1 /*
2 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.misc.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.Set;
58 import java.util.concurrent.ConcurrentHashMap;
59 import java.util.stream.Collectors;
60 import java.util.stream.Stream;
61
62 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
63 import static java.lang.invoke.MethodHandleNatives.Constants.*;
64 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
65 import static java.lang.invoke.MethodType.methodType;
66
67 /**
68 * This class consists exclusively of static methods that operate on or return
69 * method handles. They fall into several categories:
70 * <ul>
71 * <li>Lookup methods which help create method handles for methods and fields.
72 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
73 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
74 * </ul>
75 * A lookup, combinator, or factory method will fail and throw an
76 * {@code IllegalArgumentException} if the created method handle's type
77 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
78 *
79 * @author John Rose, JSR 292 EG
80 * @since 1.7
81 */
82 public class MethodHandles {
83
84 private MethodHandles() { } // do not instantiate
85
86 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
87
88 // See IMPL_LOOKUP below.
89
90 //// Method handle creation from ordinary methods.
91
92 /**
93 * Returns a {@link Lookup lookup object} with
94 * full capabilities to emulate all supported bytecode behaviors of the caller.
95 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
96 * Factory methods on the lookup object can create
97 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
98 * for any member that the caller has access to via bytecodes,
99 * including protected and private fields and methods.
100 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
101 * Do not store it in place where untrusted code can access it.
102 * <p>
103 * This method is caller sensitive, which means that it may return different
104 * values to different callers.
105 * @return a lookup object for the caller of this method, with private access
106 */
107 @CallerSensitive
108 @ForceInline // to ensure Reflection.getCallerClass optimization
109 public static Lookup lookup() {
110 return new Lookup(Reflection.getCallerClass());
111 }
112
113 /**
114 * This reflected$lookup method is the alternate implementation of
115 * the lookup method when being invoked by reflection.
116 */
117 @CallerSensitive
118 private static Lookup reflected$lookup() {
119 Class<?> caller = Reflection.getCallerClass();
120 if (caller.getClassLoader() == null) {
121 throw newIllegalArgumentException("illegal lookupClass: "+caller);
122 }
123 return new Lookup(caller);
124 }
125
126 /**
127 * Returns a {@link Lookup lookup object} which is trusted minimally.
128 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
129 * It can only be used to create method handles to public members of
130 * public classes in packages that are exported unconditionally.
131 * <p>
132 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
133 * of this lookup object will be {@link java.lang.Object}.
134 *
135 * @apiNote The use of Object is conventional, and because the lookup modes are
136 * limited, there is no special access provided to the internals of Object, its package
137 * or its module. Consequently, the lookup context of this lookup object will be the
138 * bootstrap class loader, which means it cannot find user classes.
139 *
140 * <p style="font-size:smaller;">
141 * <em>Discussion:</em>
142 * The lookup class can be changed to any other class {@code C} using an expression of the form
143 * {@link Lookup#in publicLookup().in(C.class)}.
144 * but may change the lookup context by virtue of changing the class loader.
145 * A public lookup object is always subject to
146 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
147 * Also, it cannot access
148 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
149 * @return a lookup object which is trusted minimally
150 *
151 * @revised 9
152 * @spec JPMS
153 */
154 public static Lookup publicLookup() {
155 return Lookup.PUBLIC_LOOKUP;
156 }
157
158 /**
159 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
160 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
161 * private access</a>, on a target class.
162 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
163 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
164 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
165 * the target class, then this check ensures that
166 * <ul>
167 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
168 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
169 * the target class to at least {@code m1}.</li>
170 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
171 * </ul>
172 * <p>
173 * If there is a security manager, its {@code checkPermission} method is called to
174 * check {@code ReflectPermission("suppressAccessChecks")}.
175 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
176 * was created by code in the caller module (or derived from a lookup object originally
177 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
178 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
179 * access to the caller.
180 * @param targetClass the target class
181 * @param lookup the caller lookup object
182 * @return a lookup object for the target class, with private access
183 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
184 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
185 * @throws IllegalAccessException if the access check specified above fails
186 * @throws SecurityException if denied by the security manager
187 * @since 9
188 * @spec JPMS
189 * @see Lookup#dropLookupMode
190 */
191 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
192 SecurityManager sm = System.getSecurityManager();
193 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
194 if (targetClass.isPrimitive())
195 throw new IllegalArgumentException(targetClass + " is a primitive class");
196 if (targetClass.isArray())
197 throw new IllegalArgumentException(targetClass + " is an array class");
198 Module targetModule = targetClass.getModule();
199 Module callerModule = lookup.lookupClass().getModule();
200 if (!callerModule.canRead(targetModule))
201 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
202 if (targetModule.isNamed()) {
203 String pn = targetClass.getPackageName();
204 assert pn.length() > 0 : "unnamed package cannot be in named module";
205 if (!targetModule.isOpen(pn, callerModule))
206 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
207 }
208 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
209 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
210 if (!callerModule.isNamed() && targetModule.isNamed()) {
211 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
212 if (logger != null) {
213 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
214 }
215 }
216 return new Lookup(targetClass);
217 }
218
219 /**
220 * Performs an unchecked "crack" of a
221 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
222 * The result is as if the user had obtained a lookup object capable enough
223 * to crack the target method handle, called
224 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
225 * on the target to obtain its symbolic reference, and then called
226 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
227 * to resolve the symbolic reference to a member.
228 * <p>
229 * If there is a security manager, its {@code checkPermission} method
230 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
231 * @param <T> the desired type of the result, either {@link Member} or a subtype
232 * @param target a direct method handle to crack into symbolic reference components
233 * @param expected a class object representing the desired result type {@code T}
234 * @return a reference to the method, constructor, or field object
235 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
236 * @exception NullPointerException if either argument is {@code null}
237 * @exception IllegalArgumentException if the target is not a direct method handle
238 * @exception ClassCastException if the member is not of the expected type
239 * @since 1.8
240 */
241 public static <T extends Member> T
242 reflectAs(Class<T> expected, MethodHandle target) {
243 SecurityManager smgr = System.getSecurityManager();
244 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
245 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
246 return lookup.revealDirect(target).reflectAs(expected, lookup);
247 }
248 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
249 private static final java.security.Permission ACCESS_PERMISSION =
250 new ReflectPermission("suppressAccessChecks");
251
252 /**
253 * A <em>lookup object</em> is a factory for creating method handles,
254 * when the creation requires access checking.
255 * Method handles do not perform
256 * access checks when they are called, but rather when they are created.
257 * Therefore, method handle access
258 * restrictions must be enforced when a method handle is created.
259 * The caller class against which those restrictions are enforced
260 * is known as the {@linkplain #lookupClass() lookup class}.
261 * <p>
262 * A lookup class which needs to create method handles will call
263 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
264 * When the {@code Lookup} factory object is created, the identity of the lookup class is
265 * determined, and securely stored in the {@code Lookup} object.
266 * The lookup class (or its delegates) may then use factory methods
267 * on the {@code Lookup} object to create method handles for access-checked members.
268 * This includes all methods, constructors, and fields which are allowed to the lookup class,
269 * even private ones.
270 *
271 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
272 * The factory methods on a {@code Lookup} object correspond to all major
273 * use cases for methods, constructors, and fields.
274 * Each method handle created by a factory method is the functional
275 * equivalent of a particular <em>bytecode behavior</em>.
276 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
277 * Here is a summary of the correspondence between these factory methods and
278 * the behavior of the resulting method handles:
279 * <table class="striped">
280 * <caption style="display:none">lookup method behaviors</caption>
281 * <thead>
282 * <tr>
283 * <th scope="col"><a id="equiv"></a>lookup expression</th>
284 * <th scope="col">member</th>
285 * <th scope="col">bytecode behavior</th>
286 * </tr>
287 * </thead>
288 * <tbody>
289 * <tr>
290 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
291 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
292 * </tr>
293 * <tr>
294 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
295 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
296 * </tr>
297 * <tr>
298 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
299 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
300 * </tr>
301 * <tr>
302 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
303 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
304 * </tr>
305 * <tr>
306 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
307 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
308 * </tr>
309 * <tr>
310 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
311 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
312 * </tr>
313 * <tr>
314 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
315 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
316 * </tr>
317 * <tr>
318 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
319 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
320 * </tr>
321 * <tr>
322 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
323 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
324 * </tr>
325 * <tr>
326 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
327 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
328 * </tr>
329 * <tr>
330 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
331 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
332 * </tr>
333 * <tr>
334 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
335 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
336 * </tr>
337 * <tr>
338 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
339 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
340 * </tr>
341 * <tr>
342 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
343 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
344 * </tr>
345 * </tbody>
346 * </table>
347 *
348 * Here, the type {@code C} is the class or interface being searched for a member,
349 * documented as a parameter named {@code refc} in the lookup methods.
350 * The method type {@code MT} is composed from the return type {@code T}
351 * and the sequence of argument types {@code A*}.
352 * The constructor also has a sequence of argument types {@code A*} and
353 * is deemed to return the newly-created object of type {@code C}.
354 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
355 * The formal parameter {@code this} stands for the self-reference of type {@code C};
356 * if it is present, it is always the leading argument to the method handle invocation.
357 * (In the case of some {@code protected} members, {@code this} may be
358 * restricted in type to the lookup class; see below.)
359 * The name {@code arg} stands for all the other method handle arguments.
360 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
361 * stands for a null reference if the accessed method or field is static,
362 * and {@code this} otherwise.
363 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
364 * for reflective objects corresponding to the given members.
365 * <p>
366 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
367 * as if by {@code ldc CONSTANT_Class}.
368 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
369 * <p>
370 * In cases where the given member is of variable arity (i.e., a method or constructor)
371 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
372 * In all other cases, the returned method handle will be of fixed arity.
373 * <p style="font-size:smaller;">
374 * <em>Discussion:</em>
375 * The equivalence between looked-up method handles and underlying
376 * class members and bytecode behaviors
377 * can break down in a few ways:
378 * <ul style="font-size:smaller;">
379 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
380 * the lookup can still succeed, even when there is no equivalent
381 * Java expression or bytecoded constant.
382 * <li>Likewise, if {@code T} or {@code MT}
383 * is not symbolically accessible from the lookup class's loader,
384 * the lookup can still succeed.
385 * For example, lookups for {@code MethodHandle.invokeExact} and
386 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
387 * <li>If there is a security manager installed, it can forbid the lookup
388 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
389 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
390 * constant is not subject to security manager checks.
391 * <li>If the looked-up method has a
392 * <a href="MethodHandle.html#maxarity">very large arity</a>,
393 * the method handle creation may fail with an
394 * {@code IllegalArgumentException}, due to the method handle type having
395 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
396 * </ul>
397 *
398 * <h1><a id="access"></a>Access checking</h1>
399 * Access checks are applied in the factory methods of {@code Lookup},
400 * when a method handle is created.
401 * This is a key difference from the Core Reflection API, since
402 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
403 * performs access checking against every caller, on every call.
404 * <p>
405 * All access checks start from a {@code Lookup} object, which
406 * compares its recorded lookup class against all requests to
407 * create method handles.
408 * A single {@code Lookup} object can be used to create any number
409 * of access-checked method handles, all checked against a single
410 * lookup class.
411 * <p>
412 * A {@code Lookup} object can be shared with other trusted code,
413 * such as a metaobject protocol.
414 * A shared {@code Lookup} object delegates the capability
415 * to create method handles on private members of the lookup class.
416 * Even if privileged code uses the {@code Lookup} object,
417 * the access checking is confined to the privileges of the
418 * original lookup class.
419 * <p>
420 * A lookup can fail, because
421 * the containing class is not accessible to the lookup class, or
422 * because the desired class member is missing, or because the
423 * desired class member is not accessible to the lookup class, or
424 * because the lookup object is not trusted enough to access the member.
425 * In any of these cases, a {@code ReflectiveOperationException} will be
426 * thrown from the attempted lookup. The exact class will be one of
427 * the following:
428 * <ul>
429 * <li>NoSuchMethodException — if a method is requested but does not exist
430 * <li>NoSuchFieldException — if a field is requested but does not exist
431 * <li>IllegalAccessException — if the member exists but an access check fails
432 * </ul>
433 * <p>
434 * In general, the conditions under which a method handle may be
435 * looked up for a method {@code M} are no more restrictive than the conditions
436 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
437 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
438 * a method handle lookup will generally raise a corresponding
439 * checked exception, such as {@code NoSuchMethodException}.
440 * And the effect of invoking the method handle resulting from the lookup
441 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
442 * to executing the compiled, verified, and resolved call to {@code M}.
443 * The same point is true of fields and constructors.
444 * <p style="font-size:smaller;">
445 * <em>Discussion:</em>
446 * Access checks only apply to named and reflected methods,
447 * constructors, and fields.
448 * Other method handle creation methods, such as
449 * {@link MethodHandle#asType MethodHandle.asType},
450 * do not require any access checks, and are used
451 * independently of any {@code Lookup} object.
452 * <p>
453 * If the desired member is {@code protected}, the usual JVM rules apply,
454 * including the requirement that the lookup class must either be in the
455 * same package as the desired member, or must inherit that member.
456 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
457 * In addition, if the desired member is a non-static field or method
458 * in a different package, the resulting method handle may only be applied
459 * to objects of the lookup class or one of its subclasses.
460 * This requirement is enforced by narrowing the type of the leading
461 * {@code this} parameter from {@code C}
462 * (which will necessarily be a superclass of the lookup class)
463 * to the lookup class itself.
464 * <p>
465 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
466 * that the receiver argument must match both the resolved method <em>and</em>
467 * the current class. Again, this requirement is enforced by narrowing the
468 * type of the leading parameter to the resulting method handle.
469 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
470 * <p>
471 * The JVM represents constructors and static initializer blocks as internal methods
472 * with special names ({@code "<init>"} and {@code "<clinit>"}).
473 * The internal syntax of invocation instructions allows them to refer to such internal
474 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
475 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
476 * <p>
477 * If the relationship between nested types is expressed directly through the
478 * {@code NestHost} and {@code NestMembers} attributes
479 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
480 * then the associated {@code Lookup} object provides direct access to
481 * the lookup class and all of its nestmates
482 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
483 * Otherwise, access between nested classes is obtained by the Java compiler creating
484 * a wrapper method to access a private method of another class in the same nest.
485 * For example, a nested class {@code C.D}
486 * can access private members within other related classes such as
487 * {@code C}, {@code C.D.E}, or {@code C.B},
488 * but the Java compiler may need to generate wrapper methods in
489 * those related classes. In such cases, a {@code Lookup} object on
490 * {@code C.E} would be unable to access those private members.
491 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
492 * which can transform a lookup on {@code C.E} into one on any of those other
493 * classes, without special elevation of privilege.
494 * <p>
495 * The accesses permitted to a given lookup object may be limited,
496 * according to its set of {@link #lookupModes lookupModes},
497 * to a subset of members normally accessible to the lookup class.
498 * For example, the {@link MethodHandles#publicLookup publicLookup}
499 * method produces a lookup object which is only allowed to access
500 * public members in public classes of exported packages.
501 * The caller sensitive method {@link MethodHandles#lookup lookup}
502 * produces a lookup object with full capabilities relative to
503 * its caller class, to emulate all supported bytecode behaviors.
504 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
505 * with fewer access modes than the original lookup object.
506 *
507 * <p style="font-size:smaller;">
508 * <a id="privacc"></a>
509 * <em>Discussion of private access:</em>
510 * We say that a lookup has <em>private access</em>
511 * if its {@linkplain #lookupModes lookup modes}
512 * include the possibility of accessing {@code private} members
513 * (which includes the private members of nestmates).
514 * As documented in the relevant methods elsewhere,
515 * only lookups with private access possess the following capabilities:
516 * <ul style="font-size:smaller;">
517 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
518 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
519 * such as {@code Class.forName}
520 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
521 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
522 * for classes accessible to the lookup class
523 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
524 * within the same package member
525 * </ul>
526 * <p style="font-size:smaller;">
527 * Each of these permissions is a consequence of the fact that a lookup object
528 * with private access can be securely traced back to an originating class,
529 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
530 * can be reliably determined and emulated by method handles.
531 *
532 * <h1><a id="secmgr"></a>Security manager interactions</h1>
533 * Although bytecode instructions can only refer to classes in
534 * a related class loader, this API can search for methods in any
535 * class, as long as a reference to its {@code Class} object is
536 * available. Such cross-loader references are also possible with the
537 * Core Reflection API, and are impossible to bytecode instructions
538 * such as {@code invokestatic} or {@code getfield}.
539 * There is a {@linkplain java.lang.SecurityManager security manager API}
540 * to allow applications to check such cross-loader references.
541 * These checks apply to both the {@code MethodHandles.Lookup} API
542 * and the Core Reflection API
543 * (as found on {@link java.lang.Class Class}).
544 * <p>
545 * If a security manager is present, member and class lookups are subject to
546 * additional checks.
547 * From one to three calls are made to the security manager.
548 * Any of these calls can refuse access by throwing a
549 * {@link java.lang.SecurityException SecurityException}.
550 * Define {@code smgr} as the security manager,
551 * {@code lookc} as the lookup class of the current lookup object,
552 * {@code refc} as the containing class in which the member
553 * is being sought, and {@code defc} as the class in which the
554 * member is actually defined.
555 * (If a class or other type is being accessed,
556 * the {@code refc} and {@code defc} values are the class itself.)
557 * The value {@code lookc} is defined as <em>not present</em>
558 * if the current lookup object does not have
559 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
560 * The calls are made according to the following rules:
561 * <ul>
562 * <li><b>Step 1:</b>
563 * If {@code lookc} is not present, or if its class loader is not
564 * the same as or an ancestor of the class loader of {@code refc},
565 * then {@link SecurityManager#checkPackageAccess
566 * smgr.checkPackageAccess(refcPkg)} is called,
567 * where {@code refcPkg} is the package of {@code refc}.
568 * <li><b>Step 2a:</b>
569 * If the retrieved member is not public and
570 * {@code lookc} is not present, then
571 * {@link SecurityManager#checkPermission smgr.checkPermission}
572 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
573 * <li><b>Step 2b:</b>
574 * If the retrieved class has a {@code null} class loader,
575 * and {@code lookc} is not present, then
576 * {@link SecurityManager#checkPermission smgr.checkPermission}
577 * with {@code RuntimePermission("getClassLoader")} is called.
578 * <li><b>Step 3:</b>
579 * If the retrieved member is not public,
580 * and if {@code lookc} is not present,
581 * and if {@code defc} and {@code refc} are different,
582 * then {@link SecurityManager#checkPackageAccess
583 * smgr.checkPackageAccess(defcPkg)} is called,
584 * where {@code defcPkg} is the package of {@code defc}.
585 * </ul>
586 * Security checks are performed after other access checks have passed.
587 * Therefore, the above rules presuppose a member or class that is public,
588 * or else that is being accessed from a lookup class that has
589 * rights to access the member or class.
590 *
591 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
592 * A small number of Java methods have a special property called caller sensitivity.
593 * A <em>caller-sensitive</em> method can behave differently depending on the
594 * identity of its immediate caller.
595 * <p>
596 * If a method handle for a caller-sensitive method is requested,
597 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
598 * but they take account of the lookup class in a special way.
599 * The resulting method handle behaves as if it were called
600 * from an instruction contained in the lookup class,
601 * so that the caller-sensitive method detects the lookup class.
602 * (By contrast, the invoker of the method handle is disregarded.)
603 * Thus, in the case of caller-sensitive methods,
604 * different lookup classes may give rise to
605 * differently behaving method handles.
606 * <p>
607 * In cases where the lookup object is
608 * {@link MethodHandles#publicLookup() publicLookup()},
609 * or some other lookup object without
610 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
611 * the lookup class is disregarded.
612 * In such cases, no caller-sensitive method handle can be created,
613 * access is forbidden, and the lookup fails with an
614 * {@code IllegalAccessException}.
615 * <p style="font-size:smaller;">
616 * <em>Discussion:</em>
617 * For example, the caller-sensitive method
618 * {@link java.lang.Class#forName(String) Class.forName(x)}
619 * can return varying classes or throw varying exceptions,
620 * depending on the class loader of the class that calls it.
621 * A public lookup of {@code Class.forName} will fail, because
622 * there is no reasonable way to determine its bytecode behavior.
623 * <p style="font-size:smaller;">
624 * If an application caches method handles for broad sharing,
625 * it should use {@code publicLookup()} to create them.
626 * If there is a lookup of {@code Class.forName}, it will fail,
627 * and the application must take appropriate action in that case.
628 * It may be that a later lookup, perhaps during the invocation of a
629 * bootstrap method, can incorporate the specific identity
630 * of the caller, making the method accessible.
631 * <p style="font-size:smaller;">
632 * The function {@code MethodHandles.lookup} is caller sensitive
633 * so that there can be a secure foundation for lookups.
634 * Nearly all other methods in the JSR 292 API rely on lookup
635 * objects to check access requests.
636 *
637 * @revised 9
638 */
639 public static final
640 class Lookup {
641 /** The class on behalf of whom the lookup is being performed. */
642 private final Class<?> lookupClass;
643
644 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
645 private final int allowedModes;
646
647 static {
648 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
649 }
650
651 /** A single-bit mask representing {@code public} access,
652 * which may contribute to the result of {@link #lookupModes lookupModes}.
653 * The value, {@code 0x01}, happens to be the same as the value of the
654 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
655 */
656 public static final int PUBLIC = Modifier.PUBLIC;
657
658 /** A single-bit mask representing {@code private} access,
659 * which may contribute to the result of {@link #lookupModes lookupModes}.
660 * The value, {@code 0x02}, happens to be the same as the value of the
661 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
662 */
663 public static final int PRIVATE = Modifier.PRIVATE;
664
665 /** A single-bit mask representing {@code protected} access,
666 * which may contribute to the result of {@link #lookupModes lookupModes}.
667 * The value, {@code 0x04}, happens to be the same as the value of the
668 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
669 */
670 public static final int PROTECTED = Modifier.PROTECTED;
671
672 /** A single-bit mask representing {@code package} access (default access),
673 * which may contribute to the result of {@link #lookupModes lookupModes}.
674 * The value is {@code 0x08}, which does not correspond meaningfully to
675 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
676 */
677 public static final int PACKAGE = Modifier.STATIC;
678
679 /** A single-bit mask representing {@code module} access (default access),
680 * which may contribute to the result of {@link #lookupModes lookupModes}.
681 * The value is {@code 0x10}, which does not correspond meaningfully to
682 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
683 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
684 * with this lookup mode can access all public types in the module of the
685 * lookup class and public types in packages exported by other modules
686 * to the module of the lookup class.
687 * @since 9
688 * @spec JPMS
689 */
690 public static final int MODULE = PACKAGE << 1;
691
692 /** A single-bit mask representing {@code unconditional} access
693 * which may contribute to the result of {@link #lookupModes lookupModes}.
694 * The value is {@code 0x20}, which does not correspond meaningfully to
695 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
696 * A {@code Lookup} with this lookup mode assumes {@linkplain
697 * java.lang.Module#canRead(java.lang.Module) readability}.
698 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
699 * with this lookup mode can access all public members of public types
700 * of all modules where the type is in a package that is {@link
701 * java.lang.Module#isExported(String) exported unconditionally}.
702 * @since 9
703 * @spec JPMS
704 * @see #publicLookup()
705 */
706 public static final int UNCONDITIONAL = PACKAGE << 2;
707
708 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
709 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
710 private static final int TRUSTED = -1;
711
712 private static int fixmods(int mods) {
713 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
714 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
715 }
716
717 /** Tells which class is performing the lookup. It is this class against
718 * which checks are performed for visibility and access permissions.
719 * <p>
720 * The class implies a maximum level of access permission,
721 * but the permissions may be additionally limited by the bitmask
722 * {@link #lookupModes lookupModes}, which controls whether non-public members
723 * can be accessed.
724 * @return the lookup class, on behalf of which this lookup object finds members
725 */
726 public Class<?> lookupClass() {
727 return lookupClass;
728 }
729
730 // This is just for calling out to MethodHandleImpl.
731 private Class<?> lookupClassOrNull() {
732 return (allowedModes == TRUSTED) ? null : lookupClass;
733 }
734
735 /** Tells which access-protection classes of members this lookup object can produce.
736 * The result is a bit-mask of the bits
737 * {@linkplain #PUBLIC PUBLIC (0x01)},
738 * {@linkplain #PRIVATE PRIVATE (0x02)},
739 * {@linkplain #PROTECTED PROTECTED (0x04)},
740 * {@linkplain #PACKAGE PACKAGE (0x08)},
741 * {@linkplain #MODULE MODULE (0x10)},
742 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
743 * <p>
744 * A freshly-created lookup object
745 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
746 * all possible bits set, except {@code UNCONDITIONAL}.
747 * A lookup object on a new lookup class
748 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
749 * may have some mode bits set to zero.
750 * Mode bits can also be
751 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
752 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
753 * The purpose of this is to restrict access via the new lookup object,
754 * so that it can access only names which can be reached by the original
755 * lookup object, and also by the new lookup class.
756 * @return the lookup modes, which limit the kinds of access performed by this lookup object
757 * @see #in
758 * @see #dropLookupMode
759 *
760 * @revised 9
761 * @spec JPMS
762 */
763 public int lookupModes() {
764 return allowedModes & ALL_MODES;
765 }
766
767 /** Embody the current class (the lookupClass) as a lookup class
768 * for method handle creation.
