1 /*
2 * Copyright (c) 2008, 2019, 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.access.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.Set;
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.MethodHandleImpl.Intrinsic;
63 import static java.lang.invoke.MethodHandleNatives.Constants.*;
64 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
65 import static java.lang.invoke.MethodType.methodType;
66
67 /**
68 * This class consists exclusively of static methods that operate on or return
69 * method handles. They fall into several categories:
70 * <ul>
71 * <li>Lookup methods which help create method handles for methods and fields.
72 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
73 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
74 * </ul>
75 * A lookup, combinator, or factory method will fail and throw an
76 * {@code IllegalArgumentException} if the created method handle's type
77 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
78 *
79 * @author John Rose, JSR 292 EG
80 * @since 1.7
81 */
82 public class MethodHandles {
83
84 private MethodHandles() { } // do not instantiate
85
86 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
87
88 // See IMPL_LOOKUP below.
89
90 //// Method handle creation from ordinary methods.
91
92 /**
93 * Returns a {@link Lookup lookup object} with
94 * full capabilities to emulate all supported bytecode behaviors of the caller.
95 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
96 * Factory methods on the lookup object can create
97 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
98 * for any member that the caller has access to via bytecodes,
99 * including protected and private fields and methods.
100 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
101 * Do not store it in place where untrusted code can access it.
102 * <p>
103 * This method is caller sensitive, which means that it may return different
104 * values to different callers.
105 * @return a lookup object for the caller of this method, with private access
106 */
107 @CallerSensitive
108 @ForceInline // to ensure Reflection.getCallerClass optimization
109 public static Lookup lookup() {
110 return new Lookup(Reflection.getCallerClass());
111 }
112
113 /**
114 * This reflected$lookup method is the alternate implementation of
115 * the lookup method when being invoked by reflection.
116 */
117 @CallerSensitive
118 private static Lookup reflected$lookup() {
119 Class<?> caller = Reflection.getCallerClass();
120 if (caller.getClassLoader() == null) {
121 throw newIllegalArgumentException("illegal lookupClass: "+caller);
122 }
123 return new Lookup(caller);
124 }
125
126 /**
127 * Returns a {@link Lookup lookup object} which is trusted minimally.
128 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
129 * It can only be used to create method handles to public members of
130 * public classes in packages that are exported unconditionally.
131 * <p>
132 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
133 * of this lookup object will be {@link java.lang.Object}.
134 *
135 * @apiNote The use of Object is conventional, and because the lookup modes are
136 * limited, there is no special access provided to the internals of Object, its package
137 * or its module. Consequently, the lookup context of this lookup object will be the
138 * bootstrap class loader, which means it cannot find user classes.
139 *
140 * <p style="font-size:smaller;">
141 * <em>Discussion:</em>
142 * The lookup class can be changed to any other class {@code C} using an expression of the form
143 * {@link Lookup#in publicLookup().in(C.class)}.
144 * but may change the lookup context by virtue of changing the class loader.
145 * A public lookup object is always subject to
146 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
147 * Also, it cannot access
148 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
149 * @return a lookup object which is trusted minimally
150 *
151 * @revised 9
152 * @spec JPMS
153 */
154 public static Lookup publicLookup() {
155 return Lookup.PUBLIC_LOOKUP;
156 }
157
158 /**
159 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
160 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
161 * private access</a>, on a target class.
162 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
163 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
164 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
165 * the target class, then this check ensures that
166 * <ul>
167 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
168 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
169 * the target class to at least {@code m1}.</li>
170 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
171 * </ul>
172 * <p>
173 * If there is a security manager, its {@code checkPermission} method is called to
174 * check {@code ReflectPermission("suppressAccessChecks")}.
175 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
176 * was created by code in the caller module (or derived from a lookup object originally
177 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
178 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
179 * access to the caller.
180 * @param targetClass the target class
181 * @param lookup the caller lookup object
182 * @return a lookup object for the target class, with private access
183 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
184 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
185 * @throws IllegalAccessException if the access check specified above fails
186 * @throws SecurityException if denied by the security manager
187 * @since 9
188 * @spec JPMS
189 * @see Lookup#dropLookupMode
190 */
191 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
192 SecurityManager sm = System.getSecurityManager();
193 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
194 if (targetClass.isPrimitive())
195 throw new IllegalArgumentException(targetClass + " is a primitive class");
196 if (targetClass.isArray())
197 throw new IllegalArgumentException(targetClass + " is an array class");
198 Module targetModule = targetClass.getModule();
199 Module callerModule = lookup.lookupClass().getModule();
200 if (!callerModule.canRead(targetModule))
201 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
202 if (targetModule.isNamed()) {
203 String pn = targetClass.getPackageName();
204 assert !pn.isEmpty() : "unnamed package cannot be in named module";
205 if (!targetModule.isOpen(pn, callerModule))
206 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
207 }
208 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
209 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
210 if (!callerModule.isNamed() && targetModule.isNamed()) {
211 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
212 if (logger != null) {
213 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
214 }
215 }
216 return new Lookup(targetClass);
217 }
218
219 /**
220 * Performs an unchecked "crack" of a
221 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
222 * The result is as if the user had obtained a lookup object capable enough
223 * to crack the target method handle, called
224 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
225 * on the target to obtain its symbolic reference, and then called
226 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
227 * to resolve the symbolic reference to a member.
228 * <p>
229 * If there is a security manager, its {@code checkPermission} method
230 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
231 * @param <T> the desired type of the result, either {@link Member} or a subtype
232 * @param target a direct method handle to crack into symbolic reference components
233 * @param expected a class object representing the desired result type {@code T}
234 * @return a reference to the method, constructor, or field object
235 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
236 * @exception NullPointerException if either argument is {@code null}
237 * @exception IllegalArgumentException if the target is not a direct method handle
238 * @exception ClassCastException if the member is not of the expected type
239 * @since 1.8
240 */
241 public static <T extends Member> T
242 reflectAs(Class<T> expected, MethodHandle target) {
243 SecurityManager smgr = System.getSecurityManager();
244 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
245 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
246 return lookup.revealDirect(target).reflectAs(expected, lookup);
247 }
248 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
249 private static final java.security.Permission ACCESS_PERMISSION =
250 new ReflectPermission("suppressAccessChecks");
251
252 /**
253 * A <em>lookup object</em> is a factory for creating method handles,
254 * when the creation requires access checking.
255 * Method handles do not perform
256 * access checks when they are called, but rather when they are created.
257 * Therefore, method handle access
258 * restrictions must be enforced when a method handle is created.
259 * The caller class against which those restrictions are enforced
260 * is known as the {@linkplain #lookupClass() lookup class}.
261 * <p>
262 * A lookup class which needs to create method handles will call
263 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
264 * When the {@code Lookup} factory object is created, the identity of the lookup class is
265 * determined, and securely stored in the {@code Lookup} object.
266 * The lookup class (or its delegates) may then use factory methods
267 * on the {@code Lookup} object to create method handles for access-checked members.
268 * This includes all methods, constructors, and fields which are allowed to the lookup class,
269 * even private ones.
270 *
271 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
272 * The factory methods on a {@code Lookup} object correspond to all major
273 * use cases for methods, constructors, and fields.
274 * Each method handle created by a factory method is the functional
275 * equivalent of a particular <em>bytecode behavior</em>.
276 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
277 * Here is a summary of the correspondence between these factory methods and
278 * the behavior of the resulting method handles:
279 * <table class="striped">
280 * <caption style="display:none">lookup method behaviors</caption>
281 * <thead>
282 * <tr>
283 * <th scope="col"><a id="equiv"></a>lookup expression</th>
284 * <th scope="col">member</th>
285 * <th scope="col">bytecode behavior</th>
286 * </tr>
287 * </thead>
288 * <tbody>
289 * <tr>
290 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
291 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
292 * </tr>
293 * <tr>
294 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
295 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
296 * </tr>
297 * <tr>
298 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
299 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
300 * </tr>
301 * <tr>
302 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
303 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
304 * </tr>
305 * <tr>
306 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
307 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
308 * </tr>
309 * <tr>
310 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
311 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
312 * </tr>
313 * <tr>
314 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
315 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
316 * </tr>
317 * <tr>
318 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
319 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
320 * </tr>
321 * <tr>
322 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
323 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
324 * </tr>
325 * <tr>
326 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
327 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
328 * </tr>
329 * <tr>
330 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
331 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
332 * </tr>
333 * <tr>
334 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
335 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
336 * </tr>
337 * <tr>
338 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
339 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
340 * </tr>
341 * <tr>
342 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
343 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
344 * </tr>
345 * </tbody>
346 * </table>
347 *
348 * Here, the type {@code C} is the class or interface being searched for a member,
349 * documented as a parameter named {@code refc} in the lookup methods.
350 * The method type {@code MT} is composed from the return type {@code T}
351 * and the sequence of argument types {@code A*}.
352 * The constructor also has a sequence of argument types {@code A*} and
353 * is deemed to return the newly-created object of type {@code C}.
354 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
355 * The formal parameter {@code this} stands for the self-reference of type {@code C};
356 * if it is present, it is always the leading argument to the method handle invocation.
357 * (In the case of some {@code protected} members, {@code this} may be
358 * restricted in type to the lookup class; see below.)
359 * The name {@code arg} stands for all the other method handle arguments.
360 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
361 * stands for a null reference if the accessed method or field is static,
362 * and {@code this} otherwise.
363 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
364 * for reflective objects corresponding to the given members.
365 * <p>
366 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
367 * as if by {@code ldc CONSTANT_Class}.
368 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
369 * <p>
370 * In cases where the given member is of variable arity (i.e., a method or constructor)
371 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
372 * In all other cases, the returned method handle will be of fixed arity.
373 * <p style="font-size:smaller;">
374 * <em>Discussion:</em>
375 * The equivalence between looked-up method handles and underlying
376 * class members and bytecode behaviors
377 * can break down in a few ways:
378 * <ul style="font-size:smaller;">
379 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
380 * the lookup can still succeed, even when there is no equivalent
381 * Java expression or bytecoded constant.
382 * <li>Likewise, if {@code T} or {@code MT}
383 * is not symbolically accessible from the lookup class's loader,
384 * the lookup can still succeed.
385 * For example, lookups for {@code MethodHandle.invokeExact} and
386 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
387 * <li>If there is a security manager installed, it can forbid the lookup
388 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
389 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
390 * constant is not subject to security manager checks.
391 * <li>If the looked-up method has a
392 * <a href="MethodHandle.html#maxarity">very large arity</a>,
393 * the method handle creation may fail with an
394 * {@code IllegalArgumentException}, due to the method handle type having
395 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
396 * </ul>
397 *
398 * <h2><a id="access"></a>Access checking</h2>
399 * Access checks are applied in the factory methods of {@code Lookup},
400 * when a method handle is created.
401 * This is a key difference from the Core Reflection API, since
402 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
403 * performs access checking against every caller, on every call.
404 * <p>
405 * All access checks start from a {@code Lookup} object, which
406 * compares its recorded lookup class against all requests to
407 * create method handles.
408 * A single {@code Lookup} object can be used to create any number
409 * of access-checked method handles, all checked against a single
410 * lookup class.
411 * <p>
412 * A {@code Lookup} object can be shared with other trusted code,
413 * such as a metaobject protocol.
414 * A shared {@code Lookup} object delegates the capability
415 * to create method handles on private members of the lookup class.
416 * Even if privileged code uses the {@code Lookup} object,
417 * the access checking is confined to the privileges of the
418 * original lookup class.
419 * <p>
420 * A lookup can fail, because
421 * the containing class is not accessible to the lookup class, or
422 * because the desired class member is missing, or because the
423 * desired class member is not accessible to the lookup class, or
424 * because the lookup object is not trusted enough to access the member.
425 * In the case of a field setter function on a {@code final} field,
426 * finality enforcement is treated as a kind of access control,
427 * and the lookup will fail, except in special cases of
428 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
429 * In any of these cases, a {@code ReflectiveOperationException} will be
430 * thrown from the attempted lookup. The exact class will be one of
431 * the following:
432 * <ul>
433 * <li>NoSuchMethodException — if a method is requested but does not exist
434 * <li>NoSuchFieldException — if a field is requested but does not exist
435 * <li>IllegalAccessException — if the member exists but an access check fails
436 * </ul>
437 * <p>
438 * In general, the conditions under which a method handle may be
439 * looked up for a method {@code M} are no more restrictive than the conditions
440 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
441 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
442 * a method handle lookup will generally raise a corresponding
443 * checked exception, such as {@code NoSuchMethodException}.
444 * And the effect of invoking the method handle resulting from the lookup
445 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
446 * to executing the compiled, verified, and resolved call to {@code M}.
447 * The same point is true of fields and constructors.
448 * <p style="font-size:smaller;">
449 * <em>Discussion:</em>
450 * Access checks only apply to named and reflected methods,
451 * constructors, and fields.
452 * Other method handle creation methods, such as
453 * {@link MethodHandle#asType MethodHandle.asType},
454 * do not require any access checks, and are used
455 * independently of any {@code Lookup} object.
456 * <p>
457 * If the desired member is {@code protected}, the usual JVM rules apply,
458 * including the requirement that the lookup class must either be in the
459 * same package as the desired member, or must inherit that member.
460 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
461 * In addition, if the desired member is a non-static field or method
462 * in a different package, the resulting method handle may only be applied
463 * to objects of the lookup class or one of its subclasses.
464 * This requirement is enforced by narrowing the type of the leading
465 * {@code this} parameter from {@code C}
466 * (which will necessarily be a superclass of the lookup class)
467 * to the lookup class itself.
468 * <p>
469 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
470 * that the receiver argument must match both the resolved method <em>and</em>
471 * the current class. Again, this requirement is enforced by narrowing the
472 * type of the leading parameter to the resulting method handle.
473 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
474 * <p>
475 * The JVM represents constructors and static initializer blocks as internal methods
476 * with special names ({@code "<init>"} and {@code "<clinit>"}).
477 * The internal syntax of invocation instructions allows them to refer to such internal
478 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
479 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
480 * <p>
481 * If the relationship between nested types is expressed directly through the
482 * {@code NestHost} and {@code NestMembers} attributes
483 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
484 * then the associated {@code Lookup} object provides direct access to
485 * the lookup class and all of its nestmates
486 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
487 * Otherwise, access between nested classes is obtained by the Java compiler creating
488 * a wrapper method to access a private method of another class in the same nest.
489 * For example, a nested class {@code C.D}
490 * can access private members within other related classes such as
491 * {@code C}, {@code C.D.E}, or {@code C.B},
492 * but the Java compiler may need to generate wrapper methods in
493 * those related classes. In such cases, a {@code Lookup} object on
494 * {@code C.E} would be unable to access those private members.
495 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
496 * which can transform a lookup on {@code C.E} into one on any of those other
497 * classes, without special elevation of privilege.
498 * <p>
499 * The accesses permitted to a given lookup object may be limited,
500 * according to its set of {@link #lookupModes lookupModes},
501 * to a subset of members normally accessible to the lookup class.
502 * For example, the {@link MethodHandles#publicLookup publicLookup}
503 * method produces a lookup object which is only allowed to access
504 * public members in public classes of exported packages.
505 * The caller sensitive method {@link MethodHandles#lookup lookup}
506 * produces a lookup object with full capabilities relative to
507 * its caller class, to emulate all supported bytecode behaviors.
508 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
509 * with fewer access modes than the original lookup object.
510 *
511 * <p style="font-size:smaller;">
512 * <a id="privacc"></a>
513 * <em>Discussion of private access:</em>
514 * We say that a lookup has <em>private access</em>
515 * if its {@linkplain #lookupModes lookup modes}
516 * include the possibility of accessing {@code private} members
517 * (which includes the private members of nestmates).
518 * As documented in the relevant methods elsewhere,
519 * only lookups with private access possess the following capabilities:
520 * <ul style="font-size:smaller;">
521 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
522 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
523 * such as {@code Class.forName}
524 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
525 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
526 * for classes accessible to the lookup class
527 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
528 * within the same package member
529 * </ul>
530 * <p style="font-size:smaller;">
531 * Each of these permissions is a consequence of the fact that a lookup object
532 * with private access can be securely traced back to an originating class,
533 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
534 * can be reliably determined and emulated by method handles.
535 *
536 * <h2><a id="secmgr"></a>Security manager interactions</h2>
537 * Although bytecode instructions can only refer to classes in
538 * a related class loader, this API can search for methods in any
539 * class, as long as a reference to its {@code Class} object is
540 * available. Such cross-loader references are also possible with the
541 * Core Reflection API, and are impossible to bytecode instructions
542 * such as {@code invokestatic} or {@code getfield}.
543 * There is a {@linkplain java.lang.SecurityManager security manager API}
544 * to allow applications to check such cross-loader references.
545 * These checks apply to both the {@code MethodHandles.Lookup} API
546 * and the Core Reflection API
547 * (as found on {@link java.lang.Class Class}).
548 * <p>
549 * If a security manager is present, member and class lookups are subject to
550 * additional checks.
551 * From one to three calls are made to the security manager.
552 * Any of these calls can refuse access by throwing a
553 * {@link java.lang.SecurityException SecurityException}.
554 * Define {@code smgr} as the security manager,
555 * {@code lookc} as the lookup class of the current lookup object,
556 * {@code refc} as the containing class in which the member
557 * is being sought, and {@code defc} as the class in which the
558 * member is actually defined.
559 * (If a class or other type is being accessed,
560 * the {@code refc} and {@code defc} values are the class itself.)
561 * The value {@code lookc} is defined as <em>not present</em>
562 * if the current lookup object does not have
563 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
564 * The calls are made according to the following rules:
565 * <ul>
566 * <li><b>Step 1:</b>
567 * If {@code lookc} is not present, or if its class loader is not
568 * the same as or an ancestor of the class loader of {@code refc},
569 * then {@link SecurityManager#checkPackageAccess
570 * smgr.checkPackageAccess(refcPkg)} is called,
571 * where {@code refcPkg} is the package of {@code refc}.
572 * <li><b>Step 2a:</b>
573 * If the retrieved member is not public and
574 * {@code lookc} is not present, then
575 * {@link SecurityManager#checkPermission smgr.checkPermission}
576 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
577 * <li><b>Step 2b:</b>
578 * If the retrieved class has a {@code null} class loader,
579 * and {@code lookc} is not present, then
580 * {@link SecurityManager#checkPermission smgr.checkPermission}
581 * with {@code RuntimePermission("getClassLoader")} is called.
582 * <li><b>Step 3:</b>
583 * If the retrieved member is not public,
584 * and if {@code lookc} is not present,
585 * and if {@code defc} and {@code refc} are different,
586 * then {@link SecurityManager#checkPackageAccess
587 * smgr.checkPackageAccess(defcPkg)} is called,
588 * where {@code defcPkg} is the package of {@code defc}.
589 * </ul>
590 * Security checks are performed after other access checks have passed.
591 * Therefore, the above rules presuppose a member or class that is public,
592 * or else that is being accessed from a lookup class that has
593 * rights to access the member or class.
594 *
595 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
596 * A small number of Java methods have a special property called caller sensitivity.
597 * A <em>caller-sensitive</em> method can behave differently depending on the
598 * identity of its immediate caller.
599 * <p>
600 * If a method handle for a caller-sensitive method is requested,
601 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
602 * but they take account of the lookup class in a special way.
603 * The resulting method handle behaves as if it were called
604 * from an instruction contained in the lookup class,
605 * so that the caller-sensitive method detects the lookup class.
606 * (By contrast, the invoker of the method handle is disregarded.)
607 * Thus, in the case of caller-sensitive methods,
608 * different lookup classes may give rise to
609 * differently behaving method handles.
610 * <p>
611 * In cases where the lookup object is
612 * {@link MethodHandles#publicLookup() publicLookup()},
613 * or some other lookup object without
614 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
615 * the lookup class is disregarded.
616 * In such cases, no caller-sensitive method handle can be created,
617 * access is forbidden, and the lookup fails with an
618 * {@code IllegalAccessException}.
619 * <p style="font-size:smaller;">
620 * <em>Discussion:</em>
621 * For example, the caller-sensitive method
622 * {@link java.lang.Class#forName(String) Class.forName(x)}
623 * can return varying classes or throw varying exceptions,
624 * depending on the class loader of the class that calls it.
625 * A public lookup of {@code Class.forName} will fail, because
626 * there is no reasonable way to determine its bytecode behavior.
627 * <p style="font-size:smaller;">
628 * If an application caches method handles for broad sharing,
629 * it should use {@code publicLookup()} to create them.
630 * If there is a lookup of {@code Class.forName}, it will fail,
631 * and the application must take appropriate action in that case.
632 * It may be that a later lookup, perhaps during the invocation of a
633 * bootstrap method, can incorporate the specific identity
634 * of the caller, making the method accessible.
635 * <p style="font-size:smaller;">
636 * The function {@code MethodHandles.lookup} is caller sensitive
637 * so that there can be a secure foundation for lookups.
638 * Nearly all other methods in the JSR 292 API rely on lookup
639 * objects to check access requests.
640 *
641 * @revised 9
642 */
643 public static final
644 class Lookup {
645 /** The class on behalf of whom the lookup is being performed. */
646 private final Class<?> lookupClass;
647
648 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
649 private final int allowedModes;
650
651 static {
652 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
653 }
654
655 /** A single-bit mask representing {@code public} access,
656 * which may contribute to the result of {@link #lookupModes lookupModes}.
657 * The value, {@code 0x01}, happens to be the same as the value of the
658 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
659 */
660 public static final int PUBLIC = Modifier.PUBLIC;
661
662 /** A single-bit mask representing {@code private} access,
663 * which may contribute to the result of {@link #lookupModes lookupModes}.
664 * The value, {@code 0x02}, happens to be the same as the value of the
665 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
666 */
667 public static final int PRIVATE = Modifier.PRIVATE;
668
669 /** A single-bit mask representing {@code protected} access,
670 * which may contribute to the result of {@link #lookupModes lookupModes}.
671 * The value, {@code 0x04}, happens to be the same as the value of the
672 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
673 */
674 public static final int PROTECTED = Modifier.PROTECTED;
675
676 /** A single-bit mask representing {@code package} access (default access),
677 * which may contribute to the result of {@link #lookupModes lookupModes}.
678 * The value is {@code 0x08}, which does not correspond meaningfully to
679 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
680 */
681 public static final int PACKAGE = Modifier.STATIC;
682
683 /** A single-bit mask representing {@code module} access (default access),
684 * which may contribute to the result of {@link #lookupModes lookupModes}.
685 * The value is {@code 0x10}, which does not correspond meaningfully to
686 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
687 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
688 * with this lookup mode can access all public types in the module of the
689 * lookup class and public types in packages exported by other modules
690 * to the module of the lookup class.
691 * @since 9
692 * @spec JPMS
693 */
694 public static final int MODULE = PACKAGE << 1;
695
696 /** A single-bit mask representing {@code unconditional} access
697 * which may contribute to the result of {@link #lookupModes lookupModes}.
698 * The value is {@code 0x20}, which does not correspond meaningfully to
699 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
700 * A {@code Lookup} with this lookup mode assumes {@linkplain
701 * java.lang.Module#canRead(java.lang.Module) readability}.
702 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
703 * with this lookup mode can access all public members of public types
704 * of all modules where the type is in a package that is {@link
705 * java.lang.Module#isExported(String) exported unconditionally}.
706 * @since 9
707 * @spec JPMS
708 * @see #publicLookup()
709 */
710 public static final int UNCONDITIONAL = PACKAGE << 2;
711
712 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
713 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
714 private static final int TRUSTED = -1;
715
716 private static int fixmods(int mods) {
717 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
718 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
719 }
720
721 /** Tells which class is performing the lookup. It is this class against
722 * which checks are performed for visibility and access permissions.
723 * <p>
724 * The class implies a maximum level of access permission,
725 * but the permissions may be additionally limited by the bitmask
726 * {@link #lookupModes lookupModes}, which controls whether non-public members
727 * can be accessed.
728 * @return the lookup class, on behalf of which this lookup object finds members
729 */
730 public Class<?> lookupClass() {
731 return lookupClass;
732 }
733
734 // This is just for calling out to MethodHandleImpl.
735 private Class<?> lookupClassOrNull() {
736 return (allowedModes == TRUSTED) ? null : lookupClass;
737 }
738
739 /** Tells which access-protection classes of members this lookup object can produce.
740 * The result is a bit-mask of the bits
741 * {@linkplain #PUBLIC PUBLIC (0x01)},
742 * {@linkplain #PRIVATE PRIVATE (0x02)},
743 * {@linkplain #PROTECTED PROTECTED (0x04)},
744 * {@linkplain #PACKAGE PACKAGE (0x08)},
745 * {@linkplain #MODULE MODULE (0x10)},
746 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
747 * <p>
748 * A freshly-created lookup object
749 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
750 * all possible bits set, except {@code UNCONDITIONAL}.
751 * A lookup object on a new lookup class
752 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
753 * may have some mode bits set to zero.
754 * Mode bits can also be
755 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
756 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
757 * The purpose of this is to restrict access via the new lookup object,
758 * so that it can access only names which can be reached by the original
759 * lookup object, and also by the new lookup class.
760 * @return the lookup modes, which limit the kinds of access performed by this lookup object
761 * @see #in
762 * @see #dropLookupMode
763 *
764 * @revised 9
765 * @spec JPMS
766 */
767 public int lookupModes() {
768 return allowedModes & ALL_MODES;
769 }
770
771 /** Embody the current class (the lookupClass) as a lookup class
772 * for method handle creation.
773 * Must be called by from a method in this package,
774 * which in turn is called by a method not in this package.
