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 UNCONDITIONAL} mode.
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. This public lookup object or other lookup object with
138 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
139 * is not used to determine the lookup context.
140 *
141 * <p style="font-size:smaller;">
142 * <em>Discussion:</em>
143 * The lookup class can be changed to any other class {@code C} using an expression of the form
144 * {@link Lookup#in publicLookup().in(C.class)}.
145 * 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 on a target class to emulate all supported
160 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc"> private access</a>.
161 * The returned lookup object can provide access to classes in modules and packages,
162 * and members of those classes, outside the normal rules of Java access control,
163 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
164 * <p>
165 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
166 * allowed to do deep reflection on module {@code M2} and package of the target class
167 * if and only if all of the following conditions are {@code true}:
168 * <ul>
169 * <li>If there is a security manager, its {@code checkPermission} method is
170 * called to check {@code ReflectPermission("suppressAccessChecks")} and
171 * that must return normally.
172 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
173 * (This is because otherwise there would be no way to ensure the original lookup
174 * creator was a member of any particular module, and so any subsequent checks
175 * for readability and qualified exports would become ineffective.)
176 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
177 * (This is because an application intending to share intra-module access
178 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
179 * deep reflection to its own module.)
180 * <li>The target class must be a proper class, not a primitive or array class.
181 * (Thus, {@code M2} is well-defined.)
182 * <li>If the caller module {@code M1} differs from
183 * the target module {@code M2} then both of the following must be true:
184 * <ul>
185 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
186 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
187 * containing the target class to at least {@code M1}.</li>
188 * </ul>
189 * </ul>
190 * <p>
191 * If any of the above checks is violated, this method fails with an
192 * exception.
193 * <p>
194 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
195 * returns a {@code Lookup} on {@code targetClass} with full capabilities and
196 * {@code null} previous lookup class.
197 * <p>
198 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
199 * returns a {@code Lookup} on {@code targetClass} that records
200 * the lookup class of the caller as the new previous lookup class and
201 * drops {@code MODULE} access from the full capabilities mode.
202 *
203 * @param targetClass the target class
204 * @param caller the caller lookup object
205 * @return a lookup object for the target class, with private access
206 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or array class
207 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
208 * @throws SecurityException if denied by the security manager
209 * @throws IllegalAccessException if any of the other access checks specified above fails
210 * @since 9
211 * @spec JPMS
212 * @see Lookup#dropLookupMode
213 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
214 */
215 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
216 SecurityManager sm = System.getSecurityManager();
217 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
218 if (targetClass.isPrimitive())
219 throw new IllegalArgumentException(targetClass + " is a primitive class");
220 if (targetClass.isArray())
221 throw new IllegalArgumentException(targetClass + " is an array class");
222 // Ensure that we can reason accurately about private and module access.
223 if ((caller.lookupModes() & Lookup.PRIVATE) == 0)
224 throw new IllegalAccessException("caller does not have PRIVATE lookup mode");
225 if ((caller.lookupModes() & Lookup.MODULE) == 0)
226 throw new IllegalAccessException("caller does not have MODULE lookup mode");
227
228 // previous lookup class is never set if it has MODULE access
229 assert caller.previousLookupClass() == null;
230
231 Class<?> callerClass = caller.lookupClass();
232 Module callerModule = callerClass.getModule(); // M1
233 Module targetModule = targetClass.getModule(); // M2
234 Class<?> newPreviousClass = null;
235 int newModes = Lookup.FULL_POWER_MODES;
236
237 if (targetModule != callerModule) {
238 if (!callerModule.canRead(targetModule))
239 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
240 if (targetModule.isNamed()) {
241 String pn = targetClass.getPackageName();
242 assert !pn.isEmpty() : "unnamed package cannot be in named module";
243 if (!targetModule.isOpen(pn, callerModule))
244 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
245 }
246
247 // M2 != M1, set previous lookup class to M1 and drop MODULE access
248 newPreviousClass = callerClass;
249 newModes &= ~Lookup.MODULE;
250 }
251
252 if (!callerModule.isNamed() && targetModule.isNamed()) {
253 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
254 if (logger != null) {
255 logger.logIfOpenedForIllegalAccess(caller, targetClass);
256 }
257 }
258 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
259 }
260
261 /**
262 * Performs an unchecked "crack" of a
263 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
264 * The result is as if the user had obtained a lookup object capable enough
265 * to crack the target method handle, called
266 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
267 * on the target to obtain its symbolic reference, and then called
268 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
269 * to resolve the symbolic reference to a member.
270 * <p>
271 * If there is a security manager, its {@code checkPermission} method
272 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
273 * @param <T> the desired type of the result, either {@link Member} or a subtype
274 * @param target a direct method handle to crack into symbolic reference components
275 * @param expected a class object representing the desired result type {@code T}
276 * @return a reference to the method, constructor, or field object
277 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
278 * @exception NullPointerException if either argument is {@code null}
279 * @exception IllegalArgumentException if the target is not a direct method handle
280 * @exception ClassCastException if the member is not of the expected type
281 * @since 1.8
282 */
283 public static <T extends Member> T
284 reflectAs(Class<T> expected, MethodHandle target) {
285 SecurityManager smgr = System.getSecurityManager();
286 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
287 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
288 return lookup.revealDirect(target).reflectAs(expected, lookup);
289 }
290 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
291 private static final java.security.Permission ACCESS_PERMISSION =
292 new ReflectPermission("suppressAccessChecks");
293
294 /**
295 * A <em>lookup object</em> is a factory for creating method handles,
296 * when the creation requires access checking.
297 * Method handles do not perform
298 * access checks when they are called, but rather when they are created.
299 * Therefore, method handle access
300 * restrictions must be enforced when a method handle is created.
301 * The caller class against which those restrictions are enforced
302 * is known as the {@linkplain #lookupClass() lookup class}.
303 * <p>
304 * A lookup class which needs to create method handles will call
305 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
306 * When the {@code Lookup} factory object is created, the identity of the lookup class is
307 * determined, and securely stored in the {@code Lookup} object.
308 * The lookup class (or its delegates) may then use factory methods
309 * on the {@code Lookup} object to create method handles for access-checked members.
310 * This includes all methods, constructors, and fields which are allowed to the lookup class,
311 * even private ones.
312 *
313 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
314 * The factory methods on a {@code Lookup} object correspond to all major
315 * use cases for methods, constructors, and fields.
316 * Each method handle created by a factory method is the functional
317 * equivalent of a particular <em>bytecode behavior</em>.
318 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
319 * Here is a summary of the correspondence between these factory methods and
320 * the behavior of the resulting method handles:
321 * <table class="striped">
322 * <caption style="display:none">lookup method behaviors</caption>
323 * <thead>
324 * <tr>
325 * <th scope="col"><a id="equiv"></a>lookup expression</th>
326 * <th scope="col">member</th>
327 * <th scope="col">bytecode behavior</th>
328 * </tr>
329 * </thead>
330 * <tbody>
331 * <tr>
332 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
333 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
334 * </tr>
335 * <tr>
336 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
337 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
338 * </tr>
339 * <tr>
340 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
341 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
342 * </tr>
343 * <tr>
344 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
345 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
346 * </tr>
347 * <tr>
348 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
349 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
350 * </tr>
351 * <tr>
352 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
353 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
354 * </tr>
355 * <tr>
356 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
357 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
358 * </tr>
359 * <tr>
360 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
361 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
362 * </tr>
363 * <tr>
364 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
365 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
366 * </tr>
367 * <tr>
368 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
369 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
370 * </tr>
371 * <tr>
372 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
373 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
374 * </tr>
375 * <tr>
376 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
377 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
378 * </tr>
379 * <tr>
380 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
381 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
382 * </tr>
383 * <tr>
384 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
385 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
386 * </tr>
387 * </tbody>
388 * </table>
389 *
390 * Here, the type {@code C} is the class or interface being searched for a member,
391 * documented as a parameter named {@code refc} in the lookup methods.
392 * The method type {@code MT} is composed from the return type {@code T}
393 * and the sequence of argument types {@code A*}.
394 * The constructor also has a sequence of argument types {@code A*} and
395 * is deemed to return the newly-created object of type {@code C}.
396 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
397 * The formal parameter {@code this} stands for the self-reference of type {@code C};
398 * if it is present, it is always the leading argument to the method handle invocation.
399 * (In the case of some {@code protected} members, {@code this} may be
400 * restricted in type to the lookup class; see below.)
401 * The name {@code arg} stands for all the other method handle arguments.
402 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
403 * stands for a null reference if the accessed method or field is static,
404 * and {@code this} otherwise.
405 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
406 * for reflective objects corresponding to the given members declared in type {@code C}.
407 * <p>
408 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
409 * as if by {@code ldc CONSTANT_Class}.
410 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
411 * <p>
412 * In cases where the given member is of variable arity (i.e., a method or constructor)
413 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
414 * In all other cases, the returned method handle will be of fixed arity.
415 * <p style="font-size:smaller;">
416 * <em>Discussion:</em>
417 * The equivalence between looked-up method handles and underlying
418 * class members and bytecode behaviors
419 * can break down in a few ways:
420 * <ul style="font-size:smaller;">
421 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
422 * the lookup can still succeed, even when there is no equivalent
423 * Java expression or bytecoded constant.
424 * <li>Likewise, if {@code T} or {@code MT}
425 * is not symbolically accessible from the lookup class's loader,
426 * the lookup can still succeed.
427 * For example, lookups for {@code MethodHandle.invokeExact} and
428 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
429 * <li>If there is a security manager installed, it can forbid the lookup
430 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
431 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
432 * constant is not subject to security manager checks.
433 * <li>If the looked-up method has a
434 * <a href="MethodHandle.html#maxarity">very large arity</a>,
435 * the method handle creation may fail with an
436 * {@code IllegalArgumentException}, due to the method handle type having
437 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
438 * </ul>
439 *
440 * <h2><a id="access"></a>Access checking</h2>
441 * Access checks are applied in the factory methods of {@code Lookup},
442 * when a method handle is created.
443 * This is a key difference from the Core Reflection API, since
444 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
445 * performs access checking against every caller, on every call.
446 * <p>
447 * All access checks start from a {@code Lookup} object, which
448 * compares its recorded lookup class against all requests to
449 * create method handles.
450 * A single {@code Lookup} object can be used to create any number
451 * of access-checked method handles, all checked against a single
452 * lookup class.
453 * <p>
454 * A {@code Lookup} object can be shared with other trusted code,
455 * such as a metaobject protocol.
456 * A shared {@code Lookup} object delegates the capability
457 * to create method handles on private members of the lookup class.
458 * Even if privileged code uses the {@code Lookup} object,
459 * the access checking is confined to the privileges of the
460 * original lookup class.
461 * <p>
462 * A lookup can fail, because
463 * the containing class is not accessible to the lookup class, or
464 * because the desired class member is missing, or because the
465 * desired class member is not accessible to the lookup class, or
466 * because the lookup object is not trusted enough to access the member.
467 * In the case of a field setter function on a {@code final} field,
468 * finality enforcement is treated as a kind of access control,
469 * and the lookup will fail, except in special cases of
470 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
471 * In any of these cases, a {@code ReflectiveOperationException} will be
472 * thrown from the attempted lookup. The exact class will be one of
473 * the following:
474 * <ul>
475 * <li>NoSuchMethodException — if a method is requested but does not exist
476 * <li>NoSuchFieldException — if a field is requested but does not exist
477 * <li>IllegalAccessException — if the member exists but an access check fails
478 * </ul>
479 * <p>
480 * In general, the conditions under which a method handle may be
481 * looked up for a method {@code M} are no more restrictive than the conditions
482 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
483 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
484 * a method handle lookup will generally raise a corresponding
485 * checked exception, such as {@code NoSuchMethodException}.
486 * And the effect of invoking the method handle resulting from the lookup
487 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
488 * to executing the compiled, verified, and resolved call to {@code M}.
489 * The same point is true of fields and constructors.
490 * <p style="font-size:smaller;">
491 * <em>Discussion:</em>
492 * Access checks only apply to named and reflected methods,
493 * constructors, and fields.
494 * Other method handle creation methods, such as
495 * {@link MethodHandle#asType MethodHandle.asType},
496 * do not require any access checks, and are used
497 * independently of any {@code Lookup} object.
498 * <p>
499 * If the desired member is {@code protected}, the usual JVM rules apply,
500 * including the requirement that the lookup class must either be in the
501 * same package as the desired member, or must inherit that member.
502 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
503 * In addition, if the desired member is a non-static field or method
504 * in a different package, the resulting method handle may only be applied
505 * to objects of the lookup class or one of its subclasses.
506 * This requirement is enforced by narrowing the type of the leading
507 * {@code this} parameter from {@code C}
508 * (which will necessarily be a superclass of the lookup class)
509 * to the lookup class itself.
510 * <p>
511 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
512 * that the receiver argument must match both the resolved method <em>and</em>
513 * the current class. Again, this requirement is enforced by narrowing the
514 * type of the leading parameter to the resulting method handle.
515 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
516 * <p>
517 * The JVM represents constructors and static initializer blocks as internal methods
518 * with special names ({@code "<init>"} and {@code "<clinit>"}).
519 * The internal syntax of invocation instructions allows them to refer to such internal
520 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
521 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
522 * <p>
523 * If the relationship between nested types is expressed directly through the
524 * {@code NestHost} and {@code NestMembers} attributes
525 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
526 * then the associated {@code Lookup} object provides direct access to
527 * the lookup class and all of its nestmates
528 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
529 * Otherwise, access between nested classes is obtained by the Java compiler creating
530 * a wrapper method to access a private method of another class in the same nest.
531 * For example, a nested class {@code C.D}
532 * can access private members within other related classes such as
533 * {@code C}, {@code C.D.E}, or {@code C.B},
534 * but the Java compiler may need to generate wrapper methods in
535 * those related classes. In such cases, a {@code Lookup} object on
536 * {@code C.E} would be unable to access those private members.
537 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
538 * which can transform a lookup on {@code C.E} into one on any of those other
539 * classes, without special elevation of privilege.
540 * <p>
541 * The accesses permitted to a given lookup object may be limited,
542 * according to its set of {@link #lookupModes lookupModes},
543 * to a subset of members normally accessible to the lookup class.
544 * For example, the {@link MethodHandles#publicLookup publicLookup}
545 * method produces a lookup object which is only allowed to access
546 * public members in public classes of exported packages.
547 * The caller sensitive method {@link MethodHandles#lookup lookup}
548 * produces a lookup object with full capabilities relative to
549 * its caller class, to emulate all supported bytecode behaviors.
550 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
551 * with fewer access modes than the original lookup object.
552 *
553 * <p style="font-size:smaller;">
554 * <a id="privacc"></a>
555 * <em>Discussion of private access:</em>
556 * We say that a lookup has <em>private access</em>
557 * if its {@linkplain #lookupModes lookup modes}
558 * include the possibility of accessing {@code private} members
559 * (which includes the private members of nestmates).
560 * As documented in the relevant methods elsewhere,
561 * only lookups with private access possess the following capabilities:
562 * <ul style="font-size:smaller;">
563 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
564 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
565 * such as {@code Class.forName}
566 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
567 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
568 * for classes accessible to the lookup class
569 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
570 * within the same package member
571 * </ul>
572 * <p style="font-size:smaller;">
573 * Each of these permissions is a consequence of the fact that a lookup object
574 * with private access can be securely traced back to an originating class,
575 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
576 * can be reliably determined and emulated by method handles.
577 *
578 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
579 * When a lookup class in one module {@code M1} accesses a class in another module
580 * {@code M2}, extra access checking is performed beyond the access mode bits.
581 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
582 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
583 * and when the type is in a package of {@code M2} that is exported to
584 * at least {@code M1}.
585 * <p>
586 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
587 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
588 * MethodHandles.privateLookupIn} methods.
589 * Teleporting across modules will always record the original lookup class as
590 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
591 * and drops {@link Lookup#MODULE MODULE} access.
592 * If the target class is in the same module as the lookup class {@code C},
593 * then the target class becomes the new lookup class
594 * and there is no change to the previous lookup class.
595 * If the target class is in a different module from {@code M1} ({@code C}'s module),
596 * {@code C} becomes the new previous lookup class
597 * and the target class becomes the new lookup class.
598 * In that case, if there was already a previous lookup class in {@code M0},
599 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
600 * drops all privileges.
601 * For example,
602 * <blockquote><pre>
603 * {@code
604 * Lookup lookup = MethodHandles.lookup(); // in class C
605 * Lookup lookup2 = lookup.in(D.class);
606 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
607 * }</pre></blockquote>
608 * <p>
609 * The {@link #lookup()} factory method produces a {@code Lookup} object
610 * with {@code null} previous lookup class.
611 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
612 * to class {@code D} without elevation of privileges.
613 * If {@code C} and {@code D} are in the same module,
614 * {@code lookup2} records {@code D} as the new lookup class and keeps the
615 * same previous lookup class as the original {@code lookup}, or
616 * {@code null} if not present.
617 * <p>
618 * When a {@code Lookup} teleports from a class
619 * in one nest to another nest, {@code PRIVATE} access is dropped.
620 * When a {@code Lookup} teleports from a class in one package to
621 * another package, {@code PACKAGE} access is dropped.
622 * When a {@code Lookup} teleports from a class in one module to another module,
623 * {@code MODULE} access is dropped.
624 * Teleporting across modules drops the ability to access non-exported classes
625 * in both the module of the new lookup class and the module of the old lookup class
626 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
627 * A {@code Lookup} can teleport back and forth to a class in the module of
628 * the lookup class and the module of the previous class lookup.
629 * Teleporting across modules can only decrease access but cannot increase it.
630 * Teleporting to some third module drops all accesses.
631 * <p>
632 * In the above example, if {@code C} and {@code D} are in different modules,
633 * {@code lookup2} records {@code D} as its lookup class and
634 * {@code C} as its previous lookup class and {@code lookup2} has only
635 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
636 * {@code C}'s module and {@code D}'s module.
637 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
638 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
639 * class {@code D} is recorded as its previous lookup class.
640 * <p>
641 * Teleporting across modules restricts access to the public types that
642 * both the lookup class and the previous lookup class can equally access
643 * (see below).
644 * <p>
645 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
646 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
647 * and create a new {@code Lookup} with <a href="#privcc">private access</a>
648 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
649 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
650 * to call {@code privateLookupIn}.
651 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
652 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
653 * produces a new {@code Lookup} on {@code T} with full capabilities.
654 * A {@code lookup} on {@code C} is also allowed
655 * to do deep reflection on {@code T} in another module {@code M2} if
656 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
657 * the package containing {@code T} to at least {@code M1}.
658 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
659 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
660 * The resulting {@code Lookup} can be used to do member lookup or teleport
661 * to another lookup class by calling {@link #in Lookup::in}. But
662 * it cannot be used to obtain another private {@code Lookup} by calling
663 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
664 * because it has no {@code MODULE} access.
665 *
666 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
667 *
668 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
669 * allows cross-module access. The access checking is performed with respect
670 * to both the lookup class and the previous lookup class if present.
671 * <p>
672 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
673 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
674 * exported unconditionally}.
675 * <p>
676 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
677 * the lookup with {@link #PUBLIC} mode can access all public types in modules
678 * that are readable to {@code M1} and the type is in a package that is exported
679 * at least to {@code M1}.
680 * <p>
681 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
682 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
683 * the intersection of all public types that are accessible to {@code M1}
684 * with all public types that are accessible to {@code M0}. {@code M0}
685 * reads {@code M1} and hence the set of accessible types includes:
686 *
687 * <table class="striped">
688 * <caption style="display:none">
689 * Public types in the following packages are accessible to the
690 * lookup class and the previous lookup class.
691 * </caption>
692 * <thead>
693 * <tr>
694 * <th scope="col">Equally accessible types to {@code M0} and {@code M1}</th>
695 * </tr>
696 * </thead>
697 * <tbody>
698 * <tr>
699 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M1}</th>
700 * </tr>
701 * <tr>
702 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</th>
703 * </tr>
704 * <tr>
705 * <th scope="row" style="text-align:left">unconditional-exported packages from a third module {@code M2}
706 * if both {@code M0} and {@code M1} read {@code M2}</th>
707 * </tr>
708 * <tr>
709 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M1} to {@code M0}</th>
710 * </tr>
711 * <tr>
712 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M0} to {@code M1}
713 * if {@code M1} reads {@code M0}</th>
714 * </tr>
715 * <tr>
716 * <th scope="row" style="text-align:left">qualified-exported packages from a third module {@code M2} to
717 * both {@code M0} and {@code M1} if both {@code M0} and {@code M1} read {@code M2}</th>
718 * </tr>
719 * </tbody>
720 * </table>
721 *
722 * <h2><a id="access-modes"></a>Access modes</h2>
723 *
724 * The table below shows the access modes of a {@code Lookup} produced by
725 * any of the following factory or transformation methods:
726 * <ul>
727 * <li>{@link #lookup() MethodHandles.lookup()}</li>
728 * <li>{@link #publicLookup() MethodHandles.publicLookup()}</li>
729 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn}</li>
730 * <li>{@link Lookup#in}</li>
731 * <li>{@link Lookup#dropLookupMode(int)}</li>
732 * </ul>
733 *
734 * <table class="striped">
735 * <caption style="display:none">
736 * Access mode summary
737 * </caption>
738 * <thead>
739 * <tr>
740 * <th scope="col">Lookup object</th>
741 * <th style="text-align:center">protected</th>
742 * <th style="text-align:center">private</th>
743 * <th style="text-align:center">package</th>
744 * <th style="text-align:center">module</th>
745 * <th style="text-align:center">public</th>
746 * </tr>
747 * </thead>
748 * <tbody>
749 * <tr>
750 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
751 * <td style="text-align:center">PRO</td>
752 * <td style="text-align:center">PRI</td>
753 * <td style="text-align:center">PAC</td>
754 * <td style="text-align:center">MOD</td>
755 * <td style="text-align:center">1R</td>
756 * </tr>
757 * <tr>
758 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
759 * <td></td>
760 * <td></td>
761 * <td style="text-align:center">PAC</td>
762 * <td style="text-align:center">MOD</td>
763 * <td style="text-align:center">1R</td>
764 * </tr>
765 * <tr>
766 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
767 * <td></td>
768 * <td></td>
769 * <td></td>
770 * <td style="text-align:center">MOD</td>
771 * <td style="text-align:center">1R</td>
772 * </tr>
773 * <tr>
774 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
775 * <td></td>
776 * <td></td>
777 * <td></td>
778 * <td></td>
779 * <td style="text-align:center">2R</td>
780 * </tr>
781 * <tr>
782 * <td>{@code CL.in(D).in(C)} hop back to module</td>
783 * <td></td>
784 * <td></td>
785 * <td></td>
786 * <td></td>
787 * <td style="text-align:center">2R</td>
788 * </tr>
789 * <tr>
790 * <td>{@code PRI1 = privateLookupIn(C1,CL)}</td>
791 * <td style="text-align:center">PRO</td>
792 * <td style="text-align:center">PRI</td>
793 * <td style="text-align:center">PAC</td>
794 * <td style="text-align:center">MOD</td>
795 * <td style="text-align:center">1R</td>
796 * </tr>
797 * <tr>
798 * <td>{@code PRI1a = privateLookupIn(C,PRI1)}</td>
799 * <td style="text-align:center">PRO</td>
800 * <td style="text-align:center">PRI</td>
801 * <td style="text-align:center">PAC</td>
802 * <td style="text-align:center">MOD</td>
803 * <td style="text-align:center">1R</td>
804 * </tr>
805 * <tr>
806 * <td>{@code PRI1.in(C1)} same package</td>
807 * <td></td>
808 * <td></td>
809 * <td style="text-align:center">PAC</td>
810 * <td style="text-align:center">MOD</td>
811 * <td style="text-align:center">1R</td>
812 * </tr>
813 * <tr>
814 * <td>{@code PRI1.in(C1)} different package</td>
815 * <td></td>
816 * <td></td>
817 * <td></td>
818 * <td style="text-align:center">MOD</td>
819 * <td style="text-align:center">1R</td>
820 * </tr>
821 * <tr>
822 * <td>{@code PRI1.in(D)} different module</td>
823 * <td></td>
824 * <td></td>
825 * <td></td>
826 * <td></td>
827 * <td style="text-align:center">2R</td>
828 * </tr>
829 * <tr>
830 * <td>{@code PRI1.dropLookupMode(PROTECTED)}</td>
831 * <td></td>
832 * <td style="text-align:center">PRI</td>
833 * <td style="text-align:center">PAC</td>
834 * <td style="text-align:center">MOD</td>
835 * <td style="text-align:center">1R</td>
836 * </tr>
837 * <tr>
838 * <td>{@code PRI1.dropLookupMode(PRIVATE)}</td>
839 * <td></td>
840 * <td></td>
841 * <td style="text-align:center">PAC</td>
842 * <td style="text-align:center">MOD</td>
843 * <td style="text-align:center">1R</td>
844 * </tr>
845 * <tr>
846 * <td>{@code PRI1.dropLookupMode(PACKAGE)}</td>
847 * <td></td>
848 * <td></td>
849 * <td></td>
850 * <td style="text-align:center">MOD</td>
851 * <td style="text-align:center">1R</td>
852 * </tr>
853 * <tr>
854 * <td>{@code PRI1.dropLookupMode(MODULE)}</td>
855 * <td></td>
856 * <td></td>
857 * <td></td>
858 * <td></td>
859 * <td style="text-align:center">1R</td>
860 * </tr>
861 * <tr>
862 * <td>{@code PRI1.dropLookupMode(PUBLIC)}</td>
863 * <td></td>
864 * <td></td>
865 * <td></td>
866 * <td></td>
867 * <td style="text-align:center">none</td>
868 * <tr>
869 * <td>{@code PRI2 = privateLookupIn(D,CL)}</td>
870 * <td style="text-align:center">PRO</td>
871 * <td style="text-align:center">PRI</td>
872 * <td style="text-align:center">PAC</td>
873 * <td></td>
874 * <td style="text-align:center">2R</td>
875 * </tr>
876 * <tr>
877 * <td>{@code privateLookupIn(D,PRI1)}</td>
878 * <td style="text-align:center">PRO</td>
879 * <td style="text-align:center">PRI</td>
880 * <td style="text-align:center">PAC</td>
881 * <td></td>
882 * <td style="text-align:center">2R</td>
883 * </tr>
884 * <tr>
885 * <td>{@code privateLookupIn(C,PRI2)} fails</td>
886 * <td></td>
887 * <td></td>
888 * <td></td>
889 * <td></td>
890 * <td style="text-align:center">IAE</td>
891 * </tr>
892 * <tr>
893 * <td>{@code PRI2.in(D2)} same package</td>
894 * <td></td>
895 * <td></td>
896 * <td style="text-align:center">PAC</td>
897 * <td></td>
898 * <td style="text-align:center">2R</td>
899 * </tr>
900 * <tr>
901 * <td>{@code PRI2.in(D2)} different package</td>
902 * <td></td>
903 * <td></td>
904 * <td></td>
905 * <td></td>
906 * <td style="text-align:center">2R</td>
907 * </tr>
908 * <tr>
909 * <td>{@code PRI2.in(C1)} hop back to module</td>
910 * <td></td>
911 * <td></td>
912 * <td></td>
913 * <td></td>
914 * <td style="text-align:center">2R</td>
915 * </tr>
916 * <tr>
917 * <td>{@code PRI2.in(E)} hop to third module</td>
918 * <td></td>
919 * <td></td>
920 * <td></td>
921 * <td></td>
922 * <td style="text-align:center">none</td>
923 * </tr>
924 * <tr>
925 * <td>{@code PRI2.dropLookupMode(PROTECTED)}</td>
926 * <td></td>
927 * <td style="text-align:center">PRI</td>
928 * <td style="text-align:center">PAC</td>
929 * <td></td>
930 * <td style="text-align:center">2R</td>
931 * </tr>
932 * <tr>
933 * <td>{@code PRI2.dropLookupMode(PRIVATE)}</td>
934 * <td></td>
935 * <td></td>
936 * <td style="text-align:center">PAC</td>
937 * <td></td>
938 * <td style="text-align:center">2R</td>
939 * </tr>
940 * <tr>
941 * <td>{@code PRI2.dropLookupMode(PACKAGE)}</td>
942 * <td></td>
943 * <td></td>
944 * <td></td>
945 * <td></td>
946 * <td style="text-align:center">2R</td>
947 * </tr>
948 * <tr>
949 * <td>{@code PRI2.dropLookupMode(MODULE)}</td>
950 * <td></td>
951 * <td></td>
952 * <td></td>
953 * <td></td>
954 * <td style="text-align:center">2R</td>
955 * </tr>
956 * <tr>
957 * <td>{@code PRI2.dropLookupMode(PUBLIC)}</td>
958 * <td></td>
959 * <td></td>
960 * <td></td>
961 * <td></td>
962 * <td style="text-align:center">none</td>
963 * </tr>
964 * <tr>
965 * <td>{@code CL.dropLookupMode(PROTECTED)}</td>
966 * <td></td>
967 * <td style="text-align:center">PRI</td>
968 * <td style="text-align:center">PAC</td>
969 * <td style="text-align:center">MOD</td>
970 * <td style="text-align:center">1R</td>
971 * </tr>
972 * <tr>
973 * <td>{@code CL.dropLookupMode(PRIVATE)}</td>
974 * <td></td>
975 * <td></td>
976 * <td style="text-align:center">PAC</td>
977 * <td style="text-align:center">MOD</td>
978 * <td style="text-align:center">1R</td>
979 * </tr>
980 * <tr>
981 * <td>{@code CL.dropLookupMode(PACKAGE)}</td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td style="text-align:center">MOD</td>
986 * <td style="text-align:center">1R</td>
987 * </tr>
988 * <tr>
989 * <td>{@code CL.dropLookupMode(MODULE)}</td>
990 * <td></td>
991 * <td></td>
992 * <td></td>
993 * <td></td>
994 * <td style="text-align:center">1R</td>
995 * </tr>
996 * <tr>
997 * <td>{@code CL.dropLookupMode(PUBLIC)}</td>
998 * <td></td>
999 * <td></td>
1000 * <td></td>
1001 * <td></td>
1002 * <td style="text-align:center">none</td>
1003 * </tr>
1004 * <tr>
1005 * <td>{@code PUB = publicLookup()}</td>
1006 * <td></td>
1007 * <td></td>
1008 * <td></td>
1009 * <td></td>
1010 * <td style="text-align:center">U</td>
1011 * </tr>
1012 * <tr>
1013 * <td>{@code PUB.in(D)} different module</td>
1014 * <td></td>
1015 * <td></td>
1016 * <td></td>
1017 * <td></td>
1018 * <td style="text-align:center">U</td>
1019 * </tr>
1020 * <tr>
1021 * <td>{@code PUB.in(D).in(E)} third module</td>
1022 * <td></td>
1023 * <td></td>
1024 * <td></td>
1025 * <td></td>
1026 * <td style="text-align:center">U</td>
1027 * </tr>
1028 * <tr>
1029 * <td>{@code PUB.dropLookupMode(UNCONDITIONAL)}</td>
1030 * <td></td>
1031 * <td></td>
1032 * <td></td>
1033 * <td></td>
1034 * <td style="text-align:center">none</td>
1035 * </tr>
1036 * <tr>
1037 * <td>{@code privateLookupIn(C1,PUB)} fails</td>
1038 * <td></td>
1039 * <td></td>
1040 * <td></td>
1041 * <td></td>
1042 * <td style="text-align:center">IAE</td>
1043 * </tr>
1044 * <tr>
1045 * <td>{@code ANY.in(X)}, for inaccessible <code>X</code></td>
1046 * <td></td>
1047 * <td></td>
1048 * <td></td>
1049 * <td></td>
1050 * <td style="text-align:center">none</td>
1051 * </tr>
1052 * </tbody>
1053 * </table>
1054 *
1055 * <p>
1056 * Notes:
1057 * <ul>
1058 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1059 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1060 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1061 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1062 * <li>{@code PRO} indicates {@link #PROTECTED} bit set,
1063 * {@code PRI} indicates {@link #PRIVATE} bit set,
1064 * {@code PAC} indicates {@link #PACKAGE} bit set,
1065 * {@code MOD} indicates {@link #MODULE} bit set,
1066 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1067 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1068 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1069 * <li>Public access comes in three kinds:
1070 * <ul>
1071 * <li>unconditional ({@code U}): the lookup assumes readability.
