1 /*
2 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.misc.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.concurrent.ConcurrentHashMap;
58 import java.util.stream.Collectors;
59 import java.util.stream.Stream;
60
61 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
62 import static java.lang.invoke.MethodHandleNatives.Constants.*;
63 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
64 import static java.lang.invoke.MethodType.methodType;
65
66 /**
67 * This class consists exclusively of static methods that operate on or return
68 * method handles. They fall into several categories:
69 * <ul>
70 * <li>Lookup methods which help create method handles for methods and fields.
71 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
72 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
73 * </ul>
74 * A lookup, combinator, or factory method will fail and throw an
75 * {@code IllegalArgumentException} if the created method handle's type
76 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
77 *
78 * @author John Rose, JSR 292 EG
79 * @since 1.7
80 */
81 public class MethodHandles {
82
83 private MethodHandles() { } // do not instantiate
84
85 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
86
87 // See IMPL_LOOKUP below.
88
89 //// Method handle creation from ordinary methods.
90
91 /**
92 * Returns a {@link Lookup lookup object} with
93 * full capabilities to emulate all supported bytecode behaviors of the caller.
94 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
95 * Factory methods on the lookup object can create
96 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
97 * for any member that the caller has access to via bytecodes,
98 * including protected and private fields and methods.
99 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
100 * Do not store it in place where untrusted code can access it.
101 * <p>
102 * This method is caller sensitive, which means that it may return different
103 * values to different callers.
104 * @return a lookup object for the caller of this method, with private access
105 */
106 @CallerSensitive
107 @ForceInline // to ensure Reflection.getCallerClass optimization
108 public static Lookup lookup() {
109 return new Lookup(Reflection.getCallerClass());
110 }
111
112 /**
113 * This reflected$lookup method is the alternate implementation of
114 * the lookup method when being invoked by reflection.
115 */
116 @CallerSensitive
117 private static Lookup reflected$lookup() {
118 Class<?> caller = Reflection.getCallerClass();
119 if (caller.getClassLoader() == null) {
120 throw newIllegalArgumentException("illegal lookupClass: "+caller);
121 }
122 return new Lookup(caller);
123 }
124
125 /**
126 * Returns a {@link Lookup lookup object} which is trusted minimally.
127 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
128 * It can only be used to create method handles to public members of
129 * public classes in packages that are exported unconditionally.
130 * <p>
131 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
132 * of this lookup object will be {@link java.lang.Object}.
133 *
134 * @apiNote The use of Object is conventional, and because the lookup modes are
135 * limited, there is no special access provided to the internals of Object, its package
136 * or its module. Consequently, the lookup context of this lookup object will be the
137 * bootstrap class loader, which means it cannot find user classes.
138 *
139 * <p style="font-size:smaller;">
140 * <em>Discussion:</em>
141 * The lookup class can be changed to any other class {@code C} using an expression of the form
142 * {@link Lookup#in publicLookup().in(C.class)}.
143 * but may change the lookup context by virtue of changing the class loader.
144 * A public lookup object is always subject to
145 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
146 * Also, it cannot access
147 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
148 * @return a lookup object which is trusted minimally
149 *
150 * @revised 9
151 * @spec JPMS
152 */
153 public static Lookup publicLookup() {
154 return Lookup.PUBLIC_LOOKUP;
155 }
156
157 /**
158 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
159 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
160 * private access</a>, on a target class.
161 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
162 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
163 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
164 * the target class, then this check ensures that
165 * <ul>
166 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
167 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
168 * the target class to at least {@code m1}.</li>
169 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
170 * </ul>
171 * <p>
172 * If there is a security manager, its {@code checkPermission} method is called to
173 * check {@code ReflectPermission("suppressAccessChecks")}.
174 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
175 * was created by code in the caller module (or derived from a lookup object originally
176 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
177 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
178 * access to the caller.
179 * @param targetClass the target class
180 * @param lookup the caller lookup object
181 * @return a lookup object for the target class, with private access
182 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
183 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
184 * @throws IllegalAccessException if the access check specified above fails
185 * @throws SecurityException if denied by the security manager
186 * @since 9
187 * @spec JPMS
188 * @see Lookup#dropLookupMode
189 */
190 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
191 SecurityManager sm = System.getSecurityManager();
192 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
193 if (targetClass.isPrimitive())
194 throw new IllegalArgumentException(targetClass + " is a primitive class");
195 if (targetClass.isArray())
196 throw new IllegalArgumentException(targetClass + " is an array class");
197 Module targetModule = targetClass.getModule();
198 Module callerModule = lookup.lookupClass().getModule();
199 if (!callerModule.canRead(targetModule))
200 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
201 if (targetModule.isNamed()) {
202 String pn = targetClass.getPackageName();
203 assert pn.length() > 0 : "unnamed package cannot be in named module";
204 if (!targetModule.isOpen(pn, callerModule))
205 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
206 }
207 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
208 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
209 if (!callerModule.isNamed() && targetModule.isNamed()) {
210 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
211 if (logger != null) {
212 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
213 }
214 }
215 return new Lookup(targetClass);
216 }
217
218 /**
219 * Performs an unchecked "crack" of a
220 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
221 * The result is as if the user had obtained a lookup object capable enough
222 * to crack the target method handle, called
223 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
224 * on the target to obtain its symbolic reference, and then called
225 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
226 * to resolve the symbolic reference to a member.
227 * <p>
228 * If there is a security manager, its {@code checkPermission} method
229 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
230 * @param <T> the desired type of the result, either {@link Member} or a subtype
231 * @param target a direct method handle to crack into symbolic reference components
232 * @param expected a class object representing the desired result type {@code T}
233 * @return a reference to the method, constructor, or field object
234 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
235 * @exception NullPointerException if either argument is {@code null}
236 * @exception IllegalArgumentException if the target is not a direct method handle
237 * @exception ClassCastException if the member is not of the expected type
238 * @since 1.8
239 */
240 public static <T extends Member> T
241 reflectAs(Class<T> expected, MethodHandle target) {
242 SecurityManager smgr = System.getSecurityManager();
243 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
244 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
245 return lookup.revealDirect(target).reflectAs(expected, lookup);
246 }
247 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
248 private static final java.security.Permission ACCESS_PERMISSION =
249 new ReflectPermission("suppressAccessChecks");
250
251 /**
252 * A <em>lookup object</em> is a factory for creating method handles,
253 * when the creation requires access checking.
254 * Method handles do not perform
255 * access checks when they are called, but rather when they are created.
256 * Therefore, method handle access
257 * restrictions must be enforced when a method handle is created.
258 * The caller class against which those restrictions are enforced
259 * is known as the {@linkplain #lookupClass() lookup class}.
260 * <p>
261 * A lookup class which needs to create method handles will call
262 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
263 * When the {@code Lookup} factory object is created, the identity of the lookup class is
264 * determined, and securely stored in the {@code Lookup} object.
265 * The lookup class (or its delegates) may then use factory methods
266 * on the {@code Lookup} object to create method handles for access-checked members.
267 * This includes all methods, constructors, and fields which are allowed to the lookup class,
268 * even private ones.
269 *
270 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
271 * The factory methods on a {@code Lookup} object correspond to all major
272 * use cases for methods, constructors, and fields.
273 * Each method handle created by a factory method is the functional
274 * equivalent of a particular <em>bytecode behavior</em>.
275 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
276 * Here is a summary of the correspondence between these factory methods and
277 * the behavior of the resulting method handles:
278 * <table class="striped">
279 * <caption style="display:none">lookup method behaviors</caption>
280 * <thead>
281 * <tr>
282 * <th scope="col"><a id="equiv"></a>lookup expression</th>
283 * <th scope="col">member</th>
284 * <th scope="col">bytecode behavior</th>
285 * </tr>
286 * </thead>
287 * <tbody>
288 * <tr>
289 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
290 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
291 * </tr>
292 * <tr>
293 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
294 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
295 * </tr>
296 * <tr>
297 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
298 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
299 * </tr>
300 * <tr>
301 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
302 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
303 * </tr>
304 * <tr>
305 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
306 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
307 * </tr>
308 * <tr>
309 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
310 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
311 * </tr>
312 * <tr>
313 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
314 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
315 * </tr>
316 * <tr>
317 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
318 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
319 * </tr>
320 * <tr>
321 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
322 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
323 * </tr>
324 * <tr>
325 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
326 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
327 * </tr>
328 * <tr>
329 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
330 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
331 * </tr>
332 * <tr>
333 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
334 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
335 * </tr>
336 * <tr>
337 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
338 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
339 * </tr>
340 * <tr>
341 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
342 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
343 * </tr>
344 * </tbody>
345 * </table>
346 *
347 * Here, the type {@code C} is the class or interface being searched for a member,
348 * documented as a parameter named {@code refc} in the lookup methods.
349 * The method type {@code MT} is composed from the return type {@code T}
350 * and the sequence of argument types {@code A*}.
351 * The constructor also has a sequence of argument types {@code A*} and
352 * is deemed to return the newly-created object of type {@code C}.
353 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
354 * The formal parameter {@code this} stands for the self-reference of type {@code C};
355 * if it is present, it is always the leading argument to the method handle invocation.
356 * (In the case of some {@code protected} members, {@code this} may be
357 * restricted in type to the lookup class; see below.)
358 * The name {@code arg} stands for all the other method handle arguments.
359 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
360 * stands for a null reference if the accessed method or field is static,
361 * and {@code this} otherwise.
362 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
363 * for reflective objects corresponding to the given members.
364 * <p>
365 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
366 * as if by {@code ldc CONSTANT_Class}.
367 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
368 * <p>
369 * In cases where the given member is of variable arity (i.e., a method or constructor)
370 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
371 * In all other cases, the returned method handle will be of fixed arity.
372 * <p style="font-size:smaller;">
373 * <em>Discussion:</em>
374 * The equivalence between looked-up method handles and underlying
375 * class members and bytecode behaviors
376 * can break down in a few ways:
377 * <ul style="font-size:smaller;">
378 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
379 * the lookup can still succeed, even when there is no equivalent
380 * Java expression or bytecoded constant.
381 * <li>Likewise, if {@code T} or {@code MT}
382 * is not symbolically accessible from the lookup class's loader,
383 * the lookup can still succeed.
384 * For example, lookups for {@code MethodHandle.invokeExact} and
385 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
386 * <li>If there is a security manager installed, it can forbid the lookup
387 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
388 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
389 * constant is not subject to security manager checks.
390 * <li>If the looked-up method has a
391 * <a href="MethodHandle.html#maxarity">very large arity</a>,
392 * the method handle creation may fail with an
393 * {@code IllegalArgumentException}, due to the method handle type having
394 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
395 * </ul>
396 *
397 * <h1><a id="access"></a>Access checking</h1>
398 * Access checks are applied in the factory methods of {@code Lookup},
399 * when a method handle is created.
400 * This is a key difference from the Core Reflection API, since
401 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
402 * performs access checking against every caller, on every call.
403 * <p>
404 * All access checks start from a {@code Lookup} object, which
405 * compares its recorded lookup class against all requests to
406 * create method handles.
407 * A single {@code Lookup} object can be used to create any number
408 * of access-checked method handles, all checked against a single
409 * lookup class.
410 * <p>
411 * A {@code Lookup} object can be shared with other trusted code,
412 * such as a metaobject protocol.
413 * A shared {@code Lookup} object delegates the capability
414 * to create method handles on private members of the lookup class.
415 * Even if privileged code uses the {@code Lookup} object,
416 * the access checking is confined to the privileges of the
417 * original lookup class.
418 * <p>
419 * A lookup can fail, because
420 * the containing class is not accessible to the lookup class, or
421 * because the desired class member is missing, or because the
422 * desired class member is not accessible to the lookup class, or
423 * because the lookup object is not trusted enough to access the member.
424 * In any of these cases, a {@code ReflectiveOperationException} will be
425 * thrown from the attempted lookup. The exact class will be one of
426 * the following:
427 * <ul>
428 * <li>NoSuchMethodException — if a method is requested but does not exist
429 * <li>NoSuchFieldException — if a field is requested but does not exist
430 * <li>IllegalAccessException — if the member exists but an access check fails
431 * </ul>
432 * <p>
433 * In general, the conditions under which a method handle may be
434 * looked up for a method {@code M} are no more restrictive than the conditions
435 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
436 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
437 * a method handle lookup will generally raise a corresponding
438 * checked exception, such as {@code NoSuchMethodException}.
439 * And the effect of invoking the method handle resulting from the lookup
440 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
441 * to executing the compiled, verified, and resolved call to {@code M}.
442 * The same point is true of fields and constructors.
443 * <p style="font-size:smaller;">
444 * <em>Discussion:</em>
445 * Access checks only apply to named and reflected methods,
446 * constructors, and fields.
447 * Other method handle creation methods, such as
448 * {@link MethodHandle#asType MethodHandle.asType},
449 * do not require any access checks, and are used
450 * independently of any {@code Lookup} object.
451 * <p>
452 * If the desired member is {@code protected}, the usual JVM rules apply,
453 * including the requirement that the lookup class must either be in the
454 * same package as the desired member, or must inherit that member.
455 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
456 * In addition, if the desired member is a non-static field or method
457 * in a different package, the resulting method handle may only be applied
458 * to objects of the lookup class or one of its subclasses.
459 * This requirement is enforced by narrowing the type of the leading
460 * {@code this} parameter from {@code C}
461 * (which will necessarily be a superclass of the lookup class)
462 * to the lookup class itself.
463 * <p>
464 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
465 * that the receiver argument must match both the resolved method <em>and</em>
466 * the current class. Again, this requirement is enforced by narrowing the
467 * type of the leading parameter to the resulting method handle.
468 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
469 * <p>
470 * The JVM represents constructors and static initializer blocks as internal methods
471 * with special names ({@code "<init>"} and {@code "<clinit>"}).
472 * The internal syntax of invocation instructions allows them to refer to such internal
473 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
474 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
475 * <p>
476 * If the relationship between nested types is expressed directly through the
477 * {@code NestHost} and {@code NestMembers} attributes
478 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
479 * then the associated {@code Lookup} object provides direct access to
480 * the lookup class and all of its nestmates
481 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
482 * Otherwise, access between nested classes is obtained by the Java compiler creating
483 * a wrapper method to access a private method of another class in the same nest.
484 * For example, a nested class {@code C.D}
485 * can access private members within other related classes such as
486 * {@code C}, {@code C.D.E}, or {@code C.B},
487 * but the Java compiler may need to generate wrapper methods in
488 * those related classes. In such cases, a {@code Lookup} object on
489 * {@code C.E} would be unable to access those private members.
490 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
491 * which can transform a lookup on {@code C.E} into one on any of those other
492 * classes, without special elevation of privilege.
493 * <p>
494 * The accesses permitted to a given lookup object may be limited,
495 * according to its set of {@link #lookupModes lookupModes},
496 * to a subset of members normally accessible to the lookup class.
497 * For example, the {@link MethodHandles#publicLookup publicLookup}
498 * method produces a lookup object which is only allowed to access
499 * public members in public classes of exported packages.
500 * The caller sensitive method {@link MethodHandles#lookup lookup}
501 * produces a lookup object with full capabilities relative to
502 * its caller class, to emulate all supported bytecode behaviors.
503 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
504 * with fewer access modes than the original lookup object.
505 *
506 * <p style="font-size:smaller;">
507 * <a id="privacc"></a>
508 * <em>Discussion of private access:</em>
509 * We say that a lookup has <em>private access</em>
510 * if its {@linkplain #lookupModes lookup modes}
511 * include the possibility of accessing {@code private} members
512 * (which includes the private members of nestmates).
513 * As documented in the relevant methods elsewhere,
514 * only lookups with private access possess the following capabilities:
515 * <ul style="font-size:smaller;">
516 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
517 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
518 * such as {@code Class.forName}
519 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
520 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
521 * for classes accessible to the lookup class
522 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
523 * within the same package member
524 * </ul>
525 * <p style="font-size:smaller;">
526 * Each of these permissions is a consequence of the fact that a lookup object
527 * with private access can be securely traced back to an originating class,
528 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
529 * can be reliably determined and emulated by method handles.
530 *
531 * <h1><a id="secmgr"></a>Security manager interactions</h1>
532 * Although bytecode instructions can only refer to classes in
533 * a related class loader, this API can search for methods in any
534 * class, as long as a reference to its {@code Class} object is
535 * available. Such cross-loader references are also possible with the
536 * Core Reflection API, and are impossible to bytecode instructions
537 * such as {@code invokestatic} or {@code getfield}.
538 * There is a {@linkplain java.lang.SecurityManager security manager API}
539 * to allow applications to check such cross-loader references.
540 * These checks apply to both the {@code MethodHandles.Lookup} API
541 * and the Core Reflection API
542 * (as found on {@link java.lang.Class Class}).
543 * <p>
544 * If a security manager is present, member and class lookups are subject to
545 * additional checks.
546 * From one to three calls are made to the security manager.
547 * Any of these calls can refuse access by throwing a
548 * {@link java.lang.SecurityException SecurityException}.
549 * Define {@code smgr} as the security manager,
550 * {@code lookc} as the lookup class of the current lookup object,
551 * {@code refc} as the containing class in which the member
552 * is being sought, and {@code defc} as the class in which the
553 * member is actually defined.
554 * (If a class or other type is being accessed,
555 * the {@code refc} and {@code defc} values are the class itself.)
556 * The value {@code lookc} is defined as <em>not present</em>
557 * if the current lookup object does not have
558 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
559 * The calls are made according to the following rules:
560 * <ul>
561 * <li><b>Step 1:</b>
562 * If {@code lookc} is not present, or if its class loader is not
563 * the same as or an ancestor of the class loader of {@code refc},
564 * then {@link SecurityManager#checkPackageAccess
565 * smgr.checkPackageAccess(refcPkg)} is called,
566 * where {@code refcPkg} is the package of {@code refc}.
567 * <li><b>Step 2a:</b>
568 * If the retrieved member is not public and
569 * {@code lookc} is not present, then
570 * {@link SecurityManager#checkPermission smgr.checkPermission}
571 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
572 * <li><b>Step 2b:</b>
573 * If the retrieved class has a {@code null} class loader,
574 * and {@code lookc} is not present, then
575 * {@link SecurityManager#checkPermission smgr.checkPermission}
576 * with {@code RuntimePermission("getClassLoader")} is called.
577 * <li><b>Step 3:</b>
578 * If the retrieved member is not public,
579 * and if {@code lookc} is not present,
580 * and if {@code defc} and {@code refc} are different,
581 * then {@link SecurityManager#checkPackageAccess
582 * smgr.checkPackageAccess(defcPkg)} is called,
583 * where {@code defcPkg} is the package of {@code defc}.
584 * </ul>
585 * Security checks are performed after other access checks have passed.
586 * Therefore, the above rules presuppose a member or class that is public,
587 * or else that is being accessed from a lookup class that has
588 * rights to access the member or class.
589 *
590 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
591 * A small number of Java methods have a special property called caller sensitivity.
592 * A <em>caller-sensitive</em> method can behave differently depending on the
593 * identity of its immediate caller.
594 * <p>
595 * If a method handle for a caller-sensitive method is requested,
596 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
597 * but they take account of the lookup class in a special way.
598 * The resulting method handle behaves as if it were called
599 * from an instruction contained in the lookup class,
600 * so that the caller-sensitive method detects the lookup class.
601 * (By contrast, the invoker of the method handle is disregarded.)
602 * Thus, in the case of caller-sensitive methods,
603 * different lookup classes may give rise to
604 * differently behaving method handles.
605 * <p>
606 * In cases where the lookup object is
607 * {@link MethodHandles#publicLookup() publicLookup()},
608 * or some other lookup object without
609 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
610 * the lookup class is disregarded.
611 * In such cases, no caller-sensitive method handle can be created,
612 * access is forbidden, and the lookup fails with an
613 * {@code IllegalAccessException}.
614 * <p style="font-size:smaller;">
615 * <em>Discussion:</em>
616 * For example, the caller-sensitive method
617 * {@link java.lang.Class#forName(String) Class.forName(x)}
618 * can return varying classes or throw varying exceptions,
619 * depending on the class loader of the class that calls it.
620 * A public lookup of {@code Class.forName} will fail, because
621 * there is no reasonable way to determine its bytecode behavior.
622 * <p style="font-size:smaller;">
623 * If an application caches method handles for broad sharing,
624 * it should use {@code publicLookup()} to create them.
625 * If there is a lookup of {@code Class.forName}, it will fail,
626 * and the application must take appropriate action in that case.
627 * It may be that a later lookup, perhaps during the invocation of a
628 * bootstrap method, can incorporate the specific identity
629 * of the caller, making the method accessible.
630 * <p style="font-size:smaller;">
631 * The function {@code MethodHandles.lookup} is caller sensitive
632 * so that there can be a secure foundation for lookups.
633 * Nearly all other methods in the JSR 292 API rely on lookup
634 * objects to check access requests.
635 *
636 * @revised 9
637 */
638 public static final
639 class Lookup {
640 /** The class on behalf of whom the lookup is being performed. */
641 private final Class<?> lookupClass;
642
643 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
644 private final int allowedModes;
645
646 /** A single-bit mask representing {@code public} access,
647 * which may contribute to the result of {@link #lookupModes lookupModes}.
648 * The value, {@code 0x01}, happens to be the same as the value of the
649 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
650 */
651 public static final int PUBLIC = Modifier.PUBLIC;
652
653 /** A single-bit mask representing {@code private} access,
654 * which may contribute to the result of {@link #lookupModes lookupModes}.
655 * The value, {@code 0x02}, happens to be the same as the value of the
656 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
657 */
658 public static final int PRIVATE = Modifier.PRIVATE;
659
660 /** A single-bit mask representing {@code protected} access,
661 * which may contribute to the result of {@link #lookupModes lookupModes}.
662 * The value, {@code 0x04}, happens to be the same as the value of the
663 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
664 */
665 public static final int PROTECTED = Modifier.PROTECTED;
666
667 /** A single-bit mask representing {@code package} access (default access),
668 * which may contribute to the result of {@link #lookupModes lookupModes}.
669 * The value is {@code 0x08}, which does not correspond meaningfully to
670 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
671 */
672 public static final int PACKAGE = Modifier.STATIC;
673
674 /** A single-bit mask representing {@code module} access (default access),
675 * which may contribute to the result of {@link #lookupModes lookupModes}.
676 * The value is {@code 0x10}, which does not correspond meaningfully to
677 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
678 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
679 * with this lookup mode can access all public types in the module of the
680 * lookup class and public types in packages exported by other modules
681 * to the module of the lookup class.
682 * @since 9
683 * @spec JPMS
684 */
685 public static final int MODULE = PACKAGE << 1;
686
687 /** A single-bit mask representing {@code unconditional} access
688 * which may contribute to the result of {@link #lookupModes lookupModes}.
689 * The value is {@code 0x20}, which does not correspond meaningfully to
690 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
691 * A {@code Lookup} with this lookup mode assumes {@linkplain
692 * java.lang.Module#canRead(java.lang.Module) readability}.
693 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
694 * with this lookup mode can access all public members of public types
695 * of all modules where the type is in a package that is {@link
696 * java.lang.Module#isExported(String) exported unconditionally}.
697 * @since 9
698 * @spec JPMS
699 * @see #publicLookup()
700 */
701 public static final int UNCONDITIONAL = PACKAGE << 2;
702
703 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
704 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
705 private static final int TRUSTED = -1;
706
707 private static int fixmods(int mods) {
708 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
709 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
710 }
711
712 /** Tells which class is performing the lookup. It is this class against
713 * which checks are performed for visibility and access permissions.
714 * <p>
715 * The class implies a maximum level of access permission,
716 * but the permissions may be additionally limited by the bitmask
717 * {@link #lookupModes lookupModes}, which controls whether non-public members
718 * can be accessed.
719 * @return the lookup class, on behalf of which this lookup object finds members
720 */
721 public Class<?> lookupClass() {
722 return lookupClass;
723 }
724
725 // This is just for calling out to MethodHandleImpl.
726 private Class<?> lookupClassOrNull() {
727 return (allowedModes == TRUSTED) ? null : lookupClass;
728 }
729
730 /** Tells which access-protection classes of members this lookup object can produce.
731 * The result is a bit-mask of the bits
732 * {@linkplain #PUBLIC PUBLIC (0x01)},
733 * {@linkplain #PRIVATE PRIVATE (0x02)},
734 * {@linkplain #PROTECTED PROTECTED (0x04)},
735 * {@linkplain #PACKAGE PACKAGE (0x08)},
736 * {@linkplain #MODULE MODULE (0x10)},
737 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
738 * <p>
739 * A freshly-created lookup object
740 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
741 * all possible bits set, except {@code UNCONDITIONAL}.
742 * A lookup object on a new lookup class
743 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
744 * may have some mode bits set to zero.
745 * Mode bits can also be
746 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
747 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
748 * The purpose of this is to restrict access via the new lookup object,
749 * so that it can access only names which can be reached by the original
750 * lookup object, and also by the new lookup class.
751 * @return the lookup modes, which limit the kinds of access performed by this lookup object
752 * @see #in
753 * @see #dropLookupMode
754 *
755 * @revised 9
756 * @spec JPMS
757 */
758 public int lookupModes() {
759 return allowedModes & ALL_MODES;
760 }
761
762 /** Embody the current class (the lookupClass) as a lookup class
763 * for method handle creation.