775 */
776 Lookup(Class<?> lookupClass) {
777 this(lookupClass, FULL_POWER_MODES);
778 // make sure we haven't accidentally picked up a privileged class:
779 checkUnprivilegedlookupClass(lookupClass);
780 }
781
782 private Lookup(Class<?> lookupClass, int allowedModes) {
783 this.lookupClass = lookupClass;
784 this.allowedModes = allowedModes;
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 NullPointerException if the argument is null
823 *
824 * @revised 9
825 * @spec JPMS
826 */
827 public Lookup in(Class<?> requestedLookupClass) {
828 Objects.requireNonNull(requestedLookupClass);
829 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
830 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
831 if (requestedLookupClass == this.lookupClass)
832 return this; // keep same capabilities
833 int newModes = (allowedModes & FULL_POWER_MODES);
834 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
835 // Need to drop all access when teleporting from a named module to another
836 // module. The exception is publicLookup where PUBLIC is not lost.
837 if (this.lookupClass.getModule().isNamed()
838 && (this.allowedModes & UNCONDITIONAL) == 0)
839 newModes = 0;
840 else
841 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
842 }
843 if ((newModes & PACKAGE) != 0
844 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
845 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
846 }
847 // Allow nestmate lookups to be created without special privilege:
848 if ((newModes & PRIVATE) != 0
849 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
850 newModes &= ~(PRIVATE|PROTECTED);
851 }
852 if ((newModes & PUBLIC) != 0
853 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
854 // The requested class it not accessible from the lookup class.
855 // No permissions.
856 newModes = 0;
857 }
858
859 checkUnprivilegedlookupClass(requestedLookupClass);
860 return new Lookup(requestedLookupClass, newModes);
861 }
862
863
864 /**
865 * Creates a lookup on the same lookup class which this lookup object
866 * finds members, but with a lookup mode that has lost the given lookup mode.
867 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
868 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
869 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
870 * dropped and so the resulting lookup mode will never have these access capabilities.
871 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
872 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
873 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
874 * is dropped then the resulting lookup has no access.
875 * @param modeToDrop the lookup mode to drop
876 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
877 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
878 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
879 * @see MethodHandles#privateLookupIn
880 * @since 9
881 */
882 public Lookup dropLookupMode(int modeToDrop) {
883 int oldModes = lookupModes();
884 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
885 switch (modeToDrop) {
886 case PUBLIC: newModes &= ~(ALL_MODES); break;
887 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
888 case PACKAGE: newModes &= ~(PRIVATE); break;
889 case PROTECTED:
890 case PRIVATE:
891 case UNCONDITIONAL: break;
892 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
893 }
894 if (newModes == oldModes) return this; // return self if no change
895 return new Lookup(lookupClass(), newModes);
896 }
897
898 /**
899 * Defines a class to the same class loader and in the same runtime package and
900 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
901 * {@linkplain #lookupClass() lookup class}.
902 *
903 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
904 * {@link #PACKAGE PACKAGE} access as default (package) members will be
905 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
906 * that the lookup object was created by a caller in the runtime package (or derived
907 * from a lookup originally created by suitably privileged code to a target class in
908 * the runtime package). </p>
909 *
910 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
911 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
912 * same package as the lookup class. </p>
913 *
914 * <p> This method does not run the class initializer. The class initializer may
915 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
916 * Specification</em>. </p>
917 *
918 * <p> If there is a security manager, its {@code checkPermission} method is first called
919 * to check {@code RuntimePermission("defineClass")}. </p>
920 *
921 * @param bytes the class bytes
922 * @return the {@code Class} object for the class
923 * @throws IllegalArgumentException the bytes are for a class in a different package
924 * to the lookup class
925 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
926 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
927 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
928 * @throws SecurityException if denied by the security manager
929 * @throws NullPointerException if {@code bytes} is {@code null}
930 * @since 9
931 * @spec JPMS
932 * @see Lookup#privateLookupIn
933 * @see Lookup#dropLookupMode
934 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
935 */
936 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
937 SecurityManager sm = System.getSecurityManager();
938 if (sm != null)
939 sm.checkPermission(new RuntimePermission("defineClass"));
940 if ((lookupModes() & PACKAGE) == 0)
941 throw new IllegalAccessException("Lookup does not have PACKAGE access");
942 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
943
944 // parse class bytes to get class name (in internal form)
945 bytes = bytes.clone();
946 String name;
947 try {
948 ClassReader reader = new ClassReader(bytes);
949 name = reader.getClassName();
950 } catch (RuntimeException e) {
951 // ASM exceptions are poorly specified
952 ClassFormatError cfe = new ClassFormatError();
953 cfe.initCause(e);
954 throw cfe;
955 }
956
957 // get package and class name in binary form
958 String cn, pn;
959 int index = name.lastIndexOf('/');
960 if (index == -1) {
961 cn = name;
962 pn = "";
963 } else {
964 cn = name.replace('/', '.');
965 pn = cn.substring(0, index);
966 }
967 if (!pn.equals(lookupClass.getPackageName())) {
968 throw new IllegalArgumentException("Class not in same package as lookup class");
969 }
970
971 // invoke the class loader's defineClass method
972 ClassLoader loader = lookupClass.getClassLoader();
973 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
974 String source = "__Lookup_defineClass__";
975 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
976 return clazz;
977 }
978
979 private ProtectionDomain lookupClassProtectionDomain() {
980 ProtectionDomain pd = cachedProtectionDomain;
981 if (pd == null) {
982 cachedProtectionDomain = pd = protectionDomain(lookupClass);
983 }
984 return pd;
985 }
986
987 private ProtectionDomain protectionDomain(Class<?> clazz) {
988 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
989 return AccessController.doPrivileged(pa);
990 }
991
992 // cached protection domain
993 private volatile ProtectionDomain cachedProtectionDomain;
994
995
996 // Make sure outer class is initialized first.
997 static { IMPL_NAMES.getClass(); }
998
999 /** Package-private version of lookup which is trusted. */
1000 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
1001
1002 /** Version of lookup which is trusted minimally.
1003 * It can only be used to create method handles to publicly accessible
1004 * members in packages that are exported unconditionally.
1005 */
1006 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
1007
1008 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1009 String name = lookupClass.getName();
1010 if (name.startsWith("java.lang.invoke."))
1011 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1012 }
1013
1014 /**
1015 * Displays the name of the class from which lookups are to be made.
1016 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1017 * If there are restrictions on the access permitted to this lookup,
1018 * this is indicated by adding a suffix to the class name, consisting
1019 * of a slash and a keyword. The keyword represents the strongest
1020 * allowed access, and is chosen as follows:
1021 * <ul>
1022 * <li>If no access is allowed, the suffix is "/noaccess".
1023 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1024 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1025 * <li>If only public and module access are allowed, the suffix is "/module".
1026 * <li>If only public, module and package access are allowed, the suffix is "/package".
1027 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1028 * </ul>
1029 * If none of the above cases apply, it is the case that full
1030 * access (public, module, package, private, and protected) is allowed.
1031 * In this case, no suffix is added.
1032 * This is true only of an object obtained originally from
1033 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1034 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1035 * always have restricted access, and will display a suffix.
1036 * <p>
1037 * (It may seem strange that protected access should be
1038 * stronger than private access. Viewed independently from
1039 * package access, protected access is the first to be lost,
1040 * because it requires a direct subclass relationship between
1041 * caller and callee.)
1042 * @see #in
1043 *
1044 * @revised 9
1045 * @spec JPMS
1046 */
1047 @Override
1048 public String toString() {
1049 String cname = lookupClass.getName();
1050 switch (allowedModes) {
1051 case 0: // no privileges
1052 return cname + "/noaccess";
1053 case PUBLIC:
1054 return cname + "/public";
1055 case PUBLIC|UNCONDITIONAL:
1056 return cname + "/publicLookup";
1057 case PUBLIC|MODULE:
1058 return cname + "/module";
1059 case PUBLIC|MODULE|PACKAGE:
1060 return cname + "/package";
1061 case FULL_POWER_MODES & ~PROTECTED:
1062 return cname + "/private";
1063 case FULL_POWER_MODES:
1064 return cname;
1065 case TRUSTED:
1066 return "/trusted"; // internal only; not exported
1067 default: // Should not happen, but it's a bitfield...
1068 cname = cname + "/" + Integer.toHexString(allowedModes);
1069 assert(false) : cname;
1070 return cname;
1071 }
1072 }
1073
1074 /**
1075 * Produces a method handle for a static method.
1076 * The type of the method handle will be that of the method.
1077 * (Since static methods do not take receivers, there is no
1078 * additional receiver argument inserted into the method handle type,
1079 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1080 * The method and all its argument types must be accessible to the lookup object.
1081 * <p>
1082 * The returned method handle will have
1083 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1084 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1085 * <p>
1086 * If the returned method handle is invoked, the method's class will
1087 * be initialized, if it has not already been initialized.
1088 * <p><b>Example:</b>
1089 * <blockquote><pre>{@code
1090 import static java.lang.invoke.MethodHandles.*;
1091 import static java.lang.invoke.MethodType.*;
1092 ...
1093 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1094 "asList", methodType(List.class, Object[].class));
1095 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1096 * }</pre></blockquote>
1097 * @param refc the class from which the method is accessed
1098 * @param name the name of the method
1099 * @param type the type of the method
1100 * @return the desired method handle
1101 * @throws NoSuchMethodException if the method does not exist
1102 * @throws IllegalAccessException if access checking fails,
1103 * or if the method is not {@code static},
1104 * or if the method's variable arity modifier bit
1105 * is set and {@code asVarargsCollector} fails
1106 * @exception SecurityException if a security manager is present and it
1107 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1108 * @throws NullPointerException if any argument is null
1109 */
1110 public
1111 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1112 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1113 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1114 }
1115
1116 /**
1117 * Produces a method handle for a virtual method.
1118 * The type of the method handle will be that of the method,
1119 * with the receiver type (usually {@code refc}) prepended.
1120 * The method and all its argument types must be accessible to the lookup object.
1121 * <p>
1122 * When called, the handle will treat the first argument as a receiver
1123 * and, for non-private methods, dispatch on the receiver's type to determine which method
1124 * implementation to enter.
1125 * For private methods the named method in {@code refc} will be invoked on the receiver.
1126 * (The dispatching action is identical with that performed by an
1127 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1128 * <p>
1129 * The first argument will be of type {@code refc} if the lookup
1130 * class has full privileges to access the member. Otherwise
1131 * the member must be {@code protected} and the first argument
1132 * will be restricted in type to the lookup class.
1133 * <p>
1134 * The returned method handle will have
1135 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1136 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1137 * <p>
1138 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1139 * instructions and method handles produced by {@code findVirtual},
1140 * if the class is {@code MethodHandle} and the name string is
1141 * {@code invokeExact} or {@code invoke}, the resulting
1142 * method handle is equivalent to one produced by
1143 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1144 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1145 * with the same {@code type} argument.
1146 * <p>
1147 * If the class is {@code VarHandle} and the name string corresponds to
1148 * the name of a signature-polymorphic access mode method, the resulting
1149 * method handle is equivalent to one produced by
1150 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1151 * the access mode corresponding to the name string and with the same
1152 * {@code type} arguments.
1153 * <p>
1154 * <b>Example:</b>
1155 * <blockquote><pre>{@code
1156 import static java.lang.invoke.MethodHandles.*;
1157 import static java.lang.invoke.MethodType.*;
1158 ...
1159 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1160 "concat", methodType(String.class, String.class));
1161 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1162 "hashCode", methodType(int.class));
1163 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1164 "hashCode", methodType(int.class));
1165 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1166 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1167 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1168 // interface method:
1169 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1170 "subSequence", methodType(CharSequence.class, int.class, int.class));
1171 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1172 // constructor "internal method" must be accessed differently:
1173 MethodType MT_newString = methodType(void.class); //()V for new String()
1174 try { assertEquals("impossible", lookup()
1175 .findVirtual(String.class, "<init>", MT_newString));
1176 } catch (NoSuchMethodException ex) { } // OK
1177 MethodHandle MH_newString = publicLookup()
1178 .findConstructor(String.class, MT_newString);
1179 assertEquals("", (String) MH_newString.invokeExact());
1180 * }</pre></blockquote>
1181 *
1182 * @param refc the class or interface from which the method is accessed
1183 * @param name the name of the method
1184 * @param type the type of the method, with the receiver argument omitted
1185 * @return the desired method handle
1186 * @throws NoSuchMethodException if the method does not exist
1187 * @throws IllegalAccessException if access checking fails,
1188 * or if the method is {@code static},
1189 * or if the method's variable arity modifier bit
1190 * is set and {@code asVarargsCollector} fails
1191 * @exception SecurityException if a security manager is present and it
1192 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1193 * @throws NullPointerException if any argument is null
1194 */
1195 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1196 if (refc == MethodHandle.class) {
1197 MethodHandle mh = findVirtualForMH(name, type);
1198 if (mh != null) return mh;
1199 } else if (refc == VarHandle.class) {
1200 MethodHandle mh = findVirtualForVH(name, type);
1201 if (mh != null) return mh;
1202 }
1203 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1204 MemberName method = resolveOrFail(refKind, refc, name, type);
1205 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1206 }
1207 private MethodHandle findVirtualForMH(String name, MethodType type) {
1208 // these names require special lookups because of the implicit MethodType argument
1209 if ("invoke".equals(name))
1210 return invoker(type);
1211 if ("invokeExact".equals(name))
1212 return exactInvoker(type);
1213 assert(!MemberName.isMethodHandleInvokeName(name));
1214 return null;
1215 }
1216 private MethodHandle findVirtualForVH(String name, MethodType type) {
1217 try {
1218 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1219 } catch (IllegalArgumentException e) {
1220 return null;
1221 }
1222 }
1223
1224 /**
1225 * Produces a method handle which creates an object and initializes it, using
1226 * the constructor of the specified type.
1227 * The parameter types of the method handle will be those of the constructor,
1228 * while the return type will be a reference to the constructor's class.
1229 * The constructor and all its argument types must be accessible to the lookup object.
1230 * <p>
1231 * The requested type must have a return type of {@code void}.
1232 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1233 * <p>
1234 * The returned method handle will have
1235 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1236 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1237 * <p>
1238 * If the returned method handle is invoked, the constructor's class will
1239 * be initialized, if it has not already been initialized.
1240 * <p><b>Example:</b>
1241 * <blockquote><pre>{@code
1242 import static java.lang.invoke.MethodHandles.*;
1243 import static java.lang.invoke.MethodType.*;
1244 ...
1245 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1246 ArrayList.class, methodType(void.class, Collection.class));
1247 Collection orig = Arrays.asList("x", "y");
1248 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1249 assert(orig != copy);
1250 assertEquals(orig, copy);
1251 // a variable-arity constructor:
1252 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1253 ProcessBuilder.class, methodType(void.class, String[].class));
1254 ProcessBuilder pb = (ProcessBuilder)
1255 MH_newProcessBuilder.invoke("x", "y", "z");
1256 assertEquals("[x, y, z]", pb.command().toString());
1257 * }</pre></blockquote>
1258 * @param refc the class or interface from which the method is accessed
1259 * @param type the type of the method, with the receiver argument omitted, and a void return type
1260 * @return the desired method handle
1261 * @throws NoSuchMethodException if the constructor does not exist
1262 * @throws IllegalAccessException if access checking fails
1263 * or if the method's variable arity modifier bit
1264 * is set and {@code asVarargsCollector} fails
1265 * @exception SecurityException if a security manager is present and it
1266 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1267 * @throws NullPointerException if any argument is null
1268 */
1269 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1270 if (refc.isArray()) {
1271 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1272 }
1273 String name = "<init>";
1274 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1275 return getDirectConstructor(refc, ctor);
1276 }
1277
1278 /**
1279 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1280 * initializer of the class is not run.
1281 * <p>
1282 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1283 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1284 * load the requested class, and then determines whether the class is accessible to this lookup object.
1285 *
1286 * @param targetName the fully qualified name of the class to be looked up.
1287 * @return the requested class.
1288 * @exception SecurityException if a security manager is present and it
1289 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1290 * @throws LinkageError if the linkage fails
1291 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1292 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1293 * modes.
1294 * @exception SecurityException if a security manager is present and it
1295 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1296 * @since 9
1297 */
1298 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1299 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1300 return accessClass(targetClass);
1301 }
1302
1303 /**
1304 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1305 * static initializer of the class is not run.
1306 * <p>
1307 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1308 * {@linkplain #lookupModes() lookup modes}.
1309 *
1310 * @param targetClass the class to be access-checked
1311 *
1312 * @return the class that has been access-checked
1313 *
1314 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1315 * modes.
1316 * @exception SecurityException if a security manager is present and it
1317 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1318 * @since 9
1319 */
1320 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1321 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1322 throw new MemberName(targetClass).makeAccessException("access violation", this);
1323 }
1324 checkSecurityManager(targetClass, null);
1325 return targetClass;
1326 }
1327
1328 /**
1329 * Produces an early-bound method handle for a virtual method.
1330 * It will bypass checks for overriding methods on the receiver,
1331 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1332 * instruction from within the explicitly specified {@code specialCaller}.
1333 * The type of the method handle will be that of the method,
1334 * with a suitably restricted receiver type prepended.
1335 * (The receiver type will be {@code specialCaller} or a subtype.)
1336 * The method and all its argument types must be accessible
1337 * to the lookup object.
1338 * <p>
1339 * Before method resolution,
1340 * if the explicitly specified caller class is not identical with the
1341 * lookup class, or if this lookup object does not have
1342 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1343 * privileges, the access fails.
1344 * <p>
1345 * The returned method handle will have
1346 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1347 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1348 * <p style="font-size:smaller;">
1349 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1350 * even though the {@code invokespecial} instruction can refer to them
1351 * in special circumstances. Use {@link #findConstructor findConstructor}
1352 * to access instance initialization methods in a safe manner.)</em>
1353 * <p><b>Example:</b>
1354 * <blockquote><pre>{@code
1355 import static java.lang.invoke.MethodHandles.*;
1356 import static java.lang.invoke.MethodType.*;
1357 ...
1358 static class Listie extends ArrayList {
1359 public String toString() { return "[wee Listie]"; }
1360 static Lookup lookup() { return MethodHandles.lookup(); }
1361 }
1362 ...
1363 // no access to constructor via invokeSpecial:
1364 MethodHandle MH_newListie = Listie.lookup()
1365 .findConstructor(Listie.class, methodType(void.class));
1366 Listie l = (Listie) MH_newListie.invokeExact();
1367 try { assertEquals("impossible", Listie.lookup().findSpecial(
1368 Listie.class, "<init>", methodType(void.class), Listie.class));
1369 } catch (NoSuchMethodException ex) { } // OK
1370 // access to super and self methods via invokeSpecial:
1371 MethodHandle MH_super = Listie.lookup().findSpecial(
1372 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1373 MethodHandle MH_this = Listie.lookup().findSpecial(
1374 Listie.class, "toString" , methodType(String.class), Listie.class);
1375 MethodHandle MH_duper = Listie.lookup().findSpecial(
1376 Object.class, "toString" , methodType(String.class), Listie.class);
1377 assertEquals("[]", (String) MH_super.invokeExact(l));
1378 assertEquals(""+l, (String) MH_this.invokeExact(l));
1379 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1380 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1381 String.class, "toString", methodType(String.class), Listie.class));
1382 } catch (IllegalAccessException ex) { } // OK
1383 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1384 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1385 * }</pre></blockquote>
1386 *
1387 * @param refc the class or interface from which the method is accessed
1388 * @param name the name of the method (which must not be "<init>")
1389 * @param type the type of the method, with the receiver argument omitted
1390 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1391 * @return the desired method handle
1392 * @throws NoSuchMethodException if the method does not exist
1393 * @throws IllegalAccessException if access checking fails,
1394 * or if the method is {@code static},
1395 * or if the method's variable arity modifier bit
1396 * is set and {@code asVarargsCollector} fails
1397 * @exception SecurityException if a security manager is present and it
1398 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1399 * @throws NullPointerException if any argument is null
1400 */
1401 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1402 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1403 checkSpecialCaller(specialCaller, refc);
1404 Lookup specialLookup = this.in(specialCaller);
1405 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1406 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1407 }
1408
1409 /**
1410 * Produces a method handle giving read access to a non-static field.
1411 * The type of the method handle will have a return type of the field's
1412 * value type.
1413 * The method handle's single argument will be the instance containing
1414 * the field.
1415 * Access checking is performed immediately on behalf of the lookup class.
1416 * @param refc the class or interface from which the method is accessed
1417 * @param name the field's name
1418 * @param type the field's type
1419 * @return a method handle which can load values from the field
1420 * @throws NoSuchFieldException if the field does not exist
1421 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1422 * @exception SecurityException if a security manager is present and it
1423 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1424 * @throws NullPointerException if any argument is null
1425 * @see #findVarHandle(Class, String, Class)
1426 */
1427 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1428 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1429 return getDirectField(REF_getField, refc, field);
1430 }
1431
1432 /**
1433 * Produces a method handle giving write access to a non-static field.
1434 * The type of the method handle will have a void return type.
1435 * The method handle will take two arguments, the instance containing
1436 * the field, and the value to be stored.
1437 * The second argument will be of the field's value type.
1438 * Access checking is performed immediately on behalf of the lookup class.
1439 * @param refc the class or interface from which the method is accessed
1440 * @param name the field's name
1441 * @param type the field's type
1442 * @return a method handle which can store values into the field
1443 * @throws NoSuchFieldException if the field does not exist
1444 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1445 * or {@code final}
1446 * @exception SecurityException if a security manager is present and it
1447 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1448 * @throws NullPointerException if any argument is null
1449 * @see #findVarHandle(Class, String, Class)
1450 */
1451 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1452 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1453 return getDirectField(REF_putField, refc, field);
1454 }
1455
1456 /**
1457 * Produces a VarHandle giving access to a non-static field {@code name}
1458 * of type {@code type} declared in a class of type {@code recv}.
1459 * The VarHandle's variable type is {@code type} and it has one
1460 * coordinate type, {@code recv}.
1461 * <p>
1462 * Access checking is performed immediately on behalf of the lookup
1463 * class.
1464 * <p>
1465 * Certain access modes of the returned VarHandle are unsupported under
1466 * the following conditions:
1467 * <ul>
1468 * <li>if the field is declared {@code final}, then the write, atomic
1469 * update, numeric atomic update, and bitwise atomic update access
1470 * modes are unsupported.
1471 * <li>if the field type is anything other than {@code byte},
1472 * {@code short}, {@code char}, {@code int}, {@code long},
1473 * {@code float}, or {@code double} then numeric atomic update
1474 * access modes are unsupported.
1475 * <li>if the field type is anything other than {@code boolean},
1476 * {@code byte}, {@code short}, {@code char}, {@code int} or
1477 * {@code long} then bitwise atomic update access modes are
1478 * unsupported.
1479 * </ul>
1480 * <p>
1481 * If the field is declared {@code volatile} then the returned VarHandle
1482 * will override access to the field (effectively ignore the
1483 * {@code volatile} declaration) in accordance to its specified
1484 * access modes.
1485 * <p>
1486 * If the field type is {@code float} or {@code double} then numeric
1487 * and atomic update access modes compare values using their bitwise
1488 * representation (see {@link Float#floatToRawIntBits} and
1489 * {@link Double#doubleToRawLongBits}, respectively).
1490 * @apiNote
1491 * Bitwise comparison of {@code float} values or {@code double} values,
1492 * as performed by the numeric and atomic update access modes, differ
1493 * from the primitive {@code ==} operator and the {@link Float#equals}
1494 * and {@link Double#equals} methods, specifically with respect to
1495 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1496 * Care should be taken when performing a compare and set or a compare
1497 * and exchange operation with such values since the operation may
1498 * unexpectedly fail.
1499 * There are many possible NaN values that are considered to be
1500 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1501 * provided by Java can distinguish between them. Operation failure can
1502 * occur if the expected or witness value is a NaN value and it is
1503 * transformed (perhaps in a platform specific manner) into another NaN
1504 * value, and thus has a different bitwise representation (see
1505 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1506 * details).
1507 * The values {@code -0.0} and {@code +0.0} have different bitwise
1508 * representations but are considered equal when using the primitive
1509 * {@code ==} operator. Operation failure can occur if, for example, a
1510 * numeric algorithm computes an expected value to be say {@code -0.0}
1511 * and previously computed the witness value to be say {@code +0.0}.
1512 * @param recv the receiver class, of type {@code R}, that declares the
1513 * non-static field
1514 * @param name the field's name
1515 * @param type the field's type, of type {@code T}
1516 * @return a VarHandle giving access to non-static fields.
1517 * @throws NoSuchFieldException if the field does not exist
1518 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1519 * @exception SecurityException if a security manager is present and it
1520 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1521 * @throws NullPointerException if any argument is null
1522 * @since 9
1523 */
1524 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1525 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1526 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1527 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1528 }
1529
1530 /**
1531 * Produces a method handle giving read access to a static field.
1532 * The type of the method handle will have a return type of the field's
1533 * value type.
1534 * The method handle will take no arguments.
1535 * Access checking is performed immediately on behalf of the lookup class.
1536 * <p>
1537 * If the returned method handle is invoked, the field's class will
1538 * be initialized, if it has not already been initialized.
1539 * @param refc the class or interface from which the method is accessed
1540 * @param name the field's name
1541 * @param type the field's type
1542 * @return a method handle which can load values from the field
1543 * @throws NoSuchFieldException if the field does not exist
1544 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1545 * @exception SecurityException if a security manager is present and it
1546 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1547 * @throws NullPointerException if any argument is null
1548 */
1549 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1550 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1551 return getDirectField(REF_getStatic, refc, field);
1552 }
1553
1554 /**
1555 * Produces a method handle giving write access to a static field.