1072 * The lookup has {@code null} previous lookup class.
1073 * <li>one-module-reads ({@code 1R}): the module access checking is
1074 * performed with respect to the lookup class. The lookup has {@code null}
1075 * previous lookup class.
1076 * <li>two-module-reads ({@code 2R}): the module access checking is
1077 * performed with respect to the lookup class and the previous lookup class.
1078 * The lookup has a non-null previous lookup class which is in a
1079 * different module from the current lookup class.
1080 * </ul>
1081 * <li>Any attempt to reach a third module loses all access.</li>
1082 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1083 * all access modes are dropped.</li>
1084 * </ul>
1085 *
1086 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1087 * Although bytecode instructions can only refer to classes in
1088 * a related class loader, this API can search for methods in any
1089 * class, as long as a reference to its {@code Class} object is
1090 * available. Such cross-loader references are also possible with the
1091 * Core Reflection API, and are impossible to bytecode instructions
1092 * such as {@code invokestatic} or {@code getfield}.
1093 * There is a {@linkplain java.lang.SecurityManager security manager API}
1094 * to allow applications to check such cross-loader references.
1095 * These checks apply to both the {@code MethodHandles.Lookup} API
1096 * and the Core Reflection API
1097 * (as found on {@link java.lang.Class Class}).
1098 * <p>
1099 * If a security manager is present, member and class lookups are subject to
1100 * additional checks.
1101 * From one to three calls are made to the security manager.
1102 * Any of these calls can refuse access by throwing a
1103 * {@link java.lang.SecurityException SecurityException}.
1104 * Define {@code smgr} as the security manager,
1105 * {@code lookc} as the lookup class of the current lookup object,
1106 * {@code refc} as the containing class in which the member
1107 * is being sought, and {@code defc} as the class in which the
1108 * member is actually defined.
1109 * (If a class or other type is being accessed,
1110 * the {@code refc} and {@code defc} values are the class itself.)
1111 * The value {@code lookc} is defined as <em>not present</em>
1112 * if the current lookup object does not have
1113 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1114 * The calls are made according to the following rules:
1115 * <ul>
1116 * <li><b>Step 1:</b>
1117 * If {@code lookc} is not present, or if its class loader is not
1118 * the same as or an ancestor of the class loader of {@code refc},
1119 * then {@link SecurityManager#checkPackageAccess
1120 * smgr.checkPackageAccess(refcPkg)} is called,
1121 * where {@code refcPkg} is the package of {@code refc}.
1122 * <li><b>Step 2a:</b>
1123 * If the retrieved member is not public and
1124 * {@code lookc} is not present, then
1125 * {@link SecurityManager#checkPermission smgr.checkPermission}
1126 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1127 * <li><b>Step 2b:</b>
1128 * If the retrieved class has a {@code null} class loader,
1129 * and {@code lookc} is not present, then
1130 * {@link SecurityManager#checkPermission smgr.checkPermission}
1131 * with {@code RuntimePermission("getClassLoader")} is called.
1132 * <li><b>Step 3:</b>
1133 * If the retrieved member is not public,
1134 * and if {@code lookc} is not present,
1135 * and if {@code defc} and {@code refc} are different,
1136 * then {@link SecurityManager#checkPackageAccess
1137 * smgr.checkPackageAccess(defcPkg)} is called,
1138 * where {@code defcPkg} is the package of {@code defc}.
1139 * </ul>
1140 * Security checks are performed after other access checks have passed.
1141 * Therefore, the above rules presuppose a member or class that is public,
1142 * or else that is being accessed from a lookup class that has
1143 * rights to access the member or class.
1144 *
1145 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1146 * A small number of Java methods have a special property called caller sensitivity.
1147 * A <em>caller-sensitive</em> method can behave differently depending on the
1148 * identity of its immediate caller.
1149 * <p>
1150 * If a method handle for a caller-sensitive method is requested,
1151 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1152 * but they take account of the lookup class in a special way.
1153 * The resulting method handle behaves as if it were called
1154 * from an instruction contained in the lookup class,
1155 * so that the caller-sensitive method detects the lookup class.
1156 * (By contrast, the invoker of the method handle is disregarded.)
1157 * Thus, in the case of caller-sensitive methods,
1158 * different lookup classes may give rise to
1159 * differently behaving method handles.
1160 * <p>
1161 * In cases where the lookup object is
1162 * {@link MethodHandles#publicLookup() publicLookup()},
1163 * or some other lookup object without
1164 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
1165 * the lookup class is disregarded.
1166 * In such cases, no caller-sensitive method handle can be created,
1167 * access is forbidden, and the lookup fails with an
1168 * {@code IllegalAccessException}.
1169 * <p style="font-size:smaller;">
1170 * <em>Discussion:</em>
1171 * For example, the caller-sensitive method
1172 * {@link java.lang.Class#forName(String) Class.forName(x)}
1173 * can return varying classes or throw varying exceptions,
1174 * depending on the class loader of the class that calls it.
1175 * A public lookup of {@code Class.forName} will fail, because
1176 * there is no reasonable way to determine its bytecode behavior.
1177 * <p style="font-size:smaller;">
1178 * If an application caches method handles for broad sharing,
1179 * it should use {@code publicLookup()} to create them.
1180 * If there is a lookup of {@code Class.forName}, it will fail,
1181 * and the application must take appropriate action in that case.
1182 * It may be that a later lookup, perhaps during the invocation of a
1183 * bootstrap method, can incorporate the specific identity
1184 * of the caller, making the method accessible.
1185 * <p style="font-size:smaller;">
1186 * The function {@code MethodHandles.lookup} is caller sensitive
1187 * so that there can be a secure foundation for lookups.
1188 * Nearly all other methods in the JSR 292 API rely on lookup
1189 * objects to check access requests.
1190 *
1191 * @revised 9
1192 */
1193 public static final
1194 class Lookup {
1195 /** The class on behalf of whom the lookup is being performed. */
1196 private final Class<?> lookupClass;
1197
1198 /** previous lookup class */
1199 private final Class<?> prevLookupClass;
1200
1201 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1202 private final int allowedModes;
1203
1204 static {
1205 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1206 }
1207
1208 /** A single-bit mask representing {@code public} access,
1209 * which may contribute to the result of {@link #lookupModes lookupModes}.
1210 * The value, {@code 0x01}, happens to be the same as the value of the
1211 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1212 * <p>
1213 * A {@code Lookup} with this lookup mode performs cross-module access check
1214 * with respect to the {@linkplain #lookupClass() lookup class} and
1215 * {@linkplain #previousLookupClass() previous lookup class} if present.
1216 */
1217 public static final int PUBLIC = Modifier.PUBLIC;
1218
1219 /** A single-bit mask representing {@code private} access,
1220 * which may contribute to the result of {@link #lookupModes lookupModes}.
1221 * The value, {@code 0x02}, happens to be the same as the value of the
1222 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1223 */
1224 public static final int PRIVATE = Modifier.PRIVATE;
1225
1226 /** A single-bit mask representing {@code protected} access,
1227 * which may contribute to the result of {@link #lookupModes lookupModes}.
1228 * The value, {@code 0x04}, happens to be the same as the value of the
1229 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1230 */
1231 public static final int PROTECTED = Modifier.PROTECTED;
1232
1233 /** A single-bit mask representing {@code package} access (default access),
1234 * which may contribute to the result of {@link #lookupModes lookupModes}.
1235 * The value is {@code 0x08}, which does not correspond meaningfully to
1236 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1237 */
1238 public static final int PACKAGE = Modifier.STATIC;
1239
1240 /** A single-bit mask representing {@code module} access,
1241 * which may contribute to the result of {@link #lookupModes lookupModes}.
1242 * The value is {@code 0x10}, which does not correspond meaningfully to
1243 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1244 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1245 * with this lookup mode can access all public types in the module of the
1246 * lookup class and public types in packages exported by other modules
1247 * to the module of the lookup class.
1248 * <p>
1249 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1250 * previous lookup class} is always {@code null}.
1251 *
1252 * @since 9
1253 * @spec JPMS
1254 */
1255 public static final int MODULE = PACKAGE << 1;
1256
1257 /** A single-bit mask representing {@code unconditional} access
1258 * which may contribute to the result of {@link #lookupModes lookupModes}.
1259 * The value is {@code 0x20}, which does not correspond meaningfully to
1260 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1261 * A {@code Lookup} with this lookup mode assumes {@linkplain
1262 * java.lang.Module#canRead(java.lang.Module) readability}.
1263 * This lookup mode can access all public members of public types
1264 * of all modules when the type is in a package that is {@link
1265 * java.lang.Module#isExported(String) exported unconditionally}.
1266 *
1267 * <p>
1268 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1269 * previous lookup class} is always {@code null}.
1270 *
1271 * @since 9
1272 * @spec JPMS
1273 * @see #publicLookup()
1274 */
1275 public static final int UNCONDITIONAL = PACKAGE << 2;
1276
1277 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
1278 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
1279 private static final int TRUSTED = -1;
1280
1281 /*
1282 * Adjust PUBLIC => PUBLIC|MODULE|UNCONDITIONAL
1283 * Adjust 0 => PACKAGE
1284 */
1285 private static int fixmods(int mods) {
1286 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
1287 if (Modifier.isPublic(mods))
1288 mods |= UNCONDITIONAL;
1289 return (mods != 0) ? mods : PACKAGE;
1290 }
1291
1292 /** Tells which class is performing the lookup. It is this class against
1293 * which checks are performed for visibility and access permissions.
1294 * <p>
1295 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1296 * access checks are performed against both the lookup class and the previous lookup class.
1297 * <p>
1298 * The class implies a maximum level of access permission,
1299 * but the permissions may be additionally limited by the bitmask
1300 * {@link #lookupModes lookupModes}, which controls whether non-public members
1301 * can be accessed.
1302 * @return the lookup class, on behalf of which this lookup object finds members
1303 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1304 */
1305 public Class<?> lookupClass() {
1306 return lookupClass;
1307 }
1308
1309 /** Reports a lookup class in another module that this lookup object
1310 * was previously teleported from, or {@code null}.
1311 * <p>
1312 * A {@code Lookup} object produced by the factory methods, such as the
1313 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1314 * has {@code null} previous lookup class.
1315 * A {@code Lookup} object has a non-null previous lookup class
1316 * when this lookup was teleported from an old lookup class
1317 * in one module to a new lookup class in another module.
1318 *
1319 * @return the lookup class in another module that this lookup object was
1320 * previously teleported from, or {@code null}
1321 * @since 14
1322 * @see #in(Class)
1323 * @see MethodHandles#privateLookupIn(Class, Lookup)
1324 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1325 */
1326 public Class<?> previousLookupClass() {
1327 return prevLookupClass;
1328 }
1329
1330 // This is just for calling out to MethodHandleImpl.
1331 private Class<?> lookupClassOrNull() {
1332 if (allowedModes == TRUSTED) {
1333 return null;
1334 }
1335 if (allowedModes == UNCONDITIONAL) {
1336 // use Object as the caller to pass to VM doing resolution
1337 return Object.class;
1338 }
1339 return lookupClass;
1340 }
1341
1342 /** Tells which access-protection classes of members this lookup object can produce.
1343 * The result is a bit-mask of the bits
1344 * {@linkplain #PUBLIC PUBLIC (0x01)},
1345 * {@linkplain #PRIVATE PRIVATE (0x02)},
1346 * {@linkplain #PROTECTED PROTECTED (0x04)},
1347 * {@linkplain #PACKAGE PACKAGE (0x08)},
1348 * {@linkplain #MODULE MODULE (0x10)},
1349 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
1350 * <p>
1351 * A freshly-created lookup object
1352 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1353 * all possible bits set, except {@code UNCONDITIONAL}.
1354 * A lookup object on a new lookup class
1355 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1356 * may have some mode bits set to zero.
1357 * Mode bits can also be
1358 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1359 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1360 * The purpose of this is to restrict access via the new lookup object,
1361 * so that it can access only names which can be reached by the original
1362 * lookup object, and also by the new lookup class.
1363 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1364 * @see #in
1365 * @see #dropLookupMode
1366 *
1367 * @revised 9
1368 * @spec JPMS
1369 */
1370 public int lookupModes() {
1371 return allowedModes & ALL_MODES;
1372 }
1373
1374 /** Embody the current class (the lookupClass) as a lookup class
1375 * for method handle creation.
1376 * Must be called by from a method in this package,
1377 * which in turn is called by a method not in this package.
1378 */
1379 Lookup(Class<?> lookupClass) {
1380 this(lookupClass, null, FULL_POWER_MODES);
1381 // make sure we haven't accidentally picked up a privileged class:
1382 checkUnprivilegedlookupClass(lookupClass);
1383 }
1384
1385 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1386 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1387 && prevLookupClass.getModule() != lookupClass.getModule());
1388
1389 this.lookupClass = lookupClass;
1390 this.prevLookupClass = prevLookupClass;
1391 this.allowedModes = allowedModes;
1392 }
1393
1394 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1395 // make sure we haven't accidentally picked up a privileged class:
1396 checkUnprivilegedlookupClass(lookupClass);
1397 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1398 }
1399
1400 /**
1401 * Creates a lookup on the specified new lookup class.
1402 * The resulting object will report the specified
1403 * class as its own {@link #lookupClass() lookupClass}.
1404 *
1405 * <p>
1406 * However, the resulting {@code Lookup} object is guaranteed
1407 * to have no more access capabilities than the original.
1408 * In particular, access capabilities can be lost as follows:<ul>
1409 * <li>If the new lookup class is in a different module from the old one,
1410 * i.e. {@link #MODULE MODULE} access is lost.
1411 * <li>If the new lookup class is in a different package
1412 * than the old one, protected and default (package) members will not be accessible,
1413 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1414 * <li>If the new lookup class is not within the same package member
1415 * as the old one, private members will not be accessible, and protected members
1416 * will not be accessible by virtue of inheritance,
1417 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1418 * (Protected members may continue to be accessible because of package sharing.)
1419 * <li>If the new lookup class is not
1420 * {@linkplain #accessClass(Class) accessible} to this lookup,
1421 * then no members, not even public members, will be accessible
1422 * i.e. all access modes are lost.
1423 * <li>If the new lookup class, the old lookup class and the previous lookup class
1424 * are all in different modules i.e. teleporting to a third module,
1425 * all access modes are lost.
1426 * </ul>
1427 * <p>
1428 * The new previous lookup class is chosen as follows:
1429 * <ul>
1430 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1431 * the new previous lookup class is {@code null}.
1432 * <li>If the new lookup class is in the same module as the old lookup class,
1433 * the new previous lookup class is the old previous lookup class.
1434 * <li>If the new lookup class is in a different module from the old lookup class,
1435 * the new previous lookup class is the the old lookup class.
1436 *</ul>
1437 * <p>
1438 * The resulting lookup's capabilities for loading classes
1439 * (used during {@link #findClass} invocations)
1440 * are determined by the lookup class' loader,
1441 * which may change due to this operation.
1442 * <p>
1443 * @param requestedLookupClass the desired lookup class for the new lookup object
1444 * @return a lookup object which reports the desired lookup class, or the same object
1445 * if there is no change
1446 * @throws NullPointerException if the argument is null
1447 *
1448 * @revised 9
1449 * @spec JPMS
1450 * @see #accessClass(Class)
1451 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1452 */
1453 public Lookup in(Class<?> requestedLookupClass) {
1454 Objects.requireNonNull(requestedLookupClass);
1455 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1456 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1457 if (requestedLookupClass == this.lookupClass)
1458 return this; // keep same capabilities
1459 int newModes = (allowedModes & FULL_POWER_MODES);
1460 Module fromModule = this.lookupClass.getModule();
1461 Module targetModule = requestedLookupClass.getModule();
1462 Class<?> plc = this.previousLookupClass();
1463 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1464 assert plc == null;
1465 newModes = UNCONDITIONAL;
1466 } else if (fromModule != targetModule) {
1467 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1468 // allow hopping back and forth between fromModule and plc's module
1469 // but not the third module
1470 newModes = 0;
1471 }
1472 // drop MODULE access
1473 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1474 // teleport from this lookup class
1475 plc = this.lookupClass;
1476 }
1477 if ((newModes & PACKAGE) != 0
1478 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1479 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1480 }
1481 // Allow nestmate lookups to be created without special privilege:
1482 if ((newModes & PRIVATE) != 0
1483 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1484 newModes &= ~(PRIVATE|PROTECTED);
1485 }
1486 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1487 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1488 // The requested class it not accessible from the lookup class.
1489 // No permissions.
1490 newModes = 0;
1491 }
1492 return newLookup(requestedLookupClass, plc, newModes);
1493 }
1494
1495 /**
1496 * Creates a lookup on the same lookup class which this lookup object
1497 * finds members, but with a lookup mode that has lost the given lookup mode.
1498 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1499 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
1500 * {@link #PROTECTED PROTECTED} is always
1501 * dropped and so the resulting lookup mode will never have this access capability.
1502 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
1503 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
1504 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
1505 * is dropped then the resulting lookup has no access. If {@code UNCONDITIONAL}
1506 * is dropped then the resulting lookup has no access.
1507 *
1508 * @apiNote
1509 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1510 * delegate non-public access within the package of the lookup class without
1511 * conferring private access. A lookup with {@code MODULE} but not
1512 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1513 * the module of the lookup class without conferring package access.
1514 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1515 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1516 * to public classes accessible to both the module of the lookup class
1517 * and the module of the previous lookup class.
1518 *
1519 * @param modeToDrop the lookup mode to drop
1520 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1521 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1522 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
1523 * @see MethodHandles#privateLookupIn
1524 * @since 9
1525 */
1526 public Lookup dropLookupMode(int modeToDrop) {
1527 int oldModes = lookupModes();
1528 int newModes = oldModes & ~(modeToDrop | PROTECTED);
1529 switch (modeToDrop) {
1530 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1531 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1532 case PACKAGE: newModes &= ~(PRIVATE); break;
1533 case PROTECTED:
1534 case PRIVATE:
1535 case UNCONDITIONAL: break;
1536 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1537 }
1538 if (newModes == oldModes) return this; // return self if no change
1539 return newLookup(lookupClass(), previousLookupClass(), newModes);
1540 }
1541
1542 /**
1543 * Defines a class to the same class loader and in the same runtime package and
1544 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1545 * {@linkplain #lookupClass() lookup class}.
1546 *
1547 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1548 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1549 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1550 * that the lookup object was created by a caller in the runtime package (or derived
1551 * from a lookup originally created by suitably privileged code to a target class in
1552 * the runtime package). </p>
1553 *
1554 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1555 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1556 * same package as the lookup class. </p>
1557 *
1558 * <p> This method does not run the class initializer. The class initializer may
1559 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1560 * Specification</em>. </p>
1561 *
1562 * <p> If there is a security manager, its {@code checkPermission} method is first called
1563 * to check {@code RuntimePermission("defineClass")}. </p>
1564 *
1565 * @param bytes the class bytes
1566 * @return the {@code Class} object for the class
1567 * @throws IllegalArgumentException the bytes are for a class in a different package
1568 * to the lookup class
1569 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1570 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1571 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
1572 * @throws SecurityException if denied by the security manager
1573 * @throws NullPointerException if {@code bytes} is {@code null}
1574 * @since 9
1575 * @spec JPMS
1576 * @see Lookup#privateLookupIn
1577 * @see Lookup#dropLookupMode
1578 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1579 */
1580 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1581 SecurityManager sm = System.getSecurityManager();
1582 if (sm != null)
1583 sm.checkPermission(new RuntimePermission("defineClass"));
1584 if ((lookupModes() & PACKAGE) == 0)
1585 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1586 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
1587
1588 // parse class bytes to get class name (in internal form)
1589 bytes = bytes.clone();
1590 String name;
1591 try {
1592 ClassReader reader = new ClassReader(bytes);
1593 name = reader.getClassName();
1594 } catch (RuntimeException e) {
1595 // ASM exceptions are poorly specified
1596 ClassFormatError cfe = new ClassFormatError();
1597 cfe.initCause(e);
1598 throw cfe;
1599 }
1600
1601 // get package and class name in binary form
1602 String cn, pn;
1603 int index = name.lastIndexOf('/');
1604 if (index == -1) {
1605 cn = name;
1606 pn = "";
1607 } else {
1608 cn = name.replace('/', '.');
1609 pn = cn.substring(0, index);
1610 }
1611 if (!pn.equals(lookupClass.getPackageName())) {
1612 throw new IllegalArgumentException("Class not in same package as lookup class");
1613 }
1614
1615 // invoke the class loader's defineClass method
1616 ClassLoader loader = lookupClass.getClassLoader();
1617 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
1618 String source = "__Lookup_defineClass__";
1619 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
1620 return clazz;
1621 }
1622
1623 private ProtectionDomain lookupClassProtectionDomain() {
1624 ProtectionDomain pd = cachedProtectionDomain;
1625 if (pd == null) {
1626 cachedProtectionDomain = pd = protectionDomain(lookupClass);
1627 }
1628 return pd;
1629 }
1630
1631 private ProtectionDomain protectionDomain(Class<?> clazz) {
1632 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
1633 return AccessController.doPrivileged(pa);
1634 }
1635
1636 // cached protection domain
1637 private volatile ProtectionDomain cachedProtectionDomain;
1638
1639
1640 // Make sure outer class is initialized first.
1641 static { IMPL_NAMES.getClass(); }
1642
1643 /** Package-private version of lookup which is trusted. */
1644 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
1645
1646 /** Version of lookup which is trusted minimally.
1647 * It can only be used to create method handles to publicly accessible
1648 * members in packages that are exported unconditionally.
1649 */
1650 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
1651
1652 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1653 String name = lookupClass.getName();
1654 if (name.startsWith("java.lang.invoke."))
1655 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1656 }
1657
1658 /**
1659 * Displays the name of the class from which lookups are to be made.
1660 * followed with "/" and the name of the {@linkplain #previousLookupClass()
1661 * previous lookup class} if present.
1662 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1663 * If there are restrictions on the access permitted to this lookup,
1664 * this is indicated by adding a suffix to the class name, consisting
1665 * of a slash and a keyword. The keyword represents the strongest
1666 * allowed access, and is chosen as follows:
1667 * <ul>
1668 * <li>If no access is allowed, the suffix is "/noaccess".
1669 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
1670 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1671 * <li>If only public and module access are allowed, the suffix is "/module".
1672 * <li>If public and package access are allowed, the suffix is "/package".
1673 * <li>If public, package, and private access are allowed, the suffix is "/private".
1674 * </ul>
1675 * If none of the above cases apply, it is the case that full access
1676 * (public, module, package, private, and protected) is allowed.
1677 * In this case, no suffix is added.
1678 * This is true only of an object obtained originally from
1679 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1680 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1681 * always have restricted access, and will display a suffix.
1682 * <p>
1683 * (It may seem strange that protected access should be
1684 * stronger than private access. Viewed independently from
1685 * package access, protected access is the first to be lost,
1686 * because it requires a direct subclass relationship between
1687 * caller and callee.)
1688 * @see #in
1689 *
1690 * @revised 9
1691 * @spec JPMS
1692 */
1693 @Override
1694 public String toString() {
1695 String cname = lookupClass.getName();
1696 if (prevLookupClass != null)
1697 cname += "/" + prevLookupClass.getName();
1698 switch (allowedModes) {
1699 case 0: // no privileges
1700 return cname + "/noaccess";
1701 case UNCONDITIONAL:
1702 return cname + "/publicLookup";
1703 case PUBLIC:
1704 return cname + "/public";
1705 case PUBLIC|MODULE:
1706 return cname + "/module";
1707 case PUBLIC|PACKAGE:
1708 case PUBLIC|MODULE|PACKAGE:
1709 return cname + "/package";
1710 case FULL_POWER_MODES & (~PROTECTED):
1711 case FULL_POWER_MODES & ~(PROTECTED|MODULE):
1712 return cname + "/private";
1713 case FULL_POWER_MODES:
1714 case FULL_POWER_MODES & (~MODULE):
1715 return cname;
1716 case TRUSTED:
1717 return "/trusted"; // internal only; not exported
1718 default: // Should not happen, but it's a bitfield...
1719 cname = cname + "/" + Integer.toHexString(allowedModes);
1720 assert(false) : cname;
1721 return cname;
1722 }
1723 }
1724
1725 /**
1726 * Produces a method handle for a static method.
1727 * The type of the method handle will be that of the method.
1728 * (Since static methods do not take receivers, there is no
1729 * additional receiver argument inserted into the method handle type,
1730 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1731 * The method and all its argument types must be accessible to the lookup object.
1732 * <p>
1733 * The returned method handle will have
1734 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1735 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1736 * <p>
1737 * If the returned method handle is invoked, the method's class will
1738 * be initialized, if it has not already been initialized.
1739 * <p><b>Example:</b>
1740 * <blockquote><pre>{@code
1741 import static java.lang.invoke.MethodHandles.*;
1742 import static java.lang.invoke.MethodType.*;
1743 ...
1744 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1745 "asList", methodType(List.class, Object[].class));
1746 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1747 * }</pre></blockquote>
1748 * @param refc the class from which the method is accessed
1749 * @param name the name of the method
1750 * @param type the type of the method
1751 * @return the desired method handle
1752 * @throws NoSuchMethodException if the method does not exist
1753 * @throws IllegalAccessException if access checking fails,
1754 * or if the method is not {@code static},
1755 * or if the method's variable arity modifier bit
1756 * is set and {@code asVarargsCollector} fails
1757 * @exception SecurityException if a security manager is present and it
1758 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1759 * @throws NullPointerException if any argument is null
1760 */
1761 public
1762 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1763 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1764 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1765 }
1766
1767 /**
1768 * Produces a method handle for a virtual method.
1769 * The type of the method handle will be that of the method,
1770 * with the receiver type (usually {@code refc}) prepended.
1771 * The method and all its argument types must be accessible to the lookup object.