764 * Must be called by from a method in this package,
765 * which in turn is called by a method not in this package.
766 */
767 Lookup(Class<?> lookupClass) {
768 this(lookupClass, FULL_POWER_MODES);
769 // make sure we haven't accidentally picked up a privileged class:
770 checkUnprivilegedlookupClass(lookupClass);
771 }
772
773 private Lookup(Class<?> lookupClass, int allowedModes) {
774 this.lookupClass = lookupClass;
775 this.allowedModes = allowedModes;
776 }
777
778 /**
779 * Creates a lookup on the specified new lookup class.
780 * The resulting object will report the specified
781 * class as its own {@link #lookupClass() lookupClass}.
782 * <p>
783 * However, the resulting {@code Lookup} object is guaranteed
784 * to have no more access capabilities than the original.
785 * In particular, access capabilities can be lost as follows:<ul>
786 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
787 * the new lookup class is in a different module {@code M}, then no members, not
788 * even public members in {@code M}'s exported packages, will be accessible.
789 * The exception to this is when this lookup is {@link #publicLookup()
790 * publicLookup}, in which case {@code PUBLIC} access is not lost.
791 * <li>If the old lookup class is in an unnamed module, and the new lookup class
792 * is a different module then {@link #MODULE MODULE} access is lost.
793 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
794 * <li>If the new lookup class is in a different package
795 * than the old one, protected and default (package) members will not be accessible.
796 * <li>If the new lookup class is not within the same package member
797 * as the old one, private members will not be accessible, and protected members
798 * will not be accessible by virtue of inheritance.
799 * (Protected members may continue to be accessible because of package sharing.)
800 * <li>If the new lookup class is not accessible to the old lookup class,
801 * then no members, not even public members, will be accessible.
802 * (In all other cases, public members will continue to be accessible.)
803 * </ul>
804 * <p>
805 * The resulting lookup's capabilities for loading classes
806 * (used during {@link #findClass} invocations)
807 * are determined by the lookup class' loader,
808 * which may change due to this operation.
809 *
810 * @param requestedLookupClass the desired lookup class for the new lookup object
811 * @return a lookup object which reports the desired lookup class, or the same object
812 * if there is no change
813 * @throws NullPointerException if the argument is null
814 *
815 * @revised 9
816 * @spec JPMS
817 */
818 public Lookup in(Class<?> requestedLookupClass) {
819 Objects.requireNonNull(requestedLookupClass);
820 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
821 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
822 if (requestedLookupClass == this.lookupClass)
823 return this; // keep same capabilities
824 int newModes = (allowedModes & FULL_POWER_MODES);
825 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
826 // Need to drop all access when teleporting from a named module to another
827 // module. The exception is publicLookup where PUBLIC is not lost.
828 if (this.lookupClass.getModule().isNamed()
829 && (this.allowedModes & UNCONDITIONAL) == 0)
830 newModes = 0;
831 else
832 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
833 }
834 if ((newModes & PACKAGE) != 0
835 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
836 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
837 }
838 // Allow nestmate lookups to be created without special privilege:
839 if ((newModes & PRIVATE) != 0
840 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
841 newModes &= ~(PRIVATE|PROTECTED);
842 }
843 if ((newModes & PUBLIC) != 0
844 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
845 // The requested class it not accessible from the lookup class.
846 // No permissions.
847 newModes = 0;
848 }
849
850 checkUnprivilegedlookupClass(requestedLookupClass);
851 return new Lookup(requestedLookupClass, newModes);
852 }
853
854
855 /**
856 * Creates a lookup on the same lookup class which this lookup object
857 * finds members, but with a lookup mode that has lost the given lookup mode.
858 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
859 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
860 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
861 * dropped and so the resulting lookup mode will never have these access capabilities.
862 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
863 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
864 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
865 * is dropped then the resulting lookup has no access.
866 * @param modeToDrop the lookup mode to drop
867 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
868 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
869 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
870 * @see MethodHandles#privateLookupIn
871 * @since 9
872 */
873 public Lookup dropLookupMode(int modeToDrop) {
874 int oldModes = lookupModes();
875 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
876 switch (modeToDrop) {
877 case PUBLIC: newModes &= ~(ALL_MODES); break;
878 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
879 case PACKAGE: newModes &= ~(PRIVATE); break;
880 case PROTECTED:
881 case PRIVATE:
882 case UNCONDITIONAL: break;
883 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
884 }
885 if (newModes == oldModes) return this; // return self if no change
886 return new Lookup(lookupClass(), newModes);
887 }
888
889 /**
890 * Defines a class to the same class loader and in the same runtime package and
891 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
892 * {@linkplain #lookupClass() lookup class}.
893 *
894 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
895 * {@link #PACKAGE PACKAGE} access as default (package) members will be
896 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
897 * that the lookup object was created by a caller in the runtime package (or derived
898 * from a lookup originally created by suitably privileged code to a target class in
899 * the runtime package). </p>
900 *
901 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
902 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
903 * same package as the lookup class. </p>
904 *
905 * <p> This method does not run the class initializer. The class initializer may
906 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
907 * Specification</em>. </p>
908 *
909 * <p> If there is a security manager, its {@code checkPermission} method is first called
910 * to check {@code RuntimePermission("defineClass")}. </p>
911 *
912 * @param bytes the class bytes
913 * @return the {@code Class} object for the class
914 * @throws IllegalArgumentException the bytes are for a class in a different package
915 * to the lookup class
916 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
917 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
918 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
919 * @throws SecurityException if denied by the security manager
920 * @throws NullPointerException if {@code bytes} is {@code null}
921 * @since 9
922 * @spec JPMS
923 * @see Lookup#privateLookupIn
924 * @see Lookup#dropLookupMode
925 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
926 */
927 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
928 SecurityManager sm = System.getSecurityManager();
929 if (sm != null)
930 sm.checkPermission(new RuntimePermission("defineClass"));
931 if ((lookupModes() & PACKAGE) == 0)
932 throw new IllegalAccessException("Lookup does not have PACKAGE access");
933 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
934
935 // parse class bytes to get class name (in internal form)
936 bytes = bytes.clone();
937 String name;
938 try {
939 ClassReader reader = new ClassReader(bytes);
940 name = reader.getClassName();
941 } catch (RuntimeException e) {
942 // ASM exceptions are poorly specified
943 ClassFormatError cfe = new ClassFormatError();
944 cfe.initCause(e);
945 throw cfe;
946 }
947
948 // get package and class name in binary form
949 String cn, pn;
950 int index = name.lastIndexOf('/');
951 if (index == -1) {
952 cn = name;
953 pn = "";
954 } else {
955 cn = name.replace('/', '.');
956 pn = cn.substring(0, index);
957 }
958 if (!pn.equals(lookupClass.getPackageName())) {
959 throw new IllegalArgumentException("Class not in same package as lookup class");
960 }
961
962 // invoke the class loader's defineClass method
963 ClassLoader loader = lookupClass.getClassLoader();
964 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
965 String source = "__Lookup_defineClass__";
966 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
967 assert clazz.getClassLoader() == lookupClass.getClassLoader()
968 && clazz.getPackageName().equals(lookupClass.getPackageName())
969 && protectionDomain(clazz) == lookupClassProtectionDomain();
970 return clazz;
971 }
972
973 private ProtectionDomain lookupClassProtectionDomain() {
974 ProtectionDomain pd = cachedProtectionDomain;
975 if (pd == null) {
976 cachedProtectionDomain = pd = protectionDomain(lookupClass);
977 }
978 return pd;
979 }
980
981 private ProtectionDomain protectionDomain(Class<?> clazz) {
982 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
983 return AccessController.doPrivileged(pa);
984 }
985
986 // cached protection domain
987 private volatile ProtectionDomain cachedProtectionDomain;
988
989
990 // Make sure outer class is initialized first.
991 static { IMPL_NAMES.getClass(); }
992
993 /** Package-private version of lookup which is trusted. */
994 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
995
996 /** Version of lookup which is trusted minimally.
997 * It can only be used to create method handles to publicly accessible
998 * members in packages that are exported unconditionally.
999 */
1000 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
1001
1002 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1003 String name = lookupClass.getName();
1004 if (name.startsWith("java.lang.invoke."))
1005 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1006 }
1007
1008 /**
1009 * Displays the name of the class from which lookups are to be made.
1010 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1011 * If there are restrictions on the access permitted to this lookup,
1012 * this is indicated by adding a suffix to the class name, consisting
1013 * of a slash and a keyword. The keyword represents the strongest
1014 * allowed access, and is chosen as follows:
1015 * <ul>
1016 * <li>If no access is allowed, the suffix is "/noaccess".
1017 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1018 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1019 * <li>If only public and module access are allowed, the suffix is "/module".
1020 * <li>If only public, module and package access are allowed, the suffix is "/package".
1021 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1022 * </ul>
1023 * If none of the above cases apply, it is the case that full
1024 * access (public, module, package, private, and protected) is allowed.
1025 * In this case, no suffix is added.
1026 * This is true only of an object obtained originally from
1027 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1028 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1029 * always have restricted access, and will display a suffix.
1030 * <p>
1031 * (It may seem strange that protected access should be
1032 * stronger than private access. Viewed independently from
1033 * package access, protected access is the first to be lost,
1034 * because it requires a direct subclass relationship between
1035 * caller and callee.)
1036 * @see #in
1037 *
1038 * @revised 9
1039 * @spec JPMS
1040 */
1041 @Override
1042 public String toString() {
1043 String cname = lookupClass.getName();
1044 switch (allowedModes) {
1045 case 0: // no privileges
1046 return cname + "/noaccess";
1047 case PUBLIC:
1048 return cname + "/public";
1049 case PUBLIC|UNCONDITIONAL:
1050 return cname + "/publicLookup";
1051 case PUBLIC|MODULE:
1052 return cname + "/module";
1053 case PUBLIC|MODULE|PACKAGE:
1054 return cname + "/package";
1055 case FULL_POWER_MODES & ~PROTECTED:
1056 return cname + "/private";
1057 case FULL_POWER_MODES:
1058 return cname;
1059 case TRUSTED:
1060 return "/trusted"; // internal only; not exported
1061 default: // Should not happen, but it's a bitfield...
1062 cname = cname + "/" + Integer.toHexString(allowedModes);
1063 assert(false) : cname;
1064 return cname;
1065 }
1066 }
1067
1068 /**
1069 * Produces a method handle for a static method.
1070 * The type of the method handle will be that of the method.
1071 * (Since static methods do not take receivers, there is no
1072 * additional receiver argument inserted into the method handle type,
1073 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1074 * The method and all its argument types must be accessible to the lookup object.
1075 * <p>
1076 * The returned method handle will have
1077 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1078 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1079 * <p>
1080 * If the returned method handle is invoked, the method's class will
1081 * be initialized, if it has not already been initialized.
1082 * <p><b>Example:</b>
1083 * <blockquote><pre>{@code
1084 import static java.lang.invoke.MethodHandles.*;
1085 import static java.lang.invoke.MethodType.*;
1086 ...
1087 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1088 "asList", methodType(List.class, Object[].class));
1089 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1090 * }</pre></blockquote>
1091 * @param refc the class from which the method is accessed
1092 * @param name the name of the method
1093 * @param type the type of the method
1094 * @return the desired method handle
1095 * @throws NoSuchMethodException if the method does not exist
1096 * @throws IllegalAccessException if access checking fails,
1097 * or if the method is not {@code static},
1098 * or if the method's variable arity modifier bit
1099 * is set and {@code asVarargsCollector} fails
1100 * @exception SecurityException if a security manager is present and it
1101 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1102 * @throws NullPointerException if any argument is null
1103 */
1104 public
1105 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1106 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1107 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1108 }
1109
1110 /**
1111 * Produces a method handle for a virtual method.
1112 * The type of the method handle will be that of the method,
1113 * with the receiver type (usually {@code refc}) prepended.
1114 * The method and all its argument types must be accessible to the lookup object.
1115 * <p>
1116 * When called, the handle will treat the first argument as a receiver
1117 * and, for non-private methods, dispatch on the receiver's type to determine which method
1118 * implementation to enter.
1119 * For private methods the named method in {@code refc} will be invoked on the receiver.
1120 * (The dispatching action is identical with that performed by an
1121 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1122 * <p>
1123 * The first argument will be of type {@code refc} if the lookup
1124 * class has full privileges to access the member. Otherwise
1125 * the member must be {@code protected} and the first argument
1126 * will be restricted in type to the lookup class.
1127 * <p>
1128 * The returned method handle will have
1129 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1130 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1131 * <p>
1132 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1133 * instructions and method handles produced by {@code findVirtual},
1134 * if the class is {@code MethodHandle} and the name string is
1135 * {@code invokeExact} or {@code invoke}, the resulting
1136 * method handle is equivalent to one produced by
1137 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1138 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1139 * with the same {@code type} argument.
1140 * <p>
1141 * If the class is {@code VarHandle} and the name string corresponds to
1142 * the name of a signature-polymorphic access mode method, the resulting
1143 * method handle is equivalent to one produced by
1144 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1145 * the access mode corresponding to the name string and with the same
1146 * {@code type} arguments.
1147 * <p>
1148 * <b>Example:</b>
1149 * <blockquote><pre>{@code
1150 import static java.lang.invoke.MethodHandles.*;
1151 import static java.lang.invoke.MethodType.*;
1152 ...
1153 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1154 "concat", methodType(String.class, String.class));
1155 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1156 "hashCode", methodType(int.class));
1157 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1158 "hashCode", methodType(int.class));
1159 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1160 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1161 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1162 // interface method:
1163 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1164 "subSequence", methodType(CharSequence.class, int.class, int.class));
1165 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1166 // constructor "internal method" must be accessed differently:
1167 MethodType MT_newString = methodType(void.class); //()V for new String()
1168 try { assertEquals("impossible", lookup()
1169 .findVirtual(String.class, "<init>", MT_newString));
1170 } catch (NoSuchMethodException ex) { } // OK
1171 MethodHandle MH_newString = publicLookup()
1172 .findConstructor(String.class, MT_newString);
1173 assertEquals("", (String) MH_newString.invokeExact());
1174 * }</pre></blockquote>
1175 *
1176 * @param refc the class or interface from which the method is accessed
1177 * @param name the name of the method
1178 * @param type the type of the method, with the receiver argument omitted
1179 * @return the desired method handle
1180 * @throws NoSuchMethodException if the method does not exist
1181 * @throws IllegalAccessException if access checking fails,
1182 * or if the method is {@code static},
1183 * or if the method's variable arity modifier bit
1184 * is set and {@code asVarargsCollector} fails
1185 * @exception SecurityException if a security manager is present and it
1186 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1187 * @throws NullPointerException if any argument is null
1188 */
1189 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1190 if (refc == MethodHandle.class) {
1191 MethodHandle mh = findVirtualForMH(name, type);
1192 if (mh != null) return mh;
1193 } else if (refc == VarHandle.class) {
1194 MethodHandle mh = findVirtualForVH(name, type);
1195 if (mh != null) return mh;
1196 }
1197 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1198 MemberName method = resolveOrFail(refKind, refc, name, type);
1199 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1200 }
1201 private MethodHandle findVirtualForMH(String name, MethodType type) {
1202 // these names require special lookups because of the implicit MethodType argument
1203 if ("invoke".equals(name))
1204 return invoker(type);
1205 if ("invokeExact".equals(name))
1206 return exactInvoker(type);
1207 assert(!MemberName.isMethodHandleInvokeName(name));
1208 return null;
1209 }
1210 private MethodHandle findVirtualForVH(String name, MethodType type) {
1211 try {
1212 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1213 } catch (IllegalArgumentException e) {
1214 return null;
1215 }
1216 }
1217
1218 /**
1219 * Produces a method handle which creates an object and initializes it, using
1220 * the constructor of the specified type.
1221 * The parameter types of the method handle will be those of the constructor,
1222 * while the return type will be a reference to the constructor's class.
1223 * The constructor and all its argument types must be accessible to the lookup object.
1224 * <p>
1225 * The requested type must have a return type of {@code void}.
1226 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1227 * <p>
1228 * The returned method handle will have
1229 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1230 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1231 * <p>
1232 * If the returned method handle is invoked, the constructor's class will
1233 * be initialized, if it has not already been initialized.
1234 * <p><b>Example:</b>
1235 * <blockquote><pre>{@code
1236 import static java.lang.invoke.MethodHandles.*;
1237 import static java.lang.invoke.MethodType.*;
1238 ...
1239 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1240 ArrayList.class, methodType(void.class, Collection.class));
1241 Collection orig = Arrays.asList("x", "y");
1242 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1243 assert(orig != copy);
1244 assertEquals(orig, copy);
1245 // a variable-arity constructor:
1246 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1247 ProcessBuilder.class, methodType(void.class, String[].class));
1248 ProcessBuilder pb = (ProcessBuilder)
1249 MH_newProcessBuilder.invoke("x", "y", "z");
1250 assertEquals("[x, y, z]", pb.command().toString());
1251 * }</pre></blockquote>
1252 * @param refc the class or interface from which the method is accessed
1253 * @param type the type of the method, with the receiver argument omitted, and a void return type
1254 * @return the desired method handle
1255 * @throws NoSuchMethodException if the constructor does not exist
1256 * @throws IllegalAccessException if access checking fails
1257 * or if the method's variable arity modifier bit
1258 * is set and {@code asVarargsCollector} fails
1259 * @exception SecurityException if a security manager is present and it
1260 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1261 * @throws NullPointerException if any argument is null
1262 */
1263 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1264 if (refc.isArray()) {
1265 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1266 }
1267 String name = "<init>";
1268 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1269 return getDirectConstructor(refc, ctor);
1270 }
1271
1272 /**
1273 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1274 * initializer of the class is not run.
1275 * <p>
1276 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1277 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1278 * load the requested class, and then determines whether the class is accessible to this lookup object.
1279 *
1280 * @param targetName the fully qualified name of the class to be looked up.
1281 * @return the requested class.
1282 * @exception SecurityException if a security manager is present and it
1283 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1284 * @throws LinkageError if the linkage fails
1285 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1286 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1287 * modes.
1288 * @exception SecurityException if a security manager is present and it
1289 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1290 * @since 9
1291 */
1292 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1293 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1294 return accessClass(targetClass);
1295 }
1296
1297 /**
1298 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1299 * static initializer of the class is not run.
1300 * <p>
1301 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1302 * {@linkplain #lookupModes() lookup modes}.
1303 *
1304 * @param targetClass the class to be access-checked
1305 *
1306 * @return the class that has been access-checked
1307 *
1308 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1309 * modes.
1310 * @exception SecurityException if a security manager is present and it
1311 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1312 * @since 9
1313 */
1314 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1315 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1316 throw new MemberName(targetClass).makeAccessException("access violation", this);
1317 }
1318 checkSecurityManager(targetClass, null);
1319 return targetClass;
1320 }
1321
1322 /**
1323 * Produces an early-bound method handle for a virtual method.
1324 * It will bypass checks for overriding methods on the receiver,
1325 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1326 * instruction from within the explicitly specified {@code specialCaller}.
1327 * The type of the method handle will be that of the method,
1328 * with a suitably restricted receiver type prepended.
1329 * (The receiver type will be {@code specialCaller} or a subtype.)
1330 * The method and all its argument types must be accessible
1331 * to the lookup object.
1332 * <p>
1333 * Before method resolution,
1334 * if the explicitly specified caller class is not identical with the
1335 * lookup class, or if this lookup object does not have
1336 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1337 * privileges, the access fails.
1338 * <p>
1339 * The returned method handle will have
1340 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1341 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1342 * <p style="font-size:smaller;">
1343 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1344 * even though the {@code invokespecial} instruction can refer to them
1345 * in special circumstances. Use {@link #findConstructor findConstructor}
1346 * to access instance initialization methods in a safe manner.)</em>
1347 * <p><b>Example:</b>
1348 * <blockquote><pre>{@code
1349 import static java.lang.invoke.MethodHandles.*;
1350 import static java.lang.invoke.MethodType.*;
1351 ...
1352 static class Listie extends ArrayList {
1353 public String toString() { return "[wee Listie]"; }
1354 static Lookup lookup() { return MethodHandles.lookup(); }
1355 }
1356 ...
1357 // no access to constructor via invokeSpecial:
1358 MethodHandle MH_newListie = Listie.lookup()
1359 .findConstructor(Listie.class, methodType(void.class));
1360 Listie l = (Listie) MH_newListie.invokeExact();
1361 try { assertEquals("impossible", Listie.lookup().findSpecial(
1362 Listie.class, "<init>", methodType(void.class), Listie.class));
1363 } catch (NoSuchMethodException ex) { } // OK
1364 // access to super and self methods via invokeSpecial:
1365 MethodHandle MH_super = Listie.lookup().findSpecial(
1366 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1367 MethodHandle MH_this = Listie.lookup().findSpecial(
1368 Listie.class, "toString" , methodType(String.class), Listie.class);
1369 MethodHandle MH_duper = Listie.lookup().findSpecial(
1370 Object.class, "toString" , methodType(String.class), Listie.class);
1371 assertEquals("[]", (String) MH_super.invokeExact(l));
1372 assertEquals(""+l, (String) MH_this.invokeExact(l));
1373 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1374 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1375 String.class, "toString", methodType(String.class), Listie.class));
1376 } catch (IllegalAccessException ex) { } // OK
1377 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1378 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1379 * }</pre></blockquote>
1380 *
1381 * @param refc the class or interface from which the method is accessed
1382 * @param name the name of the method (which must not be "<init>")
1383 * @param type the type of the method, with the receiver argument omitted
1384 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1385 * @return the desired method handle
1386 * @throws NoSuchMethodException if the method does not exist
1387 * @throws IllegalAccessException if access checking fails,
1388 * or if the method is {@code static},
1389 * or if the method's variable arity modifier bit
1390 * is set and {@code asVarargsCollector} fails
1391 * @exception SecurityException if a security manager is present and it
1392 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1393 * @throws NullPointerException if any argument is null
1394 */
1395 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1396 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1397 checkSpecialCaller(specialCaller, refc);
1398 Lookup specialLookup = this.in(specialCaller);
1399 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1400 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1401 }
1402
1403 /**
1404 * Produces a method handle giving read access to a non-static field.
1405 * The type of the method handle will have a return type of the field's
1406 * value type.
1407 * The method handle's single argument will be the instance containing
1408 * the field.
1409 * Access checking is performed immediately on behalf of the lookup class.
1410 * @param refc the class or interface from which the method is accessed
1411 * @param name the field's name
1412 * @param type the field's type
1413 * @return a method handle which can load values from the field
1414 * @throws NoSuchFieldException if the field does not exist
1415 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1416 * @exception SecurityException if a security manager is present and it
1417 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1418 * @throws NullPointerException if any argument is null
1419 * @see #findVarHandle(Class, String, Class)
1420 */
1421 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1422 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1423 return getDirectField(REF_getField, refc, field);
1424 }
1425
1426 /**
1427 * Produces a method handle giving write access to a non-static field.
1428 * The type of the method handle will have a void return type.
1429 * The method handle will take two arguments, the instance containing
1430 * the field, and the value to be stored.
1431 * The second argument will be of the field's value type.
1432 * Access checking is performed immediately on behalf of the lookup class.
1433 * @param refc the class or interface from which the method is accessed
1434 * @param name the field's name
1435 * @param type the field's type
1436 * @return a method handle which can store values into the field
1437 * @throws NoSuchFieldException if the field does not exist
1438 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1439 * @exception SecurityException if a security manager is present and it
1440 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1441 * @throws NullPointerException if any argument is null
1442 * @see #findVarHandle(Class, String, Class)
1443 */
1444 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1445 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1446 return getDirectField(REF_putField, refc, field);
1447 }
1448
1449 /**
1450 * Produces a VarHandle giving access to a non-static field {@code name}
1451 * of type {@code type} declared in a class of type {@code recv}.
1452 * The VarHandle's variable type is {@code type} and it has one
1453 * coordinate type, {@code recv}.
1454 * <p>
1455 * Access checking is performed immediately on behalf of the lookup
1456 * class.
1457 * <p>
1458 * Certain access modes of the returned VarHandle are unsupported under
1459 * the following conditions:
1460 * <ul>
1461 * <li>if the field is declared {@code final}, then the write, atomic
1462 * update, numeric atomic update, and bitwise atomic update access
1463 * modes are unsupported.
1464 * <li>if the field type is anything other than {@code byte},
1465 * {@code short}, {@code char}, {@code int}, {@code long},
1466 * {@code float}, or {@code double} then numeric atomic update
1467 * access modes are unsupported.
1468 * <li>if the field type is anything other than {@code boolean},
1469 * {@code byte}, {@code short}, {@code char}, {@code int} or
1470 * {@code long} then bitwise atomic update access modes are
1471 * unsupported.
1472 * </ul>
1473 * <p>
1474 * If the field is declared {@code volatile} then the returned VarHandle
1475 * will override access to the field (effectively ignore the
1476 * {@code volatile} declaration) in accordance to its specified
1477 * access modes.
1478 * <p>
1479 * If the field type is {@code float} or {@code double} then numeric
1480 * and atomic update access modes compare values using their bitwise
1481 * representation (see {@link Float#floatToRawIntBits} and
1482 * {@link Double#doubleToRawLongBits}, respectively).
