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 {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} 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
106 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
107 */
108 @CallerSensitive
109 @ForceInline // to ensure Reflection.getCallerClass optimization
110 public static Lookup lookup() {
111 return new Lookup(Reflection.getCallerClass());
112 }
113
114 /**
115 * This reflected$lookup method is the alternate implementation of
116 * the lookup method when being invoked by reflection.
117 */
118 @CallerSensitive
119 private static Lookup reflected$lookup() {
120 Class<?> caller = Reflection.getCallerClass();
121 if (caller.getClassLoader() == null) {
122 throw newIllegalArgumentException("illegal lookupClass: "+caller);
123 }
124 return new Lookup(caller);
125 }
126
127 /**
128 * Returns a {@link Lookup lookup object} which is trusted minimally.
129 * The lookup has the {@code UNCONDITIONAL} mode.
130 * It can only be used to create method handles to public members of
131 * public classes in packages that are exported unconditionally.
132 * <p>
133 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
134 * of this lookup object will be {@link java.lang.Object}.
135 *
136 * @apiNote The use of Object is conventional, and because the lookup modes are
137 * limited, there is no special access provided to the internals of Object, its package
138 * or its module. This public lookup object or other lookup object with
139 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
140 * is not used to determine the lookup context.
141 *
142 * <p style="font-size:smaller;">
143 * <em>Discussion:</em>
144 * The lookup class can be changed to any other class {@code C} using an expression of the form
145 * {@link Lookup#in publicLookup().in(C.class)}.
146 * A public lookup object is always subject to
147 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
148 * Also, it cannot access
149 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
150 * @return a lookup object which is trusted minimally
151 *
152 * @revised 9
153 * @spec JPMS
154 */
155 public static Lookup publicLookup() {
156 return Lookup.PUBLIC_LOOKUP;
157 }
158
159 /**
160 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
161 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
162 * The returned lookup object can provide access to classes in modules and packages,
163 * and members of those classes, outside the normal rules of Java access control,
164 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
165 * <p>
166 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
167 * allowed to do deep reflection on module {@code M2} and package of the target class
168 * if and only if all of the following conditions are {@code true}:
169 * <ul>
170 * <li>If there is a security manager, its {@code checkPermission} method is
171 * called to check {@code ReflectPermission("suppressAccessChecks")} and
172 * that must return normally.
173 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
174 * full privilege access}. Specifically:
175 * <ul>
176 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
177 * (This is because otherwise there would be no way to ensure the original lookup
178 * creator was a member of any particular module, and so any subsequent checks
179 * for readability and qualified exports would become ineffective.)
180 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
181 * (This is because an application intending to share intra-module access
182 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
183 * deep reflection to its own module.)
184 * </ul>
185 * <li>The target class must be a proper class, not a primitive or array class.
186 * (Thus, {@code M2} is well-defined.)
187 * <li>If the caller module {@code M1} differs from
188 * the target module {@code M2} then both of the following must be true:
189 * <ul>
190 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
191 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
192 * containing the target class to at least {@code M1}.</li>
193 * </ul>
194 * </ul>
195 * <p>
196 * If any of the above checks is violated, this method fails with an
197 * exception.
198 * <p>
199 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
200 * returns a {@code Lookup} on {@code targetClass} with
201 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} and
202 * {@code null} previous lookup class.
203 * <p>
204 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
205 * returns a {@code Lookup} on {@code targetClass} that records
206 * the lookup class of the caller as the new previous lookup class and
207 * drops {@code MODULE} access from the full privilege access.
208 *
209 * @param targetClass the target class
210 * @param caller the caller lookup object
211 * @return a lookup object for the target class, with private access
212 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
213 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
214 * @throws SecurityException if denied by the security manager
215 * @throws IllegalAccessException if any of the other access checks specified above fails
216 * @since 9
217 * @spec JPMS
218 * @see Lookup#dropLookupMode
219 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
220 */
221 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
222 SecurityManager sm = System.getSecurityManager();
223 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
224 if (targetClass.isPrimitive())
225 throw new IllegalArgumentException(targetClass + " is a primitive class");
226 if (targetClass.isArray())
227 throw new IllegalArgumentException(targetClass + " is an array class");
228 // Ensure that we can reason accurately about private and module access.
229 if (!caller.hasFullPrivilegeAccess())
230 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
231
232 // previous lookup class is never set if it has MODULE access
233 assert caller.previousLookupClass() == null;
234
235 Class<?> callerClass = caller.lookupClass();
236 Module callerModule = callerClass.getModule(); // M1
237 Module targetModule = targetClass.getModule(); // M2
238 Class<?> newPreviousClass = null;
239 int newModes = Lookup.FULL_POWER_MODES;
240
241 if (targetModule != callerModule) {
242 if (!callerModule.canRead(targetModule))
243 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
244 if (targetModule.isNamed()) {
245 String pn = targetClass.getPackageName();
246 assert !pn.isEmpty() : "unnamed package cannot be in named module";
247 if (!targetModule.isOpen(pn, callerModule))
248 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
249 }
250
251 // M2 != M1, set previous lookup class to M1 and drop MODULE access
252 newPreviousClass = callerClass;
253 newModes &= ~Lookup.MODULE;
254 }
255
256 if (!callerModule.isNamed() && targetModule.isNamed()) {
257 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
258 if (logger != null) {
259 logger.logIfOpenedForIllegalAccess(caller, targetClass);
260 }
261 }
262 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
263 }
264
265 /**
266 * Performs an unchecked "crack" of a
267 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
268 * The result is as if the user had obtained a lookup object capable enough
269 * to crack the target method handle, called
270 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
271 * on the target to obtain its symbolic reference, and then called
272 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
273 * to resolve the symbolic reference to a member.
274 * <p>
275 * If there is a security manager, its {@code checkPermission} method
276 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
277 * @param <T> the desired type of the result, either {@link Member} or a subtype
278 * @param target a direct method handle to crack into symbolic reference components
279 * @param expected a class object representing the desired result type {@code T}
280 * @return a reference to the method, constructor, or field object
281 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
282 * @throws NullPointerException if either argument is {@code null}
283 * @throws IllegalArgumentException if the target is not a direct method handle
284 * @throws ClassCastException if the member is not of the expected type
285 * @since 1.8
286 */
287 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
288 SecurityManager smgr = System.getSecurityManager();
289 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
290 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
291 return lookup.revealDirect(target).reflectAs(expected, lookup);
292 }
293 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
294 private static final java.security.Permission ACCESS_PERMISSION =
295 new ReflectPermission("suppressAccessChecks");
296
297 /**
298 * A <em>lookup object</em> is a factory for creating method handles,
299 * when the creation requires access checking.
300 * Method handles do not perform
301 * access checks when they are called, but rather when they are created.
302 * Therefore, method handle access
303 * restrictions must be enforced when a method handle is created.
304 * The caller class against which those restrictions are enforced
305 * is known as the {@linkplain #lookupClass() lookup class}.
306 * <p>
307 * A lookup class which needs to create method handles will call
308 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
309 * When the {@code Lookup} factory object is created, the identity of the lookup class is
310 * determined, and securely stored in the {@code Lookup} object.
311 * The lookup class (or its delegates) may then use factory methods
312 * on the {@code Lookup} object to create method handles for access-checked members.
313 * This includes all methods, constructors, and fields which are allowed to the lookup class,
314 * even private ones.
315 *
316 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
317 * The factory methods on a {@code Lookup} object correspond to all major
318 * use cases for methods, constructors, and fields.
319 * Each method handle created by a factory method is the functional
320 * equivalent of a particular <em>bytecode behavior</em>.
321 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of the Java Virtual Machine Specification.)
322 * Here is a summary of the correspondence between these factory methods and
323 * the behavior of the resulting method handles:
324 * <table class="striped">
325 * <caption style="display:none">lookup method behaviors</caption>
326 * <thead>
327 * <tr>
328 * <th scope="col"><a id="equiv"></a>lookup expression</th>
329 * <th scope="col">member</th>
330 * <th scope="col">bytecode behavior</th>
331 * </tr>
332 * </thead>
333 * <tbody>
334 * <tr>
335 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
336 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
337 * </tr>
338 * <tr>
339 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
340 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
341 * </tr>
342 * <tr>
343 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
344 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
345 * </tr>
346 * <tr>
347 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
348 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
349 * </tr>
350 * <tr>
351 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
352 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
353 * </tr>
354 * <tr>
355 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
356 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
357 * </tr>
358 * <tr>
359 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
360 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
361 * </tr>
362 * <tr>
363 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
364 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
365 * </tr>
366 * <tr>
367 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
368 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
369 * </tr>
370 * <tr>
371 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
372 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
373 * </tr>
374 * <tr>
375 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
376 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
377 * </tr>
378 * <tr>
379 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
380 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
381 * </tr>
382 * <tr>
383 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
384 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
385 * </tr>
386 * <tr>
387 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
388 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
389 * </tr>
390 * </tbody>
391 * </table>
392 *
393 * Here, the type {@code C} is the class or interface being searched for a member,
394 * documented as a parameter named {@code refc} in the lookup methods.
395 * The method type {@code MT} is composed from the return type {@code T}
396 * and the sequence of argument types {@code A*}.
397 * The constructor also has a sequence of argument types {@code A*} and
398 * is deemed to return the newly-created object of type {@code C}.
399 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
400 * The formal parameter {@code this} stands for the self-reference of type {@code C};
401 * if it is present, it is always the leading argument to the method handle invocation.
402 * (In the case of some {@code protected} members, {@code this} may be
403 * restricted in type to the lookup class; see below.)
404 * The name {@code arg} stands for all the other method handle arguments.
405 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
406 * stands for a null reference if the accessed method or field is static,
407 * and {@code this} otherwise.
408 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
409 * for reflective objects corresponding to the given members declared in type {@code C}.
410 * <p>
411 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
412 * as if by {@code ldc CONSTANT_Class}.
413 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
414 * <p>
415 * In cases where the given member is of variable arity (i.e., a method or constructor)
416 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
417 * In all other cases, the returned method handle will be of fixed arity.
418 * <p style="font-size:smaller;">
419 * <em>Discussion:</em>
420 * The equivalence between looked-up method handles and underlying
421 * class members and bytecode behaviors
422 * can break down in a few ways:
423 * <ul style="font-size:smaller;">
424 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
425 * the lookup can still succeed, even when there is no equivalent
426 * Java expression or bytecoded constant.
427 * <li>Likewise, if {@code T} or {@code MT}
428 * is not symbolically accessible from the lookup class's loader,
429 * the lookup can still succeed.
430 * For example, lookups for {@code MethodHandle.invokeExact} and
431 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
432 * <li>If there is a security manager installed, it can forbid the lookup
433 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
434 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
435 * constant is not subject to security manager checks.
436 * <li>If the looked-up method has a
437 * <a href="MethodHandle.html#maxarity">very large arity</a>,
438 * the method handle creation may fail with an
439 * {@code IllegalArgumentException}, due to the method handle type having
440 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
441 * </ul>
442 *
443 * <h2><a id="access"></a>Access checking</h2>
444 * Access checks are applied in the factory methods of {@code Lookup},
445 * when a method handle is created.
446 * This is a key difference from the Core Reflection API, since
447 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
448 * performs access checking against every caller, on every call.
449 * <p>
450 * All access checks start from a {@code Lookup} object, which
451 * compares its recorded lookup class against all requests to
452 * create method handles.
453 * A single {@code Lookup} object can be used to create any number
454 * of access-checked method handles, all checked against a single
455 * lookup class.
456 * <p>
457 * A {@code Lookup} object can be shared with other trusted code,
458 * such as a metaobject protocol.
459 * A shared {@code Lookup} object delegates the capability
460 * to create method handles on private members of the lookup class.
461 * Even if privileged code uses the {@code Lookup} object,
462 * the access checking is confined to the privileges of the
463 * original lookup class.
464 * <p>
465 * A lookup can fail, because
466 * the containing class is not accessible to the lookup class, or
467 * because the desired class member is missing, or because the
468 * desired class member is not accessible to the lookup class, or
469 * because the lookup object is not trusted enough to access the member.
470 * In the case of a field setter function on a {@code final} field,
471 * finality enforcement is treated as a kind of access control,
472 * and the lookup will fail, except in special cases of
473 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
474 * In any of these cases, a {@code ReflectiveOperationException} will be
475 * thrown from the attempted lookup. The exact class will be one of
476 * the following:
477 * <ul>
478 * <li>NoSuchMethodException — if a method is requested but does not exist
479 * <li>NoSuchFieldException — if a field is requested but does not exist
480 * <li>IllegalAccessException — if the member exists but an access check fails
481 * </ul>
482 * <p>
483 * In general, the conditions under which a method handle may be
484 * looked up for a method {@code M} are no more restrictive than the conditions
485 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
486 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
487 * a method handle lookup will generally raise a corresponding
488 * checked exception, such as {@code NoSuchMethodException}.
489 * And the effect of invoking the method handle resulting from the lookup
490 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
491 * to executing the compiled, verified, and resolved call to {@code M}.
492 * The same point is true of fields and constructors.
493 * <p style="font-size:smaller;">
494 * <em>Discussion:</em>
495 * Access checks only apply to named and reflected methods,
496 * constructors, and fields.
497 * Other method handle creation methods, such as
498 * {@link MethodHandle#asType MethodHandle.asType},
499 * do not require any access checks, and are used
500 * independently of any {@code Lookup} object.
501 * <p>
502 * If the desired member is {@code protected}, the usual JVM rules apply,
503 * including the requirement that the lookup class must either be in the
504 * same package as the desired member, or must inherit that member.
505 * (See the Java Virtual Machine Specification, sections {@jvms 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
506 * In addition, if the desired member is a non-static field or method
507 * in a different package, the resulting method handle may only be applied
508 * to objects of the lookup class or one of its subclasses.
509 * This requirement is enforced by narrowing the type of the leading
510 * {@code this} parameter from {@code C}
511 * (which will necessarily be a superclass of the lookup class)
512 * to the lookup class itself.
513 * <p>
514 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
515 * that the receiver argument must match both the resolved method <em>and</em>
516 * the current class. Again, this requirement is enforced by narrowing the
517 * type of the leading parameter to the resulting method handle.
518 * (See the Java Virtual Machine Specification, section {@jmvs 4.10.1.9}.)
519 * <p>
520 * The JVM represents constructors and static initializer blocks as internal methods
521 * with special names ({@code "<init>"} and {@code "<clinit>"}).
522 * The internal syntax of invocation instructions allows them to refer to such internal
523 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
524 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
525 * <p>
526 * If the relationship between nested types is expressed directly through the
527 * {@code NestHost} and {@code NestMembers} attributes
528 * (see the Java Virtual Machine Specification, sections {@jvms 4.7.28} and {@jvms 4.7.29}),
529 * then the associated {@code Lookup} object provides direct access to
530 * the lookup class and all of its nestmates
531 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
532 * Otherwise, access between nested classes is obtained by the Java compiler creating
533 * a wrapper method to access a private method of another class in the same nest.
534 * For example, a nested class {@code C.D}
535 * can access private members within other related classes such as
536 * {@code C}, {@code C.D.E}, or {@code C.B},
537 * but the Java compiler may need to generate wrapper methods in
538 * those related classes. In such cases, a {@code Lookup} object on
539 * {@code C.E} would be unable to access those private members.
540 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
541 * which can transform a lookup on {@code C.E} into one on any of those other
542 * classes, without special elevation of privilege.
543 * <p>
544 * The accesses permitted to a given lookup object may be limited,
545 * according to its set of {@link #lookupModes lookupModes},
546 * to a subset of members normally accessible to the lookup class.
547 * For example, the {@link MethodHandles#publicLookup publicLookup}
548 * method produces a lookup object which is only allowed to access
549 * public members in public classes of exported packages.
550 * The caller sensitive method {@link MethodHandles#lookup lookup}
551 * produces a lookup object with full capabilities relative to
552 * its caller class, to emulate all supported bytecode behaviors.
553 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
554 * with fewer access modes than the original lookup object.
555 *
556 * <p style="font-size:smaller;">
557 * <a id="privacc"></a>
558 * <em>Discussion of private and module access:</em>
559 * We say that a lookup has <em>private access</em>
560 * if its {@linkplain #lookupModes lookup modes}
561 * include the possibility of accessing {@code private} members
562 * (which includes the private members of nestmates).
563 * As documented in the relevant methods elsewhere,
564 * only lookups with private access possess the following capabilities:
565 * <ul style="font-size:smaller;">
566 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
567 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
568 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
569 * for classes accessible to the lookup class
570 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
571 * within the same package member
572 * </ul>
573 * <p style="font-size:smaller;">
574 * Similarly, a lookup with module access ensures that the original lookup creator was
575 * a member in the same module as the lookup class.
576 * <p style="font-size:smaller;">
577 * Private and module access are independently determined modes; a lookup may have
578 * either or both or neither. A lookup which possesses both access modes is said to
579 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}. Such a lookup has
580 * the following additional capability:
581 * <ul style="font-size:smaller;">
582 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
583 * such as {@code Class.forName}
584 * </ul>
585 * <p style="font-size:smaller;">
586 * Each of these permissions is a consequence of the fact that a lookup object
587 * with private access can be securely traced back to an originating class,
588 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
589 * can be reliably determined and emulated by method handles.
590 *
591 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
592 * When a lookup class in one module {@code M1} accesses a class in another module
593 * {@code M2}, extra access checking is performed beyond the access mode bits.
594 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
595 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
596 * and when the type is in a package of {@code M2} that is exported to
597 * at least {@code M1}.
598 * <p>
599 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
600 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
601 * MethodHandles.privateLookupIn} methods.
602 * Teleporting across modules will always record the original lookup class as
603 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
604 * and drops {@link Lookup#MODULE MODULE} access.
605 * If the target class is in the same module as the lookup class {@code C},
606 * then the target class becomes the new lookup class
607 * and there is no change to the previous lookup class.
608 * If the target class is in a different module from {@code M1} ({@code C}'s module),
609 * {@code C} becomes the new previous lookup class
610 * and the target class becomes the new lookup class.
611 * In that case, if there was already a previous lookup class in {@code M0},
612 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
613 * drops all privileges.
614 * For example,
615 * <blockquote><pre>
616 * {@code
617 * Lookup lookup = MethodHandles.lookup(); // in class C
618 * Lookup lookup2 = lookup.in(D.class);
619 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
620 * }</pre></blockquote>
621 * <p>
622 * The {@link #lookup()} factory method produces a {@code Lookup} object
623 * with {@code null} previous lookup class.
624 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
625 * to class {@code D} without elevation of privileges.
626 * If {@code C} and {@code D} are in the same module,
627 * {@code lookup2} records {@code D} as the new lookup class and keeps the
628 * same previous lookup class as the original {@code lookup}, or
629 * {@code null} if not present.
630 * <p>
631 * When a {@code Lookup} teleports from a class
632 * in one nest to another nest, {@code PRIVATE} access is dropped.
633 * When a {@code Lookup} teleports from a class in one package to
634 * another package, {@code PACKAGE} access is dropped.
635 * When a {@code Lookup} teleports from a class in one module to another module,
636 * {@code MODULE} access is dropped.
637 * Teleporting across modules drops the ability to access non-exported classes
638 * in both the module of the new lookup class and the module of the old lookup class
639 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
640 * A {@code Lookup} can teleport back and forth to a class in the module of
641 * the lookup class and the module of the previous class lookup.
642 * Teleporting across modules can only decrease access but cannot increase it.
643 * Teleporting to some third module drops all accesses.
644 * <p>
645 * In the above example, if {@code C} and {@code D} are in different modules,
646 * {@code lookup2} records {@code D} as its lookup class and
647 * {@code C} as its previous lookup class and {@code lookup2} has only
648 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
649 * {@code C}'s module and {@code D}'s module.
650 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
651 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
652 * class {@code D} is recorded as its previous lookup class.
653 * <p>
654 * Teleporting across modules restricts access to the public types that
655 * both the lookup class and the previous lookup class can equally access
656 * (see below).
657 * <p>
658 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
659 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
660 * and create a new {@code Lookup} with <a href="#privacc">private access</a>
661 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
662 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
663 * to call {@code privateLookupIn}.
664 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
665 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
666 * produces a new {@code Lookup} on {@code T} with full capabilities.
667 * A {@code lookup} on {@code C} is also allowed
668 * to do deep reflection on {@code T} in another module {@code M2} if
669 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
670 * the package containing {@code T} to at least {@code M1}.
671 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
672 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
673 * The resulting {@code Lookup} can be used to do member lookup or teleport
674 * to another lookup class by calling {@link #in Lookup::in}. But
675 * it cannot be used to obtain another private {@code Lookup} by calling
676 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
677 * because it has no {@code MODULE} access.
678 *
679 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
680 *
681 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
682 * allows cross-module access. The access checking is performed with respect
683 * to both the lookup class and the previous lookup class if present.
684 * <p>
685 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
686 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
687 * exported unconditionally}.
688 * <p>
689 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
690 * the lookup with {@link #PUBLIC} mode can access all public types in modules
691 * that are readable to {@code M1} and the type is in a package that is exported
692 * at least to {@code M1}.
693 * <p>
694 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
695 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
696 * the intersection of all public types that are accessible to {@code M1}
697 * with all public types that are accessible to {@code M0}. {@code M0}
698 * reads {@code M1} and hence the set of accessible types includes:
699 *
700 * <table class="striped">
701 * <caption style="display:none">
702 * Public types in the following packages are accessible to the
703 * lookup class and the previous lookup class.
704 * </caption>
705 * <thead>
706 * <tr>
707 * <th scope="col">Equally accessible types to {@code M0} and {@code M1}</th>
708 * </tr>
709 * </thead>
710 * <tbody>
711 * <tr>
712 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M1}</th>
713 * </tr>
714 * <tr>
715 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</th>
716 * </tr>
717 * <tr>
718 * <th scope="row" style="text-align:left">unconditional-exported packages from a third module {@code M2}
719 * if both {@code M0} and {@code M1} read {@code M2}</th>
720 * </tr>
721 * <tr>
722 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M1} to {@code M0}</th>
723 * </tr>
724 * <tr>
725 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M0} to {@code M1}
726 * if {@code M1} reads {@code M0}</th>
727 * </tr>
728 * <tr>
729 * <th scope="row" style="text-align:left">qualified-exported packages from a third module {@code M2} to
730 * both {@code M0} and {@code M1} if both {@code M0} and {@code M1} read {@code M2}</th>
731 * </tr>
732 * </tbody>
733 * </table>
734 *
735 * <h2><a id="access-modes"></a>Access modes</h2>
736 *
737 * The table below shows the access modes of a {@code Lookup} produced by
738 * any of the following factory or transformation methods:
739 * <ul>
740 * <li>{@link #lookup() MethodHandles.lookup()}</li>
741 * <li>{@link #publicLookup() MethodHandles.publicLookup()}</li>
742 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn}</li>
743 * <li>{@link Lookup#in}</li>
744 * <li>{@link Lookup#dropLookupMode(int)}</li>
745 * </ul>
746 *
747 * <table class="striped">
748 * <caption style="display:none">
749 * Access mode summary
750 * </caption>
751 * <thead>
752 * <tr>
753 * <th scope="col">Lookup object</th>
754 * <th style="text-align:center">protected</th>
755 * <th style="text-align:center">private</th>
756 * <th style="text-align:center">package</th>
757 * <th style="text-align:center">module</th>
758 * <th style="text-align:center">public</th>
759 * </tr>
760 * </thead>
761 * <tbody>
762 * <tr>
763 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
764 * <td style="text-align:center">PRO</td>
765 * <td style="text-align:center">PRI</td>
766 * <td style="text-align:center">PAC</td>
767 * <td style="text-align:center">MOD</td>
768 * <td style="text-align:center">1R</td>
769 * </tr>
770 * <tr>
771 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
772 * <td></td>
773 * <td></td>
774 * <td style="text-align:center">PAC</td>
775 * <td style="text-align:center">MOD</td>
776 * <td style="text-align:center">1R</td>
777 * </tr>
778 * <tr>
779 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
780 * <td></td>
781 * <td></td>
782 * <td></td>
783 * <td style="text-align:center">MOD</td>
784 * <td style="text-align:center">1R</td>
785 * </tr>
786 * <tr>
787 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
788 * <td></td>
789 * <td></td>
790 * <td></td>
791 * <td></td>
792 * <td style="text-align:center">2R</td>
793 * </tr>
794 * <tr>
795 * <td>{@code CL.in(D).in(C)} hop back to module</td>
796 * <td></td>
797 * <td></td>
798 * <td></td>
799 * <td></td>
800 * <td style="text-align:center">2R</td>
801 * </tr>
802 * <tr>
803 * <td>{@code PRI1 = privateLookupIn(C1,CL)}</td>
804 * <td style="text-align:center">PRO</td>
805 * <td style="text-align:center">PRI</td>
806 * <td style="text-align:center">PAC</td>
807 * <td style="text-align:center">MOD</td>
808 * <td style="text-align:center">1R</td>
809 * </tr>
810 * <tr>
811 * <td>{@code PRI1a = privateLookupIn(C,PRI1)}</td>
812 * <td style="text-align:center">PRO</td>
813 * <td style="text-align:center">PRI</td>
814 * <td style="text-align:center">PAC</td>
815 * <td style="text-align:center">MOD</td>
816 * <td style="text-align:center">1R</td>
817 * </tr>
818 * <tr>
819 * <td>{@code PRI1.in(C1)} same package</td>
820 * <td></td>
821 * <td></td>
822 * <td style="text-align:center">PAC</td>
823 * <td style="text-align:center">MOD</td>
824 * <td style="text-align:center">1R</td>
825 * </tr>
826 * <tr>
827 * <td>{@code PRI1.in(C1)} different package</td>
828 * <td></td>
829 * <td></td>
830 * <td></td>
831 * <td style="text-align:center">MOD</td>
832 * <td style="text-align:center">1R</td>
833 * </tr>
834 * <tr>
835 * <td>{@code PRI1.in(D)} different module</td>
836 * <td></td>
837 * <td></td>
838 * <td></td>
839 * <td></td>
840 * <td style="text-align:center">2R</td>
841 * </tr>
842 * <tr>
843 * <td>{@code PRI1.dropLookupMode(PROTECTED)}</td>
844 * <td></td>
845 * <td style="text-align:center">PRI</td>
846 * <td style="text-align:center">PAC</td>
847 * <td style="text-align:center">MOD</td>
848 * <td style="text-align:center">1R</td>
849 * </tr>
850 * <tr>
851 * <td>{@code PRI1.dropLookupMode(PRIVATE)}</td>
852 * <td></td>
853 * <td></td>
854 * <td style="text-align:center">PAC</td>
855 * <td style="text-align:center">MOD</td>
856 * <td style="text-align:center">1R</td>
857 * </tr>
858 * <tr>
859 * <td>{@code PRI1.dropLookupMode(PACKAGE)}</td>
860 * <td></td>
861 * <td></td>
862 * <td></td>
863 * <td style="text-align:center">MOD</td>
864 * <td style="text-align:center">1R</td>
865 * </tr>
866 * <tr>
867 * <td>{@code PRI1.dropLookupMode(MODULE)}</td>
868 * <td></td>
869 * <td></td>
870 * <td></td>
871 * <td></td>
872 * <td style="text-align:center">1R</td>
873 * </tr>
874 * <tr>
875 * <td>{@code PRI1.dropLookupMode(PUBLIC)}</td>
876 * <td></td>
877 * <td></td>
878 * <td></td>
879 * <td></td>
880 * <td style="text-align:center">none</td>
881 * <tr>
882 * <td>{@code PRI2 = privateLookupIn(D,CL)}</td>
883 * <td style="text-align:center">PRO</td>
884 * <td style="text-align:center">PRI</td>
885 * <td style="text-align:center">PAC</td>
886 * <td></td>
887 * <td style="text-align:center">2R</td>
888 * </tr>
889 * <tr>
890 * <td>{@code privateLookupIn(D,PRI1)}</td>
891 * <td style="text-align:center">PRO</td>
892 * <td style="text-align:center">PRI</td>
893 * <td style="text-align:center">PAC</td>
894 * <td></td>
895 * <td style="text-align:center">2R</td>
896 * </tr>
897 * <tr>
898 * <td>{@code privateLookupIn(C,PRI2)} fails</td>
899 * <td></td>
900 * <td></td>
901 * <td></td>
902 * <td></td>
903 * <td style="text-align:center">IAE</td>
904 * </tr>
905 * <tr>
906 * <td>{@code PRI2.in(D2)} same package</td>
907 * <td></td>
908 * <td></td>
909 * <td style="text-align:center">PAC</td>
910 * <td></td>
911 * <td style="text-align:center">2R</td>
912 * </tr>
913 * <tr>
914 * <td>{@code PRI2.in(D2)} different package</td>
915 * <td></td>
916 * <td></td>
917 * <td></td>
918 * <td></td>
919 * <td style="text-align:center">2R</td>
920 * </tr>
921 * <tr>
922 * <td>{@code PRI2.in(C1)} hop back to module</td>
923 * <td></td>
924 * <td></td>
925 * <td></td>
926 * <td></td>
927 * <td style="text-align:center">2R</td>
928 * </tr>
929 * <tr>
930 * <td>{@code PRI2.in(E)} hop to third module</td>
931 * <td></td>
932 * <td></td>
933 * <td></td>
934 * <td></td>
935 * <td style="text-align:center">none</td>
936 * </tr>
937 * <tr>
938 * <td>{@code PRI2.dropLookupMode(PROTECTED)}</td>
939 * <td></td>
940 * <td style="text-align:center">PRI</td>
941 * <td style="text-align:center">PAC</td>
942 * <td></td>
943 * <td style="text-align:center">2R</td>
944 * </tr>
945 * <tr>
946 * <td>{@code PRI2.dropLookupMode(PRIVATE)}</td>
947 * <td></td>
948 * <td></td>
949 * <td style="text-align:center">PAC</td>
950 * <td></td>
951 * <td style="text-align:center">2R</td>
952 * </tr>
953 * <tr>
954 * <td>{@code PRI2.dropLookupMode(PACKAGE)}</td>
955 * <td></td>
956 * <td></td>
957 * <td></td>
958 * <td></td>
959 * <td style="text-align:center">2R</td>
960 * </tr>
961 * <tr>
962 * <td>{@code PRI2.dropLookupMode(MODULE)}</td>
963 * <td></td>
964 * <td></td>
965 * <td></td>
966 * <td></td>
967 * <td style="text-align:center">2R</td>
968 * </tr>
969 * <tr>
970 * <td>{@code PRI2.dropLookupMode(PUBLIC)}</td>
971 * <td></td>
972 * <td></td>
973 * <td></td>
974 * <td></td>
975 * <td style="text-align:center">none</td>
976 * </tr>
977 * <tr>
978 * <td>{@code CL.dropLookupMode(PROTECTED)}</td>
979 * <td></td>
980 * <td style="text-align:center">PRI</td>
981 * <td style="text-align:center">PAC</td>
982 * <td style="text-align:center">MOD</td>
983 * <td style="text-align:center">1R</td>
984 * </tr>
985 * <tr>
986 * <td>{@code CL.dropLookupMode(PRIVATE)}</td>
987 * <td></td>
988 * <td></td>
989 * <td style="text-align:center">PAC</td>
990 * <td style="text-align:center">MOD</td>
991 * <td style="text-align:center">1R</td>
992 * </tr>
993 * <tr>
994 * <td>{@code CL.dropLookupMode(PACKAGE)}</td>
995 * <td></td>
996 * <td></td>
997 * <td></td>
998 * <td style="text-align:center">MOD</td>
999 * <td style="text-align:center">1R</td>
1000 * </tr>
1001 * <tr>
1002 * <td>{@code CL.dropLookupMode(MODULE)}</td>
1003 * <td></td>
1004 * <td></td>
1005 * <td></td>
1006 * <td></td>
1007 * <td style="text-align:center">1R</td>
1008 * </tr>
1009 * <tr>
1010 * <td>{@code CL.dropLookupMode(PUBLIC)}</td>
1011 * <td></td>
1012 * <td></td>
1013 * <td></td>
1014 * <td></td>
1015 * <td style="text-align:center">none</td>
1016 * </tr>
1017 * <tr>
1018 * <td>{@code PUB = publicLookup()}</td>
1019 * <td></td>
1020 * <td></td>
1021 * <td></td>
1022 * <td></td>
1023 * <td style="text-align:center">U</td>
1024 * </tr>
1025 * <tr>
1026 * <td>{@code PUB.in(D)} different module</td>
1027 * <td></td>
1028 * <td></td>
1029 * <td></td>
1030 * <td></td>
1031 * <td style="text-align:center">U</td>
1032 * </tr>
1033 * <tr>
1034 * <td>{@code PUB.in(D).in(E)} third module</td>
1035 * <td></td>
1036 * <td></td>
1037 * <td></td>
1038 * <td></td>
1039 * <td style="text-align:center">U</td>
1040 * </tr>
1041 * <tr>
1042 * <td>{@code PUB.dropLookupMode(UNCONDITIONAL)}</td>
1043 * <td></td>
1044 * <td></td>
1045 * <td></td>
1046 * <td></td>
1047 * <td style="text-align:center">none</td>
1048 * </tr>
1049 * <tr>
1050 * <td>{@code privateLookupIn(C1,PUB)} fails</td>
1051 * <td></td>
1052 * <td></td>
1053 * <td></td>
1054 * <td></td>
1055 * <td style="text-align:center">IAE</td>
1056 * </tr>
1057 * <tr>
1058 * <td>{@code ANY.in(X)}, for inaccessible {@code X}</td>
1059 * <td></td>
1060 * <td></td>
1061 * <td></td>
1062 * <td></td>
1063 * <td style="text-align:center">none</td>
1064 * </tr>
1065 * </tbody>
1066 * </table>
1067 *
1068 * <p>
1069 * Notes:
1070 * <ul>
1071 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1072 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1073 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1074 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1075 * <li>{@code PRO} indicates {@link #PROTECTED} bit set,
1076 * {@code PRI} indicates {@link #PRIVATE} bit set,
1077 * {@code PAC} indicates {@link #PACKAGE} bit set,
1078 * {@code MOD} indicates {@link #MODULE} bit set,
1079 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1080 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1081 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1082 * <li>Public access comes in three kinds:
1083 * <ul>
1084 * <li>unconditional ({@code U}): the lookup assumes readability.
