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.access.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.Set;
58 import java.util.concurrent.ConcurrentHashMap;
59 import java.util.stream.Collectors;
60 import java.util.stream.Stream;
61
62 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
63 import static java.lang.invoke.MethodHandleNatives.Constants.*;
64 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
65 import static java.lang.invoke.MethodType.methodType;
66
67 /**
68 * This class consists exclusively of static methods that operate on or return
69 * method handles. They fall into several categories:
70 * <ul>
71 * <li>Lookup methods which help create method handles for methods and fields.
72 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
73 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
74 * </ul>
75 * A lookup, combinator, or factory method will fail and throw an
76 * {@code IllegalArgumentException} if the created method handle's type
77 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
78 *
79 * @author John Rose, JSR 292 EG
80 * @since 1.7
81 */
82 public class MethodHandles {
83
84 private MethodHandles() { } // do not instantiate
85
86 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
87
88 // See IMPL_LOOKUP below.
89
90 //// Method handle creation from ordinary methods.
91
92 /**
93 * Returns a {@link Lookup lookup object} with
94 * full capabilities to emulate all supported bytecode behaviors of the caller.
95 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
96 * Factory methods on the lookup object can create
97 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
98 * for any member that the caller has access to via bytecodes,
99 * including protected and private fields and methods.
100 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
101 * Do not store it in place where untrusted code can access it.
102 * <p>
103 * This method is caller sensitive, which means that it may return different
104 * values to different callers.
105 * @return a lookup object for the caller of this method, with private access
106 */
107 @CallerSensitive
108 @ForceInline // to ensure Reflection.getCallerClass optimization
109 public static Lookup lookup() {
110 return new Lookup(Reflection.getCallerClass());
111 }
112
113 /**
114 * This reflected$lookup method is the alternate implementation of
115 * the lookup method when being invoked by reflection.
116 */
117 @CallerSensitive
118 private static Lookup reflected$lookup() {
119 Class<?> caller = Reflection.getCallerClass();
120 if (caller.getClassLoader() == null) {
121 throw newIllegalArgumentException("illegal lookupClass: "+caller);
122 }
123 return new Lookup(caller);
124 }
125
126 /**
127 * Returns a {@link Lookup lookup object} which is trusted minimally.
128 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
129 * It can only be used to create method handles to public members of
130 * public classes in packages that are exported unconditionally.
131 * <p>
132 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
133 * of this lookup object will be {@link java.lang.Object}.
134 *
135 * @apiNote The use of Object is conventional, and because the lookup modes are
136 * limited, there is no special access provided to the internals of Object, its package
137 * or its module. Consequently, the lookup context of this lookup object will be the
138 * bootstrap class loader, which means it cannot find user classes.
139 *
140 * <p style="font-size:smaller;">
141 * <em>Discussion:</em>
142 * The lookup class can be changed to any other class {@code C} using an expression of the form
143 * {@link Lookup#in publicLookup().in(C.class)}.
144 * but may change the lookup context by virtue of changing the class loader.
145 * A public lookup object is always subject to
146 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
147 * Also, it cannot access
148 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
149 * @return a lookup object which is trusted minimally
150 *
151 * @revised 9
152 * @spec JPMS
153 */
154 public static Lookup publicLookup() {
155 return Lookup.PUBLIC_LOOKUP;
156 }
157
158 /**
159 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
160 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
161 * private access</a>, on a target class.
162 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
163 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
164 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
165 * the target class, then this check ensures that
166 * <ul>
167 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
168 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
169 * the target class to at least {@code m1}.</li>
170 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
171 * </ul>
172 * <p>
173 * If there is a security manager, its {@code checkPermission} method is called to
174 * check {@code ReflectPermission("suppressAccessChecks")}.
175 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
176 * was created by code in the caller module (or derived from a lookup object originally
177 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
178 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
179 * access to the caller.
180 * @param targetClass the target class
181 * @param lookup the caller lookup object
182 * @return a lookup object for the target class, with private access
183 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
184 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
185 * @throws IllegalAccessException if the access check specified above fails
186 * @throws SecurityException if denied by the security manager
187 * @since 9
188 * @spec JPMS
189 * @see Lookup#dropLookupMode
190 */
191 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
192 SecurityManager sm = System.getSecurityManager();
193 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
194 if (targetClass.isPrimitive())
195 throw new IllegalArgumentException(targetClass + " is a primitive class");
196 if (targetClass.isArray())
197 throw new IllegalArgumentException(targetClass + " is an array class");
198 Module targetModule = targetClass.getModule();
199 Module callerModule = lookup.lookupClass().getModule();
200 if (!callerModule.canRead(targetModule))
201 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
202 if (targetModule.isNamed()) {
203 String pn = targetClass.getPackageName();
204 assert !pn.isEmpty() : "unnamed package cannot be in named module";
205 if (!targetModule.isOpen(pn, callerModule))
206 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
207 }
208 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
209 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
210 if (!callerModule.isNamed() && targetModule.isNamed()) {
211 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
212 if (logger != null) {
213 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
214 }
215 }
216 return new Lookup(targetClass);
217 }
218
219 /**
220 * Performs an unchecked "crack" of a
221 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
222 * The result is as if the user had obtained a lookup object capable enough
223 * to crack the target method handle, called
224 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
225 * on the target to obtain its symbolic reference, and then called
226 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
227 * to resolve the symbolic reference to a member.
228 * <p>
229 * If there is a security manager, its {@code checkPermission} method
230 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
231 * @param <T> the desired type of the result, either {@link Member} or a subtype
232 * @param target a direct method handle to crack into symbolic reference components
233 * @param expected a class object representing the desired result type {@code T}
234 * @return a reference to the method, constructor, or field object
235 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
236 * @exception NullPointerException if either argument is {@code null}
237 * @exception IllegalArgumentException if the target is not a direct method handle
238 * @exception ClassCastException if the member is not of the expected type
239 * @since 1.8
240 */
241 public static <T extends Member> T
242 reflectAs(Class<T> expected, MethodHandle target) {
243 SecurityManager smgr = System.getSecurityManager();
244 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
245 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
246 return lookup.revealDirect(target).reflectAs(expected, lookup);
247 }
248 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
249 private static final java.security.Permission ACCESS_PERMISSION =
250 new ReflectPermission("suppressAccessChecks");
251
252 /**
253 * A <em>lookup object</em> is a factory for creating method handles,
254 * when the creation requires access checking.
255 * Method handles do not perform
256 * access checks when they are called, but rather when they are created.
257 * Therefore, method handle access
258 * restrictions must be enforced when a method handle is created.
259 * The caller class against which those restrictions are enforced
260 * is known as the {@linkplain #lookupClass() lookup class}.
261 * <p>
262 * A lookup class which needs to create method handles will call
263 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
264 * When the {@code Lookup} factory object is created, the identity of the lookup class is
265 * determined, and securely stored in the {@code Lookup} object.
266 * The lookup class (or its delegates) may then use factory methods
267 * on the {@code Lookup} object to create method handles for access-checked members.
268 * This includes all methods, constructors, and fields which are allowed to the lookup class,
269 * even private ones.
270 *
271 * <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 return clazz;
973 }
974
975 private ProtectionDomain lookupClassProtectionDomain() {
976 ProtectionDomain pd = cachedProtectionDomain;
977 if (pd == null) {
978 cachedProtectionDomain = pd = protectionDomain(lookupClass);
979 }
980 return pd;
981 }
982
983 private ProtectionDomain protectionDomain(Class<?> clazz) {
984 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
985 return AccessController.doPrivileged(pa);
986 }
987
988 // cached protection domain
989 private volatile ProtectionDomain cachedProtectionDomain;
990
991
992 // Make sure outer class is initialized first.
993 static { IMPL_NAMES.getClass(); }
994
995 /** Package-private version of lookup which is trusted. */
996 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
997
998 /** Version of lookup which is trusted minimally.
999 * It can only be used to create method handles to publicly accessible
1000 * members in packages that are exported unconditionally.
1001 */
1002 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
1003
1004 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1005 String name = lookupClass.getName();
1006 if (name.startsWith("java.lang.invoke."))
1007 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1008 }
1009
1010 /**
1011 * Displays the name of the class from which lookups are to be made.
1012 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1013 * If there are restrictions on the access permitted to this lookup,
1014 * this is indicated by adding a suffix to the class name, consisting
1015 * of a slash and a keyword. The keyword represents the strongest
1016 * allowed access, and is chosen as follows:
1017 * <ul>
1018 * <li>If no access is allowed, the suffix is "/noaccess".
1019 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1020 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1021 * <li>If only public and module access are allowed, the suffix is "/module".
1022 * <li>If only public, module and package access are allowed, the suffix is "/package".
1023 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1024 * </ul>
1025 * If none of the above cases apply, it is the case that full
1026 * access (public, module, package, private, and protected) is allowed.
1027 * In this case, no suffix is added.
1028 * This is true only of an object obtained originally from
1029 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1030 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1031 * always have restricted access, and will display a suffix.
1032 * <p>
1033 * (It may seem strange that protected access should be
1034 * stronger than private access. Viewed independently from
1035 * package access, protected access is the first to be lost,
1036 * because it requires a direct subclass relationship between
1037 * caller and callee.)
1038 * @see #in
1039 *
1040 * @revised 9
1041 * @spec JPMS
1042 */
1043 @Override
1044 public String toString() {
1045 String cname = lookupClass.getName();
1046 switch (allowedModes) {
1047 case 0: // no privileges
1048 return cname + "/noaccess";
1049 case PUBLIC:
1050 return cname + "/public";
1051 case PUBLIC|UNCONDITIONAL:
1052 return cname + "/publicLookup";
1053 case PUBLIC|MODULE:
1054 return cname + "/module";
1055 case PUBLIC|MODULE|PACKAGE:
1056 return cname + "/package";
1057 case FULL_POWER_MODES & ~PROTECTED:
1058 return cname + "/private";
1059 case FULL_POWER_MODES:
1060 return cname;
1061 case TRUSTED:
1062 return "/trusted"; // internal only; not exported
1063 default: // Should not happen, but it's a bitfield...
1064 cname = cname + "/" + Integer.toHexString(allowedModes);
1065 assert(false) : cname;
1066 return cname;
1067 }
1068 }
1069
1070 /**
1071 * Produces a method handle for a static method.
1072 * The type of the method handle will be that of the method.
1073 * (Since static methods do not take receivers, there is no
1074 * additional receiver argument inserted into the method handle type,
1075 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1076 * The method and all its argument types must be accessible to the lookup object.
1077 * <p>
1078 * The returned method handle will have
1079 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1080 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1081 * <p>
1082 * If the returned method handle is invoked, the method's class will
1083 * be initialized, if it has not already been initialized.
1084 * <p><b>Example:</b>
1085 * <blockquote><pre>{@code
1086 import static java.lang.invoke.MethodHandles.*;
1087 import static java.lang.invoke.MethodType.*;
1088 ...
1089 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1090 "asList", methodType(List.class, Object[].class));
1091 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1092 * }</pre></blockquote>
1093 * @param refc the class from which the method is accessed
1094 * @param name the name of the method
1095 * @param type the type of the method
1096 * @return the desired method handle
1097 * @throws NoSuchMethodException if the method does not exist
1098 * @throws IllegalAccessException if access checking fails,
1099 * or if the method is not {@code static},
1100 * or if the method's variable arity modifier bit
1101 * is set and {@code asVarargsCollector} fails
1102 * @exception SecurityException if a security manager is present and it
1103 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1104 * @throws NullPointerException if any argument is null
1105 */
1106 public
1107 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1108 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1109 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1110 }
1111
1112 /**
1113 * Produces a method handle for a virtual method.
1114 * The type of the method handle will be that of the method,
1115 * with the receiver type (usually {@code refc}) prepended.
1116 * The method and all its argument types must be accessible to the lookup object.
1117 * <p>
1118 * When called, the handle will treat the first argument as a receiver
1119 * and, for non-private methods, dispatch on the receiver's type to determine which method
1120 * implementation to enter.
1121 * For private methods the named method in {@code refc} will be invoked on the receiver.
1122 * (The dispatching action is identical with that performed by an
1123 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1124 * <p>
1125 * The first argument will be of type {@code refc} if the lookup
1126 * class has full privileges to access the member. Otherwise
1127 * the member must be {@code protected} and the first argument
1128 * will be restricted in type to the lookup class.
1129 * <p>
1130 * The returned method handle will have
1131 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1132 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1133 * <p>
1134 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1135 * instructions and method handles produced by {@code findVirtual},
1136 * if the class is {@code MethodHandle} and the name string is
1137 * {@code invokeExact} or {@code invoke}, the resulting
1138 * method handle is equivalent to one produced by
1139 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1140 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1141 * with the same {@code type} argument.
1142 * <p>
1143 * If the class is {@code VarHandle} and the name string corresponds to
1144 * the name of a signature-polymorphic access mode method, the resulting
1145 * method handle is equivalent to one produced by
1146 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1147 * the access mode corresponding to the name string and with the same
1148 * {@code type} arguments.
1149 * <p>
1150 * <b>Example:</b>
1151 * <blockquote><pre>{@code
1152 import static java.lang.invoke.MethodHandles.*;
1153 import static java.lang.invoke.MethodType.*;
1154 ...
1155 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1156 "concat", methodType(String.class, String.class));
1157 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1158 "hashCode", methodType(int.class));
1159 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1160 "hashCode", methodType(int.class));
1161 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1162 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1163 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1164 // interface method:
1165 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1166 "subSequence", methodType(CharSequence.class, int.class, int.class));
1167 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1168 // constructor "internal method" must be accessed differently:
1169 MethodType MT_newString = methodType(void.class); //()V for new String()
1170 try { assertEquals("impossible", lookup()
1171 .findVirtual(String.class, "<init>", MT_newString));
1172 } catch (NoSuchMethodException ex) { } // OK
1173 MethodHandle MH_newString = publicLookup()
1174 .findConstructor(String.class, MT_newString);
1175 assertEquals("", (String) MH_newString.invokeExact());
1176 * }</pre></blockquote>
1177 *
1178 * @param refc the class or interface from which the method is accessed
1179 * @param name the name of the method
1180 * @param type the type of the method, with the receiver argument omitted
1181 * @return the desired method handle
1182 * @throws NoSuchMethodException if the method does not exist
1183 * @throws IllegalAccessException if access checking fails,
1184 * or if the method is {@code static},
1185 * or if the method's variable arity modifier bit
1186 * is set and {@code asVarargsCollector} fails
1187 * @exception SecurityException if a security manager is present and it
1188 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1189 * @throws NullPointerException if any argument is null
1190 */
1191 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1192 if (refc == MethodHandle.class) {
1193 MethodHandle mh = findVirtualForMH(name, type);
1194 if (mh != null) return mh;
1195 } else if (refc == VarHandle.class) {
1196 MethodHandle mh = findVirtualForVH(name, type);
1197 if (mh != null) return mh;
1198 }
1199 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1200 MemberName method = resolveOrFail(refKind, refc, name, type);
1201 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1202 }
1203 private MethodHandle findVirtualForMH(String name, MethodType type) {
1204 // these names require special lookups because of the implicit MethodType argument
1205 if ("invoke".equals(name))
1206 return invoker(type);
1207 if ("invokeExact".equals(name))
1208 return exactInvoker(type);
1209 assert(!MemberName.isMethodHandleInvokeName(name));
1210 return null;
1211 }
1212 private MethodHandle findVirtualForVH(String name, MethodType type) {
1213 try {
1214 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1215 } catch (IllegalArgumentException e) {
1216 return null;
1217 }
1218 }
1219
1220 /**
1221 * Produces a method handle which creates an object and initializes it, using
1222 * the constructor of the specified type.
1223 * The parameter types of the method handle will be those of the constructor,
1224 * while the return type will be a reference to the constructor's class.
1225 * The constructor and all its argument types must be accessible to the lookup object.
1226 * <p>
1227 * The requested type must have a return type of {@code void}.
1228 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1229 * <p>
1230 * The returned method handle will have
1231 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1232 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1233 * <p>
1234 * If the returned method handle is invoked, the constructor's class will
1235 * be initialized, if it has not already been initialized.
1236 * <p><b>Example:</b>
1237 * <blockquote><pre>{@code
1238 import static java.lang.invoke.MethodHandles.*;
1239 import static java.lang.invoke.MethodType.*;
1240 ...
1241 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1242 ArrayList.class, methodType(void.class, Collection.class));
1243 Collection orig = Arrays.asList("x", "y");
1244 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1245 assert(orig != copy);
1246 assertEquals(orig, copy);
1247 // a variable-arity constructor:
1248 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1249 ProcessBuilder.class, methodType(void.class, String[].class));
1250 ProcessBuilder pb = (ProcessBuilder)
1251 MH_newProcessBuilder.invoke("x", "y", "z");
1252 assertEquals("[x, y, z]", pb.command().toString());
1253 * }</pre></blockquote>
1254 * @param refc the class or interface from which the method is accessed
1255 * @param type the type of the method, with the receiver argument omitted, and a void return type
1256 * @return the desired method handle
1257 * @throws NoSuchMethodException if the constructor does not exist
1258 * @throws IllegalAccessException if access checking fails
1259 * or if the method's variable arity modifier bit
1260 * is set and {@code asVarargsCollector} fails
1261 * @exception SecurityException if a security manager is present and it
1262 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1263 * @throws NullPointerException if any argument is null
1264 */
1265 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1266 if (refc.isArray()) {
1267 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1268 }
1269 String name = "<init>";
1270 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1271 return getDirectConstructor(refc, ctor);
1272 }
1273
1274 /**
1275 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1276 * initializer of the class is not run.
1277 * <p>
1278 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1279 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1280 * load the requested class, and then determines whether the class is accessible to this lookup object.
1281 *
1282 * @param targetName the fully qualified name of the class to be looked up.
1283 * @return the requested class.
1284 * @exception SecurityException if a security manager is present and it
1285 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1286 * @throws LinkageError if the linkage fails
1287 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1288 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1289 * modes.
1290 * @exception SecurityException if a security manager is present and it
1291 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1292 * @since 9
1293 */
1294 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1295 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1296 return accessClass(targetClass);
1297 }
1298
1299 /**
1300 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1301 * static initializer of the class is not run.
1302 * <p>
1303 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1304 * {@linkplain #lookupModes() lookup modes}.
1305 *
1306 * @param targetClass the class to be access-checked
1307 *
1308 * @return the class that has been access-checked
1309 *
1310 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1311 * modes.
1312 * @exception SecurityException if a security manager is present and it
1313 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1314 * @since 9
1315 */
1316 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1317 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1318 throw new MemberName(targetClass).makeAccessException("access violation", this);
1319 }
1320 checkSecurityManager(targetClass, null);
1321 return targetClass;
1322 }
1323
1324 /**
1325 * Produces an early-bound method handle for a virtual method.
1326 * It will bypass checks for overriding methods on the receiver,
1327 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1328 * instruction from within the explicitly specified {@code specialCaller}.
1329 * The type of the method handle will be that of the method,
1330 * with a suitably restricted receiver type prepended.
1331 * (The receiver type will be {@code specialCaller} or a subtype.)
1332 * The method and all its argument types must be accessible
1333 * to the lookup object.
1334 * <p>
1335 * Before method resolution,
1336 * if the explicitly specified caller class is not identical with the
1337 * lookup class, or if this lookup object does not have
1338 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1339 * privileges, the access fails.
1340 * <p>
1341 * The returned method handle will have
1342 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1343 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1344 * <p style="font-size:smaller;">
1345 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1346 * even though the {@code invokespecial} instruction can refer to them
1347 * in special circumstances. Use {@link #findConstructor findConstructor}
1348 * to access instance initialization methods in a safe manner.)</em>
1349 * <p><b>Example:</b>
1350 * <blockquote><pre>{@code
1351 import static java.lang.invoke.MethodHandles.*;
1352 import static java.lang.invoke.MethodType.*;
1353 ...
1354 static class Listie extends ArrayList {
1355 public String toString() { return "[wee Listie]"; }
1356 static Lookup lookup() { return MethodHandles.lookup(); }
1357 }
1358 ...
1359 // no access to constructor via invokeSpecial:
1360 MethodHandle MH_newListie = Listie.lookup()
1361 .findConstructor(Listie.class, methodType(void.class));
1362 Listie l = (Listie) MH_newListie.invokeExact();
1363 try { assertEquals("impossible", Listie.lookup().findSpecial(
1364 Listie.class, "<init>", methodType(void.class), Listie.class));
1365 } catch (NoSuchMethodException ex) { } // OK
1366 // access to super and self methods via invokeSpecial:
1367 MethodHandle MH_super = Listie.lookup().findSpecial(
1368 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1369 MethodHandle MH_this = Listie.lookup().findSpecial(
1370 Listie.class, "toString" , methodType(String.class), Listie.class);
1371 MethodHandle MH_duper = Listie.lookup().findSpecial(
1372 Object.class, "toString" , methodType(String.class), Listie.class);
1373 assertEquals("[]", (String) MH_super.invokeExact(l));
1374 assertEquals(""+l, (String) MH_this.invokeExact(l));
1375 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1376 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1377 String.class, "toString", methodType(String.class), Listie.class));
1378 } catch (IllegalAccessException ex) { } // OK
1379 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1380 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1381 * }</pre></blockquote>
1382 *
1383 * @param refc the class or interface from which the method is accessed
1384 * @param name the name of the method (which must not be "<init>")
1385 * @param type the type of the method, with the receiver argument omitted
1386 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1387 * @return the desired method handle
1388 * @throws NoSuchMethodException if the method does not exist
1389 * @throws IllegalAccessException if access checking fails,
1390 * or if the method is {@code static},
1391 * or if the method's variable arity modifier bit
1392 * is set and {@code asVarargsCollector} fails
1393 * @exception SecurityException if a security manager is present and it
1394 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1395 * @throws NullPointerException if any argument is null
1396 */
1397 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1398 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1399 checkSpecialCaller(specialCaller, refc);
1400 Lookup specialLookup = this.in(specialCaller);
1401 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1402 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1403 }
1404
1405 /**
1406 * Produces a method handle giving read access to a non-static field.
1407 * The type of the method handle will have a return type of the field's
1408 * value type.
1409 * The method handle's single argument will be the instance containing
1410 * the field.
1411 * Access checking is performed immediately on behalf of the lookup class.