769 * Must be called by from a method in this package,
770 * which in turn is called by a method not in this package.
771 */
772 Lookup(Class<?> lookupClass) {
773 this(lookupClass, FULL_POWER_MODES);
774 // make sure we haven't accidentally picked up a privileged class:
775 checkUnprivilegedlookupClass(lookupClass);
776 }
777
778 private Lookup(Class<?> lookupClass, int allowedModes) {
779 this.lookupClass = lookupClass;
780 this.allowedModes = allowedModes;
781 }
782
783 /**
784 * Creates a lookup on the specified new lookup class.
785 * The resulting object will report the specified
786 * class as its own {@link #lookupClass() lookupClass}.
787 * <p>
788 * However, the resulting {@code Lookup} object is guaranteed
789 * to have no more access capabilities than the original.
790 * In particular, access capabilities can be lost as follows:<ul>
791 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
792 * the new lookup class is in a different module {@code M}, then no members, not
793 * even public members in {@code M}'s exported packages, will be accessible.
794 * The exception to this is when this lookup is {@link #publicLookup()
795 * publicLookup}, in which case {@code PUBLIC} access is not lost.
796 * <li>If the old lookup class is in an unnamed module, and the new lookup class
797 * is a different module then {@link #MODULE MODULE} access is lost.
798 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
799 * <li>If the new lookup class is in a different package
800 * than the old one, protected and default (package) members will not be accessible.
801 * <li>If the new lookup class is not within the same package member
802 * as the old one, private members will not be accessible, and protected members
803 * will not be accessible by virtue of inheritance.
804 * (Protected members may continue to be accessible because of package sharing.)
805 * <li>If the new lookup class is not accessible to the old lookup class,
806 * then no members, not even public members, will be accessible.
807 * (In all other cases, public members will continue to be accessible.)
808 * </ul>
809 * <p>
810 * The resulting lookup's capabilities for loading classes
811 * (used during {@link #findClass} invocations)
812 * are determined by the lookup class' loader,
813 * which may change due to this operation.
814 *
815 * @param requestedLookupClass the desired lookup class for the new lookup object
816 * @return a lookup object which reports the desired lookup class, or the same object
817 * if there is no change
818 * @throws NullPointerException if the argument is null
819 *
820 * @revised 9
821 * @spec JPMS
822 */
823 public Lookup in(Class<?> requestedLookupClass) {
824 Objects.requireNonNull(requestedLookupClass);
825 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
826 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
827 if (requestedLookupClass == this.lookupClass)
828 return this; // keep same capabilities
829 int newModes = (allowedModes & FULL_POWER_MODES);
830 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
831 // Need to drop all access when teleporting from a named module to another
832 // module. The exception is publicLookup where PUBLIC is not lost.
833 if (this.lookupClass.getModule().isNamed()
834 && (this.allowedModes & UNCONDITIONAL) == 0)
835 newModes = 0;
836 else
837 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
838 }
839 if ((newModes & PACKAGE) != 0
840 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
841 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
842 }
843 // Allow nestmate lookups to be created without special privilege:
844 if ((newModes & PRIVATE) != 0
845 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
846 newModes &= ~(PRIVATE|PROTECTED);
847 }
848 if ((newModes & PUBLIC) != 0
849 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
850 // The requested class it not accessible from the lookup class.
851 // No permissions.
852 newModes = 0;
853 }
854
855 checkUnprivilegedlookupClass(requestedLookupClass);
856 return new Lookup(requestedLookupClass, newModes);
857 }
858
859
860 /**
861 * Creates a lookup on the same lookup class which this lookup object
862 * finds members, but with a lookup mode that has lost the given lookup mode.
863 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
864 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
865 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
866 * dropped and so the resulting lookup mode will never have these access capabilities.
867 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
868 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
869 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
870 * is dropped then the resulting lookup has no access.
871 * @param modeToDrop the lookup mode to drop
872 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
873 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
874 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
875 * @see MethodHandles#privateLookupIn
876 * @since 9
877 */
878 public Lookup dropLookupMode(int modeToDrop) {
879 int oldModes = lookupModes();
880 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
881 switch (modeToDrop) {
882 case PUBLIC: newModes &= ~(ALL_MODES); break;
883 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
884 case PACKAGE: newModes &= ~(PRIVATE); break;
885 case PROTECTED:
886 case PRIVATE:
887 case UNCONDITIONAL: break;
888 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
889 }
890 if (newModes == oldModes) return this; // return self if no change
891 return new Lookup(lookupClass(), newModes);
892 }
893
894 /**
895 * Defines a class to the same class loader and in the same runtime package and
896 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
897 * {@linkplain #lookupClass() lookup class}.
898 *
899 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
900 * {@link #PACKAGE PACKAGE} access as default (package) members will be
901 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
902 * that the lookup object was created by a caller in the runtime package (or derived
903 * from a lookup originally created by suitably privileged code to a target class in
904 * the runtime package). </p>
905 *
906 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
907 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
908 * same package as the lookup class. </p>
909 *
910 * <p> This method does not run the class initializer. The class initializer may
911 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
912 * Specification</em>. </p>
913 *
914 * <p> If there is a security manager, its {@code checkPermission} method is first called
915 * to check {@code RuntimePermission("defineClass")}. </p>
916 *
917 * @param bytes the class bytes
918 * @return the {@code Class} object for the class
919 * @throws IllegalArgumentException the bytes are for a class in a different package
920 * to the lookup class
921 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
922 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
923 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
924 * @throws SecurityException if denied by the security manager
925 * @throws NullPointerException if {@code bytes} is {@code null}
926 * @since 9
927 * @spec JPMS
928 * @see Lookup#privateLookupIn
929 * @see Lookup#dropLookupMode
930 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
931 */
932 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
933 SecurityManager sm = System.getSecurityManager();
934 if (sm != null)
935 sm.checkPermission(new RuntimePermission("defineClass"));
936 if ((lookupModes() & PACKAGE) == 0)
937 throw new IllegalAccessException("Lookup does not have PACKAGE access");
938 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
939
940 // parse class bytes to get class name (in internal form)
941 bytes = bytes.clone();
942 String name;
943 try {
944 ClassReader reader = new ClassReader(bytes);
945 name = reader.getClassName();
946 } catch (RuntimeException e) {
947 // ASM exceptions are poorly specified
948 ClassFormatError cfe = new ClassFormatError();
949 cfe.initCause(e);
950 throw cfe;
951 }
952
953 // get package and class name in binary form
954 String cn, pn;
955 int index = name.lastIndexOf('/');
956 if (index == -1) {
957 cn = name;
958 pn = "";
959 } else {
960 cn = name.replace('/', '.');
961 pn = cn.substring(0, index);
962 }
963 if (!pn.equals(lookupClass.getPackageName())) {
964 throw new IllegalArgumentException("Class not in same package as lookup class");
965 }
966
967 // invoke the class loader's defineClass method
968 ClassLoader loader = lookupClass.getClassLoader();
969 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
970 String source = "__Lookup_defineClass__";
971 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
972 assert clazz.getClassLoader() == lookupClass.getClassLoader()
973 && clazz.getPackageName().equals(lookupClass.getPackageName())
974 && protectionDomain(clazz) == lookupClassProtectionDomain();
975 return clazz;
976 }
977
978 private ProtectionDomain lookupClassProtectionDomain() {
979 ProtectionDomain pd = cachedProtectionDomain;
980 if (pd == null) {
981 cachedProtectionDomain = pd = protectionDomain(lookupClass);
982 }
983 return pd;
984 }
985
986 private ProtectionDomain protectionDomain(Class<?> clazz) {
987 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
988 return AccessController.doPrivileged(pa);
989 }
990
991 // cached protection domain
992 private volatile ProtectionDomain cachedProtectionDomain;
993
994
995 // Make sure outer class is initialized first.
996 static { IMPL_NAMES.getClass(); }
997
998 /** Package-private version of lookup which is trusted. */
999 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
1000
1001 /** Version of lookup which is trusted minimally.
1002 * It can only be used to create method handles to publicly accessible
1003 * members in packages that are exported unconditionally.
1004 */
1005 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
1006
1007 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1008 String name = lookupClass.getName();
1009 if (name.startsWith("java.lang.invoke."))
1010 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1011 }
1012
1013 /**
1014 * Displays the name of the class from which lookups are to be made.
1015 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1016 * If there are restrictions on the access permitted to this lookup,
1017 * this is indicated by adding a suffix to the class name, consisting
1018 * of a slash and a keyword. The keyword represents the strongest
1019 * allowed access, and is chosen as follows:
1020 * <ul>
1021 * <li>If no access is allowed, the suffix is "/noaccess".
1022 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1023 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1024 * <li>If only public and module access are allowed, the suffix is "/module".
1025 * <li>If only public, module and package access are allowed, the suffix is "/package".
1026 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1027 * </ul>
1028 * If none of the above cases apply, it is the case that full
1029 * access (public, module, package, private, and protected) is allowed.
1030 * In this case, no suffix is added.
1031 * This is true only of an object obtained originally from
1032 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1033 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1034 * always have restricted access, and will display a suffix.
1035 * <p>
1036 * (It may seem strange that protected access should be
1037 * stronger than private access. Viewed independently from
1038 * package access, protected access is the first to be lost,
1039 * because it requires a direct subclass relationship between
1040 * caller and callee.)
1041 * @see #in
1042 *
1043 * @revised 9
1044 * @spec JPMS
1045 */
1046 @Override
1047 public String toString() {
1048 String cname = lookupClass.getName();
1049 switch (allowedModes) {
1050 case 0: // no privileges
1051 return cname + "/noaccess";
1052 case PUBLIC:
1053 return cname + "/public";
1054 case PUBLIC|UNCONDITIONAL:
1055 return cname + "/publicLookup";
1056 case PUBLIC|MODULE:
1057 return cname + "/module";
1058 case PUBLIC|MODULE|PACKAGE:
1059 return cname + "/package";
1060 case FULL_POWER_MODES & ~PROTECTED:
1061 return cname + "/private";
1062 case FULL_POWER_MODES:
1063 return cname;
1064 case TRUSTED:
1065 return "/trusted"; // internal only; not exported
1066 default: // Should not happen, but it's a bitfield...
1067 cname = cname + "/" + Integer.toHexString(allowedModes);
1068 assert(false) : cname;
1069 return cname;
1070 }
1071 }
1072
1073 /**
1074 * Produces a method handle for a static method.
1075 * The type of the method handle will be that of the method.
1076 * (Since static methods do not take receivers, there is no
1077 * additional receiver argument inserted into the method handle type,
1078 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1079 * The method and all its argument types must be accessible to the lookup object.
1080 * <p>
1081 * The returned method handle will have
1082 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1083 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1084 * <p>
1085 * If the returned method handle is invoked, the method's class will
1086 * be initialized, if it has not already been initialized.
1087 * <p><b>Example:</b>
1088 * <blockquote><pre>{@code
1089 import static java.lang.invoke.MethodHandles.*;
1090 import static java.lang.invoke.MethodType.*;
1091 ...
1092 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1093 "asList", methodType(List.class, Object[].class));
1094 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1095 * }</pre></blockquote>
1096 * @param refc the class from which the method is accessed
1097 * @param name the name of the method
1098 * @param type the type of the method
1099 * @return the desired method handle
1100 * @throws NoSuchMethodException if the method does not exist
1101 * @throws IllegalAccessException if access checking fails,
1102 * or if the method is not {@code static},
1103 * or if the method's variable arity modifier bit
1104 * is set and {@code asVarargsCollector} fails
1105 * @exception SecurityException if a security manager is present and it
1106 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1107 * @throws NullPointerException if any argument is null
1108 */
1109 public
1110 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1111 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1112 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1113 }
1114
1115 /**
1116 * Produces a method handle for a virtual method.
1117 * The type of the method handle will be that of the method,
1118 * with the receiver type (usually {@code refc}) prepended.
1119 * The method and all its argument types must be accessible to the lookup object.
1120 * <p>
1121 * When called, the handle will treat the first argument as a receiver
1122 * and, for non-private methods, dispatch on the receiver's type to determine which method
1123 * implementation to enter.
1124 * For private methods the named method in {@code refc} will be invoked on the receiver.
1125 * (The dispatching action is identical with that performed by an
1126 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1127 * <p>
1128 * The first argument will be of type {@code refc} if the lookup
1129 * class has full privileges to access the member. Otherwise
1130 * the member must be {@code protected} and the first argument
1131 * will be restricted in type to the lookup class.
1132 * <p>
1133 * The returned method handle will have
1134 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1135 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1136 * <p>
1137 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1138 * instructions and method handles produced by {@code findVirtual},
1139 * if the class is {@code MethodHandle} and the name string is
1140 * {@code invokeExact} or {@code invoke}, the resulting
1141 * method handle is equivalent to one produced by
1142 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1143 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1144 * with the same {@code type} argument.
1145 * <p>
1146 * If the class is {@code VarHandle} and the name string corresponds to
1147 * the name of a signature-polymorphic access mode method, the resulting
1148 * method handle is equivalent to one produced by
1149 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1150 * the access mode corresponding to the name string and with the same
1151 * {@code type} arguments.
1152 * <p>
1153 * <b>Example:</b>
1154 * <blockquote><pre>{@code
1155 import static java.lang.invoke.MethodHandles.*;
1156 import static java.lang.invoke.MethodType.*;
1157 ...
1158 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1159 "concat", methodType(String.class, String.class));
1160 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1161 "hashCode", methodType(int.class));
1162 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1163 "hashCode", methodType(int.class));
1164 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1165 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1166 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1167 // interface method:
1168 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1169 "subSequence", methodType(CharSequence.class, int.class, int.class));
1170 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1171 // constructor "internal method" must be accessed differently:
1172 MethodType MT_newString = methodType(void.class); //()V for new String()
1173 try { assertEquals("impossible", lookup()
1174 .findVirtual(String.class, "<init>", MT_newString));
1175 } catch (NoSuchMethodException ex) { } // OK
1176 MethodHandle MH_newString = publicLookup()
1177 .findConstructor(String.class, MT_newString);
1178 assertEquals("", (String) MH_newString.invokeExact());
1179 * }</pre></blockquote>
1180 *
1181 * @param refc the class or interface from which the method is accessed
1182 * @param name the name of the method
1183 * @param type the type of the method, with the receiver argument omitted
1184 * @return the desired method handle
1185 * @throws NoSuchMethodException if the method does not exist
1186 * @throws IllegalAccessException if access checking fails,
1187 * or if the method is {@code static},
1188 * or if the method's variable arity modifier bit
1189 * is set and {@code asVarargsCollector} fails
1190 * @exception SecurityException if a security manager is present and it
1191 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1192 * @throws NullPointerException if any argument is null
1193 */
1194 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1195 if (refc == MethodHandle.class) {
1196 MethodHandle mh = findVirtualForMH(name, type);
1197 if (mh != null) return mh;
1198 } else if (refc == VarHandle.class) {
1199 MethodHandle mh = findVirtualForVH(name, type);
1200 if (mh != null) return mh;
1201 }
1202 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1203 MemberName method = resolveOrFail(refKind, refc, name, type);
1204 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1205 }
1206 private MethodHandle findVirtualForMH(String name, MethodType type) {
1207 // these names require special lookups because of the implicit MethodType argument
1208 if ("invoke".equals(name))
1209 return invoker(type);
1210 if ("invokeExact".equals(name))
1211 return exactInvoker(type);
1212 assert(!MemberName.isMethodHandleInvokeName(name));
1213 return null;
1214 }
1215 private MethodHandle findVirtualForVH(String name, MethodType type) {
1216 try {
1217 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1218 } catch (IllegalArgumentException e) {
1219 return null;
1220 }
1221 }
1222
1223 /**
1224 * Produces a method handle which creates an object and initializes it, using
1225 * the constructor of the specified type.
1226 * The parameter types of the method handle will be those of the constructor,
1227 * while the return type will be a reference to the constructor's class.
1228 * The constructor and all its argument types must be accessible to the lookup object.
1229 * <p>
1230 * The requested type must have a return type of {@code void}.
1231 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1232 * <p>
1233 * The returned method handle will have
1234 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1235 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1236 * <p>
1237 * If the returned method handle is invoked, the constructor's class will
1238 * be initialized, if it has not already been initialized.
1239 * <p><b>Example:</b>
1240 * <blockquote><pre>{@code
1241 import static java.lang.invoke.MethodHandles.*;
1242 import static java.lang.invoke.MethodType.*;
1243 ...
1244 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1245 ArrayList.class, methodType(void.class, Collection.class));
1246 Collection orig = Arrays.asList("x", "y");
1247 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1248 assert(orig != copy);
1249 assertEquals(orig, copy);
1250 // a variable-arity constructor:
1251 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1252 ProcessBuilder.class, methodType(void.class, String[].class));
1253 ProcessBuilder pb = (ProcessBuilder)
1254 MH_newProcessBuilder.invoke("x", "y", "z");
1255 assertEquals("[x, y, z]", pb.command().toString());
1256 * }</pre></blockquote>
1257 * @param refc the class or interface from which the method is accessed
1258 * @param type the type of the method, with the receiver argument omitted, and a void return type
1259 * @return the desired method handle
1260 * @throws NoSuchMethodException if the constructor does not exist
1261 * @throws IllegalAccessException if access checking fails
1262 * or if the method's variable arity modifier bit
1263 * is set and {@code asVarargsCollector} fails
1264 * @exception SecurityException if a security manager is present and it
1265 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1266 * @throws NullPointerException if any argument is null
1267 */
1268 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1269 if (refc.isArray()) {
1270 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1271 }
1272 String name = "<init>";
1273 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1274 return getDirectConstructor(refc, ctor);
1275 }
1276
1277 /**
1278 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1279 * initializer of the class is not run.
1280 * <p>
1281 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1282 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1283 * load the requested class, and then determines whether the class is accessible to this lookup object.
1284 *
1285 * @param targetName the fully qualified name of the class to be looked up.
1286 * @return the requested class.
1287 * @exception SecurityException if a security manager is present and it
1288 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1289 * @throws LinkageError if the linkage fails
1290 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1291 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1292 * modes.
1293 * @exception SecurityException if a security manager is present and it
1294 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1295 * @since 9
1296 */
1297 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1298 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1299 return accessClass(targetClass);
1300 }
1301
1302 /**
1303 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1304 * static initializer of the class is not run.
1305 * <p>
1306 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1307 * {@linkplain #lookupModes() lookup modes}.
1308 *
1309 * @param targetClass the class to be access-checked
1310 *
1311 * @return the class that has been access-checked
1312 *
1313 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1314 * modes.
1315 * @exception SecurityException if a security manager is present and it
1316 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1317 * @since 9
1318 */
1319 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1320 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1321 throw new MemberName(targetClass).makeAccessException("access violation", this);
1322 }
1323 checkSecurityManager(targetClass, null);
1324 return targetClass;
1325 }
1326
1327 /**
1328 * Produces an early-bound method handle for a virtual method.
1329 * It will bypass checks for overriding methods on the receiver,
1330 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1331 * instruction from within the explicitly specified {@code specialCaller}.
1332 * The type of the method handle will be that of the method,
1333 * with a suitably restricted receiver type prepended.
1334 * (The receiver type will be {@code specialCaller} or a subtype.)
1335 * The method and all its argument types must be accessible
1336 * to the lookup object.
1337 * <p>
1338 * Before method resolution,
1339 * if the explicitly specified caller class is not identical with the
1340 * lookup class, or if this lookup object does not have
1341 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1342 * privileges, the access fails.
1343 * <p>
1344 * The returned method handle will have
1345 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1346 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1347 * <p style="font-size:smaller;">
1348 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1349 * even though the {@code invokespecial} instruction can refer to them
1350 * in special circumstances. Use {@link #findConstructor findConstructor}
1351 * to access instance initialization methods in a safe manner.)</em>
1352 * <p><b>Example:</b>
1353 * <blockquote><pre>{@code
1354 import static java.lang.invoke.MethodHandles.*;
1355 import static java.lang.invoke.MethodType.*;
1356 ...
1357 static class Listie extends ArrayList {
1358 public String toString() { return "[wee Listie]"; }
1359 static Lookup lookup() { return MethodHandles.lookup(); }
1360 }
1361 ...
1362 // no access to constructor via invokeSpecial:
1363 MethodHandle MH_newListie = Listie.lookup()
1364 .findConstructor(Listie.class, methodType(void.class));
1365 Listie l = (Listie) MH_newListie.invokeExact();
1366 try { assertEquals("impossible", Listie.lookup().findSpecial(
1367 Listie.class, "<init>", methodType(void.class), Listie.class));
1368 } catch (NoSuchMethodException ex) { } // OK
1369 // access to super and self methods via invokeSpecial:
1370 MethodHandle MH_super = Listie.lookup().findSpecial(
1371 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1372 MethodHandle MH_this = Listie.lookup().findSpecial(
1373 Listie.class, "toString" , methodType(String.class), Listie.class);
1374 MethodHandle MH_duper = Listie.lookup().findSpecial(
1375 Object.class, "toString" , methodType(String.class), Listie.class);
1376 assertEquals("[]", (String) MH_super.invokeExact(l));
1377 assertEquals(""+l, (String) MH_this.invokeExact(l));
1378 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1379 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1380 String.class, "toString", methodType(String.class), Listie.class));
1381 } catch (IllegalAccessException ex) { } // OK
1382 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1383 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1384 * }</pre></blockquote>
1385 *
1386 * @param refc the class or interface from which the method is accessed
1387 * @param name the name of the method (which must not be "<init>")
1388 * @param type the type of the method, with the receiver argument omitted
1389 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1390 * @return the desired method handle
1391 * @throws NoSuchMethodException if the method does not exist
1392 * @throws IllegalAccessException if access checking fails,
1393 * or if the method is {@code static},
1394 * or if the method's variable arity modifier bit
1395 * is set and {@code asVarargsCollector} fails
1396 * @exception SecurityException if a security manager is present and it
1397 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1398 * @throws NullPointerException if any argument is null
1399 */
1400 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1401 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1402 checkSpecialCaller(specialCaller, refc);
1403 Lookup specialLookup = this.in(specialCaller);
1404 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1405 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1406 }
1407
1408 /**
1409 * Produces a method handle giving read access to a non-static field.
1410 * The type of the method handle will have a return type of the field's
1411 * value type.
1412 * The method handle's single argument will be the instance containing
1413 * the field.
1414 * Access checking is performed immediately on behalf of the lookup class.
1415 * @param refc the class or interface from which the method is accessed
1416 * @param name the field's name
1417 * @param type the field's type
1418 * @return a method handle which can load values from the field
1419 * @throws NoSuchFieldException if the field does not exist
1420 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1421 * @exception SecurityException if a security manager is present and it
1422 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1423 * @throws NullPointerException if any argument is null
1424 * @see #findVarHandle(Class, String, Class)
1425 */
1426 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1427 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1428 return getDirectField(REF_getField, refc, field);
1429 }
1430
1431 /**
1432 * Produces a method handle giving write access to a non-static field.
1433 * The type of the method handle will have a void return type.
1434 * The method handle will take two arguments, the instance containing
1435 * the field, and the value to be stored.
1436 * The second argument will be of the field's value type.
1437 * Access checking is performed immediately on behalf of the lookup class.
1438 * @param refc the class or interface from which the method is accessed
1439 * @param name the field's name
1440 * @param type the field's type
1441 * @return a method handle which can store values into the field
1442 * @throws NoSuchFieldException if the field does not exist
1443 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1444 * @exception SecurityException if a security manager is present and it
1445 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1446 * @throws NullPointerException if any argument is null
1447 * @see #findVarHandle(Class, String, Class)
1448 */
1449 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1450 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1451 return getDirectField(REF_putField, refc, field);
1452 }
1453
1454 /**
1455 * Produces a VarHandle giving access to a non-static field {@code name}
1456 * of type {@code type} declared in a class of type {@code recv}.
1457 * The VarHandle's variable type is {@code type} and it has one
1458 * coordinate type, {@code recv}.
1459 * <p>
1460 * Access checking is performed immediately on behalf of the lookup
1461 * class.
1462 * <p>
1463 * Certain access modes of the returned VarHandle are unsupported under
1464 * the following conditions:
1465 * <ul>
1466 * <li>if the field is declared {@code final}, then the write, atomic
1467 * update, numeric atomic update, and bitwise atomic update access
1468 * modes are unsupported.
1469 * <li>if the field type is anything other than {@code byte},
1470 * {@code short}, {@code char}, {@code int}, {@code long},
1471 * {@code float}, or {@code double} then numeric atomic update
1472 * access modes are unsupported.
1473 * <li>if the field type is anything other than {@code boolean},
1474 * {@code byte}, {@code short}, {@code char}, {@code int} or
1475 * {@code long} then bitwise atomic update access modes are
1476 * unsupported.
1477 * </ul>
1478 * <p>
1479 * If the field is declared {@code volatile} then the returned VarHandle
1480 * will override access to the field (effectively ignore the
1481 * {@code volatile} declaration) in accordance to its specified
1482 * access modes.
1483 * <p>
1484 * If the field type is {@code float} or {@code double} then numeric
1485 * and atomic update access modes compare values using their bitwise
1486 * representation (see {@link Float#floatToRawIntBits} and
1487 * {@link Double#doubleToRawLongBits}, respectively).
