1 /*
2 * Copyright (c) 2008, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.Set;
58 import java.util.concurrent.ConcurrentHashMap;
59 import java.util.stream.Collectors;
60 import java.util.stream.Stream;
61
62 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
63 import static java.lang.invoke.MethodHandleNatives.Constants.*;
64 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
65 import static java.lang.invoke.MethodType.methodType;
66
67 /**
68 * This class consists exclusively of static methods that operate on or return
69 * method handles. They fall into several categories:
70 * <ul>
71 * <li>Lookup methods which help create method handles for methods and fields.
72 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
73 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
74 * </ul>
75 * A lookup, combinator, or factory method will fail and throw an
76 * {@code IllegalArgumentException} if the created method handle's type
77 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
78 *
79 * @author John Rose, JSR 292 EG
80 * @since 1.7
81 */
82 public class MethodHandles {
83
84 private MethodHandles() { } // do not instantiate
85
86 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
87
88 // See IMPL_LOOKUP below.
89
90 //// Method handle creation from ordinary methods.
91
92 /**
93 * Returns a {@link Lookup lookup object} with
94 * full capabilities to emulate all supported bytecode behaviors of the caller.
95 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
96 * Factory methods on the lookup object can create
97 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
98 * for any member that the caller has access to via bytecodes,
99 * including protected and private fields and methods.
100 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
101 * Do not store it in place where untrusted code can access it.
102 * <p>
103 * This method is caller sensitive, which means that it may return different
104 * values to different callers.
105 * @return a lookup object for the caller of this method, with private access
106 */
107 @CallerSensitive
108 @ForceInline // to ensure Reflection.getCallerClass optimization
109 public static Lookup lookup() {
110 return new Lookup(Reflection.getCallerClass());
111 }
112
113 /**
114 * This reflected$lookup method is the alternate implementation of
115 * the lookup method when being invoked by reflection.
116 */
117 @CallerSensitive
118 private static Lookup reflected$lookup() {
119 Class<?> caller = Reflection.getCallerClass();
120 if (caller.getClassLoader() == null) {
121 throw newIllegalArgumentException("illegal lookupClass: "+caller);
122 }
123 return new Lookup(caller);
124 }
125
126 /**
127 * Returns a {@link Lookup lookup object} which is trusted minimally.
128 * The lookup has the {@code UNCONDITIONAL} mode.
129 * It can only be used to create method handles to public members of
130 * public classes in packages that are exported unconditionally.
131 * <p>
132 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
133 * of this lookup object will be {@link java.lang.Object}.
134 *
135 * @apiNote The use of Object is conventional, and because the lookup modes are
136 * limited, there is no special access provided to the internals of Object, its package
137 * or its module. This public lookup object or other lookup object with
138 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
139 * is not used to determine the lookup context.
140 *
141 * <p style="font-size:smaller;">
142 * <em>Discussion:</em>
143 * The lookup class can be changed to any other class {@code C} using an expression of the form
144 * {@link Lookup#in publicLookup().in(C.class)}.
145 * A public lookup object is always subject to
146 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
147 * Also, it cannot access
148 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
149 * @return a lookup object which is trusted minimally
150 *
151 * @revised 9
152 * @spec JPMS
153 */
154 public static Lookup publicLookup() {
155 return Lookup.PUBLIC_LOOKUP;
156 }
157
158 /**
159 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
160 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc"> private access</a>.
161 * The returned lookup object can provide access to classes in modules and packages,
162 * and members of those classes, outside the normal rules of Java access control,
163 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
164 * <p>
165 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
166 * allowed to do deep reflection on module {@code M2} and package of the target class
167 * if and only if all of the following conditions are {@code true}:
168 * <ul>
169 * <li>If there is a security manager, its {@code checkPermission} method is
170 * called to check {@code ReflectPermission("suppressAccessChecks")} and
171 * that must return normally.
172 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
173 * (This is because otherwise there would be no way to ensure the original lookup
174 * creator was a member of any particular module, and so any subsequent checks
175 * for readability and qualified exports would become ineffective.)
176 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
177 * (This is because an application intending to share intra-module access
178 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
179 * deep reflection to its own module.)
180 * <li>The target class must be a proper class, not a primitive or array class.
181 * (Thus, {@code M2} is well-defined.)
182 * <li>If the caller module {@code M1} differs from
183 * the target module {@code M2} then both of the following must be true:
184 * <ul>
185 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
186 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
187 * containing the target class to at least {@code M1}.</li>
188 * </ul>
189 * </ul>
190 * <p>
191 * If any of the above checks is violated, this method fails with an
192 * exception.
193 * <p>
194 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
195 * returns a {@code Lookup} on {@code targetClass} with full capabilities and
196 * {@code null} previous lookup class.
197 * <p>
198 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
199 * returns a {@code Lookup} on {@code targetClass} that records
200 * the lookup class of the caller as the new previous lookup class and
201 * drops {@code MODULE} access from the full capabilities mode.
202 *
203 * @param targetClass the target class
204 * @param caller the caller lookup object
205 * @return a lookup object for the target class, with private access
206 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or array class
207 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
208 * @throws SecurityException if denied by the security manager
209 * @throws IllegalAccessException if any of the other access checks specified above fails
210 * @since 9
211 * @spec JPMS
212 * @see Lookup#dropLookupMode
213 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
214 */
215 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
216 SecurityManager sm = System.getSecurityManager();
217 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
218 if (targetClass.isPrimitive())
219 throw new IllegalArgumentException(targetClass + " is a primitive class");
220 if (targetClass.isArray())
221 throw new IllegalArgumentException(targetClass + " is an array class");
222 // Ensure that we can reason accurately about private and module access.
223 if ((caller.lookupModes() & Lookup.PRIVATE) == 0)
224 throw new IllegalAccessException("caller does not have PRIVATE lookup mode");
225 if ((caller.lookupModes() & Lookup.MODULE) == 0)
226 throw new IllegalAccessException("caller does not have MODULE lookup mode");
227
228 // previous lookup class is never set if it has MODULE access
229 assert caller.previousLookupClass() == null;
230
231 Class<?> callerClass = caller.lookupClass();
232 Module callerModule = callerClass.getModule(); // M1
233 Module targetModule = targetClass.getModule(); // M2
234 Class<?> newPreviousClass = null;
235 int newModes = Lookup.FULL_POWER_MODES;
236
237 if (targetModule != callerModule) {
238 if (!callerModule.canRead(targetModule))
239 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
240 if (targetModule.isNamed()) {
241 String pn = targetClass.getPackageName();
242 assert !pn.isEmpty() : "unnamed package cannot be in named module";
243 if (!targetModule.isOpen(pn, callerModule))
244 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
245 }
246
247 // M2 != M1, set previous lookup class to M1 and drop MODULE access
248 newPreviousClass = callerClass;
249 newModes &= ~Lookup.MODULE;
250 }
251
252 if (!callerModule.isNamed() && targetModule.isNamed()) {
253 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
254 if (logger != null) {
255 logger.logIfOpenedForIllegalAccess(caller, targetClass);
256 }
257 }
258 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
259 }
260
261 /**
262 * Performs an unchecked "crack" of a
263 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
264 * The result is as if the user had obtained a lookup object capable enough
265 * to crack the target method handle, called
266 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
267 * on the target to obtain its symbolic reference, and then called
268 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
269 * to resolve the symbolic reference to a member.
270 * <p>
271 * If there is a security manager, its {@code checkPermission} method
272 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
273 * @param <T> the desired type of the result, either {@link Member} or a subtype
274 * @param target a direct method handle to crack into symbolic reference components
275 * @param expected a class object representing the desired result type {@code T}
276 * @return a reference to the method, constructor, or field object
277 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
278 * @exception NullPointerException if either argument is {@code null}
279 * @exception IllegalArgumentException if the target is not a direct method handle
280 * @exception ClassCastException if the member is not of the expected type
281 * @since 1.8
282 */
283 public static <T extends Member> T
284 reflectAs(Class<T> expected, MethodHandle target) {
285 SecurityManager smgr = System.getSecurityManager();
286 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
287 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
288 return lookup.revealDirect(target).reflectAs(expected, lookup);
289 }
290 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
291 private static final java.security.Permission ACCESS_PERMISSION =
292 new ReflectPermission("suppressAccessChecks");
293
294 /**
295 * A <em>lookup object</em> is a factory for creating method handles,
296 * when the creation requires access checking.
297 * Method handles do not perform
298 * access checks when they are called, but rather when they are created.
299 * Therefore, method handle access
300 * restrictions must be enforced when a method handle is created.
301 * The caller class against which those restrictions are enforced
302 * is known as the {@linkplain #lookupClass() lookup class}.
303 * <p>
304 * A lookup class which needs to create method handles will call
305 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
306 * When the {@code Lookup} factory object is created, the identity of the lookup class is
307 * determined, and securely stored in the {@code Lookup} object.
308 * The lookup class (or its delegates) may then use factory methods
309 * on the {@code Lookup} object to create method handles for access-checked members.
310 * This includes all methods, constructors, and fields which are allowed to the lookup class,
311 * even private ones.
312 *
313 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
314 * The factory methods on a {@code Lookup} object correspond to all major
315 * use cases for methods, constructors, and fields.
316 * Each method handle created by a factory method is the functional
317 * equivalent of a particular <em>bytecode behavior</em>.
318 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
319 * Here is a summary of the correspondence between these factory methods and
320 * the behavior of the resulting method handles:
321 * <table class="striped">
322 * <caption style="display:none">lookup method behaviors</caption>
323 * <thead>
324 * <tr>
325 * <th scope="col"><a id="equiv"></a>lookup expression</th>
326 * <th scope="col">member</th>
327 * <th scope="col">bytecode behavior</th>
328 * </tr>
329 * </thead>
330 * <tbody>
331 * <tr>
332 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
333 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
334 * </tr>
335 * <tr>
336 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
337 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
338 * </tr>
339 * <tr>
340 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
341 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
342 * </tr>
343 * <tr>
344 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
345 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
346 * </tr>
347 * <tr>
348 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
349 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
350 * </tr>
351 * <tr>
352 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
353 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
354 * </tr>
355 * <tr>
356 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
357 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
358 * </tr>
359 * <tr>
360 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
361 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
362 * </tr>
363 * <tr>
364 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
365 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
366 * </tr>
367 * <tr>
368 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
369 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
370 * </tr>
371 * <tr>
372 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
373 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
374 * </tr>
375 * <tr>
376 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
377 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
378 * </tr>
379 * <tr>
380 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
381 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
382 * </tr>
383 * <tr>
384 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
385 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
386 * </tr>
387 * </tbody>
388 * </table>
389 *
390 * Here, the type {@code C} is the class or interface being searched for a member,
391 * documented as a parameter named {@code refc} in the lookup methods.
392 * The method type {@code MT} is composed from the return type {@code T}
393 * and the sequence of argument types {@code A*}.
394 * The constructor also has a sequence of argument types {@code A*} and
395 * is deemed to return the newly-created object of type {@code C}.
396 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
397 * The formal parameter {@code this} stands for the self-reference of type {@code C};
398 * if it is present, it is always the leading argument to the method handle invocation.
399 * (In the case of some {@code protected} members, {@code this} may be
400 * restricted in type to the lookup class; see below.)
401 * The name {@code arg} stands for all the other method handle arguments.
402 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
403 * stands for a null reference if the accessed method or field is static,
404 * and {@code this} otherwise.
405 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
406 * for reflective objects corresponding to the given members.
407 * <p>
408 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
409 * as if by {@code ldc CONSTANT_Class}.
410 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
411 * <p>
412 * In cases where the given member is of variable arity (i.e., a method or constructor)
413 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
414 * In all other cases, the returned method handle will be of fixed arity.
415 * <p style="font-size:smaller;">
416 * <em>Discussion:</em>
417 * The equivalence between looked-up method handles and underlying
418 * class members and bytecode behaviors
419 * can break down in a few ways:
420 * <ul style="font-size:smaller;">
421 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
422 * the lookup can still succeed, even when there is no equivalent
423 * Java expression or bytecoded constant.
424 * <li>Likewise, if {@code T} or {@code MT}
425 * is not symbolically accessible from the lookup class's loader,
426 * the lookup can still succeed.
427 * For example, lookups for {@code MethodHandle.invokeExact} and
428 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
429 * <li>If there is a security manager installed, it can forbid the lookup
430 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
431 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
432 * constant is not subject to security manager checks.
433 * <li>If the looked-up method has a
434 * <a href="MethodHandle.html#maxarity">very large arity</a>,
435 * the method handle creation may fail with an
436 * {@code IllegalArgumentException}, due to the method handle type having
437 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
438 * </ul>
439 *
440 * <h2><a id="access"></a>Access checking</h2>
441 * Access checks are applied in the factory methods of {@code Lookup},
442 * when a method handle is created.
443 * This is a key difference from the Core Reflection API, since
444 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
445 * performs access checking against every caller, on every call.
446 * <p>
447 * All access checks start from a {@code Lookup} object, which
448 * compares its recorded lookup class against all requests to
449 * create method handles.
450 * A single {@code Lookup} object can be used to create any number
451 * of access-checked method handles, all checked against a single
452 * lookup class.
453 * <p>
454 * A {@code Lookup} object can be shared with other trusted code,
455 * such as a metaobject protocol.
456 * A shared {@code Lookup} object delegates the capability
457 * to create method handles on private members of the lookup class.
458 * Even if privileged code uses the {@code Lookup} object,
459 * the access checking is confined to the privileges of the
460 * original lookup class.
461 * <p>
462 * A lookup can fail, because
463 * the containing class is not accessible to the lookup class, or
464 * because the desired class member is missing, or because the
465 * desired class member is not accessible to the lookup class, or
466 * because the lookup object is not trusted enough to access the member.
467 * In the case of a field setter function on a {@code final} field,
468 * finality enforcement is treated as a kind of access control,
469 * and the lookup will fail, except in special cases of
470 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
471 * In any of these cases, a {@code ReflectiveOperationException} will be
472 * thrown from the attempted lookup. The exact class will be one of
473 * the following:
474 * <ul>
475 * <li>NoSuchMethodException — if a method is requested but does not exist
476 * <li>NoSuchFieldException — if a field is requested but does not exist
477 * <li>IllegalAccessException — if the member exists but an access check fails
478 * </ul>
479 * <p>
480 * In general, the conditions under which a method handle may be
481 * looked up for a method {@code M} are no more restrictive than the conditions
482 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
483 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
484 * a method handle lookup will generally raise a corresponding
485 * checked exception, such as {@code NoSuchMethodException}.
486 * And the effect of invoking the method handle resulting from the lookup
487 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
488 * to executing the compiled, verified, and resolved call to {@code M}.
489 * The same point is true of fields and constructors.
490 * <p style="font-size:smaller;">
491 * <em>Discussion:</em>
492 * Access checks only apply to named and reflected methods,
493 * constructors, and fields.
494 * Other method handle creation methods, such as
495 * {@link MethodHandle#asType MethodHandle.asType},
496 * do not require any access checks, and are used
497 * independently of any {@code Lookup} object.
498 * <p>
499 * If the desired member is {@code protected}, the usual JVM rules apply,
500 * including the requirement that the lookup class must either be in the
501 * same package as the desired member, or must inherit that member.
502 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
503 * In addition, if the desired member is a non-static field or method
504 * in a different package, the resulting method handle may only be applied
505 * to objects of the lookup class or one of its subclasses.
506 * This requirement is enforced by narrowing the type of the leading
507 * {@code this} parameter from {@code C}
508 * (which will necessarily be a superclass of the lookup class)
509 * to the lookup class itself.
510 * <p>
511 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
512 * that the receiver argument must match both the resolved method <em>and</em>
513 * the current class. Again, this requirement is enforced by narrowing the
514 * type of the leading parameter to the resulting method handle.
515 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
516 * <p>
517 * The JVM represents constructors and static initializer blocks as internal methods
518 * with special names ({@code "<init>"} and {@code "<clinit>"}).
519 * The internal syntax of invocation instructions allows them to refer to such internal
520 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
521 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
522 * <p>
523 * If the relationship between nested types is expressed directly through the
524 * {@code NestHost} and {@code NestMembers} attributes
525 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
526 * then the associated {@code Lookup} object provides direct access to
527 * the lookup class and all of its nestmates
528 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
529 * Otherwise, access between nested classes is obtained by the Java compiler creating
530 * a wrapper method to access a private method of another class in the same nest.
531 * For example, a nested class {@code C.D}
532 * can access private members within other related classes such as
533 * {@code C}, {@code C.D.E}, or {@code C.B},
534 * but the Java compiler may need to generate wrapper methods in
535 * those related classes. In such cases, a {@code Lookup} object on
536 * {@code C.E} would be unable to access those private members.
537 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
538 * which can transform a lookup on {@code C.E} into one on any of those other
539 * classes, without special elevation of privilege.
540 * <p>
541 * The accesses permitted to a given lookup object may be limited,
542 * according to its set of {@link #lookupModes lookupModes},
543 * to a subset of members normally accessible to the lookup class.
544 * For example, the {@link MethodHandles#publicLookup publicLookup}
545 * method produces a lookup object which is only allowed to access
546 * public members in public classes of exported packages.
547 * The caller sensitive method {@link MethodHandles#lookup lookup}
548 * produces a lookup object with full capabilities relative to
549 * its caller class, to emulate all supported bytecode behaviors.
550 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
551 * with fewer access modes than the original lookup object.
552 *
553 * <p style="font-size:smaller;">
554 * <a id="privacc"></a>
555 * <em>Discussion of private access:</em>
556 * We say that a lookup has <em>private access</em>
557 * if its {@linkplain #lookupModes lookup modes}
558 * include the possibility of accessing {@code private} members
559 * (which includes the private members of nestmates).
560 * As documented in the relevant methods elsewhere,
561 * only lookups with private access possess the following capabilities:
562 * <ul style="font-size:smaller;">
563 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
564 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
565 * such as {@code Class.forName}
566 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
567 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
568 * for classes accessible to the lookup class
569 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
570 * within the same package member
571 * </ul>
572 * <p style="font-size:smaller;">
573 * Each of these permissions is a consequence of the fact that a lookup object
574 * with private access can be securely traced back to an originating class,
575 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
576 * can be reliably determined and emulated by method handles.
577 *
578 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
579 * When a lookup class in one module {@code M1} accesses a class in another module
580 * {@code M2}, extra access checking is performed beyond the access mode bits.
581 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
582 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
583 * and when the type is in a package of {@code M2} that is exported to
584 * at least {@code M1}.
585 * <p>
586 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
587 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
588 * MethodHandles.privateLookupIn} methods.
589 * Teleporting across modules will always record the original lookup class as
590 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
591 * and drops {@link Lookup#MODULE MODULE} access.
592 * If the target class is in the same module as the lookup class {@code C},
593 * then the target class becomes the new lookup class
594 * and there is no change to the previous lookup class.
595 * If the target class is in a different module from {@code M1} ({@code C}'s module),
596 * {@code C} becomes the new previous lookup class
597 * and the target class becomes the new lookup class.
598 * In that case, if there was already a previous lookup class in {@code M0},
599 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
600 * drops all privileges.
601 * For example,
602 * <blockquote><pre>
603 * {@code
604 * Lookup lookup = MethodHandles.lookup(); // in class C
605 * Lookup lookup2 = lookup.in(D.class);
606 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
607 * }</pre></blockquote>
608 * <p>
609 * The {@link #lookup()} factory method produces a {@code Lookup} object
610 * with {@code null} previous lookup class.
611 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
612 * to class {@code D} without elevation of privileges.
613 * If {@code C} and {@code D} are in the same module,
614 * {@code lookup2} records {@code D} as the new lookup class and keeps the
615 * same previous lookup class as the original {@code lookup}, or
616 * {@code null} if not present.
617 * <p>
618 * When a {@code Lookup} teleports from a class
619 * in one nest to another nest, {@code PRIVATE} access is dropped.
620 * When a {@code Lookup} teleports from a class in one package to
621 * another package, {@code PACKAGE} access is dropped.
622 * When a {@code Lookup} teleports from a class in one module to another module,
623 * {@code MODULE} access is dropped.
624 * Teleporting across modules drops the ability to access non-exported classes
625 * in both the module of the new lookup class and the module of the old lookup class
626 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
627 * A {@code Lookup} can teleport back and forth to a class in the module of
628 * the lookup class and the module of the previous class lookup.
629 * Teleporting across modules can only decrease access but cannot increase it.
630 * Teleporting to some third module drops all accesses.
631 * <p>
632 * In the above example, if {@code C} and {@code D} are in different modules,
633 * {@code lookup2} records {@code D} as its lookup class and
634 * {@code C} as its previous lookup class and {@code lookup2} has only
635 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
636 * {@code C}'s module and {@code D}'s module.
637 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
638 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
639 * class {@code D} is recorded as its previous lookup class.
640 * <p>
641 * Teleporting across modules restricts access to the public types that
642 * both the lookup class and the previous lookup class can equally access
643 * (see below).
644 * <p>
645 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
646 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
647 * and create a new {@code Lookup} with <a href="#privcc">private access</a>
648 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
649 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
650 * to call {@code privateLookupIn}.
651 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
652 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
653 * produces a new {@code Lookup} on {@code T} with full capabilities.
654 * A {@code lookup} on {@code C} is also allowed
655 * to do deep reflection on {@code T} in another module {@code M2} if
656 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
657 * the package containing {@code T} to at least {@code M1}.
658 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
659 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
660 * The resulting {@code Lookup} can be used to do member lookup or teleport
661 * to another lookup class by calling {@link #in Lookup::in}. But
662 * it cannot be used to obtain another private {@code Lookup} by calling
663 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
664 * because it has no {@code MODULE} access.
665 *
666 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
667 *
668 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
669 * allows cross-module access. The access checking is performed with respect
670 * to both the lookup class and the previous lookup class if present.
671 * <p>
672 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
673 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
674 * exported unconditionally}.
675 * <p>
676 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
677 * the lookup with {@link #PUBLIC} mode can access all public types in modules
678 * that are readable to {@code M1} and the type is in a package that is exported
679 * at least to {@code M1}.
680 * <p>
681 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
682 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
683 * the intersection of all public types that are accessible to {@code M1}
684 * with all public types that are accessible to {@code M0}. {@code M0}
685 * reads {@code M1} and hence the set of accessible types includes:
686 *
687 * <table class="striped">
688 * <caption style="display:none">
689 * Public types in the following packages are accessible to the
690 * lookup class and the previous lookup class.
691 * </caption>
692 * <thead>
693 * <tr>
694 * <th scope="col">Equally accessible types to {@code M0} and {@code M1}</th>
695 * </tr>
696 * </thead>
697 * <tbody>
698 * <tr>
699 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M1}</th>
700 * </tr>
701 * <tr>
702 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</th>
703 * </tr>
704 * <tr>
705 * <th scope="row" style="text-align:left">unconditional-exported packages from a third module {@code M2}
706 * if both {@code M0} and {@code M1} read {@code M2}</th>
707 * </tr>
708 * <tr>
709 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M1} to {@code M0}</th>
710 * </tr>
711 * <tr>
712 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M0} to {@code M1}
713 * if {@code M1} reads {@code M0}</th>
714 * </tr>
715 * <tr>
716 * <th scope="row" style="text-align:left">qualified-exported packages from a third module {@code M2} to
717 * both {@code M0} and {@code M1} if both {@code M0} and {@code M1} read {@code M2}</th>
718 * </tr>
719 * </tbody>
720 * </table>
721 *
722 * <h2><a id="access-modes"></a>Access modes</h2>
723 *
724 * The table below shows the access modes of a {@code Lookup} produced by
725 * any of the following factory or transformation methods:
726 * <ul>
727 * <li>{@link #lookup() MethodHandles.lookup()}</li>
728 * <li>{@link #publicLookup() MethodHandles.publicLookup()}</li>
729 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn}</li>
730 * <li>{@link Lookup#in}</li>
731 * <li>{@link Lookup#dropLookupMode(int)}</li>
732 * </ul>
733 *
734 * <table class="striped">
735 * <caption style="display:none">
736 * Access mode summary
737 * </caption>
738 * <thead>
739 * <tr>
740 * <th scope="col">Lookup object</th>
741 * <th style="text-align:center">protected</th>
742 * <th style="text-align:center">private</th>
743 * <th style="text-align:center">package</th>
744 * <th style="text-align:center">module</th>
745 * <th style="text-align:center">public</th>
746 * </tr>
747 * </thead>
748 * <tbody>
749 * <tr>
750 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
751 * <td style="text-align:center">PRO</td>
752 * <td style="text-align:center">PRI</td>
753 * <td style="text-align:center">PAC</td>
754 * <td style="text-align:center">MOD</td>
755 * <td style="text-align:center">1R</td>
756 * </tr>
757 * <tr>
758 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
759 * <td></td>
760 * <td></td>
761 * <td style="text-align:center">PAC</td>
762 * <td style="text-align:center">MOD</td>
763 * <td style="text-align:center">1R</td>
764 * </tr>
765 * <tr>
766 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
767 * <td></td>
768 * <td></td>
769 * <td></td>
770 * <td style="text-align:center">MOD</td>
771 * <td style="text-align:center">1R</td>
772 * </tr>
773 * <tr>
774 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
775 * <td></td>
776 * <td></td>
777 * <td></td>
778 * <td></td>
779 * <td style="text-align:center">2R</td>
780 * </tr>
781 * <tr>
782 * <td>{@code CL.in(D).in(C)} hop back to module</td>
783 * <td></td>
784 * <td></td>
785 * <td></td>
786 * <td></td>
787 * <td style="text-align:center">2R</td>
788 * </tr>
789 * <tr>
790 * <td>{@code PRI1 = privateLookupIn(C1,CL)}</td>
791 * <td style="text-align:center">PRO</td>
792 * <td style="text-align:center">PRI</td>
793 * <td style="text-align:center">PAC</td>
794 * <td style="text-align:center">MOD</td>
795 * <td style="text-align:center">1R</td>
796 * </tr>
797 * <tr>
798 * <td>{@code PRI1a = privateLookupIn(C,PRI1)}</td>
799 * <td style="text-align:center">PRO</td>
800 * <td style="text-align:center">PRI</td>
801 * <td style="text-align:center">PAC</td>
802 * <td style="text-align:center">MOD</td>
803 * <td style="text-align:center">1R</td>
804 * </tr>
805 * <tr>
806 * <td>{@code PRI1.in(C1)} same package</td>
807 * <td></td>
808 * <td></td>
809 * <td style="text-align:center">PAC</td>
810 * <td style="text-align:center">MOD</td>
811 * <td style="text-align:center">1R</td>
812 * </tr>
813 * <tr>
814 * <td>{@code PRI1.in(C1)} different package</td>
815 * <td></td>
816 * <td></td>
817 * <td></td>
818 * <td style="text-align:center">MOD</td>
819 * <td style="text-align:center">1R</td>
820 * </tr>
821 * <tr>
822 * <td>{@code PRI1.in(D)} different module</td>
823 * <td></td>
824 * <td></td>
825 * <td></td>
826 * <td></td>
827 * <td style="text-align:center">2R</td>
828 * </tr>
829 * <tr>
830 * <td>{@code PRI1.dropLookupMode(PROTECTED)}</td>
831 * <td></td>
832 * <td style="text-align:center">PRI</td>
833 * <td style="text-align:center">PAC</td>
834 * <td style="text-align:center">MOD</td>
835 * <td style="text-align:center">1R</td>
836 * </tr>
837 * <tr>
838 * <td>{@code PRI1.dropLookupMode(PRIVATE)}</td>
839 * <td></td>
840 * <td></td>
841 * <td style="text-align:center">PAC</td>
842 * <td style="text-align:center">MOD</td>
843 * <td style="text-align:center">1R</td>
844 * </tr>
845 * <tr>
846 * <td>{@code PRI1.dropLookupMode(PACKAGE)}</td>
847 * <td></td>
848 * <td></td>
849 * <td></td>
850 * <td style="text-align:center">MOD</td>
851 * <td style="text-align:center">1R</td>
852 * </tr>
853 * <tr>
854 * <td>{@code PRI1.dropLookupMode(MODULE)}</td>
855 * <td></td>
856 * <td></td>
857 * <td></td>
858 * <td></td>
859 * <td style="text-align:center">1R</td>
860 * </tr>
861 * <tr>
862 * <td>{@code PRI1.dropLookupMode(PUBLIC)}</td>
863 * <td></td>
864 * <td></td>
865 * <td></td>
866 * <td></td>
867 * <td style="text-align:center">none</td>
868 * <tr>
869 * <td>{@code PRI2 = privateLookupIn(D,CL)}</td>
870 * <td style="text-align:center">PRO</td>
871 * <td style="text-align:center">PRI</td>
872 * <td style="text-align:center">PAC</td>
873 * <td></td>
874 * <td style="text-align:center">2R</td>
875 * </tr>
876 * <tr>
877 * <td>{@code privateLookupIn(D,PRI1)}</td>
878 * <td style="text-align:center">PRO</td>
879 * <td style="text-align:center">PRI</td>
880 * <td style="text-align:center">PAC</td>
881 * <td></td>
882 * <td style="text-align:center">2R</td>
883 * </tr>
884 * <tr>
885 * <td>{@code privateLookupIn(C,PRI2)} fails</td>
886 * <td></td>
887 * <td></td>
888 * <td></td>
889 * <td></td>
890 * <td style="text-align:center">IAE</td>
891 * </tr>
892 * <tr>
893 * <td>{@code PRI2.in(D2)} same package</td>
894 * <td></td>
895 * <td></td>
896 * <td style="text-align:center">PAC</td>
897 * <td></td>
898 * <td style="text-align:center">2R</td>
899 * </tr>
900 * <tr>
901 * <td>{@code PRI2.in(D2)} different package</td>
902 * <td></td>
903 * <td></td>
904 * <td></td>
905 * <td></td>
906 * <td style="text-align:center">2R</td>
907 * </tr>
908 * <tr>
909 * <td>{@code PRI2.in(C1)} hop back to module</td>
910 * <td></td>
911 * <td></td>
912 * <td></td>
913 * <td></td>
914 * <td style="text-align:center">2R</td>
915 * </tr>
916 * <tr>
917 * <td>{@code PRI2.in(E)} hop to third module</td>
918 * <td></td>
919 * <td></td>
920 * <td></td>
921 * <td></td>
922 * <td style="text-align:center">none</td>
923 * </tr>
924 * <tr>
925 * <td>{@code PRI2.dropLookupMode(PROTECTED)}</td>
926 * <td></td>
927 * <td style="text-align:center">PRI</td>
928 * <td style="text-align:center">PAC</td>
929 * <td></td>
930 * <td style="text-align:center">2R</td>
931 * </tr>
932 * <tr>
933 * <td>{@code PRI2.dropLookupMode(PRIVATE)}</td>
934 * <td></td>
935 * <td></td>
936 * <td style="text-align:center">PAC</td>
937 * <td></td>
938 * <td style="text-align:center">2R</td>
939 * </tr>
940 * <tr>
941 * <td>{@code PRI2.dropLookupMode(PACKAGE)}</td>
942 * <td></td>
943 * <td></td>
944 * <td></td>
945 * <td></td>
946 * <td style="text-align:center">2R</td>
947 * </tr>
948 * <tr>
949 * <td>{@code PRI2.dropLookupMode(MODULE)}</td>
950 * <td></td>
951 * <td></td>
952 * <td></td>
953 * <td></td>
954 * <td style="text-align:center">2R</td>
955 * </tr>
956 * <tr>
957 * <td>{@code PRI2.dropLookupMode(PUBLIC)}</td>
958 * <td></td>
959 * <td></td>
960 * <td></td>
961 * <td></td>
962 * <td style="text-align:center">none</td>
963 * </tr>
964 * <tr>
965 * <td>{@code CL.dropLookupMode(PROTECTED)}</td>
966 * <td></td>
967 * <td style="text-align:center">PRI</td>
968 * <td style="text-align:center">PAC</td>
969 * <td style="text-align:center">MOD</td>
970 * <td style="text-align:center">1R</td>
971 * </tr>
972 * <tr>
973 * <td>{@code CL.dropLookupMode(PRIVATE)}</td>
974 * <td></td>
975 * <td></td>
976 * <td style="text-align:center">PAC</td>
977 * <td style="text-align:center">MOD</td>
978 * <td style="text-align:center">1R</td>
979 * </tr>
980 * <tr>
981 * <td>{@code CL.dropLookupMode(PACKAGE)}</td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td style="text-align:center">MOD</td>
986 * <td style="text-align:center">1R</td>
987 * </tr>
988 * <tr>
989 * <td>{@code CL.dropLookupMode(MODULE)}</td>
990 * <td></td>
991 * <td></td>
992 * <td></td>
993 * <td></td>
994 * <td style="text-align:center">1R</td>
995 * </tr>
996 * <tr>
997 * <td>{@code CL.dropLookupMode(PUBLIC)}</td>
998 * <td></td>
999 * <td></td>
1000 * <td></td>
1001 * <td></td>
1002 * <td style="text-align:center">none</td>
1003 * </tr>
1004 * <tr>
1005 * <td>{@code PUB = publicLookup()}</td>
1006 * <td></td>
1007 * <td></td>
1008 * <td></td>
1009 * <td></td>
1010 * <td style="text-align:center">U</td>
1011 * </tr>
1012 * <tr>
1013 * <td>{@code PUB.in(D)} different module</td>
1014 * <td></td>
1015 * <td></td>
1016 * <td></td>
1017 * <td></td>
1018 * <td style="text-align:center">U</td>
1019 * </tr>
1020 * <tr>
1021 * <td>{@code PUB.in(D).in(E)} third module</td>
1022 * <td></td>
1023 * <td></td>
1024 * <td></td>
1025 * <td></td>
1026 * <td style="text-align:center">U</td>
1027 * </tr>
1028 * <tr>
1029 * <td>{@code PUB.dropLookupMode(UNCONDITIONAL)}</td>
1030 * <td></td>
1031 * <td></td>
1032 * <td></td>
1033 * <td></td>
1034 * <td style="text-align:center">none</td>
1035 * </tr>
1036 * <tr>
1037 * <td>{@code privateLookupIn(C1,PUB)} fails</td>
1038 * <td></td>
1039 * <td></td>
1040 * <td></td>
1041 * <td></td>
1042 * <td style="text-align:center">IAE</td>
1043 * </tr>
1044 * <tr>
1045 * <td>{@code ANY.in(X)}, for inaccessible <code>X</code></td>
1046 * <td></td>
1047 * <td></td>
1048 * <td></td>
1049 * <td></td>
1050 * <td style="text-align:center">none</td>
1051 * </tr>
1052 * </tbody>
1053 * </table>
1054 *
1055 * <p>
1056 * Notes:
1057 * <ul>
1058 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1059 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1060 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1061 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1062 * <li>{@code PRO} indicates {@link #PROTECTED} bit set,
1063 * {@code PRI} indicates {@link #PRIVATE} bit set,
1064 * {@code PAC} indicates {@link #PACKAGE} bit set,
1065 * {@code MOD} indicates {@link #MODULE} bit set,
1066 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1067 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1068 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1069 * <li>Public access comes in three kinds:
1070 * <ul>
1071 * <li>unconditional ({@code U}): the lookup assumes readability.