1412 * @param refc the class or interface from which the method is accessed
1413 * @param name the field's name
1414 * @param type the field's type
1415 * @return a method handle which can load values from the field
1416 * @throws NoSuchFieldException if the field does not exist
1417 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1418 * @exception SecurityException if a security manager is present and it
1419 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1420 * @throws NullPointerException if any argument is null
1421 * @see #findVarHandle(Class, String, Class)
1422 */
1423 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1424 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1425 return getDirectField(REF_getField, refc, field);
1426 }
1427
1428 /**
1429 * Produces a method handle giving write access to a non-static field.
1430 * The type of the method handle will have a void return type.
1431 * The method handle will take two arguments, the instance containing
1432 * the field, and the value to be stored.
1433 * The second argument will be of the field's value type.
1434 * Access checking is performed immediately on behalf of the lookup class.
1435 * @param refc the class or interface from which the method is accessed
1436 * @param name the field's name
1437 * @param type the field's type
1438 * @return a method handle which can store values into the field
1439 * @throws NoSuchFieldException if the field does not exist
1440 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1441 * @exception SecurityException if a security manager is present and it
1442 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1443 * @throws NullPointerException if any argument is null
1444 * @see #findVarHandle(Class, String, Class)
1445 */
1446 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1447 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1448 return getDirectField(REF_putField, refc, field);
1449 }
1450
1451 /**
1452 * Produces a VarHandle giving access to a non-static field {@code name}
1453 * of type {@code type} declared in a class of type {@code recv}.
1454 * The VarHandle's variable type is {@code type} and it has one
1455 * coordinate type, {@code recv}.
1456 * <p>
1457 * Access checking is performed immediately on behalf of the lookup
1458 * class.
1459 * <p>
1460 * Certain access modes of the returned VarHandle are unsupported under
1461 * the following conditions:
1462 * <ul>
1463 * <li>if the field is declared {@code final}, then the write, atomic
1464 * update, numeric atomic update, and bitwise atomic update access
1465 * modes are unsupported.
1466 * <li>if the field type is anything other than {@code byte},
1467 * {@code short}, {@code char}, {@code int}, {@code long},
1468 * {@code float}, or {@code double} then numeric atomic update
1469 * access modes are unsupported.
1470 * <li>if the field type is anything other than {@code boolean},
1471 * {@code byte}, {@code short}, {@code char}, {@code int} or
1472 * {@code long} then bitwise atomic update access modes are
1473 * unsupported.
1474 * </ul>
1475 * <p>
1476 * If the field is declared {@code volatile} then the returned VarHandle
1477 * will override access to the field (effectively ignore the
1478 * {@code volatile} declaration) in accordance to its specified
1479 * access modes.
1480 * <p>
1481 * If the field type is {@code float} or {@code double} then numeric
1482 * and atomic update access modes compare values using their bitwise
1483 * representation (see {@link Float#floatToRawIntBits} and
1484 * {@link Double#doubleToRawLongBits}, respectively).
1485 * @apiNote
1486 * Bitwise comparison of {@code float} values or {@code double} values,
1487 * as performed by the numeric and atomic update access modes, differ
1488 * from the primitive {@code ==} operator and the {@link Float#equals}
1489 * and {@link Double#equals} methods, specifically with respect to
1490 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1491 * Care should be taken when performing a compare and set or a compare
1492 * and exchange operation with such values since the operation may
1493 * unexpectedly fail.
1494 * There are many possible NaN values that are considered to be
1495 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1496 * provided by Java can distinguish between them. Operation failure can
1497 * occur if the expected or witness value is a NaN value and it is
1498 * transformed (perhaps in a platform specific manner) into another NaN
1499 * value, and thus has a different bitwise representation (see
1500 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1501 * details).
1502 * The values {@code -0.0} and {@code +0.0} have different bitwise
1503 * representations but are considered equal when using the primitive
1504 * {@code ==} operator. Operation failure can occur if, for example, a
1505 * numeric algorithm computes an expected value to be say {@code -0.0}
1506 * and previously computed the witness value to be say {@code +0.0}.
1507 * @param recv the receiver class, of type {@code R}, that declares the
1508 * non-static field
1509 * @param name the field's name
1510 * @param type the field's type, of type {@code T}
1511 * @return a VarHandle giving access to non-static fields.
1512 * @throws NoSuchFieldException if the field does not exist
1513 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1514 * @exception SecurityException if a security manager is present and it
1515 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1516 * @throws NullPointerException if any argument is null
1517 * @since 9
1518 */
1519 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1520 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1521 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1522 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1523 }
1524
1525 /**
1526 * Produces a method handle giving read access to a static field.
1527 * The type of the method handle will have a return type of the field's
1528 * value type.
1529 * The method handle will take no arguments.
1530 * Access checking is performed immediately on behalf of the lookup class.
1531 * <p>
1532 * If the returned method handle is invoked, the field's class will
1533 * be initialized, if it has not already been initialized.
1534 * @param refc the class or interface from which the method is accessed
1535 * @param name the field's name
1536 * @param type the field's type
1537 * @return a method handle which can load values from the field
1538 * @throws NoSuchFieldException if the field does not exist
1539 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1540 * @exception SecurityException if a security manager is present and it
1541 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1542 * @throws NullPointerException if any argument is null
1543 */
1544 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1545 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1546 return getDirectField(REF_getStatic, refc, field);
1547 }
1548
1549 /**
1550 * Produces a method handle giving write access to a static field.
1551 * The type of the method handle will have a void return type.
1552 * The method handle will take a single
1553 * argument, of the field's value type, the value to be stored.
1554 * Access checking is performed immediately on behalf of the lookup class.
1555 * <p>
1556 * If the returned method handle is invoked, the field's class will
1557 * be initialized, if it has not already been initialized.
1558 * @param refc the class or interface from which the method is accessed
1559 * @param name the field's name
1560 * @param type the field's type
1561 * @return a method handle which can store values into the field
1562 * @throws NoSuchFieldException if the field does not exist
1563 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1564 * @exception SecurityException if a security manager is present and it
1565 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1566 * @throws NullPointerException if any argument is null
1567 */
1568 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1569 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1570 return getDirectField(REF_putStatic, refc, field);
1571 }
1572
1573 /**
1574 * Produces a VarHandle giving access to a static field {@code name} of
1575 * type {@code type} declared in a class of type {@code decl}.
1576 * The VarHandle's variable type is {@code type} and it has no
1577 * coordinate types.
1578 * <p>
1579 * Access checking is performed immediately on behalf of the lookup
1580 * class.
1581 * <p>
1582 * If the returned VarHandle is operated on, the declaring class will be
1583 * initialized, if it has not already been initialized.
1584 * <p>
1585 * Certain access modes of the returned VarHandle are unsupported under
1586 * the following conditions:
1587 * <ul>
1588 * <li>if the field is declared {@code final}, then the write, atomic
1589 * update, numeric atomic update, and bitwise atomic update access
1590 * modes are unsupported.
1591 * <li>if the field type is anything other than {@code byte},
1592 * {@code short}, {@code char}, {@code int}, {@code long},
1593 * {@code float}, or {@code double}, then numeric atomic update
1594 * access modes are unsupported.
1595 * <li>if the field type is anything other than {@code boolean},
1596 * {@code byte}, {@code short}, {@code char}, {@code int} or
1597 * {@code long} then bitwise atomic update access modes are
1598 * unsupported.
1599 * </ul>
1600 * <p>
1601 * If the field is declared {@code volatile} then the returned VarHandle
1602 * will override access to the field (effectively ignore the
1603 * {@code volatile} declaration) in accordance to its specified
1604 * access modes.
1605 * <p>
1606 * If the field type is {@code float} or {@code double} then numeric
1607 * and atomic update access modes compare values using their bitwise
1608 * representation (see {@link Float#floatToRawIntBits} and
1609 * {@link Double#doubleToRawLongBits}, respectively).
1610 * @apiNote
1611 * Bitwise comparison of {@code float} values or {@code double} values,
1612 * as performed by the numeric and atomic update access modes, differ
1613 * from the primitive {@code ==} operator and the {@link Float#equals}
1614 * and {@link Double#equals} methods, specifically with respect to
1615 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1616 * Care should be taken when performing a compare and set or a compare
1617 * and exchange operation with such values since the operation may
1618 * unexpectedly fail.
1619 * There are many possible NaN values that are considered to be
1620 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1621 * provided by Java can distinguish between them. Operation failure can
1622 * occur if the expected or witness value is a NaN value and it is
1623 * transformed (perhaps in a platform specific manner) into another NaN
1624 * value, and thus has a different bitwise representation (see
1625 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1626 * details).
1627 * The values {@code -0.0} and {@code +0.0} have different bitwise
1628 * representations but are considered equal when using the primitive
1629 * {@code ==} operator. Operation failure can occur if, for example, a
1630 * numeric algorithm computes an expected value to be say {@code -0.0}
1631 * and previously computed the witness value to be say {@code +0.0}.
1632 * @param decl the class that declares the static field
1633 * @param name the field's name
1634 * @param type the field's type, of type {@code T}
1635 * @return a VarHandle giving access to a static field
1636 * @throws NoSuchFieldException if the field does not exist
1637 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1638 * @exception SecurityException if a security manager is present and it
1639 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1640 * @throws NullPointerException if any argument is null
1641 * @since 9
1642 */
1643 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1644 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1645 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1646 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1647 }
1648
1649 /**
1650 * Produces an early-bound method handle for a non-static method.
1651 * The receiver must have a supertype {@code defc} in which a method
1652 * of the given name and type is accessible to the lookup class.
1653 * The method and all its argument types must be accessible to the lookup object.
1654 * The type of the method handle will be that of the method,
1655 * without any insertion of an additional receiver parameter.
1656 * The given receiver will be bound into the method handle,
1657 * so that every call to the method handle will invoke the
1658 * requested method on the given receiver.
1659 * <p>
1660 * The returned method handle will have
1661 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1662 * the method's variable arity modifier bit ({@code 0x0080}) is set
1663 * <em>and</em> the trailing array argument is not the only argument.
1664 * (If the trailing array argument is the only argument,
1665 * the given receiver value will be bound to it.)
1666 * <p>
1667 * This is almost equivalent to the following code, with some differences noted below:
1668 * <blockquote><pre>{@code
1669 import static java.lang.invoke.MethodHandles.*;
1670 import static java.lang.invoke.MethodType.*;
1671 ...
1672 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1673 MethodHandle mh1 = mh0.bindTo(receiver);
1674 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1675 return mh1;
1676 * }</pre></blockquote>
1677 * where {@code defc} is either {@code receiver.getClass()} or a super
1678 * type of that class, in which the requested method is accessible
1679 * to the lookup class.
1680 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1681 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1682 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1683 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1684 * @param receiver the object from which the method is accessed
1685 * @param name the name of the method
1686 * @param type the type of the method, with the receiver argument omitted
1687 * @return the desired method handle
1688 * @throws NoSuchMethodException if the method does not exist
1689 * @throws IllegalAccessException if access checking fails
1690 * or if the method's variable arity modifier bit
1691 * is set and {@code asVarargsCollector} fails
1692 * @exception SecurityException if a security manager is present and it
1693 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1694 * @throws NullPointerException if any argument is null
1695 * @see MethodHandle#bindTo
1696 * @see #findVirtual
1697 */
1698 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1699 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1700 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1701 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1702 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1703 throw new IllegalAccessException("The restricted defining class " +
1704 mh.type().leadingReferenceParameter().getName() +
1705 " is not assignable from receiver class " +
1706 receiver.getClass().getName());
1707 }
1708 return mh.bindArgumentL(0, receiver).setVarargs(method);
1709 }
1710
1711 /**
1712 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1713 * to <i>m</i>, if the lookup class has permission.
1714 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1715 * If <i>m</i> is virtual, overriding is respected on every call.
1716 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1717 * The type of the method handle will be that of the method,
1718 * with the receiver type prepended (but only if it is non-static).
1719 * If the method's {@code accessible} flag is not set,
1720 * access checking is performed immediately on behalf of the lookup class.
1721 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1722 * <p>
1723 * The returned method handle will have
1724 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1725 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1726 * <p>
1727 * If <i>m</i> is static, and
1728 * if the returned method handle is invoked, the method's class will
1729 * be initialized, if it has not already been initialized.
1730 * @param m the reflected method
1731 * @return a method handle which can invoke the reflected method
1732 * @throws IllegalAccessException if access checking fails
1733 * or if the method's variable arity modifier bit
1734 * is set and {@code asVarargsCollector} fails
1735 * @throws NullPointerException if the argument is null
1736 */
1737 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1738 if (m.getDeclaringClass() == MethodHandle.class) {
1739 MethodHandle mh = unreflectForMH(m);
1740 if (mh != null) return mh;
1741 }
1742 if (m.getDeclaringClass() == VarHandle.class) {
1743 MethodHandle mh = unreflectForVH(m);
1744 if (mh != null) return mh;
1745 }
1746 MemberName method = new MemberName(m);
1747 byte refKind = method.getReferenceKind();
1748 if (refKind == REF_invokeSpecial)
1749 refKind = REF_invokeVirtual;
1750 assert(method.isMethod());
1751 @SuppressWarnings("deprecation")
1752 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1753 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1754 }
1755 private MethodHandle unreflectForMH(Method m) {
1756 // these names require special lookups because they throw UnsupportedOperationException
1757 if (MemberName.isMethodHandleInvokeName(m.getName()))
1758 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1759 return null;
1760 }
1761 private MethodHandle unreflectForVH(Method m) {
1762 // these names require special lookups because they throw UnsupportedOperationException
1763 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1764 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1765 return null;
1766 }
1767
1768 /**
1769 * Produces a method handle for a reflected method.
1770 * It will bypass checks for overriding methods on the receiver,
1771 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1772 * instruction from within the explicitly specified {@code specialCaller}.
1773 * The type of the method handle will be that of the method,
1774 * with a suitably restricted receiver type prepended.
1775 * (The receiver type will be {@code specialCaller} or a subtype.)
1776 * If the method's {@code accessible} flag is not set,
1777 * access checking is performed immediately on behalf of the lookup class,
1778 * as if {@code invokespecial} instruction were being linked.
1779 * <p>
1780 * Before method resolution,
1781 * if the explicitly specified caller class is not identical with the
1782 * lookup class, or if this lookup object does not have
1783 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1784 * privileges, the access fails.
1785 * <p>
1786 * The returned method handle will have
1787 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1788 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1789 * @param m the reflected method
1790 * @param specialCaller the class nominally calling the method
1791 * @return a method handle which can invoke the reflected method
1792 * @throws IllegalAccessException if access checking fails,
1793 * or if the method is {@code static},
1794 * or if the method's variable arity modifier bit
1795 * is set and {@code asVarargsCollector} fails
1796 * @throws NullPointerException if any argument is null
1797 */
1798 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1799 checkSpecialCaller(specialCaller, null);
1800 Lookup specialLookup = this.in(specialCaller);
1801 MemberName method = new MemberName(m, true);
1802 assert(method.isMethod());
1803 // ignore m.isAccessible: this is a new kind of access
1804 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1805 }
1806
1807 /**
1808 * Produces a method handle for a reflected constructor.
1809 * The type of the method handle will be that of the constructor,
1810 * with the return type changed to the declaring class.
1811 * The method handle will perform a {@code newInstance} operation,
1812 * creating a new instance of the constructor's class on the
1813 * arguments passed to the method handle.
1814 * <p>
1815 * If the constructor's {@code accessible} flag is not set,
1816 * access checking is performed immediately on behalf of the lookup class.
1817 * <p>
1818 * The returned method handle will have
1819 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1820 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1821 * <p>
1822 * If the returned method handle is invoked, the constructor's class will
1823 * be initialized, if it has not already been initialized.
1824 * @param c the reflected constructor
1825 * @return a method handle which can invoke the reflected constructor
1826 * @throws IllegalAccessException if access checking fails
1827 * or if the method's variable arity modifier bit
1828 * is set and {@code asVarargsCollector} fails
1829 * @throws NullPointerException if the argument is null
1830 */
1831 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1832 MemberName ctor = new MemberName(c);
1833 assert(ctor.isConstructor());
1834 @SuppressWarnings("deprecation")
1835 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1836 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1837 }
1838
1839 /**
1840 * Produces a method handle giving read access to a reflected field.
1841 * The type of the method handle will have a return type of the field's
1842 * value type.
1843 * If the field is static, the method handle will take no arguments.
1844 * Otherwise, its single argument will be the instance containing
1845 * the field.
1846 * If the field's {@code accessible} flag is not set,
1847 * access checking is performed immediately on behalf of the lookup class.
1848 * <p>
1849 * If the field is static, and
1850 * if the returned method handle is invoked, the field's class will
1851 * be initialized, if it has not already been initialized.
1852 * @param f the reflected field
1853 * @return a method handle which can load values from the reflected field
1854 * @throws IllegalAccessException if access checking fails
1855 * @throws NullPointerException if the argument is null
1856 */
1857 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1858 return unreflectField(f, false);
1859 }
1860 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1861 MemberName field = new MemberName(f, isSetter);
1862 assert(isSetter
1863 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1864 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1865 @SuppressWarnings("deprecation")
1866 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1867 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1868 }
1869
1870 /**
1871 * Produces a method handle giving write access to a reflected field.
1872 * The type of the method handle will have a void return type.
1873 * If the field is static, the method handle will take a single
1874 * argument, of the field's value type, the value to be stored.
1875 * Otherwise, the two arguments will be the instance containing
1876 * the field, and the value to be stored.
1877 * If the field's {@code accessible} flag is not set,
1878 * access checking is performed immediately on behalf of the lookup class.
1879 * <p>
1880 * If the field is static, and
1881 * if the returned method handle is invoked, the field's class will
1882 * be initialized, if it has not already been initialized.
1883 * @param f the reflected field
1884 * @return a method handle which can store values into the reflected field
1885 * @throws IllegalAccessException if access checking fails
1886 * @throws NullPointerException if the argument is null
1887 */
1888 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1889 return unreflectField(f, true);
1890 }
1891
1892 /**
1893 * Produces a VarHandle giving access to a reflected field {@code f}
1894 * of type {@code T} declared in a class of type {@code R}.
1895 * The VarHandle's variable type is {@code T}.
1896 * If the field is non-static the VarHandle has one coordinate type,
1897 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1898 * coordinate types.
1899 * <p>
1900 * Access checking is performed immediately on behalf of the lookup
1901 * class, regardless of the value of the field's {@code accessible}
1902 * flag.
1903 * <p>
1904 * If the field is static, and if the returned VarHandle is operated
1905 * on, the field's declaring class will be initialized, if it has not
1906 * already been initialized.
1907 * <p>
1908 * Certain access modes of the returned VarHandle are unsupported under
1909 * the following conditions:
1910 * <ul>
1911 * <li>if the field is declared {@code final}, then the write, atomic
1912 * update, numeric atomic update, and bitwise atomic update access
1913 * modes are unsupported.
1914 * <li>if the field type is anything other than {@code byte},
1915 * {@code short}, {@code char}, {@code int}, {@code long},
1916 * {@code float}, or {@code double} then numeric atomic update
1917 * access modes are unsupported.
1918 * <li>if the field type is anything other than {@code boolean},
1919 * {@code byte}, {@code short}, {@code char}, {@code int} or
1920 * {@code long} then bitwise atomic update access modes are
1921 * unsupported.
1922 * </ul>
1923 * <p>
1924 * If the field is declared {@code volatile} then the returned VarHandle
1925 * will override access to the field (effectively ignore the
1926 * {@code volatile} declaration) in accordance to its specified
1927 * access modes.
1928 * <p>
1929 * If the field type is {@code float} or {@code double} then numeric
1930 * and atomic update access modes compare values using their bitwise
1931 * representation (see {@link Float#floatToRawIntBits} and
1932 * {@link Double#doubleToRawLongBits}, respectively).
1933 * @apiNote
1934 * Bitwise comparison of {@code float} values or {@code double} values,
1935 * as performed by the numeric and atomic update access modes, differ
1936 * from the primitive {@code ==} operator and the {@link Float#equals}
1937 * and {@link Double#equals} methods, specifically with respect to
1938 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1939 * Care should be taken when performing a compare and set or a compare
1940 * and exchange operation with such values since the operation may
1941 * unexpectedly fail.
1942 * There are many possible NaN values that are considered to be
1943 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1944 * provided by Java can distinguish between them. Operation failure can
1945 * occur if the expected or witness value is a NaN value and it is
1946 * transformed (perhaps in a platform specific manner) into another NaN
1947 * value, and thus has a different bitwise representation (see
1948 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1949 * details).
1950 * The values {@code -0.0} and {@code +0.0} have different bitwise
1951 * representations but are considered equal when using the primitive
1952 * {@code ==} operator. Operation failure can occur if, for example, a
1953 * numeric algorithm computes an expected value to be say {@code -0.0}
1954 * and previously computed the witness value to be say {@code +0.0}.
1955 * @param f the reflected field, with a field of type {@code T}, and
1956 * a declaring class of type {@code R}
1957 * @return a VarHandle giving access to non-static fields or a static
1958 * field
1959 * @throws IllegalAccessException if access checking fails
1960 * @throws NullPointerException if the argument is null
1961 * @since 9
1962 */
1963 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1964 MemberName getField = new MemberName(f, false);
1965 MemberName putField = new MemberName(f, true);
1966 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1967 f.getDeclaringClass(), getField, putField);
1968 }
1969
1970 /**
1971 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1972 * created by this lookup object or a similar one.
1973 * Security and access checks are performed to ensure that this lookup object
1974 * is capable of reproducing the target method handle.
1975 * This means that the cracking may fail if target is a direct method handle
1976 * but was created by an unrelated lookup object.
1977 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1978 * and was created by a lookup object for a different class.
1979 * @param target a direct method handle to crack into symbolic reference components
1980 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1981 * @exception SecurityException if a security manager is present and it
1982 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1983 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1984 * @exception NullPointerException if the target is {@code null}
1985 * @see MethodHandleInfo
1986 * @since 1.8
1987 */
1988 public MethodHandleInfo revealDirect(MethodHandle target) {
1989 MemberName member = target.internalMemberName();
1990 if (member == null || (!member.isResolved() &&
1991 !member.isMethodHandleInvoke() &&
1992 !member.isVarHandleMethodInvoke()))
1993 throw newIllegalArgumentException("not a direct method handle");
1994 Class<?> defc = member.getDeclaringClass();
1995 byte refKind = member.getReferenceKind();
1996 assert(MethodHandleNatives.refKindIsValid(refKind));
1997 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1998 // Devirtualized method invocation is usually formally virtual.