1488 * @apiNote
1489 * Bitwise comparison of {@code float} values or {@code double} values,
1490 * as performed by the numeric and atomic update access modes, differ
1491 * from the primitive {@code ==} operator and the {@link Float#equals}
1492 * and {@link Double#equals} methods, specifically with respect to
1493 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1494 * Care should be taken when performing a compare and set or a compare
1495 * and exchange operation with such values since the operation may
1496 * unexpectedly fail.
1497 * There are many possible NaN values that are considered to be
1498 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1499 * provided by Java can distinguish between them. Operation failure can
1500 * occur if the expected or witness value is a NaN value and it is
1501 * transformed (perhaps in a platform specific manner) into another NaN
1502 * value, and thus has a different bitwise representation (see
1503 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1504 * details).
1505 * The values {@code -0.0} and {@code +0.0} have different bitwise
1506 * representations but are considered equal when using the primitive
1507 * {@code ==} operator. Operation failure can occur if, for example, a
1508 * numeric algorithm computes an expected value to be say {@code -0.0}
1509 * and previously computed the witness value to be say {@code +0.0}.
1510 * @param recv the receiver class, of type {@code R}, that declares the
1511 * non-static field
1512 * @param name the field's name
1513 * @param type the field's type, of type {@code T}
1514 * @return a VarHandle giving access to non-static fields.
1515 * @throws NoSuchFieldException if the field does not exist
1516 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1517 * @exception SecurityException if a security manager is present and it
1518 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1519 * @throws NullPointerException if any argument is null
1520 * @since 9
1521 */
1522 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1523 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1524 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1525 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1526 }
1527
1528 /**
1529 * Produces a method handle giving read access to a static field.
1530 * The type of the method handle will have a return type of the field's
1531 * value type.
1532 * The method handle will take no arguments.
1533 * Access checking is performed immediately on behalf of the lookup class.
1534 * <p>
1535 * If the returned method handle is invoked, the field's class will
1536 * be initialized, if it has not already been initialized.
1537 * @param refc the class or interface from which the method is accessed
1538 * @param name the field's name
1539 * @param type the field's type
1540 * @return a method handle which can load values from the field
1541 * @throws NoSuchFieldException if the field does not exist
1542 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1543 * @exception SecurityException if a security manager is present and it
1544 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1545 * @throws NullPointerException if any argument is null
1546 */
1547 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1548 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1549 return getDirectField(REF_getStatic, refc, field);
1550 }
1551
1552 /**
1553 * Produces a method handle giving write access to a static field.
1554 * The type of the method handle will have a void return type.
1555 * The method handle will take a single
1556 * argument, of the field's value type, the value to be stored.
1557 * Access checking is performed immediately on behalf of the lookup class.
1558 * <p>
1559 * If the returned method handle is invoked, the field's class will
1560 * be initialized, if it has not already been initialized.
1561 * @param refc the class or interface from which the method is accessed
1562 * @param name the field's name
1563 * @param type the field's type
1564 * @return a method handle which can store values into the field
1565 * @throws NoSuchFieldException if the field does not exist
1566 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1567 * @exception SecurityException if a security manager is present and it
1568 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1569 * @throws NullPointerException if any argument is null
1570 */
1571 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1572 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1573 return getDirectField(REF_putStatic, refc, field);
1574 }
1575
1576 /**
1577 * Produces a VarHandle giving access to a static field {@code name} of
1578 * type {@code type} declared in a class of type {@code decl}.
1579 * The VarHandle's variable type is {@code type} and it has no
1580 * coordinate types.
1581 * <p>
1582 * Access checking is performed immediately on behalf of the lookup
1583 * class.
1584 * <p>
1585 * If the returned VarHandle is operated on, the declaring class will be
1586 * initialized, if it has not already been initialized.
1587 * <p>
1588 * Certain access modes of the returned VarHandle are unsupported under
1589 * the following conditions:
1590 * <ul>
1591 * <li>if the field is declared {@code final}, then the write, atomic
1592 * update, numeric atomic update, and bitwise atomic update access
1593 * modes are unsupported.
1594 * <li>if the field type is anything other than {@code byte},
1595 * {@code short}, {@code char}, {@code int}, {@code long},
1596 * {@code float}, or {@code double}, then numeric atomic update
1597 * access modes are unsupported.
1598 * <li>if the field type is anything other than {@code boolean},
1599 * {@code byte}, {@code short}, {@code char}, {@code int} or
1600 * {@code long} then bitwise atomic update access modes are
1601 * unsupported.
1602 * </ul>
1603 * <p>
1604 * If the field is declared {@code volatile} then the returned VarHandle
1605 * will override access to the field (effectively ignore the
1606 * {@code volatile} declaration) in accordance to its specified
1607 * access modes.
1608 * <p>
1609 * If the field type is {@code float} or {@code double} then numeric
1610 * and atomic update access modes compare values using their bitwise
1611 * representation (see {@link Float#floatToRawIntBits} and
1612 * {@link Double#doubleToRawLongBits}, respectively).
1613 * @apiNote
1614 * Bitwise comparison of {@code float} values or {@code double} values,
1615 * as performed by the numeric and atomic update access modes, differ
1616 * from the primitive {@code ==} operator and the {@link Float#equals}
1617 * and {@link Double#equals} methods, specifically with respect to
1618 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1619 * Care should be taken when performing a compare and set or a compare
1620 * and exchange operation with such values since the operation may
1621 * unexpectedly fail.
1622 * There are many possible NaN values that are considered to be
1623 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1624 * provided by Java can distinguish between them. Operation failure can
1625 * occur if the expected or witness value is a NaN value and it is
1626 * transformed (perhaps in a platform specific manner) into another NaN
1627 * value, and thus has a different bitwise representation (see
1628 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1629 * details).
1630 * The values {@code -0.0} and {@code +0.0} have different bitwise
1631 * representations but are considered equal when using the primitive
1632 * {@code ==} operator. Operation failure can occur if, for example, a
1633 * numeric algorithm computes an expected value to be say {@code -0.0}
1634 * and previously computed the witness value to be say {@code +0.0}.
1635 * @param decl the class that declares the static field
1636 * @param name the field's name
1637 * @param type the field's type, of type {@code T}
1638 * @return a VarHandle giving access to a static field
1639 * @throws NoSuchFieldException if the field does not exist
1640 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1641 * @exception SecurityException if a security manager is present and it
1642 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1643 * @throws NullPointerException if any argument is null
1644 * @since 9
1645 */
1646 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1647 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1648 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1649 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1650 }
1651
1652 /**
1653 * Produces an early-bound method handle for a non-static method.
1654 * The receiver must have a supertype {@code defc} in which a method
1655 * of the given name and type is accessible to the lookup class.
1656 * The method and all its argument types must be accessible to the lookup object.
1657 * The type of the method handle will be that of the method,
1658 * without any insertion of an additional receiver parameter.
1659 * The given receiver will be bound into the method handle,
1660 * so that every call to the method handle will invoke the
1661 * requested method on the given receiver.
1662 * <p>
1663 * The returned method handle will have
1664 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1665 * the method's variable arity modifier bit ({@code 0x0080}) is set
1666 * <em>and</em> the trailing array argument is not the only argument.
1667 * (If the trailing array argument is the only argument,
1668 * the given receiver value will be bound to it.)
1669 * <p>
1670 * This is almost equivalent to the following code, with some differences noted below:
1671 * <blockquote><pre>{@code
1672 import static java.lang.invoke.MethodHandles.*;
1673 import static java.lang.invoke.MethodType.*;
1674 ...
1675 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1676 MethodHandle mh1 = mh0.bindTo(receiver);
1677 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1678 return mh1;
1679 * }</pre></blockquote>
1680 * where {@code defc} is either {@code receiver.getClass()} or a super
1681 * type of that class, in which the requested method is accessible
1682 * to the lookup class.
1683 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1684 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1685 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1686 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1687 * @param receiver the object from which the method is accessed
1688 * @param name the name of the method
1689 * @param type the type of the method, with the receiver argument omitted
1690 * @return the desired method handle
1691 * @throws NoSuchMethodException if the method does not exist
1692 * @throws IllegalAccessException if access checking fails
1693 * or if the method's variable arity modifier bit
1694 * is set and {@code asVarargsCollector} fails
1695 * @exception SecurityException if a security manager is present and it
1696 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1697 * @throws NullPointerException if any argument is null
1698 * @see MethodHandle#bindTo
1699 * @see #findVirtual
1700 */
1701 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1702 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1703 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1704 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1705 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1706 throw new IllegalAccessException("The restricted defining class " +
1707 mh.type().leadingReferenceParameter().getName() +
1708 " is not assignable from receiver class " +
1709 receiver.getClass().getName());
1710 }
1711 return mh.bindArgumentL(0, receiver).setVarargs(method);
1712 }
1713
1714 /**
1715 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1716 * to <i>m</i>, if the lookup class has permission.
1717 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1718 * If <i>m</i> is virtual, overriding is respected on every call.
1719 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1720 * The type of the method handle will be that of the method,
1721 * with the receiver type prepended (but only if it is non-static).
1722 * If the method's {@code accessible} flag is not set,
1723 * access checking is performed immediately on behalf of the lookup class.
1724 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
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 <i>m</i> is static, and
1731 * if the returned method handle is invoked, the method's class will
1732 * be initialized, if it has not already been initialized.
1733 * @param m the reflected method
1734 * @return a method handle which can invoke the reflected method
1735 * @throws IllegalAccessException if access checking fails
1736 * or if the method's variable arity modifier bit
1737 * is set and {@code asVarargsCollector} fails
1738 * @throws NullPointerException if the argument is null
1739 */
1740 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1741 if (m.getDeclaringClass() == MethodHandle.class) {
1742 MethodHandle mh = unreflectForMH(m);
1743 if (mh != null) return mh;
1744 }
1745 if (m.getDeclaringClass() == VarHandle.class) {
1746 MethodHandle mh = unreflectForVH(m);
1747 if (mh != null) return mh;
1748 }
1749 MemberName method = new MemberName(m);
1750 byte refKind = method.getReferenceKind();
1751 if (refKind == REF_invokeSpecial)
1752 refKind = REF_invokeVirtual;
1753 assert(method.isMethod());
1754 @SuppressWarnings("deprecation")
1755 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1756 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1757 }
1758 private MethodHandle unreflectForMH(Method m) {
1759 // these names require special lookups because they throw UnsupportedOperationException
1760 if (MemberName.isMethodHandleInvokeName(m.getName()))
1761 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1762 return null;
1763 }
1764 private MethodHandle unreflectForVH(Method m) {
1765 // these names require special lookups because they throw UnsupportedOperationException
1766 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1767 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1768 return null;
1769 }
1770
1771 /**
1772 * Produces a method handle for a reflected method.
1773 * It will bypass checks for overriding methods on the receiver,
1774 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1775 * instruction from within the explicitly specified {@code specialCaller}.
1776 * The type of the method handle will be that of the method,
1777 * with a suitably restricted receiver type prepended.
1778 * (The receiver type will be {@code specialCaller} or a subtype.)
1779 * If the method's {@code accessible} flag is not set,
1780 * access checking is performed immediately on behalf of the lookup class,
1781 * as if {@code invokespecial} instruction were being linked.
1782 * <p>
1783 * Before method resolution,
1784 * if the explicitly specified caller class is not identical with the
1785 * lookup class, or if this lookup object does not have
1786 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1787 * privileges, the access fails.
1788 * <p>
1789 * The returned method handle will have
1790 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1791 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1792 * @param m the reflected method
1793 * @param specialCaller the class nominally calling the method
1794 * @return a method handle which can invoke the reflected method
1795 * @throws IllegalAccessException if access checking fails,
1796 * or if the method is {@code static},
1797 * or if the method's variable arity modifier bit
1798 * is set and {@code asVarargsCollector} fails
1799 * @throws NullPointerException if any argument is null
1800 */
1801 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1802 checkSpecialCaller(specialCaller, null);
1803 Lookup specialLookup = this.in(specialCaller);
1804 MemberName method = new MemberName(m, true);
1805 assert(method.isMethod());
1806 // ignore m.isAccessible: this is a new kind of access
1807 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1808 }
1809
1810 /**
1811 * Produces a method handle for a reflected constructor.
1812 * The type of the method handle will be that of the constructor,
1813 * with the return type changed to the declaring class.
1814 * The method handle will perform a {@code newInstance} operation,
1815 * creating a new instance of the constructor's class on the
1816 * arguments passed to the method handle.
1817 * <p>
1818 * If the constructor's {@code accessible} flag is not set,
1819 * access checking is performed immediately on behalf of the lookup class.
1820 * <p>
1821 * The returned method handle will have
1822 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1823 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1824 * <p>
1825 * If the returned method handle is invoked, the constructor's class will
1826 * be initialized, if it has not already been initialized.
1827 * @param c the reflected constructor
1828 * @return a method handle which can invoke the reflected constructor
1829 * @throws IllegalAccessException if access checking fails
1830 * or if the method's variable arity modifier bit
1831 * is set and {@code asVarargsCollector} fails
1832 * @throws NullPointerException if the argument is null
1833 */
1834 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1835 MemberName ctor = new MemberName(c);
1836 assert(ctor.isConstructor());
1837 @SuppressWarnings("deprecation")
1838 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1839 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1840 }
1841
1842 /**
1843 * Produces a method handle giving read access to a reflected field.
1844 * The type of the method handle will have a return type of the field's
1845 * value type.
1846 * If the field is static, the method handle will take no arguments.
1847 * Otherwise, its single argument will be the instance containing
1848 * the field.
1849 * If the field's {@code accessible} flag is not set,
1850 * access checking is performed immediately on behalf of the lookup class.
1851 * <p>
1852 * If the field is static, and
1853 * if the returned method handle is invoked, the field's class will
1854 * be initialized, if it has not already been initialized.
1855 * @param f the reflected field
1856 * @return a method handle which can load values from the reflected field
1857 * @throws IllegalAccessException if access checking fails
1858 * @throws NullPointerException if the argument is null
1859 */
1860 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1861 return unreflectField(f, false);
1862 }
1863 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1864 MemberName field = new MemberName(f, isSetter);
1865 assert(isSetter
1866 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1867 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1868 @SuppressWarnings("deprecation")
1869 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1870 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1871 }
1872
1873 /**
1874 * Produces a method handle giving write access to a reflected field.
1875 * The type of the method handle will have a void return type.
1876 * If the field is static, the method handle will take a single
1877 * argument, of the field's value type, the value to be stored.
1878 * Otherwise, the two arguments will be the instance containing
1879 * the field, and the value to be stored.
1880 * If the field's {@code accessible} flag is not set,
1881 * access checking is performed immediately on behalf of the lookup class.
1882 * <p>
1883 * If the field is static, and
1884 * if the returned method handle is invoked, the field's class will
1885 * be initialized, if it has not already been initialized.
1886 * @param f the reflected field
1887 * @return a method handle which can store values into the reflected field
1888 * @throws IllegalAccessException if access checking fails
1889 * @throws NullPointerException if the argument is null
1890 */
1891 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1892 return unreflectField(f, true);
1893 }
1894
1895 /**
1896 * Produces a VarHandle giving access to a reflected field {@code f}
1897 * of type {@code T} declared in a class of type {@code R}.
1898 * The VarHandle's variable type is {@code T}.
1899 * If the field is non-static the VarHandle has one coordinate type,
1900 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1901 * coordinate types.
1902 * <p>
1903 * Access checking is performed immediately on behalf of the lookup
1904 * class, regardless of the value of the field's {@code accessible}
1905 * flag.
1906 * <p>
1907 * If the field is static, and if the returned VarHandle is operated
1908 * on, the field's declaring class will be initialized, if it has not
1909 * already been initialized.
1910 * <p>
1911 * Certain access modes of the returned VarHandle are unsupported under
1912 * the following conditions:
1913 * <ul>
1914 * <li>if the field is declared {@code final}, then the write, atomic
1915 * update, numeric atomic update, and bitwise atomic update access
1916 * modes are unsupported.
1917 * <li>if the field type is anything other than {@code byte},
1918 * {@code short}, {@code char}, {@code int}, {@code long},
1919 * {@code float}, or {@code double} then numeric atomic update
1920 * access modes are unsupported.
1921 * <li>if the field type is anything other than {@code boolean},
1922 * {@code byte}, {@code short}, {@code char}, {@code int} or
1923 * {@code long} then bitwise atomic update access modes are
1924 * unsupported.
1925 * </ul>
1926 * <p>
1927 * If the field is declared {@code volatile} then the returned VarHandle
1928 * will override access to the field (effectively ignore the
1929 * {@code volatile} declaration) in accordance to its specified
1930 * access modes.
1931 * <p>
1932 * If the field type is {@code float} or {@code double} then numeric
1933 * and atomic update access modes compare values using their bitwise
1934 * representation (see {@link Float#floatToRawIntBits} and
1935 * {@link Double#doubleToRawLongBits}, respectively).
1936 * @apiNote
1937 * Bitwise comparison of {@code float} values or {@code double} values,
1938 * as performed by the numeric and atomic update access modes, differ
1939 * from the primitive {@code ==} operator and the {@link Float#equals}
1940 * and {@link Double#equals} methods, specifically with respect to
1941 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1942 * Care should be taken when performing a compare and set or a compare
1943 * and exchange operation with such values since the operation may
1944 * unexpectedly fail.
1945 * There are many possible NaN values that are considered to be
1946 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1947 * provided by Java can distinguish between them. Operation failure can
1948 * occur if the expected or witness value is a NaN value and it is
1949 * transformed (perhaps in a platform specific manner) into another NaN
1950 * value, and thus has a different bitwise representation (see
1951 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1952 * details).
1953 * The values {@code -0.0} and {@code +0.0} have different bitwise
1954 * representations but are considered equal when using the primitive
1955 * {@code ==} operator. Operation failure can occur if, for example, a
1956 * numeric algorithm computes an expected value to be say {@code -0.0}
1957 * and previously computed the witness value to be say {@code +0.0}.
1958 * @param f the reflected field, with a field of type {@code T}, and
1959 * a declaring class of type {@code R}
1960 * @return a VarHandle giving access to non-static fields or a static
1961 * field
1962 * @throws IllegalAccessException if access checking fails
1963 * @throws NullPointerException if the argument is null
1964 * @since 9
1965 */
1966 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1967 MemberName getField = new MemberName(f, false);
1968 MemberName putField = new MemberName(f, true);
1969 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1970 f.getDeclaringClass(), getField, putField);
1971 }
1972
1973 /**
1974 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1975 * created by this lookup object or a similar one.
1976 * Security and access checks are performed to ensure that this lookup object
1977 * is capable of reproducing the target method handle.
1978 * This means that the cracking may fail if target is a direct method handle
1979 * but was created by an unrelated lookup object.
1980 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1981 * and was created by a lookup object for a different class.
1982 * @param target a direct method handle to crack into symbolic reference components
1983 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1984 * @exception SecurityException if a security manager is present and it
1985 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1986 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1987 * @exception NullPointerException if the target is {@code null}
1988 * @see MethodHandleInfo
1989 * @since 1.8
1990 */
1991 public MethodHandleInfo revealDirect(MethodHandle target) {
1992 MemberName member = target.internalMemberName();
1993 if (member == null || (!member.isResolved() &&
1994 !member.isMethodHandleInvoke() &&
1995 !member.isVarHandleMethodInvoke()))
1996 throw newIllegalArgumentException("not a direct method handle");
1997 Class<?> defc = member.getDeclaringClass();
1998 byte refKind = member.getReferenceKind();
1999 assert(MethodHandleNatives.refKindIsValid(refKind));
2000 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2001 // Devirtualized method invocation is usually formally virtual.
2002 // To avoid creating extra MemberName objects for this common case,
2003 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2004 refKind = REF_invokeVirtual;
2005 if (refKind == REF_invokeVirtual && defc.isInterface())
2006 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2007 refKind = REF_invokeInterface;
2008 // Check SM permissions and member access before cracking.
2009 try {
2010 checkAccess(refKind, defc, member);
2011 checkSecurityManager(defc, member);
2012 } catch (IllegalAccessException ex) {
2013 throw new IllegalArgumentException(ex);
2014 }
2015 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2016 Class<?> callerClass = target.internalCallerClass();
2017 if (!hasPrivateAccess() || callerClass != lookupClass())
2018 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2019 }
2020 // Produce the handle to the results.
2021 return new InfoFromMemberName(this, member, refKind);
2022 }
2023
2024 /// Helper methods, all package-private.
2025
2026 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2027 checkSymbolicClass(refc); // do this before attempting to resolve
2028 Objects.requireNonNull(name);
2029 Objects.requireNonNull(type);
2030 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2031 NoSuchFieldException.class);
2032 }
2033
2034 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2035 checkSymbolicClass(refc); // do this before attempting to resolve
2036 Objects.requireNonNull(name);
2037 Objects.requireNonNull(type);
2038 checkMethodName(refKind, name); // NPE check on name
2039 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2040 NoSuchMethodException.class);
2041 }
2042
2043 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2044 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2045 Objects.requireNonNull(member.getName());
2046 Objects.requireNonNull(member.getType());
2047 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2048 ReflectiveOperationException.class);
2049 }
2050
2051 MemberName resolveOrNull(byte refKind, MemberName member) {
2052 // do this before attempting to resolve
2053 if (!isClassAccessible(member.getDeclaringClass())) {
2054 return null;
2055 }
2056 Objects.requireNonNull(member.getName());
2057 Objects.requireNonNull(member.getType());
2058 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2059 }
2060
2061 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2062 if (!isClassAccessible(refc)) {
2063 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2064 }
2065 }
2066
2067 boolean isClassAccessible(Class<?> refc) {
2068 Objects.requireNonNull(refc);
2069 Class<?> caller = lookupClassOrNull();
2070 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes);
2071 }
2072
2073 /** Check name for an illegal leading "<" character. */
2074 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2075 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2076 throw new NoSuchMethodException("illegal method name: "+name);
2077 }
2078
2079
2080 /**
2081 * Find my trustable caller class if m is a caller sensitive method.
2082 * If this lookup object has private access, then the caller class is the lookupClass.
2083 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2084 */
2085 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2086 Class<?> callerClass = null;
2087 if (MethodHandleNatives.isCallerSensitive(m)) {
2088 // Only lookups with private access are allowed to resolve caller-sensitive methods
2089 if (hasPrivateAccess()) {
2090 callerClass = lookupClass;
2091 } else {
2092 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2093 }
2094 }
2095 return callerClass;
2096 }
2097
2098 /**
2099 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2100 * @return {@code true} if this lookup has {@code PRIVATE} access.
2101 * @since 9
2102 */
2103 public boolean hasPrivateAccess() {
2104 return (allowedModes & PRIVATE) != 0;
2105 }
2106
2107 /**
2108 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2109 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2110 * If this lookup object has private access, then the caller class is the lookupClass.
2111 */
2112 void checkSecurityManager(Class<?> refc, MemberName m) {
2113 SecurityManager smgr = System.getSecurityManager();
2114 if (smgr == null) return;
2115 if (allowedModes == TRUSTED) return;
2116
2117 // Step 1:
2118 boolean fullPowerLookup = hasPrivateAccess();
2119 if (!fullPowerLookup ||
2120 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2121 ReflectUtil.checkPackageAccess(refc);
2122 }
2123
2124 if (m == null) { // findClass or accessClass
2125 // Step 2b:
2126 if (!fullPowerLookup) {
2127 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2128 }
2129 return;
2130 }
2131
2132 // Step 2a:
2133 if (m.isPublic()) return;
2134 if (!fullPowerLookup) {
2135 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2136 }
2137
2138 // Step 3:
2139 Class<?> defc = m.getDeclaringClass();
2140 if (!fullPowerLookup && defc != refc) {
2141 ReflectUtil.checkPackageAccess(defc);
2142 }
2143 }
2144
2145 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2146 boolean wantStatic = (refKind == REF_invokeStatic);
2147 String message;
2148 if (m.isConstructor())
2149 message = "expected a method, not a constructor";
2150 else if (!m.isMethod())
2151 message = "expected a method";
2152 else if (wantStatic != m.isStatic())
2153 message = wantStatic ? "expected a static method" : "expected a non-static method";
2154 else
2155 { checkAccess(refKind, refc, m); return; }
2156 throw m.makeAccessException(message, this);
2157 }
2158
2159 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2160 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2161 String message;
2162 if (wantStatic != m.isStatic())
2163 message = wantStatic ? "expected a static field" : "expected a non-static field";
2164 else
2165 { checkAccess(refKind, refc, m); return; }
2166 throw m.makeAccessException(message, this);
2167 }
2168
2169 /** Check public/protected/private bits on the symbolic reference class and its member. */
2170 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2171 assert(m.referenceKindIsConsistentWith(refKind) &&
2172 MethodHandleNatives.refKindIsValid(refKind) &&
2173 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2174 int allowedModes = this.allowedModes;
2175 if (allowedModes == TRUSTED) return;
2176 int mods = m.getModifiers();
2177 if (Modifier.isProtected(mods) &&
2178 refKind == REF_invokeVirtual &&
2179 m.getDeclaringClass() == Object.class &&
2180 m.getName().equals("clone") &&
2181 refc.isArray()) {
2182 // The JVM does this hack also.
2183 // (See ClassVerifier::verify_invoke_instructions
2184 // and LinkResolver::check_method_accessability.)