1072 * The lookup has {@code null} previous lookup class.
1073 * <li>one-module-reads ({@code 1R}): the module access checking is
1074 * performed with respect to the lookup class. The lookup has {@code null}
1075 * previous lookup class.
1076 * <li>two-module-reads ({@code 2R}): the module access checking is
1077 * performed with respect to the lookup class and the previous lookup class.
1078 * The lookup has a non-null previous lookup class which is in a
1079 * different module from the current lookup class.
1080 * </ul>
1081 * <li>Any attempt to reach a third module loses all access.</li>
1082 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1083 * all access modes are dropped.</li>
1084 * </ul>
1085 *
1086 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1087 * Although bytecode instructions can only refer to classes in
1088 * a related class loader, this API can search for methods in any
1089 * class, as long as a reference to its {@code Class} object is
1090 * available. Such cross-loader references are also possible with the
1091 * Core Reflection API, and are impossible to bytecode instructions
1092 * such as {@code invokestatic} or {@code getfield}.
1093 * There is a {@linkplain java.lang.SecurityManager security manager API}
1094 * to allow applications to check such cross-loader references.
1095 * These checks apply to both the {@code MethodHandles.Lookup} API
1096 * and the Core Reflection API
1097 * (as found on {@link java.lang.Class Class}).
1098 * <p>
1099 * If a security manager is present, member and class lookups are subject to
1100 * additional checks.
1101 * From one to three calls are made to the security manager.
1102 * Any of these calls can refuse access by throwing a
1103 * {@link java.lang.SecurityException SecurityException}.
1104 * Define {@code smgr} as the security manager,
1105 * {@code lookc} as the lookup class of the current lookup object,
1106 * {@code refc} as the containing class in which the member
1107 * is being sought, and {@code defc} as the class in which the
1108 * member is actually defined.
1109 * (If a class or other type is being accessed,
1110 * the {@code refc} and {@code defc} values are the class itself.)
1111 * The value {@code lookc} is defined as <em>not present</em>
1112 * if the current lookup object does not have
1113 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1114 * The calls are made according to the following rules:
1115 * <ul>
1116 * <li><b>Step 1:</b>
1117 * If {@code lookc} is not present, or if its class loader is not
1118 * the same as or an ancestor of the class loader of {@code refc},
1119 * then {@link SecurityManager#checkPackageAccess
1120 * smgr.checkPackageAccess(refcPkg)} is called,
1121 * where {@code refcPkg} is the package of {@code refc}.
1122 * <li><b>Step 2a:</b>
1123 * If the retrieved member is not public and
1124 * {@code lookc} is not present, then
1125 * {@link SecurityManager#checkPermission smgr.checkPermission}
1126 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1127 * <li><b>Step 2b:</b>
1128 * If the retrieved class has a {@code null} class loader,
1129 * and {@code lookc} is not present, then
1130 * {@link SecurityManager#checkPermission smgr.checkPermission}
1131 * with {@code RuntimePermission("getClassLoader")} is called.
1132 * <li><b>Step 3:</b>
1133 * If the retrieved member is not public,
1134 * and if {@code lookc} is not present,
1135 * and if {@code defc} and {@code refc} are different,
1136 * then {@link SecurityManager#checkPackageAccess
1137 * smgr.checkPackageAccess(defcPkg)} is called,
1138 * where {@code defcPkg} is the package of {@code defc}.
1139 * </ul>
1140 * Security checks are performed after other access checks have passed.
1141 * Therefore, the above rules presuppose a member or class that is public,
1142 * or else that is being accessed from a lookup class that has
1143 * rights to access the member or class.
1144 *
1145 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1146 * A small number of Java methods have a special property called caller sensitivity.
1147 * A <em>caller-sensitive</em> method can behave differently depending on the
1148 * identity of its immediate caller.
1149 * <p>
1150 * If a method handle for a caller-sensitive method is requested,
1151 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1152 * but they take account of the lookup class in a special way.
1153 * The resulting method handle behaves as if it were called
1154 * from an instruction contained in the lookup class,
1155 * so that the caller-sensitive method detects the lookup class.
1156 * (By contrast, the invoker of the method handle is disregarded.)
1157 * Thus, in the case of caller-sensitive methods,
1158 * different lookup classes may give rise to
1159 * differently behaving method handles.
1160 * <p>
1161 * In cases where the lookup object is
1162 * {@link MethodHandles#publicLookup() publicLookup()},
1163 * or some other lookup object without
1164 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
1165 * the lookup class is disregarded.
1166 * In such cases, no caller-sensitive method handle can be created,
1167 * access is forbidden, and the lookup fails with an
1168 * {@code IllegalAccessException}.
1169 * <p style="font-size:smaller;">
1170 * <em>Discussion:</em>
1171 * For example, the caller-sensitive method
1172 * {@link java.lang.Class#forName(String) Class.forName(x)}
1173 * can return varying classes or throw varying exceptions,
1174 * depending on the class loader of the class that calls it.
1175 * A public lookup of {@code Class.forName} will fail, because
1176 * there is no reasonable way to determine its bytecode behavior.
1177 * <p style="font-size:smaller;">
1178 * If an application caches method handles for broad sharing,
1179 * it should use {@code publicLookup()} to create them.
1180 * If there is a lookup of {@code Class.forName}, it will fail,
1181 * and the application must take appropriate action in that case.
1182 * It may be that a later lookup, perhaps during the invocation of a
1183 * bootstrap method, can incorporate the specific identity
1184 * of the caller, making the method accessible.
1185 * <p style="font-size:smaller;">
1186 * The function {@code MethodHandles.lookup} is caller sensitive
1187 * so that there can be a secure foundation for lookups.
1188 * Nearly all other methods in the JSR 292 API rely on lookup
1189 * objects to check access requests.
1190 *
1191 * @revised 9
1192 */
1193 public static final
1194 class Lookup {
1195 /** The class on behalf of whom the lookup is being performed. */
1196 private final Class<?> lookupClass;
1197
1198 /** previous lookup class */
1199 private final Class<?> prevLookupClass;
1200
1201 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1202 private final int allowedModes;
1203
1204 static {
1205 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1206 }
1207
1208 /** A single-bit mask representing {@code public} access,
1209 * which may contribute to the result of {@link #lookupModes lookupModes}.
1210 * The value, {@code 0x01}, happens to be the same as the value of the
1211 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1212 * <p>
1213 * A {@code Lookup} with this lookup mode performs cross-module access check
1214 * with respect to the {@linkplain #lookupClass() lookup class} and
1215 * {@linkplain #previousLookupClass() previous lookup class} if present.
1216 */
1217 public static final int PUBLIC = Modifier.PUBLIC;
1218
1219 /** A single-bit mask representing {@code private} access,
1220 * which may contribute to the result of {@link #lookupModes lookupModes}.
1221 * The value, {@code 0x02}, happens to be the same as the value of the
1222 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1223 */
1224 public static final int PRIVATE = Modifier.PRIVATE;
1225
1226 /** A single-bit mask representing {@code protected} access,
1227 * which may contribute to the result of {@link #lookupModes lookupModes}.
1228 * The value, {@code 0x04}, happens to be the same as the value of the
1229 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1230 */
1231 public static final int PROTECTED = Modifier.PROTECTED;
1232
1233 /** A single-bit mask representing {@code package} access (default access),
1234 * which may contribute to the result of {@link #lookupModes lookupModes}.
1235 * The value is {@code 0x08}, which does not correspond meaningfully to
1236 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1237 */
1238 public static final int PACKAGE = Modifier.STATIC;
1239
1240 /** A single-bit mask representing {@code module} access,
1241 * which may contribute to the result of {@link #lookupModes lookupModes}.
1242 * The value is {@code 0x10}, which does not correspond meaningfully to
1243 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1244 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1245 * with this lookup mode can access all public types in the module of the
1246 * lookup class and public types in packages exported by other modules
1247 * to the module of the lookup class.
1248 * <p>
1249 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1250 * previous lookup class} is always {@code null}.
1251 *
1252 * @since 9
1253 * @spec JPMS
1254 */
1255 public static final int MODULE = PACKAGE << 1;
1256
1257 /** A single-bit mask representing {@code unconditional} access
1258 * which may contribute to the result of {@link #lookupModes lookupModes}.
1259 * The value is {@code 0x20}, which does not correspond meaningfully to
1260 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1261 * A {@code Lookup} with this lookup mode assumes {@linkplain
1262 * java.lang.Module#canRead(java.lang.Module) readability}.
1263 * This lookup mode can access all public members of public types
1264 * of all modules when the type is in a package that is {@link
1265 * java.lang.Module#isExported(String) exported unconditionally}.
1266 *
1267 * <p>
1268 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1269 * previous lookup class} is always {@code null}.
1270 *
1271 * @since 9
1272 * @spec JPMS
1273 * @see #publicLookup()
1274 */
1275 public static final int UNCONDITIONAL = PACKAGE << 2;
1276
1277 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
1278 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
1279 private static final int TRUSTED = -1;
1280
1281 /*
1282 * Adjust PUBLIC => PUBLIC|MODULE|UNCONDITIONAL
1283 * Adjust 0 => PACKAGE
1284 */
1285 private static int fixmods(int mods) {
1286 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
1287 if (Modifier.isPublic(mods))
1288 mods |= UNCONDITIONAL;
1289 return (mods != 0) ? mods : PACKAGE;
1290 }
1291
1292 /** Tells which class is performing the lookup. It is this class against
1293 * which checks are performed for visibility and access permissions.
1294 * <p>
1295 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1296 * access checks are performed against both the lookup class and the previous lookup class.
1297 * <p>
1298 * The class implies a maximum level of access permission,
1299 * but the permissions may be additionally limited by the bitmask
1300 * {@link #lookupModes lookupModes}, which controls whether non-public members
1301 * can be accessed.
1302 * @return the lookup class, on behalf of which this lookup object finds members
1303 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1304 */
1305 public Class<?> lookupClass() {
1306 return lookupClass;
1307 }
1308
1309 /** Reports a lookup class in another module that this lookup object
1310 * was previously teleported from, or {@code null}.
1311 * <p>
1312 * A {@code Lookup} object produced by the factory methods, such as the
1313 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1314 * has {@code null} previous lookup class.
1315 * A {@code Lookup} object has a non-null previous lookup class
1316 * when this lookup was teleported from an old lookup class
1317 * in one module to a new lookup class in another module.
1318 *
1319 * @return the lookup class in another module that this lookup object was
1320 * previously teleported from, or {@code null}
1321 * @since 14
1322 * @see #in(Class)
1323 * @see MethodHandles#privateLookupIn(Class, Lookup)
1324 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1325 */
1326 public Class<?> previousLookupClass() {
1327 return prevLookupClass;
1328 }
1329
1330 // This is just for calling out to MethodHandleImpl.
1331 private Class<?> lookupClassOrNull() {
1332 return (allowedModes == TRUSTED) ? null : lookupClass;
1333 }
1334
1335 /** Tells which access-protection classes of members this lookup object can produce.
1336 * The result is a bit-mask of the bits
1337 * {@linkplain #PUBLIC PUBLIC (0x01)},
1338 * {@linkplain #PRIVATE PRIVATE (0x02)},
1339 * {@linkplain #PROTECTED PROTECTED (0x04)},
1340 * {@linkplain #PACKAGE PACKAGE (0x08)},
1341 * {@linkplain #MODULE MODULE (0x10)},
1342 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
1343 * <p>
1344 * A freshly-created lookup object
1345 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1346 * all possible bits set, except {@code UNCONDITIONAL}.
1347 * A lookup object on a new lookup class
1348 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1349 * may have some mode bits set to zero.
1350 * Mode bits can also be
1351 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1352 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1353 * The purpose of this is to restrict access via the new lookup object,
1354 * so that it can access only names which can be reached by the original
1355 * lookup object, and also by the new lookup class.
1356 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1357 * @see #in
1358 * @see #dropLookupMode
1359 *
1360 * @revised 9
1361 * @spec JPMS
1362 */
1363 public int lookupModes() {
1364 return allowedModes & ALL_MODES;
1365 }
1366
1367 /** Embody the current class (the lookupClass) as a lookup class
1368 * for method handle creation.
1369 * Must be called by from a method in this package,
1370 * which in turn is called by a method not in this package.
1371 */
1372 Lookup(Class<?> lookupClass) {
1373 this(lookupClass, null, FULL_POWER_MODES);
1374 // make sure we haven't accidentally picked up a privileged class:
1375 checkUnprivilegedlookupClass(lookupClass);
1376 }
1377
1378 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1379 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1380 && prevLookupClass.getModule() != lookupClass.getModule());
1381
1382 this.lookupClass = lookupClass;
1383 this.prevLookupClass = prevLookupClass;
1384 this.allowedModes = allowedModes;
1385 }
1386
1387 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1388 // make sure we haven't accidentally picked up a privileged class:
1389 checkUnprivilegedlookupClass(lookupClass);
1390 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1391 }
1392
1393 /**
1394 * Creates a lookup on the specified new lookup class.
1395 * The resulting object will report the specified
1396 * class as its own {@link #lookupClass() lookupClass}.
1397 *
1398 * <p>
1399 * However, the resulting {@code Lookup} object is guaranteed
1400 * to have no more access capabilities than the original.
1401 * In particular, access capabilities can be lost as follows:<ul>
1402 * <li>If the new lookup class is in a different module from the old one,
1403 * i.e. {@link #MODULE MODULE} access is lost.
1404 * <li>If the new lookup class is in a different package
1405 * than the old one, protected and default (package) members will not be accessible,
1406 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1407 * <li>If the new lookup class is not within the same package member
1408 * as the old one, private members will not be accessible, and protected members
1409 * will not be accessible by virtue of inheritance,
1410 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1411 * (Protected members may continue to be accessible because of package sharing.)
1412 * <li>If the new lookup class is not
1413 * {@linkplain #accessClass(Class) accessible} to this lookup,
1414 * then no members, not even public members, will be accessible
1415 * i.e. all access modes are lost.
1416 * <li>If the new lookup class, the old lookup class and the previous lookup class
1417 * are all in different modules i.e. teleporting to a third module,
1418 * all access modes are lost.
1419 * </ul>
1420 * <p>
1421 * The new previous lookup class is chosen as follows:
1422 * <ul>
1423 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1424 * the new previous lookup class is {@code null}.
1425 * <li>If the new lookup class is in the same module as the old lookup class,
1426 * the new previous lookup class is the old previous lookup class.
1427 * <li>If the new lookup class is in a different module from the old lookup class,
1428 * the new previous lookup class is the the old lookup class.
1429 *</ul>
1430 * <p>
1431 * The resulting lookup's capabilities for loading classes
1432 * (used during {@link #findClass} invocations)
1433 * are determined by the lookup class' loader,
1434 * which may change due to this operation.
1435 * <p>
1436 * @param requestedLookupClass the desired lookup class for the new lookup object
1437 * @return a lookup object which reports the desired lookup class, or the same object
1438 * if there is no change
1439 * @throws NullPointerException if the argument is null
1440 *
1441 * @revised 9
1442 * @spec JPMS
1443 * @see #accessClass(Class)
1444 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1445 */
1446 public Lookup in(Class<?> requestedLookupClass) {
1447 Objects.requireNonNull(requestedLookupClass);
1448 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1449 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1450 if (requestedLookupClass == this.lookupClass)
1451 return this; // keep same capabilities
1452 int newModes = (allowedModes & FULL_POWER_MODES);
1453 Module fromModule = this.lookupClass.getModule();
1454 Module targetModule = requestedLookupClass.getModule();
1455 Class<?> plc = this.previousLookupClass();
1456 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1457 assert plc == null;
1458 newModes = UNCONDITIONAL;
1459 } else if (fromModule != targetModule) {
1460 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1461 // allow hopping back and forth between fromModule and plc's module
1462 // but not the third module
1463 newModes = 0;
1464 }
1465 // drop MODULE access
1466 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1467 // teleport from this lookup class
1468 plc = this.lookupClass;
1469 }
1470 if ((newModes & PACKAGE) != 0
1471 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1472 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1473 }
1474 // Allow nestmate lookups to be created without special privilege:
1475 if ((newModes & PRIVATE) != 0
1476 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1477 newModes &= ~(PRIVATE|PROTECTED);
1478 }
1479 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1480 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1481 // The requested class it not accessible from the lookup class.
1482 // No permissions.
1483 newModes = 0;
1484 }
1485 return newLookup(requestedLookupClass, plc, newModes);
1486 }
1487
1488 /**
1489 * Creates a lookup on the same lookup class which this lookup object
1490 * finds members, but with a lookup mode that has lost the given lookup mode.
1491 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1492 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
1493 * {@link #PROTECTED PROTECTED} is always
1494 * dropped and so the resulting lookup mode will never have this access capability.
1495 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
1496 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
1497 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
1498 * is dropped then the resulting lookup has no access. If {@code UNCONDITIONAL}
1499 * is dropped then the resulting lookup has no access.
1500 *
1501 * @apiNote
1502 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1503 * delegate non-public access within the package of the lookup class without
1504 * conferring private access. A lookup with {@code MODULE} but not
1505 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1506 * the module of the lookup class without conferring package access.
1507 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1508 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1509 * to public classes accessible to both the module of the lookup class
1510 * and the module of the previous lookup class.
1511 *
1512 * @param modeToDrop the lookup mode to drop
1513 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1514 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1515 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
1516 * @see MethodHandles#privateLookupIn
1517 * @since 9
1518 */
1519 public Lookup dropLookupMode(int modeToDrop) {
1520 int oldModes = lookupModes();
1521 int newModes = oldModes & ~(modeToDrop | PROTECTED);
1522 switch (modeToDrop) {
1523 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1524 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1525 case PACKAGE: newModes &= ~(PRIVATE); break;
1526 case PROTECTED:
1527 case PRIVATE:
1528 case UNCONDITIONAL: break;
1529 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1530 }
1531 if (newModes == oldModes) return this; // return self if no change
1532 return newLookup(lookupClass(), previousLookupClass(), newModes);
1533 }
1534
1535 /**
1536 * Defines a class to the same class loader and in the same runtime package and
1537 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1538 * {@linkplain #lookupClass() lookup class}.
1539 *
1540 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1541 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1542 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1543 * that the lookup object was created by a caller in the runtime package (or derived
1544 * from a lookup originally created by suitably privileged code to a target class in
1545 * the runtime package). </p>
1546 *
1547 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1548 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1549 * same package as the lookup class. </p>
1550 *
1551 * <p> This method does not run the class initializer. The class initializer may
1552 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1553 * Specification</em>. </p>
1554 *
1555 * <p> If there is a security manager, its {@code checkPermission} method is first called
1556 * to check {@code RuntimePermission("defineClass")}. </p>
1557 *
1558 * @param bytes the class bytes
1559 * @return the {@code Class} object for the class
1560 * @throws IllegalArgumentException the bytes are for a class in a different package
1561 * to the lookup class
1562 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1563 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1564 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
1565 * @throws SecurityException if denied by the security manager
1566 * @throws NullPointerException if {@code bytes} is {@code null}
1567 * @since 9
1568 * @spec JPMS
1569 * @see Lookup#privateLookupIn
1570 * @see Lookup#dropLookupMode
1571 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1572 */
1573 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1574 SecurityManager sm = System.getSecurityManager();
1575 if (sm != null)
1576 sm.checkPermission(new RuntimePermission("defineClass"));
1577 if ((lookupModes() & PACKAGE) == 0)
1578 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1579 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
1580
1581 // parse class bytes to get class name (in internal form)
1582 bytes = bytes.clone();
1583 String name;
1584 try {
1585 ClassReader reader = new ClassReader(bytes);
1586 name = reader.getClassName();
1587 } catch (RuntimeException e) {
1588 // ASM exceptions are poorly specified
1589 ClassFormatError cfe = new ClassFormatError();
1590 cfe.initCause(e);
1591 throw cfe;
1592 }
1593
1594 // get package and class name in binary form
1595 String cn, pn;
1596 int index = name.lastIndexOf('/');
1597 if (index == -1) {
1598 cn = name;
1599 pn = "";
1600 } else {
1601 cn = name.replace('/', '.');
1602 pn = cn.substring(0, index);
1603 }
1604 if (!pn.equals(lookupClass.getPackageName())) {
1605 throw new IllegalArgumentException("Class not in same package as lookup class");
1606 }
1607
1608 // invoke the class loader's defineClass method
1609 ClassLoader loader = lookupClass.getClassLoader();
1610 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
1611 String source = "__Lookup_defineClass__";
1612 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
1613 return clazz;
1614 }
1615
1616 private ProtectionDomain lookupClassProtectionDomain() {
1617 ProtectionDomain pd = cachedProtectionDomain;
1618 if (pd == null) {
1619 cachedProtectionDomain = pd = protectionDomain(lookupClass);
1620 }
1621 return pd;
1622 }
1623
1624 private ProtectionDomain protectionDomain(Class<?> clazz) {
1625 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
1626 return AccessController.doPrivileged(pa);
1627 }
1628
1629 // cached protection domain
1630 private volatile ProtectionDomain cachedProtectionDomain;
1631
1632
1633 // Make sure outer class is initialized first.
1634 static { IMPL_NAMES.getClass(); }
1635
1636 /** Package-private version of lookup which is trusted. */
1637 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
1638
1639 /** Version of lookup which is trusted minimally.
1640 * It can only be used to create method handles to publicly accessible
1641 * members in packages that are exported unconditionally.
1642 */
1643 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
1644
1645 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1646 String name = lookupClass.getName();
1647 if (name.startsWith("java.lang.invoke."))
1648 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1649 }
1650
1651 /**
1652 * Displays the name of the class from which lookups are to be made.
1653 * followed with "/" and the name of the {@linkplain #previousLookupClass()
1654 * previous lookup class} if present.
1655 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1656 * If there are restrictions on the access permitted to this lookup,
1657 * this is indicated by adding a suffix to the class name, consisting
1658 * of a slash and a keyword. The keyword represents the strongest
1659 * allowed access, and is chosen as follows:
1660 * <ul>
1661 * <li>If no access is allowed, the suffix is "/noaccess".
1662 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
1663 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1664 * <li>If only public and module access are allowed, the suffix is "/module".
1665 * <li>If public and package access are allowed, the suffix is "/package".
1666 * <li>If public, package, and private access are allowed, the suffix is "/private".
1667 * </ul>
1668 * If none of the above cases apply, it is the case that full access
1669 * (public, module, package, private, and protected) is allowed.
1670 * In this case, no suffix is added.
1671 * This is true only of an object obtained originally from
1672 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1673 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1674 * always have restricted access, and will display a suffix.
1675 * <p>
1676 * (It may seem strange that protected access should be
1677 * stronger than private access. Viewed independently from
1678 * package access, protected access is the first to be lost,
1679 * because it requires a direct subclass relationship between
1680 * caller and callee.)
1681 * @see #in
1682 *
1683 * @revised 9
1684 * @spec JPMS
1685 */
1686 @Override
1687 public String toString() {
1688 String cname = lookupClass.getName();
1689 if (prevLookupClass != null)
1690 cname += "/" + prevLookupClass.getName();
1691 switch (allowedModes) {
1692 case 0: // no privileges
1693 return cname + "/noaccess";
1694 case UNCONDITIONAL:
1695 return cname + "/publicLookup";
1696 case PUBLIC:
1697 return cname + "/public";
1698 case PUBLIC|MODULE:
1699 return cname + "/module";
1700 case PUBLIC|PACKAGE:
1701 case PUBLIC|MODULE|PACKAGE:
1702 return cname + "/package";
1703 case FULL_POWER_MODES & (~PROTECTED):
1704 case FULL_POWER_MODES & ~(PROTECTED|MODULE):
1705 return cname + "/private";
1706 case FULL_POWER_MODES:
1707 case FULL_POWER_MODES & (~MODULE):
1708 return cname;
1709 case TRUSTED:
1710 return "/trusted"; // internal only; not exported
1711 default: // Should not happen, but it's a bitfield...