1483 * @apiNote
1484 * Bitwise comparison of {@code float} values or {@code double} values,
1485 * as performed by the numeric and atomic update access modes, differ
1486 * from the primitive {@code ==} operator and the {@link Float#equals}
1487 * and {@link Double#equals} methods, specifically with respect to
1488 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1489 * Care should be taken when performing a compare and set or a compare
1490 * and exchange operation with such values since the operation may
1491 * unexpectedly fail.
1492 * There are many possible NaN values that are considered to be
1493 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1494 * provided by Java can distinguish between them. Operation failure can
1495 * occur if the expected or witness value is a NaN value and it is
1496 * transformed (perhaps in a platform specific manner) into another NaN
1497 * value, and thus has a different bitwise representation (see
1498 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1499 * details).
1500 * The values {@code -0.0} and {@code +0.0} have different bitwise
1501 * representations but are considered equal when using the primitive
1502 * {@code ==} operator. Operation failure can occur if, for example, a
1503 * numeric algorithm computes an expected value to be say {@code -0.0}
1504 * and previously computed the witness value to be say {@code +0.0}.
1505 * @param recv the receiver class, of type {@code R}, that declares the
1506 * non-static field
1507 * @param name the field's name
1508 * @param type the field's type, of type {@code T}
1509 * @return a VarHandle giving access to non-static fields.
1510 * @throws NoSuchFieldException if the field does not exist
1511 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1512 * @exception SecurityException if a security manager is present and it
1513 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1514 * @throws NullPointerException if any argument is null
1515 * @since 9
1516 */
1517 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1518 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1519 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1520 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1521 }
1522
1523 /**
1524 * Produces a method handle giving read access to a static field.
1525 * The type of the method handle will have a return type of the field's
1526 * value type.
1527 * The method handle will take no arguments.
1528 * Access checking is performed immediately on behalf of the lookup class.
1529 * <p>
1530 * If the returned method handle is invoked, the field's class will
1531 * be initialized, if it has not already been initialized.
1532 * @param refc the class or interface from which the method is accessed
1533 * @param name the field's name
1534 * @param type the field's type
1535 * @return a method handle which can load values from the field
1536 * @throws NoSuchFieldException if the field does not exist
1537 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1538 * @exception SecurityException if a security manager is present and it
1539 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1540 * @throws NullPointerException if any argument is null
1541 */
1542 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1543 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1544 return getDirectField(REF_getStatic, refc, field);
1545 }
1546
1547 /**
1548 * Produces a method handle giving write access to a static field.
1549 * The type of the method handle will have a void return type.
1550 * The method handle will take a single
1551 * argument, of the field's value type, the value to be stored.
1552 * Access checking is performed immediately on behalf of the lookup class.
1553 * <p>
1554 * If the returned method handle is invoked, the field's class will
1555 * be initialized, if it has not already been initialized.
1556 * @param refc the class or interface from which the method is accessed
1557 * @param name the field's name
1558 * @param type the field's type
1559 * @return a method handle which can store values into the field
1560 * @throws NoSuchFieldException if the field does not exist
1561 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1562 * @exception SecurityException if a security manager is present and it
1563 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1564 * @throws NullPointerException if any argument is null
1565 */
1566 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1567 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1568 return getDirectField(REF_putStatic, refc, field);
1569 }
1570
1571 /**
1572 * Produces a VarHandle giving access to a static field {@code name} of
1573 * type {@code type} declared in a class of type {@code decl}.
1574 * The VarHandle's variable type is {@code type} and it has no
1575 * coordinate types.
1576 * <p>
1577 * Access checking is performed immediately on behalf of the lookup
1578 * class.
1579 * <p>
1580 * If the returned VarHandle is operated on, the declaring class will be
1581 * initialized, if it has not already been initialized.
1582 * <p>
1583 * Certain access modes of the returned VarHandle are unsupported under
1584 * the following conditions:
1585 * <ul>
1586 * <li>if the field is declared {@code final}, then the write, atomic
1587 * update, numeric atomic update, and bitwise atomic update access
1588 * modes are unsupported.
1589 * <li>if the field type is anything other than {@code byte},
1590 * {@code short}, {@code char}, {@code int}, {@code long},
1591 * {@code float}, or {@code double}, then numeric atomic update
1592 * access modes are unsupported.
1593 * <li>if the field type is anything other than {@code boolean},
1594 * {@code byte}, {@code short}, {@code char}, {@code int} or
1595 * {@code long} then bitwise atomic update access modes are
1596 * unsupported.
1597 * </ul>
1598 * <p>
1599 * If the field is declared {@code volatile} then the returned VarHandle
1600 * will override access to the field (effectively ignore the
1601 * {@code volatile} declaration) in accordance to its specified
1602 * access modes.
1603 * <p>
1604 * If the field type is {@code float} or {@code double} then numeric
1605 * and atomic update access modes compare values using their bitwise
1606 * representation (see {@link Float#floatToRawIntBits} and
1607 * {@link Double#doubleToRawLongBits}, respectively).
1608 * @apiNote
1609 * Bitwise comparison of {@code float} values or {@code double} values,
1610 * as performed by the numeric and atomic update access modes, differ
1611 * from the primitive {@code ==} operator and the {@link Float#equals}
1612 * and {@link Double#equals} methods, specifically with respect to
1613 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1614 * Care should be taken when performing a compare and set or a compare
1615 * and exchange operation with such values since the operation may
1616 * unexpectedly fail.
1617 * There are many possible NaN values that are considered to be
1618 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1619 * provided by Java can distinguish between them. Operation failure can
1620 * occur if the expected or witness value is a NaN value and it is
1621 * transformed (perhaps in a platform specific manner) into another NaN
1622 * value, and thus has a different bitwise representation (see
1623 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1624 * details).
1625 * The values {@code -0.0} and {@code +0.0} have different bitwise
1626 * representations but are considered equal when using the primitive
1627 * {@code ==} operator. Operation failure can occur if, for example, a
1628 * numeric algorithm computes an expected value to be say {@code -0.0}
1629 * and previously computed the witness value to be say {@code +0.0}.
1630 * @param decl the class that declares the static field
1631 * @param name the field's name
1632 * @param type the field's type, of type {@code T}
1633 * @return a VarHandle giving access to a static field
1634 * @throws NoSuchFieldException if the field does not exist
1635 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1636 * @exception SecurityException if a security manager is present and it
1637 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1638 * @throws NullPointerException if any argument is null
1639 * @since 9
1640 */
1641 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1642 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1643 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1644 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1645 }
1646
1647 /**
1648 * Produces an early-bound method handle for a non-static method.
1649 * The receiver must have a supertype {@code defc} in which a method
1650 * of the given name and type is accessible to the lookup class.
1651 * The method and all its argument types must be accessible to the lookup object.
1652 * The type of the method handle will be that of the method,
1653 * without any insertion of an additional receiver parameter.
1654 * The given receiver will be bound into the method handle,
1655 * so that every call to the method handle will invoke the
1656 * requested method on the given receiver.
1657 * <p>
1658 * The returned method handle will have
1659 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1660 * the method's variable arity modifier bit ({@code 0x0080}) is set
1661 * <em>and</em> the trailing array argument is not the only argument.
1662 * (If the trailing array argument is the only argument,
1663 * the given receiver value will be bound to it.)
1664 * <p>
1665 * This is almost equivalent to the following code, with some differences noted below:
1666 * <blockquote><pre>{@code
1667 import static java.lang.invoke.MethodHandles.*;
1668 import static java.lang.invoke.MethodType.*;
1669 ...
1670 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1671 MethodHandle mh1 = mh0.bindTo(receiver);
1672 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1673 return mh1;
1674 * }</pre></blockquote>
1675 * where {@code defc} is either {@code receiver.getClass()} or a super
1676 * type of that class, in which the requested method is accessible
1677 * to the lookup class.
1678 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1679 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1680 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1681 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1682 * @param receiver the object from which the method is accessed
1683 * @param name the name of the method
1684 * @param type the type of the method, with the receiver argument omitted
1685 * @return the desired method handle
1686 * @throws NoSuchMethodException if the method does not exist
1687 * @throws IllegalAccessException if access checking fails
1688 * or if the method's variable arity modifier bit
1689 * is set and {@code asVarargsCollector} fails
1690 * @exception SecurityException if a security manager is present and it
1691 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1692 * @throws NullPointerException if any argument is null
1693 * @see MethodHandle#bindTo
1694 * @see #findVirtual
1695 */
1696 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1697 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1698 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1699 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1700 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1701 throw new IllegalAccessException("The restricted defining class " +
1702 mh.type().leadingReferenceParameter().getName() +
1703 " is not assignable from receiver class " +
1704 receiver.getClass().getName());
1705 }
1706 return mh.bindArgumentL(0, receiver).setVarargs(method);
1707 }
1708
1709 /**
1710 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1711 * to <i>m</i>, if the lookup class has permission.
1712 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1713 * If <i>m</i> is virtual, overriding is respected on every call.
1714 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1715 * The type of the method handle will be that of the method,
1716 * with the receiver type prepended (but only if it is non-static).
1717 * If the method's {@code accessible} flag is not set,
1718 * access checking is performed immediately on behalf of the lookup class.
1719 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1720 * <p>
1721 * The returned method handle will have
1722 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1723 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1724 * <p>
1725 * If <i>m</i> is static, and
1726 * if the returned method handle is invoked, the method's class will
1727 * be initialized, if it has not already been initialized.
1728 * @param m the reflected method
1729 * @return a method handle which can invoke the reflected method
1730 * @throws IllegalAccessException if access checking fails
1731 * or if the method's variable arity modifier bit
1732 * is set and {@code asVarargsCollector} fails
1733 * @throws NullPointerException if the argument is null
1734 */
1735 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1736 if (m.getDeclaringClass() == MethodHandle.class) {
1737 MethodHandle mh = unreflectForMH(m);
1738 if (mh != null) return mh;
1739 }
1740 if (m.getDeclaringClass() == VarHandle.class) {
1741 MethodHandle mh = unreflectForVH(m);
1742 if (mh != null) return mh;
1743 }
1744 MemberName method = new MemberName(m);
1745 byte refKind = method.getReferenceKind();
1746 if (refKind == REF_invokeSpecial)
1747 refKind = REF_invokeVirtual;
1748 assert(method.isMethod());
1749 @SuppressWarnings("deprecation")
1750 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1751 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1752 }
1753 private MethodHandle unreflectForMH(Method m) {
1754 // these names require special lookups because they throw UnsupportedOperationException
1755 if (MemberName.isMethodHandleInvokeName(m.getName()))
1756 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1757 return null;
1758 }
1759 private MethodHandle unreflectForVH(Method m) {
1760 // these names require special lookups because they throw UnsupportedOperationException
1761 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1762 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1763 return null;
1764 }
1765
1766 /**
1767 * Produces a method handle for a reflected method.
1768 * It will bypass checks for overriding methods on the receiver,
1769 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1770 * instruction from within the explicitly specified {@code specialCaller}.
1771 * The type of the method handle will be that of the method,
1772 * with a suitably restricted receiver type prepended.
1773 * (The receiver type will be {@code specialCaller} or a subtype.)
1774 * If the method's {@code accessible} flag is not set,
1775 * access checking is performed immediately on behalf of the lookup class,
1776 * as if {@code invokespecial} instruction were being linked.
1777 * <p>
1778 * Before method resolution,
1779 * if the explicitly specified caller class is not identical with the
1780 * lookup class, or if this lookup object does not have
1781 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1782 * privileges, the access fails.
1783 * <p>
1784 * The returned method handle will have
1785 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1786 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1787 * @param m the reflected method
1788 * @param specialCaller the class nominally calling the method
1789 * @return a method handle which can invoke the reflected method
1790 * @throws IllegalAccessException if access checking fails,
1791 * or if the method is {@code static},
1792 * or if the method's variable arity modifier bit
1793 * is set and {@code asVarargsCollector} fails
1794 * @throws NullPointerException if any argument is null
1795 */
1796 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1797 checkSpecialCaller(specialCaller, null);
1798 Lookup specialLookup = this.in(specialCaller);
1799 MemberName method = new MemberName(m, true);
1800 assert(method.isMethod());
1801 // ignore m.isAccessible: this is a new kind of access
1802 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1803 }
1804
1805 /**
1806 * Produces a method handle for a reflected constructor.
1807 * The type of the method handle will be that of the constructor,
1808 * with the return type changed to the declaring class.
1809 * The method handle will perform a {@code newInstance} operation,
1810 * creating a new instance of the constructor's class on the
1811 * arguments passed to the method handle.
1812 * <p>
1813 * If the constructor's {@code accessible} flag is not set,
1814 * access checking is performed immediately on behalf of the lookup class.
1815 * <p>
1816 * The returned method handle will have
1817 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1818 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1819 * <p>
1820 * If the returned method handle is invoked, the constructor's class will
1821 * be initialized, if it has not already been initialized.
1822 * @param c the reflected constructor
1823 * @return a method handle which can invoke the reflected constructor
1824 * @throws IllegalAccessException if access checking fails
1825 * or if the method's variable arity modifier bit
1826 * is set and {@code asVarargsCollector} fails
1827 * @throws NullPointerException if the argument is null
1828 */
1829 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1830 MemberName ctor = new MemberName(c);
1831 assert(ctor.isConstructor());
1832 @SuppressWarnings("deprecation")
1833 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1834 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1835 }
1836
1837 /**
1838 * Produces a method handle giving read access to a reflected field.
1839 * The type of the method handle will have a return type of the field's
1840 * value type.
1841 * If the field is static, the method handle will take no arguments.
1842 * Otherwise, its single argument will be the instance containing
1843 * the field.
1844 * If the field's {@code accessible} flag is not set,
1845 * access checking is performed immediately on behalf of the lookup class.
1846 * <p>
1847 * If the field is static, and
1848 * if the returned method handle is invoked, the field's class will
1849 * be initialized, if it has not already been initialized.
1850 * @param f the reflected field
1851 * @return a method handle which can load values from the reflected field
1852 * @throws IllegalAccessException if access checking fails
1853 * @throws NullPointerException if the argument is null
1854 */
1855 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1856 return unreflectField(f, false);
1857 }
1858 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1859 MemberName field = new MemberName(f, isSetter);
1860 assert(isSetter
1861 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1862 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1863 @SuppressWarnings("deprecation")
1864 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1865 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1866 }
1867
1868 /**
1869 * Produces a method handle giving write access to a reflected field.
1870 * The type of the method handle will have a void return type.
1871 * If the field is static, the method handle will take a single
1872 * argument, of the field's value type, the value to be stored.
1873 * Otherwise, the two arguments will be the instance containing
1874 * the field, and the value to be stored.
1875 * If the field's {@code accessible} flag is not set,
1876 * access checking is performed immediately on behalf of the lookup class.
1877 * <p>
1878 * If the field is static, and
1879 * if the returned method handle is invoked, the field's class will
1880 * be initialized, if it has not already been initialized.
1881 * @param f the reflected field
1882 * @return a method handle which can store values into the reflected field
1883 * @throws IllegalAccessException if access checking fails
1884 * @throws NullPointerException if the argument is null
1885 */
1886 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1887 return unreflectField(f, true);
1888 }
1889
1890 /**
1891 * Produces a VarHandle giving access to a reflected field {@code f}
1892 * of type {@code T} declared in a class of type {@code R}.
1893 * The VarHandle's variable type is {@code T}.
1894 * If the field is non-static the VarHandle has one coordinate type,
1895 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1896 * coordinate types.
1897 * <p>
1898 * Access checking is performed immediately on behalf of the lookup
1899 * class, regardless of the value of the field's {@code accessible}
1900 * flag.
1901 * <p>
1902 * If the field is static, and if the returned VarHandle is operated
1903 * on, the field's declaring class will be initialized, if it has not
1904 * already been initialized.
1905 * <p>
1906 * Certain access modes of the returned VarHandle are unsupported under
1907 * the following conditions:
1908 * <ul>
1909 * <li>if the field is declared {@code final}, then the write, atomic
1910 * update, numeric atomic update, and bitwise atomic update access
1911 * modes are unsupported.
1912 * <li>if the field type is anything other than {@code byte},
1913 * {@code short}, {@code char}, {@code int}, {@code long},
1914 * {@code float}, or {@code double} then numeric atomic update
1915 * access modes are unsupported.
1916 * <li>if the field type is anything other than {@code boolean},
1917 * {@code byte}, {@code short}, {@code char}, {@code int} or
1918 * {@code long} then bitwise atomic update access modes are
1919 * unsupported.
1920 * </ul>
1921 * <p>
1922 * If the field is declared {@code volatile} then the returned VarHandle
1923 * will override access to the field (effectively ignore the
1924 * {@code volatile} declaration) in accordance to its specified
1925 * access modes.
1926 * <p>
1927 * If the field type is {@code float} or {@code double} then numeric
1928 * and atomic update access modes compare values using their bitwise
1929 * representation (see {@link Float#floatToRawIntBits} and
1930 * {@link Double#doubleToRawLongBits}, respectively).
1931 * @apiNote
1932 * Bitwise comparison of {@code float} values or {@code double} values,
1933 * as performed by the numeric and atomic update access modes, differ
1934 * from the primitive {@code ==} operator and the {@link Float#equals}
1935 * and {@link Double#equals} methods, specifically with respect to
1936 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1937 * Care should be taken when performing a compare and set or a compare
1938 * and exchange operation with such values since the operation may
1939 * unexpectedly fail.
1940 * There are many possible NaN values that are considered to be
1941 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1942 * provided by Java can distinguish between them. Operation failure can
1943 * occur if the expected or witness value is a NaN value and it is
1944 * transformed (perhaps in a platform specific manner) into another NaN
1945 * value, and thus has a different bitwise representation (see
1946 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1947 * details).
1948 * The values {@code -0.0} and {@code +0.0} have different bitwise
1949 * representations but are considered equal when using the primitive
1950 * {@code ==} operator. Operation failure can occur if, for example, a
1951 * numeric algorithm computes an expected value to be say {@code -0.0}
1952 * and previously computed the witness value to be say {@code +0.0}.
1953 * @param f the reflected field, with a field of type {@code T}, and
1954 * a declaring class of type {@code R}
1955 * @return a VarHandle giving access to non-static fields or a static
1956 * field
1957 * @throws IllegalAccessException if access checking fails
1958 * @throws NullPointerException if the argument is null
1959 * @since 9
1960 */
1961 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1962 MemberName getField = new MemberName(f, false);
1963 MemberName putField = new MemberName(f, true);
1964 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1965 f.getDeclaringClass(), getField, putField);
1966 }
1967
1968 /**
1969 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1970 * created by this lookup object or a similar one.
1971 * Security and access checks are performed to ensure that this lookup object
1972 * is capable of reproducing the target method handle.
1973 * This means that the cracking may fail if target is a direct method handle
1974 * but was created by an unrelated lookup object.
1975 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1976 * and was created by a lookup object for a different class.
1977 * @param target a direct method handle to crack into symbolic reference components
1978 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1979 * @exception SecurityException if a security manager is present and it
1980 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1981 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1982 * @exception NullPointerException if the target is {@code null}
1983 * @see MethodHandleInfo
1984 * @since 1.8
1985 */
1986 public MethodHandleInfo revealDirect(MethodHandle target) {
1987 MemberName member = target.internalMemberName();
1988 if (member == null || (!member.isResolved() &&
1989 !member.isMethodHandleInvoke() &&
1990 !member.isVarHandleMethodInvoke()))
1991 throw newIllegalArgumentException("not a direct method handle");
1992 Class<?> defc = member.getDeclaringClass();
1993 byte refKind = member.getReferenceKind();
1994 assert(MethodHandleNatives.refKindIsValid(refKind));
1995 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1996 // Devirtualized method invocation is usually formally virtual.
1997 // To avoid creating extra MemberName objects for this common case,
1998 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1999 refKind = REF_invokeVirtual;
2000 if (refKind == REF_invokeVirtual && defc.isInterface())
2001 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2002 refKind = REF_invokeInterface;
2003 // Check SM permissions and member access before cracking.
2004 try {
2005 checkAccess(refKind, defc, member);
2006 checkSecurityManager(defc, member);
2007 } catch (IllegalAccessException ex) {
2008 throw new IllegalArgumentException(ex);
2009 }
2010 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2011 Class<?> callerClass = target.internalCallerClass();
2012 if (!hasPrivateAccess() || callerClass != lookupClass())
2013 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2014 }
2015 // Produce the handle to the results.
2016 return new InfoFromMemberName(this, member, refKind);
2017 }
2018
2019 /// Helper methods, all package-private.
2020
2021 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2022 checkSymbolicClass(refc); // do this before attempting to resolve
2023 Objects.requireNonNull(name);
2024 Objects.requireNonNull(type);
2025 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2026 NoSuchFieldException.class);
2027 }
2028
2029 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2030 checkSymbolicClass(refc); // do this before attempting to resolve
2031 Objects.requireNonNull(name);
2032 Objects.requireNonNull(type);
2033 checkMethodName(refKind, name); // NPE check on name
2034 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2035 NoSuchMethodException.class);
2036 }
2037
2038 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2039 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2040 Objects.requireNonNull(member.getName());
2041 Objects.requireNonNull(member.getType());
2042 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2043 ReflectiveOperationException.class);
2044 }
2045
2046 MemberName resolveOrNull(byte refKind, MemberName member) {
2047 // do this before attempting to resolve
2048 if (!isClassAccessible(member.getDeclaringClass())) {
2049 return null;
2050 }
2051 Objects.requireNonNull(member.getName());
2052 Objects.requireNonNull(member.getType());
2053 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2054 }
2055
2056 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2057 if (!isClassAccessible(refc)) {
2058 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2059 }
2060 }
2061
2062 boolean isClassAccessible(Class<?> refc) {
2063 Objects.requireNonNull(refc);
2064 Class<?> caller = lookupClassOrNull();
2065 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes);
2066 }
2067
2068 /** Check name for an illegal leading "<" character. */
2069 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2070 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2071 throw new NoSuchMethodException("illegal method name: "+name);
2072 }
2073
2074
2075 /**
2076 * Find my trustable caller class if m is a caller sensitive method.
2077 * If this lookup object has private access, then the caller class is the lookupClass.
2078 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2079 */
2080 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2081 Class<?> callerClass = null;
2082 if (MethodHandleNatives.isCallerSensitive(m)) {
2083 // Only lookups with private access are allowed to resolve caller-sensitive methods
2084 if (hasPrivateAccess()) {
2085 callerClass = lookupClass;
2086 } else {
2087 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2088 }
2089 }
2090 return callerClass;
2091 }
2092
2093 /**
2094 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2095 * @return {@code true} if this lookup has {@code PRIVATE} access.
2096 * @since 9
2097 */
2098 public boolean hasPrivateAccess() {
2099 return (allowedModes & PRIVATE) != 0;
2100 }
2101
2102 /**
2103 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2104 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2105 * If this lookup object has private access, then the caller class is the lookupClass.
2106 */
2107 void checkSecurityManager(Class<?> refc, MemberName m) {
2108 SecurityManager smgr = System.getSecurityManager();
2109 if (smgr == null) return;
2110 if (allowedModes == TRUSTED) return;
2111
2112 // Step 1:
2113 boolean fullPowerLookup = hasPrivateAccess();
2114 if (!fullPowerLookup ||
2115 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2116 ReflectUtil.checkPackageAccess(refc);
2117 }
2118
2119 if (m == null) { // findClass or accessClass
2120 // Step 2b:
2121 if (!fullPowerLookup) {
2122 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2123 }
2124 return;
2125 }
2126
2127 // Step 2a:
2128 if (m.isPublic()) return;
2129 if (!fullPowerLookup) {
2130 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2131 }
2132
2133 // Step 3:
2134 Class<?> defc = m.getDeclaringClass();
2135 if (!fullPowerLookup && defc != refc) {
2136 ReflectUtil.checkPackageAccess(defc);
2137 }
2138 }
2139
2140 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2141 boolean wantStatic = (refKind == REF_invokeStatic);
2142 String message;
2143 if (m.isConstructor())
2144 message = "expected a method, not a constructor";
2145 else if (!m.isMethod())
2146 message = "expected a method";
2147 else if (wantStatic != m.isStatic())
2148 message = wantStatic ? "expected a static method" : "expected a non-static method";
2149 else
2150 { checkAccess(refKind, refc, m); return; }
2151 throw m.makeAccessException(message, this);
2152 }
2153
2154 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2155 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2156 String message;
2157 if (wantStatic != m.isStatic())
2158 message = wantStatic ? "expected a static field" : "expected a non-static field";
2159 else
2160 { checkAccess(refKind, refc, m); return; }
2161 throw m.makeAccessException(message, this);
2162 }
2163
2164 /** Check public/protected/private bits on the symbolic reference class and its member. */
2165 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2166 assert(m.referenceKindIsConsistentWith(refKind) &&
2167 MethodHandleNatives.refKindIsValid(refKind) &&
2168 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2169 int allowedModes = this.allowedModes;
2170 if (allowedModes == TRUSTED) return;
2171 int mods = m.getModifiers();
2172 if (Modifier.isProtected(mods) &&
2173 refKind == REF_invokeVirtual &&
2174 m.getDeclaringClass() == Object.class &&
2175 m.getName().equals("clone") &&
2176 refc.isArray()) {
2177 // The JVM does this hack also.
2178 // (See ClassVerifier::verify_invoke_instructions
2179 // and LinkResolver::check_method_accessability.)