1085 * The lookup has {@code null} previous lookup class.
1086 * <li>one-module-reads ({@code 1R}): the module access checking is
1087 * performed with respect to the lookup class. The lookup has {@code null}
1088 * previous lookup class.
1089 * <li>two-module-reads ({@code 2R}): the module access checking is
1090 * performed with respect to the lookup class and the previous lookup class.
1091 * The lookup has a non-null previous lookup class which is in a
1092 * different module from the current lookup class.
1093 * </ul>
1094 * <li>Any attempt to reach a third module loses all access.</li>
1095 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1096 * all access modes are dropped.</li>
1097 * </ul>
1098 *
1099 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1100 * Although bytecode instructions can only refer to classes in
1101 * a related class loader, this API can search for methods in any
1102 * class, as long as a reference to its {@code Class} object is
1103 * available. Such cross-loader references are also possible with the
1104 * Core Reflection API, and are impossible to bytecode instructions
1105 * such as {@code invokestatic} or {@code getfield}.
1106 * There is a {@linkplain java.lang.SecurityManager security manager API}
1107 * to allow applications to check such cross-loader references.
1108 * These checks apply to both the {@code MethodHandles.Lookup} API
1109 * and the Core Reflection API
1110 * (as found on {@link java.lang.Class Class}).
1111 * <p>
1112 * If a security manager is present, member and class lookups are subject to
1113 * additional checks.
1114 * From one to three calls are made to the security manager.
1115 * Any of these calls can refuse access by throwing a
1116 * {@link java.lang.SecurityException SecurityException}.
1117 * Define {@code smgr} as the security manager,
1118 * {@code lookc} as the lookup class of the current lookup object,
1119 * {@code refc} as the containing class in which the member
1120 * is being sought, and {@code defc} as the class in which the
1121 * member is actually defined.
1122 * (If a class or other type is being accessed,
1123 * the {@code refc} and {@code defc} values are the class itself.)
1124 * The value {@code lookc} is defined as <em>not present</em>
1125 * if the current lookup object does not have
1126 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1127 * The calls are made according to the following rules:
1128 * <ul>
1129 * <li><b>Step 1:</b>
1130 * If {@code lookc} is not present, or if its class loader is not
1131 * the same as or an ancestor of the class loader of {@code refc},
1132 * then {@link SecurityManager#checkPackageAccess
1133 * smgr.checkPackageAccess(refcPkg)} is called,
1134 * where {@code refcPkg} is the package of {@code refc}.
1135 * <li><b>Step 2a:</b>
1136 * If the retrieved member is not public and
1137 * {@code lookc} is not present, then
1138 * {@link SecurityManager#checkPermission smgr.checkPermission}
1139 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1140 * <li><b>Step 2b:</b>
1141 * If the retrieved class has a {@code null} class loader,
1142 * and {@code lookc} is not present, then
1143 * {@link SecurityManager#checkPermission smgr.checkPermission}
1144 * with {@code RuntimePermission("getClassLoader")} is called.
1145 * <li><b>Step 3:</b>
1146 * If the retrieved member is not public,
1147 * and if {@code lookc} is not present,
1148 * and if {@code defc} and {@code refc} are different,
1149 * then {@link SecurityManager#checkPackageAccess
1150 * smgr.checkPackageAccess(defcPkg)} is called,
1151 * where {@code defcPkg} is the package of {@code defc}.
1152 * </ul>
1153 * Security checks are performed after other access checks have passed.
1154 * Therefore, the above rules presuppose a member or class that is public,
1155 * or else that is being accessed from a lookup class that has
1156 * rights to access the member or class.
1157 * <p>
1158 * If a security manager is present and the current lookup object does not have
1159 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1160 * {@link #defineClass(byte[]) defineClass}
1161 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1162 * with {@code RuntimePermission("defineClass")}.
1163 *
1164 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1165 * A small number of Java methods have a special property called caller sensitivity.
1166 * A <em>caller-sensitive</em> method can behave differently depending on the
1167 * identity of its immediate caller.
1168 * <p>
1169 * If a method handle for a caller-sensitive method is requested,
1170 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1171 * but they take account of the lookup class in a special way.
1172 * The resulting method handle behaves as if it were called
1173 * from an instruction contained in the lookup class,
1174 * so that the caller-sensitive method detects the lookup class.
1175 * (By contrast, the invoker of the method handle is disregarded.)
1176 * Thus, in the case of caller-sensitive methods,
1177 * different lookup classes may give rise to
1178 * differently behaving method handles.
1179 * <p>
1180 * In cases where the lookup object is
1181 * {@link MethodHandles#publicLookup() publicLookup()},
1182 * or some other lookup object without the
1183 * {@linkplain #hasFullPrivilegeAccess() full privilege access},
1184 * the lookup class is disregarded.
1185 * In such cases, no caller-sensitive method handle can be created,
1186 * access is forbidden, and the lookup fails with an
1187 * {@code IllegalAccessException}.
1188 * <p style="font-size:smaller;">
1189 * <em>Discussion:</em>
1190 * For example, the caller-sensitive method
1191 * {@link java.lang.Class#forName(String) Class.forName(x)}
1192 * can return varying classes or throw varying exceptions,
1193 * depending on the class loader of the class that calls it.
1194 * A public lookup of {@code Class.forName} will fail, because
1195 * there is no reasonable way to determine its bytecode behavior.
1196 * <p style="font-size:smaller;">
1197 * If an application caches method handles for broad sharing,
1198 * it should use {@code publicLookup()} to create them.
1199 * If there is a lookup of {@code Class.forName}, it will fail,
1200 * and the application must take appropriate action in that case.
1201 * It may be that a later lookup, perhaps during the invocation of a
1202 * bootstrap method, can incorporate the specific identity
1203 * of the caller, making the method accessible.
1204 * <p style="font-size:smaller;">
1205 * The function {@code MethodHandles.lookup} is caller sensitive
1206 * so that there can be a secure foundation for lookups.
1207 * Nearly all other methods in the JSR 292 API rely on lookup
1208 * objects to check access requests.
1209 *
1210 * @revised 9
1211 */
1212 public static final
1213 class Lookup {
1214 /** The class on behalf of whom the lookup is being performed. */
1215 private final Class<?> lookupClass;
1216
1217 /** previous lookup class */
1218 private final Class<?> prevLookupClass;
1219
1220 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1221 private final int allowedModes;
1222
1223 static {
1224 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1225 }
1226
1227 /** A single-bit mask representing {@code public} access,
1228 * which may contribute to the result of {@link #lookupModes lookupModes}.
1229 * The value, {@code 0x01}, happens to be the same as the value of the
1230 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1231 * <p>
1232 * A {@code Lookup} with this lookup mode performs cross-module access check
1233 * with respect to the {@linkplain #lookupClass() lookup class} and
1234 * {@linkplain #previousLookupClass() previous lookup class} if present.
1235 */
1236 public static final int PUBLIC = Modifier.PUBLIC;
1237
1238 /** A single-bit mask representing {@code private} access,
1239 * which may contribute to the result of {@link #lookupModes lookupModes}.
1240 * The value, {@code 0x02}, happens to be the same as the value of the
1241 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1242 */
1243 public static final int PRIVATE = Modifier.PRIVATE;
1244
1245 /** A single-bit mask representing {@code protected} access,
1246 * which may contribute to the result of {@link #lookupModes lookupModes}.
1247 * The value, {@code 0x04}, happens to be the same as the value of the
1248 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1249 */
1250 public static final int PROTECTED = Modifier.PROTECTED;
1251
1252 /** A single-bit mask representing {@code package} access (default access),
1253 * which may contribute to the result of {@link #lookupModes lookupModes}.
1254 * The value is {@code 0x08}, which does not correspond meaningfully to
1255 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1256 */
1257 public static final int PACKAGE = Modifier.STATIC;
1258
1259 /** A single-bit mask representing {@code module} access,
1260 * which may contribute to the result of {@link #lookupModes lookupModes}.
1261 * The value is {@code 0x10}, which does not correspond meaningfully to
1262 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1263 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1264 * with this lookup mode can access all public types in the module of the
1265 * lookup class and public types in packages exported by other modules
1266 * to the module of the lookup class.
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 */
1274 public static final int MODULE = PACKAGE << 1;
1275
1276 /** A single-bit mask representing {@code unconditional} access
1277 * which may contribute to the result of {@link #lookupModes lookupModes}.
1278 * The value is {@code 0x20}, which does not correspond meaningfully to
1279 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1280 * A {@code Lookup} with this lookup mode assumes {@linkplain
1281 * java.lang.Module#canRead(java.lang.Module) readability}.
1282 * This lookup mode can access all public members of public types
1283 * of all modules when the type is in a package that is {@link
1284 * java.lang.Module#isExported(String) exported unconditionally}.
1285 *
1286 * <p>
1287 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1288 * previous lookup class} is always {@code null}.
1289 *
1290 * @since 9
1291 * @spec JPMS
1292 * @see #publicLookup()
1293 */
1294 public static final int UNCONDITIONAL = PACKAGE << 2;
1295
1296 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
1297 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
1298 private static final int TRUSTED = -1;
1299
1300 /*
1301 * Adjust PUBLIC => PUBLIC|MODULE|UNCONDITIONAL
1302 * Adjust 0 => PACKAGE
1303 */
1304 private static int fixmods(int mods) {
1305 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
1306 if (Modifier.isPublic(mods))
1307 mods |= UNCONDITIONAL;
1308 return (mods != 0) ? mods : PACKAGE;
1309 }
1310
1311 /** Tells which class is performing the lookup. It is this class against
1312 * which checks are performed for visibility and access permissions.
1313 * <p>
1314 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1315 * access checks are performed against both the lookup class and the previous lookup class.
1316 * <p>
1317 * The class implies a maximum level of access permission,
1318 * but the permissions may be additionally limited by the bitmask
1319 * {@link #lookupModes lookupModes}, which controls whether non-public members
1320 * can be accessed.
1321 * @return the lookup class, on behalf of which this lookup object finds members
1322 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1323 */
1324 public Class<?> lookupClass() {
1325 return lookupClass;
1326 }
1327
1328 /** Reports a lookup class in another module that this lookup object
1329 * was previously teleported from, or {@code null}.
1330 * <p>
1331 * A {@code Lookup} object produced by the factory methods, such as the
1332 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1333 * has {@code null} previous lookup class.
1334 * A {@code Lookup} object has a non-null previous lookup class
1335 * when this lookup was teleported from an old lookup class
1336 * in one module to a new lookup class in another module.
1337 *
1338 * @return the lookup class in another module that this lookup object was
1339 * previously teleported from, or {@code null}
1340 * @since 14
1341 * @see #in(Class)
1342 * @see MethodHandles#privateLookupIn(Class, Lookup)
1343 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1344 */
1345 public Class<?> previousLookupClass() {
1346 return prevLookupClass;
1347 }
1348
1349 // This is just for calling out to MethodHandleImpl.
1350 private Class<?> lookupClassOrNull() {
1351 if (allowedModes == TRUSTED) {
1352 return null;
1353 }
1354 if (allowedModes == UNCONDITIONAL) {
1355 // use Object as the caller to pass to VM doing resolution
1356 return Object.class;
1357 }
1358 return lookupClass;
1359 }
1360
1361 /** Tells which access-protection classes of members this lookup object can produce.
1362 * The result is a bit-mask of the bits
1363 * {@linkplain #PUBLIC PUBLIC (0x01)},
1364 * {@linkplain #PRIVATE PRIVATE (0x02)},
1365 * {@linkplain #PROTECTED PROTECTED (0x04)},
1366 * {@linkplain #PACKAGE PACKAGE (0x08)},
1367 * {@linkplain #MODULE MODULE (0x10)},
1368 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
1369 * <p>
1370 * A freshly-created lookup object
1371 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1372 * all possible bits set, except {@code UNCONDITIONAL}.
1373 * A lookup object on a new lookup class
1374 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1375 * may have some mode bits set to zero.
1376 * Mode bits can also be
1377 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1378 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1379 * The purpose of this is to restrict access via the new lookup object,
1380 * so that it can access only names which can be reached by the original
1381 * lookup object, and also by the new lookup class.
1382 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1383 * @see #in
1384 * @see #dropLookupMode
1385 *
1386 * @revised 9
1387 * @spec JPMS
1388 */
1389 public int lookupModes() {
1390 return allowedModes & ALL_MODES;
1391 }
1392
1393 /** Embody the current class (the lookupClass) as a lookup class
1394 * for method handle creation.
1395 * Must be called by from a method in this package,
1396 * which in turn is called by a method not in this package.
1397 */
1398 Lookup(Class<?> lookupClass) {
1399 this(lookupClass, null, FULL_POWER_MODES);
1400 // make sure we haven't accidentally picked up a privileged class:
1401 checkUnprivilegedlookupClass(lookupClass);
1402 }
1403
1404 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1405 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1406 && prevLookupClass.getModule() != lookupClass.getModule());
1407 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1408 this.lookupClass = lookupClass;
1409 this.prevLookupClass = prevLookupClass;
1410 this.allowedModes = allowedModes;
1411 }
1412
1413 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1414 // make sure we haven't accidentally picked up a privileged class:
1415 checkUnprivilegedlookupClass(lookupClass);
1416 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1417 }
1418
1419 /**
1420 * Creates a lookup on the specified new lookup class.
1421 * The resulting object will report the specified
1422 * class as its own {@link #lookupClass() lookupClass}.
1423 *
1424 * <p>
1425 * However, the resulting {@code Lookup} object is guaranteed
1426 * to have no more access capabilities than the original.
1427 * In particular, access capabilities can be lost as follows:<ul>
1428 * <li>If the new lookup class is in a different module from the old one,
1429 * i.e. {@link #MODULE MODULE} access is lost.
1430 * <li>If the new lookup class is in a different package
1431 * than the old one, protected and default (package) members will not be accessible,
1432 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1433 * <li>If the new lookup class is not within the same package member
1434 * as the old one, private members will not be accessible, and protected members
1435 * will not be accessible by virtue of inheritance,
1436 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1437 * (Protected members may continue to be accessible because of package sharing.)
1438 * <li>If the new lookup class is not
1439 * {@linkplain #accessClass(Class) accessible} to this lookup,
1440 * then no members, not even public members, will be accessible
1441 * i.e. all access modes are lost.
1442 * <li>If the new lookup class, the old lookup class and the previous lookup class
1443 * are all in different modules i.e. teleporting to a third module,
1444 * all access modes are lost.
1445 * </ul>
1446 * <p>
1447 * The new previous lookup class is chosen as follows:
1448 * <ul>
1449 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1450 * the new previous lookup class is {@code null}.
1451 * <li>If the new lookup class is in the same module as the old lookup class,
1452 * the new previous lookup class is the old previous lookup class.
1453 * <li>If the new lookup class is in a different module from the old lookup class,
1454 * the new previous lookup class is the old lookup class.
1455 *</ul>
1456 * <p>
1457 * The resulting lookup's capabilities for loading classes
1458 * (used during {@link #findClass} invocations)
1459 * are determined by the lookup class' loader,
1460 * which may change due to this operation.
1461 * <p>
1462 * @param requestedLookupClass the desired lookup class for the new lookup object
1463 * @return a lookup object which reports the desired lookup class, or the same object
1464 * if there is no change
1465 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1466 * @throws NullPointerException if the argument is null
1467 *
1468 * @revised 9
1469 * @spec JPMS
1470 * @see #accessClass(Class)
1471 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1472 */
1473 public Lookup in(Class<?> requestedLookupClass) {
1474 Objects.requireNonNull(requestedLookupClass);
1475 if (requestedLookupClass.isPrimitive())
1476 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1477 if (requestedLookupClass.isArray())
1478 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1479
1480 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1481 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1482 if (requestedLookupClass == this.lookupClass)
1483 return this; // keep same capabilities
1484 int newModes = (allowedModes & FULL_POWER_MODES);
1485 Module fromModule = this.lookupClass.getModule();
1486 Module targetModule = requestedLookupClass.getModule();
1487 Class<?> plc = this.previousLookupClass();
1488 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1489 assert plc == null;
1490 newModes = UNCONDITIONAL;
1491 } else if (fromModule != targetModule) {
1492 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1493 // allow hopping back and forth between fromModule and plc's module
1494 // but not the third module
1495 newModes = 0;
1496 }
1497 // drop MODULE access
1498 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1499 // teleport from this lookup class
1500 plc = this.lookupClass;
1501 }
1502 if ((newModes & PACKAGE) != 0
1503 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1504 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1505 }
1506 // Allow nestmate lookups to be created without special privilege:
1507 if ((newModes & PRIVATE) != 0
1508 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1509 newModes &= ~(PRIVATE|PROTECTED);
1510 }
1511 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1512 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1513 // The requested class it not accessible from the lookup class.
1514 // No permissions.
1515 newModes = 0;
1516 }
1517 return newLookup(requestedLookupClass, plc, newModes);
1518 }
1519
1520 /**
1521 * Creates a lookup on the same lookup class which this lookup object
1522 * finds members, but with a lookup mode that has lost the given lookup mode.
1523 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1524 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
1525 * {@link #PROTECTED PROTECTED} is always
1526 * dropped and so the resulting lookup mode will never have this access capability.
1527 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
1528 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
1529 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
1530 * is dropped then the resulting lookup has no access. If {@code UNCONDITIONAL}
1531 * is dropped then the resulting lookup has no access.
1532 *
1533 * @apiNote
1534 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1535 * delegate non-public access within the package of the lookup class without
1536 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1537 * A lookup with {@code MODULE} but not
1538 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1539 * the module of the lookup class without conferring package access.
1540 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1541 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1542 * to public classes accessible to both the module of the lookup class
1543 * and the module of the previous lookup class.
1544 *
1545 * @param modeToDrop the lookup mode to drop
1546 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1547 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1548 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
1549 * @see MethodHandles#privateLookupIn
1550 * @since 9
1551 */
1552 public Lookup dropLookupMode(int modeToDrop) {
1553 int oldModes = lookupModes();
1554 int newModes = oldModes & ~(modeToDrop | PROTECTED);
1555 switch (modeToDrop) {
1556 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1557 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1558 case PACKAGE: newModes &= ~(PRIVATE); break;
1559 case PROTECTED:
1560 case PRIVATE:
1561 case UNCONDITIONAL: break;
1562 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1563 }
1564 if (newModes == oldModes) return this; // return self if no change
1565 return newLookup(lookupClass(), previousLookupClass(), newModes);
1566 }
1567
1568 /**
1569 * Defines a class to the same class loader and in the same runtime package and
1570 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1571 * {@linkplain #lookupClass() lookup class}.
1572 *
1573 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1574 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1575 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1576 * that the lookup object was created by a caller in the runtime package (or derived
1577 * from a lookup originally created by suitably privileged code to a target class in
1578 * the runtime package). </p>
1579 *
1580 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1581 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1582 * same package as the lookup class. </p>
1583 *
1584 * <p> This method does not run the class initializer. The class initializer may
1585 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1586 * Specification</em>. </p>
1587 *
1588 * <p> If there is a security manager and this lookup does not have {@linkplain
1589 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1590 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1591 *
1592 * @param bytes the class bytes
1593 * @return the {@code Class} object for the class
1594 * @throws IllegalArgumentException the bytes are for a class in a different package
1595 * to the lookup class
1596 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1597 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1598 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
1599 * @throws SecurityException if a security manager is present and it
1600 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1601 * @throws NullPointerException if {@code bytes} is {@code null}
1602 * @since 9
1603 * @spec JPMS
1604 * @see Lookup#privateLookupIn
1605 * @see Lookup#dropLookupMode
1606 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1607 */
1608 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1609 if (!hasFullPrivilegeAccess()) {
1610 SecurityManager sm = System.getSecurityManager();
1611 if (sm != null)
1612 sm.checkPermission(new RuntimePermission("defineClass"));
1613 }
1614 if ((lookupModes() & PACKAGE) == 0)
1615 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1616
1617 // parse class bytes to get class name (in internal form)
1618 bytes = bytes.clone();
1619 String name;
1620 try {
1621 ClassReader reader = new ClassReader(bytes);
1622 name = reader.getClassName();
1623 } catch (RuntimeException e) {
1624 // ASM exceptions are poorly specified
1625 ClassFormatError cfe = new ClassFormatError();
1626 cfe.initCause(e);
1627 throw cfe;
1628 }
1629
1630 // get package and class name in binary form
1631 String cn, pn;
1632 int index = name.lastIndexOf('/');
1633 if (index == -1) {
1634 cn = name;
1635 pn = "";
1636 } else {
1637 cn = name.replace('/', '.');
1638 pn = cn.substring(0, index);
1639 }
1640 if (!pn.equals(lookupClass.getPackageName())) {
1641 throw new IllegalArgumentException("Class not in same package as lookup class");
1642 }
1643
1644 // invoke the class loader's defineClass method
1645 ClassLoader loader = lookupClass.getClassLoader();
1646 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
1647 String source = "__Lookup_defineClass__";
1648 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
1649 return clazz;
1650 }
1651
1652 private ProtectionDomain lookupClassProtectionDomain() {
1653 ProtectionDomain pd = cachedProtectionDomain;
1654 if (pd == null) {
1655 cachedProtectionDomain = pd = protectionDomain(lookupClass);
1656 }
1657 return pd;
1658 }
1659
1660 private ProtectionDomain protectionDomain(Class<?> clazz) {
1661 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
1662 return AccessController.doPrivileged(pa);
1663 }
1664
1665 // cached protection domain
1666 private volatile ProtectionDomain cachedProtectionDomain;
1667
1668
1669 // Make sure outer class is initialized first.
1670 static { IMPL_NAMES.getClass(); }
1671
1672 /** Package-private version of lookup which is trusted. */
1673 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
1674
1675 /** Version of lookup which is trusted minimally.
1676 * It can only be used to create method handles to publicly accessible
1677 * members in packages that are exported unconditionally.
1678 */
1679 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
1680
1681 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1682 String name = lookupClass.getName();
1683 if (name.startsWith("java.lang.invoke."))
1684 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1685 }
1686
1687 /**
1688 * Displays the name of the class from which lookups are to be made.
1689 * followed with "/" and the name of the {@linkplain #previousLookupClass()
1690 * previous lookup class} if present.
1691 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1692 * If there are restrictions on the access permitted to this lookup,
1693 * this is indicated by adding a suffix to the class name, consisting
1694 * of a slash and a keyword. The keyword represents the strongest
1695 * allowed access, and is chosen as follows:
1696 * <ul>
1697 * <li>If no access is allowed, the suffix is "/noaccess".
1698 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
1699 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1700 * <li>If only public and module access are allowed, the suffix is "/module".
1701 * <li>If public and package access are allowed, the suffix is "/package".
1702 * <li>If public, package, and private access are allowed, the suffix is "/private".
1703 * </ul>
1704 * If none of the above cases apply, it is the case that full access
1705 * (public, module, package, private, and protected) is allowed.
1706 * In this case, no suffix is added.
1707 * This is true only of an object obtained originally from
1708 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1709 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1710 * always have restricted access, and will display a suffix.
1711 * <p>
1712 * (It may seem strange that protected access should be
1713 * stronger than private access. Viewed independently from
1714 * package access, protected access is the first to be lost,
1715 * because it requires a direct subclass relationship between
1716 * caller and callee.)
1717 * @see #in
1718 *
1719 * @revised 9
1720 * @spec JPMS
1721 */
1722 @Override
1723 public String toString() {
1724 String cname = lookupClass.getName();
1725 if (prevLookupClass != null)
1726 cname += "/" + prevLookupClass.getName();
1727 switch (allowedModes) {
1728 case 0: // no privileges
1729 return cname + "/noaccess";
1730 case UNCONDITIONAL:
1731 return cname + "/publicLookup";
1732 case PUBLIC:
1733 return cname + "/public";
1734 case PUBLIC|MODULE:
1735 return cname + "/module";
1736 case PUBLIC|PACKAGE:
1737 case PUBLIC|MODULE|PACKAGE:
1738 return cname + "/package";
1739 case FULL_POWER_MODES & (~PROTECTED):
1740 case FULL_POWER_MODES & ~(PROTECTED|MODULE):
1741 return cname + "/private";
1742 case FULL_POWER_MODES:
1743 case FULL_POWER_MODES & (~MODULE):
1744 return cname;
1745 case TRUSTED:
1746 return "/trusted"; // internal only; not exported
1747 default: // Should not happen, but it's a bitfield...