1712 cname = cname + "/" + Integer.toHexString(allowedModes);
1713 assert(false) : cname;
1714 return cname;
1715 }
1716 }
1717
1718 /**
1719 * Produces a method handle for a static method.
1720 * The type of the method handle will be that of the method.
1721 * (Since static methods do not take receivers, there is no
1722 * additional receiver argument inserted into the method handle type,
1723 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1724 * The method and all its argument types must be accessible to the lookup object.
1725 * <p>
1726 * The returned method handle will have
1727 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1728 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1729 * <p>
1730 * If the returned method handle is invoked, the method's class will
1731 * be initialized, if it has not already been initialized.
1732 * <p><b>Example:</b>
1733 * <blockquote><pre>{@code
1734 import static java.lang.invoke.MethodHandles.*;
1735 import static java.lang.invoke.MethodType.*;
1736 ...
1737 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1738 "asList", methodType(List.class, Object[].class));
1739 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1740 * }</pre></blockquote>
1741 * @param refc the class from which the method is accessed
1742 * @param name the name of the method
1743 * @param type the type of the method
1744 * @return the desired method handle
1745 * @throws NoSuchMethodException if the method does not exist
1746 * @throws IllegalAccessException if access checking fails,
1747 * or if the method is not {@code static},
1748 * or if the method's variable arity modifier bit
1749 * is set and {@code asVarargsCollector} fails
1750 * @exception SecurityException if a security manager is present and it
1751 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1752 * @throws NullPointerException if any argument is null
1753 */
1754 public
1755 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1756 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1757 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1758 }
1759
1760 /**
1761 * Produces a method handle for a virtual method.
1762 * The type of the method handle will be that of the method,
1763 * with the receiver type (usually {@code refc}) prepended.
1764 * The method and all its argument types must be accessible to the lookup object.
1765 * <p>
1766 * When called, the handle will treat the first argument as a receiver
1767 * and, for non-private methods, dispatch on the receiver's type to determine which method
1768 * implementation to enter.
1769 * For private methods the named method in {@code refc} will be invoked on the receiver.
1770 * (The dispatching action is identical with that performed by an
1771 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1772 * <p>
1773 * The first argument will be of type {@code refc} if the lookup
1774 * class has full privileges to access the member. Otherwise
1775 * the member must be {@code protected} and the first argument
1776 * will be restricted in type to the lookup class.
1777 * <p>
1778 * The returned method handle will have
1779 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1780 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1781 * <p>
1782 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1783 * instructions and method handles produced by {@code findVirtual},
1784 * if the class is {@code MethodHandle} and the name string is
1785 * {@code invokeExact} or {@code invoke}, the resulting
1786 * method handle is equivalent to one produced by
1787 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1788 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1789 * with the same {@code type} argument.
1790 * <p>
1791 * If the class is {@code VarHandle} and the name string corresponds to
1792 * the name of a signature-polymorphic access mode method, the resulting
1793 * method handle is equivalent to one produced by
1794 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1795 * the access mode corresponding to the name string and with the same
1796 * {@code type} arguments.
1797 * <p>
1798 * <b>Example:</b>
1799 * <blockquote><pre>{@code
1800 import static java.lang.invoke.MethodHandles.*;
1801 import static java.lang.invoke.MethodType.*;
1802 ...
1803 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1804 "concat", methodType(String.class, String.class));
1805 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1806 "hashCode", methodType(int.class));
1807 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1808 "hashCode", methodType(int.class));
1809 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1810 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1811 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1812 // interface method:
1813 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1814 "subSequence", methodType(CharSequence.class, int.class, int.class));
1815 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1816 // constructor "internal method" must be accessed differently:
1817 MethodType MT_newString = methodType(void.class); //()V for new String()
1818 try { assertEquals("impossible", lookup()
1819 .findVirtual(String.class, "<init>", MT_newString));
1820 } catch (NoSuchMethodException ex) { } // OK
1821 MethodHandle MH_newString = publicLookup()
1822 .findConstructor(String.class, MT_newString);
1823 assertEquals("", (String) MH_newString.invokeExact());
1824 * }</pre></blockquote>
1825 *
1826 * @param refc the class or interface from which the method is accessed
1827 * @param name the name of the method
1828 * @param type the type of the method, with the receiver argument omitted
1829 * @return the desired method handle
1830 * @throws NoSuchMethodException if the method does not exist
1831 * @throws IllegalAccessException if access checking fails,
1832 * or if the method is {@code static},
1833 * or if the method's variable arity modifier bit
1834 * is set and {@code asVarargsCollector} fails
1835 * @exception SecurityException if a security manager is present and it
1836 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1837 * @throws NullPointerException if any argument is null
1838 */
1839 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1840 if (refc == MethodHandle.class) {
1841 MethodHandle mh = findVirtualForMH(name, type);
1842 if (mh != null) return mh;
1843 } else if (refc == VarHandle.class) {
1844 MethodHandle mh = findVirtualForVH(name, type);
1845 if (mh != null) return mh;
1846 }
1847 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1848 MemberName method = resolveOrFail(refKind, refc, name, type);
1849 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1850 }
1851 private MethodHandle findVirtualForMH(String name, MethodType type) {
1852 // these names require special lookups because of the implicit MethodType argument
1853 if ("invoke".equals(name))
1854 return invoker(type);
1855 if ("invokeExact".equals(name))
1856 return exactInvoker(type);
1857 assert(!MemberName.isMethodHandleInvokeName(name));
1858 return null;
1859 }
1860 private MethodHandle findVirtualForVH(String name, MethodType type) {
1861 try {
1862 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1863 } catch (IllegalArgumentException e) {
1864 return null;
1865 }
1866 }
1867
1868 /**
1869 * Produces a method handle which creates an object and initializes it, using
1870 * the constructor of the specified type.
1871 * The parameter types of the method handle will be those of the constructor,
1872 * while the return type will be a reference to the constructor's class.
1873 * The constructor and all its argument types must be accessible to the lookup object.
1874 * <p>
1875 * The requested type must have a return type of {@code void}.
1876 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1877 * <p>
1878 * The returned method handle will have
1879 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1880 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1881 * <p>
1882 * If the returned method handle is invoked, the constructor's class will
1883 * be initialized, if it has not already been initialized.
1884 * <p><b>Example:</b>
1885 * <blockquote><pre>{@code
1886 import static java.lang.invoke.MethodHandles.*;
1887 import static java.lang.invoke.MethodType.*;
1888 ...
1889 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1890 ArrayList.class, methodType(void.class, Collection.class));
1891 Collection orig = Arrays.asList("x", "y");
1892 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1893 assert(orig != copy);
1894 assertEquals(orig, copy);
1895 // a variable-arity constructor:
1896 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1897 ProcessBuilder.class, methodType(void.class, String[].class));
1898 ProcessBuilder pb = (ProcessBuilder)
1899 MH_newProcessBuilder.invoke("x", "y", "z");
1900 assertEquals("[x, y, z]", pb.command().toString());
1901 * }</pre></blockquote>
1902 * @param refc the class or interface from which the method is accessed
1903 * @param type the type of the method, with the receiver argument omitted, and a void return type
1904 * @return the desired method handle
1905 * @throws NoSuchMethodException if the constructor does not exist
1906 * @throws IllegalAccessException if access checking fails
1907 * or if the method's variable arity modifier bit
1908 * is set and {@code asVarargsCollector} fails
1909 * @exception SecurityException if a security manager is present and it
1910 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1911 * @throws NullPointerException if any argument is null
1912 */
1913 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1914 if (refc.isArray()) {
1915 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1916 }
1917 String name = "<init>";
1918 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1919 return getDirectConstructor(refc, ctor);
1920 }
1921
1922 /**
1923 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1924 * initializer of the class is not run.
1925 * <p>
1926 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1927 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1928 * load the requested class, and then determines whether the class is accessible to this lookup object.
1929 *
1930 * @param targetName the fully qualified name of the class to be looked up.
1931 * @return the requested class.
1932 * @exception SecurityException if a security manager is present and it
1933 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1934 * @throws LinkageError if the linkage fails
1935 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1936 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1937 * modes.
1938 * @exception SecurityException if a security manager is present and it
1939 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1940 * @since 9
1941 */
1942 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1943 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1944 return accessClass(targetClass);
1945 }
1946
1947 /**
1948 * Determines if a class can be accessed from the lookup context defined by
1949 * this {@code Lookup} object. The static initializer of the class is not run.
1950 * <p>
1951 * If the {@code targetClass} is in the same module as the lookup class,
1952 * the lookup class is {@code LC} in module {@code M1} and
1953 * the previous lookup class is in module {@code M0} or
1954 * {@code null} if not present,
1955 * {@code targetClass} is accessible if and only if one of the following is true:
1956 * <ul>
1957 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
1958 * {@code LC} or other class in the same nest of {@code LC}.</li>
1959 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
1960 * in the same runtime package of {@code LC}.</li>
1961 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
1962 * a public type in {@code M1}.</li>
1963 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
1964 * a public type in a package exported by {@code M1} to at least {@code M0}
1965 * if the previous lookup class is present; otherwise, {@code targetClass}
1966 * is a public type in a package exported by {@code M1} unconditionally.</li>
1967 * </ul>
1968 *
1969 * <p>
1970 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
1971 * can access public types in all modules when the type is in a package
1972 * that is exported unconditionally.
1973 * <p>
1974 * Otherwise, the target class is in a different module from {@code lookupClass},
1975 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
1976 * is inaccessible.
1977 * <p>
1978 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
1979 * {@code M1} is the module containing {@code lookupClass} and
1980 * {@code M2} is the module containing {@code targetClass},
1981 * then {@code targetClass} is accessible if and only if
1982 * <ul>
1983 * <li>{@code M1} reads {@code M2}, and
1984 * <li>{@code targetClass} is public and in a package exported by
1985 * {@code M2} at least to {@code M1}.
1986 * </ul>
1987 * <p>
1988 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
1989 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
1990 * containing the previous lookup class, then {@code targetClass} is accessible
1991 * if and only if one of the following is true:
1992 * <ul>
1993 * <li>{@code targetClass} is in {@code M0} and {@code M1}
1994 * {@linkplain Module#reads reads} {@code M0} and the type is
1995 * in a package that is exported to at least {@code M1}.
1996 * <li>{@code targetClass} is in {@code M1} and {@code M0}
1997 * {@linkplain Module#reads reads} {@code M1} and the type is
1998 * in a package that is exported to at least {@code M0}.
1999 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2000 * and {@code M1} reads {@code M2} and the type is in a package
2001 * that is exported to at least both {@code M0} and {@code M2}.
2002 * </ul>
2003 * <p>
2004 * Otherwise, {@code targetClass} is not accessible.
2005 *
2006 * @param targetClass the class to be access-checked
2007 * @return the class that has been access-checked
2008 * @throws IllegalAccessException if the class is not accessible from the lookup class
2009 * and previous lookup class, if present, using the allowed access modes.
2010 * @exception SecurityException if a security manager is present and it
2011 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2012 * @since 9
2013 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2014 */
2015 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2016 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2017 throw new MemberName(targetClass).makeAccessException("access violation", this);
2018 }
2019 checkSecurityManager(targetClass, null);
2020 return targetClass;
2021 }
2022
2023 /**
2024 * Produces an early-bound method handle for a virtual method.
2025 * It will bypass checks for overriding methods on the receiver,
2026 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2027 * instruction from within the explicitly specified {@code specialCaller}.
2028 * The type of the method handle will be that of the method,
2029 * with a suitably restricted receiver type prepended.
2030 * (The receiver type will be {@code specialCaller} or a subtype.)
2031 * The method and all its argument types must be accessible
2032 * to the lookup object.
2033 * <p>
2034 * Before method resolution,
2035 * if the explicitly specified caller class is not identical with the
2036 * lookup class, or if this lookup object does not have
2037 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2038 * privileges, the access fails.
2039 * <p>
2040 * The returned method handle will have
2041 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2042 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2043 * <p style="font-size:smaller;">
2044 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2045 * even though the {@code invokespecial} instruction can refer to them
2046 * in special circumstances. Use {@link #findConstructor findConstructor}
2047 * to access instance initialization methods in a safe manner.)</em>
2048 * <p><b>Example:</b>
2049 * <blockquote><pre>{@code
2050 import static java.lang.invoke.MethodHandles.*;
2051 import static java.lang.invoke.MethodType.*;
2052 ...
2053 static class Listie extends ArrayList {
2054 public String toString() { return "[wee Listie]"; }
2055 static Lookup lookup() { return MethodHandles.lookup(); }
2056 }
2057 ...
2058 // no access to constructor via invokeSpecial:
2059 MethodHandle MH_newListie = Listie.lookup()
2060 .findConstructor(Listie.class, methodType(void.class));
2061 Listie l = (Listie) MH_newListie.invokeExact();
2062 try { assertEquals("impossible", Listie.lookup().findSpecial(
2063 Listie.class, "<init>", methodType(void.class), Listie.class));
2064 } catch (NoSuchMethodException ex) { } // OK
2065 // access to super and self methods via invokeSpecial:
2066 MethodHandle MH_super = Listie.lookup().findSpecial(
2067 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2068 MethodHandle MH_this = Listie.lookup().findSpecial(
2069 Listie.class, "toString" , methodType(String.class), Listie.class);
2070 MethodHandle MH_duper = Listie.lookup().findSpecial(
2071 Object.class, "toString" , methodType(String.class), Listie.class);
2072 assertEquals("[]", (String) MH_super.invokeExact(l));
2073 assertEquals(""+l, (String) MH_this.invokeExact(l));
2074 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2075 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2076 String.class, "toString", methodType(String.class), Listie.class));
2077 } catch (IllegalAccessException ex) { } // OK
2078 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2079 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2080 * }</pre></blockquote>
2081 *
2082 * @param refc the class or interface from which the method is accessed
2083 * @param name the name of the method (which must not be "<init>")
2084 * @param type the type of the method, with the receiver argument omitted
2085 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2086 * @return the desired method handle
2087 * @throws NoSuchMethodException if the method does not exist
2088 * @throws IllegalAccessException if access checking fails,
2089 * or if the method is {@code static},
2090 * or if the method's variable arity modifier bit
2091 * is set and {@code asVarargsCollector} fails
2092 * @exception SecurityException if a security manager is present and it
2093 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2094 * @throws NullPointerException if any argument is null
2095 */
2096 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2097 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2098 checkSpecialCaller(specialCaller, refc);
2099 Lookup specialLookup = this.in(specialCaller);
2100 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2101 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
2102 }
2103
2104 /**
2105 * Produces a method handle giving read access to a non-static field.
2106 * The type of the method handle will have a return type of the field's
2107 * value type.
2108 * The method handle's single argument will be the instance containing
2109 * the field.
2110 * Access checking is performed immediately on behalf of the lookup class.
2111 * @param refc the class or interface from which the method is accessed
2112 * @param name the field's name
2113 * @param type the field's type
2114 * @return a method handle which can load values from the field
2115 * @throws NoSuchFieldException if the field does not exist
2116 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2117 * @exception SecurityException if a security manager is present and it
2118 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2119 * @throws NullPointerException if any argument is null
2120 * @see #findVarHandle(Class, String, Class)
2121 */
2122 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2123 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2124 return getDirectField(REF_getField, refc, field);
2125 }
2126
2127 /**
2128 * Produces a method handle giving write access to a non-static field.
2129 * The type of the method handle will have a void return type.
2130 * The method handle will take two arguments, the instance containing
2131 * the field, and the value to be stored.
2132 * The second argument will be of the field's value type.
2133 * Access checking is performed immediately on behalf of the lookup class.
2134 * @param refc the class or interface from which the method is accessed
2135 * @param name the field's name
2136 * @param type the field's type
2137 * @return a method handle which can store values into the field
2138 * @throws NoSuchFieldException if the field does not exist
2139 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2140 * or {@code final}
2141 * @exception SecurityException if a security manager is present and it
2142 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2143 * @throws NullPointerException if any argument is null
2144 * @see #findVarHandle(Class, String, Class)
2145 */
2146 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2147 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2148 return getDirectField(REF_putField, refc, field);
2149 }
2150
2151 /**
2152 * Produces a VarHandle giving access to a non-static field {@code name}
2153 * of type {@code type} declared in a class of type {@code recv}.
2154 * The VarHandle's variable type is {@code type} and it has one
2155 * coordinate type, {@code recv}.
2156 * <p>
2157 * Access checking is performed immediately on behalf of the lookup
2158 * class.
2159 * <p>
2160 * Certain access modes of the returned VarHandle are unsupported under
2161 * the following conditions:
2162 * <ul>
2163 * <li>if the field is declared {@code final}, then the write, atomic
2164 * update, numeric atomic update, and bitwise atomic update access
2165 * modes are unsupported.
2166 * <li>if the field type is anything other than {@code byte},
2167 * {@code short}, {@code char}, {@code int}, {@code long},
2168 * {@code float}, or {@code double} then numeric atomic update
2169 * access modes are unsupported.
2170 * <li>if the field type is anything other than {@code boolean},
2171 * {@code byte}, {@code short}, {@code char}, {@code int} or
2172 * {@code long} then bitwise atomic update access modes are
2173 * unsupported.
2174 * </ul>
2175 * <p>
2176 * If the field is declared {@code volatile} then the returned VarHandle
2177 * will override access to the field (effectively ignore the
2178 * {@code volatile} declaration) in accordance to its specified
2179 * access modes.
2180 * <p>
2181 * If the field type is {@code float} or {@code double} then numeric
2182 * and atomic update access modes compare values using their bitwise
2183 * representation (see {@link Float#floatToRawIntBits} and
2184 * {@link Double#doubleToRawLongBits}, respectively).
2185 * @apiNote
2186 * Bitwise comparison of {@code float} values or {@code double} values,
2187 * as performed by the numeric and atomic update access modes, differ
2188 * from the primitive {@code ==} operator and the {@link Float#equals}
2189 * and {@link Double#equals} methods, specifically with respect to
2190 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2191 * Care should be taken when performing a compare and set or a compare
2192 * and exchange operation with such values since the operation may
2193 * unexpectedly fail.
2194 * There are many possible NaN values that are considered to be
2195 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2196 * provided by Java can distinguish between them. Operation failure can
2197 * occur if the expected or witness value is a NaN value and it is
2198 * transformed (perhaps in a platform specific manner) into another NaN
2199 * value, and thus has a different bitwise representation (see
2200 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2201 * details).
2202 * The values {@code -0.0} and {@code +0.0} have different bitwise
2203 * representations but are considered equal when using the primitive
2204 * {@code ==} operator. Operation failure can occur if, for example, a
2205 * numeric algorithm computes an expected value to be say {@code -0.0}
2206 * and previously computed the witness value to be say {@code +0.0}.
2207 * @param recv the receiver class, of type {@code R}, that declares the
2208 * non-static field
2209 * @param name the field's name
2210 * @param type the field's type, of type {@code T}
2211 * @return a VarHandle giving access to non-static fields.
2212 * @throws NoSuchFieldException if the field does not exist
2213 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2214 * @exception SecurityException if a security manager is present and it
2215 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2216 * @throws NullPointerException if any argument is null
2217 * @since 9
2218 */
2219 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2220 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
2221 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
2222 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
2223 }
2224
2225 /**
2226 * Produces a method handle giving read access to a static field.
2227 * The type of the method handle will have a return type of the field's
2228 * value type.
2229 * The method handle will take no arguments.
2230 * Access checking is performed immediately on behalf of the lookup class.
2231 * <p>
2232 * If the returned method handle is invoked, the field's class will
2233 * be initialized, if it has not already been initialized.
2234 * @param refc the class or interface from which the method is accessed
2235 * @param name the field's name
2236 * @param type the field's type
2237 * @return a method handle which can load values from the field
2238 * @throws NoSuchFieldException if the field does not exist
2239 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2240 * @exception SecurityException if a security manager is present and it
2241 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2242 * @throws NullPointerException if any argument is null
2243 */
2244 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2245 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
2246 return getDirectField(REF_getStatic, refc, field);
2247 }
2248
2249 /**
2250 * Produces a method handle giving write access to a static field.
2251 * The type of the method handle will have a void return type.
2252 * The method handle will take a single
2253 * argument, of the field's value type, the value to be stored.
2254 * Access checking is performed immediately on behalf of the lookup class.
2255 * <p>
2256 * If the returned method handle is invoked, the field's class will
2257 * be initialized, if it has not already been initialized.
2258 * @param refc the class or interface from which the method is accessed
2259 * @param name the field's name
2260 * @param type the field's type
2261 * @return a method handle which can store values into the field
2262 * @throws NoSuchFieldException if the field does not exist
2263 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2264 * or is {@code final}
2265 * @exception SecurityException if a security manager is present and it
2266 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2267 * @throws NullPointerException if any argument is null
2268 */
2269 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2270 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
2271 return getDirectField(REF_putStatic, refc, field);
2272 }
2273
2274 /**
2275 * Produces a VarHandle giving access to a static field {@code name} of
2276 * type {@code type} declared in a class of type {@code decl}.
2277 * The VarHandle's variable type is {@code type} and it has no
2278 * coordinate types.
2279 * <p>
2280 * Access checking is performed immediately on behalf of the lookup
2281 * class.
2282 * <p>
2283 * If the returned VarHandle is operated on, the declaring class will be
2284 * initialized, if it has not already been initialized.
2285 * <p>
2286 * Certain access modes of the returned VarHandle are unsupported under
2287 * the following conditions:
2288 * <ul>
2289 * <li>if the field is declared {@code final}, then the write, atomic
2290 * update, numeric atomic update, and bitwise atomic update access
2291 * modes are unsupported.
2292 * <li>if the field type is anything other than {@code byte},
2293 * {@code short}, {@code char}, {@code int}, {@code long},
2294 * {@code float}, or {@code double}, then numeric atomic update
2295 * access modes are unsupported.
2296 * <li>if the field type is anything other than {@code boolean},
2297 * {@code byte}, {@code short}, {@code char}, {@code int} or
2298 * {@code long} then bitwise atomic update access modes are
2299 * unsupported.
2300 * </ul>
2301 * <p>
2302 * If the field is declared {@code volatile} then the returned VarHandle
2303 * will override access to the field (effectively ignore the
2304 * {@code volatile} declaration) in accordance to its specified
2305 * access modes.
2306 * <p>
2307 * If the field type is {@code float} or {@code double} then numeric
2308 * and atomic update access modes compare values using their bitwise
2309 * representation (see {@link Float#floatToRawIntBits} and
2310 * {@link Double#doubleToRawLongBits}, respectively).
2311 * @apiNote
2312 * Bitwise comparison of {@code float} values or {@code double} values,
2313 * as performed by the numeric and atomic update access modes, differ
2314 * from the primitive {@code ==} operator and the {@link Float#equals}
2315 * and {@link Double#equals} methods, specifically with respect to
2316 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2317 * Care should be taken when performing a compare and set or a compare
2318 * and exchange operation with such values since the operation may
2319 * unexpectedly fail.
2320 * There are many possible NaN values that are considered to be
2321 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2322 * provided by Java can distinguish between them. Operation failure can
2323 * occur if the expected or witness value is a NaN value and it is
2324 * transformed (perhaps in a platform specific manner) into another NaN
2325 * value, and thus has a different bitwise representation (see
2326 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2327 * details).
2328 * The values {@code -0.0} and {@code +0.0} have different bitwise
2329 * representations but are considered equal when using the primitive
2330 * {@code ==} operator. Operation failure can occur if, for example, a
2331 * numeric algorithm computes an expected value to be say {@code -0.0}
2332 * and previously computed the witness value to be say {@code +0.0}.
2333 * @param decl the class that declares the static field
2334 * @param name the field's name
2335 * @param type the field's type, of type {@code T}
2336 * @return a VarHandle giving access to a static field
2337 * @throws NoSuchFieldException if the field does not exist
2338 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
2339 * @exception SecurityException if a security manager is present and it
2340 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2341 * @throws NullPointerException if any argument is null
2342 * @since 9
2343 */
2344 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2345 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
2346 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
2347 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
2348 }
2349
2350 /**
2351 * Produces an early-bound method handle for a non-static method.
2352 * The receiver must have a supertype {@code defc} in which a method
2353 * of the given name and type is accessible to the lookup class.
2354 * The method and all its argument types must be accessible to the lookup object.
2355 * The type of the method handle will be that of the method,
2356 * without any insertion of an additional receiver parameter.
2357 * The given receiver will be bound into the method handle,
2358 * so that every call to the method handle will invoke the
2359 * requested method on the given receiver.
2360 * <p>
2361 * The returned method handle will have
2362 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2363 * the method's variable arity modifier bit ({@code 0x0080}) is set
2364 * <em>and</em> the trailing array argument is not the only argument.
2365 * (If the trailing array argument is the only argument,
2366 * the given receiver value will be bound to it.)
2367 * <p>
2368 * This is almost equivalent to the following code, with some differences noted below:
2369 * <blockquote><pre>{@code
2370 import static java.lang.invoke.MethodHandles.*;
2371 import static java.lang.invoke.MethodType.*;
2372 ...
2373 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
2374 MethodHandle mh1 = mh0.bindTo(receiver);
2375 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
2376 return mh1;
2377 * }</pre></blockquote>
2378 * where {@code defc} is either {@code receiver.getClass()} or a super
2379 * type of that class, in which the requested method is accessible
2380 * to the lookup class.
2381 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
2382 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
2383 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
2384 * the receiver is restricted by {@code findVirtual} to the lookup class.)
2385 * @param receiver the object from which the method is accessed
2386 * @param name the name of the method
2387 * @param type the type of the method, with the receiver argument omitted
2388 * @return the desired method handle
2389 * @throws NoSuchMethodException if the method does not exist
2390 * @throws IllegalAccessException if access checking fails
2391 * or if the method's variable arity modifier bit
2392 * is set and {@code asVarargsCollector} fails
2393 * @exception SecurityException if a security manager is present and it
2394 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2395 * @throws NullPointerException if any argument is null
2396 * @see MethodHandle#bindTo
2397 * @see #findVirtual
2398 */
2399 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2400 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2401 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2402 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
2403 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2404 throw new IllegalAccessException("The restricted defining class " +
2405 mh.type().leadingReferenceParameter().getName() +
2406 " is not assignable from receiver class " +
2407 receiver.getClass().getName());
2408 }
2409 return mh.bindArgumentL(0, receiver).setVarargs(method);
2410 }
2411
2412 /**
2413 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2414 * to <i>m</i>, if the lookup class has permission.
2415 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2416 * If <i>m</i> is virtual, overriding is respected on every call.
2417 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2418 * The type of the method handle will be that of the method,
2419 * with the receiver type prepended (but only if it is non-static).
2420 * If the method's {@code accessible} flag is not set,
2421 * access checking is performed immediately on behalf of the lookup class.
2422 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2423 * <p>
2424 * The returned method handle will have
2425 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2426 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2427 * <p>
2428 * If <i>m</i> is static, and
2429 * if the returned method handle is invoked, the method's class will
2430 * be initialized, if it has not already been initialized.
2431 * @param m the reflected method
2432 * @return a method handle which can invoke the reflected method
2433 * @throws IllegalAccessException if access checking fails
2434 * or if the method's variable arity modifier bit
2435 * is set and {@code asVarargsCollector} fails
2436 * @throws NullPointerException if the argument is null
2437 */
2438 public MethodHandle unreflect(Method m) throws IllegalAccessException {
2439 if (m.getDeclaringClass() == MethodHandle.class) {
2440 MethodHandle mh = unreflectForMH(m);
2441 if (mh != null) return mh;
2442 }
2443 if (m.getDeclaringClass() == VarHandle.class) {
2444 MethodHandle mh = unreflectForVH(m);
2445 if (mh != null) return mh;
2446 }
2447 MemberName method = new MemberName(m);
2448 byte refKind = method.getReferenceKind();
2449 if (refKind == REF_invokeSpecial)
2450 refKind = REF_invokeVirtual;
2451 assert(method.isMethod());
2452 @SuppressWarnings("deprecation")
2453 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
2454 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
2455 }
2456 private MethodHandle unreflectForMH(Method m) {
2457 // these names require special lookups because they throw UnsupportedOperationException
2458 if (MemberName.isMethodHandleInvokeName(m.getName()))
2459 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
2460 return null;
2461 }
2462 private MethodHandle unreflectForVH(Method m) {
2463 // these names require special lookups because they throw UnsupportedOperationException
2464 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
2465 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
2466 return null;
2467 }
2468
2469 /**
2470 * Produces a method handle for a reflected method.
2471 * It will bypass checks for overriding methods on the receiver,
2472 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2473 * instruction from within the explicitly specified {@code specialCaller}.
2474 * The type of the method handle will be that of the method,
2475 * with a suitably restricted receiver type prepended.
2476 * (The receiver type will be {@code specialCaller} or a subtype.)
2477 * If the method's {@code accessible} flag is not set,
2478 * access checking is performed immediately on behalf of the lookup class,
2479 * as if {@code invokespecial} instruction were being linked.
2480 * <p>
2481 * Before method resolution,
2482 * if the explicitly specified caller class is not identical with the
2483 * lookup class, or if this lookup object does not have
2484 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2485 * privileges, the access fails.