1772 * <p>
1773 * When called, the handle will treat the first argument as a receiver
1774 * and, for non-private methods, dispatch on the receiver's type to determine which method
1775 * implementation to enter.
1776 * For private methods the named method in {@code refc} will be invoked on the receiver.
1777 * (The dispatching action is identical with that performed by an
1778 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1779 * <p>
1780 * The first argument will be of type {@code refc} if the lookup
1781 * class has full privileges to access the member. Otherwise
1782 * the member must be {@code protected} and the first argument
1783 * will be restricted in type to the lookup class.
1784 * <p>
1785 * The returned method handle will have
1786 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1787 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1788 * <p>
1789 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1790 * instructions and method handles produced by {@code findVirtual},
1791 * if the class is {@code MethodHandle} and the name string is
1792 * {@code invokeExact} or {@code invoke}, the resulting
1793 * method handle is equivalent to one produced by
1794 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1795 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1796 * with the same {@code type} argument.
1797 * <p>
1798 * If the class is {@code VarHandle} and the name string corresponds to
1799 * the name of a signature-polymorphic access mode method, the resulting
1800 * method handle is equivalent to one produced by
1801 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1802 * the access mode corresponding to the name string and with the same
1803 * {@code type} arguments.
1804 * <p>
1805 * <b>Example:</b>
1806 * <blockquote><pre>{@code
1807 import static java.lang.invoke.MethodHandles.*;
1808 import static java.lang.invoke.MethodType.*;
1809 ...
1810 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1811 "concat", methodType(String.class, String.class));
1812 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1813 "hashCode", methodType(int.class));
1814 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1815 "hashCode", methodType(int.class));
1816 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1817 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1818 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1819 // interface method:
1820 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1821 "subSequence", methodType(CharSequence.class, int.class, int.class));
1822 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1823 // constructor "internal method" must be accessed differently:
1824 MethodType MT_newString = methodType(void.class); //()V for new String()
1825 try { assertEquals("impossible", lookup()
1826 .findVirtual(String.class, "<init>", MT_newString));
1827 } catch (NoSuchMethodException ex) { } // OK
1828 MethodHandle MH_newString = publicLookup()
1829 .findConstructor(String.class, MT_newString);
1830 assertEquals("", (String) MH_newString.invokeExact());
1831 * }</pre></blockquote>
1832 *
1833 * @param refc the class or interface from which the method is accessed
1834 * @param name the name of the method
1835 * @param type the type of the method, with the receiver argument omitted
1836 * @return the desired method handle
1837 * @throws NoSuchMethodException if the method does not exist
1838 * @throws IllegalAccessException if access checking fails,
1839 * or if the method is {@code static},
1840 * or if the method's variable arity modifier bit
1841 * is set and {@code asVarargsCollector} fails
1842 * @exception SecurityException if a security manager is present and it
1843 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1844 * @throws NullPointerException if any argument is null
1845 */
1846 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1847 if (refc == MethodHandle.class) {
1848 MethodHandle mh = findVirtualForMH(name, type);
1849 if (mh != null) return mh;
1850 } else if (refc == VarHandle.class) {
1851 MethodHandle mh = findVirtualForVH(name, type);
1852 if (mh != null) return mh;
1853 }
1854 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1855 MemberName method = resolveOrFail(refKind, refc, name, type);
1856 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1857 }
1858 private MethodHandle findVirtualForMH(String name, MethodType type) {
1859 // these names require special lookups because of the implicit MethodType argument
1860 if ("invoke".equals(name))
1861 return invoker(type);
1862 if ("invokeExact".equals(name))
1863 return exactInvoker(type);
1864 assert(!MemberName.isMethodHandleInvokeName(name));
1865 return null;
1866 }
1867 private MethodHandle findVirtualForVH(String name, MethodType type) {
1868 try {
1869 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1870 } catch (IllegalArgumentException e) {
1871 return null;
1872 }
1873 }
1874
1875 /**
1876 * Produces a method handle which creates an object and initializes it, using
1877 * the constructor of the specified type.
1878 * The parameter types of the method handle will be those of the constructor,
1879 * while the return type will be a reference to the constructor's class.
1880 * The constructor and all its argument types must be accessible to the lookup object.
1881 * <p>
1882 * The requested type must have a return type of {@code void}.
1883 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1884 * <p>
1885 * The returned method handle will have
1886 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1887 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1888 * <p>
1889 * If the returned method handle is invoked, the constructor's class will
1890 * be initialized, if it has not already been initialized.
1891 * <p><b>Example:</b>
1892 * <blockquote><pre>{@code
1893 import static java.lang.invoke.MethodHandles.*;
1894 import static java.lang.invoke.MethodType.*;
1895 ...
1896 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1897 ArrayList.class, methodType(void.class, Collection.class));
1898 Collection orig = Arrays.asList("x", "y");
1899 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1900 assert(orig != copy);
1901 assertEquals(orig, copy);
1902 // a variable-arity constructor:
1903 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1904 ProcessBuilder.class, methodType(void.class, String[].class));
1905 ProcessBuilder pb = (ProcessBuilder)
1906 MH_newProcessBuilder.invoke("x", "y", "z");
1907 assertEquals("[x, y, z]", pb.command().toString());
1908 * }</pre></blockquote>
1909 * @param refc the class or interface from which the method is accessed
1910 * @param type the type of the method, with the receiver argument omitted, and a void return type
1911 * @return the desired method handle
1912 * @throws NoSuchMethodException if the constructor does not exist
1913 * @throws IllegalAccessException if access checking fails
1914 * or if the method's variable arity modifier bit
1915 * is set and {@code asVarargsCollector} fails
1916 * @exception SecurityException if a security manager is present and it
1917 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1918 * @throws NullPointerException if any argument is null
1919 */
1920 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1921 if (refc.isArray()) {
1922 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1923 }
1924 String name = "<init>";
1925 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1926 return getDirectConstructor(refc, ctor);
1927 }
1928
1929 /**
1930 * Looks up a class by name from the lookup context defined by this {@code Lookup} object.
1931 * This method attempts to locate, load, and link the class. The static
1932 * initializer of the class is not run.
1933 * <p>
1934 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1935 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1936 * load the requested class, and then determines whether the class is accessible to this lookup object.
1937 * <p>
1938 * Note that this method throws errors related to loading and linking as
1939 * specified in Sections 12.2 and 12.3 of <em>The Java Language
1940 * Specification</em>.
1941 *
1942 * @param targetName the fully qualified name of the class to be looked up.
1943 * @return the requested class.
1944 * @exception SecurityException if a security manager is present and it
1945 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1946 * @throws LinkageError if the linkage fails
1947 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1948 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1949 * modes.
1950 * @exception SecurityException if a security manager is present and it
1951 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1952 *
1953 * @jls 12.2 Loading of Classes and Interfaces
1954 * @jls 12.3 Linking of Classes and Interfaces
1955 * @since 9
1956 */
1957 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1958 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1959 return accessClass(targetClass);
1960 }
1961
1962 /**
1963 * Determines if a class can be accessed from the lookup context defined by
1964 * this {@code Lookup} object. The static initializer of the class is not run.
1965 * <p>
1966 * If the {@code targetClass} is in the same module as the lookup class,
1967 * the lookup class is {@code LC} in module {@code M1} and
1968 * the previous lookup class is in module {@code M0} or
1969 * {@code null} if not present,
1970 * {@code targetClass} is accessible if and only if one of the following is true:
1971 * <ul>
1972 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
1973 * {@code LC} or other class in the same nest of {@code LC}.</li>
1974 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
1975 * in the same runtime package of {@code LC}.</li>
1976 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
1977 * a public type in {@code M1}.</li>
1978 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
1979 * a public type in a package exported by {@code M1} to at least {@code M0}
1980 * if the previous lookup class is present; otherwise, {@code targetClass}
1981 * is a public type in a package exported by {@code M1} unconditionally.</li>
1982 * </ul>
1983 *
1984 * <p>
1985 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
1986 * can access public types in all modules when the type is in a package
1987 * that is exported unconditionally.
1988 * <p>
1989 * Otherwise, the target class is in a different module from {@code lookupClass},
1990 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
1991 * is inaccessible.
1992 * <p>
1993 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
1994 * {@code M1} is the module containing {@code lookupClass} and
1995 * {@code M2} is the module containing {@code targetClass},
1996 * then {@code targetClass} is accessible if and only if
1997 * <ul>
1998 * <li>{@code M1} reads {@code M2}, and
1999 * <li>{@code targetClass} is public and in a package exported by
2000 * {@code M2} at least to {@code M1}.
2001 * </ul>
2002 * <p>
2003 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2004 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2005 * containing the previous lookup class, then {@code targetClass} is accessible
2006 * if and only if one of the following is true:
2007 * <ul>
2008 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2009 * {@linkplain Module#reads reads} {@code M0} and the type is
2010 * in a package that is exported to at least {@code M1}.
2011 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2012 * {@linkplain Module#reads reads} {@code M1} and the type is
2013 * in a package that is exported to at least {@code M0}.
2014 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2015 * and {@code M1} reads {@code M2} and the type is in a package
2016 * that is exported to at least both {@code M0} and {@code M2}.
2017 * </ul>
2018 * <p>
2019 * Otherwise, {@code targetClass} is not accessible.
2020 *
2021 * @param targetClass the class to be access-checked
2022 * @return the class that has been access-checked
2023 * @throws IllegalAccessException if the class is not accessible from the lookup class
2024 * and previous lookup class, if present, using the allowed access modes.
2025 * @exception SecurityException if a security manager is present and it
2026 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2027 * @since 9
2028 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2029 */
2030 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2031 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2032 throw new MemberName(targetClass).makeAccessException("access violation", this);
2033 }
2034 checkSecurityManager(targetClass, null);
2035 return targetClass;
2036 }
2037
2038 /**
2039 * Produces an early-bound method handle for a virtual method.
2040 * It will bypass checks for overriding methods on the receiver,
2041 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2042 * instruction from within the explicitly specified {@code specialCaller}.
2043 * The type of the method handle will be that of the method,
2044 * with a suitably restricted receiver type prepended.
2045 * (The receiver type will be {@code specialCaller} or a subtype.)
2046 * The method and all its argument types must be accessible
2047 * to the lookup object.
2048 * <p>
2049 * Before method resolution,
2050 * if the explicitly specified caller class is not identical with the
2051 * lookup class, or if this lookup object does not have
2052 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2053 * privileges, the access fails.
2054 * <p>
2055 * The returned method handle will have
2056 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2057 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2058 * <p style="font-size:smaller;">
2059 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2060 * even though the {@code invokespecial} instruction can refer to them
2061 * in special circumstances. Use {@link #findConstructor findConstructor}
2062 * to access instance initialization methods in a safe manner.)</em>
2063 * <p><b>Example:</b>
2064 * <blockquote><pre>{@code
2065 import static java.lang.invoke.MethodHandles.*;
2066 import static java.lang.invoke.MethodType.*;
2067 ...
2068 static class Listie extends ArrayList {
2069 public String toString() { return "[wee Listie]"; }
2070 static Lookup lookup() { return MethodHandles.lookup(); }
2071 }
2072 ...
2073 // no access to constructor via invokeSpecial:
2074 MethodHandle MH_newListie = Listie.lookup()
2075 .findConstructor(Listie.class, methodType(void.class));
2076 Listie l = (Listie) MH_newListie.invokeExact();
2077 try { assertEquals("impossible", Listie.lookup().findSpecial(
2078 Listie.class, "<init>", methodType(void.class), Listie.class));
2079 } catch (NoSuchMethodException ex) { } // OK
2080 // access to super and self methods via invokeSpecial:
2081 MethodHandle MH_super = Listie.lookup().findSpecial(
2082 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2083 MethodHandle MH_this = Listie.lookup().findSpecial(
2084 Listie.class, "toString" , methodType(String.class), Listie.class);
2085 MethodHandle MH_duper = Listie.lookup().findSpecial(
2086 Object.class, "toString" , methodType(String.class), Listie.class);
2087 assertEquals("[]", (String) MH_super.invokeExact(l));
2088 assertEquals(""+l, (String) MH_this.invokeExact(l));
2089 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2090 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2091 String.class, "toString", methodType(String.class), Listie.class));
2092 } catch (IllegalAccessException ex) { } // OK
2093 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2094 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2095 * }</pre></blockquote>
2096 *
2097 * @param refc the class or interface from which the method is accessed
2098 * @param name the name of the method (which must not be "<init>")
2099 * @param type the type of the method, with the receiver argument omitted
2100 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2101 * @return the desired method handle
2102 * @throws NoSuchMethodException if the method does not exist
2103 * @throws IllegalAccessException if access checking fails,
2104 * or if the method is {@code static},
2105 * or if the method's variable arity modifier bit
2106 * is set and {@code asVarargsCollector} fails
2107 * @exception SecurityException if a security manager is present and it
2108 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2109 * @throws NullPointerException if any argument is null
2110 */
2111 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2112 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2113 checkSpecialCaller(specialCaller, refc);
2114 Lookup specialLookup = this.in(specialCaller);
2115 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2116 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
2117 }
2118
2119 /**
2120 * Produces a method handle giving read access to a non-static field.
2121 * The type of the method handle will have a return type of the field's
2122 * value type.
2123 * The method handle's single argument will be the instance containing
2124 * the field.
2125 * Access checking is performed immediately on behalf of the lookup class.
2126 * @param refc the class or interface from which the method is accessed
2127 * @param name the field's name
2128 * @param type the field's type
2129 * @return a method handle which can load values from the field
2130 * @throws NoSuchFieldException if the field does not exist
2131 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2132 * @exception SecurityException if a security manager is present and it
2133 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2134 * @throws NullPointerException if any argument is null
2135 * @see #findVarHandle(Class, String, Class)
2136 */
2137 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2138 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2139 return getDirectField(REF_getField, refc, field);
2140 }
2141
2142 /**
2143 * Produces a method handle giving write access to a non-static field.
2144 * The type of the method handle will have a void return type.
2145 * The method handle will take two arguments, the instance containing
2146 * the field, and the value to be stored.
2147 * The second argument will be of the field's value type.
2148 * Access checking is performed immediately on behalf of the lookup class.
2149 * @param refc the class or interface from which the method is accessed
2150 * @param name the field's name
2151 * @param type the field's type
2152 * @return a method handle which can store values into the field
2153 * @throws NoSuchFieldException if the field does not exist
2154 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2155 * or {@code final}
2156 * @exception SecurityException if a security manager is present and it
2157 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2158 * @throws NullPointerException if any argument is null
2159 * @see #findVarHandle(Class, String, Class)
2160 */
2161 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2162 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2163 return getDirectField(REF_putField, refc, field);
2164 }
2165
2166 /**
2167 * Produces a VarHandle giving access to a non-static field {@code name}
2168 * of type {@code type} declared in a class of type {@code recv}.
2169 * The VarHandle's variable type is {@code type} and it has one
2170 * coordinate type, {@code recv}.
2171 * <p>
2172 * Access checking is performed immediately on behalf of the lookup
2173 * class.
2174 * <p>
2175 * Certain access modes of the returned VarHandle are unsupported under
2176 * the following conditions:
2177 * <ul>
2178 * <li>if the field is declared {@code final}, then the write, atomic
2179 * update, numeric atomic update, and bitwise atomic update access
2180 * modes are unsupported.
2181 * <li>if the field type is anything other than {@code byte},
2182 * {@code short}, {@code char}, {@code int}, {@code long},
2183 * {@code float}, or {@code double} then numeric atomic update
2184 * access modes are unsupported.
2185 * <li>if the field type is anything other than {@code boolean},
2186 * {@code byte}, {@code short}, {@code char}, {@code int} or
2187 * {@code long} then bitwise atomic update access modes are
2188 * unsupported.
2189 * </ul>
2190 * <p>
2191 * If the field is declared {@code volatile} then the returned VarHandle
2192 * will override access to the field (effectively ignore the
2193 * {@code volatile} declaration) in accordance to its specified
2194 * access modes.
2195 * <p>
2196 * If the field type is {@code float} or {@code double} then numeric
2197 * and atomic update access modes compare values using their bitwise
2198 * representation (see {@link Float#floatToRawIntBits} and
2199 * {@link Double#doubleToRawLongBits}, respectively).
2200 * @apiNote
2201 * Bitwise comparison of {@code float} values or {@code double} values,
2202 * as performed by the numeric and atomic update access modes, differ
2203 * from the primitive {@code ==} operator and the {@link Float#equals}
2204 * and {@link Double#equals} methods, specifically with respect to
2205 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2206 * Care should be taken when performing a compare and set or a compare
2207 * and exchange operation with such values since the operation may
2208 * unexpectedly fail.
2209 * There are many possible NaN values that are considered to be
2210 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2211 * provided by Java can distinguish between them. Operation failure can
2212 * occur if the expected or witness value is a NaN value and it is
2213 * transformed (perhaps in a platform specific manner) into another NaN
2214 * value, and thus has a different bitwise representation (see
2215 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2216 * details).
2217 * The values {@code -0.0} and {@code +0.0} have different bitwise
2218 * representations but are considered equal when using the primitive
2219 * {@code ==} operator. Operation failure can occur if, for example, a
2220 * numeric algorithm computes an expected value to be say {@code -0.0}
2221 * and previously computed the witness value to be say {@code +0.0}.
2222 * @param recv the receiver class, of type {@code R}, that declares the
2223 * non-static field
2224 * @param name the field's name
2225 * @param type the field's type, of type {@code T}
2226 * @return a VarHandle giving access to non-static fields.
2227 * @throws NoSuchFieldException if the field does not exist
2228 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2229 * @exception SecurityException if a security manager is present and it
2230 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2231 * @throws NullPointerException if any argument is null
2232 * @since 9
2233 */
2234 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2235 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
2236 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
2237 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
2238 }
2239
2240 /**
2241 * Produces a method handle giving read access to a static field.
2242 * The type of the method handle will have a return type of the field's
2243 * value type.
2244 * The method handle will take no arguments.
2245 * Access checking is performed immediately on behalf of the lookup class.
2246 * <p>
2247 * If the returned method handle is invoked, the field's class will
2248 * be initialized, if it has not already been initialized.
2249 * @param refc the class or interface from which the method is accessed
2250 * @param name the field's name
2251 * @param type the field's type
2252 * @return a method handle which can load values from the field
2253 * @throws NoSuchFieldException if the field does not exist
2254 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2255 * @exception SecurityException if a security manager is present and it
2256 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2257 * @throws NullPointerException if any argument is null
2258 */
2259 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2260 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
2261 return getDirectField(REF_getStatic, refc, field);
2262 }
2263
2264 /**
2265 * Produces a method handle giving write access to a static field.
2266 * The type of the method handle will have a void return type.
2267 * The method handle will take a single
2268 * argument, of the field's value type, the value to be stored.
2269 * Access checking is performed immediately on behalf of the lookup class.
2270 * <p>
2271 * If the returned method handle is invoked, the field's class will
2272 * be initialized, if it has not already been initialized.
2273 * @param refc the class or interface from which the method is accessed
2274 * @param name the field's name
2275 * @param type the field's type
2276 * @return a method handle which can store values into the field
2277 * @throws NoSuchFieldException if the field does not exist
2278 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2279 * or is {@code final}
2280 * @exception SecurityException if a security manager is present and it
2281 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2282 * @throws NullPointerException if any argument is null
2283 */
2284 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2285 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
2286 return getDirectField(REF_putStatic, refc, field);
2287 }
2288
2289 /**
2290 * Produces a VarHandle giving access to a static field {@code name} of
2291 * type {@code type} declared in a class of type {@code decl}.
2292 * The VarHandle's variable type is {@code type} and it has no
2293 * coordinate types.
2294 * <p>
2295 * Access checking is performed immediately on behalf of the lookup
2296 * class.
2297 * <p>
2298 * If the returned VarHandle is operated on, the declaring class will be
2299 * initialized, if it has not already been initialized.
2300 * <p>
2301 * Certain access modes of the returned VarHandle are unsupported under
2302 * the following conditions:
2303 * <ul>
2304 * <li>if the field is declared {@code final}, then the write, atomic
2305 * update, numeric atomic update, and bitwise atomic update access
2306 * modes are unsupported.
2307 * <li>if the field type is anything other than {@code byte},
2308 * {@code short}, {@code char}, {@code int}, {@code long},
2309 * {@code float}, or {@code double}, then numeric atomic update
2310 * access modes are unsupported.
2311 * <li>if the field type is anything other than {@code boolean},
2312 * {@code byte}, {@code short}, {@code char}, {@code int} or
2313 * {@code long} then bitwise atomic update access modes are
2314 * unsupported.
2315 * </ul>
2316 * <p>
2317 * If the field is declared {@code volatile} then the returned VarHandle
2318 * will override access to the field (effectively ignore the
2319 * {@code volatile} declaration) in accordance to its specified
2320 * access modes.
2321 * <p>
2322 * If the field type is {@code float} or {@code double} then numeric
2323 * and atomic update access modes compare values using their bitwise
2324 * representation (see {@link Float#floatToRawIntBits} and
2325 * {@link Double#doubleToRawLongBits}, respectively).
2326 * @apiNote
2327 * Bitwise comparison of {@code float} values or {@code double} values,
2328 * as performed by the numeric and atomic update access modes, differ
2329 * from the primitive {@code ==} operator and the {@link Float#equals}
2330 * and {@link Double#equals} methods, specifically with respect to
2331 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2332 * Care should be taken when performing a compare and set or a compare
2333 * and exchange operation with such values since the operation may
2334 * unexpectedly fail.
2335 * There are many possible NaN values that are considered to be
2336 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2337 * provided by Java can distinguish between them. Operation failure can
2338 * occur if the expected or witness value is a NaN value and it is
2339 * transformed (perhaps in a platform specific manner) into another NaN
2340 * value, and thus has a different bitwise representation (see
2341 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2342 * details).
2343 * The values {@code -0.0} and {@code +0.0} have different bitwise
2344 * representations but are considered equal when using the primitive
2345 * {@code ==} operator. Operation failure can occur if, for example, a
2346 * numeric algorithm computes an expected value to be say {@code -0.0}
2347 * and previously computed the witness value to be say {@code +0.0}.
2348 * @param decl the class that declares the static field
2349 * @param name the field's name
2350 * @param type the field's type, of type {@code T}
2351 * @return a VarHandle giving access to a static field
2352 * @throws NoSuchFieldException if the field does not exist
2353 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2354 * @exception SecurityException if a security manager is present and it
2355 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2356 * @throws NullPointerException if any argument is null
2357 * @since 9
2358 */
2359 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2360 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
2361 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
2362 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
2363 }
2364
2365 /**
2366 * Produces an early-bound method handle for a non-static method.
2367 * The receiver must have a supertype {@code defc} in which a method
2368 * of the given name and type is accessible to the lookup class.
2369 * The method and all its argument types must be accessible to the lookup object.
2370 * The type of the method handle will be that of the method,
2371 * without any insertion of an additional receiver parameter.
2372 * The given receiver will be bound into the method handle,
2373 * so that every call to the method handle will invoke the
2374 * requested method on the given receiver.
2375 * <p>
2376 * The returned method handle will have
2377 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2378 * the method's variable arity modifier bit ({@code 0x0080}) is set
2379 * <em>and</em> the trailing array argument is not the only argument.
2380 * (If the trailing array argument is the only argument,
2381 * the given receiver value will be bound to it.)
2382 * <p>
2383 * This is almost equivalent to the following code, with some differences noted below:
2384 * <blockquote><pre>{@code
2385 import static java.lang.invoke.MethodHandles.*;
2386 import static java.lang.invoke.MethodType.*;
2387 ...
2388 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
2389 MethodHandle mh1 = mh0.bindTo(receiver);
2390 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
2391 return mh1;
2392 * }</pre></blockquote>
2393 * where {@code defc} is either {@code receiver.getClass()} or a super
2394 * type of that class, in which the requested method is accessible
2395 * to the lookup class.
2396 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
2397 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
2398 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
2399 * the receiver is restricted by {@code findVirtual} to the lookup class.)
2400 * @param receiver the object from which the method is accessed
2401 * @param name the name of the method
2402 * @param type the type of the method, with the receiver argument omitted
2403 * @return the desired method handle
2404 * @throws NoSuchMethodException if the method does not exist
2405 * @throws IllegalAccessException if access checking fails
2406 * or if the method's variable arity modifier bit
2407 * is set and {@code asVarargsCollector} fails
2408 * @exception SecurityException if a security manager is present and it
2409 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2410 * @throws NullPointerException if any argument is null
2411 * @see MethodHandle#bindTo
2412 * @see #findVirtual
2413 */
2414 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2415 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2416 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2417 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
2418 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2419 throw new IllegalAccessException("The restricted defining class " +
2420 mh.type().leadingReferenceParameter().getName() +
2421 " is not assignable from receiver class " +
2422 receiver.getClass().getName());
2423 }
2424 return mh.bindArgumentL(0, receiver).setVarargs(method);
2425 }
2426
2427 /**
2428 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2429 * to <i>m</i>, if the lookup class has permission.
2430 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2431 * If <i>m</i> is virtual, overriding is respected on every call.
2432 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2433 * The type of the method handle will be that of the method,
2434 * with the receiver type prepended (but only if it is non-static).
2435 * If the method's {@code accessible} flag is not set,
2436 * access checking is performed immediately on behalf of the lookup class.
2437 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2438 * <p>
2439 * The returned method handle will have
2440 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2441 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2442 * <p>
2443 * If <i>m</i> is static, and
2444 * if the returned method handle is invoked, the method's class will
2445 * be initialized, if it has not already been initialized.
2446 * @param m the reflected method
2447 * @return a method handle which can invoke the reflected method
2448 * @throws IllegalAccessException if access checking fails
2449 * or if the method's variable arity modifier bit
2450 * is set and {@code asVarargsCollector} fails
2451 * @throws NullPointerException if the argument is null
2452 */
2453 public MethodHandle unreflect(Method m) throws IllegalAccessException {
2454 if (m.getDeclaringClass() == MethodHandle.class) {
2455 MethodHandle mh = unreflectForMH(m);
2456 if (mh != null) return mh;
2457 }
2458 if (m.getDeclaringClass() == VarHandle.class) {
2459 MethodHandle mh = unreflectForVH(m);
2460 if (mh != null) return mh;
2461 }
2462 MemberName method = new MemberName(m);
2463 byte refKind = method.getReferenceKind();
2464 if (refKind == REF_invokeSpecial)
2465 refKind = REF_invokeVirtual;
2466 assert(method.isMethod());
2467 @SuppressWarnings("deprecation")
2468 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
2469 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
2470 }
2471 private MethodHandle unreflectForMH(Method m) {
2472 // these names require special lookups because they throw UnsupportedOperationException
2473 if (MemberName.isMethodHandleInvokeName(m.getName()))
2474 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
2475 return null;
2476 }
2477 private MethodHandle unreflectForVH(Method m) {
2478 // these names require special lookups because they throw UnsupportedOperationException
2479 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
2480 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
2481 return null;
2482 }
2483
2484 /**
2485 * Produces a method handle for a reflected method.
2486 * It will bypass checks for overriding methods on the receiver,
2487 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2488 * instruction from within the explicitly specified {@code specialCaller}.
2489 * The type of the method handle will be that of the method,
2490 * with a suitably restricted receiver type prepended.
2491 * (The receiver type will be {@code specialCaller} or a subtype.)
2492 * If the method's {@code accessible} flag is not set,
2493 * access checking is performed immediately on behalf of the lookup class,
2494 * as if {@code invokespecial} instruction were being linked.
2495 * <p>
2496 * Before method resolution,
2497 * if the explicitly specified caller class is not identical with the
2498 * lookup class, or if this lookup object does not have
2499 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2500 * privileges, the access fails.
2501 * <p>
2502 * The returned method handle will have
2503 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2504 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2505 * @param m the reflected method
2506 * @param specialCaller the class nominally calling the method
2507 * @return a method handle which can invoke the reflected method
2508 * @throws IllegalAccessException if access checking fails,
2509 * or if the method is {@code static},
2510 * or if the method's variable arity modifier bit
2511 * is set and {@code asVarargsCollector} fails
2512 * @throws NullPointerException if any argument is null
2513 */
2514 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
2515 checkSpecialCaller(specialCaller, m.getDeclaringClass());
2516 Lookup specialLookup = this.in(specialCaller);
2517 MemberName method = new MemberName(m, true);
2518 assert(method.isMethod());
2519 // ignore m.isAccessible: this is a new kind of access
2520 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
2521 }
2522
2523 /**
2524 * Produces a method handle for a reflected constructor.
2525 * The type of the method handle will be that of the constructor,
2526 * with the return type changed to the declaring class.
2527 * The method handle will perform a {@code newInstance} operation,
2528 * creating a new instance of the constructor's class on the
2529 * arguments passed to the method handle.
2530 * <p>
2531 * If the constructor's {@code accessible} flag is not set,
2532 * access checking is performed immediately on behalf of the lookup class.
2533 * <p>
2534 * The returned method handle will have
2535 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2536 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2537 * <p>
2538 * If the returned method handle is invoked, the constructor's class will
2539 * be initialized, if it has not already been initialized.