2185 // Because the JVM does not allow separate methods on array types,
2186 // there is no separate method for int[].clone.
2187 // All arrays simply inherit Object.clone.
2188 // But for access checking logic, we make Object.clone
2189 // (normally protected) appear to be public.
2190 // Later on, when the DirectMethodHandle is created,
2191 // its leading argument will be restricted to the
2192 // requested array type.
2193 // N.B. The return type is not adjusted, because
2194 // that is *not* the bytecode behavior.
2195 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2196 }
2197 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2198 // cannot "new" a protected ctor in a different package
2199 mods ^= Modifier.PROTECTED;
2200 }
2201 if (Modifier.isFinal(mods) &&
2202 MethodHandleNatives.refKindIsSetter(refKind))
2203 throw m.makeAccessException("unexpected set of a final field", this);
2204 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2205 if ((requestedModes & allowedModes) != 0) {
2206 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2207 mods, lookupClass(), allowedModes))
2208 return;
2209 } else {
2210 // Protected members can also be checked as if they were package-private.
2211 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2212 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2213 return;
2214 }
2215 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2216 }
2217
2218 String accessFailedMessage(Class<?> refc, MemberName m) {
2219 Class<?> defc = m.getDeclaringClass();
2220 int mods = m.getModifiers();
2221 // check the class first:
2222 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2223 (defc == refc ||
2224 Modifier.isPublic(refc.getModifiers())));
2225 if (!classOK && (allowedModes & PACKAGE) != 0) {
2226 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2227 (defc == refc ||
2228 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2229 }
2230 if (!classOK)
2231 return "class is not public";
2232 if (Modifier.isPublic(mods))
2233 return "access to public member failed"; // (how?, module not readable?)
2234 if (Modifier.isPrivate(mods))
2235 return "member is private";
2236 if (Modifier.isProtected(mods))
2237 return "member is protected";
2238 return "member is private to package";
2239 }
2240
2241 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2242 int allowedModes = this.allowedModes;
2243 if (allowedModes == TRUSTED) return;
2244 if (!hasPrivateAccess()
2245 || (specialCaller != lookupClass()
2246 // ensure non-abstract methods in superinterfaces can be special-invoked
2247 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2248 throw new MemberName(specialCaller).
2249 makeAccessException("no private access for invokespecial", this);
2250 }
2251
2252 private boolean restrictProtectedReceiver(MemberName method) {
2253 // The accessing class only has the right to use a protected member
2254 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2255 if (!method.isProtected() || method.isStatic()
2256 || allowedModes == TRUSTED
2257 || method.getDeclaringClass() == lookupClass()
2258 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2259 return false;
2260 return true;
2261 }
2262 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2263 assert(!method.isStatic());
2264 // receiver type of mh is too wide; narrow to caller
2265 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2266 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2267 }
2268 MethodType rawType = mh.type();
2269 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2270 MethodType narrowType = rawType.changeParameterType(0, caller);
2271 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2272 assert(mh.viewAsTypeChecks(narrowType, true));
2273 return mh.copyWith(narrowType, mh.form);
2274 }
2275
2276 /** Check access and get the requested method. */
2277 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2278 final boolean doRestrict = true;
2279 final boolean checkSecurity = true;
2280 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2281 }
2282 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2283 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2284 final boolean doRestrict = false;
2285 final boolean checkSecurity = true;
2286 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2287 }
2288 /** Check access and get the requested method, eliding security manager checks. */
2289 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2290 final boolean doRestrict = true;
2291 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2292 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2293 }
2294 /** Common code for all methods; do not call directly except from immediately above. */
2295 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2296 boolean checkSecurity,
2297 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
2298
2299 checkMethod(refKind, refc, method);
2300 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2301 if (checkSecurity)
2302 checkSecurityManager(refc, method);
2303 assert(!method.isMethodHandleInvoke());
2304
2305 if (refKind == REF_invokeSpecial &&
2306 refc != lookupClass() &&
2307 !refc.isInterface() &&
2308 refc != lookupClass().getSuperclass() &&
2309 refc.isAssignableFrom(lookupClass())) {
2310 assert(!method.getName().equals("<init>")); // not this code path
2311
2312 // Per JVMS 6.5, desc. of invokespecial instruction:
2313 // If the method is in a superclass of the LC,
2314 // and if our original search was above LC.super,
2315 // repeat the search (symbolic lookup) from LC.super
2316 // and continue with the direct superclass of that class,
2317 // and so forth, until a match is found or no further superclasses exist.
2318 // FIXME: MemberName.resolve should handle this instead.
2319 Class<?> refcAsSuper = lookupClass();
2320 MemberName m2;
2321 do {
2322 refcAsSuper = refcAsSuper.getSuperclass();
2323 m2 = new MemberName(refcAsSuper,
2324 method.getName(),
2325 method.getMethodType(),
2326 REF_invokeSpecial);
2327 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2328 } while (m2 == null && // no method is found yet
2329 refc != refcAsSuper); // search up to refc
2330 if (m2 == null) throw new InternalError(method.toString());
2331 method = m2;
2332 refc = refcAsSuper;
2333 // redo basic checks
2334 checkMethod(refKind, refc, method);
2335 }
2336
2337 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
2338 MethodHandle mh = dmh;
2339 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
2340 if ((doRestrict && refKind == REF_invokeSpecial) ||
2341 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2342 mh = restrictReceiver(method, dmh, lookupClass());
2343 }
2344 mh = maybeBindCaller(method, mh, boundCallerClass);
2345 mh = mh.setVarargs(method);
2346 return mh;
2347 }
2348 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2349 Class<?> boundCallerClass)
2350 throws IllegalAccessException {
2351 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2352 return mh;
2353 Class<?> hostClass = lookupClass;
2354 if (!hasPrivateAccess()) // caller must have private access
2355 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
2356 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2357 // Note: caller will apply varargs after this step happens.
2358 return cbmh;
2359 }
2360 /** Check access and get the requested field. */
2361 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2362 final boolean checkSecurity = true;
2363 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2364 }
2365 /** Check access and get the requested field, eliding security manager checks. */
2366 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2367 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2368 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2369 }
2370 /** Common code for all fields; do not call directly except from immediately above. */
2371 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2372 boolean checkSecurity) throws IllegalAccessException {
2373 checkField(refKind, refc, field);
2374 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2375 if (checkSecurity)
2376 checkSecurityManager(refc, field);
2377 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2378 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2379 restrictProtectedReceiver(field));
2380 if (doRestrict)
2381 return restrictReceiver(field, dmh, lookupClass());
2382 return dmh;
2383 }
2384 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2385 Class<?> refc, MemberName getField, MemberName putField)
2386 throws IllegalAccessException {
2387 final boolean checkSecurity = true;
2388 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2389 }
2390 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2391 Class<?> refc, MemberName getField, MemberName putField)
2392 throws IllegalAccessException {
2393 final boolean checkSecurity = false;
2394 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2395 }
2396 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2397 Class<?> refc, MemberName getField, MemberName putField,
2398 boolean checkSecurity) throws IllegalAccessException {
2399 assert getField.isStatic() == putField.isStatic();
2400 assert getField.isGetter() && putField.isSetter();
2401 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2402 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2403
2404 checkField(getRefKind, refc, getField);
2405 if (checkSecurity)
2406 checkSecurityManager(refc, getField);
2407
2408 if (!putField.isFinal()) {
2409 // A VarHandle does not support updates to final fields, any
2410 // such VarHandle to a final field will be read-only and
2411 // therefore the following write-based accessibility checks are
2412 // only required for non-final fields
2413 checkField(putRefKind, refc, putField);
2414 if (checkSecurity)
2415 checkSecurityManager(refc, putField);
2416 }
2417
2418 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2419 restrictProtectedReceiver(getField));
2420 if (doRestrict) {
2421 assert !getField.isStatic();
2422 // receiver type of VarHandle is too wide; narrow to caller
2423 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2424 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2425 }
2426 refc = lookupClass();
2427 }
2428 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2429 }
2430 /** Check access and get the requested constructor. */
2431 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2432 final boolean checkSecurity = true;
2433 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2434 }
2435 /** Check access and get the requested constructor, eliding security manager checks. */
2436 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2437 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2438 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2439 }
2440 /** Common code for all constructors; do not call directly except from immediately above. */
2441 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2442 boolean checkSecurity) throws IllegalAccessException {
2443 assert(ctor.isConstructor());
2444 checkAccess(REF_newInvokeSpecial, refc, ctor);
2445 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2446 if (checkSecurity)
2447 checkSecurityManager(refc, ctor);
2448 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2449 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2450 }
2451
2452 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2453 */
2454 /*non-public*/
2455 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2456 if (!(type instanceof Class || type instanceof MethodType))
2457 throw new InternalError("unresolved MemberName");
2458 MemberName member = new MemberName(refKind, defc, name, type);
2459 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2460 if (mh != null) {
2461 checkSymbolicClass(defc);
2462 return mh;
2463 }
2464 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2465 // Treat MethodHandle.invoke and invokeExact specially.
2466 mh = findVirtualForMH(member.getName(), member.getMethodType());
2467 if (mh != null) {
2468 return mh;
2469 }
2470 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
2471 // Treat signature-polymorphic methods on VarHandle specially.
2472 mh = findVirtualForVH(member.getName(), member.getMethodType());
2473 if (mh != null) {
2474 return mh;
2475 }
2476 }
2477 MemberName resolved = resolveOrFail(refKind, member);
2478 mh = getDirectMethodForConstant(refKind, defc, resolved);
2479 if (mh instanceof DirectMethodHandle
2480 && canBeCached(refKind, defc, resolved)) {
2481 MemberName key = mh.internalMemberName();
2482 if (key != null) {
2483 key = key.asNormalOriginal();
2484 }
2485 if (member.equals(key)) { // better safe than sorry
2486 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2487 }
2488 }
2489 return mh;
2490 }
2491 private
2492 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2493 if (refKind == REF_invokeSpecial) {
2494 return false;
2495 }
2496 if (!Modifier.isPublic(defc.getModifiers()) ||
2497 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2498 !member.isPublic() ||
2499 member.isCallerSensitive()) {
2500 return false;
2501 }
2502 ClassLoader loader = defc.getClassLoader();
2503 if (loader != null) {
2504 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2505 boolean found = false;
2506 while (sysl != null) {
2507 if (loader == sysl) { found = true; break; }
2508 sysl = sysl.getParent();
2509 }
2510 if (!found) {
2511 return false;
2512 }
2513 }
2514 try {
2515 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
2516 new MemberName(refKind, defc, member.getName(), member.getType()));
2517 if (resolved2 == null) {
2518 return false;
2519 }
2520 checkSecurityManager(defc, resolved2);
2521 } catch (SecurityException ex) {
2522 return false;
2523 }
2524 return true;
2525 }
2526 private
2527 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2528 throws ReflectiveOperationException {
2529 if (MethodHandleNatives.refKindIsField(refKind)) {
2530 return getDirectFieldNoSecurityManager(refKind, defc, member);
2531 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2532 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2533 } else if (refKind == REF_newInvokeSpecial) {
2534 return getDirectConstructorNoSecurityManager(defc, member);
2535 }
2536 // oops
2537 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2538 }
2539
2540 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2541 }
2542
2543 /**
2544 * Produces a method handle constructing arrays of a desired type,
2545 * as if by the {@code anewarray} bytecode.
2546 * The return type of the method handle will be the array type.
2547 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2548 *
2549 * <p> If the returned method handle is invoked with a negative
2550 * array size, a {@code NegativeArraySizeException} will be thrown.
2551 *
2552 * @param arrayClass an array type
2553 * @return a method handle which can create arrays of the given type
2554 * @throws NullPointerException if the argument is {@code null}
2555 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2556 * @see java.lang.reflect.Array#newInstance(Class, int)
2557 * @jvms 6.5 {@code anewarray} Instruction
2558 * @since 9
2559 */
2560 public static
2561 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2562 if (!arrayClass.isArray()) {
2563 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2564 }
2565 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2566 bindTo(arrayClass.getComponentType());
2567 return ani.asType(ani.type().changeReturnType(arrayClass));
2568 }
2569
2570 /**
2571 * Produces a method handle returning the length of an array,
2572 * as if by the {@code arraylength} bytecode.
2573 * The type of the method handle will have {@code int} as return type,
2574 * and its sole argument will be the array type.
2575 *
2576 * <p> If the returned method handle is invoked with a {@code null}
2577 * array reference, a {@code NullPointerException} will be thrown.
2578 *
2579 * @param arrayClass an array type
2580 * @return a method handle which can retrieve the length of an array of the given array type
2581 * @throws NullPointerException if the argument is {@code null}
2582 * @throws IllegalArgumentException if arrayClass is not an array type
2583 * @jvms 6.5 {@code arraylength} Instruction
2584 * @since 9
2585 */
2586 public static
2587 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2588 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2589 }
2590
2591 /**
2592 * Produces a method handle giving read access to elements of an array,
2593 * as if by the {@code aaload} bytecode.
2594 * The type of the method handle will have a return type of the array's
2595 * element type. Its first argument will be the array type,
2596 * and the second will be {@code int}.
2597 *
2598 * <p> When the returned method handle is invoked,
2599 * the array reference and array index are checked.
2600 * A {@code NullPointerException} will be thrown if the array reference
2601 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2602 * thrown if the index is negative or if it is greater than or equal to
2603 * the length of the array.
2604 *
2605 * @param arrayClass an array type
2606 * @return a method handle which can load values from the given array type
2607 * @throws NullPointerException if the argument is null
2608 * @throws IllegalArgumentException if arrayClass is not an array type
2609 * @jvms 6.5 {@code aaload} Instruction
2610 */
2611 public static
2612 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2613 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2614 }
2615
2616 /**
2617 * Produces a method handle giving write access to elements of an array,
2618 * as if by the {@code astore} bytecode.
2619 * The type of the method handle will have a void return type.
2620 * Its last argument will be the array's element type.
2621 * The first and second arguments will be the array type and int.
2622 *
2623 * <p> When the returned method handle is invoked,
2624 * the array reference and array index are checked.
2625 * A {@code NullPointerException} will be thrown if the array reference
2626 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2627 * thrown if the index is negative or if it is greater than or equal to
2628 * the length of the array.
2629 *
2630 * @param arrayClass the class of an array
2631 * @return a method handle which can store values into the array type
2632 * @throws NullPointerException if the argument is null
2633 * @throws IllegalArgumentException if arrayClass is not an array type
2634 * @jvms 6.5 {@code aastore} Instruction
2635 */
2636 public static
2637 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2638 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2639 }
2640
2641 /**
2642 * Produces a VarHandle giving access to elements of an array of type
2643 * {@code arrayClass}. The VarHandle's variable type is the component type
2644 * of {@code arrayClass} and the list of coordinate types is
2645 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2646 * corresponds to an argument that is an index into an array.
2647 * <p>
2648 * Certain access modes of the returned VarHandle are unsupported under
2649 * the following conditions:
2650 * <ul>
2651 * <li>if the component type is anything other than {@code byte},
2652 * {@code short}, {@code char}, {@code int}, {@code long},
2653 * {@code float}, or {@code double} then numeric atomic update access
2654 * modes are unsupported.
2655 * <li>if the field type is anything other than {@code boolean},
2656 * {@code byte}, {@code short}, {@code char}, {@code int} or
2657 * {@code long} then bitwise atomic update access modes are
2658 * unsupported.
2659 * </ul>
2660 * <p>
2661 * If the component type is {@code float} or {@code double} then numeric
2662 * and atomic update access modes compare values using their bitwise
2663 * representation (see {@link Float#floatToRawIntBits} and
2664 * {@link Double#doubleToRawLongBits}, respectively).
2665 *
2666 * <p> When the returned {@code VarHandle} is invoked,
2667 * the array reference and array index are checked.
2668 * A {@code NullPointerException} will be thrown if the array reference
2669 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2670 * thrown if the index is negative or if it is greater than or equal to
2671 * the length of the array.
2672 *
2673 * @apiNote
2674 * Bitwise comparison of {@code float} values or {@code double} values,
2675 * as performed by the numeric and atomic update access modes, differ
2676 * from the primitive {@code ==} operator and the {@link Float#equals}
2677 * and {@link Double#equals} methods, specifically with respect to
2678 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2679 * Care should be taken when performing a compare and set or a compare
2680 * and exchange operation with such values since the operation may
2681 * unexpectedly fail.
2682 * There are many possible NaN values that are considered to be
2683 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2684 * provided by Java can distinguish between them. Operation failure can
2685 * occur if the expected or witness value is a NaN value and it is
2686 * transformed (perhaps in a platform specific manner) into another NaN
2687 * value, and thus has a different bitwise representation (see
2688 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2689 * details).
2690 * The values {@code -0.0} and {@code +0.0} have different bitwise
2691 * representations but are considered equal when using the primitive
2692 * {@code ==} operator. Operation failure can occur if, for example, a
2693 * numeric algorithm computes an expected value to be say {@code -0.0}
2694 * and previously computed the witness value to be say {@code +0.0}.
2695 * @param arrayClass the class of an array, of type {@code T[]}
2696 * @return a VarHandle giving access to elements of an array
2697 * @throws NullPointerException if the arrayClass is null
2698 * @throws IllegalArgumentException if arrayClass is not an array type
2699 * @since 9
2700 */
2701 public static
2702 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2703 return VarHandles.makeArrayElementHandle(arrayClass);
2704 }
2705
2706 /**
2707 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2708 * viewed as if it were a different primitive array type, such as
2709 * {@code int[]} or {@code long[]}.
2710 * The VarHandle's variable type is the component type of
2711 * {@code viewArrayClass} and the list of coordinate types is
2712 * {@code (byte[], int)}, where the {@code int} coordinate type
2713 * corresponds to an argument that is an index into a {@code byte[]} array.
2714 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2715 * array, composing bytes to or from a value of the component type of
2716 * {@code viewArrayClass} according to the given endianness.
2717 * <p>
2718 * The supported component types (variables types) are {@code short},
2719 * {@code char}, {@code int}, {@code long}, {@code float} and
2720 * {@code double}.
2721 * <p>
2722 * Access of bytes at a given index will result in an
2723 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2724 * or greater than the {@code byte[]} array length minus the size (in bytes)
2725 * of {@code T}.
2726 * <p>
2727 * Access of bytes at an index may be aligned or misaligned for {@code T},
2728 * with respect to the underlying memory address, {@code A} say, associated
2729 * with the array and index.
2730 * If access is misaligned then access for anything other than the
2731 * {@code get} and {@code set} access modes will result in an
2732 * {@code IllegalStateException}. In such cases atomic access is only
2733 * guaranteed with respect to the largest power of two that divides the GCD
2734 * of {@code A} and the size (in bytes) of {@code T}.
2735 * If access is aligned then following access modes are supported and are
2736 * guaranteed to support atomic access:
2737 * <ul>
2738 * <li>read write access modes for all {@code T}, with the exception of
2739 * access modes {@code get} and {@code set} for {@code long} and
2740 * {@code double} on 32-bit platforms.
2741 * <li>atomic update access modes for {@code int}, {@code long},
2742 * {@code float} or {@code double}.
2743 * (Future major platform releases of the JDK may support additional
2744 * types for certain currently unsupported access modes.)
2745 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2746 * (Future major platform releases of the JDK may support additional
2747 * numeric types for certain currently unsupported access modes.)
2748 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2749 * (Future major platform releases of the JDK may support additional
2750 * numeric types for certain currently unsupported access modes.)
2751 * </ul>
2752 * <p>
2753 * Misaligned access, and therefore atomicity guarantees, may be determined
2754 * for {@code byte[]} arrays without operating on a specific array. Given
2755 * an {@code index}, {@code T} and it's corresponding boxed type,
2756 * {@code T_BOX}, misalignment may be determined as follows:
2757 * <pre>{@code
2758 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2759 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2760 * alignmentOffset(0, sizeOfT);
2761 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2762 * boolean isMisaligned = misalignedAtIndex != 0;
2763 * }</pre>
2764 * <p>
2765 * If the variable type is {@code float} or {@code double} then atomic
2766 * update access modes compare values using their bitwise representation
2767 * (see {@link Float#floatToRawIntBits} and
2768 * {@link Double#doubleToRawLongBits}, respectively).
2769 * @param viewArrayClass the view array class, with a component type of
2770 * type {@code T}
2771 * @param byteOrder the endianness of the view array elements, as
2772 * stored in the underlying {@code byte} array
2773 * @return a VarHandle giving access to elements of a {@code byte[]} array
2774 * viewed as if elements corresponding to the components type of the view
2775 * array class
2776 * @throws NullPointerException if viewArrayClass or byteOrder is null
2777 * @throws IllegalArgumentException if viewArrayClass is not an array type
2778 * @throws UnsupportedOperationException if the component type of
2779 * viewArrayClass is not supported as a variable type
2780 * @since 9
2781 */
2782 public static
2783 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2784 ByteOrder byteOrder) throws IllegalArgumentException {
2785 Objects.requireNonNull(byteOrder);
2786 return VarHandles.byteArrayViewHandle(viewArrayClass,
2787 byteOrder == ByteOrder.BIG_ENDIAN);
2788 }
2789
2790 /**
2791 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2792 * viewed as if it were an array of elements of a different primitive
2793 * component type to that of {@code byte}, such as {@code int[]} or
2794 * {@code long[]}.
2795 * The VarHandle's variable type is the component type of
2796 * {@code viewArrayClass} and the list of coordinate types is
2797 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2798 * corresponds to an argument that is an index into a {@code byte[]} array.
2799 * The returned VarHandle accesses bytes at an index in a
2800 * {@code ByteBuffer}, composing bytes to or from a value of the component
2801 * type of {@code viewArrayClass} according to the given endianness.
2802 * <p>
2803 * The supported component types (variables types) are {@code short},
2804 * {@code char}, {@code int}, {@code long}, {@code float} and
2805 * {@code double}.
2806 * <p>
2807 * Access will result in a {@code ReadOnlyBufferException} for anything
2808 * other than the read access modes if the {@code ByteBuffer} is read-only.
2809 * <p>
2810 * Access of bytes at a given index will result in an
2811 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2812 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2813 * {@code T}.
2814 * <p>
2815 * Access of bytes at an index may be aligned or misaligned for {@code T},
2816 * with respect to the underlying memory address, {@code A} say, associated
2817 * with the {@code ByteBuffer} and index.
2818 * If access is misaligned then access for anything other than the
2819 * {@code get} and {@code set} access modes will result in an
2820 * {@code IllegalStateException}. In such cases atomic access is only
2821 * guaranteed with respect to the largest power of two that divides the GCD
2822 * of {@code A} and the size (in bytes) of {@code T}.
2823 * If access is aligned then following access modes are supported and are
2824 * guaranteed to support atomic access:
2825 * <ul>
2826 * <li>read write access modes for all {@code T}, with the exception of
2827 * access modes {@code get} and {@code set} for {@code long} and
2828 * {@code double} on 32-bit platforms.
2829 * <li>atomic update access modes for {@code int}, {@code long},
2830 * {@code float} or {@code double}.
2831 * (Future major platform releases of the JDK may support additional
2832 * types for certain currently unsupported access modes.)
2833 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2834 * (Future major platform releases of the JDK may support additional
2835 * numeric types for certain currently unsupported access modes.)
2836 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2837 * (Future major platform releases of the JDK may support additional
2838 * numeric types for certain currently unsupported access modes.)
2839 * </ul>
2840 * <p>
2841 * Misaligned access, and therefore atomicity guarantees, may be determined
2842 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2843 * {@code index}, {@code T} and it's corresponding boxed type,
2844 * {@code T_BOX}, as follows:
2845 * <pre>{@code
2846 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2847 * ByteBuffer bb = ...
2848 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2849 * boolean isMisaligned = misalignedAtIndex != 0;
2850 * }</pre>
2851 * <p>
2852 * If the variable type is {@code float} or {@code double} then atomic
2853 * update access modes compare values using their bitwise representation
2854 * (see {@link Float#floatToRawIntBits} and
2855 * {@link Double#doubleToRawLongBits}, respectively).
2856 * @param viewArrayClass the view array class, with a component type of
2857 * type {@code T}
2858 * @param byteOrder the endianness of the view array elements, as
2859 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2860 * endianness of a {@code ByteBuffer})
2861 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2862 * viewed as if elements corresponding to the components type of the view
2863 * array class
2864 * @throws NullPointerException if viewArrayClass or byteOrder is null
2865 * @throws IllegalArgumentException if viewArrayClass is not an array type
2866 * @throws UnsupportedOperationException if the component type of
2867 * viewArrayClass is not supported as a variable type
2868 * @since 9
2869 */
2870 public static
2871 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2872 ByteOrder byteOrder) throws IllegalArgumentException {
2873 Objects.requireNonNull(byteOrder);
2874 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2875 byteOrder == ByteOrder.BIG_ENDIAN);
2876 }
2877
2878
2879 /// method handle invocation (reflective style)
2880
2881 /**
2882 * Produces a method handle which will invoke any method handle of the
2883 * given {@code type}, with a given number of trailing arguments replaced by
2884 * a single trailing {@code Object[]} array.
2885 * The resulting invoker will be a method handle with the following
2886 * arguments:
2887 * <ul>
2888 * <li>a single {@code MethodHandle} target
2889 * <li>zero or more leading values (counted by {@code leadingArgCount})
2890 * <li>an {@code Object[]} array containing trailing arguments
2891 * </ul>
2892 * <p>
2893 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2894 * the indicated {@code type}.