1748 cname = cname + "/" + Integer.toHexString(allowedModes);
1749 assert(false) : cname;
1750 return cname;
1751 }
1752 }
1753
1754 /**
1755 * Produces a method handle for a static method.
1756 * The type of the method handle will be that of the method.
1757 * (Since static methods do not take receivers, there is no
1758 * additional receiver argument inserted into the method handle type,
1759 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1760 * The method and all its argument types must be accessible to the lookup object.
1761 * <p>
1762 * The returned method handle will have
1763 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1764 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1765 * <p>
1766 * If the returned method handle is invoked, the method's class will
1767 * be initialized, if it has not already been initialized.
1768 * <p><b>Example:</b>
1769 * <blockquote><pre>{@code
1770 import static java.lang.invoke.MethodHandles.*;
1771 import static java.lang.invoke.MethodType.*;
1772 ...
1773 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1774 "asList", methodType(List.class, Object[].class));
1775 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1776 * }</pre></blockquote>
1777 * @param refc the class from which the method is accessed
1778 * @param name the name of the method
1779 * @param type the type of the method
1780 * @return the desired method handle
1781 * @throws NoSuchMethodException if the method does not exist
1782 * @throws IllegalAccessException if access checking fails,
1783 * or if the method is not {@code static},
1784 * or if the method's variable arity modifier bit
1785 * is set and {@code asVarargsCollector} fails
1786 * @throws SecurityException if a security manager is present and it
1787 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1788 * @throws NullPointerException if any argument is null
1789 */
1790 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1791 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1792 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
1793 }
1794
1795 /**
1796 * Produces a method handle for a virtual method.
1797 * The type of the method handle will be that of the method,
1798 * with the receiver type (usually {@code refc}) prepended.
1799 * The method and all its argument types must be accessible to the lookup object.
1800 * <p>
1801 * When called, the handle will treat the first argument as a receiver
1802 * and, for non-private methods, dispatch on the receiver's type to determine which method
1803 * implementation to enter.
1804 * For private methods the named method in {@code refc} will be invoked on the receiver.
1805 * (The dispatching action is identical with that performed by an
1806 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1807 * <p>
1808 * The first argument will be of type {@code refc} if the lookup
1809 * class has full privileges to access the member. Otherwise
1810 * the member must be {@code protected} and the first argument
1811 * will be restricted in type to the lookup class.
1812 * <p>
1813 * The returned method handle will have
1814 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1815 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1816 * <p>
1817 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1818 * instructions and method handles produced by {@code findVirtual},
1819 * if the class is {@code MethodHandle} and the name string is
1820 * {@code invokeExact} or {@code invoke}, the resulting
1821 * method handle is equivalent to one produced by
1822 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1823 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1824 * with the same {@code type} argument.
1825 * <p>
1826 * If the class is {@code VarHandle} and the name string corresponds to
1827 * the name of a signature-polymorphic access mode method, the resulting
1828 * method handle is equivalent to one produced by
1829 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1830 * the access mode corresponding to the name string and with the same
1831 * {@code type} arguments.
1832 * <p>
1833 * <b>Example:</b>
1834 * <blockquote><pre>{@code
1835 import static java.lang.invoke.MethodHandles.*;
1836 import static java.lang.invoke.MethodType.*;
1837 ...
1838 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1839 "concat", methodType(String.class, String.class));
1840 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1841 "hashCode", methodType(int.class));
1842 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1843 "hashCode", methodType(int.class));
1844 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1845 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1846 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1847 // interface method:
1848 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1849 "subSequence", methodType(CharSequence.class, int.class, int.class));
1850 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1851 // constructor "internal method" must be accessed differently:
1852 MethodType MT_newString = methodType(void.class); //()V for new String()
1853 try { assertEquals("impossible", lookup()
1854 .findVirtual(String.class, "<init>", MT_newString));
1855 } catch (NoSuchMethodException ex) { } // OK
1856 MethodHandle MH_newString = publicLookup()
1857 .findConstructor(String.class, MT_newString);
1858 assertEquals("", (String) MH_newString.invokeExact());
1859 * }</pre></blockquote>
1860 *
1861 * @param refc the class or interface from which the method is accessed
1862 * @param name the name of the method
1863 * @param type the type of the method, with the receiver argument omitted
1864 * @return the desired method handle
1865 * @throws NoSuchMethodException if the method does not exist
1866 * @throws IllegalAccessException if access checking fails,
1867 * or if the method is {@code static},
1868 * or if the method's variable arity modifier bit
1869 * is set and {@code asVarargsCollector} fails
1870 * @throws SecurityException if a security manager is present and it
1871 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1872 * @throws NullPointerException if any argument is null
1873 */
1874 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1875 if (refc == MethodHandle.class) {
1876 MethodHandle mh = findVirtualForMH(name, type);
1877 if (mh != null) return mh;
1878 } else if (refc == VarHandle.class) {
1879 MethodHandle mh = findVirtualForVH(name, type);
1880 if (mh != null) return mh;
1881 }
1882 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1883 MemberName method = resolveOrFail(refKind, refc, name, type);
1884 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
1885 }
1886 private MethodHandle findVirtualForMH(String name, MethodType type) {
1887 // these names require special lookups because of the implicit MethodType argument
1888 if ("invoke".equals(name))
1889 return invoker(type);
1890 if ("invokeExact".equals(name))
1891 return exactInvoker(type);
1892 assert(!MemberName.isMethodHandleInvokeName(name));
1893 return null;
1894 }
1895 private MethodHandle findVirtualForVH(String name, MethodType type) {
1896 try {
1897 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1898 } catch (IllegalArgumentException e) {
1899 return null;
1900 }
1901 }
1902
1903 /**
1904 * Produces a method handle which creates an object and initializes it, using
1905 * the constructor of the specified type.
1906 * The parameter types of the method handle will be those of the constructor,
1907 * while the return type will be a reference to the constructor's class.
1908 * The constructor and all its argument types must be accessible to the lookup object.
1909 * <p>
1910 * The requested type must have a return type of {@code void}.
1911 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1912 * <p>
1913 * The returned method handle will have
1914 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1915 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1916 * <p>
1917 * If the returned method handle is invoked, the constructor's class will
1918 * be initialized, if it has not already been initialized.
1919 * <p><b>Example:</b>
1920 * <blockquote><pre>{@code
1921 import static java.lang.invoke.MethodHandles.*;
1922 import static java.lang.invoke.MethodType.*;
1923 ...
1924 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1925 ArrayList.class, methodType(void.class, Collection.class));
1926 Collection orig = Arrays.asList("x", "y");
1927 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1928 assert(orig != copy);
1929 assertEquals(orig, copy);
1930 // a variable-arity constructor:
1931 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1932 ProcessBuilder.class, methodType(void.class, String[].class));
1933 ProcessBuilder pb = (ProcessBuilder)
1934 MH_newProcessBuilder.invoke("x", "y", "z");
1935 assertEquals("[x, y, z]", pb.command().toString());
1936 * }</pre></blockquote>
1937 * @param refc the class or interface from which the method is accessed
1938 * @param type the type of the method, with the receiver argument omitted, and a void return type
1939 * @return the desired method handle
1940 * @throws NoSuchMethodException if the constructor does not exist
1941 * @throws IllegalAccessException if access checking fails
1942 * or if the method's variable arity modifier bit
1943 * is set and {@code asVarargsCollector} fails
1944 * @throws SecurityException if a security manager is present and it
1945 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1946 * @throws NullPointerException if any argument is null
1947 */
1948 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1949 if (refc.isArray()) {
1950 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1951 }
1952 String name = "<init>";
1953 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1954 return getDirectConstructor(refc, ctor);
1955 }
1956
1957 /**
1958 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
1959 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
1960 * Such a resolution, as specified in JVMS 5.4.3.1 section, attempts to locate and load the class,
1961 * and then determines whether the class is accessible to this lookup object.
1962 * <p>
1963 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
1964 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
1965 *
1966 * @param targetName the fully qualified name of the class to be looked up.
1967 * @return the requested class.
1968 * @throws SecurityException if a security manager is present and it
1969 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1970 * @throws LinkageError if the linkage fails
1971 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1972 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1973 * modes.
1974 * @since 9
1975 * @jvms 5.4.3.1 Class and Interface Resolution
1976 */
1977 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1978 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1979 return accessClass(targetClass);
1980 }
1981
1982 /**
1983 * Determines if a class can be accessed from the lookup context defined by
1984 * this {@code Lookup} object. The static initializer of the class is not run.
1985 * <p>
1986 * If the {@code targetClass} is in the same module as the lookup class,
1987 * the lookup class is {@code LC} in module {@code M1} and
1988 * the previous lookup class is in module {@code M0} or
1989 * {@code null} if not present,
1990 * {@code targetClass} is accessible if and only if one of the following is true:
1991 * <ul>
1992 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
1993 * {@code LC} or other class in the same nest of {@code LC}.</li>
1994 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
1995 * in the same runtime package of {@code LC}.</li>
1996 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
1997 * a public type in {@code M1}.</li>
1998 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
1999 * a public type in a package exported by {@code M1} to at least {@code M0}
2000 * if the previous lookup class is present; otherwise, {@code targetClass}
2001 * is a public type in a package exported by {@code M1} unconditionally.</li>
2002 * </ul>
2003 *
2004 * <p>
2005 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2006 * can access public types in all modules when the type is in a package
2007 * that is exported unconditionally.
2008 * <p>
2009 * Otherwise, the target class is in a different module from {@code lookupClass},
2010 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2011 * is inaccessible.
2012 * <p>
2013 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2014 * {@code M1} is the module containing {@code lookupClass} and
2015 * {@code M2} is the module containing {@code targetClass},
2016 * then {@code targetClass} is accessible if and only if
2017 * <ul>
2018 * <li>{@code M1} reads {@code M2}, and
2019 * <li>{@code targetClass} is public and in a package exported by
2020 * {@code M2} at least to {@code M1}.
2021 * </ul>
2022 * <p>
2023 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2024 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2025 * containing the previous lookup class, then {@code targetClass} is accessible
2026 * if and only if one of the following is true:
2027 * <ul>
2028 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2029 * {@linkplain Module#reads reads} {@code M0} and the type is
2030 * in a package that is exported to at least {@code M1}.
2031 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2032 * {@linkplain Module#reads reads} {@code M1} and the type is
2033 * in a package that is exported to at least {@code M0}.
2034 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2035 * and {@code M1} reads {@code M2} and the type is in a package
2036 * that is exported to at least both {@code M0} and {@code M2}.
2037 * </ul>
2038 * <p>
2039 * Otherwise, {@code targetClass} is not accessible.
2040 *
2041 * @param targetClass the class to be access-checked
2042 * @return the class that has been access-checked
2043 * @throws IllegalAccessException if the class is not accessible from the lookup class
2044 * and previous lookup class, if present, using the allowed access modes.
2045 * @throws SecurityException if a security manager is present and it
2046 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2047 * @since 9
2048 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2049 */
2050 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2051 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2052 throw new MemberName(targetClass).makeAccessException("access violation", this);
2053 }
2054 checkSecurityManager(targetClass, null);
2055 return targetClass;
2056 }
2057
2058 /**
2059 * Produces an early-bound method handle for a virtual method.
2060 * It will bypass checks for overriding methods on the receiver,
2061 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2062 * instruction from within the explicitly specified {@code specialCaller}.
2063 * The type of the method handle will be that of the method,
2064 * with a suitably restricted receiver type prepended.
2065 * (The receiver type will be {@code specialCaller} or a subtype.)
2066 * The method and all its argument types must be accessible
2067 * to the lookup object.
2068 * <p>
2069 * Before method resolution,
2070 * if the explicitly specified caller class is not identical with the
2071 * lookup class, or if this lookup object does not have
2072 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2073 * privileges, the access fails.
2074 * <p>
2075 * The returned method handle will have
2076 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2077 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2078 * <p style="font-size:smaller;">
2079 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2080 * even though the {@code invokespecial} instruction can refer to them
2081 * in special circumstances. Use {@link #findConstructor findConstructor}
2082 * to access instance initialization methods in a safe manner.)</em>
2083 * <p><b>Example:</b>
2084 * <blockquote><pre>{@code
2085 import static java.lang.invoke.MethodHandles.*;
2086 import static java.lang.invoke.MethodType.*;
2087 ...
2088 static class Listie extends ArrayList {
2089 public String toString() { return "[wee Listie]"; }
2090 static Lookup lookup() { return MethodHandles.lookup(); }
2091 }
2092 ...
2093 // no access to constructor via invokeSpecial:
2094 MethodHandle MH_newListie = Listie.lookup()
2095 .findConstructor(Listie.class, methodType(void.class));
2096 Listie l = (Listie) MH_newListie.invokeExact();
2097 try { assertEquals("impossible", Listie.lookup().findSpecial(
2098 Listie.class, "<init>", methodType(void.class), Listie.class));
2099 } catch (NoSuchMethodException ex) { } // OK
2100 // access to super and self methods via invokeSpecial:
2101 MethodHandle MH_super = Listie.lookup().findSpecial(
2102 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2103 MethodHandle MH_this = Listie.lookup().findSpecial(
2104 Listie.class, "toString" , methodType(String.class), Listie.class);
2105 MethodHandle MH_duper = Listie.lookup().findSpecial(
2106 Object.class, "toString" , methodType(String.class), Listie.class);
2107 assertEquals("[]", (String) MH_super.invokeExact(l));
2108 assertEquals(""+l, (String) MH_this.invokeExact(l));
2109 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2110 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2111 String.class, "toString", methodType(String.class), Listie.class));
2112 } catch (IllegalAccessException ex) { } // OK
2113 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2114 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2115 * }</pre></blockquote>
2116 *
2117 * @param refc the class or interface from which the method is accessed
2118 * @param name the name of the method (which must not be "<init>")
2119 * @param type the type of the method, with the receiver argument omitted
2120 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2121 * @return the desired method handle
2122 * @throws NoSuchMethodException if the method does not exist
2123 * @throws IllegalAccessException if access checking fails,
2124 * or if the method is {@code static},
2125 * or if the method's variable arity modifier bit
2126 * is set and {@code asVarargsCollector} fails
2127 * @throws SecurityException if a security manager is present and it
2128 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2129 * @throws NullPointerException if any argument is null
2130 */
2131 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2132 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2133 checkSpecialCaller(specialCaller, refc);
2134 Lookup specialLookup = this.in(specialCaller);
2135 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2136 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
2137 }
2138
2139 /**
2140 * Produces a method handle giving read access to a non-static field.
2141 * The type of the method handle will have a return type of the field's
2142 * value type.
2143 * The method handle's single argument will be the instance containing
2144 * the field.
2145 * Access checking is performed immediately on behalf of the lookup class.
2146 * @param refc the class or interface from which the method is accessed
2147 * @param name the field's name
2148 * @param type the field's type
2149 * @return a method handle which can load values from the field
2150 * @throws NoSuchFieldException if the field does not exist
2151 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2152 * @throws SecurityException if a security manager is present and it
2153 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2154 * @throws NullPointerException if any argument is null
2155 * @see #findVarHandle(Class, String, Class)
2156 */
2157 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2158 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2159 return getDirectField(REF_getField, refc, field);
2160 }
2161
2162 /**
2163 * Produces a method handle giving write access to a non-static field.
2164 * The type of the method handle will have a void return type.
2165 * The method handle will take two arguments, the instance containing
2166 * the field, and the value to be stored.
2167 * The second argument will be of the field's value type.
2168 * Access checking is performed immediately on behalf of the lookup class.
2169 * @param refc the class or interface from which the method is accessed
2170 * @param name the field's name
2171 * @param type the field's type
2172 * @return a method handle which can store values into the field
2173 * @throws NoSuchFieldException if the field does not exist
2174 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2175 * or {@code final}
2176 * @throws SecurityException if a security manager is present and it
2177 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2178 * @throws NullPointerException if any argument is null
2179 * @see #findVarHandle(Class, String, Class)
2180 */
2181 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2182 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2183 return getDirectField(REF_putField, refc, field);
2184 }
2185
2186 /**
2187 * Produces a VarHandle giving access to a non-static field {@code name}
2188 * of type {@code type} declared in a class of type {@code recv}.
2189 * The VarHandle's variable type is {@code type} and it has one
2190 * coordinate type, {@code recv}.
2191 * <p>
2192 * Access checking is performed immediately on behalf of the lookup
2193 * class.
2194 * <p>
2195 * Certain access modes of the returned VarHandle are unsupported under
2196 * the following conditions:
2197 * <ul>
2198 * <li>if the field is declared {@code final}, then the write, atomic
2199 * update, numeric atomic update, and bitwise atomic update access
2200 * modes are unsupported.
2201 * <li>if the field type is anything other than {@code byte},
2202 * {@code short}, {@code char}, {@code int}, {@code long},
2203 * {@code float}, or {@code double} then numeric atomic update
2204 * access modes are unsupported.
2205 * <li>if the field type is anything other than {@code boolean},
2206 * {@code byte}, {@code short}, {@code char}, {@code int} or
2207 * {@code long} then bitwise atomic update access modes are
2208 * unsupported.
2209 * </ul>
2210 * <p>
2211 * If the field is declared {@code volatile} then the returned VarHandle
2212 * will override access to the field (effectively ignore the
2213 * {@code volatile} declaration) in accordance to its specified
2214 * access modes.
2215 * <p>
2216 * If the field type is {@code float} or {@code double} then numeric
2217 * and atomic update access modes compare values using their bitwise
2218 * representation (see {@link Float#floatToRawIntBits} and
2219 * {@link Double#doubleToRawLongBits}, respectively).
2220 * @apiNote
2221 * Bitwise comparison of {@code float} values or {@code double} values,
2222 * as performed by the numeric and atomic update access modes, differ
2223 * from the primitive {@code ==} operator and the {@link Float#equals}
2224 * and {@link Double#equals} methods, specifically with respect to
2225 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2226 * Care should be taken when performing a compare and set or a compare
2227 * and exchange operation with such values since the operation may
2228 * unexpectedly fail.
2229 * There are many possible NaN values that are considered to be
2230 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2231 * provided by Java can distinguish between them. Operation failure can
2232 * occur if the expected or witness value is a NaN value and it is
2233 * transformed (perhaps in a platform specific manner) into another NaN
2234 * value, and thus has a different bitwise representation (see
2235 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2236 * details).
2237 * The values {@code -0.0} and {@code +0.0} have different bitwise
2238 * representations but are considered equal when using the primitive
2239 * {@code ==} operator. Operation failure can occur if, for example, a
2240 * numeric algorithm computes an expected value to be say {@code -0.0}
2241 * and previously computed the witness value to be say {@code +0.0}.
2242 * @param recv the receiver class, of type {@code R}, that declares the
2243 * non-static field
2244 * @param name the field's name
2245 * @param type the field's type, of type {@code T}
2246 * @return a VarHandle giving access to non-static fields.
2247 * @throws NoSuchFieldException if the field does not exist
2248 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2249 * @throws SecurityException if a security manager is present and it
2250 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2251 * @throws NullPointerException if any argument is null
2252 * @since 9
2253 */
2254 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2255 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
2256 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
2257 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
2258 }
2259
2260 /**
2261 * Produces a method handle giving read access to a static field.
2262 * The type of the method handle will have a return type of the field's
2263 * value type.
2264 * The method handle will take no arguments.
2265 * Access checking is performed immediately on behalf of the lookup class.
2266 * <p>
2267 * If the returned method handle is invoked, the field's class will
2268 * be initialized, if it has not already been initialized.
2269 * @param refc the class or interface from which the method is accessed
2270 * @param name the field's name
2271 * @param type the field's type
2272 * @return a method handle which can load values from the field
2273 * @throws NoSuchFieldException if the field does not exist
2274 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2275 * @throws SecurityException if a security manager is present and it
2276 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2277 * @throws NullPointerException if any argument is null
2278 */
2279 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2280 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
2281 return getDirectField(REF_getStatic, refc, field);
2282 }
2283
2284 /**
2285 * Produces a method handle giving write access to a static field.
2286 * The type of the method handle will have a void return type.
2287 * The method handle will take a single
2288 * argument, of the field's value type, the value to be stored.
2289 * Access checking is performed immediately on behalf of the lookup class.
2290 * <p>
2291 * If the returned method handle is invoked, the field's class will
2292 * be initialized, if it has not already been initialized.
2293 * @param refc the class or interface from which the method is accessed
2294 * @param name the field's name
2295 * @param type the field's type
2296 * @return a method handle which can store values into the field
2297 * @throws NoSuchFieldException if the field does not exist
2298 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2299 * or is {@code final}
2300 * @throws SecurityException if a security manager is present and it
2301 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2302 * @throws NullPointerException if any argument is null
2303 */
2304 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2305 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
2306 return getDirectField(REF_putStatic, refc, field);
2307 }
2308
2309 /**
2310 * Produces a VarHandle giving access to a static field {@code name} of
2311 * type {@code type} declared in a class of type {@code decl}.
2312 * The VarHandle's variable type is {@code type} and it has no
2313 * coordinate types.
2314 * <p>
2315 * Access checking is performed immediately on behalf of the lookup
2316 * class.
2317 * <p>
2318 * If the returned VarHandle is operated on, the declaring class will be
2319 * initialized, if it has not already been initialized.
2320 * <p>
2321 * Certain access modes of the returned VarHandle are unsupported under
2322 * the following conditions:
2323 * <ul>
2324 * <li>if the field is declared {@code final}, then the write, atomic
2325 * update, numeric atomic update, and bitwise atomic update access
2326 * modes are unsupported.
2327 * <li>if the field type is anything other than {@code byte},
2328 * {@code short}, {@code char}, {@code int}, {@code long},
2329 * {@code float}, or {@code double}, then numeric atomic update
2330 * access modes are unsupported.
2331 * <li>if the field type is anything other than {@code boolean},
2332 * {@code byte}, {@code short}, {@code char}, {@code int} or
2333 * {@code long} then bitwise atomic update access modes are
2334 * unsupported.
2335 * </ul>
2336 * <p>
2337 * If the field is declared {@code volatile} then the returned VarHandle
2338 * will override access to the field (effectively ignore the
2339 * {@code volatile} declaration) in accordance to its specified
2340 * access modes.
2341 * <p>
2342 * If the field type is {@code float} or {@code double} then numeric
2343 * and atomic update access modes compare values using their bitwise
2344 * representation (see {@link Float#floatToRawIntBits} and
2345 * {@link Double#doubleToRawLongBits}, respectively).
2346 * @apiNote
2347 * Bitwise comparison of {@code float} values or {@code double} values,
2348 * as performed by the numeric and atomic update access modes, differ
2349 * from the primitive {@code ==} operator and the {@link Float#equals}
2350 * and {@link Double#equals} methods, specifically with respect to
2351 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2352 * Care should be taken when performing a compare and set or a compare
2353 * and exchange operation with such values since the operation may
2354 * unexpectedly fail.
2355 * There are many possible NaN values that are considered to be
2356 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2357 * provided by Java can distinguish between them. Operation failure can
2358 * occur if the expected or witness value is a NaN value and it is
2359 * transformed (perhaps in a platform specific manner) into another NaN
2360 * value, and thus has a different bitwise representation (see
2361 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2362 * details).
2363 * The values {@code -0.0} and {@code +0.0} have different bitwise
2364 * representations but are considered equal when using the primitive
2365 * {@code ==} operator. Operation failure can occur if, for example, a
2366 * numeric algorithm computes an expected value to be say {@code -0.0}
2367 * and previously computed the witness value to be say {@code +0.0}.
2368 * @param decl the class that declares the static field
2369 * @param name the field's name
2370 * @param type the field's type, of type {@code T}
2371 * @return a VarHandle giving access to a static field
2372 * @throws NoSuchFieldException if the field does not exist
2373 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2374 * @throws SecurityException if a security manager is present and it
2375 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2376 * @throws NullPointerException if any argument is null
2377 * @since 9
2378 */
2379 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2380 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
2381 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
2382 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
2383 }
2384
2385 /**
2386 * Produces an early-bound method handle for a non-static method.
2387 * The receiver must have a supertype {@code defc} in which a method
2388 * of the given name and type is accessible to the lookup class.
2389 * The method and all its argument types must be accessible to the lookup object.
2390 * The type of the method handle will be that of the method,
2391 * without any insertion of an additional receiver parameter.
2392 * The given receiver will be bound into the method handle,
2393 * so that every call to the method handle will invoke the
2394 * requested method on the given receiver.
2395 * <p>
2396 * The returned method handle will have
2397 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2398 * the method's variable arity modifier bit ({@code 0x0080}) is set
2399 * <em>and</em> the trailing array argument is not the only argument.
2400 * (If the trailing array argument is the only argument,
2401 * the given receiver value will be bound to it.)
2402 * <p>
2403 * This is almost equivalent to the following code, with some differences noted below:
2404 * <blockquote><pre>{@code
2405 import static java.lang.invoke.MethodHandles.*;
2406 import static java.lang.invoke.MethodType.*;
2407 ...
2408 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
2409 MethodHandle mh1 = mh0.bindTo(receiver);
2410 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
2411 return mh1;
2412 * }</pre></blockquote>
2413 * where {@code defc} is either {@code receiver.getClass()} or a super
2414 * type of that class, in which the requested method is accessible
2415 * to the lookup class.
2416 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
2417 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
2418 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
2419 * the receiver is restricted by {@code findVirtual} to the lookup class.)
2420 * @param receiver the object from which the method is accessed
2421 * @param name the name of the method
2422 * @param type the type of the method, with the receiver argument omitted
2423 * @return the desired method handle
2424 * @throws NoSuchMethodException if the method does not exist
2425 * @throws IllegalAccessException if access checking fails
2426 * or if the method's variable arity modifier bit
2427 * is set and {@code asVarargsCollector} fails
2428 * @throws SecurityException if a security manager is present and it
2429 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2430 * @throws NullPointerException if any argument is null
2431 * @see MethodHandle#bindTo
2432 * @see #findVirtual
2433 */
2434 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2435 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2436 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2437 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
2438 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2439 throw new IllegalAccessException("The restricted defining class " +
2440 mh.type().leadingReferenceParameter().getName() +
2441 " is not assignable from receiver class " +
2442 receiver.getClass().getName());
2443 }
2444 return mh.bindArgumentL(0, receiver).setVarargs(method);
2445 }
2446
2447 /**
2448 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2449 * to <i>m</i>, if the lookup class has permission.
2450 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2451 * If <i>m</i> is virtual, overriding is respected on every call.
2452 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2453 * The type of the method handle will be that of the method,
2454 * with the receiver type prepended (but only if it is non-static).
2455 * If the method's {@code accessible} flag is not set,
2456 * access checking is performed immediately on behalf of the lookup class.
2457 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2458 * <p>
2459 * The returned method handle will have
2460 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2461 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2462 * <p>
2463 * If <i>m</i> is static, and
2464 * if the returned method handle is invoked, the method's class will
2465 * be initialized, if it has not already been initialized.
2466 * @param m the reflected method
2467 * @return a method handle which can invoke the reflected method
2468 * @throws IllegalAccessException if access checking fails
2469 * or if the method's variable arity modifier bit
2470 * is set and {@code asVarargsCollector} fails
2471 * @throws NullPointerException if the argument is null
2472 */
2473 public MethodHandle unreflect(Method m) throws IllegalAccessException {
2474 if (m.getDeclaringClass() == MethodHandle.class) {
2475 MethodHandle mh = unreflectForMH(m);
2476 if (mh != null) return mh;
2477 }
2478 if (m.getDeclaringClass() == VarHandle.class) {
2479 MethodHandle mh = unreflectForVH(m);
2480 if (mh != null) return mh;
2481 }
2482 MemberName method = new MemberName(m);
2483 byte refKind = method.getReferenceKind();
2484 if (refKind == REF_invokeSpecial)
2485 refKind = REF_invokeVirtual;
2486 assert(method.isMethod());
2487 @SuppressWarnings("deprecation")
2488 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
2489 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
2490 }
2491 private MethodHandle unreflectForMH(Method m) {
2492 // these names require special lookups because they throw UnsupportedOperationException
2493 if (MemberName.isMethodHandleInvokeName(m.getName()))
2494 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
2495 return null;
2496 }
2497 private MethodHandle unreflectForVH(Method m) {
2498 // these names require special lookups because they throw UnsupportedOperationException
2499 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
2500 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
2501 return null;
2502 }
2503
2504 /**
2505 * Produces a method handle for a reflected method.
2506 * It will bypass checks for overriding methods on the receiver,
2507 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2508 * instruction from within the explicitly specified {@code specialCaller}.
2509 * The type of the method handle will be that of the method,
2510 * with a suitably restricted receiver type prepended.
2511 * (The receiver type will be {@code specialCaller} or a subtype.)
2512 * If the method's {@code accessible} flag is not set,
2513 * access checking is performed immediately on behalf of the lookup class,
2514 * as if {@code invokespecial} instruction were being linked.
2515 * <p>
2516 * Before method resolution,
2517 * if the explicitly specified caller class is not identical with the
2518 * lookup class, or if this lookup object does not have
2519 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2520 * privileges, the access fails.