2540 * @param c the reflected constructor
2541 * @return a method handle which can invoke the reflected constructor
2542 * @throws IllegalAccessException if access checking fails
2543 * or if the method's variable arity modifier bit
2544 * is set and {@code asVarargsCollector} fails
2545 * @throws NullPointerException if the argument is null
2546 */
2547 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
2548 MemberName ctor = new MemberName(c);
2549 assert(ctor.isConstructor());
2550 @SuppressWarnings("deprecation")
2551 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
2552 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
2553 }
2554
2555 /**
2556 * Produces a method handle giving read access to a reflected field.
2557 * The type of the method handle will have a return type of the field's
2558 * value type.
2559 * If the field is {@code static}, the method handle will take no arguments.
2560 * Otherwise, its single argument will be the instance containing
2561 * the field.
2562 * If the {@code Field} object's {@code accessible} flag is not set,
2563 * access checking is performed immediately on behalf of the lookup class.
2564 * <p>
2565 * If the field is static, and
2566 * if the returned method handle is invoked, the field's class will
2567 * be initialized, if it has not already been initialized.
2568 * @param f the reflected field
2569 * @return a method handle which can load values from the reflected field
2570 * @throws IllegalAccessException if access checking fails
2571 * @throws NullPointerException if the argument is null
2572 */
2573 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
2574 return unreflectField(f, false);
2575 }
2576
2577 /**
2578 * Produces a method handle giving write access to a reflected field.
2579 * The type of the method handle will have a void return type.
2580 * If the field is {@code static}, the method handle will take a single
2581 * argument, of the field's value type, the value to be stored.
2582 * Otherwise, the two arguments will be the instance containing
2583 * the field, and the value to be stored.
2584 * If the {@code Field} object's {@code accessible} flag is not set,
2585 * access checking is performed immediately on behalf of the lookup class.
2586 * <p>
2587 * If the field is {@code final}, write access will not be
2588 * allowed and access checking will fail, except under certain
2589 * narrow circumstances documented for {@link Field#set Field.set}.
2590 * A method handle is returned only if a corresponding call to
2591 * the {@code Field} object's {@code set} method could return
2592 * normally. In particular, fields which are both {@code static}
2593 * and {@code final} may never be set.
2594 * <p>
2595 * If the field is {@code static}, and
2596 * if the returned method handle is invoked, the field's class will
2597 * be initialized, if it has not already been initialized.
2598 * @param f the reflected field
2599 * @return a method handle which can store values into the reflected field
2600 * @throws IllegalAccessException if access checking fails,
2601 * or if the field is {@code final} and write access
2602 * is not enabled on the {@code Field} object
2603 * @throws NullPointerException if the argument is null
2604 */
2605 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
2606 return unreflectField(f, true);
2607 }
2608
2609 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
2610 MemberName field = new MemberName(f, isSetter);
2611 if (isSetter && field.isStatic() && field.isFinal())
2612 throw field.makeAccessException("static final field has no write access", this);
2613 assert(isSetter
2614 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
2615 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
2616 @SuppressWarnings("deprecation")
2617 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
2618 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
2619 }
2620
2621 /**
2622 * Produces a VarHandle giving access to a reflected field {@code f}
2623 * of type {@code T} declared in a class of type {@code R}.
2624 * The VarHandle's variable type is {@code T}.
2625 * If the field is non-static the VarHandle has one coordinate type,
2626 * {@code R}. Otherwise, the field is static, and the VarHandle has no
2627 * coordinate types.
2628 * <p>
2629 * Access checking is performed immediately on behalf of the lookup
2630 * class, regardless of the value of the field's {@code accessible}
2631 * flag.
2632 * <p>
2633 * If the field is static, and if the returned VarHandle is operated
2634 * on, the field's declaring class will be initialized, if it has not
2635 * already been initialized.
2636 * <p>
2637 * Certain access modes of the returned VarHandle are unsupported under
2638 * the following conditions:
2639 * <ul>
2640 * <li>if the field is declared {@code final}, then the write, atomic
2641 * update, numeric atomic update, and bitwise atomic update access
2642 * modes are unsupported.
2643 * <li>if the field type is anything other than {@code byte},
2644 * {@code short}, {@code char}, {@code int}, {@code long},
2645 * {@code float}, or {@code double} then numeric atomic update
2646 * access modes are unsupported.
2647 * <li>if the field type is anything other than {@code boolean},
2648 * {@code byte}, {@code short}, {@code char}, {@code int} or
2649 * {@code long} then bitwise atomic update access modes are
2650 * unsupported.
2651 * </ul>
2652 * <p>
2653 * If the field is declared {@code volatile} then the returned VarHandle
2654 * will override access to the field (effectively ignore the
2655 * {@code volatile} declaration) in accordance to its specified
2656 * access modes.
2657 * <p>
2658 * If the field type is {@code float} or {@code double} then numeric
2659 * and atomic update access modes compare values using their bitwise
2660 * representation (see {@link Float#floatToRawIntBits} and
2661 * {@link Double#doubleToRawLongBits}, respectively).
2662 * @apiNote
2663 * Bitwise comparison of {@code float} values or {@code double} values,
2664 * as performed by the numeric and atomic update access modes, differ
2665 * from the primitive {@code ==} operator and the {@link Float#equals}
2666 * and {@link Double#equals} methods, specifically with respect to
2667 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2668 * Care should be taken when performing a compare and set or a compare
2669 * and exchange operation with such values since the operation may
2670 * unexpectedly fail.
2671 * There are many possible NaN values that are considered to be
2672 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2673 * provided by Java can distinguish between them. Operation failure can
2674 * occur if the expected or witness value is a NaN value and it is
2675 * transformed (perhaps in a platform specific manner) into another NaN
2676 * value, and thus has a different bitwise representation (see
2677 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2678 * details).
2679 * The values {@code -0.0} and {@code +0.0} have different bitwise
2680 * representations but are considered equal when using the primitive
2681 * {@code ==} operator. Operation failure can occur if, for example, a
2682 * numeric algorithm computes an expected value to be say {@code -0.0}
2683 * and previously computed the witness value to be say {@code +0.0}.
2684 * @param f the reflected field, with a field of type {@code T}, and
2685 * a declaring class of type {@code R}
2686 * @return a VarHandle giving access to non-static fields or a static
2687 * field
2688 * @throws IllegalAccessException if access checking fails
2689 * @throws NullPointerException if the argument is null
2690 * @since 9
2691 */
2692 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
2693 MemberName getField = new MemberName(f, false);
2694 MemberName putField = new MemberName(f, true);
2695 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
2696 f.getDeclaringClass(), getField, putField);
2697 }
2698
2699 /**
2700 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2701 * created by this lookup object or a similar one.
2702 * Security and access checks are performed to ensure that this lookup object
2703 * is capable of reproducing the target method handle.
2704 * This means that the cracking may fail if target is a direct method handle
2705 * but was created by an unrelated lookup object.
2706 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
2707 * and was created by a lookup object for a different class.
2708 * @param target a direct method handle to crack into symbolic reference components
2709 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
2710 * @exception SecurityException if a security manager is present and it
2711 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2712 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
2713 * @exception NullPointerException if the target is {@code null}
2714 * @see MethodHandleInfo
2715 * @since 1.8
2716 */
2717 public MethodHandleInfo revealDirect(MethodHandle target) {
2718 MemberName member = target.internalMemberName();
2719 if (member == null || (!member.isResolved() &&
2720 !member.isMethodHandleInvoke() &&
2721 !member.isVarHandleMethodInvoke()))
2722 throw newIllegalArgumentException("not a direct method handle");
2723 Class<?> defc = member.getDeclaringClass();
2724 byte refKind = member.getReferenceKind();
2725 assert(MethodHandleNatives.refKindIsValid(refKind));
2726 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2727 // Devirtualized method invocation is usually formally virtual.
2728 // To avoid creating extra MemberName objects for this common case,
2729 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2730 refKind = REF_invokeVirtual;
2731 if (refKind == REF_invokeVirtual && defc.isInterface())
2732 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2733 refKind = REF_invokeInterface;
2734 // Check SM permissions and member access before cracking.
2735 try {
2736 checkAccess(refKind, defc, member);
2737 checkSecurityManager(defc, member);
2738 } catch (IllegalAccessException ex) {
2739 throw new IllegalArgumentException(ex);
2740 }
2741 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2742 Class<?> callerClass = target.internalCallerClass();
2743 if (!hasPrivateAccess() || callerClass != lookupClass())
2744 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2745 }
2746 // Produce the handle to the results.
2747 return new InfoFromMemberName(this, member, refKind);
2748 }
2749
2750 /// Helper methods, all package-private.
2751
2752 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2753 checkSymbolicClass(refc); // do this before attempting to resolve
2754 Objects.requireNonNull(name);
2755 Objects.requireNonNull(type);
2756 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2757 NoSuchFieldException.class);
2758 }
2759
2760 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2761 checkSymbolicClass(refc); // do this before attempting to resolve
2762 Objects.requireNonNull(name);
2763 Objects.requireNonNull(type);
2764 checkMethodName(refKind, name); // NPE check on name
2765 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2766 NoSuchMethodException.class);
2767 }
2768
2769 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2770 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2771 Objects.requireNonNull(member.getName());
2772 Objects.requireNonNull(member.getType());
2773 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2774 ReflectiveOperationException.class);
2775 }
2776
2777 MemberName resolveOrNull(byte refKind, MemberName member) {
2778 // do this before attempting to resolve
2779 if (!isClassAccessible(member.getDeclaringClass())) {
2780 return null;
2781 }
2782 Objects.requireNonNull(member.getName());
2783 Objects.requireNonNull(member.getType());
2784 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2785 }
2786
2787 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2788 if (!isClassAccessible(refc)) {
2789 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2790 }
2791 }
2792
2793 boolean isClassAccessible(Class<?> refc) {
2794 Objects.requireNonNull(refc);
2795 Class<?> caller = lookupClassOrNull();
2796 return caller == null || VerifyAccess.isClassAccessible(refc, caller, prevLookupClass, allowedModes);
2797 }
2798
2799 /** Check name for an illegal leading "<" character. */
2800 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2801 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2802 throw new NoSuchMethodException("illegal method name: "+name);
2803 }
2804
2805
2806 /**
2807 * Find my trustable caller class if m is a caller sensitive method.
2808 * If this lookup object has private access, then the caller class is the lookupClass.
2809 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2810 */
2811 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2812 Class<?> callerClass = null;
2813 if (MethodHandleNatives.isCallerSensitive(m)) {
2814 // Only lookups with private access are allowed to resolve caller-sensitive methods
2815 if (hasPrivateAccess()) {
2816 callerClass = lookupClass;
2817 } else {
2818 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2819 }
2820 }
2821 return callerClass;
2822 }
2823
2824 /**
2825 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2826 * @return {@code true} if this lookup has {@code PRIVATE} access.
2827 * @since 9
2828 */
2829 public boolean hasPrivateAccess() {
2830 return (allowedModes & PRIVATE) != 0;
2831 }
2832
2833 /**
2834 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2835 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2836 * If this lookup object has private access, then the caller class is the lookupClass.
2837 */
2838 void checkSecurityManager(Class<?> refc, MemberName m) {
2839 SecurityManager smgr = System.getSecurityManager();
2840 if (smgr == null) return;
2841 if (allowedModes == TRUSTED) return;
2842
2843 // Step 1:
2844 boolean fullPowerLookup = hasPrivateAccess();
2845 if (!fullPowerLookup ||
2846 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2847 ReflectUtil.checkPackageAccess(refc);
2848 }
2849
2850 if (m == null) { // findClass or accessClass
2851 // Step 2b:
2852 if (!fullPowerLookup) {
2853 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2854 }
2855 return;
2856 }
2857
2858 // Step 2a:
2859 if (m.isPublic()) return;
2860 if (!fullPowerLookup) {
2861 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2862 }
2863
2864 // Step 3:
2865 Class<?> defc = m.getDeclaringClass();
2866 if (!fullPowerLookup && defc != refc) {
2867 ReflectUtil.checkPackageAccess(defc);
2868 }
2869 }
2870
2871 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2872 boolean wantStatic = (refKind == REF_invokeStatic);
2873 String message;
2874 if (m.isConstructor())
2875 message = "expected a method, not a constructor";
2876 else if (!m.isMethod())
2877 message = "expected a method";
2878 else if (wantStatic != m.isStatic())
2879 message = wantStatic ? "expected a static method" : "expected a non-static method";
2880 else
2881 { checkAccess(refKind, refc, m); return; }
2882 throw m.makeAccessException(message, this);
2883 }
2884
2885 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2886 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2887 String message;
2888 if (wantStatic != m.isStatic())
2889 message = wantStatic ? "expected a static field" : "expected a non-static field";
2890 else
2891 { checkAccess(refKind, refc, m); return; }
2892 throw m.makeAccessException(message, this);
2893 }
2894
2895 /** Check public/protected/private bits on the symbolic reference class and its member. */
2896 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2897 assert(m.referenceKindIsConsistentWith(refKind) &&
2898 MethodHandleNatives.refKindIsValid(refKind) &&
2899 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2900 int allowedModes = this.allowedModes;
2901 if (allowedModes == TRUSTED) return;
2902 int mods = m.getModifiers();
2903 if (Modifier.isProtected(mods) &&
2904 refKind == REF_invokeVirtual &&
2905 m.getDeclaringClass() == Object.class &&
2906 m.getName().equals("clone") &&
2907 refc.isArray()) {
2908 // The JVM does this hack also.
2909 // (See ClassVerifier::verify_invoke_instructions
2910 // and LinkResolver::check_method_accessability.)
2911 // Because the JVM does not allow separate methods on array types,
2912 // there is no separate method for int[].clone.
2913 // All arrays simply inherit Object.clone.
2914 // But for access checking logic, we make Object.clone
2915 // (normally protected) appear to be public.
2916 // Later on, when the DirectMethodHandle is created,
2917 // its leading argument will be restricted to the
2918 // requested array type.
2919 // N.B. The return type is not adjusted, because
2920 // that is *not* the bytecode behavior.
2921 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2922 }
2923 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2924 // cannot "new" a protected ctor in a different package
2925 mods ^= Modifier.PROTECTED;
2926 }
2927 if (Modifier.isFinal(mods) &&
2928 MethodHandleNatives.refKindIsSetter(refKind))
2929 throw m.makeAccessException("unexpected set of a final field", this);
2930 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2931 if ((requestedModes & allowedModes) != 0) {
2932 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2933 mods, lookupClass(), previousLookupClass(), allowedModes))
2934 return;
2935 } else {
2936 // Protected members can also be checked as if they were package-private.
2937 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2938 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2939 return;
2940 }
2941 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2942 }
2943
2944 String accessFailedMessage(Class<?> refc, MemberName m) {
2945 Class<?> defc = m.getDeclaringClass();
2946 int mods = m.getModifiers();
2947 // check the class first:
2948 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2949 (defc == refc ||
2950 Modifier.isPublic(refc.getModifiers())));
2951 if (!classOK && (allowedModes & PACKAGE) != 0) {
2952 // ignore previous lookup class to check if default package access
2953 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
2954 (defc == refc ||
2955 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
2956 }
2957 if (!classOK)
2958 return "class is not public";
2959 if (Modifier.isPublic(mods))
2960 return "access to public member failed"; // (how?, module not readable?)
2961 if (Modifier.isPrivate(mods))
2962 return "member is private";
2963 if (Modifier.isProtected(mods))
2964 return "member is protected";
2965 return "member is private to package";
2966 }
2967
2968 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2969 int allowedModes = this.allowedModes;
2970 if (allowedModes == TRUSTED) return;
2971 if (!hasPrivateAccess()
2972 || (specialCaller != lookupClass()
2973 // ensure non-abstract methods in superinterfaces can be special-invoked
2974 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2975 throw new MemberName(specialCaller).
2976 makeAccessException("no private access for invokespecial", this);
2977 }
2978
2979 private boolean restrictProtectedReceiver(MemberName method) {
2980 // The accessing class only has the right to use a protected member
2981 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2982 if (!method.isProtected() || method.isStatic()
2983 || allowedModes == TRUSTED
2984 || method.getDeclaringClass() == lookupClass()
2985 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2986 return false;
2987 return true;
2988 }
2989 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2990 assert(!method.isStatic());
2991 // receiver type of mh is too wide; narrow to caller
2992 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2993 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2994 }
2995 MethodType rawType = mh.type();
2996 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2997 MethodType narrowType = rawType.changeParameterType(0, caller);
2998 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2999 assert(mh.viewAsTypeChecks(narrowType, true));
3000 return mh.copyWith(narrowType, mh.form);
3001 }
3002
3003 /** Check access and get the requested method. */
3004 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
3005 final boolean doRestrict = true;
3006 final boolean checkSecurity = true;
3007 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
3008 }
3009 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3010 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
3011 final boolean doRestrict = false;
3012 final boolean checkSecurity = true;
3013 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
3014 }
3015 /** Check access and get the requested method, eliding security manager checks. */
3016 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
3017 final boolean doRestrict = true;
3018 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3019 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
3020 }
3021 /** Common code for all methods; do not call directly except from immediately above. */
3022 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3023 boolean checkSecurity,
3024 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
3025
3026 checkMethod(refKind, refc, method);
3027 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3028 if (checkSecurity)
3029 checkSecurityManager(refc, method);
3030 assert(!method.isMethodHandleInvoke());
3031
3032 if (refKind == REF_invokeSpecial &&
3033 refc != lookupClass() &&
3034 !refc.isInterface() &&
3035 refc != lookupClass().getSuperclass() &&
3036 refc.isAssignableFrom(lookupClass())) {
3037 assert(!method.getName().equals("<init>")); // not this code path
3038
3039 // Per JVMS 6.5, desc. of invokespecial instruction:
3040 // If the method is in a superclass of the LC,
3041 // and if our original search was above LC.super,
3042 // repeat the search (symbolic lookup) from LC.super
3043 // and continue with the direct superclass of that class,
3044 // and so forth, until a match is found or no further superclasses exist.
3045 // FIXME: MemberName.resolve should handle this instead.
3046 Class<?> refcAsSuper = lookupClass();
3047 MemberName m2;
3048 do {
3049 refcAsSuper = refcAsSuper.getSuperclass();
3050 m2 = new MemberName(refcAsSuper,
3051 method.getName(),
3052 method.getMethodType(),
3053 REF_invokeSpecial);
3054 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
3055 } while (m2 == null && // no method is found yet
3056 refc != refcAsSuper); // search up to refc
3057 if (m2 == null) throw new InternalError(method.toString());
3058 method = m2;
3059 refc = refcAsSuper;
3060 // redo basic checks
3061 checkMethod(refKind, refc, method);
3062 }
3063
3064 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3065 MethodHandle mh = dmh;
3066 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3067 if ((doRestrict && refKind == REF_invokeSpecial) ||
3068 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
3069 mh = restrictReceiver(method, dmh, lookupClass());
3070 }
3071 mh = maybeBindCaller(method, mh, boundCallerClass);
3072 mh = mh.setVarargs(method);
3073 return mh;
3074 }
3075 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
3076 Class<?> boundCallerClass)
3077 throws IllegalAccessException {
3078 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3079 return mh;
3080 Class<?> hostClass = lookupClass;
3081 if (!hasPrivateAccess()) // caller must have private access
3082 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
3083 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
3084 // Note: caller will apply varargs after this step happens.
3085 return cbmh;
3086 }
3087 /** Check access and get the requested field. */
3088 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3089 final boolean checkSecurity = true;
3090 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3091 }
3092 /** Check access and get the requested field, eliding security manager checks. */
3093 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3094 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3095 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3096 }
3097 /** Common code for all fields; do not call directly except from immediately above. */
3098 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
3099 boolean checkSecurity) throws IllegalAccessException {
3100 checkField(refKind, refc, field);
3101 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3102 if (checkSecurity)
3103 checkSecurityManager(refc, field);
3104 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3105 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3106 restrictProtectedReceiver(field));
3107 if (doRestrict)
3108 return restrictReceiver(field, dmh, lookupClass());
3109 return dmh;
3110 }
3111 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3112 Class<?> refc, MemberName getField, MemberName putField)
3113 throws IllegalAccessException {
3114 final boolean checkSecurity = true;
3115 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3116 }
3117 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
3118 Class<?> refc, MemberName getField, MemberName putField)
3119 throws IllegalAccessException {
3120 final boolean checkSecurity = false;
3121 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3122 }
3123 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3124 Class<?> refc, MemberName getField, MemberName putField,
3125 boolean checkSecurity) throws IllegalAccessException {
3126 assert getField.isStatic() == putField.isStatic();
3127 assert getField.isGetter() && putField.isSetter();
3128 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3129 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3130
3131 checkField(getRefKind, refc, getField);
3132 if (checkSecurity)
3133 checkSecurityManager(refc, getField);
3134
3135 if (!putField.isFinal()) {
3136 // A VarHandle does not support updates to final fields, any
3137 // such VarHandle to a final field will be read-only and
3138 // therefore the following write-based accessibility checks are
3139 // only required for non-final fields
3140 checkField(putRefKind, refc, putField);
3141 if (checkSecurity)
3142 checkSecurityManager(refc, putField);
3143 }
3144
3145 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3146 restrictProtectedReceiver(getField));
3147 if (doRestrict) {
3148 assert !getField.isStatic();
3149 // receiver type of VarHandle is too wide; narrow to caller
3150 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3151 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3152 }
3153 refc = lookupClass();
3154 }
3155 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
3156 }
3157 /** Check access and get the requested constructor. */
3158 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3159 final boolean checkSecurity = true;
3160 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3161 }
3162 /** Check access and get the requested constructor, eliding security manager checks. */
3163 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3164 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3165 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3166 }
3167 /** Common code for all constructors; do not call directly except from immediately above. */
3168 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
3169 boolean checkSecurity) throws IllegalAccessException {
3170 assert(ctor.isConstructor());
3171 checkAccess(REF_newInvokeSpecial, refc, ctor);
3172 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3173 if (checkSecurity)
3174 checkSecurityManager(refc, ctor);
3175 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3176 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3177 }
3178
3179 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3180 */
3181 /*non-public*/
3182 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
3183 if (!(type instanceof Class || type instanceof MethodType))
3184 throw new InternalError("unresolved MemberName");
3185 MemberName member = new MemberName(refKind, defc, name, type);
3186 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3187 if (mh != null) {
3188 checkSymbolicClass(defc);
3189 return mh;
3190 }
3191 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3192 // Treat MethodHandle.invoke and invokeExact specially.
3193 mh = findVirtualForMH(member.getName(), member.getMethodType());
3194 if (mh != null) {
3195 return mh;
3196 }
3197 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3198 // Treat signature-polymorphic methods on VarHandle specially.
3199 mh = findVirtualForVH(member.getName(), member.getMethodType());
3200 if (mh != null) {
3201 return mh;
3202 }
3203 }
3204 MemberName resolved = resolveOrFail(refKind, member);
3205 mh = getDirectMethodForConstant(refKind, defc, resolved);
3206 if (mh instanceof DirectMethodHandle
3207 && canBeCached(refKind, defc, resolved)) {
3208 MemberName key = mh.internalMemberName();
3209 if (key != null) {
3210 key = key.asNormalOriginal();
3211 }
3212 if (member.equals(key)) { // better safe than sorry
3213 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
3214 }
3215 }
3216 return mh;
3217 }
3218 private
3219 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
3220 if (refKind == REF_invokeSpecial) {
3221 return false;
3222 }
3223 if (!Modifier.isPublic(defc.getModifiers()) ||
3224 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
3225 !member.isPublic() ||
3226 member.isCallerSensitive()) {
3227 return false;
3228 }
3229 ClassLoader loader = defc.getClassLoader();
3230 if (loader != null) {
3231 ClassLoader sysl = ClassLoader.getSystemClassLoader();
3232 boolean found = false;
3233 while (sysl != null) {
3234 if (loader == sysl) { found = true; break; }
3235 sysl = sysl.getParent();
3236 }
3237 if (!found) {
3238 return false;
3239 }
3240 }
3241 try {
3242 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
3243 new MemberName(refKind, defc, member.getName(), member.getType()));
3244 if (resolved2 == null) {
3245 return false;
3246 }
3247 checkSecurityManager(defc, resolved2);
3248 } catch (SecurityException ex) {
3249 return false;
3250 }
3251 return true;
3252 }
3253 private
3254 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
3255 throws ReflectiveOperationException {
3256 if (MethodHandleNatives.refKindIsField(refKind)) {
3257 return getDirectFieldNoSecurityManager(refKind, defc, member);
3258 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
3259 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
3260 } else if (refKind == REF_newInvokeSpecial) {
3261 return getDirectConstructorNoSecurityManager(defc, member);
3262 }
3263 // oops
3264 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
3265 }
3266
3267 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
3268 }
3269
3270 /**
3271 * Produces a method handle constructing arrays of a desired type,
3272 * as if by the {@code anewarray} bytecode.
3273 * The return type of the method handle will be the array type.
3274 * The type of its sole argument will be {@code int}, which specifies the size of the array.
3275 *
3276 * <p> If the returned method handle is invoked with a negative
3277 * array size, a {@code NegativeArraySizeException} will be thrown.
3278 *
3279 * @param arrayClass an array type
3280 * @return a method handle which can create arrays of the given type
3281 * @throws NullPointerException if the argument is {@code null}
3282 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
3283 * @see java.lang.reflect.Array#newInstance(Class, int)
3284 * @jvms 6.5 {@code anewarray} Instruction
3285 * @since 9
3286 */
3287 public static
3288 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
3289 if (!arrayClass.isArray()) {
3290 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
3291 }
3292 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
3293 bindTo(arrayClass.getComponentType());
3294 return ani.asType(ani.type().changeReturnType(arrayClass));
3295 }
3296
3297 /**
3298 * Produces a method handle returning the length of an array,
3299 * as if by the {@code arraylength} bytecode.
3300 * The type of the method handle will have {@code int} as return type,
3301 * and its sole argument will be the array type.
3302 *
3303 * <p> If the returned method handle is invoked with a {@code null}
3304 * array reference, a {@code NullPointerException} will be thrown.
3305 *
3306 * @param arrayClass an array type
3307 * @return a method handle which can retrieve the length of an array of the given array type
3308 * @throws NullPointerException if the argument is {@code null}
3309 * @throws IllegalArgumentException if arrayClass is not an array type
3310 * @jvms 6.5 {@code arraylength} Instruction
3311 * @since 9
3312 */
3313 public static
3314 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
3315 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
3316 }
3317
3318 /**
3319 * Produces a method handle giving read access to elements of an array,
3320 * as if by the {@code aaload} bytecode.
3321 * The type of the method handle will have a return type of the array's
3322 * element type. Its first argument will be the array type,
3323 * and the second will be {@code int}.
3324 *
3325 * <p> When the returned method handle is invoked,
3326 * the array reference and array index are checked.
3327 * A {@code NullPointerException} will be thrown if the array reference
3328 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3329 * thrown if the index is negative or if it is greater than or equal to
3330 * the length of the array.
3331 *
3332 * @param arrayClass an array type
3333 * @return a method handle which can load values from the given array type
3334 * @throws NullPointerException if the argument is null
3335 * @throws IllegalArgumentException if arrayClass is not an array type
3336 * @jvms 6.5 {@code aaload} Instruction
3337 */
3338 public static
3339 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
3340 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
3341 }
3342
3343 /**
3344 * Produces a method handle giving write access to elements of an array,
3345 * as if by the {@code astore} bytecode.
3346 * The type of the method handle will have a void return type.
3347 * Its last argument will be the array's element type.
3348 * The first and second arguments will be the array type and int.
3349 *
3350 * <p> When the returned method handle is invoked,
3351 * the array reference and array index are checked.
3352 * A {@code NullPointerException} will be thrown if the array reference
3353 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3354 * thrown if the index is negative or if it is greater than or equal to
3355 * the length of the array.
3356 *
3357 * @param arrayClass the class of an array
3358 * @return a method handle which can store values into the array type
3359 * @throws NullPointerException if the argument is null
3360 * @throws IllegalArgumentException if arrayClass is not an array type
3361 * @jvms 6.5 {@code aastore} Instruction
3362 */
3363 public static
3364 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
3365 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
3366 }
3367
3368 /**
3369 * Produces a VarHandle giving access to elements of an array of type
3370 * {@code arrayClass}. The VarHandle's variable type is the component type
3371 * of {@code arrayClass} and the list of coordinate types is
3372 * {@code (arrayClass, int)}, where the {@code int} coordinate type
3373 * corresponds to an argument that is an index into an array.
3374 * <p>
3375 * Certain access modes of the returned VarHandle are unsupported under
3376 * the following conditions:
3377 * <ul>
3378 * <li>if the component type is anything other than {@code byte},
3379 * {@code short}, {@code char}, {@code int}, {@code long},
3380 * {@code float}, or {@code double} then numeric atomic update access
3381 * modes are unsupported.
3382 * <li>if the field type is anything other than {@code boolean},
3383 * {@code byte}, {@code short}, {@code char}, {@code int} or
3384 * {@code long} then bitwise atomic update access modes are
3385 * unsupported.
