .findConstructor(String.class, MT_newString);
1484 assertEquals("", (String) MH_newString.invokeExact());
1485 * }</pre></blockquote>
1486 *
1487 * @param refc the class or interface from which the method is accessed
1488 * @param name the name of the method
1489 * @param type the type of the method, with the receiver argument omitted
1490 * @return the desired method handle
1491 * @throws NoSuchMethodException if the method does not exist
1492 * @throws IllegalAccessException if access checking fails,
1493 * or if the method is {@code static},
1494 * or if the method's variable arity modifier bit
1495 * is set and {@code asVarargsCollector} fails
1496 * @exception SecurityException if a security manager is present and it
1497 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1498 * @throws NullPointerException if any argument is null
1499 */
1500 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1501 if (refc == MethodHandle.class) {
1502 MethodHandle mh = findVirtualForMH(name, type);
1503 if (mh != null) return mh;
1504 } else if (refc == VarHandle.class) {
1505 MethodHandle mh = findVirtualForVH(name, type);
1506 if (mh != null) return mh;
1507 }
1508 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1509 MemberName method = resolveOrFail(refKind, refc, name, type);
1510 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1511 }
1512 private MethodHandle findVirtualForMH(String name, MethodType type) {
1513 // these names require special lookups because of the implicit MethodType argument
1514 if ("invoke".equals(name))
1515 return invoker(type);
1516 if ("invokeExact".equals(name))
1517 return exactInvoker(type);
1518 assert(!MemberName.isMethodHandleInvokeName(name));
1519 return null;
1520 }
1521 private MethodHandle findVirtualForVH(String name, MethodType type) {
1522 try {
1523 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1524 } catch (IllegalArgumentException e) {
1525 return null;
1526 }
1527 }
1528
1529 /**
1530 * Produces a method handle which creates an object and initializes it, using
1531 * the constructor of the specified type.
1532 * The parameter types of the method handle will be those of the constructor,
1533 * while the return type will be a reference to the constructor's class.
1534 * The constructor and all its argument types must be accessible to the lookup object.
1535 * <p>
1536 * The requested type must have a return type of {@code void}.
1537 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1538 * <p>
1539 * The returned method handle will have
1540 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1541 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1542 * <p>
1543 * If the returned method handle is invoked, the constructor's class will
1544 * be initialized, if it has not already been initialized.
1545 * <p><b>Example:</b>
1546 * <blockquote><pre>{@code
1547 import static java.lang.invoke.MethodHandles.*;
1548 import static java.lang.invoke.MethodType.*;
1549 ...
1550 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1551 ArrayList.class, methodType(void.class, Collection.class));
1552 Collection orig = Arrays.asList("x", "y");
1553 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1554 assert(orig != copy);
1555 assertEquals(orig, copy);
1556 // a variable-arity constructor:
1557 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1558 ProcessBuilder.class, methodType(void.class, String[].class));
1559 ProcessBuilder pb = (ProcessBuilder)
1560 MH_newProcessBuilder.invoke("x", "y", "z");
1561 assertEquals("[x, y, z]", pb.command().toString());
1562 * }</pre></blockquote>
1563 * @param refc the class or interface from which the method is accessed
1564 * @param type the type of the method, with the receiver argument omitted, and a void return type
1565 * @return the desired method handle
1566 * @throws NoSuchMethodException if the constructor does not exist
1567 * @throws IllegalAccessException if access checking fails
1568 * or if the method's variable arity modifier bit
1569 * is set and {@code asVarargsCollector} fails
1570 * @exception SecurityException if a security manager is present and it
1571 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1572 * @throws NullPointerException if any argument is null
1573 */
1574 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1575 if (refc.isArray()) {
1576 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1577 }
1578 String name = "<init>";
1579 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1580 return getDirectConstructor(refc, ctor);
1581 }
1582
1583 /**
1584 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1585 * initializer of the class is not run.
1586 * <p>
1587 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1588 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1589 * load the requested class, and then determines whether the class is accessible to this lookup object.
1590 *
1591 * @param targetName the fully qualified name of the class to be looked up.
1592 * @return the requested class.
1593 * @exception SecurityException if a security manager is present and it
1594 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1595 * @throws LinkageError if the linkage fails
1596 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader
1597 * or the class is not {@linkplain Class#isHidden hidden}
1598 * @throws IllegalAccessException if the class is not accessible, using the allowed access modes.
1599
1600 * @since 9
1601 * @see Class#isHidden
1602 */
1603 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1604 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1605 return accessClass(targetClass);
1606 }
1607
1608 /**
1609 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1610 * static initializer of the class is not run.
1611 * <p>
1612 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1613 * {@linkplain #lookupModes() lookup modes}.
1614 *
1615 * @param targetClass the class to be access-checked
1616 *
1617 * @return the class that has been access-checked
1618 *
1619 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1620 * modes.
1621 * @exception SecurityException if a security manager is present and it
1622 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1623 * @since 9
1624 */
1625 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1626 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1627 throw new MemberName(targetClass).makeAccessException("access violation", this);
1628 }
1629 checkSecurityManager(targetClass, null);
1630 return targetClass;
1631 }
1632
1633 /**
1634 * Produces an early-bound method handle for a virtual method.
1635 * It will bypass checks for overriding methods on the receiver,
1636 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1637 * instruction from within the explicitly specified {@code specialCaller}.
1638 * The type of the method handle will be that of the method,
1639 * with a suitably restricted receiver type prepended.
1640 * (The receiver type will be {@code specialCaller} or a subtype.)
1641 * The method and all its argument types must be accessible
1642 * to the lookup object.
1643 * <p>
1644 * Before method resolution,
1645 * if the explicitly specified caller class is not identical with the
1646 * lookup class, or if this lookup object does not have
1647 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1648 * privileges, the access fails.
1649 * <p>
1650 * The returned method handle will have
1651 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1652 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1653 * <p style="font-size:smaller;">
1654 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1655 * even though the {@code invokespecial} instruction can refer to them
1656 * in special circumstances. Use {@link #findConstructor findConstructor}
1657 * to access instance initialization methods in a safe manner.)</em>
1658 * <p><b>Example:</b>
1659 * <blockquote><pre>{@code
1660 import static java.lang.invoke.MethodHandles.*;
1661 import static java.lang.invoke.MethodType.*;
1662 ...
1663 static class Listie extends ArrayList {
1664 public String toString() { return "[wee Listie]"; }
1665 static Lookup lookup() { return MethodHandles.lookup(); }
1666 }
1667 ...
1668 // no access to constructor via invokeSpecial:
1669 MethodHandle MH_newListie = Listie.lookup()
1670 .findConstructor(Listie.class, methodType(void.class));
1671 Listie l = (Listie) MH_newListie.invokeExact();
1672 try { assertEquals("impossible", Listie.lookup().findSpecial(
1673 Listie.class, "<init>", methodType(void.class), Listie.class));
1674 } catch (NoSuchMethodException ex) { } // OK
1675 // access to super and self methods via invokeSpecial:
1676 MethodHandle MH_super = Listie.lookup().findSpecial(
1677 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1678 MethodHandle MH_this = Listie.lookup().findSpecial(
1679 Listie.class, "toString" , methodType(String.class), Listie.class);
1680 MethodHandle MH_duper = Listie.lookup().findSpecial(
1681 Object.class, "toString" , methodType(String.class), Listie.class);
1682 assertEquals("[]", (String) MH_super.invokeExact(l));
1683 assertEquals(""+l, (String) MH_this.invokeExact(l));
1684 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1685 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1686 String.class, "toString", methodType(String.class), Listie.class));
1687 } catch (IllegalAccessException ex) { } // OK
1688 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1689 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1690 * }</pre></blockquote>
1691 *
1692 * @param refc the class or interface from which the method is accessed
1693 * @param name the name of the method (which must not be "<init>")
1694 * @param type the type of the method, with the receiver argument omitted
1695 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1696 * @return the desired method handle
1697 * @throws NoSuchMethodException if the method does not exist
1698 * @throws IllegalAccessException if access checking fails,
1699 * or if the method is {@code static},
1700 * or if the method's variable arity modifier bit
1701 * is set and {@code asVarargsCollector} fails
1702 * @exception SecurityException if a security manager is present and it
1703 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1704 * @throws NullPointerException if any argument is null
1705 */
1706 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1707 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1708 checkSpecialCaller(specialCaller, refc);
1709 Lookup specialLookup = this.in(specialCaller);
1710 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1711 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1712 }
1713
1714 /**
1715 * Produces a method handle giving read access to a non-static field.
1716 * The type of the method handle will have a return type of the field's
1717 * value type.
1718 * The method handle's single argument will be the instance containing
1719 * the field.
1720 * Access checking is performed immediately on behalf of the lookup class.
1721 * @param refc the class or interface from which the method is accessed
1722 * @param name the field's name
1723 * @param type the field's type
1724 * @return a method handle which can load values from the field
1725 * @throws NoSuchFieldException if the field does not exist
1726 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1727 * @exception SecurityException if a security manager is present and it
1728 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1729 * @throws NullPointerException if any argument is null
1730 * @see #findVarHandle(Class, String, Class)
1731 */
1732 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1733 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1734 return getDirectField(REF_getField, refc, field);
1735 }
1736
1737 /**
1738 * Produces a method handle giving write access to a non-static field.
1739 * The type of the method handle will have a void return type.
1740 * The method handle will take two arguments, the instance containing
1741 * the field, and the value to be stored.
1742 * The second argument will be of the field's value type.
1743 * Access checking is performed immediately on behalf of the lookup class.
1744 * @param refc the class or interface from which the method is accessed
1745 * @param name the field's name
1746 * @param type the field's type
1747 * @return a method handle which can store values into the field
1748 * @throws NoSuchFieldException if the field does not exist
1749 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1750 * @exception SecurityException if a security manager is present and it
1751 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1752 * @throws NullPointerException if any argument is null
1753 * @see #findVarHandle(Class, String, Class)
1754 */
1755 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1756 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1757 return getDirectField(REF_putField, refc, field);
1758 }
1759
1760 /**
1761 * Produces a VarHandle giving access to a non-static field {@code name}
1762 * of type {@code type} declared in a class of type {@code recv}.
1763 * The VarHandle's variable type is {@code type} and it has one
1764 * coordinate type, {@code recv}.
1765 * <p>
1766 * Access checking is performed immediately on behalf of the lookup
1767 * class.
1768 * <p>
1769 * Certain access modes of the returned VarHandle are unsupported under
1770 * the following conditions:
1771 * <ul>
1772 * <li>if the field is declared {@code final}, then the write, atomic
1773 * update, numeric atomic update, and bitwise atomic update access
1774 * modes are unsupported.
1775 * <li>if the field type is anything other than {@code byte},
1776 * {@code short}, {@code char}, {@code int}, {@code long},
1777 * {@code float}, or {@code double} then numeric atomic update
1778 * access modes are unsupported.
1779 * <li>if the field type is anything other than {@code boolean},
1780 * {@code byte}, {@code short}, {@code char}, {@code int} or
1781 * {@code long} then bitwise atomic update access modes are
1782 * unsupported.
1783 * </ul>
1784 * <p>
1785 * If the field is declared {@code volatile} then the returned VarHandle
1786 * will override access to the field (effectively ignore the
1787 * {@code volatile} declaration) in accordance to its specified
1788 * access modes.
1789 * <p>
1790 * If the field type is {@code float} or {@code double} then numeric
1791 * and atomic update access modes compare values using their bitwise
1792 * representation (see {@link Float#floatToRawIntBits} and
1793 * {@link Double#doubleToRawLongBits}, respectively).
1794 * @apiNote
1795 * Bitwise comparison of {@code float} values or {@code double} values,
1796 * as performed by the numeric and atomic update access modes, differ
1797 * from the primitive {@code ==} operator and the {@link Float#equals}
1798 * and {@link Double#equals} methods, specifically with respect to
1799 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1800 * Care should be taken when performing a compare and set or a compare
1801 * and exchange operation with such values since the operation may
1802 * unexpectedly fail.
1803 * There are many possible NaN values that are considered to be
1804 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1805 * provided by Java can distinguish between them. Operation failure can
1806 * occur if the expected or witness value is a NaN value and it is
1807 * transformed (perhaps in a platform specific manner) into another NaN
1808 * value, and thus has a different bitwise representation (see
1809 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1810 * details).
1811 * The values {@code -0.0} and {@code +0.0} have different bitwise
1812 * representations but are considered equal when using the primitive
1813 * {@code ==} operator. Operation failure can occur if, for example, a
1814 * numeric algorithm computes an expected value to be say {@code -0.0}
1815 * and previously computed the witness value to be say {@code +0.0}.
1816 * @param recv the receiver class, of type {@code R}, that declares the
1817 * non-static field
1818 * @param name the field's name
1819 * @param type the field's type, of type {@code T}
1820 * @return a VarHandle giving access to non-static fields.
1821 * @throws NoSuchFieldException if the field does not exist
1822 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1823 * @exception SecurityException if a security manager is present and it
1824 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1825 * @throws NullPointerException if any argument is null
1826 * @since 9
1827 */
1828 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1829 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1830 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1831 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1832 }
1833
1834 /**
1835 * Produces a method handle giving read access to a static field.
1836 * The type of the method handle will have a return type of the field's
1837 * value type.
1838 * The method handle will take no arguments.
1839 * Access checking is performed immediately on behalf of the lookup class.
1840 * <p>
1841 * If the returned method handle is invoked, the field's class will
1842 * be initialized, if it has not already been initialized.
1843 * @param refc the class or interface from which the method is accessed
1844 * @param name the field's name
1845 * @param type the field's type
1846 * @return a method handle which can load values from the field
1847 * @throws NoSuchFieldException if the field does not exist
1848 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1849 * @exception SecurityException if a security manager is present and it
1850 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1851 * @throws NullPointerException if any argument is null
1852 */
1853 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1854 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1855 return getDirectField(REF_getStatic, refc, field);
1856 }
1857
1858 /**
1859 * Produces a method handle giving write access to a static field.
1860 * The type of the method handle will have a void return type.
1861 * The method handle will take a single
1862 * argument, of the field's value type, the value to be stored.
1863 * Access checking is performed immediately on behalf of the lookup class.
1864 * <p>
1865 * If the returned method handle is invoked, the field's class will
1866 * be initialized, if it has not already been initialized.
1867 * @param refc the class or interface from which the method is accessed
1868 * @param name the field's name
1869 * @param type the field's type
1870 * @return a method handle which can store values into the field
1871 * @throws NoSuchFieldException if the field does not exist
1872 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1873 * @exception SecurityException if a security manager is present and it
1874 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1875 * @throws NullPointerException if any argument is null
1876 */
1877 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1878 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1879 return getDirectField(REF_putStatic, refc, field);
1880 }
1881
1882 /**
1883 * Produces a VarHandle giving access to a static field {@code name} of
1884 * type {@code type} declared in a class of type {@code decl}.
1885 * The VarHandle's variable type is {@code type} and it has no
1886 * coordinate types.
1887 * <p>
1888 * Access checking is performed immediately on behalf of the lookup
1889 * class.
1890 * <p>
1891 * If the returned VarHandle is operated on, the declaring class will be
1892 * initialized, if it has not already been initialized.
1893 * <p>
1894 * Certain access modes of the returned VarHandle are unsupported under
1895 * the following conditions:
1896 * <ul>
1897 * <li>if the field is declared {@code final}, then the write, atomic
1898 * update, numeric atomic update, and bitwise atomic update access
1899 * modes are unsupported.
1900 * <li>if the field type is anything other than {@code byte},
1901 * {@code short}, {@code char}, {@code int}, {@code long},
1902 * {@code float}, or {@code double}, then numeric atomic update
1903 * access modes are unsupported.
1904 * <li>if the field type is anything other than {@code boolean},
1905 * {@code byte}, {@code short}, {@code char}, {@code int} or
1906 * {@code long} then bitwise atomic update access modes are
1907 * unsupported.
1908 * </ul>
1909 * <p>
1910 * If the field is declared {@code volatile} then the returned VarHandle
1911 * will override access to the field (effectively ignore the
1912 * {@code volatile} declaration) in accordance to its specified
1913 * access modes.
1914 * <p>
1915 * If the field type is {@code float} or {@code double} then numeric
1916 * and atomic update access modes compare values using their bitwise
1917 * representation (see {@link Float#floatToRawIntBits} and
1918 * {@link Double#doubleToRawLongBits}, respectively).
1919 * @apiNote
1920 * Bitwise comparison of {@code float} values or {@code double} values,
1921 * as performed by the numeric and atomic update access modes, differ
1922 * from the primitive {@code ==} operator and the {@link Float#equals}
1923 * and {@link Double#equals} methods, specifically with respect to
1924 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1925 * Care should be taken when performing a compare and set or a compare
1926 * and exchange operation with such values since the operation may
1927 * unexpectedly fail.
1928 * There are many possible NaN values that are considered to be
1929 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1930 * provided by Java can distinguish between them. Operation failure can
1931 * occur if the expected or witness value is a NaN value and it is
1932 * transformed (perhaps in a platform specific manner) into another NaN
1933 * value, and thus has a different bitwise representation (see
1934 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1935 * details).
1936 * The values {@code -0.0} and {@code +0.0} have different bitwise
1937 * representations but are considered equal when using the primitive
1938 * {@code ==} operator. Operation failure can occur if, for example, a
1939 * numeric algorithm computes an expected value to be say {@code -0.0}
1940 * and previously computed the witness value to be say {@code +0.0}.
1941 * @param decl the class that declares the static field
1942 * @param name the field's name
1943 * @param type the field's type, of type {@code T}
1944 * @return a VarHandle giving access to a static field
1945 * @throws NoSuchFieldException if the field does not exist
1946 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1947 * @exception SecurityException if a security manager is present and it
1948 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1949 * @throws NullPointerException if any argument is null
1950 * @since 9
1951 */
1952 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1953 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1954 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1955 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1956 }
1957
1958 /**
1959 * Produces an early-bound method handle for a non-static method.
1960 * The receiver must have a supertype {@code defc} in which a method
1961 * of the given name and type is accessible to the lookup class.
1962 * The method and all its argument types must be accessible to the lookup object.
1963 * The type of the method handle will be that of the method,
1964 * without any insertion of an additional receiver parameter.
1965 * The given receiver will be bound into the method handle,
1966 * so that every call to the method handle will invoke the
1967 * requested method on the given receiver.
1968 * <p>
1969 * The returned method handle will have
1970 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1971 * the method's variable arity modifier bit ({@code 0x0080}) is set
1972 * <em>and</em> the trailing array argument is not the only argument.
1973 * (If the trailing array argument is the only argument,
1974 * the given receiver value will be bound to it.)
1975 * <p>
1976 * This is almost equivalent to the following code, with some differences noted below:
1977 * <blockquote><pre>{@code
1978 import static java.lang.invoke.MethodHandles.*;
1979 import static java.lang.invoke.MethodType.*;
1980 ...
1981 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1982 MethodHandle mh1 = mh0.bindTo(receiver);
1983 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1984 return mh1;
1985 * }</pre></blockquote>
1986 * where {@code defc} is either {@code receiver.getClass()} or a super
1987 * type of that class, in which the requested method is accessible
1988 * to the lookup class.
1989 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1990 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1991 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1992 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1993 * @param receiver the object from which the method is accessed
1994 * @param name the name of the method
1995 * @param type the type of the method, with the receiver argument omitted
1996 * @return the desired method handle
1997 * @throws NoSuchMethodException if the method does not exist
1998 * @throws IllegalAccessException if access checking fails
1999 * or if the method's variable arity modifier bit
2000 * is set and {@code asVarargsCollector} fails
2001 * @exception SecurityException if a security manager is present and it
2002 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2003 * @throws NullPointerException if any argument is null
2004 * @see MethodHandle#bindTo
2005 * @see #findVirtual
2006 */
2007 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2008 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2009 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2010 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
2011 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2012 throw new IllegalAccessException("The restricted defining class " +
2013 mh.type().leadingReferenceParameter().getName() +
2014 " is not assignable from receiver class " +
2015 receiver.getClass().getName());
2016 }
2017 return mh.bindArgumentL(0, receiver).setVarargs(method);
2018 }
2019
2020 /**
2021 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2022 * to <i>m</i>, if the lookup class has permission.
2023 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2024 * If <i>m</i> is virtual, overriding is respected on every call.
2025 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2026 * The type of the method handle will be that of the method,
2027 * with the receiver type prepended (but only if it is non-static).
2028 * If the method's {@code accessible} flag is not set,
2029 * access checking is performed immediately on behalf of the lookup class.
2030 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2031 * <p>
2032 * The returned method handle will have
2033 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2034 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2035 * <p>
2036 * If <i>m</i> is static, and
2037 * if the returned method handle is invoked, the method's class will
2038 * be initialized, if it has not already been initialized.