2521 * <p>
2522 * The returned method handle will have
2523 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2524 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2525 * @param m the reflected method
2526 * @param specialCaller the class nominally calling the method
2527 * @return a method handle which can invoke the reflected method
2528 * @throws IllegalAccessException if access checking fails,
2529 * or if the method is {@code static},
2530 * or if the method's variable arity modifier bit
2531 * is set and {@code asVarargsCollector} fails
2532 * @throws NullPointerException if any argument is null
2533 */
2534 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
2535 checkSpecialCaller(specialCaller, m.getDeclaringClass());
2536 Lookup specialLookup = this.in(specialCaller);
2537 MemberName method = new MemberName(m, true);
2538 assert(method.isMethod());
2539 // ignore m.isAccessible: this is a new kind of access
2540 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
2541 }
2542
2543 /**
2544 * Produces a method handle for a reflected constructor.
2545 * The type of the method handle will be that of the constructor,
2546 * with the return type changed to the declaring class.
2547 * The method handle will perform a {@code newInstance} operation,
2548 * creating a new instance of the constructor's class on the
2549 * arguments passed to the method handle.
2550 * <p>
2551 * If the constructor's {@code accessible} flag is not set,
2552 * access checking is performed immediately on behalf of the lookup class.
2553 * <p>
2554 * The returned method handle will have
2555 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2556 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2557 * <p>
2558 * If the returned method handle is invoked, the constructor's class will
2559 * be initialized, if it has not already been initialized.
2560 * @param c the reflected constructor
2561 * @return a method handle which can invoke the reflected constructor
2562 * @throws IllegalAccessException if access checking fails
2563 * or if the method's variable arity modifier bit
2564 * is set and {@code asVarargsCollector} fails
2565 * @throws NullPointerException if the argument is null
2566 */
2567 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
2568 MemberName ctor = new MemberName(c);
2569 assert(ctor.isConstructor());
2570 @SuppressWarnings("deprecation")
2571 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
2572 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
2573 }
2574
2575 /**
2576 * Produces a method handle giving read access to a reflected field.
2577 * The type of the method handle will have a return type of the field's
2578 * value type.
2579 * If the field is {@code static}, the method handle will take no arguments.
2580 * Otherwise, its single argument will be the instance containing
2581 * the field.
2582 * If the {@code Field} object's {@code accessible} flag is not set,
2583 * access checking is performed immediately on behalf of the lookup class.
2584 * <p>
2585 * If the field is static, and
2586 * if the returned method handle is invoked, the field's class will
2587 * be initialized, if it has not already been initialized.
2588 * @param f the reflected field
2589 * @return a method handle which can load values from the reflected field
2590 * @throws IllegalAccessException if access checking fails
2591 * @throws NullPointerException if the argument is null
2592 */
2593 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
2594 return unreflectField(f, false);
2595 }
2596
2597 /**
2598 * Produces a method handle giving write access to a reflected field.
2599 * The type of the method handle will have a void return type.
2600 * If the field is {@code static}, the method handle will take a single
2601 * argument, of the field's value type, the value to be stored.
2602 * Otherwise, the two arguments will be the instance containing
2603 * the field, and the value to be stored.
2604 * If the {@code Field} object's {@code accessible} flag is not set,
2605 * access checking is performed immediately on behalf of the lookup class.
2606 * <p>
2607 * If the field is {@code final}, write access will not be
2608 * allowed and access checking will fail, except under certain
2609 * narrow circumstances documented for {@link Field#set Field.set}.
2610 * A method handle is returned only if a corresponding call to
2611 * the {@code Field} object's {@code set} method could return
2612 * normally. In particular, fields which are both {@code static}
2613 * and {@code final} may never be set.
2614 * <p>
2615 * If the field is {@code static}, and
2616 * if the returned method handle is invoked, the field's class will
2617 * be initialized, if it has not already been initialized.
2618 * @param f the reflected field
2619 * @return a method handle which can store values into the reflected field
2620 * @throws IllegalAccessException if access checking fails,
2621 * or if the field is {@code final} and write access
2622 * is not enabled on the {@code Field} object
2623 * @throws NullPointerException if the argument is null
2624 */
2625 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
2626 return unreflectField(f, true);
2627 }
2628
2629 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
2630 MemberName field = new MemberName(f, isSetter);
2631 if (isSetter && field.isStatic() && field.isFinal())
2632 throw field.makeAccessException("static final field has no write access", this);
2633 assert(isSetter
2634 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
2635 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
2636 @SuppressWarnings("deprecation")
2637 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
2638 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
2639 }
2640
2641 /**
2642 * Produces a VarHandle giving access to a reflected field {@code f}
2643 * of type {@code T} declared in a class of type {@code R}.
2644 * The VarHandle's variable type is {@code T}.
2645 * If the field is non-static the VarHandle has one coordinate type,
2646 * {@code R}. Otherwise, the field is static, and the VarHandle has no
2647 * coordinate types.
2648 * <p>
2649 * Access checking is performed immediately on behalf of the lookup
2650 * class, regardless of the value of the field's {@code accessible}
2651 * flag.
2652 * <p>
2653 * If the field is static, and if the returned VarHandle is operated
2654 * on, the field's declaring class will be initialized, if it has not
2655 * already been initialized.
2656 * <p>
2657 * Certain access modes of the returned VarHandle are unsupported under
2658 * the following conditions:
2659 * <ul>
2660 * <li>if the field is declared {@code final}, then the write, atomic
2661 * update, numeric atomic update, and bitwise atomic update access
2662 * modes are unsupported.
2663 * <li>if the field type is anything other than {@code byte},
2664 * {@code short}, {@code char}, {@code int}, {@code long},
2665 * {@code float}, or {@code double} then numeric atomic update
2666 * access modes are unsupported.
2667 * <li>if the field type is anything other than {@code boolean},
2668 * {@code byte}, {@code short}, {@code char}, {@code int} or
2669 * {@code long} then bitwise atomic update access modes are
2670 * unsupported.
2671 * </ul>
2672 * <p>
2673 * If the field is declared {@code volatile} then the returned VarHandle
2674 * will override access to the field (effectively ignore the
2675 * {@code volatile} declaration) in accordance to its specified
2676 * access modes.
2677 * <p>
2678 * If the field type is {@code float} or {@code double} then numeric
2679 * and atomic update access modes compare values using their bitwise
2680 * representation (see {@link Float#floatToRawIntBits} and
2681 * {@link Double#doubleToRawLongBits}, respectively).
2682 * @apiNote
2683 * Bitwise comparison of {@code float} values or {@code double} values,
2684 * as performed by the numeric and atomic update access modes, differ
2685 * from the primitive {@code ==} operator and the {@link Float#equals}
2686 * and {@link Double#equals} methods, specifically with respect to
2687 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2688 * Care should be taken when performing a compare and set or a compare
2689 * and exchange operation with such values since the operation may
2690 * unexpectedly fail.
2691 * There are many possible NaN values that are considered to be
2692 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2693 * provided by Java can distinguish between them. Operation failure can
2694 * occur if the expected or witness value is a NaN value and it is
2695 * transformed (perhaps in a platform specific manner) into another NaN
2696 * value, and thus has a different bitwise representation (see
2697 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2698 * details).
2699 * The values {@code -0.0} and {@code +0.0} have different bitwise
2700 * representations but are considered equal when using the primitive
2701 * {@code ==} operator. Operation failure can occur if, for example, a
2702 * numeric algorithm computes an expected value to be say {@code -0.0}
2703 * and previously computed the witness value to be say {@code +0.0}.
2704 * @param f the reflected field, with a field of type {@code T}, and
2705 * a declaring class of type {@code R}
2706 * @return a VarHandle giving access to non-static fields or a static
2707 * field
2708 * @throws IllegalAccessException if access checking fails
2709 * @throws NullPointerException if the argument is null
2710 * @since 9
2711 */
2712 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
2713 MemberName getField = new MemberName(f, false);
2714 MemberName putField = new MemberName(f, true);
2715 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
2716 f.getDeclaringClass(), getField, putField);
2717 }
2718
2719 /**
2720 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2721 * created by this lookup object or a similar one.
2722 * Security and access checks are performed to ensure that this lookup object
2723 * is capable of reproducing the target method handle.
2724 * This means that the cracking may fail if target is a direct method handle
2725 * but was created by an unrelated lookup object.
2726 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
2727 * and was created by a lookup object for a different class.
2728 * @param target a direct method handle to crack into symbolic reference components
2729 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
2730 * @throws SecurityException if a security manager is present and it
2731 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2732 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
2733 * @throws NullPointerException if the target is {@code null}
2734 * @see MethodHandleInfo
2735 * @since 1.8
2736 */
2737 public MethodHandleInfo revealDirect(MethodHandle target) {
2738 MemberName member = target.internalMemberName();
2739 if (member == null || (!member.isResolved() &&
2740 !member.isMethodHandleInvoke() &&
2741 !member.isVarHandleMethodInvoke()))
2742 throw newIllegalArgumentException("not a direct method handle");
2743 Class<?> defc = member.getDeclaringClass();
2744 byte refKind = member.getReferenceKind();
2745 assert(MethodHandleNatives.refKindIsValid(refKind));
2746 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2747 // Devirtualized method invocation is usually formally virtual.
2748 // To avoid creating extra MemberName objects for this common case,
2749 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2750 refKind = REF_invokeVirtual;
2751 if (refKind == REF_invokeVirtual && defc.isInterface())
2752 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2753 refKind = REF_invokeInterface;
2754 // Check SM permissions and member access before cracking.
2755 try {
2756 checkAccess(refKind, defc, member);
2757 checkSecurityManager(defc, member);
2758 } catch (IllegalAccessException ex) {
2759 throw new IllegalArgumentException(ex);
2760 }
2761 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2762 Class<?> callerClass = target.internalCallerClass();
2763 if (!hasFullPrivilegeAccess() || callerClass != lookupClass())
2764 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2765 }
2766 // Produce the handle to the results.
2767 return new InfoFromMemberName(this, member, refKind);
2768 }
2769
2770 /// Helper methods, all package-private.
2771
2772 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2773 checkSymbolicClass(refc); // do this before attempting to resolve
2774 Objects.requireNonNull(name);
2775 Objects.requireNonNull(type);
2776 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2777 NoSuchFieldException.class);
2778 }
2779
2780 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2781 checkSymbolicClass(refc); // do this before attempting to resolve
2782 Objects.requireNonNull(name);
2783 Objects.requireNonNull(type);
2784 checkMethodName(refKind, name); // NPE check on name
2785 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2786 NoSuchMethodException.class);
2787 }
2788
2789 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2790 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2791 Objects.requireNonNull(member.getName());
2792 Objects.requireNonNull(member.getType());
2793 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2794 ReflectiveOperationException.class);
2795 }
2796
2797 MemberName resolveOrNull(byte refKind, MemberName member) {
2798 // do this before attempting to resolve
2799 if (!isClassAccessible(member.getDeclaringClass())) {
2800 return null;
2801 }
2802 Objects.requireNonNull(member.getName());
2803 Objects.requireNonNull(member.getType());
2804 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2805 }
2806
2807 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2808 if (!isClassAccessible(refc)) {
2809 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2810 }
2811 }
2812
2813 boolean isClassAccessible(Class<?> refc) {
2814 Objects.requireNonNull(refc);
2815 Class<?> caller = lookupClassOrNull();
2816 return caller == null || VerifyAccess.isClassAccessible(refc, caller, prevLookupClass, allowedModes);
2817 }
2818
2819 /** Check name for an illegal leading "<" character. */
2820 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2821 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2822 throw new NoSuchMethodException("illegal method name: "+name);
2823 }
2824
2825
2826 /**
2827 * Find my trustable caller class if m is a caller sensitive method.
2828 * If this lookup object has full privilege access, then the caller class is the lookupClass.
2829 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2830 */
2831 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
2832 if (MethodHandleNatives.isCallerSensitive(m) && !hasFullPrivilegeAccess()) {
2833 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
2834 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2835 }
2836 return this;
2837 }
2838
2839 /**
2840 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
2841 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
2842 *
2843 * @deprecated This method was originally designed to test {@code PRIVATE} access
2844 * that implies full privilege access but {@code MODULE} access has since become
2845 * independent of {@code PRIVATE} access. It is recommended to call
2846 * {@link #hasFullPrivilegeAccess()} instead.
2847 * @since 9
2848 */
2849 @Deprecated(since="14")
2850 public boolean hasPrivateAccess() {
2851 return hasFullPrivilegeAccess();
2852 }
2853
2854 /**
2855 * Returns {@code true} if this lookup has <em>full privilege access</em>,
2856 * i.e. {@code PRIVATE} and {@code MODULE} access.
2857 * A {@code Lookup} object must have full privilege access in order to
2858 * access all members that are allowed to the {@linkplain #lookupClass() lookup class}.
2859 *
2860 * @return {@code true} if this lookup has full privilege access.
2861 * @since 14
2862 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
2863 */
2864 public boolean hasFullPrivilegeAccess() {
2865 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
2866 }
2867
2868 /**
2869 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2870 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2871 * If this lookup object has full privilege access, then the caller class is the lookupClass.
2872 */
2873 void checkSecurityManager(Class<?> refc, MemberName m) {
2874 if (allowedModes == TRUSTED) return;
2875
2876 SecurityManager smgr = System.getSecurityManager();
2877 if (smgr == null) return;
2878
2879 // Step 1:
2880 boolean fullPowerLookup = hasFullPrivilegeAccess();
2881 if (!fullPowerLookup ||
2882 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2883 ReflectUtil.checkPackageAccess(refc);
2884 }
2885
2886 if (m == null) { // findClass or accessClass
2887 // Step 2b:
2888 if (!fullPowerLookup) {
2889 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2890 }
2891 return;
2892 }
2893
2894 // Step 2a:
2895 if (m.isPublic()) return;
2896 if (!fullPowerLookup) {
2897 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2898 }
2899
2900 // Step 3:
2901 Class<?> defc = m.getDeclaringClass();
2902 if (!fullPowerLookup && defc != refc) {
2903 ReflectUtil.checkPackageAccess(defc);
2904 }
2905 }
2906
2907 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2908 boolean wantStatic = (refKind == REF_invokeStatic);
2909 String message;
2910 if (m.isConstructor())
2911 message = "expected a method, not a constructor";
2912 else if (!m.isMethod())
2913 message = "expected a method";
2914 else if (wantStatic != m.isStatic())
2915 message = wantStatic ? "expected a static method" : "expected a non-static method";
2916 else
2917 { checkAccess(refKind, refc, m); return; }
2918 throw m.makeAccessException(message, this);
2919 }
2920
2921 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2922 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2923 String message;
2924 if (wantStatic != m.isStatic())
2925 message = wantStatic ? "expected a static field" : "expected a non-static field";
2926 else
2927 { checkAccess(refKind, refc, m); return; }
2928 throw m.makeAccessException(message, this);
2929 }
2930
2931 /** Check public/protected/private bits on the symbolic reference class and its member. */
2932 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2933 assert(m.referenceKindIsConsistentWith(refKind) &&
2934 MethodHandleNatives.refKindIsValid(refKind) &&
2935 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2936 int allowedModes = this.allowedModes;
2937 if (allowedModes == TRUSTED) return;
2938 int mods = m.getModifiers();
2939 if (Modifier.isProtected(mods) &&
2940 refKind == REF_invokeVirtual &&
2941 m.getDeclaringClass() == Object.class &&
2942 m.getName().equals("clone") &&
2943 refc.isArray()) {
2944 // The JVM does this hack also.
2945 // (See ClassVerifier::verify_invoke_instructions
2946 // and LinkResolver::check_method_accessability.)
2947 // Because the JVM does not allow separate methods on array types,
2948 // there is no separate method for int[].clone.
2949 // All arrays simply inherit Object.clone.
2950 // But for access checking logic, we make Object.clone
2951 // (normally protected) appear to be public.
2952 // Later on, when the DirectMethodHandle is created,
2953 // its leading argument will be restricted to the
2954 // requested array type.
2955 // N.B. The return type is not adjusted, because
2956 // that is *not* the bytecode behavior.
2957 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2958 }
2959 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2960 // cannot "new" a protected ctor in a different package
2961 mods ^= Modifier.PROTECTED;
2962 }
2963 if (Modifier.isFinal(mods) &&
2964 MethodHandleNatives.refKindIsSetter(refKind))
2965 throw m.makeAccessException("unexpected set of a final field", this);
2966 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2967 if ((requestedModes & allowedModes) != 0) {
2968 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2969 mods, lookupClass(), previousLookupClass(), allowedModes))
2970 return;
2971 } else {
2972 // Protected members can also be checked as if they were package-private.
2973 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2974 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2975 return;
2976 }
2977 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2978 }
2979
2980 String accessFailedMessage(Class<?> refc, MemberName m) {
2981 Class<?> defc = m.getDeclaringClass();
2982 int mods = m.getModifiers();
2983 // check the class first:
2984 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2985 (defc == refc ||
2986 Modifier.isPublic(refc.getModifiers())));
2987 if (!classOK && (allowedModes & PACKAGE) != 0) {
2988 // ignore previous lookup class to check if default package access
2989 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
2990 (defc == refc ||
2991 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
2992 }
2993 if (!classOK)
2994 return "class is not public";
2995 if (Modifier.isPublic(mods))
2996 return "access to public member failed"; // (how?, module not readable?)
2997 if (Modifier.isPrivate(mods))
2998 return "member is private";
2999 if (Modifier.isProtected(mods))
3000 return "member is protected";
3001 return "member is private to package";
3002 }
3003
3004 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3005 int allowedModes = this.allowedModes;
3006 if (allowedModes == TRUSTED) return;
3007 if ((lookupModes() & PRIVATE) == 0
3008 || (specialCaller != lookupClass()
3009 // ensure non-abstract methods in superinterfaces can be special-invoked
3010 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3011 throw new MemberName(specialCaller).
3012 makeAccessException("no private access for invokespecial", this);
3013 }
3014
3015 private boolean restrictProtectedReceiver(MemberName method) {
3016 // The accessing class only has the right to use a protected member
3017 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3018 if (!method.isProtected() || method.isStatic()
3019 || allowedModes == TRUSTED
3020 || method.getDeclaringClass() == lookupClass()
3021 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3022 return false;
3023 return true;
3024 }
3025 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3026 assert(!method.isStatic());
3027 // receiver type of mh is too wide; narrow to caller
3028 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3029 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3030 }
3031 MethodType rawType = mh.type();
3032 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3033 MethodType narrowType = rawType.changeParameterType(0, caller);
3034 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3035 assert(mh.viewAsTypeChecks(narrowType, true));
3036 return mh.copyWith(narrowType, mh.form);
3037 }
3038
3039 /** Check access and get the requested method. */
3040 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3041 final boolean doRestrict = true;
3042 final boolean checkSecurity = true;
3043 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3044 }
3045 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3046 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3047 final boolean doRestrict = false;
3048 final boolean checkSecurity = true;
3049 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
3050 }
3051 /** Check access and get the requested method, eliding security manager checks. */
3052 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3053 final boolean doRestrict = true;
3054 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3055 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3056 }
3057 /** Common code for all methods; do not call directly except from immediately above. */
3058 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3059 boolean checkSecurity,
3060 boolean doRestrict,
3061 Lookup boundCaller) throws IllegalAccessException {
3062 checkMethod(refKind, refc, method);
3063 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3064 if (checkSecurity)
3065 checkSecurityManager(refc, method);
3066 assert(!method.isMethodHandleInvoke());
3067
3068 if (refKind == REF_invokeSpecial &&
3069 refc != lookupClass() &&
3070 !refc.isInterface() &&
3071 refc != lookupClass().getSuperclass() &&
3072 refc.isAssignableFrom(lookupClass())) {
3073 assert(!method.getName().equals("<init>")); // not this code path
3074
3075 // Per JVMS 6.5, desc. of invokespecial instruction:
3076 // If the method is in a superclass of the LC,
3077 // and if our original search was above LC.super,
3078 // repeat the search (symbolic lookup) from LC.super
3079 // and continue with the direct superclass of that class,
3080 // and so forth, until a match is found or no further superclasses exist.
3081 // FIXME: MemberName.resolve should handle this instead.
3082 Class<?> refcAsSuper = lookupClass();
3083 MemberName m2;
3084 do {
3085 refcAsSuper = refcAsSuper.getSuperclass();
3086 m2 = new MemberName(refcAsSuper,
3087 method.getName(),
3088 method.getMethodType(),
3089 REF_invokeSpecial);
3090 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
3091 } while (m2 == null && // no method is found yet
3092 refc != refcAsSuper); // search up to refc
3093 if (m2 == null) throw new InternalError(method.toString());
3094 method = m2;
3095 refc = refcAsSuper;
3096 // redo basic checks
3097 checkMethod(refKind, refc, method);
3098 }
3099 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3100 MethodHandle mh = dmh;
3101 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3102 if ((doRestrict && refKind == REF_invokeSpecial) ||
3103 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
3104 mh = restrictReceiver(method, dmh, lookupClass());
3105 }
3106 mh = maybeBindCaller(method, mh, boundCaller);
3107 mh = mh.setVarargs(method);
3108 return mh;
3109 }
3110 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
3111 throws IllegalAccessException {
3112 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3113 return mh;
3114
3115 // boundCaller must have full privilege access.
3116 // It should have been checked by findBoundCallerLookup. Safe to check this again.
3117 if (!boundCaller.hasFullPrivilegeAccess())
3118 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3119
3120 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
3121 // Note: caller will apply varargs after this step happens.
3122 return cbmh;
3123 }
3124
3125 /** Check access and get the requested field. */
3126 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3127 final boolean checkSecurity = true;
3128 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3129 }
3130 /** Check access and get the requested field, eliding security manager checks. */
3131 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3132 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3133 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3134 }
3135 /** Common code for all fields; do not call directly except from immediately above. */
3136 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
3137 boolean checkSecurity) throws IllegalAccessException {
3138 checkField(refKind, refc, field);
3139 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3140 if (checkSecurity)
3141 checkSecurityManager(refc, field);
3142 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3143 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3144 restrictProtectedReceiver(field));
3145 if (doRestrict)
3146 return restrictReceiver(field, dmh, lookupClass());
3147 return dmh;
3148 }
3149 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3150 Class<?> refc, MemberName getField, MemberName putField)
3151 throws IllegalAccessException {
3152 final boolean checkSecurity = true;
3153 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3154 }
3155 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
3156 Class<?> refc, MemberName getField, MemberName putField)
3157 throws IllegalAccessException {
3158 final boolean checkSecurity = false;
3159 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3160 }
3161 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3162 Class<?> refc, MemberName getField, MemberName putField,
3163 boolean checkSecurity) throws IllegalAccessException {
3164 assert getField.isStatic() == putField.isStatic();
3165 assert getField.isGetter() && putField.isSetter();
3166 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3167 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3168
3169 checkField(getRefKind, refc, getField);
3170 if (checkSecurity)
3171 checkSecurityManager(refc, getField);
3172
3173 if (!putField.isFinal()) {
3174 // A VarHandle does not support updates to final fields, any
3175 // such VarHandle to a final field will be read-only and
3176 // therefore the following write-based accessibility checks are
3177 // only required for non-final fields
3178 checkField(putRefKind, refc, putField);
3179 if (checkSecurity)
3180 checkSecurityManager(refc, putField);
3181 }
3182
3183 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3184 restrictProtectedReceiver(getField));
3185 if (doRestrict) {
3186 assert !getField.isStatic();
3187 // receiver type of VarHandle is too wide; narrow to caller
3188 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3189 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3190 }
3191 refc = lookupClass();
3192 }
3193 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
3194 }
3195 /** Check access and get the requested constructor. */
3196 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3197 final boolean checkSecurity = true;
3198 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3199 }
3200 /** Check access and get the requested constructor, eliding security manager checks. */
3201 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3202 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3203 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3204 }
3205 /** Common code for all constructors; do not call directly except from immediately above. */
3206 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
3207 boolean checkSecurity) throws IllegalAccessException {
3208 assert(ctor.isConstructor());
3209 checkAccess(REF_newInvokeSpecial, refc, ctor);
3210 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3211 if (checkSecurity)
3212 checkSecurityManager(refc, ctor);
3213 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3214 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3215 }
3216
3217 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3218 */
3219 /*non-public*/
3220 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
3221 throws ReflectiveOperationException {
3222 if (!(type instanceof Class || type instanceof MethodType))
3223 throw new InternalError("unresolved MemberName");
3224 MemberName member = new MemberName(refKind, defc, name, type);
3225 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3226 if (mh != null) {
3227 checkSymbolicClass(defc);
3228 return mh;
3229 }
3230 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3231 // Treat MethodHandle.invoke and invokeExact specially.
3232 mh = findVirtualForMH(member.getName(), member.getMethodType());
3233 if (mh != null) {
3234 return mh;
3235 }
3236 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3237 // Treat signature-polymorphic methods on VarHandle specially.
3238 mh = findVirtualForVH(member.getName(), member.getMethodType());
3239 if (mh != null) {
3240 return mh;
3241 }
3242 }
3243 MemberName resolved = resolveOrFail(refKind, member);
3244 mh = getDirectMethodForConstant(refKind, defc, resolved);
3245 if (mh instanceof DirectMethodHandle
3246 && canBeCached(refKind, defc, resolved)) {
3247 MemberName key = mh.internalMemberName();
3248 if (key != null) {
3249 key = key.asNormalOriginal();
3250 }
3251 if (member.equals(key)) { // better safe than sorry
3252 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
3253 }
3254 }
3255 return mh;
3256 }
3257 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
3258 if (refKind == REF_invokeSpecial) {
3259 return false;
3260 }
3261 if (!Modifier.isPublic(defc.getModifiers()) ||
3262 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
3263 !member.isPublic() ||
3264 member.isCallerSensitive()) {
3265 return false;
3266 }
3267 ClassLoader loader = defc.getClassLoader();
3268 if (loader != null) {
3269 ClassLoader sysl = ClassLoader.getSystemClassLoader();
3270 boolean found = false;
3271 while (sysl != null) {
3272 if (loader == sysl) { found = true; break; }
3273 sysl = sysl.getParent();
3274 }
3275 if (!found) {
3276 return false;
3277 }
3278 }
3279 try {
3280 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
3281 new MemberName(refKind, defc, member.getName(), member.getType()));
3282 if (resolved2 == null) {
3283 return false;
3284 }
3285 checkSecurityManager(defc, resolved2);
3286 } catch (SecurityException ex) {
3287 return false;
3288 }
3289 return true;
3290 }
3291 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
3292 throws ReflectiveOperationException {
3293 if (MethodHandleNatives.refKindIsField(refKind)) {
3294 return getDirectFieldNoSecurityManager(refKind, defc, member);
3295 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
3296 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
3297 } else if (refKind == REF_newInvokeSpecial) {
3298 return getDirectConstructorNoSecurityManager(defc, member);
3299 }
3300 // oops
3301 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
3302 }
3303
3304 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
3305 }
3306
3307 /**
3308 * Produces a method handle constructing arrays of a desired type,
3309 * as if by the {@code anewarray} bytecode.
3310 * The return type of the method handle will be the array type.
3311 * The type of its sole argument will be {@code int}, which specifies the size of the array.
3312 *
3313 * <p> If the returned method handle is invoked with a negative
3314 * array size, a {@code NegativeArraySizeException} will be thrown.
3315 *
3316 * @param arrayClass an array type
3317 * @return a method handle which can create arrays of the given type
3318 * @throws NullPointerException if the argument is {@code null}
3319 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
3320 * @see java.lang.reflect.Array#newInstance(Class, int)
3321 * @jvms 6.5 {@code anewarray} Instruction
3322 * @since 9
3323 */
3324 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
3325 if (!arrayClass.isArray()) {
3326 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
3327 }
3328 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
3329 bindTo(arrayClass.getComponentType());
3330 return ani.asType(ani.type().changeReturnType(arrayClass));
3331 }
3332
3333 /**
3334 * Produces a method handle returning the length of an array,
3335 * as if by the {@code arraylength} bytecode.
3336 * The type of the method handle will have {@code int} as return type,
3337 * and its sole argument will be the array type.
3338 *
3339 * <p> If the returned method handle is invoked with a {@code null}
3340 * array reference, a {@code NullPointerException} will be thrown.
3341 *
3342 * @param arrayClass an array type
3343 * @return a method handle which can retrieve the length of an array of the given array type
3344 * @throws NullPointerException if the argument is {@code null}
3345 * @throws IllegalArgumentException if arrayClass is not an array type
3346 * @jvms 6.5 {@code arraylength} Instruction
3347 * @since 9
3348 */
3349 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
3350 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
3351 }
3352
3353 /**
3354 * Produces a method handle giving read access to elements of an array,
3355 * as if by the {@code aaload} bytecode.
3356 * The type of the method handle will have a return type of the array's
3357 * element type. Its first argument will be the array type,
3358 * and the second will be {@code int}.
3359 *
3360 * <p> When the returned method handle is invoked,
3361 * the array reference and array index are checked.
3362 * A {@code NullPointerException} will be thrown if the array reference
3363 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3364 * thrown if the index is negative or if it is greater than or equal to
3365 * the length of the array.
3366 *
3367 * @param arrayClass an array type
3368 * @return a method handle which can load values from the given array type
3369 * @throws NullPointerException if the argument is null
3370 * @throws IllegalArgumentException if arrayClass is not an array type
3371 * @jvms 6.5 {@code aaload} Instruction
3372 */
3373 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
3374 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
3375 }
3376
3377 /**
3378 * Produces a method handle giving write access to elements of an array,
3379 * as if by the {@code astore} bytecode.
3380 * The type of the method handle will have a void return type.
3381 * Its last argument will be the array's element type.
3382 * The first and second arguments will be the array type and int.
3383 *
3384 * <p> When the returned method handle is invoked,
3385 * the array reference and array index are checked.