3386 * </ul>
3387 * <p>
3388 * If the component type is {@code float} or {@code double} then numeric
3389 * and atomic update access modes compare values using their bitwise
3390 * representation (see {@link Float#floatToRawIntBits} and
3391 * {@link Double#doubleToRawLongBits}, respectively).
3392 *
3393 * <p> When the returned {@code VarHandle} is invoked,
3394 * the array reference and array index are checked.
3395 * A {@code NullPointerException} will be thrown if the array reference
3396 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3397 * thrown if the index is negative or if it is greater than or equal to
3398 * the length of the array.
3399 *
3400 * @apiNote
3401 * Bitwise comparison of {@code float} values or {@code double} values,
3402 * as performed by the numeric and atomic update access modes, differ
3403 * from the primitive {@code ==} operator and the {@link Float#equals}
3404 * and {@link Double#equals} methods, specifically with respect to
3405 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3406 * Care should be taken when performing a compare and set or a compare
3407 * and exchange operation with such values since the operation may
3408 * unexpectedly fail.
3409 * There are many possible NaN values that are considered to be
3410 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3411 * provided by Java can distinguish between them. Operation failure can
3412 * occur if the expected or witness value is a NaN value and it is
3413 * transformed (perhaps in a platform specific manner) into another NaN
3414 * value, and thus has a different bitwise representation (see
3415 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3416 * details).
3417 * The values {@code -0.0} and {@code +0.0} have different bitwise
3418 * representations but are considered equal when using the primitive
3419 * {@code ==} operator. Operation failure can occur if, for example, a
3420 * numeric algorithm computes an expected value to be say {@code -0.0}
3421 * and previously computed the witness value to be say {@code +0.0}.
3422 * @param arrayClass the class of an array, of type {@code T[]}
3423 * @return a VarHandle giving access to elements of an array
3424 * @throws NullPointerException if the arrayClass is null
3425 * @throws IllegalArgumentException if arrayClass is not an array type
3426 * @since 9
3427 */
3428 public static
3429 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
3430 return VarHandles.makeArrayElementHandle(arrayClass);
3431 }
3432
3433 /**
3434 * Produces a VarHandle giving access to elements of a {@code byte[]} array
3435 * viewed as if it were a different primitive array type, such as
3436 * {@code int[]} or {@code long[]}.
3437 * The VarHandle's variable type is the component type of
3438 * {@code viewArrayClass} and the list of coordinate types is
3439 * {@code (byte[], int)}, where the {@code int} coordinate type
3440 * corresponds to an argument that is an index into a {@code byte[]} array.
3441 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
3442 * array, composing bytes to or from a value of the component type of
3443 * {@code viewArrayClass} according to the given endianness.
3444 * <p>
3445 * The supported component types (variables types) are {@code short},
3446 * {@code char}, {@code int}, {@code long}, {@code float} and
3447 * {@code double}.
3448 * <p>
3449 * Access of bytes at a given index will result in an
3450 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3451 * or greater than the {@code byte[]} array length minus the size (in bytes)
3452 * of {@code T}.
3453 * <p>
3454 * Access of bytes at an index may be aligned or misaligned for {@code T},
3455 * with respect to the underlying memory address, {@code A} say, associated
3456 * with the array and index.
3457 * If access is misaligned then access for anything other than the
3458 * {@code get} and {@code set} access modes will result in an
3459 * {@code IllegalStateException}. In such cases atomic access is only
3460 * guaranteed with respect to the largest power of two that divides the GCD
3461 * of {@code A} and the size (in bytes) of {@code T}.
3462 * If access is aligned then following access modes are supported and are
3463 * guaranteed to support atomic access:
3464 * <ul>
3465 * <li>read write access modes for all {@code T}, with the exception of
3466 * access modes {@code get} and {@code set} for {@code long} and
3467 * {@code double} on 32-bit platforms.
3468 * <li>atomic update access modes for {@code int}, {@code long},
3469 * {@code float} or {@code double}.
3470 * (Future major platform releases of the JDK may support additional
3471 * types for certain currently unsupported access modes.)
3472 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3473 * (Future major platform releases of the JDK may support additional
3474 * numeric types for certain currently unsupported access modes.)
3475 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3476 * (Future major platform releases of the JDK may support additional
3477 * numeric types for certain currently unsupported access modes.)
3478 * </ul>
3479 * <p>
3480 * Misaligned access, and therefore atomicity guarantees, may be determined
3481 * for {@code byte[]} arrays without operating on a specific array. Given
3482 * an {@code index}, {@code T} and it's corresponding boxed type,
3483 * {@code T_BOX}, misalignment may be determined as follows:
3484 * <pre>{@code
3485 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3486 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
3487 * alignmentOffset(0, sizeOfT);
3488 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
3489 * boolean isMisaligned = misalignedAtIndex != 0;
3490 * }</pre>
3491 * <p>
3492 * If the variable type is {@code float} or {@code double} then atomic
3493 * update access modes compare values using their bitwise representation
3494 * (see {@link Float#floatToRawIntBits} and
3495 * {@link Double#doubleToRawLongBits}, respectively).
3496 * @param viewArrayClass the view array class, with a component type of
3497 * type {@code T}
3498 * @param byteOrder the endianness of the view array elements, as
3499 * stored in the underlying {@code byte} array
3500 * @return a VarHandle giving access to elements of a {@code byte[]} array
3501 * viewed as if elements corresponding to the components type of the view
3502 * array class
3503 * @throws NullPointerException if viewArrayClass or byteOrder is null
3504 * @throws IllegalArgumentException if viewArrayClass is not an array type
3505 * @throws UnsupportedOperationException if the component type of
3506 * viewArrayClass is not supported as a variable type
3507 * @since 9
3508 */
3509 public static
3510 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
3511 ByteOrder byteOrder) throws IllegalArgumentException {
3512 Objects.requireNonNull(byteOrder);
3513 return VarHandles.byteArrayViewHandle(viewArrayClass,
3514 byteOrder == ByteOrder.BIG_ENDIAN);
3515 }
3516
3517 /**
3518 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
3519 * viewed as if it were an array of elements of a different primitive
3520 * component type to that of {@code byte}, such as {@code int[]} or
3521 * {@code long[]}.
3522 * The VarHandle's variable type is the component type of
3523 * {@code viewArrayClass} and the list of coordinate types is
3524 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
3525 * corresponds to an argument that is an index into a {@code byte[]} array.
3526 * The returned VarHandle accesses bytes at an index in a
3527 * {@code ByteBuffer}, composing bytes to or from a value of the component
3528 * type of {@code viewArrayClass} according to the given endianness.
3529 * <p>
3530 * The supported component types (variables types) are {@code short},
3531 * {@code char}, {@code int}, {@code long}, {@code float} and
3532 * {@code double}.
3533 * <p>
3534 * Access will result in a {@code ReadOnlyBufferException} for anything
3535 * other than the read access modes if the {@code ByteBuffer} is read-only.
3536 * <p>
3537 * Access of bytes at a given index will result in an
3538 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3539 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
3540 * {@code T}.
3541 * <p>
3542 * Access of bytes at an index may be aligned or misaligned for {@code T},
3543 * with respect to the underlying memory address, {@code A} say, associated
3544 * with the {@code ByteBuffer} and index.
3545 * If access is misaligned then access for anything other than the
3546 * {@code get} and {@code set} access modes will result in an
3547 * {@code IllegalStateException}. In such cases atomic access is only
3548 * guaranteed with respect to the largest power of two that divides the GCD
3549 * of {@code A} and the size (in bytes) of {@code T}.
3550 * If access is aligned then following access modes are supported and are
3551 * guaranteed to support atomic access:
3552 * <ul>
3553 * <li>read write access modes for all {@code T}, with the exception of
3554 * access modes {@code get} and {@code set} for {@code long} and
3555 * {@code double} on 32-bit platforms.
3556 * <li>atomic update access modes for {@code int}, {@code long},
3557 * {@code float} or {@code double}.
3558 * (Future major platform releases of the JDK may support additional
3559 * types for certain currently unsupported access modes.)
3560 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3561 * (Future major platform releases of the JDK may support additional
3562 * numeric types for certain currently unsupported access modes.)
3563 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3564 * (Future major platform releases of the JDK may support additional
3565 * numeric types for certain currently unsupported access modes.)
3566 * </ul>
3567 * <p>
3568 * Misaligned access, and therefore atomicity guarantees, may be determined
3569 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
3570 * {@code index}, {@code T} and it's corresponding boxed type,
3571 * {@code T_BOX}, as follows:
3572 * <pre>{@code
3573 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3574 * ByteBuffer bb = ...
3575 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
3576 * boolean isMisaligned = misalignedAtIndex != 0;
3577 * }</pre>
3578 * <p>
3579 * If the variable type is {@code float} or {@code double} then atomic
3580 * update access modes compare values using their bitwise representation
3581 * (see {@link Float#floatToRawIntBits} and
3582 * {@link Double#doubleToRawLongBits}, respectively).
3583 * @param viewArrayClass the view array class, with a component type of
3584 * type {@code T}
3585 * @param byteOrder the endianness of the view array elements, as
3586 * stored in the underlying {@code ByteBuffer} (Note this overrides the
3587 * endianness of a {@code ByteBuffer})
3588 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
3589 * viewed as if elements corresponding to the components type of the view
3590 * array class
3591 * @throws NullPointerException if viewArrayClass or byteOrder is null
3592 * @throws IllegalArgumentException if viewArrayClass is not an array type
3593 * @throws UnsupportedOperationException if the component type of
3594 * viewArrayClass is not supported as a variable type
3595 * @since 9
3596 */
3597 public static
3598 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
3599 ByteOrder byteOrder) throws IllegalArgumentException {
3600 Objects.requireNonNull(byteOrder);
3601 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
3602 byteOrder == ByteOrder.BIG_ENDIAN);
3603 }
3604
3605
3606 /// method handle invocation (reflective style)
3607
3608 /**
3609 * Produces a method handle which will invoke any method handle of the
3610 * given {@code type}, with a given number of trailing arguments replaced by
3611 * a single trailing {@code Object[]} array.
3612 * The resulting invoker will be a method handle with the following
3613 * arguments:
3614 * <ul>
3615 * <li>a single {@code MethodHandle} target
3616 * <li>zero or more leading values (counted by {@code leadingArgCount})
3617 * <li>an {@code Object[]} array containing trailing arguments
3618 * </ul>
3619 * <p>
3620 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
3621 * the indicated {@code type}.
3622 * That is, if the target is exactly of the given {@code type}, it will behave
3623 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
3624 * is used to convert the target to the required {@code type}.
3625 * <p>
3626 * The type of the returned invoker will not be the given {@code type}, but rather
3627 * will have all parameters except the first {@code leadingArgCount}
3628 * replaced by a single array of type {@code Object[]}, which will be
3629 * the final parameter.
3630 * <p>
3631 * Before invoking its target, the invoker will spread the final array, apply
3632 * reference casts as necessary, and unbox and widen primitive arguments.
3633 * If, when the invoker is called, the supplied array argument does
3634 * not have the correct number of elements, the invoker will throw
3635 * an {@link IllegalArgumentException} instead of invoking the target.
3636 * <p>
3637 * This method is equivalent to the following code (though it may be more efficient):
3638 * <blockquote><pre>{@code
3639 MethodHandle invoker = MethodHandles.invoker(type);
3640 int spreadArgCount = type.parameterCount() - leadingArgCount;
3641 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
3642 return invoker;
3643 * }</pre></blockquote>
3644 * This method throws no reflective or security exceptions.
3645 * @param type the desired target type
3646 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
3647 * @return a method handle suitable for invoking any method handle of the given type
3648 * @throws NullPointerException if {@code type} is null
3649 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
3650 * the range from 0 to {@code type.parameterCount()} inclusive,
3651 * or if the resulting method handle's type would have
3652 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3653 */
3654 public static
3655 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
3656 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
3657 throw newIllegalArgumentException("bad argument count", leadingArgCount);
3658 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
3659 return type.invokers().spreadInvoker(leadingArgCount);
3660 }
3661
3662 /**
3663 * Produces a special <em>invoker method handle</em> which can be used to
3664 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
3665 * The resulting invoker will have a type which is
3666 * exactly equal to the desired type, except that it will accept
3667 * an additional leading argument of type {@code MethodHandle}.
3668 * <p>
3669 * This method is equivalent to the following code (though it may be more efficient):
3670 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
3671 *
3672 * <p style="font-size:smaller;">
3673 * <em>Discussion:</em>
3674 * Invoker method handles can be useful when working with variable method handles
3675 * of unknown types.
3676 * For example, to emulate an {@code invokeExact} call to a variable method
3677 * handle {@code M}, extract its type {@code T},
3678 * look up the invoker method {@code X} for {@code T},
3679 * and call the invoker method, as {@code X.invoke(T, A...)}.
3680 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
3681 * is unknown.)
3682 * If spreading, collecting, or other argument transformations are required,
3683 * they can be applied once to the invoker {@code X} and reused on many {@code M}
3684 * method handle values, as long as they are compatible with the type of {@code X}.
3685 * <p style="font-size:smaller;">
3686 * <em>(Note: The invoker method is not available via the Core Reflection API.
3687 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3688 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3689 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3690 * <p>
3691 * This method throws no reflective or security exceptions.
3692 * @param type the desired target type
3693 * @return a method handle suitable for invoking any method handle of the given type
3694 * @throws IllegalArgumentException if the resulting method handle's type would have
3695 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3696 */
3697 public static
3698 MethodHandle exactInvoker(MethodType type) {
3699 return type.invokers().exactInvoker();
3700 }
3701
3702 /**
3703 * Produces a special <em>invoker method handle</em> which can be used to
3704 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
3705 * The resulting invoker will have a type which is
3706 * exactly equal to the desired type, except that it will accept
3707 * an additional leading argument of type {@code MethodHandle}.
3708 * <p>
3709 * Before invoking its target, if the target differs from the expected type,
3710 * the invoker will apply reference casts as
3711 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
3712 * Similarly, the return value will be converted as necessary.
3713 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
3714 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
3715 * <p>
3716 * This method is equivalent to the following code (though it may be more efficient):
3717 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
3718 * <p style="font-size:smaller;">
3719 * <em>Discussion:</em>
3720 * A {@linkplain MethodType#genericMethodType general method type} is one which
3721 * mentions only {@code Object} arguments and return values.
3722 * An invoker for such a type is capable of calling any method handle
3723 * of the same arity as the general type.
3724 * <p style="font-size:smaller;">
3725 * <em>(Note: The invoker method is not available via the Core Reflection API.
3726 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3727 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3728 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3729 * <p>
3730 * This method throws no reflective or security exceptions.
3731 * @param type the desired target type
3732 * @return a method handle suitable for invoking any method handle convertible to the given type
3733 * @throws IllegalArgumentException if the resulting method handle's type would have
3734 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3735 */
3736 public static
3737 MethodHandle invoker(MethodType type) {
3738 return type.invokers().genericInvoker();
3739 }
3740
3741 /**
3742 * Produces a special <em>invoker method handle</em> which can be used to
3743 * invoke a signature-polymorphic access mode method on any VarHandle whose
3744 * associated access mode type is compatible with the given type.
3745 * The resulting invoker will have a type which is exactly equal to the
3746 * desired given type, except that it will accept an additional leading
3747 * argument of type {@code VarHandle}.
3748 *
3749 * @param accessMode the VarHandle access mode
3750 * @param type the desired target type
3751 * @return a method handle suitable for invoking an access mode method of
3752 * any VarHandle whose access mode type is of the given type.
3753 * @since 9
3754 */
3755 static public
3756 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3757 return type.invokers().varHandleMethodExactInvoker(accessMode);
3758 }
3759
3760 /**
3761 * Produces a special <em>invoker method handle</em> which can be used to
3762 * invoke a signature-polymorphic access mode method on any VarHandle whose
3763 * associated access mode type is compatible with the given type.
3764 * The resulting invoker will have a type which is exactly equal to the
3765 * desired given type, except that it will accept an additional leading
3766 * argument of type {@code VarHandle}.
3767 * <p>
3768 * Before invoking its target, if the access mode type differs from the
3769 * desired given type, the invoker will apply reference casts as necessary
3770 * and box, unbox, or widen primitive values, as if by
3771 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3772 * converted as necessary.
3773 * <p>
3774 * This method is equivalent to the following code (though it may be more
3775 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3776 *
3777 * @param accessMode the VarHandle access mode
3778 * @param type the desired target type
3779 * @return a method handle suitable for invoking an access mode method of
3780 * any VarHandle whose access mode type is convertible to the given
3781 * type.
3782 * @since 9
3783 */
3784 static public
3785 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3786 return type.invokers().varHandleMethodInvoker(accessMode);
3787 }
3788
3789 static /*non-public*/
3790 MethodHandle basicInvoker(MethodType type) {
3791 return type.invokers().basicInvoker();
3792 }
3793
3794 /// method handle modification (creation from other method handles)
3795
3796 /**
3797 * Produces a method handle which adapts the type of the
3798 * given method handle to a new type by pairwise argument and return type conversion.
3799 * The original type and new type must have the same number of arguments.
3800 * The resulting method handle is guaranteed to report a type
3801 * which is equal to the desired new type.
3802 * <p>
3803 * If the original type and new type are equal, returns target.
3804 * <p>
3805 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3806 * and some additional conversions are also applied if those conversions fail.
3807 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3808 * if possible, before or instead of any conversions done by {@code asType}:
3809 * <ul>
3810 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3811 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3812 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3813 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3814 * the boolean is converted to a byte value, 1 for true, 0 for false.
3815 * (This treatment follows the usage of the bytecode verifier.)
3816 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3817 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3818 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3819 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3820 * then a Java casting conversion (JLS 5.5) is applied.
3821 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3822 * widening and/or narrowing.)
3823 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3824 * conversion will be applied at runtime, possibly followed
3825 * by a Java casting conversion (JLS 5.5) on the primitive value,
3826 * possibly followed by a conversion from byte to boolean by testing
3827 * the low-order bit.
3828 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3829 * and if the reference is null at runtime, a zero value is introduced.
3830 * </ul>
3831 * @param target the method handle to invoke after arguments are retyped
3832 * @param newType the expected type of the new method handle
3833 * @return a method handle which delegates to the target after performing
3834 * any necessary argument conversions, and arranges for any
3835 * necessary return value conversions
3836 * @throws NullPointerException if either argument is null
3837 * @throws WrongMethodTypeException if the conversion cannot be made
3838 * @see MethodHandle#asType
3839 */
3840 public static
3841 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3842 explicitCastArgumentsChecks(target, newType);
3843 // use the asTypeCache when possible:
3844 MethodType oldType = target.type();
3845 if (oldType == newType) return target;
3846 if (oldType.explicitCastEquivalentToAsType(newType)) {
3847 return target.asFixedArity().asType(newType);
3848 }
3849 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3850 }
3851
3852 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3853 if (target.type().parameterCount() != newType.parameterCount()) {
3854 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3855 }
3856 }
3857
3858 /**
3859 * Produces a method handle which adapts the calling sequence of the
3860 * given method handle to a new type, by reordering the arguments.
3861 * The resulting method handle is guaranteed to report a type
3862 * which is equal to the desired new type.
3863 * <p>
3864 * The given array controls the reordering.
3865 * Call {@code #I} the number of incoming parameters (the value
3866 * {@code newType.parameterCount()}, and call {@code #O} the number
3867 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3868 * Then the length of the reordering array must be {@code #O},
3869 * and each element must be a non-negative number less than {@code #I}.
3870 * For every {@code N} less than {@code #O}, the {@code N}-th
3871 * outgoing argument will be taken from the {@code I}-th incoming
3872 * argument, where {@code I} is {@code reorder[N]}.
3873 * <p>
3874 * No argument or return value conversions are applied.
3875 * The type of each incoming argument, as determined by {@code newType},
3876 * must be identical to the type of the corresponding outgoing parameter
3877 * or parameters in the target method handle.
3878 * The return type of {@code newType} must be identical to the return
3879 * type of the original target.
3880 * <p>
3881 * The reordering array need not specify an actual permutation.
3882 * An incoming argument will be duplicated if its index appears
3883 * more than once in the array, and an incoming argument will be dropped
3884 * if its index does not appear in the array.
3885 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3886 * incoming arguments which are not mentioned in the reordering array
3887 * may be of any type, as determined only by {@code newType}.
3888 * <blockquote><pre>{@code
3889 import static java.lang.invoke.MethodHandles.*;
3890 import static java.lang.invoke.MethodType.*;
3891 ...
3892 MethodType intfn1 = methodType(int.class, int.class);
3893 MethodType intfn2 = methodType(int.class, int.class, int.class);
3894 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3895 assert(sub.type().equals(intfn2));
3896 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3897 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3898 assert((int)rsub.invokeExact(1, 100) == 99);
3899 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3900 assert(add.type().equals(intfn2));
3901 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3902 assert(twice.type().equals(intfn1));
3903 assert((int)twice.invokeExact(21) == 42);
3904 * }</pre></blockquote>
3905 * <p>
3906 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3907 * variable-arity method handle}, even if the original target method handle was.
3908 * @param target the method handle to invoke after arguments are reordered
3909 * @param newType the expected type of the new method handle
3910 * @param reorder an index array which controls the reordering
3911 * @return a method handle which delegates to the target after it
3912 * drops unused arguments and moves and/or duplicates the other arguments
3913 * @throws NullPointerException if any argument is null
3914 * @throws IllegalArgumentException if the index array length is not equal to
3915 * the arity of the target, or if any index array element
3916 * not a valid index for a parameter of {@code newType},
3917 * or if two corresponding parameter types in
3918 * {@code target.type()} and {@code newType} are not identical,
3919 */
3920 public static
3921 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3922 reorder = reorder.clone(); // get a private copy
3923 MethodType oldType = target.type();
3924 permuteArgumentChecks(reorder, newType, oldType);
3925 // first detect dropped arguments and handle them separately
3926 int[] originalReorder = reorder;
3927 BoundMethodHandle result = target.rebind();
3928 LambdaForm form = result.form;
3929 int newArity = newType.parameterCount();
3930 // Normalize the reordering into a real permutation,
3931 // by removing duplicates and adding dropped elements.
3932 // This somewhat improves lambda form caching, as well
3933 // as simplifying the transform by breaking it up into steps.
3934 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3935 if (ddIdx > 0) {
3936 // We found a duplicated entry at reorder[ddIdx].
3937 // Example: (x,y,z)->asList(x,y,z)
3938 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3939 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3940 // The starred element corresponds to the argument
3941 // deleted by the dupArgumentForm transform.
3942 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3943 boolean killFirst = false;
3944 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3945 // Set killFirst if the dup is larger than an intervening position.
3946 // This will remove at least one inversion from the permutation.
3947 if (dupVal > val) killFirst = true;
3948 }
3949 if (!killFirst) {
3950 srcPos = dstPos;
3951 dstPos = ddIdx;
3952 }
3953 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3954 assert (reorder[srcPos] == reorder[dstPos]);
3955 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3956 // contract the reordering by removing the element at dstPos
3957 int tailPos = dstPos + 1;
3958 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3959 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3960 } else {
3961 int dropVal = ~ddIdx, insPos = 0;
3962 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3963 // Find first element of reorder larger than dropVal.
3964 // This is where we will insert the dropVal.
3965 insPos += 1;
3966 }
3967 Class<?> ptype = newType.parameterType(dropVal);
3968 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3969 oldType = oldType.insertParameterTypes(insPos, ptype);
3970 // expand the reordering by inserting an element at insPos
3971 int tailPos = insPos + 1;
3972 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3973 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3974 reorder[insPos] = dropVal;
3975 }
3976 assert (permuteArgumentChecks(reorder, newType, oldType));
3977 }
3978 assert (reorder.length == newArity); // a perfect permutation
3979 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3980 form = form.editor().permuteArgumentsForm(1, reorder);
3981 if (newType == result.type() && form == result.internalForm())
3982 return result;
3983 return result.copyWith(newType, form);
3984 }
3985
3986 /**
3987 * Return an indication of any duplicate or omission in reorder.
3988 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3989 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3990 * Otherwise, return zero.
3991 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3992 */
3993 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3994 final int BIT_LIMIT = 63; // max number of bits in bit mask
3995 if (newArity < BIT_LIMIT) {
3996 long mask = 0;
3997 for (int i = 0; i < reorder.length; i++) {
3998 int arg = reorder[i];
3999 if (arg >= newArity) {
4000 return reorder.length;
4001 }
4002 long bit = 1L << arg;
4003 if ((mask & bit) != 0) {
4004 return i; // >0 indicates a dup
4005 }
4006 mask |= bit;
4007 }
4008 if (mask == (1L << newArity) - 1) {
4009 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4010 return 0;
4011 }
4012 // find first zero
4013 long zeroBit = Long.lowestOneBit(~mask);
4014 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4015 assert(zeroPos <= newArity);
4016 if (zeroPos == newArity) {
4017 return 0;
4018 }
4019 return ~zeroPos;
4020 } else {
4021 // same algorithm, different bit set
4022 BitSet mask = new BitSet(newArity);
4023 for (int i = 0; i < reorder.length; i++) {
4024 int arg = reorder[i];
4025 if (arg >= newArity) {
4026 return reorder.length;
4027 }
4028 if (mask.get(arg)) {
4029 return i; // >0 indicates a dup
4030 }
4031 mask.set(arg);
4032 }
4033 int zeroPos = mask.nextClearBit(0);
4034 assert(zeroPos <= newArity);
4035 if (zeroPos == newArity) {
4036 return 0;
4037 }
4038 return ~zeroPos;
4039 }
4040 }
4041
4042 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4043 if (newType.returnType() != oldType.returnType())
4044 throw newIllegalArgumentException("return types do not match",
4045 oldType, newType);
4046 if (reorder.length == oldType.parameterCount()) {
4047 int limit = newType.parameterCount();
4048 boolean bad = false;
4049 for (int j = 0; j < reorder.length; j++) {
4050 int i = reorder[j];
4051 if (i < 0 || i >= limit) {
4052 bad = true; break;
4053 }
4054 Class<?> src = newType.parameterType(i);
4055 Class<?> dst = oldType.parameterType(j);
4056 if (src != dst)
4057 throw newIllegalArgumentException("parameter types do not match after reorder",
4058 oldType, newType);
4059 }
4060 if (!bad) return true;
4061 }
4062 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
4063 }
4064
4065 /**
4066 * Produces a method handle of the requested return type which returns the given
4067 * constant value every time it is invoked.
4068 * <p>
4069 * Before the method handle is returned, the passed-in value is converted to the requested type.
4070 * If the requested type is primitive, widening primitive conversions are attempted,
4071 * else reference conversions are attempted.
4072 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4073 * @param type the return type of the desired method handle
4074 * @param value the value to return
4075 * @return a method handle of the given return type and no arguments, which always returns the given value
4076 * @throws NullPointerException if the {@code type} argument is null
4077 * @throws ClassCastException if the value cannot be converted to the required return type
4078 * @throws IllegalArgumentException if the given type is {@code void.class}
4079 */
4080 public static
4081 MethodHandle constant(Class<?> type, Object value) {
4082 if (type.isPrimitive()) {
4083 if (type == void.class)
4084 throw newIllegalArgumentException("void type");
4085 Wrapper w = Wrapper.forPrimitiveType(type);
4086 value = w.convert(value, type);
4087 if (w.zero().equals(value))
4088 return zero(w, type);
4089 return insertArguments(identity(type), 0, value);
4090 } else {
4091 if (value == null)
4092 return zero(Wrapper.OBJECT, type);
4093 return identity(type).bindTo(value);
4094 }
4095 }
4096
4097 /**
4098 * Produces a method handle which returns its sole argument when invoked.
4099 * @param type the type of the sole parameter and return value of the desired method handle
4100 * @return a unary method handle which accepts and returns the given type
4101 * @throws NullPointerException if the argument is null
4102 * @throws IllegalArgumentException if the given type is {@code void.class}
4103 */
4104 public static
4105 MethodHandle identity(Class<?> type) {
4106 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4107 int pos = btw.ordinal();
4108 MethodHandle ident = IDENTITY_MHS[pos];
4109 if (ident == null) {
4110 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4111 }
4112 if (ident.type().returnType() == type)
4113 return ident;
4114 // something like identity(Foo.class); do not bother to intern these
4115 assert (btw == Wrapper.OBJECT);
4116 return makeIdentity(type);
4117 }
4118
4119 /**
4120 * Produces a constant method handle of the requested return type which
4121 * returns the default value for that type every time it is invoked.
4122 * The resulting constant method handle will have no side effects.
4123 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4124 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4125 * since {@code explicitCastArguments} converts {@code null} to default values.
4126 * @param type the expected return type of the desired method handle
4127 * @return a constant method handle that takes no arguments
4128 * and returns the default value of the given type (or void, if the type is void)
4129 * @throws NullPointerException if the argument is null
4130 * @see MethodHandles#constant
4131 * @see MethodHandles#empty
4132 * @see MethodHandles#explicitCastArguments
4133 * @since 9
4134 */
4135 public static MethodHandle zero(Class<?> type) {
4136 Objects.requireNonNull(type);
4137 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
4138 }
4139
4140 private static MethodHandle identityOrVoid(Class<?> type) {
4141 return type == void.class ? zero(type) : identity(type);
4142 }
4143
4144 /**
4145 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4146 * and returns a suitable default depending on the return type.