2180 // Because the JVM does not allow separate methods on array types,
2181 // there is no separate method for int[].clone.
2182 // All arrays simply inherit Object.clone.
2183 // But for access checking logic, we make Object.clone
2184 // (normally protected) appear to be public.
2185 // Later on, when the DirectMethodHandle is created,
2186 // its leading argument will be restricted to the
2187 // requested array type.
2188 // N.B. The return type is not adjusted, because
2189 // that is *not* the bytecode behavior.
2190 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2191 }
2192 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2193 // cannot "new" a protected ctor in a different package
2194 mods ^= Modifier.PROTECTED;
2195 }
2196 if (Modifier.isFinal(mods) &&
2197 MethodHandleNatives.refKindIsSetter(refKind))
2198 throw m.makeAccessException("unexpected set of a final field", this);
2199 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2200 if ((requestedModes & allowedModes) != 0) {
2201 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2202 mods, lookupClass(), allowedModes))
2203 return;
2204 } else {
2205 // Protected members can also be checked as if they were package-private.
2206 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2207 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2208 return;
2209 }
2210 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2211 }
2212
2213 String accessFailedMessage(Class<?> refc, MemberName m) {
2214 Class<?> defc = m.getDeclaringClass();
2215 int mods = m.getModifiers();
2216 // check the class first:
2217 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2218 (defc == refc ||
2219 Modifier.isPublic(refc.getModifiers())));
2220 if (!classOK && (allowedModes & PACKAGE) != 0) {
2221 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2222 (defc == refc ||
2223 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2224 }
2225 if (!classOK)
2226 return "class is not public";
2227 if (Modifier.isPublic(mods))
2228 return "access to public member failed"; // (how?, module not readable?)
2229 if (Modifier.isPrivate(mods))
2230 return "member is private";
2231 if (Modifier.isProtected(mods))
2232 return "member is protected";
2233 return "member is private to package";
2234 }
2235
2236 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2237 int allowedModes = this.allowedModes;
2238 if (allowedModes == TRUSTED) return;
2239 if (!hasPrivateAccess()
2240 || (specialCaller != lookupClass()
2241 // ensure non-abstract methods in superinterfaces can be special-invoked
2242 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2243 throw new MemberName(specialCaller).
2244 makeAccessException("no private access for invokespecial", this);
2245 }
2246
2247 private boolean restrictProtectedReceiver(MemberName method) {
2248 // The accessing class only has the right to use a protected member
2249 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2250 if (!method.isProtected() || method.isStatic()
2251 || allowedModes == TRUSTED
2252 || method.getDeclaringClass() == lookupClass()
2253 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2254 return false;
2255 return true;
2256 }
2257 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2258 assert(!method.isStatic());
2259 // receiver type of mh is too wide; narrow to caller
2260 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2261 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2262 }
2263 MethodType rawType = mh.type();
2264 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2265 MethodType narrowType = rawType.changeParameterType(0, caller);
2266 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2267 assert(mh.viewAsTypeChecks(narrowType, true));
2268 return mh.copyWith(narrowType, mh.form);
2269 }
2270
2271 /** Check access and get the requested method. */
2272 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2273 final boolean doRestrict = true;
2274 final boolean checkSecurity = true;
2275 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2276 }
2277 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2278 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2279 final boolean doRestrict = false;
2280 final boolean checkSecurity = true;
2281 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2282 }
2283 /** Check access and get the requested method, eliding security manager checks. */
2284 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2285 final boolean doRestrict = true;
2286 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2287 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2288 }
2289 /** Common code for all methods; do not call directly except from immediately above. */
2290 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2291 boolean checkSecurity,
2292 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
2293
2294 checkMethod(refKind, refc, method);
2295 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2296 if (checkSecurity)
2297 checkSecurityManager(refc, method);
2298 assert(!method.isMethodHandleInvoke());
2299
2300 if (refKind == REF_invokeSpecial &&
2301 refc != lookupClass() &&
2302 !refc.isInterface() &&
2303 refc != lookupClass().getSuperclass() &&
2304 refc.isAssignableFrom(lookupClass())) {
2305 assert(!method.getName().equals("<init>")); // not this code path
2306
2307 // Per JVMS 6.5, desc. of invokespecial instruction:
2308 // If the method is in a superclass of the LC,
2309 // and if our original search was above LC.super,
2310 // repeat the search (symbolic lookup) from LC.super
2311 // and continue with the direct superclass of that class,
2312 // and so forth, until a match is found or no further superclasses exist.
2313 // FIXME: MemberName.resolve should handle this instead.
2314 Class<?> refcAsSuper = lookupClass();
2315 MemberName m2;
2316 do {
2317 refcAsSuper = refcAsSuper.getSuperclass();
2318 m2 = new MemberName(refcAsSuper,
2319 method.getName(),
2320 method.getMethodType(),
2321 REF_invokeSpecial);
2322 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2323 } while (m2 == null && // no method is found yet
2324 refc != refcAsSuper); // search up to refc
2325 if (m2 == null) throw new InternalError(method.toString());
2326 method = m2;
2327 refc = refcAsSuper;
2328 // redo basic checks
2329 checkMethod(refKind, refc, method);
2330 }
2331
2332 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
2333 MethodHandle mh = dmh;
2334 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
2335 if ((doRestrict && refKind == REF_invokeSpecial) ||
2336 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2337 mh = restrictReceiver(method, dmh, lookupClass());
2338 }
2339 mh = maybeBindCaller(method, mh, boundCallerClass);
2340 mh = mh.setVarargs(method);
2341 return mh;
2342 }
2343 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2344 Class<?> boundCallerClass)
2345 throws IllegalAccessException {
2346 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2347 return mh;
2348 Class<?> hostClass = lookupClass;
2349 if (!hasPrivateAccess()) // caller must have private access
2350 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
2351 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2352 // Note: caller will apply varargs after this step happens.
2353 return cbmh;
2354 }
2355 /** Check access and get the requested field. */
2356 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2357 final boolean checkSecurity = true;
2358 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2359 }
2360 /** Check access and get the requested field, eliding security manager checks. */
2361 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2362 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2363 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2364 }
2365 /** Common code for all fields; do not call directly except from immediately above. */
2366 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2367 boolean checkSecurity) throws IllegalAccessException {
2368 checkField(refKind, refc, field);
2369 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2370 if (checkSecurity)
2371 checkSecurityManager(refc, field);
2372 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2373 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2374 restrictProtectedReceiver(field));
2375 if (doRestrict)
2376 return restrictReceiver(field, dmh, lookupClass());
2377 return dmh;
2378 }
2379 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2380 Class<?> refc, MemberName getField, MemberName putField)
2381 throws IllegalAccessException {
2382 final boolean checkSecurity = true;
2383 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2384 }
2385 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2386 Class<?> refc, MemberName getField, MemberName putField)
2387 throws IllegalAccessException {
2388 final boolean checkSecurity = false;
2389 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2390 }
2391 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2392 Class<?> refc, MemberName getField, MemberName putField,
2393 boolean checkSecurity) throws IllegalAccessException {
2394 assert getField.isStatic() == putField.isStatic();
2395 assert getField.isGetter() && putField.isSetter();
2396 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2397 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2398
2399 checkField(getRefKind, refc, getField);
2400 if (checkSecurity)
2401 checkSecurityManager(refc, getField);
2402
2403 if (!putField.isFinal()) {
2404 // A VarHandle does not support updates to final fields, any
2405 // such VarHandle to a final field will be read-only and
2406 // therefore the following write-based accessibility checks are
2407 // only required for non-final fields
2408 checkField(putRefKind, refc, putField);
2409 if (checkSecurity)
2410 checkSecurityManager(refc, putField);
2411 }
2412
2413 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2414 restrictProtectedReceiver(getField));
2415 if (doRestrict) {
2416 assert !getField.isStatic();
2417 // receiver type of VarHandle is too wide; narrow to caller
2418 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2419 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2420 }
2421 refc = lookupClass();
2422 }
2423 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2424 }
2425 /** Check access and get the requested constructor. */
2426 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2427 final boolean checkSecurity = true;
2428 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2429 }
2430 /** Check access and get the requested constructor, eliding security manager checks. */
2431 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2432 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2433 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2434 }
2435 /** Common code for all constructors; do not call directly except from immediately above. */
2436 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2437 boolean checkSecurity) throws IllegalAccessException {
2438 assert(ctor.isConstructor());
2439 checkAccess(REF_newInvokeSpecial, refc, ctor);
2440 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2441 if (checkSecurity)
2442 checkSecurityManager(refc, ctor);
2443 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2444 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2445 }
2446
2447 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2448 */
2449 /*non-public*/
2450 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2451 if (!(type instanceof Class || type instanceof MethodType))
2452 throw new InternalError("unresolved MemberName");
2453 MemberName member = new MemberName(refKind, defc, name, type);
2454 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2455 if (mh != null) {
2456 checkSymbolicClass(defc);
2457 return mh;
2458 }
2459 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2460 // Treat MethodHandle.invoke and invokeExact specially.
2461 mh = findVirtualForMH(member.getName(), member.getMethodType());
2462 if (mh != null) {
2463 return mh;
2464 }
2465 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
2466 // Treat signature-polymorphic methods on VarHandle specially.
2467 mh = findVirtualForVH(member.getName(), member.getMethodType());
2468 if (mh != null) {
2469 return mh;
2470 }
2471 }
2472 MemberName resolved = resolveOrFail(refKind, member);
2473 mh = getDirectMethodForConstant(refKind, defc, resolved);
2474 if (mh instanceof DirectMethodHandle
2475 && canBeCached(refKind, defc, resolved)) {
2476 MemberName key = mh.internalMemberName();
2477 if (key != null) {
2478 key = key.asNormalOriginal();
2479 }
2480 if (member.equals(key)) { // better safe than sorry
2481 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2482 }
2483 }
2484 return mh;
2485 }
2486 private
2487 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2488 if (refKind == REF_invokeSpecial) {
2489 return false;
2490 }
2491 if (!Modifier.isPublic(defc.getModifiers()) ||
2492 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2493 !member.isPublic() ||
2494 member.isCallerSensitive()) {
2495 return false;
2496 }
2497 ClassLoader loader = defc.getClassLoader();
2498 if (loader != null) {
2499 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2500 boolean found = false;
2501 while (sysl != null) {
2502 if (loader == sysl) { found = true; break; }
2503 sysl = sysl.getParent();
2504 }
2505 if (!found) {
2506 return false;
2507 }
2508 }
2509 try {
2510 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
2511 new MemberName(refKind, defc, member.getName(), member.getType()));
2512 if (resolved2 == null) {
2513 return false;
2514 }
2515 checkSecurityManager(defc, resolved2);
2516 } catch (SecurityException ex) {
2517 return false;
2518 }
2519 return true;
2520 }
2521 private
2522 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2523 throws ReflectiveOperationException {
2524 if (MethodHandleNatives.refKindIsField(refKind)) {
2525 return getDirectFieldNoSecurityManager(refKind, defc, member);
2526 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2527 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2528 } else if (refKind == REF_newInvokeSpecial) {
2529 return getDirectConstructorNoSecurityManager(defc, member);
2530 }
2531 // oops
2532 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2533 }
2534
2535 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2536 }
2537
2538 /**
2539 * Produces a method handle constructing arrays of a desired type,
2540 * as if by the {@code anewarray} bytecode.
2541 * The return type of the method handle will be the array type.
2542 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2543 *
2544 * <p> If the returned method handle is invoked with a negative
2545 * array size, a {@code NegativeArraySizeException} will be thrown.
2546 *
2547 * @param arrayClass an array type
2548 * @return a method handle which can create arrays of the given type
2549 * @throws NullPointerException if the argument is {@code null}
2550 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2551 * @see java.lang.reflect.Array#newInstance(Class, int)
2552 * @jvms 6.5 {@code anewarray} Instruction
2553 * @since 9
2554 */
2555 public static
2556 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2557 if (!arrayClass.isArray()) {
2558 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2559 }
2560 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2561 bindTo(arrayClass.getComponentType());
2562 return ani.asType(ani.type().changeReturnType(arrayClass));
2563 }
2564
2565 /**
2566 * Produces a method handle returning the length of an array,
2567 * as if by the {@code arraylength} bytecode.
2568 * The type of the method handle will have {@code int} as return type,
2569 * and its sole argument will be the array type.
2570 *
2571 * <p> If the returned method handle is invoked with a {@code null}
2572 * array reference, a {@code NullPointerException} will be thrown.
2573 *
2574 * @param arrayClass an array type
2575 * @return a method handle which can retrieve the length of an array of the given array type
2576 * @throws NullPointerException if the argument is {@code null}
2577 * @throws IllegalArgumentException if arrayClass is not an array type
2578 * @jvms 6.5 {@code arraylength} Instruction
2579 * @since 9
2580 */
2581 public static
2582 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2583 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2584 }
2585
2586 /**
2587 * Produces a method handle giving read access to elements of an array,
2588 * as if by the {@code aaload} bytecode.
2589 * The type of the method handle will have a return type of the array's
2590 * element type. Its first argument will be the array type,
2591 * and the second will be {@code int}.
2592 *
2593 * <p> When the returned method handle is invoked,
2594 * the array reference and array index are checked.
2595 * A {@code NullPointerException} will be thrown if the array reference
2596 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2597 * thrown if the index is negative or if it is greater than or equal to
2598 * the length of the array.
2599 *
2600 * @param arrayClass an array type
2601 * @return a method handle which can load values from the given array type
2602 * @throws NullPointerException if the argument is null
2603 * @throws IllegalArgumentException if arrayClass is not an array type
2604 * @jvms 6.5 {@code aaload} Instruction
2605 */
2606 public static
2607 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2608 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2609 }
2610
2611 /**
2612 * Produces a method handle giving write access to elements of an array,
2613 * as if by the {@code astore} bytecode.
2614 * The type of the method handle will have a void return type.
2615 * Its last argument will be the array's element type.
2616 * The first and second arguments will be the array type and int.
2617 *
2618 * <p> When the returned method handle is invoked,
2619 * the array reference and array index are checked.
2620 * A {@code NullPointerException} will be thrown if the array reference
2621 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2622 * thrown if the index is negative or if it is greater than or equal to
2623 * the length of the array.
2624 *
2625 * @param arrayClass the class of an array
2626 * @return a method handle which can store values into the array type
2627 * @throws NullPointerException if the argument is null
2628 * @throws IllegalArgumentException if arrayClass is not an array type
2629 * @jvms 6.5 {@code aastore} Instruction
2630 */
2631 public static
2632 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2633 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2634 }
2635
2636 /**
2637 * Produces a VarHandle giving access to elements of an array of type
2638 * {@code arrayClass}. The VarHandle's variable type is the component type
2639 * of {@code arrayClass} and the list of coordinate types is
2640 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2641 * corresponds to an argument that is an index into an array.
2642 * <p>
2643 * Certain access modes of the returned VarHandle are unsupported under
2644 * the following conditions:
2645 * <ul>
2646 * <li>if the component type is anything other than {@code byte},
2647 * {@code short}, {@code char}, {@code int}, {@code long},
2648 * {@code float}, or {@code double} then numeric atomic update access
2649 * modes are unsupported.
2650 * <li>if the field type is anything other than {@code boolean},
2651 * {@code byte}, {@code short}, {@code char}, {@code int} or
2652 * {@code long} then bitwise atomic update access modes are
2653 * unsupported.
2654 * </ul>
2655 * <p>
2656 * If the component type is {@code float} or {@code double} then numeric
2657 * and atomic update access modes compare values using their bitwise
2658 * representation (see {@link Float#floatToRawIntBits} and
2659 * {@link Double#doubleToRawLongBits}, respectively).
2660 *
2661 * <p> When the returned {@code VarHandle} is invoked,
2662 * the array reference and array index are checked.
2663 * A {@code NullPointerException} will be thrown if the array reference
2664 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2665 * thrown if the index is negative or if it is greater than or equal to
2666 * the length of the array.
2667 *
2668 * @apiNote
2669 * Bitwise comparison of {@code float} values or {@code double} values,
2670 * as performed by the numeric and atomic update access modes, differ
2671 * from the primitive {@code ==} operator and the {@link Float#equals}
2672 * and {@link Double#equals} methods, specifically with respect to
2673 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2674 * Care should be taken when performing a compare and set or a compare
2675 * and exchange operation with such values since the operation may
2676 * unexpectedly fail.
2677 * There are many possible NaN values that are considered to be
2678 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2679 * provided by Java can distinguish between them. Operation failure can
2680 * occur if the expected or witness value is a NaN value and it is
2681 * transformed (perhaps in a platform specific manner) into another NaN
2682 * value, and thus has a different bitwise representation (see
2683 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2684 * details).
2685 * The values {@code -0.0} and {@code +0.0} have different bitwise
2686 * representations but are considered equal when using the primitive
2687 * {@code ==} operator. Operation failure can occur if, for example, a
2688 * numeric algorithm computes an expected value to be say {@code -0.0}
2689 * and previously computed the witness value to be say {@code +0.0}.
2690 * @param arrayClass the class of an array, of type {@code T[]}
2691 * @return a VarHandle giving access to elements of an array
2692 * @throws NullPointerException if the arrayClass is null
2693 * @throws IllegalArgumentException if arrayClass is not an array type
2694 * @since 9
2695 */
2696 public static
2697 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2698 return VarHandles.makeArrayElementHandle(arrayClass);
2699 }
2700
2701 /**
2702 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2703 * viewed as if it were a different primitive array type, such as
2704 * {@code int[]} or {@code long[]}.
2705 * The VarHandle's variable type is the component type of
2706 * {@code viewArrayClass} and the list of coordinate types is
2707 * {@code (byte[], int)}, where the {@code int} coordinate type
2708 * corresponds to an argument that is an index into a {@code byte[]} array.
2709 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2710 * array, composing bytes to or from a value of the component type of
2711 * {@code viewArrayClass} according to the given endianness.
2712 * <p>
2713 * The supported component types (variables types) are {@code short},
2714 * {@code char}, {@code int}, {@code long}, {@code float} and
2715 * {@code double}.
2716 * <p>
2717 * Access of bytes at a given index will result in an
2718 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2719 * or greater than the {@code byte[]} array length minus the size (in bytes)
2720 * of {@code T}.
2721 * <p>
2722 * Access of bytes at an index may be aligned or misaligned for {@code T},
2723 * with respect to the underlying memory address, {@code A} say, associated
2724 * with the array and index.
2725 * If access is misaligned then access for anything other than the
2726 * {@code get} and {@code set} access modes will result in an
2727 * {@code IllegalStateException}. In such cases atomic access is only
2728 * guaranteed with respect to the largest power of two that divides the GCD
2729 * of {@code A} and the size (in bytes) of {@code T}.
2730 * If access is aligned then following access modes are supported and are
2731 * guaranteed to support atomic access:
2732 * <ul>
2733 * <li>read write access modes for all {@code T}, with the exception of
2734 * access modes {@code get} and {@code set} for {@code long} and
2735 * {@code double} on 32-bit platforms.
2736 * <li>atomic update access modes for {@code int}, {@code long},
2737 * {@code float} or {@code double}.
2738 * (Future major platform releases of the JDK may support additional
2739 * types for certain currently unsupported access modes.)
2740 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2741 * (Future major platform releases of the JDK may support additional
2742 * numeric types for certain currently unsupported access modes.)
2743 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2744 * (Future major platform releases of the JDK may support additional
2745 * numeric types for certain currently unsupported access modes.)
2746 * </ul>
2747 * <p>
2748 * Misaligned access, and therefore atomicity guarantees, may be determined
2749 * for {@code byte[]} arrays without operating on a specific array. Given
2750 * an {@code index}, {@code T} and it's corresponding boxed type,
2751 * {@code T_BOX}, misalignment may be determined as follows:
2752 * <pre>{@code
2753 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2754 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2755 * alignmentOffset(0, sizeOfT);
2756 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2757 * boolean isMisaligned = misalignedAtIndex != 0;
2758 * }</pre>
2759 * <p>
2760 * If the variable type is {@code float} or {@code double} then atomic
2761 * update access modes compare values using their bitwise representation
2762 * (see {@link Float#floatToRawIntBits} and
2763 * {@link Double#doubleToRawLongBits}, respectively).
2764 * @param viewArrayClass the view array class, with a component type of
2765 * type {@code T}
2766 * @param byteOrder the endianness of the view array elements, as
2767 * stored in the underlying {@code byte} array
2768 * @return a VarHandle giving access to elements of a {@code byte[]} array
2769 * viewed as if elements corresponding to the components type of the view
2770 * array class
2771 * @throws NullPointerException if viewArrayClass or byteOrder is null
2772 * @throws IllegalArgumentException if viewArrayClass is not an array type
2773 * @throws UnsupportedOperationException if the component type of
2774 * viewArrayClass is not supported as a variable type
2775 * @since 9
2776 */
2777 public static
2778 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2779 ByteOrder byteOrder) throws IllegalArgumentException {
2780 Objects.requireNonNull(byteOrder);
2781 return VarHandles.byteArrayViewHandle(viewArrayClass,
2782 byteOrder == ByteOrder.BIG_ENDIAN);
2783 }
2784
2785 /**
2786 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2787 * viewed as if it were an array of elements of a different primitive
2788 * component type to that of {@code byte}, such as {@code int[]} or
2789 * {@code long[]}.
2790 * The VarHandle's variable type is the component type of
2791 * {@code viewArrayClass} and the list of coordinate types is
2792 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2793 * corresponds to an argument that is an index into a {@code byte[]} array.
2794 * The returned VarHandle accesses bytes at an index in a
2795 * {@code ByteBuffer}, composing bytes to or from a value of the component
2796 * type of {@code viewArrayClass} according to the given endianness.
2797 * <p>
2798 * The supported component types (variables types) are {@code short},
2799 * {@code char}, {@code int}, {@code long}, {@code float} and
2800 * {@code double}.
2801 * <p>
2802 * Access will result in a {@code ReadOnlyBufferException} for anything
2803 * other than the read access modes if the {@code ByteBuffer} is read-only.
2804 * <p>
2805 * Access of bytes at a given index will result in an
2806 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2807 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2808 * {@code T}.
2809 * <p>
2810 * Access of bytes at an index may be aligned or misaligned for {@code T},
2811 * with respect to the underlying memory address, {@code A} say, associated
2812 * with the {@code ByteBuffer} and index.
2813 * If access is misaligned then access for anything other than the
2814 * {@code get} and {@code set} access modes will result in an
2815 * {@code IllegalStateException}. In such cases atomic access is only
2816 * guaranteed with respect to the largest power of two that divides the GCD
2817 * of {@code A} and the size (in bytes) of {@code T}.
2818 * If access is aligned then following access modes are supported and are
2819 * guaranteed to support atomic access:
2820 * <ul>
2821 * <li>read write access modes for all {@code T}, with the exception of
2822 * access modes {@code get} and {@code set} for {@code long} and
2823 * {@code double} on 32-bit platforms.
2824 * <li>atomic update access modes for {@code int}, {@code long},
2825 * {@code float} or {@code double}.
2826 * (Future major platform releases of the JDK may support additional
2827 * types for certain currently unsupported access modes.)
2828 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2829 * (Future major platform releases of the JDK may support additional
2830 * numeric types for certain currently unsupported access modes.)
2831 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2832 * (Future major platform releases of the JDK may support additional
2833 * numeric types for certain currently unsupported access modes.)
2834 * </ul>
2835 * <p>
2836 * Misaligned access, and therefore atomicity guarantees, may be determined
2837 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2838 * {@code index}, {@code T} and it's corresponding boxed type,
2839 * {@code T_BOX}, as follows:
2840 * <pre>{@code
2841 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2842 * ByteBuffer bb = ...
2843 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2844 * boolean isMisaligned = misalignedAtIndex != 0;
2845 * }</pre>
2846 * <p>
2847 * If the variable type is {@code float} or {@code double} then atomic
2848 * update access modes compare values using their bitwise representation
2849 * (see {@link Float#floatToRawIntBits} and
2850 * {@link Double#doubleToRawLongBits}, respectively).
2851 * @param viewArrayClass the view array class, with a component type of
2852 * type {@code T}
2853 * @param byteOrder the endianness of the view array elements, as
2854 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2855 * endianness of a {@code ByteBuffer})
2856 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2857 * viewed as if elements corresponding to the components type of the view
2858 * array class
2859 * @throws NullPointerException if viewArrayClass or byteOrder is null
2860 * @throws IllegalArgumentException if viewArrayClass is not an array type
2861 * @throws UnsupportedOperationException if the component type of
2862 * viewArrayClass is not supported as a variable type
2863 * @since 9
2864 */
2865 public static
2866 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2867 ByteOrder byteOrder) throws IllegalArgumentException {
2868 Objects.requireNonNull(byteOrder);
2869 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2870 byteOrder == ByteOrder.BIG_ENDIAN);
2871 }
2872
2873
2874 /// method handle invocation (reflective style)
2875
2876 /**
2877 * Produces a method handle which will invoke any method handle of the
2878 * given {@code type}, with a given number of trailing arguments replaced by
2879 * a single trailing {@code Object[]} array.
2880 * The resulting invoker will be a method handle with the following
2881 * arguments:
2882 * <ul>
2883 * <li>a single {@code MethodHandle} target
2884 * <li>zero or more leading values (counted by {@code leadingArgCount})
2885 * <li>an {@code Object[]} array containing trailing arguments
2886 * </ul>
2887 * <p>
2888 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2889 * the indicated {@code type}.