3386 * A {@code NullPointerException} will be thrown if the array reference
3387 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3388 * thrown if the index is negative or if it is greater than or equal to
3389 * the length of the array.
3390 *
3391 * @param arrayClass the class of an array
3392 * @return a method handle which can store values into the array type
3393 * @throws NullPointerException if the argument is null
3394 * @throws IllegalArgumentException if arrayClass is not an array type
3395 * @jvms 6.5 {@code aastore} Instruction
3396 */
3397 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
3398 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
3399 }
3400
3401 /**
3402 * Produces a VarHandle giving access to elements of an array of type
3403 * {@code arrayClass}. The VarHandle's variable type is the component type
3404 * of {@code arrayClass} and the list of coordinate types is
3405 * {@code (arrayClass, int)}, where the {@code int} coordinate type
3406 * corresponds to an argument that is an index into an array.
3407 * <p>
3408 * Certain access modes of the returned VarHandle are unsupported under
3409 * the following conditions:
3410 * <ul>
3411 * <li>if the component type is anything other than {@code byte},
3412 * {@code short}, {@code char}, {@code int}, {@code long},
3413 * {@code float}, or {@code double} then numeric atomic update access
3414 * modes are unsupported.
3415 * <li>if the field type is anything other than {@code boolean},
3416 * {@code byte}, {@code short}, {@code char}, {@code int} or
3417 * {@code long} then bitwise atomic update access modes are
3418 * unsupported.
3419 * </ul>
3420 * <p>
3421 * If the component type is {@code float} or {@code double} then numeric
3422 * and atomic update access modes compare values using their bitwise
3423 * representation (see {@link Float#floatToRawIntBits} and
3424 * {@link Double#doubleToRawLongBits}, respectively).
3425 *
3426 * <p> When the returned {@code VarHandle} is invoked,
3427 * the array reference and array index are checked.
3428 * A {@code NullPointerException} will be thrown if the array reference
3429 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3430 * thrown if the index is negative or if it is greater than or equal to
3431 * the length of the array.
3432 *
3433 * @apiNote
3434 * Bitwise comparison of {@code float} values or {@code double} values,
3435 * as performed by the numeric and atomic update access modes, differ
3436 * from the primitive {@code ==} operator and the {@link Float#equals}
3437 * and {@link Double#equals} methods, specifically with respect to
3438 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3439 * Care should be taken when performing a compare and set or a compare
3440 * and exchange operation with such values since the operation may
3441 * unexpectedly fail.
3442 * There are many possible NaN values that are considered to be
3443 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3444 * provided by Java can distinguish between them. Operation failure can
3445 * occur if the expected or witness value is a NaN value and it is
3446 * transformed (perhaps in a platform specific manner) into another NaN
3447 * value, and thus has a different bitwise representation (see
3448 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3449 * details).
3450 * The values {@code -0.0} and {@code +0.0} have different bitwise
3451 * representations but are considered equal when using the primitive
3452 * {@code ==} operator. Operation failure can occur if, for example, a
3453 * numeric algorithm computes an expected value to be say {@code -0.0}
3454 * and previously computed the witness value to be say {@code +0.0}.
3455 * @param arrayClass the class of an array, of type {@code T[]}
3456 * @return a VarHandle giving access to elements of an array
3457 * @throws NullPointerException if the arrayClass is null
3458 * @throws IllegalArgumentException if arrayClass is not an array type
3459 * @since 9
3460 */
3461 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
3462 return VarHandles.makeArrayElementHandle(arrayClass);
3463 }
3464
3465 /**
3466 * Produces a VarHandle giving access to elements of a {@code byte[]} array
3467 * viewed as if it were a different primitive array type, such as
3468 * {@code int[]} or {@code long[]}.
3469 * The VarHandle's variable type is the component type of
3470 * {@code viewArrayClass} and the list of coordinate types is
3471 * {@code (byte[], int)}, where the {@code int} coordinate type
3472 * corresponds to an argument that is an index into a {@code byte[]} array.
3473 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
3474 * array, composing bytes to or from a value of the component type of
3475 * {@code viewArrayClass} according to the given endianness.
3476 * <p>
3477 * The supported component types (variables types) are {@code short},
3478 * {@code char}, {@code int}, {@code long}, {@code float} and
3479 * {@code double}.
3480 * <p>
3481 * Access of bytes at a given index will result in an
3482 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3483 * or greater than the {@code byte[]} array length minus the size (in bytes)
3484 * of {@code T}.
3485 * <p>
3486 * Access of bytes at an index may be aligned or misaligned for {@code T},
3487 * with respect to the underlying memory address, {@code A} say, associated
3488 * with the array and index.
3489 * If access is misaligned then access for anything other than the
3490 * {@code get} and {@code set} access modes will result in an
3491 * {@code IllegalStateException}. In such cases atomic access is only
3492 * guaranteed with respect to the largest power of two that divides the GCD
3493 * of {@code A} and the size (in bytes) of {@code T}.
3494 * If access is aligned then following access modes are supported and are
3495 * guaranteed to support atomic access:
3496 * <ul>
3497 * <li>read write access modes for all {@code T}, with the exception of
3498 * access modes {@code get} and {@code set} for {@code long} and
3499 * {@code double} on 32-bit platforms.
3500 * <li>atomic update access modes for {@code int}, {@code long},
3501 * {@code float} or {@code double}.
3502 * (Future major platform releases of the JDK may support additional
3503 * types for certain currently unsupported access modes.)
3504 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3505 * (Future major platform releases of the JDK may support additional
3506 * numeric types for certain currently unsupported access modes.)
3507 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3508 * (Future major platform releases of the JDK may support additional
3509 * numeric types for certain currently unsupported access modes.)
3510 * </ul>
3511 * <p>
3512 * Misaligned access, and therefore atomicity guarantees, may be determined
3513 * for {@code byte[]} arrays without operating on a specific array. Given
3514 * an {@code index}, {@code T} and it's corresponding boxed type,
3515 * {@code T_BOX}, misalignment may be determined as follows:
3516 * <pre>{@code
3517 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3518 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
3519 * alignmentOffset(0, sizeOfT);
3520 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
3521 * boolean isMisaligned = misalignedAtIndex != 0;
3522 * }</pre>
3523 * <p>
3524 * If the variable type is {@code float} or {@code double} then atomic
3525 * update access modes compare values using their bitwise representation
3526 * (see {@link Float#floatToRawIntBits} and
3527 * {@link Double#doubleToRawLongBits}, respectively).
3528 * @param viewArrayClass the view array class, with a component type of
3529 * type {@code T}
3530 * @param byteOrder the endianness of the view array elements, as
3531 * stored in the underlying {@code byte} array
3532 * @return a VarHandle giving access to elements of a {@code byte[]} array
3533 * viewed as if elements corresponding to the components type of the view
3534 * array class
3535 * @throws NullPointerException if viewArrayClass or byteOrder is null
3536 * @throws IllegalArgumentException if viewArrayClass is not an array type
3537 * @throws UnsupportedOperationException if the component type of
3538 * viewArrayClass is not supported as a variable type
3539 * @since 9
3540 */
3541 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
3542 ByteOrder byteOrder) throws IllegalArgumentException {
3543 Objects.requireNonNull(byteOrder);
3544 return VarHandles.byteArrayViewHandle(viewArrayClass,
3545 byteOrder == ByteOrder.BIG_ENDIAN);
3546 }
3547
3548 /**
3549 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
3550 * viewed as if it were an array of elements of a different primitive
3551 * component type to that of {@code byte}, such as {@code int[]} or
3552 * {@code long[]}.
3553 * The VarHandle's variable type is the component type of
3554 * {@code viewArrayClass} and the list of coordinate types is
3555 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
3556 * corresponds to an argument that is an index into a {@code byte[]} array.
3557 * The returned VarHandle accesses bytes at an index in a
3558 * {@code ByteBuffer}, composing bytes to or from a value of the component
3559 * type of {@code viewArrayClass} according to the given endianness.
3560 * <p>
3561 * The supported component types (variables types) are {@code short},
3562 * {@code char}, {@code int}, {@code long}, {@code float} and
3563 * {@code double}.
3564 * <p>
3565 * Access will result in a {@code ReadOnlyBufferException} for anything
3566 * other than the read access modes if the {@code ByteBuffer} is read-only.
3567 * <p>
3568 * Access of bytes at a given index will result in an
3569 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3570 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
3571 * {@code T}.
3572 * <p>
3573 * Access of bytes at an index may be aligned or misaligned for {@code T},
3574 * with respect to the underlying memory address, {@code A} say, associated
3575 * with the {@code ByteBuffer} and index.
3576 * If access is misaligned then access for anything other than the
3577 * {@code get} and {@code set} access modes will result in an
3578 * {@code IllegalStateException}. In such cases atomic access is only
3579 * guaranteed with respect to the largest power of two that divides the GCD
3580 * of {@code A} and the size (in bytes) of {@code T}.
3581 * If access is aligned then following access modes are supported and are
3582 * guaranteed to support atomic access:
3583 * <ul>
3584 * <li>read write access modes for all {@code T}, with the exception of
3585 * access modes {@code get} and {@code set} for {@code long} and
3586 * {@code double} on 32-bit platforms.
3587 * <li>atomic update access modes for {@code int}, {@code long},
3588 * {@code float} or {@code double}.
3589 * (Future major platform releases of the JDK may support additional
3590 * types for certain currently unsupported access modes.)
3591 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3592 * (Future major platform releases of the JDK may support additional
3593 * numeric types for certain currently unsupported access modes.)
3594 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3595 * (Future major platform releases of the JDK may support additional
3596 * numeric types for certain currently unsupported access modes.)
3597 * </ul>
3598 * <p>
3599 * Misaligned access, and therefore atomicity guarantees, may be determined
3600 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
3601 * {@code index}, {@code T} and it's corresponding boxed type,
3602 * {@code T_BOX}, as follows:
3603 * <pre>{@code
3604 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3605 * ByteBuffer bb = ...
3606 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
3607 * boolean isMisaligned = misalignedAtIndex != 0;
3608 * }</pre>
3609 * <p>
3610 * If the variable type is {@code float} or {@code double} then atomic
3611 * update access modes compare values using their bitwise representation
3612 * (see {@link Float#floatToRawIntBits} and
3613 * {@link Double#doubleToRawLongBits}, respectively).
3614 * @param viewArrayClass the view array class, with a component type of
3615 * type {@code T}
3616 * @param byteOrder the endianness of the view array elements, as
3617 * stored in the underlying {@code ByteBuffer} (Note this overrides the
3618 * endianness of a {@code ByteBuffer})
3619 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
3620 * viewed as if elements corresponding to the components type of the view
3621 * array class
3622 * @throws NullPointerException if viewArrayClass or byteOrder is null
3623 * @throws IllegalArgumentException if viewArrayClass is not an array type
3624 * @throws UnsupportedOperationException if the component type of
3625 * viewArrayClass is not supported as a variable type
3626 * @since 9
3627 */
3628 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
3629 ByteOrder byteOrder) throws IllegalArgumentException {
3630 Objects.requireNonNull(byteOrder);
3631 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
3632 byteOrder == ByteOrder.BIG_ENDIAN);
3633 }
3634
3635
3636 /// method handle invocation (reflective style)
3637
3638 /**
3639 * Produces a method handle which will invoke any method handle of the
3640 * given {@code type}, with a given number of trailing arguments replaced by
3641 * a single trailing {@code Object[]} array.
3642 * The resulting invoker will be a method handle with the following
3643 * arguments:
3644 * <ul>
3645 * <li>a single {@code MethodHandle} target
3646 * <li>zero or more leading values (counted by {@code leadingArgCount})
3647 * <li>an {@code Object[]} array containing trailing arguments
3648 * </ul>
3649 * <p>
3650 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
3651 * the indicated {@code type}.
3652 * That is, if the target is exactly of the given {@code type}, it will behave
3653 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
3654 * is used to convert the target to the required {@code type}.
3655 * <p>
3656 * The type of the returned invoker will not be the given {@code type}, but rather
3657 * will have all parameters except the first {@code leadingArgCount}
3658 * replaced by a single array of type {@code Object[]}, which will be
3659 * the final parameter.
3660 * <p>
3661 * Before invoking its target, the invoker will spread the final array, apply
3662 * reference casts as necessary, and unbox and widen primitive arguments.
3663 * If, when the invoker is called, the supplied array argument does
3664 * not have the correct number of elements, the invoker will throw
3665 * an {@link IllegalArgumentException} instead of invoking the target.
3666 * <p>
3667 * This method is equivalent to the following code (though it may be more efficient):
3668 * <blockquote><pre>{@code
3669 MethodHandle invoker = MethodHandles.invoker(type);
3670 int spreadArgCount = type.parameterCount() - leadingArgCount;
3671 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
3672 return invoker;
3673 * }</pre></blockquote>
3674 * This method throws no reflective or security exceptions.
3675 * @param type the desired target type
3676 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
3677 * @return a method handle suitable for invoking any method handle of the given type
3678 * @throws NullPointerException if {@code type} is null
3679 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
3680 * the range from 0 to {@code type.parameterCount()} inclusive,
3681 * or if the resulting method handle's type would have
3682 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3683 */
3684 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
3685 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
3686 throw newIllegalArgumentException("bad argument count", leadingArgCount);
3687 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
3688 return type.invokers().spreadInvoker(leadingArgCount);
3689 }
3690
3691 /**
3692 * Produces a special <em>invoker method handle</em> which can be used to
3693 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
3694 * The resulting invoker will have a type which is
3695 * exactly equal to the desired type, except that it will accept
3696 * an additional leading argument of type {@code MethodHandle}.
3697 * <p>
3698 * This method is equivalent to the following code (though it may be more efficient):
3699 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
3700 *
3701 * <p style="font-size:smaller;">
3702 * <em>Discussion:</em>
3703 * Invoker method handles can be useful when working with variable method handles
3704 * of unknown types.
3705 * For example, to emulate an {@code invokeExact} call to a variable method
3706 * handle {@code M}, extract its type {@code T},
3707 * look up the invoker method {@code X} for {@code T},
3708 * and call the invoker method, as {@code X.invoke(T, A...)}.
3709 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
3710 * is unknown.)
3711 * If spreading, collecting, or other argument transformations are required,
3712 * they can be applied once to the invoker {@code X} and reused on many {@code M}
3713 * method handle values, as long as they are compatible with the type of {@code X}.
3714 * <p style="font-size:smaller;">
3715 * <em>(Note: The invoker method is not available via the Core Reflection API.
3716 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3717 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3718 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3719 * <p>
3720 * This method throws no reflective or security exceptions.
3721 * @param type the desired target type
3722 * @return a method handle suitable for invoking any method handle of the given type
3723 * @throws IllegalArgumentException if the resulting method handle's type would have
3724 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3725 */
3726 public static MethodHandle exactInvoker(MethodType type) {
3727 return type.invokers().exactInvoker();
3728 }
3729
3730 /**
3731 * Produces a special <em>invoker method handle</em> which can be used to
3732 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
3733 * The resulting invoker will have a type which is
3734 * exactly equal to the desired type, except that it will accept
3735 * an additional leading argument of type {@code MethodHandle}.
3736 * <p>
3737 * Before invoking its target, if the target differs from the expected type,
3738 * the invoker will apply reference casts as
3739 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
3740 * Similarly, the return value will be converted as necessary.
3741 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
3742 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
3743 * <p>
3744 * This method is equivalent to the following code (though it may be more efficient):
3745 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
3746 * <p style="font-size:smaller;">
3747 * <em>Discussion:</em>
3748 * A {@linkplain MethodType#genericMethodType general method type} is one which
3749 * mentions only {@code Object} arguments and return values.
3750 * An invoker for such a type is capable of calling any method handle
3751 * of the same arity as the general type.
3752 * <p style="font-size:smaller;">
3753 * <em>(Note: The invoker method is not available via the Core Reflection API.
3754 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3755 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3756 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3757 * <p>
3758 * This method throws no reflective or security exceptions.
3759 * @param type the desired target type
3760 * @return a method handle suitable for invoking any method handle convertible to the given type
3761 * @throws IllegalArgumentException if the resulting method handle's type would have
3762 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3763 */
3764 public static MethodHandle invoker(MethodType type) {
3765 return type.invokers().genericInvoker();
3766 }
3767
3768 /**
3769 * Produces a special <em>invoker method handle</em> which can be used to
3770 * invoke a signature-polymorphic access mode method on any VarHandle whose
3771 * associated access mode type is compatible with the given type.
3772 * The resulting invoker will have a type which is exactly equal to the
3773 * desired given type, except that it will accept an additional leading
3774 * argument of type {@code VarHandle}.
3775 *
3776 * @param accessMode the VarHandle access mode
3777 * @param type the desired target type
3778 * @return a method handle suitable for invoking an access mode method of
3779 * any VarHandle whose access mode type is of the given type.
3780 * @since 9
3781 */
3782 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3783 return type.invokers().varHandleMethodExactInvoker(accessMode);
3784 }
3785
3786 /**
3787 * Produces a special <em>invoker method handle</em> which can be used to
3788 * invoke a signature-polymorphic access mode method on any VarHandle whose
3789 * associated access mode type is compatible with the given type.
3790 * The resulting invoker will have a type which is exactly equal to the
3791 * desired given type, except that it will accept an additional leading
3792 * argument of type {@code VarHandle}.
3793 * <p>
3794 * Before invoking its target, if the access mode type differs from the
3795 * desired given type, the invoker will apply reference casts as necessary
3796 * and box, unbox, or widen primitive values, as if by
3797 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3798 * converted as necessary.
3799 * <p>
3800 * This method is equivalent to the following code (though it may be more
3801 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3802 *
3803 * @param accessMode the VarHandle access mode
3804 * @param type the desired target type
3805 * @return a method handle suitable for invoking an access mode method of
3806 * any VarHandle whose access mode type is convertible to the given
3807 * type.
3808 * @since 9
3809 */
3810 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3811 return type.invokers().varHandleMethodInvoker(accessMode);
3812 }
3813
3814 /*non-public*/
3815 static MethodHandle basicInvoker(MethodType type) {
3816 return type.invokers().basicInvoker();
3817 }
3818
3819 /// method handle modification (creation from other method handles)
3820
3821 /**
3822 * Produces a method handle which adapts the type of the
3823 * given method handle to a new type by pairwise argument and return type conversion.
3824 * The original type and new type must have the same number of arguments.
3825 * The resulting method handle is guaranteed to report a type
3826 * which is equal to the desired new type.
3827 * <p>
3828 * If the original type and new type are equal, returns target.
3829 * <p>
3830 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3831 * and some additional conversions are also applied if those conversions fail.
3832 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3833 * if possible, before or instead of any conversions done by {@code asType}:
3834 * <ul>
3835 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3836 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3837 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3838 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3839 * the boolean is converted to a byte value, 1 for true, 0 for false.
3840 * (This treatment follows the usage of the bytecode verifier.)
3841 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3842 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3843 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3844 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3845 * then a Java casting conversion (JLS 5.5) is applied.
3846 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3847 * widening and/or narrowing.)
3848 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3849 * conversion will be applied at runtime, possibly followed
3850 * by a Java casting conversion (JLS 5.5) on the primitive value,
3851 * possibly followed by a conversion from byte to boolean by testing
3852 * the low-order bit.
3853 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3854 * and if the reference is null at runtime, a zero value is introduced.
3855 * </ul>
3856 * @param target the method handle to invoke after arguments are retyped
3857 * @param newType the expected type of the new method handle
3858 * @return a method handle which delegates to the target after performing
3859 * any necessary argument conversions, and arranges for any
3860 * necessary return value conversions
3861 * @throws NullPointerException if either argument is null
3862 * @throws WrongMethodTypeException if the conversion cannot be made
3863 * @see MethodHandle#asType
3864 */
3865 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3866 explicitCastArgumentsChecks(target, newType);
3867 // use the asTypeCache when possible:
3868 MethodType oldType = target.type();
3869 if (oldType == newType) return target;
3870 if (oldType.explicitCastEquivalentToAsType(newType)) {
3871 return target.asFixedArity().asType(newType);
3872 }
3873 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3874 }
3875
3876 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3877 if (target.type().parameterCount() != newType.parameterCount()) {
3878 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3879 }
3880 }
3881
3882 /**
3883 * Produces a method handle which adapts the calling sequence of the
3884 * given method handle to a new type, by reordering the arguments.
3885 * The resulting method handle is guaranteed to report a type
3886 * which is equal to the desired new type.
3887 * <p>
3888 * The given array controls the reordering.
3889 * Call {@code #I} the number of incoming parameters (the value
3890 * {@code newType.parameterCount()}, and call {@code #O} the number
3891 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3892 * Then the length of the reordering array must be {@code #O},
3893 * and each element must be a non-negative number less than {@code #I}.
3894 * For every {@code N} less than {@code #O}, the {@code N}-th
3895 * outgoing argument will be taken from the {@code I}-th incoming
3896 * argument, where {@code I} is {@code reorder[N]}.
3897 * <p>
3898 * No argument or return value conversions are applied.
3899 * The type of each incoming argument, as determined by {@code newType},
3900 * must be identical to the type of the corresponding outgoing parameter
3901 * or parameters in the target method handle.
3902 * The return type of {@code newType} must be identical to the return
3903 * type of the original target.
3904 * <p>
3905 * The reordering array need not specify an actual permutation.
3906 * An incoming argument will be duplicated if its index appears
3907 * more than once in the array, and an incoming argument will be dropped
3908 * if its index does not appear in the array.
3909 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3910 * incoming arguments which are not mentioned in the reordering array
3911 * may be of any type, as determined only by {@code newType}.
3912 * <blockquote><pre>{@code
3913 import static java.lang.invoke.MethodHandles.*;
3914 import static java.lang.invoke.MethodType.*;
3915 ...
3916 MethodType intfn1 = methodType(int.class, int.class);
3917 MethodType intfn2 = methodType(int.class, int.class, int.class);
3918 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3919 assert(sub.type().equals(intfn2));
3920 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3921 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3922 assert((int)rsub.invokeExact(1, 100) == 99);
3923 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3924 assert(add.type().equals(intfn2));
3925 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3926 assert(twice.type().equals(intfn1));
3927 assert((int)twice.invokeExact(21) == 42);
3928 * }</pre></blockquote>
3929 * <p>
3930 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3931 * variable-arity method handle}, even if the original target method handle was.
3932 * @param target the method handle to invoke after arguments are reordered
3933 * @param newType the expected type of the new method handle
3934 * @param reorder an index array which controls the reordering
3935 * @return a method handle which delegates to the target after it
3936 * drops unused arguments and moves and/or duplicates the other arguments
3937 * @throws NullPointerException if any argument is null
3938 * @throws IllegalArgumentException if the index array length is not equal to
3939 * the arity of the target, or if any index array element
3940 * not a valid index for a parameter of {@code newType},
3941 * or if two corresponding parameter types in
3942 * {@code target.type()} and {@code newType} are not identical,
3943 */
3944 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3945 reorder = reorder.clone(); // get a private copy
3946 MethodType oldType = target.type();
3947 permuteArgumentChecks(reorder, newType, oldType);
3948 // first detect dropped arguments and handle them separately
3949 int[] originalReorder = reorder;
3950 BoundMethodHandle result = target.rebind();
3951 LambdaForm form = result.form;
3952 int newArity = newType.parameterCount();
3953 // Normalize the reordering into a real permutation,
3954 // by removing duplicates and adding dropped elements.
3955 // This somewhat improves lambda form caching, as well
3956 // as simplifying the transform by breaking it up into steps.
3957 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3958 if (ddIdx > 0) {
3959 // We found a duplicated entry at reorder[ddIdx].
3960 // Example: (x,y,z)->asList(x,y,z)
3961 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3962 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3963 // The starred element corresponds to the argument
3964 // deleted by the dupArgumentForm transform.
3965 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3966 boolean killFirst = false;
3967 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3968 // Set killFirst if the dup is larger than an intervening position.
3969 // This will remove at least one inversion from the permutation.
3970 if (dupVal > val) killFirst = true;
3971 }
3972 if (!killFirst) {
3973 srcPos = dstPos;
3974 dstPos = ddIdx;
3975 }
3976 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3977 assert (reorder[srcPos] == reorder[dstPos]);
3978 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3979 // contract the reordering by removing the element at dstPos
3980 int tailPos = dstPos + 1;
3981 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3982 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3983 } else {
3984 int dropVal = ~ddIdx, insPos = 0;
3985 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3986 // Find first element of reorder larger than dropVal.
3987 // This is where we will insert the dropVal.
3988 insPos += 1;
3989 }
3990 Class<?> ptype = newType.parameterType(dropVal);
3991 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3992 oldType = oldType.insertParameterTypes(insPos, ptype);
3993 // expand the reordering by inserting an element at insPos
3994 int tailPos = insPos + 1;
3995 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3996 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3997 reorder[insPos] = dropVal;
3998 }
3999 assert (permuteArgumentChecks(reorder, newType, oldType));
4000 }
4001 assert (reorder.length == newArity); // a perfect permutation
4002 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4003 form = form.editor().permuteArgumentsForm(1, reorder);
4004 if (newType == result.type() && form == result.internalForm())
4005 return result;
4006 return result.copyWith(newType, form);
4007 }
4008
4009 /**
4010 * Return an indication of any duplicate or omission in reorder.
4011 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4012 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4013 * Otherwise, return zero.
4014 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4015 */
4016 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4017 final int BIT_LIMIT = 63; // max number of bits in bit mask
4018 if (newArity < BIT_LIMIT) {
4019 long mask = 0;
4020 for (int i = 0; i < reorder.length; i++) {
4021 int arg = reorder[i];
4022 if (arg >= newArity) {
4023 return reorder.length;
4024 }
4025 long bit = 1L << arg;
4026 if ((mask & bit) != 0) {
4027 return i; // >0 indicates a dup
4028 }
4029 mask |= bit;
4030 }
4031 if (mask == (1L << newArity) - 1) {
4032 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4033 return 0;
4034 }
4035 // find first zero
4036 long zeroBit = Long.lowestOneBit(~mask);
4037 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4038 assert(zeroPos <= newArity);
4039 if (zeroPos == newArity) {
4040 return 0;
4041 }
4042 return ~zeroPos;
4043 } else {
4044 // same algorithm, different bit set
4045 BitSet mask = new BitSet(newArity);
4046 for (int i = 0; i < reorder.length; i++) {
4047 int arg = reorder[i];
4048 if (arg >= newArity) {
4049 return reorder.length;
4050 }
4051 if (mask.get(arg)) {
4052 return i; // >0 indicates a dup
4053 }
4054 mask.set(arg);
4055 }
4056 int zeroPos = mask.nextClearBit(0);
4057 assert(zeroPos <= newArity);
4058 if (zeroPos == newArity) {
4059 return 0;
4060 }
4061 return ~zeroPos;
4062 }
4063 }
4064
4065 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4066 if (newType.returnType() != oldType.returnType())
4067 throw newIllegalArgumentException("return types do not match",
4068 oldType, newType);
4069 if (reorder.length == oldType.parameterCount()) {
4070 int limit = newType.parameterCount();
4071 boolean bad = false;
4072 for (int j = 0; j < reorder.length; j++) {
4073 int i = reorder[j];
4074 if (i < 0 || i >= limit) {
4075 bad = true; break;
4076 }
4077 Class<?> src = newType.parameterType(i);
4078 Class<?> dst = oldType.parameterType(j);
4079 if (src != dst)
4080 throw newIllegalArgumentException("parameter types do not match after reorder",
4081 oldType, newType);
4082 }
4083 if (!bad) return true;
4084 }
4085 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
4086 }
4087
4088 /**
4089 * Produces a method handle of the requested return type which returns the given
4090 * constant value every time it is invoked.
4091 * <p>
4092 * Before the method handle is returned, the passed-in value is converted to the requested type.
4093 * If the requested type is primitive, widening primitive conversions are attempted,
4094 * else reference conversions are attempted.
4095 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4096 * @param type the return type of the desired method handle
4097 * @param value the value to return
4098 * @return a method handle of the given return type and no arguments, which always returns the given value
4099 * @throws NullPointerException if the {@code type} argument is null
4100 * @throws ClassCastException if the value cannot be converted to the required return type
4101 * @throws IllegalArgumentException if the given type is {@code void.class}
4102 */
4103 public static MethodHandle constant(Class<?> type, Object value) {
4104 if (type.isPrimitive()) {
4105 if (type == void.class)
4106 throw newIllegalArgumentException("void type");
4107 Wrapper w = Wrapper.forPrimitiveType(type);
4108 value = w.convert(value, type);
4109 if (w.zero().equals(value))
4110 return zero(w, type);
4111 return insertArguments(identity(type), 0, value);
4112 } else {
4113 if (value == null)
4114 return zero(Wrapper.OBJECT, type);
4115 return identity(type).bindTo(value);
4116 }
4117 }
4118
4119 /**
4120 * Produces a method handle which returns its sole argument when invoked.
4121 * @param type the type of the sole parameter and return value of the desired method handle
4122 * @return a unary method handle which accepts and returns the given type
4123 * @throws NullPointerException if the argument is null
4124 * @throws IllegalArgumentException if the given type is {@code void.class}
4125 */
4126 public static MethodHandle identity(Class<?> type) {
4127 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4128 int pos = btw.ordinal();
4129 MethodHandle ident = IDENTITY_MHS[pos];
4130 if (ident == null) {
4131 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4132 }
4133 if (ident.type().returnType() == type)
4134 return ident;
4135 // something like identity(Foo.class); do not bother to intern these
4136 assert (btw == Wrapper.OBJECT);
4137 return makeIdentity(type);
4138 }
4139
4140 /**
4141 * Produces a constant method handle of the requested return type which
4142 * returns the default value for that type every time it is invoked.