2039 * @param m the reflected method
2040 * @return a method handle which can invoke the reflected method
2041 * @throws IllegalAccessException if access checking fails
2042 * or if the method's variable arity modifier bit
2043 * is set and {@code asVarargsCollector} fails
2044 * @throws NullPointerException if the argument is null
2045 */
2046 public MethodHandle unreflect(Method m) throws IllegalAccessException {
2047 if (m.getDeclaringClass() == MethodHandle.class) {
2048 MethodHandle mh = unreflectForMH(m);
2049 if (mh != null) return mh;
2050 }
2051 if (m.getDeclaringClass() == VarHandle.class) {
2052 MethodHandle mh = unreflectForVH(m);
2053 if (mh != null) return mh;
2054 }
2055 MemberName method = new MemberName(m);
2056 byte refKind = method.getReferenceKind();
2057 if (refKind == REF_invokeSpecial)
2058 refKind = REF_invokeVirtual;
2059 assert(method.isMethod());
2060 @SuppressWarnings("deprecation")
2061 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
2062 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
2063 }
2064 private MethodHandle unreflectForMH(Method m) {
2065 // these names require special lookups because they throw UnsupportedOperationException
2066 if (MemberName.isMethodHandleInvokeName(m.getName()))
2067 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
2068 return null;
2069 }
2070 private MethodHandle unreflectForVH(Method m) {
2071 // these names require special lookups because they throw UnsupportedOperationException
2072 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
2073 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
2074 return null;
2075 }
2076
2077 /**
2078 * Produces a method handle for a reflected method.
2079 * It will bypass checks for overriding methods on the receiver,
2080 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2081 * instruction from within the explicitly specified {@code specialCaller}.
2082 * The type of the method handle will be that of the method,
2083 * with a suitably restricted receiver type prepended.
2084 * (The receiver type will be {@code specialCaller} or a subtype.)
2085 * If the method's {@code accessible} flag is not set,
2086 * access checking is performed immediately on behalf of the lookup class,
2087 * as if {@code invokespecial} instruction were being linked.
2088 * <p>
2089 * Before method resolution,
2090 * if the explicitly specified caller class is not identical with the
2091 * lookup class, or if this lookup object does not have
2092 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2093 * privileges, the access fails.
2094 * <p>
2095 * The returned method handle will have
2096 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2097 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2098 * @param m the reflected method
2099 * @param specialCaller the class nominally calling the method
2100 * @return a method handle which can invoke the reflected method
2101 * @throws IllegalAccessException if access checking fails,
2102 * or if the method is {@code static},
2103 * or if the method's variable arity modifier bit
2104 * is set and {@code asVarargsCollector} fails
2105 * @throws NullPointerException if any argument is null
2106 */
2107 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
2108 checkSpecialCaller(specialCaller, null);
2109 Lookup specialLookup = this.in(specialCaller);
2110 MemberName method = new MemberName(m, true);
2111 assert(method.isMethod());
2112 // ignore m.isAccessible: this is a new kind of access
2113 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
2114 }
2115
2116 /**
2117 * Produces a method handle for a reflected constructor.
2118 * The type of the method handle will be that of the constructor,
2119 * with the return type changed to the declaring class.
2120 * The method handle will perform a {@code newInstance} operation,
2121 * creating a new instance of the constructor's class on the
2122 * arguments passed to the method handle.
2123 * <p>
2124 * If the constructor's {@code accessible} flag is not set,
2125 * access checking is performed immediately on behalf of the lookup class.
2126 * <p>
2127 * The returned method handle will have
2128 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2129 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2130 * <p>
2131 * If the returned method handle is invoked, the constructor's class will
2132 * be initialized, if it has not already been initialized.
2133 * @param c the reflected constructor
2134 * @return a method handle which can invoke the reflected constructor
2135 * @throws IllegalAccessException if access checking fails
2136 * or if the method's variable arity modifier bit
2137 * is set and {@code asVarargsCollector} fails
2138 * @throws NullPointerException if the argument is null
2139 */
2140 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
2141 MemberName ctor = new MemberName(c);
2142 assert(ctor.isConstructor());
2143 @SuppressWarnings("deprecation")
2144 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
2145 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
2146 }
2147
2148 /**
2149 * Produces a method handle giving read access to a reflected field.
2150 * The type of the method handle will have a return type of the field's
2151 * value type.
2152 * If the field is static, the method handle will take no arguments.
2153 * Otherwise, its single argument will be the instance containing
2154 * the field.
2155 * If the field's {@code accessible} flag is not set,
2156 * access checking is performed immediately on behalf of the lookup class.
2157 * <p>
2158 * If the field is static, and
2159 * if the returned method handle is invoked, the field's class will
2160 * be initialized, if it has not already been initialized.
2161 * @param f the reflected field
2162 * @return a method handle which can load values from the reflected field
2163 * @throws IllegalAccessException if access checking fails
2164 * @throws NullPointerException if the argument is null
2165 */
2166 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
2167 return unreflectField(f, false);
2168 }
2169 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
2170 MemberName field = new MemberName(f, isSetter);
2171 assert(isSetter
2172 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
2173 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
2174 @SuppressWarnings("deprecation")
2175 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
2176 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
2177 }
2178
2179 /**
2180 * Produces a method handle giving write access to a reflected field.
2181 * The type of the method handle will have a void return type.
2182 * If the field is static, the method handle will take a single
2183 * argument, of the field's value type, the value to be stored.
2184 * Otherwise, the two arguments will be the instance containing
2185 * the field, and the value to be stored.
2186 * If the field's {@code accessible} flag is not set,
2187 * access checking is performed immediately on behalf of the lookup class.
2188 * <p>
2189 * If the field is static, and
2190 * if the returned method handle is invoked, the field's class will
2191 * be initialized, if it has not already been initialized.
2192 * @param f the reflected field
2193 * @return a method handle which can store values into the reflected field
2194 * @throws IllegalAccessException if access checking fails
2195 * @throws NullPointerException if the argument is null
2196 */
2197 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
2198 return unreflectField(f, true);
2199 }
2200
2201 /**
2202 * Produces a VarHandle giving access to a reflected field {@code f}
2203 * of type {@code T} declared in a class of type {@code R}.
2204 * The VarHandle's variable type is {@code T}.
2205 * If the field is non-static the VarHandle has one coordinate type,
2206 * {@code R}. Otherwise, the field is static, and the VarHandle has no
2207 * coordinate types.
2208 * <p>
2209 * Access checking is performed immediately on behalf of the lookup
2210 * class, regardless of the value of the field's {@code accessible}
2211 * flag.
2212 * <p>
2213 * If the field is static, and if the returned VarHandle is operated
2214 * on, the field's declaring class will be initialized, if it has not
2215 * already been initialized.
2216 * <p>
2217 * Certain access modes of the returned VarHandle are unsupported under
2218 * the following conditions:
2219 * <ul>
2220 * <li>if the field is declared {@code final}, then the write, atomic
2221 * update, numeric atomic update, and bitwise atomic update access
2222 * modes are unsupported.
2223 * <li>if the field type is anything other than {@code byte},
2224 * {@code short}, {@code char}, {@code int}, {@code long},
2225 * {@code float}, or {@code double} then numeric atomic update
2226 * access modes are unsupported.
2227 * <li>if the field type is anything other than {@code boolean},
2228 * {@code byte}, {@code short}, {@code char}, {@code int} or
2229 * {@code long} then bitwise atomic update access modes are
2230 * unsupported.
2231 * </ul>
2232 * <p>
2233 * If the field is declared {@code volatile} then the returned VarHandle
2234 * will override access to the field (effectively ignore the
2235 * {@code volatile} declaration) in accordance to its specified
2236 * access modes.
2237 * <p>
2238 * If the field type is {@code float} or {@code double} then numeric
2239 * and atomic update access modes compare values using their bitwise
2240 * representation (see {@link Float#floatToRawIntBits} and
2241 * {@link Double#doubleToRawLongBits}, respectively).
2242 * @apiNote
2243 * Bitwise comparison of {@code float} values or {@code double} values,
2244 * as performed by the numeric and atomic update access modes, differ
2245 * from the primitive {@code ==} operator and the {@link Float#equals}
2246 * and {@link Double#equals} methods, specifically with respect to
2247 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2248 * Care should be taken when performing a compare and set or a compare
2249 * and exchange operation with such values since the operation may
2250 * unexpectedly fail.
2251 * There are many possible NaN values that are considered to be
2252 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2253 * provided by Java can distinguish between them. Operation failure can
2254 * occur if the expected or witness value is a NaN value and it is
2255 * transformed (perhaps in a platform specific manner) into another NaN
2256 * value, and thus has a different bitwise representation (see
2257 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2258 * details).
2259 * The values {@code -0.0} and {@code +0.0} have different bitwise
2260 * representations but are considered equal when using the primitive
2261 * {@code ==} operator. Operation failure can occur if, for example, a
2262 * numeric algorithm computes an expected value to be say {@code -0.0}
2263 * and previously computed the witness value to be say {@code +0.0}.
2264 * @param f the reflected field, with a field of type {@code T}, and
2265 * a declaring class of type {@code R}
2266 * @return a VarHandle giving access to non-static fields or a static
2267 * field
2268 * @throws IllegalAccessException if access checking fails
2269 * @throws NullPointerException if the argument is null
2270 * @since 9
2271 */
2272 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
2273 MemberName getField = new MemberName(f, false);
2274 MemberName putField = new MemberName(f, true);
2275 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
2276 f.getDeclaringClass(), getField, putField);
2277 }
2278
2279 /**
2280 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2281 * created by this lookup object or a similar one.
2282 * Security and access checks are performed to ensure that this lookup object
2283 * is capable of reproducing the target method handle.
2284 * This means that the cracking may fail if target is a direct method handle
2285 * but was created by an unrelated lookup object.
2286 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
2287 * and was created by a lookup object for a different class.
2288 * @param target a direct method handle to crack into symbolic reference components
2289 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
2290 * @exception SecurityException if a security manager is present and it
2291 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2292 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
2293 * @exception NullPointerException if the target is {@code null}
2294 * @see MethodHandleInfo
2295 * @since 1.8
2296 */
2297 public MethodHandleInfo revealDirect(MethodHandle target) {
2298 MemberName member = target.internalMemberName();
2299 if (member == null || (!member.isResolved() &&
2300 !member.isMethodHandleInvoke() &&
2301 !member.isVarHandleMethodInvoke()))
2302 throw newIllegalArgumentException("not a direct method handle");
2303 Class<?> defc = member.getDeclaringClass();
2304 byte refKind = member.getReferenceKind();
2305 assert(MethodHandleNatives.refKindIsValid(refKind));
2306 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2307 // Devirtualized method invocation is usually formally virtual.
2308 // To avoid creating extra MemberName objects for this common case,
2309 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2310 refKind = REF_invokeVirtual;
2311 if (refKind == REF_invokeVirtual && defc.isInterface())
2312 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2313 refKind = REF_invokeInterface;
2314 // Check SM permissions and member access before cracking.
2315 try {
2316 checkAccess(refKind, defc, member);
2317 checkSecurityManager(defc, member);
2318 } catch (IllegalAccessException ex) {
2319 throw new IllegalArgumentException(ex);
2320 }
2321 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2322 Class<?> callerClass = target.internalCallerClass();
2323 if (!hasPrivateAccess() || callerClass != lookupClass())
2324 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2325 }
2326 // Produce the handle to the results.
2327 return new InfoFromMemberName(this, member, refKind);
2328 }
2329
2330 /// Helper methods, all package-private.
2331
2332 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2333 checkSymbolicClass(refc); // do this before attempting to resolve
2334 Objects.requireNonNull(name);
2335 Objects.requireNonNull(type);
2336 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2337 NoSuchFieldException.class);
2338 }
2339
2340 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2341 checkSymbolicClass(refc); // do this before attempting to resolve
2342 Objects.requireNonNull(name);
2343 Objects.requireNonNull(type);
2344 checkMethodName(refKind, name); // NPE check on name
2345 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2346 NoSuchMethodException.class);
2347 }
2348
2349 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2350 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2351 Objects.requireNonNull(member.getName());
2352 Objects.requireNonNull(member.getType());
2353 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2354 ReflectiveOperationException.class);
2355 }
2356
2357 MemberName resolveOrNull(byte refKind, MemberName member) {
2358 // do this before attempting to resolve
2359 if (!isClassAccessible(member.getDeclaringClass())) {
2360 return null;
2361 }
2362 Objects.requireNonNull(member.getName());
2363 Objects.requireNonNull(member.getType());
2364 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2365 }
2366
2367 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2368 if (!isClassAccessible(refc)) {
2369 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2370 }
2371 }
2372
2373 boolean isClassAccessible(Class<?> refc) {
2374 Objects.requireNonNull(refc);
2375 Class<?> caller = lookupClassOrNull();
2376 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes);
2377 }
2378
2379 /** Check name for an illegal leading "<" character. */
2380 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2381 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2382 throw new NoSuchMethodException("illegal method name: "+name);
2383 }
2384
2385
2386 /**
2387 * Find my trustable caller class if m is a caller sensitive method.
2388 * If this lookup object has private access, then the caller class is the lookupClass.
2389 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2390 */
2391 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2392 Class<?> callerClass = null;
2393 if (MethodHandleNatives.isCallerSensitive(m)) {
2394 // Only lookups with private access are allowed to resolve caller-sensitive methods
2395 if (hasPrivateAccess()) {
2396 callerClass = lookupClass;
2397 } else {
2398 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2399 }
2400 }
2401 return callerClass;
2402 }
2403
2404 /**
2405 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2406 * @return {@code true} if this lookup has {@code PRIVATE} access.
2407 * @since 9
2408 */
2409 public boolean hasPrivateAccess() {
2410 return (allowedModes & PRIVATE) != 0;
2411 }
2412
2413 /**
2414 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2415 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2416 * If this lookup object has private access, then the caller class is the lookupClass.
2417 */
2418 void checkSecurityManager(Class<?> refc, MemberName m) {
2419 SecurityManager smgr = System.getSecurityManager();
2420 if (smgr == null) return;
2421 if (allowedModes == TRUSTED) return;
2422
2423 // Step 1:
2424 boolean fullPowerLookup = hasPrivateAccess();
2425 if (!fullPowerLookup ||
2426 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2427 ReflectUtil.checkPackageAccess(refc);
2428 }
2429
2430 if (m == null) { // findClass or accessClass
2431 // Step 2b:
2432 if (!fullPowerLookup) {
2433 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2434 }
2435 return;
2436 }
2437
2438 // Step 2a:
2439 if (m.isPublic()) return;
2440 if (!fullPowerLookup) {
2441 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2442 }
2443
2444 // Step 3:
2445 Class<?> defc = m.getDeclaringClass();
2446 if (!fullPowerLookup && defc != refc) {
2447 ReflectUtil.checkPackageAccess(defc);
2448 }
2449 }
2450
2451 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2452 boolean wantStatic = (refKind == REF_invokeStatic);
2453 String message;
2454 if (m.isConstructor())
2455 message = "expected a method, not a constructor";
2456 else if (!m.isMethod())
2457 message = "expected a method";
2458 else if (wantStatic != m.isStatic())
2459 message = wantStatic ? "expected a static method" : "expected a non-static method";
2460 else
2461 { checkAccess(refKind, refc, m); return; }
2462 throw m.makeAccessException(message, this);
2463 }
2464
2465 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2466 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2467 String message;
2468 if (wantStatic != m.isStatic())
2469 message = wantStatic ? "expected a static field" : "expected a non-static field";
2470 else
2471 { checkAccess(refKind, refc, m); return; }
2472 throw m.makeAccessException(message, this);
2473 }
2474
2475 /** Check public/protected/private bits on the symbolic reference class and its member. */
2476 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2477 assert(m.referenceKindIsConsistentWith(refKind) &&
2478 MethodHandleNatives.refKindIsValid(refKind) &&
2479 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2480 int allowedModes = this.allowedModes;
2481 if (allowedModes == TRUSTED) return;
2482 int mods = m.getModifiers();
2483 if (Modifier.isProtected(mods) &&
2484 refKind == REF_invokeVirtual &&
2485 m.getDeclaringClass() == Object.class &&
2486 m.getName().equals("clone") &&
2487 refc.isArray()) {
2488 // The JVM does this hack also.
2489 // (See ClassVerifier::verify_invoke_instructions
2490 // and LinkResolver::check_method_accessability.)
2491 // Because the JVM does not allow separate methods on array types,
2492 // there is no separate method for int[].clone.
2493 // All arrays simply inherit Object.clone.
2494 // But for access checking logic, we make Object.clone
2495 // (normally protected) appear to be public.
2496 // Later on, when the DirectMethodHandle is created,
2497 // its leading argument will be restricted to the
2498 // requested array type.
2499 // N.B. The return type is not adjusted, because
2500 // that is *not* the bytecode behavior.
2501 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2502 }
2503 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2504 // cannot "new" a protected ctor in a different package
2505 mods ^= Modifier.PROTECTED;
2506 }
2507 if (Modifier.isFinal(mods) &&
2508 MethodHandleNatives.refKindIsSetter(refKind))
2509 throw m.makeAccessException("unexpected set of a final field", this);
2510 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2511 if ((requestedModes & allowedModes) != 0) {
2512 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2513 mods, lookupClass(), allowedModes))
2514 return;
2515 } else {
2516 // Protected members can also be checked as if they were package-private.
2517 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2518 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2519 return;
2520 }
2521 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2522 }
2523
2524 String accessFailedMessage(Class<?> refc, MemberName m) {
2525 Class<?> defc = m.getDeclaringClass();
2526 int mods = m.getModifiers();
2527 // check the class first:
2528 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2529 (defc == refc ||
2530 Modifier.isPublic(refc.getModifiers())));
2531 if (!classOK && (allowedModes & PACKAGE) != 0) {
2532 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2533 (defc == refc ||
2534 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2535 }
2536 if (!classOK)
2537 return "class is not public";
2538 if (Modifier.isPublic(mods))
2539 return "access to public member failed"; // (how?, module not readable?)
2540 if (Modifier.isPrivate(mods))
2541 return "member is private";
2542 if (Modifier.isProtected(mods))
2543 return "member is protected";
2544 return "member is private to package";
2545 }
2546
2547 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2548 int allowedModes = this.allowedModes;
2549 if (allowedModes == TRUSTED) return;
2550 if (!hasPrivateAccess()
2551 || (specialCaller != lookupClass()
2552 // ensure non-abstract methods in superinterfaces can be special-invoked
2553 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2554 throw new MemberName(specialCaller).
2555 makeAccessException("no private access for invokespecial", this);
2556 }
2557
2558 private boolean restrictProtectedReceiver(MemberName method) {
2559 // The accessing class only has the right to use a protected member
2560 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2561 if (!method.isProtected() || method.isStatic()
2562 || allowedModes == TRUSTED
2563 || method.getDeclaringClass() == lookupClass()
2564 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2565 return false;
2566 return true;
2567 }
2568 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2569 assert(!method.isStatic());
2570 // receiver type of mh is too wide; narrow to caller
2571 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2572 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2573 }
2574 MethodType rawType = mh.type();
2575 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2576 MethodType narrowType = rawType.changeParameterType(0, caller);
2577 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2578 assert(mh.viewAsTypeChecks(narrowType, true));
2579 return mh.copyWith(narrowType, mh.form);
2580 }
2581
2582 /** Check access and get the requested method. */
2583 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2584 final boolean doRestrict = true;
2585 final boolean checkSecurity = true;
2586 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2587 }
2588 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2589 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2590 final boolean doRestrict = false;
2591 final boolean checkSecurity = true;
2592 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2593 }
2594 /** Check access and get the requested method, eliding security manager checks. */
2595 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2596 final boolean doRestrict = true;
2597 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2598 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2599 }
2600 /** Common code for all methods; do not call directly except from immediately above. */
2601 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2602 boolean checkSecurity,
2603 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
2604
2605 checkMethod(refKind, refc, method);
2606 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2607 if (checkSecurity)
2608 checkSecurityManager(refc, method);
2609 assert(!method.isMethodHandleInvoke());
2610
2611 if (refKind == REF_invokeSpecial &&
2612 refc != lookupClass() &&
2613 !refc.isInterface() &&
2614 refc != lookupClass().getSuperclass() &&
2615 refc.isAssignableFrom(lookupClass())) {
2616 assert(!method.getName().equals("<init>")); // not this code path
2617
2618 // Per JVMS 6.5, desc. of invokespecial instruction:
2619 // If the method is in a superclass of the LC,
2620 // and if our original search was above LC.super,
2621 // repeat the search (symbolic lookup) from LC.super
2622 // and continue with the direct superclass of that class,
2623 // and so forth, until a match is found or no further superclasses exist.
2624 // FIXME: MemberName.resolve should handle this instead.
