1 /*
2 * Copyright (c) 2008, 2017, 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 import valhalla.shady.MinimalValueTypes_1_0;
40 import valhalla.shady.ValueTypeHolder;
41
42 import java.lang.invoke.LambdaForm.BasicType;
43 import java.lang.reflect.Constructor;
44 import java.lang.reflect.Field;
45 import java.lang.reflect.Member;
46 import java.lang.reflect.Method;
47 import java.lang.reflect.Modifier;
48 import java.lang.reflect.ReflectPermission;
49 import java.nio.ByteOrder;
50 import java.security.AccessController;
51 import java.security.PrivilegedAction;
52 import java.security.ProtectionDomain;
53 import java.util.ArrayList;
54 import java.util.Arrays;
55 import java.util.BitSet;
56 import java.util.Iterator;
57 import java.util.List;
58 import java.util.Objects;
59 import java.util.concurrent.ConcurrentHashMap;
60 import java.util.stream.Collectors;
61 import java.util.stream.Stream;
62
63 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
64 import static java.lang.invoke.MethodHandleNatives.Constants.*;
65 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
66 import static java.lang.invoke.MethodType.methodType;
67
68 /**
69 * This class consists exclusively of static methods that operate on or return
70 * method handles. They fall into several categories:
71 * <ul>
72 * <li>Lookup methods which help create method handles for methods and fields.
73 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
74 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
75 * </ul>
76 *
77 * @author John Rose, JSR 292 EG
78 * @since 1.7
79 */
80 public class MethodHandles {
81
82 private MethodHandles() { } // do not instantiate
83
84 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
85
86 // See IMPL_LOOKUP below.
87
88 //// Method handle creation from ordinary methods.
89
90 /**
91 * Returns a {@link Lookup lookup object} with
92 * full capabilities to emulate all supported bytecode behaviors of the caller.
93 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
94 * Factory methods on the lookup object can create
95 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
96 * for any member that the caller has access to via bytecodes,
97 * including protected and private fields and methods.
98 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
99 * Do not store it in place where untrusted code can access it.
100 * <p>
101 * This method is caller sensitive, which means that it may return different
102 * values to different callers.
103 * <p>
104 * For any given caller class {@code C}, the lookup object returned by this call
105 * has equivalent capabilities to any lookup object
106 * supplied by the JVM to the bootstrap method of an
107 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
108 * executing in the same caller class {@code C}.
109 * @return a lookup object for the caller of this method, with private access
110 */
111 @CallerSensitive
112 @ForceInline // to ensure Reflection.getCallerClass optimization
113 public static Lookup lookup() {
114 return new Lookup(Reflection.getCallerClass());
115 }
116
117 /**
118 * This reflected$lookup method is the alternate implementation of
119 * the lookup method when being invoked by reflection.
120 */
121 @CallerSensitive
122 private static Lookup reflected$lookup() {
123 Class<?> caller = Reflection.getCallerClass();
124 if (caller.getClassLoader() == null) {
125 throw newIllegalArgumentException("illegal lookupClass: "+caller);
126 }
127 return new Lookup(caller);
128 }
129
130 /**
131 * Returns a {@link Lookup lookup object} which is trusted minimally.
132 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
133 * It can only be used to create method handles to public members of
134 * public classes in packages that are exported unconditionally.
135 * <p>
136 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
137 * of this lookup object will be {@link java.lang.Object}.
138 *
139 * @apiNote The use of Object is conventional, and because the lookup modes are
140 * limited, there is no special access provided to the internals of Object, its package
141 * or its module. Consequently, the lookup context of this lookup object will be the
142 * bootstrap class loader, which means it cannot find user classes.
143 *
144 * <p style="font-size:smaller;">
145 * <em>Discussion:</em>
146 * The lookup class can be changed to any other class {@code C} using an expression of the form
147 * {@link Lookup#in publicLookup().in(C.class)}.
148 * but may change the lookup context by virtue of changing the class loader.
149 * A public lookup object is always subject to
150 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
151 * Also, it cannot access
152 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
153 * @return a lookup object which is trusted minimally
154 *
155 * @revised 9
156 * @spec JPMS
157 */
158 public static Lookup publicLookup() {
159 return Lookup.PUBLIC_LOOKUP;
160 }
161
162 /**
163 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
164 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
165 * private access</a>, on a target class.
166 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
167 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
168 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
169 * the target class, then this check ensures that
170 * <ul>
171 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
172 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
173 * the target class to at least {@code m1}.</li>
174 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
175 * </ul>
176 * <p>
177 * If there is a security manager, its {@code checkPermission} method is called to
178 * check {@code ReflectPermission("suppressAccessChecks")}.