4143 * The resulting constant method handle will have no side effects.
4144 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4145 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4146 * since {@code explicitCastArguments} converts {@code null} to default values.
4147 * @param type the expected return type of the desired method handle
4148 * @return a constant method handle that takes no arguments
4149 * and returns the default value of the given type (or void, if the type is void)
4150 * @throws NullPointerException if the argument is null
4151 * @see MethodHandles#constant
4152 * @see MethodHandles#empty
4153 * @see MethodHandles#explicitCastArguments
4154 * @since 9
4155 */
4156 public static MethodHandle zero(Class<?> type) {
4157 Objects.requireNonNull(type);
4158 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
4159 }
4160
4161 private static MethodHandle identityOrVoid(Class<?> type) {
4162 return type == void.class ? zero(type) : identity(type);
4163 }
4164
4165 /**
4166 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4167 * and returns a suitable default depending on the return type.
4168 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4169 * <p>The returned method handle is equivalent to
4170 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4171 *
4172 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4173 * {@code guardWithTest(pred, target, empty(target.type())}.
4174 * @param type the type of the desired method handle
4175 * @return a constant method handle of the given type, which returns a default value of the given return type
4176 * @throws NullPointerException if the argument is null
4177 * @see MethodHandles#zero
4178 * @see MethodHandles#constant
4179 * @since 9
4180 */
4181 public static MethodHandle empty(MethodType type) {
4182 Objects.requireNonNull(type);
4183 return dropArguments(zero(type.returnType()), 0, type.parameterList());
4184 }
4185
4186 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4187 private static MethodHandle makeIdentity(Class<?> ptype) {
4188 MethodType mtype = methodType(ptype, ptype);
4189 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4190 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4191 }
4192
4193 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
4194 int pos = btw.ordinal();
4195 MethodHandle zero = ZERO_MHS[pos];
4196 if (zero == null) {
4197 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
4198 }
4199 if (zero.type().returnType() == rtype)
4200 return zero;
4201 assert(btw == Wrapper.OBJECT);
4202 return makeZero(rtype);
4203 }
4204 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4205 private static MethodHandle makeZero(Class<?> rtype) {
4206 MethodType mtype = methodType(rtype);
4207 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
4208 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
4209 }
4210
4211 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4212 // Simulate a CAS, to avoid racy duplication of results.
4213 MethodHandle prev = cache[pos];
4214 if (prev != null) return prev;
4215 return cache[pos] = value;
4216 }
4217
4218 /**
4219 * Provides a target method handle with one or more <em>bound arguments</em>
4220 * in advance of the method handle's invocation.
4221 * The formal parameters to the target corresponding to the bound
4222 * arguments are called <em>bound parameters</em>.
4223 * Returns a new method handle which saves away the bound arguments.
4224 * When it is invoked, it receives arguments for any non-bound parameters,
4225 * binds the saved arguments to their corresponding parameters,
4226 * and calls the original target.
4227 * <p>
4228 * The type of the new method handle will drop the types for the bound
4229 * parameters from the original target type, since the new method handle
4230 * will no longer require those arguments to be supplied by its callers.
4231 * <p>
4232 * Each given argument object must match the corresponding bound parameter type.
4233 * If a bound parameter type is a primitive, the argument object
4234 * must be a wrapper, and will be unboxed to produce the primitive value.
4235 * <p>
4236 * The {@code pos} argument selects which parameters are to be bound.
4237 * It may range between zero and <i>N-L</i> (inclusively),
4238 * where <i>N</i> is the arity of the target method handle
4239 * and <i>L</i> is the length of the values array.
4240 * <p>
4241 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4242 * variable-arity method handle}, even if the original target method handle was.
4243 * @param target the method handle to invoke after the argument is inserted
4244 * @param pos where to insert the argument (zero for the first)
4245 * @param values the series of arguments to insert
4246 * @return a method handle which inserts an additional argument,
4247 * before calling the original method handle
4248 * @throws NullPointerException if the target or the {@code values} array is null
4249 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
4250 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4251 * is the length of the values array.
4252 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4253 * type.
4254 * @see MethodHandle#bindTo
4255 */
4256 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4257 int insCount = values.length;
4258 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4259 if (insCount == 0) return target;
4260 BoundMethodHandle result = target.rebind();
4261 for (int i = 0; i < insCount; i++) {
4262 Object value = values[i];
4263 Class<?> ptype = ptypes[pos+i];
4264 if (ptype.isPrimitive()) {
4265 result = insertArgumentPrimitive(result, pos, ptype, value);
4266 } else {
4267 value = ptype.cast(value); // throw CCE if needed
4268 result = result.bindArgumentL(pos, value);
4269 }
4270 }
4271 return result;
4272 }
4273
4274 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4275 Class<?> ptype, Object value) {
4276 Wrapper w = Wrapper.forPrimitiveType(ptype);
4277 // perform unboxing and/or primitive conversion
4278 value = w.convert(value, ptype);
4279 switch (w) {
4280 case INT: return result.bindArgumentI(pos, (int)value);
4281 case LONG: return result.bindArgumentJ(pos, (long)value);
4282 case FLOAT: return result.bindArgumentF(pos, (float)value);
4283 case DOUBLE: return result.bindArgumentD(pos, (double)value);
4284 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
4285 }
4286 }
4287
4288 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
4289 MethodType oldType = target.type();
4290 int outargs = oldType.parameterCount();
4291 int inargs = outargs - insCount;
4292 if (inargs < 0)
4293 throw newIllegalArgumentException("too many values to insert");
4294 if (pos < 0 || pos > inargs)
4295 throw newIllegalArgumentException("no argument type to append");
4296 return oldType.ptypes();
4297 }
4298
4299 /**
4300 * Produces a method handle which will discard some dummy arguments
4301 * before calling some other specified <i>target</i> method handle.
4302 * The type of the new method handle will be the same as the target's type,
4303 * except it will also include the dummy argument types,
4304 * at some given position.
4305 * <p>
4306 * The {@code pos} argument may range between zero and <i>N</i>,
4307 * where <i>N</i> is the arity of the target.
4308 * If {@code pos} is zero, the dummy arguments will precede
4309 * the target's real arguments; if {@code pos} is <i>N</i>
4310 * they will come after.
4311 * <p>
4312 * <b>Example:</b>
4313 * <blockquote><pre>{@code
4314 import static java.lang.invoke.MethodHandles.*;
4315 import static java.lang.invoke.MethodType.*;
4316 ...
4317 MethodHandle cat = lookup().findVirtual(String.class,
4318 "concat", methodType(String.class, String.class));
4319 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4320 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
4321 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
4322 assertEquals(bigType, d0.type());
4323 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
4324 * }</pre></blockquote>
4325 * <p>
4326 * This method is also equivalent to the following code:
4327 * <blockquote><pre>
4328 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
4329 * </pre></blockquote>
4330 * @param target the method handle to invoke after the arguments are dropped
4331 * @param pos position of first argument to drop (zero for the leftmost)
4332 * @param valueTypes the type(s) of the argument(s) to drop
4333 * @return a method handle which drops arguments of the given types,
4334 * before calling the original method handle
4335 * @throws NullPointerException if the target is null,
4336 * or if the {@code valueTypes} list or any of its elements is null
4337 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4338 * or if {@code pos} is negative or greater than the arity of the target,
4339 * or if the new method handle's type would have too many parameters
4340 */
4341 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4342 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
4343 }
4344
4345 private static List<Class<?>> copyTypes(Object[] array) {
4346 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
4347 }
4348
4349 private static MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4350 MethodType oldType = target.type(); // get NPE
4351 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
4352 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
4353 if (dropped == 0) return target;
4354 BoundMethodHandle result = target.rebind();
4355 LambdaForm lform = result.form;
4356 int insertFormArg = 1 + pos;
4357 for (Class<?> ptype : valueTypes) {
4358 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
4359 }
4360 result = result.copyWith(newType, lform);
4361 return result;
4362 }
4363
4364 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
4365 int dropped = valueTypes.size();
4366 MethodType.checkSlotCount(dropped);
4367 int outargs = oldType.parameterCount();
4368 int inargs = outargs + dropped;
4369 if (pos < 0 || pos > outargs)
4370 throw newIllegalArgumentException("no argument type to remove"
4371 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
4372 );
4373 return dropped;
4374 }
4375
4376 /**
4377 * Produces a method handle which will discard some dummy arguments
4378 * before calling some other specified <i>target</i> method handle.
4379 * The type of the new method handle will be the same as the target's type,
4380 * except it will also include the dummy argument types,
4381 * at some given position.
4382 * <p>
4383 * The {@code pos} argument may range between zero and <i>N</i>,
4384 * where <i>N</i> is the arity of the target.
4385 * If {@code pos} is zero, the dummy arguments will precede
4386 * the target's real arguments; if {@code pos} is <i>N</i>
4387 * they will come after.
4388 * @apiNote
4389 * <blockquote><pre>{@code
4390 import static java.lang.invoke.MethodHandles.*;
4391 import static java.lang.invoke.MethodType.*;
4392 ...
4393 MethodHandle cat = lookup().findVirtual(String.class,
4394 "concat", methodType(String.class, String.class));
4395 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4396 MethodHandle d0 = dropArguments(cat, 0, String.class);
4397 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
4398 MethodHandle d1 = dropArguments(cat, 1, String.class);
4399 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4400 MethodHandle d2 = dropArguments(cat, 2, String.class);
4401 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4402 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4403 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4404 * }</pre></blockquote>
4405 * <p>
4406 * This method is also equivalent to the following code:
4407 * <blockquote><pre>
4408 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4409 * </pre></blockquote>
4410 * @param target the method handle to invoke after the arguments are dropped
4411 * @param pos position of first argument to drop (zero for the leftmost)
4412 * @param valueTypes the type(s) of the argument(s) to drop
4413 * @return a method handle which drops arguments of the given types,
4414 * before calling the original method handle
4415 * @throws NullPointerException if the target is null,
4416 * or if the {@code valueTypes} array or any of its elements is null
4417 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4418 * or if {@code pos} is negative or greater than the arity of the target,
4419 * or if the new method handle's type would have
4420 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4421 */
4422 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4423 return dropArguments0(target, pos, copyTypes(valueTypes));
4424 }
4425
4426 // private version which allows caller some freedom with error handling
4427 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4428 boolean nullOnFailure) {
4429 newTypes = copyTypes(newTypes.toArray());
4430 List<Class<?>> oldTypes = target.type().parameterList();
4431 int match = oldTypes.size();
4432 if (skip != 0) {
4433 if (skip < 0 || skip > match) {
4434 throw newIllegalArgumentException("illegal skip", skip, target);
4435 }
4436 oldTypes = oldTypes.subList(skip, match);
4437 match -= skip;
4438 }
4439 List<Class<?>> addTypes = newTypes;
4440 int add = addTypes.size();
4441 if (pos != 0) {
4442 if (pos < 0 || pos > add) {
4443 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4444 }
4445 addTypes = addTypes.subList(pos, add);
4446 add -= pos;
4447 assert(addTypes.size() == add);
4448 }
4449 // Do not add types which already match the existing arguments.
4450 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4451 if (nullOnFailure) {
4452 return null;
4453 }
4454 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
4455 }
4456 addTypes = addTypes.subList(match, add);
4457 add -= match;
4458 assert(addTypes.size() == add);
4459 // newTypes: ( P*[pos], M*[match], A*[add] )
4460 // target: ( S*[skip], M*[match] )
4461 MethodHandle adapter = target;
4462 if (add > 0) {
4463 adapter = dropArguments0(adapter, skip+ match, addTypes);
4464 }
4465 // adapter: (S*[skip], M*[match], A*[add] )
4466 if (pos > 0) {
4467 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
4468 }
4469 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
4470 return adapter;
4471 }
4472
4473 /**
4474 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
4475 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
4476 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
4477 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
4478 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
4479 * {@link #dropArguments(MethodHandle, int, Class[])}.
4480 * <p>
4481 * The resulting handle will have the same return type as the target handle.
4482 * <p>
4483 * In more formal terms, assume these two type lists:<ul>
4484 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
4485 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
4486 * {@code newTypes}.
4487 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
4488 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
4489 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
4490 * sub-list.
4491 * </ul>
4492 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
4493 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
4494 * {@link #dropArguments(MethodHandle, int, Class[])}.
4495 *
4496 * @apiNote
4497 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
4498 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
4499 * <blockquote><pre>{@code
4500 import static java.lang.invoke.MethodHandles.*;
4501 import static java.lang.invoke.MethodType.*;
4502 ...
4503 ...
4504 MethodHandle h0 = constant(boolean.class, true);
4505 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
4506 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
4507 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
4508 if (h1.type().parameterCount() < h2.type().parameterCount())
4509 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
4510 else
4511 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
4512 MethodHandle h3 = guardWithTest(h0, h1, h2);
4513 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
4514 * }</pre></blockquote>
4515 * @param target the method handle to adapt
4516 * @param skip number of targets parameters to disregard (they will be unchanged)
4517 * @param newTypes the list of types to match {@code target}'s parameter type list to
4518 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
4519 * @return a possibly adapted method handle
4520 * @throws NullPointerException if either argument is null
4521 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
4522 * or if {@code skip} is negative or greater than the arity of the target,
4523 * or if {@code pos} is negative or greater than the newTypes list size,
4524 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
4525 * {@code pos}.
4526 * @since 9
4527 */
4528 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
4529 Objects.requireNonNull(target);
4530 Objects.requireNonNull(newTypes);
4531 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
4532 }
4533
4534 /**
4535 * Adapts a target method handle by pre-processing
4536 * one or more of its arguments, each with its own unary filter function,
4537 * and then calling the target with each pre-processed argument
4538 * replaced by the result of its corresponding filter function.
4539 * <p>
4540 * The pre-processing is performed by one or more method handles,
4541 * specified in the elements of the {@code filters} array.
4542 * The first element of the filter array corresponds to the {@code pos}
4543 * argument of the target, and so on in sequence.
4544 * The filter functions are invoked in left to right order.
4545 * <p>
4546 * Null arguments in the array are treated as identity functions,
4547 * and the corresponding arguments left unchanged.
4548 * (If there are no non-null elements in the array, the original target is returned.)
4549 * Each filter is applied to the corresponding argument of the adapter.
4550 * <p>
4551 * If a filter {@code F} applies to the {@code N}th argument of
4552 * the target, then {@code F} must be a method handle which
4553 * takes exactly one argument. The type of {@code F}'s sole argument
4554 * replaces the corresponding argument type of the target
4555 * in the resulting adapted method handle.
4556 * The return type of {@code F} must be identical to the corresponding
4557 * parameter type of the target.
4558 * <p>
4559 * It is an error if there are elements of {@code filters}
4560 * (null or not)
4561 * which do not correspond to argument positions in the target.
4562 * <p><b>Example:</b>
4563 * <blockquote><pre>{@code
4564 import static java.lang.invoke.MethodHandles.*;
4565 import static java.lang.invoke.MethodType.*;
4566 ...
4567 MethodHandle cat = lookup().findVirtual(String.class,
4568 "concat", methodType(String.class, String.class));
4569 MethodHandle upcase = lookup().findVirtual(String.class,
4570 "toUpperCase", methodType(String.class));
4571 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4572 MethodHandle f0 = filterArguments(cat, 0, upcase);
4573 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
4574 MethodHandle f1 = filterArguments(cat, 1, upcase);
4575 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
4576 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
4577 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
4578 * }</pre></blockquote>
4579 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4580 * denotes the return type of both the {@code target} and resulting adapter.
4581 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
4582 * of the parameters and arguments that precede and follow the filter position
4583 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
4584 * values of the filtered parameters and arguments; they also represent the
4585 * return types of the {@code filter[i]} handles. The latter accept arguments
4586 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
4587 * the resulting adapter.
4588 * <blockquote><pre>{@code
4589 * T target(P... p, A[i]... a[i], B... b);
4590 * A[i] filter[i](V[i]);
4591 * T adapter(P... p, V[i]... v[i], B... b) {
4592 * return target(p..., filter[i](v[i])..., b...);
4593 * }
4594 * }</pre></blockquote>
4595 * <p>
4596 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4597 * variable-arity method handle}, even if the original target method handle was.
4598 *
4599 * @param target the method handle to invoke after arguments are filtered
4600 * @param pos the position of the first argument to filter
4601 * @param filters method handles to call initially on filtered arguments
4602 * @return method handle which incorporates the specified argument filtering logic
4603 * @throws NullPointerException if the target is null
4604 * or if the {@code filters} array is null
4605 * @throws IllegalArgumentException if a non-null element of {@code filters}
4606 * does not match a corresponding argument type of target as described above,
4607 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
4608 * or if the resulting method handle's type would have
4609 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4610 */
4611 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
4612 // In method types arguments start at index 0, while the LF
4613 // editor have the MH receiver at position 0 - adjust appropriately.
4614 final int MH_RECEIVER_OFFSET = 1;
4615 filterArgumentsCheckArity(target, pos, filters);
4616 MethodHandle adapter = target;
4617
4618 // keep track of currently matched filters, as to optimize repeated filters
4619 int index = 0;
4620 int[] positions = new int[filters.length];
4621 MethodHandle filter = null;
4622
4623 // process filters in reverse order so that the invocation of
4624 // the resulting adapter will invoke the filters in left-to-right order
4625 for (int i = filters.length - 1; i >= 0; --i) {
4626 MethodHandle newFilter = filters[i];
4627 if (newFilter == null) continue; // ignore null elements of filters
4628
4629 // flush changes on update
4630 if (filter != newFilter) {
4631 if (filter != null) {
4632 if (index > 1) {
4633 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4634 } else {
4635 adapter = filterArgument(adapter, positions[0] - 1, filter);
4636 }
4637 }
4638 filter = newFilter;
4639 index = 0;
4640 }
4641
4642 filterArgumentChecks(target, pos + i, newFilter);
4643 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
4644 }
4645 if (index > 1) {
4646 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4647 } else if (index == 1) {
4648 adapter = filterArgument(adapter, positions[0] - 1, filter);
4649 }
4650 return adapter;
4651 }
4652
4653 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
4654 MethodType targetType = adapter.type();
4655 MethodType filterType = filter.type();
4656 BoundMethodHandle result = adapter.rebind();
4657 Class<?> newParamType = filterType.parameterType(0);
4658
4659 Class<?>[] ptypes = targetType.ptypes().clone();
4660 for (int pos : positions) {
4661 ptypes[pos - 1] = newParamType;
4662 }
4663 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
4664
4665 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
4666 return result.copyWithExtendL(newType, lform, filter);
4667 }
4668
4669 /*non-public*/
4670 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
4671 filterArgumentChecks(target, pos, filter);
4672 MethodType targetType = target.type();
4673 MethodType filterType = filter.type();
4674 BoundMethodHandle result = target.rebind();
4675 Class<?> newParamType = filterType.parameterType(0);
4676 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
4677 MethodType newType = targetType.changeParameterType(pos, newParamType);
4678 result = result.copyWithExtendL(newType, lform, filter);
4679 return result;
4680 }
4681
4682 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
4683 MethodType targetType = target.type();
4684 int maxPos = targetType.parameterCount();
4685 if (pos + filters.length > maxPos)
4686 throw newIllegalArgumentException("too many filters");
4687 }
4688
4689 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4690 MethodType targetType = target.type();
4691 MethodType filterType = filter.type();
4692 if (filterType.parameterCount() != 1
4693 || filterType.returnType() != targetType.parameterType(pos))
4694 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4695 }
4696
4697 /**
4698 * Adapts a target method handle by pre-processing
4699 * a sub-sequence of its arguments with a filter (another method handle).
4700 * The pre-processed arguments are replaced by the result (if any) of the
4701 * filter function.
4702 * The target is then called on the modified (usually shortened) argument list.
4703 * <p>
4704 * If the filter returns a value, the target must accept that value as
4705 * its argument in position {@code pos}, preceded and/or followed by
4706 * any arguments not passed to the filter.
4707 * If the filter returns void, the target must accept all arguments
4708 * not passed to the filter.
4709 * No arguments are reordered, and a result returned from the filter
4710 * replaces (in order) the whole subsequence of arguments originally
4711 * passed to the adapter.
4712 * <p>
4713 * The argument types (if any) of the filter
4714 * replace zero or one argument types of the target, at position {@code pos},
4715 * in the resulting adapted method handle.
4716 * The return type of the filter (if any) must be identical to the
4717 * argument type of the target at position {@code pos}, and that target argument
4718 * is supplied by the return value of the filter.
4719 * <p>
4720 * In all cases, {@code pos} must be greater than or equal to zero, and
4721 * {@code pos} must also be less than or equal to the target's arity.
4722 * <p><b>Example:</b>
4723 * <blockquote><pre>{@code
4724 import static java.lang.invoke.MethodHandles.*;
4725 import static java.lang.invoke.MethodType.*;
4726 ...
4727 MethodHandle deepToString = publicLookup()
4728 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
4729
4730 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
4731 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
4732
4733 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
4734 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
4735
4736 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
4737 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
4738 assertEquals("[top, [up, down], strange]",
4739 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
4740
4741 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
4742 assertEquals("[top, [up, down], [strange]]",
4743 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
4744
4745 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4746 assertEquals("[top, [[up, down, strange], charm], bottom]",
4747 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4748 * }</pre></blockquote>
4749 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4750 * represents the return type of the {@code target} and resulting adapter.
4751 * {@code V}/{@code v} stand for the return type and value of the
4752 * {@code filter}, which are also found in the signature and arguments of
4753 * the {@code target}, respectively, unless {@code V} is {@code void}.
4754 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4755 * and values preceding and following the collection position, {@code pos},
4756 * in the {@code target}'s signature. They also turn up in the resulting
4757 * adapter's signature and arguments, where they surround
4758 * {@code B}/{@code b}, which represent the parameter types and arguments
4759 * to the {@code filter} (if any).
4760 * <blockquote><pre>{@code
4761 * T target(A...,V,C...);
4762 * V filter(B...);
4763 * T adapter(A... a,B... b,C... c) {
4764 * V v = filter(b...);
4765 * return target(a...,v,c...);
4766 * }
4767 * // and if the filter has no arguments:
4768 * T target2(A...,V,C...);
4769 * V filter2();
4770 * T adapter2(A... a,C... c) {
4771 * V v = filter2();
4772 * return target2(a...,v,c...);
4773 * }
4774 * // and if the filter has a void return:
4775 * T target3(A...,C...);
4776 * void filter3(B...);
4777 * T adapter3(A... a,B... b,C... c) {
4778 * filter3(b...);
4779 * return target3(a...,c...);
4780 * }
4781 * }</pre></blockquote>
4782 * <p>
4783 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
4784 * one which first "folds" the affected arguments, and then drops them, in separate
4785 * steps as follows:
4786 * <blockquote><pre>{@code
4787 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4788 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4789 * }</pre></blockquote>
4790 * If the target method handle consumes no arguments besides than the result
4791 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4792 * is equivalent to {@code filterReturnValue(coll, mh)}.
4793 * If the filter method handle {@code coll} consumes one argument and produces
4794 * a non-void result, then {@code collectArguments(mh, N, coll)}
4795 * is equivalent to {@code filterArguments(mh, N, coll)}.
4796 * Other equivalences are possible but would require argument permutation.
4797 * <p>
4798 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4799 * variable-arity method handle}, even if the original target method handle was.
4800 *
4801 * @param target the method handle to invoke after filtering the subsequence of arguments
4802 * @param pos the position of the first adapter argument to pass to the filter,
4803 * and/or the target argument which receives the result of the filter
4804 * @param filter method handle to call on the subsequence of arguments
4805 * @return method handle which incorporates the specified argument subsequence filtering logic
4806 * @throws NullPointerException if either argument is null
4807 * @throws IllegalArgumentException if the return type of {@code filter}
4808 * is non-void and is not the same as the {@code pos} argument of the target,
4809 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4810 * or if the resulting method handle's type would have
4811 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4812 * @see MethodHandles#foldArguments
4813 * @see MethodHandles#filterArguments
4814 * @see MethodHandles#filterReturnValue
4815 */
4816 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4817 MethodType newType = collectArgumentsChecks(target, pos, filter);
4818 MethodType collectorType = filter.type();
4819 BoundMethodHandle result = target.rebind();
4820 LambdaForm lform;
4821 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4822 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4823 if (lform != null) {
4824 return result.copyWith(newType, lform);
4825 }
4826 }
4827 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4828 return result.copyWithExtendL(newType, lform, filter);
4829 }
4830
4831 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4832 MethodType targetType = target.type();
4833 MethodType filterType = filter.type();
4834 Class<?> rtype = filterType.returnType();
4835 List<Class<?>> filterArgs = filterType.parameterList();
4836 if (rtype == void.class) {
4837 return targetType.insertParameterTypes(pos, filterArgs);
4838 }
4839 if (rtype != targetType.parameterType(pos)) {
4840 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4841 }
4842 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4843 }
4844
4845 /**
4846 * Adapts a target method handle by post-processing
4847 * its return value (if any) with a filter (another method handle).
4848 * The result of the filter is returned from the adapter.
4849 * <p>
4850 * If the target returns a value, the filter must accept that value as
4851 * its only argument.
4852 * If the target returns void, the filter must accept no arguments.
4853 * <p>
4854 * The return type of the filter
4855 * replaces the return type of the target
4856 * in the resulting adapted method handle.
4857 * The argument type of the filter (if any) must be identical to the
4858 * return type of the target.
4859 * <p><b>Example:</b>
4860 * <blockquote><pre>{@code
4861 import static java.lang.invoke.MethodHandles.*;
4862 import static java.lang.invoke.MethodType.*;
4863 ...
4864 MethodHandle cat = lookup().findVirtual(String.class,
4865 "concat", methodType(String.class, String.class));
4866 MethodHandle length = lookup().findVirtual(String.class,
4867 "length", methodType(int.class));
4868 System.out.println((String) cat.invokeExact("x", "y")); // xy
4869 MethodHandle f0 = filterReturnValue(cat, length);
4870 System.out.println((int) f0.invokeExact("x", "y")); // 2
4871 * }</pre></blockquote>
4872 * <p>Here is pseudocode for the resulting adapter. In the code,
4873 * {@code T}/{@code t} represent the result type and value of the
4874 * {@code target}; {@code V}, the result type of the {@code filter}; and
4875 * {@code A}/{@code a}, the types and values of the parameters and arguments
4876 * of the {@code target} as well as the resulting adapter.
4877 * <blockquote><pre>{@code
4878 * T target(A...);
4879 * V filter(T);
4880 * V adapter(A... a) {
4881 * T t = target(a...);
4882 * return filter(t);
4883 * }
4884 * // and if the target has a void return:
4885 * void target2(A...);
4886 * V filter2();
4887 * V adapter2(A... a) {
4888 * target2(a...);
4889 * return filter2();
4890 * }
4891 * // and if the filter has a void return:
4892 * T target3(A...);
4893 * void filter3(V);
4894 * void adapter3(A... a) {
4895 * T t = target3(a...);
4896 * filter3(t);
4897 * }
4898 * }</pre></blockquote>
4899 * <p>
4900 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4901 * variable-arity method handle}, even if the original target method handle was.
4902 * @param target the method handle to invoke before filtering the return value
4903 * @param filter method handle to call on the return value
4904 * @return method handle which incorporates the specified return value filtering logic
4905 * @throws NullPointerException if either argument is null
4906 * @throws IllegalArgumentException if the argument list of {@code filter}
4907 * does not match the return type of target as described above
4908 */
4909 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4910 MethodType targetType = target.type();
4911 MethodType filterType = filter.type();
4912 filterReturnValueChecks(targetType, filterType);
4913 BoundMethodHandle result = target.rebind();
4914 BasicType rtype = BasicType.basicType(filterType.returnType());
4915 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4916 MethodType newType = targetType.changeReturnType(filterType.returnType());
4917 result = result.copyWithExtendL(newType, lform, filter);
4918 return result;
4919 }
4920
4921 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4922 Class<?> rtype = targetType.returnType();
4923 int filterValues = filterType.parameterCount();
4924 if (filterValues == 0
4925 ? (rtype != void.class)
4926 : (rtype != filterType.parameterType(0) || filterValues != 1))
4927 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4928 }
4929
4930 /**
4931 * Adapts a target method handle by pre-processing
4932 * some of its arguments, and then calling the target with
4933 * the result of the pre-processing, inserted into the original
4934 * sequence of arguments.
4935 * <p>
4936 * The pre-processing is performed by {@code combiner}, a second method handle.
4937 * Of the arguments passed to the adapter, the first {@code N} arguments
4938 * are copied to the combiner, which is then called.
4939 * (Here, {@code N} is defined as the parameter count of the combiner.)
4940 * After this, control passes to the target, with any result
4941 * from the combiner inserted before the original {@code N} incoming
4942 * arguments.
4943 * <p>
4944 * If the combiner returns a value, the first parameter type of the target
4945 * must be identical with the return type of the combiner, and the next
4946 * {@code N} parameter types of the target must exactly match the parameters
4947 * of the combiner.