2895 * That is, if the target is exactly of the given {@code type}, it will behave
2896 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2897 * is used to convert the target to the required {@code type}.
2898 * <p>
2899 * The type of the returned invoker will not be the given {@code type}, but rather
2900 * will have all parameters except the first {@code leadingArgCount}
2901 * replaced by a single array of type {@code Object[]}, which will be
2902 * the final parameter.
2903 * <p>
2904 * Before invoking its target, the invoker will spread the final array, apply
2905 * reference casts as necessary, and unbox and widen primitive arguments.
2906 * If, when the invoker is called, the supplied array argument does
2907 * not have the correct number of elements, the invoker will throw
2908 * an {@link IllegalArgumentException} instead of invoking the target.
2909 * <p>
2910 * This method is equivalent to the following code (though it may be more efficient):
2911 * <blockquote><pre>{@code
2912 MethodHandle invoker = MethodHandles.invoker(type);
2913 int spreadArgCount = type.parameterCount() - leadingArgCount;
2914 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2915 return invoker;
2916 * }</pre></blockquote>
2917 * This method throws no reflective or security exceptions.
2918 * @param type the desired target type
2919 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2920 * @return a method handle suitable for invoking any method handle of the given type
2921 * @throws NullPointerException if {@code type} is null
2922 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2923 * the range from 0 to {@code type.parameterCount()} inclusive,
2924 * or if the resulting method handle's type would have
2925 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2926 */
2927 public static
2928 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2929 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2930 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2931 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2932 return type.invokers().spreadInvoker(leadingArgCount);
2933 }
2934
2935 /**
2936 * Produces a special <em>invoker method handle</em> which can be used to
2937 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2938 * The resulting invoker will have a type which is
2939 * exactly equal to the desired type, except that it will accept
2940 * an additional leading argument of type {@code MethodHandle}.
2941 * <p>
2942 * This method is equivalent to the following code (though it may be more efficient):
2943 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2944 *
2945 * <p style="font-size:smaller;">
2946 * <em>Discussion:</em>
2947 * Invoker method handles can be useful when working with variable method handles
2948 * of unknown types.
2949 * For example, to emulate an {@code invokeExact} call to a variable method
2950 * handle {@code M}, extract its type {@code T},
2951 * look up the invoker method {@code X} for {@code T},
2952 * and call the invoker method, as {@code X.invoke(T, A...)}.
2953 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2954 * is unknown.)
2955 * If spreading, collecting, or other argument transformations are required,
2956 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2957 * method handle values, as long as they are compatible with the type of {@code X}.
2958 * <p style="font-size:smaller;">
2959 * <em>(Note: The invoker method is not available via the Core Reflection API.
2960 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2961 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2962 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2963 * <p>
2964 * This method throws no reflective or security exceptions.
2965 * @param type the desired target type
2966 * @return a method handle suitable for invoking any method handle of the given type
2967 * @throws IllegalArgumentException if the resulting method handle's type would have
2968 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2969 */
2970 public static
2971 MethodHandle exactInvoker(MethodType type) {
2972 return type.invokers().exactInvoker();
2973 }
2974
2975 /**
2976 * Produces a special <em>invoker method handle</em> which can be used to
2977 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2978 * The resulting invoker will have a type which is
2979 * exactly equal to the desired type, except that it will accept
2980 * an additional leading argument of type {@code MethodHandle}.
2981 * <p>
2982 * Before invoking its target, if the target differs from the expected type,
2983 * the invoker will apply reference casts as
2984 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2985 * Similarly, the return value will be converted as necessary.
2986 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2987 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2988 * <p>
2989 * This method is equivalent to the following code (though it may be more efficient):
2990 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2991 * <p style="font-size:smaller;">
2992 * <em>Discussion:</em>
2993 * A {@linkplain MethodType#genericMethodType general method type} is one which
2994 * mentions only {@code Object} arguments and return values.
2995 * An invoker for such a type is capable of calling any method handle
2996 * of the same arity as the general type.
2997 * <p style="font-size:smaller;">
2998 * <em>(Note: The invoker method is not available via the Core Reflection API.
2999 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3000 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3001 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3002 * <p>
3003 * This method throws no reflective or security exceptions.
3004 * @param type the desired target type
3005 * @return a method handle suitable for invoking any method handle convertible to the given type
3006 * @throws IllegalArgumentException if the resulting method handle's type would have
3007 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3008 */
3009 public static
3010 MethodHandle invoker(MethodType type) {
3011 return type.invokers().genericInvoker();
3012 }
3013
3014 /**
3015 * Produces a special <em>invoker method handle</em> which can be used to
3016 * invoke a signature-polymorphic access mode method on any VarHandle whose
3017 * associated access mode type is compatible with the given type.
3018 * The resulting invoker will have a type which is exactly equal to the
3019 * desired given type, except that it will accept an additional leading
3020 * argument of type {@code VarHandle}.
3021 *
3022 * @param accessMode the VarHandle access mode
3023 * @param type the desired target type
3024 * @return a method handle suitable for invoking an access mode method of
3025 * any VarHandle whose access mode type is of the given type.
3026 * @since 9
3027 */
3028 static public
3029 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3030 return type.invokers().varHandleMethodExactInvoker(accessMode);
3031 }
3032
3033 /**
3034 * Produces a special <em>invoker method handle</em> which can be used to
3035 * invoke a signature-polymorphic access mode method on any VarHandle whose
3036 * associated access mode type is compatible with the given type.
3037 * The resulting invoker will have a type which is exactly equal to the
3038 * desired given type, except that it will accept an additional leading
3039 * argument of type {@code VarHandle}.
3040 * <p>
3041 * Before invoking its target, if the access mode type differs from the
3042 * desired given type, the invoker will apply reference casts as necessary
3043 * and box, unbox, or widen primitive values, as if by
3044 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3045 * converted as necessary.
3046 * <p>
3047 * This method is equivalent to the following code (though it may be more
3048 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3049 *
3050 * @param accessMode the VarHandle access mode
3051 * @param type the desired target type
3052 * @return a method handle suitable for invoking an access mode method of
3053 * any VarHandle whose access mode type is convertible to the given
3054 * type.
3055 * @since 9
3056 */
3057 static public
3058 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3059 return type.invokers().varHandleMethodInvoker(accessMode);
3060 }
3061
3062 static /*non-public*/
3063 MethodHandle basicInvoker(MethodType type) {
3064 return type.invokers().basicInvoker();
3065 }
3066
3067 /// method handle modification (creation from other method handles)
3068
3069 /**
3070 * Produces a method handle which adapts the type of the
3071 * given method handle to a new type by pairwise argument and return type conversion.
3072 * The original type and new type must have the same number of arguments.
3073 * The resulting method handle is guaranteed to report a type
3074 * which is equal to the desired new type.
3075 * <p>
3076 * If the original type and new type are equal, returns target.
3077 * <p>
3078 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3079 * and some additional conversions are also applied if those conversions fail.
3080 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3081 * if possible, before or instead of any conversions done by {@code asType}:
3082 * <ul>
3083 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3084 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3085 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3086 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3087 * the boolean is converted to a byte value, 1 for true, 0 for false.
3088 * (This treatment follows the usage of the bytecode verifier.)
3089 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3090 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3091 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3092 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3093 * then a Java casting conversion (JLS 5.5) is applied.
3094 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3095 * widening and/or narrowing.)
3096 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3097 * conversion will be applied at runtime, possibly followed
3098 * by a Java casting conversion (JLS 5.5) on the primitive value,
3099 * possibly followed by a conversion from byte to boolean by testing
3100 * the low-order bit.
3101 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3102 * and if the reference is null at runtime, a zero value is introduced.
3103 * </ul>
3104 * @param target the method handle to invoke after arguments are retyped
3105 * @param newType the expected type of the new method handle
3106 * @return a method handle which delegates to the target after performing
3107 * any necessary argument conversions, and arranges for any
3108 * necessary return value conversions
3109 * @throws NullPointerException if either argument is null
3110 * @throws WrongMethodTypeException if the conversion cannot be made
3111 * @see MethodHandle#asType
3112 */
3113 public static
3114 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3115 explicitCastArgumentsChecks(target, newType);
3116 // use the asTypeCache when possible:
3117 MethodType oldType = target.type();
3118 if (oldType == newType) return target;
3119 if (oldType.explicitCastEquivalentToAsType(newType)) {
3120 return target.asFixedArity().asType(newType);
3121 }
3122 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3123 }
3124
3125 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3126 if (target.type().parameterCount() != newType.parameterCount()) {
3127 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3128 }
3129 }
3130
3131 /**
3132 * Produces a method handle which adapts the calling sequence of the
3133 * given method handle to a new type, by reordering the arguments.
3134 * The resulting method handle is guaranteed to report a type
3135 * which is equal to the desired new type.
3136 * <p>
3137 * The given array controls the reordering.
3138 * Call {@code #I} the number of incoming parameters (the value
3139 * {@code newType.parameterCount()}, and call {@code #O} the number
3140 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3141 * Then the length of the reordering array must be {@code #O},
3142 * and each element must be a non-negative number less than {@code #I}.
3143 * For every {@code N} less than {@code #O}, the {@code N}-th
3144 * outgoing argument will be taken from the {@code I}-th incoming
3145 * argument, where {@code I} is {@code reorder[N]}.
3146 * <p>
3147 * No argument or return value conversions are applied.
3148 * The type of each incoming argument, as determined by {@code newType},
3149 * must be identical to the type of the corresponding outgoing parameter
3150 * or parameters in the target method handle.
3151 * The return type of {@code newType} must be identical to the return
3152 * type of the original target.
3153 * <p>
3154 * The reordering array need not specify an actual permutation.
3155 * An incoming argument will be duplicated if its index appears
3156 * more than once in the array, and an incoming argument will be dropped
3157 * if its index does not appear in the array.
3158 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3159 * incoming arguments which are not mentioned in the reordering array
3160 * may be of any type, as determined only by {@code newType}.
3161 * <blockquote><pre>{@code
3162 import static java.lang.invoke.MethodHandles.*;
3163 import static java.lang.invoke.MethodType.*;
3164 ...
3165 MethodType intfn1 = methodType(int.class, int.class);
3166 MethodType intfn2 = methodType(int.class, int.class, int.class);
3167 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3168 assert(sub.type().equals(intfn2));
3169 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3170 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3171 assert((int)rsub.invokeExact(1, 100) == 99);
3172 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3173 assert(add.type().equals(intfn2));
3174 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3175 assert(twice.type().equals(intfn1));
3176 assert((int)twice.invokeExact(21) == 42);
3177 * }</pre></blockquote>
3178 * <p>
3179 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3180 * variable-arity method handle}, even if the original target method handle was.
3181 * @param target the method handle to invoke after arguments are reordered
3182 * @param newType the expected type of the new method handle
3183 * @param reorder an index array which controls the reordering
3184 * @return a method handle which delegates to the target after it
3185 * drops unused arguments and moves and/or duplicates the other arguments
3186 * @throws NullPointerException if any argument is null
3187 * @throws IllegalArgumentException if the index array length is not equal to
3188 * the arity of the target, or if any index array element
3189 * not a valid index for a parameter of {@code newType},
3190 * or if two corresponding parameter types in
3191 * {@code target.type()} and {@code newType} are not identical,
3192 */
3193 public static
3194 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3195 reorder = reorder.clone(); // get a private copy
3196 MethodType oldType = target.type();
3197 permuteArgumentChecks(reorder, newType, oldType);
3198 // first detect dropped arguments and handle them separately
3199 int[] originalReorder = reorder;
3200 BoundMethodHandle result = target.rebind();
3201 LambdaForm form = result.form;
3202 int newArity = newType.parameterCount();
3203 // Normalize the reordering into a real permutation,
3204 // by removing duplicates and adding dropped elements.
3205 // This somewhat improves lambda form caching, as well
3206 // as simplifying the transform by breaking it up into steps.
3207 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3208 if (ddIdx > 0) {
3209 // We found a duplicated entry at reorder[ddIdx].
3210 // Example: (x,y,z)->asList(x,y,z)
3211 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3212 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3213 // The starred element corresponds to the argument
3214 // deleted by the dupArgumentForm transform.
3215 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3216 boolean killFirst = false;
3217 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3218 // Set killFirst if the dup is larger than an intervening position.
3219 // This will remove at least one inversion from the permutation.
3220 if (dupVal > val) killFirst = true;
3221 }
3222 if (!killFirst) {
3223 srcPos = dstPos;
3224 dstPos = ddIdx;
3225 }
3226 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3227 assert (reorder[srcPos] == reorder[dstPos]);
3228 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3229 // contract the reordering by removing the element at dstPos
3230 int tailPos = dstPos + 1;
3231 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3232 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3233 } else {
3234 int dropVal = ~ddIdx, insPos = 0;
3235 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3236 // Find first element of reorder larger than dropVal.
3237 // This is where we will insert the dropVal.
3238 insPos += 1;
3239 }
3240 Class<?> ptype = newType.parameterType(dropVal);
3241 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3242 oldType = oldType.insertParameterTypes(insPos, ptype);
3243 // expand the reordering by inserting an element at insPos
3244 int tailPos = insPos + 1;
3245 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3246 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3247 reorder[insPos] = dropVal;
3248 }
3249 assert (permuteArgumentChecks(reorder, newType, oldType));
3250 }
3251 assert (reorder.length == newArity); // a perfect permutation
3252 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3253 form = form.editor().permuteArgumentsForm(1, reorder);
3254 if (newType == result.type() && form == result.internalForm())
3255 return result;
3256 return result.copyWith(newType, form);
3257 }
3258
3259 /**
3260 * Return an indication of any duplicate or omission in reorder.
3261 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3262 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3263 * Otherwise, return zero.
3264 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3265 */
3266 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3267 final int BIT_LIMIT = 63; // max number of bits in bit mask
3268 if (newArity < BIT_LIMIT) {
3269 long mask = 0;
3270 for (int i = 0; i < reorder.length; i++) {
3271 int arg = reorder[i];
3272 if (arg >= newArity) {
3273 return reorder.length;
3274 }
3275 long bit = 1L << arg;
3276 if ((mask & bit) != 0) {
3277 return i; // >0 indicates a dup
3278 }
3279 mask |= bit;
3280 }
3281 if (mask == (1L << newArity) - 1) {
3282 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3283 return 0;
3284 }
3285 // find first zero
3286 long zeroBit = Long.lowestOneBit(~mask);
3287 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3288 assert(zeroPos <= newArity);
3289 if (zeroPos == newArity) {
3290 return 0;
3291 }
3292 return ~zeroPos;
3293 } else {
3294 // same algorithm, different bit set
3295 BitSet mask = new BitSet(newArity);
3296 for (int i = 0; i < reorder.length; i++) {
3297 int arg = reorder[i];
3298 if (arg >= newArity) {
3299 return reorder.length;
3300 }
3301 if (mask.get(arg)) {
3302 return i; // >0 indicates a dup
3303 }
3304 mask.set(arg);
3305 }
3306 int zeroPos = mask.nextClearBit(0);
3307 assert(zeroPos <= newArity);
3308 if (zeroPos == newArity) {
3309 return 0;
3310 }
3311 return ~zeroPos;
3312 }
3313 }
3314
3315 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3316 if (newType.returnType() != oldType.returnType())
3317 throw newIllegalArgumentException("return types do not match",
3318 oldType, newType);
3319 if (reorder.length == oldType.parameterCount()) {
3320 int limit = newType.parameterCount();
3321 boolean bad = false;
3322 for (int j = 0; j < reorder.length; j++) {
3323 int i = reorder[j];
3324 if (i < 0 || i >= limit) {
3325 bad = true; break;
3326 }
3327 Class<?> src = newType.parameterType(i);
3328 Class<?> dst = oldType.parameterType(j);
3329 if (src != dst)
3330 throw newIllegalArgumentException("parameter types do not match after reorder",
3331 oldType, newType);
3332 }
3333 if (!bad) return true;
3334 }
3335 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3336 }
3337
3338 /**
3339 * Produces a method handle of the requested return type which returns the given
3340 * constant value every time it is invoked.
3341 * <p>
3342 * Before the method handle is returned, the passed-in value is converted to the requested type.
3343 * If the requested type is primitive, widening primitive conversions are attempted,
3344 * else reference conversions are attempted.
3345 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3346 * @param type the return type of the desired method handle
3347 * @param value the value to return
3348 * @return a method handle of the given return type and no arguments, which always returns the given value
3349 * @throws NullPointerException if the {@code type} argument is null
3350 * @throws ClassCastException if the value cannot be converted to the required return type
3351 * @throws IllegalArgumentException if the given type is {@code void.class}
3352 */
3353 public static
3354 MethodHandle constant(Class<?> type, Object value) {
3355 if (type.isPrimitive()) {
3356 if (type == void.class)
3357 throw newIllegalArgumentException("void type");
3358 Wrapper w = Wrapper.forPrimitiveType(type);
3359 value = w.convert(value, type);
3360 if (w.zero().equals(value))
3361 return zero(w, type);
3362 return insertArguments(identity(type), 0, value);
3363 } else {
3364 if (value == null)
3365 return zero(Wrapper.OBJECT, type);
3366 return identity(type).bindTo(value);
3367 }
3368 }
3369
3370 /**
3371 * Produces a method handle which returns its sole argument when invoked.
3372 * @param type the type of the sole parameter and return value of the desired method handle
3373 * @return a unary method handle which accepts and returns the given type
3374 * @throws NullPointerException if the argument is null
3375 * @throws IllegalArgumentException if the given type is {@code void.class}
3376 */
3377 public static
3378 MethodHandle identity(Class<?> type) {
3379 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3380 int pos = btw.ordinal();
3381 MethodHandle ident = IDENTITY_MHS[pos];
3382 if (ident == null) {
3383 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3384 }
3385 if (ident.type().returnType() == type)
3386 return ident;
3387 // something like identity(Foo.class); do not bother to intern these
3388 assert (btw == Wrapper.OBJECT);
3389 return makeIdentity(type);
3390 }
3391
3392 /**
3393 * Produces a constant method handle of the requested return type which
3394 * returns the default value for that type every time it is invoked.
3395 * The resulting constant method handle will have no side effects.
3396 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3397 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3398 * since {@code explicitCastArguments} converts {@code null} to default values.
3399 * @param type the expected return type of the desired method handle
3400 * @return a constant method handle that takes no arguments
3401 * and returns the default value of the given type (or void, if the type is void)
3402 * @throws NullPointerException if the argument is null
3403 * @see MethodHandles#constant
3404 * @see MethodHandles#empty
3405 * @see MethodHandles#explicitCastArguments
3406 * @since 9
3407 */
3408 public static MethodHandle zero(Class<?> type) {
3409 Objects.requireNonNull(type);
3410 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3411 }
3412
3413 private static MethodHandle identityOrVoid(Class<?> type) {
3414 return type == void.class ? zero(type) : identity(type);
3415 }
3416
3417 /**
3418 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3419 * and returns a suitable default depending on the return type.
3420 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3421 * <p>The returned method handle is equivalent to
3422 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3423 *
3424 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3425 * {@code guardWithTest(pred, target, empty(target.type())}.
3426 * @param type the type of the desired method handle
3427 * @return a constant method handle of the given type, which returns a default value of the given return type
3428 * @throws NullPointerException if the argument is null
3429 * @see MethodHandles#zero
3430 * @see MethodHandles#constant
3431 * @since 9
3432 */
3433 public static MethodHandle empty(MethodType type) {
3434 Objects.requireNonNull(type);
3435 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3436 }
3437
3438 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3439 private static MethodHandle makeIdentity(Class<?> ptype) {
3440 MethodType mtype = methodType(ptype, ptype);
3441 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3442 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3443 }
3444
3445 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3446 int pos = btw.ordinal();
3447 MethodHandle zero = ZERO_MHS[pos];
3448 if (zero == null) {
3449 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3450 }
3451 if (zero.type().returnType() == rtype)
3452 return zero;
3453 assert(btw == Wrapper.OBJECT);
3454 return makeZero(rtype);
3455 }
3456 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3457 private static MethodHandle makeZero(Class<?> rtype) {
3458 MethodType mtype = methodType(rtype);
3459 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3460 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3461 }
3462
3463 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3464 // Simulate a CAS, to avoid racy duplication of results.
3465 MethodHandle prev = cache[pos];
3466 if (prev != null) return prev;
3467 return cache[pos] = value;
3468 }
3469
3470 /**
3471 * Provides a target method handle with one or more <em>bound arguments</em>
3472 * in advance of the method handle's invocation.
3473 * The formal parameters to the target corresponding to the bound
3474 * arguments are called <em>bound parameters</em>.
3475 * Returns a new method handle which saves away the bound arguments.
3476 * When it is invoked, it receives arguments for any non-bound parameters,
3477 * binds the saved arguments to their corresponding parameters,
3478 * and calls the original target.
3479 * <p>
3480 * The type of the new method handle will drop the types for the bound
3481 * parameters from the original target type, since the new method handle
3482 * will no longer require those arguments to be supplied by its callers.
3483 * <p>
3484 * Each given argument object must match the corresponding bound parameter type.
3485 * If a bound parameter type is a primitive, the argument object
3486 * must be a wrapper, and will be unboxed to produce the primitive value.
3487 * <p>
3488 * The {@code pos} argument selects which parameters are to be bound.
3489 * It may range between zero and <i>N-L</i> (inclusively),
3490 * where <i>N</i> is the arity of the target method handle
3491 * and <i>L</i> is the length of the values array.
3492 * <p>
3493 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3494 * variable-arity method handle}, even if the original target method handle was.
3495 * @param target the method handle to invoke after the argument is inserted
3496 * @param pos where to insert the argument (zero for the first)
3497 * @param values the series of arguments to insert
3498 * @return a method handle which inserts an additional argument,
3499 * before calling the original method handle
3500 * @throws NullPointerException if the target or the {@code values} array is null
3501 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
3502 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
3503 * is the length of the values array.
3504 * @throws ClassCastException if an argument does not match the corresponding bound parameter
3505 * type.
3506 * @see MethodHandle#bindTo
3507 */
3508 public static
3509 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3510 int insCount = values.length;
3511 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3512 if (insCount == 0) return target;
3513 BoundMethodHandle result = target.rebind();
3514 for (int i = 0; i < insCount; i++) {
3515 Object value = values[i];
3516 Class<?> ptype = ptypes[pos+i];
3517 if (ptype.isPrimitive()) {
3518 result = insertArgumentPrimitive(result, pos, ptype, value);
3519 } else {
3520 value = ptype.cast(value); // throw CCE if needed
3521 result = result.bindArgumentL(pos, value);
3522 }
3523 }
3524 return result;
3525 }
3526
3527 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3528 Class<?> ptype, Object value) {
3529 Wrapper w = Wrapper.forPrimitiveType(ptype);
3530 // perform unboxing and/or primitive conversion
3531 value = w.convert(value, ptype);
3532 switch (w) {
3533 case INT: return result.bindArgumentI(pos, (int)value);
3534 case LONG: return result.bindArgumentJ(pos, (long)value);
3535 case FLOAT: return result.bindArgumentF(pos, (float)value);
3536 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3537 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3538 }
3539 }
3540
3541 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3542 MethodType oldType = target.type();
3543 int outargs = oldType.parameterCount();
3544 int inargs = outargs - insCount;
3545 if (inargs < 0)
3546 throw newIllegalArgumentException("too many values to insert");
3547 if (pos < 0 || pos > inargs)
3548 throw newIllegalArgumentException("no argument type to append");
3549 return oldType.ptypes();
3550 }
3551
3552 /**
3553 * Produces a method handle which will discard some dummy arguments
3554 * before calling some other specified <i>target</i> method handle.
3555 * The type of the new method handle will be the same as the target's type,
3556 * except it will also include the dummy argument types,
3557 * at some given position.
3558 * <p>
3559 * The {@code pos} argument may range between zero and <i>N</i>,
3560 * where <i>N</i> is the arity of the target.
3561 * If {@code pos} is zero, the dummy arguments will precede
3562 * the target's real arguments; if {@code pos} is <i>N</i>
3563 * they will come after.
3564 * <p>
3565 * <b>Example:</b>
3566 * <blockquote><pre>{@code
3567 import static java.lang.invoke.MethodHandles.*;
3568 import static java.lang.invoke.MethodType.*;
3569 ...