1556 * The type of the method handle will have a void return type.
1557 * The method handle will take a single
1558 * argument, of the field's value type, the value to be stored.
1559 * Access checking is performed immediately on behalf of the lookup class.
1560 * <p>
1561 * If the returned method handle is invoked, the field's class will
1562 * be initialized, if it has not already been initialized.
1563 * @param refc the class or interface from which the method is accessed
1564 * @param name the field's name
1565 * @param type the field's type
1566 * @return a method handle which can store values into the field
1567 * @throws NoSuchFieldException if the field does not exist
1568 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1569 * or is {@code final}
1570 * @exception SecurityException if a security manager is present and it
1571 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1572 * @throws NullPointerException if any argument is null
1573 */
1574 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1575 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1576 return getDirectField(REF_putStatic, refc, field);
1577 }
1578
1579 /**
1580 * Produces a VarHandle giving access to a static field {@code name} of
1581 * type {@code type} declared in a class of type {@code decl}.
1582 * The VarHandle's variable type is {@code type} and it has no
1583 * coordinate types.
1584 * <p>
1585 * Access checking is performed immediately on behalf of the lookup
1586 * class.
1587 * <p>
1588 * If the returned VarHandle is operated on, the declaring class will be
1589 * initialized, if it has not already been initialized.
1590 * <p>
1591 * Certain access modes of the returned VarHandle are unsupported under
1592 * the following conditions:
1593 * <ul>
1594 * <li>if the field is declared {@code final}, then the write, atomic
1595 * update, numeric atomic update, and bitwise atomic update access
1596 * modes are unsupported.
1597 * <li>if the field type is anything other than {@code byte},
1598 * {@code short}, {@code char}, {@code int}, {@code long},
1599 * {@code float}, or {@code double}, then numeric atomic update
1600 * access modes are unsupported.
1601 * <li>if the field type is anything other than {@code boolean},
1602 * {@code byte}, {@code short}, {@code char}, {@code int} or
1603 * {@code long} then bitwise atomic update access modes are
1604 * unsupported.
1605 * </ul>
1606 * <p>
1607 * If the field is declared {@code volatile} then the returned VarHandle
1608 * will override access to the field (effectively ignore the
1609 * {@code volatile} declaration) in accordance to its specified
1610 * access modes.
1611 * <p>
1612 * If the field type is {@code float} or {@code double} then numeric
1613 * and atomic update access modes compare values using their bitwise
1614 * representation (see {@link Float#floatToRawIntBits} and
1615 * {@link Double#doubleToRawLongBits}, respectively).
1616 * @apiNote
1617 * Bitwise comparison of {@code float} values or {@code double} values,
1618 * as performed by the numeric and atomic update access modes, differ
1619 * from the primitive {@code ==} operator and the {@link Float#equals}
1620 * and {@link Double#equals} methods, specifically with respect to
1621 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1622 * Care should be taken when performing a compare and set or a compare
1623 * and exchange operation with such values since the operation may
1624 * unexpectedly fail.
1625 * There are many possible NaN values that are considered to be
1626 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1627 * provided by Java can distinguish between them. Operation failure can
1628 * occur if the expected or witness value is a NaN value and it is
1629 * transformed (perhaps in a platform specific manner) into another NaN
1630 * value, and thus has a different bitwise representation (see
1631 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1632 * details).
1633 * The values {@code -0.0} and {@code +0.0} have different bitwise
1634 * representations but are considered equal when using the primitive
1635 * {@code ==} operator. Operation failure can occur if, for example, a
1636 * numeric algorithm computes an expected value to be say {@code -0.0}
1637 * and previously computed the witness value to be say {@code +0.0}.
1638 * @param decl the class that declares the static field
1639 * @param name the field's name
1640 * @param type the field's type, of type {@code T}
1641 * @return a VarHandle giving access to a static field
1642 * @throws NoSuchFieldException if the field does not exist
1643 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1644 * @exception SecurityException if a security manager is present and it
1645 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1646 * @throws NullPointerException if any argument is null
1647 * @since 9
1648 */
1649 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1650 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1651 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1652 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1653 }
1654
1655 /**
1656 * Produces an early-bound method handle for a non-static method.
1657 * The receiver must have a supertype {@code defc} in which a method
1658 * of the given name and type is accessible to the lookup class.
1659 * The method and all its argument types must be accessible to the lookup object.
1660 * The type of the method handle will be that of the method,
1661 * without any insertion of an additional receiver parameter.
1662 * The given receiver will be bound into the method handle,
1663 * so that every call to the method handle will invoke the
1664 * requested method on the given receiver.
1665 * <p>
1666 * The returned method handle will have
1667 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1668 * the method's variable arity modifier bit ({@code 0x0080}) is set
1669 * <em>and</em> the trailing array argument is not the only argument.
1670 * (If the trailing array argument is the only argument,
1671 * the given receiver value will be bound to it.)
1672 * <p>
1673 * This is almost equivalent to the following code, with some differences noted below:
1674 * <blockquote><pre>{@code
1675 import static java.lang.invoke.MethodHandles.*;
1676 import static java.lang.invoke.MethodType.*;
1677 ...
1678 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1679 MethodHandle mh1 = mh0.bindTo(receiver);
1680 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1681 return mh1;
1682 * }</pre></blockquote>
1683 * where {@code defc} is either {@code receiver.getClass()} or a super
1684 * type of that class, in which the requested method is accessible
1685 * to the lookup class.
1686 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1687 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1688 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1689 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1690 * @param receiver the object from which the method is accessed
1691 * @param name the name of the method
1692 * @param type the type of the method, with the receiver argument omitted
1693 * @return the desired method handle
1694 * @throws NoSuchMethodException if the method does not exist
1695 * @throws IllegalAccessException if access checking fails
1696 * or if the method's variable arity modifier bit
1697 * is set and {@code asVarargsCollector} fails
1698 * @exception SecurityException if a security manager is present and it
1699 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1700 * @throws NullPointerException if any argument is null
1701 * @see MethodHandle#bindTo
1702 * @see #findVirtual
1703 */
1704 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1705 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1706 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1707 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1708 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1709 throw new IllegalAccessException("The restricted defining class " +
1710 mh.type().leadingReferenceParameter().getName() +
1711 " is not assignable from receiver class " +
1712 receiver.getClass().getName());
1713 }
1714 return mh.bindArgumentL(0, receiver).setVarargs(method);
1715 }
1716
1717 /**
1718 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1719 * to <i>m</i>, if the lookup class has permission.
1720 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1721 * If <i>m</i> is virtual, overriding is respected on every call.
1722 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1723 * The type of the method handle will be that of the method,
1724 * with the receiver type prepended (but only if it is non-static).
1725 * If the method's {@code accessible} flag is not set,
1726 * access checking is performed immediately on behalf of the lookup class.
1727 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1728 * <p>
1729 * The returned method handle will have
1730 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1731 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1732 * <p>
1733 * If <i>m</i> is static, and
1734 * if the returned method handle is invoked, the method's class will
1735 * be initialized, if it has not already been initialized.
1736 * @param m the reflected method
1737 * @return a method handle which can invoke the reflected method
1738 * @throws IllegalAccessException if access checking fails
1739 * or if the method's variable arity modifier bit
1740 * is set and {@code asVarargsCollector} fails
1741 * @throws NullPointerException if the argument is null
1742 */
1743 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1744 if (m.getDeclaringClass() == MethodHandle.class) {
1745 MethodHandle mh = unreflectForMH(m);
1746 if (mh != null) return mh;
1747 }
1748 if (m.getDeclaringClass() == VarHandle.class) {
1749 MethodHandle mh = unreflectForVH(m);
1750 if (mh != null) return mh;
1751 }
1752 MemberName method = new MemberName(m);
1753 byte refKind = method.getReferenceKind();
1754 if (refKind == REF_invokeSpecial)
1755 refKind = REF_invokeVirtual;
1756 assert(method.isMethod());
1757 @SuppressWarnings("deprecation")
1758 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1759 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1760 }
1761 private MethodHandle unreflectForMH(Method m) {
1762 // these names require special lookups because they throw UnsupportedOperationException
1763 if (MemberName.isMethodHandleInvokeName(m.getName()))
1764 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1765 return null;
1766 }
1767 private MethodHandle unreflectForVH(Method m) {
1768 // these names require special lookups because they throw UnsupportedOperationException
1769 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1770 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1771 return null;
1772 }
1773
1774 /**
1775 * Produces a method handle for a reflected method.
1776 * It will bypass checks for overriding methods on the receiver,
1777 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1778 * instruction from within the explicitly specified {@code specialCaller}.
1779 * The type of the method handle will be that of the method,
1780 * with a suitably restricted receiver type prepended.
1781 * (The receiver type will be {@code specialCaller} or a subtype.)
1782 * If the method's {@code accessible} flag is not set,
1783 * access checking is performed immediately on behalf of the lookup class,
1784 * as if {@code invokespecial} instruction were being linked.
1785 * <p>
1786 * Before method resolution,
1787 * if the explicitly specified caller class is not identical with the
1788 * lookup class, or if this lookup object does not have
1789 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1790 * privileges, the access fails.
1791 * <p>
1792 * The returned method handle will have
1793 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1794 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1795 * @param m the reflected method
1796 * @param specialCaller the class nominally calling the method
1797 * @return a method handle which can invoke the reflected method
1798 * @throws IllegalAccessException if access checking fails,
1799 * or if the method is {@code static},
1800 * or if the method's variable arity modifier bit
1801 * is set and {@code asVarargsCollector} fails
1802 * @throws NullPointerException if any argument is null
1803 */
1804 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1805 checkSpecialCaller(specialCaller, null);
1806 Lookup specialLookup = this.in(specialCaller);
1807 MemberName method = new MemberName(m, true);
1808 assert(method.isMethod());
1809 // ignore m.isAccessible: this is a new kind of access
1810 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1811 }
1812
1813 /**
1814 * Produces a method handle for a reflected constructor.
1815 * The type of the method handle will be that of the constructor,
1816 * with the return type changed to the declaring class.
1817 * The method handle will perform a {@code newInstance} operation,
1818 * creating a new instance of the constructor's class on the
1819 * arguments passed to the method handle.
1820 * <p>
1821 * If the constructor's {@code accessible} flag is not set,
1822 * access checking is performed immediately on behalf of the lookup class.
1823 * <p>
1824 * The returned method handle will have
1825 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1826 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1827 * <p>
1828 * If the returned method handle is invoked, the constructor's class will
1829 * be initialized, if it has not already been initialized.
1830 * @param c the reflected constructor
1831 * @return a method handle which can invoke the reflected constructor
1832 * @throws IllegalAccessException if access checking fails
1833 * or if the method's variable arity modifier bit
1834 * is set and {@code asVarargsCollector} fails
1835 * @throws NullPointerException if the argument is null
1836 */
1837 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1838 MemberName ctor = new MemberName(c);
1839 assert(ctor.isConstructor());
1840 @SuppressWarnings("deprecation")
1841 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1842 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1843 }
1844
1845 /**
1846 * Produces a method handle giving read access to a reflected field.
1847 * The type of the method handle will have a return type of the field's
1848 * value type.
1849 * If the field is {@code static}, the method handle will take no arguments.
1850 * Otherwise, its single argument will be the instance containing
1851 * the field.
1852 * If the {@code Field} object's {@code accessible} flag is not set,
1853 * access checking is performed immediately on behalf of the lookup class.
1854 * <p>
1855 * If the field is static, and
1856 * if the returned method handle is invoked, the field's class will
1857 * be initialized, if it has not already been initialized.
1858 * @param f the reflected field
1859 * @return a method handle which can load values from the reflected field
1860 * @throws IllegalAccessException if access checking fails
1861 * @throws NullPointerException if the argument is null
1862 */
1863 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1864 return unreflectField(f, false);
1865 }
1866
1867 /**
1868 * Produces a method handle giving write access to a reflected field.
1869 * The type of the method handle will have a void return type.
1870 * If the field is {@code static}, the method handle will take a single
1871 * argument, of the field's value type, the value to be stored.
1872 * Otherwise, the two arguments will be the instance containing
1873 * the field, and the value to be stored.
1874 * If the {@code Field} object's {@code accessible} flag is not set,
1875 * access checking is performed immediately on behalf of the lookup class.
1876 * <p>
1877 * If the field is {@code final}, write access will not be
1878 * allowed and access checking will fail, except under certain
1879 * narrow circumstances documented for {@link Field#set Field.set}.
1880 * A method handle is returned only if a corresponding call to
1881 * the {@code Field} object's {@code set} method could return
1882 * normally. In particular, fields which are both {@code static}
1883 * and {@code final} may never be set.
1884 * <p>
1885 * If the field is {@code static}, and
1886 * if the returned method handle is invoked, the field's class will
1887 * be initialized, if it has not already been initialized.
1888 * @param f the reflected field
1889 * @return a method handle which can store values into the reflected field
1890 * @throws IllegalAccessException if access checking fails,
1891 * or if the field is {@code final} and write access
1892 * is not enabled on the {@code Field} object
1893 * @throws NullPointerException if the argument is null
1894 */
1895 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1896 return unreflectField(f, true);
1897 }
1898
1899 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1900 MemberName field = new MemberName(f, isSetter);
1901 if (isSetter && field.isStatic() && field.isFinal())
1902 throw field.makeAccessException("static final field has no write access", this);
1903 assert(isSetter
1904 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1905 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1906 @SuppressWarnings("deprecation")
1907 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1908 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1909 }
1910
1911 /**
1912 * Produces a VarHandle giving access to a reflected field {@code f}
1913 * of type {@code T} declared in a class of type {@code R}.
1914 * The VarHandle's variable type is {@code T}.
1915 * If the field is non-static the VarHandle has one coordinate type,
1916 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1917 * coordinate types.
1918 * <p>
1919 * Access checking is performed immediately on behalf of the lookup
1920 * class, regardless of the value of the field's {@code accessible}
1921 * flag.
1922 * <p>
1923 * If the field is static, and if the returned VarHandle is operated
1924 * on, the field's declaring class will be initialized, if it has not
1925 * already been initialized.
1926 * <p>
1927 * Certain access modes of the returned VarHandle are unsupported under
1928 * the following conditions:
1929 * <ul>
1930 * <li>if the field is declared {@code final}, then the write, atomic
1931 * update, numeric atomic update, and bitwise atomic update access
1932 * modes are unsupported.
1933 * <li>if the field type is anything other than {@code byte},
1934 * {@code short}, {@code char}, {@code int}, {@code long},
1935 * {@code float}, or {@code double} then numeric atomic update
1936 * access modes are unsupported.
1937 * <li>if the field type is anything other than {@code boolean},
1938 * {@code byte}, {@code short}, {@code char}, {@code int} or
1939 * {@code long} then bitwise atomic update access modes are
1940 * unsupported.
1941 * </ul>
1942 * <p>
1943 * If the field is declared {@code volatile} then the returned VarHandle
1944 * will override access to the field (effectively ignore the
1945 * {@code volatile} declaration) in accordance to its specified
1946 * access modes.
1947 * <p>
1948 * If the field type is {@code float} or {@code double} then numeric
1949 * and atomic update access modes compare values using their bitwise
1950 * representation (see {@link Float#floatToRawIntBits} and
1951 * {@link Double#doubleToRawLongBits}, respectively).
1952 * @apiNote
1953 * Bitwise comparison of {@code float} values or {@code double} values,
1954 * as performed by the numeric and atomic update access modes, differ
1955 * from the primitive {@code ==} operator and the {@link Float#equals}
1956 * and {@link Double#equals} methods, specifically with respect to
1957 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1958 * Care should be taken when performing a compare and set or a compare
1959 * and exchange operation with such values since the operation may
1960 * unexpectedly fail.
1961 * There are many possible NaN values that are considered to be
1962 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1963 * provided by Java can distinguish between them. Operation failure can
1964 * occur if the expected or witness value is a NaN value and it is
1965 * transformed (perhaps in a platform specific manner) into another NaN
1966 * value, and thus has a different bitwise representation (see
1967 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1968 * details).
1969 * The values {@code -0.0} and {@code +0.0} have different bitwise
1970 * representations but are considered equal when using the primitive
1971 * {@code ==} operator. Operation failure can occur if, for example, a
1972 * numeric algorithm computes an expected value to be say {@code -0.0}
1973 * and previously computed the witness value to be say {@code +0.0}.
1974 * @param f the reflected field, with a field of type {@code T}, and
1975 * a declaring class of type {@code R}
1976 * @return a VarHandle giving access to non-static fields or a static
1977 * field
1978 * @throws IllegalAccessException if access checking fails
1979 * @throws NullPointerException if the argument is null
1980 * @since 9
1981 */
1982 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1983 MemberName getField = new MemberName(f, false);
1984 MemberName putField = new MemberName(f, true);
1985 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1986 f.getDeclaringClass(), getField, putField);
1987 }
1988
1989 /**
1990 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1991 * created by this lookup object or a similar one.
1992 * Security and access checks are performed to ensure that this lookup object
1993 * is capable of reproducing the target method handle.
1994 * This means that the cracking may fail if target is a direct method handle
1995 * but was created by an unrelated lookup object.
1996 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1997 * and was created by a lookup object for a different class.
1998 * @param target a direct method handle to crack into symbolic reference components
1999 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
2000 * @exception SecurityException if a security manager is present and it
2001 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2002 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
2003 * @exception NullPointerException if the target is {@code null}
2004 * @see MethodHandleInfo
2005 * @since 1.8
2006 */
2007 public MethodHandleInfo revealDirect(MethodHandle target) {
2008 MemberName member = target.internalMemberName();
2009 if (member == null || (!member.isResolved() &&
2010 !member.isMethodHandleInvoke() &&
2011 !member.isVarHandleMethodInvoke()))
2012 throw newIllegalArgumentException("not a direct method handle");
2013 Class<?> defc = member.getDeclaringClass();
2014 byte refKind = member.getReferenceKind();
2015 assert(MethodHandleNatives.refKindIsValid(refKind));
2016 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2017 // Devirtualized method invocation is usually formally virtual.
2018 // To avoid creating extra MemberName objects for this common case,
2019 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2020 refKind = REF_invokeVirtual;
2021 if (refKind == REF_invokeVirtual && defc.isInterface())
2022 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2023 refKind = REF_invokeInterface;
2024 // Check SM permissions and member access before cracking.
2025 try {
2026 checkAccess(refKind, defc, member);
2027 checkSecurityManager(defc, member);
2028 } catch (IllegalAccessException ex) {
2029 throw new IllegalArgumentException(ex);
2030 }
2031 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2032 Class<?> callerClass = target.internalCallerClass();
2033 if (!hasPrivateAccess() || callerClass != lookupClass())
2034 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2035 }
2036 // Produce the handle to the results.
2037 return new InfoFromMemberName(this, member, refKind);
2038 }
2039
2040 /// Helper methods, all package-private.
2041
2042 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2043 checkSymbolicClass(refc); // do this before attempting to resolve
2044 Objects.requireNonNull(name);
2045 Objects.requireNonNull(type);
2046 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2047 NoSuchFieldException.class);
2048 }
2049
2050 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2051 checkSymbolicClass(refc); // do this before attempting to resolve
2052 Objects.requireNonNull(name);
2053 Objects.requireNonNull(type);
2054 checkMethodName(refKind, name); // NPE check on name
2055 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2056 NoSuchMethodException.class);
2057 }
2058
2059 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2060 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2061 Objects.requireNonNull(member.getName());
2062 Objects.requireNonNull(member.getType());
2063 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2064 ReflectiveOperationException.class);
2065 }
2066
2067 MemberName resolveOrNull(byte refKind, MemberName member) {
2068 // do this before attempting to resolve
2069 if (!isClassAccessible(member.getDeclaringClass())) {
2070 return null;
2071 }
2072 Objects.requireNonNull(member.getName());
2073 Objects.requireNonNull(member.getType());
2074 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2075 }
2076
2077 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2078 if (!isClassAccessible(refc)) {
2079 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2080 }
2081 }
2082
2083 boolean isClassAccessible(Class<?> refc) {
2084 Objects.requireNonNull(refc);
2085 Class<?> caller = lookupClassOrNull();
2086 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes);
2087 }
2088
2089 /** Check name for an illegal leading "<" character. */
2090 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2091 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2092 throw new NoSuchMethodException("illegal method name: "+name);
2093 }
2094
2095
2096 /**
2097 * Find my trustable caller class if m is a caller sensitive method.
2098 * If this lookup object has private access, then the caller class is the lookupClass.
2099 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2100 */
2101 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2102 Class<?> callerClass = null;
2103 if (MethodHandleNatives.isCallerSensitive(m)) {
2104 // Only lookups with private access are allowed to resolve caller-sensitive methods
2105 if (hasPrivateAccess()) {
2106 callerClass = lookupClass;
2107 } else {
2108 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2109 }
2110 }
2111 return callerClass;
2112 }
2113
2114 /**
2115 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2116 * @return {@code true} if this lookup has {@code PRIVATE} access.
2117 * @since 9
2118 */
2119 public boolean hasPrivateAccess() {
2120 return (allowedModes & PRIVATE) != 0;
2121 }
2122
2123 /**
2124 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2125 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2126 * If this lookup object has private access, then the caller class is the lookupClass.
2127 */
2128 void checkSecurityManager(Class<?> refc, MemberName m) {
2129 SecurityManager smgr = System.getSecurityManager();
2130 if (smgr == null) return;
2131 if (allowedModes == TRUSTED) return;
2132
2133 // Step 1:
2134 boolean fullPowerLookup = hasPrivateAccess();
2135 if (!fullPowerLookup ||
2136 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2137 ReflectUtil.checkPackageAccess(refc);
2138 }
2139
2140 if (m == null) { // findClass or accessClass
2141 // Step 2b:
2142 if (!fullPowerLookup) {
2143 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2144 }
2145 return;
2146 }
2147
2148 // Step 2a:
2149 if (m.isPublic()) return;
2150 if (!fullPowerLookup) {
2151 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2152 }
2153
2154 // Step 3:
2155 Class<?> defc = m.getDeclaringClass();
2156 if (!fullPowerLookup && defc != refc) {
2157 ReflectUtil.checkPackageAccess(defc);
2158 }
2159 }
2160
2161 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2162 boolean wantStatic = (refKind == REF_invokeStatic);
2163 String message;
2164 if (m.isConstructor())
2165 message = "expected a method, not a constructor";
2166 else if (!m.isMethod())
2167 message = "expected a method";
2168 else if (wantStatic != m.isStatic())
2169 message = wantStatic ? "expected a static method" : "expected a non-static method";
2170 else
2171 { checkAccess(refKind, refc, m); return; }
2172 throw m.makeAccessException(message, this);
2173 }
2174
2175 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2176 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2177 String message;
2178 if (wantStatic != m.isStatic())
2179 message = wantStatic ? "expected a static field" : "expected a non-static field";
2180 else
2181 { checkAccess(refKind, refc, m); return; }
2182 throw m.makeAccessException(message, this);
2183 }
2184
2185 /** Check public/protected/private bits on the symbolic reference class and its member. */
2186 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2187 assert(m.referenceKindIsConsistentWith(refKind) &&
2188 MethodHandleNatives.refKindIsValid(refKind) &&
2189 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2190 int allowedModes = this.allowedModes;
2191 if (allowedModes == TRUSTED) return;
2192 int mods = m.getModifiers();
2193 if (Modifier.isProtected(mods) &&
2194 refKind == REF_invokeVirtual &&
2195 m.getDeclaringClass() == Object.class &&
2196 m.getName().equals("clone") &&
2197 refc.isArray()) {
2198 // The JVM does this hack also.
2199 // (See ClassVerifier::verify_invoke_instructions
2200 // and LinkResolver::check_method_accessability.)
2201 // Because the JVM does not allow separate methods on array types,
2202 // there is no separate method for int[].clone.
2203 // All arrays simply inherit Object.clone.
2204 // But for access checking logic, we make Object.clone
2205 // (normally protected) appear to be public.
2206 // Later on, when the DirectMethodHandle is created,
2207 // its leading argument will be restricted to the
2208 // requested array type.
2209 // N.B. The return type is not adjusted, because
2210 // that is *not* the bytecode behavior.
2211 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2212 }
2213 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2214 // cannot "new" a protected ctor in a different package
2215 mods ^= Modifier.PROTECTED;
2216 }
2217 if (Modifier.isFinal(mods) &&
2218 MethodHandleNatives.refKindIsSetter(refKind))
2219 throw m.makeAccessException("unexpected set of a final field", this);
2220 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2221 if ((requestedModes & allowedModes) != 0) {
2222 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2223 mods, lookupClass(), allowedModes))
2224 return;
2225 } else {
2226 // Protected members can also be checked as if they were package-private.
2227 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2228 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2229 return;
2230 }
2231 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2232 }
2233
2234 String accessFailedMessage(Class<?> refc, MemberName m) {
2235 Class<?> defc = m.getDeclaringClass();
2236 int mods = m.getModifiers();
2237 // check the class first:
2238 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2239 (defc == refc ||
2240 Modifier.isPublic(refc.getModifiers())));
2241 if (!classOK && (allowedModes & PACKAGE) != 0) {
2242 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2243 (defc == refc ||
2244 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2245 }
2246 if (!classOK)
2247 return "class is not public";
2248 if (Modifier.isPublic(mods))
2249 return "access to public member failed"; // (how?, module not readable?)