2486 * <p>
2487 * The returned method handle will have
2488 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2489 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2490 * @param m the reflected method
2491 * @param specialCaller the class nominally calling the method
2492 * @return a method handle which can invoke the reflected method
2493 * @throws IllegalAccessException if access checking fails,
2494 * or if the method is {@code static},
2495 * or if the method's variable arity modifier bit
2496 * is set and {@code asVarargsCollector} fails
2497 * @throws NullPointerException if any argument is null
2498 */
2499 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
2500 checkSpecialCaller(specialCaller, null);
2501 Lookup specialLookup = this.in(specialCaller);
2502 MemberName method = new MemberName(m, true);
2503 assert(method.isMethod());
2504 // ignore m.isAccessible: this is a new kind of access
2505 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
2506 }
2507
2508 /**
2509 * Produces a method handle for a reflected constructor.
2510 * The type of the method handle will be that of the constructor,
2511 * with the return type changed to the declaring class.
2512 * The method handle will perform a {@code newInstance} operation,
2513 * creating a new instance of the constructor's class on the
2514 * arguments passed to the method handle.
2515 * <p>
2516 * If the constructor's {@code accessible} flag is not set,
2517 * access checking is performed immediately on behalf of the lookup class.
2518 * <p>
2519 * The returned method handle will have
2520 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2521 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2522 * <p>
2523 * If the returned method handle is invoked, the constructor's class will
2524 * be initialized, if it has not already been initialized.
2525 * @param c the reflected constructor
2526 * @return a method handle which can invoke the reflected constructor
2527 * @throws IllegalAccessException if access checking fails
2528 * or if the method's variable arity modifier bit
2529 * is set and {@code asVarargsCollector} fails
2530 * @throws NullPointerException if the argument is null
2531 */
2532 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
2533 MemberName ctor = new MemberName(c);
2534 assert(ctor.isConstructor());
2535 @SuppressWarnings("deprecation")
2536 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
2537 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
2538 }
2539
2540 /**
2541 * Produces a method handle giving read access to a reflected field.
2542 * The type of the method handle will have a return type of the field's
2543 * value type.
2544 * If the field is {@code static}, the method handle will take no arguments.
2545 * Otherwise, its single argument will be the instance containing
2546 * the field.
2547 * If the {@code Field} object's {@code accessible} flag is not set,
2548 * access checking is performed immediately on behalf of the lookup class.
2549 * <p>
2550 * If the field is static, and
2551 * if the returned method handle is invoked, the field's class will
2552 * be initialized, if it has not already been initialized.
2553 * @param f the reflected field
2554 * @return a method handle which can load values from the reflected field
2555 * @throws IllegalAccessException if access checking fails
2556 * @throws NullPointerException if the argument is null
2557 */
2558 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
2559 return unreflectField(f, false);
2560 }
2561
2562 /**
2563 * Produces a method handle giving write access to a reflected field.
2564 * The type of the method handle will have a void return type.
2565 * If the field is {@code static}, the method handle will take a single
2566 * argument, of the field's value type, the value to be stored.
2567 * Otherwise, the two arguments will be the instance containing
2568 * the field, and the value to be stored.
2569 * If the {@code Field} object's {@code accessible} flag is not set,
2570 * access checking is performed immediately on behalf of the lookup class.
2571 * <p>
2572 * If the field is {@code final}, write access will not be
2573 * allowed and access checking will fail, except under certain
2574 * narrow circumstances documented for {@link Field#set Field.set}.
2575 * A method handle is returned only if a corresponding call to
2576 * the {@code Field} object's {@code set} method could return
2577 * normally. In particular, fields which are both {@code static}
2578 * and {@code final} may never be set.
2579 * <p>
2580 * If the field is {@code static}, and
2581 * if the returned method handle is invoked, the field's class will
2582 * be initialized, if it has not already been initialized.
2583 * @param f the reflected field
2584 * @return a method handle which can store values into the reflected field
2585 * @throws IllegalAccessException if access checking fails,
2586 * or if the field is {@code final} and write access
2587 * is not enabled on the {@code Field} object
2588 * @throws NullPointerException if the argument is null
2589 */
2590 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
2591 return unreflectField(f, true);
2592 }
2593
2594 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
2595 MemberName field = new MemberName(f, isSetter);
2596 if (isSetter && field.isStatic() && field.isFinal())
2597 throw field.makeAccessException("static final field has no write access", this);
2598 assert(isSetter
2599 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
2600 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
2601 @SuppressWarnings("deprecation")
2602 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
2603 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
2604 }
2605
2606 /**
2607 * Produces a VarHandle giving access to a reflected field {@code f}
2608 * of type {@code T} declared in a class of type {@code R}.
2609 * The VarHandle's variable type is {@code T}.
2610 * If the field is non-static the VarHandle has one coordinate type,
2611 * {@code R}. Otherwise, the field is static, and the VarHandle has no
2612 * coordinate types.
2613 * <p>
2614 * Access checking is performed immediately on behalf of the lookup
2615 * class, regardless of the value of the field's {@code accessible}
2616 * flag.
2617 * <p>
2618 * If the field is static, and if the returned VarHandle is operated
2619 * on, the field's declaring class will be initialized, if it has not
2620 * already been initialized.
2621 * <p>
2622 * Certain access modes of the returned VarHandle are unsupported under
2623 * the following conditions:
2624 * <ul>
2625 * <li>if the field is declared {@code final}, then the write, atomic
2626 * update, numeric atomic update, and bitwise atomic update access
2627 * modes are unsupported.
2628 * <li>if the field type is anything other than {@code byte},
2629 * {@code short}, {@code char}, {@code int}, {@code long},
2630 * {@code float}, or {@code double} then numeric atomic update
2631 * access modes are unsupported.
2632 * <li>if the field type is anything other than {@code boolean},
2633 * {@code byte}, {@code short}, {@code char}, {@code int} or
2634 * {@code long} then bitwise atomic update access modes are
2635 * unsupported.
2636 * </ul>
2637 * <p>
2638 * If the field is declared {@code volatile} then the returned VarHandle
2639 * will override access to the field (effectively ignore the
2640 * {@code volatile} declaration) in accordance to its specified
2641 * access modes.
2642 * <p>
2643 * If the field type is {@code float} or {@code double} then numeric
2644 * and atomic update access modes compare values using their bitwise
2645 * representation (see {@link Float#floatToRawIntBits} and
2646 * {@link Double#doubleToRawLongBits}, respectively).
2647 * @apiNote
2648 * Bitwise comparison of {@code float} values or {@code double} values,
2649 * as performed by the numeric and atomic update access modes, differ
2650 * from the primitive {@code ==} operator and the {@link Float#equals}
2651 * and {@link Double#equals} methods, specifically with respect to
2652 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2653 * Care should be taken when performing a compare and set or a compare
2654 * and exchange operation with such values since the operation may
2655 * unexpectedly fail.
2656 * There are many possible NaN values that are considered to be
2657 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2658 * provided by Java can distinguish between them. Operation failure can
2659 * occur if the expected or witness value is a NaN value and it is
2660 * transformed (perhaps in a platform specific manner) into another NaN
2661 * value, and thus has a different bitwise representation (see
2662 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2663 * details).
2664 * The values {@code -0.0} and {@code +0.0} have different bitwise
2665 * representations but are considered equal when using the primitive
2666 * {@code ==} operator. Operation failure can occur if, for example, a
2667 * numeric algorithm computes an expected value to be say {@code -0.0}
2668 * and previously computed the witness value to be say {@code +0.0}.
2669 * @param f the reflected field, with a field of type {@code T}, and
2670 * a declaring class of type {@code R}
2671 * @return a VarHandle giving access to non-static fields or a static
2672 * field
2673 * @throws IllegalAccessException if access checking fails
2674 * @throws NullPointerException if the argument is null
2675 * @since 9
2676 */
2677 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
2678 MemberName getField = new MemberName(f, false);
2679 MemberName putField = new MemberName(f, true);
2680 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
2681 f.getDeclaringClass(), getField, putField);
2682 }
2683
2684 /**
2685 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2686 * created by this lookup object or a similar one.
2687 * Security and access checks are performed to ensure that this lookup object
2688 * is capable of reproducing the target method handle.
2689 * This means that the cracking may fail if target is a direct method handle
2690 * but was created by an unrelated lookup object.
2691 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
2692 * and was created by a lookup object for a different class.
2693 * @param target a direct method handle to crack into symbolic reference components
2694 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
2695 * @exception SecurityException if a security manager is present and it
2696 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2697 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
2698 * @exception NullPointerException if the target is {@code null}
2699 * @see MethodHandleInfo
2700 * @since 1.8
2701 */
2702 public MethodHandleInfo revealDirect(MethodHandle target) {
2703 MemberName member = target.internalMemberName();
2704 if (member == null || (!member.isResolved() &&
2705 !member.isMethodHandleInvoke() &&
2706 !member.isVarHandleMethodInvoke()))
2707 throw newIllegalArgumentException("not a direct method handle");
2708 Class<?> defc = member.getDeclaringClass();
2709 byte refKind = member.getReferenceKind();
2710 assert(MethodHandleNatives.refKindIsValid(refKind));
2711 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2712 // Devirtualized method invocation is usually formally virtual.
2713 // To avoid creating extra MemberName objects for this common case,
2714 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2715 refKind = REF_invokeVirtual;
2716 if (refKind == REF_invokeVirtual && defc.isInterface())
2717 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2718 refKind = REF_invokeInterface;
2719 // Check SM permissions and member access before cracking.
2720 try {
2721 checkAccess(refKind, defc, member);
2722 checkSecurityManager(defc, member);
2723 } catch (IllegalAccessException ex) {
2724 throw new IllegalArgumentException(ex);
2725 }
2726 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2727 Class<?> callerClass = target.internalCallerClass();
2728 if (!hasPrivateAccess() || callerClass != lookupClass())
2729 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2730 }
2731 // Produce the handle to the results.
2732 return new InfoFromMemberName(this, member, refKind);
2733 }
2734
2735 /// Helper methods, all package-private.
2736
2737 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2738 checkSymbolicClass(refc); // do this before attempting to resolve
2739 Objects.requireNonNull(name);
2740 Objects.requireNonNull(type);
2741 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2742 NoSuchFieldException.class);
2743 }
2744
2745 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2746 checkSymbolicClass(refc); // do this before attempting to resolve
2747 Objects.requireNonNull(name);
2748 Objects.requireNonNull(type);
2749 checkMethodName(refKind, name); // NPE check on name
2750 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2751 NoSuchMethodException.class);
2752 }
2753
2754 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2755 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2756 Objects.requireNonNull(member.getName());
2757 Objects.requireNonNull(member.getType());
2758 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2759 ReflectiveOperationException.class);
2760 }
2761
2762 MemberName resolveOrNull(byte refKind, MemberName member) {
2763 // do this before attempting to resolve
2764 if (!isClassAccessible(member.getDeclaringClass())) {
2765 return null;
2766 }
2767 Objects.requireNonNull(member.getName());
2768 Objects.requireNonNull(member.getType());
2769 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2770 }
2771
2772 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2773 if (!isClassAccessible(refc)) {
2774 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2775 }
2776 }
2777
2778 boolean isClassAccessible(Class<?> refc) {
2779 Objects.requireNonNull(refc);
2780 Class<?> caller = lookupClassOrNull();
2781 return caller == null || VerifyAccess.isClassAccessible(refc, caller, prevLookupClass, allowedModes);
2782 }
2783
2784 /** Check name for an illegal leading "<" character. */
2785 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2786 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2787 throw new NoSuchMethodException("illegal method name: "+name);
2788 }
2789
2790
2791 /**
2792 * Find my trustable caller class if m is a caller sensitive method.
2793 * If this lookup object has private access, then the caller class is the lookupClass.
2794 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2795 */
2796 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2797 Class<?> callerClass = null;
2798 if (MethodHandleNatives.isCallerSensitive(m)) {
2799 // Only lookups with private access are allowed to resolve caller-sensitive methods
2800 if (hasPrivateAccess()) {
2801 callerClass = lookupClass;
2802 } else {
2803 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2804 }
2805 }
2806 return callerClass;
2807 }
2808
2809 /**
2810 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2811 * @return {@code true} if this lookup has {@code PRIVATE} access.
2812 * @since 9
2813 */
2814 public boolean hasPrivateAccess() {
2815 return (allowedModes & PRIVATE) != 0;
2816 }
2817
2818 /**
2819 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2820 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2821 * If this lookup object has private access, then the caller class is the lookupClass.
2822 */
2823 void checkSecurityManager(Class<?> refc, MemberName m) {
2824 SecurityManager smgr = System.getSecurityManager();
2825 if (smgr == null) return;
2826 if (allowedModes == TRUSTED) return;
2827
2828 // Step 1:
2829 boolean fullPowerLookup = hasPrivateAccess();
2830 if (!fullPowerLookup ||
2831 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2832 ReflectUtil.checkPackageAccess(refc);
2833 }
2834
2835 if (m == null) { // findClass or accessClass
2836 // Step 2b:
2837 if (!fullPowerLookup) {
2838 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2839 }
2840 return;
2841 }
2842
2843 // Step 2a:
2844 if (m.isPublic()) return;
2845 if (!fullPowerLookup) {
2846 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2847 }
2848
2849 // Step 3:
2850 Class<?> defc = m.getDeclaringClass();
2851 if (!fullPowerLookup && defc != refc) {
2852 ReflectUtil.checkPackageAccess(defc);
2853 }
2854 }
2855
2856 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2857 boolean wantStatic = (refKind == REF_invokeStatic);
2858 String message;
2859 if (m.isConstructor())
2860 message = "expected a method, not a constructor";
2861 else if (!m.isMethod())
2862 message = "expected a method";
2863 else if (wantStatic != m.isStatic())
2864 message = wantStatic ? "expected a static method" : "expected a non-static method";
2865 else
2866 { checkAccess(refKind, refc, m); return; }
2867 throw m.makeAccessException(message, this);
2868 }
2869
2870 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2871 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2872 String message;
2873 if (wantStatic != m.isStatic())
2874 message = wantStatic ? "expected a static field" : "expected a non-static field";
2875 else
2876 { checkAccess(refKind, refc, m); return; }
2877 throw m.makeAccessException(message, this);
2878 }
2879
2880 /** Check public/protected/private bits on the symbolic reference class and its member. */
2881 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2882 assert(m.referenceKindIsConsistentWith(refKind) &&
2883 MethodHandleNatives.refKindIsValid(refKind) &&
2884 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2885 int allowedModes = this.allowedModes;
2886 if (allowedModes == TRUSTED) return;
2887 int mods = m.getModifiers();
2888 if (Modifier.isProtected(mods) &&
2889 refKind == REF_invokeVirtual &&
2890 m.getDeclaringClass() == Object.class &&
2891 m.getName().equals("clone") &&
2892 refc.isArray()) {
2893 // The JVM does this hack also.
2894 // (See ClassVerifier::verify_invoke_instructions
2895 // and LinkResolver::check_method_accessability.)
2896 // Because the JVM does not allow separate methods on array types,
2897 // there is no separate method for int[].clone.
2898 // All arrays simply inherit Object.clone.
2899 // But for access checking logic, we make Object.clone
2900 // (normally protected) appear to be public.
2901 // Later on, when the DirectMethodHandle is created,
2902 // its leading argument will be restricted to the
2903 // requested array type.
2904 // N.B. The return type is not adjusted, because
2905 // that is *not* the bytecode behavior.
2906 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2907 }
2908 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2909 // cannot "new" a protected ctor in a different package
2910 mods ^= Modifier.PROTECTED;
2911 }
2912 if (Modifier.isFinal(mods) &&
2913 MethodHandleNatives.refKindIsSetter(refKind))
2914 throw m.makeAccessException("unexpected set of a final field", this);
2915 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2916 if ((requestedModes & allowedModes) != 0) {
2917 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2918 mods, lookupClass(), previousLookupClass(), allowedModes))
2919 return;
2920 } else {
2921 // Protected members can also be checked as if they were package-private.
2922 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2923 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2924 return;
2925 }
2926 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2927 }
2928
2929 String accessFailedMessage(Class<?> refc, MemberName m) {
2930 Class<?> defc = m.getDeclaringClass();
2931 int mods = m.getModifiers();
2932 // check the class first:
2933 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2934 (defc == refc ||
2935 Modifier.isPublic(refc.getModifiers())));
2936 if (!classOK && (allowedModes & PACKAGE) != 0) {
2937 // ignore previous lookup class to check if default package access
2938 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
2939 (defc == refc ||
2940 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
2941 }
2942 if (!classOK)
2943 return "class is not public";
2944 if (Modifier.isPublic(mods))
2945 return "access to public member failed"; // (how?, module not readable?)
2946 if (Modifier.isPrivate(mods))
2947 return "member is private";
2948 if (Modifier.isProtected(mods))
2949 return "member is protected";
2950 return "member is private to package";
2951 }
2952
2953 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2954 int allowedModes = this.allowedModes;
2955 if (allowedModes == TRUSTED) return;
2956 if (!hasPrivateAccess()
2957 || (specialCaller != lookupClass()
2958 // ensure non-abstract methods in superinterfaces can be special-invoked
2959 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2960 throw new MemberName(specialCaller).
2961 makeAccessException("no private access for invokespecial", this);
2962 }
2963
2964 private boolean restrictProtectedReceiver(MemberName method) {
2965 // The accessing class only has the right to use a protected member
2966 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2967 if (!method.isProtected() || method.isStatic()
2968 || allowedModes == TRUSTED
2969 || method.getDeclaringClass() == lookupClass()
2970 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2971 return false;
2972 return true;
2973 }
2974 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2975 assert(!method.isStatic());
2976 // receiver type of mh is too wide; narrow to caller
2977 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2978 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2979 }
2980 MethodType rawType = mh.type();
2981 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2982 MethodType narrowType = rawType.changeParameterType(0, caller);
2983 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2984 assert(mh.viewAsTypeChecks(narrowType, true));
2985 return mh.copyWith(narrowType, mh.form);
2986 }
2987
2988 /** Check access and get the requested method. */
2989 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2990 final boolean doRestrict = true;
2991 final boolean checkSecurity = true;
2992 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2993 }
2994 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2995 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2996 final boolean doRestrict = false;
2997 final boolean checkSecurity = true;
2998 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2999 }
3000 /** Check access and get the requested method, eliding security manager checks. */
3001 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
3002 final boolean doRestrict = true;
3003 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3004 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
3005 }
3006 /** Common code for all methods; do not call directly except from immediately above. */
3007 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3008 boolean checkSecurity,
3009 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
3010
3011 checkMethod(refKind, refc, method);
3012 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3013 if (checkSecurity)
3014 checkSecurityManager(refc, method);
3015 assert(!method.isMethodHandleInvoke());
3016
3017 if (refKind == REF_invokeSpecial &&
3018 refc != lookupClass() &&
3019 !refc.isInterface() &&
3020 refc != lookupClass().getSuperclass() &&
3021 refc.isAssignableFrom(lookupClass())) {
3022 assert(!method.getName().equals("<init>")); // not this code path
3023
3024 // Per JVMS 6.5, desc. of invokespecial instruction:
3025 // If the method is in a superclass of the LC,
3026 // and if our original search was above LC.super,
3027 // repeat the search (symbolic lookup) from LC.super
3028 // and continue with the direct superclass of that class,
3029 // and so forth, until a match is found or no further superclasses exist.
3030 // FIXME: MemberName.resolve should handle this instead.
3031 Class<?> refcAsSuper = lookupClass();
3032 MemberName m2;
3033 do {
3034 refcAsSuper = refcAsSuper.getSuperclass();
3035 m2 = new MemberName(refcAsSuper,
3036 method.getName(),
3037 method.getMethodType(),
3038 REF_invokeSpecial);
3039 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
3040 } while (m2 == null && // no method is found yet
3041 refc != refcAsSuper); // search up to refc
3042 if (m2 == null) throw new InternalError(method.toString());
3043 method = m2;
3044 refc = refcAsSuper;
3045 // redo basic checks
3046 checkMethod(refKind, refc, method);
3047 }
3048
3049 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3050 MethodHandle mh = dmh;
3051 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3052 if ((doRestrict && refKind == REF_invokeSpecial) ||
3053 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
3054 mh = restrictReceiver(method, dmh, lookupClass());
3055 }
3056 mh = maybeBindCaller(method, mh, boundCallerClass);
3057 mh = mh.setVarargs(method);
3058 return mh;
3059 }
3060 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
3061 Class<?> boundCallerClass)
3062 throws IllegalAccessException {
3063 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3064 return mh;
3065 Class<?> hostClass = lookupClass;
3066 if (!hasPrivateAccess()) // caller must have private access
3067 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
3068 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
3069 // Note: caller will apply varargs after this step happens.
3070 return cbmh;
3071 }
3072 /** Check access and get the requested field. */
3073 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3074 final boolean checkSecurity = true;
3075 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3076 }
3077 /** Check access and get the requested field, eliding security manager checks. */
3078 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3079 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3080 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
3081 }
3082 /** Common code for all fields; do not call directly except from immediately above. */
3083 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
3084 boolean checkSecurity) throws IllegalAccessException {
3085 checkField(refKind, refc, field);
3086 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3087 if (checkSecurity)
3088 checkSecurityManager(refc, field);
3089 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3090 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3091 restrictProtectedReceiver(field));
3092 if (doRestrict)
3093 return restrictReceiver(field, dmh, lookupClass());
3094 return dmh;
3095 }
3096 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3097 Class<?> refc, MemberName getField, MemberName putField)
3098 throws IllegalAccessException {
3099 final boolean checkSecurity = true;
3100 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3101 }
3102 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
3103 Class<?> refc, MemberName getField, MemberName putField)
3104 throws IllegalAccessException {
3105 final boolean checkSecurity = false;
3106 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
3107 }
3108 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3109 Class<?> refc, MemberName getField, MemberName putField,
3110 boolean checkSecurity) throws IllegalAccessException {
3111 assert getField.isStatic() == putField.isStatic();
3112 assert getField.isGetter() && putField.isSetter();
3113 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3114 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3115
3116 checkField(getRefKind, refc, getField);
3117 if (checkSecurity)
3118 checkSecurityManager(refc, getField);
3119
3120 if (!putField.isFinal()) {
3121 // A VarHandle does not support updates to final fields, any
3122 // such VarHandle to a final field will be read-only and
3123 // therefore the following write-based accessibility checks are
3124 // only required for non-final fields
3125 checkField(putRefKind, refc, putField);
3126 if (checkSecurity)
3127 checkSecurityManager(refc, putField);
3128 }
3129
3130 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3131 restrictProtectedReceiver(getField));
3132 if (doRestrict) {
3133 assert !getField.isStatic();
3134 // receiver type of VarHandle is too wide; narrow to caller
3135 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3136 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3137 }
3138 refc = lookupClass();
3139 }
3140 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
3141 }
3142 /** Check access and get the requested constructor. */
3143 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3144 final boolean checkSecurity = true;
3145 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3146 }
3147 /** Check access and get the requested constructor, eliding security manager checks. */
3148 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3149 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3150 return getDirectConstructorCommon(refc, ctor, checkSecurity);
3151 }
3152 /** Common code for all constructors; do not call directly except from immediately above. */
3153 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
3154 boolean checkSecurity) throws IllegalAccessException {
3155 assert(ctor.isConstructor());
3156 checkAccess(REF_newInvokeSpecial, refc, ctor);
3157 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3158 if (checkSecurity)
3159 checkSecurityManager(refc, ctor);
3160 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3161 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3162 }
3163
3164 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3165 */
3166 /*non-public*/
3167 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
3168 if (!(type instanceof Class || type instanceof MethodType))
3169 throw new InternalError("unresolved MemberName");
3170 MemberName member = new MemberName(refKind, defc, name, type);
3171 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3172 if (mh != null) {
3173 checkSymbolicClass(defc);
3174 return mh;
3175 }
3176 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3177 // Treat MethodHandle.invoke and invokeExact specially.
3178 mh = findVirtualForMH(member.getName(), member.getMethodType());
3179 if (mh != null) {
3180 return mh;
3181 }
3182 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3183 // Treat signature-polymorphic methods on VarHandle specially.
3184 mh = findVirtualForVH(member.getName(), member.getMethodType());
3185 if (mh != null) {
3186 return mh;
3187 }
3188 }
3189 MemberName resolved = resolveOrFail(refKind, member);
3190 mh = getDirectMethodForConstant(refKind, defc, resolved);
3191 if (mh instanceof DirectMethodHandle
3192 && canBeCached(refKind, defc, resolved)) {
3193 MemberName key = mh.internalMemberName();
3194 if (key != null) {
3195 key = key.asNormalOriginal();
3196 }
3197 if (member.equals(key)) { // better safe than sorry
3198 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
3199 }
3200 }
3201 return mh;
3202 }
3203 private
3204 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
3205 if (refKind == REF_invokeSpecial) {
3206 return false;
3207 }
3208 if (!Modifier.isPublic(defc.getModifiers()) ||
3209 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
3210 !member.isPublic() ||
3211 member.isCallerSensitive()) {
3212 return false;
3213 }
3214 ClassLoader loader = defc.getClassLoader();
3215 if (loader != null) {
3216 ClassLoader sysl = ClassLoader.getSystemClassLoader();
3217 boolean found = false;
3218 while (sysl != null) {
3219 if (loader == sysl) { found = true; break; }
3220 sysl = sysl.getParent();
3221 }
3222 if (!found) {
3223 return false;
3224 }
3225 }
3226 try {
3227 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
3228 new MemberName(refKind, defc, member.getName(), member.getType()));
3229 if (resolved2 == null) {
3230 return false;
3231 }
3232 checkSecurityManager(defc, resolved2);
3233 } catch (SecurityException ex) {
3234 return false;
3235 }
3236 return true;
3237 }
3238 private
3239 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
3240 throws ReflectiveOperationException {
3241 if (MethodHandleNatives.refKindIsField(refKind)) {
3242 return getDirectFieldNoSecurityManager(refKind, defc, member);
3243 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
3244 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
3245 } else if (refKind == REF_newInvokeSpecial) {
3246 return getDirectConstructorNoSecurityManager(defc, member);
3247 }
3248 // oops
3249 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
3250 }
3251
3252 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
3253 }
3254
3255 /**
3256 * Produces a method handle constructing arrays of a desired type,
3257 * as if by the {@code anewarray} bytecode.
3258 * The return type of the method handle will be the array type.
3259 * The type of its sole argument will be {@code int}, which specifies the size of the array.
3260 *
3261 * <p> If the returned method handle is invoked with a negative
3262 * array size, a {@code NegativeArraySizeException} will be thrown.
3263 *
3264 * @param arrayClass an array type
3265 * @return a method handle which can create arrays of the given type
3266 * @throws NullPointerException if the argument is {@code null}
3267 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
3268 * @see java.lang.reflect.Array#newInstance(Class, int)
3269 * @jvms 6.5 {@code anewarray} Instruction
3270 * @since 9
3271 */
3272 public static
3273 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
3274 if (!arrayClass.isArray()) {
3275 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
3276 }
3277 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
3278 bindTo(arrayClass.getComponentType());
3279 return ani.asType(ani.type().changeReturnType(arrayClass));
3280 }
3281
3282 /**
3283 * Produces a method handle returning the length of an array,
3284 * as if by the {@code arraylength} bytecode.
3285 * The type of the method handle will have {@code int} as return type,
3286 * and its sole argument will be the array type.
3287 *
3288 * <p> If the returned method handle is invoked with a {@code null}
3289 * array reference, a {@code NullPointerException} will be thrown.
3290 *
3291 * @param arrayClass an array type
3292 * @return a method handle which can retrieve the length of an array of the given array type
3293 * @throws NullPointerException if the argument is {@code null}
3294 * @throws IllegalArgumentException if arrayClass is not an array type
3295 * @jvms 6.5 {@code arraylength} Instruction
3296 * @since 9
3297 */
3298 public static
3299 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
3300 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
3301 }
3302
3303 /**
3304 * Produces a method handle giving read access to elements of an array,
3305 * as if by the {@code aaload} bytecode.
3306 * The type of the method handle will have a return type of the array's
3307 * element type. Its first argument will be the array type,
3308 * and the second will be {@code int}.
3309 *
3310 * <p> When the returned method handle is invoked,
3311 * the array reference and array index are checked.
3312 * A {@code NullPointerException} will be thrown if the array reference
3313 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3314 * thrown if the index is negative or if it is greater than or equal to
3315 * the length of the array.
3316 *
3317 * @param arrayClass an array type
3318 * @return a method handle which can load values from the given array type
3319 * @throws NullPointerException if the argument is null
3320 * @throws IllegalArgumentException if arrayClass is not an array type
3321 * @jvms 6.5 {@code aaload} Instruction
3322 */
3323 public static
3324 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
3325 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
3326 }
3327
3328 /**
3329 * Produces a method handle giving write access to elements of an array,
3330 * as if by the {@code astore} bytecode.
3331 * The type of the method handle will have a void return type.
3332 * Its last argument will be the array's element type.
3333 * The first and second arguments will be the array type and int.
3334 *
3335 * <p> When the returned method handle is invoked,
3336 * the array reference and array index are checked.
3337 * A {@code NullPointerException} will be thrown if the array reference
3338 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3339 * thrown if the index is negative or if it is greater than or equal to
3340 * the length of the array.