3570 MethodHandle cat = lookup().findVirtual(String.class,
3571 "concat", methodType(String.class, String.class));
3572 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3573 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3574 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3575 assertEquals(bigType, d0.type());
3576 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3577 * }</pre></blockquote>
3578 * <p>
3579 * This method is also equivalent to the following code:
3580 * <blockquote><pre>
3581 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3582 * </pre></blockquote>
3583 * @param target the method handle to invoke after the arguments are dropped
3584 * @param valueTypes the type(s) of the argument(s) to drop
3585 * @param pos position of first argument to drop (zero for the leftmost)
3586 * @return a method handle which drops arguments of the given types,
3587 * before calling the original method handle
3588 * @throws NullPointerException if the target is null,
3589 * or if the {@code valueTypes} list or any of its elements is null
3590 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3591 * or if {@code pos} is negative or greater than the arity of the target,
3592 * or if the new method handle's type would have too many parameters
3593 */
3594 public static
3595 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3596 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3597 }
3598
3599 private static List<Class<?>> copyTypes(Object[] array) {
3600 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3601 }
3602
3603 private static
3604 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3605 MethodType oldType = target.type(); // get NPE
3606 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3607 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3608 if (dropped == 0) return target;
3609 BoundMethodHandle result = target.rebind();
3610 LambdaForm lform = result.form;
3611 int insertFormArg = 1 + pos;
3612 for (Class<?> ptype : valueTypes) {
3613 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3614 }
3615 result = result.copyWith(newType, lform);
3616 return result;
3617 }
3618
3619 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3620 int dropped = valueTypes.size();
3621 MethodType.checkSlotCount(dropped);
3622 int outargs = oldType.parameterCount();
3623 int inargs = outargs + dropped;
3624 if (pos < 0 || pos > outargs)
3625 throw newIllegalArgumentException("no argument type to remove"
3626 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3627 );
3628 return dropped;
3629 }
3630
3631 /**
3632 * Produces a method handle which will discard some dummy arguments
3633 * before calling some other specified <i>target</i> method handle.
3634 * The type of the new method handle will be the same as the target's type,
3635 * except it will also include the dummy argument types,
3636 * at some given position.
3637 * <p>
3638 * The {@code pos} argument may range between zero and <i>N</i>,
3639 * where <i>N</i> is the arity of the target.
3640 * If {@code pos} is zero, the dummy arguments will precede
3641 * the target's real arguments; if {@code pos} is <i>N</i>
3642 * they will come after.
3643 * @apiNote
3644 * <blockquote><pre>{@code
3645 import static java.lang.invoke.MethodHandles.*;
3646 import static java.lang.invoke.MethodType.*;
3647 ...
3648 MethodHandle cat = lookup().findVirtual(String.class,
3649 "concat", methodType(String.class, String.class));
3650 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3651 MethodHandle d0 = dropArguments(cat, 0, String.class);
3652 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3653 MethodHandle d1 = dropArguments(cat, 1, String.class);
3654 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3655 MethodHandle d2 = dropArguments(cat, 2, String.class);
3656 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3657 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3658 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3659 * }</pre></blockquote>
3660 * <p>
3661 * This method is also equivalent to the following code:
3662 * <blockquote><pre>
3663 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3664 * </pre></blockquote>
3665 * @param target the method handle to invoke after the arguments are dropped
3666 * @param valueTypes the type(s) of the argument(s) to drop
3667 * @param pos position of first argument to drop (zero for the leftmost)
3668 * @return a method handle which drops arguments of the given types,
3669 * before calling the original method handle
3670 * @throws NullPointerException if the target is null,
3671 * or if the {@code valueTypes} array or any of its elements is null
3672 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3673 * or if {@code pos} is negative or greater than the arity of the target,
3674 * or if the new method handle's type would have
3675 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3676 */
3677 public static
3678 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3679 return dropArguments0(target, pos, copyTypes(valueTypes));
3680 }
3681
3682 // private version which allows caller some freedom with error handling
3683 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3684 boolean nullOnFailure) {
3685 newTypes = copyTypes(newTypes.toArray());
3686 List<Class<?>> oldTypes = target.type().parameterList();
3687 int match = oldTypes.size();
3688 if (skip != 0) {
3689 if (skip < 0 || skip > match) {
3690 throw newIllegalArgumentException("illegal skip", skip, target);
3691 }
3692 oldTypes = oldTypes.subList(skip, match);
3693 match -= skip;
3694 }
3695 List<Class<?>> addTypes = newTypes;
3696 int add = addTypes.size();
3697 if (pos != 0) {
3698 if (pos < 0 || pos > add) {
3699 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3700 }
3701 addTypes = addTypes.subList(pos, add);
3702 add -= pos;
3703 assert(addTypes.size() == add);
3704 }
3705 // Do not add types which already match the existing arguments.
3706 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3707 if (nullOnFailure) {
3708 return null;
3709 }
3710 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3711 }
3712 addTypes = addTypes.subList(match, add);
3713 add -= match;
3714 assert(addTypes.size() == add);
3715 // newTypes: ( P*[pos], M*[match], A*[add] )
3716 // target: ( S*[skip], M*[match] )
3717 MethodHandle adapter = target;
3718 if (add > 0) {
3719 adapter = dropArguments0(adapter, skip+ match, addTypes);
3720 }
3721 // adapter: (S*[skip], M*[match], A*[add] )
3722 if (pos > 0) {
3723 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3724 }
3725 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3726 return adapter;
3727 }
3728
3729 /**
3730 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3731 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3732 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3733 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3734 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3735 * {@link #dropArguments(MethodHandle, int, Class[])}.
3736 * <p>
3737 * The resulting handle will have the same return type as the target handle.
3738 * <p>
3739 * In more formal terms, assume these two type lists:<ul>
3740 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3741 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3742 * {@code newTypes}.
3743 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3744 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3745 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3746 * sub-list.
3747 * </ul>
3748 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3749 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3750 * {@link #dropArguments(MethodHandle, int, Class[])}.
3751 *
3752 * @apiNote
3753 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3754 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3755 * <blockquote><pre>{@code
3756 import static java.lang.invoke.MethodHandles.*;
3757 import static java.lang.invoke.MethodType.*;
3758 ...
3759 ...
3760 MethodHandle h0 = constant(boolean.class, true);
3761 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3762 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3763 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3764 if (h1.type().parameterCount() < h2.type().parameterCount())
3765 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3766 else
3767 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3768 MethodHandle h3 = guardWithTest(h0, h1, h2);
3769 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3770 * }</pre></blockquote>
3771 * @param target the method handle to adapt
3772 * @param skip number of targets parameters to disregard (they will be unchanged)
3773 * @param newTypes the list of types to match {@code target}'s parameter type list to
3774 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3775 * @return a possibly adapted method handle
3776 * @throws NullPointerException if either argument is null
3777 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3778 * or if {@code skip} is negative or greater than the arity of the target,
3779 * or if {@code pos} is negative or greater than the newTypes list size,
3780 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3781 * {@code pos}.
3782 * @since 9
3783 */
3784 public static
3785 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3786 Objects.requireNonNull(target);
3787 Objects.requireNonNull(newTypes);
3788 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3789 }
3790
3791 /**
3792 * Adapts a target method handle by pre-processing
3793 * one or more of its arguments, each with its own unary filter function,
3794 * and then calling the target with each pre-processed argument
3795 * replaced by the result of its corresponding filter function.
3796 * <p>
3797 * The pre-processing is performed by one or more method handles,
3798 * specified in the elements of the {@code filters} array.
3799 * The first element of the filter array corresponds to the {@code pos}
3800 * argument of the target, and so on in sequence.
3801 * The filter functions are invoked in left to right order.
3802 * <p>
3803 * Null arguments in the array are treated as identity functions,
3804 * and the corresponding arguments left unchanged.
3805 * (If there are no non-null elements in the array, the original target is returned.)
3806 * Each filter is applied to the corresponding argument of the adapter.
3807 * <p>
3808 * If a filter {@code F} applies to the {@code N}th argument of
3809 * the target, then {@code F} must be a method handle which
3810 * takes exactly one argument. The type of {@code F}'s sole argument
3811 * replaces the corresponding argument type of the target
3812 * in the resulting adapted method handle.
3813 * The return type of {@code F} must be identical to the corresponding
3814 * parameter type of the target.
3815 * <p>
3816 * It is an error if there are elements of {@code filters}
3817 * (null or not)
3818 * which do not correspond to argument positions in the target.
3819 * <p><b>Example:</b>
3820 * <blockquote><pre>{@code
3821 import static java.lang.invoke.MethodHandles.*;
3822 import static java.lang.invoke.MethodType.*;
3823 ...
3824 MethodHandle cat = lookup().findVirtual(String.class,
3825 "concat", methodType(String.class, String.class));
3826 MethodHandle upcase = lookup().findVirtual(String.class,
3827 "toUpperCase", methodType(String.class));
3828 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3829 MethodHandle f0 = filterArguments(cat, 0, upcase);
3830 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3831 MethodHandle f1 = filterArguments(cat, 1, upcase);
3832 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3833 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3834 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3835 * }</pre></blockquote>
3836 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3837 * denotes the return type of both the {@code target} and resulting adapter.
3838 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3839 * of the parameters and arguments that precede and follow the filter position
3840 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3841 * values of the filtered parameters and arguments; they also represent the
3842 * return types of the {@code filter[i]} handles. The latter accept arguments
3843 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3844 * the resulting adapter.
3845 * <blockquote><pre>{@code
3846 * T target(P... p, A[i]... a[i], B... b);
3847 * A[i] filter[i](V[i]);
3848 * T adapter(P... p, V[i]... v[i], B... b) {
3849 * return target(p..., filter[i](v[i])..., b...);
3850 * }
3851 * }</pre></blockquote>
3852 * <p>
3853 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3854 * variable-arity method handle}, even if the original target method handle was.
3855 *
3856 * @param target the method handle to invoke after arguments are filtered
3857 * @param pos the position of the first argument to filter
3858 * @param filters method handles to call initially on filtered arguments
3859 * @return method handle which incorporates the specified argument filtering logic
3860 * @throws NullPointerException if the target is null
3861 * or if the {@code filters} array is null
3862 * @throws IllegalArgumentException if a non-null element of {@code filters}
3863 * does not match a corresponding argument type of target as described above,
3864 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3865 * or if the resulting method handle's type would have
3866 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3867 */
3868 public static
3869 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3870 filterArgumentsCheckArity(target, pos, filters);
3871 MethodHandle adapter = target;
3872 // process filters in reverse order so that the invocation of
3873 // the resulting adapter will invoke the filters in left-to-right order
3874 for (int i = filters.length - 1; i >= 0; --i) {
3875 MethodHandle filter = filters[i];
3876 if (filter == null) continue; // ignore null elements of filters
3877 adapter = filterArgument(adapter, pos + i, filter);
3878 }
3879 return adapter;
3880 }
3881
3882 /*non-public*/ static
3883 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3884 filterArgumentChecks(target, pos, filter);
3885 MethodType targetType = target.type();
3886 MethodType filterType = filter.type();
3887 BoundMethodHandle result = target.rebind();
3888 Class<?> newParamType = filterType.parameterType(0);
3889 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3890 MethodType newType = targetType.changeParameterType(pos, newParamType);
3891 result = result.copyWithExtendL(newType, lform, filter);
3892 return result;
3893 }
3894
3895 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3896 MethodType targetType = target.type();
3897 int maxPos = targetType.parameterCount();
3898 if (pos + filters.length > maxPos)
3899 throw newIllegalArgumentException("too many filters");
3900 }
3901
3902 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3903 MethodType targetType = target.type();
3904 MethodType filterType = filter.type();
3905 if (filterType.parameterCount() != 1
3906 || filterType.returnType() != targetType.parameterType(pos))
3907 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3908 }
3909
3910 /**
3911 * Adapts a target method handle by pre-processing
3912 * a sub-sequence of its arguments with a filter (another method handle).
3913 * The pre-processed arguments are replaced by the result (if any) of the
3914 * filter function.
3915 * The target is then called on the modified (usually shortened) argument list.
3916 * <p>
3917 * If the filter returns a value, the target must accept that value as
3918 * its argument in position {@code pos}, preceded and/or followed by
3919 * any arguments not passed to the filter.
3920 * If the filter returns void, the target must accept all arguments
3921 * not passed to the filter.
3922 * No arguments are reordered, and a result returned from the filter
3923 * replaces (in order) the whole subsequence of arguments originally
3924 * passed to the adapter.
3925 * <p>
3926 * The argument types (if any) of the filter
3927 * replace zero or one argument types of the target, at position {@code pos},
3928 * in the resulting adapted method handle.
3929 * The return type of the filter (if any) must be identical to the
3930 * argument type of the target at position {@code pos}, and that target argument
3931 * is supplied by the return value of the filter.
3932 * <p>
3933 * In all cases, {@code pos} must be greater than or equal to zero, and
3934 * {@code pos} must also be less than or equal to the target's arity.
3935 * <p><b>Example:</b>
3936 * <blockquote><pre>{@code
3937 import static java.lang.invoke.MethodHandles.*;
3938 import static java.lang.invoke.MethodType.*;
3939 ...
3940 MethodHandle deepToString = publicLookup()
3941 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3942
3943 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3944 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3945
3946 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3947 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3948
3949 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3950 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3951 assertEquals("[top, [up, down], strange]",
3952 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3953
3954 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3955 assertEquals("[top, [up, down], [strange]]",
3956 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3957
3958 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3959 assertEquals("[top, [[up, down, strange], charm], bottom]",
3960 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3961 * }</pre></blockquote>
3962 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3963 * represents the return type of the {@code target} and resulting adapter.
3964 * {@code V}/{@code v} stand for the return type and value of the
3965 * {@code filter}, which are also found in the signature and arguments of
3966 * the {@code target}, respectively, unless {@code V} is {@code void}.
3967 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3968 * and values preceding and following the collection position, {@code pos},
3969 * in the {@code target}'s signature. They also turn up in the resulting
3970 * adapter's signature and arguments, where they surround
3971 * {@code B}/{@code b}, which represent the parameter types and arguments
3972 * to the {@code filter} (if any).
3973 * <blockquote><pre>{@code
3974 * T target(A...,V,C...);
3975 * V filter(B...);
3976 * T adapter(A... a,B... b,C... c) {
3977 * V v = filter(b...);
3978 * return target(a...,v,c...);
3979 * }
3980 * // and if the filter has no arguments:
3981 * T target2(A...,V,C...);
3982 * V filter2();
3983 * T adapter2(A... a,C... c) {
3984 * V v = filter2();
3985 * return target2(a...,v,c...);
3986 * }
3987 * // and if the filter has a void return:
3988 * T target3(A...,C...);
3989 * void filter3(B...);
3990 * T adapter3(A... a,B... b,C... c) {
3991 * filter3(b...);
3992 * return target3(a...,c...);
3993 * }
3994 * }</pre></blockquote>
3995 * <p>
3996 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3997 * one which first "folds" the affected arguments, and then drops them, in separate
3998 * steps as follows:
3999 * <blockquote><pre>{@code
4000 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4001 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4002 * }</pre></blockquote>
4003 * If the target method handle consumes no arguments besides than the result
4004 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4005 * is equivalent to {@code filterReturnValue(coll, mh)}.
4006 * If the filter method handle {@code coll} consumes one argument and produces
4007 * a non-void result, then {@code collectArguments(mh, N, coll)}
4008 * is equivalent to {@code filterArguments(mh, N, coll)}.
4009 * Other equivalences are possible but would require argument permutation.
4010 * <p>
4011 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4012 * variable-arity method handle}, even if the original target method handle was.
4013 *
4014 * @param target the method handle to invoke after filtering the subsequence of arguments
4015 * @param pos the position of the first adapter argument to pass to the filter,
4016 * and/or the target argument which receives the result of the filter
4017 * @param filter method handle to call on the subsequence of arguments
4018 * @return method handle which incorporates the specified argument subsequence filtering logic
4019 * @throws NullPointerException if either argument is null
4020 * @throws IllegalArgumentException if the return type of {@code filter}
4021 * is non-void and is not the same as the {@code pos} argument of the target,
4022 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4023 * or if the resulting method handle's type would have
4024 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4025 * @see MethodHandles#foldArguments
4026 * @see MethodHandles#filterArguments
4027 * @see MethodHandles#filterReturnValue
4028 */
4029 public static
4030 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4031 MethodType newType = collectArgumentsChecks(target, pos, filter);
4032 MethodType collectorType = filter.type();
4033 BoundMethodHandle result = target.rebind();
4034 LambdaForm lform;
4035 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4036 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4037 if (lform != null) {
4038 return result.copyWith(newType, lform);
4039 }
4040 }
4041 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4042 return result.copyWithExtendL(newType, lform, filter);
4043 }
4044
4045 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4046 MethodType targetType = target.type();
4047 MethodType filterType = filter.type();
4048 Class<?> rtype = filterType.returnType();
4049 List<Class<?>> filterArgs = filterType.parameterList();
4050 if (rtype == void.class) {
4051 return targetType.insertParameterTypes(pos, filterArgs);
4052 }
4053 if (rtype != targetType.parameterType(pos)) {
4054 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4055 }
4056 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4057 }
4058
4059 /**
4060 * Adapts a target method handle by post-processing
4061 * its return value (if any) with a filter (another method handle).
4062 * The result of the filter is returned from the adapter.
4063 * <p>
4064 * If the target returns a value, the filter must accept that value as
4065 * its only argument.
4066 * If the target returns void, the filter must accept no arguments.
4067 * <p>
4068 * The return type of the filter
4069 * replaces the return type of the target
4070 * in the resulting adapted method handle.
4071 * The argument type of the filter (if any) must be identical to the
4072 * return type of the target.
4073 * <p><b>Example:</b>
4074 * <blockquote><pre>{@code
4075 import static java.lang.invoke.MethodHandles.*;
4076 import static java.lang.invoke.MethodType.*;
4077 ...
4078 MethodHandle cat = lookup().findVirtual(String.class,
4079 "concat", methodType(String.class, String.class));
4080 MethodHandle length = lookup().findVirtual(String.class,
4081 "length", methodType(int.class));
4082 System.out.println((String) cat.invokeExact("x", "y")); // xy
4083 MethodHandle f0 = filterReturnValue(cat, length);
4084 System.out.println((int) f0.invokeExact("x", "y")); // 2
4085 * }</pre></blockquote>
4086 * <p>Here is pseudocode for the resulting adapter. In the code,
4087 * {@code T}/{@code t} represent the result type and value of the
4088 * {@code target}; {@code V}, the result type of the {@code filter}; and
4089 * {@code A}/{@code a}, the types and values of the parameters and arguments
4090 * of the {@code target} as well as the resulting adapter.
4091 * <blockquote><pre>{@code
4092 * T target(A...);
4093 * V filter(T);
4094 * V adapter(A... a) {
4095 * T t = target(a...);
4096 * return filter(t);
4097 * }
4098 * // and if the target has a void return:
4099 * void target2(A...);
4100 * V filter2();
4101 * V adapter2(A... a) {
4102 * target2(a...);
4103 * return filter2();
4104 * }
4105 * // and if the filter has a void return:
4106 * T target3(A...);
4107 * void filter3(V);
4108 * void adapter3(A... a) {
4109 * T t = target3(a...);
4110 * filter3(t);
4111 * }
4112 * }</pre></blockquote>
4113 * <p>
4114 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4115 * variable-arity method handle}, even if the original target method handle was.
4116 * @param target the method handle to invoke before filtering the return value
4117 * @param filter method handle to call on the return value
4118 * @return method handle which incorporates the specified return value filtering logic
4119 * @throws NullPointerException if either argument is null
4120 * @throws IllegalArgumentException if the argument list of {@code filter}
4121 * does not match the return type of target as described above
4122 */
4123 public static
4124 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4125 MethodType targetType = target.type();
4126 MethodType filterType = filter.type();
4127 filterReturnValueChecks(targetType, filterType);
4128 BoundMethodHandle result = target.rebind();
4129 BasicType rtype = BasicType.basicType(filterType.returnType());
4130 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4131 MethodType newType = targetType.changeReturnType(filterType.returnType());
4132 result = result.copyWithExtendL(newType, lform, filter);
4133 return result;
4134 }
4135
4136 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4137 Class<?> rtype = targetType.returnType();
4138 int filterValues = filterType.parameterCount();
4139 if (filterValues == 0
4140 ? (rtype != void.class)
4141 : (rtype != filterType.parameterType(0) || filterValues != 1))
4142 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4143 }
4144
4145 /**
4146 * Adapts a target method handle by pre-processing
4147 * some of its arguments, and then calling the target with
4148 * the result of the pre-processing, inserted into the original
4149 * sequence of arguments.
4150 * <p>
4151 * The pre-processing is performed by {@code combiner}, a second method handle.
4152 * Of the arguments passed to the adapter, the first {@code N} arguments
4153 * are copied to the combiner, which is then called.
4154 * (Here, {@code N} is defined as the parameter count of the combiner.)
4155 * After this, control passes to the target, with any result
4156 * from the combiner inserted before the original {@code N} incoming
4157 * arguments.
4158 * <p>
4159 * If the combiner returns a value, the first parameter type of the target
4160 * must be identical with the return type of the combiner, and the next
4161 * {@code N} parameter types of the target must exactly match the parameters
4162 * of the combiner.
4163 * <p>
4164 * If the combiner has a void return, no result will be inserted,
4165 * and the first {@code N} parameter types of the target
4166 * must exactly match the parameters of the combiner.
4167 * <p>
4168 * The resulting adapter is the same type as the target, except that the
4169 * first parameter type is dropped,
4170 * if it corresponds to the result of the combiner.
4171 * <p>
4172 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4173 * that either the combiner or the target does not wish to receive.
4174 * If some of the incoming arguments are destined only for the combiner,
4175 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4176 * arguments will not need to be live on the stack on entry to the
4177 * target.)
4178 * <p><b>Example:</b>
4179 * <blockquote><pre>{@code
4180 import static java.lang.invoke.MethodHandles.*;
4181 import static java.lang.invoke.MethodType.*;
4182 ...
4183 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4184 "println", methodType(void.class, String.class))
4185 .bindTo(System.out);
4186 MethodHandle cat = lookup().findVirtual(String.class,
4187 "concat", methodType(String.class, String.class));
4188 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4189 MethodHandle catTrace = foldArguments(cat, trace);
4190 // also prints "boo":
4191 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4192 * }</pre></blockquote>
4193 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4194 * represents the result type of the {@code target} and resulting adapter.
4195 * {@code V}/{@code v} represent the type and value of the parameter and argument
4196 * of {@code target} that precedes the folding position; {@code V} also is
4197 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4198 * types and values of the {@code N} parameters and arguments at the folding
4199 * position. {@code B}/{@code b} represent the types and values of the
4200 * {@code target} parameters and arguments that follow the folded parameters
4201 * and arguments.
4202 * <blockquote><pre>{@code
4203 * // there are N arguments in A...
4204 * T target(V, A[N]..., B...);
4205 * V combiner(A...);
4206 * T adapter(A... a, B... b) {
4207 * V v = combiner(a...);
4208 * return target(v, a..., b...);
4209 * }
4210 * // and if the combiner has a void return:
4211 * T target2(A[N]..., B...);
4212 * void combiner2(A...);
4213 * T adapter2(A... a, B... b) {
4214 * combiner2(a...);
4215 * return target2(a..., b...);
4216 * }
4217 * }</pre></blockquote>
4218 * <p>
4219 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4220 * variable-arity method handle}, even if the original target method handle was.
4221 * @param target the method handle to invoke after arguments are combined
4222 * @param combiner method handle to call initially on the incoming arguments
4223 * @return method handle which incorporates the specified argument folding logic
4224 * @throws NullPointerException if either argument is null
4225 * @throws IllegalArgumentException if {@code combiner}'s return type
4226 * is non-void and not the same as the first argument type of
4227 * the target, or if the initial {@code N} argument types
4228 * of the target
4229 * (skipping one matching the {@code combiner}'s return type)
4230 * are not identical with the argument types of {@code combiner}
4231 */
4232 public static
4233 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4234 return foldArguments(target, 0, combiner);
4235 }
4236
4237 /**
4238 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4239 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4240 * before the folded arguments.
4241 * <p>
4242 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4243 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4244 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4245 * 0.
4246 *
4247 * @apiNote Example:
4248 * <blockquote><pre>{@code
4249 import static java.lang.invoke.MethodHandles.*;
4250 import static java.lang.invoke.MethodType.*;
4251 ...
4252 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4253 "println", methodType(void.class, String.class))
4254 .bindTo(System.out);
4255 MethodHandle cat = lookup().findVirtual(String.class,
4256 "concat", methodType(String.class, String.class));
4257 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4258 MethodHandle catTrace = foldArguments(cat, 1, trace);
4259 // also prints "jum":
4260 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4261 * }</pre></blockquote>
4262 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4263 * represents the result type of the {@code target} and resulting adapter.
4264 * {@code V}/{@code v} represent the type and value of the parameter and argument
4265 * of {@code target} that precedes the folding position; {@code V} also is
4266 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4267 * types and values of the {@code N} parameters and arguments at the folding
4268 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4269 * and values of the {@code target} parameters and arguments that precede and
4270 * follow the folded parameters and arguments starting at {@code pos},
4271 * respectively.
4272 * <blockquote><pre>{@code
4273 * // there are N arguments in A...
4274 * T target(Z..., V, A[N]..., B...);
4275 * V combiner(A...);
4276 * T adapter(Z... z, A... a, B... b) {
4277 * V v = combiner(a...);
4278 * return target(z..., v, a..., b...);
4279 * }
4280 * // and if the combiner has a void return:
4281 * T target2(Z..., A[N]..., B...);
4282 * void combiner2(A...);
4283 * T adapter2(Z... z, A... a, B... b) {
4284 * combiner2(a...);
4285 * return target2(z..., a..., b...);
4286 * }
4287 * }</pre></blockquote>
4288 * <p>
4289 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4290 * variable-arity method handle}, even if the original target method handle was.
