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