1999 // To avoid creating extra MemberName objects for this common case,
2000 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2001 refKind = REF_invokeVirtual;
2002 if (refKind == REF_invokeVirtual && defc.isInterface())
2003 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2004 refKind = REF_invokeInterface;
2005 // Check SM permissions and member access before cracking.
2006 try {
2007 checkAccess(refKind, defc, member);
2008 checkSecurityManager(defc, member);
2009 } catch (IllegalAccessException ex) {
2010 throw new IllegalArgumentException(ex);
2011 }
2012 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2013 Class<?> callerClass = target.internalCallerClass();
2014 if (!hasPrivateAccess() || callerClass != lookupClass())
2015 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2016 }
2017 // Produce the handle to the results.
2018 return new InfoFromMemberName(this, member, refKind);
2019 }
2020
2021 /// Helper methods, all package-private.
2022
2023 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2024 checkSymbolicClass(refc); // do this before attempting to resolve
2025 Objects.requireNonNull(name);
2026 Objects.requireNonNull(type);
2027 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2028 NoSuchFieldException.class);
2029 }
2030
2031 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2032 checkSymbolicClass(refc); // do this before attempting to resolve
2033 Objects.requireNonNull(name);
2034 Objects.requireNonNull(type);
2035 checkMethodName(refKind, name); // NPE check on name
2036 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2037 NoSuchMethodException.class);
2038 }
2039
2040 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2041 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2042 Objects.requireNonNull(member.getName());
2043 Objects.requireNonNull(member.getType());
2044 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2045 ReflectiveOperationException.class);
2046 }
2047
2048 MemberName resolveOrNull(byte refKind, MemberName member) {
2049 // do this before attempting to resolve
2050 if (!isClassAccessible(member.getDeclaringClass())) {
2051 return null;
2052 }
2053 Objects.requireNonNull(member.getName());
2054 Objects.requireNonNull(member.getType());
2055 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2056 }
2057
2058 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2059 if (!isClassAccessible(refc)) {
2060 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2061 }
2062 }
2063
2064 boolean isClassAccessible(Class<?> refc) {
2065 Objects.requireNonNull(refc);
2066 Class<?> caller = lookupClassOrNull();
2067 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes);
2068 }
2069
2070 /** Check name for an illegal leading "<" character. */
2071 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2072 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2073 throw new NoSuchMethodException("illegal method name: "+name);
2074 }
2075
2076
2077 /**
2078 * Find my trustable caller class if m is a caller sensitive method.
2079 * If this lookup object has private access, then the caller class is the lookupClass.
2080 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2081 */
2082 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2083 Class<?> callerClass = null;
2084 if (MethodHandleNatives.isCallerSensitive(m)) {
2085 // Only lookups with private access are allowed to resolve caller-sensitive methods
2086 if (hasPrivateAccess()) {
2087 callerClass = lookupClass;
2088 } else {
2089 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2090 }
2091 }
2092 return callerClass;
2093 }
2094
2095 /**
2096 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2097 * @return {@code true} if this lookup has {@code PRIVATE} access.
2098 * @since 9
2099 */
2100 public boolean hasPrivateAccess() {
2101 return (allowedModes & PRIVATE) != 0;
2102 }
2103
2104 /**
2105 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2106 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2107 * If this lookup object has private access, then the caller class is the lookupClass.
2108 */
2109 void checkSecurityManager(Class<?> refc, MemberName m) {
2110 SecurityManager smgr = System.getSecurityManager();
2111 if (smgr == null) return;
2112 if (allowedModes == TRUSTED) return;
2113
2114 // Step 1:
2115 boolean fullPowerLookup = hasPrivateAccess();
2116 if (!fullPowerLookup ||
2117 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2118 ReflectUtil.checkPackageAccess(refc);
2119 }
2120
2121 if (m == null) { // findClass or accessClass
2122 // Step 2b:
2123 if (!fullPowerLookup) {
2124 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2125 }
2126 return;
2127 }
2128
2129 // Step 2a:
2130 if (m.isPublic()) return;
2131 if (!fullPowerLookup) {
2132 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2133 }
2134
2135 // Step 3:
2136 Class<?> defc = m.getDeclaringClass();
2137 if (!fullPowerLookup && defc != refc) {
2138 ReflectUtil.checkPackageAccess(defc);
2139 }
2140 }
2141
2142 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2143 boolean wantStatic = (refKind == REF_invokeStatic);
2144 String message;
2145 if (m.isConstructor())
2146 message = "expected a method, not a constructor";
2147 else if (!m.isMethod())
2148 message = "expected a method";
2149 else if (wantStatic != m.isStatic())
2150 message = wantStatic ? "expected a static method" : "expected a non-static method";
2151 else
2152 { checkAccess(refKind, refc, m); return; }
2153 throw m.makeAccessException(message, this);
2154 }
2155
2156 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2157 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2158 String message;
2159 if (wantStatic != m.isStatic())
2160 message = wantStatic ? "expected a static field" : "expected a non-static field";
2161 else
2162 { checkAccess(refKind, refc, m); return; }
2163 throw m.makeAccessException(message, this);
2164 }
2165
2166 /** Check public/protected/private bits on the symbolic reference class and its member. */
2167 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2168 assert(m.referenceKindIsConsistentWith(refKind) &&
2169 MethodHandleNatives.refKindIsValid(refKind) &&
2170 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2171 int allowedModes = this.allowedModes;
2172 if (allowedModes == TRUSTED) return;
2173 int mods = m.getModifiers();
2174 if (Modifier.isProtected(mods) &&
2175 refKind == REF_invokeVirtual &&
2176 m.getDeclaringClass() == Object.class &&
2177 m.getName().equals("clone") &&
2178 refc.isArray()) {
2179 // The JVM does this hack also.
2180 // (See ClassVerifier::verify_invoke_instructions
2181 // and LinkResolver::check_method_accessability.)
2182 // Because the JVM does not allow separate methods on array types,
2183 // there is no separate method for int[].clone.
2184 // All arrays simply inherit Object.clone.
2185 // But for access checking logic, we make Object.clone
2186 // (normally protected) appear to be public.
2187 // Later on, when the DirectMethodHandle is created,
2188 // its leading argument will be restricted to the
2189 // requested array type.
2190 // N.B. The return type is not adjusted, because
2191 // that is *not* the bytecode behavior.
2192 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2193 }
2194 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2195 // cannot "new" a protected ctor in a different package
2196 mods ^= Modifier.PROTECTED;
2197 }
2198 if (Modifier.isFinal(mods) &&
2199 MethodHandleNatives.refKindIsSetter(refKind))
2200 throw m.makeAccessException("unexpected set of a final field", this);
2201 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2202 if ((requestedModes & allowedModes) != 0) {
2203 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2204 mods, lookupClass(), allowedModes))
2205 return;
2206 } else {
2207 // Protected members can also be checked as if they were package-private.
2208 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2209 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2210 return;
2211 }
2212 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2213 }
2214
2215 String accessFailedMessage(Class<?> refc, MemberName m) {
2216 Class<?> defc = m.getDeclaringClass();
2217 int mods = m.getModifiers();
2218 // check the class first:
2219 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2220 (defc == refc ||
2221 Modifier.isPublic(refc.getModifiers())));
2222 if (!classOK && (allowedModes & PACKAGE) != 0) {
2223 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2224 (defc == refc ||
2225 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2226 }
2227 if (!classOK)
2228 return "class is not public";
2229 if (Modifier.isPublic(mods))
2230 return "access to public member failed"; // (how?, module not readable?)
2231 if (Modifier.isPrivate(mods))
2232 return "member is private";
2233 if (Modifier.isProtected(mods))
2234 return "member is protected";
2235 return "member is private to package";
2236 }
2237
2238 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2239 int allowedModes = this.allowedModes;
2240 if (allowedModes == TRUSTED) return;
2241 if (!hasPrivateAccess()
2242 || (specialCaller != lookupClass()
2243 // ensure non-abstract methods in superinterfaces can be special-invoked
2244 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2245 throw new MemberName(specialCaller).
2246 makeAccessException("no private access for invokespecial", this);
2247 }
2248
2249 private boolean restrictProtectedReceiver(MemberName method) {
2250 // The accessing class only has the right to use a protected member
2251 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2252 if (!method.isProtected() || method.isStatic()
2253 || allowedModes == TRUSTED
2254 || method.getDeclaringClass() == lookupClass()
2255 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2256 return false;
2257 return true;
2258 }
2259 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2260 assert(!method.isStatic());
2261 // receiver type of mh is too wide; narrow to caller
2262 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2263 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2264 }
2265 MethodType rawType = mh.type();
2266 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2267 MethodType narrowType = rawType.changeParameterType(0, caller);
2268 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2269 assert(mh.viewAsTypeChecks(narrowType, true));
2270 return mh.copyWith(narrowType, mh.form);
2271 }
2272
2273 /** Check access and get the requested method. */
2274 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2275 final boolean doRestrict = true;
2276 final boolean checkSecurity = true;
2277 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2278 }
2279 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2280 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2281 final boolean doRestrict = false;
2282 final boolean checkSecurity = true;
2283 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2284 }
2285 /** Check access and get the requested method, eliding security manager checks. */
2286 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2287 final boolean doRestrict = true;
2288 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2289 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2290 }
2291 /** Common code for all methods; do not call directly except from immediately above. */
2292 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2293 boolean checkSecurity,
2294 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
2295
2296 checkMethod(refKind, refc, method);
2297 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2298 if (checkSecurity)
2299 checkSecurityManager(refc, method);
2300 assert(!method.isMethodHandleInvoke());
2301
2302 if (refKind == REF_invokeSpecial &&
2303 refc != lookupClass() &&
2304 !refc.isInterface() &&
2305 refc != lookupClass().getSuperclass() &&
2306 refc.isAssignableFrom(lookupClass())) {
2307 assert(!method.getName().equals("<init>")); // not this code path
2308
2309 // Per JVMS 6.5, desc. of invokespecial instruction:
2310 // If the method is in a superclass of the LC,
2311 // and if our original search was above LC.super,
2312 // repeat the search (symbolic lookup) from LC.super
2313 // and continue with the direct superclass of that class,
2314 // and so forth, until a match is found or no further superclasses exist.
2315 // FIXME: MemberName.resolve should handle this instead.
2316 Class<?> refcAsSuper = lookupClass();
2317 MemberName m2;
2318 do {
2319 refcAsSuper = refcAsSuper.getSuperclass();
2320 m2 = new MemberName(refcAsSuper,
2321 method.getName(),
2322 method.getMethodType(),
2323 REF_invokeSpecial);
2324 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2325 } while (m2 == null && // no method is found yet
2326 refc != refcAsSuper); // search up to refc
2327 if (m2 == null) throw new InternalError(method.toString());
2328 method = m2;
2329 refc = refcAsSuper;
2330 // redo basic checks
2331 checkMethod(refKind, refc, method);
2332 }
2333
2334 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
2335 MethodHandle mh = dmh;
2336 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
2337 if ((doRestrict && refKind == REF_invokeSpecial) ||
2338 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2339 mh = restrictReceiver(method, dmh, lookupClass());
2340 }
2341 mh = maybeBindCaller(method, mh, boundCallerClass);
2342 mh = mh.setVarargs(method);
2343 return mh;
2344 }
2345 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2346 Class<?> boundCallerClass)
2347 throws IllegalAccessException {
2348 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2349 return mh;
2350 Class<?> hostClass = lookupClass;
2351 if (!hasPrivateAccess()) // caller must have private access
2352 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
2353 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2354 // Note: caller will apply varargs after this step happens.
2355 return cbmh;
2356 }
2357 /** Check access and get the requested field. */
2358 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2359 final boolean checkSecurity = true;
2360 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2361 }
2362 /** Check access and get the requested field, eliding security manager checks. */
2363 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2364 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2365 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2366 }
2367 /** Common code for all fields; do not call directly except from immediately above. */
2368 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2369 boolean checkSecurity) throws IllegalAccessException {
2370 checkField(refKind, refc, field);
2371 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2372 if (checkSecurity)
2373 checkSecurityManager(refc, field);
2374 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2375 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2376 restrictProtectedReceiver(field));
2377 if (doRestrict)
2378 return restrictReceiver(field, dmh, lookupClass());
2379 return dmh;
2380 }
2381 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2382 Class<?> refc, MemberName getField, MemberName putField)
2383 throws IllegalAccessException {
2384 final boolean checkSecurity = true;
2385 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2386 }
2387 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2388 Class<?> refc, MemberName getField, MemberName putField)
2389 throws IllegalAccessException {
2390 final boolean checkSecurity = false;
2391 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2392 }
2393 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2394 Class<?> refc, MemberName getField, MemberName putField,
2395 boolean checkSecurity) throws IllegalAccessException {
2396 assert getField.isStatic() == putField.isStatic();
2397 assert getField.isGetter() && putField.isSetter();
2398 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2399 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2400
2401 checkField(getRefKind, refc, getField);
2402 if (checkSecurity)
2403 checkSecurityManager(refc, getField);
2404
2405 if (!putField.isFinal()) {
2406 // A VarHandle does not support updates to final fields, any
2407 // such VarHandle to a final field will be read-only and
2408 // therefore the following write-based accessibility checks are
2409 // only required for non-final fields
2410 checkField(putRefKind, refc, putField);
2411 if (checkSecurity)
2412 checkSecurityManager(refc, putField);
2413 }
2414
2415 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2416 restrictProtectedReceiver(getField));
2417 if (doRestrict) {
2418 assert !getField.isStatic();
2419 // receiver type of VarHandle is too wide; narrow to caller
2420 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2421 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2422 }
2423 refc = lookupClass();
2424 }
2425 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2426 }
2427 /** Check access and get the requested constructor. */
2428 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2429 final boolean checkSecurity = true;
2430 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2431 }
2432 /** Check access and get the requested constructor, eliding security manager checks. */
2433 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2434 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2435 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2436 }
2437 /** Common code for all constructors; do not call directly except from immediately above. */
2438 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2439 boolean checkSecurity) throws IllegalAccessException {
2440 assert(ctor.isConstructor());
2441 checkAccess(REF_newInvokeSpecial, refc, ctor);
2442 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2443 if (checkSecurity)
2444 checkSecurityManager(refc, ctor);
2445 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2446 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2447 }
2448
2449 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2450 */
2451 /*non-public*/
2452 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2453 if (!(type instanceof Class || type instanceof MethodType))
2454 throw new InternalError("unresolved MemberName");
2455 MemberName member = new MemberName(refKind, defc, name, type);
2456 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2457 if (mh != null) {
2458 checkSymbolicClass(defc);
2459 return mh;
2460 }
2461 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2462 // Treat MethodHandle.invoke and invokeExact specially.
2463 mh = findVirtualForMH(member.getName(), member.getMethodType());
2464 if (mh != null) {
2465 return mh;
2466 }
2467 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
2468 // Treat signature-polymorphic methods on VarHandle specially.
2469 mh = findVirtualForVH(member.getName(), member.getMethodType());
2470 if (mh != null) {
2471 return mh;
2472 }
2473 }
2474 MemberName resolved = resolveOrFail(refKind, member);
2475 mh = getDirectMethodForConstant(refKind, defc, resolved);
2476 if (mh instanceof DirectMethodHandle
2477 && canBeCached(refKind, defc, resolved)) {
2478 MemberName key = mh.internalMemberName();
2479 if (key != null) {
2480 key = key.asNormalOriginal();
2481 }
2482 if (member.equals(key)) { // better safe than sorry
2483 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2484 }
2485 }
2486 return mh;
2487 }
2488 private
2489 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2490 if (refKind == REF_invokeSpecial) {
2491 return false;
2492 }
2493 if (!Modifier.isPublic(defc.getModifiers()) ||
2494 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2495 !member.isPublic() ||
2496 member.isCallerSensitive()) {
2497 return false;
2498 }
2499 ClassLoader loader = defc.getClassLoader();
2500 if (loader != null) {
2501 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2502 boolean found = false;
2503 while (sysl != null) {
2504 if (loader == sysl) { found = true; break; }
2505 sysl = sysl.getParent();
2506 }
2507 if (!found) {
2508 return false;
2509 }
2510 }
2511 try {
2512 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
2513 new MemberName(refKind, defc, member.getName(), member.getType()));
2514 if (resolved2 == null) {
2515 return false;
2516 }
2517 checkSecurityManager(defc, resolved2);
2518 } catch (SecurityException ex) {
2519 return false;
2520 }
2521 return true;
2522 }
2523 private
2524 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2525 throws ReflectiveOperationException {
2526 if (MethodHandleNatives.refKindIsField(refKind)) {
2527 return getDirectFieldNoSecurityManager(refKind, defc, member);
2528 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2529 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2530 } else if (refKind == REF_newInvokeSpecial) {
2531 return getDirectConstructorNoSecurityManager(defc, member);
2532 }
2533 // oops
2534 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2535 }
2536
2537 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2538 }
2539
2540 /**
2541 * Produces a method handle constructing arrays of a desired type,
2542 * as if by the {@code anewarray} bytecode.
2543 * The return type of the method handle will be the array type.
2544 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2545 *
2546 * <p> If the returned method handle is invoked with a negative
2547 * array size, a {@code NegativeArraySizeException} will be thrown.
2548 *
2549 * @param arrayClass an array type
2550 * @return a method handle which can create arrays of the given type
2551 * @throws NullPointerException if the argument is {@code null}
2552 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2553 * @see java.lang.reflect.Array#newInstance(Class, int)
2554 * @jvms 6.5 {@code anewarray} Instruction
2555 * @since 9
2556 */
2557 public static
2558 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2559 if (!arrayClass.isArray()) {
2560 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2561 }
2562 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2563 bindTo(arrayClass.getComponentType());
2564 return ani.asType(ani.type().changeReturnType(arrayClass));
2565 }
2566
2567 /**
2568 * Produces a method handle returning the length of an array,
2569 * as if by the {@code arraylength} bytecode.
2570 * The type of the method handle will have {@code int} as return type,
2571 * and its sole argument will be the array type.
2572 *
2573 * <p> If the returned method handle is invoked with a {@code null}
2574 * array reference, a {@code NullPointerException} will be thrown.
2575 *
2576 * @param arrayClass an array type
2577 * @return a method handle which can retrieve the length of an array of the given array type
2578 * @throws NullPointerException if the argument is {@code null}
2579 * @throws IllegalArgumentException if arrayClass is not an array type
2580 * @jvms 6.5 {@code arraylength} Instruction
2581 * @since 9
2582 */
2583 public static
2584 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2585 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2586 }
2587
2588 /**
2589 * Produces a method handle giving read access to elements of an array,
2590 * as if by the {@code aaload} bytecode.
2591 * The type of the method handle will have a return type of the array's
2592 * element type. Its first argument will be the array type,
2593 * and the second will be {@code int}.
2594 *
2595 * <p> When the returned method handle is invoked,
2596 * the array reference and array index are checked.
2597 * A {@code NullPointerException} will be thrown if the array reference
2598 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2599 * thrown if the index is negative or if it is greater than or equal to
2600 * the length of the array.
2601 *
2602 * @param arrayClass an array type
2603 * @return a method handle which can load values from the given array type
2604 * @throws NullPointerException if the argument is null
2605 * @throws IllegalArgumentException if arrayClass is not an array type
2606 * @jvms 6.5 {@code aaload} Instruction
2607 */
2608 public static
2609 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2610 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2611 }
2612
2613 /**
2614 * Produces a method handle giving write access to elements of an array,
2615 * as if by the {@code astore} bytecode.
2616 * The type of the method handle will have a void return type.
2617 * Its last argument will be the array's element type.
2618 * The first and second arguments will be the array type and int.
2619 *
2620 * <p> When the returned method handle is invoked,
2621 * the array reference and array index are checked.
2622 * A {@code NullPointerException} will be thrown if the array reference
2623 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2624 * thrown if the index is negative or if it is greater than or equal to
2625 * the length of the array.
2626 *
2627 * @param arrayClass the class of an array
2628 * @return a method handle which can store values into the array type
2629 * @throws NullPointerException if the argument is null
2630 * @throws IllegalArgumentException if arrayClass is not an array type
2631 * @jvms 6.5 {@code aastore} Instruction
2632 */
2633 public static
2634 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2635 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2636 }
2637
2638 /**
2639 * Produces a VarHandle giving access to elements of an array of type
2640 * {@code arrayClass}. The VarHandle's variable type is the component type
2641 * of {@code arrayClass} and the list of coordinate types is
2642 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2643 * corresponds to an argument that is an index into an array.
2644 * <p>
2645 * Certain access modes of the returned VarHandle are unsupported under
2646 * the following conditions:
2647 * <ul>
2648 * <li>if the component type is anything other than {@code byte},
2649 * {@code short}, {@code char}, {@code int}, {@code long},
2650 * {@code float}, or {@code double} then numeric atomic update access
2651 * modes are unsupported.
2652 * <li>if the field type is anything other than {@code boolean},
2653 * {@code byte}, {@code short}, {@code char}, {@code int} or
2654 * {@code long} then bitwise atomic update access modes are
2655 * unsupported.
2656 * </ul>
2657 * <p>
2658 * If the component type is {@code float} or {@code double} then numeric
2659 * and atomic update access modes compare values using their bitwise
2660 * representation (see {@link Float#floatToRawIntBits} and
2661 * {@link Double#doubleToRawLongBits}, respectively).
2662 *
2663 * <p> When the returned {@code VarHandle} is invoked,
2664 * the array reference and array index are checked.
2665 * A {@code NullPointerException} will be thrown if the array reference
2666 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2667 * thrown if the index is negative or if it is greater than or equal to
2668 * the length of the array.
2669 *
2670 * @apiNote
2671 * Bitwise comparison of {@code float} values or {@code double} values,
2672 * as performed by the numeric and atomic update access modes, differ
2673 * from the primitive {@code ==} operator and the {@link Float#equals}
2674 * and {@link Double#equals} methods, specifically with respect to
2675 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2676 * Care should be taken when performing a compare and set or a compare
2677 * and exchange operation with such values since the operation may
2678 * unexpectedly fail.
2679 * There are many possible NaN values that are considered to be
2680 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2681 * provided by Java can distinguish between them. Operation failure can
2682 * occur if the expected or witness value is a NaN value and it is
2683 * transformed (perhaps in a platform specific manner) into another NaN
2684 * value, and thus has a different bitwise representation (see
2685 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2686 * details).
2687 * The values {@code -0.0} and {@code +0.0} have different bitwise
2688 * representations but are considered equal when using the primitive
2689 * {@code ==} operator. Operation failure can occur if, for example, a
2690 * numeric algorithm computes an expected value to be say {@code -0.0}
2691 * and previously computed the witness value to be say {@code +0.0}.