179 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
180 * was created by code in the caller module (or derived from a lookup object originally
181 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
182 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
183 * access to the caller.
184 * @param targetClass the target class
185 * @param lookup the caller lookup object
186 * @return a lookup object for the target class, with private access
187 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
188 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
189 * @throws IllegalAccessException if the access check specified above fails
190 * @throws SecurityException if denied by the security manager
191 * @since 9
192 * @spec JPMS
193 * @see Lookup#dropLookupMode
194 */
195 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
196 SecurityManager sm = System.getSecurityManager();
197 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
198 if (targetClass.isPrimitive())
199 throw new IllegalArgumentException(targetClass + " is a primitive class");
200 if (targetClass.isArray())
201 throw new IllegalArgumentException(targetClass + " is an array class");
202 Module targetModule = targetClass.getModule();
203 Module callerModule = lookup.lookupClass().getModule();
204 if (!callerModule.canRead(targetModule))
205 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
206 if (targetModule.isNamed()) {
207 String pn = targetClass.getPackageName();
208 assert pn.length() > 0 : "unnamed package cannot be in named module";
209 if (!targetModule.isOpen(pn, callerModule))
210 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
211 }
212 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
213 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
214 if (!callerModule.isNamed() && targetModule.isNamed()) {
215 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
216 if (logger != null) {
217 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
218 }
219 }
220 return new Lookup(targetClass);
221 }
222
223 /**
224 * Performs an unchecked "crack" of a
225 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
226 * The result is as if the user had obtained a lookup object capable enough
227 * to crack the target method handle, called
228 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
229 * on the target to obtain its symbolic reference, and then called
230 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
231 * to resolve the symbolic reference to a member.
232 * <p>
233 * If there is a security manager, its {@code checkPermission} method
234 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
235 * @param <T> the desired type of the result, either {@link Member} or a subtype
236 * @param target a direct method handle to crack into symbolic reference components
237 * @param expected a class object representing the desired result type {@code T}
238 * @return a reference to the method, constructor, or field object
239 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
240 * @exception NullPointerException if either argument is {@code null}
241 * @exception IllegalArgumentException if the target is not a direct method handle
242 * @exception ClassCastException if the member is not of the expected type
243 * @since 1.8
244 */
245 public static <T extends Member> T
246 reflectAs(Class<T> expected, MethodHandle target) {
247 SecurityManager smgr = System.getSecurityManager();
248 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
249 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
250 return lookup.revealDirect(target).reflectAs(expected, lookup);
251 }
252 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
253 private static final java.security.Permission ACCESS_PERMISSION =
254 new ReflectPermission("suppressAccessChecks");
255
256 /**
257 * A <em>lookup object</em> is a factory for creating method handles,
258 * when the creation requires access checking.
259 * Method handles do not perform
260 * access checks when they are called, but rather when they are created.
261 * Therefore, method handle access
262 * restrictions must be enforced when a method handle is created.
263 * The caller class against which those restrictions are enforced
264 * is known as the {@linkplain #lookupClass lookup class}.
265 * <p>
266 * A lookup class which needs to create method handles will call
267 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
268 * When the {@code Lookup} factory object is created, the identity of the lookup class is
269 * determined, and securely stored in the {@code Lookup} object.
270 * The lookup class (or its delegates) may then use factory methods
271 * on the {@code Lookup} object to create method handles for access-checked members.
272 * This includes all methods, constructors, and fields which are allowed to the lookup class,
273 * even private ones.
274 *
275 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
276 * The factory methods on a {@code Lookup} object correspond to all major
277 * use cases for methods, constructors, and fields.
278 * Each method handle created by a factory method is the functional
279 * equivalent of a particular <em>bytecode behavior</em>.
280 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
281 * Here is a summary of the correspondence between these factory methods and
282 * the behavior of the resulting method handles:
283 * <table class="striped">
284 * <caption style="display:none">lookup method behaviors</caption>
285 * <thead>
286 * <tr>
287 * <th scope="col"><a id="equiv"></a>lookup expression</th>
288 * <th scope="col">member</th>
289 * <th scope="col">bytecode behavior</th>
290 * </tr>
291 * </thead>
292 * <tbody>
293 * <tr>
294 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
295 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
296 * </tr>
297 * <tr>
298 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
299 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
300 * </tr>
301 * <tr>
302 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
303 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
304 * </tr>
305 * <tr>
306 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
307 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
308 * </tr>
309 * <tr>
310 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
311 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
312 * </tr>
313 * <tr>
314 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
315 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
316 * </tr>
317 * <tr>
318 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
319 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
320 * </tr>
321 * <tr>
322 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
323 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
324 * </tr>
325 * <tr>
326 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
327 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
328 * </tr>
329 * <tr>
330 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
331 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, 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#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
339 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
340 * </tr>
341 * <tr>
342 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
343 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
344 * </tr>
345 * <tr>
346 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
347 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
348 * </tr>
349 * </tbody>
350 * </table>
351 *
352 * Here, the type {@code C} is the class or interface being searched for a member,
353 * documented as a parameter named {@code refc} in the lookup methods.