4948 * <p>
4949 * If the combiner has a void return, no result will be inserted,
4950 * and the first {@code N} parameter types of the target
4951 * must exactly match the parameters of the combiner.
4952 * <p>
4953 * The resulting adapter is the same type as the target, except that the
4954 * first parameter type is dropped,
4955 * if it corresponds to the result of the combiner.
4956 * <p>
4957 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4958 * that either the combiner or the target does not wish to receive.
4959 * If some of the incoming arguments are destined only for the combiner,
4960 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4961 * arguments will not need to be live on the stack on entry to the
4962 * target.)
4963 * <p><b>Example:</b>
4964 * <blockquote><pre>{@code
4965 import static java.lang.invoke.MethodHandles.*;
4966 import static java.lang.invoke.MethodType.*;
4967 ...
4968 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4969 "println", methodType(void.class, String.class))
4970 .bindTo(System.out);
4971 MethodHandle cat = lookup().findVirtual(String.class,
4972 "concat", methodType(String.class, String.class));
4973 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4974 MethodHandle catTrace = foldArguments(cat, trace);
4975 // also prints "boo":
4976 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4977 * }</pre></blockquote>
4978 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4979 * represents the result type of the {@code target} and resulting adapter.
4980 * {@code V}/{@code v} represent the type and value of the parameter and argument
4981 * of {@code target} that precedes the folding position; {@code V} also is
4982 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4983 * types and values of the {@code N} parameters and arguments at the folding
4984 * position. {@code B}/{@code b} represent the types and values of the
4985 * {@code target} parameters and arguments that follow the folded parameters
4986 * and arguments.
4987 * <blockquote><pre>{@code
4988 * // there are N arguments in A...
4989 * T target(V, A[N]..., B...);
4990 * V combiner(A...);
4991 * T adapter(A... a, B... b) {
4992 * V v = combiner(a...);
4993 * return target(v, a..., b...);
4994 * }
4995 * // and if the combiner has a void return:
4996 * T target2(A[N]..., B...);
4997 * void combiner2(A...);
4998 * T adapter2(A... a, B... b) {
4999 * combiner2(a...);
5000 * return target2(a..., b...);
5001 * }
5002 * }</pre></blockquote>
5003 * <p>
5004 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5005 * variable-arity method handle}, even if the original target method handle was.
5006 * @param target the method handle to invoke after arguments are combined
5007 * @param combiner method handle to call initially on the incoming arguments
5008 * @return method handle which incorporates the specified argument folding logic
5009 * @throws NullPointerException if either argument is null
5010 * @throws IllegalArgumentException if {@code combiner}'s return type
5011 * is non-void and not the same as the first argument type of
5012 * the target, or if the initial {@code N} argument types
5013 * of the target
5014 * (skipping one matching the {@code combiner}'s return type)
5015 * are not identical with the argument types of {@code combiner}
5016 */
5017 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5018 return foldArguments(target, 0, combiner);
5019 }
5020
5021 /**
5022 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5023 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5024 * before the folded arguments.
5025 * <p>
5026 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5027 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5028 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5029 * 0.
5030 *
5031 * @apiNote Example:
5032 * <blockquote><pre>{@code
5033 import static java.lang.invoke.MethodHandles.*;
5034 import static java.lang.invoke.MethodType.*;
5035 ...
5036 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5037 "println", methodType(void.class, String.class))
5038 .bindTo(System.out);
5039 MethodHandle cat = lookup().findVirtual(String.class,
5040 "concat", methodType(String.class, String.class));
5041 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5042 MethodHandle catTrace = foldArguments(cat, 1, trace);
5043 // also prints "jum":
5044 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5045 * }</pre></blockquote>
5046 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5047 * represents the result type of the {@code target} and resulting adapter.
5048 * {@code V}/{@code v} represent the type and value of the parameter and argument
5049 * of {@code target} that precedes the folding position; {@code V} also is
5050 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5051 * types and values of the {@code N} parameters and arguments at the folding
5052 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5053 * and values of the {@code target} parameters and arguments that precede and
5054 * follow the folded parameters and arguments starting at {@code pos},
5055 * respectively.
5056 * <blockquote><pre>{@code
5057 * // there are N arguments in A...
5058 * T target(Z..., V, A[N]..., B...);
5059 * V combiner(A...);
5060 * T adapter(Z... z, A... a, B... b) {
5061 * V v = combiner(a...);
5062 * return target(z..., v, a..., b...);
5063 * }
5064 * // and if the combiner has a void return:
5065 * T target2(Z..., A[N]..., B...);
5066 * void combiner2(A...);
5067 * T adapter2(Z... z, A... a, B... b) {
5068 * combiner2(a...);
5069 * return target2(z..., a..., b...);
5070 * }
5071 * }</pre></blockquote>
5072 * <p>
5073 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5074 * variable-arity method handle}, even if the original target method handle was.
5075 *
5076 * @param target the method handle to invoke after arguments are combined
5077 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5078 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5079 * @param combiner method handle to call initially on the incoming arguments
5080 * @return method handle which incorporates the specified argument folding logic
5081 * @throws NullPointerException if either argument is null
5082 * @throws IllegalArgumentException if either of the following two conditions holds:
5083 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5084 * {@code pos} of the target signature;
5085 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5086 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5087 *
5088 * @see #foldArguments(MethodHandle, MethodHandle)
5089 * @since 9
5090 */
5091 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5092 MethodType targetType = target.type();
5093 MethodType combinerType = combiner.type();
5094 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5095 BoundMethodHandle result = target.rebind();
5096 boolean dropResult = rtype == void.class;
5097 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5098 MethodType newType = targetType;
5099 if (!dropResult) {
5100 newType = newType.dropParameterTypes(pos, pos + 1);
5101 }
5102 result = result.copyWithExtendL(newType, lform, combiner);
5103 return result;
5104 }
5105
5106 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5107 int foldArgs = combinerType.parameterCount();
5108 Class<?> rtype = combinerType.returnType();
5109 int foldVals = rtype == void.class ? 0 : 1;
5110 int afterInsertPos = foldPos + foldVals;
5111 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5112 if (ok) {
5113 for (int i = 0; i < foldArgs; i++) {
5114 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5115 ok = false;
5116 break;
5117 }
5118 }
5119 }
5120 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5121 ok = false;
5122 if (!ok)
5123 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5124 return rtype;
5125 }
5126
5127 /**
5128 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5129 * of the pre-processing replacing the argument at the given position.
5130 *
5131 * @param target the method handle to invoke after arguments are combined
5132 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5133 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5134 * @param combiner method handle to call initially on the incoming arguments
5135 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5136 * @return method handle which incorporates the specified argument folding logic
5137 * @throws NullPointerException if either argument is null
5138 * @throws IllegalArgumentException if either of the following two conditions holds:
5139 * (1) {@code combiner}'s return type is not the same as the argument type at position
5140 * {@code pos} of the target signature;
5141 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5142 * not identical with the argument types of {@code combiner}.
5143 */
5144 /*non-public*/
5145 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5146 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5147 }
5148
5149 /**
5150 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5151 * the pre-processing inserted into the original sequence of arguments at the given position.
5152 *
5153 * @param target the method handle to invoke after arguments are combined
5154 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5155 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5156 * @param combiner method handle to call initially on the incoming arguments
5157 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5158 * @return method handle which incorporates the specified argument folding logic
5159 * @throws NullPointerException if either argument is null
5160 * @throws IllegalArgumentException if either of the following two conditions holds:
5161 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5162 * {@code pos} of the target signature;
5163 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5164 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5165 * with the argument types of {@code combiner}.
5166 */
5167 /*non-public*/
5168 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5169 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5170 }
5171
5172 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5173 MethodType targetType = target.type();
5174 MethodType combinerType = combiner.type();
5175 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5176 BoundMethodHandle result = target.rebind();
5177
5178 MethodType newType = targetType;
5179 LambdaForm lform;
5180 if (filter) {
5181 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5182 } else {
5183 boolean dropResult = rtype == void.class;
5184 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5185 if (!dropResult) {
5186 newType = newType.dropParameterTypes(position, position + 1);
5187 }
5188 }
5189 result = result.copyWithExtendL(newType, lform, combiner);
5190 return result;
5191 }
5192
5193 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5194 int combinerArgs = combinerType.parameterCount();
5195 if (argPos.length != combinerArgs) {
5196 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5197 }
5198 Class<?> rtype = combinerType.returnType();
5199
5200 for (int i = 0; i < combinerArgs; i++) {
5201 int arg = argPos[i];
5202 if (arg < 0 || arg > targetType.parameterCount()) {
5203 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5204 }
5205 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5206 throw newIllegalArgumentException("target argument type at position " + arg
5207 + " must match combiner argument type at index " + i + ": " + targetType
5208 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5209 }
5210 }
5211 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5212 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5213 }
5214 return rtype;
5215 }
5216
5217 /**
5218 * Makes a method handle which adapts a target method handle,
5219 * by guarding it with a test, a boolean-valued method handle.
5220 * If the guard fails, a fallback handle is called instead.
5221 * All three method handles must have the same corresponding
5222 * argument and return types, except that the return type
5223 * of the test must be boolean, and the test is allowed
5224 * to have fewer arguments than the other two method handles.
5225 * <p>
5226 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5227 * represents the uniform result type of the three involved handles;
5228 * {@code A}/{@code a}, the types and values of the {@code target}
5229 * parameters and arguments that are consumed by the {@code test}; and
5230 * {@code B}/{@code b}, those types and values of the {@code target}
5231 * parameters and arguments that are not consumed by the {@code test}.
5232 * <blockquote><pre>{@code
5233 * boolean test(A...);
5234 * T target(A...,B...);
5235 * T fallback(A...,B...);
5236 * T adapter(A... a,B... b) {
5237 * if (test(a...))
5238 * return target(a..., b...);
5239 * else
5240 * return fallback(a..., b...);
5241 * }
5242 * }</pre></blockquote>
5243 * Note that the test arguments ({@code a...} in the pseudocode) cannot
5244 * be modified by execution of the test, and so are passed unchanged
5245 * from the caller to the target or fallback as appropriate.
5246 * @param test method handle used for test, must return boolean
5247 * @param target method handle to call if test passes
5248 * @param fallback method handle to call if test fails
5249 * @return method handle which incorporates the specified if/then/else logic
5250 * @throws NullPointerException if any argument is null
5251 * @throws IllegalArgumentException if {@code test} does not return boolean,
5252 * or if all three method types do not match (with the return
5253 * type of {@code test} changed to match that of the target).
5254 */
5255 public static MethodHandle guardWithTest(MethodHandle test,
5256 MethodHandle target,
5257 MethodHandle fallback) {
5258 MethodType gtype = test.type();
5259 MethodType ttype = target.type();
5260 MethodType ftype = fallback.type();
5261 if (!ttype.equals(ftype))
5262 throw misMatchedTypes("target and fallback types", ttype, ftype);
5263 if (gtype.returnType() != boolean.class)
5264 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
5265 List<Class<?>> targs = ttype.parameterList();
5266 test = dropArgumentsToMatch(test, 0, targs, 0, true);
5267 if (test == null) {
5268 throw misMatchedTypes("target and test types", ttype, gtype);
5269 }
5270 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
5271 }
5272
5273 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
5274 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
5275 }
5276
5277 /**
5278 * Makes a method handle which adapts a target method handle,
5279 * by running it inside an exception handler.
5280 * If the target returns normally, the adapter returns that value.
5281 * If an exception matching the specified type is thrown, the fallback
5282 * handle is called instead on the exception, plus the original arguments.
5283 * <p>
5284 * The target and handler must have the same corresponding
5285 * argument and return types, except that handler may omit trailing arguments
5286 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
5287 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
5288 * <p>
5289 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5290 * represents the return type of the {@code target} and {@code handler},
5291 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
5292 * the types and values of arguments to the resulting handle consumed by
5293 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
5294 * resulting handle discarded by {@code handler}.
5295 * <blockquote><pre>{@code
5296 * T target(A..., B...);
5297 * T handler(ExType, A...);
5298 * T adapter(A... a, B... b) {
5299 * try {
5300 * return target(a..., b...);
5301 * } catch (ExType ex) {
5302 * return handler(ex, a...);
5303 * }
5304 * }
5305 * }</pre></blockquote>
5306 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5307 * be modified by execution of the target, and so are passed unchanged
5308 * from the caller to the handler, if the handler is invoked.
5309 * <p>
5310 * The target and handler must return the same type, even if the handler
5311 * always throws. (This might happen, for instance, because the handler
5312 * is simulating a {@code finally} clause).
5313 * To create such a throwing handler, compose the handler creation logic
5314 * with {@link #throwException throwException},
5315 * in order to create a method handle of the correct return type.
5316 * @param target method handle to call
5317 * @param exType the type of exception which the handler will catch
5318 * @param handler method handle to call if a matching exception is thrown
5319 * @return method handle which incorporates the specified try/catch logic
5320 * @throws NullPointerException if any argument is null
5321 * @throws IllegalArgumentException if {@code handler} does not accept
5322 * the given exception type, or if the method handle types do
5323 * not match in their return types and their
5324 * corresponding parameters
5325 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
5326 */
5327 public static MethodHandle catchException(MethodHandle target,
5328 Class<? extends Throwable> exType,
5329 MethodHandle handler) {
5330 MethodType ttype = target.type();
5331 MethodType htype = handler.type();
5332 if (!Throwable.class.isAssignableFrom(exType))
5333 throw new ClassCastException(exType.getName());
5334 if (htype.parameterCount() < 1 ||
5335 !htype.parameterType(0).isAssignableFrom(exType))
5336 throw newIllegalArgumentException("handler does not accept exception type "+exType);
5337 if (htype.returnType() != ttype.returnType())
5338 throw misMatchedTypes("target and handler return types", ttype, htype);
5339 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
5340 if (handler == null) {
5341 throw misMatchedTypes("target and handler types", ttype, htype);
5342 }
5343 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
5344 }
5345
5346 /**
5347 * Produces a method handle which will throw exceptions of the given {@code exType}.
5348 * The method handle will accept a single argument of {@code exType},
5349 * and immediately throw it as an exception.
5350 * The method type will nominally specify a return of {@code returnType}.
5351 * The return type may be anything convenient: It doesn't matter to the
5352 * method handle's behavior, since it will never return normally.
5353 * @param returnType the return type of the desired method handle
5354 * @param exType the parameter type of the desired method handle
5355 * @return method handle which can throw the given exceptions
5356 * @throws NullPointerException if either argument is null
5357 */
5358 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
5359 if (!Throwable.class.isAssignableFrom(exType))
5360 throw new ClassCastException(exType.getName());
5361 return MethodHandleImpl.throwException(methodType(returnType, exType));
5362 }
5363
5364 /**
5365 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
5366 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
5367 * delivers the loop's result, which is the return value of the resulting handle.
5368 * <p>
5369 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
5370 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
5371 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
5372 * terms of method handles, each clause will specify up to four independent actions:<ul>
5373 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
5374 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
5375 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
5376 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
5377 * </ul>
5378 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
5379 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
5380 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
5381 * <p>
5382 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
5383 * this case. See below for a detailed description.
5384 * <p>
5385 * <em>Parameters optional everywhere:</em>
5386 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
5387 * As an exception, the init functions cannot take any {@code v} parameters,
5388 * because those values are not yet computed when the init functions are executed.
5389 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
5390 * In fact, any clause function may take no arguments at all.
5391 * <p>
5392 * <em>Loop parameters:</em>
5393 * A clause function may take all the iteration variable values it is entitled to, in which case
5394 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
5395 * with their types and values notated as {@code (A...)} and {@code (a...)}.
5396 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
5397 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
5398 * init function is automatically a loop parameter {@code a}.)
5399 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
5400 * These loop parameters act as loop-invariant values visible across the whole loop.
5401 * <p>
5402 * <em>Parameters visible everywhere:</em>
5403 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
5404 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
5405 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
5406 * Most clause functions will not need all of this information, but they will be formally connected to it
5407 * as if by {@link #dropArguments}.
5408 * <a id="astar"></a>
5409 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
5410 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
5411 * In that notation, the general form of an init function parameter list
5412 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
5413 * <p>
5414 * <em>Checking clause structure:</em>
5415 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
5416 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
5417 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
5418 * met by the inputs to the loop combinator.
5419 * <p>
5420 * <em>Effectively identical sequences:</em>
5421 * <a id="effid"></a>
5422 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
5423 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
5424 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
5425 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
5426 * that longest list.
5427 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
5428 * and the same is true if more sequences of the form {@code (V... A*)} are added.
5429 * <p>
5430 * <em>Step 0: Determine clause structure.</em><ol type="a">
5431 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
5432 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
5433 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
5434 * four. Padding takes place by appending elements to the array.
5435 * <li>Clauses with all {@code null}s are disregarded.
5436 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
5437 * </ol>
5438 * <p>
5439 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
5440 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
5441 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
5442 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
5443 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
5444 * iteration variable type.
5445 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
5446 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
5447 * </ol>
5448 * <p>
5449 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
5450 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
5451 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
5452 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
5453 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
5454 * (These types will be checked in step 2, along with all the clause function types.)
5455 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
5456 * <li>All of the collected parameter lists must be effectively identical.
5457 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
5458 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
5459 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
5460 * the "internal parameter list".
5461 * </ul>
5462 * <p>
5463 * <em>Step 1C: Determine loop return type.</em><ol type="a">
5464 * <li>Examine fini function return types, disregarding omitted fini functions.
5465 * <li>If there are no fini functions, the loop return type is {@code void}.
5466 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
5467 * type.
5468 * </ol>
5469 * <p>
5470 * <em>Step 1D: Check other types.</em><ol type="a">
5471 * <li>There must be at least one non-omitted pred function.
5472 * <li>Every non-omitted pred function must have a {@code boolean} return type.
5473 * </ol>
5474 * <p>
5475 * <em>Step 2: Determine parameter lists.</em><ol type="a">
5476 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
5477 * <li>The parameter list for init functions will be adjusted to the external parameter list.
5478 * (Note that their parameter lists are already effectively identical to this list.)
5479 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
5480 * effectively identical to the internal parameter list {@code (V... A...)}.
5481 * </ol>
5482 * <p>
5483 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
5484 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
5485 * type.
5486 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
5487 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
5488 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
5489 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
5490 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
5491 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
5492 * loop return type.
5493 * </ol>
5494 * <p>
5495 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
5496 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
5497 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
5498 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
5499 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
5500 * pad out the end of the list.
5501 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
5502 * </ol>
5503 * <p>
5504 * <em>Final observations.</em><ol type="a">
5505 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
5506 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
5507 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
5508 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
5509 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
5510 * <li>Each pair of init and step functions agrees in their return type {@code V}.
5511 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
5512 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
5513 * </ol>
5514 * <p>
5515 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
5516 * <ul>
5517 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
5518 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
5519 * (Only one {@code Pn} has to be non-{@code null}.)
5520 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
5521 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
5522 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
5523 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
5524 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
5525 * the resulting loop handle's parameter types {@code (A...)}.
5526 * </ul>
5527 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
5528 * which is natural if most of the loop computation happens in the steps. For some loops,
5529 * the burden of computation might be heaviest in the pred functions, and so the pred functions
5530 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
5531 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
5532 * where the init functions will need the extra parameters. For such reasons, the rules for
5533 * determining these parameters are as symmetric as possible, across all clause parts.
5534 * In general, the loop parameters function as common invariant values across the whole
5535 * loop, while the iteration variables function as common variant values, or (if there is
5536 * no step function) as internal loop invariant temporaries.
5537 * <p>
5538 * <em>Loop execution.</em><ol type="a">
5539 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
5540 * every clause function. These locals are loop invariant.
5541 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
5542 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
5543 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
5544 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
5545 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
5546 * (in argument order).
5547 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
5548 * returns {@code false}.
5549 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
5550 * sequence {@code (v...)} of loop variables.
5551 * The updated value is immediately visible to all subsequent function calls.
5552 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
5553 * (of type {@code R}) is returned from the loop as a whole.
5554 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
5555 * except by throwing an exception.
5556 * </ol>
5557 * <p>
5558 * <em>Usage tips.</em>
5559 * <ul>
5560 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
5561 * sometimes a step function only needs to observe the current value of its own variable.
5562 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
5563 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
5564 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
5565 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
5566 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
5567 * <li>If some of the clause functions are virtual methods on an instance, the instance
5568 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
5569 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
5570 * will be the first iteration variable value, and it will be easy to use virtual
5571 * methods as clause parts, since all of them will take a leading instance reference matching that value.
5572 * </ul>
5573 * <p>
5574 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
5575 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
5576 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
5577 * <blockquote><pre>{@code
5578 * V... init...(A...);
5579 * boolean pred...(V..., A...);
5580 * V... step...(V..., A...);
5581 * R fini...(V..., A...);
5582 * R loop(A... a) {
5583 * V... v... = init...(a...);
5584 * for (;;) {
5585 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
5586 * v = s(v..., a...);
5587 * if (!p(v..., a...)) {
5588 * return f(v..., a...);
5589 * }
5590 * }
5591 * }
5592 * }
5593 * }</pre></blockquote>
5594 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
5595 * to their full length, even though individual clause functions may neglect to take them all.
5596 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
5597 *
5598 * @apiNote Example:
5599 * <blockquote><pre>{@code
5600 * // iterative implementation of the factorial function as a loop handle
5601 * static int one(int k) { return 1; }
5602 * static int inc(int i, int acc, int k) { return i + 1; }
5603 * static int mult(int i, int acc, int k) { return i * acc; }
5604 * static boolean pred(int i, int acc, int k) { return i < k; }
5605 * static int fin(int i, int acc, int k) { return acc; }
5606 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5607 * // null initializer for counter, should initialize to 0
5608 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5609 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5610 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5611 * assertEquals(120, loop.invoke(5));
5612 * }</pre></blockquote>
5613 * The same example, dropping arguments and using combinators:
5614 * <blockquote><pre>{@code
5615 * // simplified implementation of the factorial function as a loop handle
5616 * static int inc(int i) { return i + 1; } // drop acc, k
5617 * static int mult(int i, int acc) { return i * acc; } //drop k
5618 * static boolean cmp(int i, int k) { return i < k; }
5619 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
5620 * // null initializer for counter, should initialize to 0
5621 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5622 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
5623 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
5624 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5625 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5626 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5627 * assertEquals(720, loop.invoke(6));
5628 * }</pre></blockquote>
5629 * A similar example, using a helper object to hold a loop parameter:
5630 * <blockquote><pre>{@code
5631 * // instance-based implementation of the factorial function as a loop handle
5632 * static class FacLoop {
5633 * final int k;
5634 * FacLoop(int k) { this.k = k; }
5635 * int inc(int i) { return i + 1; }
5636 * int mult(int i, int acc) { return i * acc; }
5637 * boolean pred(int i) { return i < k; }
5638 * int fin(int i, int acc) { return acc; }
5639 * }
5640 * // assume MH_FacLoop is a handle to the constructor
5641 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5642 * // null initializer for counter, should initialize to 0
5643 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5644 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
5645 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5646 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5647 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
5648 * assertEquals(5040, loop.invoke(7));
5649 * }</pre></blockquote>
5650 *
5651 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
5652 *
5653 * @return a method handle embodying the looping behavior as defined by the arguments.
5654 *
5655 * @throws IllegalArgumentException in case any of the constraints described above is violated.
5656 *
5657 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
5658 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5659 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
5660 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
5661 * @since 9
5662 */
5663 public static MethodHandle loop(MethodHandle[]... clauses) {
5664 // Step 0: determine clause structure.
5665 loopChecks0(clauses);
5666
5667 List<MethodHandle> init = new ArrayList<>();
5668 List<MethodHandle> step = new ArrayList<>();
5669 List<MethodHandle> pred = new ArrayList<>();
5670 List<MethodHandle> fini = new ArrayList<>();
5671
5672 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
5673 init.add(clause[0]); // all clauses have at least length 1
5674 step.add(clause.length <= 1 ? null : clause[1]);
5675 pred.add(clause.length <= 2 ? null : clause[2]);
5676 fini.add(clause.length <= 3 ? null : clause[3]);
5677 });
5678
5679 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
5680 final int nclauses = init.size();
5681
5682 // Step 1A: determine iteration variables (V...).
5683 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
5684 for (int i = 0; i < nclauses; ++i) {
5685 MethodHandle in = init.get(i);
5686 MethodHandle st = step.get(i);
5687 if (in == null && st == null) {
5688 iterationVariableTypes.add(void.class);
5689 } else if (in != null && st != null) {
5690 loopChecks1a(i, in, st);
5691 iterationVariableTypes.add(in.type().returnType());
5692 } else {
5693 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
5694 }
5695 }
5696 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
5697 collect(Collectors.toList());
5698
5699 // Step 1B: determine loop parameters (A...).
5700 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
5701 loopChecks1b(init, commonSuffix);
5702
5703 // Step 1C: determine loop return type.
5704 // Step 1D: check other types.
5705 // local variable required here; see JDK-8223553
5706 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
5707 .map(MethodType::returnType);
5708 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
5709 loopChecks1cd(pred, fini, loopReturnType);
5710
5711 // Step 2: determine parameter lists.
5712 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
5713 commonParameterSequence.addAll(commonSuffix);
5714 loopChecks2(step, pred, fini, commonParameterSequence);
5715
5716 // Step 3: fill in omitted functions.
5717 for (int i = 0; i < nclauses; ++i) {
5718 Class<?> t = iterationVariableTypes.get(i);
5719 if (init.get(i) == null) {
5720 init.set(i, empty(methodType(t, commonSuffix)));
5721 }
5722 if (step.get(i) == null) {
5723 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
5724 }
5725 if (pred.get(i) == null) {
5726 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
5727 }
5728 if (fini.get(i) == null) {
5729 fini.set(i, empty(methodType(t, commonParameterSequence)));
5730 }
5731 }
5732
5733 // Step 4: fill in missing parameter types.
5734 // Also convert all handles to fixed-arity handles.
5735 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
5736 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
5737 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
5738 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
5739
5740 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
5741 allMatch(pl -> pl.equals(commonSuffix));
5742 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5743 allMatch(pl -> pl.equals(commonParameterSequence));
5744
5745 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5746 }
5747
5748 private static void loopChecks0(MethodHandle[][] clauses) {
5749 if (clauses == null || clauses.length == 0) {
5750 throw newIllegalArgumentException("null or no clauses passed");
5751 }
5752 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5753 throw newIllegalArgumentException("null clauses are not allowed");
5754 }
5755 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5756 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5757 }
5758 }
5759
5760 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5761 if (in.type().returnType() != st.type().returnType()) {
5762 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5763 st.type().returnType());
5764 }
5765 }
5766
5767 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
5768 final List<Class<?>> empty = List.of();
5769 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
5770 // take only those that can contribute to a common suffix because they are longer than the prefix
5771 map(MethodHandle::type).
5772 filter(t -> t.parameterCount() > skipSize).
5773 map(MethodType::parameterList).
5774 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5775 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
5776 }
5777
5778 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
5779 final List<Class<?>> empty = List.of();
5780 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5781 }
5782
5783 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
5784 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
5785 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
5786 return longestParameterList(Arrays.asList(longest1, longest2));
5787 }
5788
5789 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
5790 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
5791 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
5792 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
5793 " (common suffix: " + commonSuffix + ")");
5794 }
5795 }
5796
5797 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
5798 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5799 anyMatch(t -> t != loopReturnType)) {
5800 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
5801 loopReturnType + ")");
5802 }
5803
5804 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5805 throw newIllegalArgumentException("no predicate found", pred);
5806 }
5807 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5808 anyMatch(t -> t != boolean.class)) {
5809 throw newIllegalArgumentException("predicates must have boolean return type", pred);
5810 }
5811 }
5812
5813 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5814 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5815 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
5816 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5817 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5818 }
5819 }
5820
5821 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
5822 return hs.stream().map(h -> {
5823 int pc = h.type().parameterCount();
5824 int tpsize = targetParams.size();
5825 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5826 }).collect(Collectors.toList());
5827 }
5828
5829 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5830 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5831 }
5832
5833 /**
5834 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5835 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5836 * <p>
5837 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5838 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5839 * evaluates to {@code true}).
5840 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5841 * <p>
5842 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5843 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5844 * and updated with the value returned from its invocation. The result of loop execution will be
5845 * the final value of the additional loop-local variable (if present).
5846 * <p>
5847 * The following rules hold for these argument handles:<ul>
5848 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5849 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5850 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5851 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5852 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5853 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5854 * It will constrain the parameter lists of the other loop parts.
5855 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5856 * list {@code (A...)} is called the <em>external parameter list</em>.
5857 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5858 * additional state variable of the loop.
5859 * The body must both accept and return a value of this type {@code V}.
5860 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5861 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5862 * <a href="MethodHandles.html#effid">effectively identical</a>
5863 * to the external parameter list {@code (A...)}.
5864 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5865 * {@linkplain #empty default value}.
5866 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5867 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5868 * effectively identical to the internal parameter list.
5869 * </ul>
5870 * <p>
5871 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5872 * <li>The loop handle's result type is the result type {@code V} of the body.
5873 * <li>The loop handle's parameter types are the types {@code (A...)},
5874 * from the external parameter list.
5875 * </ul>
5876 * <p>
5877 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5878 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5879 * passed to the loop.