2250 if (Modifier.isPrivate(mods))
2251 return "member is private";
2252 if (Modifier.isProtected(mods))
2253 return "member is protected";
2254 return "member is private to package";
2255 }
2256
2257 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2258 int allowedModes = this.allowedModes;
2259 if (allowedModes == TRUSTED) return;
2260 if (!hasPrivateAccess()
2261 || (specialCaller != lookupClass()
2262 // ensure non-abstract methods in superinterfaces can be special-invoked
2263 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2264 throw new MemberName(specialCaller).
2265 makeAccessException("no private access for invokespecial", this);
2266 }
2267
2268 private boolean restrictProtectedReceiver(MemberName method) {
2269 // The accessing class only has the right to use a protected member
2270 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2271 if (!method.isProtected() || method.isStatic()
2272 || allowedModes == TRUSTED
2273 || method.getDeclaringClass() == lookupClass()
2274 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2275 return false;
2276 return true;
2277 }
2278 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2279 assert(!method.isStatic());
2280 // receiver type of mh is too wide; narrow to caller
2281 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2282 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2283 }
2284 MethodType rawType = mh.type();
2285 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2286 MethodType narrowType = rawType.changeParameterType(0, caller);
2287 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2288 assert(mh.viewAsTypeChecks(narrowType, true));
2289 return mh.copyWith(narrowType, mh.form);
2290 }
2291
2292 /** Check access and get the requested method. */
2293 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2294 final boolean doRestrict = true;
2295 final boolean checkSecurity = true;
2296 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2297 }
2298 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2299 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2300 final boolean doRestrict = false;
2301 final boolean checkSecurity = true;
2302 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2303 }
2304 /** Check access and get the requested method, eliding security manager checks. */
2305 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2306 final boolean doRestrict = true;
2307 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2308 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2309 }
2310 /** Common code for all methods; do not call directly except from immediately above. */
2311 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2312 boolean checkSecurity,
2313 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
2314
2315 checkMethod(refKind, refc, method);
2316 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2317 if (checkSecurity)
2318 checkSecurityManager(refc, method);
2319 assert(!method.isMethodHandleInvoke());
2320
2321 if (refKind == REF_invokeSpecial &&
2322 refc != lookupClass() &&
2323 !refc.isInterface() &&
2324 refc != lookupClass().getSuperclass() &&
2325 refc.isAssignableFrom(lookupClass())) {
2326 assert(!method.getName().equals("<init>")); // not this code path
2327
2328 // Per JVMS 6.5, desc. of invokespecial instruction:
2329 // If the method is in a superclass of the LC,
2330 // and if our original search was above LC.super,
2331 // repeat the search (symbolic lookup) from LC.super
2332 // and continue with the direct superclass of that class,
2333 // and so forth, until a match is found or no further superclasses exist.
2334 // FIXME: MemberName.resolve should handle this instead.
2335 Class<?> refcAsSuper = lookupClass();
2336 MemberName m2;
2337 do {
2338 refcAsSuper = refcAsSuper.getSuperclass();
2339 m2 = new MemberName(refcAsSuper,
2340 method.getName(),
2341 method.getMethodType(),
2342 REF_invokeSpecial);
2343 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2344 } while (m2 == null && // no method is found yet
2345 refc != refcAsSuper); // search up to refc
2346 if (m2 == null) throw new InternalError(method.toString());
2347 method = m2;
2348 refc = refcAsSuper;
2349 // redo basic checks
2350 checkMethod(refKind, refc, method);
2351 }
2352
2353 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
2354 MethodHandle mh = dmh;
2355 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
2356 if ((doRestrict && refKind == REF_invokeSpecial) ||
2357 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2358 mh = restrictReceiver(method, dmh, lookupClass());
2359 }
2360 mh = maybeBindCaller(method, mh, boundCallerClass);
2361 mh = mh.setVarargs(method);
2362 return mh;
2363 }
2364 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2365 Class<?> boundCallerClass)
2366 throws IllegalAccessException {
2367 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2368 return mh;
2369 Class<?> hostClass = lookupClass;
2370 if (!hasPrivateAccess()) // caller must have private access
2371 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
2372 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2373 // Note: caller will apply varargs after this step happens.
2374 return cbmh;
2375 }
2376 /** Check access and get the requested field. */
2377 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2378 final boolean checkSecurity = true;
2379 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2380 }
2381 /** Check access and get the requested field, eliding security manager checks. */
2382 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2383 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2384 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2385 }
2386 /** Common code for all fields; do not call directly except from immediately above. */
2387 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2388 boolean checkSecurity) throws IllegalAccessException {
2389 checkField(refKind, refc, field);
2390 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2391 if (checkSecurity)
2392 checkSecurityManager(refc, field);
2393 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2394 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2395 restrictProtectedReceiver(field));
2396 if (doRestrict)
2397 return restrictReceiver(field, dmh, lookupClass());
2398 return dmh;
2399 }
2400 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2401 Class<?> refc, MemberName getField, MemberName putField)
2402 throws IllegalAccessException {
2403 final boolean checkSecurity = true;
2404 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2405 }
2406 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2407 Class<?> refc, MemberName getField, MemberName putField)
2408 throws IllegalAccessException {
2409 final boolean checkSecurity = false;
2410 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2411 }
2412 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2413 Class<?> refc, MemberName getField, MemberName putField,
2414 boolean checkSecurity) throws IllegalAccessException {
2415 assert getField.isStatic() == putField.isStatic();
2416 assert getField.isGetter() && putField.isSetter();
2417 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2418 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2419
2420 checkField(getRefKind, refc, getField);
2421 if (checkSecurity)
2422 checkSecurityManager(refc, getField);
2423
2424 if (!putField.isFinal()) {
2425 // A VarHandle does not support updates to final fields, any
2426 // such VarHandle to a final field will be read-only and
2427 // therefore the following write-based accessibility checks are
2428 // only required for non-final fields
2429 checkField(putRefKind, refc, putField);
2430 if (checkSecurity)
2431 checkSecurityManager(refc, putField);
2432 }
2433
2434 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2435 restrictProtectedReceiver(getField));
2436 if (doRestrict) {
2437 assert !getField.isStatic();
2438 // receiver type of VarHandle is too wide; narrow to caller
2439 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2440 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2441 }
2442 refc = lookupClass();
2443 }
2444 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2445 }
2446 /** Check access and get the requested constructor. */
2447 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2448 final boolean checkSecurity = true;
2449 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2450 }
2451 /** Check access and get the requested constructor, eliding security manager checks. */
2452 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2453 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2454 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2455 }
2456 /** Common code for all constructors; do not call directly except from immediately above. */
2457 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2458 boolean checkSecurity) throws IllegalAccessException {
2459 assert(ctor.isConstructor());
2460 checkAccess(REF_newInvokeSpecial, refc, ctor);
2461 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2462 if (checkSecurity)
2463 checkSecurityManager(refc, ctor);
2464 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2465 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2466 }
2467
2468 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2469 */
2470 /*non-public*/
2471 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2472 if (!(type instanceof Class || type instanceof MethodType))
2473 throw new InternalError("unresolved MemberName");
2474 MemberName member = new MemberName(refKind, defc, name, type);
2475 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2476 if (mh != null) {
2477 checkSymbolicClass(defc);
2478 return mh;
2479 }
2480 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2481 // Treat MethodHandle.invoke and invokeExact specially.
2482 mh = findVirtualForMH(member.getName(), member.getMethodType());
2483 if (mh != null) {
2484 return mh;
2485 }
2486 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
2487 // Treat signature-polymorphic methods on VarHandle specially.
2488 mh = findVirtualForVH(member.getName(), member.getMethodType());
2489 if (mh != null) {
2490 return mh;
2491 }
2492 }
2493 MemberName resolved = resolveOrFail(refKind, member);
2494 mh = getDirectMethodForConstant(refKind, defc, resolved);
2495 if (mh instanceof DirectMethodHandle
2496 && canBeCached(refKind, defc, resolved)) {
2497 MemberName key = mh.internalMemberName();
2498 if (key != null) {
2499 key = key.asNormalOriginal();
2500 }
2501 if (member.equals(key)) { // better safe than sorry
2502 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2503 }
2504 }
2505 return mh;
2506 }
2507 private
2508 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2509 if (refKind == REF_invokeSpecial) {
2510 return false;
2511 }
2512 if (!Modifier.isPublic(defc.getModifiers()) ||
2513 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2514 !member.isPublic() ||
2515 member.isCallerSensitive()) {
2516 return false;
2517 }
2518 ClassLoader loader = defc.getClassLoader();
2519 if (loader != null) {
2520 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2521 boolean found = false;
2522 while (sysl != null) {
2523 if (loader == sysl) { found = true; break; }
2524 sysl = sysl.getParent();
2525 }
2526 if (!found) {
2527 return false;
2528 }
2529 }
2530 try {
2531 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
2532 new MemberName(refKind, defc, member.getName(), member.getType()));
2533 if (resolved2 == null) {
2534 return false;
2535 }
2536 checkSecurityManager(defc, resolved2);
2537 } catch (SecurityException ex) {
2538 return false;
2539 }
2540 return true;
2541 }
2542 private
2543 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2544 throws ReflectiveOperationException {
2545 if (MethodHandleNatives.refKindIsField(refKind)) {
2546 return getDirectFieldNoSecurityManager(refKind, defc, member);
2547 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2548 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2549 } else if (refKind == REF_newInvokeSpecial) {
2550 return getDirectConstructorNoSecurityManager(defc, member);
2551 }
2552 // oops
2553 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2554 }
2555
2556 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2557 }
2558
2559 /**
2560 * Produces a method handle constructing arrays of a desired type,
2561 * as if by the {@code anewarray} bytecode.
2562 * The return type of the method handle will be the array type.
2563 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2564 *
2565 * <p> If the returned method handle is invoked with a negative
2566 * array size, a {@code NegativeArraySizeException} will be thrown.
2567 *
2568 * @param arrayClass an array type
2569 * @return a method handle which can create arrays of the given type
2570 * @throws NullPointerException if the argument is {@code null}
2571 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2572 * @see java.lang.reflect.Array#newInstance(Class, int)
2573 * @jvms 6.5 {@code anewarray} Instruction
2574 * @since 9
2575 */
2576 public static
2577 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2578 if (!arrayClass.isArray()) {
2579 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2580 }
2581 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2582 bindTo(arrayClass.getComponentType());
2583 return ani.asType(ani.type().changeReturnType(arrayClass));
2584 }
2585
2586 /**
2587 * Produces a method handle returning the length of an array,
2588 * as if by the {@code arraylength} bytecode.
2589 * The type of the method handle will have {@code int} as return type,
2590 * and its sole argument will be the array type.
2591 *
2592 * <p> If the returned method handle is invoked with a {@code null}
2593 * array reference, a {@code NullPointerException} will be thrown.
2594 *
2595 * @param arrayClass an array type
2596 * @return a method handle which can retrieve the length of an array of the given array type
2597 * @throws NullPointerException if the argument is {@code null}
2598 * @throws IllegalArgumentException if arrayClass is not an array type
2599 * @jvms 6.5 {@code arraylength} Instruction
2600 * @since 9
2601 */
2602 public static
2603 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2604 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2605 }
2606
2607 /**
2608 * Produces a method handle giving read access to elements of an array,
2609 * as if by the {@code aaload} bytecode.
2610 * The type of the method handle will have a return type of the array's
2611 * element type. Its first argument will be the array type,
2612 * and the second will be {@code int}.
2613 *
2614 * <p> When the returned method handle is invoked,
2615 * the array reference and array index are checked.
2616 * A {@code NullPointerException} will be thrown if the array reference
2617 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2618 * thrown if the index is negative or if it is greater than or equal to
2619 * the length of the array.
2620 *
2621 * @param arrayClass an array type
2622 * @return a method handle which can load values from the given array type
2623 * @throws NullPointerException if the argument is null
2624 * @throws IllegalArgumentException if arrayClass is not an array type
2625 * @jvms 6.5 {@code aaload} Instruction
2626 */
2627 public static
2628 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2629 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2630 }
2631
2632 /**
2633 * Produces a method handle giving write access to elements of an array,
2634 * as if by the {@code astore} bytecode.
2635 * The type of the method handle will have a void return type.
2636 * Its last argument will be the array's element type.
2637 * The first and second arguments will be the array type and int.
2638 *
2639 * <p> When the returned method handle is invoked,
2640 * the array reference and array index are checked.
2641 * A {@code NullPointerException} will be thrown if the array reference
2642 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2643 * thrown if the index is negative or if it is greater than or equal to
2644 * the length of the array.
2645 *
2646 * @param arrayClass the class of an array
2647 * @return a method handle which can store values into the array type
2648 * @throws NullPointerException if the argument is null
2649 * @throws IllegalArgumentException if arrayClass is not an array type
2650 * @jvms 6.5 {@code aastore} Instruction
2651 */
2652 public static
2653 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2654 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2655 }
2656
2657 /**
2658 * Produces a VarHandle giving access to elements of an array of type
2659 * {@code arrayClass}. The VarHandle's variable type is the component type
2660 * of {@code arrayClass} and the list of coordinate types is
2661 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2662 * corresponds to an argument that is an index into an array.
2663 * <p>
2664 * Certain access modes of the returned VarHandle are unsupported under
2665 * the following conditions:
2666 * <ul>
2667 * <li>if the component type is anything other than {@code byte},
2668 * {@code short}, {@code char}, {@code int}, {@code long},
2669 * {@code float}, or {@code double} then numeric atomic update access
2670 * modes are unsupported.
2671 * <li>if the field type is anything other than {@code boolean},
2672 * {@code byte}, {@code short}, {@code char}, {@code int} or
2673 * {@code long} then bitwise atomic update access modes are
2674 * unsupported.
2675 * </ul>
2676 * <p>
2677 * If the component type is {@code float} or {@code double} then numeric
2678 * and atomic update access modes compare values using their bitwise
2679 * representation (see {@link Float#floatToRawIntBits} and
2680 * {@link Double#doubleToRawLongBits}, respectively).
2681 *
2682 * <p> When the returned {@code VarHandle} is invoked,
2683 * the array reference and array index are checked.
2684 * A {@code NullPointerException} will be thrown if the array reference
2685 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2686 * thrown if the index is negative or if it is greater than or equal to
2687 * the length of the array.
2688 *
2689 * @apiNote
2690 * Bitwise comparison of {@code float} values or {@code double} values,
2691 * as performed by the numeric and atomic update access modes, differ
2692 * from the primitive {@code ==} operator and the {@link Float#equals}
2693 * and {@link Double#equals} methods, specifically with respect to
2694 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2695 * Care should be taken when performing a compare and set or a compare
2696 * and exchange operation with such values since the operation may
2697 * unexpectedly fail.
2698 * There are many possible NaN values that are considered to be
2699 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2700 * provided by Java can distinguish between them. Operation failure can
2701 * occur if the expected or witness value is a NaN value and it is
2702 * transformed (perhaps in a platform specific manner) into another NaN
2703 * value, and thus has a different bitwise representation (see
2704 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2705 * details).
2706 * The values {@code -0.0} and {@code +0.0} have different bitwise
2707 * representations but are considered equal when using the primitive
2708 * {@code ==} operator. Operation failure can occur if, for example, a
2709 * numeric algorithm computes an expected value to be say {@code -0.0}
2710 * and previously computed the witness value to be say {@code +0.0}.
2711 * @param arrayClass the class of an array, of type {@code T[]}
2712 * @return a VarHandle giving access to elements of an array
2713 * @throws NullPointerException if the arrayClass is null
2714 * @throws IllegalArgumentException if arrayClass is not an array type
2715 * @since 9
2716 */
2717 public static
2718 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2719 return VarHandles.makeArrayElementHandle(arrayClass);
2720 }
2721
2722 /**
2723 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2724 * viewed as if it were a different primitive array type, such as
2725 * {@code int[]} or {@code long[]}.
2726 * The VarHandle's variable type is the component type of
2727 * {@code viewArrayClass} and the list of coordinate types is
2728 * {@code (byte[], int)}, where the {@code int} coordinate type
2729 * corresponds to an argument that is an index into a {@code byte[]} array.
2730 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2731 * array, composing bytes to or from a value of the component type of
2732 * {@code viewArrayClass} according to the given endianness.
2733 * <p>
2734 * The supported component types (variables types) are {@code short},
2735 * {@code char}, {@code int}, {@code long}, {@code float} and
2736 * {@code double}.
2737 * <p>
2738 * Access of bytes at a given index will result in an
2739 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2740 * or greater than the {@code byte[]} array length minus the size (in bytes)
2741 * of {@code T}.
2742 * <p>
2743 * Access of bytes at an index may be aligned or misaligned for {@code T},
2744 * with respect to the underlying memory address, {@code A} say, associated
2745 * with the array and index.
2746 * If access is misaligned then access for anything other than the
2747 * {@code get} and {@code set} access modes will result in an
2748 * {@code IllegalStateException}. In such cases atomic access is only
2749 * guaranteed with respect to the largest power of two that divides the GCD
2750 * of {@code A} and the size (in bytes) of {@code T}.
2751 * If access is aligned then following access modes are supported and are
2752 * guaranteed to support atomic access:
2753 * <ul>
2754 * <li>read write access modes for all {@code T}, with the exception of
2755 * access modes {@code get} and {@code set} for {@code long} and
2756 * {@code double} on 32-bit platforms.
2757 * <li>atomic update access modes for {@code int}, {@code long},
2758 * {@code float} or {@code double}.
2759 * (Future major platform releases of the JDK may support additional
2760 * types for certain currently unsupported access modes.)
2761 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2762 * (Future major platform releases of the JDK may support additional
2763 * numeric types for certain currently unsupported access modes.)
2764 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2765 * (Future major platform releases of the JDK may support additional
2766 * numeric types for certain currently unsupported access modes.)
2767 * </ul>
2768 * <p>
2769 * Misaligned access, and therefore atomicity guarantees, may be determined
2770 * for {@code byte[]} arrays without operating on a specific array. Given
2771 * an {@code index}, {@code T} and it's corresponding boxed type,
2772 * {@code T_BOX}, misalignment may be determined as follows:
2773 * <pre>{@code
2774 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2775 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2776 * alignmentOffset(0, sizeOfT);
2777 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2778 * boolean isMisaligned = misalignedAtIndex != 0;
2779 * }</pre>
2780 * <p>
2781 * If the variable type is {@code float} or {@code double} then atomic
2782 * update access modes compare values using their bitwise representation
2783 * (see {@link Float#floatToRawIntBits} and
2784 * {@link Double#doubleToRawLongBits}, respectively).
2785 * @param viewArrayClass the view array class, with a component type of
2786 * type {@code T}
2787 * @param byteOrder the endianness of the view array elements, as
2788 * stored in the underlying {@code byte} array
2789 * @return a VarHandle giving access to elements of a {@code byte[]} array
2790 * viewed as if elements corresponding to the components type of the view
2791 * array class
2792 * @throws NullPointerException if viewArrayClass or byteOrder is null
2793 * @throws IllegalArgumentException if viewArrayClass is not an array type
2794 * @throws UnsupportedOperationException if the component type of
2795 * viewArrayClass is not supported as a variable type
2796 * @since 9
2797 */
2798 public static
2799 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2800 ByteOrder byteOrder) throws IllegalArgumentException {
2801 Objects.requireNonNull(byteOrder);
2802 return VarHandles.byteArrayViewHandle(viewArrayClass,
2803 byteOrder == ByteOrder.BIG_ENDIAN);
2804 }
2805
2806 /**
2807 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2808 * viewed as if it were an array of elements of a different primitive
2809 * component type to that of {@code byte}, such as {@code int[]} or
2810 * {@code long[]}.
2811 * The VarHandle's variable type is the component type of
2812 * {@code viewArrayClass} and the list of coordinate types is
2813 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2814 * corresponds to an argument that is an index into a {@code byte[]} array.
2815 * The returned VarHandle accesses bytes at an index in a
2816 * {@code ByteBuffer}, composing bytes to or from a value of the component
2817 * type of {@code viewArrayClass} according to the given endianness.
2818 * <p>
2819 * The supported component types (variables types) are {@code short},
2820 * {@code char}, {@code int}, {@code long}, {@code float} and
2821 * {@code double}.
2822 * <p>
2823 * Access will result in a {@code ReadOnlyBufferException} for anything
2824 * other than the read access modes if the {@code ByteBuffer} is read-only.
2825 * <p>
2826 * Access of bytes at a given index will result in an
2827 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2828 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2829 * {@code T}.
2830 * <p>
2831 * Access of bytes at an index may be aligned or misaligned for {@code T},
2832 * with respect to the underlying memory address, {@code A} say, associated
2833 * with the {@code ByteBuffer} and index.
2834 * If access is misaligned then access for anything other than the
2835 * {@code get} and {@code set} access modes will result in an
2836 * {@code IllegalStateException}. In such cases atomic access is only
2837 * guaranteed with respect to the largest power of two that divides the GCD
2838 * of {@code A} and the size (in bytes) of {@code T}.
2839 * If access is aligned then following access modes are supported and are
2840 * guaranteed to support atomic access:
2841 * <ul>
2842 * <li>read write access modes for all {@code T}, with the exception of
2843 * access modes {@code get} and {@code set} for {@code long} and
2844 * {@code double} on 32-bit platforms.
2845 * <li>atomic update access modes for {@code int}, {@code long},
2846 * {@code float} or {@code double}.
2847 * (Future major platform releases of the JDK may support additional
2848 * types for certain currently unsupported access modes.)
2849 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2850 * (Future major platform releases of the JDK may support additional
2851 * numeric types for certain currently unsupported access modes.)
2852 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2853 * (Future major platform releases of the JDK may support additional
2854 * numeric types for certain currently unsupported access modes.)
2855 * </ul>
2856 * <p>
2857 * Misaligned access, and therefore atomicity guarantees, may be determined
2858 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2859 * {@code index}, {@code T} and it's corresponding boxed type,
2860 * {@code T_BOX}, as follows:
2861 * <pre>{@code
2862 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2863 * ByteBuffer bb = ...
2864 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2865 * boolean isMisaligned = misalignedAtIndex != 0;
2866 * }</pre>
2867 * <p>
2868 * If the variable type is {@code float} or {@code double} then atomic
2869 * update access modes compare values using their bitwise representation
2870 * (see {@link Float#floatToRawIntBits} and
2871 * {@link Double#doubleToRawLongBits}, respectively).
2872 * @param viewArrayClass the view array class, with a component type of
2873 * type {@code T}
2874 * @param byteOrder the endianness of the view array elements, as
2875 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2876 * endianness of a {@code ByteBuffer})
2877 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2878 * viewed as if elements corresponding to the components type of the view
2879 * array class
2880 * @throws NullPointerException if viewArrayClass or byteOrder is null
2881 * @throws IllegalArgumentException if viewArrayClass is not an array type
2882 * @throws UnsupportedOperationException if the component type of
2883 * viewArrayClass is not supported as a variable type
2884 * @since 9
2885 */
2886 public static
2887 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2888 ByteOrder byteOrder) throws IllegalArgumentException {
2889 Objects.requireNonNull(byteOrder);
2890 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2891 byteOrder == ByteOrder.BIG_ENDIAN);
2892 }
2893
2894
2895 /// method handle invocation (reflective style)
2896
2897 /**
2898 * Produces a method handle which will invoke any method handle of the
2899 * given {@code type}, with a given number of trailing arguments replaced by
2900 * a single trailing {@code Object[]} array.
2901 * The resulting invoker will be a method handle with the following
2902 * arguments:
2903 * <ul>
2904 * <li>a single {@code MethodHandle} target
2905 * <li>zero or more leading values (counted by {@code leadingArgCount})
2906 * <li>an {@code Object[]} array containing trailing arguments
2907 * </ul>
2908 * <p>
2909 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2910 * the indicated {@code type}.
2911 * That is, if the target is exactly of the given {@code type}, it will behave
2912 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2913 * is used to convert the target to the required {@code type}.
2914 * <p>
2915 * The type of the returned invoker will not be the given {@code type}, but rather
2916 * will have all parameters except the first {@code leadingArgCount}
2917 * replaced by a single array of type {@code Object[]}, which will be
2918 * the final parameter.
2919 * <p>
2920 * Before invoking its target, the invoker will spread the final array, apply
2921 * reference casts as necessary, and unbox and widen primitive arguments.
2922 * If, when the invoker is called, the supplied array argument does
2923 * not have the correct number of elements, the invoker will throw
2924 * an {@link IllegalArgumentException} instead of invoking the target.
2925 * <p>
2926 * This method is equivalent to the following code (though it may be more efficient):
2927 * <blockquote><pre>{@code
2928 MethodHandle invoker = MethodHandles.invoker(type);
2929 int spreadArgCount = type.parameterCount() - leadingArgCount;
2930 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2931 return invoker;
2932 * }</pre></blockquote>
2933 * This method throws no reflective or security exceptions.
2934 * @param type the desired target type
2935 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2936 * @return a method handle suitable for invoking any method handle of the given type
2937 * @throws NullPointerException if {@code type} is null
2938 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2939 * the range from 0 to {@code type.parameterCount()} inclusive,
2940 * or if the resulting method handle's type would have
2941 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2942 */
2943 public static
2944 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2945 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2946 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2947 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2948 return type.invokers().spreadInvoker(leadingArgCount);
2949 }
2950
2951 /**
2952 * Produces a special <em>invoker method handle</em> which can be used to
2953 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2954 * The resulting invoker will have a type which is
2955 * exactly equal to the desired type, except that it will accept
2956 * an additional leading argument of type {@code MethodHandle}.