3341 *
3342 * @param arrayClass the class of an array
3343 * @return a method handle which can store values into the array type
3344 * @throws NullPointerException if the argument is null
3345 * @throws IllegalArgumentException if arrayClass is not an array type
3346 * @jvms 6.5 {@code aastore} Instruction
3347 */
3348 public static
3349 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
3350 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
3351 }
3352
3353 /**
3354 * Produces a VarHandle giving access to elements of an array of type
3355 * {@code arrayClass}. The VarHandle's variable type is the component type
3356 * of {@code arrayClass} and the list of coordinate types is
3357 * {@code (arrayClass, int)}, where the {@code int} coordinate type
3358 * corresponds to an argument that is an index into an array.
3359 * <p>
3360 * Certain access modes of the returned VarHandle are unsupported under
3361 * the following conditions:
3362 * <ul>
3363 * <li>if the component type is anything other than {@code byte},
3364 * {@code short}, {@code char}, {@code int}, {@code long},
3365 * {@code float}, or {@code double} then numeric atomic update access
3366 * modes are unsupported.
3367 * <li>if the field type is anything other than {@code boolean},
3368 * {@code byte}, {@code short}, {@code char}, {@code int} or
3369 * {@code long} then bitwise atomic update access modes are
3370 * unsupported.
3371 * </ul>
3372 * <p>
3373 * If the component type is {@code float} or {@code double} then numeric
3374 * and atomic update access modes compare values using their bitwise
3375 * representation (see {@link Float#floatToRawIntBits} and
3376 * {@link Double#doubleToRawLongBits}, respectively).
3377 *
3378 * <p> When the returned {@code VarHandle} is invoked,
3379 * the array reference and array index are checked.
3380 * A {@code NullPointerException} will be thrown if the array reference
3381 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3382 * thrown if the index is negative or if it is greater than or equal to
3383 * the length of the array.
3384 *
3385 * @apiNote
3386 * Bitwise comparison of {@code float} values or {@code double} values,
3387 * as performed by the numeric and atomic update access modes, differ
3388 * from the primitive {@code ==} operator and the {@link Float#equals}
3389 * and {@link Double#equals} methods, specifically with respect to
3390 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3391 * Care should be taken when performing a compare and set or a compare
3392 * and exchange operation with such values since the operation may
3393 * unexpectedly fail.
3394 * There are many possible NaN values that are considered to be
3395 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3396 * provided by Java can distinguish between them. Operation failure can
3397 * occur if the expected or witness value is a NaN value and it is
3398 * transformed (perhaps in a platform specific manner) into another NaN
3399 * value, and thus has a different bitwise representation (see
3400 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3401 * details).
3402 * The values {@code -0.0} and {@code +0.0} have different bitwise
3403 * representations but are considered equal when using the primitive
3404 * {@code ==} operator. Operation failure can occur if, for example, a
3405 * numeric algorithm computes an expected value to be say {@code -0.0}
3406 * and previously computed the witness value to be say {@code +0.0}.
3407 * @param arrayClass the class of an array, of type {@code T[]}
3408 * @return a VarHandle giving access to elements of an array
3409 * @throws NullPointerException if the arrayClass is null
3410 * @throws IllegalArgumentException if arrayClass is not an array type
3411 * @since 9
3412 */
3413 public static
3414 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
3415 return VarHandles.makeArrayElementHandle(arrayClass);
3416 }
3417
3418 /**
3419 * Produces a VarHandle giving access to elements of a {@code byte[]} array
3420 * viewed as if it were a different primitive array type, such as
3421 * {@code int[]} or {@code long[]}.
3422 * The VarHandle's variable type is the component type of
3423 * {@code viewArrayClass} and the list of coordinate types is
3424 * {@code (byte[], int)}, where the {@code int} coordinate type
3425 * corresponds to an argument that is an index into a {@code byte[]} array.
3426 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
3427 * array, composing bytes to or from a value of the component type of
3428 * {@code viewArrayClass} according to the given endianness.
3429 * <p>
3430 * The supported component types (variables types) are {@code short},
3431 * {@code char}, {@code int}, {@code long}, {@code float} and
3432 * {@code double}.
3433 * <p>
3434 * Access of bytes at a given index will result in an
3435 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3436 * or greater than the {@code byte[]} array length minus the size (in bytes)
3437 * of {@code T}.
3438 * <p>
3439 * Access of bytes at an index may be aligned or misaligned for {@code T},
3440 * with respect to the underlying memory address, {@code A} say, associated
3441 * with the array and index.
3442 * If access is misaligned then access for anything other than the
3443 * {@code get} and {@code set} access modes will result in an
3444 * {@code IllegalStateException}. In such cases atomic access is only
3445 * guaranteed with respect to the largest power of two that divides the GCD
3446 * of {@code A} and the size (in bytes) of {@code T}.
3447 * If access is aligned then following access modes are supported and are
3448 * guaranteed to support atomic access:
3449 * <ul>
3450 * <li>read write access modes for all {@code T}, with the exception of
3451 * access modes {@code get} and {@code set} for {@code long} and
3452 * {@code double} on 32-bit platforms.
3453 * <li>atomic update access modes for {@code int}, {@code long},
3454 * {@code float} or {@code double}.
3455 * (Future major platform releases of the JDK may support additional
3456 * types for certain currently unsupported access modes.)
3457 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3458 * (Future major platform releases of the JDK may support additional
3459 * numeric types for certain currently unsupported access modes.)
3460 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3461 * (Future major platform releases of the JDK may support additional
3462 * numeric types for certain currently unsupported access modes.)
3463 * </ul>
3464 * <p>
3465 * Misaligned access, and therefore atomicity guarantees, may be determined
3466 * for {@code byte[]} arrays without operating on a specific array. Given
3467 * an {@code index}, {@code T} and it's corresponding boxed type,
3468 * {@code T_BOX}, misalignment may be determined as follows:
3469 * <pre>{@code
3470 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3471 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
3472 * alignmentOffset(0, sizeOfT);
3473 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
3474 * boolean isMisaligned = misalignedAtIndex != 0;
3475 * }</pre>
3476 * <p>
3477 * If the variable type is {@code float} or {@code double} then atomic
3478 * update access modes compare values using their bitwise representation
3479 * (see {@link Float#floatToRawIntBits} and
3480 * {@link Double#doubleToRawLongBits}, respectively).
3481 * @param viewArrayClass the view array class, with a component type of
3482 * type {@code T}
3483 * @param byteOrder the endianness of the view array elements, as
3484 * stored in the underlying {@code byte} array
3485 * @return a VarHandle giving access to elements of a {@code byte[]} array
3486 * viewed as if elements corresponding to the components type of the view
3487 * array class
3488 * @throws NullPointerException if viewArrayClass or byteOrder is null
3489 * @throws IllegalArgumentException if viewArrayClass is not an array type
3490 * @throws UnsupportedOperationException if the component type of
3491 * viewArrayClass is not supported as a variable type
3492 * @since 9
3493 */
3494 public static
3495 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
3496 ByteOrder byteOrder) throws IllegalArgumentException {
3497 Objects.requireNonNull(byteOrder);
3498 return VarHandles.byteArrayViewHandle(viewArrayClass,
3499 byteOrder == ByteOrder.BIG_ENDIAN);
3500 }
3501
3502 /**
3503 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
3504 * viewed as if it were an array of elements of a different primitive
3505 * component type to that of {@code byte}, such as {@code int[]} or
3506 * {@code long[]}.
3507 * The VarHandle's variable type is the component type of
3508 * {@code viewArrayClass} and the list of coordinate types is
3509 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
3510 * corresponds to an argument that is an index into a {@code byte[]} array.
3511 * The returned VarHandle accesses bytes at an index in a
3512 * {@code ByteBuffer}, composing bytes to or from a value of the component
3513 * type of {@code viewArrayClass} according to the given endianness.
3514 * <p>
3515 * The supported component types (variables types) are {@code short},
3516 * {@code char}, {@code int}, {@code long}, {@code float} and
3517 * {@code double}.
3518 * <p>
3519 * Access will result in a {@code ReadOnlyBufferException} for anything
3520 * other than the read access modes if the {@code ByteBuffer} is read-only.
3521 * <p>
3522 * Access of bytes at a given index will result in an
3523 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3524 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
3525 * {@code T}.
3526 * <p>
3527 * Access of bytes at an index may be aligned or misaligned for {@code T},
3528 * with respect to the underlying memory address, {@code A} say, associated
3529 * with the {@code ByteBuffer} and index.
3530 * If access is misaligned then access for anything other than the
3531 * {@code get} and {@code set} access modes will result in an
3532 * {@code IllegalStateException}. In such cases atomic access is only
3533 * guaranteed with respect to the largest power of two that divides the GCD
3534 * of {@code A} and the size (in bytes) of {@code T}.
3535 * If access is aligned then following access modes are supported and are
3536 * guaranteed to support atomic access:
3537 * <ul>
3538 * <li>read write access modes for all {@code T}, with the exception of
3539 * access modes {@code get} and {@code set} for {@code long} and
3540 * {@code double} on 32-bit platforms.
3541 * <li>atomic update access modes for {@code int}, {@code long},
3542 * {@code float} or {@code double}.
3543 * (Future major platform releases of the JDK may support additional
3544 * types for certain currently unsupported access modes.)
3545 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3546 * (Future major platform releases of the JDK may support additional
3547 * numeric types for certain currently unsupported access modes.)
3548 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3549 * (Future major platform releases of the JDK may support additional
3550 * numeric types for certain currently unsupported access modes.)
3551 * </ul>
3552 * <p>
3553 * Misaligned access, and therefore atomicity guarantees, may be determined
3554 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
3555 * {@code index}, {@code T} and it's corresponding boxed type,
3556 * {@code T_BOX}, as follows:
3557 * <pre>{@code
3558 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3559 * ByteBuffer bb = ...
3560 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
3561 * boolean isMisaligned = misalignedAtIndex != 0;
3562 * }</pre>
3563 * <p>
3564 * If the variable type is {@code float} or {@code double} then atomic
3565 * update access modes compare values using their bitwise representation
3566 * (see {@link Float#floatToRawIntBits} and
3567 * {@link Double#doubleToRawLongBits}, respectively).
3568 * @param viewArrayClass the view array class, with a component type of
3569 * type {@code T}
3570 * @param byteOrder the endianness of the view array elements, as
3571 * stored in the underlying {@code ByteBuffer} (Note this overrides the
3572 * endianness of a {@code ByteBuffer})
3573 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
3574 * viewed as if elements corresponding to the components type of the view
3575 * array class
3576 * @throws NullPointerException if viewArrayClass or byteOrder is null
3577 * @throws IllegalArgumentException if viewArrayClass is not an array type
3578 * @throws UnsupportedOperationException if the component type of
3579 * viewArrayClass is not supported as a variable type
3580 * @since 9
3581 */
3582 public static
3583 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
3584 ByteOrder byteOrder) throws IllegalArgumentException {
3585 Objects.requireNonNull(byteOrder);
3586 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
3587 byteOrder == ByteOrder.BIG_ENDIAN);
3588 }
3589
3590
3591 /// method handle invocation (reflective style)
3592
3593 /**
3594 * Produces a method handle which will invoke any method handle of the
3595 * given {@code type}, with a given number of trailing arguments replaced by
3596 * a single trailing {@code Object[]} array.
3597 * The resulting invoker will be a method handle with the following
3598 * arguments:
3599 * <ul>
3600 * <li>a single {@code MethodHandle} target
3601 * <li>zero or more leading values (counted by {@code leadingArgCount})
3602 * <li>an {@code Object[]} array containing trailing arguments
3603 * </ul>
3604 * <p>
3605 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
3606 * the indicated {@code type}.
3607 * That is, if the target is exactly of the given {@code type}, it will behave
3608 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
3609 * is used to convert the target to the required {@code type}.
3610 * <p>
3611 * The type of the returned invoker will not be the given {@code type}, but rather
3612 * will have all parameters except the first {@code leadingArgCount}
3613 * replaced by a single array of type {@code Object[]}, which will be
3614 * the final parameter.
3615 * <p>
3616 * Before invoking its target, the invoker will spread the final array, apply
3617 * reference casts as necessary, and unbox and widen primitive arguments.
3618 * If, when the invoker is called, the supplied array argument does
3619 * not have the correct number of elements, the invoker will throw
3620 * an {@link IllegalArgumentException} instead of invoking the target.
3621 * <p>
3622 * This method is equivalent to the following code (though it may be more efficient):
3623 * <blockquote><pre>{@code
3624 MethodHandle invoker = MethodHandles.invoker(type);
3625 int spreadArgCount = type.parameterCount() - leadingArgCount;
3626 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
3627 return invoker;
3628 * }</pre></blockquote>
3629 * This method throws no reflective or security exceptions.
3630 * @param type the desired target type
3631 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
3632 * @return a method handle suitable for invoking any method handle of the given type
3633 * @throws NullPointerException if {@code type} is null
3634 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
3635 * the range from 0 to {@code type.parameterCount()} inclusive,
3636 * or if the resulting method handle's type would have
3637 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3638 */
3639 public static
3640 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
3641 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
3642 throw newIllegalArgumentException("bad argument count", leadingArgCount);
3643 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
3644 return type.invokers().spreadInvoker(leadingArgCount);
3645 }
3646
3647 /**
3648 * Produces a special <em>invoker method handle</em> which can be used to
3649 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
3650 * The resulting invoker will have a type which is
3651 * exactly equal to the desired type, except that it will accept
3652 * an additional leading argument of type {@code MethodHandle}.
3653 * <p>
3654 * This method is equivalent to the following code (though it may be more efficient):
3655 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
3656 *
3657 * <p style="font-size:smaller;">
3658 * <em>Discussion:</em>
3659 * Invoker method handles can be useful when working with variable method handles
3660 * of unknown types.
3661 * For example, to emulate an {@code invokeExact} call to a variable method
3662 * handle {@code M}, extract its type {@code T},
3663 * look up the invoker method {@code X} for {@code T},
3664 * and call the invoker method, as {@code X.invoke(T, A...)}.
3665 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
3666 * is unknown.)
3667 * If spreading, collecting, or other argument transformations are required,
3668 * they can be applied once to the invoker {@code X} and reused on many {@code M}
3669 * method handle values, as long as they are compatible with the type of {@code X}.
3670 * <p style="font-size:smaller;">
3671 * <em>(Note: The invoker method is not available via the Core Reflection API.
3672 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3673 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3674 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3675 * <p>
3676 * This method throws no reflective or security exceptions.
3677 * @param type the desired target type
3678 * @return a method handle suitable for invoking any method handle of the given type
3679 * @throws IllegalArgumentException if the resulting method handle's type would have
3680 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3681 */
3682 public static
3683 MethodHandle exactInvoker(MethodType type) {
3684 return type.invokers().exactInvoker();
3685 }
3686
3687 /**
3688 * Produces a special <em>invoker method handle</em> which can be used to
3689 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
3690 * The resulting invoker will have a type which is
3691 * exactly equal to the desired type, except that it will accept
3692 * an additional leading argument of type {@code MethodHandle}.
3693 * <p>
3694 * Before invoking its target, if the target differs from the expected type,
3695 * the invoker will apply reference casts as
3696 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
3697 * Similarly, the return value will be converted as necessary.
3698 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
3699 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
3700 * <p>
3701 * This method is equivalent to the following code (though it may be more efficient):
3702 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
3703 * <p style="font-size:smaller;">
3704 * <em>Discussion:</em>
3705 * A {@linkplain MethodType#genericMethodType general method type} is one which
3706 * mentions only {@code Object} arguments and return values.
3707 * An invoker for such a type is capable of calling any method handle
3708 * of the same arity as the general type.
3709 * <p style="font-size:smaller;">
3710 * <em>(Note: The invoker method is not available via the Core Reflection API.
3711 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3712 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3713 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3714 * <p>
3715 * This method throws no reflective or security exceptions.
3716 * @param type the desired target type
3717 * @return a method handle suitable for invoking any method handle convertible to the given type
3718 * @throws IllegalArgumentException if the resulting method handle's type would have
3719 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3720 */
3721 public static
3722 MethodHandle invoker(MethodType type) {
3723 return type.invokers().genericInvoker();
3724 }
3725
3726 /**
3727 * Produces a special <em>invoker method handle</em> which can be used to
3728 * invoke a signature-polymorphic access mode method on any VarHandle whose
3729 * associated access mode type is compatible with the given type.
3730 * The resulting invoker will have a type which is exactly equal to the
3731 * desired given type, except that it will accept an additional leading
3732 * argument of type {@code VarHandle}.
3733 *
3734 * @param accessMode the VarHandle access mode
3735 * @param type the desired target type
3736 * @return a method handle suitable for invoking an access mode method of
3737 * any VarHandle whose access mode type is of the given type.
3738 * @since 9
3739 */
3740 static public
3741 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3742 return type.invokers().varHandleMethodExactInvoker(accessMode);
3743 }
3744
3745 /**
3746 * Produces a special <em>invoker method handle</em> which can be used to
3747 * invoke a signature-polymorphic access mode method on any VarHandle whose
3748 * associated access mode type is compatible with the given type.
3749 * The resulting invoker will have a type which is exactly equal to the
3750 * desired given type, except that it will accept an additional leading
3751 * argument of type {@code VarHandle}.
3752 * <p>
3753 * Before invoking its target, if the access mode type differs from the
3754 * desired given type, the invoker will apply reference casts as necessary
3755 * and box, unbox, or widen primitive values, as if by
3756 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3757 * converted as necessary.
3758 * <p>
3759 * This method is equivalent to the following code (though it may be more
3760 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3761 *
3762 * @param accessMode the VarHandle access mode
3763 * @param type the desired target type
3764 * @return a method handle suitable for invoking an access mode method of
3765 * any VarHandle whose access mode type is convertible to the given
3766 * type.
3767 * @since 9
3768 */
3769 static public
3770 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3771 return type.invokers().varHandleMethodInvoker(accessMode);
3772 }
3773
3774 static /*non-public*/
3775 MethodHandle basicInvoker(MethodType type) {
3776 return type.invokers().basicInvoker();
3777 }
3778
3779 /// method handle modification (creation from other method handles)
3780
3781 /**
3782 * Produces a method handle which adapts the type of the
3783 * given method handle to a new type by pairwise argument and return type conversion.
3784 * The original type and new type must have the same number of arguments.
3785 * The resulting method handle is guaranteed to report a type
3786 * which is equal to the desired new type.
3787 * <p>
3788 * If the original type and new type are equal, returns target.
3789 * <p>
3790 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3791 * and some additional conversions are also applied if those conversions fail.
3792 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3793 * if possible, before or instead of any conversions done by {@code asType}:
3794 * <ul>
3795 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3796 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3797 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3798 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3799 * the boolean is converted to a byte value, 1 for true, 0 for false.
3800 * (This treatment follows the usage of the bytecode verifier.)
3801 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3802 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3803 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3804 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3805 * then a Java casting conversion (JLS 5.5) is applied.
3806 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3807 * widening and/or narrowing.)
3808 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3809 * conversion will be applied at runtime, possibly followed
3810 * by a Java casting conversion (JLS 5.5) on the primitive value,
3811 * possibly followed by a conversion from byte to boolean by testing
3812 * the low-order bit.
3813 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3814 * and if the reference is null at runtime, a zero value is introduced.
3815 * </ul>
3816 * @param target the method handle to invoke after arguments are retyped
3817 * @param newType the expected type of the new method handle
3818 * @return a method handle which delegates to the target after performing
3819 * any necessary argument conversions, and arranges for any
3820 * necessary return value conversions
3821 * @throws NullPointerException if either argument is null
3822 * @throws WrongMethodTypeException if the conversion cannot be made
3823 * @see MethodHandle#asType
3824 */
3825 public static
3826 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3827 explicitCastArgumentsChecks(target, newType);
3828 // use the asTypeCache when possible:
3829 MethodType oldType = target.type();
3830 if (oldType == newType) return target;
3831 if (oldType.explicitCastEquivalentToAsType(newType)) {
3832 return target.asFixedArity().asType(newType);
3833 }
3834 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3835 }
3836
3837 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3838 if (target.type().parameterCount() != newType.parameterCount()) {
3839 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3840 }
3841 }
3842
3843 /**
3844 * Produces a method handle which adapts the calling sequence of the
3845 * given method handle to a new type, by reordering the arguments.
3846 * The resulting method handle is guaranteed to report a type
3847 * which is equal to the desired new type.
3848 * <p>
3849 * The given array controls the reordering.
3850 * Call {@code #I} the number of incoming parameters (the value
3851 * {@code newType.parameterCount()}, and call {@code #O} the number
3852 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3853 * Then the length of the reordering array must be {@code #O},
3854 * and each element must be a non-negative number less than {@code #I}.
3855 * For every {@code N} less than {@code #O}, the {@code N}-th
3856 * outgoing argument will be taken from the {@code I}-th incoming
3857 * argument, where {@code I} is {@code reorder[N]}.
3858 * <p>
3859 * No argument or return value conversions are applied.
3860 * The type of each incoming argument, as determined by {@code newType},
3861 * must be identical to the type of the corresponding outgoing parameter
3862 * or parameters in the target method handle.
3863 * The return type of {@code newType} must be identical to the return
3864 * type of the original target.
3865 * <p>
3866 * The reordering array need not specify an actual permutation.
3867 * An incoming argument will be duplicated if its index appears
3868 * more than once in the array, and an incoming argument will be dropped
3869 * if its index does not appear in the array.
3870 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3871 * incoming arguments which are not mentioned in the reordering array
3872 * may be of any type, as determined only by {@code newType}.
3873 * <blockquote><pre>{@code
3874 import static java.lang.invoke.MethodHandles.*;
3875 import static java.lang.invoke.MethodType.*;
3876 ...
3877 MethodType intfn1 = methodType(int.class, int.class);
3878 MethodType intfn2 = methodType(int.class, int.class, int.class);
3879 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3880 assert(sub.type().equals(intfn2));
3881 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3882 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3883 assert((int)rsub.invokeExact(1, 100) == 99);
3884 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3885 assert(add.type().equals(intfn2));
3886 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3887 assert(twice.type().equals(intfn1));
3888 assert((int)twice.invokeExact(21) == 42);
3889 * }</pre></blockquote>
3890 * <p>
3891 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3892 * variable-arity method handle}, even if the original target method handle was.
3893 * @param target the method handle to invoke after arguments are reordered
3894 * @param newType the expected type of the new method handle
3895 * @param reorder an index array which controls the reordering
3896 * @return a method handle which delegates to the target after it
3897 * drops unused arguments and moves and/or duplicates the other arguments
3898 * @throws NullPointerException if any argument is null
3899 * @throws IllegalArgumentException if the index array length is not equal to
3900 * the arity of the target, or if any index array element
3901 * not a valid index for a parameter of {@code newType},
3902 * or if two corresponding parameter types in
3903 * {@code target.type()} and {@code newType} are not identical,
3904 */
3905 public static
3906 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3907 reorder = reorder.clone(); // get a private copy
3908 MethodType oldType = target.type();
3909 permuteArgumentChecks(reorder, newType, oldType);
3910 // first detect dropped arguments and handle them separately
3911 int[] originalReorder = reorder;
3912 BoundMethodHandle result = target.rebind();
3913 LambdaForm form = result.form;
3914 int newArity = newType.parameterCount();
3915 // Normalize the reordering into a real permutation,
3916 // by removing duplicates and adding dropped elements.
3917 // This somewhat improves lambda form caching, as well
3918 // as simplifying the transform by breaking it up into steps.
3919 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3920 if (ddIdx > 0) {
3921 // We found a duplicated entry at reorder[ddIdx].
3922 // Example: (x,y,z)->asList(x,y,z)
3923 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3924 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3925 // The starred element corresponds to the argument
3926 // deleted by the dupArgumentForm transform.
3927 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3928 boolean killFirst = false;
3929 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3930 // Set killFirst if the dup is larger than an intervening position.
3931 // This will remove at least one inversion from the permutation.
3932 if (dupVal > val) killFirst = true;
3933 }
3934 if (!killFirst) {
3935 srcPos = dstPos;
3936 dstPos = ddIdx;
3937 }
3938 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3939 assert (reorder[srcPos] == reorder[dstPos]);
3940 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3941 // contract the reordering by removing the element at dstPos
3942 int tailPos = dstPos + 1;
3943 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3944 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3945 } else {
3946 int dropVal = ~ddIdx, insPos = 0;
3947 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3948 // Find first element of reorder larger than dropVal.
3949 // This is where we will insert the dropVal.
3950 insPos += 1;
3951 }
3952 Class<?> ptype = newType.parameterType(dropVal);
3953 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3954 oldType = oldType.insertParameterTypes(insPos, ptype);
3955 // expand the reordering by inserting an element at insPos
3956 int tailPos = insPos + 1;
3957 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3958 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3959 reorder[insPos] = dropVal;
3960 }
3961 assert (permuteArgumentChecks(reorder, newType, oldType));
3962 }
3963 assert (reorder.length == newArity); // a perfect permutation
3964 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3965 form = form.editor().permuteArgumentsForm(1, reorder);
3966 if (newType == result.type() && form == result.internalForm())
3967 return result;
3968 return result.copyWith(newType, form);
3969 }
3970
3971 /**
3972 * Return an indication of any duplicate or omission in reorder.
3973 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3974 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3975 * Otherwise, return zero.
3976 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3977 */
3978 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3979 final int BIT_LIMIT = 63; // max number of bits in bit mask
3980 if (newArity < BIT_LIMIT) {
3981 long mask = 0;
3982 for (int i = 0; i < reorder.length; i++) {
3983 int arg = reorder[i];
3984 if (arg >= newArity) {
3985 return reorder.length;
3986 }
3987 long bit = 1L << arg;
3988 if ((mask & bit) != 0) {
3989 return i; // >0 indicates a dup
3990 }
3991 mask |= bit;
3992 }
3993 if (mask == (1L << newArity) - 1) {
3994 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3995 return 0;
3996 }
3997 // find first zero
3998 long zeroBit = Long.lowestOneBit(~mask);
3999 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4000 assert(zeroPos <= newArity);
4001 if (zeroPos == newArity) {
4002 return 0;
4003 }
4004 return ~zeroPos;
4005 } else {
4006 // same algorithm, different bit set
4007 BitSet mask = new BitSet(newArity);
4008 for (int i = 0; i < reorder.length; i++) {
4009 int arg = reorder[i];
4010 if (arg >= newArity) {
4011 return reorder.length;
4012 }
4013 if (mask.get(arg)) {
4014 return i; // >0 indicates a dup
4015 }
4016 mask.set(arg);
4017 }
4018 int zeroPos = mask.nextClearBit(0);
4019 assert(zeroPos <= newArity);
4020 if (zeroPos == newArity) {
4021 return 0;
4022 }
4023 return ~zeroPos;
4024 }
4025 }
4026
4027 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4028 if (newType.returnType() != oldType.returnType())
4029 throw newIllegalArgumentException("return types do not match",
4030 oldType, newType);
4031 if (reorder.length == oldType.parameterCount()) {
4032 int limit = newType.parameterCount();
4033 boolean bad = false;
4034 for (int j = 0; j < reorder.length; j++) {
4035 int i = reorder[j];
4036 if (i < 0 || i >= limit) {
4037 bad = true; break;
4038 }
4039 Class<?> src = newType.parameterType(i);
4040 Class<?> dst = oldType.parameterType(j);
4041 if (src != dst)
4042 throw newIllegalArgumentException("parameter types do not match after reorder",
4043 oldType, newType);
4044 }
4045 if (!bad) return true;
4046 }
4047 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
4048 }
4049
4050 /**
4051 * Produces a method handle of the requested return type which returns the given
4052 * constant value every time it is invoked.
4053 * <p>
4054 * Before the method handle is returned, the passed-in value is converted to the requested type.
4055 * If the requested type is primitive, widening primitive conversions are attempted,
4056 * else reference conversions are attempted.
4057 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4058 * @param type the return type of the desired method handle
4059 * @param value the value to return
4060 * @return a method handle of the given return type and no arguments, which always returns the given value
4061 * @throws NullPointerException if the {@code type} argument is null
4062 * @throws ClassCastException if the value cannot be converted to the required return type
4063 * @throws IllegalArgumentException if the given type is {@code void.class}
4064 */
4065 public static
4066 MethodHandle constant(Class<?> type, Object value) {
4067 if (type.isPrimitive()) {
4068 if (type == void.class)
4069 throw newIllegalArgumentException("void type");
4070 Wrapper w = Wrapper.forPrimitiveType(type);
4071 value = w.convert(value, type);
4072 if (w.zero().equals(value))
4073 return zero(w, type);
4074 return insertArguments(identity(type), 0, value);
4075 } else {
4076 if (value == null)
4077 return zero(Wrapper.OBJECT, type);
4078 return identity(type).bindTo(value);
4079 }
4080 }
4081
4082 /**
4083 * Produces a method handle which returns its sole argument when invoked.
4084 * @param type the type of the sole parameter and return value of the desired method handle
4085 * @return a unary method handle which accepts and returns the given type
4086 * @throws NullPointerException if the argument is null
4087 * @throws IllegalArgumentException if the given type is {@code void.class}
4088 */
4089 public static
4090 MethodHandle identity(Class<?> type) {
4091 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4092 int pos = btw.ordinal();
4093 MethodHandle ident = IDENTITY_MHS[pos];
4094 if (ident == null) {
4095 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4096 }
4097 if (ident.type().returnType() == type)
4098 return ident;
4099 // something like identity(Foo.class); do not bother to intern these
4100 assert (btw == Wrapper.OBJECT);
4101 return makeIdentity(type);
4102 }
4103
4104 /**
4105 * Produces a constant method handle of the requested return type which
4106 * returns the default value for that type every time it is invoked.