5880 * <blockquote><pre>{@code
5881 * V init(A...);
5882 * boolean pred(V, A...);
5883 * V body(V, A...);
5884 * V whileLoop(A... a...) {
5885 * V v = init(a...);
5886 * while (pred(v, a...)) {
5887 * v = body(v, a...);
5888 * }
5889 * return v;
5890 * }
5891 * }</pre></blockquote>
5892 *
5893 * @apiNote Example:
5894 * <blockquote><pre>{@code
5895 * // implement the zip function for lists as a loop handle
5896 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5897 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5898 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5899 * zip.add(a.next());
5900 * zip.add(b.next());
5901 * return zip;
5902 * }
5903 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5904 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5905 * List<String> a = Arrays.asList("a", "b", "c", "d");
5906 * List<String> b = Arrays.asList("e", "f", "g", "h");
5907 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5908 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5909 * }</pre></blockquote>
5910 *
5911 *
5912 * @apiNote The implementation of this method can be expressed as follows:
5913 * <blockquote><pre>{@code
5914 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5915 * MethodHandle fini = (body.type().returnType() == void.class
5916 * ? null : identity(body.type().returnType()));
5917 * MethodHandle[]
5918 * checkExit = { null, null, pred, fini },
5919 * varBody = { init, body };
5920 * return loop(checkExit, varBody);
5921 * }
5922 * }</pre></blockquote>
5923 *
5924 * @param init optional initializer, providing the initial value of the loop variable.
5925 * May be {@code null}, implying a default initial value. See above for other constraints.
5926 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5927 * above for other constraints.
5928 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5929 * See above for other constraints.
5930 *
5931 * @return a method handle implementing the {@code while} loop as described by the arguments.
5932 * @throws IllegalArgumentException if the rules for the arguments are violated.
5933 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5934 *
5935 * @see #loop(MethodHandle[][])
5936 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5937 * @since 9
5938 */
5939 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5940 whileLoopChecks(init, pred, body);
5941 MethodHandle fini = identityOrVoid(body.type().returnType());
5942 MethodHandle[] checkExit = { null, null, pred, fini };
5943 MethodHandle[] varBody = { init, body };
5944 return loop(checkExit, varBody);
5945 }
5946
5947 /**
5948 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5949 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5950 * <p>
5951 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5952 * method will, in each iteration, first execute its body and then evaluate the predicate.
5953 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5954 * <p>
5955 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5956 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5957 * and updated with the value returned from its invocation. The result of loop execution will be
5958 * the final value of the additional loop-local variable (if present).
5959 * <p>
5960 * The following rules hold for these argument handles:<ul>
5961 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5962 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5963 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5964 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5965 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5966 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5967 * It will constrain the parameter lists of the other loop parts.
5968 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5969 * list {@code (A...)} is called the <em>external parameter list</em>.
5970 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5971 * additional state variable of the loop.
5972 * The body must both accept and return a value of this type {@code V}.
5973 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5974 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5975 * <a href="MethodHandles.html#effid">effectively identical</a>
5976 * to the external parameter list {@code (A...)}.
5977 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5978 * {@linkplain #empty default value}.
5979 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5980 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5981 * effectively identical to the internal parameter list.
5982 * </ul>
5983 * <p>
5984 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5985 * <li>The loop handle's result type is the result type {@code V} of the body.
5986 * <li>The loop handle's parameter types are the types {@code (A...)},
5987 * from the external parameter list.
5988 * </ul>
5989 * <p>
5990 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5991 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5992 * passed to the loop.
5993 * <blockquote><pre>{@code
5994 * V init(A...);
5995 * boolean pred(V, A...);
5996 * V body(V, A...);
5997 * V doWhileLoop(A... a...) {
5998 * V v = init(a...);
5999 * do {
6000 * v = body(v, a...);
6001 * } while (pred(v, a...));
6002 * return v;
6003 * }
6004 * }</pre></blockquote>
6005 *
6006 * @apiNote Example:
6007 * <blockquote><pre>{@code
6008 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6009 * static int zero(int limit) { return 0; }
6010 * static int step(int i, int limit) { return i + 1; }
6011 * static boolean pred(int i, int limit) { return i < limit; }
6012 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6013 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6014 * assertEquals(23, loop.invoke(23));
6015 * }</pre></blockquote>
6016 *
6017 *
6018 * @apiNote The implementation of this method can be expressed as follows:
6019 * <blockquote><pre>{@code
6020 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6021 * MethodHandle fini = (body.type().returnType() == void.class
6022 * ? null : identity(body.type().returnType()));
6023 * MethodHandle[] clause = { init, body, pred, fini };
6024 * return loop(clause);
6025 * }
6026 * }</pre></blockquote>
6027 *
6028 * @param init optional initializer, providing the initial value of the loop variable.
6029 * May be {@code null}, implying a default initial value. See above for other constraints.
6030 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6031 * See above for other constraints.
6032 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6033 * above for other constraints.
6034 *
6035 * @return a method handle implementing the {@code while} loop as described by the arguments.
6036 * @throws IllegalArgumentException if the rules for the arguments are violated.
6037 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6038 *
6039 * @see #loop(MethodHandle[][])
6040 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6041 * @since 9
6042 */
6043 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6044 whileLoopChecks(init, pred, body);
6045 MethodHandle fini = identityOrVoid(body.type().returnType());
6046 MethodHandle[] clause = {init, body, pred, fini };
6047 return loop(clause);
6048 }
6049
6050 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6051 Objects.requireNonNull(pred);
6052 Objects.requireNonNull(body);
6053 MethodType bodyType = body.type();
6054 Class<?> returnType = bodyType.returnType();
6055 List<Class<?>> innerList = bodyType.parameterList();
6056 List<Class<?>> outerList = innerList;
6057 if (returnType == void.class) {
6058 // OK
6059 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
6060 // leading V argument missing => error
6061 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6062 throw misMatchedTypes("body function", bodyType, expected);
6063 } else {
6064 outerList = innerList.subList(1, innerList.size());
6065 }
6066 MethodType predType = pred.type();
6067 if (predType.returnType() != boolean.class ||
6068 !predType.effectivelyIdenticalParameters(0, innerList)) {
6069 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6070 }
6071 if (init != null) {
6072 MethodType initType = init.type();
6073 if (initType.returnType() != returnType ||
6074 !initType.effectivelyIdenticalParameters(0, outerList)) {
6075 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6076 }
6077 }
6078 }
6079
6080 /**
6081 * Constructs a loop that runs a given number of iterations.
6082 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6083 * <p>
6084 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6085 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6086 * It will be initialized to 0 and incremented by 1 in each iteration.
6087 * <p>
6088 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6089 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6090 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6091 * <p>
6092 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6093 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6094 * iteration variable.
6095 * The result of the loop handle execution will be the final {@code V} value of that variable
6096 * (or {@code void} if there is no {@code V} variable).
6097 * <p>
6098 * The following rules hold for the argument handles:<ul>
6099 * <li>The {@code iterations} handle must not be {@code null}, and must return
6100 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6101 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6102 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6103 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6104 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6105 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6106 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6107 * of types called the <em>internal parameter list</em>.
6108 * It will constrain the parameter lists of the other loop parts.
6109 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6110 * with no additional {@code A} types, then the internal parameter list is extended by
6111 * the argument types {@code A...} of the {@code iterations} handle.
6112 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6113 * list {@code (A...)} is called the <em>external parameter list</em>.
6114 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6115 * additional state variable of the loop.
6116 * The body must both accept a leading parameter and return a value of this type {@code V}.
6117 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6118 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6119 * <a href="MethodHandles.html#effid">effectively identical</a>
6120 * to the external parameter list {@code (A...)}.
6121 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6122 * {@linkplain #empty default value}.
6123 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6124 * effectively identical to the external parameter list {@code (A...)}.
6125 * </ul>
6126 * <p>
6127 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6128 * <li>The loop handle's result type is the result type {@code V} of the body.
6129 * <li>The loop handle's parameter types are the types {@code (A...)},
6130 * from the external parameter list.
6131 * </ul>
6132 * <p>
6133 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6134 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6135 * arguments passed to the loop.
6136 * <blockquote><pre>{@code
6137 * int iterations(A...);
6138 * V init(A...);
6139 * V body(V, int, A...);
6140 * V countedLoop(A... a...) {
6141 * int end = iterations(a...);
6142 * V v = init(a...);
6143 * for (int i = 0; i < end; ++i) {
6144 * v = body(v, i, a...);
6145 * }
6146 * return v;
6147 * }
6148 * }</pre></blockquote>
6149 *
6150 * @apiNote Example with a fully conformant body method:
6151 * <blockquote><pre>{@code
6152 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6153 * // => a variation on a well known theme
6154 * static String step(String v, int counter, String init) { return "na " + v; }
6155 * // assume MH_step is a handle to the method above
6156 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6157 * MethodHandle start = MethodHandles.identity(String.class);
6158 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6159 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6160 * }</pre></blockquote>
6161 *
6162 * @apiNote Example with the simplest possible body method type,
6163 * and passing the number of iterations to the loop invocation:
6164 * <blockquote><pre>{@code
6165 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6166 * // => a variation on a well known theme
6167 * static String step(String v, int counter ) { return "na " + v; }
6168 * // assume MH_step is a handle to the method above
6169 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6170 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6171 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6172 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6173 * }</pre></blockquote>
6174 *
6175 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6176 * as loop parameters:
6177 * <blockquote><pre>{@code
6178 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6179 * // => a variation on a well known theme
6180 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6181 * // assume MH_step is a handle to the method above
6182 * MethodHandle count = MethodHandles.identity(int.class);
6183 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6184 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6185 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6186 * }</pre></blockquote>
6187 *
6188 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6189 * to enforce a loop type:
6190 * <blockquote><pre>{@code
6191 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6192 * // => a variation on a well known theme
6193 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6194 * // assume MH_step is a handle to the method above
6195 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6196 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6197 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6198 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6199 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6200 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6201 * }</pre></blockquote>
6202 *
6203 * @apiNote The implementation of this method can be expressed as follows:
6204 * <blockquote><pre>{@code
6205 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6206 * return countedLoop(empty(iterations.type()), iterations, init, body);
6207 * }
6208 * }</pre></blockquote>
6209 *
6210 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6211 * result type must be {@code int}. See above for other constraints.
6212 * @param init optional initializer, providing the initial value of the loop variable.
6213 * May be {@code null}, implying a default initial value. See above for other constraints.
6214 * @param body body of the loop, which may not be {@code null}.
6215 * It controls the loop parameters and result type in the standard case (see above for details).
6216 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6217 * and may accept any number of additional types.
6218 * See above for other constraints.
6219 *
6220 * @return a method handle representing the loop.
6221 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6222 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6223 *
6224 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6225 * @since 9
6226 */
6227 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6228 return countedLoop(empty(iterations.type()), iterations, init, body);
6229 }
6230
6231 /**
6232 * Constructs a loop that counts over a range of numbers.
6233 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6234 * <p>
6235 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
6236 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
6237 * values of the loop counter.
6238 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
6239 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
6240 * <p>
6241 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6242 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6243 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6244 * <p>
6245 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6246 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6247 * iteration variable.
6248 * The result of the loop handle execution will be the final {@code V} value of that variable
6249 * (or {@code void} if there is no {@code V} variable).
6250 * <p>
6251 * The following rules hold for the argument handles:<ul>
6252 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
6253 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
6254 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6255 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6256 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6257 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6258 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6259 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6260 * of types called the <em>internal parameter list</em>.
6261 * It will constrain the parameter lists of the other loop parts.
6262 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6263 * with no additional {@code A} types, then the internal parameter list is extended by
6264 * the argument types {@code A...} of the {@code end} handle.
6265 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6266 * list {@code (A...)} is called the <em>external parameter list</em>.
6267 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6268 * additional state variable of the loop.
6269 * The body must both accept a leading parameter and return a value of this type {@code V}.
6270 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6271 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6272 * <a href="MethodHandles.html#effid">effectively identical</a>
6273 * to the external parameter list {@code (A...)}.
6274 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6275 * {@linkplain #empty default value}.
6276 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
6277 * effectively identical to the external parameter list {@code (A...)}.
6278 * <li>Likewise, the parameter list of {@code end} must be effectively identical
6279 * to the external parameter list.
6280 * </ul>
6281 * <p>
6282 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6283 * <li>The loop handle's result type is the result type {@code V} of the body.
6284 * <li>The loop handle's parameter types are the types {@code (A...)},
6285 * from the external parameter list.
6286 * </ul>
6287 * <p>
6288 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6289 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6290 * arguments passed to the loop.
6291 * <blockquote><pre>{@code
6292 * int start(A...);
6293 * int end(A...);
6294 * V init(A...);
6295 * V body(V, int, A...);
6296 * V countedLoop(A... a...) {
6297 * int e = end(a...);
6298 * int s = start(a...);
6299 * V v = init(a...);
6300 * for (int i = s; i < e; ++i) {
6301 * v = body(v, i, a...);
6302 * }
6303 * return v;
6304 * }
6305 * }</pre></blockquote>
6306 *
6307 * @apiNote The implementation of this method can be expressed as follows:
6308 * <blockquote><pre>{@code
6309 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6310 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
6311 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
6312 * // the following semantics:
6313 * // MH_increment: (int limit, int counter) -> counter + 1
6314 * // MH_predicate: (int limit, int counter) -> counter < limit
6315 * Class<?> counterType = start.type().returnType(); // int
6316 * Class<?> returnType = body.type().returnType();
6317 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
6318 * if (returnType != void.class) { // ignore the V variable
6319 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6320 * pred = dropArguments(pred, 1, returnType); // ditto
6321 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
6322 * }
6323 * body = dropArguments(body, 0, counterType); // ignore the limit variable
6324 * MethodHandle[]
6325 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6326 * bodyClause = { init, body }, // v = init(); v = body(v, i)
6327 * indexVar = { start, incr }; // i = start(); i = i + 1
6328 * return loop(loopLimit, bodyClause, indexVar);
6329 * }
6330 * }</pre></blockquote>
6331 *
6332 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
6333 * See above for other constraints.
6334 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
6335 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
6336 * @param init optional initializer, providing the initial value of the loop variable.
6337 * May be {@code null}, implying a default initial value. See above for other constraints.
6338 * @param body body of the loop, which may not be {@code null}.
6339 * It controls the loop parameters and result type in the standard case (see above for details).
6340 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6341 * and may accept any number of additional types.
6342 * See above for other constraints.
6343 *
6344 * @return a method handle representing the loop.
6345 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
6346 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6347 *
6348 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
6349 * @since 9
6350 */
6351 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6352 countedLoopChecks(start, end, init, body);
6353 Class<?> counterType = start.type().returnType(); // int, but who's counting?
6354 Class<?> limitType = end.type().returnType(); // yes, int again
6355 Class<?> returnType = body.type().returnType();
6356 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
6357 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
6358 MethodHandle retv = null;
6359 if (returnType != void.class) {
6360 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6361 pred = dropArguments(pred, 1, returnType); // ditto
6362 retv = dropArguments(identity(returnType), 0, counterType);
6363 }
6364 body = dropArguments(body, 0, counterType); // ignore the limit variable
6365 MethodHandle[]
6366 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6367 bodyClause = { init, body }, // v = init(); v = body(v, i)
6368 indexVar = { start, incr }; // i = start(); i = i + 1
6369 return loop(loopLimit, bodyClause, indexVar);
6370 }
6371
6372 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6373 Objects.requireNonNull(start);
6374 Objects.requireNonNull(end);
6375 Objects.requireNonNull(body);
6376 Class<?> counterType = start.type().returnType();
6377 if (counterType != int.class) {
6378 MethodType expected = start.type().changeReturnType(int.class);
6379 throw misMatchedTypes("start function", start.type(), expected);
6380 } else if (end.type().returnType() != counterType) {
6381 MethodType expected = end.type().changeReturnType(counterType);
6382 throw misMatchedTypes("end function", end.type(), expected);
6383 }
6384 MethodType bodyType = body.type();
6385 Class<?> returnType = bodyType.returnType();
6386 List<Class<?>> innerList = bodyType.parameterList();
6387 // strip leading V value if present
6388 int vsize = (returnType == void.class ? 0 : 1);
6389 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
6390 // argument list has no "V" => error
6391 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6392 throw misMatchedTypes("body function", bodyType, expected);
6393 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
6394 // missing I type => error
6395 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
6396 throw misMatchedTypes("body function", bodyType, expected);
6397 }
6398 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
6399 if (outerList.isEmpty()) {
6400 // special case; take lists from end handle
6401 outerList = end.type().parameterList();
6402 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
6403 }
6404 MethodType expected = methodType(counterType, outerList);
6405 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
6406 throw misMatchedTypes("start parameter types", start.type(), expected);
6407 }
6408 if (end.type() != start.type() &&
6409 !end.type().effectivelyIdenticalParameters(0, outerList)) {
6410 throw misMatchedTypes("end parameter types", end.type(), expected);
6411 }
6412 if (init != null) {
6413 MethodType initType = init.type();
6414 if (initType.returnType() != returnType ||
6415 !initType.effectivelyIdenticalParameters(0, outerList)) {
6416 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6417 }
6418 }
6419 }
6420
6421 /**
6422 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
6423 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6424 * <p>
6425 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
6426 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
6427 * <p>
6428 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6429 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6430 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6431 * <p>
6432 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6433 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6434 * iteration variable.
6435 * The result of the loop handle execution will be the final {@code V} value of that variable
6436 * (or {@code void} if there is no {@code V} variable).
6437 * <p>
6438 * The following rules hold for the argument handles:<ul>
6439 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6440 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
6441 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6442 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
6443 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
6444 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
6445 * of types called the <em>internal parameter list</em>.
6446 * It will constrain the parameter lists of the other loop parts.
6447 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
6448 * with no additional {@code A} types, then the internal parameter list is extended by
6449 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
6450 * single type {@code Iterable} is added and constitutes the {@code A...} list.
6451 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
6452 * list {@code (A...)} is called the <em>external parameter list</em>.
6453 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6454 * additional state variable of the loop.
6455 * The body must both accept a leading parameter and return a value of this type {@code V}.
6456 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6457 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6458 * <a href="MethodHandles.html#effid">effectively identical</a>
6459 * to the external parameter list {@code (A...)}.
6460 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6461 * {@linkplain #empty default value}.
6462 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
6463 * type {@code java.util.Iterator} or a subtype thereof.
6464 * The iterator it produces when the loop is executed will be assumed
6465 * to yield values which can be converted to type {@code T}.
6466 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
6467 * effectively identical to the external parameter list {@code (A...)}.
6468 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
6469 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
6470 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
6471 * handle parameter is adjusted to accept the leading {@code A} type, as if by
6472 * the {@link MethodHandle#asType asType} conversion method.
6473 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
6474 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
6475 * </ul>
6476 * <p>
6477 * The type {@code T} may be either a primitive or reference.
6478 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
6479 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
6480 * as if by the {@link MethodHandle#asType asType} conversion method.
6481 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
6482 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
6483 * <p>
6484 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6485 * <li>The loop handle's result type is the result type {@code V} of the body.
6486 * <li>The loop handle's parameter types are the types {@code (A...)},
6487 * from the external parameter list.
6488 * </ul>
6489 * <p>
6490 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6491 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
6492 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
6493 * <blockquote><pre>{@code
6494 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
6495 * V init(A...);
6496 * V body(V,T,A...);
6497 * V iteratedLoop(A... a...) {
6498 * Iterator<T> it = iterator(a...);
6499 * V v = init(a...);
6500 * while (it.hasNext()) {
6501 * T t = it.next();
6502 * v = body(v, t, a...);
6503 * }
6504 * return v;
6505 * }
6506 * }</pre></blockquote>
6507 *
6508 * @apiNote Example:
6509 * <blockquote><pre>{@code
6510 * // get an iterator from a list
6511 * static List<String> reverseStep(List<String> r, String e) {
6512 * r.add(0, e);
6513 * return r;
6514 * }
6515 * static List<String> newArrayList() { return new ArrayList<>(); }
6516 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
6517 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
6518 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
6519 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
6520 * assertEquals(reversedList, (List<String>) loop.invoke(list));
6521 * }</pre></blockquote>
6522 *
6523 * @apiNote The implementation of this method can be expressed approximately as follows:
6524 * <blockquote><pre>{@code
6525 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6526 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
6527 * Class<?> returnType = body.type().returnType();
6528 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6529 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
6530 * MethodHandle retv = null, step = body, startIter = iterator;
6531 * if (returnType != void.class) {
6532 * // the simple thing first: in (I V A...), drop the I to get V
6533 * retv = dropArguments(identity(returnType), 0, Iterator.class);
6534 * // body type signature (V T A...), internal loop types (I V A...)
6535 * step = swapArguments(body, 0, 1); // swap V <-> T
6536 * }
6537 * if (startIter == null) startIter = MH_getIter;
6538 * MethodHandle[]
6539 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
6540 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
6541 * return loop(iterVar, bodyClause);
6542 * }
6543 * }</pre></blockquote>
6544 *
6545 * @param iterator an optional handle to return the iterator to start the loop.
6546 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
6547 * See above for other constraints.
6548 * @param init optional initializer, providing the initial value of the loop variable.
6549 * May be {@code null}, implying a default initial value. See above for other constraints.
6550 * @param body body of the loop, which may not be {@code null}.
6551 * It controls the loop parameters and result type in the standard case (see above for details).
6552 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
6553 * and may accept any number of additional types.
6554 * See above for other constraints.
6555 *
6556 * @return a method handle embodying the iteration loop functionality.
6557 * @throws NullPointerException if the {@code body} handle is {@code null}.
6558 * @throws IllegalArgumentException if any argument violates the above requirements.
6559 *
6560 * @since 9
6561 */
6562 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6563 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
6564 Class<?> returnType = body.type().returnType();
6565 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
6566 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
6567 MethodHandle startIter;
6568 MethodHandle nextVal;
6569 {
6570 MethodType iteratorType;
6571 if (iterator == null) {
6572 // derive argument type from body, if available, else use Iterable
6573 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
6574 iteratorType = startIter.type().changeParameterType(0, iterableType);
6575 } else {
6576 // force return type to the internal iterator class
6577 iteratorType = iterator.type().changeReturnType(Iterator.class);
6578 startIter = iterator;
6579 }
6580 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6581 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
6582
6583 // perform the asType transforms under an exception transformer, as per spec.:
6584 try {
6585 startIter = startIter.asType(iteratorType);
6586 nextVal = nextRaw.asType(nextValType);
6587 } catch (WrongMethodTypeException ex) {
6588 throw new IllegalArgumentException(ex);
6589 }
6590 }
6591
6592 MethodHandle retv = null, step = body;
6593 if (returnType != void.class) {
6594 // the simple thing first: in (I V A...), drop the I to get V
6595 retv = dropArguments(identity(returnType), 0, Iterator.class);
6596 // body type signature (V T A...), internal loop types (I V A...)
6597 step = swapArguments(body, 0, 1); // swap V <-> T
6598 }
6599
6600 MethodHandle[]
6601 iterVar = { startIter, null, hasNext, retv },
6602 bodyClause = { init, filterArgument(step, 0, nextVal) };
6603 return loop(iterVar, bodyClause);
6604 }
6605
6606 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6607 Objects.requireNonNull(body);
6608 MethodType bodyType = body.type();
6609 Class<?> returnType = bodyType.returnType();
6610 List<Class<?>> internalParamList = bodyType.parameterList();
6611 // strip leading V value if present
6612 int vsize = (returnType == void.class ? 0 : 1);
6613 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
6614 // argument list has no "V" => error
6615 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6616 throw misMatchedTypes("body function", bodyType, expected);
6617 } else if (internalParamList.size() <= vsize) {
6618 // missing T type => error
6619 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
6620 throw misMatchedTypes("body function", bodyType, expected);
6621 }
6622 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
6623 Class<?> iterableType = null;
6624 if (iterator != null) {
6625 // special case; if the body handle only declares V and T then
6626 // the external parameter list is obtained from iterator handle
6627 if (externalParamList.isEmpty()) {
6628 externalParamList = iterator.type().parameterList();
6629 }
6630 MethodType itype = iterator.type();
6631 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
6632 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
6633 }
6634 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
6635 MethodType expected = methodType(itype.returnType(), externalParamList);
6636 throw misMatchedTypes("iterator parameters", itype, expected);
6637 }
6638 } else {
6639 if (externalParamList.isEmpty()) {
6640 // special case; if the iterator handle is null and the body handle
6641 // only declares V and T then the external parameter list consists
6642 // of Iterable
6643 externalParamList = Arrays.asList(Iterable.class);
6644 iterableType = Iterable.class;
6645 } else {
6646 // special case; if the iterator handle is null and the external
6647 // parameter list is not empty then the first parameter must be
6648 // assignable to Iterable
6649 iterableType = externalParamList.get(0);
6650 if (!Iterable.class.isAssignableFrom(iterableType)) {
6651 throw newIllegalArgumentException(
6652 "inferred first loop argument must inherit from Iterable: " + iterableType);
6653 }
6654 }
6655 }
6656 if (init != null) {
6657 MethodType initType = init.type();
6658 if (initType.returnType() != returnType ||
6659 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
6660 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
6661 }
6662 }
6663 return iterableType; // help the caller a bit
6664 }
6665
6666 /*non-public*/
6667 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
6668 // there should be a better way to uncross my wires
6669 int arity = mh.type().parameterCount();
6670 int[] order = new int[arity];
6671 for (int k = 0; k < arity; k++) order[k] = k;
6672 order[i] = j; order[j] = i;
6673 Class<?>[] types = mh.type().parameterArray();
6674 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
6675 MethodType swapType = methodType(mh.type().returnType(), types);
6676 return permuteArguments(mh, swapType, order);
6677 }
6678
6679 /**
6680 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
6681 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
6682 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
6683 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
6684 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
6685 * {@code try-finally} handle.
6686 * <p>
6687 * The {@code cleanup} handle will be passed one or two additional leading arguments.
6688 * The first is the exception thrown during the
6689 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
6690 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
6691 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
6692 * The second argument is not present if the {@code target} handle has a {@code void} return type.
6693 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
6694 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
6695 * <p>
6696 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
6697 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
6698 * two extra leading parameters:<ul>
6699 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
6700 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
6701 * the result from the execution of the {@code target} handle.
6702 * This parameter is not present if the {@code target} returns {@code void}.
6703 * </ul>
6704 * <p>
6705 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
6706 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
6707 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
6708 * the cleanup.
6709 * <blockquote><pre>{@code
6710 * V target(A..., B...);
6711 * V cleanup(Throwable, V, A...);
6712 * V adapter(A... a, B... b) {
6713 * V result = (zero value for V);
6714 * Throwable throwable = null;
6715 * try {
6716 * result = target(a..., b...);
6717 * } catch (Throwable t) {
6718 * throwable = t;
6719 * throw t;
6720 * } finally {
6721 * result = cleanup(throwable, result, a...);
6722 * }
6723 * return result;
6724 * }
6725 * }</pre></blockquote>
6726 * <p>
6727 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6728 * be modified by execution of the target, and so are passed unchanged
6729 * from the caller to the cleanup, if it is invoked.
6730 * <p>
6731 * The target and cleanup must return the same type, even if the cleanup
6732 * always throws.
6733 * To create such a throwing cleanup, compose the cleanup logic
6734 * with {@link #throwException throwException},
6735 * in order to create a method handle of the correct return type.
6736 * <p>
6737 * Note that {@code tryFinally} never converts exceptions into normal returns.
6738 * In rare cases where exceptions must be converted in that way, first wrap
6739 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
6740 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
6741 * <p>
6742 * It is recommended that the first parameter type of {@code cleanup} be
6743 * declared {@code Throwable} rather than a narrower subtype. This ensures
6744 * {@code cleanup} will always be invoked with whatever exception that
6745 * {@code target} throws. Declaring a narrower type may result in a
6746 * {@code ClassCastException} being thrown by the {@code try-finally}
6747 * handle if the type of the exception thrown by {@code target} is not
6748 * assignable to the first parameter type of {@code cleanup}. Note that
6749 * various exception types of {@code VirtualMachineError},
6750 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6751 * thrown by almost any kind of Java code, and a finally clause that
6752 * catches (say) only {@code IOException} would mask any of the others
6753 * behind a {@code ClassCastException}.
6754 *
6755 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6756 * @param cleanup the handle that is invoked in the finally block.
6757 *
6758 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6759 * @throws NullPointerException if any argument is null
6760 * @throws IllegalArgumentException if {@code cleanup} does not accept
6761 * the required leading arguments, or if the method handle types do
6762 * not match in their return types and their
6763 * corresponding trailing parameters
6764 *
6765 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
6766 * @since 9
6767 */
6768 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
6769 List<Class<?>> targetParamTypes = target.type().parameterList();
6770 Class<?> rtype = target.type().returnType();
6771
6772 tryFinallyChecks(target, cleanup);
6773
6774 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
6775 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6776 // target parameter list.
6777 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
6778
6779 // Ensure that the intrinsic type checks the instance thrown by the
6780 // target against the first parameter of cleanup
6781 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
6782
6783 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
6784 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
6785 }
6786
6787 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
6788 Class<?> rtype = target.type().returnType();
6789 if (rtype != cleanup.type().returnType()) {
6790 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
6791 }
6792 MethodType cleanupType = cleanup.type();
6793 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
6794 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
6795 }
6796 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
6797 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
6798 }
6799 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6800 // target parameter list.
6801 int cleanupArgIndex = rtype == void.class ? 1 : 2;
6802 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
6803 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
6804 cleanup.type(), target.type());
6805 }
6806 }
6807
6808 }