2957 * <p>
2958 * This method is equivalent to the following code (though it may be more efficient):
2959 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2960 *
2961 * <p style="font-size:smaller;">
2962 * <em>Discussion:</em>
2963 * Invoker method handles can be useful when working with variable method handles
2964 * of unknown types.
2965 * For example, to emulate an {@code invokeExact} call to a variable method
2966 * handle {@code M}, extract its type {@code T},
2967 * look up the invoker method {@code X} for {@code T},
2968 * and call the invoker method, as {@code X.invoke(T, A...)}.
2969 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2970 * is unknown.)
2971 * If spreading, collecting, or other argument transformations are required,
2972 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2973 * method handle values, as long as they are compatible with the type of {@code X}.
2974 * <p style="font-size:smaller;">
2975 * <em>(Note: The invoker method is not available via the Core Reflection API.
2976 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2977 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2978 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2979 * <p>
2980 * This method throws no reflective or security exceptions.
2981 * @param type the desired target type
2982 * @return a method handle suitable for invoking any method handle of the given type
2983 * @throws IllegalArgumentException if the resulting method handle's type would have
2984 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2985 */
2986 public static
2987 MethodHandle exactInvoker(MethodType type) {
2988 return type.invokers().exactInvoker();
2989 }
2990
2991 /**
2992 * Produces a special <em>invoker method handle</em> which can be used to
2993 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2994 * The resulting invoker will have a type which is
2995 * exactly equal to the desired type, except that it will accept
2996 * an additional leading argument of type {@code MethodHandle}.
2997 * <p>
2998 * Before invoking its target, if the target differs from the expected type,
2999 * the invoker will apply reference casts as
3000 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
3001 * Similarly, the return value will be converted as necessary.
3002 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
3003 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
3004 * <p>
3005 * This method is equivalent to the following code (though it may be more efficient):
3006 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
3007 * <p style="font-size:smaller;">
3008 * <em>Discussion:</em>
3009 * A {@linkplain MethodType#genericMethodType general method type} is one which
3010 * mentions only {@code Object} arguments and return values.
3011 * An invoker for such a type is capable of calling any method handle
3012 * of the same arity as the general type.
3013 * <p style="font-size:smaller;">
3014 * <em>(Note: The invoker method is not available via the Core Reflection API.
3015 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3016 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3017 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3018 * <p>
3019 * This method throws no reflective or security exceptions.
3020 * @param type the desired target type
3021 * @return a method handle suitable for invoking any method handle convertible to the given type
3022 * @throws IllegalArgumentException if the resulting method handle's type would have
3023 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3024 */
3025 public static
3026 MethodHandle invoker(MethodType type) {
3027 return type.invokers().genericInvoker();
3028 }
3029
3030 /**
3031 * Produces a special <em>invoker method handle</em> which can be used to
3032 * invoke a signature-polymorphic access mode method on any VarHandle whose
3033 * associated access mode type is compatible with the given type.
3034 * The resulting invoker will have a type which is exactly equal to the
3035 * desired given type, except that it will accept an additional leading
3036 * argument of type {@code VarHandle}.
3037 *
3038 * @param accessMode the VarHandle access mode
3039 * @param type the desired target type
3040 * @return a method handle suitable for invoking an access mode method of
3041 * any VarHandle whose access mode type is of the given type.
3042 * @since 9
3043 */
3044 static public
3045 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3046 return type.invokers().varHandleMethodExactInvoker(accessMode);
3047 }
3048
3049 /**
3050 * Produces a special <em>invoker method handle</em> which can be used to
3051 * invoke a signature-polymorphic access mode method on any VarHandle whose
3052 * associated access mode type is compatible with the given type.
3053 * The resulting invoker will have a type which is exactly equal to the
3054 * desired given type, except that it will accept an additional leading
3055 * argument of type {@code VarHandle}.
3056 * <p>
3057 * Before invoking its target, if the access mode type differs from the
3058 * desired given type, the invoker will apply reference casts as necessary
3059 * and box, unbox, or widen primitive values, as if by
3060 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3061 * converted as necessary.
3062 * <p>
3063 * This method is equivalent to the following code (though it may be more
3064 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3065 *
3066 * @param accessMode the VarHandle access mode
3067 * @param type the desired target type
3068 * @return a method handle suitable for invoking an access mode method of
3069 * any VarHandle whose access mode type is convertible to the given
3070 * type.
3071 * @since 9
3072 */
3073 static public
3074 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3075 return type.invokers().varHandleMethodInvoker(accessMode);
3076 }
3077
3078 static /*non-public*/
3079 MethodHandle basicInvoker(MethodType type) {
3080 return type.invokers().basicInvoker();
3081 }
3082
3083 /// method handle modification (creation from other method handles)
3084
3085 /**
3086 * Produces a method handle which adapts the type of the
3087 * given method handle to a new type by pairwise argument and return type conversion.
3088 * The original type and new type must have the same number of arguments.
3089 * The resulting method handle is guaranteed to report a type
3090 * which is equal to the desired new type.
3091 * <p>
3092 * If the original type and new type are equal, returns target.
3093 * <p>
3094 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3095 * and some additional conversions are also applied if those conversions fail.
3096 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3097 * if possible, before or instead of any conversions done by {@code asType}:
3098 * <ul>
3099 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3100 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3101 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3102 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3103 * the boolean is converted to a byte value, 1 for true, 0 for false.
3104 * (This treatment follows the usage of the bytecode verifier.)
3105 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3106 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3107 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3108 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3109 * then a Java casting conversion (JLS 5.5) is applied.
3110 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3111 * widening and/or narrowing.)
3112 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3113 * conversion will be applied at runtime, possibly followed
3114 * by a Java casting conversion (JLS 5.5) on the primitive value,
3115 * possibly followed by a conversion from byte to boolean by testing
3116 * the low-order bit.
3117 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3118 * and if the reference is null at runtime, a zero value is introduced.
3119 * </ul>
3120 * @param target the method handle to invoke after arguments are retyped
3121 * @param newType the expected type of the new method handle
3122 * @return a method handle which delegates to the target after performing
3123 * any necessary argument conversions, and arranges for any
3124 * necessary return value conversions
3125 * @throws NullPointerException if either argument is null
3126 * @throws WrongMethodTypeException if the conversion cannot be made
3127 * @see MethodHandle#asType
3128 */
3129 public static
3130 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3131 explicitCastArgumentsChecks(target, newType);
3132 // use the asTypeCache when possible:
3133 MethodType oldType = target.type();
3134 if (oldType == newType) return target;
3135 if (oldType.explicitCastEquivalentToAsType(newType)) {
3136 return target.asFixedArity().asType(newType);
3137 }
3138 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3139 }
3140
3141 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3142 if (target.type().parameterCount() != newType.parameterCount()) {
3143 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3144 }
3145 }
3146
3147 /**
3148 * Produces a method handle which adapts the calling sequence of the
3149 * given method handle to a new type, by reordering the arguments.
3150 * The resulting method handle is guaranteed to report a type
3151 * which is equal to the desired new type.
3152 * <p>
3153 * The given array controls the reordering.
3154 * Call {@code #I} the number of incoming parameters (the value
3155 * {@code newType.parameterCount()}, and call {@code #O} the number
3156 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3157 * Then the length of the reordering array must be {@code #O},
3158 * and each element must be a non-negative number less than {@code #I}.
3159 * For every {@code N} less than {@code #O}, the {@code N}-th
3160 * outgoing argument will be taken from the {@code I}-th incoming
3161 * argument, where {@code I} is {@code reorder[N]}.
3162 * <p>
3163 * No argument or return value conversions are applied.
3164 * The type of each incoming argument, as determined by {@code newType},
3165 * must be identical to the type of the corresponding outgoing parameter
3166 * or parameters in the target method handle.
3167 * The return type of {@code newType} must be identical to the return
3168 * type of the original target.
3169 * <p>
3170 * The reordering array need not specify an actual permutation.
3171 * An incoming argument will be duplicated if its index appears
3172 * more than once in the array, and an incoming argument will be dropped
3173 * if its index does not appear in the array.
3174 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3175 * incoming arguments which are not mentioned in the reordering array
3176 * may be of any type, as determined only by {@code newType}.
3177 * <blockquote><pre>{@code
3178 import static java.lang.invoke.MethodHandles.*;
3179 import static java.lang.invoke.MethodType.*;
3180 ...
3181 MethodType intfn1 = methodType(int.class, int.class);
3182 MethodType intfn2 = methodType(int.class, int.class, int.class);
3183 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3184 assert(sub.type().equals(intfn2));
3185 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3186 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3187 assert((int)rsub.invokeExact(1, 100) == 99);
3188 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3189 assert(add.type().equals(intfn2));
3190 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3191 assert(twice.type().equals(intfn1));
3192 assert((int)twice.invokeExact(21) == 42);
3193 * }</pre></blockquote>
3194 * <p>
3195 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3196 * variable-arity method handle}, even if the original target method handle was.
3197 * @param target the method handle to invoke after arguments are reordered
3198 * @param newType the expected type of the new method handle
3199 * @param reorder an index array which controls the reordering
3200 * @return a method handle which delegates to the target after it
3201 * drops unused arguments and moves and/or duplicates the other arguments
3202 * @throws NullPointerException if any argument is null
3203 * @throws IllegalArgumentException if the index array length is not equal to
3204 * the arity of the target, or if any index array element
3205 * not a valid index for a parameter of {@code newType},
3206 * or if two corresponding parameter types in
3207 * {@code target.type()} and {@code newType} are not identical,
3208 */
3209 public static
3210 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3211 reorder = reorder.clone(); // get a private copy
3212 MethodType oldType = target.type();
3213 permuteArgumentChecks(reorder, newType, oldType);
3214 // first detect dropped arguments and handle them separately
3215 int[] originalReorder = reorder;
3216 BoundMethodHandle result = target.rebind();
3217 LambdaForm form = result.form;
3218 int newArity = newType.parameterCount();
3219 // Normalize the reordering into a real permutation,
3220 // by removing duplicates and adding dropped elements.
3221 // This somewhat improves lambda form caching, as well
3222 // as simplifying the transform by breaking it up into steps.
3223 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3224 if (ddIdx > 0) {
3225 // We found a duplicated entry at reorder[ddIdx].
3226 // Example: (x,y,z)->asList(x,y,z)
3227 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3228 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3229 // The starred element corresponds to the argument
3230 // deleted by the dupArgumentForm transform.
3231 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3232 boolean killFirst = false;
3233 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3234 // Set killFirst if the dup is larger than an intervening position.
3235 // This will remove at least one inversion from the permutation.
3236 if (dupVal > val) killFirst = true;
3237 }
3238 if (!killFirst) {
3239 srcPos = dstPos;
3240 dstPos = ddIdx;
3241 }
3242 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3243 assert (reorder[srcPos] == reorder[dstPos]);
3244 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3245 // contract the reordering by removing the element at dstPos
3246 int tailPos = dstPos + 1;
3247 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3248 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3249 } else {
3250 int dropVal = ~ddIdx, insPos = 0;
3251 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3252 // Find first element of reorder larger than dropVal.
3253 // This is where we will insert the dropVal.
3254 insPos += 1;
3255 }
3256 Class<?> ptype = newType.parameterType(dropVal);
3257 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3258 oldType = oldType.insertParameterTypes(insPos, ptype);
3259 // expand the reordering by inserting an element at insPos
3260 int tailPos = insPos + 1;
3261 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3262 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3263 reorder[insPos] = dropVal;
3264 }
3265 assert (permuteArgumentChecks(reorder, newType, oldType));
3266 }
3267 assert (reorder.length == newArity); // a perfect permutation
3268 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3269 form = form.editor().permuteArgumentsForm(1, reorder);
3270 if (newType == result.type() && form == result.internalForm())
3271 return result;
3272 return result.copyWith(newType, form);
3273 }
3274
3275 /**
3276 * Return an indication of any duplicate or omission in reorder.
3277 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3278 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3279 * Otherwise, return zero.
3280 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3281 */
3282 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3283 final int BIT_LIMIT = 63; // max number of bits in bit mask
3284 if (newArity < BIT_LIMIT) {
3285 long mask = 0;
3286 for (int i = 0; i < reorder.length; i++) {
3287 int arg = reorder[i];
3288 if (arg >= newArity) {
3289 return reorder.length;
3290 }
3291 long bit = 1L << arg;
3292 if ((mask & bit) != 0) {
3293 return i; // >0 indicates a dup
3294 }
3295 mask |= bit;
3296 }
3297 if (mask == (1L << newArity) - 1) {
3298 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3299 return 0;
3300 }
3301 // find first zero
3302 long zeroBit = Long.lowestOneBit(~mask);
3303 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3304 assert(zeroPos <= newArity);
3305 if (zeroPos == newArity) {
3306 return 0;
3307 }
3308 return ~zeroPos;
3309 } else {
3310 // same algorithm, different bit set
3311 BitSet mask = new BitSet(newArity);
3312 for (int i = 0; i < reorder.length; i++) {
3313 int arg = reorder[i];
3314 if (arg >= newArity) {
3315 return reorder.length;
3316 }
3317 if (mask.get(arg)) {
3318 return i; // >0 indicates a dup
3319 }
3320 mask.set(arg);
3321 }
3322 int zeroPos = mask.nextClearBit(0);
3323 assert(zeroPos <= newArity);
3324 if (zeroPos == newArity) {
3325 return 0;
3326 }
3327 return ~zeroPos;
3328 }
3329 }
3330
3331 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3332 if (newType.returnType() != oldType.returnType())
3333 throw newIllegalArgumentException("return types do not match",
3334 oldType, newType);
3335 if (reorder.length == oldType.parameterCount()) {
3336 int limit = newType.parameterCount();
3337 boolean bad = false;
3338 for (int j = 0; j < reorder.length; j++) {
3339 int i = reorder[j];
3340 if (i < 0 || i >= limit) {
3341 bad = true; break;
3342 }
3343 Class<?> src = newType.parameterType(i);
3344 Class<?> dst = oldType.parameterType(j);
3345 if (src != dst)
3346 throw newIllegalArgumentException("parameter types do not match after reorder",
3347 oldType, newType);
3348 }
3349 if (!bad) return true;
3350 }
3351 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3352 }
3353
3354 /**
3355 * Produces a method handle of the requested return type which returns the given
3356 * constant value every time it is invoked.
3357 * <p>
3358 * Before the method handle is returned, the passed-in value is converted to the requested type.
3359 * If the requested type is primitive, widening primitive conversions are attempted,
3360 * else reference conversions are attempted.
3361 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3362 * @param type the return type of the desired method handle
3363 * @param value the value to return
3364 * @return a method handle of the given return type and no arguments, which always returns the given value
3365 * @throws NullPointerException if the {@code type} argument is null
3366 * @throws ClassCastException if the value cannot be converted to the required return type
3367 * @throws IllegalArgumentException if the given type is {@code void.class}
3368 */
3369 public static
3370 MethodHandle constant(Class<?> type, Object value) {
3371 if (type.isPrimitive()) {
3372 if (type == void.class)
3373 throw newIllegalArgumentException("void type");
3374 Wrapper w = Wrapper.forPrimitiveType(type);
3375 value = w.convert(value, type);
3376 if (w.zero().equals(value))
3377 return zero(w, type);
3378 return insertArguments(identity(type), 0, value);
3379 } else {
3380 if (value == null)
3381 return zero(Wrapper.OBJECT, type);
3382 return identity(type).bindTo(value);
3383 }
3384 }
3385
3386 /**
3387 * Produces a method handle which returns its sole argument when invoked.
3388 * @param type the type of the sole parameter and return value of the desired method handle
3389 * @return a unary method handle which accepts and returns the given type
3390 * @throws NullPointerException if the argument is null
3391 * @throws IllegalArgumentException if the given type is {@code void.class}
3392 */
3393 public static
3394 MethodHandle identity(Class<?> type) {
3395 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3396 int pos = btw.ordinal();
3397 MethodHandle ident = IDENTITY_MHS[pos];
3398 if (ident == null) {
3399 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3400 }
3401 if (ident.type().returnType() == type)
3402 return ident;
3403 // something like identity(Foo.class); do not bother to intern these
3404 assert (btw == Wrapper.OBJECT);
3405 return makeIdentity(type);
3406 }
3407
3408 /**
3409 * Produces a constant method handle of the requested return type which
3410 * returns the default value for that type every time it is invoked.
3411 * The resulting constant method handle will have no side effects.
3412 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3413 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3414 * since {@code explicitCastArguments} converts {@code null} to default values.
3415 * @param type the expected return type of the desired method handle
3416 * @return a constant method handle that takes no arguments
3417 * and returns the default value of the given type (or void, if the type is void)
3418 * @throws NullPointerException if the argument is null
3419 * @see MethodHandles#constant
3420 * @see MethodHandles#empty
3421 * @see MethodHandles#explicitCastArguments
3422 * @since 9
3423 */
3424 public static MethodHandle zero(Class<?> type) {
3425 Objects.requireNonNull(type);
3426 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3427 }
3428
3429 private static MethodHandle identityOrVoid(Class<?> type) {
3430 return type == void.class ? zero(type) : identity(type);
3431 }
3432
3433 /**
3434 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3435 * and returns a suitable default depending on the return type.
3436 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3437 * <p>The returned method handle is equivalent to
3438 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3439 *
3440 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3441 * {@code guardWithTest(pred, target, empty(target.type())}.
3442 * @param type the type of the desired method handle
3443 * @return a constant method handle of the given type, which returns a default value of the given return type
3444 * @throws NullPointerException if the argument is null
3445 * @see MethodHandles#zero
3446 * @see MethodHandles#constant
3447 * @since 9
3448 */
3449 public static MethodHandle empty(MethodType type) {
3450 Objects.requireNonNull(type);
3451 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3452 }
3453
3454 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3455 private static MethodHandle makeIdentity(Class<?> ptype) {
3456 MethodType mtype = methodType(ptype, ptype);
3457 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3458 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3459 }
3460
3461 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3462 int pos = btw.ordinal();
3463 MethodHandle zero = ZERO_MHS[pos];
3464 if (zero == null) {
3465 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3466 }
3467 if (zero.type().returnType() == rtype)
3468 return zero;
3469 assert(btw == Wrapper.OBJECT);
3470 return makeZero(rtype);
3471 }
3472 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3473 private static MethodHandle makeZero(Class<?> rtype) {
3474 MethodType mtype = methodType(rtype);
3475 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3476 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3477 }
3478
3479 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3480 // Simulate a CAS, to avoid racy duplication of results.
3481 MethodHandle prev = cache[pos];
3482 if (prev != null) return prev;
3483 return cache[pos] = value;
3484 }
3485
3486 /**
3487 * Provides a target method handle with one or more <em>bound arguments</em>
3488 * in advance of the method handle's invocation.
3489 * The formal parameters to the target corresponding to the bound
3490 * arguments are called <em>bound parameters</em>.
3491 * Returns a new method handle which saves away the bound arguments.
3492 * When it is invoked, it receives arguments for any non-bound parameters,
3493 * binds the saved arguments to their corresponding parameters,
3494 * and calls the original target.
3495 * <p>
3496 * The type of the new method handle will drop the types for the bound
3497 * parameters from the original target type, since the new method handle
3498 * will no longer require those arguments to be supplied by its callers.
3499 * <p>
3500 * Each given argument object must match the corresponding bound parameter type.
3501 * If a bound parameter type is a primitive, the argument object
3502 * must be a wrapper, and will be unboxed to produce the primitive value.
3503 * <p>
3504 * The {@code pos} argument selects which parameters are to be bound.
3505 * It may range between zero and <i>N-L</i> (inclusively),
3506 * where <i>N</i> is the arity of the target method handle
3507 * and <i>L</i> is the length of the values array.
3508 * <p>
3509 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3510 * variable-arity method handle}, even if the original target method handle was.
3511 * @param target the method handle to invoke after the argument is inserted
3512 * @param pos where to insert the argument (zero for the first)
3513 * @param values the series of arguments to insert
3514 * @return a method handle which inserts an additional argument,
3515 * before calling the original method handle
3516 * @throws NullPointerException if the target or the {@code values} array is null
3517 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
3518 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
3519 * is the length of the values array.
3520 * @throws ClassCastException if an argument does not match the corresponding bound parameter
3521 * type.
3522 * @see MethodHandle#bindTo
3523 */
3524 public static
3525 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3526 int insCount = values.length;
3527 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3528 if (insCount == 0) return target;
3529 BoundMethodHandle result = target.rebind();
3530 for (int i = 0; i < insCount; i++) {
3531 Object value = values[i];
3532 Class<?> ptype = ptypes[pos+i];
3533 if (ptype.isPrimitive()) {
3534 result = insertArgumentPrimitive(result, pos, ptype, value);
3535 } else {
3536 value = ptype.cast(value); // throw CCE if needed
3537 result = result.bindArgumentL(pos, value);
3538 }
3539 }
3540 return result;
3541 }
3542
3543 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3544 Class<?> ptype, Object value) {
3545 Wrapper w = Wrapper.forPrimitiveType(ptype);
3546 // perform unboxing and/or primitive conversion
3547 value = w.convert(value, ptype);
3548 switch (w) {
3549 case INT: return result.bindArgumentI(pos, (int)value);
3550 case LONG: return result.bindArgumentJ(pos, (long)value);
3551 case FLOAT: return result.bindArgumentF(pos, (float)value);
3552 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3553 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3554 }
3555 }
3556
3557 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3558 MethodType oldType = target.type();
3559 int outargs = oldType.parameterCount();
3560 int inargs = outargs - insCount;
3561 if (inargs < 0)
3562 throw newIllegalArgumentException("too many values to insert");
3563 if (pos < 0 || pos > inargs)
3564 throw newIllegalArgumentException("no argument type to append");
3565 return oldType.ptypes();
3566 }
3567
3568 /**
3569 * Produces a method handle which will discard some dummy arguments
3570 * before calling some other specified <i>target</i> method handle.
3571 * The type of the new method handle will be the same as the target's type,
3572 * except it will also include the dummy argument types,
3573 * at some given position.
3574 * <p>
3575 * The {@code pos} argument may range between zero and <i>N</i>,
3576 * where <i>N</i> is the arity of the target.
3577 * If {@code pos} is zero, the dummy arguments will precede
3578 * the target's real arguments; if {@code pos} is <i>N</i>
3579 * they will come after.
3580 * <p>
3581 * <b>Example:</b>
3582 * <blockquote><pre>{@code
3583 import static java.lang.invoke.MethodHandles.*;
3584 import static java.lang.invoke.MethodType.*;
3585 ...
3586 MethodHandle cat = lookup().findVirtual(String.class,
3587 "concat", methodType(String.class, String.class));
3588 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3589 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3590 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3591 assertEquals(bigType, d0.type());
3592 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3593 * }</pre></blockquote>
3594 * <p>
3595 * This method is also equivalent to the following code:
3596 * <blockquote><pre>
3597 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3598 * </pre></blockquote>
3599 * @param target the method handle to invoke after the arguments are dropped
3600 * @param valueTypes the type(s) of the argument(s) to drop
3601 * @param pos position of first argument to drop (zero for the leftmost)
3602 * @return a method handle which drops arguments of the given types,
3603 * before calling the original method handle
3604 * @throws NullPointerException if the target is null,
3605 * or if the {@code valueTypes} list or any of its elements is null
3606 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3607 * or if {@code pos} is negative or greater than the arity of the target,
3608 * or if the new method handle's type would have too many parameters
3609 */
3610 public static
3611 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3612 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3613 }
3614
3615 private static List<Class<?>> copyTypes(Object[] array) {
3616 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3617 }
3618
3619 private static
3620 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3621 MethodType oldType = target.type(); // get NPE
3622 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3623 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3624 if (dropped == 0) return target;
3625 BoundMethodHandle result = target.rebind();
3626 LambdaForm lform = result.form;
3627 int insertFormArg = 1 + pos;
3628 for (Class<?> ptype : valueTypes) {
3629 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3630 }
3631 result = result.copyWith(newType, lform);
3632 return result;
3633 }
3634
3635 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3636 int dropped = valueTypes.size();
3637 MethodType.checkSlotCount(dropped);
3638 int outargs = oldType.parameterCount();
3639 int inargs = outargs + dropped;
3640 if (pos < 0 || pos > outargs)
3641 throw newIllegalArgumentException("no argument type to remove"
3642 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3643 );
3644 return dropped;
3645 }
3646
3647 /**
3648 * Produces a method handle which will discard some dummy arguments
3649 * before calling some other specified <i>target</i> method handle.
3650 * The type of the new method handle will be the same as the target's type,
3651 * except it will also include the dummy argument types,
3652 * at some given position.
3653 * <p>
3654 * The {@code pos} argument may range between zero and <i>N</i>,
3655 * where <i>N</i> is the arity of the target.
3656 * If {@code pos} is zero, the dummy arguments will precede
3657 * the target's real arguments; if {@code pos} is <i>N</i>
3658 * they will come after.
3659 * @apiNote
3660 * <blockquote><pre>{@code
3661 import static java.lang.invoke.MethodHandles.*;
3662 import static java.lang.invoke.MethodType.*;
3663 ...