2625 Class<?> refcAsSuper = lookupClass();
2626 MemberName m2;
2627 do {
2628 refcAsSuper = refcAsSuper.getSuperclass();
2629 m2 = new MemberName(refcAsSuper,
2630 method.getName(),
2631 method.getMethodType(),
2632 REF_invokeSpecial);
2633 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2634 } while (m2 == null && // no method is found yet
2635 refc != refcAsSuper); // search up to refc
2636 if (m2 == null) throw new InternalError(method.toString());
2637 method = m2;
2638 refc = refcAsSuper;
2639 // redo basic checks
2640 checkMethod(refKind, refc, method);
2641 }
2642
2643 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
2644 MethodHandle mh = dmh;
2645 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
2646 if ((doRestrict && refKind == REF_invokeSpecial) ||
2647 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2648 mh = restrictReceiver(method, dmh, lookupClass());
2649 }
2650 mh = maybeBindCaller(method, mh, boundCallerClass);
2651 mh = mh.setVarargs(method);
2652 return mh;
2653 }
2654 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2655 Class<?> boundCallerClass)
2656 throws IllegalAccessException {
2657 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2658 return mh;
2659 Class<?> hostClass = lookupClass;
2660 if (!hasPrivateAccess()) // caller must have private access
2661 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
2662 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2663 // Note: caller will apply varargs after this step happens.
2664 return cbmh;
2665 }
2666 /** Check access and get the requested field. */
2667 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2668 final boolean checkSecurity = true;
2669 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2670 }
2671 /** Check access and get the requested field, eliding security manager checks. */
2672 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2673 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2674 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2675 }
2676 /** Common code for all fields; do not call directly except from immediately above. */
2677 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2678 boolean checkSecurity) throws IllegalAccessException {
2679 checkField(refKind, refc, field);
2680 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2681 if (checkSecurity)
2682 checkSecurityManager(refc, field);
2683 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2684 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2685 restrictProtectedReceiver(field));
2686 if (doRestrict)
2687 return restrictReceiver(field, dmh, lookupClass());
2688 return dmh;
2689 }
2690 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2691 Class<?> refc, MemberName getField, MemberName putField)
2692 throws IllegalAccessException {
2693 final boolean checkSecurity = true;
2694 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2695 }
2696 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2697 Class<?> refc, MemberName getField, MemberName putField)
2698 throws IllegalAccessException {
2699 final boolean checkSecurity = false;
2700 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2701 }
2702 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2703 Class<?> refc, MemberName getField, MemberName putField,
2704 boolean checkSecurity) throws IllegalAccessException {
2705 assert getField.isStatic() == putField.isStatic();
2706 assert getField.isGetter() && putField.isSetter();
2707 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2708 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2709
2710 checkField(getRefKind, refc, getField);
2711 if (checkSecurity)
2712 checkSecurityManager(refc, getField);
2713
2714 if (!putField.isFinal()) {
2715 // A VarHandle does not support updates to final fields, any
2716 // such VarHandle to a final field will be read-only and
2717 // therefore the following write-based accessibility checks are
2718 // only required for non-final fields
2719 checkField(putRefKind, refc, putField);
2720 if (checkSecurity)
2721 checkSecurityManager(refc, putField);
2722 }
2723
2724 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2725 restrictProtectedReceiver(getField));
2726 if (doRestrict) {
2727 assert !getField.isStatic();
2728 // receiver type of VarHandle is too wide; narrow to caller
2729 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2730 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2731 }
2732 refc = lookupClass();
2733 }
2734 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2735 }
2736 /** Check access and get the requested constructor. */
2737 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2738 final boolean checkSecurity = true;
2739 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2740 }
2741 /** Check access and get the requested constructor, eliding security manager checks. */
2742 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2743 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2744 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2745 }
2746 /** Common code for all constructors; do not call directly except from immediately above. */
2747 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2748 boolean checkSecurity) throws IllegalAccessException {
2749 assert(ctor.isConstructor());
2750 checkAccess(REF_newInvokeSpecial, refc, ctor);
2751 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2752 if (checkSecurity)
2753 checkSecurityManager(refc, ctor);
2754 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2755 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2756 }
2757
2758 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2759 */
2760 /*non-public*/
2761 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2762 if (!(type instanceof Class || type instanceof MethodType))
2763 throw new InternalError("unresolved MemberName");
2764 MemberName member = new MemberName(refKind, defc, name, type);
2765 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2766 if (mh != null) {
2767 checkSymbolicClass(defc);
2768 return mh;
2769 }
2770 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2771 // Treat MethodHandle.invoke and invokeExact specially.
2772 mh = findVirtualForMH(member.getName(), member.getMethodType());
2773 if (mh != null) {
2774 return mh;
2775 }
2776 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
2777 // Treat signature-polymorphic methods on VarHandle specially.
2778 mh = findVirtualForVH(member.getName(), member.getMethodType());
2779 if (mh != null) {
2780 return mh;
2781 }
2782 }
2783 MemberName resolved = resolveOrFail(refKind, member);
2784 mh = getDirectMethodForConstant(refKind, defc, resolved);
2785 if (mh instanceof DirectMethodHandle
2786 && canBeCached(refKind, defc, resolved)) {
2787 MemberName key = mh.internalMemberName();
2788 if (key != null) {
2789 key = key.asNormalOriginal();
2790 }
2791 if (member.equals(key)) { // better safe than sorry
2792 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2793 }
2794 }
2795 return mh;
2796 }
2797 private
2798 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2799 if (refKind == REF_invokeSpecial) {
2800 return false;
2801 }
2802 if (!Modifier.isPublic(defc.getModifiers()) ||
2803 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2804 !member.isPublic() ||
2805 member.isCallerSensitive()) {
2806 return false;
2807 }
2808 ClassLoader loader = defc.getClassLoader();
2809 if (loader != null) {
2810 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2811 boolean found = false;
2812 while (sysl != null) {
2813 if (loader == sysl) { found = true; break; }
2814 sysl = sysl.getParent();
2815 }
2816 if (!found) {
2817 return false;
2818 }
2819 }
2820 try {
2821 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
2822 new MemberName(refKind, defc, member.getName(), member.getType()));
2823 if (resolved2 == null) {
2824 return false;
2825 }
2826 checkSecurityManager(defc, resolved2);
2827 } catch (SecurityException ex) {
2828 return false;
2829 }
2830 return true;
2831 }
2832 private
2833 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2834 throws ReflectiveOperationException {
2835 if (MethodHandleNatives.refKindIsField(refKind)) {
2836 return getDirectFieldNoSecurityManager(refKind, defc, member);
2837 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2838 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2839 } else if (refKind == REF_newInvokeSpecial) {
2840 return getDirectConstructorNoSecurityManager(defc, member);
2841 }
2842 // oops
2843 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2844 }
2845
2846 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2847
2848 /**
2849 * Property of a class to be defined via the
2850 * {@link Lookup#defineClass(byte[], ClassProperty[]) Lookup.defineClass} method.
2851 *
2852 * @since 12
2853 * @see Lookup#defineClass(byte[], ClassProperty[])
2854 * @see Lookup#defineClassWithClassData(byte[], Object, ClassProperty[])
2855 */
2856 public enum ClassProperty {
2857 /**
2858 * A nestmate is a class that is in the same {@linkplain Class#getNestHost nest}
2859 * of a lookup class. It has access to the private members of all
2860 * classes and interfaces in the same nest.
2861 *
2862 * @see Class#getNestHost()
2863 */
2864 NESTMATE(NESTMATE_CLASS),
2865
2866 /**
2867 * A hidden class is a class that cannot be referenced by other
2868 * classes. A Java Virtual Machine implementation may hide
2869 * the hidden frames from {@linkplain Throwable#getStackTrace()
2870 * stack traces}.
2871 *
2872 * @see Class#isHidden()
2873 * @see StackWalker.Option#SHOW_HIDDEN_FRAMES
2874 */
2875 HIDDEN(NONFINDABLE_CLASS),
2876
2877 /**
2878 * A weak class is a class that may be unloaded even if
2879 * its defining class loader is
2880 * <a href="../ref/package.html#reachability">reachable</a>.
2881 * A weak class is {@linkplain #HIDDEN hidden}.
2882 *
2883 * @jls 12.7 Unloading of Classes and Interfaces
2884 */
2885 WEAK(WEAK_CLASS);
2886
2887 /* the flag value is used by VM at define class time */
2888 final int flag;
2889 ClassProperty(int flag) {
2890 this.flag = flag;
2891 }
2892 }
2893 }
2894
2895 /**
2896 * Produces a method handle constructing arrays of a desired type,
2897 * as if by the {@code anewarray} bytecode.
2898 * The return type of the method handle will be the array type.
2899 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2900 *
2901 * <p> If the returned method handle is invoked with a negative
2902 * array size, a {@code NegativeArraySizeException} will be thrown.
2903 *
2904 * @param arrayClass an array type
2905 * @return a method handle which can create arrays of the given type
2906 * @throws NullPointerException if the argument is {@code null}
2907 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2908 * @see java.lang.reflect.Array#newInstance(Class, int)
2909 * @jvms 6.5 {@code anewarray} Instruction
2910 * @since 9
2911 */
2912 public static
2913 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2914 if (!arrayClass.isArray()) {
2915 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2916 }
2917 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2918 bindTo(arrayClass.getComponentType());
2919 return ani.asType(ani.type().changeReturnType(arrayClass));
2920 }
2921
2922 /**
2923 * Produces a method handle returning the length of an array,
2924 * as if by the {@code arraylength} bytecode.
2925 * The type of the method handle will have {@code int} as return type,
2926 * and its sole argument will be the array type.
2927 *
2928 * <p> If the returned method handle is invoked with a {@code null}
2929 * array reference, a {@code NullPointerException} will be thrown.
2930 *
2931 * @param arrayClass an array type
2932 * @return a method handle which can retrieve the length of an array of the given array type
2933 * @throws NullPointerException if the argument is {@code null}
2934 * @throws IllegalArgumentException if arrayClass is not an array type
2935 * @jvms 6.5 {@code arraylength} Instruction
2936 * @since 9
2937 */
2938 public static
2939 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2940 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2941 }
2942
2943 /**
2944 * Produces a method handle giving read access to elements of an array,
2945 * as if by the {@code aaload} bytecode.
2946 * The type of the method handle will have a return type of the array's
2947 * element type. Its first argument will be the array type,
2948 * and the second will be {@code int}.
2949 *
2950 * <p> When the returned method handle is invoked,
2951 * the array reference and array index are checked.
2952 * A {@code NullPointerException} will be thrown if the array reference
2953 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2954 * thrown if the index is negative or if it is greater than or equal to
2955 * the length of the array.
2956 *
2957 * @param arrayClass an array type
2958 * @return a method handle which can load values from the given array type
2959 * @throws NullPointerException if the argument is null
2960 * @throws IllegalArgumentException if arrayClass is not an array type
2961 * @jvms 6.5 {@code aaload} Instruction
2962 */
2963 public static
2964 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2965 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2966 }
2967
2968 /**
2969 * Produces a method handle giving write access to elements of an array,
2970 * as if by the {@code astore} bytecode.
2971 * The type of the method handle will have a void return type.
2972 * Its last argument will be the array's element type.
2973 * The first and second arguments will be the array type and int.
2974 *
2975 * <p> When the returned method handle is invoked,
2976 * the array reference and array index are checked.
2977 * A {@code NullPointerException} will be thrown if the array reference
2978 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2979 * thrown if the index is negative or if it is greater than or equal to
2980 * the length of the array.
2981 *
2982 * @param arrayClass the class of an array
2983 * @return a method handle which can store values into the array type
2984 * @throws NullPointerException if the argument is null
2985 * @throws IllegalArgumentException if arrayClass is not an array type
2986 * @jvms 6.5 {@code aastore} Instruction
2987 */
2988 public static
2989 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2990 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2991 }
2992
2993 /**
2994 * Produces a VarHandle giving access to elements of an array of type
2995 * {@code arrayClass}. The VarHandle's variable type is the component type
2996 * of {@code arrayClass} and the list of coordinate types is
2997 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2998 * corresponds to an argument that is an index into an array.
2999 * <p>
3000 * Certain access modes of the returned VarHandle are unsupported under
3001 * the following conditions:
3002 * <ul>
3003 * <li>if the component type is anything other than {@code byte},
3004 * {@code short}, {@code char}, {@code int}, {@code long},
3005 * {@code float}, or {@code double} then numeric atomic update access
3006 * modes are unsupported.
3007 * <li>if the field type is anything other than {@code boolean},
3008 * {@code byte}, {@code short}, {@code char}, {@code int} or
3009 * {@code long} then bitwise atomic update access modes are
3010 * unsupported.
3011 * </ul>
3012 * <p>
3013 * If the component type is {@code float} or {@code double} then numeric
3014 * and atomic update access modes compare values using their bitwise
3015 * representation (see {@link Float#floatToRawIntBits} and
3016 * {@link Double#doubleToRawLongBits}, respectively).
3017 *
3018 * <p> When the returned {@code VarHandle} is invoked,
3019 * the array reference and array index are checked.
3020 * A {@code NullPointerException} will be thrown if the array reference
3021 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3022 * thrown if the index is negative or if it is greater than or equal to
3023 * the length of the array.
3024 *
3025 * @apiNote
3026 * Bitwise comparison of {@code float} values or {@code double} values,
3027 * as performed by the numeric and atomic update access modes, differ
3028 * from the primitive {@code ==} operator and the {@link Float#equals}
3029 * and {@link Double#equals} methods, specifically with respect to
3030 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3031 * Care should be taken when performing a compare and set or a compare
3032 * and exchange operation with such values since the operation may
3033 * unexpectedly fail.
3034 * There are many possible NaN values that are considered to be
3035 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3036 * provided by Java can distinguish between them. Operation failure can
3037 * occur if the expected or witness value is a NaN value and it is
3038 * transformed (perhaps in a platform specific manner) into another NaN
3039 * value, and thus has a different bitwise representation (see
3040 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3041 * details).
3042 * The values {@code -0.0} and {@code +0.0} have different bitwise
3043 * representations but are considered equal when using the primitive
3044 * {@code ==} operator. Operation failure can occur if, for example, a
3045 * numeric algorithm computes an expected value to be say {@code -0.0}
3046 * and previously computed the witness value to be say {@code +0.0}.
3047 * @param arrayClass the class of an array, of type {@code T[]}
3048 * @return a VarHandle giving access to elements of an array
3049 * @throws NullPointerException if the arrayClass is null
3050 * @throws IllegalArgumentException if arrayClass is not an array type
3051 * @since 9
3052 */
3053 public static
3054 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
3055 return VarHandles.makeArrayElementHandle(arrayClass);
3056 }
3057
3058 /**
3059 * Produces a VarHandle giving access to elements of a {@code byte[]} array
3060 * viewed as if it were a different primitive array type, such as
3061 * {@code int[]} or {@code long[]}.
3062 * The VarHandle's variable type is the component type of
3063 * {@code viewArrayClass} and the list of coordinate types is
3064 * {@code (byte[], int)}, where the {@code int} coordinate type
3065 * corresponds to an argument that is an index into a {@code byte[]} array.
3066 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
3067 * array, composing bytes to or from a value of the component type of
3068 * {@code viewArrayClass} according to the given endianness.
3069 * <p>
3070 * The supported component types (variables types) are {@code short},
3071 * {@code char}, {@code int}, {@code long}, {@code float} and
3072 * {@code double}.
3073 * <p>
3074 * Access of bytes at a given index will result in an
3075 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3076 * or greater than the {@code byte[]} array length minus the size (in bytes)
3077 * of {@code T}.
3078 * <p>
3079 * Access of bytes at an index may be aligned or misaligned for {@code T},
3080 * with respect to the underlying memory address, {@code A} say, associated
3081 * with the array and index.
3082 * If access is misaligned then access for anything other than the
3083 * {@code get} and {@code set} access modes will result in an
3084 * {@code IllegalStateException}. In such cases atomic access is only
3085 * guaranteed with respect to the largest power of two that divides the GCD
3086 * of {@code A} and the size (in bytes) of {@code T}.
3087 * If access is aligned then following access modes are supported and are
3088 * guaranteed to support atomic access:
3089 * <ul>
3090 * <li>read write access modes for all {@code T}, with the exception of
3091 * access modes {@code get} and {@code set} for {@code long} and
3092 * {@code double} on 32-bit platforms.
3093 * <li>atomic update access modes for {@code int}, {@code long},
3094 * {@code float} or {@code double}.
3095 * (Future major platform releases of the JDK may support additional
3096 * types for certain currently unsupported access modes.)
3097 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3098 * (Future major platform releases of the JDK may support additional
3099 * numeric types for certain currently unsupported access modes.)
3100 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3101 * (Future major platform releases of the JDK may support additional
3102 * numeric types for certain currently unsupported access modes.)
3103 * </ul>
3104 * <p>
3105 * Misaligned access, and therefore atomicity guarantees, may be determined
3106 * for {@code byte[]} arrays without operating on a specific array. Given
3107 * an {@code index}, {@code T} and it's corresponding boxed type,
3108 * {@code T_BOX}, misalignment may be determined as follows:
3109 * <pre>{@code
3110 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3111 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
3112 * alignmentOffset(0, sizeOfT);
3113 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
3114 * boolean isMisaligned = misalignedAtIndex != 0;
3115 * }</pre>
3116 * <p>
3117 * If the variable type is {@code float} or {@code double} then atomic
3118 * update access modes compare values using their bitwise representation
3119 * (see {@link Float#floatToRawIntBits} and
3120 * {@link Double#doubleToRawLongBits}, respectively).
3121 * @param viewArrayClass the view array class, with a component type of
3122 * type {@code T}
3123 * @param byteOrder the endianness of the view array elements, as
3124 * stored in the underlying {@code byte} array
3125 * @return a VarHandle giving access to elements of a {@code byte[]} array
3126 * viewed as if elements corresponding to the components type of the view
3127 * array class
3128 * @throws NullPointerException if viewArrayClass or byteOrder is null
3129 * @throws IllegalArgumentException if viewArrayClass is not an array type
3130 * @throws UnsupportedOperationException if the component type of
3131 * viewArrayClass is not supported as a variable type
3132 * @since 9
3133 */
3134 public static
3135 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
3136 ByteOrder byteOrder) throws IllegalArgumentException {
3137 Objects.requireNonNull(byteOrder);
3138 return VarHandles.byteArrayViewHandle(viewArrayClass,
3139 byteOrder == ByteOrder.BIG_ENDIAN);
3140 }
3141
3142 /**
3143 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
3144 * viewed as if it were an array of elements of a different primitive
3145 * component type to that of {@code byte}, such as {@code int[]} or
3146 * {@code long[]}.
3147 * The VarHandle's variable type is the component type of
3148 * {@code viewArrayClass} and the list of coordinate types is
3149 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
3150 * corresponds to an argument that is an index into a {@code byte[]} array.
3151 * The returned VarHandle accesses bytes at an index in a
3152 * {@code ByteBuffer}, composing bytes to or from a value of the component
3153 * type of {@code viewArrayClass} according to the given endianness.
3154 * <p>
3155 * The supported component types (variables types) are {@code short},
3156 * {@code char}, {@code int}, {@code long}, {@code float} and
3157 * {@code double}.
3158 * <p>
3159 * Access will result in a {@code ReadOnlyBufferException} for anything
3160 * other than the read access modes if the {@code ByteBuffer} is read-only.
3161 * <p>
3162 * Access of bytes at a given index will result in an
3163 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3164 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
3165 * {@code T}.
3166 * <p>
3167 * Access of bytes at an index may be aligned or misaligned for {@code T},
3168 * with respect to the underlying memory address, {@code A} say, associated
3169 * with the {@code ByteBuffer} and index.
3170 * If access is misaligned then access for anything other than the
3171 * {@code get} and {@code set} access modes will result in an
3172 * {@code IllegalStateException}. In such cases atomic access is only
3173 * guaranteed with respect to the largest power of two that divides the GCD
3174 * of {@code A} and the size (in bytes) of {@code T}.
3175 * If access is aligned then following access modes are supported and are
3176 * guaranteed to support atomic access:
3177 * <ul>
3178 * <li>read write access modes for all {@code T}, with the exception of
3179 * access modes {@code get} and {@code set} for {@code long} and
3180 * {@code double} on 32-bit platforms.
3181 * <li>atomic update access modes for {@code int}, {@code long},
3182 * {@code float} or {@code double}.
3183 * (Future major platform releases of the JDK may support additional
3184 * types for certain currently unsupported access modes.)
3185 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3186 * (Future major platform releases of the JDK may support additional
3187 * numeric types for certain currently unsupported access modes.)
3188 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3189 * (Future major platform releases of the JDK may support additional
3190 * numeric types for certain currently unsupported access modes.)
3191 * </ul>
3192 * <p>
3193 * Misaligned access, and therefore atomicity guarantees, may be determined
3194 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
3195 * {@code index}, {@code T} and it's corresponding boxed type,
3196 * {@code T_BOX}, as follows:
3197 * <pre>{@code
3198 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3199 * ByteBuffer bb = ...