4107 * The resulting constant method handle will have no side effects.
4108 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4109 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4110 * since {@code explicitCastArguments} converts {@code null} to default values.
4111 * @param type the expected return type of the desired method handle
4112 * @return a constant method handle that takes no arguments
4113 * and returns the default value of the given type (or void, if the type is void)
4114 * @throws NullPointerException if the argument is null
4115 * @see MethodHandles#constant
4116 * @see MethodHandles#empty
4117 * @see MethodHandles#explicitCastArguments
4118 * @since 9
4119 */
4120 public static MethodHandle zero(Class<?> type) {
4121 Objects.requireNonNull(type);
4122 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
4123 }
4124
4125 private static MethodHandle identityOrVoid(Class<?> type) {
4126 return type == void.class ? zero(type) : identity(type);
4127 }
4128
4129 /**
4130 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4131 * and returns a suitable default depending on the return type.
4132 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4133 * <p>The returned method handle is equivalent to
4134 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4135 *
4136 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4137 * {@code guardWithTest(pred, target, empty(target.type())}.
4138 * @param type the type of the desired method handle
4139 * @return a constant method handle of the given type, which returns a default value of the given return type
4140 * @throws NullPointerException if the argument is null
4141 * @see MethodHandles#zero
4142 * @see MethodHandles#constant
4143 * @since 9
4144 */
4145 public static MethodHandle empty(MethodType type) {
4146 Objects.requireNonNull(type);
4147 return dropArguments(zero(type.returnType()), 0, type.parameterList());
4148 }
4149
4150 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4151 private static MethodHandle makeIdentity(Class<?> ptype) {
4152 MethodType mtype = methodType(ptype, ptype);
4153 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4154 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4155 }
4156
4157 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
4158 int pos = btw.ordinal();
4159 MethodHandle zero = ZERO_MHS[pos];
4160 if (zero == null) {
4161 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
4162 }
4163 if (zero.type().returnType() == rtype)
4164 return zero;
4165 assert(btw == Wrapper.OBJECT);
4166 return makeZero(rtype);
4167 }
4168 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4169 private static MethodHandle makeZero(Class<?> rtype) {
4170 MethodType mtype = methodType(rtype);
4171 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
4172 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
4173 }
4174
4175 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4176 // Simulate a CAS, to avoid racy duplication of results.
4177 MethodHandle prev = cache[pos];
4178 if (prev != null) return prev;
4179 return cache[pos] = value;
4180 }
4181
4182 /**
4183 * Provides a target method handle with one or more <em>bound arguments</em>
4184 * in advance of the method handle's invocation.
4185 * The formal parameters to the target corresponding to the bound
4186 * arguments are called <em>bound parameters</em>.
4187 * Returns a new method handle which saves away the bound arguments.
4188 * When it is invoked, it receives arguments for any non-bound parameters,
4189 * binds the saved arguments to their corresponding parameters,
4190 * and calls the original target.
4191 * <p>
4192 * The type of the new method handle will drop the types for the bound
4193 * parameters from the original target type, since the new method handle
4194 * will no longer require those arguments to be supplied by its callers.
4195 * <p>
4196 * Each given argument object must match the corresponding bound parameter type.
4197 * If a bound parameter type is a primitive, the argument object
4198 * must be a wrapper, and will be unboxed to produce the primitive value.
4199 * <p>
4200 * The {@code pos} argument selects which parameters are to be bound.
4201 * It may range between zero and <i>N-L</i> (inclusively),
4202 * where <i>N</i> is the arity of the target method handle
4203 * and <i>L</i> is the length of the values array.
4204 * <p>
4205 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4206 * variable-arity method handle}, even if the original target method handle was.
4207 * @param target the method handle to invoke after the argument is inserted
4208 * @param pos where to insert the argument (zero for the first)
4209 * @param values the series of arguments to insert
4210 * @return a method handle which inserts an additional argument,
4211 * before calling the original method handle
4212 * @throws NullPointerException if the target or the {@code values} array is null
4213 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
4214 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4215 * is the length of the values array.
4216 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4217 * type.
4218 * @see MethodHandle#bindTo
4219 */
4220 public static
4221 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4222 int insCount = values.length;
4223 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4224 if (insCount == 0) return target;
4225 BoundMethodHandle result = target.rebind();
4226 for (int i = 0; i < insCount; i++) {
4227 Object value = values[i];
4228 Class<?> ptype = ptypes[pos+i];
4229 if (ptype.isPrimitive()) {
4230 result = insertArgumentPrimitive(result, pos, ptype, value);
4231 } else {
4232 value = ptype.cast(value); // throw CCE if needed
4233 result = result.bindArgumentL(pos, value);
4234 }
4235 }
4236 return result;
4237 }
4238
4239 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4240 Class<?> ptype, Object value) {
4241 Wrapper w = Wrapper.forPrimitiveType(ptype);
4242 // perform unboxing and/or primitive conversion
4243 value = w.convert(value, ptype);
4244 switch (w) {
4245 case INT: return result.bindArgumentI(pos, (int)value);
4246 case LONG: return result.bindArgumentJ(pos, (long)value);
4247 case FLOAT: return result.bindArgumentF(pos, (float)value);
4248 case DOUBLE: return result.bindArgumentD(pos, (double)value);
4249 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
4250 }
4251 }
4252
4253 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
4254 MethodType oldType = target.type();
4255 int outargs = oldType.parameterCount();
4256 int inargs = outargs - insCount;
4257 if (inargs < 0)
4258 throw newIllegalArgumentException("too many values to insert");
4259 if (pos < 0 || pos > inargs)
4260 throw newIllegalArgumentException("no argument type to append");
4261 return oldType.ptypes();
4262 }
4263
4264 /**
4265 * Produces a method handle which will discard some dummy arguments
4266 * before calling some other specified <i>target</i> method handle.
4267 * The type of the new method handle will be the same as the target's type,
4268 * except it will also include the dummy argument types,
4269 * at some given position.
4270 * <p>
4271 * The {@code pos} argument may range between zero and <i>N</i>,
4272 * where <i>N</i> is the arity of the target.
4273 * If {@code pos} is zero, the dummy arguments will precede
4274 * the target's real arguments; if {@code pos} is <i>N</i>
4275 * they will come after.
4276 * <p>
4277 * <b>Example:</b>
4278 * <blockquote><pre>{@code
4279 import static java.lang.invoke.MethodHandles.*;
4280 import static java.lang.invoke.MethodType.*;
4281 ...
4282 MethodHandle cat = lookup().findVirtual(String.class,
4283 "concat", methodType(String.class, String.class));
4284 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4285 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
4286 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
4287 assertEquals(bigType, d0.type());
4288 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
4289 * }</pre></blockquote>
4290 * <p>
4291 * This method is also equivalent to the following code:
4292 * <blockquote><pre>
4293 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
4294 * </pre></blockquote>
4295 * @param target the method handle to invoke after the arguments are dropped
4296 * @param valueTypes the type(s) of the argument(s) to drop
4297 * @param pos position of first argument to drop (zero for the leftmost)
4298 * @return a method handle which drops arguments of the given types,
4299 * before calling the original method handle
4300 * @throws NullPointerException if the target is null,
4301 * or if the {@code valueTypes} list or any of its elements is null
4302 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4303 * or if {@code pos} is negative or greater than the arity of the target,
4304 * or if the new method handle's type would have too many parameters
4305 */
4306 public static
4307 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4308 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
4309 }
4310
4311 private static List<Class<?>> copyTypes(Object[] array) {
4312 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
4313 }
4314
4315 private static
4316 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
4317 MethodType oldType = target.type(); // get NPE
4318 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
4319 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
4320 if (dropped == 0) return target;
4321 BoundMethodHandle result = target.rebind();
4322 LambdaForm lform = result.form;
4323 int insertFormArg = 1 + pos;
4324 for (Class<?> ptype : valueTypes) {
4325 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
4326 }
4327 result = result.copyWith(newType, lform);
4328 return result;
4329 }
4330
4331 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
4332 int dropped = valueTypes.size();
4333 MethodType.checkSlotCount(dropped);
4334 int outargs = oldType.parameterCount();
4335 int inargs = outargs + dropped;
4336 if (pos < 0 || pos > outargs)
4337 throw newIllegalArgumentException("no argument type to remove"
4338 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
4339 );
4340 return dropped;
4341 }
4342
4343 /**
4344 * Produces a method handle which will discard some dummy arguments
4345 * before calling some other specified <i>target</i> method handle.
4346 * The type of the new method handle will be the same as the target's type,
4347 * except it will also include the dummy argument types,
4348 * at some given position.
4349 * <p>
4350 * The {@code pos} argument may range between zero and <i>N</i>,
4351 * where <i>N</i> is the arity of the target.
4352 * If {@code pos} is zero, the dummy arguments will precede
4353 * the target's real arguments; if {@code pos} is <i>N</i>
4354 * they will come after.
4355 * @apiNote
4356 * <blockquote><pre>{@code
4357 import static java.lang.invoke.MethodHandles.*;
4358 import static java.lang.invoke.MethodType.*;
4359 ...
4360 MethodHandle cat = lookup().findVirtual(String.class,
4361 "concat", methodType(String.class, String.class));
4362 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4363 MethodHandle d0 = dropArguments(cat, 0, String.class);
4364 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
4365 MethodHandle d1 = dropArguments(cat, 1, String.class);
4366 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4367 MethodHandle d2 = dropArguments(cat, 2, String.class);
4368 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4369 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4370 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4371 * }</pre></blockquote>
4372 * <p>
4373 * This method is also equivalent to the following code:
4374 * <blockquote><pre>
4375 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4376 * </pre></blockquote>
4377 * @param target the method handle to invoke after the arguments are dropped
4378 * @param valueTypes the type(s) of the argument(s) to drop
4379 * @param pos position of first argument to drop (zero for the leftmost)
4380 * @return a method handle which drops arguments of the given types,
4381 * before calling the original method handle
4382 * @throws NullPointerException if the target is null,
4383 * or if the {@code valueTypes} array or any of its elements is null
4384 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4385 * or if {@code pos} is negative or greater than the arity of the target,
4386 * or if the new method handle's type would have
4387 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4388 */
4389 public static
4390 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4391 return dropArguments0(target, pos, copyTypes(valueTypes));
4392 }
4393
4394 // private version which allows caller some freedom with error handling
4395 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4396 boolean nullOnFailure) {
4397 newTypes = copyTypes(newTypes.toArray());
4398 List<Class<?>> oldTypes = target.type().parameterList();
4399 int match = oldTypes.size();
4400 if (skip != 0) {
4401 if (skip < 0 || skip > match) {
4402 throw newIllegalArgumentException("illegal skip", skip, target);
4403 }
4404 oldTypes = oldTypes.subList(skip, match);
4405 match -= skip;
4406 }
4407 List<Class<?>> addTypes = newTypes;
4408 int add = addTypes.size();
4409 if (pos != 0) {
4410 if (pos < 0 || pos > add) {
4411 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4412 }
4413 addTypes = addTypes.subList(pos, add);
4414 add -= pos;
4415 assert(addTypes.size() == add);
4416 }
4417 // Do not add types which already match the existing arguments.
4418 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4419 if (nullOnFailure) {
4420 return null;
4421 }
4422 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
4423 }
4424 addTypes = addTypes.subList(match, add);
4425 add -= match;
4426 assert(addTypes.size() == add);
4427 // newTypes: ( P*[pos], M*[match], A*[add] )
4428 // target: ( S*[skip], M*[match] )
4429 MethodHandle adapter = target;
4430 if (add > 0) {
4431 adapter = dropArguments0(adapter, skip+ match, addTypes);
4432 }
4433 // adapter: (S*[skip], M*[match], A*[add] )
4434 if (pos > 0) {
4435 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
4436 }
4437 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
4438 return adapter;
4439 }
4440
4441 /**
4442 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
4443 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
4444 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
4445 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
4446 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
4447 * {@link #dropArguments(MethodHandle, int, Class[])}.
4448 * <p>
4449 * The resulting handle will have the same return type as the target handle.
4450 * <p>
4451 * In more formal terms, assume these two type lists:<ul>
4452 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
4453 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
4454 * {@code newTypes}.
4455 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
4456 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
4457 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
4458 * sub-list.
4459 * </ul>
4460 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
4461 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
4462 * {@link #dropArguments(MethodHandle, int, Class[])}.
4463 *
4464 * @apiNote
4465 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
4466 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
4467 * <blockquote><pre>{@code
4468 import static java.lang.invoke.MethodHandles.*;
4469 import static java.lang.invoke.MethodType.*;
4470 ...
4471 ...
4472 MethodHandle h0 = constant(boolean.class, true);
4473 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
4474 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
4475 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
4476 if (h1.type().parameterCount() < h2.type().parameterCount())
4477 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
4478 else
4479 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
4480 MethodHandle h3 = guardWithTest(h0, h1, h2);
4481 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
4482 * }</pre></blockquote>
4483 * @param target the method handle to adapt
4484 * @param skip number of targets parameters to disregard (they will be unchanged)
4485 * @param newTypes the list of types to match {@code target}'s parameter type list to
4486 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
4487 * @return a possibly adapted method handle
4488 * @throws NullPointerException if either argument is null
4489 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
4490 * or if {@code skip} is negative or greater than the arity of the target,
4491 * or if {@code pos} is negative or greater than the newTypes list size,
4492 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
4493 * {@code pos}.
4494 * @since 9
4495 */
4496 public static
4497 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
4498 Objects.requireNonNull(target);
4499 Objects.requireNonNull(newTypes);
4500 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
4501 }
4502
4503 /**
4504 * Adapts a target method handle by pre-processing
4505 * one or more of its arguments, each with its own unary filter function,
4506 * and then calling the target with each pre-processed argument
4507 * replaced by the result of its corresponding filter function.
4508 * <p>
4509 * The pre-processing is performed by one or more method handles,
4510 * specified in the elements of the {@code filters} array.
4511 * The first element of the filter array corresponds to the {@code pos}
4512 * argument of the target, and so on in sequence.
4513 * The filter functions are invoked in left to right order.
4514 * <p>
4515 * Null arguments in the array are treated as identity functions,
4516 * and the corresponding arguments left unchanged.
4517 * (If there are no non-null elements in the array, the original target is returned.)
4518 * Each filter is applied to the corresponding argument of the adapter.
4519 * <p>
4520 * If a filter {@code F} applies to the {@code N}th argument of
4521 * the target, then {@code F} must be a method handle which
4522 * takes exactly one argument. The type of {@code F}'s sole argument
4523 * replaces the corresponding argument type of the target
4524 * in the resulting adapted method handle.
4525 * The return type of {@code F} must be identical to the corresponding
4526 * parameter type of the target.
4527 * <p>
4528 * It is an error if there are elements of {@code filters}
4529 * (null or not)
4530 * which do not correspond to argument positions in the target.
4531 * <p><b>Example:</b>
4532 * <blockquote><pre>{@code
4533 import static java.lang.invoke.MethodHandles.*;
4534 import static java.lang.invoke.MethodType.*;
4535 ...
4536 MethodHandle cat = lookup().findVirtual(String.class,
4537 "concat", methodType(String.class, String.class));
4538 MethodHandle upcase = lookup().findVirtual(String.class,
4539 "toUpperCase", methodType(String.class));
4540 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4541 MethodHandle f0 = filterArguments(cat, 0, upcase);
4542 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
4543 MethodHandle f1 = filterArguments(cat, 1, upcase);
4544 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
4545 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
4546 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
4547 * }</pre></blockquote>
4548 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4549 * denotes the return type of both the {@code target} and resulting adapter.
4550 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
4551 * of the parameters and arguments that precede and follow the filter position
4552 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
4553 * values of the filtered parameters and arguments; they also represent the
4554 * return types of the {@code filter[i]} handles. The latter accept arguments
4555 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
4556 * the resulting adapter.
4557 * <blockquote><pre>{@code
4558 * T target(P... p, A[i]... a[i], B... b);
4559 * A[i] filter[i](V[i]);
4560 * T adapter(P... p, V[i]... v[i], B... b) {
4561 * return target(p..., filter[i](v[i])..., b...);
4562 * }
4563 * }</pre></blockquote>
4564 * <p>
4565 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4566 * variable-arity method handle}, even if the original target method handle was.
4567 *
4568 * @param target the method handle to invoke after arguments are filtered
4569 * @param pos the position of the first argument to filter
4570 * @param filters method handles to call initially on filtered arguments
4571 * @return method handle which incorporates the specified argument filtering logic
4572 * @throws NullPointerException if the target is null
4573 * or if the {@code filters} array is null
4574 * @throws IllegalArgumentException if a non-null element of {@code filters}
4575 * does not match a corresponding argument type of target as described above,
4576 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
4577 * or if the resulting method handle's type would have
4578 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4579 */
4580 public static
4581 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
4582 // In method types arguments start at index 0, while the LF
4583 // editor have the MH receiver at position 0 - adjust appropriately.
4584 final int MH_RECEIVER_OFFSET = 1;
4585 filterArgumentsCheckArity(target, pos, filters);
4586 MethodHandle adapter = target;
4587
4588 // keep track of currently matched filters, as to optimize repeated filters
4589 int index = 0;
4590 int[] positions = new int[filters.length];
4591 MethodHandle filter = null;
4592
4593 // process filters in reverse order so that the invocation of
4594 // the resulting adapter will invoke the filters in left-to-right order
4595 for (int i = filters.length - 1; i >= 0; --i) {
4596 MethodHandle newFilter = filters[i];
4597 if (newFilter == null) continue; // ignore null elements of filters
4598
4599 // flush changes on update
4600 if (filter != newFilter) {
4601 if (filter != null) {
4602 if (index > 1) {
4603 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4604 } else {
4605 adapter = filterArgument(adapter, positions[0] - 1, filter);
4606 }
4607 }
4608 filter = newFilter;
4609 index = 0;
4610 }
4611
4612 filterArgumentChecks(target, pos + i, newFilter);
4613 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
4614 }
4615 if (index > 1) {
4616 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
4617 } else if (index == 1) {
4618 adapter = filterArgument(adapter, positions[0] - 1, filter);
4619 }
4620 return adapter;
4621 }
4622
4623 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
4624 MethodType targetType = adapter.type();
4625 MethodType filterType = filter.type();
4626 BoundMethodHandle result = adapter.rebind();
4627 Class<?> newParamType = filterType.parameterType(0);
4628
4629 Class<?>[] ptypes = targetType.ptypes().clone();
4630 for (int pos : positions) {
4631 ptypes[pos - 1] = newParamType;
4632 }
4633 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
4634
4635 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
4636 return result.copyWithExtendL(newType, lform, filter);
4637 }
4638
4639 /*non-public*/ static
4640 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
4641 filterArgumentChecks(target, pos, filter);
4642 MethodType targetType = target.type();
4643 MethodType filterType = filter.type();
4644 BoundMethodHandle result = target.rebind();
4645 Class<?> newParamType = filterType.parameterType(0);
4646 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
4647 MethodType newType = targetType.changeParameterType(pos, newParamType);
4648 result = result.copyWithExtendL(newType, lform, filter);
4649 return result;
4650 }
4651
4652 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
4653 MethodType targetType = target.type();
4654 int maxPos = targetType.parameterCount();
4655 if (pos + filters.length > maxPos)
4656 throw newIllegalArgumentException("too many filters");
4657 }
4658
4659 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4660 MethodType targetType = target.type();
4661 MethodType filterType = filter.type();
4662 if (filterType.parameterCount() != 1
4663 || filterType.returnType() != targetType.parameterType(pos))
4664 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4665 }
4666
4667 /**
4668 * Adapts a target method handle by pre-processing
4669 * a sub-sequence of its arguments with a filter (another method handle).
4670 * The pre-processed arguments are replaced by the result (if any) of the
4671 * filter function.
4672 * The target is then called on the modified (usually shortened) argument list.
4673 * <p>
4674 * If the filter returns a value, the target must accept that value as
4675 * its argument in position {@code pos}, preceded and/or followed by
4676 * any arguments not passed to the filter.
4677 * If the filter returns void, the target must accept all arguments
4678 * not passed to the filter.
4679 * No arguments are reordered, and a result returned from the filter
4680 * replaces (in order) the whole subsequence of arguments originally
4681 * passed to the adapter.
4682 * <p>
4683 * The argument types (if any) of the filter
4684 * replace zero or one argument types of the target, at position {@code pos},
4685 * in the resulting adapted method handle.
4686 * The return type of the filter (if any) must be identical to the
4687 * argument type of the target at position {@code pos}, and that target argument
4688 * is supplied by the return value of the filter.
4689 * <p>
4690 * In all cases, {@code pos} must be greater than or equal to zero, and
4691 * {@code pos} must also be less than or equal to the target's arity.
4692 * <p><b>Example:</b>
4693 * <blockquote><pre>{@code
4694 import static java.lang.invoke.MethodHandles.*;
4695 import static java.lang.invoke.MethodType.*;
4696 ...
4697 MethodHandle deepToString = publicLookup()
4698 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
4699
4700 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
4701 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
4702
4703 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
4704 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
4705
4706 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
4707 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
4708 assertEquals("[top, [up, down], strange]",
4709 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
4710
4711 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
4712 assertEquals("[top, [up, down], [strange]]",
4713 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
4714
4715 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4716 assertEquals("[top, [[up, down, strange], charm], bottom]",
4717 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4718 * }</pre></blockquote>
4719 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4720 * represents the return type of the {@code target} and resulting adapter.
4721 * {@code V}/{@code v} stand for the return type and value of the
4722 * {@code filter}, which are also found in the signature and arguments of
4723 * the {@code target}, respectively, unless {@code V} is {@code void}.
4724 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4725 * and values preceding and following the collection position, {@code pos},
4726 * in the {@code target}'s signature. They also turn up in the resulting
4727 * adapter's signature and arguments, where they surround
4728 * {@code B}/{@code b}, which represent the parameter types and arguments
4729 * to the {@code filter} (if any).
4730 * <blockquote><pre>{@code
4731 * T target(A...,V,C...);
4732 * V filter(B...);
4733 * T adapter(A... a,B... b,C... c) {
4734 * V v = filter(b...);
4735 * return target(a...,v,c...);
4736 * }
4737 * // and if the filter has no arguments:
4738 * T target2(A...,V,C...);
4739 * V filter2();
4740 * T adapter2(A... a,C... c) {
4741 * V v = filter2();
4742 * return target2(a...,v,c...);
4743 * }
4744 * // and if the filter has a void return:
4745 * T target3(A...,C...);
4746 * void filter3(B...);
4747 * T adapter3(A... a,B... b,C... c) {
4748 * filter3(b...);
4749 * return target3(a...,c...);
4750 * }
4751 * }</pre></blockquote>
4752 * <p>
4753 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
4754 * one which first "folds" the affected arguments, and then drops them, in separate
4755 * steps as follows:
4756 * <blockquote><pre>{@code
4757 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4758 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4759 * }</pre></blockquote>
4760 * If the target method handle consumes no arguments besides than the result
4761 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4762 * is equivalent to {@code filterReturnValue(coll, mh)}.
4763 * If the filter method handle {@code coll} consumes one argument and produces
4764 * a non-void result, then {@code collectArguments(mh, N, coll)}
4765 * is equivalent to {@code filterArguments(mh, N, coll)}.
4766 * Other equivalences are possible but would require argument permutation.
4767 * <p>
4768 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4769 * variable-arity method handle}, even if the original target method handle was.
4770 *
4771 * @param target the method handle to invoke after filtering the subsequence of arguments
4772 * @param pos the position of the first adapter argument to pass to the filter,
4773 * and/or the target argument which receives the result of the filter
4774 * @param filter method handle to call on the subsequence of arguments
4775 * @return method handle which incorporates the specified argument subsequence filtering logic
4776 * @throws NullPointerException if either argument is null
4777 * @throws IllegalArgumentException if the return type of {@code filter}
4778 * is non-void and is not the same as the {@code pos} argument of the target,
4779 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4780 * or if the resulting method handle's type would have
4781 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4782 * @see MethodHandles#foldArguments
4783 * @see MethodHandles#filterArguments
4784 * @see MethodHandles#filterReturnValue
4785 */
4786 public static
4787 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4788 MethodType newType = collectArgumentsChecks(target, pos, filter);
4789 MethodType collectorType = filter.type();
4790 BoundMethodHandle result = target.rebind();
4791 LambdaForm lform;
4792 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4793 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4794 if (lform != null) {
4795 return result.copyWith(newType, lform);
4796 }
4797 }
4798 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4799 return result.copyWithExtendL(newType, lform, filter);
4800 }
4801
4802 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4803 MethodType targetType = target.type();
4804 MethodType filterType = filter.type();
4805 Class<?> rtype = filterType.returnType();
4806 List<Class<?>> filterArgs = filterType.parameterList();
4807 if (rtype == void.class) {
4808 return targetType.insertParameterTypes(pos, filterArgs);
4809 }
4810 if (rtype != targetType.parameterType(pos)) {
4811 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4812 }
4813 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4814 }
4815
4816 /**
4817 * Adapts a target method handle by post-processing
4818 * its return value (if any) with a filter (another method handle).
4819 * The result of the filter is returned from the adapter.
4820 * <p>
4821 * If the target returns a value, the filter must accept that value as
4822 * its only argument.
4823 * If the target returns void, the filter must accept no arguments.
4824 * <p>
4825 * The return type of the filter
4826 * replaces the return type of the target
4827 * in the resulting adapted method handle.
4828 * The argument type of the filter (if any) must be identical to the
4829 * return type of the target.
4830 * <p><b>Example:</b>
4831 * <blockquote><pre>{@code
4832 import static java.lang.invoke.MethodHandles.*;
4833 import static java.lang.invoke.MethodType.*;
4834 ...
4835 MethodHandle cat = lookup().findVirtual(String.class,
4836 "concat", methodType(String.class, String.class));
4837 MethodHandle length = lookup().findVirtual(String.class,
4838 "length", methodType(int.class));
4839 System.out.println((String) cat.invokeExact("x", "y")); // xy
4840 MethodHandle f0 = filterReturnValue(cat, length);
4841 System.out.println((int) f0.invokeExact("x", "y")); // 2
4842 * }</pre></blockquote>
4843 * <p>Here is pseudocode for the resulting adapter. In the code,
4844 * {@code T}/{@code t} represent the result type and value of the
4845 * {@code target}; {@code V}, the result type of the {@code filter}; and
4846 * {@code A}/{@code a}, the types and values of the parameters and arguments
4847 * of the {@code target} as well as the resulting adapter.
4848 * <blockquote><pre>{@code
4849 * T target(A...);
4850 * V filter(T);
4851 * V adapter(A... a) {
4852 * T t = target(a...);
4853 * return filter(t);
4854 * }
4855 * // and if the target has a void return:
4856 * void target2(A...);
4857 * V filter2();
4858 * V adapter2(A... a) {
4859 * target2(a...);
4860 * return filter2();
4861 * }
4862 * // and if the filter has a void return:
4863 * T target3(A...);
4864 * void filter3(V);
4865 * void adapter3(A... a) {
4866 * T t = target3(a...);
4867 * filter3(t);
4868 * }
4869 * }</pre></blockquote>
4870 * <p>
4871 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4872 * variable-arity method handle}, even if the original target method handle was.
4873 * @param target the method handle to invoke before filtering the return value
4874 * @param filter method handle to call on the return value
4875 * @return method handle which incorporates the specified return value filtering logic
4876 * @throws NullPointerException if either argument is null
4877 * @throws IllegalArgumentException if the argument list of {@code filter}
4878 * does not match the return type of target as described above
4879 */
4880 public static
4881 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4882 MethodType targetType = target.type();
4883 MethodType filterType = filter.type();
4884 filterReturnValueChecks(targetType, filterType);
4885 BoundMethodHandle result = target.rebind();
4886 BasicType rtype = BasicType.basicType(filterType.returnType());
4887 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4888 MethodType newType = targetType.changeReturnType(filterType.returnType());
4889 result = result.copyWithExtendL(newType, lform, filter);
4890 return result;
4891 }
4892
4893 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4894 Class<?> rtype = targetType.returnType();
4895 int filterValues = filterType.parameterCount();
4896 if (filterValues == 0
4897 ? (rtype != void.class)
4898 : (rtype != filterType.parameterType(0) || filterValues != 1))
4899 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4900 }
4901
4902 /**
4903 * Adapts a target method handle by pre-processing
4904 * some of its arguments, and then calling the target with
4905 * the result of the pre-processing, inserted into the original
4906 * sequence of arguments.
4907 * <p>
4908 * The pre-processing is performed by {@code combiner}, a second method handle.
4909 * Of the arguments passed to the adapter, the first {@code N} arguments
4910 * are copied to the combiner, which is then called.
4911 * (Here, {@code N} is defined as the parameter count of the combiner.)
4912 * After this, control passes to the target, with any result
4913 * from the combiner inserted before the original {@code N} incoming
4914 * arguments.
4915 * <p>
4916 * If the combiner returns a value, the first parameter type of the target
4917 * must be identical with the return type of the combiner, and the next
4918 * {@code N} parameter types of the target must exactly match the parameters
4919 * of the combiner.
4920 * <p>
4921 * If the combiner has a void return, no result will be inserted,
4922 * and the first {@code N} parameter types of the target
4923 * must exactly match the parameters of the combiner.