4147 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4148 * <p>The returned method handle is equivalent to
4149 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4150 *
4151 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4152 * {@code guardWithTest(pred, target, empty(target.type())}.
4153 * @param type the type of the desired method handle
4154 * @return a constant method handle of the given type, which returns a default value of the given return type
4155 * @throws NullPointerException if the argument is null
4156 * @see MethodHandles#zero
4157 * @see MethodHandles#constant
4158 * @since 9
4159 */
4160 public static MethodHandle empty(MethodType type) {
4161 Objects.requireNonNull(type);
4162 return dropArguments(zero(type.returnType()), 0, type.parameterList());
4163 }
4164
4165 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4166 private static MethodHandle makeIdentity(Class<?> ptype) {
4167 MethodType mtype = methodType(ptype, ptype);
4168 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4169 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4170 }
4171
4172 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
4173 int pos = btw.ordinal();
4174 MethodHandle zero = ZERO_MHS[pos];
4175 if (zero == null) {
4176 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
4177 }
4178 if (zero.type().returnType() == rtype)
4179 return zero;
4180 assert(btw == Wrapper.OBJECT);
4181 return makeZero(rtype);
4182 }
4183 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4184 private static MethodHandle makeZero(Class<?> rtype) {
4185 MethodType mtype = methodType(rtype);
4186 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
4187 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
4188 }
4189
4190 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4191 // Simulate a CAS, to avoid racy duplication of results.
4192 MethodHandle prev = cache[pos];
4193 if (prev != null) return prev;
4194 return cache[pos] = value;
4195 }
4196
4197 /**
4198 * Provides a target method handle with one or more <em>bound arguments</em>
4199 * in advance of the method handle's invocation.
4200 * The formal parameters to the target corresponding to the bound
4201 * arguments are called <em>bound parameters</em>.
4202 * Returns a new method handle which saves away the bound arguments.
4203 * When it is invoked, it receives arguments for any non-bound parameters,
4204 * binds the saved arguments to their corresponding parameters,
4205 * and calls the original target.
4206 * <p>
4207 * The type of the new method handle will drop the types for the bound
4208 * parameters from the original target type, since the new method handle
4209 * will no longer require those arguments to be supplied by its callers.
4210 * <p>
4211 * Each given argument object must match the corresponding bound parameter type.
4212 * If a bound parameter type is a primitive, the argument object
4213 * must be a wrapper, and will be unboxed to produce the primitive value.
4214 * <p>
4215 * The {@code pos} argument selects which parameters are to be bound.
4216 * It may range between zero and <i>N-L</i> (inclusively),
4217 * where <i>N</i> is the arity of the target method handle
4218 * and <i>L</i> is the length of the values array.
4219 * <p>
4220 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4221 * variable-arity method handle}, even if the original target method handle was.
4222 * @param target the method handle to invoke after the argument is inserted
4223 * @param pos where to insert the argument (zero for the first)
4224 * @param values the series of arguments to insert
4225 * @return a method handle which inserts an additional argument,
4226 * before calling the original method handle
4227 * @throws NullPointerException if the target or the {@code values} array is null
4228 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
4229 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4230 * is the length of the values array.
4231 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4232 * type.
4233 * @see MethodHandle#bindTo
4234 */
4235 public static
4236 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4237 int insCount = values.length;
4238 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4239 if (insCount == 0) return target;
4240 BoundMethodHandle result = target.rebind();
4241 for (int i = 0; i < insCount; i++) {
4242 Object value = values[i];
4243 Class<?> ptype = ptypes[pos+i];
4244 if (ptype.isPrimitive()) {
4245 result = insertArgumentPrimitive(result, pos, ptype, value);
4246 } else {
4247 value = ptype.cast(value); // throw CCE if needed
4248 result = result.bindArgumentL(pos, value);
4249 }
4250 }
4251 return result;
4252 }
4253
4254 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4255 Class<?> ptype, Object value) {
4256 Wrapper w = Wrapper.forPrimitiveType(ptype);
4257 // perform unboxing and/or primitive conversion
4258 value = w.convert(value, ptype);
4259 switch (w) {
4260 case INT: return result.bindArgumentI(pos, (int)value);
4261 case LONG: return result.bindArgumentJ(pos, (long)value);
4262 case FLOAT: return result.bindArgumentF(pos, (float)value);
4263 case DOUBLE: return result.bindArgumentD(pos, (double)value);
4264 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
4265 }
4266 }
4267
4268 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
4269 MethodType oldType = target.type();
4270 int outargs = oldType.parameterCount();
4271 int inargs = outargs - insCount;
4272 if (inargs < 0)
4273 throw newIllegalArgumentException("too many values to insert");
4274 if (pos < 0 || pos > inargs)
4275 throw newIllegalArgumentException("no argument type to append");
4276 return oldType.ptypes();
4277 }
4278
4279 /**
4280 * Produces a method handle which will discard some dummy arguments
4281 * before calling some other specified <i>target</i> method handle.
4282 * The type of the new method handle will be the same as the target's type,
4283 * except it will also include the dummy argument types,
4284 * at some given position.
4285 * <p>
4286 * The {@code pos} argument may range between zero and <i>N</i>,
4287 * where <i>N</i> is the arity of the target.
4288 * If {@code pos} is zero, the dummy arguments will precede
4289 * the target's real arguments; if {@code pos} is <i>N</i>
4290 * they will come after.
4291 * <p>
4292 * <b>Example:</b>
4293 * <blockquote><pre>{@code
4294 import static java.lang.invoke.MethodHandles.*;
4295 import static java.lang.invoke.MethodType.*;
4296 ...
4297 MethodHandle cat = lookup().findVirtual(String.class,
4298 "concat", methodType(String.class, String.class));
4299 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4300 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
4301 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
4302 assertEquals(bigType, d0.type());
4303 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
4304 * }</pre></blockquote>
4305 * <p>
4306 * This method is also equivalent to the following code:
4307 * <blockquote><pre>
4308 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
4309 * </pre></blockquote>
4310 * @param target the method handle to invoke after the arguments are dropped
4311 * @param valueTypes the type(s) of the argument(s) to drop
4312 * @param pos position of first argument to drop (zero for the leftmost)
4313 * @return a method handle which drops arguments of the given types,
4314 * before calling the original method handle
4315 * @throws NullPointerException if the target is null,
4316 * or if the {@code valueTypes} list or any of its elements is null
4317 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4318 * or if {@code pos} is negative or greater than the arity of the target,
4319 * or if the new method handle's type would have too many parameters
4320 */
4321 public static
4322 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4323 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
4324 }
4325
4326 private static List<Class<?>> copyTypes(Object[] array) {
4327 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
4328 }
4329
4330 private static
4331 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4332 MethodType oldType = target.type(); // get NPE
4333 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
4334 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
4335 if (dropped == 0) return target;
4336 BoundMethodHandle result = target.rebind();
4337 LambdaForm lform = result.form;
4338 int insertFormArg = 1 + pos;
4339 for (Class<?> ptype : valueTypes) {
4340 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
4341 }
4342 result = result.copyWith(newType, lform);
4343 return result;
4344 }
4345
4346 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
4347 int dropped = valueTypes.size();
4348 MethodType.checkSlotCount(dropped);
4349 int outargs = oldType.parameterCount();
4350 int inargs = outargs + dropped;
4351 if (pos < 0 || pos > outargs)
4352 throw newIllegalArgumentException("no argument type to remove"
4353 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
4354 );
4355 return dropped;
4356 }
4357
4358 /**
4359 * Produces a method handle which will discard some dummy arguments
4360 * before calling some other specified <i>target</i> method handle.
4361 * The type of the new method handle will be the same as the target's type,
4362 * except it will also include the dummy argument types,
4363 * at some given position.
4364 * <p>
4365 * The {@code pos} argument may range between zero and <i>N</i>,
4366 * where <i>N</i> is the arity of the target.
4367 * If {@code pos} is zero, the dummy arguments will precede
4368 * the target's real arguments; if {@code pos} is <i>N</i>
4369 * they will come after.
4370 * @apiNote
4371 * <blockquote><pre>{@code
4372 import static java.lang.invoke.MethodHandles.*;
4373 import static java.lang.invoke.MethodType.*;
4374 ...
4375 MethodHandle cat = lookup().findVirtual(String.class,
4376 "concat", methodType(String.class, String.class));
4377 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4378 MethodHandle d0 = dropArguments(cat, 0, String.class);
4379 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
4380 MethodHandle d1 = dropArguments(cat, 1, String.class);
4381 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4382 MethodHandle d2 = dropArguments(cat, 2, String.class);
4383 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4384 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4385 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4386 * }</pre></blockquote>
4387 * <p>
4388 * This method is also equivalent to the following code:
4389 * <blockquote><pre>
4390 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4391 * </pre></blockquote>
4392 * @param target the method handle to invoke after the arguments are dropped
4393 * @param valueTypes the type(s) of the argument(s) to drop
4394 * @param pos position of first argument to drop (zero for the leftmost)
4395 * @return a method handle which drops arguments of the given types,
4396 * before calling the original method handle
4397 * @throws NullPointerException if the target is null,
4398 * or if the {@code valueTypes} array or any of its elements is null
4399 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4400 * or if {@code pos} is negative or greater than the arity of the target,
4401 * or if the new method handle's type would have
4402 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4403 */
4404 public static
4405 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4406 return dropArguments0(target, pos, copyTypes(valueTypes));
4407 }
4408
4409 // private version which allows caller some freedom with error handling
4410 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4411 boolean nullOnFailure) {
4412 newTypes = copyTypes(newTypes.toArray());
4413 List<Class<?>> oldTypes = target.type().parameterList();
4414 int match = oldTypes.size();
4415 if (skip != 0) {
4416 if (skip < 0 || skip > match) {
4417 throw newIllegalArgumentException("illegal skip", skip, target);
4418 }
4419 oldTypes = oldTypes.subList(skip, match);
4420 match -= skip;
4421 }
4422 List<Class<?>> addTypes = newTypes;
4423 int add = addTypes.size();
4424 if (pos != 0) {
4425 if (pos < 0 || pos > add) {
4426 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4427 }
4428 addTypes = addTypes.subList(pos, add);
4429 add -= pos;
4430 assert(addTypes.size() == add);
4431 }
4432 // Do not add types which already match the existing arguments.
4433 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4434 if (nullOnFailure) {
4435 return null;
4436 }
4437 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
4438 }
4439 addTypes = addTypes.subList(match, add);
4440 add -= match;
4441 assert(addTypes.size() == add);
4442 // newTypes: ( P*[pos], M*[match], A*[add] )
4443 // target: ( S*[skip], M*[match] )
4444 MethodHandle adapter = target;
4445 if (add > 0) {
4446 adapter = dropArguments0(adapter, skip+ match, addTypes);
4447 }
4448 // adapter: (S*[skip], M*[match], A*[add] )
4449 if (pos > 0) {
4450 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
4451 }
4452 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
4453 return adapter;
4454 }
4455
4456 /**
4457 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
4458 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
4459 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
4460 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
4461 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
4462 * {@link #dropArguments(MethodHandle, int, Class[])}.
4463 * <p>
4464 * The resulting handle will have the same return type as the target handle.
4465 * <p>
4466 * In more formal terms, assume these two type lists:<ul>
4467 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
4468 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
4469 * {@code newTypes}.
4470 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
4471 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
4472 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
4473 * sub-list.
4474 * </ul>
4475 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
4476 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
4477 * {@link #dropArguments(MethodHandle, int, Class[])}.
4478 *
4479 * @apiNote
4480 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
4481 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
4482 * <blockquote><pre>{@code
4483 import static java.lang.invoke.MethodHandles.*;
4484 import static java.lang.invoke.MethodType.*;
4485 ...
4486 ...
4487 MethodHandle h0 = constant(boolean.class, true);
4488 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
4489 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
4490 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
4491 if (h1.type().parameterCount() < h2.type().parameterCount())
4492 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
4493 else
4494 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
4495 MethodHandle h3 = guardWithTest(h0, h1, h2);
4496 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
4497 * }</pre></blockquote>
4498 * @param target the method handle to adapt
4499 * @param skip number of targets parameters to disregard (they will be unchanged)
4500 * @param newTypes the list of types to match {@code target}'s parameter type list to
4501 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
4502 * @return a possibly adapted method handle
4503 * @throws NullPointerException if either argument is null
4504 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
4505 * or if {@code skip} is negative or greater than the arity of the target,
4506 * or if {@code pos} is negative or greater than the newTypes list size,
4507 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
4508 * {@code pos}.
4509 * @since 9
4510 */
4511 public static
4512 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
4513 Objects.requireNonNull(target);
4514 Objects.requireNonNull(newTypes);
4515 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
4516 }
4517
4518 /**
4519 * Adapts a target method handle by pre-processing
4520 * one or more of its arguments, each with its own unary filter function,
4521 * and then calling the target with each pre-processed argument
4522 * replaced by the result of its corresponding filter function.
4523 * <p>
4524 * The pre-processing is performed by one or more method handles,
4525 * specified in the elements of the {@code filters} array.
4526 * The first element of the filter array corresponds to the {@code pos}
4527 * argument of the target, and so on in sequence.
4528 * The filter functions are invoked in left to right order.
4529 * <p>
4530 * Null arguments in the array are treated as identity functions,
4531 * and the corresponding arguments left unchanged.
4532 * (If there are no non-null elements in the array, the original target is returned.)
4533 * Each filter is applied to the corresponding argument of the adapter.
4534 * <p>
4535 * If a filter {@code F} applies to the {@code N}th argument of
4536 * the target, then {@code F} must be a method handle which
4537 * takes exactly one argument. The type of {@code F}'s sole argument
4538 * replaces the corresponding argument type of the target
4539 * in the resulting adapted method handle.
4540 * The return type of {@code F} must be identical to the corresponding
4541 * parameter type of the target.
4542 * <p>
4543 * It is an error if there are elements of {@code filters}
4544 * (null or not)
4545 * which do not correspond to argument positions in the target.
4546 * <p><b>Example:</b>
4547 * <blockquote><pre>{@code
4548 import static java.lang.invoke.MethodHandles.*;
4549 import static java.lang.invoke.MethodType.*;
4550 ...
4551 MethodHandle cat = lookup().findVirtual(String.class,
4552 "concat", methodType(String.class, String.class));
4553 MethodHandle upcase = lookup().findVirtual(String.class,
4554 "toUpperCase", methodType(String.class));
4555 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4556 MethodHandle f0 = filterArguments(cat, 0, upcase);
4557 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
4558 MethodHandle f1 = filterArguments(cat, 1, upcase);
4559 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
4560 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
4561 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
4562 * }</pre></blockquote>
4563 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4564 * denotes the return type of both the {@code target} and resulting adapter.
4565 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
4566 * of the parameters and arguments that precede and follow the filter position
4567 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
4568 * values of the filtered parameters and arguments; they also represent the
4569 * return types of the {@code filter[i]} handles. The latter accept arguments
4570 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
4571 * the resulting adapter.
4572 * <blockquote><pre>{@code
4573 * T target(P... p, A[i]... a[i], B... b);
4574 * A[i] filter[i](V[i]);
4575 * T adapter(P... p, V[i]... v[i], B... b) {
4576 * return target(p..., filter[i](v[i])..., b...);
4577 * }
4578 * }</pre></blockquote>
4579 * <p>
4580 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4581 * variable-arity method handle}, even if the original target method handle was.
4582 *
4583 * @param target the method handle to invoke after arguments are filtered
4584 * @param pos the position of the first argument to filter
4585 * @param filters method handles to call initially on filtered arguments
4586 * @return method handle which incorporates the specified argument filtering logic
4587 * @throws NullPointerException if the target is null
4588 * or if the {@code filters} array is null
4589 * @throws IllegalArgumentException if a non-null element of {@code filters}
4590 * does not match a corresponding argument type of target as described above,
4591 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
4592 * or if the resulting method handle's type would have
4593 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4594 */
4595 public static
4596 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
4597 // In method types arguments start at index 0, while the LF
4598 // editor have the MH receiver at position 0 - adjust appropriately.
4599 final int MH_RECEIVER_OFFSET = 1;
4600 filterArgumentsCheckArity(target, pos, filters);
4601 MethodHandle adapter = target;
4602
4603 // keep track of currently matched filters, as to optimize repeated filters
4604 int index = 0;
4605 int[] positions = new int[filters.length];
4606 MethodHandle filter = null;
4607
4608 // process filters in reverse order so that the invocation of
4609 // the resulting adapter will invoke the filters in left-to-right order
4610 for (int i = filters.length - 1; i >= 0; --i) {
4611 MethodHandle newFilter = filters[i];
4612 if (newFilter == null) continue; // ignore null elements of filters
4613
4614 // flush changes on update
4615 if (filter != newFilter) {
4616 if (filter != null) {
4617 if (index > 1) {
4618 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4619 } else {
4620 adapter = filterArgument(adapter, positions[0] - 1, filter);
4621 }
4622 }
4623 filter = newFilter;
4624 index = 0;
4625 }
4626
4627 filterArgumentChecks(target, pos + i, newFilter);
4628 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
4629 }
4630 if (index > 1) {
4631 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4632 } else if (index == 1) {
4633 adapter = filterArgument(adapter, positions[0] - 1, filter);
4634 }
4635 return adapter;
4636 }
4637
4638 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
4639 MethodType targetType = adapter.type();
4640 MethodType filterType = filter.type();
4641 BoundMethodHandle result = adapter.rebind();
4642 Class<?> newParamType = filterType.parameterType(0);
4643
4644 Class<?>[] ptypes = targetType.ptypes().clone();
4645 for (int pos : positions) {
4646 ptypes[pos - 1] = newParamType;
4647 }
4648 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
4649
4650 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
4651 return result.copyWithExtendL(newType, lform, filter);
4652 }
4653
4654 /*non-public*/ static
4655 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
4656 filterArgumentChecks(target, pos, filter);
4657 MethodType targetType = target.type();
4658 MethodType filterType = filter.type();
4659 BoundMethodHandle result = target.rebind();
4660 Class<?> newParamType = filterType.parameterType(0);
4661 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
4662 MethodType newType = targetType.changeParameterType(pos, newParamType);
4663 result = result.copyWithExtendL(newType, lform, filter);
4664 return result;
4665 }
4666
4667 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
4668 MethodType targetType = target.type();
4669 int maxPos = targetType.parameterCount();
4670 if (pos + filters.length > maxPos)
4671 throw newIllegalArgumentException("too many filters");
4672 }
4673
4674 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4675 MethodType targetType = target.type();
4676 MethodType filterType = filter.type();
4677 if (filterType.parameterCount() != 1
4678 || filterType.returnType() != targetType.parameterType(pos))
4679 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4680 }
4681
4682 /**
4683 * Adapts a target method handle by pre-processing
4684 * a sub-sequence of its arguments with a filter (another method handle).
4685 * The pre-processed arguments are replaced by the result (if any) of the
4686 * filter function.
4687 * The target is then called on the modified (usually shortened) argument list.
4688 * <p>
4689 * If the filter returns a value, the target must accept that value as
4690 * its argument in position {@code pos}, preceded and/or followed by
4691 * any arguments not passed to the filter.
4692 * If the filter returns void, the target must accept all arguments
4693 * not passed to the filter.
4694 * No arguments are reordered, and a result returned from the filter
4695 * replaces (in order) the whole subsequence of arguments originally
4696 * passed to the adapter.
4697 * <p>
4698 * The argument types (if any) of the filter
4699 * replace zero or one argument types of the target, at position {@code pos},
4700 * in the resulting adapted method handle.
4701 * The return type of the filter (if any) must be identical to the
4702 * argument type of the target at position {@code pos}, and that target argument
4703 * is supplied by the return value of the filter.
4704 * <p>
4705 * In all cases, {@code pos} must be greater than or equal to zero, and
4706 * {@code pos} must also be less than or equal to the target's arity.
4707 * <p><b>Example:</b>
4708 * <blockquote><pre>{@code
4709 import static java.lang.invoke.MethodHandles.*;
4710 import static java.lang.invoke.MethodType.*;
4711 ...
4712 MethodHandle deepToString = publicLookup()
4713 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
4714
4715 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
4716 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
4717
4718 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
4719 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
4720
4721 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
4722 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
4723 assertEquals("[top, [up, down], strange]",
4724 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
4725
4726 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
4727 assertEquals("[top, [up, down], [strange]]",
4728 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
4729
4730 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4731 assertEquals("[top, [[up, down, strange], charm], bottom]",
4732 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4733 * }</pre></blockquote>
4734 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4735 * represents the return type of the {@code target} and resulting adapter.
4736 * {@code V}/{@code v} stand for the return type and value of the
4737 * {@code filter}, which are also found in the signature and arguments of
4738 * the {@code target}, respectively, unless {@code V} is {@code void}.
4739 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4740 * and values preceding and following the collection position, {@code pos},
4741 * in the {@code target}'s signature. They also turn up in the resulting
4742 * adapter's signature and arguments, where they surround
4743 * {@code B}/{@code b}, which represent the parameter types and arguments
4744 * to the {@code filter} (if any).
4745 * <blockquote><pre>{@code
4746 * T target(A...,V,C...);
4747 * V filter(B...);
4748 * T adapter(A... a,B... b,C... c) {
4749 * V v = filter(b...);
4750 * return target(a...,v,c...);
4751 * }
4752 * // and if the filter has no arguments:
4753 * T target2(A...,V,C...);
4754 * V filter2();
4755 * T adapter2(A... a,C... c) {
4756 * V v = filter2();
4757 * return target2(a...,v,c...);
4758 * }
4759 * // and if the filter has a void return:
4760 * T target3(A...,C...);
4761 * void filter3(B...);
4762 * T adapter3(A... a,B... b,C... c) {
4763 * filter3(b...);
4764 * return target3(a...,c...);
4765 * }
4766 * }</pre></blockquote>
4767 * <p>
4768 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
4769 * one which first "folds" the affected arguments, and then drops them, in separate
4770 * steps as follows:
4771 * <blockquote><pre>{@code
4772 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4773 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4774 * }</pre></blockquote>
4775 * If the target method handle consumes no arguments besides than the result
4776 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4777 * is equivalent to {@code filterReturnValue(coll, mh)}.
4778 * If the filter method handle {@code coll} consumes one argument and produces
4779 * a non-void result, then {@code collectArguments(mh, N, coll)}
4780 * is equivalent to {@code filterArguments(mh, N, coll)}.
4781 * Other equivalences are possible but would require argument permutation.
4782 * <p>
4783 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4784 * variable-arity method handle}, even if the original target method handle was.
4785 *
4786 * @param target the method handle to invoke after filtering the subsequence of arguments
4787 * @param pos the position of the first adapter argument to pass to the filter,
4788 * and/or the target argument which receives the result of the filter
4789 * @param filter method handle to call on the subsequence of arguments
4790 * @return method handle which incorporates the specified argument subsequence filtering logic
4791 * @throws NullPointerException if either argument is null
4792 * @throws IllegalArgumentException if the return type of {@code filter}
4793 * is non-void and is not the same as the {@code pos} argument of the target,
4794 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4795 * or if the resulting method handle's type would have
4796 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4797 * @see MethodHandles#foldArguments
4798 * @see MethodHandles#filterArguments
4799 * @see MethodHandles#filterReturnValue
4800 */
4801 public static
4802 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4803 MethodType newType = collectArgumentsChecks(target, pos, filter);
4804 MethodType collectorType = filter.type();
4805 BoundMethodHandle result = target.rebind();
4806 LambdaForm lform;
4807 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4808 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4809 if (lform != null) {
4810 return result.copyWith(newType, lform);
4811 }
4812 }
4813 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4814 return result.copyWithExtendL(newType, lform, filter);
4815 }
4816
4817 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4818 MethodType targetType = target.type();
4819 MethodType filterType = filter.type();
4820 Class<?> rtype = filterType.returnType();
4821 List<Class<?>> filterArgs = filterType.parameterList();
4822 if (rtype == void.class) {
4823 return targetType.insertParameterTypes(pos, filterArgs);
4824 }
4825 if (rtype != targetType.parameterType(pos)) {
4826 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4827 }
4828 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4829 }
4830
4831 /**
4832 * Adapts a target method handle by post-processing
4833 * its return value (if any) with a filter (another method handle).
4834 * The result of the filter is returned from the adapter.
4835 * <p>
4836 * If the target returns a value, the filter must accept that value as
4837 * its only argument.
4838 * If the target returns void, the filter must accept no arguments.
4839 * <p>
4840 * The return type of the filter
4841 * replaces the return type of the target
4842 * in the resulting adapted method handle.
4843 * The argument type of the filter (if any) must be identical to the
4844 * return type of the target.
4845 * <p><b>Example:</b>
4846 * <blockquote><pre>{@code
4847 import static java.lang.invoke.MethodHandles.*;
4848 import static java.lang.invoke.MethodType.*;
4849 ...
4850 MethodHandle cat = lookup().findVirtual(String.class,
4851 "concat", methodType(String.class, String.class));
4852 MethodHandle length = lookup().findVirtual(String.class,
4853 "length", methodType(int.class));
4854 System.out.println((String) cat.invokeExact("x", "y")); // xy
4855 MethodHandle f0 = filterReturnValue(cat, length);
4856 System.out.println((int) f0.invokeExact("x", "y")); // 2
4857 * }</pre></blockquote>
4858 * <p>Here is pseudocode for the resulting adapter. In the code,
4859 * {@code T}/{@code t} represent the result type and value of the
4860 * {@code target}; {@code V}, the result type of the {@code filter}; and
4861 * {@code A}/{@code a}, the types and values of the parameters and arguments
4862 * of the {@code target} as well as the resulting adapter.
4863 * <blockquote><pre>{@code
4864 * T target(A...);
4865 * V filter(T);
4866 * V adapter(A... a) {
4867 * T t = target(a...);
4868 * return filter(t);
4869 * }
4870 * // and if the target has a void return:
4871 * void target2(A...);
4872 * V filter2();
4873 * V adapter2(A... a) {
4874 * target2(a...);
4875 * return filter2();
4876 * }
4877 * // and if the filter has a void return:
4878 * T target3(A...);
4879 * void filter3(V);
4880 * void adapter3(A... a) {
4881 * T t = target3(a...);
4882 * filter3(t);
4883 * }
4884 * }</pre></blockquote>
4885 * <p>
4886 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4887 * variable-arity method handle}, even if the original target method handle was.
4888 * @param target the method handle to invoke before filtering the return value
4889 * @param filter method handle to call on the return value
4890 * @return method handle which incorporates the specified return value filtering logic
4891 * @throws NullPointerException if either argument is null
4892 * @throws IllegalArgumentException if the argument list of {@code filter}
4893 * does not match the return type of target as described above
4894 */
4895 public static
4896 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4897 MethodType targetType = target.type();
4898 MethodType filterType = filter.type();
4899 filterReturnValueChecks(targetType, filterType);
4900 BoundMethodHandle result = target.rebind();
4901 BasicType rtype = BasicType.basicType(filterType.returnType());
4902 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4903 MethodType newType = targetType.changeReturnType(filterType.returnType());
4904 result = result.copyWithExtendL(newType, lform, filter);
4905 return result;
4906 }
4907
4908 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4909 Class<?> rtype = targetType.returnType();
4910 int filterValues = filterType.parameterCount();
4911 if (filterValues == 0
4912 ? (rtype != void.class)
4913 : (rtype != filterType.parameterType(0) || filterValues != 1))
4914 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4915 }
4916
4917 /**
4918 * Adapts a target method handle by pre-processing
4919 * some of its arguments, and then calling the target with
4920 * the result of the pre-processing, inserted into the original
4921 * sequence of arguments.
4922 * <p>
4923 * The pre-processing is performed by {@code combiner}, a second method handle.
4924 * Of the arguments passed to the adapter, the first {@code N} arguments
4925 * are copied to the combiner, which is then called.
4926 * (Here, {@code N} is defined as the parameter count of the combiner.)
4927 * After this, control passes to the target, with any result
4928 * from the combiner inserted before the original {@code N} incoming
4929 * arguments.
4930 * <p>
4931 * If the combiner returns a value, the first parameter type of the target
4932 * must be identical with the return type of the combiner, and the next
4933 * {@code N} parameter types of the target must exactly match the parameters
4934 * of the combiner.
4935 * <p>
4936 * If the combiner has a void return, no result will be inserted,
4937 * and the first {@code N} parameter types of the target
4938 * must exactly match the parameters of the combiner.
4939 * <p>
4940 * The resulting adapter is the same type as the target, except that the
4941 * first parameter type is dropped,
4942 * if it corresponds to the result of the combiner.
4943 * <p>
4944 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4945 * that either the combiner or the target does not wish to receive.
4946 * If some of the incoming arguments are destined only for the combiner,
4947 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4948 * arguments will not need to be live on the stack on entry to the
4949 * target.)