3664 MethodHandle cat = lookup().findVirtual(String.class,
3665 "concat", methodType(String.class, String.class));
3666 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3667 MethodHandle d0 = dropArguments(cat, 0, String.class);
3668 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3669 MethodHandle d1 = dropArguments(cat, 1, String.class);
3670 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3671 MethodHandle d2 = dropArguments(cat, 2, String.class);
3672 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3673 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3674 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3675 * }</pre></blockquote>
3676 * <p>
3677 * This method is also equivalent to the following code:
3678 * <blockquote><pre>
3679 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3680 * </pre></blockquote>
3681 * @param target the method handle to invoke after the arguments are dropped
3682 * @param valueTypes the type(s) of the argument(s) to drop
3683 * @param pos position of first argument to drop (zero for the leftmost)
3684 * @return a method handle which drops arguments of the given types,
3685 * before calling the original method handle
3686 * @throws NullPointerException if the target is null,
3687 * or if the {@code valueTypes} array or any of its elements is null
3688 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3689 * or if {@code pos} is negative or greater than the arity of the target,
3690 * or if the new method handle's type would have
3691 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3692 */
3693 public static
3694 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3695 return dropArguments0(target, pos, copyTypes(valueTypes));
3696 }
3697
3698 // private version which allows caller some freedom with error handling
3699 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3700 boolean nullOnFailure) {
3701 newTypes = copyTypes(newTypes.toArray());
3702 List<Class<?>> oldTypes = target.type().parameterList();
3703 int match = oldTypes.size();
3704 if (skip != 0) {
3705 if (skip < 0 || skip > match) {
3706 throw newIllegalArgumentException("illegal skip", skip, target);
3707 }
3708 oldTypes = oldTypes.subList(skip, match);
3709 match -= skip;
3710 }
3711 List<Class<?>> addTypes = newTypes;
3712 int add = addTypes.size();
3713 if (pos != 0) {
3714 if (pos < 0 || pos > add) {
3715 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3716 }
3717 addTypes = addTypes.subList(pos, add);
3718 add -= pos;
3719 assert(addTypes.size() == add);
3720 }
3721 // Do not add types which already match the existing arguments.
3722 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3723 if (nullOnFailure) {
3724 return null;
3725 }
3726 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3727 }
3728 addTypes = addTypes.subList(match, add);
3729 add -= match;
3730 assert(addTypes.size() == add);
3731 // newTypes: ( P*[pos], M*[match], A*[add] )
3732 // target: ( S*[skip], M*[match] )
3733 MethodHandle adapter = target;
3734 if (add > 0) {
3735 adapter = dropArguments0(adapter, skip+ match, addTypes);
3736 }
3737 // adapter: (S*[skip], M*[match], A*[add] )
3738 if (pos > 0) {
3739 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3740 }
3741 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3742 return adapter;
3743 }
3744
3745 /**
3746 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3747 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3748 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3749 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3750 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3751 * {@link #dropArguments(MethodHandle, int, Class[])}.
3752 * <p>
3753 * The resulting handle will have the same return type as the target handle.
3754 * <p>
3755 * In more formal terms, assume these two type lists:<ul>
3756 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3757 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3758 * {@code newTypes}.
3759 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3760 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3761 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3762 * sub-list.
3763 * </ul>
3764 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3765 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3766 * {@link #dropArguments(MethodHandle, int, Class[])}.
3767 *
3768 * @apiNote
3769 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3770 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3771 * <blockquote><pre>{@code
3772 import static java.lang.invoke.MethodHandles.*;
3773 import static java.lang.invoke.MethodType.*;
3774 ...
3775 ...
3776 MethodHandle h0 = constant(boolean.class, true);
3777 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3778 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3779 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3780 if (h1.type().parameterCount() < h2.type().parameterCount())
3781 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3782 else
3783 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3784 MethodHandle h3 = guardWithTest(h0, h1, h2);
3785 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3786 * }</pre></blockquote>
3787 * @param target the method handle to adapt
3788 * @param skip number of targets parameters to disregard (they will be unchanged)
3789 * @param newTypes the list of types to match {@code target}'s parameter type list to
3790 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3791 * @return a possibly adapted method handle
3792 * @throws NullPointerException if either argument is null
3793 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3794 * or if {@code skip} is negative or greater than the arity of the target,
3795 * or if {@code pos} is negative or greater than the newTypes list size,
3796 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3797 * {@code pos}.
3798 * @since 9
3799 */
3800 public static
3801 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3802 Objects.requireNonNull(target);
3803 Objects.requireNonNull(newTypes);
3804 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3805 }
3806
3807 /**
3808 * Adapts a target method handle by pre-processing
3809 * one or more of its arguments, each with its own unary filter function,
3810 * and then calling the target with each pre-processed argument
3811 * replaced by the result of its corresponding filter function.
3812 * <p>
3813 * The pre-processing is performed by one or more method handles,
3814 * specified in the elements of the {@code filters} array.
3815 * The first element of the filter array corresponds to the {@code pos}
3816 * argument of the target, and so on in sequence.
3817 * The filter functions are invoked in left to right order.
3818 * <p>
3819 * Null arguments in the array are treated as identity functions,
3820 * and the corresponding arguments left unchanged.
3821 * (If there are no non-null elements in the array, the original target is returned.)
3822 * Each filter is applied to the corresponding argument of the adapter.
3823 * <p>
3824 * If a filter {@code F} applies to the {@code N}th argument of
3825 * the target, then {@code F} must be a method handle which
3826 * takes exactly one argument. The type of {@code F}'s sole argument
3827 * replaces the corresponding argument type of the target
3828 * in the resulting adapted method handle.
3829 * The return type of {@code F} must be identical to the corresponding
3830 * parameter type of the target.
3831 * <p>
3832 * It is an error if there are elements of {@code filters}
3833 * (null or not)
3834 * which do not correspond to argument positions in the target.
3835 * <p><b>Example:</b>
3836 * <blockquote><pre>{@code
3837 import static java.lang.invoke.MethodHandles.*;
3838 import static java.lang.invoke.MethodType.*;
3839 ...
3840 MethodHandle cat = lookup().findVirtual(String.class,
3841 "concat", methodType(String.class, String.class));
3842 MethodHandle upcase = lookup().findVirtual(String.class,
3843 "toUpperCase", methodType(String.class));
3844 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3845 MethodHandle f0 = filterArguments(cat, 0, upcase);
3846 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3847 MethodHandle f1 = filterArguments(cat, 1, upcase);
3848 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3849 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3850 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3851 * }</pre></blockquote>
3852 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3853 * denotes the return type of both the {@code target} and resulting adapter.
3854 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3855 * of the parameters and arguments that precede and follow the filter position
3856 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3857 * values of the filtered parameters and arguments; they also represent the
3858 * return types of the {@code filter[i]} handles. The latter accept arguments
3859 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3860 * the resulting adapter.
3861 * <blockquote><pre>{@code
3862 * T target(P... p, A[i]... a[i], B... b);
3863 * A[i] filter[i](V[i]);
3864 * T adapter(P... p, V[i]... v[i], B... b) {
3865 * return target(p..., filter[i](v[i])..., b...);
3866 * }
3867 * }</pre></blockquote>
3868 * <p>
3869 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3870 * variable-arity method handle}, even if the original target method handle was.
3871 *
3872 * @param target the method handle to invoke after arguments are filtered
3873 * @param pos the position of the first argument to filter
3874 * @param filters method handles to call initially on filtered arguments
3875 * @return method handle which incorporates the specified argument filtering logic
3876 * @throws NullPointerException if the target is null
3877 * or if the {@code filters} array is null
3878 * @throws IllegalArgumentException if a non-null element of {@code filters}
3879 * does not match a corresponding argument type of target as described above,
3880 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3881 * or if the resulting method handle's type would have
3882 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3883 */
3884 public static
3885 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3886 // In method types arguments start at index 0, while the LF
3887 // editor have the MH receiver at position 0 - adjust appropriately.
3888 final int MH_RECEIVER_OFFSET = 1;
3889 filterArgumentsCheckArity(target, pos, filters);
3890 MethodHandle adapter = target;
3891
3892 // keep track of currently matched filters, as to optimize repeated filters
3893 int index = 0;
3894 int[] positions = new int[filters.length];
3895 MethodHandle filter = null;
3896
3897 // process filters in reverse order so that the invocation of
3898 // the resulting adapter will invoke the filters in left-to-right order
3899 for (int i = filters.length - 1; i >= 0; --i) {
3900 MethodHandle newFilter = filters[i];
3901 if (newFilter == null) continue; // ignore null elements of filters
3902
3903 // flush changes on update
3904 if (filter != newFilter) {
3905 if (filter != null) {
3906 if (index > 1) {
3907 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
3908 } else {
3909 adapter = filterArgument(adapter, positions[0] - 1, filter);
3910 }
3911 }
3912 filter = newFilter;
3913 index = 0;
3914 }
3915
3916 filterArgumentChecks(target, pos + i, newFilter);
3917 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
3918 }
3919 if (index > 1) {
3920 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
3921 } else if (index == 1) {
3922 adapter = filterArgument(adapter, positions[0] - 1, filter);
3923 }
3924 return adapter;
3925 }
3926
3927 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
3928 MethodType targetType = adapter.type();
3929 MethodType filterType = filter.type();
3930 BoundMethodHandle result = adapter.rebind();
3931 Class<?> newParamType = filterType.parameterType(0);
3932
3933 Class<?>[] ptypes = targetType.ptypes().clone();
3934 for (int pos : positions) {
3935 ptypes[pos - 1] = newParamType;
3936 }
3937 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
3938
3939 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
3940 return result.copyWithExtendL(newType, lform, filter);
3941 }
3942
3943 /*non-public*/ static
3944 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3945 filterArgumentChecks(target, pos, filter);
3946 MethodType targetType = target.type();
3947 MethodType filterType = filter.type();
3948 BoundMethodHandle result = target.rebind();
3949 Class<?> newParamType = filterType.parameterType(0);
3950 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3951 MethodType newType = targetType.changeParameterType(pos, newParamType);
3952 result = result.copyWithExtendL(newType, lform, filter);
3953 return result;
3954 }
3955
3956 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3957 MethodType targetType = target.type();
3958 int maxPos = targetType.parameterCount();
3959 if (pos + filters.length > maxPos)
3960 throw newIllegalArgumentException("too many filters");
3961 }
3962
3963 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3964 MethodType targetType = target.type();
3965 MethodType filterType = filter.type();
3966 if (filterType.parameterCount() != 1
3967 || filterType.returnType() != targetType.parameterType(pos))
3968 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3969 }
3970
3971 /**
3972 * Adapts a target method handle by pre-processing
3973 * a sub-sequence of its arguments with a filter (another method handle).
3974 * The pre-processed arguments are replaced by the result (if any) of the
3975 * filter function.
3976 * The target is then called on the modified (usually shortened) argument list.
3977 * <p>
3978 * If the filter returns a value, the target must accept that value as
3979 * its argument in position {@code pos}, preceded and/or followed by
3980 * any arguments not passed to the filter.
3981 * If the filter returns void, the target must accept all arguments
3982 * not passed to the filter.
3983 * No arguments are reordered, and a result returned from the filter
3984 * replaces (in order) the whole subsequence of arguments originally
3985 * passed to the adapter.
3986 * <p>
3987 * The argument types (if any) of the filter
3988 * replace zero or one argument types of the target, at position {@code pos},
3989 * in the resulting adapted method handle.
3990 * The return type of the filter (if any) must be identical to the
3991 * argument type of the target at position {@code pos}, and that target argument
3992 * is supplied by the return value of the filter.
3993 * <p>
3994 * In all cases, {@code pos} must be greater than or equal to zero, and
3995 * {@code pos} must also be less than or equal to the target's arity.
3996 * <p><b>Example:</b>
3997 * <blockquote><pre>{@code
3998 import static java.lang.invoke.MethodHandles.*;
3999 import static java.lang.invoke.MethodType.*;
4000 ...
4001 MethodHandle deepToString = publicLookup()
4002 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
4003
4004 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
4005 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
4006
4007 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
4008 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
4009
4010 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
4011 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
4012 assertEquals("[top, [up, down], strange]",
4013 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
4014
4015 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
4016 assertEquals("[top, [up, down], [strange]]",
4017 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
4018
4019 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4020 assertEquals("[top, [[up, down, strange], charm], bottom]",
4021 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4022 * }</pre></blockquote>
4023 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4024 * represents the return type of the {@code target} and resulting adapter.
4025 * {@code V}/{@code v} stand for the return type and value of the
4026 * {@code filter}, which are also found in the signature and arguments of
4027 * the {@code target}, respectively, unless {@code V} is {@code void}.
4028 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4029 * and values preceding and following the collection position, {@code pos},
4030 * in the {@code target}'s signature. They also turn up in the resulting
4031 * adapter's signature and arguments, where they surround
4032 * {@code B}/{@code b}, which represent the parameter types and arguments
4033 * to the {@code filter} (if any).
4034 * <blockquote><pre>{@code
4035 * T target(A...,V,C...);
4036 * V filter(B...);
4037 * T adapter(A... a,B... b,C... c) {
4038 * V v = filter(b...);
4039 * return target(a...,v,c...);
4040 * }
4041 * // and if the filter has no arguments:
4042 * T target2(A...,V,C...);
4043 * V filter2();
4044 * T adapter2(A... a,C... c) {
4045 * V v = filter2();
4046 * return target2(a...,v,c...);
4047 * }
4048 * // and if the filter has a void return:
4049 * T target3(A...,C...);
4050 * void filter3(B...);
4051 * T adapter3(A... a,B... b,C... c) {
4052 * filter3(b...);
4053 * return target3(a...,c...);
4054 * }
4055 * }</pre></blockquote>
4056 * <p>
4057 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
4058 * one which first "folds" the affected arguments, and then drops them, in separate
4059 * steps as follows:
4060 * <blockquote><pre>{@code
4061 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4062 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4063 * }</pre></blockquote>
4064 * If the target method handle consumes no arguments besides than the result
4065 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4066 * is equivalent to {@code filterReturnValue(coll, mh)}.
4067 * If the filter method handle {@code coll} consumes one argument and produces
4068 * a non-void result, then {@code collectArguments(mh, N, coll)}
4069 * is equivalent to {@code filterArguments(mh, N, coll)}.
4070 * Other equivalences are possible but would require argument permutation.
4071 * <p>
4072 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4073 * variable-arity method handle}, even if the original target method handle was.
4074 *
4075 * @param target the method handle to invoke after filtering the subsequence of arguments
4076 * @param pos the position of the first adapter argument to pass to the filter,
4077 * and/or the target argument which receives the result of the filter
4078 * @param filter method handle to call on the subsequence of arguments
4079 * @return method handle which incorporates the specified argument subsequence filtering logic
4080 * @throws NullPointerException if either argument is null
4081 * @throws IllegalArgumentException if the return type of {@code filter}
4082 * is non-void and is not the same as the {@code pos} argument of the target,
4083 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4084 * or if the resulting method handle's type would have
4085 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4086 * @see MethodHandles#foldArguments
4087 * @see MethodHandles#filterArguments
4088 * @see MethodHandles#filterReturnValue
4089 */
4090 public static
4091 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4092 MethodType newType = collectArgumentsChecks(target, pos, filter);
4093 MethodType collectorType = filter.type();
4094 BoundMethodHandle result = target.rebind();
4095 LambdaForm lform;
4096 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4097 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4098 if (lform != null) {
4099 return result.copyWith(newType, lform);
4100 }
4101 }
4102 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4103 return result.copyWithExtendL(newType, lform, filter);
4104 }
4105
4106 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4107 MethodType targetType = target.type();
4108 MethodType filterType = filter.type();
4109 Class<?> rtype = filterType.returnType();
4110 List<Class<?>> filterArgs = filterType.parameterList();
4111 if (rtype == void.class) {
4112 return targetType.insertParameterTypes(pos, filterArgs);
4113 }
4114 if (rtype != targetType.parameterType(pos)) {
4115 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4116 }
4117 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4118 }
4119
4120 /**
4121 * Adapts a target method handle by post-processing
4122 * its return value (if any) with a filter (another method handle).
4123 * The result of the filter is returned from the adapter.
4124 * <p>
4125 * If the target returns a value, the filter must accept that value as
4126 * its only argument.
4127 * If the target returns void, the filter must accept no arguments.
4128 * <p>
4129 * The return type of the filter
4130 * replaces the return type of the target
4131 * in the resulting adapted method handle.
4132 * The argument type of the filter (if any) must be identical to the
4133 * return type of the target.
4134 * <p><b>Example:</b>
4135 * <blockquote><pre>{@code
4136 import static java.lang.invoke.MethodHandles.*;
4137 import static java.lang.invoke.MethodType.*;
4138 ...
4139 MethodHandle cat = lookup().findVirtual(String.class,
4140 "concat", methodType(String.class, String.class));
4141 MethodHandle length = lookup().findVirtual(String.class,
4142 "length", methodType(int.class));
4143 System.out.println((String) cat.invokeExact("x", "y")); // xy
4144 MethodHandle f0 = filterReturnValue(cat, length);
4145 System.out.println((int) f0.invokeExact("x", "y")); // 2
4146 * }</pre></blockquote>
4147 * <p>Here is pseudocode for the resulting adapter. In the code,
4148 * {@code T}/{@code t} represent the result type and value of the
4149 * {@code target}; {@code V}, the result type of the {@code filter}; and
4150 * {@code A}/{@code a}, the types and values of the parameters and arguments
4151 * of the {@code target} as well as the resulting adapter.
4152 * <blockquote><pre>{@code
4153 * T target(A...);
4154 * V filter(T);
4155 * V adapter(A... a) {
4156 * T t = target(a...);
4157 * return filter(t);
4158 * }
4159 * // and if the target has a void return:
4160 * void target2(A...);
4161 * V filter2();
4162 * V adapter2(A... a) {
4163 * target2(a...);
4164 * return filter2();
4165 * }
4166 * // and if the filter has a void return:
4167 * T target3(A...);
4168 * void filter3(V);
4169 * void adapter3(A... a) {
4170 * T t = target3(a...);
4171 * filter3(t);
4172 * }
4173 * }</pre></blockquote>
4174 * <p>
4175 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4176 * variable-arity method handle}, even if the original target method handle was.
4177 * @param target the method handle to invoke before filtering the return value
4178 * @param filter method handle to call on the return value
4179 * @return method handle which incorporates the specified return value filtering logic
4180 * @throws NullPointerException if either argument is null
4181 * @throws IllegalArgumentException if the argument list of {@code filter}
4182 * does not match the return type of target as described above
4183 */
4184 public static
4185 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4186 MethodType targetType = target.type();
4187 MethodType filterType = filter.type();
4188 filterReturnValueChecks(targetType, filterType);
4189 BoundMethodHandle result = target.rebind();
4190 BasicType rtype = BasicType.basicType(filterType.returnType());
4191 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4192 MethodType newType = targetType.changeReturnType(filterType.returnType());
4193 result = result.copyWithExtendL(newType, lform, filter);
4194 return result;
4195 }
4196
4197 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4198 Class<?> rtype = targetType.returnType();
4199 int filterValues = filterType.parameterCount();
4200 if (filterValues == 0
4201 ? (rtype != void.class)
4202 : (rtype != filterType.parameterType(0) || filterValues != 1))
4203 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4204 }
4205
4206 /**
4207 * Adapts a target method handle by pre-processing
4208 * some of its arguments, and then calling the target with
4209 * the result of the pre-processing, inserted into the original
4210 * sequence of arguments.
4211 * <p>
4212 * The pre-processing is performed by {@code combiner}, a second method handle.
4213 * Of the arguments passed to the adapter, the first {@code N} arguments
4214 * are copied to the combiner, which is then called.
4215 * (Here, {@code N} is defined as the parameter count of the combiner.)
4216 * After this, control passes to the target, with any result
4217 * from the combiner inserted before the original {@code N} incoming
4218 * arguments.
4219 * <p>
4220 * If the combiner returns a value, the first parameter type of the target
4221 * must be identical with the return type of the combiner, and the next
4222 * {@code N} parameter types of the target must exactly match the parameters
4223 * of the combiner.
4224 * <p>
4225 * If the combiner has a void return, no result will be inserted,
4226 * and the first {@code N} parameter types of the target
4227 * must exactly match the parameters of the combiner.
4228 * <p>
4229 * The resulting adapter is the same type as the target, except that the
4230 * first parameter type is dropped,
4231 * if it corresponds to the result of the combiner.
4232 * <p>
4233 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4234 * that either the combiner or the target does not wish to receive.
4235 * If some of the incoming arguments are destined only for the combiner,
4236 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4237 * arguments will not need to be live on the stack on entry to the
4238 * target.)
4239 * <p><b>Example:</b>
4240 * <blockquote><pre>{@code
4241 import static java.lang.invoke.MethodHandles.*;
4242 import static java.lang.invoke.MethodType.*;
4243 ...
4244 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4245 "println", methodType(void.class, String.class))
4246 .bindTo(System.out);
4247 MethodHandle cat = lookup().findVirtual(String.class,
4248 "concat", methodType(String.class, String.class));
4249 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4250 MethodHandle catTrace = foldArguments(cat, trace);
4251 // also prints "boo":
4252 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4253 * }</pre></blockquote>
4254 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4255 * represents the result type of the {@code target} and resulting adapter.
4256 * {@code V}/{@code v} represent the type and value of the parameter and argument
4257 * of {@code target} that precedes the folding position; {@code V} also is
4258 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4259 * types and values of the {@code N} parameters and arguments at the folding
4260 * position. {@code B}/{@code b} represent the types and values of the
4261 * {@code target} parameters and arguments that follow the folded parameters
4262 * and arguments.
4263 * <blockquote><pre>{@code
4264 * // there are N arguments in A...
4265 * T target(V, A[N]..., B...);
4266 * V combiner(A...);
4267 * T adapter(A... a, B... b) {
4268 * V v = combiner(a...);
4269 * return target(v, a..., b...);
4270 * }
4271 * // and if the combiner has a void return:
4272 * T target2(A[N]..., B...);
4273 * void combiner2(A...);
4274 * T adapter2(A... a, B... b) {
4275 * combiner2(a...);
4276 * return target2(a..., b...);
4277 * }
4278 * }</pre></blockquote>
4279 * <p>
4280 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4281 * variable-arity method handle}, even if the original target method handle was.
4282 * @param target the method handle to invoke after arguments are combined
4283 * @param combiner method handle to call initially on the incoming arguments
4284 * @return method handle which incorporates the specified argument folding logic
4285 * @throws NullPointerException if either argument is null
4286 * @throws IllegalArgumentException if {@code combiner}'s return type
4287 * is non-void and not the same as the first argument type of
4288 * the target, or if the initial {@code N} argument types
4289 * of the target
4290 * (skipping one matching the {@code combiner}'s return type)
4291 * are not identical with the argument types of {@code combiner}
4292 */
4293 public static
4294 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4295 return foldArguments(target, 0, combiner);
4296 }
4297
4298 /**
4299 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4300 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4301 * before the folded arguments.
4302 * <p>
4303 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4304 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4305 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4306 * 0.
4307 *
4308 * @apiNote Example:
4309 * <blockquote><pre>{@code
4310 import static java.lang.invoke.MethodHandles.*;
4311 import static java.lang.invoke.MethodType.*;
4312 ...
4313 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4314 "println", methodType(void.class, String.class))
4315 .bindTo(System.out);
4316 MethodHandle cat = lookup().findVirtual(String.class,
4317 "concat", methodType(String.class, String.class));
4318 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4319 MethodHandle catTrace = foldArguments(cat, 1, trace);
4320 // also prints "jum":
4321 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4322 * }</pre></blockquote>
4323 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4324 * represents the result type of the {@code target} and resulting adapter.
4325 * {@code V}/{@code v} represent the type and value of the parameter and argument
4326 * of {@code target} that precedes the folding position; {@code V} also is
4327 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4328 * types and values of the {@code N} parameters and arguments at the folding
4329 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4330 * and values of the {@code target} parameters and arguments that precede and
4331 * follow the folded parameters and arguments starting at {@code pos},
4332 * respectively.
4333 * <blockquote><pre>{@code
4334 * // there are N arguments in A...
4335 * T target(Z..., V, A[N]..., B...);
4336 * V combiner(A...);
4337 * T adapter(Z... z, A... a, B... b) {
4338 * V v = combiner(a...);
4339 * return target(z..., v, a..., b...);
4340 * }
4341 * // and if the combiner has a void return:
4342 * T target2(Z..., A[N]..., B...);
4343 * void combiner2(A...);
4344 * T adapter2(Z... z, A... a, B... b) {
4345 * combiner2(a...);
4346 * return target2(z..., a..., b...);
4347 * }
4348 * }</pre></blockquote>
4349 * <p>
4350 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4351 * variable-arity method handle}, even if the original target method handle was.
4352 *
4353 * @param target the method handle to invoke after arguments are combined
4354 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4355 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4356 * @param combiner method handle to call initially on the incoming arguments
4357 * @return method handle which incorporates the specified argument folding logic
4358 * @throws NullPointerException if either argument is null
4359 * @throws IllegalArgumentException if either of the following two conditions holds:
4360 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4361 * {@code pos} of the target signature;
4362 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4363 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4364 *
4365 * @see #foldArguments(MethodHandle, MethodHandle)
4366 * @since 9
4367 */
4368 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4369 MethodType targetType = target.type();
4370 MethodType combinerType = combiner.type();
4371 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4372 BoundMethodHandle result = target.rebind();
4373 boolean dropResult = rtype == void.class;
4374 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4375 MethodType newType = targetType;
4376 if (!dropResult) {
4377 newType = newType.dropParameterTypes(pos, pos + 1);
4378 }
4379 result = result.copyWithExtendL(newType, lform, combiner);
4380 return result;
4381 }
4382
4383 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4384 int foldArgs = combinerType.parameterCount();
4385 Class<?> rtype = combinerType.returnType();
4386 int foldVals = rtype == void.class ? 0 : 1;
4387 int afterInsertPos = foldPos + foldVals;
4388 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4389 if (ok) {
4390 for (int i = 0; i < foldArgs; i++) {
4391 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4392 ok = false;
4393 break;
4394 }
4395 }
4396 }
4397 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4398 ok = false;
4399 if (!ok)
4400 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4401 return rtype;
4402 }
4403
4404 /**
4405 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
4406 * of the pre-processing replacing the argument at the given position.