4924 * <p>
4925 * The resulting adapter is the same type as the target, except that the
4926 * first parameter type is dropped,
4927 * if it corresponds to the result of the combiner.
4928 * <p>
4929 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4930 * that either the combiner or the target does not wish to receive.
4931 * If some of the incoming arguments are destined only for the combiner,
4932 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4933 * arguments will not need to be live on the stack on entry to the
4934 * target.)
4935 * <p><b>Example:</b>
4936 * <blockquote><pre>{@code
4937 import static java.lang.invoke.MethodHandles.*;
4938 import static java.lang.invoke.MethodType.*;
4939 ...
4940 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4941 "println", methodType(void.class, String.class))
4942 .bindTo(System.out);
4943 MethodHandle cat = lookup().findVirtual(String.class,
4944 "concat", methodType(String.class, String.class));
4945 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4946 MethodHandle catTrace = foldArguments(cat, trace);
4947 // also prints "boo":
4948 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4949 * }</pre></blockquote>
4950 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4951 * represents the result type of the {@code target} and resulting adapter.
4952 * {@code V}/{@code v} represent the type and value of the parameter and argument
4953 * of {@code target} that precedes the folding position; {@code V} also is
4954 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4955 * types and values of the {@code N} parameters and arguments at the folding
4956 * position. {@code B}/{@code b} represent the types and values of the
4957 * {@code target} parameters and arguments that follow the folded parameters
4958 * and arguments.
4959 * <blockquote><pre>{@code
4960 * // there are N arguments in A...
4961 * T target(V, A[N]..., B...);
4962 * V combiner(A...);
4963 * T adapter(A... a, B... b) {
4964 * V v = combiner(a...);
4965 * return target(v, a..., b...);
4966 * }
4967 * // and if the combiner has a void return:
4968 * T target2(A[N]..., B...);
4969 * void combiner2(A...);
4970 * T adapter2(A... a, B... b) {
4971 * combiner2(a...);
4972 * return target2(a..., b...);
4973 * }
4974 * }</pre></blockquote>
4975 * <p>
4976 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4977 * variable-arity method handle}, even if the original target method handle was.
4978 * @param target the method handle to invoke after arguments are combined
4979 * @param combiner method handle to call initially on the incoming arguments
4980 * @return method handle which incorporates the specified argument folding logic
4981 * @throws NullPointerException if either argument is null
4982 * @throws IllegalArgumentException if {@code combiner}'s return type
4983 * is non-void and not the same as the first argument type of
4984 * the target, or if the initial {@code N} argument types
4985 * of the target
4986 * (skipping one matching the {@code combiner}'s return type)
4987 * are not identical with the argument types of {@code combiner}
4988 */
4989 public static
4990 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4991 return foldArguments(target, 0, combiner);
4992 }
4993
4994 /**
4995 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4996 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4997 * before the folded arguments.
4998 * <p>
4999 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5000 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5001 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5002 * 0.
5003 *
5004 * @apiNote Example:
5005 * <blockquote><pre>{@code
5006 import static java.lang.invoke.MethodHandles.*;
5007 import static java.lang.invoke.MethodType.*;
5008 ...
5009 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5010 "println", methodType(void.class, String.class))
5011 .bindTo(System.out);
5012 MethodHandle cat = lookup().findVirtual(String.class,
5013 "concat", methodType(String.class, String.class));
5014 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5015 MethodHandle catTrace = foldArguments(cat, 1, trace);
5016 // also prints "jum":
5017 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5018 * }</pre></blockquote>
5019 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5020 * represents the result type of the {@code target} and resulting adapter.
5021 * {@code V}/{@code v} represent the type and value of the parameter and argument
5022 * of {@code target} that precedes the folding position; {@code V} also is
5023 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5024 * types and values of the {@code N} parameters and arguments at the folding
5025 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5026 * and values of the {@code target} parameters and arguments that precede and
5027 * follow the folded parameters and arguments starting at {@code pos},
5028 * respectively.
5029 * <blockquote><pre>{@code
5030 * // there are N arguments in A...
5031 * T target(Z..., V, A[N]..., B...);
5032 * V combiner(A...);
5033 * T adapter(Z... z, A... a, B... b) {
5034 * V v = combiner(a...);
5035 * return target(z..., v, a..., b...);
5036 * }
5037 * // and if the combiner has a void return:
5038 * T target2(Z..., A[N]..., B...);
5039 * void combiner2(A...);
5040 * T adapter2(Z... z, A... a, B... b) {
5041 * combiner2(a...);
5042 * return target2(z..., a..., b...);
5043 * }
5044 * }</pre></blockquote>
5045 * <p>
5046 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5047 * variable-arity method handle}, even if the original target method handle was.
5048 *
5049 * @param target the method handle to invoke after arguments are combined
5050 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5051 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5052 * @param combiner method handle to call initially on the incoming arguments
5053 * @return method handle which incorporates the specified argument folding logic
5054 * @throws NullPointerException if either argument is null
5055 * @throws IllegalArgumentException if either of the following two conditions holds:
5056 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5057 * {@code pos} of the target signature;
5058 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5059 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5060 *
5061 * @see #foldArguments(MethodHandle, MethodHandle)
5062 * @since 9
5063 */
5064 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5065 MethodType targetType = target.type();
5066 MethodType combinerType = combiner.type();
5067 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5068 BoundMethodHandle result = target.rebind();
5069 boolean dropResult = rtype == void.class;
5070 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5071 MethodType newType = targetType;
5072 if (!dropResult) {
5073 newType = newType.dropParameterTypes(pos, pos + 1);
5074 }
5075 result = result.copyWithExtendL(newType, lform, combiner);
5076 return result;
5077 }
5078
5079 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5080 int foldArgs = combinerType.parameterCount();
5081 Class<?> rtype = combinerType.returnType();
5082 int foldVals = rtype == void.class ? 0 : 1;
5083 int afterInsertPos = foldPos + foldVals;
5084 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5085 if (ok) {
5086 for (int i = 0; i < foldArgs; i++) {
5087 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5088 ok = false;
5089 break;
5090 }
5091 }
5092 }
5093 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5094 ok = false;
5095 if (!ok)
5096 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5097 return rtype;
5098 }
5099
5100 /**
5101 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5102 * of the pre-processing replacing the argument at the given position.
5103 *
5104 * @param target the method handle to invoke after arguments are combined
5105 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5106 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5107 * @param combiner method handle to call initially on the incoming arguments
5108 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5109 * @return method handle which incorporates the specified argument folding logic
5110 * @throws NullPointerException if either argument is null
5111 * @throws IllegalArgumentException if either of the following two conditions holds:
5112 * (1) {@code combiner}'s return type is not the same as the argument type at position
5113 * {@code pos} of the target signature;
5114 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5115 * not identical with the argument types of {@code combiner}.
5116 */
5117 /*non-public*/ static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5118 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5119 }
5120
5121 /**
5122 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5123 * the pre-processing inserted into the original sequence of arguments at the given position.
5124 *
5125 * @param target the method handle to invoke after arguments are combined
5126 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5127 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5128 * @param combiner method handle to call initially on the incoming arguments
5129 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5130 * @return method handle which incorporates the specified argument folding logic
5131 * @throws NullPointerException if either argument is null
5132 * @throws IllegalArgumentException if either of the following two conditions holds:
5133 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5134 * {@code pos} of the target signature;
5135 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5136 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5137 * with the argument types of {@code combiner}.
5138 */
5139 /*non-public*/ static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5140 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5141 }
5142
5143 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5144 MethodType targetType = target.type();
5145 MethodType combinerType = combiner.type();
5146 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5147 BoundMethodHandle result = target.rebind();
5148
5149 MethodType newType = targetType;
5150 LambdaForm lform;
5151 if (filter) {
5152 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5153 } else {
5154 boolean dropResult = rtype == void.class;
5155 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5156 if (!dropResult) {
5157 newType = newType.dropParameterTypes(position, position + 1);
5158 }
5159 }
5160 result = result.copyWithExtendL(newType, lform, combiner);
5161 return result;
5162 }
5163
5164 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5165 int combinerArgs = combinerType.parameterCount();
5166 if (argPos.length != combinerArgs) {
5167 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5168 }
5169 Class<?> rtype = combinerType.returnType();
5170
5171 for (int i = 0; i < combinerArgs; i++) {
5172 int arg = argPos[i];
5173 if (arg < 0 || arg > targetType.parameterCount()) {
5174 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5175 }
5176 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5177 throw newIllegalArgumentException("target argument type at position " + arg
5178 + " must match combiner argument type at index " + i + ": " + targetType
5179 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5180 }
5181 }
5182 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5183 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5184 }
5185 return rtype;
5186 }
5187
5188 /**
5189 * Makes a method handle which adapts a target method handle,
5190 * by guarding it with a test, a boolean-valued method handle.
5191 * If the guard fails, a fallback handle is called instead.
5192 * All three method handles must have the same corresponding
5193 * argument and return types, except that the return type
5194 * of the test must be boolean, and the test is allowed
5195 * to have fewer arguments than the other two method handles.
5196 * <p>
5197 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5198 * represents the uniform result type of the three involved handles;
5199 * {@code A}/{@code a}, the types and values of the {@code target}
5200 * parameters and arguments that are consumed by the {@code test}; and
5201 * {@code B}/{@code b}, those types and values of the {@code target}
5202 * parameters and arguments that are not consumed by the {@code test}.
5203 * <blockquote><pre>{@code
5204 * boolean test(A...);
5205 * T target(A...,B...);
5206 * T fallback(A...,B...);
5207 * T adapter(A... a,B... b) {
5208 * if (test(a...))
5209 * return target(a..., b...);
5210 * else
5211 * return fallback(a..., b...);
5212 * }
5213 * }</pre></blockquote>
5214 * Note that the test arguments ({@code a...} in the pseudocode) cannot
5215 * be modified by execution of the test, and so are passed unchanged
5216 * from the caller to the target or fallback as appropriate.
5217 * @param test method handle used for test, must return boolean
5218 * @param target method handle to call if test passes
5219 * @param fallback method handle to call if test fails
5220 * @return method handle which incorporates the specified if/then/else logic
5221 * @throws NullPointerException if any argument is null
5222 * @throws IllegalArgumentException if {@code test} does not return boolean,
5223 * or if all three method types do not match (with the return
5224 * type of {@code test} changed to match that of the target).
5225 */
5226 public static
5227 MethodHandle guardWithTest(MethodHandle test,
5228 MethodHandle target,
5229 MethodHandle fallback) {
5230 MethodType gtype = test.type();
5231 MethodType ttype = target.type();
5232 MethodType ftype = fallback.type();
5233 if (!ttype.equals(ftype))
5234 throw misMatchedTypes("target and fallback types", ttype, ftype);
5235 if (gtype.returnType() != boolean.class)
5236 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
5237 List<Class<?>> targs = ttype.parameterList();
5238 test = dropArgumentsToMatch(test, 0, targs, 0, true);
5239 if (test == null) {
5240 throw misMatchedTypes("target and test types", ttype, gtype);
5241 }
5242 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
5243 }
5244
5245 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
5246 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
5247 }
5248
5249 /**
5250 * Makes a method handle which adapts a target method handle,
5251 * by running it inside an exception handler.
5252 * If the target returns normally, the adapter returns that value.
5253 * If an exception matching the specified type is thrown, the fallback
5254 * handle is called instead on the exception, plus the original arguments.
5255 * <p>
5256 * The target and handler must have the same corresponding
5257 * argument and return types, except that handler may omit trailing arguments
5258 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
5259 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
5260 * <p>
5261 * Here is pseudocode for the resulting adapter. In the code, {@code T}
5262 * represents the return type of the {@code target} and {@code handler},
5263 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
5264 * the types and values of arguments to the resulting handle consumed by
5265 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
5266 * resulting handle discarded by {@code handler}.
5267 * <blockquote><pre>{@code
5268 * T target(A..., B...);
5269 * T handler(ExType, A...);
5270 * T adapter(A... a, B... b) {
5271 * try {
5272 * return target(a..., b...);
5273 * } catch (ExType ex) {
5274 * return handler(ex, a...);
5275 * }
5276 * }
5277 * }</pre></blockquote>
5278 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5279 * be modified by execution of the target, and so are passed unchanged
5280 * from the caller to the handler, if the handler is invoked.
5281 * <p>
5282 * The target and handler must return the same type, even if the handler
5283 * always throws. (This might happen, for instance, because the handler
5284 * is simulating a {@code finally} clause).
5285 * To create such a throwing handler, compose the handler creation logic
5286 * with {@link #throwException throwException},
5287 * in order to create a method handle of the correct return type.
5288 * @param target method handle to call
5289 * @param exType the type of exception which the handler will catch
5290 * @param handler method handle to call if a matching exception is thrown
5291 * @return method handle which incorporates the specified try/catch logic
5292 * @throws NullPointerException if any argument is null
5293 * @throws IllegalArgumentException if {@code handler} does not accept
5294 * the given exception type, or if the method handle types do
5295 * not match in their return types and their
5296 * corresponding parameters
5297 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
5298 */
5299 public static
5300 MethodHandle catchException(MethodHandle target,
5301 Class<? extends Throwable> exType,
5302 MethodHandle handler) {
5303 MethodType ttype = target.type();
5304 MethodType htype = handler.type();
5305 if (!Throwable.class.isAssignableFrom(exType))
5306 throw new ClassCastException(exType.getName());
5307 if (htype.parameterCount() < 1 ||
5308 !htype.parameterType(0).isAssignableFrom(exType))
5309 throw newIllegalArgumentException("handler does not accept exception type "+exType);
5310 if (htype.returnType() != ttype.returnType())
5311 throw misMatchedTypes("target and handler return types", ttype, htype);
5312 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
5313 if (handler == null) {
5314 throw misMatchedTypes("target and handler types", ttype, htype);
5315 }
5316 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
5317 }
5318
5319 /**
5320 * Produces a method handle which will throw exceptions of the given {@code exType}.
5321 * The method handle will accept a single argument of {@code exType},
5322 * and immediately throw it as an exception.
5323 * The method type will nominally specify a return of {@code returnType}.
5324 * The return type may be anything convenient: It doesn't matter to the
5325 * method handle's behavior, since it will never return normally.
5326 * @param returnType the return type of the desired method handle
5327 * @param exType the parameter type of the desired method handle
5328 * @return method handle which can throw the given exceptions
5329 * @throws NullPointerException if either argument is null
5330 */
5331 public static
5332 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
5333 if (!Throwable.class.isAssignableFrom(exType))
5334 throw new ClassCastException(exType.getName());
5335 return MethodHandleImpl.throwException(methodType(returnType, exType));
5336 }
5337
5338 /**
5339 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
5340 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
5341 * delivers the loop's result, which is the return value of the resulting handle.
5342 * <p>
5343 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
5344 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
5345 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
5346 * terms of method handles, each clause will specify up to four independent actions:<ul>
5347 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
5348 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
5349 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
5350 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
5351 * </ul>
5352 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
5353 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
5354 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
5355 * <p>
5356 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
5357 * this case. See below for a detailed description.
5358 * <p>
5359 * <em>Parameters optional everywhere:</em>
5360 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
5361 * As an exception, the init functions cannot take any {@code v} parameters,
5362 * because those values are not yet computed when the init functions are executed.
5363 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
5364 * In fact, any clause function may take no arguments at all.
5365 * <p>
5366 * <em>Loop parameters:</em>
5367 * A clause function may take all the iteration variable values it is entitled to, in which case
5368 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
5369 * with their types and values notated as {@code (A...)} and {@code (a...)}.
5370 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
5371 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
5372 * init function is automatically a loop parameter {@code a}.)
5373 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
5374 * These loop parameters act as loop-invariant values visible across the whole loop.
5375 * <p>
5376 * <em>Parameters visible everywhere:</em>
5377 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
5378 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
5379 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
5380 * Most clause functions will not need all of this information, but they will be formally connected to it
5381 * as if by {@link #dropArguments}.
5382 * <a id="astar"></a>
5383 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
5384 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
5385 * In that notation, the general form of an init function parameter list
5386 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
5387 * <p>
5388 * <em>Checking clause structure:</em>
5389 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
5390 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
5391 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
5392 * met by the inputs to the loop combinator.
5393 * <p>
5394 * <em>Effectively identical sequences:</em>
5395 * <a id="effid"></a>
5396 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
5397 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
5398 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
5399 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
5400 * that longest list.
5401 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
5402 * and the same is true if more sequences of the form {@code (V... A*)} are added.
5403 * <p>
5404 * <em>Step 0: Determine clause structure.</em><ol type="a">
5405 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
5406 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
5407 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
5408 * four. Padding takes place by appending elements to the array.
5409 * <li>Clauses with all {@code null}s are disregarded.
5410 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
5411 * </ol>
5412 * <p>
5413 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
5414 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
5415 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
5416 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
5417 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
5418 * iteration variable type.
5419 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
5420 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
5421 * </ol>
5422 * <p>
5423 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
5424 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
5425 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
5426 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
5427 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
5428 * (These types will be checked in step 2, along with all the clause function types.)
5429 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
5430 * <li>All of the collected parameter lists must be effectively identical.
5431 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
5432 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
5433 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
5434 * the "internal parameter list".
5435 * </ul>
5436 * <p>
5437 * <em>Step 1C: Determine loop return type.</em><ol type="a">
5438 * <li>Examine fini function return types, disregarding omitted fini functions.
5439 * <li>If there are no fini functions, the loop return type is {@code void}.
5440 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
5441 * type.
5442 * </ol>
5443 * <p>
5444 * <em>Step 1D: Check other types.</em><ol type="a">
5445 * <li>There must be at least one non-omitted pred function.
5446 * <li>Every non-omitted pred function must have a {@code boolean} return type.
5447 * </ol>
5448 * <p>
5449 * <em>Step 2: Determine parameter lists.</em><ol type="a">
5450 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
5451 * <li>The parameter list for init functions will be adjusted to the external parameter list.
5452 * (Note that their parameter lists are already effectively identical to this list.)
5453 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
5454 * effectively identical to the internal parameter list {@code (V... A...)}.
5455 * </ol>
5456 * <p>
5457 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
5458 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
5459 * type.
5460 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
5461 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
5462 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
5463 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
5464 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
5465 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
5466 * loop return type.
5467 * </ol>
5468 * <p>
5469 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
5470 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
5471 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
5472 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
5473 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
5474 * pad out the end of the list.
5475 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
5476 * </ol>
5477 * <p>
5478 * <em>Final observations.</em><ol type="a">
5479 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
5480 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
5481 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
5482 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
5483 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
5484 * <li>Each pair of init and step functions agrees in their return type {@code V}.
5485 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
5486 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
5487 * </ol>
5488 * <p>
5489 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
5490 * <ul>
5491 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
5492 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
5493 * (Only one {@code Pn} has to be non-{@code null}.)
5494 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
5495 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
5496 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
5497 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
5498 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
5499 * the resulting loop handle's parameter types {@code (A...)}.
5500 * </ul>
5501 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
5502 * which is natural if most of the loop computation happens in the steps. For some loops,
5503 * the burden of computation might be heaviest in the pred functions, and so the pred functions
5504 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
5505 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
5506 * where the init functions will need the extra parameters. For such reasons, the rules for
5507 * determining these parameters are as symmetric as possible, across all clause parts.
5508 * In general, the loop parameters function as common invariant values across the whole
5509 * loop, while the iteration variables function as common variant values, or (if there is
5510 * no step function) as internal loop invariant temporaries.
5511 * <p>
5512 * <em>Loop execution.</em><ol type="a">
5513 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
5514 * every clause function. These locals are loop invariant.
5515 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
5516 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
5517 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
5518 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
5519 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
5520 * (in argument order).
5521 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
5522 * returns {@code false}.
5523 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
5524 * sequence {@code (v...)} of loop variables.
5525 * The updated value is immediately visible to all subsequent function calls.
5526 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
5527 * (of type {@code R}) is returned from the loop as a whole.
5528 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
5529 * except by throwing an exception.
5530 * </ol>
5531 * <p>
5532 * <em>Usage tips.</em>
5533 * <ul>
5534 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
5535 * sometimes a step function only needs to observe the current value of its own variable.
5536 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
5537 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
5538 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
5539 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
5540 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
5541 * <li>If some of the clause functions are virtual methods on an instance, the instance
5542 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
5543 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
5544 * will be the first iteration variable value, and it will be easy to use virtual
5545 * methods as clause parts, since all of them will take a leading instance reference matching that value.
5546 * </ul>
5547 * <p>
5548 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
5549 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
5550 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
5551 * <blockquote><pre>{@code
5552 * V... init...(A...);
5553 * boolean pred...(V..., A...);
5554 * V... step...(V..., A...);
5555 * R fini...(V..., A...);
5556 * R loop(A... a) {
5557 * V... v... = init...(a...);
5558 * for (;;) {
5559 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
5560 * v = s(v..., a...);
5561 * if (!p(v..., a...)) {
5562 * return f(v..., a...);
5563 * }
5564 * }
5565 * }
5566 * }
5567 * }</pre></blockquote>
5568 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
5569 * to their full length, even though individual clause functions may neglect to take them all.
5570 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
5571 *
5572 * @apiNote Example:
5573 * <blockquote><pre>{@code
5574 * // iterative implementation of the factorial function as a loop handle
5575 * static int one(int k) { return 1; }
5576 * static int inc(int i, int acc, int k) { return i + 1; }
5577 * static int mult(int i, int acc, int k) { return i * acc; }
5578 * static boolean pred(int i, int acc, int k) { return i < k; }
5579 * static int fin(int i, int acc, int k) { return acc; }
5580 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5581 * // null initializer for counter, should initialize to 0
5582 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5583 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5584 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5585 * assertEquals(120, loop.invoke(5));
5586 * }</pre></blockquote>
5587 * The same example, dropping arguments and using combinators:
5588 * <blockquote><pre>{@code
5589 * // simplified implementation of the factorial function as a loop handle
5590 * static int inc(int i) { return i + 1; } // drop acc, k
5591 * static int mult(int i, int acc) { return i * acc; } //drop k
5592 * static boolean cmp(int i, int k) { return i < k; }
5593 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
5594 * // null initializer for counter, should initialize to 0
5595 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5596 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
5597 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
5598 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5599 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5600 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5601 * assertEquals(720, loop.invoke(6));
5602 * }</pre></blockquote>
5603 * A similar example, using a helper object to hold a loop parameter:
5604 * <blockquote><pre>{@code
5605 * // instance-based implementation of the factorial function as a loop handle
5606 * static class FacLoop {
5607 * final int k;
5608 * FacLoop(int k) { this.k = k; }
5609 * int inc(int i) { return i + 1; }
5610 * int mult(int i, int acc) { return i * acc; }
5611 * boolean pred(int i) { return i < k; }
5612 * int fin(int i, int acc) { return acc; }
5613 * }
5614 * // assume MH_FacLoop is a handle to the constructor
5615 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5616 * // null initializer for counter, should initialize to 0
5617 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5618 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
5619 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5620 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5621 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
5622 * assertEquals(5040, loop.invoke(7));
5623 * }</pre></blockquote>
5624 *
5625 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
5626 *
5627 * @return a method handle embodying the looping behavior as defined by the arguments.
5628 *
5629 * @throws IllegalArgumentException in case any of the constraints described above is violated.
5630 *
5631 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
5632 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5633 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
5634 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
5635 * @since 9
5636 */
5637 public static MethodHandle loop(MethodHandle[]... clauses) {
5638 // Step 0: determine clause structure.
5639 loopChecks0(clauses);
5640
5641 List<MethodHandle> init = new ArrayList<>();
5642 List<MethodHandle> step = new ArrayList<>();
5643 List<MethodHandle> pred = new ArrayList<>();
5644 List<MethodHandle> fini = new ArrayList<>();
5645
5646 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
5647 init.add(clause[0]); // all clauses have at least length 1
5648 step.add(clause.length <= 1 ? null : clause[1]);
5649 pred.add(clause.length <= 2 ? null : clause[2]);
5650 fini.add(clause.length <= 3 ? null : clause[3]);
5651 });
5652
5653 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
5654 final int nclauses = init.size();
5655
5656 // Step 1A: determine iteration variables (V...).
5657 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
5658 for (int i = 0; i < nclauses; ++i) {
5659 MethodHandle in = init.get(i);
5660 MethodHandle st = step.get(i);
5661 if (in == null && st == null) {
5662 iterationVariableTypes.add(void.class);
5663 } else if (in != null && st != null) {
5664 loopChecks1a(i, in, st);
5665 iterationVariableTypes.add(in.type().returnType());
5666 } else {
5667 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
5668 }
5669 }
5670 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
5671 collect(Collectors.toList());
5672
5673 // Step 1B: determine loop parameters (A...).
5674 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
5675 loopChecks1b(init, commonSuffix);
5676
5677 // Step 1C: determine loop return type.
5678 // Step 1D: check other types.
5679 // local variable required here; see JDK-8223553
5680 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
5681 .map(MethodType::returnType);
5682 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
5683 loopChecks1cd(pred, fini, loopReturnType);
5684
5685 // Step 2: determine parameter lists.
5686 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
5687 commonParameterSequence.addAll(commonSuffix);
5688 loopChecks2(step, pred, fini, commonParameterSequence);
5689
5690 // Step 3: fill in omitted functions.
5691 for (int i = 0; i < nclauses; ++i) {
5692 Class<?> t = iterationVariableTypes.get(i);
5693 if (init.get(i) == null) {
5694 init.set(i, empty(methodType(t, commonSuffix)));
5695 }
5696 if (step.get(i) == null) {
5697 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
5698 }
5699 if (pred.get(i) == null) {
5700 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
5701 }
5702 if (fini.get(i) == null) {
5703 fini.set(i, empty(methodType(t, commonParameterSequence)));
5704 }
5705 }
5706
5707 // Step 4: fill in missing parameter types.
5708 // Also convert all handles to fixed-arity handles.
5709 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
5710 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
5711 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
5712 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
5713
5714 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
5715 allMatch(pl -> pl.equals(commonSuffix));
5716 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5717 allMatch(pl -> pl.equals(commonParameterSequence));
5718
5719 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5720 }
5721
5722 private static void loopChecks0(MethodHandle[][] clauses) {
5723 if (clauses == null || clauses.length == 0) {
5724 throw newIllegalArgumentException("null or no clauses passed");
5725 }
5726 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5727 throw newIllegalArgumentException("null clauses are not allowed");
5728 }
5729 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5730 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5731 }
5732 }
5733
5734 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5735 if (in.type().returnType() != st.type().returnType()) {
5736 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5737 st.type().returnType());
5738 }
5739 }
5740
5741 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
5742 final List<Class<?>> empty = List.of();
5743 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
5744 // take only those that can contribute to a common suffix because they are longer than the prefix
5745 map(MethodHandle::type).
5746 filter(t -> t.parameterCount() > skipSize).
5747 map(MethodType::parameterList).
5748 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5749 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
5750 }
5751
5752 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
5753 final List<Class<?>> empty = List.of();
5754 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5755 }
5756
5757 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
5758 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
5759 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
5760 return longestParameterList(Arrays.asList(longest1, longest2));
5761 }
5762
5763 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
5764 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
5765 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
5766 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
5767 " (common suffix: " + commonSuffix + ")");
5768 }
5769 }
5770
5771 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
5772 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5773 anyMatch(t -> t != loopReturnType)) {
5774 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
5775 loopReturnType + ")");
5776 }
5777
5778 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5779 throw newIllegalArgumentException("no predicate found", pred);
5780 }
5781 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5782 anyMatch(t -> t != boolean.class)) {
5783 throw newIllegalArgumentException("predicates must have boolean return type", pred);
5784 }
5785 }
5786
5787 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5788 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5789 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
5790 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5791 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5792 }
5793 }
5794
5795 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
5796 return hs.stream().map(h -> {
5797 int pc = h.type().parameterCount();
5798 int tpsize = targetParams.size();
5799 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5800 }).collect(Collectors.toList());
5801 }
5802
5803 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5804 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5805 }
5806
5807 /**
5808 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5809 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5810 * <p>
5811 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5812 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5813 * evaluates to {@code true}).
5814 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5815 * <p>
5816 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5817 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5818 * and updated with the value returned from its invocation. The result of loop execution will be
5819 * the final value of the additional loop-local variable (if present).
5820 * <p>
5821 * The following rules hold for these argument handles:<ul>
5822 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5823 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5824 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5825 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5826 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5827 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5828 * It will constrain the parameter lists of the other loop parts.
5829 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5830 * list {@code (A...)} is called the <em>external parameter list</em>.
5831 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5832 * additional state variable of the loop.
5833 * The body must both accept and return a value of this type {@code V}.
5834 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5835 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5836 * <a href="MethodHandles.html#effid">effectively identical</a>
5837 * to the external parameter list {@code (A...)}.
5838 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5839 * {@linkplain #empty default value}.
5840 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5841 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5842 * effectively identical to the internal parameter list.
5843 * </ul>
5844 * <p>
5845 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5846 * <li>The loop handle's result type is the result type {@code V} of the body.
5847 * <li>The loop handle's parameter types are the types {@code (A...)},
5848 * from the external parameter list.
5849 * </ul>
5850 * <p>
5851 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5852 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5853 * passed to the loop.