3200 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
3201 * boolean isMisaligned = misalignedAtIndex != 0;
3202 * }</pre>
3203 * <p>
3204 * If the variable type is {@code float} or {@code double} then atomic
3205 * update access modes compare values using their bitwise representation
3206 * (see {@link Float#floatToRawIntBits} and
3207 * {@link Double#doubleToRawLongBits}, respectively).
3208 * @param viewArrayClass the view array class, with a component type of
3209 * type {@code T}
3210 * @param byteOrder the endianness of the view array elements, as
3211 * stored in the underlying {@code ByteBuffer} (Note this overrides the
3212 * endianness of a {@code ByteBuffer})
3213 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
3214 * viewed as if elements corresponding to the components type of the view
3215 * array class
3216 * @throws NullPointerException if viewArrayClass or byteOrder is null
3217 * @throws IllegalArgumentException if viewArrayClass is not an array type
3218 * @throws UnsupportedOperationException if the component type of
3219 * viewArrayClass is not supported as a variable type
3220 * @since 9
3221 */
3222 public static
3223 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
3224 ByteOrder byteOrder) throws IllegalArgumentException {
3225 Objects.requireNonNull(byteOrder);
3226 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
3227 byteOrder == ByteOrder.BIG_ENDIAN);
3228 }
3229
3230
3231 /// method handle invocation (reflective style)
3232
3233 /**
3234 * Produces a method handle which will invoke any method handle of the
3235 * given {@code type}, with a given number of trailing arguments replaced by
3236 * a single trailing {@code Object[]} array.
3237 * The resulting invoker will be a method handle with the following
3238 * arguments:
3239 * <ul>
3240 * <li>a single {@code MethodHandle} target
3241 * <li>zero or more leading values (counted by {@code leadingArgCount})
3242 * <li>an {@code Object[]} array containing trailing arguments
3243 * </ul>
3244 * <p>
3245 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
3246 * the indicated {@code type}.
3247 * That is, if the target is exactly of the given {@code type}, it will behave
3248 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
3249 * is used to convert the target to the required {@code type}.
3250 * <p>
3251 * The type of the returned invoker will not be the given {@code type}, but rather
3252 * will have all parameters except the first {@code leadingArgCount}
3253 * replaced by a single array of type {@code Object[]}, which will be
3254 * the final parameter.
3255 * <p>
3256 * Before invoking its target, the invoker will spread the final array, apply
3257 * reference casts as necessary, and unbox and widen primitive arguments.
3258 * If, when the invoker is called, the supplied array argument does
3259 * not have the correct number of elements, the invoker will throw
3260 * an {@link IllegalArgumentException} instead of invoking the target.
3261 * <p>
3262 * This method is equivalent to the following code (though it may be more efficient):
3263 * <blockquote><pre>{@code
3264 MethodHandle invoker = MethodHandles.invoker(type);
3265 int spreadArgCount = type.parameterCount() - leadingArgCount;
3266 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
3267 return invoker;
3268 * }</pre></blockquote>
3269 * This method throws no reflective or security exceptions.
3270 * @param type the desired target type
3271 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
3272 * @return a method handle suitable for invoking any method handle of the given type
3273 * @throws NullPointerException if {@code type} is null
3274 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
3275 * the range from 0 to {@code type.parameterCount()} inclusive,
3276 * or if the resulting method handle's type would have
3277 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3278 */
3279 public static
3280 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
3281 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
3282 throw newIllegalArgumentException("bad argument count", leadingArgCount);
3283 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
3284 return type.invokers().spreadInvoker(leadingArgCount);
3285 }
3286
3287 /**
3288 * Produces a special <em>invoker method handle</em> which can be used to
3289 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
3290 * The resulting invoker will have a type which is
3291 * exactly equal to the desired type, except that it will accept
3292 * an additional leading argument of type {@code MethodHandle}.
3293 * <p>
3294 * This method is equivalent to the following code (though it may be more efficient):
3295 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
3296 *
3297 * <p style="font-size:smaller;">
3298 * <em>Discussion:</em>
3299 * Invoker method handles can be useful when working with variable method handles
3300 * of unknown types.
3301 * For example, to emulate an {@code invokeExact} call to a variable method
3302 * handle {@code M}, extract its type {@code T},
3303 * look up the invoker method {@code X} for {@code T},
3304 * and call the invoker method, as {@code X.invoke(T, A...)}.
3305 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
3306 * is unknown.)
3307 * If spreading, collecting, or other argument transformations are required,
3308 * they can be applied once to the invoker {@code X} and reused on many {@code M}
3309 * method handle values, as long as they are compatible with the type of {@code X}.
3310 * <p style="font-size:smaller;">
3311 * <em>(Note: The invoker method is not available via the Core Reflection API.
3312 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3313 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3314 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3315 * <p>
3316 * This method throws no reflective or security exceptions.
3317 * @param type the desired target type
3318 * @return a method handle suitable for invoking any method handle of the given type
3319 * @throws IllegalArgumentException if the resulting method handle's type would have
3320 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3321 */
3322 public static
3323 MethodHandle exactInvoker(MethodType type) {
3324 return type.invokers().exactInvoker();
3325 }
3326
3327 /**
3328 * Produces a special <em>invoker method handle</em> which can be used to
3329 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
3330 * The resulting invoker will have a type which is
3331 * exactly equal to the desired type, except that it will accept
3332 * an additional leading argument of type {@code MethodHandle}.
3333 * <p>
3334 * Before invoking its target, if the target differs from the expected type,
3335 * the invoker will apply reference casts as
3336 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
3337 * Similarly, the return value will be converted as necessary.
3338 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
3339 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
3340 * <p>
3341 * This method is equivalent to the following code (though it may be more efficient):
3342 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
3343 * <p style="font-size:smaller;">
3344 * <em>Discussion:</em>
3345 * A {@linkplain MethodType#genericMethodType general method type} is one which
3346 * mentions only {@code Object} arguments and return values.
3347 * An invoker for such a type is capable of calling any method handle
3348 * of the same arity as the general type.
3349 * <p style="font-size:smaller;">
3350 * <em>(Note: The invoker method is not available via the Core Reflection API.
3351 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3352 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3353 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3354 * <p>
3355 * This method throws no reflective or security exceptions.
3356 * @param type the desired target type
3357 * @return a method handle suitable for invoking any method handle convertible to the given type
3358 * @throws IllegalArgumentException if the resulting method handle's type would have
3359 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3360 */
3361 public static
3362 MethodHandle invoker(MethodType type) {
3363 return type.invokers().genericInvoker();
3364 }
3365
3366 /**
3367 * Produces a special <em>invoker method handle</em> which can be used to
3368 * invoke a signature-polymorphic access mode method on any VarHandle whose
3369 * associated access mode type is compatible with the given type.
3370 * The resulting invoker will have a type which is exactly equal to the
3371 * desired given type, except that it will accept an additional leading
3372 * argument of type {@code VarHandle}.
3373 *
3374 * @param accessMode the VarHandle access mode
3375 * @param type the desired target type
3376 * @return a method handle suitable for invoking an access mode method of
3377 * any VarHandle whose access mode type is of the given type.
3378 * @since 9
3379 */
3380 static public
3381 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3382 return type.invokers().varHandleMethodExactInvoker(accessMode);
3383 }
3384
3385 /**
3386 * Produces a special <em>invoker method handle</em> which can be used to
3387 * invoke a signature-polymorphic access mode method on any VarHandle whose
3388 * associated access mode type is compatible with the given type.
3389 * The resulting invoker will have a type which is exactly equal to the
3390 * desired given type, except that it will accept an additional leading
3391 * argument of type {@code VarHandle}.
3392 * <p>
3393 * Before invoking its target, if the access mode type differs from the
3394 * desired given type, the invoker will apply reference casts as necessary
3395 * and box, unbox, or widen primitive values, as if by
3396 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3397 * converted as necessary.
3398 * <p>
3399 * This method is equivalent to the following code (though it may be more
3400 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3401 *
3402 * @param accessMode the VarHandle access mode
3403 * @param type the desired target type
3404 * @return a method handle suitable for invoking an access mode method of
3405 * any VarHandle whose access mode type is convertible to the given
3406 * type.
3407 * @since 9
3408 */
3409 static public
3410 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3411 return type.invokers().varHandleMethodInvoker(accessMode);
3412 }
3413
3414 static /*non-public*/
3415 MethodHandle basicInvoker(MethodType type) {
3416 return type.invokers().basicInvoker();
3417 }
3418
3419 /// method handle modification (creation from other method handles)
3420
3421 /**
3422 * Produces a method handle which adapts the type of the
3423 * given method handle to a new type by pairwise argument and return type conversion.
3424 * The original type and new type must have the same number of arguments.
3425 * The resulting method handle is guaranteed to report a type
3426 * which is equal to the desired new type.
3427 * <p>
3428 * If the original type and new type are equal, returns target.
3429 * <p>
3430 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3431 * and some additional conversions are also applied if those conversions fail.
3432 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3433 * if possible, before or instead of any conversions done by {@code asType}:
3434 * <ul>
3435 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3436 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3437 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3438 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3439 * the boolean is converted to a byte value, 1 for true, 0 for false.
3440 * (This treatment follows the usage of the bytecode verifier.)
3441 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3442 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3443 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3444 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3445 * then a Java casting conversion (JLS 5.5) is applied.
3446 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3447 * widening and/or narrowing.)
3448 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3449 * conversion will be applied at runtime, possibly followed
3450 * by a Java casting conversion (JLS 5.5) on the primitive value,
3451 * possibly followed by a conversion from byte to boolean by testing
3452 * the low-order bit.
3453 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3454 * and if the reference is null at runtime, a zero value is introduced.
3455 * </ul>
3456 * @param target the method handle to invoke after arguments are retyped
3457 * @param newType the expected type of the new method handle
3458 * @return a method handle which delegates to the target after performing
3459 * any necessary argument conversions, and arranges for any
3460 * necessary return value conversions
3461 * @throws NullPointerException if either argument is null
3462 * @throws WrongMethodTypeException if the conversion cannot be made
3463 * @see MethodHandle#asType
3464 */
3465 public static
3466 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3467 explicitCastArgumentsChecks(target, newType);
3468 // use the asTypeCache when possible:
3469 MethodType oldType = target.type();
3470 if (oldType == newType) return target;
3471 if (oldType.explicitCastEquivalentToAsType(newType)) {
3472 return target.asFixedArity().asType(newType);
3473 }
3474 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3475 }
3476
3477 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3478 if (target.type().parameterCount() != newType.parameterCount()) {
3479 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3480 }
3481 }
3482
3483 /**
3484 * Produces a method handle which adapts the calling sequence of the
3485 * given method handle to a new type, by reordering the arguments.
3486 * The resulting method handle is guaranteed to report a type
3487 * which is equal to the desired new type.
3488 * <p>
3489 * The given array controls the reordering.
3490 * Call {@code #I} the number of incoming parameters (the value
3491 * {@code newType.parameterCount()}, and call {@code #O} the number
3492 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3493 * Then the length of the reordering array must be {@code #O},
3494 * and each element must be a non-negative number less than {@code #I}.
3495 * For every {@code N} less than {@code #O}, the {@code N}-th
3496 * outgoing argument will be taken from the {@code I}-th incoming
3497 * argument, where {@code I} is {@code reorder[N]}.
3498 * <p>
3499 * No argument or return value conversions are applied.
3500 * The type of each incoming argument, as determined by {@code newType},
3501 * must be identical to the type of the corresponding outgoing parameter
3502 * or parameters in the target method handle.
3503 * The return type of {@code newType} must be identical to the return
3504 * type of the original target.
3505 * <p>
3506 * The reordering array need not specify an actual permutation.
3507 * An incoming argument will be duplicated if its index appears
3508 * more than once in the array, and an incoming argument will be dropped
3509 * if its index does not appear in the array.
3510 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3511 * incoming arguments which are not mentioned in the reordering array
3512 * may be of any type, as determined only by {@code newType}.
3513 * <blockquote><pre>{@code
3514 import static java.lang.invoke.MethodHandles.*;
3515 import static java.lang.invoke.MethodType.*;
3516 ...
3517 MethodType intfn1 = methodType(int.class, int.class);
3518 MethodType intfn2 = methodType(int.class, int.class, int.class);
3519 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3520 assert(sub.type().equals(intfn2));
3521 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3522 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3523 assert((int)rsub.invokeExact(1, 100) == 99);
3524 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3525 assert(add.type().equals(intfn2));
3526 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3527 assert(twice.type().equals(intfn1));
3528 assert((int)twice.invokeExact(21) == 42);
3529 * }</pre></blockquote>
3530 * <p>
3531 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3532 * variable-arity method handle}, even if the original target method handle was.
3533 * @param target the method handle to invoke after arguments are reordered
3534 * @param newType the expected type of the new method handle
3535 * @param reorder an index array which controls the reordering
3536 * @return a method handle which delegates to the target after it
3537 * drops unused arguments and moves and/or duplicates the other arguments
3538 * @throws NullPointerException if any argument is null
3539 * @throws IllegalArgumentException if the index array length is not equal to
3540 * the arity of the target, or if any index array element
3541 * not a valid index for a parameter of {@code newType},
3542 * or if two corresponding parameter types in
3543 * {@code target.type()} and {@code newType} are not identical,
3544 */
3545 public static
3546 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3547 reorder = reorder.clone(); // get a private copy
3548 MethodType oldType = target.type();
3549 permuteArgumentChecks(reorder, newType, oldType);
3550 // first detect dropped arguments and handle them separately
3551 int[] originalReorder = reorder;
3552 BoundMethodHandle result = target.rebind();
3553 LambdaForm form = result.form;
3554 int newArity = newType.parameterCount();
3555 // Normalize the reordering into a real permutation,
3556 // by removing duplicates and adding dropped elements.
3557 // This somewhat improves lambda form caching, as well
3558 // as simplifying the transform by breaking it up into steps.
3559 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3560 if (ddIdx > 0) {
3561 // We found a duplicated entry at reorder[ddIdx].
3562 // Example: (x,y,z)->asList(x,y,z)
3563 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3564 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3565 // The starred element corresponds to the argument
3566 // deleted by the dupArgumentForm transform.
3567 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3568 boolean killFirst = false;
3569 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3570 // Set killFirst if the dup is larger than an intervening position.
3571 // This will remove at least one inversion from the permutation.
3572 if (dupVal > val) killFirst = true;
3573 }
3574 if (!killFirst) {
3575 srcPos = dstPos;
3576 dstPos = ddIdx;
3577 }
3578 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3579 assert (reorder[srcPos] == reorder[dstPos]);
3580 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3581 // contract the reordering by removing the element at dstPos
3582 int tailPos = dstPos + 1;
3583 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3584 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3585 } else {
3586 int dropVal = ~ddIdx, insPos = 0;
3587 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3588 // Find first element of reorder larger than dropVal.
3589 // This is where we will insert the dropVal.
3590 insPos += 1;
3591 }
3592 Class<?> ptype = newType.parameterType(dropVal);
3593 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3594 oldType = oldType.insertParameterTypes(insPos, ptype);
3595 // expand the reordering by inserting an element at insPos
3596 int tailPos = insPos + 1;
3597 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3598 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3599 reorder[insPos] = dropVal;
3600 }
3601 assert (permuteArgumentChecks(reorder, newType, oldType));
3602 }
3603 assert (reorder.length == newArity); // a perfect permutation
3604 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3605 form = form.editor().permuteArgumentsForm(1, reorder);
3606 if (newType == result.type() && form == result.internalForm())
3607 return result;
3608 return result.copyWith(newType, form);
3609 }
3610
3611 /**
3612 * Return an indication of any duplicate or omission in reorder.
3613 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3614 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3615 * Otherwise, return zero.
3616 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3617 */
3618 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3619 final int BIT_LIMIT = 63; // max number of bits in bit mask
3620 if (newArity < BIT_LIMIT) {
3621 long mask = 0;
3622 for (int i = 0; i < reorder.length; i++) {
3623 int arg = reorder[i];
3624 if (arg >= newArity) {
3625 return reorder.length;
3626 }
3627 long bit = 1L << arg;
3628 if ((mask & bit) != 0) {
3629 return i; // >0 indicates a dup
3630 }
3631 mask |= bit;
3632 }
3633 if (mask == (1L << newArity) - 1) {
3634 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3635 return 0;
3636 }
3637 // find first zero
3638 long zeroBit = Long.lowestOneBit(~mask);
3639 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3640 assert(zeroPos <= newArity);
3641 if (zeroPos == newArity) {
3642 return 0;
3643 }
3644 return ~zeroPos;
3645 } else {
3646 // same algorithm, different bit set
3647 BitSet mask = new BitSet(newArity);
3648 for (int i = 0; i < reorder.length; i++) {
3649 int arg = reorder[i];
3650 if (arg >= newArity) {
3651 return reorder.length;
3652 }
3653 if (mask.get(arg)) {
3654 return i; // >0 indicates a dup
3655 }
3656 mask.set(arg);
3657 }
3658 int zeroPos = mask.nextClearBit(0);
3659 assert(zeroPos <= newArity);
3660 if (zeroPos == newArity) {
3661 return 0;
3662 }
3663 return ~zeroPos;
3664 }
3665 }
3666
3667 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3668 if (newType.returnType() != oldType.returnType())
3669 throw newIllegalArgumentException("return types do not match",
3670 oldType, newType);
3671 if (reorder.length == oldType.parameterCount()) {
3672 int limit = newType.parameterCount();
3673 boolean bad = false;
3674 for (int j = 0; j < reorder.length; j++) {
3675 int i = reorder[j];
3676 if (i < 0 || i >= limit) {
3677 bad = true; break;
3678 }
3679 Class<?> src = newType.parameterType(i);
3680 Class<?> dst = oldType.parameterType(j);
3681 if (src != dst)
3682 throw newIllegalArgumentException("parameter types do not match after reorder",
3683 oldType, newType);
3684 }
3685 if (!bad) return true;
3686 }
3687 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3688 }
3689
3690 /**
3691 * Produces a method handle of the requested return type which returns the given
3692 * constant value every time it is invoked.
3693 * <p>
3694 * Before the method handle is returned, the passed-in value is converted to the requested type.
3695 * If the requested type is primitive, widening primitive conversions are attempted,
3696 * else reference conversions are attempted.
3697 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3698 * @param type the return type of the desired method handle
3699 * @param value the value to return
3700 * @return a method handle of the given return type and no arguments, which always returns the given value
3701 * @throws NullPointerException if the {@code type} argument is null
3702 * @throws ClassCastException if the value cannot be converted to the required return type
3703 * @throws IllegalArgumentException if the given type is {@code void.class}
3704 */
3705 public static
3706 MethodHandle constant(Class<?> type, Object value) {
3707 if (type.isPrimitive()) {
3708 if (type == void.class)
3709 throw newIllegalArgumentException("void type");
3710 Wrapper w = Wrapper.forPrimitiveType(type);
3711 value = w.convert(value, type);
3712 if (w.zero().equals(value))
3713 return zero(w, type);
3714 return insertArguments(identity(type), 0, value);
3715 } else {
3716 if (value == null)
3717 return zero(Wrapper.OBJECT, type);
3718 return identity(type).bindTo(value);
3719 }
3720 }
3721
3722 /**
3723 * Produces a method handle which returns its sole argument when invoked.
3724 * @param type the type of the sole parameter and return value of the desired method handle
3725 * @return a unary method handle which accepts and returns the given type
3726 * @throws NullPointerException if the argument is null
3727 * @throws IllegalArgumentException if the given type is {@code void.class}
3728 */
3729 public static
3730 MethodHandle identity(Class<?> type) {
3731 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3732 int pos = btw.ordinal();
3733 MethodHandle ident = IDENTITY_MHS[pos];
3734 if (ident == null) {
3735 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3736 }
3737 if (ident.type().returnType() == type)
3738 return ident;
3739 // something like identity(Foo.class); do not bother to intern these
3740 assert (btw == Wrapper.OBJECT);
3741 return makeIdentity(type);
3742 }
3743
3744 /**
3745 * Produces a constant method handle of the requested return type which
3746 * returns the default value for that type every time it is invoked.
3747 * The resulting constant method handle will have no side effects.
3748 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3749 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3750 * since {@code explicitCastArguments} converts {@code null} to default values.
3751 * @param type the expected return type of the desired method handle
3752 * @return a constant method handle that takes no arguments
3753 * and returns the default value of the given type (or void, if the type is void)
3754 * @throws NullPointerException if the argument is null
3755 * @see MethodHandles#constant
3756 * @see MethodHandles#empty
3757 * @see MethodHandles#explicitCastArguments
3758 * @since 9
3759 */
3760 public static MethodHandle zero(Class<?> type) {
3761 Objects.requireNonNull(type);
3762 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3763 }
3764
3765 private static MethodHandle identityOrVoid(Class<?> type) {
3766 return type == void.class ? zero(type) : identity(type);
3767 }
3768
3769 /**
3770 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3771 * and returns a suitable default depending on the return type.
3772 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3773 * <p>The returned method handle is equivalent to
3774 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3775 *
3776 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3777 * {@code guardWithTest(pred, target, empty(target.type())}.