354 * The method type {@code MT} is composed from the return type {@code T}
355 * and the sequence of argument types {@code A*}.
356 * The constructor also has a sequence of argument types {@code A*} and
357 * is deemed to return the newly-created object of type {@code C}.
358 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
359 * The formal parameter {@code this} stands for the self-reference of type {@code C};
360 * if it is present, it is always the leading argument to the method handle invocation.
361 * (In the case of some {@code protected} members, {@code this} may be
362 * restricted in type to the lookup class; see below.)
363 * The name {@code arg} stands for all the other method handle arguments.
364 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
365 * stands for a null reference if the accessed method or field is static,
366 * and {@code this} otherwise.
367 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
368 * for reflective objects corresponding to the given members.
369 * <p>
370 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
371 * as if by {@code ldc CONSTANT_Class}.
372 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
373 * <p>
374 * In cases where the given member is of variable arity (i.e., a method or constructor)
375 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
376 * In all other cases, the returned method handle will be of fixed arity.
377 * <p style="font-size:smaller;">
378 * <em>Discussion:</em>
379 * The equivalence between looked-up method handles and underlying
380 * class members and bytecode behaviors
381 * can break down in a few ways:
382 * <ul style="font-size:smaller;">
383 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
384 * the lookup can still succeed, even when there is no equivalent
385 * Java expression or bytecoded constant.
386 * <li>Likewise, if {@code T} or {@code MT}
387 * is not symbolically accessible from the lookup class's loader,
388 * the lookup can still succeed.
389 * For example, lookups for {@code MethodHandle.invokeExact} and
390 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
391 * <li>If there is a security manager installed, it can forbid the lookup
392 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
393 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
394 * constant is not subject to security manager checks.
395 * <li>If the looked-up method has a
396 * <a href="MethodHandle.html#maxarity">very large arity</a>,
397 * the method handle creation may fail, due to the method handle
398 * type having too many parameters.
399 * </ul>
400 *
401 * <h1><a id="access"></a>Access checking</h1>
402 * Access checks are applied in the factory methods of {@code Lookup},
403 * when a method handle is created.
404 * This is a key difference from the Core Reflection API, since
405 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
406 * performs access checking against every caller, on every call.
407 * <p>
408 * All access checks start from a {@code Lookup} object, which
409 * compares its recorded lookup class against all requests to
410 * create method handles.
411 * A single {@code Lookup} object can be used to create any number
412 * of access-checked method handles, all checked against a single
413 * lookup class.
414 * <p>
415 * A {@code Lookup} object can be shared with other trusted code,
416 * such as a metaobject protocol.
417 * A shared {@code Lookup} object delegates the capability
418 * to create method handles on private members of the lookup class.
419 * Even if privileged code uses the {@code Lookup} object,
420 * the access checking is confined to the privileges of the
421 * original lookup class.
422 * <p>
423 * A lookup can fail, because
424 * the containing class is not accessible to the lookup class, or
425 * because the desired class member is missing, or because the
426 * desired class member is not accessible to the lookup class, or
427 * because the lookup object is not trusted enough to access the member.
428 * In any of these cases, a {@code ReflectiveOperationException} will be
429 * thrown from the attempted lookup. The exact class will be one of
430 * the following:
431 * <ul>
432 * <li>NoSuchMethodException — if a method is requested but does not exist
433 * <li>NoSuchFieldException — if a field is requested but does not exist
434 * <li>IllegalAccessException — if the member exists but an access check fails
435 * </ul>
436 * <p>
437 * In general, the conditions under which a method handle may be
438 * looked up for a method {@code M} are no more restrictive than the conditions
439 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
440 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
441 * a method handle lookup will generally raise a corresponding
442 * checked exception, such as {@code NoSuchMethodException}.
443 * And the effect of invoking the method handle resulting from the lookup
444 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
445 * to executing the compiled, verified, and resolved call to {@code M}.
446 * The same point is true of fields and constructors.
447 * <p style="font-size:smaller;">
448 * <em>Discussion:</em>
449 * Access checks only apply to named and reflected methods,
450 * constructors, and fields.