2890 * That is, if the target is exactly of the given {@code type}, it will behave
2891 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2892 * is used to convert the target to the required {@code type}.
2893 * <p>
2894 * The type of the returned invoker will not be the given {@code type}, but rather
2895 * will have all parameters except the first {@code leadingArgCount}
2896 * replaced by a single array of type {@code Object[]}, which will be
2897 * the final parameter.
2898 * <p>
2899 * Before invoking its target, the invoker will spread the final array, apply
2900 * reference casts as necessary, and unbox and widen primitive arguments.
2901 * If, when the invoker is called, the supplied array argument does
2902 * not have the correct number of elements, the invoker will throw
2903 * an {@link IllegalArgumentException} instead of invoking the target.
2904 * <p>
2905 * This method is equivalent to the following code (though it may be more efficient):
2906 * <blockquote><pre>{@code
2907 MethodHandle invoker = MethodHandles.invoker(type);
2908 int spreadArgCount = type.parameterCount() - leadingArgCount;
2909 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2910 return invoker;
2911 * }</pre></blockquote>
2912 * This method throws no reflective or security exceptions.
2913 * @param type the desired target type
2914 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2915 * @return a method handle suitable for invoking any method handle of the given type
2916 * @throws NullPointerException if {@code type} is null
2917 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2918 * the range from 0 to {@code type.parameterCount()} inclusive,
2919 * or if the resulting method handle's type would have
2920 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2921 */
2922 public static
2923 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2924 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2925 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2926 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2927 return type.invokers().spreadInvoker(leadingArgCount);
2928 }
2929
2930 /**
2931 * Produces a special <em>invoker method handle</em> which can be used to
2932 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2933 * The resulting invoker will have a type which is
2934 * exactly equal to the desired type, except that it will accept
2935 * an additional leading argument of type {@code MethodHandle}.
2936 * <p>
2937 * This method is equivalent to the following code (though it may be more efficient):
2938 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2939 *
2940 * <p style="font-size:smaller;">
2941 * <em>Discussion:</em>
2942 * Invoker method handles can be useful when working with variable method handles
2943 * of unknown types.
2944 * For example, to emulate an {@code invokeExact} call to a variable method
2945 * handle {@code M}, extract its type {@code T},
2946 * look up the invoker method {@code X} for {@code T},
2947 * and call the invoker method, as {@code X.invoke(T, A...)}.
2948 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2949 * is unknown.)
2950 * If spreading, collecting, or other argument transformations are required,
2951 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2952 * method handle values, as long as they are compatible with the type of {@code X}.
2953 * <p style="font-size:smaller;">
2954 * <em>(Note: The invoker method is not available via the Core Reflection API.
2955 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2956 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2957 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2958 * <p>
2959 * This method throws no reflective or security exceptions.
2960 * @param type the desired target type
2961 * @return a method handle suitable for invoking any method handle of the given type
2962 * @throws IllegalArgumentException if the resulting method handle's type would have
2963 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2964 */
2965 public static
2966 MethodHandle exactInvoker(MethodType type) {
2967 return type.invokers().exactInvoker();
2968 }
2969
2970 /**
2971 * Produces a special <em>invoker method handle</em> which can be used to
2972 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2973 * The resulting invoker will have a type which is
2974 * exactly equal to the desired type, except that it will accept
2975 * an additional leading argument of type {@code MethodHandle}.
2976 * <p>
2977 * Before invoking its target, if the target differs from the expected type,
2978 * the invoker will apply reference casts as
2979 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2980 * Similarly, the return value will be converted as necessary.
2981 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2982 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2983 * <p>
2984 * This method is equivalent to the following code (though it may be more efficient):
2985 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2986 * <p style="font-size:smaller;">
2987 * <em>Discussion:</em>
2988 * A {@linkplain MethodType#genericMethodType general method type} is one which
2989 * mentions only {@code Object} arguments and return values.
2990 * An invoker for such a type is capable of calling any method handle
2991 * of the same arity as the general type.
2992 * <p style="font-size:smaller;">
2993 * <em>(Note: The invoker method is not available via the Core Reflection API.
2994 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2995 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2996 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2997 * <p>
2998 * This method throws no reflective or security exceptions.
2999 * @param type the desired target type
3000 * @return a method handle suitable for invoking any method handle convertible to the given type
3001 * @throws IllegalArgumentException if the resulting method handle's type would have
3002 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3003 */
3004 public static
3005 MethodHandle invoker(MethodType type) {
3006 return type.invokers().genericInvoker();
3007 }
3008
3009 /**
3010 * Produces a special <em>invoker method handle</em> which can be used to
3011 * invoke a signature-polymorphic access mode method on any VarHandle whose
3012 * associated access mode type is compatible with the given type.
3013 * The resulting invoker will have a type which is exactly equal to the
3014 * desired given type, except that it will accept an additional leading
3015 * argument of type {@code VarHandle}.
3016 *
3017 * @param accessMode the VarHandle access mode
3018 * @param type the desired target type
3019 * @return a method handle suitable for invoking an access mode method of
3020 * any VarHandle whose access mode type is of the given type.
3021 * @since 9
3022 */
3023 static public
3024 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3025 return type.invokers().varHandleMethodExactInvoker(accessMode);
3026 }
3027
3028 /**
3029 * Produces a special <em>invoker method handle</em> which can be used to
3030 * invoke a signature-polymorphic access mode method on any VarHandle whose
3031 * associated access mode type is compatible with the given type.
3032 * The resulting invoker will have a type which is exactly equal to the
3033 * desired given type, except that it will accept an additional leading
3034 * argument of type {@code VarHandle}.
3035 * <p>
3036 * Before invoking its target, if the access mode type differs from the
3037 * desired given type, the invoker will apply reference casts as necessary
3038 * and box, unbox, or widen primitive values, as if by
3039 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3040 * converted as necessary.
3041 * <p>
3042 * This method is equivalent to the following code (though it may be more
3043 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3044 *
3045 * @param accessMode the VarHandle access mode
3046 * @param type the desired target type
3047 * @return a method handle suitable for invoking an access mode method of
3048 * any VarHandle whose access mode type is convertible to the given
3049 * type.
3050 * @since 9
3051 */
3052 static public
3053 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3054 return type.invokers().varHandleMethodInvoker(accessMode);
3055 }
3056
3057 static /*non-public*/
3058 MethodHandle basicInvoker(MethodType type) {
3059 return type.invokers().basicInvoker();
3060 }
3061
3062 /// method handle modification (creation from other method handles)
3063
3064 /**
3065 * Produces a method handle which adapts the type of the
3066 * given method handle to a new type by pairwise argument and return type conversion.
3067 * The original type and new type must have the same number of arguments.
3068 * The resulting method handle is guaranteed to report a type
3069 * which is equal to the desired new type.
3070 * <p>
3071 * If the original type and new type are equal, returns target.
3072 * <p>
3073 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3074 * and some additional conversions are also applied if those conversions fail.
3075 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3076 * if possible, before or instead of any conversions done by {@code asType}:
3077 * <ul>
3078 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3079 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3080 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3081 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3082 * the boolean is converted to a byte value, 1 for true, 0 for false.
3083 * (This treatment follows the usage of the bytecode verifier.)
3084 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3085 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3086 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3087 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3088 * then a Java casting conversion (JLS 5.5) is applied.
3089 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3090 * widening and/or narrowing.)
3091 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3092 * conversion will be applied at runtime, possibly followed
3093 * by a Java casting conversion (JLS 5.5) on the primitive value,
3094 * possibly followed by a conversion from byte to boolean by testing
3095 * the low-order bit.
3096 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3097 * and if the reference is null at runtime, a zero value is introduced.
3098 * </ul>
3099 * @param target the method handle to invoke after arguments are retyped
3100 * @param newType the expected type of the new method handle
3101 * @return a method handle which delegates to the target after performing
3102 * any necessary argument conversions, and arranges for any
3103 * necessary return value conversions
3104 * @throws NullPointerException if either argument is null
3105 * @throws WrongMethodTypeException if the conversion cannot be made
3106 * @see MethodHandle#asType
3107 */
3108 public static
3109 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3110 explicitCastArgumentsChecks(target, newType);
3111 // use the asTypeCache when possible:
3112 MethodType oldType = target.type();
3113 if (oldType == newType) return target;
3114 if (oldType.explicitCastEquivalentToAsType(newType)) {
3115 return target.asFixedArity().asType(newType);
3116 }
3117 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3118 }
3119
3120 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3121 if (target.type().parameterCount() != newType.parameterCount()) {
3122 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3123 }
3124 }
3125
3126 /**
3127 * Produces a method handle which adapts the calling sequence of the
3128 * given method handle to a new type, by reordering the arguments.
3129 * The resulting method handle is guaranteed to report a type
3130 * which is equal to the desired new type.
3131 * <p>
3132 * The given array controls the reordering.
3133 * Call {@code #I} the number of incoming parameters (the value
3134 * {@code newType.parameterCount()}, and call {@code #O} the number
3135 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3136 * Then the length of the reordering array must be {@code #O},
3137 * and each element must be a non-negative number less than {@code #I}.
3138 * For every {@code N} less than {@code #O}, the {@code N}-th
3139 * outgoing argument will be taken from the {@code I}-th incoming
3140 * argument, where {@code I} is {@code reorder[N]}.
3141 * <p>
3142 * No argument or return value conversions are applied.
3143 * The type of each incoming argument, as determined by {@code newType},
3144 * must be identical to the type of the corresponding outgoing parameter
3145 * or parameters in the target method handle.
3146 * The return type of {@code newType} must be identical to the return
3147 * type of the original target.
3148 * <p>
3149 * The reordering array need not specify an actual permutation.
3150 * An incoming argument will be duplicated if its index appears
3151 * more than once in the array, and an incoming argument will be dropped
3152 * if its index does not appear in the array.
3153 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3154 * incoming arguments which are not mentioned in the reordering array
3155 * may be of any type, as determined only by {@code newType}.
3156 * <blockquote><pre>{@code
3157 import static java.lang.invoke.MethodHandles.*;
3158 import static java.lang.invoke.MethodType.*;
3159 ...
3160 MethodType intfn1 = methodType(int.class, int.class);
3161 MethodType intfn2 = methodType(int.class, int.class, int.class);
3162 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3163 assert(sub.type().equals(intfn2));
3164 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3165 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3166 assert((int)rsub.invokeExact(1, 100) == 99);
3167 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3168 assert(add.type().equals(intfn2));
3169 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3170 assert(twice.type().equals(intfn1));
3171 assert((int)twice.invokeExact(21) == 42);
3172 * }</pre></blockquote>
3173 * <p>
3174 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3175 * variable-arity method handle}, even if the original target method handle was.
3176 * @param target the method handle to invoke after arguments are reordered
3177 * @param newType the expected type of the new method handle
3178 * @param reorder an index array which controls the reordering
3179 * @return a method handle which delegates to the target after it
3180 * drops unused arguments and moves and/or duplicates the other arguments
3181 * @throws NullPointerException if any argument is null
3182 * @throws IllegalArgumentException if the index array length is not equal to
3183 * the arity of the target, or if any index array element
3184 * not a valid index for a parameter of {@code newType},
3185 * or if two corresponding parameter types in
3186 * {@code target.type()} and {@code newType} are not identical,
3187 */
3188 public static
3189 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3190 reorder = reorder.clone(); // get a private copy
3191 MethodType oldType = target.type();
3192 permuteArgumentChecks(reorder, newType, oldType);
3193 // first detect dropped arguments and handle them separately
3194 int[] originalReorder = reorder;
3195 BoundMethodHandle result = target.rebind();
3196 LambdaForm form = result.form;
3197 int newArity = newType.parameterCount();
3198 // Normalize the reordering into a real permutation,
3199 // by removing duplicates and adding dropped elements.
3200 // This somewhat improves lambda form caching, as well
3201 // as simplifying the transform by breaking it up into steps.
3202 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3203 if (ddIdx > 0) {
3204 // We found a duplicated entry at reorder[ddIdx].
3205 // Example: (x,y,z)->asList(x,y,z)
3206 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3207 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3208 // The starred element corresponds to the argument
3209 // deleted by the dupArgumentForm transform.
3210 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3211 boolean killFirst = false;
3212 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3213 // Set killFirst if the dup is larger than an intervening position.
3214 // This will remove at least one inversion from the permutation.
3215 if (dupVal > val) killFirst = true;
3216 }
3217 if (!killFirst) {
3218 srcPos = dstPos;
3219 dstPos = ddIdx;
3220 }
3221 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3222 assert (reorder[srcPos] == reorder[dstPos]);
3223 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3224 // contract the reordering by removing the element at dstPos
3225 int tailPos = dstPos + 1;
3226 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3227 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3228 } else {
3229 int dropVal = ~ddIdx, insPos = 0;
3230 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3231 // Find first element of reorder larger than dropVal.
3232 // This is where we will insert the dropVal.
3233 insPos += 1;
3234 }
3235 Class<?> ptype = newType.parameterType(dropVal);
3236 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3237 oldType = oldType.insertParameterTypes(insPos, ptype);
3238 // expand the reordering by inserting an element at insPos
3239 int tailPos = insPos + 1;
3240 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3241 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3242 reorder[insPos] = dropVal;
3243 }
3244 assert (permuteArgumentChecks(reorder, newType, oldType));
3245 }
3246 assert (reorder.length == newArity); // a perfect permutation
3247 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3248 form = form.editor().permuteArgumentsForm(1, reorder);
3249 if (newType == result.type() && form == result.internalForm())
3250 return result;
3251 return result.copyWith(newType, form);
3252 }
3253
3254 /**
3255 * Return an indication of any duplicate or omission in reorder.
3256 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3257 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3258 * Otherwise, return zero.
3259 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3260 */
3261 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3262 final int BIT_LIMIT = 63; // max number of bits in bit mask
3263 if (newArity < BIT_LIMIT) {
3264 long mask = 0;
3265 for (int i = 0; i < reorder.length; i++) {
3266 int arg = reorder[i];
3267 if (arg >= newArity) {
3268 return reorder.length;
3269 }
3270 long bit = 1L << arg;
3271 if ((mask & bit) != 0) {
3272 return i; // >0 indicates a dup
3273 }
3274 mask |= bit;
3275 }
3276 if (mask == (1L << newArity) - 1) {
3277 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3278 return 0;
3279 }
3280 // find first zero
3281 long zeroBit = Long.lowestOneBit(~mask);
3282 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3283 assert(zeroPos <= newArity);
3284 if (zeroPos == newArity) {
3285 return 0;
3286 }
3287 return ~zeroPos;
3288 } else {
3289 // same algorithm, different bit set
3290 BitSet mask = new BitSet(newArity);
3291 for (int i = 0; i < reorder.length; i++) {
3292 int arg = reorder[i];
3293 if (arg >= newArity) {
3294 return reorder.length;
3295 }
3296 if (mask.get(arg)) {
3297 return i; // >0 indicates a dup
3298 }
3299 mask.set(arg);
3300 }
3301 int zeroPos = mask.nextClearBit(0);
3302 assert(zeroPos <= newArity);
3303 if (zeroPos == newArity) {
3304 return 0;
3305 }
3306 return ~zeroPos;
3307 }
3308 }
3309
3310 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3311 if (newType.returnType() != oldType.returnType())
3312 throw newIllegalArgumentException("return types do not match",
3313 oldType, newType);
3314 if (reorder.length == oldType.parameterCount()) {
3315 int limit = newType.parameterCount();
3316 boolean bad = false;
3317 for (int j = 0; j < reorder.length; j++) {
3318 int i = reorder[j];
3319 if (i < 0 || i >= limit) {
3320 bad = true; break;
3321 }
3322 Class<?> src = newType.parameterType(i);
3323 Class<?> dst = oldType.parameterType(j);
3324 if (src != dst)
3325 throw newIllegalArgumentException("parameter types do not match after reorder",
3326 oldType, newType);
3327 }
3328 if (!bad) return true;
3329 }
3330 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3331 }
3332
3333 /**
3334 * Produces a method handle of the requested return type which returns the given
3335 * constant value every time it is invoked.
3336 * <p>
3337 * Before the method handle is returned, the passed-in value is converted to the requested type.
3338 * If the requested type is primitive, widening primitive conversions are attempted,
3339 * else reference conversions are attempted.
3340 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3341 * @param type the return type of the desired method handle
3342 * @param value the value to return
3343 * @return a method handle of the given return type and no arguments, which always returns the given value
3344 * @throws NullPointerException if the {@code type} argument is null
3345 * @throws ClassCastException if the value cannot be converted to the required return type
3346 * @throws IllegalArgumentException if the given type is {@code void.class}
3347 */
3348 public static
3349 MethodHandle constant(Class<?> type, Object value) {
3350 if (type.isPrimitive()) {
3351 if (type == void.class)
3352 throw newIllegalArgumentException("void type");
3353 Wrapper w = Wrapper.forPrimitiveType(type);
3354 value = w.convert(value, type);
3355 if (w.zero().equals(value))
3356 return zero(w, type);
3357 return insertArguments(identity(type), 0, value);
3358 } else {
3359 if (value == null)
3360 return zero(Wrapper.OBJECT, type);
3361 return identity(type).bindTo(value);
3362 }
3363 }
3364
3365 /**
3366 * Produces a method handle which returns its sole argument when invoked.
3367 * @param type the type of the sole parameter and return value of the desired method handle
3368 * @return a unary method handle which accepts and returns the given type
3369 * @throws NullPointerException if the argument is null
3370 * @throws IllegalArgumentException if the given type is {@code void.class}
3371 */
3372 public static
3373 MethodHandle identity(Class<?> type) {
3374 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3375 int pos = btw.ordinal();
3376 MethodHandle ident = IDENTITY_MHS[pos];
3377 if (ident == null) {
3378 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3379 }
3380 if (ident.type().returnType() == type)
3381 return ident;
3382 // something like identity(Foo.class); do not bother to intern these
3383 assert (btw == Wrapper.OBJECT);
3384 return makeIdentity(type);
3385 }
3386
3387 /**
3388 * Produces a constant method handle of the requested return type which
3389 * returns the default value for that type every time it is invoked.
3390 * The resulting constant method handle will have no side effects.
3391 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3392 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3393 * since {@code explicitCastArguments} converts {@code null} to default values.
3394 * @param type the expected return type of the desired method handle
3395 * @return a constant method handle that takes no arguments
3396 * and returns the default value of the given type (or void, if the type is void)
3397 * @throws NullPointerException if the argument is null
3398 * @see MethodHandles#constant
3399 * @see MethodHandles#empty
3400 * @see MethodHandles#explicitCastArguments
3401 * @since 9
3402 */
3403 public static MethodHandle zero(Class<?> type) {
3404 Objects.requireNonNull(type);
3405 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3406 }
3407
3408 private static MethodHandle identityOrVoid(Class<?> type) {
3409 return type == void.class ? zero(type) : identity(type);
3410 }
3411
3412 /**
3413 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3414 * and returns a suitable default depending on the return type.
3415 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3416 * <p>The returned method handle is equivalent to
3417 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3418 *
3419 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3420 * {@code guardWithTest(pred, target, empty(target.type())}.
3421 * @param type the type of the desired method handle
3422 * @return a constant method handle of the given type, which returns a default value of the given return type
3423 * @throws NullPointerException if the argument is null
3424 * @see MethodHandles#zero
3425 * @see MethodHandles#constant
3426 * @since 9
3427 */
3428 public static MethodHandle empty(MethodType type) {
3429 Objects.requireNonNull(type);
3430 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3431 }
3432
3433 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3434 private static MethodHandle makeIdentity(Class<?> ptype) {
3435 MethodType mtype = methodType(ptype, ptype);
3436 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3437 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3438 }
3439
3440 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3441 int pos = btw.ordinal();
3442 MethodHandle zero = ZERO_MHS[pos];
3443 if (zero == null) {
3444 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3445 }
3446 if (zero.type().returnType() == rtype)
3447 return zero;
3448 assert(btw == Wrapper.OBJECT);
3449 return makeZero(rtype);
3450 }
3451 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3452 private static MethodHandle makeZero(Class<?> rtype) {
3453 MethodType mtype = methodType(rtype);
3454 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3455 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3456 }
3457
3458 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3459 // Simulate a CAS, to avoid racy duplication of results.
3460 MethodHandle prev = cache[pos];
3461 if (prev != null) return prev;
3462 return cache[pos] = value;
3463 }
3464
3465 /**
3466 * Provides a target method handle with one or more <em>bound arguments</em>
3467 * in advance of the method handle's invocation.
3468 * The formal parameters to the target corresponding to the bound
3469 * arguments are called <em>bound parameters</em>.
3470 * Returns a new method handle which saves away the bound arguments.
3471 * When it is invoked, it receives arguments for any non-bound parameters,
3472 * binds the saved arguments to their corresponding parameters,
3473 * and calls the original target.
3474 * <p>
3475 * The type of the new method handle will drop the types for the bound
3476 * parameters from the original target type, since the new method handle
3477 * will no longer require those arguments to be supplied by its callers.
3478 * <p>
3479 * Each given argument object must match the corresponding bound parameter type.
3480 * If a bound parameter type is a primitive, the argument object
3481 * must be a wrapper, and will be unboxed to produce the primitive value.
3482 * <p>
3483 * The {@code pos} argument selects which parameters are to be bound.
3484 * It may range between zero and <i>N-L</i> (inclusively),
3485 * where <i>N</i> is the arity of the target method handle
3486 * and <i>L</i> is the length of the values array.
3487 * <p>
3488 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3489 * variable-arity method handle}, even if the original target method handle was.
3490 * @param target the method handle to invoke after the argument is inserted
3491 * @param pos where to insert the argument (zero for the first)
3492 * @param values the series of arguments to insert
3493 * @return a method handle which inserts an additional argument,
3494 * before calling the original method handle
3495 * @throws NullPointerException if the target or the {@code values} array is null
3496 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
3497 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
3498 * is the length of the values array.
3499 * @throws ClassCastException if an argument does not match the corresponding bound parameter
3500 * type.
3501 * @see MethodHandle#bindTo
3502 */
3503 public static
3504 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3505 int insCount = values.length;
3506 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3507 if (insCount == 0) return target;
3508 BoundMethodHandle result = target.rebind();
3509 for (int i = 0; i < insCount; i++) {
3510 Object value = values[i];
3511 Class<?> ptype = ptypes[pos+i];
3512 if (ptype.isPrimitive()) {
3513 result = insertArgumentPrimitive(result, pos, ptype, value);
3514 } else {
3515 value = ptype.cast(value); // throw CCE if needed
3516 result = result.bindArgumentL(pos, value);
3517 }
3518 }
3519 return result;
3520 }
3521
3522 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3523 Class<?> ptype, Object value) {
3524 Wrapper w = Wrapper.forPrimitiveType(ptype);
3525 // perform unboxing and/or primitive conversion
3526 value = w.convert(value, ptype);
3527 switch (w) {
3528 case INT: return result.bindArgumentI(pos, (int)value);
3529 case LONG: return result.bindArgumentJ(pos, (long)value);
3530 case FLOAT: return result.bindArgumentF(pos, (float)value);
3531 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3532 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3533 }
3534 }
3535
3536 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3537 MethodType oldType = target.type();
3538 int outargs = oldType.parameterCount();
3539 int inargs = outargs - insCount;
3540 if (inargs < 0)
3541 throw newIllegalArgumentException("too many values to insert");
3542 if (pos < 0 || pos > inargs)
3543 throw newIllegalArgumentException("no argument type to append");
3544 return oldType.ptypes();
3545 }
3546
3547 /**
3548 * Produces a method handle which will discard some dummy arguments
3549 * before calling some other specified <i>target</i> method handle.
3550 * The type of the new method handle will be the same as the target's type,
3551 * except it will also include the dummy argument types,
3552 * at some given position.
3553 * <p>
3554 * The {@code pos} argument may range between zero and <i>N</i>,
3555 * where <i>N</i> is the arity of the target.
3556 * If {@code pos} is zero, the dummy arguments will precede
3557 * the target's real arguments; if {@code pos} is <i>N</i>
3558 * they will come after.
3559 * <p>
3560 * <b>Example:</b>
3561 * <blockquote><pre>{@code
3562 import static java.lang.invoke.MethodHandles.*;
3563 import static java.lang.invoke.MethodType.*;
3564 ...
