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