4950 * <p><b>Example:</b>
4951 * <blockquote><pre>{@code
4952 import static java.lang.invoke.MethodHandles.*;
4953 import static java.lang.invoke.MethodType.*;
4954 ...
4955 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4956 "println", methodType(void.class, String.class))
4957 .bindTo(System.out);
4958 MethodHandle cat = lookup().findVirtual(String.class,
4959 "concat", methodType(String.class, String.class));
4960 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4961 MethodHandle catTrace = foldArguments(cat, trace);
4962 // also prints "boo":
4963 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4964 * }</pre></blockquote>
4965 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4966 * represents the result type of the {@code target} and resulting adapter.
4967 * {@code V}/{@code v} represent the type and value of the parameter and argument
4968 * of {@code target} that precedes the folding position; {@code V} also is
4969 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4970 * types and values of the {@code N} parameters and arguments at the folding
4971 * position. {@code B}/{@code b} represent the types and values of the
4972 * {@code target} parameters and arguments that follow the folded parameters
4973 * and arguments.
4974 * <blockquote><pre>{@code
4975 * // there are N arguments in A...
4976 * T target(V, A[N]..., B...);
4977 * V combiner(A...);
4978 * T adapter(A... a, B... b) {
4979 * V v = combiner(a...);
4980 * return target(v, a..., b...);
4981 * }
4982 * // and if the combiner has a void return:
4983 * T target2(A[N]..., B...);
4984 * void combiner2(A...);
4985 * T adapter2(A... a, B... b) {
4986 * combiner2(a...);
4987 * return target2(a..., b...);
4988 * }
4989 * }</pre></blockquote>
4990 * <p>
4991 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4992 * variable-arity method handle}, even if the original target method handle was.
4993 * @param target the method handle to invoke after arguments are combined
4994 * @param combiner method handle to call initially on the incoming arguments
4995 * @return method handle which incorporates the specified argument folding logic
4996 * @throws NullPointerException if either argument is null
4997 * @throws IllegalArgumentException if {@code combiner}'s return type
4998 * is non-void and not the same as the first argument type of
4999 * the target, or if the initial {@code N} argument types
5000 * of the target
5001 * (skipping one matching the {@code combiner}'s return type)
5002 * are not identical with the argument types of {@code combiner}
5003 */
5004 public static
5005 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5006 return foldArguments(target, 0, combiner);
5007 }
5008
5009 /**
5010 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5011 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5012 * before the folded arguments.
5013 * <p>
5014 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5015 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5016 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5017 * 0.
5018 *
5019 * @apiNote Example:
5020 * <blockquote><pre>{@code
5021 import static java.lang.invoke.MethodHandles.*;
5022 import static java.lang.invoke.MethodType.*;
5023 ...
5024 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5025 "println", methodType(void.class, String.class))
5026 .bindTo(System.out);
5027 MethodHandle cat = lookup().findVirtual(String.class,
5028 "concat", methodType(String.class, String.class));
5029 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5030 MethodHandle catTrace = foldArguments(cat, 1, trace);
5031 // also prints "jum":
5032 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5033 * }</pre></blockquote>
5034 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5035 * represents the result type of the {@code target} and resulting adapter.
5036 * {@code V}/{@code v} represent the type and value of the parameter and argument
5037 * of {@code target} that precedes the folding position; {@code V} also is
5038 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5039 * types and values of the {@code N} parameters and arguments at the folding
5040 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5041 * and values of the {@code target} parameters and arguments that precede and
5042 * follow the folded parameters and arguments starting at {@code pos},
5043 * respectively.
5044 * <blockquote><pre>{@code
5045 * // there are N arguments in A...
5046 * T target(Z..., V, A[N]..., B...);
5047 * V combiner(A...);
5048 * T adapter(Z... z, A... a, B... b) {
5049 * V v = combiner(a...);
5050 * return target(z..., v, a..., b...);
5051 * }
5052 * // and if the combiner has a void return:
5053 * T target2(Z..., A[N]..., B...);
5054 * void combiner2(A...);
5055 * T adapter2(Z... z, A... a, B... b) {
5056 * combiner2(a...);
5057 * return target2(z..., a..., b...);
5058 * }
5059 * }</pre></blockquote>
5060 * <p>
5061 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5062 * variable-arity method handle}, even if the original target method handle was.
5063 *
5064 * @param target the method handle to invoke after arguments are combined
5065 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5066 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5067 * @param combiner method handle to call initially on the incoming arguments
5068 * @return method handle which incorporates the specified argument folding logic
5069 * @throws NullPointerException if either argument is null
5070 * @throws IllegalArgumentException if either of the following two conditions holds:
5071 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5072 * {@code pos} of the target signature;
5073 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5074 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5075 *
5076 * @see #foldArguments(MethodHandle, MethodHandle)
5077 * @since 9
5078 */
5079 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5080 MethodType targetType = target.type();
5081 MethodType combinerType = combiner.type();
5082 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5083 BoundMethodHandle result = target.rebind();
5084 boolean dropResult = rtype == void.class;
5085 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5086 MethodType newType = targetType;
5087 if (!dropResult) {
5088 newType = newType.dropParameterTypes(pos, pos + 1);
5089 }
5090 result = result.copyWithExtendL(newType, lform, combiner);
5091 return result;
5092 }
5093
5094 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5095 int foldArgs = combinerType.parameterCount();
5096 Class<?> rtype = combinerType.returnType();
5097 int foldVals = rtype == void.class ? 0 : 1;
5098 int afterInsertPos = foldPos + foldVals;
5099 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5100 if (ok) {
5101 for (int i = 0; i < foldArgs; i++) {
5102 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5103 ok = false;
5104 break;
5105 }
5106 }
5107 }
5108 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5109 ok = false;
5110 if (!ok)
5111 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5112 return rtype;
5113 }
5114
5115 /**
5116 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5117 * of the pre-processing replacing the argument at the given position.
5118 *
5119 * @param target the method handle to invoke after arguments are combined
5120 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5121 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5122 * @param combiner method handle to call initially on the incoming arguments
5123 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5124 * @return method handle which incorporates the specified argument folding logic
5125 * @throws NullPointerException if either argument is null
5126 * @throws IllegalArgumentException if either of the following two conditions holds:
5127 * (1) {@code combiner}'s return type is not the same as the argument type at position
5128 * {@code pos} of the target signature;
5129 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5130 * not identical with the argument types of {@code combiner}.
5131 */
5132 /*non-public*/ static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5133 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5134 }
5135
5136 /**
5137 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5138 * the pre-processing inserted into the original sequence of arguments at the given position.
5139 *
5140 * @param target the method handle to invoke after arguments are combined
5141 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5142 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5143 * @param combiner method handle to call initially on the incoming arguments
5144 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5145 * @return method handle which incorporates the specified argument folding logic
5146 * @throws NullPointerException if either argument is null
5147 * @throws IllegalArgumentException if either of the following two conditions holds:
5148 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5149 * {@code pos} of the target signature;
5150 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5151 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5152 * with the argument types of {@code combiner}.
5153 */
5154 /*non-public*/ static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5155 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5156 }
5157
5158 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5159 MethodType targetType = target.type();
5160 MethodType combinerType = combiner.type();
5161 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5162 BoundMethodHandle result = target.rebind();
5163
5164 MethodType newType = targetType;
5165 LambdaForm lform;
5166 if (filter) {
5167 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5168 } else {
5169 boolean dropResult = rtype == void.class;
5170 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5171 if (!dropResult) {
5172 newType = newType.dropParameterTypes(position, position + 1);
5173 }
5174 }
5175 result = result.copyWithExtendL(newType, lform, combiner);
5176 return result;
5177 }
5178
5179 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5180 int combinerArgs = combinerType.parameterCount();
5181 if (argPos.length != combinerArgs) {
5182 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5183 }
5184 Class<?> rtype = combinerType.returnType();
5185
5186 for (int i = 0; i < combinerArgs; i++) {
5187 int arg = argPos[i];
5188 if (arg < 0 || arg > targetType.parameterCount()) {
5189 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5190 }
5191 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5192 throw newIllegalArgumentException("target argument type at position " + arg
5193 + " must match combiner argument type at index " + i + ": " + targetType
5194 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5195 }
5196 }
5197 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5198 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5199 }
5200 return rtype;
5201 }
5202
5203 /**
5204 * Makes a method handle which adapts a target method handle,
5205 * by guarding it with a test, a boolean-valued method handle.
5206 * If the guard fails, a fallback handle is called instead.
5207 * All three method handles must have the same corresponding
5208 * argument and return types, except that the return type
5209 * of the test must be boolean, and the test is allowed
5210 * to have fewer arguments than the other two method handles.
5211 * <p>
5212 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5213 * represents the uniform result type of the three involved handles;
5214 * {@code A}/{@code a}, the types and values of the {@code target}
5215 * parameters and arguments that are consumed by the {@code test}; and
5216 * {@code B}/{@code b}, those types and values of the {@code target}
5217 * parameters and arguments that are not consumed by the {@code test}.
5218 * <blockquote><pre>{@code
5219 * boolean test(A...);
5220 * T target(A...,B...);
5221 * T fallback(A...,B...);
5222 * T adapter(A... a,B... b) {
5223 * if (test(a...))
5224 * return target(a..., b...);
5225 * else
5226 * return fallback(a..., b...);
5227 * }
5228 * }</pre></blockquote>
5229 * Note that the test arguments ({@code a...} in the pseudocode) cannot
5230 * be modified by execution of the test, and so are passed unchanged
5231 * from the caller to the target or fallback as appropriate.
5232 * @param test method handle used for test, must return boolean
5233 * @param target method handle to call if test passes
5234 * @param fallback method handle to call if test fails
5235 * @return method handle which incorporates the specified if/then/else logic
5236 * @throws NullPointerException if any argument is null
5237 * @throws IllegalArgumentException if {@code test} does not return boolean,
5238 * or if all three method types do not match (with the return
5239 * type of {@code test} changed to match that of the target).
5240 */
5241 public static
5242 MethodHandle guardWithTest(MethodHandle test,
5243 MethodHandle target,
5244 MethodHandle fallback) {
5245 MethodType gtype = test.type();
5246 MethodType ttype = target.type();
5247 MethodType ftype = fallback.type();
5248 if (!ttype.equals(ftype))
5249 throw misMatchedTypes("target and fallback types", ttype, ftype);
5250 if (gtype.returnType() != boolean.class)
5251 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
5252 List<Class<?>> targs = ttype.parameterList();
5253 test = dropArgumentsToMatch(test, 0, targs, 0, true);
5254 if (test == null) {
5255 throw misMatchedTypes("target and test types", ttype, gtype);
5256 }
5257 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
5258 }
5259
5260 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
5261 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
5262 }
5263
5264 /**
5265 * Makes a method handle which adapts a target method handle,
5266 * by running it inside an exception handler.
5267 * If the target returns normally, the adapter returns that value.
5268 * If an exception matching the specified type is thrown, the fallback
5269 * handle is called instead on the exception, plus the original arguments.
5270 * <p>
5271 * The target and handler must have the same corresponding
5272 * argument and return types, except that handler may omit trailing arguments
5273 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
5274 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
5275 * <p>
5276 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5277 * represents the return type of the {@code target} and {@code handler},
5278 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
5279 * the types and values of arguments to the resulting handle consumed by
5280 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
5281 * resulting handle discarded by {@code handler}.
5282 * <blockquote><pre>{@code
5283 * T target(A..., B...);
5284 * T handler(ExType, A...);
5285 * T adapter(A... a, B... b) {
5286 * try {
5287 * return target(a..., b...);
5288 * } catch (ExType ex) {
5289 * return handler(ex, a...);
5290 * }
5291 * }
5292 * }</pre></blockquote>
5293 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5294 * be modified by execution of the target, and so are passed unchanged
5295 * from the caller to the handler, if the handler is invoked.
5296 * <p>
5297 * The target and handler must return the same type, even if the handler
5298 * always throws. (This might happen, for instance, because the handler
5299 * is simulating a {@code finally} clause).
5300 * To create such a throwing handler, compose the handler creation logic
5301 * with {@link #throwException throwException},
5302 * in order to create a method handle of the correct return type.
5303 * @param target method handle to call
5304 * @param exType the type of exception which the handler will catch
5305 * @param handler method handle to call if a matching exception is thrown
5306 * @return method handle which incorporates the specified try/catch logic
5307 * @throws NullPointerException if any argument is null
5308 * @throws IllegalArgumentException if {@code handler} does not accept
5309 * the given exception type, or if the method handle types do
5310 * not match in their return types and their
5311 * corresponding parameters
5312 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
5313 */
5314 public static
5315 MethodHandle catchException(MethodHandle target,
5316 Class<? extends Throwable> exType,
5317 MethodHandle handler) {
5318 MethodType ttype = target.type();
5319 MethodType htype = handler.type();
5320 if (!Throwable.class.isAssignableFrom(exType))
5321 throw new ClassCastException(exType.getName());
5322 if (htype.parameterCount() < 1 ||
5323 !htype.parameterType(0).isAssignableFrom(exType))
5324 throw newIllegalArgumentException("handler does not accept exception type "+exType);
5325 if (htype.returnType() != ttype.returnType())
5326 throw misMatchedTypes("target and handler return types", ttype, htype);
5327 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
5328 if (handler == null) {
5329 throw misMatchedTypes("target and handler types", ttype, htype);
5330 }
5331 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
5332 }
5333
5334 /**
5335 * Produces a method handle which will throw exceptions of the given {@code exType}.
5336 * The method handle will accept a single argument of {@code exType},
5337 * and immediately throw it as an exception.
5338 * The method type will nominally specify a return of {@code returnType}.
5339 * The return type may be anything convenient: It doesn't matter to the
5340 * method handle's behavior, since it will never return normally.
5341 * @param returnType the return type of the desired method handle
5342 * @param exType the parameter type of the desired method handle
5343 * @return method handle which can throw the given exceptions
5344 * @throws NullPointerException if either argument is null
5345 */
5346 public static
5347 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
5348 if (!Throwable.class.isAssignableFrom(exType))
5349 throw new ClassCastException(exType.getName());
5350 return MethodHandleImpl.throwException(methodType(returnType, exType));
5351 }
5352
5353 /**
5354 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
5355 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
5356 * delivers the loop's result, which is the return value of the resulting handle.
5357 * <p>
5358 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
5359 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
5360 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
5361 * terms of method handles, each clause will specify up to four independent actions:<ul>
5362 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
5363 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
5364 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
5365 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
5366 * </ul>
5367 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
5368 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
5369 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
5370 * <p>
5371 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
5372 * this case. See below for a detailed description.
5373 * <p>
5374 * <em>Parameters optional everywhere:</em>
5375 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
5376 * As an exception, the init functions cannot take any {@code v} parameters,
5377 * because those values are not yet computed when the init functions are executed.
5378 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
5379 * In fact, any clause function may take no arguments at all.
5380 * <p>
5381 * <em>Loop parameters:</em>
5382 * A clause function may take all the iteration variable values it is entitled to, in which case
5383 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
5384 * with their types and values notated as {@code (A...)} and {@code (a...)}.
5385 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
5386 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
5387 * init function is automatically a loop parameter {@code a}.)
5388 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
5389 * These loop parameters act as loop-invariant values visible across the whole loop.
5390 * <p>
5391 * <em>Parameters visible everywhere:</em>
5392 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
5393 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
5394 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
5395 * Most clause functions will not need all of this information, but they will be formally connected to it
5396 * as if by {@link #dropArguments}.
5397 * <a id="astar"></a>
5398 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
5399 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
5400 * In that notation, the general form of an init function parameter list
5401 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
5402 * <p>
5403 * <em>Checking clause structure:</em>
5404 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
5405 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
5406 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
5407 * met by the inputs to the loop combinator.
5408 * <p>
5409 * <em>Effectively identical sequences:</em>
5410 * <a id="effid"></a>
5411 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
5412 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
5413 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
5414 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
5415 * that longest list.
5416 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
5417 * and the same is true if more sequences of the form {@code (V... A*)} are added.
5418 * <p>
5419 * <em>Step 0: Determine clause structure.</em><ol type="a">
5420 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
5421 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
5422 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
5423 * four. Padding takes place by appending elements to the array.
5424 * <li>Clauses with all {@code null}s are disregarded.
5425 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
5426 * </ol>
5427 * <p>
5428 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
5429 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
5430 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
5431 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
5432 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
5433 * iteration variable type.
5434 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
5435 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
5436 * </ol>
5437 * <p>
5438 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
5439 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
5440 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
5441 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
5442 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
5443 * (These types will be checked in step 2, along with all the clause function types.)
5444 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
5445 * <li>All of the collected parameter lists must be effectively identical.
5446 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
5447 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
5448 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
5449 * the "internal parameter list".
5450 * </ul>
5451 * <p>
5452 * <em>Step 1C: Determine loop return type.</em><ol type="a">
5453 * <li>Examine fini function return types, disregarding omitted fini functions.
5454 * <li>If there are no fini functions, the loop return type is {@code void}.
5455 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
5456 * type.
5457 * </ol>
5458 * <p>
5459 * <em>Step 1D: Check other types.</em><ol type="a">
5460 * <li>There must be at least one non-omitted pred function.
5461 * <li>Every non-omitted pred function must have a {@code boolean} return type.
5462 * </ol>
5463 * <p>
5464 * <em>Step 2: Determine parameter lists.</em><ol type="a">
5465 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
5466 * <li>The parameter list for init functions will be adjusted to the external parameter list.
5467 * (Note that their parameter lists are already effectively identical to this list.)
5468 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
5469 * effectively identical to the internal parameter list {@code (V... A...)}.
5470 * </ol>
5471 * <p>
5472 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
5473 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
5474 * type.
5475 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
5476 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
5477 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
5478 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
5479 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
5480 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
5481 * loop return type.
5482 * </ol>
5483 * <p>
5484 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
5485 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
5486 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
5487 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
5488 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
5489 * pad out the end of the list.
5490 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
5491 * </ol>
5492 * <p>
5493 * <em>Final observations.</em><ol type="a">
5494 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
5495 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
5496 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
5497 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
5498 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
5499 * <li>Each pair of init and step functions agrees in their return type {@code V}.
5500 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
5501 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
5502 * </ol>
5503 * <p>
5504 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
5505 * <ul>
5506 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
5507 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
5508 * (Only one {@code Pn} has to be non-{@code null}.)
5509 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
5510 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
5511 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
5512 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
5513 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
5514 * the resulting loop handle's parameter types {@code (A...)}.
5515 * </ul>
5516 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
5517 * which is natural if most of the loop computation happens in the steps. For some loops,
5518 * the burden of computation might be heaviest in the pred functions, and so the pred functions
5519 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
5520 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
5521 * where the init functions will need the extra parameters. For such reasons, the rules for
5522 * determining these parameters are as symmetric as possible, across all clause parts.
5523 * In general, the loop parameters function as common invariant values across the whole
5524 * loop, while the iteration variables function as common variant values, or (if there is
5525 * no step function) as internal loop invariant temporaries.
5526 * <p>
5527 * <em>Loop execution.</em><ol type="a">
5528 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
5529 * every clause function. These locals are loop invariant.
5530 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
5531 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
5532 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
5533 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
5534 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
5535 * (in argument order).
5536 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
5537 * returns {@code false}.
5538 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
5539 * sequence {@code (v...)} of loop variables.
5540 * The updated value is immediately visible to all subsequent function calls.
5541 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
5542 * (of type {@code R}) is returned from the loop as a whole.
5543 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
5544 * except by throwing an exception.
5545 * </ol>
5546 * <p>
5547 * <em>Usage tips.</em>
5548 * <ul>
5549 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
5550 * sometimes a step function only needs to observe the current value of its own variable.
5551 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
5552 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
5553 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
5554 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
5555 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
5556 * <li>If some of the clause functions are virtual methods on an instance, the instance
5557 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
5558 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
5559 * will be the first iteration variable value, and it will be easy to use virtual
5560 * methods as clause parts, since all of them will take a leading instance reference matching that value.
5561 * </ul>
5562 * <p>
5563 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
5564 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
5565 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
5566 * <blockquote><pre>{@code
5567 * V... init...(A...);
5568 * boolean pred...(V..., A...);
5569 * V... step...(V..., A...);
5570 * R fini...(V..., A...);
5571 * R loop(A... a) {
5572 * V... v... = init...(a...);
5573 * for (;;) {
5574 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
5575 * v = s(v..., a...);
5576 * if (!p(v..., a...)) {
5577 * return f(v..., a...);
5578 * }
5579 * }
5580 * }
5581 * }
5582 * }</pre></blockquote>
5583 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
5584 * to their full length, even though individual clause functions may neglect to take them all.
5585 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
5586 *
5587 * @apiNote Example:
5588 * <blockquote><pre>{@code
5589 * // iterative implementation of the factorial function as a loop handle
5590 * static int one(int k) { return 1; }
5591 * static int inc(int i, int acc, int k) { return i + 1; }
5592 * static int mult(int i, int acc, int k) { return i * acc; }
5593 * static boolean pred(int i, int acc, int k) { return i < k; }
5594 * static int fin(int i, int acc, int k) { return acc; }
5595 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5596 * // null initializer for counter, should initialize to 0
5597 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5598 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5599 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5600 * assertEquals(120, loop.invoke(5));
5601 * }</pre></blockquote>
5602 * The same example, dropping arguments and using combinators:
5603 * <blockquote><pre>{@code
5604 * // simplified implementation of the factorial function as a loop handle
5605 * static int inc(int i) { return i + 1; } // drop acc, k
5606 * static int mult(int i, int acc) { return i * acc; } //drop k
5607 * static boolean cmp(int i, int k) { return i < k; }
5608 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
5609 * // null initializer for counter, should initialize to 0
5610 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5611 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
5612 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
5613 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5614 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5615 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5616 * assertEquals(720, loop.invoke(6));
5617 * }</pre></blockquote>
5618 * A similar example, using a helper object to hold a loop parameter:
5619 * <blockquote><pre>{@code
5620 * // instance-based implementation of the factorial function as a loop handle
5621 * static class FacLoop {
5622 * final int k;
5623 * FacLoop(int k) { this.k = k; }
5624 * int inc(int i) { return i + 1; }
5625 * int mult(int i, int acc) { return i * acc; }
5626 * boolean pred(int i) { return i < k; }
5627 * int fin(int i, int acc) { return acc; }
5628 * }
5629 * // assume MH_FacLoop is a handle to the constructor
5630 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5631 * // null initializer for counter, should initialize to 0
5632 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5633 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
5634 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5635 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5636 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
5637 * assertEquals(5040, loop.invoke(7));
5638 * }</pre></blockquote>
5639 *
5640 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
5641 *
5642 * @return a method handle embodying the looping behavior as defined by the arguments.
5643 *
5644 * @throws IllegalArgumentException in case any of the constraints described above is violated.
5645 *
5646 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
5647 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5648 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
5649 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
5650 * @since 9
5651 */
5652 public static MethodHandle loop(MethodHandle[]... clauses) {
5653 // Step 0: determine clause structure.
5654 loopChecks0(clauses);
5655
5656 List<MethodHandle> init = new ArrayList<>();
5657 List<MethodHandle> step = new ArrayList<>();
5658 List<MethodHandle> pred = new ArrayList<>();
5659 List<MethodHandle> fini = new ArrayList<>();
5660
5661 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
5662 init.add(clause[0]); // all clauses have at least length 1
5663 step.add(clause.length <= 1 ? null : clause[1]);
5664 pred.add(clause.length <= 2 ? null : clause[2]);
5665 fini.add(clause.length <= 3 ? null : clause[3]);
5666 });
5667
5668 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
5669 final int nclauses = init.size();
5670
5671 // Step 1A: determine iteration variables (V...).
5672 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
5673 for (int i = 0; i < nclauses; ++i) {
5674 MethodHandle in = init.get(i);
5675 MethodHandle st = step.get(i);
5676 if (in == null && st == null) {
5677 iterationVariableTypes.add(void.class);
5678 } else if (in != null && st != null) {
5679 loopChecks1a(i, in, st);
5680 iterationVariableTypes.add(in.type().returnType());
5681 } else {
5682 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
5683 }
5684 }
5685 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
5686 collect(Collectors.toList());
5687
5688 // Step 1B: determine loop parameters (A...).
5689 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
5690 loopChecks1b(init, commonSuffix);
5691
5692 // Step 1C: determine loop return type.
5693 // Step 1D: check other types.
5694 // local variable required here; see JDK-8223553
5695 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
5696 .map(MethodType::returnType);
5697 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
5698 loopChecks1cd(pred, fini, loopReturnType);
5699
5700 // Step 2: determine parameter lists.
5701 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
5702 commonParameterSequence.addAll(commonSuffix);
5703 loopChecks2(step, pred, fini, commonParameterSequence);
5704
5705 // Step 3: fill in omitted functions.
5706 for (int i = 0; i < nclauses; ++i) {
5707 Class<?> t = iterationVariableTypes.get(i);
5708 if (init.get(i) == null) {
5709 init.set(i, empty(methodType(t, commonSuffix)));
5710 }
5711 if (step.get(i) == null) {
5712 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
5713 }
5714 if (pred.get(i) == null) {
5715 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
5716 }
5717 if (fini.get(i) == null) {
5718 fini.set(i, empty(methodType(t, commonParameterSequence)));
5719 }
5720 }
5721
5722 // Step 4: fill in missing parameter types.
5723 // Also convert all handles to fixed-arity handles.
5724 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
5725 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
5726 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
5727 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
5728
5729 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
5730 allMatch(pl -> pl.equals(commonSuffix));
5731 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5732 allMatch(pl -> pl.equals(commonParameterSequence));
5733
5734 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5735 }
5736
5737 private static void loopChecks0(MethodHandle[][] clauses) {
5738 if (clauses == null || clauses.length == 0) {
5739 throw newIllegalArgumentException("null or no clauses passed");
5740 }
5741 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5742 throw newIllegalArgumentException("null clauses are not allowed");
5743 }
5744 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5745 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5746 }
5747 }
5748
5749 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5750 if (in.type().returnType() != st.type().returnType()) {
5751 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5752 st.type().returnType());
5753 }
5754 }
5755
5756 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
5757 final List<Class<?>> empty = List.of();
5758 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
5759 // take only those that can contribute to a common suffix because they are longer than the prefix
5760 map(MethodHandle::type).
5761 filter(t -> t.parameterCount() > skipSize).
5762 map(MethodType::parameterList).
5763 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5764 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
5765 }
5766
5767 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
5768 final List<Class<?>> empty = List.of();
5769 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5770 }
5771
5772 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
5773 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
5774 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
5775 return longestParameterList(Arrays.asList(longest1, longest2));
5776 }
5777
5778 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
5779 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
5780 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
5781 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
5782 " (common suffix: " + commonSuffix + ")");
5783 }
5784 }
5785
5786 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
5787 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5788 anyMatch(t -> t != loopReturnType)) {
5789 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
5790 loopReturnType + ")");
5791 }
5792
5793 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5794 throw newIllegalArgumentException("no predicate found", pred);
5795 }
5796 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5797 anyMatch(t -> t != boolean.class)) {
5798 throw newIllegalArgumentException("predicates must have boolean return type", pred);
5799 }
5800 }
5801
5802 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5803 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5804 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
5805 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5806 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5807 }
5808 }
5809
5810 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
5811 return hs.stream().map(h -> {
5812 int pc = h.type().parameterCount();
5813 int tpsize = targetParams.size();
5814 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5815 }).collect(Collectors.toList());
5816 }
5817
5818 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5819 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5820 }
5821
5822 /**
5823 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5824 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5825 * <p>
5826 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5827 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5828 * evaluates to {@code true}).
5829 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5830 * <p>
5831 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5832 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5833 * and updated with the value returned from its invocation. The result of loop execution will be
5834 * the final value of the additional loop-local variable (if present).
5835 * <p>
5836 * The following rules hold for these argument handles:<ul>
5837 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5838 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5839 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5840 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5841 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5842 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5843 * It will constrain the parameter lists of the other loop parts.
5844 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5845 * list {@code (A...)} is called the <em>external parameter list</em>.
5846 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5847 * additional state variable of the loop.
5848 * The body must both accept and return a value of this type {@code V}.
5849 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5850 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5851 * <a href="MethodHandles.html#effid">effectively identical</a>
5852 * to the external parameter list {@code (A...)}.
5853 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5854 * {@linkplain #empty default value}.
5855 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5856 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5857 * effectively identical to the internal parameter list.
5858 * </ul>
5859 * <p>
5860 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5861 * <li>The loop handle's result type is the result type {@code V} of the body.
5862 * <li>The loop handle's parameter types are the types {@code (A...)},
5863 * from the external parameter list.
5864 * </ul>
5865 * <p>
5866 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5867 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5868 * passed to the loop.