3778 * @param type the type of the desired method handle
3779 * @return a constant method handle of the given type, which returns a default value of the given return type
3780 * @throws NullPointerException if the argument is null
3781 * @see MethodHandles#zero
3782 * @see MethodHandles#constant
3783 * @since 9
3784 */
3785 public static MethodHandle empty(MethodType type) {
3786 Objects.requireNonNull(type);
3787 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3788 }
3789
3790 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3791 private static MethodHandle makeIdentity(Class<?> ptype) {
3792 MethodType mtype = methodType(ptype, ptype);
3793 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3794 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3795 }
3796
3797 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3798 int pos = btw.ordinal();
3799 MethodHandle zero = ZERO_MHS[pos];
3800 if (zero == null) {
3801 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3802 }
3803 if (zero.type().returnType() == rtype)
3804 return zero;
3805 assert(btw == Wrapper.OBJECT);
3806 return makeZero(rtype);
3807 }
3808 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3809 private static MethodHandle makeZero(Class<?> rtype) {
3810 MethodType mtype = methodType(rtype);
3811 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3812 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3813 }
3814
3815 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3816 // Simulate a CAS, to avoid racy duplication of results.
3817 MethodHandle prev = cache[pos];
3818 if (prev != null) return prev;
3819 return cache[pos] = value;
3820 }
3821
3822 /**
3823 * Provides a target method handle with one or more <em>bound arguments</em>
3824 * in advance of the method handle's invocation.
3825 * The formal parameters to the target corresponding to the bound
3826 * arguments are called <em>bound parameters</em>.
3827 * Returns a new method handle which saves away the bound arguments.
3828 * When it is invoked, it receives arguments for any non-bound parameters,
3829 * binds the saved arguments to their corresponding parameters,
3830 * and calls the original target.
3831 * <p>
3832 * The type of the new method handle will drop the types for the bound
3833 * parameters from the original target type, since the new method handle
3834 * will no longer require those arguments to be supplied by its callers.
3835 * <p>
3836 * Each given argument object must match the corresponding bound parameter type.
3837 * If a bound parameter type is a primitive, the argument object
3838 * must be a wrapper, and will be unboxed to produce the primitive value.
3839 * <p>
3840 * The {@code pos} argument selects which parameters are to be bound.
3841 * It may range between zero and <i>N-L</i> (inclusively),
3842 * where <i>N</i> is the arity of the target method handle
3843 * and <i>L</i> is the length of the values array.
3844 * <p>
3845 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3846 * variable-arity method handle}, even if the original target method handle was.
3847 * @param target the method handle to invoke after the argument is inserted
3848 * @param pos where to insert the argument (zero for the first)
3849 * @param values the series of arguments to insert
3850 * @return a method handle which inserts an additional argument,
3851 * before calling the original method handle
3852 * @throws NullPointerException if the target or the {@code values} array is null
3853 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
3854 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
3855 * is the length of the values array.
3856 * @throws ClassCastException if an argument does not match the corresponding bound parameter
3857 * type.
3858 * @see MethodHandle#bindTo
3859 */
3860 public static
3861 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3862 int insCount = values.length;
3863 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3864 if (insCount == 0) return target;
3865 BoundMethodHandle result = target.rebind();
3866 for (int i = 0; i < insCount; i++) {
3867 Object value = values[i];
3868 Class<?> ptype = ptypes[pos+i];
3869 if (ptype.isPrimitive()) {
3870 result = insertArgumentPrimitive(result, pos, ptype, value);
3871 } else {
3872 value = ptype.cast(value); // throw CCE if needed
3873 result = result.bindArgumentL(pos, value);
3874 }
3875 }
3876 return result;
3877 }
3878
3879 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3880 Class<?> ptype, Object value) {
3881 Wrapper w = Wrapper.forPrimitiveType(ptype);
3882 // perform unboxing and/or primitive conversion
3883 value = w.convert(value, ptype);
3884 switch (w) {
3885 case INT: return result.bindArgumentI(pos, (int)value);
3886 case LONG: return result.bindArgumentJ(pos, (long)value);
3887 case FLOAT: return result.bindArgumentF(pos, (float)value);
3888 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3889 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3890 }
3891 }
3892
3893 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3894 MethodType oldType = target.type();
3895 int outargs = oldType.parameterCount();
3896 int inargs = outargs - insCount;
3897 if (inargs < 0)
3898 throw newIllegalArgumentException("too many values to insert");
3899 if (pos < 0 || pos > inargs)
3900 throw newIllegalArgumentException("no argument type to append");
3901 return oldType.ptypes();
3902 }
3903
3904 /**
3905 * Produces a method handle which will discard some dummy arguments
3906 * before calling some other specified <i>target</i> method handle.
3907 * The type of the new method handle will be the same as the target's type,
3908 * except it will also include the dummy argument types,
3909 * at some given position.
3910 * <p>
3911 * The {@code pos} argument may range between zero and <i>N</i>,
3912 * where <i>N</i> is the arity of the target.
3913 * If {@code pos} is zero, the dummy arguments will precede
3914 * the target's real arguments; if {@code pos} is <i>N</i>
3915 * they will come after.
3916 * <p>
3917 * <b>Example:</b>
3918 * <blockquote><pre>{@code
3919 import static java.lang.invoke.MethodHandles.*;
3920 import static java.lang.invoke.MethodType.*;
3921 ...
3922 MethodHandle cat = lookup().findVirtual(String.class,
3923 "concat", methodType(String.class, String.class));
3924 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3925 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3926 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3927 assertEquals(bigType, d0.type());
3928 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3929 * }</pre></blockquote>
3930 * <p>
3931 * This method is also equivalent to the following code:
3932 * <blockquote><pre>
3933 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3934 * </pre></blockquote>
3935 * @param target the method handle to invoke after the arguments are dropped
3936 * @param valueTypes the type(s) of the argument(s) to drop
3937 * @param pos position of first argument to drop (zero for the leftmost)
3938 * @return a method handle which drops arguments of the given types,
3939 * before calling the original method handle
3940 * @throws NullPointerException if the target is null,
3941 * or if the {@code valueTypes} list or any of its elements is null
3942 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3943 * or if {@code pos} is negative or greater than the arity of the target,
3944 * or if the new method handle's type would have too many parameters
3945 */
3946 public static
3947 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3948 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3949 }
3950
3951 private static List<Class<?>> copyTypes(Object[] array) {
3952 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3953 }
3954
3955 private static
3956 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3957 MethodType oldType = target.type(); // get NPE
3958 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3959 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3960 if (dropped == 0) return target;
3961 BoundMethodHandle result = target.rebind();
3962 LambdaForm lform = result.form;
3963 int insertFormArg = 1 + pos;
3964 for (Class<?> ptype : valueTypes) {
3965 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3966 }
3967 result = result.copyWith(newType, lform);
3968 return result;
3969 }
3970
3971 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3972 int dropped = valueTypes.size();
3973 MethodType.checkSlotCount(dropped);
3974 int outargs = oldType.parameterCount();
3975 int inargs = outargs + dropped;
3976 if (pos < 0 || pos > outargs)
3977 throw newIllegalArgumentException("no argument type to remove"
3978 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3979 );
3980 return dropped;
3981 }
3982
3983 /**
3984 * Produces a method handle which will discard some dummy arguments
3985 * before calling some other specified <i>target</i> method handle.
3986 * The type of the new method handle will be the same as the target's type,
3987 * except it will also include the dummy argument types,
3988 * at some given position.
3989 * <p>
3990 * The {@code pos} argument may range between zero and <i>N</i>,
3991 * where <i>N</i> is the arity of the target.
3992 * If {@code pos} is zero, the dummy arguments will precede
3993 * the target's real arguments; if {@code pos} is <i>N</i>
3994 * they will come after.
3995 * @apiNote
3996 * <blockquote><pre>{@code
3997 import static java.lang.invoke.MethodHandles.*;
3998 import static java.lang.invoke.MethodType.*;
3999 ...
4000 MethodHandle cat = lookup().findVirtual(String.class,
4001 "concat", methodType(String.class, String.class));
4002 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4003 MethodHandle d0 = dropArguments(cat, 0, String.class);
4004 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
4005 MethodHandle d1 = dropArguments(cat, 1, String.class);
4006 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4007 MethodHandle d2 = dropArguments(cat, 2, String.class);
4008 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4009 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4010 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4011 * }</pre></blockquote>
4012 * <p>
4013 * This method is also equivalent to the following code:
4014 * <blockquote><pre>
4015 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4016 * </pre></blockquote>
4017 * @param target the method handle to invoke after the arguments are dropped
4018 * @param valueTypes the type(s) of the argument(s) to drop
4019 * @param pos position of first argument to drop (zero for the leftmost)
4020 * @return a method handle which drops arguments of the given types,
4021 * before calling the original method handle
4022 * @throws NullPointerException if the target is null,
4023 * or if the {@code valueTypes} array or any of its elements is null
4024 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4025 * or if {@code pos} is negative or greater than the arity of the target,
4026 * or if the new method handle's type would have
4027 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4028 */
4029 public static
4030 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4031 return dropArguments0(target, pos, copyTypes(valueTypes));
4032 }
4033
4034 // private version which allows caller some freedom with error handling
4035 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4036 boolean nullOnFailure) {
4037 newTypes = copyTypes(newTypes.toArray());
4038 List<Class<?>> oldTypes = target.type().parameterList();
4039 int match = oldTypes.size();
4040 if (skip != 0) {
4041 if (skip < 0 || skip > match) {
4042 throw newIllegalArgumentException("illegal skip", skip, target);
4043 }
4044 oldTypes = oldTypes.subList(skip, match);
4045 match -= skip;
4046 }
4047 List<Class<?>> addTypes = newTypes;
4048 int add = addTypes.size();
4049 if (pos != 0) {
4050 if (pos < 0 || pos > add) {
4051 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4052 }
4053 addTypes = addTypes.subList(pos, add);
4054 add -= pos;
4055 assert(addTypes.size() == add);
4056 }
4057 // Do not add types which already match the existing arguments.
4058 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4059 if (nullOnFailure) {
4060 return null;
4061 }
4062 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
4063 }
4064 addTypes = addTypes.subList(match, add);
4065 add -= match;
4066 assert(addTypes.size() == add);
4067 // newTypes: ( P*[pos], M*[match], A*[add] )
4068 // target: ( S*[skip], M*[match] )
4069 MethodHandle adapter = target;
4070 if (add > 0) {
4071 adapter = dropArguments0(adapter, skip+ match, addTypes);
4072 }
4073 // adapter: (S*[skip], M*[match], A*[add] )
4074 if (pos > 0) {
4075 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
4076 }
4077 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
4078 return adapter;
4079 }
4080
4081 /**
4082 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
4083 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
4084 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
4085 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
4086 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
4087 * {@link #dropArguments(MethodHandle, int, Class[])}.
4088 * <p>
4089 * The resulting handle will have the same return type as the target handle.
4090 * <p>
4091 * In more formal terms, assume these two type lists:<ul>
4092 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
4093 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
4094 * {@code newTypes}.
4095 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
4096 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
4097 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
4098 * sub-list.
4099 * </ul>
4100 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
4101 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
4102 * {@link #dropArguments(MethodHandle, int, Class[])}.
4103 *
4104 * @apiNote
4105 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
4106 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
4107 * <blockquote><pre>{@code
4108 import static java.lang.invoke.MethodHandles.*;
4109 import static java.lang.invoke.MethodType.*;
4110 ...
4111 ...
4112 MethodHandle h0 = constant(boolean.class, true);
4113 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
4114 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
4115 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
4116 if (h1.type().parameterCount() < h2.type().parameterCount())
4117 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
4118 else
4119 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
4120 MethodHandle h3 = guardWithTest(h0, h1, h2);
4121 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
4122 * }</pre></blockquote>
4123 * @param target the method handle to adapt
4124 * @param skip number of targets parameters to disregard (they will be unchanged)
4125 * @param newTypes the list of types to match {@code target}'s parameter type list to
4126 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
4127 * @return a possibly adapted method handle
4128 * @throws NullPointerException if either argument is null
4129 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
4130 * or if {@code skip} is negative or greater than the arity of the target,
4131 * or if {@code pos} is negative or greater than the newTypes list size,
4132 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
4133 * {@code pos}.
4134 * @since 9
4135 */
4136 public static
4137 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
4138 Objects.requireNonNull(target);
4139 Objects.requireNonNull(newTypes);
4140 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
4141 }
4142
4143 /**
4144 * Adapts a target method handle by pre-processing
4145 * one or more of its arguments, each with its own unary filter function,
4146 * and then calling the target with each pre-processed argument
4147 * replaced by the result of its corresponding filter function.
4148 * <p>
4149 * The pre-processing is performed by one or more method handles,
4150 * specified in the elements of the {@code filters} array.
4151 * The first element of the filter array corresponds to the {@code pos}
4152 * argument of the target, and so on in sequence.
4153 * The filter functions are invoked in left to right order.
4154 * <p>
4155 * Null arguments in the array are treated as identity functions,
4156 * and the corresponding arguments left unchanged.
4157 * (If there are no non-null elements in the array, the original target is returned.)
4158 * Each filter is applied to the corresponding argument of the adapter.
4159 * <p>
4160 * If a filter {@code F} applies to the {@code N}th argument of
4161 * the target, then {@code F} must be a method handle which
4162 * takes exactly one argument. The type of {@code F}'s sole argument
4163 * replaces the corresponding argument type of the target
4164 * in the resulting adapted method handle.
4165 * The return type of {@code F} must be identical to the corresponding
4166 * parameter type of the target.
4167 * <p>
4168 * It is an error if there are elements of {@code filters}
4169 * (null or not)
4170 * which do not correspond to argument positions in the target.
4171 * <p><b>Example:</b>
4172 * <blockquote><pre>{@code
4173 import static java.lang.invoke.MethodHandles.*;
4174 import static java.lang.invoke.MethodType.*;
4175 ...
4176 MethodHandle cat = lookup().findVirtual(String.class,
4177 "concat", methodType(String.class, String.class));
4178 MethodHandle upcase = lookup().findVirtual(String.class,
4179 "toUpperCase", methodType(String.class));
4180 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4181 MethodHandle f0 = filterArguments(cat, 0, upcase);
4182 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
4183 MethodHandle f1 = filterArguments(cat, 1, upcase);
4184 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
4185 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
4186 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
4187 * }</pre></blockquote>
4188 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4189 * denotes the return type of both the {@code target} and resulting adapter.
4190 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
4191 * of the parameters and arguments that precede and follow the filter position
4192 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
4193 * values of the filtered parameters and arguments; they also represent the
4194 * return types of the {@code filter[i]} handles. The latter accept arguments
4195 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
4196 * the resulting adapter.
4197 * <blockquote><pre>{@code
4198 * T target(P... p, A[i]... a[i], B... b);
4199 * A[i] filter[i](V[i]);
4200 * T adapter(P... p, V[i]... v[i], B... b) {
4201 * return target(p..., filter[i](v[i])..., b...);
4202 * }
4203 * }</pre></blockquote>
4204 * <p>
4205 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4206 * variable-arity method handle}, even if the original target method handle was.
4207 *
4208 * @param target the method handle to invoke after arguments are filtered
4209 * @param pos the position of the first argument to filter
4210 * @param filters method handles to call initially on filtered arguments
4211 * @return method handle which incorporates the specified argument filtering logic
4212 * @throws NullPointerException if the target is null
4213 * or if the {@code filters} array is null
4214 * @throws IllegalArgumentException if a non-null element of {@code filters}
4215 * does not match a corresponding argument type of target as described above,
4216 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
4217 * or if the resulting method handle's type would have
4218 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4219 */
4220 public static
4221 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
4222 filterArgumentsCheckArity(target, pos, filters);
4223 MethodHandle adapter = target;
4224 // process filters in reverse order so that the invocation of
4225 // the resulting adapter will invoke the filters in left-to-right order
4226 for (int i = filters.length - 1; i >= 0; --i) {
4227 MethodHandle filter = filters[i];
4228 if (filter == null) continue; // ignore null elements of filters
4229 adapter = filterArgument(adapter, pos + i, filter);
4230 }
4231 return adapter;
4232 }
4233
4234 /*non-public*/ static
4235 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
4236 filterArgumentChecks(target, pos, filter);
4237 MethodType targetType = target.type();
4238 MethodType filterType = filter.type();
4239 BoundMethodHandle result = target.rebind();
4240 Class<?> newParamType = filterType.parameterType(0);
4241 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
4242 MethodType newType = targetType.changeParameterType(pos, newParamType);
4243 result = result.copyWithExtendL(newType, lform, filter);
4244 return result;
4245 }
4246
4247 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
4248 MethodType targetType = target.type();
4249 int maxPos = targetType.parameterCount();
4250 if (pos + filters.length > maxPos)
4251 throw newIllegalArgumentException("too many filters");
4252 }
4253
4254 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4255 MethodType targetType = target.type();
4256 MethodType filterType = filter.type();
4257 if (filterType.parameterCount() != 1
4258 || filterType.returnType() != targetType.parameterType(pos))
4259 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4260 }
4261
4262 /**
4263 * Adapts a target method handle by pre-processing
4264 * a sub-sequence of its arguments with a filter (another method handle).
4265 * The pre-processed arguments are replaced by the result (if any) of the
4266 * filter function.
4267 * The target is then called on the modified (usually shortened) argument list.
4268 * <p>
4269 * If the filter returns a value, the target must accept that value as
4270 * its argument in position {@code pos}, preceded and/or followed by
4271 * any arguments not passed to the filter.
4272 * If the filter returns void, the target must accept all arguments
4273 * not passed to the filter.
4274 * No arguments are reordered, and a result returned from the filter
4275 * replaces (in order) the whole subsequence of arguments originally
4276 * passed to the adapter.
4277 * <p>
4278 * The argument types (if any) of the filter
4279 * replace zero or one argument types of the target, at position {@code pos},
4280 * in the resulting adapted method handle.
4281 * The return type of the filter (if any) must be identical to the
4282 * argument type of the target at position {@code pos}, and that target argument
4283 * is supplied by the return value of the filter.
4284 * <p>
4285 * In all cases, {@code pos} must be greater than or equal to zero, and
4286 * {@code pos} must also be less than or equal to the target's arity.
4287 * <p><b>Example:</b>
4288 * <blockquote><pre>{@code
4289 import static java.lang.invoke.MethodHandles.*;
4290 import static java.lang.invoke.MethodType.*;
4291 ...
4292 MethodHandle deepToString = publicLookup()
4293 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
4294
4295 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
4296 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
4297
4298 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
4299 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
4300
4301 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
4302 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
4303 assertEquals("[top, [up, down], strange]",
4304 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
4305
4306 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
4307 assertEquals("[top, [up, down], [strange]]",
4308 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
4309
4310 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4311 assertEquals("[top, [[up, down, strange], charm], bottom]",
4312 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4313 * }</pre></blockquote>
4314 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4315 * represents the return type of the {@code target} and resulting adapter.
4316 * {@code V}/{@code v} stand for the return type and value of the
4317 * {@code filter}, which are also found in the signature and arguments of
4318 * the {@code target}, respectively, unless {@code V} is {@code void}.
4319 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4320 * and values preceding and following the collection position, {@code pos},
4321 * in the {@code target}'s signature. They also turn up in the resulting
4322 * adapter's signature and arguments, where they surround
4323 * {@code B}/{@code b}, which represent the parameter types and arguments
4324 * to the {@code filter} (if any).
4325 * <blockquote><pre>{@code
4326 * T target(A...,V,C...);
4327 * V filter(B...);
4328 * T adapter(A... a,B... b,C... c) {
4329 * V v = filter(b...);
4330 * return target(a...,v,c...);
4331 * }
4332 * // and if the filter has no arguments:
4333 * T target2(A...,V,C...);
4334 * V filter2();
4335 * T adapter2(A... a,C... c) {
4336 * V v = filter2();
4337 * return target2(a...,v,c...);
4338 * }
4339 * // and if the filter has a void return:
4340 * T target3(A...,C...);
4341 * void filter3(B...);
4342 * T adapter3(A... a,B... b,C... c) {
4343 * filter3(b...);
4344 * return target3(a...,c...);
4345 * }
4346 * }</pre></blockquote>
4347 * <p>
4348 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
4349 * one which first "folds" the affected arguments, and then drops them, in separate
4350 * steps as follows:
4351 * <blockquote><pre>{@code
4352 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4353 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4354 * }</pre></blockquote>
4355 * If the target method handle consumes no arguments besides than the result
4356 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4357 * is equivalent to {@code filterReturnValue(coll, mh)}.
4358 * If the filter method handle {@code coll} consumes one argument and produces
4359 * a non-void result, then {@code collectArguments(mh, N, coll)}
4360 * is equivalent to {@code filterArguments(mh, N, coll)}.
4361 * Other equivalences are possible but would require argument permutation.
4362 * <p>
4363 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4364 * variable-arity method handle}, even if the original target method handle was.