2692 * @param arrayClass the class of an array, of type {@code T[]}
2693 * @return a VarHandle giving access to elements of an array
2694 * @throws NullPointerException if the arrayClass is null
2695 * @throws IllegalArgumentException if arrayClass is not an array type
2696 * @since 9
2697 */
2698 public static
2699 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2700 return VarHandles.makeArrayElementHandle(arrayClass);
2701 }
2702
2703 /**
2704 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2705 * viewed as if it were a different primitive array type, such as
2706 * {@code int[]} or {@code long[]}.
2707 * The VarHandle's variable type is the component type of
2708 * {@code viewArrayClass} and the list of coordinate types is
2709 * {@code (byte[], int)}, where the {@code int} coordinate type
2710 * corresponds to an argument that is an index into a {@code byte[]} array.
2711 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2712 * array, composing bytes to or from a value of the component type of
2713 * {@code viewArrayClass} according to the given endianness.
2714 * <p>
2715 * The supported component types (variables types) are {@code short},
2716 * {@code char}, {@code int}, {@code long}, {@code float} and
2717 * {@code double}.
2718 * <p>
2719 * Access of bytes at a given index will result in an
2720 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2721 * or greater than the {@code byte[]} array length minus the size (in bytes)
2722 * of {@code T}.
2723 * <p>
2724 * Access of bytes at an index may be aligned or misaligned for {@code T},
2725 * with respect to the underlying memory address, {@code A} say, associated
2726 * with the array and index.
2727 * If access is misaligned then access for anything other than the
2728 * {@code get} and {@code set} access modes will result in an
2729 * {@code IllegalStateException}. In such cases atomic access is only
2730 * guaranteed with respect to the largest power of two that divides the GCD
2731 * of {@code A} and the size (in bytes) of {@code T}.
2732 * If access is aligned then following access modes are supported and are
2733 * guaranteed to support atomic access:
2734 * <ul>
2735 * <li>read write access modes for all {@code T}, with the exception of
2736 * access modes {@code get} and {@code set} for {@code long} and
2737 * {@code double} on 32-bit platforms.
2738 * <li>atomic update access modes for {@code int}, {@code long},
2739 * {@code float} or {@code double}.
2740 * (Future major platform releases of the JDK may support additional
2741 * types for certain currently unsupported access modes.)
2742 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2743 * (Future major platform releases of the JDK may support additional
2744 * numeric types for certain currently unsupported access modes.)
2745 * <li>bitwise 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 * </ul>
2749 * <p>
2750 * Misaligned access, and therefore atomicity guarantees, may be determined
2751 * for {@code byte[]} arrays without operating on a specific array. Given
2752 * an {@code index}, {@code T} and it's corresponding boxed type,
2753 * {@code T_BOX}, misalignment may be determined as follows:
2754 * <pre>{@code
2755 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2756 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2757 * alignmentOffset(0, sizeOfT);
2758 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2759 * boolean isMisaligned = misalignedAtIndex != 0;
2760 * }</pre>
2761 * <p>
2762 * If the variable type is {@code float} or {@code double} then atomic
2763 * update access modes compare values using their bitwise representation
2764 * (see {@link Float#floatToRawIntBits} and
2765 * {@link Double#doubleToRawLongBits}, respectively).
2766 * @param viewArrayClass the view array class, with a component type of
2767 * type {@code T}
2768 * @param byteOrder the endianness of the view array elements, as
2769 * stored in the underlying {@code byte} array
2770 * @return a VarHandle giving access to elements of a {@code byte[]} array
2771 * viewed as if elements corresponding to the components type of the view
2772 * array class
2773 * @throws NullPointerException if viewArrayClass or byteOrder is null
2774 * @throws IllegalArgumentException if viewArrayClass is not an array type
2775 * @throws UnsupportedOperationException if the component type of
2776 * viewArrayClass is not supported as a variable type
2777 * @since 9
2778 */
2779 public static
2780 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2781 ByteOrder byteOrder) throws IllegalArgumentException {
2782 Objects.requireNonNull(byteOrder);
2783 return VarHandles.byteArrayViewHandle(viewArrayClass,
2784 byteOrder == ByteOrder.BIG_ENDIAN);
2785 }
2786
2787 /**
2788 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2789 * viewed as if it were an array of elements of a different primitive
2790 * component type to that of {@code byte}, such as {@code int[]} or
2791 * {@code long[]}.
2792 * The VarHandle's variable type is the component type of
2793 * {@code viewArrayClass} and the list of coordinate types is
2794 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2795 * corresponds to an argument that is an index into a {@code byte[]} array.
2796 * The returned VarHandle accesses bytes at an index in a
2797 * {@code ByteBuffer}, composing bytes to or from a value of the component
2798 * type of {@code viewArrayClass} according to the given endianness.
2799 * <p>
2800 * The supported component types (variables types) are {@code short},
2801 * {@code char}, {@code int}, {@code long}, {@code float} and
2802 * {@code double}.
2803 * <p>
2804 * Access will result in a {@code ReadOnlyBufferException} for anything
2805 * other than the read access modes if the {@code ByteBuffer} is read-only.
2806 * <p>
2807 * Access of bytes at a given index will result in an
2808 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2809 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2810 * {@code T}.
2811 * <p>
2812 * Access of bytes at an index may be aligned or misaligned for {@code T},
2813 * with respect to the underlying memory address, {@code A} say, associated
2814 * with the {@code ByteBuffer} and index.
2815 * If access is misaligned then access for anything other than the
2816 * {@code get} and {@code set} access modes will result in an
2817 * {@code IllegalStateException}. In such cases atomic access is only
2818 * guaranteed with respect to the largest power of two that divides the GCD
2819 * of {@code A} and the size (in bytes) of {@code T}.
2820 * If access is aligned then following access modes are supported and are
2821 * guaranteed to support atomic access:
2822 * <ul>
2823 * <li>read write access modes for all {@code T}, with the exception of
2824 * access modes {@code get} and {@code set} for {@code long} and
2825 * {@code double} on 32-bit platforms.
2826 * <li>atomic update access modes for {@code int}, {@code long},
2827 * {@code float} or {@code double}.
2828 * (Future major platform releases of the JDK may support additional
2829 * types for certain currently unsupported access modes.)
2830 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2831 * (Future major platform releases of the JDK may support additional
2832 * numeric types for certain currently unsupported access modes.)
2833 * <li>bitwise 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 * </ul>
2837 * <p>
2838 * Misaligned access, and therefore atomicity guarantees, may be determined
2839 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2840 * {@code index}, {@code T} and it's corresponding boxed type,
2841 * {@code T_BOX}, as follows:
2842 * <pre>{@code
2843 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2844 * ByteBuffer bb = ...
2845 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2846 * boolean isMisaligned = misalignedAtIndex != 0;
2847 * }</pre>
2848 * <p>
2849 * If the variable type is {@code float} or {@code double} then atomic
2850 * update access modes compare values using their bitwise representation
2851 * (see {@link Float#floatToRawIntBits} and
2852 * {@link Double#doubleToRawLongBits}, respectively).
2853 * @param viewArrayClass the view array class, with a component type of
2854 * type {@code T}
2855 * @param byteOrder the endianness of the view array elements, as
2856 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2857 * endianness of a {@code ByteBuffer})
2858 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2859 * viewed as if elements corresponding to the components type of the view
2860 * array class
2861 * @throws NullPointerException if viewArrayClass or byteOrder is null
2862 * @throws IllegalArgumentException if viewArrayClass is not an array type
2863 * @throws UnsupportedOperationException if the component type of
2864 * viewArrayClass is not supported as a variable type
2865 * @since 9
2866 */
2867 public static
2868 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2869 ByteOrder byteOrder) throws IllegalArgumentException {
2870 Objects.requireNonNull(byteOrder);
2871 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2872 byteOrder == ByteOrder.BIG_ENDIAN);
2873 }
2874
2875
2876 /// method handle invocation (reflective style)
2877
2878 /**
2879 * Produces a method handle which will invoke any method handle of the
2880 * given {@code type}, with a given number of trailing arguments replaced by
2881 * a single trailing {@code Object[]} array.
2882 * The resulting invoker will be a method handle with the following
2883 * arguments:
2884 * <ul>
2885 * <li>a single {@code MethodHandle} target
2886 * <li>zero or more leading values (counted by {@code leadingArgCount})
2887 * <li>an {@code Object[]} array containing trailing arguments
2888 * </ul>
2889 * <p>
2890 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2891 * the indicated {@code type}.
2892 * That is, if the target is exactly of the given {@code type}, it will behave
2893 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2894 * is used to convert the target to the required {@code type}.
2895 * <p>
2896 * The type of the returned invoker will not be the given {@code type}, but rather
2897 * will have all parameters except the first {@code leadingArgCount}
2898 * replaced by a single array of type {@code Object[]}, which will be
2899 * the final parameter.
2900 * <p>
2901 * Before invoking its target, the invoker will spread the final array, apply
2902 * reference casts as necessary, and unbox and widen primitive arguments.
2903 * If, when the invoker is called, the supplied array argument does
2904 * not have the correct number of elements, the invoker will throw
2905 * an {@link IllegalArgumentException} instead of invoking the target.
2906 * <p>
2907 * This method is equivalent to the following code (though it may be more efficient):
2908 * <blockquote><pre>{@code
2909 MethodHandle invoker = MethodHandles.invoker(type);
2910 int spreadArgCount = type.parameterCount() - leadingArgCount;
2911 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2912 return invoker;
2913 * }</pre></blockquote>
2914 * This method throws no reflective or security exceptions.
2915 * @param type the desired target type
2916 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2917 * @return a method handle suitable for invoking any method handle of the given type
2918 * @throws NullPointerException if {@code type} is null
2919 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2920 * the range from 0 to {@code type.parameterCount()} inclusive,
2921 * or if the resulting method handle's type would have
2922 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2923 */
2924 public static
2925 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2926 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2927 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2928 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2929 return type.invokers().spreadInvoker(leadingArgCount);
2930 }
2931
2932 /**
2933 * Produces a special <em>invoker method handle</em> which can be used to
2934 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2935 * The resulting invoker will have a type which is
2936 * exactly equal to the desired type, except that it will accept
2937 * an additional leading argument of type {@code MethodHandle}.
2938 * <p>
2939 * This method is equivalent to the following code (though it may be more efficient):
2940 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2941 *
2942 * <p style="font-size:smaller;">
2943 * <em>Discussion:</em>
2944 * Invoker method handles can be useful when working with variable method handles
2945 * of unknown types.
2946 * For example, to emulate an {@code invokeExact} call to a variable method
2947 * handle {@code M}, extract its type {@code T},
2948 * look up the invoker method {@code X} for {@code T},
2949 * and call the invoker method, as {@code X.invoke(T, A...)}.
2950 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2951 * is unknown.)
2952 * If spreading, collecting, or other argument transformations are required,
2953 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2954 * method handle values, as long as they are compatible with the type of {@code X}.
2955 * <p style="font-size:smaller;">
2956 * <em>(Note: The invoker method is not available via the Core Reflection API.
2957 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2958 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2959 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2960 * <p>
2961 * This method throws no reflective or security exceptions.
2962 * @param type the desired target type
2963 * @return a method handle suitable for invoking any method handle of the given type
2964 * @throws IllegalArgumentException if the resulting method handle's type would have
2965 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2966 */
2967 public static
2968 MethodHandle exactInvoker(MethodType type) {
2969 return type.invokers().exactInvoker();
2970 }
2971
2972 /**
2973 * Produces a special <em>invoker method handle</em> which can be used to
2974 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2975 * The resulting invoker will have a type which is
2976 * exactly equal to the desired type, except that it will accept
2977 * an additional leading argument of type {@code MethodHandle}.
2978 * <p>
2979 * Before invoking its target, if the target differs from the expected type,
2980 * the invoker will apply reference casts as
2981 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2982 * Similarly, the return value will be converted as necessary.
2983 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2984 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2985 * <p>
2986 * This method is equivalent to the following code (though it may be more efficient):
2987 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2988 * <p style="font-size:smaller;">
2989 * <em>Discussion:</em>
2990 * A {@linkplain MethodType#genericMethodType general method type} is one which
2991 * mentions only {@code Object} arguments and return values.
2992 * An invoker for such a type is capable of calling any method handle
2993 * of the same arity as the general type.
2994 * <p style="font-size:smaller;">
2995 * <em>(Note: The invoker method is not available via the Core Reflection API.
2996 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2997 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2998 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2999 * <p>
3000 * This method throws no reflective or security exceptions.
3001 * @param type the desired target type
3002 * @return a method handle suitable for invoking any method handle convertible to the given type
3003 * @throws IllegalArgumentException if the resulting method handle's type would have
3004 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3005 */
3006 public static
3007 MethodHandle invoker(MethodType type) {
3008 return type.invokers().genericInvoker();
3009 }
3010
3011 /**
3012 * Produces a special <em>invoker method handle</em> which can be used to
3013 * invoke a signature-polymorphic access mode method on any VarHandle whose
3014 * associated access mode type is compatible with the given type.
3015 * The resulting invoker will have a type which is exactly equal to the
3016 * desired given type, except that it will accept an additional leading
3017 * argument of type {@code VarHandle}.
3018 *
3019 * @param accessMode the VarHandle access mode
3020 * @param type the desired target type
3021 * @return a method handle suitable for invoking an access mode method of
3022 * any VarHandle whose access mode type is of the given type.
3023 * @since 9
3024 */
3025 static public
3026 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3027 return type.invokers().varHandleMethodExactInvoker(accessMode);
3028 }
3029
3030 /**
3031 * Produces a special <em>invoker method handle</em> which can be used to
3032 * invoke a signature-polymorphic access mode method on any VarHandle whose
3033 * associated access mode type is compatible with the given type.
3034 * The resulting invoker will have a type which is exactly equal to the
3035 * desired given type, except that it will accept an additional leading
3036 * argument of type {@code VarHandle}.
3037 * <p>
3038 * Before invoking its target, if the access mode type differs from the
3039 * desired given type, the invoker will apply reference casts as necessary
3040 * and box, unbox, or widen primitive values, as if by
3041 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3042 * converted as necessary.
3043 * <p>
3044 * This method is equivalent to the following code (though it may be more
3045 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3046 *
3047 * @param accessMode the VarHandle access mode
3048 * @param type the desired target type
3049 * @return a method handle suitable for invoking an access mode method of
3050 * any VarHandle whose access mode type is convertible to the given
3051 * type.
3052 * @since 9
3053 */
3054 static public
3055 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3056 return type.invokers().varHandleMethodInvoker(accessMode);
3057 }
3058
3059 static /*non-public*/
3060 MethodHandle basicInvoker(MethodType type) {
3061 return type.invokers().basicInvoker();
3062 }
3063
3064 /// method handle modification (creation from other method handles)
3065
3066 /**
3067 * Produces a method handle which adapts the type of the
3068 * given method handle to a new type by pairwise argument and return type conversion.
3069 * The original type and new type must have the same number of arguments.
3070 * The resulting method handle is guaranteed to report a type
3071 * which is equal to the desired new type.
3072 * <p>
3073 * If the original type and new type are equal, returns target.
3074 * <p>
3075 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3076 * and some additional conversions are also applied if those conversions fail.
3077 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3078 * if possible, before or instead of any conversions done by {@code asType}:
3079 * <ul>
3080 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3081 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3082 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3083 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3084 * the boolean is converted to a byte value, 1 for true, 0 for false.
3085 * (This treatment follows the usage of the bytecode verifier.)
3086 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3087 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3088 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3089 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3090 * then a Java casting conversion (JLS 5.5) is applied.
3091 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3092 * widening and/or narrowing.)
3093 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3094 * conversion will be applied at runtime, possibly followed
3095 * by a Java casting conversion (JLS 5.5) on the primitive value,
3096 * possibly followed by a conversion from byte to boolean by testing
3097 * the low-order bit.
3098 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3099 * and if the reference is null at runtime, a zero value is introduced.
3100 * </ul>
3101 * @param target the method handle to invoke after arguments are retyped
3102 * @param newType the expected type of the new method handle
3103 * @return a method handle which delegates to the target after performing
3104 * any necessary argument conversions, and arranges for any
3105 * necessary return value conversions
3106 * @throws NullPointerException if either argument is null
3107 * @throws WrongMethodTypeException if the conversion cannot be made
3108 * @see MethodHandle#asType
3109 */
3110 public static
3111 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3112 explicitCastArgumentsChecks(target, newType);
3113 // use the asTypeCache when possible:
3114 MethodType oldType = target.type();
3115 if (oldType == newType) return target;
3116 if (oldType.explicitCastEquivalentToAsType(newType)) {
3117 return target.asFixedArity().asType(newType);
3118 }
3119 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3120 }
3121
3122 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3123 if (target.type().parameterCount() != newType.parameterCount()) {
3124 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3125 }
3126 }
3127
3128 /**
3129 * Produces a method handle which adapts the calling sequence of the
3130 * given method handle to a new type, by reordering the arguments.
3131 * The resulting method handle is guaranteed to report a type
3132 * which is equal to the desired new type.
3133 * <p>
3134 * The given array controls the reordering.
3135 * Call {@code #I} the number of incoming parameters (the value
3136 * {@code newType.parameterCount()}, and call {@code #O} the number
3137 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3138 * Then the length of the reordering array must be {@code #O},
3139 * and each element must be a non-negative number less than {@code #I}.
3140 * For every {@code N} less than {@code #O}, the {@code N}-th
3141 * outgoing argument will be taken from the {@code I}-th incoming
3142 * argument, where {@code I} is {@code reorder[N]}.
3143 * <p>
3144 * No argument or return value conversions are applied.
3145 * The type of each incoming argument, as determined by {@code newType},
3146 * must be identical to the type of the corresponding outgoing parameter
3147 * or parameters in the target method handle.
3148 * The return type of {@code newType} must be identical to the return
3149 * type of the original target.
3150 * <p>
3151 * The reordering array need not specify an actual permutation.
3152 * An incoming argument will be duplicated if its index appears
3153 * more than once in the array, and an incoming argument will be dropped
3154 * if its index does not appear in the array.
3155 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3156 * incoming arguments which are not mentioned in the reordering array
3157 * may be of any type, as determined only by {@code newType}.
3158 * <blockquote><pre>{@code
3159 import static java.lang.invoke.MethodHandles.*;
3160 import static java.lang.invoke.MethodType.*;
3161 ...
3162 MethodType intfn1 = methodType(int.class, int.class);
3163 MethodType intfn2 = methodType(int.class, int.class, int.class);
3164 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3165 assert(sub.type().equals(intfn2));
3166 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3167 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3168 assert((int)rsub.invokeExact(1, 100) == 99);
3169 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3170 assert(add.type().equals(intfn2));
3171 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3172 assert(twice.type().equals(intfn1));
3173 assert((int)twice.invokeExact(21) == 42);
3174 * }</pre></blockquote>
3175 * <p>
3176 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3177 * variable-arity method handle}, even if the original target method handle was.
3178 * @param target the method handle to invoke after arguments are reordered
3179 * @param newType the expected type of the new method handle
3180 * @param reorder an index array which controls the reordering
3181 * @return a method handle which delegates to the target after it
3182 * drops unused arguments and moves and/or duplicates the other arguments
3183 * @throws NullPointerException if any argument is null
3184 * @throws IllegalArgumentException if the index array length is not equal to
3185 * the arity of the target, or if any index array element
3186 * not a valid index for a parameter of {@code newType},
3187 * or if two corresponding parameter types in
3188 * {@code target.type()} and {@code newType} are not identical,
3189 */
3190 public static
3191 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3192 reorder = reorder.clone(); // get a private copy
3193 MethodType oldType = target.type();
3194 permuteArgumentChecks(reorder, newType, oldType);
3195 // first detect dropped arguments and handle them separately
3196 int[] originalReorder = reorder;
3197 BoundMethodHandle result = target.rebind();
3198 LambdaForm form = result.form;
3199 int newArity = newType.parameterCount();
3200 // Normalize the reordering into a real permutation,
3201 // by removing duplicates and adding dropped elements.
3202 // This somewhat improves lambda form caching, as well
3203 // as simplifying the transform by breaking it up into steps.
3204 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3205 if (ddIdx > 0) {
3206 // We found a duplicated entry at reorder[ddIdx].
3207 // Example: (x,y,z)->asList(x,y,z)
3208 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3209 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3210 // The starred element corresponds to the argument
3211 // deleted by the dupArgumentForm transform.
3212 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3213 boolean killFirst = false;
3214 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3215 // Set killFirst if the dup is larger than an intervening position.
3216 // This will remove at least one inversion from the permutation.
3217 if (dupVal > val) killFirst = true;
3218 }
3219 if (!killFirst) {
3220 srcPos = dstPos;
3221 dstPos = ddIdx;
3222 }
3223 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3224 assert (reorder[srcPos] == reorder[dstPos]);
3225 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3226 // contract the reordering by removing the element at dstPos
3227 int tailPos = dstPos + 1;
3228 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3229 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3230 } else {
3231 int dropVal = ~ddIdx, insPos = 0;
3232 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3233 // Find first element of reorder larger than dropVal.
3234 // This is where we will insert the dropVal.
3235 insPos += 1;
3236 }
3237 Class<?> ptype = newType.parameterType(dropVal);
3238 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3239 oldType = oldType.insertParameterTypes(insPos, ptype);
3240 // expand the reordering by inserting an element at insPos
3241 int tailPos = insPos + 1;
3242 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3243 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3244 reorder[insPos] = dropVal;
3245 }
3246 assert (permuteArgumentChecks(reorder, newType, oldType));
3247 }
3248 assert (reorder.length == newArity); // a perfect permutation
3249 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3250 form = form.editor().permuteArgumentsForm(1, reorder);
3251 if (newType == result.type() && form == result.internalForm())
3252 return result;
3253 return result.copyWith(newType, form);
3254 }
3255
3256 /**
3257 * Return an indication of any duplicate or omission in reorder.
3258 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3259 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3260 * Otherwise, return zero.