3565 MethodHandle cat = lookup().findVirtual(String.class,
3566 "concat", methodType(String.class, String.class));
3567 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3568 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3569 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3570 assertEquals(bigType, d0.type());
3571 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3572 * }</pre></blockquote>
3573 * <p>
3574 * This method is also equivalent to the following code:
3575 * <blockquote><pre>
3576 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3577 * </pre></blockquote>
3578 * @param target the method handle to invoke after the arguments are dropped
3579 * @param valueTypes the type(s) of the argument(s) to drop
3580 * @param pos position of first argument to drop (zero for the leftmost)
3581 * @return a method handle which drops arguments of the given types,
3582 * before calling the original method handle
3583 * @throws NullPointerException if the target is null,
3584 * or if the {@code valueTypes} list or any of its elements is null
3585 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3586 * or if {@code pos} is negative or greater than the arity of the target,
3587 * or if the new method handle's type would have too many parameters
3588 */
3589 public static
3590 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3591 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3592 }
3593
3594 private static List<Class<?>> copyTypes(Object[] array) {
3595 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3596 }
3597
3598 private static
3599 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3600 MethodType oldType = target.type(); // get NPE
3601 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3602 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3603 if (dropped == 0) return target;
3604 BoundMethodHandle result = target.rebind();
3605 LambdaForm lform = result.form;
3606 int insertFormArg = 1 + pos;
3607 for (Class<?> ptype : valueTypes) {
3608 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3609 }
3610 result = result.copyWith(newType, lform);
3611 return result;
3612 }
3613
3614 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3615 int dropped = valueTypes.size();
3616 MethodType.checkSlotCount(dropped);
3617 int outargs = oldType.parameterCount();
3618 int inargs = outargs + dropped;
3619 if (pos < 0 || pos > outargs)
3620 throw newIllegalArgumentException("no argument type to remove"
3621 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3622 );
3623 return dropped;
3624 }
3625
3626 /**
3627 * Produces a method handle which will discard some dummy arguments
3628 * before calling some other specified <i>target</i> method handle.
3629 * The type of the new method handle will be the same as the target's type,
3630 * except it will also include the dummy argument types,
3631 * at some given position.
3632 * <p>
3633 * The {@code pos} argument may range between zero and <i>N</i>,
3634 * where <i>N</i> is the arity of the target.
3635 * If {@code pos} is zero, the dummy arguments will precede
3636 * the target's real arguments; if {@code pos} is <i>N</i>
3637 * they will come after.
3638 * @apiNote
3639 * <blockquote><pre>{@code
3640 import static java.lang.invoke.MethodHandles.*;
3641 import static java.lang.invoke.MethodType.*;
3642 ...
3643 MethodHandle cat = lookup().findVirtual(String.class,
3644 "concat", methodType(String.class, String.class));
3645 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3646 MethodHandle d0 = dropArguments(cat, 0, String.class);
3647 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3648 MethodHandle d1 = dropArguments(cat, 1, String.class);
3649 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3650 MethodHandle d2 = dropArguments(cat, 2, String.class);
3651 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3652 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3653 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3654 * }</pre></blockquote>
3655 * <p>
3656 * This method is also equivalent to the following code:
3657 * <blockquote><pre>
3658 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3659 * </pre></blockquote>
3660 * @param target the method handle to invoke after the arguments are dropped
3661 * @param valueTypes the type(s) of the argument(s) to drop
3662 * @param pos position of first argument to drop (zero for the leftmost)
3663 * @return a method handle which drops arguments of the given types,
3664 * before calling the original method handle
3665 * @throws NullPointerException if the target is null,
3666 * or if the {@code valueTypes} array or any of its elements is null
3667 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3668 * or if {@code pos} is negative or greater than the arity of the target,
3669 * or if the new method handle's type would have
3670 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3671 */
3672 public static
3673 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3674 return dropArguments0(target, pos, copyTypes(valueTypes));
3675 }
3676
3677 // private version which allows caller some freedom with error handling
3678 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3679 boolean nullOnFailure) {
3680 newTypes = copyTypes(newTypes.toArray());
3681 List<Class<?>> oldTypes = target.type().parameterList();
3682 int match = oldTypes.size();
3683 if (skip != 0) {
3684 if (skip < 0 || skip > match) {
3685 throw newIllegalArgumentException("illegal skip", skip, target);
3686 }
3687 oldTypes = oldTypes.subList(skip, match);
3688 match -= skip;
3689 }
3690 List<Class<?>> addTypes = newTypes;
3691 int add = addTypes.size();
3692 if (pos != 0) {
3693 if (pos < 0 || pos > add) {
3694 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3695 }
3696 addTypes = addTypes.subList(pos, add);
3697 add -= pos;
3698 assert(addTypes.size() == add);
3699 }
3700 // Do not add types which already match the existing arguments.
3701 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3702 if (nullOnFailure) {
3703 return null;
3704 }
3705 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3706 }
3707 addTypes = addTypes.subList(match, add);
3708 add -= match;
3709 assert(addTypes.size() == add);
3710 // newTypes: ( P*[pos], M*[match], A*[add] )
3711 // target: ( S*[skip], M*[match] )
3712 MethodHandle adapter = target;
3713 if (add > 0) {
3714 adapter = dropArguments0(adapter, skip+ match, addTypes);
3715 }
3716 // adapter: (S*[skip], M*[match], A*[add] )
3717 if (pos > 0) {
3718 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3719 }
3720 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3721 return adapter;
3722 }
3723
3724 /**
3725 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3726 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3727 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3728 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3729 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3730 * {@link #dropArguments(MethodHandle, int, Class[])}.
3731 * <p>
3732 * The resulting handle will have the same return type as the target handle.
3733 * <p>
3734 * In more formal terms, assume these two type lists:<ul>
3735 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3736 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3737 * {@code newTypes}.
3738 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3739 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3740 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3741 * sub-list.
3742 * </ul>
3743 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3744 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3745 * {@link #dropArguments(MethodHandle, int, Class[])}.
3746 *
3747 * @apiNote
3748 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3749 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3750 * <blockquote><pre>{@code
3751 import static java.lang.invoke.MethodHandles.*;
3752 import static java.lang.invoke.MethodType.*;
3753 ...
3754 ...
3755 MethodHandle h0 = constant(boolean.class, true);
3756 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3757 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3758 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3759 if (h1.type().parameterCount() < h2.type().parameterCount())
3760 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3761 else
3762 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3763 MethodHandle h3 = guardWithTest(h0, h1, h2);
3764 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3765 * }</pre></blockquote>
3766 * @param target the method handle to adapt
3767 * @param skip number of targets parameters to disregard (they will be unchanged)
3768 * @param newTypes the list of types to match {@code target}'s parameter type list to
3769 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3770 * @return a possibly adapted method handle
3771 * @throws NullPointerException if either argument is null
3772 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3773 * or if {@code skip} is negative or greater than the arity of the target,
3774 * or if {@code pos} is negative or greater than the newTypes list size,
3775 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3776 * {@code pos}.
3777 * @since 9
3778 */
3779 public static
3780 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3781 Objects.requireNonNull(target);
3782 Objects.requireNonNull(newTypes);
3783 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3784 }
3785
3786 /**
3787 * Adapts a target method handle by pre-processing
3788 * one or more of its arguments, each with its own unary filter function,
3789 * and then calling the target with each pre-processed argument
3790 * replaced by the result of its corresponding filter function.
3791 * <p>
3792 * The pre-processing is performed by one or more method handles,
3793 * specified in the elements of the {@code filters} array.
3794 * The first element of the filter array corresponds to the {@code pos}
3795 * argument of the target, and so on in sequence.
3796 * The filter functions are invoked in left to right order.
3797 * <p>
3798 * Null arguments in the array are treated as identity functions,
3799 * and the corresponding arguments left unchanged.
3800 * (If there are no non-null elements in the array, the original target is returned.)
3801 * Each filter is applied to the corresponding argument of the adapter.
3802 * <p>
3803 * If a filter {@code F} applies to the {@code N}th argument of
3804 * the target, then {@code F} must be a method handle which
3805 * takes exactly one argument. The type of {@code F}'s sole argument
3806 * replaces the corresponding argument type of the target
3807 * in the resulting adapted method handle.
3808 * The return type of {@code F} must be identical to the corresponding
3809 * parameter type of the target.
3810 * <p>
3811 * It is an error if there are elements of {@code filters}
3812 * (null or not)
3813 * which do not correspond to argument positions in the target.
3814 * <p><b>Example:</b>
3815 * <blockquote><pre>{@code
3816 import static java.lang.invoke.MethodHandles.*;
3817 import static java.lang.invoke.MethodType.*;
3818 ...
3819 MethodHandle cat = lookup().findVirtual(String.class,
3820 "concat", methodType(String.class, String.class));
3821 MethodHandle upcase = lookup().findVirtual(String.class,
3822 "toUpperCase", methodType(String.class));
3823 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3824 MethodHandle f0 = filterArguments(cat, 0, upcase);
3825 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3826 MethodHandle f1 = filterArguments(cat, 1, upcase);
3827 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3828 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3829 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3830 * }</pre></blockquote>
3831 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3832 * denotes the return type of both the {@code target} and resulting adapter.
3833 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3834 * of the parameters and arguments that precede and follow the filter position
3835 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3836 * values of the filtered parameters and arguments; they also represent the
3837 * return types of the {@code filter[i]} handles. The latter accept arguments
3838 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3839 * the resulting adapter.
3840 * <blockquote><pre>{@code
3841 * T target(P... p, A[i]... a[i], B... b);
3842 * A[i] filter[i](V[i]);
3843 * T adapter(P... p, V[i]... v[i], B... b) {
3844 * return target(p..., filter[i](v[i])..., b...);
3845 * }
3846 * }</pre></blockquote>
3847 * <p>
3848 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3849 * variable-arity method handle}, even if the original target method handle was.
3850 *
3851 * @param target the method handle to invoke after arguments are filtered
3852 * @param pos the position of the first argument to filter
3853 * @param filters method handles to call initially on filtered arguments
3854 * @return method handle which incorporates the specified argument filtering logic
3855 * @throws NullPointerException if the target is null
3856 * or if the {@code filters} array is null
3857 * @throws IllegalArgumentException if a non-null element of {@code filters}
3858 * does not match a corresponding argument type of target as described above,
3859 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3860 * or if the resulting method handle's type would have
3861 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3862 */
3863 public static
3864 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3865 filterArgumentsCheckArity(target, pos, filters);
3866 MethodHandle adapter = target;
3867 // process filters in reverse order so that the invocation of
3868 // the resulting adapter will invoke the filters in left-to-right order
3869 for (int i = filters.length - 1; i >= 0; --i) {
3870 MethodHandle filter = filters[i];
3871 if (filter == null) continue; // ignore null elements of filters
3872 adapter = filterArgument(adapter, pos + i, filter);
3873 }
3874 return adapter;
3875 }
3876
3877 /*non-public*/ static
3878 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3879 filterArgumentChecks(target, pos, filter);
3880 MethodType targetType = target.type();
3881 MethodType filterType = filter.type();
3882 BoundMethodHandle result = target.rebind();
3883 Class<?> newParamType = filterType.parameterType(0);
3884 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3885 MethodType newType = targetType.changeParameterType(pos, newParamType);
3886 result = result.copyWithExtendL(newType, lform, filter);
3887 return result;
3888 }
3889
3890 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3891 MethodType targetType = target.type();
3892 int maxPos = targetType.parameterCount();
3893 if (pos + filters.length > maxPos)
3894 throw newIllegalArgumentException("too many filters");
3895 }
3896
3897 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3898 MethodType targetType = target.type();
3899 MethodType filterType = filter.type();
3900 if (filterType.parameterCount() != 1
3901 || filterType.returnType() != targetType.parameterType(pos))
3902 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3903 }
3904
3905 /**
3906 * Adapts a target method handle by pre-processing
3907 * a sub-sequence of its arguments with a filter (another method handle).
3908 * The pre-processed arguments are replaced by the result (if any) of the
3909 * filter function.
3910 * The target is then called on the modified (usually shortened) argument list.
3911 * <p>
3912 * If the filter returns a value, the target must accept that value as
3913 * its argument in position {@code pos}, preceded and/or followed by
3914 * any arguments not passed to the filter.
3915 * If the filter returns void, the target must accept all arguments
3916 * not passed to the filter.
3917 * No arguments are reordered, and a result returned from the filter
3918 * replaces (in order) the whole subsequence of arguments originally
3919 * passed to the adapter.
3920 * <p>
3921 * The argument types (if any) of the filter
3922 * replace zero or one argument types of the target, at position {@code pos},
3923 * in the resulting adapted method handle.
3924 * The return type of the filter (if any) must be identical to the
3925 * argument type of the target at position {@code pos}, and that target argument
3926 * is supplied by the return value of the filter.
3927 * <p>
3928 * In all cases, {@code pos} must be greater than or equal to zero, and
3929 * {@code pos} must also be less than or equal to the target's arity.
3930 * <p><b>Example:</b>
3931 * <blockquote><pre>{@code
3932 import static java.lang.invoke.MethodHandles.*;
3933 import static java.lang.invoke.MethodType.*;
3934 ...
3935 MethodHandle deepToString = publicLookup()
3936 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3937
3938 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3939 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3940
3941 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3942 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3943
3944 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3945 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3946 assertEquals("[top, [up, down], strange]",
3947 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3948
3949 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3950 assertEquals("[top, [up, down], [strange]]",
3951 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3952
3953 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3954 assertEquals("[top, [[up, down, strange], charm], bottom]",
3955 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3956 * }</pre></blockquote>
3957 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3958 * represents the return type of the {@code target} and resulting adapter.
3959 * {@code V}/{@code v} stand for the return type and value of the
3960 * {@code filter}, which are also found in the signature and arguments of
3961 * the {@code target}, respectively, unless {@code V} is {@code void}.
3962 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3963 * and values preceding and following the collection position, {@code pos},
3964 * in the {@code target}'s signature. They also turn up in the resulting
3965 * adapter's signature and arguments, where they surround
3966 * {@code B}/{@code b}, which represent the parameter types and arguments
3967 * to the {@code filter} (if any).
3968 * <blockquote><pre>{@code
3969 * T target(A...,V,C...);
3970 * V filter(B...);
3971 * T adapter(A... a,B... b,C... c) {
3972 * V v = filter(b...);
3973 * return target(a...,v,c...);
3974 * }
3975 * // and if the filter has no arguments:
3976 * T target2(A...,V,C...);
3977 * V filter2();
3978 * T adapter2(A... a,C... c) {
3979 * V v = filter2();
3980 * return target2(a...,v,c...);
3981 * }
3982 * // and if the filter has a void return:
3983 * T target3(A...,C...);
3984 * void filter3(B...);
3985 * T adapter3(A... a,B... b,C... c) {
3986 * filter3(b...);
3987 * return target3(a...,c...);
3988 * }
3989 * }</pre></blockquote>
3990 * <p>
3991 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3992 * one which first "folds" the affected arguments, and then drops them, in separate
3993 * steps as follows:
3994 * <blockquote><pre>{@code
3995 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3996 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3997 * }</pre></blockquote>
3998 * If the target method handle consumes no arguments besides than the result
3999 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4000 * is equivalent to {@code filterReturnValue(coll, mh)}.
4001 * If the filter method handle {@code coll} consumes one argument and produces
4002 * a non-void result, then {@code collectArguments(mh, N, coll)}
4003 * is equivalent to {@code filterArguments(mh, N, coll)}.
4004 * Other equivalences are possible but would require argument permutation.
4005 * <p>
4006 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4007 * variable-arity method handle}, even if the original target method handle was.
4008 *
4009 * @param target the method handle to invoke after filtering the subsequence of arguments
4010 * @param pos the position of the first adapter argument to pass to the filter,
4011 * and/or the target argument which receives the result of the filter
4012 * @param filter method handle to call on the subsequence of arguments
4013 * @return method handle which incorporates the specified argument subsequence filtering logic
4014 * @throws NullPointerException if either argument is null
4015 * @throws IllegalArgumentException if the return type of {@code filter}
4016 * is non-void and is not the same as the {@code pos} argument of the target,
4017 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4018 * or if the resulting method handle's type would have
4019 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4020 * @see MethodHandles#foldArguments
4021 * @see MethodHandles#filterArguments
4022 * @see MethodHandles#filterReturnValue
4023 */
4024 public static
4025 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4026 MethodType newType = collectArgumentsChecks(target, pos, filter);
4027 MethodType collectorType = filter.type();
4028 BoundMethodHandle result = target.rebind();
4029 LambdaForm lform;
4030 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4031 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4032 if (lform != null) {
4033 return result.copyWith(newType, lform);
4034 }
4035 }
4036 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4037 return result.copyWithExtendL(newType, lform, filter);
4038 }
4039
4040 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4041 MethodType targetType = target.type();
4042 MethodType filterType = filter.type();
4043 Class<?> rtype = filterType.returnType();
4044 List<Class<?>> filterArgs = filterType.parameterList();
4045 if (rtype == void.class) {
4046 return targetType.insertParameterTypes(pos, filterArgs);
4047 }
4048 if (rtype != targetType.parameterType(pos)) {
4049 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4050 }
4051 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4052 }
4053
4054 /**
4055 * Adapts a target method handle by post-processing
4056 * its return value (if any) with a filter (another method handle).
4057 * The result of the filter is returned from the adapter.
4058 * <p>
4059 * If the target returns a value, the filter must accept that value as
4060 * its only argument.
4061 * If the target returns void, the filter must accept no arguments.
4062 * <p>
4063 * The return type of the filter
4064 * replaces the return type of the target
4065 * in the resulting adapted method handle.
4066 * The argument type of the filter (if any) must be identical to the
4067 * return type of the target.
4068 * <p><b>Example:</b>
4069 * <blockquote><pre>{@code
4070 import static java.lang.invoke.MethodHandles.*;
4071 import static java.lang.invoke.MethodType.*;
4072 ...
4073 MethodHandle cat = lookup().findVirtual(String.class,
4074 "concat", methodType(String.class, String.class));
4075 MethodHandle length = lookup().findVirtual(String.class,
4076 "length", methodType(int.class));
4077 System.out.println((String) cat.invokeExact("x", "y")); // xy
4078 MethodHandle f0 = filterReturnValue(cat, length);
4079 System.out.println((int) f0.invokeExact("x", "y")); // 2
4080 * }</pre></blockquote>
4081 * <p>Here is pseudocode for the resulting adapter. In the code,
4082 * {@code T}/{@code t} represent the result type and value of the
4083 * {@code target}; {@code V}, the result type of the {@code filter}; and
4084 * {@code A}/{@code a}, the types and values of the parameters and arguments
4085 * of the {@code target} as well as the resulting adapter.
4086 * <blockquote><pre>{@code
4087 * T target(A...);
4088 * V filter(T);
4089 * V adapter(A... a) {
4090 * T t = target(a...);
4091 * return filter(t);
4092 * }
4093 * // and if the target has a void return:
4094 * void target2(A...);
4095 * V filter2();
4096 * V adapter2(A... a) {
4097 * target2(a...);
4098 * return filter2();
4099 * }
4100 * // and if the filter has a void return:
4101 * T target3(A...);
4102 * void filter3(V);
4103 * void adapter3(A... a) {
4104 * T t = target3(a...);
4105 * filter3(t);
4106 * }
4107 * }</pre></blockquote>
4108 * <p>
4109 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4110 * variable-arity method handle}, even if the original target method handle was.
4111 * @param target the method handle to invoke before filtering the return value
4112 * @param filter method handle to call on the return value
4113 * @return method handle which incorporates the specified return value filtering logic
4114 * @throws NullPointerException if either argument is null
4115 * @throws IllegalArgumentException if the argument list of {@code filter}
4116 * does not match the return type of target as described above
4117 */
4118 public static
4119 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4120 MethodType targetType = target.type();
4121 MethodType filterType = filter.type();
4122 filterReturnValueChecks(targetType, filterType);
4123 BoundMethodHandle result = target.rebind();
4124 BasicType rtype = BasicType.basicType(filterType.returnType());
4125 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4126 MethodType newType = targetType.changeReturnType(filterType.returnType());
4127 result = result.copyWithExtendL(newType, lform, filter);
4128 return result;
4129 }
4130
4131 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4132 Class<?> rtype = targetType.returnType();
4133 int filterValues = filterType.parameterCount();
4134 if (filterValues == 0
4135 ? (rtype != void.class)
4136 : (rtype != filterType.parameterType(0) || filterValues != 1))
4137 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4138 }
4139
4140 /**
4141 * Adapts a target method handle by pre-processing
4142 * some of its arguments, and then calling the target with
4143 * the result of the pre-processing, inserted into the original
4144 * sequence of arguments.
4145 * <p>
4146 * The pre-processing is performed by {@code combiner}, a second method handle.
4147 * Of the arguments passed to the adapter, the first {@code N} arguments
4148 * are copied to the combiner, which is then called.
4149 * (Here, {@code N} is defined as the parameter count of the combiner.)
4150 * After this, control passes to the target, with any result
4151 * from the combiner inserted before the original {@code N} incoming
4152 * arguments.
4153 * <p>
4154 * If the combiner returns a value, the first parameter type of the target
4155 * must be identical with the return type of the combiner, and the next
4156 * {@code N} parameter types of the target must exactly match the parameters
4157 * of the combiner.
4158 * <p>
4159 * If the combiner has a void return, no result will be inserted,
4160 * and the first {@code N} parameter types of the target
4161 * must exactly match the parameters of the combiner.
4162 * <p>
4163 * The resulting adapter is the same type as the target, except that the
4164 * first parameter type is dropped,
4165 * if it corresponds to the result of the combiner.
4166 * <p>
4167 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4168 * that either the combiner or the target does not wish to receive.
4169 * If some of the incoming arguments are destined only for the combiner,
4170 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4171 * arguments will not need to be live on the stack on entry to the
4172 * target.)
4173 * <p><b>Example:</b>
4174 * <blockquote><pre>{@code
4175 import static java.lang.invoke.MethodHandles.*;
4176 import static java.lang.invoke.MethodType.*;
4177 ...
4178 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4179 "println", methodType(void.class, String.class))
4180 .bindTo(System.out);
4181 MethodHandle cat = lookup().findVirtual(String.class,
4182 "concat", methodType(String.class, String.class));
4183 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4184 MethodHandle catTrace = foldArguments(cat, trace);
4185 // also prints "boo":
4186 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4187 * }</pre></blockquote>
4188 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4189 * represents the result type of the {@code target} and resulting adapter.
4190 * {@code V}/{@code v} represent the type and value of the parameter and argument
4191 * of {@code target} that precedes the folding position; {@code V} also is
4192 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4193 * types and values of the {@code N} parameters and arguments at the folding
4194 * position. {@code B}/{@code b} represent the types and values of the
4195 * {@code target} parameters and arguments that follow the folded parameters
4196 * and arguments.
4197 * <blockquote><pre>{@code
4198 * // there are N arguments in A...
4199 * T target(V, A[N]..., B...);
4200 * V combiner(A...);
4201 * T adapter(A... a, B... b) {
4202 * V v = combiner(a...);
4203 * return target(v, a..., b...);
4204 * }
4205 * // and if the combiner has a void return:
4206 * T target2(A[N]..., B...);
4207 * void combiner2(A...);
4208 * T adapter2(A... a, B... b) {
4209 * combiner2(a...);
4210 * return target2(a..., b...);
4211 * }
4212 * }</pre></blockquote>
4213 * <p>
4214 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4215 * variable-arity method handle}, even if the original target method handle was.
4216 * @param target the method handle to invoke after arguments are combined
4217 * @param combiner method handle to call initially on the incoming arguments
4218 * @return method handle which incorporates the specified argument folding logic
4219 * @throws NullPointerException if either argument is null
4220 * @throws IllegalArgumentException if {@code combiner}'s return type
4221 * is non-void and not the same as the first argument type of
4222 * the target, or if the initial {@code N} argument types
4223 * of the target
4224 * (skipping one matching the {@code combiner}'s return type)
4225 * are not identical with the argument types of {@code combiner}
4226 */
4227 public static
4228 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4229 return foldArguments(target, 0, combiner);
4230 }
4231
4232 /**
4233 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4234 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4235 * before the folded arguments.
4236 * <p>
4237 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4238 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4239 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4240 * 0.
4241 *
4242 * @apiNote Example:
4243 * <blockquote><pre>{@code
4244 import static java.lang.invoke.MethodHandles.*;
4245 import static java.lang.invoke.MethodType.*;
4246 ...
4247 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4248 "println", methodType(void.class, String.class))
4249 .bindTo(System.out);
4250 MethodHandle cat = lookup().findVirtual(String.class,
4251 "concat", methodType(String.class, String.class));
4252 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4253 MethodHandle catTrace = foldArguments(cat, 1, trace);
4254 // also prints "jum":
4255 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4256 * }</pre></blockquote>
4257 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4258 * represents the result type of the {@code target} and resulting adapter.
4259 * {@code V}/{@code v} represent the type and value of the parameter and argument
4260 * of {@code target} that precedes the folding position; {@code V} also is
4261 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4262 * types and values of the {@code N} parameters and arguments at the folding
4263 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4264 * and values of the {@code target} parameters and arguments that precede and
4265 * follow the folded parameters and arguments starting at {@code pos},
4266 * respectively.
4267 * <blockquote><pre>{@code
4268 * // there are N arguments in A...
4269 * T target(Z..., V, A[N]..., B...);
4270 * V combiner(A...);
4271 * T adapter(Z... z, A... a, B... b) {
4272 * V v = combiner(a...);
4273 * return target(z..., v, a..., b...);
4274 * }
4275 * // and if the combiner has a void return:
4276 * T target2(Z..., A[N]..., B...);
4277 * void combiner2(A...);
4278 * T adapter2(Z... z, A... a, B... b) {
4279 * combiner2(a...);
4280 * return target2(z..., a..., b...);
4281 * }
4282 * }</pre></blockquote>
4283 * <p>
4284 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4285 * variable-arity method handle}, even if the original target method handle was.