4365 *
4366 * @param target the method handle to invoke after filtering the subsequence of arguments
4367 * @param pos the position of the first adapter argument to pass to the filter,
4368 * and/or the target argument which receives the result of the filter
4369 * @param filter method handle to call on the subsequence of arguments
4370 * @return method handle which incorporates the specified argument subsequence filtering logic
4371 * @throws NullPointerException if either argument is null
4372 * @throws IllegalArgumentException if the return type of {@code filter}
4373 * is non-void and is not the same as the {@code pos} argument of the target,
4374 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4375 * or if the resulting method handle's type would have
4376 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4377 * @see MethodHandles#foldArguments
4378 * @see MethodHandles#filterArguments
4379 * @see MethodHandles#filterReturnValue
4380 */
4381 public static
4382 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4383 MethodType newType = collectArgumentsChecks(target, pos, filter);
4384 MethodType collectorType = filter.type();
4385 BoundMethodHandle result = target.rebind();
4386 LambdaForm lform;
4387 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4388 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4389 if (lform != null) {
4390 return result.copyWith(newType, lform);
4391 }
4392 }
4393 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4394 return result.copyWithExtendL(newType, lform, filter);
4395 }
4396
4397 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4398 MethodType targetType = target.type();
4399 MethodType filterType = filter.type();
4400 Class<?> rtype = filterType.returnType();
4401 List<Class<?>> filterArgs = filterType.parameterList();
4402 if (rtype == void.class) {
4403 return targetType.insertParameterTypes(pos, filterArgs);
4404 }
4405 if (rtype != targetType.parameterType(pos)) {
4406 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4407 }
4408 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4409 }
4410
4411 /**
4412 * Adapts a target method handle by post-processing
4413 * its return value (if any) with a filter (another method handle).
4414 * The result of the filter is returned from the adapter.
4415 * <p>
4416 * If the target returns a value, the filter must accept that value as
4417 * its only argument.
4418 * If the target returns void, the filter must accept no arguments.
4419 * <p>
4420 * The return type of the filter
4421 * replaces the return type of the target
4422 * in the resulting adapted method handle.
4423 * The argument type of the filter (if any) must be identical to the
4424 * return type of the target.
4425 * <p><b>Example:</b>
4426 * <blockquote><pre>{@code
4427 import static java.lang.invoke.MethodHandles.*;
4428 import static java.lang.invoke.MethodType.*;
4429 ...
4430 MethodHandle cat = lookup().findVirtual(String.class,
4431 "concat", methodType(String.class, String.class));
4432 MethodHandle length = lookup().findVirtual(String.class,
4433 "length", methodType(int.class));
4434 System.out.println((String) cat.invokeExact("x", "y")); // xy
4435 MethodHandle f0 = filterReturnValue(cat, length);
4436 System.out.println((int) f0.invokeExact("x", "y")); // 2
4437 * }</pre></blockquote>
4438 * <p>Here is pseudocode for the resulting adapter. In the code,
4439 * {@code T}/{@code t} represent the result type and value of the
4440 * {@code target}; {@code V}, the result type of the {@code filter}; and
4441 * {@code A}/{@code a}, the types and values of the parameters and arguments
4442 * of the {@code target} as well as the resulting adapter.
4443 * <blockquote><pre>{@code
4444 * T target(A...);
4445 * V filter(T);
4446 * V adapter(A... a) {
4447 * T t = target(a...);
4448 * return filter(t);
4449 * }
4450 * // and if the target has a void return:
4451 * void target2(A...);
4452 * V filter2();
4453 * V adapter2(A... a) {
4454 * target2(a...);
4455 * return filter2();
4456 * }
4457 * // and if the filter has a void return:
4458 * T target3(A...);
4459 * void filter3(V);
4460 * void adapter3(A... a) {
4461 * T t = target3(a...);
4462 * filter3(t);
4463 * }
4464 * }</pre></blockquote>
4465 * <p>
4466 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4467 * variable-arity method handle}, even if the original target method handle was.
4468 * @param target the method handle to invoke before filtering the return value
4469 * @param filter method handle to call on the return value
4470 * @return method handle which incorporates the specified return value filtering logic
4471 * @throws NullPointerException if either argument is null
4472 * @throws IllegalArgumentException if the argument list of {@code filter}
4473 * does not match the return type of target as described above
4474 */
4475 public static
4476 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4477 MethodType targetType = target.type();
4478 MethodType filterType = filter.type();
4479 filterReturnValueChecks(targetType, filterType);
4480 BoundMethodHandle result = target.rebind();
4481 BasicType rtype = BasicType.basicType(filterType.returnType());
4482 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4483 MethodType newType = targetType.changeReturnType(filterType.returnType());
4484 result = result.copyWithExtendL(newType, lform, filter);
4485 return result;
4486 }
4487
4488 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4489 Class<?> rtype = targetType.returnType();
4490 int filterValues = filterType.parameterCount();
4491 if (filterValues == 0
4492 ? (rtype != void.class)
4493 : (rtype != filterType.parameterType(0) || filterValues != 1))
4494 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4495 }
4496
4497 /**
4498 * Adapts a target method handle by pre-processing
4499 * some of its arguments, and then calling the target with
4500 * the result of the pre-processing, inserted into the original
4501 * sequence of arguments.
4502 * <p>
4503 * The pre-processing is performed by {@code combiner}, a second method handle.
4504 * Of the arguments passed to the adapter, the first {@code N} arguments
4505 * are copied to the combiner, which is then called.
4506 * (Here, {@code N} is defined as the parameter count of the combiner.)
4507 * After this, control passes to the target, with any result
4508 * from the combiner inserted before the original {@code N} incoming
4509 * arguments.
4510 * <p>
4511 * If the combiner returns a value, the first parameter type of the target
4512 * must be identical with the return type of the combiner, and the next
4513 * {@code N} parameter types of the target must exactly match the parameters
4514 * of the combiner.
4515 * <p>
4516 * If the combiner has a void return, no result will be inserted,
4517 * and the first {@code N} parameter types of the target
4518 * must exactly match the parameters of the combiner.
4519 * <p>
4520 * The resulting adapter is the same type as the target, except that the
4521 * first parameter type is dropped,
4522 * if it corresponds to the result of the combiner.
4523 * <p>
4524 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4525 * that either the combiner or the target does not wish to receive.
4526 * If some of the incoming arguments are destined only for the combiner,
4527 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4528 * arguments will not need to be live on the stack on entry to the
4529 * target.)
4530 * <p><b>Example:</b>
4531 * <blockquote><pre>{@code
4532 import static java.lang.invoke.MethodHandles.*;
4533 import static java.lang.invoke.MethodType.*;
4534 ...
4535 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4536 "println", methodType(void.class, String.class))
4537 .bindTo(System.out);
4538 MethodHandle cat = lookup().findVirtual(String.class,
4539 "concat", methodType(String.class, String.class));
4540 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4541 MethodHandle catTrace = foldArguments(cat, trace);
4542 // also prints "boo":
4543 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4544 * }</pre></blockquote>
4545 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4546 * represents the result type of the {@code target} and resulting adapter.
4547 * {@code V}/{@code v} represent the type and value of the parameter and argument
4548 * of {@code target} that precedes the folding position; {@code V} also is
4549 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4550 * types and values of the {@code N} parameters and arguments at the folding
4551 * position. {@code B}/{@code b} represent the types and values of the
4552 * {@code target} parameters and arguments that follow the folded parameters
4553 * and arguments.
4554 * <blockquote><pre>{@code
4555 * // there are N arguments in A...
4556 * T target(V, A[N]..., B...);
4557 * V combiner(A...);
4558 * T adapter(A... a, B... b) {
4559 * V v = combiner(a...);
4560 * return target(v, a..., b...);
4561 * }
4562 * // and if the combiner has a void return:
4563 * T target2(A[N]..., B...);
4564 * void combiner2(A...);
4565 * T adapter2(A... a, B... b) {
4566 * combiner2(a...);
4567 * return target2(a..., b...);
4568 * }
4569 * }</pre></blockquote>
4570 * <p>
4571 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4572 * variable-arity method handle}, even if the original target method handle was.
4573 * @param target the method handle to invoke after arguments are combined
4574 * @param combiner method handle to call initially on the incoming arguments
4575 * @return method handle which incorporates the specified argument folding logic
4576 * @throws NullPointerException if either argument is null
4577 * @throws IllegalArgumentException if {@code combiner}'s return type
4578 * is non-void and not the same as the first argument type of
4579 * the target, or if the initial {@code N} argument types
4580 * of the target
4581 * (skipping one matching the {@code combiner}'s return type)
4582 * are not identical with the argument types of {@code combiner}
4583 */
4584 public static
4585 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4586 return foldArguments(target, 0, combiner);
4587 }
4588
4589 /**
4590 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4591 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4592 * before the folded arguments.
4593 * <p>
4594 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4595 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4596 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4597 * 0.
4598 *
4599 * @apiNote Example:
4600 * <blockquote><pre>{@code
4601 import static java.lang.invoke.MethodHandles.*;
4602 import static java.lang.invoke.MethodType.*;
4603 ...
4604 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4605 "println", methodType(void.class, String.class))
4606 .bindTo(System.out);
4607 MethodHandle cat = lookup().findVirtual(String.class,
4608 "concat", methodType(String.class, String.class));
4609 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4610 MethodHandle catTrace = foldArguments(cat, 1, trace);
4611 // also prints "jum":
4612 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4613 * }</pre></blockquote>
4614 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4615 * represents the result type of the {@code target} and resulting adapter.
4616 * {@code V}/{@code v} represent the type and value of the parameter and argument
4617 * of {@code target} that precedes the folding position; {@code V} also is
4618 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4619 * types and values of the {@code N} parameters and arguments at the folding
4620 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4621 * and values of the {@code target} parameters and arguments that precede and
4622 * follow the folded parameters and arguments starting at {@code pos},
4623 * respectively.
4624 * <blockquote><pre>{@code
4625 * // there are N arguments in A...
4626 * T target(Z..., V, A[N]..., B...);
4627 * V combiner(A...);
4628 * T adapter(Z... z, A... a, B... b) {
4629 * V v = combiner(a...);
4630 * return target(z..., v, a..., b...);
4631 * }
4632 * // and if the combiner has a void return:
4633 * T target2(Z..., A[N]..., B...);
4634 * void combiner2(A...);
4635 * T adapter2(Z... z, A... a, B... b) {
4636 * combiner2(a...);
4637 * return target2(z..., a..., b...);
4638 * }
4639 * }</pre></blockquote>
4640 * <p>
4641 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4642 * variable-arity method handle}, even if the original target method handle was.
4643 *
4644 * @param target the method handle to invoke after arguments are combined
4645 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4646 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4647 * @param combiner method handle to call initially on the incoming arguments
4648 * @return method handle which incorporates the specified argument folding logic
4649 * @throws NullPointerException if either argument is null
4650 * @throws IllegalArgumentException if either of the following two conditions holds:
4651 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4652 * {@code pos} of the target signature;
4653 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4654 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4655 *
4656 * @see #foldArguments(MethodHandle, MethodHandle)
4657 * @since 9
4658 */
4659 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4660 MethodType targetType = target.type();
4661 MethodType combinerType = combiner.type();
4662 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4663 BoundMethodHandle result = target.rebind();
4664 boolean dropResult = rtype == void.class;
4665 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4666 MethodType newType = targetType;
4667 if (!dropResult) {
4668 newType = newType.dropParameterTypes(pos, pos + 1);
4669 }
4670 result = result.copyWithExtendL(newType, lform, combiner);
4671 return result;
4672 }
4673
4674 /**
4675 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4676 * added capability of selecting the arguments from the targets parameters
4677 * to call the combiner with. This allows us to avoid some simple cases of
4678 * permutations and padding the combiner with dropArguments to select the
4679 * right argument, which may ultimately produce fewer intermediaries.
4680 */
4681 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4682 MethodType targetType = target.type();
4683 MethodType combinerType = combiner.type();
4684 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4685 BoundMethodHandle result = target.rebind();
4686 boolean dropResult = rtype == void.class;
4687 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4688 MethodType newType = targetType;
4689 if (!dropResult) {
4690 newType = newType.dropParameterTypes(pos, pos + 1);
4691 }
4692 result = result.copyWithExtendL(newType, lform, combiner);
4693 return result;
4694 }
4695
4696 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4697 int foldArgs = combinerType.parameterCount();
4698 Class<?> rtype = combinerType.returnType();
4699 int foldVals = rtype == void.class ? 0 : 1;
4700 int afterInsertPos = foldPos + foldVals;
4701 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4702 if (ok) {
4703 for (int i = 0; i < foldArgs; i++) {
4704 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4705 ok = false;
4706 break;
4707 }
4708 }
4709 }
4710 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4711 ok = false;
4712 if (!ok)
4713 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4714 return rtype;
4715 }
4716
4717 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4718 int foldArgs = combinerType.parameterCount();
4719 if (argPos.length != foldArgs) {
4720 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4721 }
4722 Class<?> rtype = combinerType.returnType();
4723 int foldVals = rtype == void.class ? 0 : 1;
4724 boolean ok = true;
4725 for (int i = 0; i < foldArgs; i++) {
4726 int arg = argPos[i];
4727 if (arg < 0 || arg > targetType.parameterCount()) {
4728 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4729 }
4730 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4731 throw newIllegalArgumentException("target argument type at position " + arg
4732 + " must match combiner argument type at index " + i + ": " + targetType
4733 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4734 }
4735 }
4736 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4737 ok = false;
4738 }
4739 if (!ok)
4740 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4741 return rtype;
4742 }
4743
4744 /**
4745 * Makes a method handle which adapts a target method handle,
4746 * by guarding it with a test, a boolean-valued method handle.
4747 * If the guard fails, a fallback handle is called instead.
4748 * All three method handles must have the same corresponding
4749 * argument and return types, except that the return type
4750 * of the test must be boolean, and the test is allowed
4751 * to have fewer arguments than the other two method handles.
4752 * <p>
4753 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4754 * represents the uniform result type of the three involved handles;
4755 * {@code A}/{@code a}, the types and values of the {@code target}
4756 * parameters and arguments that are consumed by the {@code test}; and
4757 * {@code B}/{@code b}, those types and values of the {@code target}
4758 * parameters and arguments that are not consumed by the {@code test}.
4759 * <blockquote><pre>{@code
4760 * boolean test(A...);
4761 * T target(A...,B...);
4762 * T fallback(A...,B...);
4763 * T adapter(A... a,B... b) {
4764 * if (test(a...))
4765 * return target(a..., b...);
4766 * else
4767 * return fallback(a..., b...);
4768 * }
4769 * }</pre></blockquote>
4770 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4771 * be modified by execution of the test, and so are passed unchanged
4772 * from the caller to the target or fallback as appropriate.
4773 * @param test method handle used for test, must return boolean
4774 * @param target method handle to call if test passes
4775 * @param fallback method handle to call if test fails
4776 * @return method handle which incorporates the specified if/then/else logic
4777 * @throws NullPointerException if any argument is null
4778 * @throws IllegalArgumentException if {@code test} does not return boolean,
4779 * or if all three method types do not match (with the return
4780 * type of {@code test} changed to match that of the target).
4781 */
4782 public static
4783 MethodHandle guardWithTest(MethodHandle test,
4784 MethodHandle target,
4785 MethodHandle fallback) {
4786 MethodType gtype = test.type();
4787 MethodType ttype = target.type();
4788 MethodType ftype = fallback.type();
4789 if (!ttype.equals(ftype))
4790 throw misMatchedTypes("target and fallback types", ttype, ftype);
4791 if (gtype.returnType() != boolean.class)
4792 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4793 List<Class<?>> targs = ttype.parameterList();
4794 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4795 if (test == null) {
4796 throw misMatchedTypes("target and test types", ttype, gtype);
4797 }
4798 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4799 }
4800
4801 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4802 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4803 }
4804
4805 /**
4806 * Makes a method handle which adapts a target method handle,
4807 * by running it inside an exception handler.
4808 * If the target returns normally, the adapter returns that value.
4809 * If an exception matching the specified type is thrown, the fallback
4810 * handle is called instead on the exception, plus the original arguments.
4811 * <p>
4812 * The target and handler must have the same corresponding
4813 * argument and return types, except that handler may omit trailing arguments
4814 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4815 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4816 * <p>
4817 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4818 * represents the return type of the {@code target} and {@code handler},
4819 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4820 * the types and values of arguments to the resulting handle consumed by
4821 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4822 * resulting handle discarded by {@code handler}.
4823 * <blockquote><pre>{@code
4824 * T target(A..., B...);
4825 * T handler(ExType, A...);
4826 * T adapter(A... a, B... b) {
4827 * try {
4828 * return target(a..., b...);
4829 * } catch (ExType ex) {
4830 * return handler(ex, a...);
4831 * }
4832 * }
4833 * }</pre></blockquote>
4834 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4835 * be modified by execution of the target, and so are passed unchanged
4836 * from the caller to the handler, if the handler is invoked.
4837 * <p>
4838 * The target and handler must return the same type, even if the handler
4839 * always throws. (This might happen, for instance, because the handler
4840 * is simulating a {@code finally} clause).
4841 * To create such a throwing handler, compose the handler creation logic
4842 * with {@link #throwException throwException},
4843 * in order to create a method handle of the correct return type.
4844 * @param target method handle to call
4845 * @param exType the type of exception which the handler will catch
4846 * @param handler method handle to call if a matching exception is thrown
4847 * @return method handle which incorporates the specified try/catch logic
4848 * @throws NullPointerException if any argument is null
4849 * @throws IllegalArgumentException if {@code handler} does not accept
4850 * the given exception type, or if the method handle types do
4851 * not match in their return types and their
4852 * corresponding parameters
4853 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4854 */
4855 public static
4856 MethodHandle catchException(MethodHandle target,
4857 Class<? extends Throwable> exType,
4858 MethodHandle handler) {
4859 MethodType ttype = target.type();
4860 MethodType htype = handler.type();
4861 if (!Throwable.class.isAssignableFrom(exType))
4862 throw new ClassCastException(exType.getName());
4863 if (htype.parameterCount() < 1 ||
4864 !htype.parameterType(0).isAssignableFrom(exType))
4865 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4866 if (htype.returnType() != ttype.returnType())
4867 throw misMatchedTypes("target and handler return types", ttype, htype);
4868 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4869 if (handler == null) {
4870 throw misMatchedTypes("target and handler types", ttype, htype);
4871 }
4872 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4873 }
4874
4875 /**
4876 * Produces a method handle which will throw exceptions of the given {@code exType}.
4877 * The method handle will accept a single argument of {@code exType},
4878 * and immediately throw it as an exception.
4879 * The method type will nominally specify a return of {@code returnType}.
4880 * The return type may be anything convenient: It doesn't matter to the
4881 * method handle's behavior, since it will never return normally.
4882 * @param returnType the return type of the desired method handle
4883 * @param exType the parameter type of the desired method handle
4884 * @return method handle which can throw the given exceptions
4885 * @throws NullPointerException if either argument is null
4886 */
4887 public static
4888 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4889 if (!Throwable.class.isAssignableFrom(exType))
4890 throw new ClassCastException(exType.getName());
4891 return MethodHandleImpl.throwException(methodType(returnType, exType));
4892 }
4893
4894 /**
4895 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4896 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4897 * delivers the loop's result, which is the return value of the resulting handle.
4898 * <p>
4899 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4900 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4901 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4902 * terms of method handles, each clause will specify up to four independent actions:<ul>
4903 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4904 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4905 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4906 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4907 * </ul>
4908 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4909 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4910 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4911 * <p>
4912 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4913 * this case. See below for a detailed description.
4914 * <p>
4915 * <em>Parameters optional everywhere:</em>
4916 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4917 * As an exception, the init functions cannot take any {@code v} parameters,
4918 * because those values are not yet computed when the init functions are executed.
4919 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4920 * In fact, any clause function may take no arguments at all.
4921 * <p>
4922 * <em>Loop parameters:</em>
4923 * A clause function may take all the iteration variable values it is entitled to, in which case
4924 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4925 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4926 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4927 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4928 * init function is automatically a loop parameter {@code a}.)
4929 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4930 * These loop parameters act as loop-invariant values visible across the whole loop.
4931 * <p>
4932 * <em>Parameters visible everywhere:</em>
4933 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4934 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4935 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4936 * Most clause functions will not need all of this information, but they will be formally connected to it
4937 * as if by {@link #dropArguments}.
4938 * <a id="astar"></a>
4939 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4940 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4941 * In that notation, the general form of an init function parameter list
4942 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4943 * <p>
4944 * <em>Checking clause structure:</em>
4945 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4946 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4947 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4948 * met by the inputs to the loop combinator.
4949 * <p>
4950 * <em>Effectively identical sequences:</em>
4951 * <a id="effid"></a>
4952 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4953 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4954 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4955 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4956 * that longest list.