4291 *
4292 * @param target the method handle to invoke after arguments are combined
4293 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4294 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4295 * @param combiner method handle to call initially on the incoming arguments
4296 * @return method handle which incorporates the specified argument folding logic
4297 * @throws NullPointerException if either argument is null
4298 * @throws IllegalArgumentException if either of the following two conditions holds:
4299 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4300 * {@code pos} of the target signature;
4301 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4302 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4303 *
4304 * @see #foldArguments(MethodHandle, MethodHandle)
4305 * @since 9
4306 */
4307 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4308 MethodType targetType = target.type();
4309 MethodType combinerType = combiner.type();
4310 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4311 BoundMethodHandle result = target.rebind();
4312 boolean dropResult = rtype == void.class;
4313 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4314 MethodType newType = targetType;
4315 if (!dropResult) {
4316 newType = newType.dropParameterTypes(pos, pos + 1);
4317 }
4318 result = result.copyWithExtendL(newType, lform, combiner);
4319 return result;
4320 }
4321
4322 /**
4323 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4324 * added capability of selecting the arguments from the targets parameters
4325 * to call the combiner with. This allows us to avoid some simple cases of
4326 * permutations and padding the combiner with dropArguments to select the
4327 * right argument, which may ultimately produce fewer intermediaries.
4328 */
4329 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4330 MethodType targetType = target.type();
4331 MethodType combinerType = combiner.type();
4332 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4333 BoundMethodHandle result = target.rebind();
4334 boolean dropResult = rtype == void.class;
4335 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4336 MethodType newType = targetType;
4337 if (!dropResult) {
4338 newType = newType.dropParameterTypes(pos, pos + 1);
4339 }
4340 result = result.copyWithExtendL(newType, lform, combiner);
4341 return result;
4342 }
4343
4344 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4345 int foldArgs = combinerType.parameterCount();
4346 Class<?> rtype = combinerType.returnType();
4347 int foldVals = rtype == void.class ? 0 : 1;
4348 int afterInsertPos = foldPos + foldVals;
4349 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4350 if (ok) {
4351 for (int i = 0; i < foldArgs; i++) {
4352 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4353 ok = false;
4354 break;
4355 }
4356 }
4357 }
4358 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4359 ok = false;
4360 if (!ok)
4361 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4362 return rtype;
4363 }
4364
4365 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4366 int foldArgs = combinerType.parameterCount();
4367 if (argPos.length != foldArgs) {
4368 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4369 }
4370 Class<?> rtype = combinerType.returnType();
4371 int foldVals = rtype == void.class ? 0 : 1;
4372 boolean ok = true;
4373 for (int i = 0; i < foldArgs; i++) {
4374 int arg = argPos[i];
4375 if (arg < 0 || arg > targetType.parameterCount()) {
4376 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4377 }
4378 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4379 throw newIllegalArgumentException("target argument type at position " + arg
4380 + " must match combiner argument type at index " + i + ": " + targetType
4381 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4382 }
4383 }
4384 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4385 ok = false;
4386 }
4387 if (!ok)
4388 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4389 return rtype;
4390 }
4391
4392 /**
4393 * Makes a method handle which adapts a target method handle,
4394 * by guarding it with a test, a boolean-valued method handle.
4395 * If the guard fails, a fallback handle is called instead.
4396 * All three method handles must have the same corresponding
4397 * argument and return types, except that the return type
4398 * of the test must be boolean, and the test is allowed
4399 * to have fewer arguments than the other two method handles.
4400 * <p>
4401 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4402 * represents the uniform result type of the three involved handles;
4403 * {@code A}/{@code a}, the types and values of the {@code target}
4404 * parameters and arguments that are consumed by the {@code test}; and
4405 * {@code B}/{@code b}, those types and values of the {@code target}
4406 * parameters and arguments that are not consumed by the {@code test}.
4407 * <blockquote><pre>{@code
4408 * boolean test(A...);
4409 * T target(A...,B...);
4410 * T fallback(A...,B...);
4411 * T adapter(A... a,B... b) {
4412 * if (test(a...))
4413 * return target(a..., b...);
4414 * else
4415 * return fallback(a..., b...);
4416 * }
4417 * }</pre></blockquote>
4418 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4419 * be modified by execution of the test, and so are passed unchanged
4420 * from the caller to the target or fallback as appropriate.
4421 * @param test method handle used for test, must return boolean
4422 * @param target method handle to call if test passes
4423 * @param fallback method handle to call if test fails
4424 * @return method handle which incorporates the specified if/then/else logic
4425 * @throws NullPointerException if any argument is null
4426 * @throws IllegalArgumentException if {@code test} does not return boolean,
4427 * or if all three method types do not match (with the return
4428 * type of {@code test} changed to match that of the target).
4429 */
4430 public static
4431 MethodHandle guardWithTest(MethodHandle test,
4432 MethodHandle target,
4433 MethodHandle fallback) {
4434 MethodType gtype = test.type();
4435 MethodType ttype = target.type();
4436 MethodType ftype = fallback.type();
4437 if (!ttype.equals(ftype))
4438 throw misMatchedTypes("target and fallback types", ttype, ftype);
4439 if (gtype.returnType() != boolean.class)
4440 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4441 List<Class<?>> targs = ttype.parameterList();
4442 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4443 if (test == null) {
4444 throw misMatchedTypes("target and test types", ttype, gtype);
4445 }
4446 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4447 }
4448
4449 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4450 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4451 }
4452
4453 /**
4454 * Makes a method handle which adapts a target method handle,
4455 * by running it inside an exception handler.
4456 * If the target returns normally, the adapter returns that value.
4457 * If an exception matching the specified type is thrown, the fallback
4458 * handle is called instead on the exception, plus the original arguments.
4459 * <p>
4460 * The target and handler must have the same corresponding
4461 * argument and return types, except that handler may omit trailing arguments
4462 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4463 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4464 * <p>
4465 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4466 * represents the return type of the {@code target} and {@code handler},
4467 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4468 * the types and values of arguments to the resulting handle consumed by
4469 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4470 * resulting handle discarded by {@code handler}.
4471 * <blockquote><pre>{@code
4472 * T target(A..., B...);
4473 * T handler(ExType, A...);
4474 * T adapter(A... a, B... b) {
4475 * try {
4476 * return target(a..., b...);
4477 * } catch (ExType ex) {
4478 * return handler(ex, a...);
4479 * }
4480 * }
4481 * }</pre></blockquote>
4482 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4483 * be modified by execution of the target, and so are passed unchanged
4484 * from the caller to the handler, if the handler is invoked.
4485 * <p>
4486 * The target and handler must return the same type, even if the handler
4487 * always throws. (This might happen, for instance, because the handler
4488 * is simulating a {@code finally} clause).
4489 * To create such a throwing handler, compose the handler creation logic
4490 * with {@link #throwException throwException},
4491 * in order to create a method handle of the correct return type.
4492 * @param target method handle to call
4493 * @param exType the type of exception which the handler will catch
4494 * @param handler method handle to call if a matching exception is thrown
4495 * @return method handle which incorporates the specified try/catch logic
4496 * @throws NullPointerException if any argument is null
4497 * @throws IllegalArgumentException if {@code handler} does not accept
4498 * the given exception type, or if the method handle types do
4499 * not match in their return types and their
4500 * corresponding parameters
4501 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4502 */
4503 public static
4504 MethodHandle catchException(MethodHandle target,
4505 Class<? extends Throwable> exType,
4506 MethodHandle handler) {
4507 MethodType ttype = target.type();
4508 MethodType htype = handler.type();
4509 if (!Throwable.class.isAssignableFrom(exType))
4510 throw new ClassCastException(exType.getName());
4511 if (htype.parameterCount() < 1 ||
4512 !htype.parameterType(0).isAssignableFrom(exType))
4513 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4514 if (htype.returnType() != ttype.returnType())
4515 throw misMatchedTypes("target and handler return types", ttype, htype);
4516 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4517 if (handler == null) {
4518 throw misMatchedTypes("target and handler types", ttype, htype);
4519 }
4520 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4521 }
4522
4523 /**
4524 * Produces a method handle which will throw exceptions of the given {@code exType}.
4525 * The method handle will accept a single argument of {@code exType},
4526 * and immediately throw it as an exception.
4527 * The method type will nominally specify a return of {@code returnType}.
4528 * The return type may be anything convenient: It doesn't matter to the
4529 * method handle's behavior, since it will never return normally.
4530 * @param returnType the return type of the desired method handle
4531 * @param exType the parameter type of the desired method handle
4532 * @return method handle which can throw the given exceptions
4533 * @throws NullPointerException if either argument is null
4534 */
4535 public static
4536 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4537 if (!Throwable.class.isAssignableFrom(exType))
4538 throw new ClassCastException(exType.getName());
4539 return MethodHandleImpl.throwException(methodType(returnType, exType));
4540 }
4541
4542 /**
4543 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4544 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4545 * delivers the loop's result, which is the return value of the resulting handle.
4546 * <p>
4547 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4548 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4549 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4550 * terms of method handles, each clause will specify up to four independent actions:<ul>
4551 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4552 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4553 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4554 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4555 * </ul>
4556 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4557 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4558 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4559 * <p>
4560 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4561 * this case. See below for a detailed description.
4562 * <p>
4563 * <em>Parameters optional everywhere:</em>
4564 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4565 * As an exception, the init functions cannot take any {@code v} parameters,
4566 * because those values are not yet computed when the init functions are executed.
4567 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4568 * In fact, any clause function may take no arguments at all.
4569 * <p>
4570 * <em>Loop parameters:</em>
4571 * A clause function may take all the iteration variable values it is entitled to, in which case
4572 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4573 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4574 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4575 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4576 * init function is automatically a loop parameter {@code a}.)
4577 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4578 * These loop parameters act as loop-invariant values visible across the whole loop.
4579 * <p>
4580 * <em>Parameters visible everywhere:</em>
4581 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4582 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4583 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4584 * Most clause functions will not need all of this information, but they will be formally connected to it
4585 * as if by {@link #dropArguments}.
4586 * <a id="astar"></a>
4587 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4588 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4589 * In that notation, the general form of an init function parameter list
4590 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4591 * <p>
4592 * <em>Checking clause structure:</em>
4593 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4594 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4595 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4596 * met by the inputs to the loop combinator.
4597 * <p>
4598 * <em>Effectively identical sequences:</em>
4599 * <a id="effid"></a>
4600 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4601 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4602 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4603 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4604 * that longest list.
4605 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4606 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4607 * <p>
4608 * <em>Step 0: Determine clause structure.</em><ol type="a">
4609 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4610 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4611 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4612 * four. Padding takes place by appending elements to the array.
4613 * <li>Clauses with all {@code null}s are disregarded.
4614 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4615 * </ol>
4616 * <p>
4617 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4618 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4619 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4620 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4621 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4622 * iteration variable type.
4623 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4624 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4625 * </ol>
4626 * <p>
4627 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4628 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4629 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4630 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4631 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4632 * (These types will checked in step 2, along with all the clause function types.)
4633 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4634 * <li>All of the collected parameter lists must be effectively identical.
4635 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4636 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4637 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4638 * the "internal parameter list".
4639 * </ul>
4640 * <p>
4641 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4642 * <li>Examine fini function return types, disregarding omitted fini functions.
4643 * <li>If there are no fini functions, the loop return type is {@code void}.
4644 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4645 * type.
4646 * </ol>
4647 * <p>
4648 * <em>Step 1D: Check other types.</em><ol type="a">
4649 * <li>There must be at least one non-omitted pred function.
4650 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4651 * </ol>
4652 * <p>
4653 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4654 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4655 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4656 * (Note that their parameter lists are already effectively identical to this list.)
4657 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4658 * effectively identical to the internal parameter list {@code (V... A...)}.
4659 * </ol>
4660 * <p>
4661 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4662 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4663 * type.
4664 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4665 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4666 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4667 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4668 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4669 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4670 * loop return type.
4671 * </ol>
4672 * <p>
4673 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4674 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4675 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4676 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4677 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4678 * pad out the end of the list.
4679 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
4680 * </ol>
4681 * <p>
4682 * <em>Final observations.</em><ol type="a">
4683 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4684 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4685 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4686 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4687 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4688 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4689 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4690 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4691 * </ol>
4692 * <p>
4693 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4694 * <ul>
4695 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4696 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4697 * (Only one {@code Pn} has to be non-{@code null}.)
4698 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4699 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4700 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4701 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4702 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4703 * the resulting loop handle's parameter types {@code (A...)}.
4704 * </ul>
4705 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4706 * which is natural if most of the loop computation happens in the steps. For some loops,
4707 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4708 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4709 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4710 * where the init functions will need the extra parameters. For such reasons, the rules for
4711 * determining these parameters are as symmetric as possible, across all clause parts.
4712 * In general, the loop parameters function as common invariant values across the whole
4713 * loop, while the iteration variables function as common variant values, or (if there is
4714 * no step function) as internal loop invariant temporaries.
4715 * <p>
4716 * <em>Loop execution.</em><ol type="a">
4717 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4718 * every clause function. These locals are loop invariant.
4719 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4720 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4721 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4722 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4723 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4724 * (in argument order).
4725 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4726 * returns {@code false}.
4727 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4728 * sequence {@code (v...)} of loop variables.
4729 * The updated value is immediately visible to all subsequent function calls.
4730 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4731 * (of type {@code R}) is returned from the loop as a whole.
4732 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4733 * except by throwing an exception.
4734 * </ol>
4735 * <p>
4736 * <em>Usage tips.</em>
4737 * <ul>
4738 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4739 * sometimes a step function only needs to observe the current value of its own variable.
4740 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4741 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4742 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4743 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4744 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4745 * <li>If some of the clause functions are virtual methods on an instance, the instance
4746 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4747 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4748 * will be the first iteration variable value, and it will be easy to use virtual
4749 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4750 * </ul>
4751 * <p>
4752 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4753 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4754 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4755 * <blockquote><pre>{@code
4756 * V... init...(A...);
4757 * boolean pred...(V..., A...);
4758 * V... step...(V..., A...);
4759 * R fini...(V..., A...);
4760 * R loop(A... a) {
4761 * V... v... = init...(a...);
4762 * for (;;) {
4763 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4764 * v = s(v..., a...);
4765 * if (!p(v..., a...)) {
4766 * return f(v..., a...);
4767 * }
4768 * }
4769 * }
4770 * }
4771 * }</pre></blockquote>
4772 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4773 * to their full length, even though individual clause functions may neglect to take them all.
4774 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
4775 *
4776 * @apiNote Example:
4777 * <blockquote><pre>{@code
4778 * // iterative implementation of the factorial function as a loop handle
4779 * static int one(int k) { return 1; }
4780 * static int inc(int i, int acc, int k) { return i + 1; }
4781 * static int mult(int i, int acc, int k) { return i * acc; }
4782 * static boolean pred(int i, int acc, int k) { return i < k; }
4783 * static int fin(int i, int acc, int k) { return acc; }
4784 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4785 * // null initializer for counter, should initialize to 0
4786 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4787 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4788 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4789 * assertEquals(120, loop.invoke(5));
4790 * }</pre></blockquote>
4791 * The same example, dropping arguments and using combinators:
4792 * <blockquote><pre>{@code
4793 * // simplified implementation of the factorial function as a loop handle
4794 * static int inc(int i) { return i + 1; } // drop acc, k
4795 * static int mult(int i, int acc) { return i * acc; } //drop k
4796 * static boolean cmp(int i, int k) { return i < k; }
4797 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4798 * // null initializer for counter, should initialize to 0
4799 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4800 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4801 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4802 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4803 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4804 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4805 * assertEquals(720, loop.invoke(6));
4806 * }</pre></blockquote>
4807 * A similar example, using a helper object to hold a loop parameter:
4808 * <blockquote><pre>{@code
4809 * // instance-based implementation of the factorial function as a loop handle
4810 * static class FacLoop {
4811 * final int k;
4812 * FacLoop(int k) { this.k = k; }
4813 * int inc(int i) { return i + 1; }
4814 * int mult(int i, int acc) { return i * acc; }
4815 * boolean pred(int i) { return i < k; }
4816 * int fin(int i, int acc) { return acc; }
4817 * }
4818 * // assume MH_FacLoop is a handle to the constructor
4819 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4820 * // null initializer for counter, should initialize to 0
4821 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4822 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4823 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4824 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4825 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4826 * assertEquals(5040, loop.invoke(7));
4827 * }</pre></blockquote>
4828 *
4829 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4830 *
4831 * @return a method handle embodying the looping behavior as defined by the arguments.
4832 *
4833 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4834 *
4835 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4836 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4837 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4838 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4839 * @since 9
4840 */
4841 public static MethodHandle loop(MethodHandle[]... clauses) {
4842 // Step 0: determine clause structure.
4843 loopChecks0(clauses);
4844
4845 List<MethodHandle> init = new ArrayList<>();
4846 List<MethodHandle> step = new ArrayList<>();
4847 List<MethodHandle> pred = new ArrayList<>();
4848 List<MethodHandle> fini = new ArrayList<>();
4849
4850 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4851 init.add(clause[0]); // all clauses have at least length 1
4852 step.add(clause.length <= 1 ? null : clause[1]);
4853 pred.add(clause.length <= 2 ? null : clause[2]);
4854 fini.add(clause.length <= 3 ? null : clause[3]);
4855 });
4856
4857 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4858 final int nclauses = init.size();
4859
4860 // Step 1A: determine iteration variables (V...).
4861 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4862 for (int i = 0; i < nclauses; ++i) {
4863 MethodHandle in = init.get(i);
4864 MethodHandle st = step.get(i);
4865 if (in == null && st == null) {
4866 iterationVariableTypes.add(void.class);
4867 } else if (in != null && st != null) {
4868 loopChecks1a(i, in, st);
4869 iterationVariableTypes.add(in.type().returnType());
4870 } else {
4871 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4872 }
4873 }
4874 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4875 collect(Collectors.toList());
4876
4877 // Step 1B: determine loop parameters (A...).
4878 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4879 loopChecks1b(init, commonSuffix);
4880
4881 // Step 1C: determine loop return type.
4882 // Step 1D: check other types.
4883 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4884 map(MethodType::returnType).findFirst().orElse(void.class);
4885 loopChecks1cd(pred, fini, loopReturnType);
4886
4887 // Step 2: determine parameter lists.
4888 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4889 commonParameterSequence.addAll(commonSuffix);
4890 loopChecks2(step, pred, fini, commonParameterSequence);
4891
4892 // Step 3: fill in omitted functions.
4893 for (int i = 0; i < nclauses; ++i) {
4894 Class<?> t = iterationVariableTypes.get(i);
4895 if (init.get(i) == null) {
4896 init.set(i, empty(methodType(t, commonSuffix)));
4897 }
4898 if (step.get(i) == null) {
4899 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4900 }
4901 if (pred.get(i) == null) {
4902 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4903 }
4904 if (fini.get(i) == null) {
4905 fini.set(i, empty(methodType(t, commonParameterSequence)));
4906 }
4907 }
4908
4909 // Step 4: fill in missing parameter types.
4910 // Also convert all handles to fixed-arity handles.
4911 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4912 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4913 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4914 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4915
4916 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4917 allMatch(pl -> pl.equals(commonSuffix));
4918 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4919 allMatch(pl -> pl.equals(commonParameterSequence));
4920
4921 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4922 }
4923
4924 private static void loopChecks0(MethodHandle[][] clauses) {
4925 if (clauses == null || clauses.length == 0) {
4926 throw newIllegalArgumentException("null or no clauses passed");
4927 }
4928 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4929 throw newIllegalArgumentException("null clauses are not allowed");
4930 }
4931 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4932 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4933 }
4934 }
4935
4936 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4937 if (in.type().returnType() != st.type().returnType()) {
4938 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4939 st.type().returnType());
4940 }
4941 }
4942
4943 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4944 final List<Class<?>> empty = List.of();
4945 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4946 // take only those that can contribute to a common suffix because they are longer than the prefix
4947 map(MethodHandle::type).
4948 filter(t -> t.parameterCount() > skipSize).
4949 map(MethodType::parameterList).
4950 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4951 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4952 }
4953
4954 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4955 final List<Class<?>> empty = List.of();
4956 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4957 }
4958
4959 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4960 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4961 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4962 return longestParameterList(Arrays.asList(longest1, longest2));
4963 }
4964
4965 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4966 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4967 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4968 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4969 " (common suffix: " + commonSuffix + ")");
4970 }
4971 }
4972
4973 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4974 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4975 anyMatch(t -> t != loopReturnType)) {
4976 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4977 loopReturnType + ")");
4978 }
4979
4980 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4981 throw newIllegalArgumentException("no predicate found", pred);
4982 }
4983 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4984 anyMatch(t -> t != boolean.class)) {
4985 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4986 }
4987 }
4988
4989 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4990 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4991 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4992 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4993 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4994 }
4995 }
4996
4997 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4998 return hs.stream().map(h -> {
4999 int pc = h.type().parameterCount();
5000 int tpsize = targetParams.size();
5001 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5002 }).collect(Collectors.toList());
5003 }
5004
5005 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5006 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5007 }
5008
5009 /**
5010 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5011 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5012 * <p>
5013 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5014 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5015 * evaluates to {@code true}).
5016 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5017 * <p>
5018 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5019 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5020 * and updated with the value returned from its invocation. The result of loop execution will be
5021 * the final value of the additional loop-local variable (if present).
5022 * <p>
5023 * The following rules hold for these argument handles:<ul>
5024 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5025 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5026 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5027 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5028 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5029 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5030 * It will constrain the parameter lists of the other loop parts.
5031 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5032 * list {@code (A...)} is called the <em>external parameter list</em>.
5033 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5034 * additional state variable of the loop.
5035 * The body must both accept and return a value of this type {@code V}.
5036 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5037 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5038 * <a href="MethodHandles.html#effid">effectively identical</a>
5039 * to the external parameter list {@code (A...)}.
5040 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5041 * {@linkplain #empty default value}.
5042 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5043 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5044 * effectively identical to the internal parameter list.
5045 * </ul>
5046 * <p>
5047 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5048 * <li>The loop handle's result type is the result type {@code V} of the body.
5049 * <li>The loop handle's parameter types are the types {@code (A...)},
5050 * from the external parameter list.
5051 * </ul>
5052 * <p>
5053 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5054 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5055 * passed to the loop.
5056 * <blockquote><pre>{@code
5057 * V init(A...);
5058 * boolean pred(V, A...);
5059 * V body(V, A...);
5060 * V whileLoop(A... a...) {
5061 * V v = init(a...);
5062 * while (pred(v, a...)) {
5063 * v = body(v, a...);
5064 * }
5065 * return v;
5066 * }
5067 * }</pre></blockquote>
5068 *
5069 * @apiNote Example:
5070 * <blockquote><pre>{@code
5071 * // implement the zip function for lists as a loop handle
5072 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5073 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5074 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5075 * zip.add(a.next());
5076 * zip.add(b.next());
5077 * return zip;
5078 * }
5079 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5080 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5081 * List<String> a = Arrays.asList("a", "b", "c", "d");
5082 * List<String> b = Arrays.asList("e", "f", "g", "h");
5083 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5084 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5085 * }</pre></blockquote>
5086 *
5087 *
5088 * @apiNote The implementation of this method can be expressed as follows:
5089 * <blockquote><pre>{@code
5090 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5091 * MethodHandle fini = (body.type().returnType() == void.class
5092 * ? null : identity(body.type().returnType()));
5093 * MethodHandle[]
5094 * checkExit = { null, null, pred, fini },
5095 * varBody = { init, body };
5096 * return loop(checkExit, varBody);
5097 * }
5098 * }</pre></blockquote>
5099 *
5100 * @param init optional initializer, providing the initial value of the loop variable.
5101 * May be {@code null}, implying a default initial value. See above for other constraints.
5102 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5103 * above for other constraints.
5104 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5105 * See above for other constraints.
5106 *
5107 * @return a method handle implementing the {@code while} loop as described by the arguments.
5108 * @throws IllegalArgumentException if the rules for the arguments are violated.
5109 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5110 *
5111 * @see #loop(MethodHandle[][])
5112 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5113 * @since 9
5114 */
5115 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5116 whileLoopChecks(init, pred, body);
5117 MethodHandle fini = identityOrVoid(body.type().returnType());
5118 MethodHandle[] checkExit = { null, null, pred, fini };
5119 MethodHandle[] varBody = { init, body };
5120 return loop(checkExit, varBody);
5121 }
5122
5123 /**
5124 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5125 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5126 * <p>
5127 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5128 * method will, in each iteration, first execute its body and then evaluate the predicate.
5129 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5130 * <p>
5131 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5132 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5133 * and updated with the value returned from its invocation. The result of loop execution will be
5134 * the final value of the additional loop-local variable (if present).
5135 * <p>
5136 * The following rules hold for these argument handles:<ul>
5137 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5138 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5139 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5140 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5141 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5142 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5143 * It will constrain the parameter lists of the other loop parts.
5144 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5145 * list {@code (A...)} is called the <em>external parameter list</em>.
5146 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5147 * additional state variable of the loop.
5148 * The body must both accept and return a value of this type {@code V}.
5149 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5150 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5151 * <a href="MethodHandles.html#effid">effectively identical</a>
5152 * to the external parameter list {@code (A...)}.
5153 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5154 * {@linkplain #empty default value}.
5155 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5156 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5157 * effectively identical to the internal parameter list.
5158 * </ul>
5159 * <p>
5160 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5161 * <li>The loop handle's result type is the result type {@code V} of the body.
5162 * <li>The loop handle's parameter types are the types {@code (A...)},
5163 * from the external parameter list.