5869 * <blockquote><pre>{@code
5870 * V init(A...);
5871 * boolean pred(V, A...);
5872 * V body(V, A...);
5873 * V whileLoop(A... a...) {
5874 * V v = init(a...);
5875 * while (pred(v, a...)) {
5876 * v = body(v, a...);
5877 * }
5878 * return v;
5879 * }
5880 * }</pre></blockquote>
5881 *
5882 * @apiNote Example:
5883 * <blockquote><pre>{@code
5884 * // implement the zip function for lists as a loop handle
5885 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5886 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5887 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5888 * zip.add(a.next());
5889 * zip.add(b.next());
5890 * return zip;
5891 * }
5892 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5893 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5894 * List<String> a = Arrays.asList("a", "b", "c", "d");
5895 * List<String> b = Arrays.asList("e", "f", "g", "h");
5896 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5897 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5898 * }</pre></blockquote>
5899 *
5900 *
5901 * @apiNote The implementation of this method can be expressed as follows:
5902 * <blockquote><pre>{@code
5903 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5904 * MethodHandle fini = (body.type().returnType() == void.class
5905 * ? null : identity(body.type().returnType()));
5906 * MethodHandle[]
5907 * checkExit = { null, null, pred, fini },
5908 * varBody = { init, body };
5909 * return loop(checkExit, varBody);
5910 * }
5911 * }</pre></blockquote>
5912 *
5913 * @param init optional initializer, providing the initial value of the loop variable.
5914 * May be {@code null}, implying a default initial value. See above for other constraints.
5915 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5916 * above for other constraints.
5917 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5918 * See above for other constraints.
5919 *
5920 * @return a method handle implementing the {@code while} loop as described by the arguments.
5921 * @throws IllegalArgumentException if the rules for the arguments are violated.
5922 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5923 *
5924 * @see #loop(MethodHandle[][])
5925 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5926 * @since 9
5927 */
5928 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5929 whileLoopChecks(init, pred, body);
5930 MethodHandle fini = identityOrVoid(body.type().returnType());
5931 MethodHandle[] checkExit = { null, null, pred, fini };
5932 MethodHandle[] varBody = { init, body };
5933 return loop(checkExit, varBody);
5934 }
5935
5936 /**
5937 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5938 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5939 * <p>
5940 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5941 * method will, in each iteration, first execute its body and then evaluate the predicate.
5942 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5943 * <p>
5944 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5945 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5946 * and updated with the value returned from its invocation. The result of loop execution will be
5947 * the final value of the additional loop-local variable (if present).
5948 * <p>
5949 * The following rules hold for these argument handles:<ul>
5950 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5951 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5952 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5953 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5954 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5955 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5956 * It will constrain the parameter lists of the other loop parts.
5957 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5958 * list {@code (A...)} is called the <em>external parameter list</em>.
5959 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5960 * additional state variable of the loop.
5961 * The body must both accept and return a value of this type {@code V}.
5962 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5963 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5964 * <a href="MethodHandles.html#effid">effectively identical</a>
5965 * to the external parameter list {@code (A...)}.
5966 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5967 * {@linkplain #empty default value}.
5968 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5969 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5970 * effectively identical to the internal parameter list.
5971 * </ul>
5972 * <p>
5973 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5974 * <li>The loop handle's result type is the result type {@code V} of the body.
5975 * <li>The loop handle's parameter types are the types {@code (A...)},
5976 * from the external parameter list.
5977 * </ul>
5978 * <p>
5979 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5980 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5981 * passed to the loop.
5982 * <blockquote><pre>{@code
5983 * V init(A...);
5984 * boolean pred(V, A...);
5985 * V body(V, A...);
5986 * V doWhileLoop(A... a...) {
5987 * V v = init(a...);
5988 * do {
5989 * v = body(v, a...);
5990 * } while (pred(v, a...));
5991 * return v;
5992 * }
5993 * }</pre></blockquote>
5994 *
5995 * @apiNote Example:
5996 * <blockquote><pre>{@code
5997 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5998 * static int zero(int limit) { return 0; }
5999 * static int step(int i, int limit) { return i + 1; }
6000 * static boolean pred(int i, int limit) { return i < limit; }
6001 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6002 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6003 * assertEquals(23, loop.invoke(23));
6004 * }</pre></blockquote>
6005 *
6006 *
6007 * @apiNote The implementation of this method can be expressed as follows:
6008 * <blockquote><pre>{@code
6009 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6010 * MethodHandle fini = (body.type().returnType() == void.class
6011 * ? null : identity(body.type().returnType()));
6012 * MethodHandle[] clause = { init, body, pred, fini };
6013 * return loop(clause);
6014 * }
6015 * }</pre></blockquote>
6016 *
6017 * @param init optional initializer, providing the initial value of the loop variable.
6018 * May be {@code null}, implying a default initial value. See above for other constraints.
6019 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6020 * See above for other constraints.
6021 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6022 * above for other constraints.
6023 *
6024 * @return a method handle implementing the {@code while} loop as described by the arguments.
6025 * @throws IllegalArgumentException if the rules for the arguments are violated.
6026 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6027 *
6028 * @see #loop(MethodHandle[][])
6029 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6030 * @since 9
6031 */
6032 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6033 whileLoopChecks(init, pred, body);
6034 MethodHandle fini = identityOrVoid(body.type().returnType());
6035 MethodHandle[] clause = {init, body, pred, fini };
6036 return loop(clause);
6037 }
6038
6039 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6040 Objects.requireNonNull(pred);
6041 Objects.requireNonNull(body);
6042 MethodType bodyType = body.type();
6043 Class<?> returnType = bodyType.returnType();
6044 List<Class<?>> innerList = bodyType.parameterList();
6045 List<Class<?>> outerList = innerList;
6046 if (returnType == void.class) {
6047 // OK
6048 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
6049 // leading V argument missing => error
6050 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6051 throw misMatchedTypes("body function", bodyType, expected);
6052 } else {
6053 outerList = innerList.subList(1, innerList.size());
6054 }
6055 MethodType predType = pred.type();
6056 if (predType.returnType() != boolean.class ||
6057 !predType.effectivelyIdenticalParameters(0, innerList)) {
6058 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6059 }
6060 if (init != null) {
6061 MethodType initType = init.type();
6062 if (initType.returnType() != returnType ||
6063 !initType.effectivelyIdenticalParameters(0, outerList)) {
6064 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6065 }
6066 }
6067 }
6068
6069 /**
6070 * Constructs a loop that runs a given number of iterations.
6071 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6072 * <p>
6073 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6074 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6075 * It will be initialized to 0 and incremented by 1 in each iteration.
6076 * <p>
6077 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6078 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6079 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6080 * <p>
6081 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6082 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6083 * iteration variable.
6084 * The result of the loop handle execution will be the final {@code V} value of that variable
6085 * (or {@code void} if there is no {@code V} variable).
6086 * <p>
6087 * The following rules hold for the argument handles:<ul>
6088 * <li>The {@code iterations} handle must not be {@code null}, and must return
6089 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6090 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6091 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6092 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6093 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6094 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6095 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6096 * of types called the <em>internal parameter list</em>.
6097 * It will constrain the parameter lists of the other loop parts.
6098 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6099 * with no additional {@code A} types, then the internal parameter list is extended by
6100 * the argument types {@code A...} of the {@code iterations} handle.
6101 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6102 * list {@code (A...)} is called the <em>external parameter list</em>.
6103 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6104 * additional state variable of the loop.
6105 * The body must both accept a leading parameter and return a value of this type {@code V}.
6106 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6107 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6108 * <a href="MethodHandles.html#effid">effectively identical</a>
6109 * to the external parameter list {@code (A...)}.
6110 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6111 * {@linkplain #empty default value}.
6112 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6113 * effectively identical to the external parameter list {@code (A...)}.
6114 * </ul>
6115 * <p>
6116 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6117 * <li>The loop handle's result type is the result type {@code V} of the body.
6118 * <li>The loop handle's parameter types are the types {@code (A...)},
6119 * from the external parameter list.
6120 * </ul>
6121 * <p>
6122 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6123 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6124 * arguments passed to the loop.
6125 * <blockquote><pre>{@code
6126 * int iterations(A...);
6127 * V init(A...);
6128 * V body(V, int, A...);
6129 * V countedLoop(A... a...) {
6130 * int end = iterations(a...);
6131 * V v = init(a...);
6132 * for (int i = 0; i < end; ++i) {
6133 * v = body(v, i, a...);
6134 * }
6135 * return v;
6136 * }
6137 * }</pre></blockquote>
6138 *
6139 * @apiNote Example with a fully conformant body method:
6140 * <blockquote><pre>{@code
6141 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6142 * // => a variation on a well known theme
6143 * static String step(String v, int counter, String init) { return "na " + v; }
6144 * // assume MH_step is a handle to the method above
6145 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6146 * MethodHandle start = MethodHandles.identity(String.class);
6147 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6148 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6149 * }</pre></blockquote>
6150 *
6151 * @apiNote Example with the simplest possible body method type,
6152 * and passing the number of iterations to the loop invocation:
6153 * <blockquote><pre>{@code
6154 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6155 * // => a variation on a well known theme
6156 * static String step(String v, int counter ) { return "na " + v; }
6157 * // assume MH_step is a handle to the method above
6158 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6159 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6160 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6161 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6162 * }</pre></blockquote>
6163 *
6164 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6165 * as loop parameters:
6166 * <blockquote><pre>{@code
6167 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6168 * // => a variation on a well known theme
6169 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6170 * // assume MH_step is a handle to the method above
6171 * MethodHandle count = MethodHandles.identity(int.class);
6172 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6173 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6174 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6175 * }</pre></blockquote>
6176 *
6177 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6178 * to enforce a loop type:
6179 * <blockquote><pre>{@code
6180 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6181 * // => a variation on a well known theme
6182 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6183 * // assume MH_step is a handle to the method above
6184 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6185 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6186 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6187 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6188 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6189 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6190 * }</pre></blockquote>
6191 *
6192 * @apiNote The implementation of this method can be expressed as follows:
6193 * <blockquote><pre>{@code
6194 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6195 * return countedLoop(empty(iterations.type()), iterations, init, body);
6196 * }
6197 * }</pre></blockquote>
6198 *
6199 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6200 * result type must be {@code int}. See above for other constraints.
6201 * @param init optional initializer, providing the initial value of the loop variable.
6202 * May be {@code null}, implying a default initial value. See above for other constraints.
6203 * @param body body of the loop, which may not be {@code null}.
6204 * It controls the loop parameters and result type in the standard case (see above for details).
6205 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6206 * and may accept any number of additional types.
6207 * See above for other constraints.
6208 *
6209 * @return a method handle representing the loop.
6210 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6211 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6212 *
6213 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6214 * @since 9
6215 */
6216 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6217 return countedLoop(empty(iterations.type()), iterations, init, body);
6218 }
6219
6220 /**
6221 * Constructs a loop that counts over a range of numbers.
6222 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6223 * <p>
6224 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
6225 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
6226 * values of the loop counter.
6227 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
6228 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
6229 * <p>
6230 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6231 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6232 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6233 * <p>
6234 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6235 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6236 * iteration variable.
6237 * The result of the loop handle execution will be the final {@code V} value of that variable
6238 * (or {@code void} if there is no {@code V} variable).
6239 * <p>
6240 * The following rules hold for the argument handles:<ul>
6241 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
6242 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
6243 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6244 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6245 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6246 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6247 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6248 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6249 * of types called the <em>internal parameter list</em>.
6250 * It will constrain the parameter lists of the other loop parts.
6251 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6252 * with no additional {@code A} types, then the internal parameter list is extended by
6253 * the argument types {@code A...} of the {@code end} handle.
6254 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6255 * list {@code (A...)} is called the <em>external parameter list</em>.
6256 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6257 * additional state variable of the loop.
6258 * The body must both accept a leading parameter and return a value of this type {@code V}.
6259 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6260 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6261 * <a href="MethodHandles.html#effid">effectively identical</a>
6262 * to the external parameter list {@code (A...)}.
6263 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6264 * {@linkplain #empty default value}.
6265 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
6266 * effectively identical to the external parameter list {@code (A...)}.
6267 * <li>Likewise, the parameter list of {@code end} must be effectively identical
6268 * to the external parameter list.
6269 * </ul>
6270 * <p>
6271 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6272 * <li>The loop handle's result type is the result type {@code V} of the body.
6273 * <li>The loop handle's parameter types are the types {@code (A...)},
6274 * from the external parameter list.
6275 * </ul>
6276 * <p>
6277 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6278 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6279 * arguments passed to the loop.
6280 * <blockquote><pre>{@code
6281 * int start(A...);
6282 * int end(A...);
6283 * V init(A...);
6284 * V body(V, int, A...);
6285 * V countedLoop(A... a...) {
6286 * int e = end(a...);
6287 * int s = start(a...);
6288 * V v = init(a...);
6289 * for (int i = s; i < e; ++i) {
6290 * v = body(v, i, a...);
6291 * }
6292 * return v;
6293 * }
6294 * }</pre></blockquote>
6295 *
6296 * @apiNote The implementation of this method can be expressed as follows:
6297 * <blockquote><pre>{@code
6298 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6299 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
6300 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
6301 * // the following semantics:
6302 * // MH_increment: (int limit, int counter) -> counter + 1
6303 * // MH_predicate: (int limit, int counter) -> counter < limit
6304 * Class<?> counterType = start.type().returnType(); // int
6305 * Class<?> returnType = body.type().returnType();
6306 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
6307 * if (returnType != void.class) { // ignore the V variable
6308 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6309 * pred = dropArguments(pred, 1, returnType); // ditto
6310 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
6311 * }
6312 * body = dropArguments(body, 0, counterType); // ignore the limit variable
6313 * MethodHandle[]
6314 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6315 * bodyClause = { init, body }, // v = init(); v = body(v, i)
6316 * indexVar = { start, incr }; // i = start(); i = i + 1
6317 * return loop(loopLimit, bodyClause, indexVar);
6318 * }
6319 * }</pre></blockquote>
6320 *
6321 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
6322 * See above for other constraints.
6323 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
6324 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
6325 * @param init optional initializer, providing the initial value of the loop variable.
6326 * May be {@code null}, implying a default initial value. See above for other constraints.
6327 * @param body body of the loop, which may not be {@code null}.
6328 * It controls the loop parameters and result type in the standard case (see above for details).
6329 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6330 * and may accept any number of additional types.
6331 * See above for other constraints.
6332 *
6333 * @return a method handle representing the loop.
6334 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
6335 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6336 *
6337 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
6338 * @since 9
6339 */
6340 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6341 countedLoopChecks(start, end, init, body);
6342 Class<?> counterType = start.type().returnType(); // int, but who's counting?
6343 Class<?> limitType = end.type().returnType(); // yes, int again
6344 Class<?> returnType = body.type().returnType();
6345 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
6346 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
6347 MethodHandle retv = null;
6348 if (returnType != void.class) {
6349 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6350 pred = dropArguments(pred, 1, returnType); // ditto
6351 retv = dropArguments(identity(returnType), 0, counterType);
6352 }
6353 body = dropArguments(body, 0, counterType); // ignore the limit variable
6354 MethodHandle[]
6355 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6356 bodyClause = { init, body }, // v = init(); v = body(v, i)
6357 indexVar = { start, incr }; // i = start(); i = i + 1
6358 return loop(loopLimit, bodyClause, indexVar);
6359 }
6360
6361 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6362 Objects.requireNonNull(start);
6363 Objects.requireNonNull(end);
6364 Objects.requireNonNull(body);
6365 Class<?> counterType = start.type().returnType();
6366 if (counterType != int.class) {
6367 MethodType expected = start.type().changeReturnType(int.class);
6368 throw misMatchedTypes("start function", start.type(), expected);
6369 } else if (end.type().returnType() != counterType) {
6370 MethodType expected = end.type().changeReturnType(counterType);
6371 throw misMatchedTypes("end function", end.type(), expected);
6372 }
6373 MethodType bodyType = body.type();
6374 Class<?> returnType = bodyType.returnType();
6375 List<Class<?>> innerList = bodyType.parameterList();
6376 // strip leading V value if present
6377 int vsize = (returnType == void.class ? 0 : 1);
6378 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
6379 // argument list has no "V" => error
6380 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6381 throw misMatchedTypes("body function", bodyType, expected);
6382 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
6383 // missing I type => error
6384 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
6385 throw misMatchedTypes("body function", bodyType, expected);
6386 }
6387 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
6388 if (outerList.isEmpty()) {
6389 // special case; take lists from end handle
6390 outerList = end.type().parameterList();
6391 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
6392 }
6393 MethodType expected = methodType(counterType, outerList);
6394 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
6395 throw misMatchedTypes("start parameter types", start.type(), expected);
6396 }
6397 if (end.type() != start.type() &&
6398 !end.type().effectivelyIdenticalParameters(0, outerList)) {
6399 throw misMatchedTypes("end parameter types", end.type(), expected);
6400 }
6401 if (init != null) {
6402 MethodType initType = init.type();
6403 if (initType.returnType() != returnType ||
6404 !initType.effectivelyIdenticalParameters(0, outerList)) {
6405 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6406 }
6407 }
6408 }
6409
6410 /**
6411 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
6412 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6413 * <p>
6414 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
6415 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
6416 * <p>
6417 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6418 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6419 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6420 * <p>
6421 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6422 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6423 * iteration variable.
6424 * The result of the loop handle execution will be the final {@code V} value of that variable
6425 * (or {@code void} if there is no {@code V} variable).
6426 * <p>
6427 * The following rules hold for the argument handles:<ul>
6428 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6429 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
6430 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6431 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
6432 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
6433 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
6434 * of types called the <em>internal parameter list</em>.
6435 * It will constrain the parameter lists of the other loop parts.
6436 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
6437 * with no additional {@code A} types, then the internal parameter list is extended by
6438 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
6439 * single type {@code Iterable} is added and constitutes the {@code A...} list.
6440 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
6441 * list {@code (A...)} is called the <em>external parameter list</em>.
6442 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6443 * additional state variable of the loop.
6444 * The body must both accept a leading parameter and return a value of this type {@code V}.
6445 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6446 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6447 * <a href="MethodHandles.html#effid">effectively identical</a>
6448 * to the external parameter list {@code (A...)}.
6449 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6450 * {@linkplain #empty default value}.
6451 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
6452 * type {@code java.util.Iterator} or a subtype thereof.
6453 * The iterator it produces when the loop is executed will be assumed
6454 * to yield values which can be converted to type {@code T}.
6455 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
6456 * effectively identical to the external parameter list {@code (A...)}.
6457 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
6458 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
6459 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
6460 * handle parameter is adjusted to accept the leading {@code A} type, as if by
6461 * the {@link MethodHandle#asType asType} conversion method.
6462 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
6463 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
6464 * </ul>
6465 * <p>
6466 * The type {@code T} may be either a primitive or reference.
6467 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
6468 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
6469 * as if by the {@link MethodHandle#asType asType} conversion method.
6470 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
6471 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
6472 * <p>
6473 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6474 * <li>The loop handle's result type is the result type {@code V} of the body.
6475 * <li>The loop handle's parameter types are the types {@code (A...)},
6476 * from the external parameter list.
6477 * </ul>
6478 * <p>
6479 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6480 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
6481 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
6482 * <blockquote><pre>{@code
6483 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
6484 * V init(A...);
6485 * V body(V,T,A...);
6486 * V iteratedLoop(A... a...) {
6487 * Iterator<T> it = iterator(a...);
6488 * V v = init(a...);
6489 * while (it.hasNext()) {
6490 * T t = it.next();
6491 * v = body(v, t, a...);
6492 * }
6493 * return v;
6494 * }
6495 * }</pre></blockquote>
6496 *
6497 * @apiNote Example:
6498 * <blockquote><pre>{@code
6499 * // get an iterator from a list
6500 * static List<String> reverseStep(List<String> r, String e) {
6501 * r.add(0, e);
6502 * return r;
6503 * }
6504 * static List<String> newArrayList() { return new ArrayList<>(); }
6505 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
6506 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
6507 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
6508 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
6509 * assertEquals(reversedList, (List<String>) loop.invoke(list));
6510 * }</pre></blockquote>
6511 *
6512 * @apiNote The implementation of this method can be expressed approximately as follows:
6513 * <blockquote><pre>{@code
6514 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6515 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
6516 * Class<?> returnType = body.type().returnType();
6517 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6518 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
6519 * MethodHandle retv = null, step = body, startIter = iterator;
6520 * if (returnType != void.class) {
6521 * // the simple thing first: in (I V A...), drop the I to get V
6522 * retv = dropArguments(identity(returnType), 0, Iterator.class);
6523 * // body type signature (V T A...), internal loop types (I V A...)
6524 * step = swapArguments(body, 0, 1); // swap V <-> T
6525 * }
6526 * if (startIter == null) startIter = MH_getIter;
6527 * MethodHandle[]
6528 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
6529 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
6530 * return loop(iterVar, bodyClause);
6531 * }
6532 * }</pre></blockquote>
6533 *
6534 * @param iterator an optional handle to return the iterator to start the loop.
6535 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
6536 * See above for other constraints.
6537 * @param init optional initializer, providing the initial value of the loop variable.
6538 * May be {@code null}, implying a default initial value. See above for other constraints.
6539 * @param body body of the loop, which may not be {@code null}.
6540 * It controls the loop parameters and result type in the standard case (see above for details).
6541 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
6542 * and may accept any number of additional types.
6543 * See above for other constraints.
6544 *
6545 * @return a method handle embodying the iteration loop functionality.
6546 * @throws NullPointerException if the {@code body} handle is {@code null}.
6547 * @throws IllegalArgumentException if any argument violates the above requirements.
6548 *
6549 * @since 9
6550 */
6551 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6552 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
6553 Class<?> returnType = body.type().returnType();
6554 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
6555 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
6556 MethodHandle startIter;
6557 MethodHandle nextVal;
6558 {
6559 MethodType iteratorType;
6560 if (iterator == null) {
6561 // derive argument type from body, if available, else use Iterable
6562 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
6563 iteratorType = startIter.type().changeParameterType(0, iterableType);
6564 } else {
6565 // force return type to the internal iterator class
6566 iteratorType = iterator.type().changeReturnType(Iterator.class);
6567 startIter = iterator;
6568 }
6569 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6570 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
6571
6572 // perform the asType transforms under an exception transformer, as per spec.:
6573 try {
6574 startIter = startIter.asType(iteratorType);
6575 nextVal = nextRaw.asType(nextValType);
6576 } catch (WrongMethodTypeException ex) {
6577 throw new IllegalArgumentException(ex);
6578 }
6579 }
6580
6581 MethodHandle retv = null, step = body;
6582 if (returnType != void.class) {
6583 // the simple thing first: in (I V A...), drop the I to get V
6584 retv = dropArguments(identity(returnType), 0, Iterator.class);
6585 // body type signature (V T A...), internal loop types (I V A...)
6586 step = swapArguments(body, 0, 1); // swap V <-> T
6587 }
6588
6589 MethodHandle[]
6590 iterVar = { startIter, null, hasNext, retv },
6591 bodyClause = { init, filterArgument(step, 0, nextVal) };
6592 return loop(iterVar, bodyClause);
6593 }
6594
6595 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6596 Objects.requireNonNull(body);
6597 MethodType bodyType = body.type();
6598 Class<?> returnType = bodyType.returnType();
6599 List<Class<?>> internalParamList = bodyType.parameterList();
6600 // strip leading V value if present
6601 int vsize = (returnType == void.class ? 0 : 1);
6602 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
6603 // argument list has no "V" => error
6604 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6605 throw misMatchedTypes("body function", bodyType, expected);
6606 } else if (internalParamList.size() <= vsize) {
6607 // missing T type => error
6608 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
6609 throw misMatchedTypes("body function", bodyType, expected);
6610 }
6611 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
6612 Class<?> iterableType = null;
6613 if (iterator != null) {
6614 // special case; if the body handle only declares V and T then
6615 // the external parameter list is obtained from iterator handle
6616 if (externalParamList.isEmpty()) {
6617 externalParamList = iterator.type().parameterList();
6618 }
6619 MethodType itype = iterator.type();
6620 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
6621 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
6622 }
6623 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
6624 MethodType expected = methodType(itype.returnType(), externalParamList);
6625 throw misMatchedTypes("iterator parameters", itype, expected);
6626 }
6627 } else {
6628 if (externalParamList.isEmpty()) {
6629 // special case; if the iterator handle is null and the body handle
6630 // only declares V and T then the external parameter list consists
6631 // of Iterable
6632 externalParamList = Arrays.asList(Iterable.class);
6633 iterableType = Iterable.class;
6634 } else {
6635 // special case; if the iterator handle is null and the external
6636 // parameter list is not empty then the first parameter must be
6637 // assignable to Iterable
6638 iterableType = externalParamList.get(0);
6639 if (!Iterable.class.isAssignableFrom(iterableType)) {
6640 throw newIllegalArgumentException(
6641 "inferred first loop argument must inherit from Iterable: " + iterableType);
6642 }
6643 }
6644 }
6645 if (init != null) {
6646 MethodType initType = init.type();
6647 if (initType.returnType() != returnType ||
6648 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
6649 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
6650 }
6651 }
6652 return iterableType; // help the caller a bit
6653 }
6654
6655 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
6656 // there should be a better way to uncross my wires
6657 int arity = mh.type().parameterCount();
6658 int[] order = new int[arity];
6659 for (int k = 0; k < arity; k++) order[k] = k;
6660 order[i] = j; order[j] = i;
6661 Class<?>[] types = mh.type().parameterArray();
6662 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
6663 MethodType swapType = methodType(mh.type().returnType(), types);
6664 return permuteArguments(mh, swapType, order);
6665 }
6666
6667 /**
6668 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
6669 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
6670 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
6671 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
6672 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
6673 * {@code try-finally} handle.
6674 * <p>
6675 * The {@code cleanup} handle will be passed one or two additional leading arguments.
6676 * The first is the exception thrown during the
6677 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
6678 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
6679 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
6680 * The second argument is not present if the {@code target} handle has a {@code void} return type.
6681 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
6682 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
6683 * <p>
6684 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
6685 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
6686 * two extra leading parameters:<ul>
6687 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
6688 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
6689 * the result from the execution of the {@code target} handle.
6690 * This parameter is not present if the {@code target} returns {@code void}.
6691 * </ul>
6692 * <p>
6693 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
6694 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
6695 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
6696 * the cleanup.
6697 * <blockquote><pre>{@code
6698 * V target(A..., B...);
6699 * V cleanup(Throwable, V, A...);
6700 * V adapter(A... a, B... b) {
6701 * V result = (zero value for V);
6702 * Throwable throwable = null;
6703 * try {
6704 * result = target(a..., b...);
6705 * } catch (Throwable t) {
6706 * throwable = t;
6707 * throw t;
6708 * } finally {
6709 * result = cleanup(throwable, result, a...);
6710 * }
6711 * return result;
6712 * }
6713 * }</pre></blockquote>
6714 * <p>
6715 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6716 * be modified by execution of the target, and so are passed unchanged
6717 * from the caller to the cleanup, if it is invoked.
6718 * <p>
6719 * The target and cleanup must return the same type, even if the cleanup
6720 * always throws.
6721 * To create such a throwing cleanup, compose the cleanup logic
6722 * with {@link #throwException throwException},
6723 * in order to create a method handle of the correct return type.
6724 * <p>
6725 * Note that {@code tryFinally} never converts exceptions into normal returns.
6726 * In rare cases where exceptions must be converted in that way, first wrap
6727 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
6728 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
6729 * <p>
6730 * It is recommended that the first parameter type of {@code cleanup} be
6731 * declared {@code Throwable} rather than a narrower subtype. This ensures
6732 * {@code cleanup} will always be invoked with whatever exception that
6733 * {@code target} throws. Declaring a narrower type may result in a
6734 * {@code ClassCastException} being thrown by the {@code try-finally}
6735 * handle if the type of the exception thrown by {@code target} is not
6736 * assignable to the first parameter type of {@code cleanup}. Note that
6737 * various exception types of {@code VirtualMachineError},
6738 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6739 * thrown by almost any kind of Java code, and a finally clause that
6740 * catches (say) only {@code IOException} would mask any of the others
6741 * behind a {@code ClassCastException}.
6742 *
6743 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6744 * @param cleanup the handle that is invoked in the finally block.
6745 *
6746 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6747 * @throws NullPointerException if any argument is null
6748 * @throws IllegalArgumentException if {@code cleanup} does not accept
6749 * the required leading arguments, or if the method handle types do
6750 * not match in their return types and their
6751 * corresponding trailing parameters
6752 *
6753 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
6754 * @since 9
6755 */
6756 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
6757 List<Class<?>> targetParamTypes = target.type().parameterList();
6758 Class<?> rtype = target.type().returnType();
6759
6760 tryFinallyChecks(target, cleanup);
6761
6762 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
6763 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6764 // target parameter list.
6765 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
6766
6767 // Ensure that the intrinsic type checks the instance thrown by the
6768 // target against the first parameter of cleanup
6769 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
6770
6771 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
6772 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
6773 }
6774
6775 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
6776 Class<?> rtype = target.type().returnType();
6777 if (rtype != cleanup.type().returnType()) {
6778 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
6779 }
6780 MethodType cleanupType = cleanup.type();
6781 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
6782 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
6783 }
6784 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
6785 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
6786 }
6787 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6788 // target parameter list.
6789 int cleanupArgIndex = rtype == void.class ? 1 : 2;
6790 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
6791 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
6792 cleanup.type(), target.type());
6793 }
6794 }
6795
6796 }