3261 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3262 */
3263 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3264 final int BIT_LIMIT = 63; // max number of bits in bit mask
3265 if (newArity < BIT_LIMIT) {
3266 long mask = 0;
3267 for (int i = 0; i < reorder.length; i++) {
3268 int arg = reorder[i];
3269 if (arg >= newArity) {
3270 return reorder.length;
3271 }
3272 long bit = 1L << arg;
3273 if ((mask & bit) != 0) {
3274 return i; // >0 indicates a dup
3275 }
3276 mask |= bit;
3277 }
3278 if (mask == (1L << newArity) - 1) {
3279 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3280 return 0;
3281 }
3282 // find first zero
3283 long zeroBit = Long.lowestOneBit(~mask);
3284 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3285 assert(zeroPos <= newArity);
3286 if (zeroPos == newArity) {
3287 return 0;
3288 }
3289 return ~zeroPos;
3290 } else {
3291 // same algorithm, different bit set
3292 BitSet mask = new BitSet(newArity);
3293 for (int i = 0; i < reorder.length; i++) {
3294 int arg = reorder[i];
3295 if (arg >= newArity) {
3296 return reorder.length;
3297 }
3298 if (mask.get(arg)) {
3299 return i; // >0 indicates a dup
3300 }
3301 mask.set(arg);
3302 }
3303 int zeroPos = mask.nextClearBit(0);
3304 assert(zeroPos <= newArity);
3305 if (zeroPos == newArity) {
3306 return 0;
3307 }
3308 return ~zeroPos;
3309 }
3310 }
3311
3312 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3313 if (newType.returnType() != oldType.returnType())
3314 throw newIllegalArgumentException("return types do not match",
3315 oldType, newType);
3316 if (reorder.length == oldType.parameterCount()) {
3317 int limit = newType.parameterCount();
3318 boolean bad = false;
3319 for (int j = 0; j < reorder.length; j++) {
3320 int i = reorder[j];
3321 if (i < 0 || i >= limit) {
3322 bad = true; break;
3323 }
3324 Class<?> src = newType.parameterType(i);
3325 Class<?> dst = oldType.parameterType(j);
3326 if (src != dst)
3327 throw newIllegalArgumentException("parameter types do not match after reorder",
3328 oldType, newType);
3329 }
3330 if (!bad) return true;
3331 }
3332 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3333 }
3334
3335 /**
3336 * Produces a method handle of the requested return type which returns the given
3337 * constant value every time it is invoked.
3338 * <p>
3339 * Before the method handle is returned, the passed-in value is converted to the requested type.
3340 * If the requested type is primitive, widening primitive conversions are attempted,
3341 * else reference conversions are attempted.
3342 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3343 * @param type the return type of the desired method handle
3344 * @param value the value to return
3345 * @return a method handle of the given return type and no arguments, which always returns the given value
3346 * @throws NullPointerException if the {@code type} argument is null
3347 * @throws ClassCastException if the value cannot be converted to the required return type
3348 * @throws IllegalArgumentException if the given type is {@code void.class}
3349 */
3350 public static
3351 MethodHandle constant(Class<?> type, Object value) {
3352 if (type.isPrimitive()) {
3353 if (type == void.class)
3354 throw newIllegalArgumentException("void type");
3355 Wrapper w = Wrapper.forPrimitiveType(type);
3356 value = w.convert(value, type);
3357 if (w.zero().equals(value))
3358 return zero(w, type);
3359 return insertArguments(identity(type), 0, value);
3360 } else {
3361 if (value == null)
3362 return zero(Wrapper.OBJECT, type);
3363 return identity(type).bindTo(value);
3364 }
3365 }
3366
3367 /**
3368 * Produces a method handle which returns its sole argument when invoked.
3369 * @param type the type of the sole parameter and return value of the desired method handle
3370 * @return a unary method handle which accepts and returns the given type
3371 * @throws NullPointerException if the argument is null
3372 * @throws IllegalArgumentException if the given type is {@code void.class}
3373 */
3374 public static
3375 MethodHandle identity(Class<?> type) {
3376 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3377 int pos = btw.ordinal();
3378 MethodHandle ident = IDENTITY_MHS[pos];
3379 if (ident == null) {
3380 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3381 }
3382 if (ident.type().returnType() == type)
3383 return ident;
3384 // something like identity(Foo.class); do not bother to intern these
3385 assert (btw == Wrapper.OBJECT);
3386 return makeIdentity(type);
3387 }
3388
3389 /**
3390 * Produces a constant method handle of the requested return type which
3391 * returns the default value for that type every time it is invoked.
3392 * The resulting constant method handle will have no side effects.
3393 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3394 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3395 * since {@code explicitCastArguments} converts {@code null} to default values.
3396 * @param type the expected return type of the desired method handle
3397 * @return a constant method handle that takes no arguments
3398 * and returns the default value of the given type (or void, if the type is void)
3399 * @throws NullPointerException if the argument is null
3400 * @see MethodHandles#constant
3401 * @see MethodHandles#empty
3402 * @see MethodHandles#explicitCastArguments
3403 * @since 9
3404 */
3405 public static MethodHandle zero(Class<?> type) {
3406 Objects.requireNonNull(type);
3407 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3408 }
3409
3410 private static MethodHandle identityOrVoid(Class<?> type) {
3411 return type == void.class ? zero(type) : identity(type);
3412 }
3413
3414 /**
3415 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3416 * and returns a suitable default depending on the return type.
3417 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3418 * <p>The returned method handle is equivalent to
3419 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3420 *
3421 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3422 * {@code guardWithTest(pred, target, empty(target.type())}.
3423 * @param type the type of the desired method handle
3424 * @return a constant method handle of the given type, which returns a default value of the given return type
3425 * @throws NullPointerException if the argument is null
3426 * @see MethodHandles#zero
3427 * @see MethodHandles#constant
3428 * @since 9
3429 */
3430 public static MethodHandle empty(MethodType type) {
3431 Objects.requireNonNull(type);
3432 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3433 }
3434
3435 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3436 private static MethodHandle makeIdentity(Class<?> ptype) {
3437 MethodType mtype = methodType(ptype, ptype);
3438 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3439 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3440 }
3441
3442 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3443 int pos = btw.ordinal();
3444 MethodHandle zero = ZERO_MHS[pos];
3445 if (zero == null) {
3446 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3447 }
3448 if (zero.type().returnType() == rtype)
3449 return zero;
3450 assert(btw == Wrapper.OBJECT);
3451 return makeZero(rtype);
3452 }
3453 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3454 private static MethodHandle makeZero(Class<?> rtype) {
3455 MethodType mtype = methodType(rtype);
3456 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3457 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3458 }
3459
3460 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3461 // Simulate a CAS, to avoid racy duplication of results.
3462 MethodHandle prev = cache[pos];
3463 if (prev != null) return prev;
3464 return cache[pos] = value;
3465 }
3466
3467 /**
3468 * Provides a target method handle with one or more <em>bound arguments</em>
3469 * in advance of the method handle's invocation.
3470 * The formal parameters to the target corresponding to the bound
3471 * arguments are called <em>bound parameters</em>.
3472 * Returns a new method handle which saves away the bound arguments.
3473 * When it is invoked, it receives arguments for any non-bound parameters,
3474 * binds the saved arguments to their corresponding parameters,
3475 * and calls the original target.
3476 * <p>
3477 * The type of the new method handle will drop the types for the bound
3478 * parameters from the original target type, since the new method handle
3479 * will no longer require those arguments to be supplied by its callers.
3480 * <p>
3481 * Each given argument object must match the corresponding bound parameter type.
3482 * If a bound parameter type is a primitive, the argument object
3483 * must be a wrapper, and will be unboxed to produce the primitive value.
3484 * <p>
3485 * The {@code pos} argument selects which parameters are to be bound.
3486 * It may range between zero and <i>N-L</i> (inclusively),
3487 * where <i>N</i> is the arity of the target method handle
3488 * and <i>L</i> is the length of the values array.
3489 * <p>
3490 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3491 * variable-arity method handle}, even if the original target method handle was.
3492 * @param target the method handle to invoke after the argument is inserted
3493 * @param pos where to insert the argument (zero for the first)
3494 * @param values the series of arguments to insert
3495 * @return a method handle which inserts an additional argument,
3496 * before calling the original method handle
3497 * @throws NullPointerException if the target or the {@code values} array is null
3498 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
3499 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
3500 * is the length of the values array.
3501 * @throws ClassCastException if an argument does not match the corresponding bound parameter
3502 * type.
3503 * @see MethodHandle#bindTo
3504 */
3505 public static
3506 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3507 int insCount = values.length;
3508 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3509 if (insCount == 0) return target;
3510 BoundMethodHandle result = target.rebind();
3511 for (int i = 0; i < insCount; i++) {
3512 Object value = values[i];
3513 Class<?> ptype = ptypes[pos+i];
3514 if (ptype.isPrimitive()) {
3515 result = insertArgumentPrimitive(result, pos, ptype, value);
3516 } else {
3517 value = ptype.cast(value); // throw CCE if needed
3518 result = result.bindArgumentL(pos, value);
3519 }
3520 }
3521 return result;
3522 }
3523
3524 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3525 Class<?> ptype, Object value) {
3526 Wrapper w = Wrapper.forPrimitiveType(ptype);
3527 // perform unboxing and/or primitive conversion
3528 value = w.convert(value, ptype);
3529 switch (w) {
3530 case INT: return result.bindArgumentI(pos, (int)value);
3531 case LONG: return result.bindArgumentJ(pos, (long)value);
3532 case FLOAT: return result.bindArgumentF(pos, (float)value);
3533 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3534 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3535 }
3536 }
3537
3538 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3539 MethodType oldType = target.type();
3540 int outargs = oldType.parameterCount();
3541 int inargs = outargs - insCount;
3542 if (inargs < 0)
3543 throw newIllegalArgumentException("too many values to insert");
3544 if (pos < 0 || pos > inargs)
3545 throw newIllegalArgumentException("no argument type to append");
3546 return oldType.ptypes();
3547 }
3548
3549 /**
3550 * Produces a method handle which will discard some dummy arguments
3551 * before calling some other specified <i>target</i> method handle.
3552 * The type of the new method handle will be the same as the target's type,
3553 * except it will also include the dummy argument types,
3554 * at some given position.
3555 * <p>
3556 * The {@code pos} argument may range between zero and <i>N</i>,
3557 * where <i>N</i> is the arity of the target.
3558 * If {@code pos} is zero, the dummy arguments will precede
3559 * the target's real arguments; if {@code pos} is <i>N</i>
3560 * they will come after.
3561 * <p>
3562 * <b>Example:</b>
3563 * <blockquote><pre>{@code
3564 import static java.lang.invoke.MethodHandles.*;
3565 import static java.lang.invoke.MethodType.*;
3566 ...
3567 MethodHandle cat = lookup().findVirtual(String.class,
3568 "concat", methodType(String.class, String.class));
3569 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3570 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3571 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3572 assertEquals(bigType, d0.type());
3573 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3574 * }</pre></blockquote>
3575 * <p>
3576 * This method is also equivalent to the following code:
3577 * <blockquote><pre>
3578 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3579 * </pre></blockquote>
3580 * @param target the method handle to invoke after the arguments are dropped
3581 * @param valueTypes the type(s) of the argument(s) to drop
3582 * @param pos position of first argument to drop (zero for the leftmost)
3583 * @return a method handle which drops arguments of the given types,
3584 * before calling the original method handle
3585 * @throws NullPointerException if the target is null,
3586 * or if the {@code valueTypes} list or any of its elements is null
3587 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3588 * or if {@code pos} is negative or greater than the arity of the target,
3589 * or if the new method handle's type would have too many parameters
3590 */
3591 public static
3592 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3593 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3594 }
3595
3596 private static List<Class<?>> copyTypes(Object[] array) {
3597 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3598 }
3599
3600 private static
3601 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3602 MethodType oldType = target.type(); // get NPE
3603 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3604 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3605 if (dropped == 0) return target;
3606 BoundMethodHandle result = target.rebind();
3607 LambdaForm lform = result.form;
3608 int insertFormArg = 1 + pos;
3609 for (Class<?> ptype : valueTypes) {
3610 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3611 }
3612 result = result.copyWith(newType, lform);
3613 return result;
3614 }
3615
3616 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3617 int dropped = valueTypes.size();
3618 MethodType.checkSlotCount(dropped);
3619 int outargs = oldType.parameterCount();
3620 int inargs = outargs + dropped;
3621 if (pos < 0 || pos > outargs)
3622 throw newIllegalArgumentException("no argument type to remove"
3623 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3624 );
3625 return dropped;
3626 }
3627
3628 /**
3629 * Produces a method handle which will discard some dummy arguments
3630 * before calling some other specified <i>target</i> method handle.
3631 * The type of the new method handle will be the same as the target's type,
3632 * except it will also include the dummy argument types,
3633 * at some given position.
3634 * <p>
3635 * The {@code pos} argument may range between zero and <i>N</i>,
3636 * where <i>N</i> is the arity of the target.
3637 * If {@code pos} is zero, the dummy arguments will precede
3638 * the target's real arguments; if {@code pos} is <i>N</i>
3639 * they will come after.
3640 * @apiNote
3641 * <blockquote><pre>{@code
3642 import static java.lang.invoke.MethodHandles.*;
3643 import static java.lang.invoke.MethodType.*;
3644 ...
3645 MethodHandle cat = lookup().findVirtual(String.class,
3646 "concat", methodType(String.class, String.class));
3647 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3648 MethodHandle d0 = dropArguments(cat, 0, String.class);
3649 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3650 MethodHandle d1 = dropArguments(cat, 1, String.class);
3651 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3652 MethodHandle d2 = dropArguments(cat, 2, String.class);
3653 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3654 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3655 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3656 * }</pre></blockquote>
3657 * <p>
3658 * This method is also equivalent to the following code:
3659 * <blockquote><pre>
3660 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3661 * </pre></blockquote>
3662 * @param target the method handle to invoke after the arguments are dropped
3663 * @param valueTypes the type(s) of the argument(s) to drop
3664 * @param pos position of first argument to drop (zero for the leftmost)
3665 * @return a method handle which drops arguments of the given types,
3666 * before calling the original method handle
3667 * @throws NullPointerException if the target is null,
3668 * or if the {@code valueTypes} array or any of its elements is null
3669 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3670 * or if {@code pos} is negative or greater than the arity of the target,
3671 * or if the new method handle's type would have
3672 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3673 */
3674 public static
3675 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3676 return dropArguments0(target, pos, copyTypes(valueTypes));
3677 }
3678
3679 // private version which allows caller some freedom with error handling
3680 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3681 boolean nullOnFailure) {
3682 newTypes = copyTypes(newTypes.toArray());
3683 List<Class<?>> oldTypes = target.type().parameterList();
3684 int match = oldTypes.size();
3685 if (skip != 0) {
3686 if (skip < 0 || skip > match) {
3687 throw newIllegalArgumentException("illegal skip", skip, target);
3688 }
3689 oldTypes = oldTypes.subList(skip, match);
3690 match -= skip;
3691 }
3692 List<Class<?>> addTypes = newTypes;
3693 int add = addTypes.size();
3694 if (pos != 0) {
3695 if (pos < 0 || pos > add) {
3696 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3697 }
3698 addTypes = addTypes.subList(pos, add);
3699 add -= pos;
3700 assert(addTypes.size() == add);
3701 }
3702 // Do not add types which already match the existing arguments.
3703 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3704 if (nullOnFailure) {
3705 return null;
3706 }
3707 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3708 }
3709 addTypes = addTypes.subList(match, add);
3710 add -= match;
3711 assert(addTypes.size() == add);
3712 // newTypes: ( P*[pos], M*[match], A*[add] )
3713 // target: ( S*[skip], M*[match] )
3714 MethodHandle adapter = target;
3715 if (add > 0) {
3716 adapter = dropArguments0(adapter, skip+ match, addTypes);
3717 }
3718 // adapter: (S*[skip], M*[match], A*[add] )
3719 if (pos > 0) {
3720 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3721 }
3722 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3723 return adapter;
3724 }
3725
3726 /**
3727 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3728 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3729 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3730 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3731 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3732 * {@link #dropArguments(MethodHandle, int, Class[])}.
3733 * <p>
3734 * The resulting handle will have the same return type as the target handle.
3735 * <p>
3736 * In more formal terms, assume these two type lists:<ul>
3737 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3738 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3739 * {@code newTypes}.
3740 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3741 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3742 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3743 * sub-list.
3744 * </ul>
3745 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3746 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3747 * {@link #dropArguments(MethodHandle, int, Class[])}.
3748 *
3749 * @apiNote
3750 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3751 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3752 * <blockquote><pre>{@code
3753 import static java.lang.invoke.MethodHandles.*;
3754 import static java.lang.invoke.MethodType.*;
3755 ...
3756 ...
3757 MethodHandle h0 = constant(boolean.class, true);
3758 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3759 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3760 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3761 if (h1.type().parameterCount() < h2.type().parameterCount())
3762 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3763 else
3764 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3765 MethodHandle h3 = guardWithTest(h0, h1, h2);
3766 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3767 * }</pre></blockquote>
3768 * @param target the method handle to adapt
3769 * @param skip number of targets parameters to disregard (they will be unchanged)
3770 * @param newTypes the list of types to match {@code target}'s parameter type list to
3771 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3772 * @return a possibly adapted method handle
3773 * @throws NullPointerException if either argument is null
3774 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3775 * or if {@code skip} is negative or greater than the arity of the target,
3776 * or if {@code pos} is negative or greater than the newTypes list size,
3777 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3778 * {@code pos}.
3779 * @since 9
3780 */
3781 public static
3782 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3783 Objects.requireNonNull(target);
3784 Objects.requireNonNull(newTypes);
3785 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3786 }
3787
3788 /**
3789 * Adapts a target method handle by pre-processing
3790 * one or more of its arguments, each with its own unary filter function,
3791 * and then calling the target with each pre-processed argument
3792 * replaced by the result of its corresponding filter function.
3793 * <p>
3794 * The pre-processing is performed by one or more method handles,
3795 * specified in the elements of the {@code filters} array.
3796 * The first element of the filter array corresponds to the {@code pos}
3797 * argument of the target, and so on in sequence.
3798 * The filter functions are invoked in left to right order.
3799 * <p>
3800 * Null arguments in the array are treated as identity functions,
3801 * and the corresponding arguments left unchanged.
3802 * (If there are no non-null elements in the array, the original target is returned.)
3803 * Each filter is applied to the corresponding argument of the adapter.
3804 * <p>
3805 * If a filter {@code F} applies to the {@code N}th argument of
3806 * the target, then {@code F} must be a method handle which
3807 * takes exactly one argument. The type of {@code F}'s sole argument
3808 * replaces the corresponding argument type of the target
3809 * in the resulting adapted method handle.
3810 * The return type of {@code F} must be identical to the corresponding
3811 * parameter type of the target.
3812 * <p>
3813 * It is an error if there are elements of {@code filters}
3814 * (null or not)
3815 * which do not correspond to argument positions in the target.
3816 * <p><b>Example:</b>
3817 * <blockquote><pre>{@code
3818 import static java.lang.invoke.MethodHandles.*;
3819 import static java.lang.invoke.MethodType.*;
3820 ...
3821 MethodHandle cat = lookup().findVirtual(String.class,
3822 "concat", methodType(String.class, String.class));
3823 MethodHandle upcase = lookup().findVirtual(String.class,
3824 "toUpperCase", methodType(String.class));
3825 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3826 MethodHandle f0 = filterArguments(cat, 0, upcase);
3827 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3828 MethodHandle f1 = filterArguments(cat, 1, upcase);
3829 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3830 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3831 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3832 * }</pre></blockquote>
3833 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3834 * denotes the return type of both the {@code target} and resulting adapter.
3835 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3836 * of the parameters and arguments that precede and follow the filter position
3837 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3838 * values of the filtered parameters and arguments; they also represent the
3839 * return types of the {@code filter[i]} handles. The latter accept arguments
3840 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3841 * the resulting adapter.
3842 * <blockquote><pre>{@code
3843 * T target(P... p, A[i]... a[i], B... b);
3844 * A[i] filter[i](V[i]);
3845 * T adapter(P... p, V[i]... v[i], B... b) {
3846 * return target(p..., filter[i](v[i])..., b...);
3847 * }
3848 * }</pre></blockquote>
3849 * <p>
3850 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3851 * variable-arity method handle}, even if the original target method handle was.
3852 *
3853 * @param target the method handle to invoke after arguments are filtered
3854 * @param pos the position of the first argument to filter
3855 * @param filters method handles to call initially on filtered arguments
3856 * @return method handle which incorporates the specified argument filtering logic
3857 * @throws NullPointerException if the target is null
3858 * or if the {@code filters} array is null
3859 * @throws IllegalArgumentException if a non-null element of {@code filters}
3860 * does not match a corresponding argument type of target as described above,
3861 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3862 * or if the resulting method handle's type would have
3863 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3864 */
3865 public static
3866 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3867 // In method types arguments start at index 0, while the LF
3868 // editor have the MH receiver at position 0 - adjust appropriately.
3869 final int MH_RECEIVER_OFFSET = 1;
3870 filterArgumentsCheckArity(target, pos, filters);
3871 MethodHandle adapter = target;
3872
3873 // keep track of currently matched filters, as to optimize repeated filters
3874 int index = 0;
3875 int[] positions = new int[filters.length];
3876 MethodHandle filter = null;
3877
3878 // process filters in reverse order so that the invocation of
3879 // the resulting adapter will invoke the filters in left-to-right order
3880 for (int i = filters.length - 1; i >= 0; --i) {
3881 MethodHandle newFilter = filters[i];
3882 if (newFilter == null) continue; // ignore null elements of filters
3883
3884 // flush changes on update
3885 if (filter != newFilter) {
3886 if (filter != null) {
3887 if (index > 1) {
3888 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
3889 } else {
3890 adapter = filterArgument(adapter, positions[0] - 1, filter);
3891 }
3892 }
3893 filter = newFilter;
3894 index = 0;
3895 }
3896
3897 filterArgumentChecks(target, pos + i, newFilter);
3898 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
3899 }
3900 if (index > 1) {
3901 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
3902 } else if (index == 1) {
3903 adapter = filterArgument(adapter, positions[0] - 1, filter);
3904 }
3905 return adapter;
3906 }
3907
3908 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
3909 MethodType targetType = adapter.type();
3910 MethodType filterType = filter.type();
3911 BoundMethodHandle result = adapter.rebind();
3912 Class<?> newParamType = filterType.parameterType(0);
3913
3914 Class<?>[] ptypes = targetType.ptypes().clone();
3915 for (int pos : positions) {
3916 ptypes[pos - 1] = newParamType;
3917 }
3918 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true);
3919
3920 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
3921 return result.copyWithExtendL(newType, lform, filter);
3922 }
3923
3924 /*non-public*/ static
3925 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3926 filterArgumentChecks(target, pos, filter);
3927 MethodType targetType = target.type();
3928 MethodType filterType = filter.type();
3929 BoundMethodHandle result = target.rebind();
3930 Class<?> newParamType = filterType.parameterType(0);
3931 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3932 MethodType newType = targetType.changeParameterType(pos, newParamType);
3933 result = result.copyWithExtendL(newType, lform, filter);
3934 return result;
3935 }
3936
3937 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3938 MethodType targetType = target.type();
3939 int maxPos = targetType.parameterCount();
3940 if (pos + filters.length > maxPos)
3941 throw newIllegalArgumentException("too many filters");
3942 }
3943
3944 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3945 MethodType targetType = target.type();
3946 MethodType filterType = filter.type();
3947 if (filterType.parameterCount() != 1
3948 || filterType.returnType() != targetType.parameterType(pos))
3949 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3950 }
3951
3952 /**
3953 * Adapts a target method handle by pre-processing
3954 * a sub-sequence of its arguments with a filter (another method handle).