4286 *
4287 * @param target the method handle to invoke after arguments are combined
4288 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4289 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4290 * @param combiner method handle to call initially on the incoming arguments
4291 * @return method handle which incorporates the specified argument folding logic
4292 * @throws NullPointerException if either argument is null
4293 * @throws IllegalArgumentException if either of the following two conditions holds:
4294 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4295 * {@code pos} of the target signature;
4296 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4297 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4298 *
4299 * @see #foldArguments(MethodHandle, MethodHandle)
4300 * @since 9
4301 */
4302 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4303 MethodType targetType = target.type();
4304 MethodType combinerType = combiner.type();
4305 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4306 BoundMethodHandle result = target.rebind();
4307 boolean dropResult = rtype == void.class;
4308 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4309 MethodType newType = targetType;
4310 if (!dropResult) {
4311 newType = newType.dropParameterTypes(pos, pos + 1);
4312 }
4313 result = result.copyWithExtendL(newType, lform, combiner);
4314 return result;
4315 }
4316
4317 /**
4318 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4319 * added capability of selecting the arguments from the targets parameters
4320 * to call the combiner with. This allows us to avoid some simple cases of
4321 * permutations and padding the combiner with dropArguments to select the
4322 * right argument, which may ultimately produce fewer intermediaries.
4323 */
4324 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4325 MethodType targetType = target.type();
4326 MethodType combinerType = combiner.type();
4327 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4328 BoundMethodHandle result = target.rebind();
4329 boolean dropResult = rtype == void.class;
4330 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4331 MethodType newType = targetType;
4332 if (!dropResult) {
4333 newType = newType.dropParameterTypes(pos, pos + 1);
4334 }
4335 result = result.copyWithExtendL(newType, lform, combiner);
4336 return result;
4337 }
4338
4339 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4340 int foldArgs = combinerType.parameterCount();
4341 Class<?> rtype = combinerType.returnType();
4342 int foldVals = rtype == void.class ? 0 : 1;
4343 int afterInsertPos = foldPos + foldVals;
4344 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4345 if (ok) {
4346 for (int i = 0; i < foldArgs; i++) {
4347 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4348 ok = false;
4349 break;
4350 }
4351 }
4352 }
4353 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4354 ok = false;
4355 if (!ok)
4356 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4357 return rtype;
4358 }
4359
4360 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4361 int foldArgs = combinerType.parameterCount();
4362 if (argPos.length != foldArgs) {
4363 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4364 }
4365 Class<?> rtype = combinerType.returnType();
4366 int foldVals = rtype == void.class ? 0 : 1;
4367 boolean ok = true;
4368 for (int i = 0; i < foldArgs; i++) {
4369 int arg = argPos[i];
4370 if (arg < 0 || arg > targetType.parameterCount()) {
4371 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4372 }
4373 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4374 throw newIllegalArgumentException("target argument type at position " + arg
4375 + " must match combiner argument type at index " + i + ": " + targetType
4376 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4377 }
4378 }
4379 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4380 ok = false;
4381 }
4382 if (!ok)
4383 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4384 return rtype;
4385 }
4386
4387 /**
4388 * Makes a method handle which adapts a target method handle,
4389 * by guarding it with a test, a boolean-valued method handle.
4390 * If the guard fails, a fallback handle is called instead.
4391 * All three method handles must have the same corresponding
4392 * argument and return types, except that the return type
4393 * of the test must be boolean, and the test is allowed
4394 * to have fewer arguments than the other two method handles.
4395 * <p>
4396 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4397 * represents the uniform result type of the three involved handles;
4398 * {@code A}/{@code a}, the types and values of the {@code target}
4399 * parameters and arguments that are consumed by the {@code test}; and
4400 * {@code B}/{@code b}, those types and values of the {@code target}
4401 * parameters and arguments that are not consumed by the {@code test}.
4402 * <blockquote><pre>{@code
4403 * boolean test(A...);
4404 * T target(A...,B...);
4405 * T fallback(A...,B...);
4406 * T adapter(A... a,B... b) {
4407 * if (test(a...))
4408 * return target(a..., b...);
4409 * else
4410 * return fallback(a..., b...);
4411 * }
4412 * }</pre></blockquote>
4413 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4414 * be modified by execution of the test, and so are passed unchanged
4415 * from the caller to the target or fallback as appropriate.
4416 * @param test method handle used for test, must return boolean
4417 * @param target method handle to call if test passes
4418 * @param fallback method handle to call if test fails
4419 * @return method handle which incorporates the specified if/then/else logic
4420 * @throws NullPointerException if any argument is null
4421 * @throws IllegalArgumentException if {@code test} does not return boolean,
4422 * or if all three method types do not match (with the return
4423 * type of {@code test} changed to match that of the target).
4424 */
4425 public static
4426 MethodHandle guardWithTest(MethodHandle test,
4427 MethodHandle target,
4428 MethodHandle fallback) {
4429 MethodType gtype = test.type();
4430 MethodType ttype = target.type();
4431 MethodType ftype = fallback.type();
4432 if (!ttype.equals(ftype))
4433 throw misMatchedTypes("target and fallback types", ttype, ftype);
4434 if (gtype.returnType() != boolean.class)
4435 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4436 List<Class<?>> targs = ttype.parameterList();
4437 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4438 if (test == null) {
4439 throw misMatchedTypes("target and test types", ttype, gtype);
4440 }
4441 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4442 }
4443
4444 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4445 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4446 }
4447
4448 /**
4449 * Makes a method handle which adapts a target method handle,
4450 * by running it inside an exception handler.
4451 * If the target returns normally, the adapter returns that value.
4452 * If an exception matching the specified type is thrown, the fallback
4453 * handle is called instead on the exception, plus the original arguments.
4454 * <p>
4455 * The target and handler must have the same corresponding
4456 * argument and return types, except that handler may omit trailing arguments
4457 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4458 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4459 * <p>
4460 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4461 * represents the return type of the {@code target} and {@code handler},
4462 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4463 * the types and values of arguments to the resulting handle consumed by
4464 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4465 * resulting handle discarded by {@code handler}.
4466 * <blockquote><pre>{@code
4467 * T target(A..., B...);
4468 * T handler(ExType, A...);
4469 * T adapter(A... a, B... b) {
4470 * try {
4471 * return target(a..., b...);
4472 * } catch (ExType ex) {
4473 * return handler(ex, a...);
4474 * }
4475 * }
4476 * }</pre></blockquote>
4477 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4478 * be modified by execution of the target, and so are passed unchanged
4479 * from the caller to the handler, if the handler is invoked.
4480 * <p>
4481 * The target and handler must return the same type, even if the handler
4482 * always throws. (This might happen, for instance, because the handler
4483 * is simulating a {@code finally} clause).
4484 * To create such a throwing handler, compose the handler creation logic
4485 * with {@link #throwException throwException},
4486 * in order to create a method handle of the correct return type.
4487 * @param target method handle to call
4488 * @param exType the type of exception which the handler will catch
4489 * @param handler method handle to call if a matching exception is thrown
4490 * @return method handle which incorporates the specified try/catch logic
4491 * @throws NullPointerException if any argument is null
4492 * @throws IllegalArgumentException if {@code handler} does not accept
4493 * the given exception type, or if the method handle types do
4494 * not match in their return types and their
4495 * corresponding parameters
4496 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4497 */
4498 public static
4499 MethodHandle catchException(MethodHandle target,
4500 Class<? extends Throwable> exType,
4501 MethodHandle handler) {
4502 MethodType ttype = target.type();
4503 MethodType htype = handler.type();
4504 if (!Throwable.class.isAssignableFrom(exType))
4505 throw new ClassCastException(exType.getName());
4506 if (htype.parameterCount() < 1 ||
4507 !htype.parameterType(0).isAssignableFrom(exType))
4508 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4509 if (htype.returnType() != ttype.returnType())
4510 throw misMatchedTypes("target and handler return types", ttype, htype);
4511 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4512 if (handler == null) {
4513 throw misMatchedTypes("target and handler types", ttype, htype);
4514 }
4515 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4516 }
4517
4518 /**
4519 * Produces a method handle which will throw exceptions of the given {@code exType}.
4520 * The method handle will accept a single argument of {@code exType},
4521 * and immediately throw it as an exception.
4522 * The method type will nominally specify a return of {@code returnType}.
4523 * The return type may be anything convenient: It doesn't matter to the
4524 * method handle's behavior, since it will never return normally.
4525 * @param returnType the return type of the desired method handle
4526 * @param exType the parameter type of the desired method handle
4527 * @return method handle which can throw the given exceptions
4528 * @throws NullPointerException if either argument is null
4529 */
4530 public static
4531 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4532 if (!Throwable.class.isAssignableFrom(exType))
4533 throw new ClassCastException(exType.getName());
4534 return MethodHandleImpl.throwException(methodType(returnType, exType));
4535 }
4536
4537 /**
4538 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4539 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4540 * delivers the loop's result, which is the return value of the resulting handle.
4541 * <p>
4542 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4543 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4544 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4545 * terms of method handles, each clause will specify up to four independent actions:<ul>
4546 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4547 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4548 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4549 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4550 * </ul>
4551 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4552 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4553 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4554 * <p>
4555 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4556 * this case. See below for a detailed description.
4557 * <p>
4558 * <em>Parameters optional everywhere:</em>
4559 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4560 * As an exception, the init functions cannot take any {@code v} parameters,
4561 * because those values are not yet computed when the init functions are executed.
4562 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4563 * In fact, any clause function may take no arguments at all.
4564 * <p>
4565 * <em>Loop parameters:</em>
4566 * A clause function may take all the iteration variable values it is entitled to, in which case
4567 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4568 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4569 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4570 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4571 * init function is automatically a loop parameter {@code a}.)
4572 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4573 * These loop parameters act as loop-invariant values visible across the whole loop.
4574 * <p>
4575 * <em>Parameters visible everywhere:</em>
4576 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4577 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4578 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4579 * Most clause functions will not need all of this information, but they will be formally connected to it
4580 * as if by {@link #dropArguments}.
4581 * <a id="astar"></a>
4582 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4583 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4584 * In that notation, the general form of an init function parameter list
4585 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4586 * <p>
4587 * <em>Checking clause structure:</em>
4588 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4589 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4590 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4591 * met by the inputs to the loop combinator.
4592 * <p>
4593 * <em>Effectively identical sequences:</em>
4594 * <a id="effid"></a>
4595 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4596 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4597 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4598 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4599 * that longest list.
4600 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4601 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4602 * <p>
4603 * <em>Step 0: Determine clause structure.</em><ol type="a">
4604 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4605 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4606 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4607 * four. Padding takes place by appending elements to the array.
4608 * <li>Clauses with all {@code null}s are disregarded.
4609 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4610 * </ol>
4611 * <p>
4612 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4613 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4614 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4615 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4616 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4617 * iteration variable type.
4618 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4619 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4620 * </ol>
4621 * <p>
4622 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4623 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4624 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4625 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4626 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4627 * (These types will checked in step 2, along with all the clause function types.)
4628 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4629 * <li>All of the collected parameter lists must be effectively identical.
4630 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4631 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4632 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4633 * the "internal parameter list".
4634 * </ul>
4635 * <p>
4636 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4637 * <li>Examine fini function return types, disregarding omitted fini functions.
4638 * <li>If there are no fini functions, the loop return type is {@code void}.
4639 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4640 * type.
4641 * </ol>
4642 * <p>
4643 * <em>Step 1D: Check other types.</em><ol type="a">
4644 * <li>There must be at least one non-omitted pred function.
4645 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4646 * </ol>
4647 * <p>
4648 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4649 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4650 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4651 * (Note that their parameter lists are already effectively identical to this list.)
4652 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4653 * effectively identical to the internal parameter list {@code (V... A...)}.
4654 * </ol>
4655 * <p>
4656 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4657 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4658 * type.
4659 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4660 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4661 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4662 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4663 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4664 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4665 * loop return type.
4666 * </ol>
4667 * <p>
4668 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4669 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4670 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4671 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4672 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4673 * pad out the end of the list.
4674 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
4675 * </ol>
4676 * <p>
4677 * <em>Final observations.</em><ol type="a">
4678 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4679 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4680 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4681 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4682 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4683 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4684 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4685 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4686 * </ol>
4687 * <p>
4688 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4689 * <ul>
4690 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4691 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4692 * (Only one {@code Pn} has to be non-{@code null}.)
4693 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4694 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4695 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4696 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4697 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4698 * the resulting loop handle's parameter types {@code (A...)}.
4699 * </ul>
4700 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4701 * which is natural if most of the loop computation happens in the steps. For some loops,
4702 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4703 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4704 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4705 * where the init functions will need the extra parameters. For such reasons, the rules for
4706 * determining these parameters are as symmetric as possible, across all clause parts.
4707 * In general, the loop parameters function as common invariant values across the whole
4708 * loop, while the iteration variables function as common variant values, or (if there is
4709 * no step function) as internal loop invariant temporaries.
4710 * <p>
4711 * <em>Loop execution.</em><ol type="a">
4712 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4713 * every clause function. These locals are loop invariant.
4714 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4715 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4716 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4717 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4718 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4719 * (in argument order).
4720 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4721 * returns {@code false}.
4722 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4723 * sequence {@code (v...)} of loop variables.
4724 * The updated value is immediately visible to all subsequent function calls.
4725 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4726 * (of type {@code R}) is returned from the loop as a whole.
4727 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4728 * except by throwing an exception.
4729 * </ol>
4730 * <p>
4731 * <em>Usage tips.</em>
4732 * <ul>
4733 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4734 * sometimes a step function only needs to observe the current value of its own variable.
4735 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4736 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4737 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4738 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4739 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4740 * <li>If some of the clause functions are virtual methods on an instance, the instance
4741 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4742 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4743 * will be the first iteration variable value, and it will be easy to use virtual
4744 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4745 * </ul>
4746 * <p>
4747 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4748 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4749 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4750 * <blockquote><pre>{@code
4751 * V... init...(A...);
4752 * boolean pred...(V..., A...);
4753 * V... step...(V..., A...);
4754 * R fini...(V..., A...);
4755 * R loop(A... a) {
4756 * V... v... = init...(a...);
4757 * for (;;) {
4758 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4759 * v = s(v..., a...);
4760 * if (!p(v..., a...)) {
4761 * return f(v..., a...);
4762 * }
4763 * }
4764 * }
4765 * }
4766 * }</pre></blockquote>
4767 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4768 * to their full length, even though individual clause functions may neglect to take them all.
4769 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
4770 *
4771 * @apiNote Example:
4772 * <blockquote><pre>{@code
4773 * // iterative implementation of the factorial function as a loop handle
4774 * static int one(int k) { return 1; }
4775 * static int inc(int i, int acc, int k) { return i + 1; }
4776 * static int mult(int i, int acc, int k) { return i * acc; }
4777 * static boolean pred(int i, int acc, int k) { return i < k; }
4778 * static int fin(int i, int acc, int k) { return acc; }
4779 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4780 * // null initializer for counter, should initialize to 0
4781 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4782 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4783 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4784 * assertEquals(120, loop.invoke(5));
4785 * }</pre></blockquote>
4786 * The same example, dropping arguments and using combinators:
4787 * <blockquote><pre>{@code
4788 * // simplified implementation of the factorial function as a loop handle
4789 * static int inc(int i) { return i + 1; } // drop acc, k
4790 * static int mult(int i, int acc) { return i * acc; } //drop k
4791 * static boolean cmp(int i, int k) { return i < k; }
4792 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4793 * // null initializer for counter, should initialize to 0
4794 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4795 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4796 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4797 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4798 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4799 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4800 * assertEquals(720, loop.invoke(6));
4801 * }</pre></blockquote>
4802 * A similar example, using a helper object to hold a loop parameter:
4803 * <blockquote><pre>{@code
4804 * // instance-based implementation of the factorial function as a loop handle
4805 * static class FacLoop {
4806 * final int k;
4807 * FacLoop(int k) { this.k = k; }
4808 * int inc(int i) { return i + 1; }
4809 * int mult(int i, int acc) { return i * acc; }
4810 * boolean pred(int i) { return i < k; }
4811 * int fin(int i, int acc) { return acc; }
4812 * }
4813 * // assume MH_FacLoop is a handle to the constructor
4814 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4815 * // null initializer for counter, should initialize to 0
4816 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4817 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4818 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4819 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4820 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4821 * assertEquals(5040, loop.invoke(7));
4822 * }</pre></blockquote>
4823 *
4824 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4825 *
4826 * @return a method handle embodying the looping behavior as defined by the arguments.
4827 *
4828 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4829 *
4830 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4831 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4832 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4833 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4834 * @since 9
4835 */
4836 public static MethodHandle loop(MethodHandle[]... clauses) {
4837 // Step 0: determine clause structure.
4838 loopChecks0(clauses);
4839
4840 List<MethodHandle> init = new ArrayList<>();
4841 List<MethodHandle> step = new ArrayList<>();
4842 List<MethodHandle> pred = new ArrayList<>();
4843 List<MethodHandle> fini = new ArrayList<>();
4844
4845 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4846 init.add(clause[0]); // all clauses have at least length 1
4847 step.add(clause.length <= 1 ? null : clause[1]);
4848 pred.add(clause.length <= 2 ? null : clause[2]);
4849 fini.add(clause.length <= 3 ? null : clause[3]);
4850 });
4851
4852 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4853 final int nclauses = init.size();
4854
4855 // Step 1A: determine iteration variables (V...).
4856 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4857 for (int i = 0; i < nclauses; ++i) {
4858 MethodHandle in = init.get(i);
4859 MethodHandle st = step.get(i);
4860 if (in == null && st == null) {
4861 iterationVariableTypes.add(void.class);
4862 } else if (in != null && st != null) {
4863 loopChecks1a(i, in, st);
4864 iterationVariableTypes.add(in.type().returnType());
4865 } else {
4866 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4867 }
4868 }
4869 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4870 collect(Collectors.toList());
4871
4872 // Step 1B: determine loop parameters (A...).
4873 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4874 loopChecks1b(init, commonSuffix);
4875
4876 // Step 1C: determine loop return type.
4877 // Step 1D: check other types.
4878 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4879 map(MethodType::returnType).findFirst().orElse(void.class);
4880 loopChecks1cd(pred, fini, loopReturnType);
4881
4882 // Step 2: determine parameter lists.
4883 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4884 commonParameterSequence.addAll(commonSuffix);
4885 loopChecks2(step, pred, fini, commonParameterSequence);
4886
4887 // Step 3: fill in omitted functions.
4888 for (int i = 0; i < nclauses; ++i) {
4889 Class<?> t = iterationVariableTypes.get(i);
4890 if (init.get(i) == null) {
4891 init.set(i, empty(methodType(t, commonSuffix)));
4892 }
4893 if (step.get(i) == null) {
4894 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4895 }
4896 if (pred.get(i) == null) {
4897 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4898 }
4899 if (fini.get(i) == null) {
4900 fini.set(i, empty(methodType(t, commonParameterSequence)));
4901 }
4902 }
4903
4904 // Step 4: fill in missing parameter types.
4905 // Also convert all handles to fixed-arity handles.
4906 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4907 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4908 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4909 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4910
4911 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4912 allMatch(pl -> pl.equals(commonSuffix));
4913 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4914 allMatch(pl -> pl.equals(commonParameterSequence));
4915
4916 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4917 }
4918
4919 private static void loopChecks0(MethodHandle[][] clauses) {
4920 if (clauses == null || clauses.length == 0) {
4921 throw newIllegalArgumentException("null or no clauses passed");
4922 }
4923 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4924 throw newIllegalArgumentException("null clauses are not allowed");
4925 }
4926 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4927 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4928 }
4929 }
4930
4931 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4932 if (in.type().returnType() != st.type().returnType()) {
4933 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4934 st.type().returnType());
4935 }
4936 }
4937
4938 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4939 final List<Class<?>> empty = List.of();
4940 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4941 // take only those that can contribute to a common suffix because they are longer than the prefix
4942 map(MethodHandle::type).
4943 filter(t -> t.parameterCount() > skipSize).
4944 map(MethodType::parameterList).
4945 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4946 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4947 }
4948
4949 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4950 final List<Class<?>> empty = List.of();
4951 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4952 }
4953
4954 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4955 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4956 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4957 return longestParameterList(Arrays.asList(longest1, longest2));
4958 }
4959
4960 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4961 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4962 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4963 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4964 " (common suffix: " + commonSuffix + ")");
4965 }
4966 }
4967
4968 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4969 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4970 anyMatch(t -> t != loopReturnType)) {
4971 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4972 loopReturnType + ")");
4973 }
4974
4975 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4976 throw newIllegalArgumentException("no predicate found", pred);
4977 }
4978 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4979 anyMatch(t -> t != boolean.class)) {
4980 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4981 }
4982 }
4983
4984 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4985 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4986 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4987 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4988 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4989 }
4990 }
4991
4992 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4993 return hs.stream().map(h -> {
4994 int pc = h.type().parameterCount();
4995 int tpsize = targetParams.size();
4996 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4997 }).collect(Collectors.toList());
4998 }
4999
5000 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5001 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5002 }
5003
5004 /**
5005 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5006 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5007 * <p>
5008 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5009 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5010 * evaluates to {@code true}).
5011 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5012 * <p>
5013 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5014 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5015 * and updated with the value returned from its invocation. The result of loop execution will be
5016 * the final value of the additional loop-local variable (if present).
5017 * <p>
5018 * The following rules hold for these argument handles:<ul>
5019 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5020 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5021 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5022 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5023 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5024 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5025 * It will constrain the parameter lists of the other loop parts.
5026 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5027 * list {@code (A...)} is called the <em>external parameter list</em>.
5028 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5029 * additional state variable of the loop.
5030 * The body must both accept and return a value of this type {@code V}.
5031 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5032 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5033 * <a href="MethodHandles.html#effid">effectively identical</a>
5034 * to the external parameter list {@code (A...)}.
5035 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5036 * {@linkplain #empty default value}.
5037 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5038 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5039 * effectively identical to the internal parameter list.
5040 * </ul>
5041 * <p>
5042 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5043 * <li>The loop handle's result type is the result type {@code V} of the body.
5044 * <li>The loop handle's parameter types are the types {@code (A...)},
5045 * from the external parameter list.
5046 * </ul>
5047 * <p>
5048 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5049 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5050 * passed to the loop.
5051 * <blockquote><pre>{@code
5052 * V init(A...);
5053 * boolean pred(V, A...);
5054 * V body(V, A...);
5055 * V whileLoop(A... a...) {
5056 * V v = init(a...);
5057 * while (pred(v, a...)) {
5058 * v = body(v, a...);
5059 * }
5060 * return v;
5061 * }
5062 * }</pre></blockquote>
5063 *
5064 * @apiNote Example:
5065 * <blockquote><pre>{@code
5066 * // implement the zip function for lists as a loop handle
5067 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5068 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5069 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5070 * zip.add(a.next());
5071 * zip.add(b.next());
5072 * return zip;
5073 * }
5074 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5075 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5076 * List<String> a = Arrays.asList("a", "b", "c", "d");
5077 * List<String> b = Arrays.asList("e", "f", "g", "h");
5078 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5079 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5080 * }</pre></blockquote>
5081 *
5082 *
5083 * @apiNote The implementation of this method can be expressed as follows:
5084 * <blockquote><pre>{@code
5085 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5086 * MethodHandle fini = (body.type().returnType() == void.class
5087 * ? null : identity(body.type().returnType()));
5088 * MethodHandle[]
5089 * checkExit = { null, null, pred, fini },
5090 * varBody = { init, body };
5091 * return loop(checkExit, varBody);
5092 * }
5093 * }</pre></blockquote>
5094 *
5095 * @param init optional initializer, providing the initial value of the loop variable.
5096 * May be {@code null}, implying a default initial value. See above for other constraints.
5097 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5098 * above for other constraints.
5099 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5100 * See above for other constraints.
5101 *
5102 * @return a method handle implementing the {@code while} loop as described by the arguments.
5103 * @throws IllegalArgumentException if the rules for the arguments are violated.
5104 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5105 *
5106 * @see #loop(MethodHandle[][])
5107 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5108 * @since 9
5109 */
5110 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5111 whileLoopChecks(init, pred, body);
5112 MethodHandle fini = identityOrVoid(body.type().returnType());
5113 MethodHandle[] checkExit = { null, null, pred, fini };
5114 MethodHandle[] varBody = { init, body };
5115 return loop(checkExit, varBody);
5116 }
5117
5118 /**
5119 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5120 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5121 * <p>
5122 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5123 * method will, in each iteration, first execute its body and then evaluate the predicate.
5124 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5125 * <p>
5126 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5127 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5128 * and updated with the value returned from its invocation. The result of loop execution will be
5129 * the final value of the additional loop-local variable (if present).
5130 * <p>
5131 * The following rules hold for these argument handles:<ul>
5132 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5133 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5134 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5135 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5136 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5137 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5138 * It will constrain the parameter lists of the other loop parts.
5139 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5140 * list {@code (A...)} is called the <em>external parameter list</em>.
5141 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5142 * additional state variable of the loop.
5143 * The body must both accept and return a value of this type {@code V}.
5144 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5145 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5146 * <a href="MethodHandles.html#effid">effectively identical</a>
5147 * to the external parameter list {@code (A...)}.
5148 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5149 * {@linkplain #empty default value}.
5150 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5151 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5152 * effectively identical to the internal parameter list.
5153 * </ul>
5154 * <p>
5155 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5156 * <li>The loop handle's result type is the result type {@code V} of the body.
5157 * <li>The loop handle's parameter types are the types {@code (A...)},
5158 * from the external parameter list.