4407 *
4408 * @param target the method handle to invoke after arguments are combined
4409 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
4410 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4411 * @param combiner method handle to call initially on the incoming arguments
4412 * @param argPositions indexes of the target to pick arguments sent to the combiner from
4413 * @return method handle which incorporates the specified argument folding logic
4414 * @throws NullPointerException if either argument is null
4415 * @throws IllegalArgumentException if either of the following two conditions holds:
4416 * (1) {@code combiner}'s return type is not the same as the argument type at position
4417 * {@code pos} of the target signature;
4418 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
4419 * not identical with the argument types of {@code combiner}.
4420 */
4421 /*non-public*/ static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4422 return argumentsWithCombiner(true, target, position, combiner, argPositions);
4423 }
4424
4425 /**
4426 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
4427 * the pre-processing inserted into the original sequence of arguments at the given position.
4428 *
4429 * @param target the method handle to invoke after arguments are combined
4430 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
4431 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4432 * @param combiner method handle to call initially on the incoming arguments
4433 * @param argPositions indexes of the target to pick arguments sent to the combiner from
4434 * @return method handle which incorporates the specified argument folding logic
4435 * @throws NullPointerException if either argument is null
4436 * @throws IllegalArgumentException if either of the following two conditions holds:
4437 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4438 * {@code pos} of the target signature;
4439 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
4440 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
4441 * with the argument types of {@code combiner}.
4442 */
4443 /*non-public*/ static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4444 return argumentsWithCombiner(false, target, position, combiner, argPositions);
4445 }
4446
4447 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4448 MethodType targetType = target.type();
4449 MethodType combinerType = combiner.type();
4450 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
4451 BoundMethodHandle result = target.rebind();
4452
4453 MethodType newType = targetType;
4454 LambdaForm lform;
4455 if (filter) {
4456 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
4457 } else {
4458 boolean dropResult = rtype == void.class;
4459 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
4460 if (!dropResult) {
4461 newType = newType.dropParameterTypes(position, position + 1);
4462 }
4463 }
4464 result = result.copyWithExtendL(newType, lform, combiner);
4465 return result;
4466 }
4467
4468 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
4469 int combinerArgs = combinerType.parameterCount();
4470 if (argPos.length != combinerArgs) {
4471 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4472 }
4473 Class<?> rtype = combinerType.returnType();
4474
4475 for (int i = 0; i < combinerArgs; i++) {
4476 int arg = argPos[i];
4477 if (arg < 0 || arg > targetType.parameterCount()) {
4478 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4479 }
4480 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4481 throw newIllegalArgumentException("target argument type at position " + arg
4482 + " must match combiner argument type at index " + i + ": " + targetType
4483 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4484 }
4485 }
4486 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
4487 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4488 }
4489 return rtype;
4490 }
4491
4492 /**
4493 * Makes a method handle which adapts a target method handle,
4494 * by guarding it with a test, a boolean-valued method handle.
4495 * If the guard fails, a fallback handle is called instead.
4496 * All three method handles must have the same corresponding
4497 * argument and return types, except that the return type
4498 * of the test must be boolean, and the test is allowed
4499 * to have fewer arguments than the other two method handles.
4500 * <p>
4501 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4502 * represents the uniform result type of the three involved handles;
4503 * {@code A}/{@code a}, the types and values of the {@code target}
4504 * parameters and arguments that are consumed by the {@code test}; and
4505 * {@code B}/{@code b}, those types and values of the {@code target}
4506 * parameters and arguments that are not consumed by the {@code test}.
4507 * <blockquote><pre>{@code
4508 * boolean test(A...);
4509 * T target(A...,B...);
4510 * T fallback(A...,B...);
4511 * T adapter(A... a,B... b) {
4512 * if (test(a...))
4513 * return target(a..., b...);
4514 * else
4515 * return fallback(a..., b...);
4516 * }
4517 * }</pre></blockquote>
4518 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4519 * be modified by execution of the test, and so are passed unchanged
4520 * from the caller to the target or fallback as appropriate.
4521 * @param test method handle used for test, must return boolean
4522 * @param target method handle to call if test passes
4523 * @param fallback method handle to call if test fails
4524 * @return method handle which incorporates the specified if/then/else logic
4525 * @throws NullPointerException if any argument is null
4526 * @throws IllegalArgumentException if {@code test} does not return boolean,
4527 * or if all three method types do not match (with the return
4528 * type of {@code test} changed to match that of the target).
4529 */
4530 public static
4531 MethodHandle guardWithTest(MethodHandle test,
4532 MethodHandle target,
4533 MethodHandle fallback) {
4534 MethodType gtype = test.type();
4535 MethodType ttype = target.type();
4536 MethodType ftype = fallback.type();
4537 if (!ttype.equals(ftype))
4538 throw misMatchedTypes("target and fallback types", ttype, ftype);
4539 if (gtype.returnType() != boolean.class)
4540 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4541 List<Class<?>> targs = ttype.parameterList();
4542 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4543 if (test == null) {
4544 throw misMatchedTypes("target and test types", ttype, gtype);
4545 }
4546 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4547 }
4548
4549 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4550 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4551 }
4552
4553 /**
4554 * Makes a method handle which adapts a target method handle,
4555 * by running it inside an exception handler.
4556 * If the target returns normally, the adapter returns that value.
4557 * If an exception matching the specified type is thrown, the fallback
4558 * handle is called instead on the exception, plus the original arguments.
4559 * <p>
4560 * The target and handler must have the same corresponding
4561 * argument and return types, except that handler may omit trailing arguments
4562 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4563 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4564 * <p>
4565 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4566 * represents the return type of the {@code target} and {@code handler},
4567 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4568 * the types and values of arguments to the resulting handle consumed by
4569 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4570 * resulting handle discarded by {@code handler}.
4571 * <blockquote><pre>{@code
4572 * T target(A..., B...);
4573 * T handler(ExType, A...);
4574 * T adapter(A... a, B... b) {
4575 * try {
4576 * return target(a..., b...);
4577 * } catch (ExType ex) {
4578 * return handler(ex, a...);
4579 * }
4580 * }
4581 * }</pre></blockquote>
4582 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4583 * be modified by execution of the target, and so are passed unchanged
4584 * from the caller to the handler, if the handler is invoked.
4585 * <p>
4586 * The target and handler must return the same type, even if the handler
4587 * always throws. (This might happen, for instance, because the handler
4588 * is simulating a {@code finally} clause).
4589 * To create such a throwing handler, compose the handler creation logic
4590 * with {@link #throwException throwException},
4591 * in order to create a method handle of the correct return type.
4592 * @param target method handle to call
4593 * @param exType the type of exception which the handler will catch
4594 * @param handler method handle to call if a matching exception is thrown
4595 * @return method handle which incorporates the specified try/catch logic
4596 * @throws NullPointerException if any argument is null
4597 * @throws IllegalArgumentException if {@code handler} does not accept
4598 * the given exception type, or if the method handle types do
4599 * not match in their return types and their
4600 * corresponding parameters
4601 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4602 */
4603 public static
4604 MethodHandle catchException(MethodHandle target,
4605 Class<? extends Throwable> exType,
4606 MethodHandle handler) {
4607 MethodType ttype = target.type();
4608 MethodType htype = handler.type();
4609 if (!Throwable.class.isAssignableFrom(exType))
4610 throw new ClassCastException(exType.getName());
4611 if (htype.parameterCount() < 1 ||
4612 !htype.parameterType(0).isAssignableFrom(exType))
4613 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4614 if (htype.returnType() != ttype.returnType())
4615 throw misMatchedTypes("target and handler return types", ttype, htype);
4616 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4617 if (handler == null) {
4618 throw misMatchedTypes("target and handler types", ttype, htype);
4619 }
4620 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4621 }
4622
4623 /**
4624 * Produces a method handle which will throw exceptions of the given {@code exType}.
4625 * The method handle will accept a single argument of {@code exType},
4626 * and immediately throw it as an exception.
4627 * The method type will nominally specify a return of {@code returnType}.
4628 * The return type may be anything convenient: It doesn't matter to the
4629 * method handle's behavior, since it will never return normally.
4630 * @param returnType the return type of the desired method handle
4631 * @param exType the parameter type of the desired method handle
4632 * @return method handle which can throw the given exceptions
4633 * @throws NullPointerException if either argument is null
4634 */
4635 public static
4636 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4637 if (!Throwable.class.isAssignableFrom(exType))
4638 throw new ClassCastException(exType.getName());
4639 return MethodHandleImpl.throwException(methodType(returnType, exType));
4640 }
4641
4642 /**
4643 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4644 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4645 * delivers the loop's result, which is the return value of the resulting handle.
4646 * <p>
4647 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4648 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4649 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4650 * terms of method handles, each clause will specify up to four independent actions:<ul>
4651 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4652 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4653 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4654 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4655 * </ul>
4656 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4657 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4658 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4659 * <p>
4660 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4661 * this case. See below for a detailed description.
4662 * <p>
4663 * <em>Parameters optional everywhere:</em>
4664 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4665 * As an exception, the init functions cannot take any {@code v} parameters,
4666 * because those values are not yet computed when the init functions are executed.
4667 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4668 * In fact, any clause function may take no arguments at all.
4669 * <p>
4670 * <em>Loop parameters:</em>
4671 * A clause function may take all the iteration variable values it is entitled to, in which case
4672 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4673 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4674 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4675 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4676 * init function is automatically a loop parameter {@code a}.)
4677 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4678 * These loop parameters act as loop-invariant values visible across the whole loop.
4679 * <p>
4680 * <em>Parameters visible everywhere:</em>
4681 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4682 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4683 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4684 * Most clause functions will not need all of this information, but they will be formally connected to it
4685 * as if by {@link #dropArguments}.
4686 * <a id="astar"></a>
4687 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4688 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4689 * In that notation, the general form of an init function parameter list
4690 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4691 * <p>
4692 * <em>Checking clause structure:</em>
4693 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4694 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4695 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4696 * met by the inputs to the loop combinator.
4697 * <p>
4698 * <em>Effectively identical sequences:</em>
4699 * <a id="effid"></a>
4700 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4701 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4702 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4703 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4704 * that longest list.
4705 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4706 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4707 * <p>
4708 * <em>Step 0: Determine clause structure.</em><ol type="a">
4709 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4710 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4711 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4712 * four. Padding takes place by appending elements to the array.
4713 * <li>Clauses with all {@code null}s are disregarded.
4714 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4715 * </ol>
4716 * <p>
4717 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4718 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4719 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4720 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4721 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4722 * iteration variable type.
4723 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4724 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4725 * </ol>
4726 * <p>
4727 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4728 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4729 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4730 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4731 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4732 * (These types will be checked in step 2, along with all the clause function types.)
4733 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4734 * <li>All of the collected parameter lists must be effectively identical.
4735 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4736 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4737 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4738 * the "internal parameter list".
4739 * </ul>
4740 * <p>
4741 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4742 * <li>Examine fini function return types, disregarding omitted fini functions.
4743 * <li>If there are no fini functions, the loop return type is {@code void}.
4744 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4745 * type.
4746 * </ol>
4747 * <p>
4748 * <em>Step 1D: Check other types.</em><ol type="a">
4749 * <li>There must be at least one non-omitted pred function.
4750 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4751 * </ol>
4752 * <p>
4753 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4754 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4755 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4756 * (Note that their parameter lists are already effectively identical to this list.)
4757 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4758 * effectively identical to the internal parameter list {@code (V... A...)}.
4759 * </ol>
4760 * <p>
4761 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4762 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4763 * type.
4764 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4765 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4766 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4767 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4768 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4769 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4770 * loop return type.
4771 * </ol>
4772 * <p>
4773 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4774 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4775 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4776 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4777 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4778 * pad out the end of the list.
4779 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
4780 * </ol>
4781 * <p>
4782 * <em>Final observations.</em><ol type="a">
4783 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4784 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4785 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4786 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4787 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4788 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4789 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4790 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4791 * </ol>
4792 * <p>
4793 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4794 * <ul>
4795 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4796 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4797 * (Only one {@code Pn} has to be non-{@code null}.)
4798 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4799 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4800 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4801 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4802 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4803 * the resulting loop handle's parameter types {@code (A...)}.
4804 * </ul>
4805 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4806 * which is natural if most of the loop computation happens in the steps. For some loops,
4807 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4808 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4809 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4810 * where the init functions will need the extra parameters. For such reasons, the rules for
4811 * determining these parameters are as symmetric as possible, across all clause parts.
4812 * In general, the loop parameters function as common invariant values across the whole
4813 * loop, while the iteration variables function as common variant values, or (if there is
4814 * no step function) as internal loop invariant temporaries.
4815 * <p>
4816 * <em>Loop execution.</em><ol type="a">
4817 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4818 * every clause function. These locals are loop invariant.
4819 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4820 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4821 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4822 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4823 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4824 * (in argument order).
4825 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4826 * returns {@code false}.
4827 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4828 * sequence {@code (v...)} of loop variables.
4829 * The updated value is immediately visible to all subsequent function calls.
4830 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4831 * (of type {@code R}) is returned from the loop as a whole.
4832 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4833 * except by throwing an exception.
4834 * </ol>
4835 * <p>
4836 * <em>Usage tips.</em>
4837 * <ul>
4838 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4839 * sometimes a step function only needs to observe the current value of its own variable.
4840 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4841 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4842 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4843 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4844 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4845 * <li>If some of the clause functions are virtual methods on an instance, the instance
4846 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4847 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4848 * will be the first iteration variable value, and it will be easy to use virtual
4849 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4850 * </ul>
4851 * <p>
4852 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4853 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4854 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4855 * <blockquote><pre>{@code
4856 * V... init...(A...);
4857 * boolean pred...(V..., A...);
4858 * V... step...(V..., A...);
4859 * R fini...(V..., A...);
4860 * R loop(A... a) {
4861 * V... v... = init...(a...);
4862 * for (;;) {
4863 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4864 * v = s(v..., a...);
4865 * if (!p(v..., a...)) {
4866 * return f(v..., a...);
4867 * }
4868 * }
4869 * }
4870 * }
4871 * }</pre></blockquote>
4872 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4873 * to their full length, even though individual clause functions may neglect to take them all.
4874 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
4875 *
4876 * @apiNote Example:
4877 * <blockquote><pre>{@code
4878 * // iterative implementation of the factorial function as a loop handle
4879 * static int one(int k) { return 1; }
4880 * static int inc(int i, int acc, int k) { return i + 1; }
4881 * static int mult(int i, int acc, int k) { return i * acc; }
4882 * static boolean pred(int i, int acc, int k) { return i < k; }
4883 * static int fin(int i, int acc, int k) { return acc; }
4884 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4885 * // null initializer for counter, should initialize to 0
4886 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4887 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4888 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4889 * assertEquals(120, loop.invoke(5));
4890 * }</pre></blockquote>
4891 * The same example, dropping arguments and using combinators:
4892 * <blockquote><pre>{@code
4893 * // simplified implementation of the factorial function as a loop handle
4894 * static int inc(int i) { return i + 1; } // drop acc, k
4895 * static int mult(int i, int acc) { return i * acc; } //drop k
4896 * static boolean cmp(int i, int k) { return i < k; }
4897 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4898 * // null initializer for counter, should initialize to 0
4899 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4900 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4901 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4902 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4903 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4904 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4905 * assertEquals(720, loop.invoke(6));
4906 * }</pre></blockquote>
4907 * A similar example, using a helper object to hold a loop parameter:
4908 * <blockquote><pre>{@code
4909 * // instance-based implementation of the factorial function as a loop handle
4910 * static class FacLoop {
4911 * final int k;
4912 * FacLoop(int k) { this.k = k; }
4913 * int inc(int i) { return i + 1; }
4914 * int mult(int i, int acc) { return i * acc; }
4915 * boolean pred(int i) { return i < k; }
4916 * int fin(int i, int acc) { return acc; }
4917 * }
4918 * // assume MH_FacLoop is a handle to the constructor
4919 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4920 * // null initializer for counter, should initialize to 0
4921 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4922 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4923 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4924 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4925 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4926 * assertEquals(5040, loop.invoke(7));
4927 * }</pre></blockquote>
4928 *
4929 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4930 *
4931 * @return a method handle embodying the looping behavior as defined by the arguments.
4932 *
4933 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4934 *
4935 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4936 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4937 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4938 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4939 * @since 9
4940 */
4941 public static MethodHandle loop(MethodHandle[]... clauses) {
4942 // Step 0: determine clause structure.
4943 loopChecks0(clauses);
4944
4945 List<MethodHandle> init = new ArrayList<>();
4946 List<MethodHandle> step = new ArrayList<>();
4947 List<MethodHandle> pred = new ArrayList<>();
4948 List<MethodHandle> fini = new ArrayList<>();
4949
4950 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4951 init.add(clause[0]); // all clauses have at least length 1
4952 step.add(clause.length <= 1 ? null : clause[1]);
4953 pred.add(clause.length <= 2 ? null : clause[2]);
4954 fini.add(clause.length <= 3 ? null : clause[3]);
4955 });
4956
4957 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4958 final int nclauses = init.size();
4959
4960 // Step 1A: determine iteration variables (V...).
4961 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4962 for (int i = 0; i < nclauses; ++i) {
4963 MethodHandle in = init.get(i);
4964 MethodHandle st = step.get(i);
4965 if (in == null && st == null) {
4966 iterationVariableTypes.add(void.class);
4967 } else if (in != null && st != null) {
4968 loopChecks1a(i, in, st);
4969 iterationVariableTypes.add(in.type().returnType());
4970 } else {
4971 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4972 }
4973 }
4974 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4975 collect(Collectors.toList());
4976
4977 // Step 1B: determine loop parameters (A...).
4978 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4979 loopChecks1b(init, commonSuffix);
4980
4981 // Step 1C: determine loop return type.
4982 // Step 1D: check other types.
4983 // local variable required here; see JDK-8223553
4984 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
4985 .map(MethodType::returnType);
4986 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
4987 loopChecks1cd(pred, fini, loopReturnType);
4988
4989 // Step 2: determine parameter lists.
4990 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4991 commonParameterSequence.addAll(commonSuffix);
4992 loopChecks2(step, pred, fini, commonParameterSequence);
4993
4994 // Step 3: fill in omitted functions.
4995 for (int i = 0; i < nclauses; ++i) {
4996 Class<?> t = iterationVariableTypes.get(i);
4997 if (init.get(i) == null) {
4998 init.set(i, empty(methodType(t, commonSuffix)));
4999 }
5000 if (step.get(i) == null) {
5001 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
5002 }
5003 if (pred.get(i) == null) {
5004 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
5005 }
5006 if (fini.get(i) == null) {
5007 fini.set(i, empty(methodType(t, commonParameterSequence)));
5008 }
5009 }
5010
5011 // Step 4: fill in missing parameter types.
5012 // Also convert all handles to fixed-arity handles.
5013 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
5014 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
5015 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
5016 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
5017
5018 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
5019 allMatch(pl -> pl.equals(commonSuffix));
5020 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5021 allMatch(pl -> pl.equals(commonParameterSequence));
5022
5023 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5024 }
5025
5026 private static void loopChecks0(MethodHandle[][] clauses) {
5027 if (clauses == null || clauses.length == 0) {
5028 throw newIllegalArgumentException("null or no clauses passed");
5029 }
5030 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5031 throw newIllegalArgumentException("null clauses are not allowed");
5032 }
5033 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5034 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5035 }
5036 }
5037
5038 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5039 if (in.type().returnType() != st.type().returnType()) {
5040 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5041 st.type().returnType());
5042 }
5043 }
5044
5045 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
5046 final List<Class<?>> empty = List.of();
5047 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
5048 // take only those that can contribute to a common suffix because they are longer than the prefix
5049 map(MethodHandle::type).
5050 filter(t -> t.parameterCount() > skipSize).
5051 map(MethodType::parameterList).
5052 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5053 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
5054 }
5055
5056 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
5057 final List<Class<?>> empty = List.of();
5058 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5059 }
5060
5061 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
5062 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
5063 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
5064 return longestParameterList(Arrays.asList(longest1, longest2));
5065 }
5066
5067 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
5068 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
5069 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
5070 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
5071 " (common suffix: " + commonSuffix + ")");
5072 }
5073 }
5074
5075 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
5076 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5077 anyMatch(t -> t != loopReturnType)) {
5078 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
5079 loopReturnType + ")");
5080 }
5081
5082 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5083 throw newIllegalArgumentException("no predicate found", pred);
5084 }
5085 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5086 anyMatch(t -> t != boolean.class)) {
5087 throw newIllegalArgumentException("predicates must have boolean return type", pred);
5088 }
5089 }
5090
5091 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5092 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5093 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
5094 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5095 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5096 }
5097 }
5098
5099 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
5100 return hs.stream().map(h -> {
5101 int pc = h.type().parameterCount();
5102 int tpsize = targetParams.size();
5103 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5104 }).collect(Collectors.toList());
5105 }
5106
5107 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5108 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5109 }
5110
5111 /**
5112 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5113 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5114 * <p>
5115 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5116 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5117 * evaluates to {@code true}).
5118 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5119 * <p>
5120 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5121 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5122 * and updated with the value returned from its invocation. The result of loop execution will be
5123 * the final value of the additional loop-local variable (if present).
5124 * <p>
5125 * The following rules hold for these argument handles:<ul>
5126 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5127 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5128 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5129 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5130 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5131 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5132 * It will constrain the parameter lists of the other loop parts.
5133 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5134 * list {@code (A...)} is called the <em>external parameter list</em>.
5135 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5136 * additional state variable of the loop.
5137 * The body must both accept and return a value of this type {@code V}.
5138 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5139 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5140 * <a href="MethodHandles.html#effid">effectively identical</a>
5141 * to the external parameter list {@code (A...)}.
5142 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5143 * {@linkplain #empty default value}.
5144 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5145 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5146 * effectively identical to the internal parameter list.
5147 * </ul>
5148 * <p>
5149 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5150 * <li>The loop handle's result type is the result type {@code V} of the body.
5151 * <li>The loop handle's parameter types are the types {@code (A...)},
5152 * from the external parameter list.
5153 * </ul>
5154 * <p>
5155 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5156 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5157 * passed to the loop.
5158 * <blockquote><pre>{@code
5159 * V init(A...);
5160 * boolean pred(V, A...);
5161 * V body(V, A...);
5162 * V whileLoop(A... a...) {
5163 * V v = init(a...);
5164 * while (pred(v, a...)) {
5165 * v = body(v, a...);
5166 * }
5167 * return v;
5168 * }
5169 * }</pre></blockquote>
5170 *
5171 * @apiNote Example:
5172 * <blockquote><pre>{@code
5173 * // implement the zip function for lists as a loop handle
5174 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5175 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5176 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5177 * zip.add(a.next());
5178 * zip.add(b.next());
5179 * return zip;
5180 * }
5181 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5182 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5183 * List<String> a = Arrays.asList("a", "b", "c", "d");
5184 * List<String> b = Arrays.asList("e", "f", "g", "h");
5185 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5186 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5187 * }</pre></blockquote>
5188 *
5189 *
5190 * @apiNote The implementation of this method can be expressed as follows:
5191 * <blockquote><pre>{@code
5192 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5193 * MethodHandle fini = (body.type().returnType() == void.class
5194 * ? null : identity(body.type().returnType()));
5195 * MethodHandle[]
5196 * checkExit = { null, null, pred, fini },
5197 * varBody = { init, body };
5198 * return loop(checkExit, varBody);
5199 * }
5200 * }</pre></blockquote>
5201 *
5202 * @param init optional initializer, providing the initial value of the loop variable.
5203 * May be {@code null}, implying a default initial value. See above for other constraints.
5204 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5205 * above for other constraints.
5206 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5207 * See above for other constraints.
5208 *
5209 * @return a method handle implementing the {@code while} loop as described by the arguments.
5210 * @throws IllegalArgumentException if the rules for the arguments are violated.
5211 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5212 *
5213 * @see #loop(MethodHandle[][])
5214 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5215 * @since 9
5216 */
5217 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5218 whileLoopChecks(init, pred, body);
5219 MethodHandle fini = identityOrVoid(body.type().returnType());
5220 MethodHandle[] checkExit = { null, null, pred, fini };
5221 MethodHandle[] varBody = { init, body };
5222 return loop(checkExit, varBody);
5223 }
5224
5225 /**
5226 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5227 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5228 * <p>
5229 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5230 * method will, in each iteration, first execute its body and then evaluate the predicate.
5231 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5232 * <p>
5233 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5234 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5235 * and updated with the value returned from its invocation. The result of loop execution will be
5236 * the final value of the additional loop-local variable (if present).
5237 * <p>
5238 * The following rules hold for these argument handles:<ul>
5239 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5240 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5241 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5242 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5243 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5244 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5245 * It will constrain the parameter lists of the other loop parts.
5246 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5247 * list {@code (A...)} is called the <em>external parameter list</em>.
5248 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5249 * additional state variable of the loop.
5250 * The body must both accept and return a value of this type {@code V}.
5251 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5252 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5253 * <a href="MethodHandles.html#effid">effectively identical</a>
5254 * to the external parameter list {@code (A...)}.
5255 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5256 * {@linkplain #empty default value}.
5257 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5258 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5259 * effectively identical to the internal parameter list.