5854 * <blockquote><pre>{@code
5855 * V init(A...);
5856 * boolean pred(V, A...);
5857 * V body(V, A...);
5858 * V whileLoop(A... a...) {
5859 * V v = init(a...);
5860 * while (pred(v, a...)) {
5861 * v = body(v, a...);
5862 * }
5863 * return v;
5864 * }
5865 * }</pre></blockquote>
5866 *
5867 * @apiNote Example:
5868 * <blockquote><pre>{@code
5869 * // implement the zip function for lists as a loop handle
5870 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5871 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5872 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5873 * zip.add(a.next());
5874 * zip.add(b.next());
5875 * return zip;
5876 * }
5877 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5878 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5879 * List<String> a = Arrays.asList("a", "b", "c", "d");
5880 * List<String> b = Arrays.asList("e", "f", "g", "h");
5881 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5882 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5883 * }</pre></blockquote>
5884 *
5885 *
5886 * @apiNote The implementation of this method can be expressed as follows:
5887 * <blockquote><pre>{@code
5888 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5889 * MethodHandle fini = (body.type().returnType() == void.class
5890 * ? null : identity(body.type().returnType()));
5891 * MethodHandle[]
5892 * checkExit = { null, null, pred, fini },
5893 * varBody = { init, body };
5894 * return loop(checkExit, varBody);
5895 * }
5896 * }</pre></blockquote>
5897 *
5898 * @param init optional initializer, providing the initial value of the loop variable.
5899 * May be {@code null}, implying a default initial value. See above for other constraints.
5900 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5901 * above for other constraints.
5902 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5903 * See above for other constraints.
5904 *
5905 * @return a method handle implementing the {@code while} loop as described by the arguments.
5906 * @throws IllegalArgumentException if the rules for the arguments are violated.
5907 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5908 *
5909 * @see #loop(MethodHandle[][])
5910 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5911 * @since 9
5912 */
5913 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5914 whileLoopChecks(init, pred, body);
5915 MethodHandle fini = identityOrVoid(body.type().returnType());
5916 MethodHandle[] checkExit = { null, null, pred, fini };
5917 MethodHandle[] varBody = { init, body };
5918 return loop(checkExit, varBody);
5919 }
5920
5921 /**
5922 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5923 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5924 * <p>
5925 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5926 * method will, in each iteration, first execute its body and then evaluate the predicate.
5927 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5928 * <p>
5929 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5930 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5931 * and updated with the value returned from its invocation. The result of loop execution will be
5932 * the final value of the additional loop-local variable (if present).
5933 * <p>
5934 * The following rules hold for these argument handles:<ul>
5935 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5936 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5937 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5938 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5939 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5940 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5941 * It will constrain the parameter lists of the other loop parts.
5942 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5943 * list {@code (A...)} is called the <em>external parameter list</em>.
5944 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5945 * additional state variable of the loop.
5946 * The body must both accept and return a value of this type {@code V}.
5947 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5948 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5949 * <a href="MethodHandles.html#effid">effectively identical</a>
5950 * to the external parameter list {@code (A...)}.
5951 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5952 * {@linkplain #empty default value}.
5953 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5954 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5955 * effectively identical to the internal parameter list.
5956 * </ul>
5957 * <p>
5958 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5959 * <li>The loop handle's result type is the result type {@code V} of the body.
5960 * <li>The loop handle's parameter types are the types {@code (A...)},
5961 * from the external parameter list.
5962 * </ul>
5963 * <p>
5964 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5965 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5966 * passed to the loop.
5967 * <blockquote><pre>{@code
5968 * V init(A...);
5969 * boolean pred(V, A...);
5970 * V body(V, A...);
5971 * V doWhileLoop(A... a...) {
5972 * V v = init(a...);
5973 * do {
5974 * v = body(v, a...);
5975 * } while (pred(v, a...));
5976 * return v;
5977 * }
5978 * }</pre></blockquote>
5979 *
5980 * @apiNote Example:
5981 * <blockquote><pre>{@code
5982 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5983 * static int zero(int limit) { return 0; }
5984 * static int step(int i, int limit) { return i + 1; }
5985 * static boolean pred(int i, int limit) { return i < limit; }
5986 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5987 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5988 * assertEquals(23, loop.invoke(23));
5989 * }</pre></blockquote>
5990 *
5991 *
5992 * @apiNote The implementation of this method can be expressed as follows:
5993 * <blockquote><pre>{@code
5994 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5995 * MethodHandle fini = (body.type().returnType() == void.class
5996 * ? null : identity(body.type().returnType()));
5997 * MethodHandle[] clause = { init, body, pred, fini };
5998 * return loop(clause);
5999 * }
6000 * }</pre></blockquote>
6001 *
6002 * @param init optional initializer, providing the initial value of the loop variable.
6003 * May be {@code null}, implying a default initial value. See above for other constraints.
6004 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6005 * See above for other constraints.
6006 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6007 * above for other constraints.
6008 *
6009 * @return a method handle implementing the {@code while} loop as described by the arguments.
6010 * @throws IllegalArgumentException if the rules for the arguments are violated.
6011 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6012 *
6013 * @see #loop(MethodHandle[][])
6014 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6015 * @since 9
6016 */
6017 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6018 whileLoopChecks(init, pred, body);
6019 MethodHandle fini = identityOrVoid(body.type().returnType());
6020 MethodHandle[] clause = {init, body, pred, fini };
6021 return loop(clause);
6022 }
6023
6024 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6025 Objects.requireNonNull(pred);
6026 Objects.requireNonNull(body);
6027 MethodType bodyType = body.type();
6028 Class<?> returnType = bodyType.returnType();
6029 List<Class<?>> innerList = bodyType.parameterList();
6030 List<Class<?>> outerList = innerList;
6031 if (returnType == void.class) {
6032 // OK
6033 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
6034 // leading V argument missing => error
6035 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6036 throw misMatchedTypes("body function", bodyType, expected);
6037 } else {
6038 outerList = innerList.subList(1, innerList.size());
6039 }
6040 MethodType predType = pred.type();
6041 if (predType.returnType() != boolean.class ||
6042 !predType.effectivelyIdenticalParameters(0, innerList)) {
6043 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6044 }
6045 if (init != null) {
6046 MethodType initType = init.type();
6047 if (initType.returnType() != returnType ||
6048 !initType.effectivelyIdenticalParameters(0, outerList)) {
6049 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6050 }
6051 }
6052 }
6053
6054 /**
6055 * Constructs a loop that runs a given number of iterations.
6056 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6057 * <p>
6058 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6059 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6060 * It will be initialized to 0 and incremented by 1 in each iteration.
6061 * <p>
6062 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6063 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6064 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6065 * <p>
6066 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6067 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6068 * iteration variable.
6069 * The result of the loop handle execution will be the final {@code V} value of that variable
6070 * (or {@code void} if there is no {@code V} variable).
6071 * <p>
6072 * The following rules hold for the argument handles:<ul>
6073 * <li>The {@code iterations} handle must not be {@code null}, and must return
6074 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6075 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6076 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6077 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6078 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6079 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6080 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6081 * of types called the <em>internal parameter list</em>.
6082 * It will constrain the parameter lists of the other loop parts.
6083 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6084 * with no additional {@code A} types, then the internal parameter list is extended by
6085 * the argument types {@code A...} of the {@code iterations} handle.
6086 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6087 * list {@code (A...)} is called the <em>external parameter list</em>.
6088 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6089 * additional state variable of the loop.
6090 * The body must both accept a leading parameter and return a value of this type {@code V}.
6091 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6092 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6093 * <a href="MethodHandles.html#effid">effectively identical</a>
6094 * to the external parameter list {@code (A...)}.
6095 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6096 * {@linkplain #empty default value}.
6097 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6098 * effectively identical to the external parameter list {@code (A...)}.
6099 * </ul>
6100 * <p>
6101 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6102 * <li>The loop handle's result type is the result type {@code V} of the body.
6103 * <li>The loop handle's parameter types are the types {@code (A...)},
6104 * from the external parameter list.
6105 * </ul>
6106 * <p>
6107 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6108 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6109 * arguments passed to the loop.
6110 * <blockquote><pre>{@code
6111 * int iterations(A...);
6112 * V init(A...);
6113 * V body(V, int, A...);
6114 * V countedLoop(A... a...) {
6115 * int end = iterations(a...);
6116 * V v = init(a...);
6117 * for (int i = 0; i < end; ++i) {
6118 * v = body(v, i, a...);
6119 * }
6120 * return v;
6121 * }
6122 * }</pre></blockquote>
6123 *
6124 * @apiNote Example with a fully conformant body method:
6125 * <blockquote><pre>{@code
6126 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6127 * // => a variation on a well known theme
6128 * static String step(String v, int counter, String init) { return "na " + v; }
6129 * // assume MH_step is a handle to the method above
6130 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6131 * MethodHandle start = MethodHandles.identity(String.class);
6132 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6133 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6134 * }</pre></blockquote>
6135 *
6136 * @apiNote Example with the simplest possible body method type,
6137 * and passing the number of iterations to the loop invocation:
6138 * <blockquote><pre>{@code
6139 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6140 * // => a variation on a well known theme
6141 * static String step(String v, int counter ) { return "na " + v; }
6142 * // assume MH_step is a handle to the method above
6143 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6144 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6145 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6146 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6147 * }</pre></blockquote>
6148 *
6149 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6150 * as loop parameters:
6151 * <blockquote><pre>{@code
6152 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6153 * // => a variation on a well known theme
6154 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6155 * // assume MH_step is a handle to the method above
6156 * MethodHandle count = MethodHandles.identity(int.class);
6157 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6158 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6159 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6160 * }</pre></blockquote>
6161 *
6162 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6163 * to enforce a loop type:
6164 * <blockquote><pre>{@code
6165 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6166 * // => a variation on a well known theme
6167 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6168 * // assume MH_step is a handle to the method above
6169 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6170 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6171 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6172 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6173 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6174 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6175 * }</pre></blockquote>
6176 *
6177 * @apiNote The implementation of this method can be expressed as follows:
6178 * <blockquote><pre>{@code
6179 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6180 * return countedLoop(empty(iterations.type()), iterations, init, body);
6181 * }
6182 * }</pre></blockquote>
6183 *
6184 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6185 * result type must be {@code int}. See above for other constraints.
6186 * @param init optional initializer, providing the initial value of the loop variable.
6187 * May be {@code null}, implying a default initial value. See above for other constraints.
6188 * @param body body of the loop, which may not be {@code null}.
6189 * It controls the loop parameters and result type in the standard case (see above for details).
6190 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6191 * and may accept any number of additional types.
6192 * See above for other constraints.
6193 *
6194 * @return a method handle representing the loop.
6195 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6196 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6197 *
6198 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6199 * @since 9
6200 */
6201 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6202 return countedLoop(empty(iterations.type()), iterations, init, body);
6203 }
6204
6205 /**
6206 * Constructs a loop that counts over a range of numbers.
6207 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6208 * <p>
6209 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
6210 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
6211 * values of the loop counter.
6212 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
6213 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
6214 * <p>
6215 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6216 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6217 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6218 * <p>
6219 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6220 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6221 * iteration variable.
6222 * The result of the loop handle execution will be the final {@code V} value of that variable
6223 * (or {@code void} if there is no {@code V} variable).
6224 * <p>
6225 * The following rules hold for the argument handles:<ul>
6226 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
6227 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
6228 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6229 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6230 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6231 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6232 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6233 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6234 * of types called the <em>internal parameter list</em>.
6235 * It will constrain the parameter lists of the other loop parts.
6236 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6237 * with no additional {@code A} types, then the internal parameter list is extended by
6238 * the argument types {@code A...} of the {@code end} handle.
6239 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6240 * list {@code (A...)} is called the <em>external parameter list</em>.
6241 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6242 * additional state variable of the loop.
6243 * The body must both accept a leading parameter and return a value of this type {@code V}.
6244 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6245 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6246 * <a href="MethodHandles.html#effid">effectively identical</a>
6247 * to the external parameter list {@code (A...)}.
6248 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6249 * {@linkplain #empty default value}.
6250 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
6251 * effectively identical to the external parameter list {@code (A...)}.
6252 * <li>Likewise, the parameter list of {@code end} must be effectively identical
6253 * to the external parameter list.
6254 * </ul>
6255 * <p>
6256 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6257 * <li>The loop handle's result type is the result type {@code V} of the body.
6258 * <li>The loop handle's parameter types are the types {@code (A...)},
6259 * from the external parameter list.
6260 * </ul>
6261 * <p>
6262 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6263 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6264 * arguments passed to the loop.
6265 * <blockquote><pre>{@code
6266 * int start(A...);
6267 * int end(A...);
6268 * V init(A...);
6269 * V body(V, int, A...);
6270 * V countedLoop(A... a...) {
6271 * int e = end(a...);
6272 * int s = start(a...);
6273 * V v = init(a...);
6274 * for (int i = s; i < e; ++i) {
6275 * v = body(v, i, a...);
6276 * }
6277 * return v;
6278 * }
6279 * }</pre></blockquote>
6280 *
6281 * @apiNote The implementation of this method can be expressed as follows:
6282 * <blockquote><pre>{@code
6283 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6284 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
6285 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
6286 * // the following semantics:
6287 * // MH_increment: (int limit, int counter) -> counter + 1
6288 * // MH_predicate: (int limit, int counter) -> counter < limit
6289 * Class<?> counterType = start.type().returnType(); // int
6290 * Class<?> returnType = body.type().returnType();
6291 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
6292 * if (returnType != void.class) { // ignore the V variable
6293 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6294 * pred = dropArguments(pred, 1, returnType); // ditto
6295 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
6296 * }
6297 * body = dropArguments(body, 0, counterType); // ignore the limit variable
6298 * MethodHandle[]
6299 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6300 * bodyClause = { init, body }, // v = init(); v = body(v, i)
6301 * indexVar = { start, incr }; // i = start(); i = i + 1
6302 * return loop(loopLimit, bodyClause, indexVar);
6303 * }
6304 * }</pre></blockquote>
6305 *
6306 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
6307 * See above for other constraints.
6308 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
6309 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
6310 * @param init optional initializer, providing the initial value of the loop variable.
6311 * May be {@code null}, implying a default initial value. See above for other constraints.
6312 * @param body body of the loop, which may not be {@code null}.
6313 * It controls the loop parameters and result type in the standard case (see above for details).
6314 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6315 * and may accept any number of additional types.
6316 * See above for other constraints.
6317 *
6318 * @return a method handle representing the loop.
6319 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
6320 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6321 *
6322 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
6323 * @since 9
6324 */
6325 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6326 countedLoopChecks(start, end, init, body);
6327 Class<?> counterType = start.type().returnType(); // int, but who's counting?
6328 Class<?> limitType = end.type().returnType(); // yes, int again
6329 Class<?> returnType = body.type().returnType();
6330 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
6331 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
6332 MethodHandle retv = null;
6333 if (returnType != void.class) {
6334 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
6335 pred = dropArguments(pred, 1, returnType); // ditto
6336 retv = dropArguments(identity(returnType), 0, counterType);
6337 }
6338 body = dropArguments(body, 0, counterType); // ignore the limit variable
6339 MethodHandle[]
6340 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
6341 bodyClause = { init, body }, // v = init(); v = body(v, i)
6342 indexVar = { start, incr }; // i = start(); i = i + 1
6343 return loop(loopLimit, bodyClause, indexVar);
6344 }
6345
6346 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
6347 Objects.requireNonNull(start);
6348 Objects.requireNonNull(end);
6349 Objects.requireNonNull(body);
6350 Class<?> counterType = start.type().returnType();
6351 if (counterType != int.class) {
6352 MethodType expected = start.type().changeReturnType(int.class);
6353 throw misMatchedTypes("start function", start.type(), expected);
6354 } else if (end.type().returnType() != counterType) {
6355 MethodType expected = end.type().changeReturnType(counterType);
6356 throw misMatchedTypes("end function", end.type(), expected);
6357 }
6358 MethodType bodyType = body.type();
6359 Class<?> returnType = bodyType.returnType();
6360 List<Class<?>> innerList = bodyType.parameterList();
6361 // strip leading V value if present
6362 int vsize = (returnType == void.class ? 0 : 1);
6363 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
6364 // argument list has no "V" => error
6365 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6366 throw misMatchedTypes("body function", bodyType, expected);
6367 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
6368 // missing I type => error
6369 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
6370 throw misMatchedTypes("body function", bodyType, expected);
6371 }
6372 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
6373 if (outerList.isEmpty()) {
6374 // special case; take lists from end handle
6375 outerList = end.type().parameterList();
6376 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
6377 }
6378 MethodType expected = methodType(counterType, outerList);
6379 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
6380 throw misMatchedTypes("start parameter types", start.type(), expected);
6381 }
6382 if (end.type() != start.type() &&
6383 !end.type().effectivelyIdenticalParameters(0, outerList)) {
6384 throw misMatchedTypes("end parameter types", end.type(), expected);
6385 }
6386 if (init != null) {
6387 MethodType initType = init.type();
6388 if (initType.returnType() != returnType ||
6389 !initType.effectivelyIdenticalParameters(0, outerList)) {
6390 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6391 }
6392 }
6393 }
6394
6395 /**
6396 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
6397 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6398 * <p>
6399 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
6400 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
6401 * <p>
6402 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6403 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6404 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6405 * <p>
6406 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6407 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6408 * iteration variable.
6409 * The result of the loop handle execution will be the final {@code V} value of that variable
6410 * (or {@code void} if there is no {@code V} variable).
6411 * <p>
6412 * The following rules hold for the argument handles:<ul>
6413 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6414 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
6415 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6416 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
6417 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
6418 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
6419 * of types called the <em>internal parameter list</em>.
6420 * It will constrain the parameter lists of the other loop parts.
6421 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
6422 * with no additional {@code A} types, then the internal parameter list is extended by
6423 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
6424 * single type {@code Iterable} is added and constitutes the {@code A...} list.
6425 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
6426 * list {@code (A...)} is called the <em>external parameter list</em>.
6427 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6428 * additional state variable of the loop.
6429 * The body must both accept a leading parameter and return a value of this type {@code V}.
6430 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6431 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6432 * <a href="MethodHandles.html#effid">effectively identical</a>
6433 * to the external parameter list {@code (A...)}.
6434 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6435 * {@linkplain #empty default value}.
6436 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
6437 * type {@code java.util.Iterator} or a subtype thereof.
6438 * The iterator it produces when the loop is executed will be assumed
6439 * to yield values which can be converted to type {@code T}.
6440 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
6441 * effectively identical to the external parameter list {@code (A...)}.
6442 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
6443 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
6444 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
6445 * handle parameter is adjusted to accept the leading {@code A} type, as if by
6446 * the {@link MethodHandle#asType asType} conversion method.
6447 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
6448 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
6449 * </ul>
6450 * <p>
6451 * The type {@code T} may be either a primitive or reference.
6452 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
6453 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
6454 * as if by the {@link MethodHandle#asType asType} conversion method.
6455 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
6456 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
6457 * <p>
6458 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6459 * <li>The loop handle's result type is the result type {@code V} of the body.
6460 * <li>The loop handle's parameter types are the types {@code (A...)},
6461 * from the external parameter list.
6462 * </ul>
6463 * <p>
6464 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6465 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
6466 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
6467 * <blockquote><pre>{@code
6468 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
6469 * V init(A...);
6470 * V body(V,T,A...);
6471 * V iteratedLoop(A... a...) {
6472 * Iterator<T> it = iterator(a...);
6473 * V v = init(a...);
6474 * while (it.hasNext()) {
6475 * T t = it.next();
6476 * v = body(v, t, a...);
6477 * }
6478 * return v;
6479 * }
6480 * }</pre></blockquote>
6481 *
6482 * @apiNote Example:
6483 * <blockquote><pre>{@code
6484 * // get an iterator from a list
6485 * static List<String> reverseStep(List<String> r, String e) {
6486 * r.add(0, e);
6487 * return r;
6488 * }
6489 * static List<String> newArrayList() { return new ArrayList<>(); }
6490 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
6491 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
6492 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
6493 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
6494 * assertEquals(reversedList, (List<String>) loop.invoke(list));
6495 * }</pre></blockquote>
6496 *
6497 * @apiNote The implementation of this method can be expressed approximately as follows:
6498 * <blockquote><pre>{@code
6499 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6500 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
6501 * Class<?> returnType = body.type().returnType();
6502 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6503 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
6504 * MethodHandle retv = null, step = body, startIter = iterator;
6505 * if (returnType != void.class) {
6506 * // the simple thing first: in (I V A...), drop the I to get V
6507 * retv = dropArguments(identity(returnType), 0, Iterator.class);
6508 * // body type signature (V T A...), internal loop types (I V A...)
6509 * step = swapArguments(body, 0, 1); // swap V <-> T
6510 * }
6511 * if (startIter == null) startIter = MH_getIter;
6512 * MethodHandle[]
6513 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
6514 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
6515 * return loop(iterVar, bodyClause);
6516 * }
6517 * }</pre></blockquote>
6518 *
6519 * @param iterator an optional handle to return the iterator to start the loop.
6520 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
6521 * See above for other constraints.
6522 * @param init optional initializer, providing the initial value of the loop variable.
6523 * May be {@code null}, implying a default initial value. See above for other constraints.
6524 * @param body body of the loop, which may not be {@code null}.
6525 * It controls the loop parameters and result type in the standard case (see above for details).
6526 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
6527 * and may accept any number of additional types.
6528 * See above for other constraints.
6529 *
6530 * @return a method handle embodying the iteration loop functionality.
6531 * @throws NullPointerException if the {@code body} handle is {@code null}.
6532 * @throws IllegalArgumentException if any argument violates the above requirements.
6533 *
6534 * @since 9
6535 */
6536 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6537 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
6538 Class<?> returnType = body.type().returnType();
6539 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
6540 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
6541 MethodHandle startIter;
6542 MethodHandle nextVal;
6543 {
6544 MethodType iteratorType;
6545 if (iterator == null) {
6546 // derive argument type from body, if available, else use Iterable
6547 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
6548 iteratorType = startIter.type().changeParameterType(0, iterableType);
6549 } else {
6550 // force return type to the internal iterator class
6551 iteratorType = iterator.type().changeReturnType(Iterator.class);
6552 startIter = iterator;
6553 }
6554 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6555 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
6556
6557 // perform the asType transforms under an exception transformer, as per spec.:
6558 try {
6559 startIter = startIter.asType(iteratorType);
6560 nextVal = nextRaw.asType(nextValType);
6561 } catch (WrongMethodTypeException ex) {
6562 throw new IllegalArgumentException(ex);
6563 }
6564 }
6565
6566 MethodHandle retv = null, step = body;
6567 if (returnType != void.class) {
6568 // the simple thing first: in (I V A...), drop the I to get V
6569 retv = dropArguments(identity(returnType), 0, Iterator.class);
6570 // body type signature (V T A...), internal loop types (I V A...)
6571 step = swapArguments(body, 0, 1); // swap V <-> T
6572 }
6573
6574 MethodHandle[]
6575 iterVar = { startIter, null, hasNext, retv },
6576 bodyClause = { init, filterArgument(step, 0, nextVal) };
6577 return loop(iterVar, bodyClause);
6578 }
6579
6580 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6581 Objects.requireNonNull(body);
6582 MethodType bodyType = body.type();
6583 Class<?> returnType = bodyType.returnType();
6584 List<Class<?>> internalParamList = bodyType.parameterList();
6585 // strip leading V value if present
6586 int vsize = (returnType == void.class ? 0 : 1);
6587 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
6588 // argument list has no "V" => error
6589 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6590 throw misMatchedTypes("body function", bodyType, expected);
6591 } else if (internalParamList.size() <= vsize) {
6592 // missing T type => error
6593 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
6594 throw misMatchedTypes("body function", bodyType, expected);
6595 }
6596 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
6597 Class<?> iterableType = null;
6598 if (iterator != null) {
6599 // special case; if the body handle only declares V and T then
6600 // the external parameter list is obtained from iterator handle
6601 if (externalParamList.isEmpty()) {
6602 externalParamList = iterator.type().parameterList();
6603 }
6604 MethodType itype = iterator.type();
6605 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
6606 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
6607 }
6608 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
6609 MethodType expected = methodType(itype.returnType(), externalParamList);
6610 throw misMatchedTypes("iterator parameters", itype, expected);
6611 }
6612 } else {
6613 if (externalParamList.isEmpty()) {
6614 // special case; if the iterator handle is null and the body handle
6615 // only declares V and T then the external parameter list consists
6616 // of Iterable
6617 externalParamList = Arrays.asList(Iterable.class);
6618 iterableType = Iterable.class;
6619 } else {
6620 // special case; if the iterator handle is null and the external
6621 // parameter list is not empty then the first parameter must be
6622 // assignable to Iterable
6623 iterableType = externalParamList.get(0);
6624 if (!Iterable.class.isAssignableFrom(iterableType)) {
6625 throw newIllegalArgumentException(
6626 "inferred first loop argument must inherit from Iterable: " + iterableType);
6627 }
6628 }
6629 }
6630 if (init != null) {
6631 MethodType initType = init.type();
6632 if (initType.returnType() != returnType ||
6633 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
6634 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
6635 }
6636 }
6637 return iterableType; // help the caller a bit
6638 }
6639
6640 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
6641 // there should be a better way to uncross my wires
6642 int arity = mh.type().parameterCount();
6643 int[] order = new int[arity];
6644 for (int k = 0; k < arity; k++) order[k] = k;
6645 order[i] = j; order[j] = i;
6646 Class<?>[] types = mh.type().parameterArray();
6647 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
6648 MethodType swapType = methodType(mh.type().returnType(), types);
6649 return permuteArguments(mh, swapType, order);
6650 }
6651
6652 /**
6653 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
6654 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
6655 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
6656 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
6657 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
6658 * {@code try-finally} handle.
6659 * <p>
6660 * The {@code cleanup} handle will be passed one or two additional leading arguments.
6661 * The first is the exception thrown during the
6662 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
6663 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
6664 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
6665 * The second argument is not present if the {@code target} handle has a {@code void} return type.
6666 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
6667 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
6668 * <p>
6669 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
6670 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
6671 * two extra leading parameters:<ul>
6672 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
6673 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
6674 * the result from the execution of the {@code target} handle.
6675 * This parameter is not present if the {@code target} returns {@code void}.
6676 * </ul>
6677 * <p>
6678 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
6679 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
6680 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
6681 * the cleanup.
6682 * <blockquote><pre>{@code
6683 * V target(A..., B...);
6684 * V cleanup(Throwable, V, A...);
6685 * V adapter(A... a, B... b) {
6686 * V result = (zero value for V);
6687 * Throwable throwable = null;
6688 * try {
6689 * result = target(a..., b...);
6690 * } catch (Throwable t) {
6691 * throwable = t;
6692 * throw t;
6693 * } finally {
6694 * result = cleanup(throwable, result, a...);
6695 * }
6696 * return result;
6697 * }
6698 * }</pre></blockquote>
6699 * <p>
6700 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6701 * be modified by execution of the target, and so are passed unchanged
6702 * from the caller to the cleanup, if it is invoked.
6703 * <p>
6704 * The target and cleanup must return the same type, even if the cleanup
6705 * always throws.
6706 * To create such a throwing cleanup, compose the cleanup logic
6707 * with {@link #throwException throwException},
6708 * in order to create a method handle of the correct return type.
6709 * <p>
6710 * Note that {@code tryFinally} never converts exceptions into normal returns.
6711 * In rare cases where exceptions must be converted in that way, first wrap
6712 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
6713 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
6714 * <p>
6715 * It is recommended that the first parameter type of {@code cleanup} be
6716 * declared {@code Throwable} rather than a narrower subtype. This ensures
6717 * {@code cleanup} will always be invoked with whatever exception that
6718 * {@code target} throws. Declaring a narrower type may result in a
6719 * {@code ClassCastException} being thrown by the {@code try-finally}
6720 * handle if the type of the exception thrown by {@code target} is not
6721 * assignable to the first parameter type of {@code cleanup}. Note that
6722 * various exception types of {@code VirtualMachineError},
6723 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6724 * thrown by almost any kind of Java code, and a finally clause that
6725 * catches (say) only {@code IOException} would mask any of the others
6726 * behind a {@code ClassCastException}.
6727 *
6728 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6729 * @param cleanup the handle that is invoked in the finally block.
6730 *
6731 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6732 * @throws NullPointerException if any argument is null
6733 * @throws IllegalArgumentException if {@code cleanup} does not accept
6734 * the required leading arguments, or if the method handle types do
6735 * not match in their return types and their
6736 * corresponding trailing parameters
6737 *
6738 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
6739 * @since 9
6740 */
6741 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
6742 List<Class<?>> targetParamTypes = target.type().parameterList();
6743 Class<?> rtype = target.type().returnType();
6744
6745 tryFinallyChecks(target, cleanup);
6746
6747 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
6748 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6749 // target parameter list.
6750 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
6751
6752 // Ensure that the intrinsic type checks the instance thrown by the
6753 // target against the first parameter of cleanup
6754 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
6755
6756 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
6757 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
6758 }
6759
6760 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
6761 Class<?> rtype = target.type().returnType();
6762 if (rtype != cleanup.type().returnType()) {
6763 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
6764 }
6765 MethodType cleanupType = cleanup.type();
6766 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
6767 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
6768 }
6769 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
6770 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
6771 }
6772 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6773 // target parameter list.
6774 int cleanupArgIndex = rtype == void.class ? 1 : 2;
6775 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
6776 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
6777 cleanup.type(), target.type());
6778 }
6779 }
6780
6781 }