451 * Other method handle creation methods, such as
452 * {@link MethodHandle#asType MethodHandle.asType},
453 * do not require any access checks, and are used
454 * independently of any {@code Lookup} object.
455 * <p>
456 * If the desired member is {@code protected}, the usual JVM rules apply,
457 * including the requirement that the lookup class must be either be in the
458 * same package as the desired member, or must inherit that member.
459 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
460 * In addition, if the desired member is a non-static field or method
461 * in a different package, the resulting method handle may only be applied
462 * to objects of the lookup class or one of its subclasses.
463 * This requirement is enforced by narrowing the type of the leading
464 * {@code this} parameter from {@code C}
465 * (which will necessarily be a superclass of the lookup class)
466 * to the lookup class itself.
467 * <p>
468 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
469 * that the receiver argument must match both the resolved method <em>and</em>
470 * the current class. Again, this requirement is enforced by narrowing the
471 * type of the leading parameter to the resulting method handle.
472 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
473 * <p>
474 * The JVM represents constructors and static initializer blocks as internal methods
475 * with special names ({@code "<init>"} and {@code "<clinit>"}).
476 * The internal syntax of invocation instructions allows them to refer to such internal
477 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
478 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
479 * <p>
480 * In some cases, access between nested classes is obtained by the Java compiler by creating
481 * an wrapper method to access a private method of another class
482 * in the same top-level declaration.
483 * For example, a nested class {@code C.D}
484 * can access private members within other related classes such as
485 * {@code C}, {@code C.D.E}, or {@code C.B},
486 * but the Java compiler may need to generate wrapper methods in
487 * those related classes. In such cases, a {@code Lookup} object on
488 * {@code C.E} would be unable to those private members.
489 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
490 * which can transform a lookup on {@code C.E} into one on any of those other
491 * classes, without special elevation of privilege.
492 * <p>
493 * The accesses permitted to a given lookup object may be limited,
494 * according to its set of {@link #lookupModes lookupModes},
495 * to a subset of members normally accessible to the lookup class.
496 * For example, the {@link MethodHandles#publicLookup publicLookup}
497 * method produces a lookup object which is only allowed to access
498 * public members in public classes of exported packages.
499 * The caller sensitive method {@link MethodHandles#lookup lookup}
500 * produces a lookup object with full capabilities relative to
501 * its caller class, to emulate all supported bytecode behaviors.
502 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
503 * with fewer access modes than the original lookup object.
504 *
505 * <p style="font-size:smaller;">
506 * <a id="privacc"></a>
507 * <em>Discussion of private access:</em>
508 * We say that a lookup has <em>private access</em>
509 * if its {@linkplain #lookupModes lookup modes}
510 * include the possibility of accessing {@code private} members.
511 * As documented in the relevant methods elsewhere,
512 * only lookups with private access possess the following capabilities:
513 * <ul style="font-size:smaller;">
514 * <li>access private fields, methods, and constructors of the lookup class
515 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
516 * such as {@code Class.forName}
517 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
518 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
519 * for classes accessible to the lookup class
520 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
521 * within the same package member
522 * </ul>
523 * <p style="font-size:smaller;">
524 * Each of these permissions is a consequence of the fact that a lookup object
525 * with private access can be securely traced back to an originating class,
526 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
527 * can be reliably determined and emulated by method handles.
528 *
529 * <h1><a id="secmgr"></a>Security manager interactions</h1>
530 * Although bytecode instructions can only refer to classes in
531 * a related class loader, this API can search for methods in any
532 * class, as long as a reference to its {@code Class} object is
533 * available. Such cross-loader references are also possible with the
534 * Core Reflection API, and are impossible to bytecode instructions
535 * such as {@code invokestatic} or {@code getfield}.
536 * There is a {@linkplain java.lang.SecurityManager security manager API}
537 * to allow applications to check such cross-loader references.
538 * These checks apply to both the {@code MethodHandles.Lookup} API
539 * and the Core Reflection API
540 * (as found on {@link java.lang.Class Class}).
541 * <p>
542 * If a security manager is present, member and class lookups are subject to
543 * additional checks.
544 * From one to three calls are made to the security manager.
545 * Any of these calls can refuse access by throwing a
546 * {@link java.lang.SecurityException SecurityException}.
547 * Define {@code smgr} as the security manager,
548 * {@code lookc} as the lookup class of the current lookup object,
549 * {@code refc} as the containing class in which the member
550 * is being sought, and {@code defc} as the class in which the
551 * member is actually defined.
552 * (If a class or other type is being accessed,
553 * the {@code refc} and {@code defc} values are the class itself.)