5260 * </ul>
5261 * <p>
5262 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5263 * <li>The loop handle's result type is the result type {@code V} of the body.
5264 * <li>The loop handle's parameter types are the types {@code (A...)},
5265 * from the external parameter list.
5266 * </ul>
5267 * <p>
5268 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5269 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5270 * passed to the loop.
5271 * <blockquote><pre>{@code
5272 * V init(A...);
5273 * boolean pred(V, A...);
5274 * V body(V, A...);
5275 * V doWhileLoop(A... a...) {
5276 * V v = init(a...);
5277 * do {
5278 * v = body(v, a...);
5279 * } while (pred(v, a...));
5280 * return v;
5281 * }
5282 * }</pre></blockquote>
5283 *
5284 * @apiNote Example:
5285 * <blockquote><pre>{@code
5286 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5287 * static int zero(int limit) { return 0; }
5288 * static int step(int i, int limit) { return i + 1; }
5289 * static boolean pred(int i, int limit) { return i < limit; }
5290 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5291 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5292 * assertEquals(23, loop.invoke(23));
5293 * }</pre></blockquote>
5294 *
5295 *
5296 * @apiNote The implementation of this method can be expressed as follows:
5297 * <blockquote><pre>{@code
5298 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5299 * MethodHandle fini = (body.type().returnType() == void.class
5300 * ? null : identity(body.type().returnType()));
5301 * MethodHandle[] clause = { init, body, pred, fini };
5302 * return loop(clause);
5303 * }
5304 * }</pre></blockquote>
5305 *
5306 * @param init optional initializer, providing the initial value of the loop variable.
5307 * May be {@code null}, implying a default initial value. See above for other constraints.
5308 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5309 * See above for other constraints.
5310 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5311 * above for other constraints.
5312 *
5313 * @return a method handle implementing the {@code while} loop as described by the arguments.
5314 * @throws IllegalArgumentException if the rules for the arguments are violated.
5315 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5316 *
5317 * @see #loop(MethodHandle[][])
5318 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5319 * @since 9
5320 */
5321 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5322 whileLoopChecks(init, pred, body);
5323 MethodHandle fini = identityOrVoid(body.type().returnType());
5324 MethodHandle[] clause = {init, body, pred, fini };
5325 return loop(clause);
5326 }
5327
5328 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5329 Objects.requireNonNull(pred);
5330 Objects.requireNonNull(body);
5331 MethodType bodyType = body.type();
5332 Class<?> returnType = bodyType.returnType();
5333 List<Class<?>> innerList = bodyType.parameterList();
5334 List<Class<?>> outerList = innerList;
5335 if (returnType == void.class) {
5336 // OK
5337 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5338 // leading V argument missing => error
5339 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5340 throw misMatchedTypes("body function", bodyType, expected);
5341 } else {
5342 outerList = innerList.subList(1, innerList.size());
5343 }
5344 MethodType predType = pred.type();
5345 if (predType.returnType() != boolean.class ||
5346 !predType.effectivelyIdenticalParameters(0, innerList)) {
5347 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5348 }
5349 if (init != null) {
5350 MethodType initType = init.type();
5351 if (initType.returnType() != returnType ||
5352 !initType.effectivelyIdenticalParameters(0, outerList)) {
5353 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5354 }
5355 }
5356 }
5357
5358 /**
5359 * Constructs a loop that runs a given number of iterations.
5360 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5361 * <p>
5362 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5363 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5364 * It will be initialized to 0 and incremented by 1 in each iteration.
5365 * <p>
5366 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5367 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5368 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5369 * <p>
5370 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5371 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5372 * iteration variable.
5373 * The result of the loop handle execution will be the final {@code V} value of that variable
5374 * (or {@code void} if there is no {@code V} variable).
5375 * <p>
5376 * The following rules hold for the argument handles:<ul>
5377 * <li>The {@code iterations} handle must not be {@code null}, and must return
5378 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5379 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5380 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5381 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5382 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5383 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5384 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5385 * of types called the <em>internal parameter list</em>.
5386 * It will constrain the parameter lists of the other loop parts.
5387 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5388 * with no additional {@code A} types, then the internal parameter list is extended by
5389 * the argument types {@code A...} of the {@code iterations} handle.
5390 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5391 * list {@code (A...)} is called the <em>external parameter list</em>.
5392 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5393 * additional state variable of the loop.
5394 * The body must both accept a leading parameter and return a value of this type {@code V}.
5395 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5396 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5397 * <a href="MethodHandles.html#effid">effectively identical</a>
5398 * to the external parameter list {@code (A...)}.
5399 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5400 * {@linkplain #empty default value}.
5401 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5402 * effectively identical to the external parameter list {@code (A...)}.
5403 * </ul>
5404 * <p>
5405 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5406 * <li>The loop handle's result type is the result type {@code V} of the body.
5407 * <li>The loop handle's parameter types are the types {@code (A...)},
5408 * from the external parameter list.
5409 * </ul>
5410 * <p>
5411 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5412 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5413 * arguments passed to the loop.
5414 * <blockquote><pre>{@code
5415 * int iterations(A...);
5416 * V init(A...);
5417 * V body(V, int, A...);
5418 * V countedLoop(A... a...) {
5419 * int end = iterations(a...);
5420 * V v = init(a...);
5421 * for (int i = 0; i < end; ++i) {
5422 * v = body(v, i, a...);
5423 * }
5424 * return v;
5425 * }
5426 * }</pre></blockquote>
5427 *
5428 * @apiNote Example with a fully conformant body method:
5429 * <blockquote><pre>{@code
5430 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5431 * // => a variation on a well known theme
5432 * static String step(String v, int counter, String init) { return "na " + v; }
5433 * // assume MH_step is a handle to the method above
5434 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5435 * MethodHandle start = MethodHandles.identity(String.class);
5436 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5437 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5438 * }</pre></blockquote>
5439 *
5440 * @apiNote Example with the simplest possible body method type,
5441 * and passing the number of iterations to the loop invocation:
5442 * <blockquote><pre>{@code
5443 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5444 * // => a variation on a well known theme
5445 * static String step(String v, int counter ) { return "na " + v; }
5446 * // assume MH_step is a handle to the method above
5447 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5448 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5449 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5450 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5451 * }</pre></blockquote>
5452 *
5453 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5454 * as loop parameters:
5455 * <blockquote><pre>{@code
5456 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5457 * // => a variation on a well known theme
5458 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5459 * // assume MH_step is a handle to the method above
5460 * MethodHandle count = MethodHandles.identity(int.class);
5461 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5462 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5463 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5464 * }</pre></blockquote>
5465 *
5466 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5467 * to enforce a loop type:
5468 * <blockquote><pre>{@code
5469 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5470 * // => a variation on a well known theme
5471 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5472 * // assume MH_step is a handle to the method above
5473 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5474 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5475 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5476 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5477 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5478 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5479 * }</pre></blockquote>
5480 *
5481 * @apiNote The implementation of this method can be expressed as follows:
5482 * <blockquote><pre>{@code
5483 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5484 * return countedLoop(empty(iterations.type()), iterations, init, body);
5485 * }
5486 * }</pre></blockquote>
5487 *
5488 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5489 * result type must be {@code int}. See above for other constraints.
5490 * @param init optional initializer, providing the initial value of the loop variable.
5491 * May be {@code null}, implying a default initial value. See above for other constraints.
5492 * @param body body of the loop, which may not be {@code null}.
5493 * It controls the loop parameters and result type in the standard case (see above for details).
5494 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5495 * and may accept any number of additional types.
5496 * See above for other constraints.
5497 *
5498 * @return a method handle representing the loop.
5499 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5500 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5501 *
5502 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5503 * @since 9
5504 */
5505 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5506 return countedLoop(empty(iterations.type()), iterations, init, body);
5507 }
5508
5509 /**
5510 * Constructs a loop that counts over a range of numbers.
5511 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5512 * <p>
5513 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5514 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5515 * values of the loop counter.
5516 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5517 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5518 * <p>
5519 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5520 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5521 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5522 * <p>
5523 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5524 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5525 * iteration variable.
5526 * The result of the loop handle execution will be the final {@code V} value of that variable
5527 * (or {@code void} if there is no {@code V} variable).
5528 * <p>
5529 * The following rules hold for the argument handles:<ul>
5530 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5531 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5532 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5533 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5534 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5535 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5536 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5537 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5538 * of types called the <em>internal parameter list</em>.
5539 * It will constrain the parameter lists of the other loop parts.
5540 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5541 * with no additional {@code A} types, then the internal parameter list is extended by
5542 * the argument types {@code A...} of the {@code end} handle.
5543 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5544 * list {@code (A...)} is called the <em>external parameter list</em>.
5545 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5546 * additional state variable of the loop.
5547 * The body must both accept a leading parameter and return a value of this type {@code V}.
5548 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5549 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5550 * <a href="MethodHandles.html#effid">effectively identical</a>
5551 * to the external parameter list {@code (A...)}.
5552 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5553 * {@linkplain #empty default value}.
5554 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5555 * effectively identical to the external parameter list {@code (A...)}.
5556 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5557 * to the external parameter list.
5558 * </ul>
5559 * <p>
5560 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5561 * <li>The loop handle's result type is the result type {@code V} of the body.
5562 * <li>The loop handle's parameter types are the types {@code (A...)},
5563 * from the external parameter list.
5564 * </ul>
5565 * <p>
5566 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5567 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5568 * arguments passed to the loop.
5569 * <blockquote><pre>{@code
5570 * int start(A...);
5571 * int end(A...);
5572 * V init(A...);
5573 * V body(V, int, A...);
5574 * V countedLoop(A... a...) {
5575 * int e = end(a...);
5576 * int s = start(a...);
5577 * V v = init(a...);
5578 * for (int i = s; i < e; ++i) {
5579 * v = body(v, i, a...);
5580 * }
5581 * return v;
5582 * }
5583 * }</pre></blockquote>
5584 *
5585 * @apiNote The implementation of this method can be expressed as follows:
5586 * <blockquote><pre>{@code
5587 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5588 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5589 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5590 * // the following semantics:
5591 * // MH_increment: (int limit, int counter) -> counter + 1
5592 * // MH_predicate: (int limit, int counter) -> counter < limit
5593 * Class<?> counterType = start.type().returnType(); // int
5594 * Class<?> returnType = body.type().returnType();
5595 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5596 * if (returnType != void.class) { // ignore the V variable
5597 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5598 * pred = dropArguments(pred, 1, returnType); // ditto
5599 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5600 * }
5601 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5602 * MethodHandle[]
5603 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5604 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5605 * indexVar = { start, incr }; // i = start(); i = i + 1
5606 * return loop(loopLimit, bodyClause, indexVar);
5607 * }
5608 * }</pre></blockquote>
5609 *
5610 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5611 * See above for other constraints.
5612 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5613 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5614 * @param init optional initializer, providing the initial value of the loop variable.
5615 * May be {@code null}, implying a default initial value. See above for other constraints.
5616 * @param body body of the loop, which may not be {@code null}.
5617 * It controls the loop parameters and result type in the standard case (see above for details).
5618 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5619 * and may accept any number of additional types.
5620 * See above for other constraints.
5621 *
5622 * @return a method handle representing the loop.
5623 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5624 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5625 *
5626 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5627 * @since 9
5628 */
5629 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5630 countedLoopChecks(start, end, init, body);
5631 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5632 Class<?> limitType = end.type().returnType(); // yes, int again
5633 Class<?> returnType = body.type().returnType();
5634 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5635 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5636 MethodHandle retv = null;
5637 if (returnType != void.class) {
5638 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5639 pred = dropArguments(pred, 1, returnType); // ditto
5640 retv = dropArguments(identity(returnType), 0, counterType);
5641 }
5642 body = dropArguments(body, 0, counterType); // ignore the limit variable
5643 MethodHandle[]
5644 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5645 bodyClause = { init, body }, // v = init(); v = body(v, i)
5646 indexVar = { start, incr }; // i = start(); i = i + 1
5647 return loop(loopLimit, bodyClause, indexVar);
5648 }
5649
5650 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5651 Objects.requireNonNull(start);
5652 Objects.requireNonNull(end);
5653 Objects.requireNonNull(body);
5654 Class<?> counterType = start.type().returnType();
5655 if (counterType != int.class) {
5656 MethodType expected = start.type().changeReturnType(int.class);
5657 throw misMatchedTypes("start function", start.type(), expected);
5658 } else if (end.type().returnType() != counterType) {
5659 MethodType expected = end.type().changeReturnType(counterType);
5660 throw misMatchedTypes("end function", end.type(), expected);
5661 }
5662 MethodType bodyType = body.type();
5663 Class<?> returnType = bodyType.returnType();
5664 List<Class<?>> innerList = bodyType.parameterList();
5665 // strip leading V value if present
5666 int vsize = (returnType == void.class ? 0 : 1);
5667 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5668 // argument list has no "V" => error
5669 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5670 throw misMatchedTypes("body function", bodyType, expected);
5671 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5672 // missing I type => error
5673 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5674 throw misMatchedTypes("body function", bodyType, expected);
5675 }
5676 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5677 if (outerList.isEmpty()) {
5678 // special case; take lists from end handle
5679 outerList = end.type().parameterList();
5680 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5681 }
5682 MethodType expected = methodType(counterType, outerList);
5683 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5684 throw misMatchedTypes("start parameter types", start.type(), expected);
5685 }
5686 if (end.type() != start.type() &&
5687 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5688 throw misMatchedTypes("end parameter types", end.type(), expected);
5689 }
5690 if (init != null) {
5691 MethodType initType = init.type();
5692 if (initType.returnType() != returnType ||
5693 !initType.effectivelyIdenticalParameters(0, outerList)) {
5694 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5695 }
5696 }
5697 }
5698
5699 /**
5700 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5701 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5702 * <p>
5703 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5704 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5705 * <p>
5706 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5707 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5708 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5709 * <p>
5710 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5711 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5712 * iteration variable.
5713 * The result of the loop handle execution will be the final {@code V} value of that variable
5714 * (or {@code void} if there is no {@code V} variable).
5715 * <p>
5716 * The following rules hold for the argument handles:<ul>
5717 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5718 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5719 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5720 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5721 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5722 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5723 * of types called the <em>internal parameter list</em>.
5724 * It will constrain the parameter lists of the other loop parts.
5725 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5726 * with no additional {@code A} types, then the internal parameter list is extended by
5727 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5728 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5729 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5730 * list {@code (A...)} is called the <em>external parameter list</em>.
5731 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5732 * additional state variable of the loop.
5733 * The body must both accept a leading parameter and return a value of this type {@code V}.
5734 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5735 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5736 * <a href="MethodHandles.html#effid">effectively identical</a>
5737 * to the external parameter list {@code (A...)}.
5738 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5739 * {@linkplain #empty default value}.
5740 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5741 * type {@code java.util.Iterator} or a subtype thereof.
5742 * The iterator it produces when the loop is executed will be assumed
5743 * to yield values which can be converted to type {@code T}.
5744 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5745 * effectively identical to the external parameter list {@code (A...)}.
5746 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5747 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5748 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5749 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5750 * the {@link MethodHandle#asType asType} conversion method.
5751 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5752 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5753 * </ul>
5754 * <p>
5755 * The type {@code T} may be either a primitive or reference.
5756 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5757 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5758 * as if by the {@link MethodHandle#asType asType} conversion method.
5759 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5760 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5761 * <p>
5762 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5763 * <li>The loop handle's result type is the result type {@code V} of the body.
5764 * <li>The loop handle's parameter types are the types {@code (A...)},
5765 * from the external parameter list.
5766 * </ul>
5767 * <p>
5768 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5769 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5770 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5771 * <blockquote><pre>{@code
5772 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5773 * V init(A...);
5774 * V body(V,T,A...);
5775 * V iteratedLoop(A... a...) {
5776 * Iterator<T> it = iterator(a...);
5777 * V v = init(a...);
5778 * while (it.hasNext()) {
5779 * T t = it.next();
5780 * v = body(v, t, a...);
5781 * }
5782 * return v;
5783 * }
5784 * }</pre></blockquote>
5785 *
5786 * @apiNote Example:
5787 * <blockquote><pre>{@code
5788 * // get an iterator from a list
5789 * static List<String> reverseStep(List<String> r, String e) {
5790 * r.add(0, e);
5791 * return r;
5792 * }
5793 * static List<String> newArrayList() { return new ArrayList<>(); }
5794 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5795 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5796 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5797 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5798 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5799 * }</pre></blockquote>
5800 *
5801 * @apiNote The implementation of this method can be expressed approximately as follows:
5802 * <blockquote><pre>{@code
5803 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5804 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5805 * Class<?> returnType = body.type().returnType();
5806 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5807 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5808 * MethodHandle retv = null, step = body, startIter = iterator;
5809 * if (returnType != void.class) {
5810 * // the simple thing first: in (I V A...), drop the I to get V
5811 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5812 * // body type signature (V T A...), internal loop types (I V A...)
5813 * step = swapArguments(body, 0, 1); // swap V <-> T
5814 * }
5815 * if (startIter == null) startIter = MH_getIter;
5816 * MethodHandle[]
5817 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5818 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5819 * return loop(iterVar, bodyClause);
5820 * }
5821 * }</pre></blockquote>
5822 *
5823 * @param iterator an optional handle to return the iterator to start the loop.
5824 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5825 * See above for other constraints.
5826 * @param init optional initializer, providing the initial value of the loop variable.
5827 * May be {@code null}, implying a default initial value. See above for other constraints.
5828 * @param body body of the loop, which may not be {@code null}.
5829 * It controls the loop parameters and result type in the standard case (see above for details).
5830 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5831 * and may accept any number of additional types.
5832 * See above for other constraints.
5833 *
5834 * @return a method handle embodying the iteration loop functionality.
5835 * @throws NullPointerException if the {@code body} handle is {@code null}.
5836 * @throws IllegalArgumentException if any argument violates the above requirements.
5837 *
5838 * @since 9
5839 */
5840 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5841 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5842 Class<?> returnType = body.type().returnType();
5843 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5844 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5845 MethodHandle startIter;
5846 MethodHandle nextVal;
5847 {
5848 MethodType iteratorType;
5849 if (iterator == null) {
5850 // derive argument type from body, if available, else use Iterable
5851 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5852 iteratorType = startIter.type().changeParameterType(0, iterableType);
5853 } else {
5854 // force return type to the internal iterator class
5855 iteratorType = iterator.type().changeReturnType(Iterator.class);
5856 startIter = iterator;
5857 }
5858 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5859 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5860
5861 // perform the asType transforms under an exception transformer, as per spec.:
5862 try {
5863 startIter = startIter.asType(iteratorType);
5864 nextVal = nextRaw.asType(nextValType);
5865 } catch (WrongMethodTypeException ex) {
5866 throw new IllegalArgumentException(ex);
5867 }
5868 }
5869
5870 MethodHandle retv = null, step = body;
5871 if (returnType != void.class) {
5872 // the simple thing first: in (I V A...), drop the I to get V
5873 retv = dropArguments(identity(returnType), 0, Iterator.class);
5874 // body type signature (V T A...), internal loop types (I V A...)
5875 step = swapArguments(body, 0, 1); // swap V <-> T
5876 }
5877
5878 MethodHandle[]
5879 iterVar = { startIter, null, hasNext, retv },
5880 bodyClause = { init, filterArgument(step, 0, nextVal) };
5881 return loop(iterVar, bodyClause);
5882 }
5883
5884 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5885 Objects.requireNonNull(body);
5886 MethodType bodyType = body.type();
5887 Class<?> returnType = bodyType.returnType();
5888 List<Class<?>> internalParamList = bodyType.parameterList();
5889 // strip leading V value if present
5890 int vsize = (returnType == void.class ? 0 : 1);
5891 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5892 // argument list has no "V" => error
5893 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5894 throw misMatchedTypes("body function", bodyType, expected);
5895 } else if (internalParamList.size() <= vsize) {
5896 // missing T type => error
5897 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5898 throw misMatchedTypes("body function", bodyType, expected);
5899 }
5900 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5901 Class<?> iterableType = null;
5902 if (iterator != null) {
5903 // special case; if the body handle only declares V and T then
5904 // the external parameter list is obtained from iterator handle
5905 if (externalParamList.isEmpty()) {
5906 externalParamList = iterator.type().parameterList();
5907 }
5908 MethodType itype = iterator.type();
5909 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5910 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5911 }
5912 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5913 MethodType expected = methodType(itype.returnType(), externalParamList);
5914 throw misMatchedTypes("iterator parameters", itype, expected);
5915 }
5916 } else {
5917 if (externalParamList.isEmpty()) {
5918 // special case; if the iterator handle is null and the body handle
5919 // only declares V and T then the external parameter list consists
5920 // of Iterable
5921 externalParamList = Arrays.asList(Iterable.class);
5922 iterableType = Iterable.class;
5923 } else {
5924 // special case; if the iterator handle is null and the external
5925 // parameter list is not empty then the first parameter must be
5926 // assignable to Iterable
5927 iterableType = externalParamList.get(0);
5928 if (!Iterable.class.isAssignableFrom(iterableType)) {
5929 throw newIllegalArgumentException(
5930 "inferred first loop argument must inherit from Iterable: " + iterableType);
5931 }
5932 }
5933 }
5934 if (init != null) {
5935 MethodType initType = init.type();
5936 if (initType.returnType() != returnType ||
5937 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5938 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5939 }
5940 }
5941 return iterableType; // help the caller a bit
5942 }
5943
5944 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5945 // there should be a better way to uncross my wires
5946 int arity = mh.type().parameterCount();
5947 int[] order = new int[arity];
5948 for (int k = 0; k < arity; k++) order[k] = k;
5949 order[i] = j; order[j] = i;
5950 Class<?>[] types = mh.type().parameterArray();
5951 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5952 MethodType swapType = methodType(mh.type().returnType(), types);
5953 return permuteArguments(mh, swapType, order);
5954 }
5955
5956 /**
5957 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5958 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5959 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5960 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5961 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5962 * {@code try-finally} handle.
5963 * <p>
5964 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5965 * The first is the exception thrown during the
5966 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5967 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5968 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5969 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5970 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5971 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5972 * <p>
5973 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5974 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5975 * two extra leading parameters:<ul>
5976 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5977 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5978 * the result from the execution of the {@code target} handle.
5979 * This parameter is not present if the {@code target} returns {@code void}.
5980 * </ul>
5981 * <p>
5982 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5983 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5984 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5985 * the cleanup.
5986 * <blockquote><pre>{@code
5987 * V target(A..., B...);
5988 * V cleanup(Throwable, V, A...);
5989 * V adapter(A... a, B... b) {
5990 * V result = (zero value for V);
5991 * Throwable throwable = null;
5992 * try {
5993 * result = target(a..., b...);
5994 * } catch (Throwable t) {
5995 * throwable = t;
5996 * throw t;
5997 * } finally {
5998 * result = cleanup(throwable, result, a...);
5999 * }
6000 * return result;
6001 * }
6002 * }</pre></blockquote>
6003 * <p>
6004 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6005 * be modified by execution of the target, and so are passed unchanged
6006 * from the caller to the cleanup, if it is invoked.
6007 * <p>
6008 * The target and cleanup must return the same type, even if the cleanup
6009 * always throws.
6010 * To create such a throwing cleanup, compose the cleanup logic
6011 * with {@link #throwException throwException},
6012 * in order to create a method handle of the correct return type.
6013 * <p>
6014 * Note that {@code tryFinally} never converts exceptions into normal returns.
6015 * In rare cases where exceptions must be converted in that way, first wrap
6016 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
6017 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
6018 * <p>
6019 * It is recommended that the first parameter type of {@code cleanup} be
6020 * declared {@code Throwable} rather than a narrower subtype. This ensures
6021 * {@code cleanup} will always be invoked with whatever exception that
6022 * {@code target} throws. Declaring a narrower type may result in a
6023 * {@code ClassCastException} being thrown by the {@code try-finally}
6024 * handle if the type of the exception thrown by {@code target} is not
6025 * assignable to the first parameter type of {@code cleanup}. Note that
6026 * various exception types of {@code VirtualMachineError},
6027 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6028 * thrown by almost any kind of Java code, and a finally clause that
6029 * catches (say) only {@code IOException} would mask any of the others
6030 * behind a {@code ClassCastException}.
6031 *
6032 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6033 * @param cleanup the handle that is invoked in the finally block.
6034 *
6035 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6036 * @throws NullPointerException if any argument is null
6037 * @throws IllegalArgumentException if {@code cleanup} does not accept
6038 * the required leading arguments, or if the method handle types do
6039 * not match in their return types and their
6040 * corresponding trailing parameters
6041 *
6042 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
6043 * @since 9
6044 */
6045 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
6046 List<Class<?>> targetParamTypes = target.type().parameterList();
6047 Class<?> rtype = target.type().returnType();
6048
6049 tryFinallyChecks(target, cleanup);
6050
6051 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
6052 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6053 // target parameter list.
6054 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
6055
6056 // Ensure that the intrinsic type checks the instance thrown by the
6057 // target against the first parameter of cleanup
6058 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
6059
6060 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
6061 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
6062 }
6063
6064 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
6065 Class<?> rtype = target.type().returnType();
6066 if (rtype != cleanup.type().returnType()) {
6067 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
6068 }
6069 MethodType cleanupType = cleanup.type();
6070 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
6071 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
6072 }
6073 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
6074 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
6075 }
6076 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6077 // target parameter list.
6078 int cleanupArgIndex = rtype == void.class ? 1 : 2;
6079 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
6080 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
6081 cleanup.type(), target.type());
6082 }
6083 }
6084
6085 }