3955 * The pre-processed arguments are replaced by the result (if any) of the
3956 * filter function.
3957 * The target is then called on the modified (usually shortened) argument list.
3958 * <p>
3959 * If the filter returns a value, the target must accept that value as
3960 * its argument in position {@code pos}, preceded and/or followed by
3961 * any arguments not passed to the filter.
3962 * If the filter returns void, the target must accept all arguments
3963 * not passed to the filter.
3964 * No arguments are reordered, and a result returned from the filter
3965 * replaces (in order) the whole subsequence of arguments originally
3966 * passed to the adapter.
3967 * <p>
3968 * The argument types (if any) of the filter
3969 * replace zero or one argument types of the target, at position {@code pos},
3970 * in the resulting adapted method handle.
3971 * The return type of the filter (if any) must be identical to the
3972 * argument type of the target at position {@code pos}, and that target argument
3973 * is supplied by the return value of the filter.
3974 * <p>
3975 * In all cases, {@code pos} must be greater than or equal to zero, and
3976 * {@code pos} must also be less than or equal to the target's arity.
3977 * <p><b>Example:</b>
3978 * <blockquote><pre>{@code
3979 import static java.lang.invoke.MethodHandles.*;
3980 import static java.lang.invoke.MethodType.*;
3981 ...
3982 MethodHandle deepToString = publicLookup()
3983 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3984
3985 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3986 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3987
3988 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3989 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3990
3991 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3992 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3993 assertEquals("[top, [up, down], strange]",
3994 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3995
3996 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3997 assertEquals("[top, [up, down], [strange]]",
3998 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3999
4000 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4001 assertEquals("[top, [[up, down, strange], charm], bottom]",
4002 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4003 * }</pre></blockquote>
4004 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4005 * represents the return type of the {@code target} and resulting adapter.
4006 * {@code V}/{@code v} stand for the return type and value of the
4007 * {@code filter}, which are also found in the signature and arguments of
4008 * the {@code target}, respectively, unless {@code V} is {@code void}.
4009 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4010 * and values preceding and following the collection position, {@code pos},
4011 * in the {@code target}'s signature. They also turn up in the resulting
4012 * adapter's signature and arguments, where they surround
4013 * {@code B}/{@code b}, which represent the parameter types and arguments
4014 * to the {@code filter} (if any).
4015 * <blockquote><pre>{@code
4016 * T target(A...,V,C...);
4017 * V filter(B...);
4018 * T adapter(A... a,B... b,C... c) {
4019 * V v = filter(b...);
4020 * return target(a...,v,c...);
4021 * }
4022 * // and if the filter has no arguments:
4023 * T target2(A...,V,C...);
4024 * V filter2();
4025 * T adapter2(A... a,C... c) {
4026 * V v = filter2();
4027 * return target2(a...,v,c...);
4028 * }
4029 * // and if the filter has a void return:
4030 * T target3(A...,C...);
4031 * void filter3(B...);
4032 * T adapter3(A... a,B... b,C... c) {
4033 * filter3(b...);
4034 * return target3(a...,c...);
4035 * }
4036 * }</pre></blockquote>
4037 * <p>
4038 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
4039 * one which first "folds" the affected arguments, and then drops them, in separate
4040 * steps as follows:
4041 * <blockquote><pre>{@code
4042 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4043 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4044 * }</pre></blockquote>
4045 * If the target method handle consumes no arguments besides than the result
4046 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4047 * is equivalent to {@code filterReturnValue(coll, mh)}.
4048 * If the filter method handle {@code coll} consumes one argument and produces
4049 * a non-void result, then {@code collectArguments(mh, N, coll)}
4050 * is equivalent to {@code filterArguments(mh, N, coll)}.
4051 * Other equivalences are possible but would require argument permutation.
4052 * <p>
4053 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4054 * variable-arity method handle}, even if the original target method handle was.
4055 *
4056 * @param target the method handle to invoke after filtering the subsequence of arguments
4057 * @param pos the position of the first adapter argument to pass to the filter,
4058 * and/or the target argument which receives the result of the filter
4059 * @param filter method handle to call on the subsequence of arguments
4060 * @return method handle which incorporates the specified argument subsequence filtering logic
4061 * @throws NullPointerException if either argument is null
4062 * @throws IllegalArgumentException if the return type of {@code filter}
4063 * is non-void and is not the same as the {@code pos} argument of the target,
4064 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4065 * or if the resulting method handle's type would have
4066 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4067 * @see MethodHandles#foldArguments
4068 * @see MethodHandles#filterArguments
4069 * @see MethodHandles#filterReturnValue
4070 */
4071 public static
4072 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4073 MethodType newType = collectArgumentsChecks(target, pos, filter);
4074 MethodType collectorType = filter.type();
4075 BoundMethodHandle result = target.rebind();
4076 LambdaForm lform;
4077 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4078 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4079 if (lform != null) {
4080 return result.copyWith(newType, lform);
4081 }
4082 }
4083 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4084 return result.copyWithExtendL(newType, lform, filter);
4085 }
4086
4087 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4088 MethodType targetType = target.type();
4089 MethodType filterType = filter.type();
4090 Class<?> rtype = filterType.returnType();
4091 List<Class<?>> filterArgs = filterType.parameterList();
4092 if (rtype == void.class) {
4093 return targetType.insertParameterTypes(pos, filterArgs);
4094 }
4095 if (rtype != targetType.parameterType(pos)) {
4096 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4097 }
4098 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4099 }
4100
4101 /**
4102 * Adapts a target method handle by post-processing
4103 * its return value (if any) with a filter (another method handle).
4104 * The result of the filter is returned from the adapter.
4105 * <p>
4106 * If the target returns a value, the filter must accept that value as
4107 * its only argument.
4108 * If the target returns void, the filter must accept no arguments.
4109 * <p>
4110 * The return type of the filter
4111 * replaces the return type of the target
4112 * in the resulting adapted method handle.
4113 * The argument type of the filter (if any) must be identical to the
4114 * return type of the target.
4115 * <p><b>Example:</b>
4116 * <blockquote><pre>{@code
4117 import static java.lang.invoke.MethodHandles.*;
4118 import static java.lang.invoke.MethodType.*;
4119 ...
4120 MethodHandle cat = lookup().findVirtual(String.class,
4121 "concat", methodType(String.class, String.class));
4122 MethodHandle length = lookup().findVirtual(String.class,
4123 "length", methodType(int.class));
4124 System.out.println((String) cat.invokeExact("x", "y")); // xy
4125 MethodHandle f0 = filterReturnValue(cat, length);
4126 System.out.println((int) f0.invokeExact("x", "y")); // 2
4127 * }</pre></blockquote>
4128 * <p>Here is pseudocode for the resulting adapter. In the code,
4129 * {@code T}/{@code t} represent the result type and value of the
4130 * {@code target}; {@code V}, the result type of the {@code filter}; and
4131 * {@code A}/{@code a}, the types and values of the parameters and arguments
4132 * of the {@code target} as well as the resulting adapter.
4133 * <blockquote><pre>{@code
4134 * T target(A...);
4135 * V filter(T);
4136 * V adapter(A... a) {
4137 * T t = target(a...);
4138 * return filter(t);
4139 * }
4140 * // and if the target has a void return:
4141 * void target2(A...);
4142 * V filter2();
4143 * V adapter2(A... a) {
4144 * target2(a...);
4145 * return filter2();
4146 * }
4147 * // and if the filter has a void return:
4148 * T target3(A...);
4149 * void filter3(V);
4150 * void adapter3(A... a) {
4151 * T t = target3(a...);
4152 * filter3(t);
4153 * }
4154 * }</pre></blockquote>
4155 * <p>
4156 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4157 * variable-arity method handle}, even if the original target method handle was.
4158 * @param target the method handle to invoke before filtering the return value
4159 * @param filter method handle to call on the return value
4160 * @return method handle which incorporates the specified return value filtering logic
4161 * @throws NullPointerException if either argument is null
4162 * @throws IllegalArgumentException if the argument list of {@code filter}
4163 * does not match the return type of target as described above
4164 */
4165 public static
4166 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4167 MethodType targetType = target.type();
4168 MethodType filterType = filter.type();
4169 filterReturnValueChecks(targetType, filterType);
4170 BoundMethodHandle result = target.rebind();
4171 BasicType rtype = BasicType.basicType(filterType.returnType());
4172 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4173 MethodType newType = targetType.changeReturnType(filterType.returnType());
4174 result = result.copyWithExtendL(newType, lform, filter);
4175 return result;
4176 }
4177
4178 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4179 Class<?> rtype = targetType.returnType();
4180 int filterValues = filterType.parameterCount();
4181 if (filterValues == 0
4182 ? (rtype != void.class)
4183 : (rtype != filterType.parameterType(0) || filterValues != 1))
4184 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4185 }
4186
4187 /**
4188 * Adapts a target method handle by pre-processing
4189 * some of its arguments, and then calling the target with
4190 * the result of the pre-processing, inserted into the original
4191 * sequence of arguments.
4192 * <p>
4193 * The pre-processing is performed by {@code combiner}, a second method handle.
4194 * Of the arguments passed to the adapter, the first {@code N} arguments
4195 * are copied to the combiner, which is then called.
4196 * (Here, {@code N} is defined as the parameter count of the combiner.)
4197 * After this, control passes to the target, with any result
4198 * from the combiner inserted before the original {@code N} incoming
4199 * arguments.
4200 * <p>
4201 * If the combiner returns a value, the first parameter type of the target
4202 * must be identical with the return type of the combiner, and the next
4203 * {@code N} parameter types of the target must exactly match the parameters
4204 * of the combiner.
4205 * <p>
4206 * If the combiner has a void return, no result will be inserted,
4207 * and the first {@code N} parameter types of the target
4208 * must exactly match the parameters of the combiner.
4209 * <p>
4210 * The resulting adapter is the same type as the target, except that the
4211 * first parameter type is dropped,
4212 * if it corresponds to the result of the combiner.
4213 * <p>
4214 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4215 * that either the combiner or the target does not wish to receive.
4216 * If some of the incoming arguments are destined only for the combiner,
4217 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4218 * arguments will not need to be live on the stack on entry to the
4219 * target.)
4220 * <p><b>Example:</b>
4221 * <blockquote><pre>{@code
4222 import static java.lang.invoke.MethodHandles.*;
4223 import static java.lang.invoke.MethodType.*;
4224 ...
4225 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4226 "println", methodType(void.class, String.class))
4227 .bindTo(System.out);
4228 MethodHandle cat = lookup().findVirtual(String.class,
4229 "concat", methodType(String.class, String.class));
4230 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4231 MethodHandle catTrace = foldArguments(cat, trace);
4232 // also prints "boo":
4233 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4234 * }</pre></blockquote>
4235 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4236 * represents the result type of the {@code target} and resulting adapter.
4237 * {@code V}/{@code v} represent the type and value of the parameter and argument
4238 * of {@code target} that precedes the folding position; {@code V} also is
4239 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4240 * types and values of the {@code N} parameters and arguments at the folding
4241 * position. {@code B}/{@code b} represent the types and values of the
4242 * {@code target} parameters and arguments that follow the folded parameters
4243 * and arguments.
4244 * <blockquote><pre>{@code
4245 * // there are N arguments in A...
4246 * T target(V, A[N]..., B...);
4247 * V combiner(A...);
4248 * T adapter(A... a, B... b) {
4249 * V v = combiner(a...);
4250 * return target(v, a..., b...);
4251 * }
4252 * // and if the combiner has a void return:
4253 * T target2(A[N]..., B...);
4254 * void combiner2(A...);
4255 * T adapter2(A... a, B... b) {
4256 * combiner2(a...);
4257 * return target2(a..., b...);
4258 * }
4259 * }</pre></blockquote>
4260 * <p>
4261 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4262 * variable-arity method handle}, even if the original target method handle was.
4263 * @param target the method handle to invoke after arguments are combined
4264 * @param combiner method handle to call initially on the incoming arguments
4265 * @return method handle which incorporates the specified argument folding logic
4266 * @throws NullPointerException if either argument is null
4267 * @throws IllegalArgumentException if {@code combiner}'s return type
4268 * is non-void and not the same as the first argument type of
4269 * the target, or if the initial {@code N} argument types
4270 * of the target
4271 * (skipping one matching the {@code combiner}'s return type)
4272 * are not identical with the argument types of {@code combiner}
4273 */
4274 public static
4275 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4276 return foldArguments(target, 0, combiner);
4277 }
4278
4279 /**
4280 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4281 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4282 * before the folded arguments.
4283 * <p>
4284 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4285 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4286 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4287 * 0.
4288 *
4289 * @apiNote Example:
4290 * <blockquote><pre>{@code
4291 import static java.lang.invoke.MethodHandles.*;
4292 import static java.lang.invoke.MethodType.*;
4293 ...
4294 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4295 "println", methodType(void.class, String.class))
4296 .bindTo(System.out);
4297 MethodHandle cat = lookup().findVirtual(String.class,
4298 "concat", methodType(String.class, String.class));
4299 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4300 MethodHandle catTrace = foldArguments(cat, 1, trace);
4301 // also prints "jum":
4302 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4303 * }</pre></blockquote>
4304 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4305 * represents the result type of the {@code target} and resulting adapter.
4306 * {@code V}/{@code v} represent the type and value of the parameter and argument
4307 * of {@code target} that precedes the folding position; {@code V} also is
4308 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4309 * types and values of the {@code N} parameters and arguments at the folding
4310 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4311 * and values of the {@code target} parameters and arguments that precede and
4312 * follow the folded parameters and arguments starting at {@code pos},
4313 * respectively.
4314 * <blockquote><pre>{@code
4315 * // there are N arguments in A...
4316 * T target(Z..., V, A[N]..., B...);
4317 * V combiner(A...);
4318 * T adapter(Z... z, A... a, B... b) {
4319 * V v = combiner(a...);
4320 * return target(z..., v, a..., b...);
4321 * }
4322 * // and if the combiner has a void return:
4323 * T target2(Z..., A[N]..., B...);
4324 * void combiner2(A...);
4325 * T adapter2(Z... z, A... a, B... b) {
4326 * combiner2(a...);
4327 * return target2(z..., a..., b...);
4328 * }
4329 * }</pre></blockquote>
4330 * <p>
4331 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4332 * variable-arity method handle}, even if the original target method handle was.
4333 *
4334 * @param target the method handle to invoke after arguments are combined
4335 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4336 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4337 * @param combiner method handle to call initially on the incoming arguments
4338 * @return method handle which incorporates the specified argument folding logic
4339 * @throws NullPointerException if either argument is null
4340 * @throws IllegalArgumentException if either of the following two conditions holds:
4341 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4342 * {@code pos} of the target signature;
4343 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4344 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4345 *
4346 * @see #foldArguments(MethodHandle, MethodHandle)
4347 * @since 9
4348 */
4349 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4350 MethodType targetType = target.type();
4351 MethodType combinerType = combiner.type();
4352 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4353 BoundMethodHandle result = target.rebind();
4354 boolean dropResult = rtype == void.class;
4355 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4356 MethodType newType = targetType;
4357 if (!dropResult) {
4358 newType = newType.dropParameterTypes(pos, pos + 1);
4359 }
4360 result = result.copyWithExtendL(newType, lform, combiner);
4361 return result;
4362 }
4363
4364 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4365 int foldArgs = combinerType.parameterCount();
4366 Class<?> rtype = combinerType.returnType();
4367 int foldVals = rtype == void.class ? 0 : 1;
4368 int afterInsertPos = foldPos + foldVals;
4369 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4370 if (ok) {
4371 for (int i = 0; i < foldArgs; i++) {
4372 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4373 ok = false;
4374 break;
4375 }
4376 }
4377 }
4378 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4379 ok = false;
4380 if (!ok)
4381 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4382 return rtype;
4383 }
4384
4385 /**
4386 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
4387 * of the pre-processing replacing the argument at the given position.
4388 *
4389 * @param target the method handle to invoke after arguments are combined
4390 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
4391 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4392 * @param combiner method handle to call initially on the incoming arguments
4393 * @param argPositions indexes of the target to pick arguments sent to the combiner from
4394 * @return method handle which incorporates the specified argument folding logic
4395 * @throws NullPointerException if either argument is null
4396 * @throws IllegalArgumentException if either of the following two conditions holds:
4397 * (1) {@code combiner}'s return type is not the same as the argument type at position
4398 * {@code pos} of the target signature;
4399 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
4400 * not identical with the argument types of {@code combiner}.
4401 */
4402 /*non-public*/ static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4403 return argumentsWithCombiner(true, target, position, combiner, argPositions);
4404 }
4405
4406 /**
4407 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
4408 * the pre-processing inserted into the original sequence of arguments at the given position.
4409 *
4410 * @param target the method handle to invoke after arguments are combined
4411 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
4412 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4413 * @param combiner method handle to call initially on the incoming arguments
4414 * @param argPositions indexes of the target to pick arguments sent to the combiner from
4415 * @return method handle which incorporates the specified argument folding logic
4416 * @throws NullPointerException if either argument is null
4417 * @throws IllegalArgumentException if either of the following two conditions holds:
4418 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4419 * {@code pos} of the target signature;
4420 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
4421 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
4422 * with the argument types of {@code combiner}.
4423 */
4424 /*non-public*/ static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4425 return argumentsWithCombiner(false, target, position, combiner, argPositions);
4426 }
4427
4428 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4429 MethodType targetType = target.type();
4430 MethodType combinerType = combiner.type();
4431 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
4432 BoundMethodHandle result = target.rebind();
4433
4434 MethodType newType = targetType;
4435 LambdaForm lform;
4436 if (filter) {
4437 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
4438 } else {
4439 boolean dropResult = rtype == void.class;
4440 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
4441 if (!dropResult) {
4442 newType = newType.dropParameterTypes(position, position + 1);
4443 }
4444 }
4445 result = result.copyWithExtendL(newType, lform, combiner);
4446 return result;
4447 }
4448
4449 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
4450 int combinerArgs = combinerType.parameterCount();
4451 if (argPos.length != combinerArgs) {
4452 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4453 }
4454 Class<?> rtype = combinerType.returnType();
4455
4456 for (int i = 0; i < combinerArgs; i++) {
4457 int arg = argPos[i];
4458 if (arg < 0 || arg > targetType.parameterCount()) {
4459 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4460 }
4461 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4462 throw newIllegalArgumentException("target argument type at position " + arg
4463 + " must match combiner argument type at index " + i + ": " + targetType
4464 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4465 }
4466 }
4467 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
4468 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4469 }
4470 return rtype;
4471 }
4472
4473 /**
4474 * Makes a method handle which adapts a target method handle,
4475 * by guarding it with a test, a boolean-valued method handle.
4476 * If the guard fails, a fallback handle is called instead.
4477 * All three method handles must have the same corresponding
4478 * argument and return types, except that the return type
4479 * of the test must be boolean, and the test is allowed
4480 * to have fewer arguments than the other two method handles.
4481 * <p>
4482 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4483 * represents the uniform result type of the three involved handles;
4484 * {@code A}/{@code a}, the types and values of the {@code target}
4485 * parameters and arguments that are consumed by the {@code test}; and
4486 * {@code B}/{@code b}, those types and values of the {@code target}
4487 * parameters and arguments that are not consumed by the {@code test}.
4488 * <blockquote><pre>{@code
4489 * boolean test(A...);
4490 * T target(A...,B...);
4491 * T fallback(A...,B...);
4492 * T adapter(A... a,B... b) {
4493 * if (test(a...))
4494 * return target(a..., b...);
4495 * else
4496 * return fallback(a..., b...);
4497 * }
4498 * }</pre></blockquote>
4499 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4500 * be modified by execution of the test, and so are passed unchanged
4501 * from the caller to the target or fallback as appropriate.
4502 * @param test method handle used for test, must return boolean
4503 * @param target method handle to call if test passes
4504 * @param fallback method handle to call if test fails
4505 * @return method handle which incorporates the specified if/then/else logic
4506 * @throws NullPointerException if any argument is null
4507 * @throws IllegalArgumentException if {@code test} does not return boolean,
4508 * or if all three method types do not match (with the return
4509 * type of {@code test} changed to match that of the target).
4510 */
4511 public static
4512 MethodHandle guardWithTest(MethodHandle test,
4513 MethodHandle target,
4514 MethodHandle fallback) {
4515 MethodType gtype = test.type();
4516 MethodType ttype = target.type();
4517 MethodType ftype = fallback.type();
4518 if (!ttype.equals(ftype))
4519 throw misMatchedTypes("target and fallback types", ttype, ftype);
4520 if (gtype.returnType() != boolean.class)
4521 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4522 List<Class<?>> targs = ttype.parameterList();
4523 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4524 if (test == null) {
4525 throw misMatchedTypes("target and test types", ttype, gtype);
4526 }
4527 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4528 }
4529
4530 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4531 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4532 }
4533
4534 /**
4535 * Makes a method handle which adapts a target method handle,
4536 * by running it inside an exception handler.
4537 * If the target returns normally, the adapter returns that value.
4538 * If an exception matching the specified type is thrown, the fallback
4539 * handle is called instead on the exception, plus the original arguments.
4540 * <p>
4541 * The target and handler must have the same corresponding
4542 * argument and return types, except that handler may omit trailing arguments
4543 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4544 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4545 * <p>
4546 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4547 * represents the return type of the {@code target} and {@code handler},
4548 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4549 * the types and values of arguments to the resulting handle consumed by
4550 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4551 * resulting handle discarded by {@code handler}.