4957 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4958 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4959 * <p>
4960 * <em>Step 0: Determine clause structure.</em><ol type="a">
4961 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4962 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4963 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4964 * four. Padding takes place by appending elements to the array.
4965 * <li>Clauses with all {@code null}s are disregarded.
4966 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4967 * </ol>
4968 * <p>
4969 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4970 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4971 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4972 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4973 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4974 * iteration variable type.
4975 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4976 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4977 * </ol>
4978 * <p>
4979 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4980 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4981 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4982 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4983 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4984 * (These types will checked in step 2, along with all the clause function types.)
4985 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4986 * <li>All of the collected parameter lists must be effectively identical.
4987 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4988 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4989 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4990 * the "internal parameter list".
4991 * </ul>
4992 * <p>
4993 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4994 * <li>Examine fini function return types, disregarding omitted fini functions.
4995 * <li>If there are no fini functions, the loop return type is {@code void}.
4996 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4997 * type.
4998 * </ol>
4999 * <p>
5000 * <em>Step 1D: Check other types.</em><ol type="a">
5001 * <li>There must be at least one non-omitted pred function.
5002 * <li>Every non-omitted pred function must have a {@code boolean} return type.
5003 * </ol>
5004 * <p>
5005 * <em>Step 2: Determine parameter lists.</em><ol type="a">
5006 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
5007 * <li>The parameter list for init functions will be adjusted to the external parameter list.
5008 * (Note that their parameter lists are already effectively identical to this list.)
5009 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
5010 * effectively identical to the internal parameter list {@code (V... A...)}.
5011 * </ol>
5012 * <p>
5013 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
5014 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
5015 * type.
5016 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
5017 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
5018 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
5019 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
5020 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
5021 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
5022 * loop return type.
5023 * </ol>
5024 * <p>
5025 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
5026 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
5027 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
5028 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
5029 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
5030 * pad out the end of the list.
5031 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
5032 * </ol>
5033 * <p>
5034 * <em>Final observations.</em><ol type="a">
5035 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
5036 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
5037 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
5038 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
5039 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
5040 * <li>Each pair of init and step functions agrees in their return type {@code V}.
5041 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
5042 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
5043 * </ol>
5044 * <p>
5045 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
5046 * <ul>
5047 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
5048 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
5049 * (Only one {@code Pn} has to be non-{@code null}.)
5050 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
5051 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
5052 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
5053 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
5054 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
5055 * the resulting loop handle's parameter types {@code (A...)}.
5056 * </ul>
5057 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
5058 * which is natural if most of the loop computation happens in the steps. For some loops,
5059 * the burden of computation might be heaviest in the pred functions, and so the pred functions
5060 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
5061 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
5062 * where the init functions will need the extra parameters. For such reasons, the rules for
5063 * determining these parameters are as symmetric as possible, across all clause parts.
5064 * In general, the loop parameters function as common invariant values across the whole
5065 * loop, while the iteration variables function as common variant values, or (if there is
5066 * no step function) as internal loop invariant temporaries.
5067 * <p>
5068 * <em>Loop execution.</em><ol type="a">
5069 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
5070 * every clause function. These locals are loop invariant.
5071 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
5072 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
5073 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
5074 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
5075 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
5076 * (in argument order).
5077 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
5078 * returns {@code false}.
5079 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
5080 * sequence {@code (v...)} of loop variables.
5081 * The updated value is immediately visible to all subsequent function calls.
5082 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
5083 * (of type {@code R}) is returned from the loop as a whole.
5084 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
5085 * except by throwing an exception.
5086 * </ol>
5087 * <p>
5088 * <em>Usage tips.</em>
5089 * <ul>
5090 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
5091 * sometimes a step function only needs to observe the current value of its own variable.
5092 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
5093 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
5094 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
5095 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
5096 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
5097 * <li>If some of the clause functions are virtual methods on an instance, the instance
5098 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
5099 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
5100 * will be the first iteration variable value, and it will be easy to use virtual
5101 * methods as clause parts, since all of them will take a leading instance reference matching that value.
5102 * </ul>
5103 * <p>
5104 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
5105 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
5106 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
5107 * <blockquote><pre>{@code
5108 * V... init...(A...);
5109 * boolean pred...(V..., A...);
5110 * V... step...(V..., A...);
5111 * R fini...(V..., A...);
5112 * R loop(A... a) {
5113 * V... v... = init...(a...);
5114 * for (;;) {
5115 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
5116 * v = s(v..., a...);
5117 * if (!p(v..., a...)) {
5118 * return f(v..., a...);
5119 * }
5120 * }
5121 * }
5122 * }
5123 * }</pre></blockquote>
5124 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
5125 * to their full length, even though individual clause functions may neglect to take them all.
5126 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
5127 *
5128 * @apiNote Example:
5129 * <blockquote><pre>{@code
5130 * // iterative implementation of the factorial function as a loop handle
5131 * static int one(int k) { return 1; }
5132 * static int inc(int i, int acc, int k) { return i + 1; }
5133 * static int mult(int i, int acc, int k) { return i * acc; }
5134 * static boolean pred(int i, int acc, int k) { return i < k; }
5135 * static int fin(int i, int acc, int k) { return acc; }
5136 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5137 * // null initializer for counter, should initialize to 0
5138 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5139 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5140 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5141 * assertEquals(120, loop.invoke(5));
5142 * }</pre></blockquote>
5143 * The same example, dropping arguments and using combinators:
5144 * <blockquote><pre>{@code
5145 * // simplified implementation of the factorial function as a loop handle
5146 * static int inc(int i) { return i + 1; } // drop acc, k
5147 * static int mult(int i, int acc) { return i * acc; } //drop k
5148 * static boolean cmp(int i, int k) { return i < k; }
5149 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
5150 * // null initializer for counter, should initialize to 0
5151 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5152 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
5153 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
5154 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5155 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5156 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5157 * assertEquals(720, loop.invoke(6));
5158 * }</pre></blockquote>
5159 * A similar example, using a helper object to hold a loop parameter:
5160 * <blockquote><pre>{@code
5161 * // instance-based implementation of the factorial function as a loop handle
5162 * static class FacLoop {
5163 * final int k;
5164 * FacLoop(int k) { this.k = k; }
5165 * int inc(int i) { return i + 1; }
5166 * int mult(int i, int acc) { return i * acc; }
5167 * boolean pred(int i) { return i < k; }
5168 * int fin(int i, int acc) { return acc; }
5169 * }
5170 * // assume MH_FacLoop is a handle to the constructor
5171 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5172 * // null initializer for counter, should initialize to 0
5173 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5174 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
5175 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5176 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5177 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
5178 * assertEquals(5040, loop.invoke(7));
5179 * }</pre></blockquote>
5180 *
5181 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
5182 *
5183 * @return a method handle embodying the looping behavior as defined by the arguments.
5184 *
5185 * @throws IllegalArgumentException in case any of the constraints described above is violated.
5186 *
5187 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
5188 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5189 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
5190 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
5191 * @since 9
5192 */
5193 public static MethodHandle loop(MethodHandle[]... clauses) {
5194 // Step 0: determine clause structure.
5195 loopChecks0(clauses);
5196
5197 List<MethodHandle> init = new ArrayList<>();
5198 List<MethodHandle> step = new ArrayList<>();
5199 List<MethodHandle> pred = new ArrayList<>();
5200 List<MethodHandle> fini = new ArrayList<>();
5201
5202 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
5203 init.add(clause[0]); // all clauses have at least length 1
5204 step.add(clause.length <= 1 ? null : clause[1]);
5205 pred.add(clause.length <= 2 ? null : clause[2]);
5206 fini.add(clause.length <= 3 ? null : clause[3]);
5207 });
5208
5209 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
5210 final int nclauses = init.size();
5211
5212 // Step 1A: determine iteration variables (V...).
5213 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
5214 for (int i = 0; i < nclauses; ++i) {
5215 MethodHandle in = init.get(i);
5216 MethodHandle st = step.get(i);
5217 if (in == null && st == null) {
5218 iterationVariableTypes.add(void.class);
5219 } else if (in != null && st != null) {
5220 loopChecks1a(i, in, st);
5221 iterationVariableTypes.add(in.type().returnType());
5222 } else {
5223 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
5224 }
5225 }
5226 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
5227 collect(Collectors.toList());
5228
5229 // Step 1B: determine loop parameters (A...).
5230 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
5231 loopChecks1b(init, commonSuffix);
5232
5233 // Step 1C: determine loop return type.
5234 // Step 1D: check other types.
5235 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
5236 map(MethodType::returnType).findFirst().orElse(void.class);
5237 loopChecks1cd(pred, fini, loopReturnType);
5238
5239 // Step 2: determine parameter lists.
5240 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
5241 commonParameterSequence.addAll(commonSuffix);
5242 loopChecks2(step, pred, fini, commonParameterSequence);
5243
5244 // Step 3: fill in omitted functions.
5245 for (int i = 0; i < nclauses; ++i) {
5246 Class<?> t = iterationVariableTypes.get(i);
5247 if (init.get(i) == null) {
5248 init.set(i, empty(methodType(t, commonSuffix)));
5249 }
5250 if (step.get(i) == null) {
5251 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
5252 }
5253 if (pred.get(i) == null) {
5254 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
5255 }
5256 if (fini.get(i) == null) {
5257 fini.set(i, empty(methodType(t, commonParameterSequence)));
5258 }
5259 }
5260
5261 // Step 4: fill in missing parameter types.
5262 // Also convert all handles to fixed-arity handles.
5263 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
5264 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
5265 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
5266 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
5267
5268 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
5269 allMatch(pl -> pl.equals(commonSuffix));
5270 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5271 allMatch(pl -> pl.equals(commonParameterSequence));
5272
5273 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5274 }
5275
5276 private static void loopChecks0(MethodHandle[][] clauses) {
5277 if (clauses == null || clauses.length == 0) {
5278 throw newIllegalArgumentException("null or no clauses passed");
5279 }
5280 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5281 throw newIllegalArgumentException("null clauses are not allowed");
5282 }
5283 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5284 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5285 }
5286 }
5287
5288 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5289 if (in.type().returnType() != st.type().returnType()) {
5290 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5291 st.type().returnType());
5292 }
5293 }
5294
5295 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
5296 final List<Class<?>> empty = List.of();
5297 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
5298 // take only those that can contribute to a common suffix because they are longer than the prefix
5299 map(MethodHandle::type).
5300 filter(t -> t.parameterCount() > skipSize).
5301 map(MethodType::parameterList).
5302 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5303 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
5304 }
5305
5306 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
5307 final List<Class<?>> empty = List.of();
5308 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5309 }
5310
5311 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
5312 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
5313 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
5314 return longestParameterList(Arrays.asList(longest1, longest2));
5315 }
5316
5317 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
5318 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
5319 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
5320 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
5321 " (common suffix: " + commonSuffix + ")");
5322 }
5323 }
5324
5325 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
5326 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5327 anyMatch(t -> t != loopReturnType)) {
5328 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
5329 loopReturnType + ")");
5330 }
5331
5332 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5333 throw newIllegalArgumentException("no predicate found", pred);
5334 }
5335 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5336 anyMatch(t -> t != boolean.class)) {
5337 throw newIllegalArgumentException("predicates must have boolean return type", pred);
5338 }
5339 }
5340
5341 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5342 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5343 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
5344 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5345 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5346 }
5347 }
5348
5349 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
5350 return hs.stream().map(h -> {
5351 int pc = h.type().parameterCount();
5352 int tpsize = targetParams.size();
5353 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5354 }).collect(Collectors.toList());
5355 }
5356
5357 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5358 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5359 }
5360
5361 /**
5362 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5363 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5364 * <p>
5365 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5366 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5367 * evaluates to {@code true}).
5368 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5369 * <p>
5370 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5371 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5372 * and updated with the value returned from its invocation. The result of loop execution will be
5373 * the final value of the additional loop-local variable (if present).
5374 * <p>
5375 * The following rules hold for these argument handles:<ul>
5376 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5377 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5378 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5379 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5380 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5381 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5382 * It will constrain the parameter lists of the other loop parts.
5383 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5384 * list {@code (A...)} is called the <em>external parameter list</em>.
5385 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5386 * additional state variable of the loop.
5387 * The body must both accept and return a value of this type {@code V}.
5388 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5389 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5390 * <a href="MethodHandles.html#effid">effectively identical</a>
5391 * to the external parameter list {@code (A...)}.
5392 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5393 * {@linkplain #empty default value}.
5394 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5395 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5396 * effectively identical to the internal parameter list.
5397 * </ul>
5398 * <p>
5399 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5400 * <li>The loop handle's result type is the result type {@code V} of the body.
5401 * <li>The loop handle's parameter types are the types {@code (A...)},
5402 * from the external parameter list.
5403 * </ul>
5404 * <p>
5405 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5406 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5407 * passed to the loop.
5408 * <blockquote><pre>{@code
5409 * V init(A...);
5410 * boolean pred(V, A...);
5411 * V body(V, A...);
5412 * V whileLoop(A... a...) {
5413 * V v = init(a...);
5414 * while (pred(v, a...)) {
5415 * v = body(v, a...);
5416 * }
5417 * return v;
5418 * }
5419 * }</pre></blockquote>
5420 *
5421 * @apiNote Example:
5422 * <blockquote><pre>{@code
5423 * // implement the zip function for lists as a loop handle
5424 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5425 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5426 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5427 * zip.add(a.next());
5428 * zip.add(b.next());
5429 * return zip;
5430 * }
5431 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5432 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5433 * List<String> a = Arrays.asList("a", "b", "c", "d");
5434 * List<String> b = Arrays.asList("e", "f", "g", "h");
5435 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5436 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5437 * }</pre></blockquote>
5438 *
5439 *
5440 * @apiNote The implementation of this method can be expressed as follows:
5441 * <blockquote><pre>{@code
5442 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5443 * MethodHandle fini = (body.type().returnType() == void.class
5444 * ? null : identity(body.type().returnType()));
5445 * MethodHandle[]
5446 * checkExit = { null, null, pred, fini },
5447 * varBody = { init, body };
5448 * return loop(checkExit, varBody);
5449 * }
5450 * }</pre></blockquote>
5451 *
5452 * @param init optional initializer, providing the initial value of the loop variable.
5453 * May be {@code null}, implying a default initial value. See above for other constraints.
5454 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5455 * above for other constraints.
5456 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5457 * See above for other constraints.
5458 *
5459 * @return a method handle implementing the {@code while} loop as described by the arguments.
5460 * @throws IllegalArgumentException if the rules for the arguments are violated.
5461 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5462 *
5463 * @see #loop(MethodHandle[][])
5464 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5465 * @since 9
5466 */
5467 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5468 whileLoopChecks(init, pred, body);
5469 MethodHandle fini = identityOrVoid(body.type().returnType());
5470 MethodHandle[] checkExit = { null, null, pred, fini };
5471 MethodHandle[] varBody = { init, body };
5472 return loop(checkExit, varBody);
5473 }
5474
5475 /**
5476 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5477 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5478 * <p>
5479 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5480 * method will, in each iteration, first execute its body and then evaluate the predicate.
5481 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5482 * <p>
5483 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5484 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5485 * and updated with the value returned from its invocation. The result of loop execution will be
5486 * the final value of the additional loop-local variable (if present).
5487 * <p>
5488 * The following rules hold for these argument handles:<ul>
5489 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5490 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5491 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5492 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5493 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5494 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5495 * It will constrain the parameter lists of the other loop parts.
5496 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5497 * list {@code (A...)} is called the <em>external parameter list</em>.
5498 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5499 * additional state variable of the loop.
5500 * The body must both accept and return a value of this type {@code V}.
5501 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5502 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5503 * <a href="MethodHandles.html#effid">effectively identical</a>
5504 * to the external parameter list {@code (A...)}.
5505 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5506 * {@linkplain #empty default value}.
5507 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5508 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5509 * effectively identical to the internal parameter list.
5510 * </ul>
5511 * <p>
5512 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5513 * <li>The loop handle's result type is the result type {@code V} of the body.
5514 * <li>The loop handle's parameter types are the types {@code (A...)},
5515 * from the external parameter list.
5516 * </ul>
5517 * <p>
5518 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5519 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5520 * passed to the loop.
5521 * <blockquote><pre>{@code
5522 * V init(A...);
5523 * boolean pred(V, A...);
5524 * V body(V, A...);
5525 * V doWhileLoop(A... a...) {
5526 * V v = init(a...);
5527 * do {
5528 * v = body(v, a...);
5529 * } while (pred(v, a...));
5530 * return v;
5531 * }
5532 * }</pre></blockquote>
5533 *
5534 * @apiNote Example:
5535 * <blockquote><pre>{@code
5536 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5537 * static int zero(int limit) { return 0; }
5538 * static int step(int i, int limit) { return i + 1; }
5539 * static boolean pred(int i, int limit) { return i < limit; }
5540 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5541 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5542 * assertEquals(23, loop.invoke(23));
5543 * }</pre></blockquote>
5544 *
5545 *
5546 * @apiNote The implementation of this method can be expressed as follows:
5547 * <blockquote><pre>{@code
5548 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5549 * MethodHandle fini = (body.type().returnType() == void.class
5550 * ? null : identity(body.type().returnType()));
5551 * MethodHandle[] clause = { init, body, pred, fini };
5552 * return loop(clause);
5553 * }
5554 * }</pre></blockquote>
5555 *
5556 * @param init optional initializer, providing the initial value of the loop variable.
5557 * May be {@code null}, implying a default initial value. See above for other constraints.
5558 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5559 * See above for other constraints.
5560 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5561 * above for other constraints.
5562 *
5563 * @return a method handle implementing the {@code while} loop as described by the arguments.
5564 * @throws IllegalArgumentException if the rules for the arguments are violated.
5565 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5566 *
5567 * @see #loop(MethodHandle[][])
5568 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5569 * @since 9
5570 */
5571 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5572 whileLoopChecks(init, pred, body);
5573 MethodHandle fini = identityOrVoid(body.type().returnType());
5574 MethodHandle[] clause = {init, body, pred, fini };
5575 return loop(clause);
5576 }
5577
5578 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5579 Objects.requireNonNull(pred);
5580 Objects.requireNonNull(body);
5581 MethodType bodyType = body.type();
5582 Class<?> returnType = bodyType.returnType();
5583 List<Class<?>> innerList = bodyType.parameterList();
5584 List<Class<?>> outerList = innerList;
5585 if (returnType == void.class) {
5586 // OK
5587 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5588 // leading V argument missing => error
5589 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5590 throw misMatchedTypes("body function", bodyType, expected);
5591 } else {
5592 outerList = innerList.subList(1, innerList.size());
5593 }
5594 MethodType predType = pred.type();
5595 if (predType.returnType() != boolean.class ||
5596 !predType.effectivelyIdenticalParameters(0, innerList)) {
5597 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5598 }
5599 if (init != null) {
5600 MethodType initType = init.type();
5601 if (initType.returnType() != returnType ||
5602 !initType.effectivelyIdenticalParameters(0, outerList)) {
5603 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5604 }
5605 }
5606 }
5607
5608 /**
5609 * Constructs a loop that runs a given number of iterations.
5610 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5611 * <p>
5612 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5613 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5614 * It will be initialized to 0 and incremented by 1 in each iteration.
5615 * <p>
5616 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5617 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5618 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5619 * <p>
5620 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5621 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5622 * iteration variable.
5623 * The result of the loop handle execution will be the final {@code V} value of that variable
5624 * (or {@code void} if there is no {@code V} variable).
5625 * <p>
5626 * The following rules hold for the argument handles:<ul>
5627 * <li>The {@code iterations} handle must not be {@code null}, and must return
5628 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5629 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5630 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5631 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5632 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5633 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5634 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5635 * of types called the <em>internal parameter list</em>.
5636 * It will constrain the parameter lists of the other loop parts.
5637 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5638 * with no additional {@code A} types, then the internal parameter list is extended by
5639 * the argument types {@code A...} of the {@code iterations} handle.
5640 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5641 * list {@code (A...)} is called the <em>external parameter list</em>.
5642 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5643 * additional state variable of the loop.
5644 * The body must both accept a leading parameter and return a value of this type {@code V}.
5645 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5646 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5647 * <a href="MethodHandles.html#effid">effectively identical</a>
5648 * to the external parameter list {@code (A...)}.
5649 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5650 * {@linkplain #empty default value}.
5651 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5652 * effectively identical to the external parameter list {@code (A...)}.
5653 * </ul>
5654 * <p>
5655 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5656 * <li>The loop handle's result type is the result type {@code V} of the body.
5657 * <li>The loop handle's parameter types are the types {@code (A...)},
5658 * from the external parameter list.
5659 * </ul>
5660 * <p>
5661 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5662 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5663 * arguments passed to the loop.