5159 * </ul>
5160 * <p>
5161 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5162 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5163 * passed to the loop.
5164 * <blockquote><pre>{@code
5165 * V init(A...);
5166 * boolean pred(V, A...);
5167 * V body(V, A...);
5168 * V doWhileLoop(A... a...) {
5169 * V v = init(a...);
5170 * do {
5171 * v = body(v, a...);
5172 * } while (pred(v, a...));
5173 * return v;
5174 * }
5175 * }</pre></blockquote>
5176 *
5177 * @apiNote Example:
5178 * <blockquote><pre>{@code
5179 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5180 * static int zero(int limit) { return 0; }
5181 * static int step(int i, int limit) { return i + 1; }
5182 * static boolean pred(int i, int limit) { return i < limit; }
5183 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5184 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5185 * assertEquals(23, loop.invoke(23));
5186 * }</pre></blockquote>
5187 *
5188 *
5189 * @apiNote The implementation of this method can be expressed as follows:
5190 * <blockquote><pre>{@code
5191 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5192 * MethodHandle fini = (body.type().returnType() == void.class
5193 * ? null : identity(body.type().returnType()));
5194 * MethodHandle[] clause = { init, body, pred, fini };
5195 * return loop(clause);
5196 * }
5197 * }</pre></blockquote>
5198 *
5199 * @param init optional initializer, providing the initial value of the loop variable.
5200 * May be {@code null}, implying a default initial value. See above for other constraints.
5201 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5202 * See above for other constraints.
5203 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5204 * above for other constraints.
5205 *
5206 * @return a method handle implementing the {@code while} loop as described by the arguments.
5207 * @throws IllegalArgumentException if the rules for the arguments are violated.
5208 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5209 *
5210 * @see #loop(MethodHandle[][])
5211 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5212 * @since 9
5213 */
5214 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5215 whileLoopChecks(init, pred, body);
5216 MethodHandle fini = identityOrVoid(body.type().returnType());
5217 MethodHandle[] clause = {init, body, pred, fini };
5218 return loop(clause);
5219 }
5220
5221 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5222 Objects.requireNonNull(pred);
5223 Objects.requireNonNull(body);
5224 MethodType bodyType = body.type();
5225 Class<?> returnType = bodyType.returnType();
5226 List<Class<?>> innerList = bodyType.parameterList();
5227 List<Class<?>> outerList = innerList;
5228 if (returnType == void.class) {
5229 // OK
5230 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5231 // leading V argument missing => error
5232 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5233 throw misMatchedTypes("body function", bodyType, expected);
5234 } else {
5235 outerList = innerList.subList(1, innerList.size());
5236 }
5237 MethodType predType = pred.type();
5238 if (predType.returnType() != boolean.class ||
5239 !predType.effectivelyIdenticalParameters(0, innerList)) {
5240 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5241 }
5242 if (init != null) {
5243 MethodType initType = init.type();
5244 if (initType.returnType() != returnType ||
5245 !initType.effectivelyIdenticalParameters(0, outerList)) {
5246 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5247 }
5248 }
5249 }
5250
5251 /**
5252 * Constructs a loop that runs a given number of iterations.
5253 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5254 * <p>
5255 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5256 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5257 * It will be initialized to 0 and incremented by 1 in each iteration.
5258 * <p>
5259 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5260 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5261 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5262 * <p>
5263 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5264 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5265 * iteration variable.
5266 * The result of the loop handle execution will be the final {@code V} value of that variable
5267 * (or {@code void} if there is no {@code V} variable).
5268 * <p>
5269 * The following rules hold for the argument handles:<ul>
5270 * <li>The {@code iterations} handle must not be {@code null}, and must return
5271 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5272 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5273 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5274 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5275 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5276 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5277 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5278 * of types called the <em>internal parameter list</em>.
5279 * It will constrain the parameter lists of the other loop parts.
5280 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5281 * with no additional {@code A} types, then the internal parameter list is extended by
5282 * the argument types {@code A...} of the {@code iterations} handle.
5283 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5284 * list {@code (A...)} is called the <em>external parameter list</em>.
5285 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5286 * additional state variable of the loop.
5287 * The body must both accept a leading parameter and return a value of this type {@code V}.
5288 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5289 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5290 * <a href="MethodHandles.html#effid">effectively identical</a>
5291 * to the external parameter list {@code (A...)}.
5292 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5293 * {@linkplain #empty default value}.
5294 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5295 * effectively identical to the external parameter list {@code (A...)}.
5296 * </ul>
5297 * <p>
5298 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5299 * <li>The loop handle's result type is the result type {@code V} of the body.
5300 * <li>The loop handle's parameter types are the types {@code (A...)},
5301 * from the external parameter list.
5302 * </ul>
5303 * <p>
5304 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5305 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5306 * arguments passed to the loop.
5307 * <blockquote><pre>{@code
5308 * int iterations(A...);
5309 * V init(A...);
5310 * V body(V, int, A...);
5311 * V countedLoop(A... a...) {
5312 * int end = iterations(a...);
5313 * V v = init(a...);
5314 * for (int i = 0; i < end; ++i) {
5315 * v = body(v, i, a...);
5316 * }
5317 * return v;
5318 * }
5319 * }</pre></blockquote>
5320 *
5321 * @apiNote Example with a fully conformant body method:
5322 * <blockquote><pre>{@code
5323 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5324 * // => a variation on a well known theme
5325 * static String step(String v, int counter, String init) { return "na " + v; }
5326 * // assume MH_step is a handle to the method above
5327 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5328 * MethodHandle start = MethodHandles.identity(String.class);
5329 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5330 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5331 * }</pre></blockquote>
5332 *
5333 * @apiNote Example with the simplest possible body method type,
5334 * and passing the number of iterations to the loop invocation:
5335 * <blockquote><pre>{@code
5336 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5337 * // => a variation on a well known theme
5338 * static String step(String v, int counter ) { return "na " + v; }
5339 * // assume MH_step is a handle to the method above
5340 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5341 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5342 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5343 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5344 * }</pre></blockquote>
5345 *
5346 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5347 * as loop parameters:
5348 * <blockquote><pre>{@code
5349 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5350 * // => a variation on a well known theme
5351 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5352 * // assume MH_step is a handle to the method above
5353 * MethodHandle count = MethodHandles.identity(int.class);
5354 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5355 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5356 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5357 * }</pre></blockquote>
5358 *
5359 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5360 * to enforce a loop type:
5361 * <blockquote><pre>{@code
5362 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5363 * // => a variation on a well known theme
5364 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5365 * // assume MH_step is a handle to the method above
5366 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5367 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5368 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5369 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5370 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5371 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5372 * }</pre></blockquote>
5373 *
5374 * @apiNote The implementation of this method can be expressed as follows:
5375 * <blockquote><pre>{@code
5376 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5377 * return countedLoop(empty(iterations.type()), iterations, init, body);
5378 * }
5379 * }</pre></blockquote>
5380 *
5381 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5382 * result type must be {@code int}. See above for other constraints.
5383 * @param init optional initializer, providing the initial value of the loop variable.
5384 * May be {@code null}, implying a default initial value. See above for other constraints.
5385 * @param body body of the loop, which may not be {@code null}.
5386 * It controls the loop parameters and result type in the standard case (see above for details).
5387 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5388 * and may accept any number of additional types.
5389 * See above for other constraints.
5390 *
5391 * @return a method handle representing the loop.
5392 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5393 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5394 *
5395 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5396 * @since 9
5397 */
5398 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5399 return countedLoop(empty(iterations.type()), iterations, init, body);
5400 }
5401
5402 /**
5403 * Constructs a loop that counts over a range of numbers.
5404 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5405 * <p>
5406 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5407 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5408 * values of the loop counter.
5409 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5410 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5411 * <p>
5412 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5413 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5414 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5415 * <p>
5416 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5417 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5418 * iteration variable.
5419 * The result of the loop handle execution will be the final {@code V} value of that variable
5420 * (or {@code void} if there is no {@code V} variable).
5421 * <p>
5422 * The following rules hold for the argument handles:<ul>
5423 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5424 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5425 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5426 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5427 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5428 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5429 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5430 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5431 * of types called the <em>internal parameter list</em>.
5432 * It will constrain the parameter lists of the other loop parts.
5433 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5434 * with no additional {@code A} types, then the internal parameter list is extended by
5435 * the argument types {@code A...} of the {@code end} handle.
5436 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5437 * list {@code (A...)} is called the <em>external parameter list</em>.
5438 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5439 * additional state variable of the loop.
5440 * The body must both accept a leading parameter and return a value of this type {@code V}.
5441 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5442 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5443 * <a href="MethodHandles.html#effid">effectively identical</a>
5444 * to the external parameter list {@code (A...)}.
5445 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5446 * {@linkplain #empty default value}.
5447 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5448 * effectively identical to the external parameter list {@code (A...)}.
5449 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5450 * to the external parameter list.
5451 * </ul>
5452 * <p>
5453 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5454 * <li>The loop handle's result type is the result type {@code V} of the body.
5455 * <li>The loop handle's parameter types are the types {@code (A...)},
5456 * from the external parameter list.
5457 * </ul>
5458 * <p>
5459 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5460 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5461 * arguments passed to the loop.
5462 * <blockquote><pre>{@code
5463 * int start(A...);
5464 * int end(A...);
5465 * V init(A...);
5466 * V body(V, int, A...);
5467 * V countedLoop(A... a...) {
5468 * int e = end(a...);
5469 * int s = start(a...);
5470 * V v = init(a...);
5471 * for (int i = s; i < e; ++i) {
5472 * v = body(v, i, a...);
5473 * }
5474 * return v;
5475 * }
5476 * }</pre></blockquote>
5477 *
5478 * @apiNote The implementation of this method can be expressed as follows:
5479 * <blockquote><pre>{@code
5480 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5481 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5482 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5483 * // the following semantics:
5484 * // MH_increment: (int limit, int counter) -> counter + 1
5485 * // MH_predicate: (int limit, int counter) -> counter < limit
5486 * Class<?> counterType = start.type().returnType(); // int
5487 * Class<?> returnType = body.type().returnType();
5488 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5489 * if (returnType != void.class) { // ignore the V variable
5490 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5491 * pred = dropArguments(pred, 1, returnType); // ditto
5492 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5493 * }
5494 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5495 * MethodHandle[]
5496 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5497 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5498 * indexVar = { start, incr }; // i = start(); i = i + 1
5499 * return loop(loopLimit, bodyClause, indexVar);
5500 * }
5501 * }</pre></blockquote>
5502 *
5503 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5504 * See above for other constraints.
5505 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5506 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5507 * @param init optional initializer, providing the initial value of the loop variable.
5508 * May be {@code null}, implying a default initial value. See above for other constraints.
5509 * @param body body of the loop, which may not be {@code null}.
5510 * It controls the loop parameters and result type in the standard case (see above for details).
5511 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5512 * and may accept any number of additional types.
5513 * See above for other constraints.
5514 *
5515 * @return a method handle representing the loop.
5516 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5517 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5518 *
5519 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5520 * @since 9
5521 */
5522 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5523 countedLoopChecks(start, end, init, body);
5524 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5525 Class<?> limitType = end.type().returnType(); // yes, int again
5526 Class<?> returnType = body.type().returnType();
5527 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5528 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5529 MethodHandle retv = null;
5530 if (returnType != void.class) {
5531 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5532 pred = dropArguments(pred, 1, returnType); // ditto
5533 retv = dropArguments(identity(returnType), 0, counterType);
5534 }
5535 body = dropArguments(body, 0, counterType); // ignore the limit variable
5536 MethodHandle[]
5537 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5538 bodyClause = { init, body }, // v = init(); v = body(v, i)
5539 indexVar = { start, incr }; // i = start(); i = i + 1
5540 return loop(loopLimit, bodyClause, indexVar);
5541 }
5542
5543 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5544 Objects.requireNonNull(start);
5545 Objects.requireNonNull(end);
5546 Objects.requireNonNull(body);
5547 Class<?> counterType = start.type().returnType();
5548 if (counterType != int.class) {
5549 MethodType expected = start.type().changeReturnType(int.class);
5550 throw misMatchedTypes("start function", start.type(), expected);
5551 } else if (end.type().returnType() != counterType) {
5552 MethodType expected = end.type().changeReturnType(counterType);
5553 throw misMatchedTypes("end function", end.type(), expected);
5554 }
5555 MethodType bodyType = body.type();
5556 Class<?> returnType = bodyType.returnType();
5557 List<Class<?>> innerList = bodyType.parameterList();
5558 // strip leading V value if present
5559 int vsize = (returnType == void.class ? 0 : 1);
5560 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5561 // argument list has no "V" => error
5562 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5563 throw misMatchedTypes("body function", bodyType, expected);
5564 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5565 // missing I type => error
5566 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5567 throw misMatchedTypes("body function", bodyType, expected);
5568 }
5569 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5570 if (outerList.isEmpty()) {
5571 // special case; take lists from end handle
5572 outerList = end.type().parameterList();
5573 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5574 }
5575 MethodType expected = methodType(counterType, outerList);
5576 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5577 throw misMatchedTypes("start parameter types", start.type(), expected);
5578 }
5579 if (end.type() != start.type() &&
5580 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5581 throw misMatchedTypes("end parameter types", end.type(), expected);
5582 }
5583 if (init != null) {
5584 MethodType initType = init.type();
5585 if (initType.returnType() != returnType ||
5586 !initType.effectivelyIdenticalParameters(0, outerList)) {
5587 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5588 }
5589 }
5590 }
5591
5592 /**
5593 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5594 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5595 * <p>
5596 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5597 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5598 * <p>
5599 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5600 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5601 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5602 * <p>
5603 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5604 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5605 * iteration variable.
5606 * The result of the loop handle execution will be the final {@code V} value of that variable
5607 * (or {@code void} if there is no {@code V} variable).
5608 * <p>
5609 * The following rules hold for the argument handles:<ul>
5610 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5611 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5612 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5613 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5614 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5615 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5616 * of types called the <em>internal parameter list</em>.
5617 * It will constrain the parameter lists of the other loop parts.
5618 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5619 * with no additional {@code A} types, then the internal parameter list is extended by
5620 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5621 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5622 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5623 * list {@code (A...)} is called the <em>external parameter list</em>.
5624 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5625 * additional state variable of the loop.
5626 * The body must both accept a leading parameter and return a value of this type {@code V}.
5627 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5628 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5629 * <a href="MethodHandles.html#effid">effectively identical</a>
5630 * to the external parameter list {@code (A...)}.
5631 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5632 * {@linkplain #empty default value}.
5633 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5634 * type {@code java.util.Iterator} or a subtype thereof.
5635 * The iterator it produces when the loop is executed will be assumed
5636 * to yield values which can be converted to type {@code T}.
5637 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5638 * effectively identical to the external parameter list {@code (A...)}.
5639 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5640 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5641 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5642 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5643 * the {@link MethodHandle#asType asType} conversion method.
5644 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5645 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5646 * </ul>
5647 * <p>
5648 * The type {@code T} may be either a primitive or reference.
5649 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5650 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5651 * as if by the {@link MethodHandle#asType asType} conversion method.
5652 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5653 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5654 * <p>
5655 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5656 * <li>The loop handle's result type is the result type {@code V} of the body.
5657 * <li>The loop handle's parameter types are the types {@code (A...)},
5658 * from the external parameter list.
5659 * </ul>
5660 * <p>
5661 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5662 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5663 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5664 * <blockquote><pre>{@code
5665 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5666 * V init(A...);
5667 * V body(V,T,A...);
5668 * V iteratedLoop(A... a...) {
5669 * Iterator<T> it = iterator(a...);
5670 * V v = init(a...);
5671 * while (it.hasNext()) {
5672 * T t = it.next();
5673 * v = body(v, t, a...);
5674 * }
5675 * return v;
5676 * }
5677 * }</pre></blockquote>
5678 *
5679 * @apiNote Example:
5680 * <blockquote><pre>{@code
5681 * // get an iterator from a list
5682 * static List<String> reverseStep(List<String> r, String e) {
5683 * r.add(0, e);
5684 * return r;
5685 * }
5686 * static List<String> newArrayList() { return new ArrayList<>(); }
5687 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5688 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5689 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5690 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5691 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5692 * }</pre></blockquote>
5693 *
5694 * @apiNote The implementation of this method can be expressed approximately as follows:
5695 * <blockquote><pre>{@code
5696 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5697 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5698 * Class<?> returnType = body.type().returnType();
5699 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5700 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5701 * MethodHandle retv = null, step = body, startIter = iterator;
5702 * if (returnType != void.class) {
5703 * // the simple thing first: in (I V A...), drop the I to get V
5704 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5705 * // body type signature (V T A...), internal loop types (I V A...)
5706 * step = swapArguments(body, 0, 1); // swap V <-> T
5707 * }
5708 * if (startIter == null) startIter = MH_getIter;
5709 * MethodHandle[]
5710 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5711 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5712 * return loop(iterVar, bodyClause);
5713 * }
5714 * }</pre></blockquote>
5715 *
5716 * @param iterator an optional handle to return the iterator to start the loop.
5717 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5718 * See above for other constraints.
5719 * @param init optional initializer, providing the initial value of the loop variable.
5720 * May be {@code null}, implying a default initial value. See above for other constraints.
5721 * @param body body of the loop, which may not be {@code null}.
5722 * It controls the loop parameters and result type in the standard case (see above for details).
5723 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5724 * and may accept any number of additional types.
5725 * See above for other constraints.
5726 *
5727 * @return a method handle embodying the iteration loop functionality.
5728 * @throws NullPointerException if the {@code body} handle is {@code null}.
5729 * @throws IllegalArgumentException if any argument violates the above requirements.
5730 *
5731 * @since 9
5732 */
5733 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5734 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5735 Class<?> returnType = body.type().returnType();
5736 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5737 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5738 MethodHandle startIter;
5739 MethodHandle nextVal;
5740 {
5741 MethodType iteratorType;
5742 if (iterator == null) {
5743 // derive argument type from body, if available, else use Iterable
5744 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5745 iteratorType = startIter.type().changeParameterType(0, iterableType);
5746 } else {
5747 // force return type to the internal iterator class
5748 iteratorType = iterator.type().changeReturnType(Iterator.class);
5749 startIter = iterator;
5750 }
5751 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5752 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5753
5754 // perform the asType transforms under an exception transformer, as per spec.:
5755 try {
5756 startIter = startIter.asType(iteratorType);
5757 nextVal = nextRaw.asType(nextValType);
5758 } catch (WrongMethodTypeException ex) {
5759 throw new IllegalArgumentException(ex);
5760 }
5761 }
5762
5763 MethodHandle retv = null, step = body;
5764 if (returnType != void.class) {
5765 // the simple thing first: in (I V A...), drop the I to get V
5766 retv = dropArguments(identity(returnType), 0, Iterator.class);
5767 // body type signature (V T A...), internal loop types (I V A...)
5768 step = swapArguments(body, 0, 1); // swap V <-> T
5769 }
5770
5771 MethodHandle[]
5772 iterVar = { startIter, null, hasNext, retv },
5773 bodyClause = { init, filterArgument(step, 0, nextVal) };
5774 return loop(iterVar, bodyClause);
5775 }
5776
5777 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5778 Objects.requireNonNull(body);
5779 MethodType bodyType = body.type();
5780 Class<?> returnType = bodyType.returnType();
5781 List<Class<?>> internalParamList = bodyType.parameterList();
5782 // strip leading V value if present
5783 int vsize = (returnType == void.class ? 0 : 1);
5784 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5785 // argument list has no "V" => error
5786 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5787 throw misMatchedTypes("body function", bodyType, expected);
5788 } else if (internalParamList.size() <= vsize) {
5789 // missing T type => error
5790 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5791 throw misMatchedTypes("body function", bodyType, expected);
5792 }
5793 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5794 Class<?> iterableType = null;
5795 if (iterator != null) {
5796 // special case; if the body handle only declares V and T then
5797 // the external parameter list is obtained from iterator handle
5798 if (externalParamList.isEmpty()) {
5799 externalParamList = iterator.type().parameterList();
5800 }
5801 MethodType itype = iterator.type();
5802 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5803 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5804 }
5805 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5806 MethodType expected = methodType(itype.returnType(), externalParamList);
5807 throw misMatchedTypes("iterator parameters", itype, expected);
5808 }
5809 } else {
5810 if (externalParamList.isEmpty()) {
5811 // special case; if the iterator handle is null and the body handle
5812 // only declares V and T then the external parameter list consists
5813 // of Iterable
5814 externalParamList = Arrays.asList(Iterable.class);
5815 iterableType = Iterable.class;
5816 } else {
5817 // special case; if the iterator handle is null and the external
5818 // parameter list is not empty then the first parameter must be
5819 // assignable to Iterable
5820 iterableType = externalParamList.get(0);
5821 if (!Iterable.class.isAssignableFrom(iterableType)) {
5822 throw newIllegalArgumentException(
5823 "inferred first loop argument must inherit from Iterable: " + iterableType);
5824 }
5825 }
5826 }
5827 if (init != null) {
5828 MethodType initType = init.type();
5829 if (initType.returnType() != returnType ||
5830 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5831 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5832 }
5833 }
5834 return iterableType; // help the caller a bit
5835 }
5836
5837 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5838 // there should be a better way to uncross my wires
5839 int arity = mh.type().parameterCount();
5840 int[] order = new int[arity];
5841 for (int k = 0; k < arity; k++) order[k] = k;
5842 order[i] = j; order[j] = i;
5843 Class<?>[] types = mh.type().parameterArray();
5844 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5845 MethodType swapType = methodType(mh.type().returnType(), types);
5846 return permuteArguments(mh, swapType, order);
5847 }
5848
5849 /**
5850 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5851 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5852 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5853 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5854 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5855 * {@code try-finally} handle.
5856 * <p>
5857 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5858 * The first is the exception thrown during the
5859 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5860 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5861 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5862 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5863 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5864 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5865 * <p>
5866 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5867 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5868 * two extra leading parameters:<ul>
5869 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5870 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5871 * the result from the execution of the {@code target} handle.
5872 * This parameter is not present if the {@code target} returns {@code void}.
5873 * </ul>
5874 * <p>
5875 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5876 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5877 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5878 * the cleanup.
5879 * <blockquote><pre>{@code
5880 * V target(A..., B...);
5881 * V cleanup(Throwable, V, A...);
5882 * V adapter(A... a, B... b) {
5883 * V result = (zero value for V);
5884 * Throwable throwable = null;
5885 * try {
5886 * result = target(a..., b...);
5887 * } catch (Throwable t) {
5888 * throwable = t;
5889 * throw t;
5890 * } finally {
5891 * result = cleanup(throwable, result, a...);
5892 * }
5893 * return result;
5894 * }
5895 * }</pre></blockquote>
5896 * <p>
5897 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5898 * be modified by execution of the target, and so are passed unchanged
5899 * from the caller to the cleanup, if it is invoked.
5900 * <p>
5901 * The target and cleanup must return the same type, even if the cleanup
5902 * always throws.
5903 * To create such a throwing cleanup, compose the cleanup logic
5904 * with {@link #throwException throwException},
5905 * in order to create a method handle of the correct return type.
5906 * <p>
5907 * Note that {@code tryFinally} never converts exceptions into normal returns.
5908 * In rare cases where exceptions must be converted in that way, first wrap
5909 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5910 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5911 * <p>
5912 * It is recommended that the first parameter type of {@code cleanup} be
5913 * declared {@code Throwable} rather than a narrower subtype. This ensures
5914 * {@code cleanup} will always be invoked with whatever exception that
5915 * {@code target} throws. Declaring a narrower type may result in a
5916 * {@code ClassCastException} being thrown by the {@code try-finally}
5917 * handle if the type of the exception thrown by {@code target} is not
5918 * assignable to the first parameter type of {@code cleanup}. Note that
5919 * various exception types of {@code VirtualMachineError},
5920 * {@code LinkageError}, and {@code RuntimeException} can in principle be
5921 * thrown by almost any kind of Java code, and a finally clause that
5922 * catches (say) only {@code IOException} would mask any of the others
5923 * behind a {@code ClassCastException}.
5924 *
5925 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5926 * @param cleanup the handle that is invoked in the finally block.
5927 *
5928 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5929 * @throws NullPointerException if any argument is null
5930 * @throws IllegalArgumentException if {@code cleanup} does not accept
5931 * the required leading arguments, or if the method handle types do
5932 * not match in their return types and their
5933 * corresponding trailing parameters
5934 *
5935 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5936 * @since 9
5937 */
5938 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5939 List<Class<?>> targetParamTypes = target.type().parameterList();
5940 Class<?> rtype = target.type().returnType();
5941
5942 tryFinallyChecks(target, cleanup);
5943
5944 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5945 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5946 // target parameter list.
5947 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5948
5949 // Ensure that the intrinsic type checks the instance thrown by the
5950 // target against the first parameter of cleanup
5951 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
5952
5953 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5954 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5955 }
5956
5957 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5958 Class<?> rtype = target.type().returnType();
5959 if (rtype != cleanup.type().returnType()) {
5960 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5961 }
5962 MethodType cleanupType = cleanup.type();
5963 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5964 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5965 }
5966 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5967 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5968 }
5969 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5970 // target parameter list.
5971 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5972 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5973 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5974 cleanup.type(), target.type());
5975 }
5976 }
5977
5978 }