4552 * <blockquote><pre>{@code
4553 * T target(A..., B...);
4554 * T handler(ExType, A...);
4555 * T adapter(A... a, B... b) {
4556 * try {
4557 * return target(a..., b...);
4558 * } catch (ExType ex) {
4559 * return handler(ex, a...);
4560 * }
4561 * }
4562 * }</pre></blockquote>
4563 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4564 * be modified by execution of the target, and so are passed unchanged
4565 * from the caller to the handler, if the handler is invoked.
4566 * <p>
4567 * The target and handler must return the same type, even if the handler
4568 * always throws. (This might happen, for instance, because the handler
4569 * is simulating a {@code finally} clause).
4570 * To create such a throwing handler, compose the handler creation logic
4571 * with {@link #throwException throwException},
4572 * in order to create a method handle of the correct return type.
4573 * @param target method handle to call
4574 * @param exType the type of exception which the handler will catch
4575 * @param handler method handle to call if a matching exception is thrown
4576 * @return method handle which incorporates the specified try/catch logic
4577 * @throws NullPointerException if any argument is null
4578 * @throws IllegalArgumentException if {@code handler} does not accept
4579 * the given exception type, or if the method handle types do
4580 * not match in their return types and their
4581 * corresponding parameters
4582 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4583 */
4584 public static
4585 MethodHandle catchException(MethodHandle target,
4586 Class<? extends Throwable> exType,
4587 MethodHandle handler) {
4588 MethodType ttype = target.type();
4589 MethodType htype = handler.type();
4590 if (!Throwable.class.isAssignableFrom(exType))
4591 throw new ClassCastException(exType.getName());
4592 if (htype.parameterCount() < 1 ||
4593 !htype.parameterType(0).isAssignableFrom(exType))
4594 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4595 if (htype.returnType() != ttype.returnType())
4596 throw misMatchedTypes("target and handler return types", ttype, htype);
4597 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4598 if (handler == null) {
4599 throw misMatchedTypes("target and handler types", ttype, htype);
4600 }
4601 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4602 }
4603
4604 /**
4605 * Produces a method handle which will throw exceptions of the given {@code exType}.
4606 * The method handle will accept a single argument of {@code exType},
4607 * and immediately throw it as an exception.
4608 * The method type will nominally specify a return of {@code returnType}.
4609 * The return type may be anything convenient: It doesn't matter to the
4610 * method handle's behavior, since it will never return normally.
4611 * @param returnType the return type of the desired method handle
4612 * @param exType the parameter type of the desired method handle
4613 * @return method handle which can throw the given exceptions
4614 * @throws NullPointerException if either argument is null
4615 */
4616 public static
4617 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4618 if (!Throwable.class.isAssignableFrom(exType))
4619 throw new ClassCastException(exType.getName());
4620 return MethodHandleImpl.throwException(methodType(returnType, exType));
4621 }
4622
4623 /**
4624 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4625 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4626 * delivers the loop's result, which is the return value of the resulting handle.
4627 * <p>
4628 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4629 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4630 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4631 * terms of method handles, each clause will specify up to four independent actions:<ul>
4632 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4633 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4634 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4635 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4636 * </ul>
4637 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4638 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4639 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4640 * <p>
4641 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4642 * this case. See below for a detailed description.
4643 * <p>
4644 * <em>Parameters optional everywhere:</em>
4645 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4646 * As an exception, the init functions cannot take any {@code v} parameters,
4647 * because those values are not yet computed when the init functions are executed.
4648 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4649 * In fact, any clause function may take no arguments at all.
4650 * <p>
4651 * <em>Loop parameters:</em>
4652 * A clause function may take all the iteration variable values it is entitled to, in which case
4653 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4654 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4655 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4656 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4657 * init function is automatically a loop parameter {@code a}.)
4658 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4659 * These loop parameters act as loop-invariant values visible across the whole loop.
4660 * <p>
4661 * <em>Parameters visible everywhere:</em>
4662 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4663 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4664 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4665 * Most clause functions will not need all of this information, but they will be formally connected to it
4666 * as if by {@link #dropArguments}.
4667 * <a id="astar"></a>
4668 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4669 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4670 * In that notation, the general form of an init function parameter list
4671 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4672 * <p>
4673 * <em>Checking clause structure:</em>
4674 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4675 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4676 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4677 * met by the inputs to the loop combinator.
4678 * <p>
4679 * <em>Effectively identical sequences:</em>
4680 * <a id="effid"></a>
4681 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4682 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4683 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4684 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4685 * that longest list.
4686 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4687 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4688 * <p>
4689 * <em>Step 0: Determine clause structure.</em><ol type="a">
4690 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4691 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4692 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4693 * four. Padding takes place by appending elements to the array.
4694 * <li>Clauses with all {@code null}s are disregarded.
4695 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4696 * </ol>
4697 * <p>
4698 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4699 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4700 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4701 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4702 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4703 * iteration variable type.
4704 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4705 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4706 * </ol>
4707 * <p>
4708 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4709 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4710 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4711 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4712 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4713 * (These types will be checked in step 2, along with all the clause function types.)
4714 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4715 * <li>All of the collected parameter lists must be effectively identical.
4716 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4717 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4718 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4719 * the "internal parameter list".
4720 * </ul>
4721 * <p>
4722 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4723 * <li>Examine fini function return types, disregarding omitted fini functions.
4724 * <li>If there are no fini functions, the loop return type is {@code void}.
4725 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4726 * type.
4727 * </ol>
4728 * <p>
4729 * <em>Step 1D: Check other types.</em><ol type="a">
4730 * <li>There must be at least one non-omitted pred function.
4731 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4732 * </ol>
4733 * <p>
4734 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4735 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4736 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4737 * (Note that their parameter lists are already effectively identical to this list.)
4738 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4739 * effectively identical to the internal parameter list {@code (V... A...)}.
4740 * </ol>
4741 * <p>
4742 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4743 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4744 * type.
4745 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4746 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4747 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4748 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4749 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4750 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4751 * loop return type.
4752 * </ol>
4753 * <p>
4754 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4755 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4756 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4757 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4758 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4759 * pad out the end of the list.
4760 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
4761 * </ol>
4762 * <p>
4763 * <em>Final observations.</em><ol type="a">
4764 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4765 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4766 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4767 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4768 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4769 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4770 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4771 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4772 * </ol>
4773 * <p>
4774 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4775 * <ul>
4776 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4777 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4778 * (Only one {@code Pn} has to be non-{@code null}.)
4779 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4780 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4781 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4782 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4783 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4784 * the resulting loop handle's parameter types {@code (A...)}.
4785 * </ul>
4786 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4787 * which is natural if most of the loop computation happens in the steps. For some loops,
4788 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4789 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4790 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4791 * where the init functions will need the extra parameters. For such reasons, the rules for
4792 * determining these parameters are as symmetric as possible, across all clause parts.
4793 * In general, the loop parameters function as common invariant values across the whole
4794 * loop, while the iteration variables function as common variant values, or (if there is
4795 * no step function) as internal loop invariant temporaries.
4796 * <p>
4797 * <em>Loop execution.</em><ol type="a">
4798 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4799 * every clause function. These locals are loop invariant.
4800 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4801 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4802 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4803 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4804 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4805 * (in argument order).
4806 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4807 * returns {@code false}.
4808 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4809 * sequence {@code (v...)} of loop variables.
4810 * The updated value is immediately visible to all subsequent function calls.
4811 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4812 * (of type {@code R}) is returned from the loop as a whole.
4813 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4814 * except by throwing an exception.
4815 * </ol>
4816 * <p>
4817 * <em>Usage tips.</em>
4818 * <ul>
4819 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4820 * sometimes a step function only needs to observe the current value of its own variable.
4821 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4822 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4823 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4824 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4825 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4826 * <li>If some of the clause functions are virtual methods on an instance, the instance
4827 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4828 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4829 * will be the first iteration variable value, and it will be easy to use virtual
4830 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4831 * </ul>
4832 * <p>
4833 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4834 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4835 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4836 * <blockquote><pre>{@code
4837 * V... init...(A...);
4838 * boolean pred...(V..., A...);
4839 * V... step...(V..., A...);
4840 * R fini...(V..., A...);
4841 * R loop(A... a) {
4842 * V... v... = init...(a...);
4843 * for (;;) {
4844 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4845 * v = s(v..., a...);
4846 * if (!p(v..., a...)) {
4847 * return f(v..., a...);
4848 * }
4849 * }
4850 * }
4851 * }
4852 * }</pre></blockquote>
4853 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4854 * to their full length, even though individual clause functions may neglect to take them all.
4855 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
4856 *
4857 * @apiNote Example:
4858 * <blockquote><pre>{@code
4859 * // iterative implementation of the factorial function as a loop handle
4860 * static int one(int k) { return 1; }
4861 * static int inc(int i, int acc, int k) { return i + 1; }
4862 * static int mult(int i, int acc, int k) { return i * acc; }
4863 * static boolean pred(int i, int acc, int k) { return i < k; }
4864 * static int fin(int i, int acc, int k) { return acc; }
4865 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4866 * // null initializer for counter, should initialize to 0
4867 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4868 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4869 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4870 * assertEquals(120, loop.invoke(5));
4871 * }</pre></blockquote>
4872 * The same example, dropping arguments and using combinators:
4873 * <blockquote><pre>{@code
4874 * // simplified implementation of the factorial function as a loop handle
4875 * static int inc(int i) { return i + 1; } // drop acc, k
4876 * static int mult(int i, int acc) { return i * acc; } //drop k
4877 * static boolean cmp(int i, int k) { return i < k; }
4878 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4879 * // null initializer for counter, should initialize to 0
4880 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4881 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4882 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4883 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4884 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4885 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4886 * assertEquals(720, loop.invoke(6));
4887 * }</pre></blockquote>
4888 * A similar example, using a helper object to hold a loop parameter:
4889 * <blockquote><pre>{@code
4890 * // instance-based implementation of the factorial function as a loop handle
4891 * static class FacLoop {
4892 * final int k;
4893 * FacLoop(int k) { this.k = k; }
4894 * int inc(int i) { return i + 1; }
4895 * int mult(int i, int acc) { return i * acc; }
4896 * boolean pred(int i) { return i < k; }
4897 * int fin(int i, int acc) { return acc; }
4898 * }
4899 * // assume MH_FacLoop is a handle to the constructor
4900 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4901 * // null initializer for counter, should initialize to 0
4902 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4903 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4904 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4905 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4906 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4907 * assertEquals(5040, loop.invoke(7));
4908 * }</pre></blockquote>
4909 *
4910 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4911 *
4912 * @return a method handle embodying the looping behavior as defined by the arguments.
4913 *
4914 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4915 *
4916 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4917 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4918 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4919 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4920 * @since 9
4921 */
4922 public static MethodHandle loop(MethodHandle[]... clauses) {
4923 // Step 0: determine clause structure.
4924 loopChecks0(clauses);
4925
4926 List<MethodHandle> init = new ArrayList<>();
4927 List<MethodHandle> step = new ArrayList<>();
4928 List<MethodHandle> pred = new ArrayList<>();
4929 List<MethodHandle> fini = new ArrayList<>();
4930
4931 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4932 init.add(clause[0]); // all clauses have at least length 1
4933 step.add(clause.length <= 1 ? null : clause[1]);
4934 pred.add(clause.length <= 2 ? null : clause[2]);
4935 fini.add(clause.length <= 3 ? null : clause[3]);
4936 });
4937
4938 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4939 final int nclauses = init.size();
4940
4941 // Step 1A: determine iteration variables (V...).
4942 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4943 for (int i = 0; i < nclauses; ++i) {
4944 MethodHandle in = init.get(i);
4945 MethodHandle st = step.get(i);
4946 if (in == null && st == null) {
4947 iterationVariableTypes.add(void.class);
4948 } else if (in != null && st != null) {
4949 loopChecks1a(i, in, st);
4950 iterationVariableTypes.add(in.type().returnType());
4951 } else {
4952 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4953 }
4954 }
4955 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4956 collect(Collectors.toList());
4957
4958 // Step 1B: determine loop parameters (A...).
4959 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4960 loopChecks1b(init, commonSuffix);
4961
4962 // Step 1C: determine loop return type.
4963 // Step 1D: check other types.
4964 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4965 map(MethodType::returnType).findFirst().orElse(void.class);
4966 loopChecks1cd(pred, fini, loopReturnType);
4967
4968 // Step 2: determine parameter lists.
4969 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4970 commonParameterSequence.addAll(commonSuffix);
4971 loopChecks2(step, pred, fini, commonParameterSequence);
4972
4973 // Step 3: fill in omitted functions.
4974 for (int i = 0; i < nclauses; ++i) {
4975 Class<?> t = iterationVariableTypes.get(i);
4976 if (init.get(i) == null) {
4977 init.set(i, empty(methodType(t, commonSuffix)));
4978 }
4979 if (step.get(i) == null) {
4980 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4981 }
4982 if (pred.get(i) == null) {
4983 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4984 }
4985 if (fini.get(i) == null) {
4986 fini.set(i, empty(methodType(t, commonParameterSequence)));
4987 }
4988 }
4989
4990 // Step 4: fill in missing parameter types.
4991 // Also convert all handles to fixed-arity handles.
4992 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4993 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4994 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4995 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4996
4997 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4998 allMatch(pl -> pl.equals(commonSuffix));
4999 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5000 allMatch(pl -> pl.equals(commonParameterSequence));
5001
5002 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5003 }
5004
5005 private static void loopChecks0(MethodHandle[][] clauses) {
5006 if (clauses == null || clauses.length == 0) {
5007 throw newIllegalArgumentException("null or no clauses passed");
5008 }
5009 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5010 throw newIllegalArgumentException("null clauses are not allowed");
5011 }
5012 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5013 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5014 }
5015 }
5016
5017 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5018 if (in.type().returnType() != st.type().returnType()) {
5019 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5020 st.type().returnType());
5021 }
5022 }
5023
5024 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
5025 final List<Class<?>> empty = List.of();
5026 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
5027 // take only those that can contribute to a common suffix because they are longer than the prefix
5028 map(MethodHandle::type).
5029 filter(t -> t.parameterCount() > skipSize).
5030 map(MethodType::parameterList).
5031 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5032 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
5033 }
5034
5035 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
5036 final List<Class<?>> empty = List.of();
5037 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5038 }
5039
5040 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
5041 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
5042 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
5043 return longestParameterList(Arrays.asList(longest1, longest2));
5044 }
5045
5046 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
5047 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
5048 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
5049 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
5050 " (common suffix: " + commonSuffix + ")");
5051 }
5052 }
5053
5054 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
5055 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5056 anyMatch(t -> t != loopReturnType)) {
5057 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
5058 loopReturnType + ")");
5059 }
5060
5061 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5062 throw newIllegalArgumentException("no predicate found", pred);
5063 }
5064 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5065 anyMatch(t -> t != boolean.class)) {
5066 throw newIllegalArgumentException("predicates must have boolean return type", pred);
5067 }
5068 }
5069
5070 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5071 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5072 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
5073 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5074 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5075 }
5076 }
5077
5078 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
5079 return hs.stream().map(h -> {
5080 int pc = h.type().parameterCount();
5081 int tpsize = targetParams.size();
5082 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5083 }).collect(Collectors.toList());
5084 }
5085
5086 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5087 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5088 }
5089
5090 /**
5091 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5092 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5093 * <p>
5094 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5095 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5096 * evaluates to {@code true}).
5097 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5098 * <p>
5099 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5100 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5101 * and updated with the value returned from its invocation. The result of loop execution will be
5102 * the final value of the additional loop-local variable (if present).
5103 * <p>
5104 * The following rules hold for these argument handles:<ul>
5105 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5106 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5107 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5108 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5109 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5110 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5111 * It will constrain the parameter lists of the other loop parts.
5112 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5113 * list {@code (A...)} is called the <em>external parameter list</em>.
5114 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5115 * additional state variable of the loop.
5116 * The body must both accept and return a value of this type {@code V}.
5117 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5118 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5119 * <a href="MethodHandles.html#effid">effectively identical</a>
5120 * to the external parameter list {@code (A...)}.
5121 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5122 * {@linkplain #empty default value}.
5123 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5124 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5125 * effectively identical to the internal parameter list.
5126 * </ul>
5127 * <p>
5128 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5129 * <li>The loop handle's result type is the result type {@code V} of the body.
5130 * <li>The loop handle's parameter types are the types {@code (A...)},
5131 * from the external parameter list.
5132 * </ul>
5133 * <p>
5134 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5135 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5136 * passed to the loop.
5137 * <blockquote><pre>{@code
5138 * V init(A...);
5139 * boolean pred(V, A...);
5140 * V body(V, A...);
5141 * V whileLoop(A... a...) {
5142 * V v = init(a...);
5143 * while (pred(v, a...)) {
5144 * v = body(v, a...);
5145 * }
5146 * return v;
5147 * }
5148 * }</pre></blockquote>
5149 *
5150 * @apiNote Example:
5151 * <blockquote><pre>{@code
5152 * // implement the zip function for lists as a loop handle
5153 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5154 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5155 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5156 * zip.add(a.next());
5157 * zip.add(b.next());
5158 * return zip;
5159 * }
5160 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5161 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5162 * List<String> a = Arrays.asList("a", "b", "c", "d");
5163 * List<String> b = Arrays.asList("e", "f", "g", "h");
5164 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5165 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5166 * }</pre></blockquote>
5167 *
5168 *
5169 * @apiNote The implementation of this method can be expressed as follows:
5170 * <blockquote><pre>{@code
5171 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5172 * MethodHandle fini = (body.type().returnType() == void.class
5173 * ? null : identity(body.type().returnType()));
5174 * MethodHandle[]
5175 * checkExit = { null, null, pred, fini },
5176 * varBody = { init, body };
5177 * return loop(checkExit, varBody);
5178 * }
5179 * }</pre></blockquote>
5180 *
5181 * @param init optional initializer, providing the initial value of the loop variable.
5182 * May be {@code null}, implying a default initial value. See above for other constraints.
5183 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5184 * above for other constraints.
5185 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5186 * See above for other constraints.
5187 *
5188 * @return a method handle implementing the {@code while} loop as described by the arguments.
5189 * @throws IllegalArgumentException if the rules for the arguments are violated.
5190 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5191 *
5192 * @see #loop(MethodHandle[][])
5193 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5194 * @since 9
5195 */
5196 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5197 whileLoopChecks(init, pred, body);
5198 MethodHandle fini = identityOrVoid(body.type().returnType());
5199 MethodHandle[] checkExit = { null, null, pred, fini };
5200 MethodHandle[] varBody = { init, body };
5201 return loop(checkExit, varBody);
5202 }
5203
5204 /**
5205 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5206 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5207 * <p>
5208 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5209 * method will, in each iteration, first execute its body and then evaluate the predicate.
5210 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5211 * <p>
5212 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5213 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5214 * and updated with the value returned from its invocation. The result of loop execution will be
5215 * the final value of the additional loop-local variable (if present).
5216 * <p>
5217 * The following rules hold for these argument handles:<ul>
5218 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5219 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5220 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5221 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5222 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5223 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5224 * It will constrain the parameter lists of the other loop parts.
5225 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5226 * list {@code (A...)} is called the <em>external parameter list</em>.
5227 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5228 * additional state variable of the loop.
5229 * The body must both accept and return a value of this type {@code V}.
5230 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5231 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5232 * <a href="MethodHandles.html#effid">effectively identical</a>
5233 * to the external parameter list {@code (A...)}.
5234 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5235 * {@linkplain #empty default value}.
5236 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5237 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5238 * effectively identical to the internal parameter list.
5239 * </ul>
5240 * <p>
5241 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5242 * <li>The loop handle's result type is the result type {@code V} of the body.
5243 * <li>The loop handle's parameter types are the types {@code (A...)},
5244 * from the external parameter list.
5245 * </ul>
5246 * <p>
5247 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5248 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5249 * passed to the loop.
5250 * <blockquote><pre>{@code
5251 * V init(A...);
5252 * boolean pred(V, A...);
5253 * V body(V, A...);
5254 * V doWhileLoop(A... a...) {
5255 * V v = init(a...);
5256 * do {
5257 * v = body(v, a...);
5258 * } while (pred(v, a...));
5259 * return v;
5260 * }
5261 * }</pre></blockquote>
5262 *
5263 * @apiNote Example:
5264 * <blockquote><pre>{@code
5265 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5266 * static int zero(int limit) { return 0; }
5267 * static int step(int i, int limit) { return i + 1; }
5268 * static boolean pred(int i, int limit) { return i < limit; }
5269 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5270 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5271 * assertEquals(23, loop.invoke(23));
5272 * }</pre></blockquote>
5273 *
5274 *
5275 * @apiNote The implementation of this method can be expressed as follows:
5276 * <blockquote><pre>{@code
5277 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5278 * MethodHandle fini = (body.type().returnType() == void.class
5279 * ? null : identity(body.type().returnType()));
5280 * MethodHandle[] clause = { init, body, pred, fini };
5281 * return loop(clause);
5282 * }
5283 * }</pre></blockquote>
5284 *
5285 * @param init optional initializer, providing the initial value of the loop variable.
5286 * May be {@code null}, implying a default initial value. See above for other constraints.
5287 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5288 * See above for other constraints.
5289 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5290 * above for other constraints.
5291 *
5292 * @return a method handle implementing the {@code while} loop as described by the arguments.
5293 * @throws IllegalArgumentException if the rules for the arguments are violated.
5294 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5295 *
5296 * @see #loop(MethodHandle[][])
5297 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5298 * @since 9
5299 */
5300 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5301 whileLoopChecks(init, pred, body);
5302 MethodHandle fini = identityOrVoid(body.type().returnType());
5303 MethodHandle[] clause = {init, body, pred, fini };
5304 return loop(clause);
5305 }
5306
5307 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5308 Objects.requireNonNull(pred);
5309 Objects.requireNonNull(body);
5310 MethodType bodyType = body.type();
5311 Class<?> returnType = bodyType.returnType();
5312 List<Class<?>> innerList = bodyType.parameterList();
5313 List<Class<?>> outerList = innerList;
5314 if (returnType == void.class) {
5315 // OK
5316 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5317 // leading V argument missing => error
5318 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5319 throw misMatchedTypes("body function", bodyType, expected);
5320 } else {
5321 outerList = innerList.subList(1, innerList.size());
5322 }
5323 MethodType predType = pred.type();
5324 if (predType.returnType() != boolean.class ||
5325 !predType.effectivelyIdenticalParameters(0, innerList)) {
5326 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5327 }
5328 if (init != null) {
5329 MethodType initType = init.type();
5330 if (initType.returnType() != returnType ||
5331 !initType.effectivelyIdenticalParameters(0, outerList)) {
5332 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5333 }
5334 }
5335 }
5336
5337 /**
5338 * Constructs a loop that runs a given number of iterations.