5664 * <blockquote><pre>{@code
5665 * int iterations(A...);
5666 * V init(A...);
5667 * V body(V, int, A...);
5668 * V countedLoop(A... a...) {
5669 * int end = iterations(a...);
5670 * V v = init(a...);
5671 * for (int i = 0; i < end; ++i) {
5672 * v = body(v, i, a...);
5673 * }
5674 * return v;
5675 * }
5676 * }</pre></blockquote>
5677 *
5678 * @apiNote Example with a fully conformant body method:
5679 * <blockquote><pre>{@code
5680 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5681 * // => a variation on a well known theme
5682 * static String step(String v, int counter, String init) { return "na " + v; }
5683 * // assume MH_step is a handle to the method above
5684 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5685 * MethodHandle start = MethodHandles.identity(String.class);
5686 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5687 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5688 * }</pre></blockquote>
5689 *
5690 * @apiNote Example with the simplest possible body method type,
5691 * and passing the number of iterations to the loop invocation:
5692 * <blockquote><pre>{@code
5693 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5694 * // => a variation on a well known theme
5695 * static String step(String v, int counter ) { return "na " + v; }
5696 * // assume MH_step is a handle to the method above
5697 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5698 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5699 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5700 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5701 * }</pre></blockquote>
5702 *
5703 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5704 * as loop parameters:
5705 * <blockquote><pre>{@code
5706 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5707 * // => a variation on a well known theme
5708 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5709 * // assume MH_step is a handle to the method above
5710 * MethodHandle count = MethodHandles.identity(int.class);
5711 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5712 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5713 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5714 * }</pre></blockquote>
5715 *
5716 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5717 * to enforce a loop type:
5718 * <blockquote><pre>{@code
5719 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5720 * // => a variation on a well known theme
5721 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5722 * // assume MH_step is a handle to the method above
5723 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5724 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5725 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5726 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5727 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5728 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5729 * }</pre></blockquote>
5730 *
5731 * @apiNote The implementation of this method can be expressed as follows:
5732 * <blockquote><pre>{@code
5733 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5734 * return countedLoop(empty(iterations.type()), iterations, init, body);
5735 * }
5736 * }</pre></blockquote>
5737 *
5738 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5739 * result type must be {@code int}. See above for other constraints.
5740 * @param init optional initializer, providing the initial value of the loop variable.
5741 * May be {@code null}, implying a default initial value. See above for other constraints.
5742 * @param body body of the loop, which may not be {@code null}.
5743 * It controls the loop parameters and result type in the standard case (see above for details).
5744 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5745 * and may accept any number of additional types.
5746 * See above for other constraints.
5747 *
5748 * @return a method handle representing the loop.
5749 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5750 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5751 *
5752 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5753 * @since 9
5754 */
5755 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5756 return countedLoop(empty(iterations.type()), iterations, init, body);
5757 }
5758
5759 /**
5760 * Constructs a loop that counts over a range of numbers.
5761 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5762 * <p>
5763 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5764 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5765 * values of the loop counter.
5766 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5767 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5768 * <p>
5769 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5770 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5771 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5772 * <p>
5773 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5774 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5775 * iteration variable.
5776 * The result of the loop handle execution will be the final {@code V} value of that variable
5777 * (or {@code void} if there is no {@code V} variable).
5778 * <p>
5779 * The following rules hold for the argument handles:<ul>
5780 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5781 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5782 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5783 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5784 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5785 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5786 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5787 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5788 * of types called the <em>internal parameter list</em>.
5789 * It will constrain the parameter lists of the other loop parts.
5790 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5791 * with no additional {@code A} types, then the internal parameter list is extended by
5792 * the argument types {@code A...} of the {@code end} handle.
5793 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5794 * list {@code (A...)} is called the <em>external parameter list</em>.
5795 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5796 * additional state variable of the loop.
5797 * The body must both accept a leading parameter and return a value of this type {@code V}.
5798 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5799 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5800 * <a href="MethodHandles.html#effid">effectively identical</a>
5801 * to the external parameter list {@code (A...)}.
5802 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5803 * {@linkplain #empty default value}.
5804 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5805 * effectively identical to the external parameter list {@code (A...)}.
5806 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5807 * to the external parameter list.
5808 * </ul>
5809 * <p>
5810 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5811 * <li>The loop handle's result type is the result type {@code V} of the body.
5812 * <li>The loop handle's parameter types are the types {@code (A...)},
5813 * from the external parameter list.
5814 * </ul>
5815 * <p>
5816 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5817 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5818 * arguments passed to the loop.
5819 * <blockquote><pre>{@code
5820 * int start(A...);
5821 * int end(A...);
5822 * V init(A...);
5823 * V body(V, int, A...);
5824 * V countedLoop(A... a...) {
5825 * int e = end(a...);
5826 * int s = start(a...);
5827 * V v = init(a...);
5828 * for (int i = s; i < e; ++i) {
5829 * v = body(v, i, a...);
5830 * }
5831 * return v;
5832 * }
5833 * }</pre></blockquote>
5834 *
5835 * @apiNote The implementation of this method can be expressed as follows:
5836 * <blockquote><pre>{@code
5837 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5838 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5839 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5840 * // the following semantics:
5841 * // MH_increment: (int limit, int counter) -> counter + 1
5842 * // MH_predicate: (int limit, int counter) -> counter < limit
5843 * Class<?> counterType = start.type().returnType(); // int
5844 * Class<?> returnType = body.type().returnType();
5845 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5846 * if (returnType != void.class) { // ignore the V variable
5847 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5848 * pred = dropArguments(pred, 1, returnType); // ditto
5849 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5850 * }
5851 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5852 * MethodHandle[]
5853 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5854 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5855 * indexVar = { start, incr }; // i = start(); i = i + 1
5856 * return loop(loopLimit, bodyClause, indexVar);
5857 * }
5858 * }</pre></blockquote>
5859 *
5860 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5861 * See above for other constraints.
5862 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5863 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5864 * @param init optional initializer, providing the initial value of the loop variable.
5865 * May be {@code null}, implying a default initial value. See above for other constraints.
5866 * @param body body of the loop, which may not be {@code null}.
5867 * It controls the loop parameters and result type in the standard case (see above for details).
5868 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5869 * and may accept any number of additional types.
5870 * See above for other constraints.
5871 *
5872 * @return a method handle representing the loop.
5873 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5874 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5875 *
5876 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5877 * @since 9
5878 */
5879 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5880 countedLoopChecks(start, end, init, body);
5881 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5882 Class<?> limitType = end.type().returnType(); // yes, int again
5883 Class<?> returnType = body.type().returnType();
5884 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5885 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5886 MethodHandle retv = null;
5887 if (returnType != void.class) {
5888 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5889 pred = dropArguments(pred, 1, returnType); // ditto
5890 retv = dropArguments(identity(returnType), 0, counterType);
5891 }
5892 body = dropArguments(body, 0, counterType); // ignore the limit variable
5893 MethodHandle[]
5894 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5895 bodyClause = { init, body }, // v = init(); v = body(v, i)
5896 indexVar = { start, incr }; // i = start(); i = i + 1
5897 return loop(loopLimit, bodyClause, indexVar);
5898 }
5899
5900 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5901 Objects.requireNonNull(start);
5902 Objects.requireNonNull(end);
5903 Objects.requireNonNull(body);
5904 Class<?> counterType = start.type().returnType();
5905 if (counterType != int.class) {
5906 MethodType expected = start.type().changeReturnType(int.class);
5907 throw misMatchedTypes("start function", start.type(), expected);
5908 } else if (end.type().returnType() != counterType) {
5909 MethodType expected = end.type().changeReturnType(counterType);
5910 throw misMatchedTypes("end function", end.type(), expected);
5911 }
5912 MethodType bodyType = body.type();
5913 Class<?> returnType = bodyType.returnType();
5914 List<Class<?>> innerList = bodyType.parameterList();
5915 // strip leading V value if present
5916 int vsize = (returnType == void.class ? 0 : 1);
5917 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5918 // argument list has no "V" => error
5919 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5920 throw misMatchedTypes("body function", bodyType, expected);
5921 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5922 // missing I type => error
5923 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5924 throw misMatchedTypes("body function", bodyType, expected);
5925 }
5926 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5927 if (outerList.isEmpty()) {
5928 // special case; take lists from end handle
5929 outerList = end.type().parameterList();
5930 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5931 }
5932 MethodType expected = methodType(counterType, outerList);
5933 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5934 throw misMatchedTypes("start parameter types", start.type(), expected);
5935 }
5936 if (end.type() != start.type() &&
5937 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5938 throw misMatchedTypes("end parameter types", end.type(), expected);
5939 }
5940 if (init != null) {
5941 MethodType initType = init.type();
5942 if (initType.returnType() != returnType ||
5943 !initType.effectivelyIdenticalParameters(0, outerList)) {
5944 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5945 }
5946 }
5947 }
5948
5949 /**
5950 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5951 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5952 * <p>
5953 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5954 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5955 * <p>
5956 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5957 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5958 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5959 * <p>
5960 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5961 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5962 * iteration variable.
5963 * The result of the loop handle execution will be the final {@code V} value of that variable
5964 * (or {@code void} if there is no {@code V} variable).
5965 * <p>
5966 * The following rules hold for the argument handles:<ul>
5967 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5968 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5969 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5970 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5971 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5972 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5973 * of types called the <em>internal parameter list</em>.
5974 * It will constrain the parameter lists of the other loop parts.
5975 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5976 * with no additional {@code A} types, then the internal parameter list is extended by
5977 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5978 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5979 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5980 * list {@code (A...)} is called the <em>external parameter list</em>.
5981 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5982 * additional state variable of the loop.
5983 * The body must both accept a leading parameter and return a value of this type {@code V}.
5984 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5985 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5986 * <a href="MethodHandles.html#effid">effectively identical</a>
5987 * to the external parameter list {@code (A...)}.
5988 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5989 * {@linkplain #empty default value}.
5990 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5991 * type {@code java.util.Iterator} or a subtype thereof.
5992 * The iterator it produces when the loop is executed will be assumed
5993 * to yield values which can be converted to type {@code T}.
5994 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5995 * effectively identical to the external parameter list {@code (A...)}.
5996 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5997 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5998 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5999 * handle parameter is adjusted to accept the leading {@code A} type, as if by
6000 * the {@link MethodHandle#asType asType} conversion method.
6001 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
6002 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
6003 * </ul>
6004 * <p>
6005 * The type {@code T} may be either a primitive or reference.
6006 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
6007 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
6008 * as if by the {@link MethodHandle#asType asType} conversion method.
6009 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
6010 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
6011 * <p>
6012 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6013 * <li>The loop handle's result type is the result type {@code V} of the body.
6014 * <li>The loop handle's parameter types are the types {@code (A...)},
6015 * from the external parameter list.
6016 * </ul>
6017 * <p>
6018 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6019 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
6020 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
6021 * <blockquote><pre>{@code
6022 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
6023 * V init(A...);
6024 * V body(V,T,A...);
6025 * V iteratedLoop(A... a...) {
6026 * Iterator<T> it = iterator(a...);
6027 * V v = init(a...);
6028 * while (it.hasNext()) {
6029 * T t = it.next();
6030 * v = body(v, t, a...);
6031 * }
6032 * return v;
6033 * }
6034 * }</pre></blockquote>
6035 *
6036 * @apiNote Example:
6037 * <blockquote><pre>{@code
6038 * // get an iterator from a list
6039 * static List<String> reverseStep(List<String> r, String e) {
6040 * r.add(0, e);
6041 * return r;
6042 * }
6043 * static List<String> newArrayList() { return new ArrayList<>(); }
6044 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
6045 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
6046 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
6047 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
6048 * assertEquals(reversedList, (List<String>) loop.invoke(list));
6049 * }</pre></blockquote>
6050 *
6051 * @apiNote The implementation of this method can be expressed approximately as follows:
6052 * <blockquote><pre>{@code
6053 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6054 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
6055 * Class<?> returnType = body.type().returnType();
6056 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6057 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
6058 * MethodHandle retv = null, step = body, startIter = iterator;
6059 * if (returnType != void.class) {
6060 * // the simple thing first: in (I V A...), drop the I to get V
6061 * retv = dropArguments(identity(returnType), 0, Iterator.class);
6062 * // body type signature (V T A...), internal loop types (I V A...)
6063 * step = swapArguments(body, 0, 1); // swap V <-> T
6064 * }
6065 * if (startIter == null) startIter = MH_getIter;
6066 * MethodHandle[]
6067 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
6068 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
6069 * return loop(iterVar, bodyClause);
6070 * }
6071 * }</pre></blockquote>
6072 *
6073 * @param iterator an optional handle to return the iterator to start the loop.
6074 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
6075 * See above for other constraints.
6076 * @param init optional initializer, providing the initial value of the loop variable.
6077 * May be {@code null}, implying a default initial value. See above for other constraints.
6078 * @param body body of the loop, which may not be {@code null}.
6079 * It controls the loop parameters and result type in the standard case (see above for details).
6080 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
6081 * and may accept any number of additional types.
6082 * See above for other constraints.
6083 *
6084 * @return a method handle embodying the iteration loop functionality.
6085 * @throws NullPointerException if the {@code body} handle is {@code null}.
6086 * @throws IllegalArgumentException if any argument violates the above requirements.
6087 *
6088 * @since 9
6089 */
6090 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6091 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
6092 Class<?> returnType = body.type().returnType();
6093 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
6094 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
6095 MethodHandle startIter;
6096 MethodHandle nextVal;
6097 {
6098 MethodType iteratorType;
6099 if (iterator == null) {
6100 // derive argument type from body, if available, else use Iterable
6101 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
6102 iteratorType = startIter.type().changeParameterType(0, iterableType);
6103 } else {
6104 // force return type to the internal iterator class
6105 iteratorType = iterator.type().changeReturnType(Iterator.class);
6106 startIter = iterator;
6107 }
6108 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6109 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
6110
6111 // perform the asType transforms under an exception transformer, as per spec.:
6112 try {
6113 startIter = startIter.asType(iteratorType);
6114 nextVal = nextRaw.asType(nextValType);
6115 } catch (WrongMethodTypeException ex) {
6116 throw new IllegalArgumentException(ex);
6117 }
6118 }
6119
6120 MethodHandle retv = null, step = body;
6121 if (returnType != void.class) {
6122 // the simple thing first: in (I V A...), drop the I to get V
6123 retv = dropArguments(identity(returnType), 0, Iterator.class);
6124 // body type signature (V T A...), internal loop types (I V A...)
6125 step = swapArguments(body, 0, 1); // swap V <-> T
6126 }
6127
6128 MethodHandle[]
6129 iterVar = { startIter, null, hasNext, retv },
6130 bodyClause = { init, filterArgument(step, 0, nextVal) };
6131 return loop(iterVar, bodyClause);
6132 }
6133
6134 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6135 Objects.requireNonNull(body);
6136 MethodType bodyType = body.type();
6137 Class<?> returnType = bodyType.returnType();
6138 List<Class<?>> internalParamList = bodyType.parameterList();
6139 // strip leading V value if present
6140 int vsize = (returnType == void.class ? 0 : 1);
6141 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
6142 // argument list has no "V" => error
6143 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6144 throw misMatchedTypes("body function", bodyType, expected);
6145 } else if (internalParamList.size() <= vsize) {
6146 // missing T type => error
6147 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
6148 throw misMatchedTypes("body function", bodyType, expected);
6149 }
6150 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
6151 Class<?> iterableType = null;
6152 if (iterator != null) {
6153 // special case; if the body handle only declares V and T then
6154 // the external parameter list is obtained from iterator handle
6155 if (externalParamList.isEmpty()) {
6156 externalParamList = iterator.type().parameterList();
6157 }
6158 MethodType itype = iterator.type();
6159 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
6160 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
6161 }
6162 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
6163 MethodType expected = methodType(itype.returnType(), externalParamList);
6164 throw misMatchedTypes("iterator parameters", itype, expected);
6165 }
6166 } else {
6167 if (externalParamList.isEmpty()) {
6168 // special case; if the iterator handle is null and the body handle
6169 // only declares V and T then the external parameter list consists
6170 // of Iterable
6171 externalParamList = Arrays.asList(Iterable.class);
6172 iterableType = Iterable.class;
6173 } else {
6174 // special case; if the iterator handle is null and the external
6175 // parameter list is not empty then the first parameter must be
6176 // assignable to Iterable
6177 iterableType = externalParamList.get(0);
6178 if (!Iterable.class.isAssignableFrom(iterableType)) {
6179 throw newIllegalArgumentException(
6180 "inferred first loop argument must inherit from Iterable: " + iterableType);
6181 }
6182 }
6183 }
6184 if (init != null) {
6185 MethodType initType = init.type();
6186 if (initType.returnType() != returnType ||
6187 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
6188 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
6189 }
6190 }
6191 return iterableType; // help the caller a bit
6192 }
6193
6194 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
6195 // there should be a better way to uncross my wires
6196 int arity = mh.type().parameterCount();
6197 int[] order = new int[arity];
6198 for (int k = 0; k < arity; k++) order[k] = k;
6199 order[i] = j; order[j] = i;
6200 Class<?>[] types = mh.type().parameterArray();
6201 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
6202 MethodType swapType = methodType(mh.type().returnType(), types);
6203 return permuteArguments(mh, swapType, order);
6204 }
6205
6206 /**
6207 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
6208 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
6209 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
6210 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
6211 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
6212 * {@code try-finally} handle.
6213 * <p>
6214 * The {@code cleanup} handle will be passed one or two additional leading arguments.
6215 * The first is the exception thrown during the
6216 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
6217 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
6218 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
6219 * The second argument is not present if the {@code target} handle has a {@code void} return type.
6220 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
6221 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
6222 * <p>
6223 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
6224 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
6225 * two extra leading parameters:<ul>
6226 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
6227 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
6228 * the result from the execution of the {@code target} handle.
6229 * This parameter is not present if the {@code target} returns {@code void}.
6230 * </ul>
6231 * <p>
6232 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
6233 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
6234 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
6235 * the cleanup.
6236 * <blockquote><pre>{@code
6237 * V target(A..., B...);
6238 * V cleanup(Throwable, V, A...);
6239 * V adapter(A... a, B... b) {
6240 * V result = (zero value for V);
6241 * Throwable throwable = null;
6242 * try {
6243 * result = target(a..., b...);
6244 * } catch (Throwable t) {
6245 * throwable = t;
6246 * throw t;
6247 * } finally {
6248 * result = cleanup(throwable, result, a...);
6249 * }
6250 * return result;
6251 * }
6252 * }</pre></blockquote>
6253 * <p>
6254 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6255 * be modified by execution of the target, and so are passed unchanged
6256 * from the caller to the cleanup, if it is invoked.
6257 * <p>
6258 * The target and cleanup must return the same type, even if the cleanup
6259 * always throws.
6260 * To create such a throwing cleanup, compose the cleanup logic
6261 * with {@link #throwException throwException},
6262 * in order to create a method handle of the correct return type.
6263 * <p>
6264 * Note that {@code tryFinally} never converts exceptions into normal returns.
6265 * In rare cases where exceptions must be converted in that way, first wrap
6266 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
6267 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
6268 * <p>
6269 * It is recommended that the first parameter type of {@code cleanup} be
6270 * declared {@code Throwable} rather than a narrower subtype. This ensures
6271 * {@code cleanup} will always be invoked with whatever exception that
6272 * {@code target} throws. Declaring a narrower type may result in a
6273 * {@code ClassCastException} being thrown by the {@code try-finally}
6274 * handle if the type of the exception thrown by {@code target} is not
6275 * assignable to the first parameter type of {@code cleanup}. Note that
6276 * various exception types of {@code VirtualMachineError},
6277 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6278 * thrown by almost any kind of Java code, and a finally clause that
6279 * catches (say) only {@code IOException} would mask any of the others
6280 * behind a {@code ClassCastException}.
6281 *
6282 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6283 * @param cleanup the handle that is invoked in the finally block.
6284 *
6285 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6286 * @throws NullPointerException if any argument is null
6287 * @throws IllegalArgumentException if {@code cleanup} does not accept
6288 * the required leading arguments, or if the method handle types do
6289 * not match in their return types and their
6290 * corresponding trailing parameters
6291 *
6292 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
6293 * @since 9
6294 */
6295 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
6296 List<Class<?>> targetParamTypes = target.type().parameterList();
6297 Class<?> rtype = target.type().returnType();
6298
6299 tryFinallyChecks(target, cleanup);
6300
6301 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
6302 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6303 // target parameter list.
6304 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
6305
6306 // Ensure that the intrinsic type checks the instance thrown by the
6307 // target against the first parameter of cleanup
6308 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
6309
6310 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
6311 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
6312 }
6313
6314 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
6315 Class<?> rtype = target.type().returnType();
6316 if (rtype != cleanup.type().returnType()) {
6317 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
6318 }
6319 MethodType cleanupType = cleanup.type();
6320 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
6321 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
6322 }
6323 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
6324 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
6325 }
6326 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6327 // target parameter list.
6328 int cleanupArgIndex = rtype == void.class ? 1 : 2;
6329 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
6330 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
6331 cleanup.type(), target.type());
6332 }
6333 }
6334
6335 }