5164 * </ul>
5165 * <p>
5166 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5167 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5168 * passed to the loop.
5169 * <blockquote><pre>{@code
5170 * V init(A...);
5171 * boolean pred(V, A...);
5172 * V body(V, A...);
5173 * V doWhileLoop(A... a...) {
5174 * V v = init(a...);
5175 * do {
5176 * v = body(v, a...);
5177 * } while (pred(v, a...));
5178 * return v;
5179 * }
5180 * }</pre></blockquote>
5181 *
5182 * @apiNote Example:
5183 * <blockquote><pre>{@code
5184 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5185 * static int zero(int limit) { return 0; }
5186 * static int step(int i, int limit) { return i + 1; }
5187 * static boolean pred(int i, int limit) { return i < limit; }
5188 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5189 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5190 * assertEquals(23, loop.invoke(23));
5191 * }</pre></blockquote>
5192 *
5193 *
5194 * @apiNote The implementation of this method can be expressed as follows:
5195 * <blockquote><pre>{@code
5196 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5197 * MethodHandle fini = (body.type().returnType() == void.class
5198 * ? null : identity(body.type().returnType()));
5199 * MethodHandle[] clause = { init, body, pred, fini };
5200 * return loop(clause);
5201 * }
5202 * }</pre></blockquote>
5203 *
5204 * @param init optional initializer, providing the initial value of the loop variable.
5205 * May be {@code null}, implying a default initial value. See above for other constraints.
5206 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5207 * See above for other constraints.
5208 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5209 * above for other constraints.
5210 *
5211 * @return a method handle implementing the {@code while} loop as described by the arguments.
5212 * @throws IllegalArgumentException if the rules for the arguments are violated.
5213 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5214 *
5215 * @see #loop(MethodHandle[][])
5216 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5217 * @since 9
5218 */
5219 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5220 whileLoopChecks(init, pred, body);
5221 MethodHandle fini = identityOrVoid(body.type().returnType());
5222 MethodHandle[] clause = {init, body, pred, fini };
5223 return loop(clause);
5224 }
5225
5226 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5227 Objects.requireNonNull(pred);
5228 Objects.requireNonNull(body);
5229 MethodType bodyType = body.type();
5230 Class<?> returnType = bodyType.returnType();
5231 List<Class<?>> innerList = bodyType.parameterList();
5232 List<Class<?>> outerList = innerList;
5233 if (returnType == void.class) {
5234 // OK
5235 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5236 // leading V argument missing => error
5237 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5238 throw misMatchedTypes("body function", bodyType, expected);
5239 } else {
5240 outerList = innerList.subList(1, innerList.size());
5241 }
5242 MethodType predType = pred.type();
5243 if (predType.returnType() != boolean.class ||
5244 !predType.effectivelyIdenticalParameters(0, innerList)) {
5245 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5246 }
5247 if (init != null) {
5248 MethodType initType = init.type();
5249 if (initType.returnType() != returnType ||
5250 !initType.effectivelyIdenticalParameters(0, outerList)) {
5251 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5252 }
5253 }
5254 }
5255
5256 /**
5257 * Constructs a loop that runs a given number of iterations.
5258 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5259 * <p>
5260 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5261 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5262 * It will be initialized to 0 and incremented by 1 in each iteration.
5263 * <p>
5264 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5265 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5266 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5267 * <p>
5268 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5269 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5270 * iteration variable.
5271 * The result of the loop handle execution will be the final {@code V} value of that variable
5272 * (or {@code void} if there is no {@code V} variable).
5273 * <p>
5274 * The following rules hold for the argument handles:<ul>
5275 * <li>The {@code iterations} handle must not be {@code null}, and must return
5276 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5277 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5278 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5279 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5280 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5281 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5282 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5283 * of types called the <em>internal parameter list</em>.
5284 * It will constrain the parameter lists of the other loop parts.
5285 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5286 * with no additional {@code A} types, then the internal parameter list is extended by
5287 * the argument types {@code A...} of the {@code iterations} handle.
5288 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5289 * list {@code (A...)} is called the <em>external parameter list</em>.
5290 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5291 * additional state variable of the loop.
5292 * The body must both accept a leading parameter and return a value of this type {@code V}.
5293 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5294 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5295 * <a href="MethodHandles.html#effid">effectively identical</a>
5296 * to the external parameter list {@code (A...)}.
5297 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5298 * {@linkplain #empty default value}.
5299 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5300 * effectively identical to the external parameter list {@code (A...)}.
5301 * </ul>
5302 * <p>
5303 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5304 * <li>The loop handle's result type is the result type {@code V} of the body.
5305 * <li>The loop handle's parameter types are the types {@code (A...)},
5306 * from the external parameter list.
5307 * </ul>
5308 * <p>
5309 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5310 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5311 * arguments passed to the loop.
5312 * <blockquote><pre>{@code
5313 * int iterations(A...);
5314 * V init(A...);
5315 * V body(V, int, A...);
5316 * V countedLoop(A... a...) {
5317 * int end = iterations(a...);
5318 * V v = init(a...);
5319 * for (int i = 0; i < end; ++i) {
5320 * v = body(v, i, a...);
5321 * }
5322 * return v;
5323 * }
5324 * }</pre></blockquote>
5325 *
5326 * @apiNote Example with a fully conformant body method:
5327 * <blockquote><pre>{@code
5328 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5329 * // => a variation on a well known theme
5330 * static String step(String v, int counter, String init) { return "na " + v; }
5331 * // assume MH_step is a handle to the method above
5332 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5333 * MethodHandle start = MethodHandles.identity(String.class);
5334 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5335 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5336 * }</pre></blockquote>
5337 *
5338 * @apiNote Example with the simplest possible body method type,
5339 * and passing the number of iterations to the loop invocation:
5340 * <blockquote><pre>{@code
5341 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5342 * // => a variation on a well known theme
5343 * static String step(String v, int counter ) { return "na " + v; }
5344 * // assume MH_step is a handle to the method above
5345 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5346 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5347 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5348 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5349 * }</pre></blockquote>
5350 *
5351 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5352 * as loop parameters:
5353 * <blockquote><pre>{@code
5354 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5355 * // => a variation on a well known theme
5356 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5357 * // assume MH_step is a handle to the method above
5358 * MethodHandle count = MethodHandles.identity(int.class);
5359 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5360 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5361 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5362 * }</pre></blockquote>
5363 *
5364 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5365 * to enforce a loop type:
5366 * <blockquote><pre>{@code
5367 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5368 * // => a variation on a well known theme
5369 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5370 * // assume MH_step is a handle to the method above
5371 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5372 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5373 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5374 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5375 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5376 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5377 * }</pre></blockquote>
5378 *
5379 * @apiNote The implementation of this method can be expressed as follows:
5380 * <blockquote><pre>{@code
5381 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5382 * return countedLoop(empty(iterations.type()), iterations, init, body);
5383 * }
5384 * }</pre></blockquote>
5385 *
5386 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5387 * result type must be {@code int}. See above for other constraints.
5388 * @param init optional initializer, providing the initial value of the loop variable.
5389 * May be {@code null}, implying a default initial value. See above for other constraints.
5390 * @param body body of the loop, which may not be {@code null}.
5391 * It controls the loop parameters and result type in the standard case (see above for details).
5392 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5393 * and may accept any number of additional types.
5394 * See above for other constraints.
5395 *
5396 * @return a method handle representing the loop.
5397 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5398 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5399 *
5400 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5401 * @since 9
5402 */
5403 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5404 return countedLoop(empty(iterations.type()), iterations, init, body);
5405 }
5406
5407 /**
5408 * Constructs a loop that counts over a range of numbers.
5409 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5410 * <p>
5411 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5412 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5413 * values of the loop counter.
5414 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5415 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5416 * <p>
5417 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5418 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5419 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5420 * <p>
5421 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5422 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5423 * iteration variable.
5424 * The result of the loop handle execution will be the final {@code V} value of that variable
5425 * (or {@code void} if there is no {@code V} variable).
5426 * <p>
5427 * The following rules hold for the argument handles:<ul>
5428 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5429 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5430 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5431 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5432 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5433 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5434 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5435 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5436 * of types called the <em>internal parameter list</em>.
5437 * It will constrain the parameter lists of the other loop parts.
5438 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5439 * with no additional {@code A} types, then the internal parameter list is extended by
5440 * the argument types {@code A...} of the {@code end} handle.
5441 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5442 * list {@code (A...)} is called the <em>external parameter list</em>.
5443 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5444 * additional state variable of the loop.
5445 * The body must both accept a leading parameter and return a value of this type {@code V}.
5446 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5447 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5448 * <a href="MethodHandles.html#effid">effectively identical</a>
5449 * to the external parameter list {@code (A...)}.
5450 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5451 * {@linkplain #empty default value}.
5452 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5453 * effectively identical to the external parameter list {@code (A...)}.
5454 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5455 * to the external parameter list.
5456 * </ul>
5457 * <p>
5458 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5459 * <li>The loop handle's result type is the result type {@code V} of the body.
5460 * <li>The loop handle's parameter types are the types {@code (A...)},
5461 * from the external parameter list.
5462 * </ul>
5463 * <p>
5464 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5465 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5466 * arguments passed to the loop.
5467 * <blockquote><pre>{@code
5468 * int start(A...);
5469 * int end(A...);
5470 * V init(A...);
5471 * V body(V, int, A...);
5472 * V countedLoop(A... a...) {
5473 * int e = end(a...);
5474 * int s = start(a...);
5475 * V v = init(a...);
5476 * for (int i = s; i < e; ++i) {
5477 * v = body(v, i, a...);
5478 * }
5479 * return v;
5480 * }
5481 * }</pre></blockquote>
5482 *
5483 * @apiNote The implementation of this method can be expressed as follows:
5484 * <blockquote><pre>{@code
5485 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5486 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5487 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5488 * // the following semantics:
5489 * // MH_increment: (int limit, int counter) -> counter + 1
5490 * // MH_predicate: (int limit, int counter) -> counter < limit
5491 * Class<?> counterType = start.type().returnType(); // int
5492 * Class<?> returnType = body.type().returnType();
5493 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5494 * if (returnType != void.class) { // ignore the V variable
5495 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5496 * pred = dropArguments(pred, 1, returnType); // ditto
5497 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5498 * }
5499 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5500 * MethodHandle[]
5501 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5502 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5503 * indexVar = { start, incr }; // i = start(); i = i + 1
5504 * return loop(loopLimit, bodyClause, indexVar);
5505 * }
5506 * }</pre></blockquote>
5507 *
5508 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5509 * See above for other constraints.
5510 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5511 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5512 * @param init optional initializer, providing the initial value of the loop variable.
5513 * May be {@code null}, implying a default initial value. See above for other constraints.
5514 * @param body body of the loop, which may not be {@code null}.
5515 * It controls the loop parameters and result type in the standard case (see above for details).
5516 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5517 * and may accept any number of additional types.
5518 * See above for other constraints.
5519 *
5520 * @return a method handle representing the loop.
5521 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5522 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5523 *
5524 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5525 * @since 9
5526 */
5527 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5528 countedLoopChecks(start, end, init, body);
5529 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5530 Class<?> limitType = end.type().returnType(); // yes, int again
5531 Class<?> returnType = body.type().returnType();
5532 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5533 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5534 MethodHandle retv = null;
5535 if (returnType != void.class) {
5536 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5537 pred = dropArguments(pred, 1, returnType); // ditto
5538 retv = dropArguments(identity(returnType), 0, counterType);
5539 }
5540 body = dropArguments(body, 0, counterType); // ignore the limit variable
5541 MethodHandle[]
5542 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5543 bodyClause = { init, body }, // v = init(); v = body(v, i)
5544 indexVar = { start, incr }; // i = start(); i = i + 1
5545 return loop(loopLimit, bodyClause, indexVar);
5546 }
5547
5548 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5549 Objects.requireNonNull(start);
5550 Objects.requireNonNull(end);
5551 Objects.requireNonNull(body);
5552 Class<?> counterType = start.type().returnType();
5553 if (counterType != int.class) {
5554 MethodType expected = start.type().changeReturnType(int.class);
5555 throw misMatchedTypes("start function", start.type(), expected);
5556 } else if (end.type().returnType() != counterType) {
5557 MethodType expected = end.type().changeReturnType(counterType);
5558 throw misMatchedTypes("end function", end.type(), expected);
5559 }
5560 MethodType bodyType = body.type();
5561 Class<?> returnType = bodyType.returnType();
5562 List<Class<?>> innerList = bodyType.parameterList();
5563 // strip leading V value if present
5564 int vsize = (returnType == void.class ? 0 : 1);
5565 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5566 // argument list has no "V" => error
5567 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5568 throw misMatchedTypes("body function", bodyType, expected);
5569 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5570 // missing I type => error
5571 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5572 throw misMatchedTypes("body function", bodyType, expected);
5573 }
5574 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5575 if (outerList.isEmpty()) {
5576 // special case; take lists from end handle
5577 outerList = end.type().parameterList();
5578 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5579 }
5580 MethodType expected = methodType(counterType, outerList);
5581 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5582 throw misMatchedTypes("start parameter types", start.type(), expected);
5583 }
5584 if (end.type() != start.type() &&
5585 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5586 throw misMatchedTypes("end parameter types", end.type(), expected);
5587 }
5588 if (init != null) {
5589 MethodType initType = init.type();
5590 if (initType.returnType() != returnType ||
5591 !initType.effectivelyIdenticalParameters(0, outerList)) {
5592 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5593 }
5594 }
5595 }
5596
5597 /**
5598 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5599 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5600 * <p>
5601 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5602 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5603 * <p>
5604 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5605 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5606 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5607 * <p>
5608 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5609 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5610 * iteration variable.
5611 * The result of the loop handle execution will be the final {@code V} value of that variable
5612 * (or {@code void} if there is no {@code V} variable).
5613 * <p>
5614 * The following rules hold for the argument handles:<ul>
5615 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5616 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5617 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5618 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5619 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5620 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5621 * of types called the <em>internal parameter list</em>.
5622 * It will constrain the parameter lists of the other loop parts.
5623 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5624 * with no additional {@code A} types, then the internal parameter list is extended by
5625 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5626 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5627 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5628 * list {@code (A...)} is called the <em>external parameter list</em>.
5629 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5630 * additional state variable of the loop.
5631 * The body must both accept a leading parameter and return a value of this type {@code V}.
5632 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5633 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5634 * <a href="MethodHandles.html#effid">effectively identical</a>
5635 * to the external parameter list {@code (A...)}.
5636 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5637 * {@linkplain #empty default value}.
5638 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5639 * type {@code java.util.Iterator} or a subtype thereof.
5640 * The iterator it produces when the loop is executed will be assumed
5641 * to yield values which can be converted to type {@code T}.
5642 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5643 * effectively identical to the external parameter list {@code (A...)}.
5644 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5645 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5646 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5647 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5648 * the {@link MethodHandle#asType asType} conversion method.
5649 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5650 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5651 * </ul>
5652 * <p>
5653 * The type {@code T} may be either a primitive or reference.
5654 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5655 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5656 * as if by the {@link MethodHandle#asType asType} conversion method.
5657 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5658 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5659 * <p>
5660 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5661 * <li>The loop handle's result type is the result type {@code V} of the body.
5662 * <li>The loop handle's parameter types are the types {@code (A...)},
5663 * from the external parameter list.
5664 * </ul>
5665 * <p>
5666 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5667 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5668 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5669 * <blockquote><pre>{@code
5670 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5671 * V init(A...);
5672 * V body(V,T,A...);
5673 * V iteratedLoop(A... a...) {
5674 * Iterator<T> it = iterator(a...);
5675 * V v = init(a...);
5676 * while (it.hasNext()) {
5677 * T t = it.next();
5678 * v = body(v, t, a...);
5679 * }
5680 * return v;
5681 * }
5682 * }</pre></blockquote>
5683 *
5684 * @apiNote Example:
5685 * <blockquote><pre>{@code
5686 * // get an iterator from a list
5687 * static List<String> reverseStep(List<String> r, String e) {
5688 * r.add(0, e);
5689 * return r;
5690 * }
5691 * static List<String> newArrayList() { return new ArrayList<>(); }
5692 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5693 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5694 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5695 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5696 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5697 * }</pre></blockquote>
5698 *
5699 * @apiNote The implementation of this method can be expressed approximately as follows:
5700 * <blockquote><pre>{@code
5701 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5702 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5703 * Class<?> returnType = body.type().returnType();
5704 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5705 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5706 * MethodHandle retv = null, step = body, startIter = iterator;
5707 * if (returnType != void.class) {
5708 * // the simple thing first: in (I V A...), drop the I to get V
5709 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5710 * // body type signature (V T A...), internal loop types (I V A...)
5711 * step = swapArguments(body, 0, 1); // swap V <-> T
5712 * }
5713 * if (startIter == null) startIter = MH_getIter;
5714 * MethodHandle[]
5715 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5716 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5717 * return loop(iterVar, bodyClause);
5718 * }
5719 * }</pre></blockquote>
5720 *
5721 * @param iterator an optional handle to return the iterator to start the loop.
5722 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5723 * See above for other constraints.
5724 * @param init optional initializer, providing the initial value of the loop variable.
5725 * May be {@code null}, implying a default initial value. See above for other constraints.
5726 * @param body body of the loop, which may not be {@code null}.
5727 * It controls the loop parameters and result type in the standard case (see above for details).
5728 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5729 * and may accept any number of additional types.
5730 * See above for other constraints.
5731 *
5732 * @return a method handle embodying the iteration loop functionality.
5733 * @throws NullPointerException if the {@code body} handle is {@code null}.
5734 * @throws IllegalArgumentException if any argument violates the above requirements.
5735 *
5736 * @since 9
5737 */
5738 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5739 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5740 Class<?> returnType = body.type().returnType();
5741 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5742 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5743 MethodHandle startIter;
5744 MethodHandle nextVal;
5745 {
5746 MethodType iteratorType;
5747 if (iterator == null) {
5748 // derive argument type from body, if available, else use Iterable
5749 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5750 iteratorType = startIter.type().changeParameterType(0, iterableType);
5751 } else {
5752 // force return type to the internal iterator class
5753 iteratorType = iterator.type().changeReturnType(Iterator.class);
5754 startIter = iterator;
5755 }
5756 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5757 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5758
5759 // perform the asType transforms under an exception transformer, as per spec.:
5760 try {
5761 startIter = startIter.asType(iteratorType);
5762 nextVal = nextRaw.asType(nextValType);
5763 } catch (WrongMethodTypeException ex) {
5764 throw new IllegalArgumentException(ex);
5765 }
5766 }
5767
5768 MethodHandle retv = null, step = body;
5769 if (returnType != void.class) {
5770 // the simple thing first: in (I V A...), drop the I to get V
5771 retv = dropArguments(identity(returnType), 0, Iterator.class);
5772 // body type signature (V T A...), internal loop types (I V A...)
5773 step = swapArguments(body, 0, 1); // swap V <-> T
5774 }
5775
5776 MethodHandle[]
5777 iterVar = { startIter, null, hasNext, retv },
5778 bodyClause = { init, filterArgument(step, 0, nextVal) };
5779 return loop(iterVar, bodyClause);
5780 }
5781
5782 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5783 Objects.requireNonNull(body);
5784 MethodType bodyType = body.type();
5785 Class<?> returnType = bodyType.returnType();
5786 List<Class<?>> internalParamList = bodyType.parameterList();
5787 // strip leading V value if present
5788 int vsize = (returnType == void.class ? 0 : 1);
5789 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5790 // argument list has no "V" => error
5791 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5792 throw misMatchedTypes("body function", bodyType, expected);
5793 } else if (internalParamList.size() <= vsize) {
5794 // missing T type => error
5795 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5796 throw misMatchedTypes("body function", bodyType, expected);
5797 }
5798 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5799 Class<?> iterableType = null;
5800 if (iterator != null) {
5801 // special case; if the body handle only declares V and T then
5802 // the external parameter list is obtained from iterator handle
5803 if (externalParamList.isEmpty()) {
5804 externalParamList = iterator.type().parameterList();
5805 }
5806 MethodType itype = iterator.type();
5807 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5808 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5809 }
5810 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5811 MethodType expected = methodType(itype.returnType(), externalParamList);
5812 throw misMatchedTypes("iterator parameters", itype, expected);
5813 }
5814 } else {
5815 if (externalParamList.isEmpty()) {
5816 // special case; if the iterator handle is null and the body handle
5817 // only declares V and T then the external parameter list consists
5818 // of Iterable
5819 externalParamList = Arrays.asList(Iterable.class);
5820 iterableType = Iterable.class;
5821 } else {
5822 // special case; if the iterator handle is null and the external
5823 // parameter list is not empty then the first parameter must be
5824 // assignable to Iterable
5825 iterableType = externalParamList.get(0);
5826 if (!Iterable.class.isAssignableFrom(iterableType)) {
5827 throw newIllegalArgumentException(
5828 "inferred first loop argument must inherit from Iterable: " + iterableType);
5829 }
5830 }
5831 }
5832 if (init != null) {
5833 MethodType initType = init.type();
5834 if (initType.returnType() != returnType ||
5835 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5836 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5837 }
5838 }
5839 return iterableType; // help the caller a bit
5840 }
5841
5842 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5843 // there should be a better way to uncross my wires
5844 int arity = mh.type().parameterCount();
5845 int[] order = new int[arity];
5846 for (int k = 0; k < arity; k++) order[k] = k;
5847 order[i] = j; order[j] = i;
5848 Class<?>[] types = mh.type().parameterArray();
5849 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5850 MethodType swapType = methodType(mh.type().returnType(), types);
5851 return permuteArguments(mh, swapType, order);
5852 }
5853
5854 /**
5855 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5856 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5857 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5858 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5859 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5860 * {@code try-finally} handle.
5861 * <p>
5862 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5863 * The first is the exception thrown during the
5864 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5865 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5866 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5867 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5868 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5869 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5870 * <p>
5871 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5872 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5873 * two extra leading parameters:<ul>
5874 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5875 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5876 * the result from the execution of the {@code target} handle.
5877 * This parameter is not present if the {@code target} returns {@code void}.
5878 * </ul>
5879 * <p>
5880 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5881 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5882 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5883 * the cleanup.
5884 * <blockquote><pre>{@code
5885 * V target(A..., B...);
5886 * V cleanup(Throwable, V, A...);
5887 * V adapter(A... a, B... b) {
5888 * V result = (zero value for V);
5889 * Throwable throwable = null;
5890 * try {
5891 * result = target(a..., b...);
5892 * } catch (Throwable t) {
5893 * throwable = t;
5894 * throw t;
5895 * } finally {
5896 * result = cleanup(throwable, result, a...);
5897 * }
5898 * return result;
5899 * }
5900 * }</pre></blockquote>
5901 * <p>
5902 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5903 * be modified by execution of the target, and so are passed unchanged
5904 * from the caller to the cleanup, if it is invoked.
5905 * <p>
5906 * The target and cleanup must return the same type, even if the cleanup
5907 * always throws.
5908 * To create such a throwing cleanup, compose the cleanup logic
5909 * with {@link #throwException throwException},
5910 * in order to create a method handle of the correct return type.
5911 * <p>
5912 * Note that {@code tryFinally} never converts exceptions into normal returns.
5913 * In rare cases where exceptions must be converted in that way, first wrap
5914 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5915 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5916 * <p>
5917 * It is recommended that the first parameter type of {@code cleanup} be
5918 * declared {@code Throwable} rather than a narrower subtype. This ensures
5919 * {@code cleanup} will always be invoked with whatever exception that
5920 * {@code target} throws. Declaring a narrower type may result in a
5921 * {@code ClassCastException} being thrown by the {@code try-finally}
5922 * handle if the type of the exception thrown by {@code target} is not
5923 * assignable to the first parameter type of {@code cleanup}. Note that
5924 * various exception types of {@code VirtualMachineError},
5925 * {@code LinkageError}, and {@code RuntimeException} can in principle be
5926 * thrown by almost any kind of Java code, and a finally clause that
5927 * catches (say) only {@code IOException} would mask any of the others
5928 * behind a {@code ClassCastException}.
5929 *
5930 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5931 * @param cleanup the handle that is invoked in the finally block.
5932 *
5933 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5934 * @throws NullPointerException if any argument is null
5935 * @throws IllegalArgumentException if {@code cleanup} does not accept
5936 * the required leading arguments, or if the method handle types do
5937 * not match in their return types and their
5938 * corresponding trailing parameters
5939 *
5940 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5941 * @since 9
5942 */
5943 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5944 List<Class<?>> targetParamTypes = target.type().parameterList();
5945 Class<?> rtype = target.type().returnType();
5946
5947 tryFinallyChecks(target, cleanup);
5948
5949 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5950 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5951 // target parameter list.
5952 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5953
5954 // Ensure that the intrinsic type checks the instance thrown by the
5955 // target against the first parameter of cleanup
5956 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
5957
5958 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5959 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5960 }
5961
5962 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5963 Class<?> rtype = target.type().returnType();
5964 if (rtype != cleanup.type().returnType()) {
5965 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5966 }
5967 MethodType cleanupType = cleanup.type();
5968 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5969 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5970 }
5971 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5972 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5973 }
5974 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5975 // target parameter list.
5976 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5977 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5978 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5979 cleanup.type(), target.type());
5980 }
5981 }
5982
5983 }