5339 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5340 * <p>
5341 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5342 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5343 * It will be initialized to 0 and incremented by 1 in each iteration.
5344 * <p>
5345 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5346 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5347 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5348 * <p>
5349 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5350 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5351 * iteration variable.
5352 * The result of the loop handle execution will be the final {@code V} value of that variable
5353 * (or {@code void} if there is no {@code V} variable).
5354 * <p>
5355 * The following rules hold for the argument handles:<ul>
5356 * <li>The {@code iterations} handle must not be {@code null}, and must return
5357 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5358 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5359 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5360 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5361 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5362 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5363 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5364 * of types called the <em>internal parameter list</em>.
5365 * It will constrain the parameter lists of the other loop parts.
5366 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5367 * with no additional {@code A} types, then the internal parameter list is extended by
5368 * the argument types {@code A...} of the {@code iterations} handle.
5369 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5370 * list {@code (A...)} is called the <em>external parameter list</em>.
5371 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5372 * additional state variable of the loop.
5373 * The body must both accept a leading parameter and return a value of this type {@code V}.
5374 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5375 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5376 * <a href="MethodHandles.html#effid">effectively identical</a>
5377 * to the external parameter list {@code (A...)}.
5378 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5379 * {@linkplain #empty default value}.
5380 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5381 * effectively identical to the external parameter list {@code (A...)}.
5382 * </ul>
5383 * <p>
5384 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5385 * <li>The loop handle's result type is the result type {@code V} of the body.
5386 * <li>The loop handle's parameter types are the types {@code (A...)},
5387 * from the external parameter list.
5388 * </ul>
5389 * <p>
5390 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5391 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5392 * arguments passed to the loop.
5393 * <blockquote><pre>{@code
5394 * int iterations(A...);
5395 * V init(A...);
5396 * V body(V, int, A...);
5397 * V countedLoop(A... a...) {
5398 * int end = iterations(a...);
5399 * V v = init(a...);
5400 * for (int i = 0; i < end; ++i) {
5401 * v = body(v, i, a...);
5402 * }
5403 * return v;
5404 * }
5405 * }</pre></blockquote>
5406 *
5407 * @apiNote Example with a fully conformant body method:
5408 * <blockquote><pre>{@code
5409 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5410 * // => a variation on a well known theme
5411 * static String step(String v, int counter, String init) { return "na " + v; }
5412 * // assume MH_step is a handle to the method above
5413 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5414 * MethodHandle start = MethodHandles.identity(String.class);
5415 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5416 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5417 * }</pre></blockquote>
5418 *
5419 * @apiNote Example with the simplest possible body method type,
5420 * and passing the number of iterations to the loop invocation:
5421 * <blockquote><pre>{@code
5422 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5423 * // => a variation on a well known theme
5424 * static String step(String v, int counter ) { return "na " + v; }
5425 * // assume MH_step is a handle to the method above
5426 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5427 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5428 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5429 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5430 * }</pre></blockquote>
5431 *
5432 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5433 * as loop parameters:
5434 * <blockquote><pre>{@code
5435 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5436 * // => a variation on a well known theme
5437 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5438 * // assume MH_step is a handle to the method above
5439 * MethodHandle count = MethodHandles.identity(int.class);
5440 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5441 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5442 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5443 * }</pre></blockquote>
5444 *
5445 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5446 * to enforce a loop type:
5447 * <blockquote><pre>{@code
5448 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5449 * // => a variation on a well known theme
5450 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5451 * // assume MH_step is a handle to the method above
5452 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5453 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5454 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5455 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5456 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5457 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5458 * }</pre></blockquote>
5459 *
5460 * @apiNote The implementation of this method can be expressed as follows:
5461 * <blockquote><pre>{@code
5462 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5463 * return countedLoop(empty(iterations.type()), iterations, init, body);
5464 * }
5465 * }</pre></blockquote>
5466 *
5467 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5468 * result type must be {@code int}. See above for other constraints.
5469 * @param init optional initializer, providing the initial value of the loop variable.
5470 * May be {@code null}, implying a default initial value. See above for other constraints.
5471 * @param body body of the loop, which may not be {@code null}.
5472 * It controls the loop parameters and result type in the standard case (see above for details).
5473 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5474 * and may accept any number of additional types.
5475 * See above for other constraints.
5476 *
5477 * @return a method handle representing the loop.
5478 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5479 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5480 *
5481 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5482 * @since 9
5483 */
5484 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5485 return countedLoop(empty(iterations.type()), iterations, init, body);
5486 }
5487
5488 /**
5489 * Constructs a loop that counts over a range of numbers.
5490 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5491 * <p>
5492 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5493 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5494 * values of the loop counter.
5495 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5496 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5497 * <p>
5498 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5499 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5500 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5501 * <p>
5502 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5503 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5504 * iteration variable.
5505 * The result of the loop handle execution will be the final {@code V} value of that variable
5506 * (or {@code void} if there is no {@code V} variable).
5507 * <p>
5508 * The following rules hold for the argument handles:<ul>
5509 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5510 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5511 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5512 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5513 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5514 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5515 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5516 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5517 * of types called the <em>internal parameter list</em>.
5518 * It will constrain the parameter lists of the other loop parts.
5519 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5520 * with no additional {@code A} types, then the internal parameter list is extended by
5521 * the argument types {@code A...} of the {@code end} handle.
5522 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5523 * list {@code (A...)} is called the <em>external parameter list</em>.
5524 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5525 * additional state variable of the loop.
5526 * The body must both accept a leading parameter and return a value of this type {@code V}.
5527 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5528 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5529 * <a href="MethodHandles.html#effid">effectively identical</a>
5530 * to the external parameter list {@code (A...)}.
5531 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5532 * {@linkplain #empty default value}.
5533 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5534 * effectively identical to the external parameter list {@code (A...)}.
5535 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5536 * to the external parameter list.
5537 * </ul>
5538 * <p>
5539 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5540 * <li>The loop handle's result type is the result type {@code V} of the body.
5541 * <li>The loop handle's parameter types are the types {@code (A...)},
5542 * from the external parameter list.
5543 * </ul>
5544 * <p>
5545 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5546 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5547 * arguments passed to the loop.
5548 * <blockquote><pre>{@code
5549 * int start(A...);
5550 * int end(A...);
5551 * V init(A...);
5552 * V body(V, int, A...);
5553 * V countedLoop(A... a...) {
5554 * int e = end(a...);
5555 * int s = start(a...);
5556 * V v = init(a...);
5557 * for (int i = s; i < e; ++i) {
5558 * v = body(v, i, a...);
5559 * }
5560 * return v;
5561 * }
5562 * }</pre></blockquote>
5563 *
5564 * @apiNote The implementation of this method can be expressed as follows:
5565 * <blockquote><pre>{@code
5566 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5567 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5568 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5569 * // the following semantics:
5570 * // MH_increment: (int limit, int counter) -> counter + 1
5571 * // MH_predicate: (int limit, int counter) -> counter < limit
5572 * Class<?> counterType = start.type().returnType(); // int
5573 * Class<?> returnType = body.type().returnType();
5574 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5575 * if (returnType != void.class) { // ignore the V variable
5576 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5577 * pred = dropArguments(pred, 1, returnType); // ditto
5578 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5579 * }
5580 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5581 * MethodHandle[]
5582 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5583 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5584 * indexVar = { start, incr }; // i = start(); i = i + 1
5585 * return loop(loopLimit, bodyClause, indexVar);
5586 * }
5587 * }</pre></blockquote>
5588 *
5589 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5590 * See above for other constraints.
5591 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5592 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5593 * @param init optional initializer, providing the initial value of the loop variable.
5594 * May be {@code null}, implying a default initial value. See above for other constraints.
5595 * @param body body of the loop, which may not be {@code null}.
5596 * It controls the loop parameters and result type in the standard case (see above for details).
5597 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5598 * and may accept any number of additional types.
5599 * See above for other constraints.
5600 *
5601 * @return a method handle representing the loop.
5602 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5603 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5604 *
5605 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5606 * @since 9
5607 */
5608 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5609 countedLoopChecks(start, end, init, body);
5610 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5611 Class<?> limitType = end.type().returnType(); // yes, int again
5612 Class<?> returnType = body.type().returnType();
5613 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5614 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5615 MethodHandle retv = null;
5616 if (returnType != void.class) {
5617 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5618 pred = dropArguments(pred, 1, returnType); // ditto
5619 retv = dropArguments(identity(returnType), 0, counterType);
5620 }
5621 body = dropArguments(body, 0, counterType); // ignore the limit variable
5622 MethodHandle[]
5623 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5624 bodyClause = { init, body }, // v = init(); v = body(v, i)
5625 indexVar = { start, incr }; // i = start(); i = i + 1
5626 return loop(loopLimit, bodyClause, indexVar);
5627 }
5628
5629 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5630 Objects.requireNonNull(start);
5631 Objects.requireNonNull(end);
5632 Objects.requireNonNull(body);
5633 Class<?> counterType = start.type().returnType();
5634 if (counterType != int.class) {
5635 MethodType expected = start.type().changeReturnType(int.class);
5636 throw misMatchedTypes("start function", start.type(), expected);
5637 } else if (end.type().returnType() != counterType) {
5638 MethodType expected = end.type().changeReturnType(counterType);
5639 throw misMatchedTypes("end function", end.type(), expected);
5640 }
5641 MethodType bodyType = body.type();
5642 Class<?> returnType = bodyType.returnType();
5643 List<Class<?>> innerList = bodyType.parameterList();
5644 // strip leading V value if present
5645 int vsize = (returnType == void.class ? 0 : 1);
5646 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5647 // argument list has no "V" => error
5648 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5649 throw misMatchedTypes("body function", bodyType, expected);
5650 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5651 // missing I type => error
5652 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5653 throw misMatchedTypes("body function", bodyType, expected);
5654 }
5655 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5656 if (outerList.isEmpty()) {
5657 // special case; take lists from end handle
5658 outerList = end.type().parameterList();
5659 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5660 }
5661 MethodType expected = methodType(counterType, outerList);
5662 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5663 throw misMatchedTypes("start parameter types", start.type(), expected);
5664 }
5665 if (end.type() != start.type() &&
5666 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5667 throw misMatchedTypes("end parameter types", end.type(), expected);
5668 }
5669 if (init != null) {
5670 MethodType initType = init.type();
5671 if (initType.returnType() != returnType ||
5672 !initType.effectivelyIdenticalParameters(0, outerList)) {
5673 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5674 }
5675 }
5676 }
5677
5678 /**
5679 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5680 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5681 * <p>
5682 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5683 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5684 * <p>
5685 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5686 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5687 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5688 * <p>
5689 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5690 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5691 * iteration variable.
5692 * The result of the loop handle execution will be the final {@code V} value of that variable
5693 * (or {@code void} if there is no {@code V} variable).
5694 * <p>
5695 * The following rules hold for the argument handles:<ul>
5696 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5697 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5698 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5699 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5700 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5701 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5702 * of types called the <em>internal parameter list</em>.
5703 * It will constrain the parameter lists of the other loop parts.
5704 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5705 * with no additional {@code A} types, then the internal parameter list is extended by
5706 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5707 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5708 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5709 * list {@code (A...)} is called the <em>external parameter list</em>.
5710 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5711 * additional state variable of the loop.
5712 * The body must both accept a leading parameter and return a value of this type {@code V}.
5713 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5714 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5715 * <a href="MethodHandles.html#effid">effectively identical</a>
5716 * to the external parameter list {@code (A...)}.
5717 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5718 * {@linkplain #empty default value}.
5719 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5720 * type {@code java.util.Iterator} or a subtype thereof.
5721 * The iterator it produces when the loop is executed will be assumed
5722 * to yield values which can be converted to type {@code T}.
5723 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5724 * effectively identical to the external parameter list {@code (A...)}.
5725 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5726 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5727 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5728 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5729 * the {@link MethodHandle#asType asType} conversion method.
5730 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5731 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5732 * </ul>
5733 * <p>
5734 * The type {@code T} may be either a primitive or reference.
5735 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5736 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5737 * as if by the {@link MethodHandle#asType asType} conversion method.
5738 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5739 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5740 * <p>
5741 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5742 * <li>The loop handle's result type is the result type {@code V} of the body.
5743 * <li>The loop handle's parameter types are the types {@code (A...)},
5744 * from the external parameter list.
5745 * </ul>
5746 * <p>
5747 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5748 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5749 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5750 * <blockquote><pre>{@code
5751 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5752 * V init(A...);
5753 * V body(V,T,A...);
5754 * V iteratedLoop(A... a...) {
5755 * Iterator<T> it = iterator(a...);
5756 * V v = init(a...);
5757 * while (it.hasNext()) {
5758 * T t = it.next();
5759 * v = body(v, t, a...);
5760 * }
5761 * return v;
5762 * }
5763 * }</pre></blockquote>
5764 *
5765 * @apiNote Example:
5766 * <blockquote><pre>{@code
5767 * // get an iterator from a list
5768 * static List<String> reverseStep(List<String> r, String e) {
5769 * r.add(0, e);
5770 * return r;
5771 * }
5772 * static List<String> newArrayList() { return new ArrayList<>(); }
5773 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5774 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5775 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5776 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5777 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5778 * }</pre></blockquote>
5779 *
5780 * @apiNote The implementation of this method can be expressed approximately as follows:
5781 * <blockquote><pre>{@code
5782 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5783 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5784 * Class<?> returnType = body.type().returnType();
5785 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5786 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5787 * MethodHandle retv = null, step = body, startIter = iterator;
5788 * if (returnType != void.class) {
5789 * // the simple thing first: in (I V A...), drop the I to get V
5790 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5791 * // body type signature (V T A...), internal loop types (I V A...)
5792 * step = swapArguments(body, 0, 1); // swap V <-> T
5793 * }
5794 * if (startIter == null) startIter = MH_getIter;
5795 * MethodHandle[]
5796 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5797 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5798 * return loop(iterVar, bodyClause);
5799 * }
5800 * }</pre></blockquote>
5801 *
5802 * @param iterator an optional handle to return the iterator to start the loop.
5803 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5804 * See above for other constraints.
5805 * @param init optional initializer, providing the initial value of the loop variable.
5806 * May be {@code null}, implying a default initial value. See above for other constraints.
5807 * @param body body of the loop, which may not be {@code null}.
5808 * It controls the loop parameters and result type in the standard case (see above for details).
5809 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5810 * and may accept any number of additional types.
5811 * See above for other constraints.
5812 *
5813 * @return a method handle embodying the iteration loop functionality.
5814 * @throws NullPointerException if the {@code body} handle is {@code null}.
5815 * @throws IllegalArgumentException if any argument violates the above requirements.
5816 *
5817 * @since 9
5818 */
5819 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5820 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5821 Class<?> returnType = body.type().returnType();
5822 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5823 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5824 MethodHandle startIter;
5825 MethodHandle nextVal;
5826 {
5827 MethodType iteratorType;
5828 if (iterator == null) {
5829 // derive argument type from body, if available, else use Iterable
5830 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5831 iteratorType = startIter.type().changeParameterType(0, iterableType);
5832 } else {
5833 // force return type to the internal iterator class
5834 iteratorType = iterator.type().changeReturnType(Iterator.class);
5835 startIter = iterator;
5836 }
5837 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5838 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5839
5840 // perform the asType transforms under an exception transformer, as per spec.:
5841 try {
5842 startIter = startIter.asType(iteratorType);
5843 nextVal = nextRaw.asType(nextValType);
5844 } catch (WrongMethodTypeException ex) {
5845 throw new IllegalArgumentException(ex);
5846 }
5847 }
5848
5849 MethodHandle retv = null, step = body;
5850 if (returnType != void.class) {
5851 // the simple thing first: in (I V A...), drop the I to get V
5852 retv = dropArguments(identity(returnType), 0, Iterator.class);
5853 // body type signature (V T A...), internal loop types (I V A...)
5854 step = swapArguments(body, 0, 1); // swap V <-> T
5855 }
5856
5857 MethodHandle[]
5858 iterVar = { startIter, null, hasNext, retv },
5859 bodyClause = { init, filterArgument(step, 0, nextVal) };
5860 return loop(iterVar, bodyClause);
5861 }
5862
5863 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5864 Objects.requireNonNull(body);
5865 MethodType bodyType = body.type();
5866 Class<?> returnType = bodyType.returnType();
5867 List<Class<?>> internalParamList = bodyType.parameterList();
5868 // strip leading V value if present
5869 int vsize = (returnType == void.class ? 0 : 1);
5870 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5871 // argument list has no "V" => error
5872 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5873 throw misMatchedTypes("body function", bodyType, expected);
5874 } else if (internalParamList.size() <= vsize) {
5875 // missing T type => error
5876 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5877 throw misMatchedTypes("body function", bodyType, expected);
5878 }
5879 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5880 Class<?> iterableType = null;
5881 if (iterator != null) {
5882 // special case; if the body handle only declares V and T then
5883 // the external parameter list is obtained from iterator handle
5884 if (externalParamList.isEmpty()) {
5885 externalParamList = iterator.type().parameterList();
5886 }
5887 MethodType itype = iterator.type();
5888 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5889 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5890 }
5891 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5892 MethodType expected = methodType(itype.returnType(), externalParamList);
5893 throw misMatchedTypes("iterator parameters", itype, expected);
5894 }
5895 } else {
5896 if (externalParamList.isEmpty()) {
5897 // special case; if the iterator handle is null and the body handle
5898 // only declares V and T then the external parameter list consists
5899 // of Iterable
5900 externalParamList = Arrays.asList(Iterable.class);
5901 iterableType = Iterable.class;
5902 } else {
5903 // special case; if the iterator handle is null and the external
5904 // parameter list is not empty then the first parameter must be
5905 // assignable to Iterable
5906 iterableType = externalParamList.get(0);
5907 if (!Iterable.class.isAssignableFrom(iterableType)) {
5908 throw newIllegalArgumentException(
5909 "inferred first loop argument must inherit from Iterable: " + iterableType);
5910 }
5911 }
5912 }
5913 if (init != null) {
5914 MethodType initType = init.type();
5915 if (initType.returnType() != returnType ||
5916 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5917 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5918 }
5919 }
5920 return iterableType; // help the caller a bit
5921 }
5922
5923 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5924 // there should be a better way to uncross my wires
5925 int arity = mh.type().parameterCount();
5926 int[] order = new int[arity];
5927 for (int k = 0; k < arity; k++) order[k] = k;
5928 order[i] = j; order[j] = i;
5929 Class<?>[] types = mh.type().parameterArray();
5930 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5931 MethodType swapType = methodType(mh.type().returnType(), types);
5932 return permuteArguments(mh, swapType, order);
5933 }
5934
5935 /**
5936 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5937 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5938 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5939 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5940 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5941 * {@code try-finally} handle.
5942 * <p>
5943 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5944 * The first is the exception thrown during the
5945 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5946 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5947 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5948 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5949 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5950 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5951 * <p>
5952 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5953 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5954 * two extra leading parameters:<ul>
5955 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5956 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5957 * the result from the execution of the {@code target} handle.
5958 * This parameter is not present if the {@code target} returns {@code void}.
5959 * </ul>
5960 * <p>
5961 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5962 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5963 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5964 * the cleanup.
5965 * <blockquote><pre>{@code
5966 * V target(A..., B...);
5967 * V cleanup(Throwable, V, A...);
5968 * V adapter(A... a, B... b) {
5969 * V result = (zero value for V);
5970 * Throwable throwable = null;
5971 * try {
5972 * result = target(a..., b...);
5973 * } catch (Throwable t) {
5974 * throwable = t;
5975 * throw t;
5976 * } finally {
5977 * result = cleanup(throwable, result, a...);
5978 * }
5979 * return result;
5980 * }
5981 * }</pre></blockquote>
5982 * <p>
5983 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5984 * be modified by execution of the target, and so are passed unchanged
5985 * from the caller to the cleanup, if it is invoked.
5986 * <p>
5987 * The target and cleanup must return the same type, even if the cleanup
5988 * always throws.
5989 * To create such a throwing cleanup, compose the cleanup logic
5990 * with {@link #throwException throwException},
5991 * in order to create a method handle of the correct return type.
5992 * <p>
5993 * Note that {@code tryFinally} never converts exceptions into normal returns.
5994 * In rare cases where exceptions must be converted in that way, first wrap
5995 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5996 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5997 * <p>
5998 * It is recommended that the first parameter type of {@code cleanup} be
5999 * declared {@code Throwable} rather than a narrower subtype. This ensures
6000 * {@code cleanup} will always be invoked with whatever exception that
6001 * {@code target} throws. Declaring a narrower type may result in a
6002 * {@code ClassCastException} being thrown by the {@code try-finally}
6003 * handle if the type of the exception thrown by {@code target} is not
6004 * assignable to the first parameter type of {@code cleanup}. Note that
6005 * various exception types of {@code VirtualMachineError},
6006 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6007 * thrown by almost any kind of Java code, and a finally clause that
6008 * catches (say) only {@code IOException} would mask any of the others
6009 * behind a {@code ClassCastException}.
6010 *
6011 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6012 * @param cleanup the handle that is invoked in the finally block.
6013 *
6014 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6015 * @throws NullPointerException if any argument is null
6016 * @throws IllegalArgumentException if {@code cleanup} does not accept
6017 * the required leading arguments, or if the method handle types do
6018 * not match in their return types and their
6019 * corresponding trailing parameters
6020 *
6021 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
6022 * @since 9
6023 */
6024 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
6025 List<Class<?>> targetParamTypes = target.type().parameterList();
6026 Class<?> rtype = target.type().returnType();
6027
6028 tryFinallyChecks(target, cleanup);
6029
6030 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
6031 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6032 // target parameter list.
6033 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
6034
6035 // Ensure that the intrinsic type checks the instance thrown by the
6036 // target against the first parameter of cleanup
6037 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
6038
6039 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
6040 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
6041 }
6042
6043 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
6044 Class<?> rtype = target.type().returnType();
6045 if (rtype != cleanup.type().returnType()) {
6046 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
6047 }
6048 MethodType cleanupType = cleanup.type();
6049 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
6050 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
6051 }
6052 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
6053 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
6054 }
6055 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6056 // target parameter list.
6057 int cleanupArgIndex = rtype == void.class ? 1 : 2;
6058 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
6059 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
6060 cleanup.type(), target.type());
6061 }
6062 }
6063
6064 }