554 * The value {@code lookc} is defined as <em>not present</em>
555 * if the current lookup object does not have
556 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
557 * The calls are made according to the following rules:
558 * <ul>
559 * <li><b>Step 1:</b>
560 * If {@code lookc} is not present, or if its class loader is not
561 * the same as or an ancestor of the class loader of {@code refc},
562 * then {@link SecurityManager#checkPackageAccess
563 * smgr.checkPackageAccess(refcPkg)} is called,
564 * where {@code refcPkg} is the package of {@code refc}.
565 * <li><b>Step 2a:</b>
566 * If the retrieved member is not public and
567 * {@code lookc} is not present, then
568 * {@link SecurityManager#checkPermission smgr.checkPermission}
569 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
570 * <li><b>Step 2b:</b>
571 * If the retrieved class has a {@code null} class loader,
572 * and {@code lookc} is not present, then
573 * {@link SecurityManager#checkPermission smgr.checkPermission}
574 * with {@code RuntimePermission("getClassLoader")} is called.
575 * <li><b>Step 3:</b>
576 * If the retrieved member is not public,
577 * and if {@code lookc} is not present,
578 * and if {@code defc} and {@code refc} are different,
579 * then {@link SecurityManager#checkPackageAccess
580 * smgr.checkPackageAccess(defcPkg)} is called,
581 * where {@code defcPkg} is the package of {@code defc}.
582 * </ul>
583 * Security checks are performed after other access checks have passed.
584 * Therefore, the above rules presuppose a member or class that is public,
585 * or else that is being accessed from a lookup class that has
586 * rights to access the member or class.
587 *
588 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
589 * A small number of Java methods have a special property called caller sensitivity.
590 * A <em>caller-sensitive</em> method can behave differently depending on the
591 * identity of its immediate caller.
592 * <p>
593 * If a method handle for a caller-sensitive method is requested,
594 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
595 * but they take account of the lookup class in a special way.
596 * The resulting method handle behaves as if it were called
597 * from an instruction contained in the lookup class,
598 * so that the caller-sensitive method detects the lookup class.
599 * (By contrast, the invoker of the method handle is disregarded.)
600 * Thus, in the case of caller-sensitive methods,
601 * different lookup classes may give rise to
602 * differently behaving method handles.
603 * <p>
604 * In cases where the lookup object is
605 * {@link MethodHandles#publicLookup() publicLookup()},
606 * or some other lookup object without
607 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
608 * the lookup class is disregarded.
609 * In such cases, no caller-sensitive method handle can be created,
610 * access is forbidden, and the lookup fails with an
611 * {@code IllegalAccessException}.
612 * <p style="font-size:smaller;">
613 * <em>Discussion:</em>
614 * For example, the caller-sensitive method
615 * {@link java.lang.Class#forName(String) Class.forName(x)}
616 * can return varying classes or throw varying exceptions,
617 * depending on the class loader of the class that calls it.
618 * A public lookup of {@code Class.forName} will fail, because
619 * there is no reasonable way to determine its bytecode behavior.
620 * <p style="font-size:smaller;">
621 * If an application caches method handles for broad sharing,
622 * it should use {@code publicLookup()} to create them.
623 * If there is a lookup of {@code Class.forName}, it will fail,
624 * and the application must take appropriate action in that case.
625 * It may be that a later lookup, perhaps during the invocation of a
626 * bootstrap method, can incorporate the specific identity
627 * of the caller, making the method accessible.
628 * <p style="font-size:smaller;">
629 * The function {@code MethodHandles.lookup} is caller sensitive
630 * so that there can be a secure foundation for lookups.
631 * Nearly all other methods in the JSR 292 API rely on lookup
632 * objects to check access requests.
633 *
634 * @revised 9
635 */
636 public static final
637 class Lookup {
638 /** The class on behalf of whom the lookup is being performed. */
639 private final Class<?> lookupClass;
640
641 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
642 private final int allowedModes;
643
644 /** A single-bit mask representing {@code public} access,
645 * which may contribute to the result of {@link #lookupModes lookupModes}.
646 * The value, {@code 0x01}, happens to be the same as the value of the
647 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
648 */
649 public static final int PUBLIC = Modifier.PUBLIC;
650
651 /** A single-bit mask representing {@code private} access,
652 * which may contribute to the result of {@link #lookupModes lookupModes}.
653 * The value, {@code 0x02}, happens to be the same as the value of the
654 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
655 */
656 public static final int PRIVATE = Modifier.PRIVATE;
657
658 /** A single-bit mask representing {@code protected} access,
659 * which may contribute to the result of {@link #lookupModes lookupModes}.
660 * The value, {@code 0x04}, happens to be the same as the value of the
661 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
662 */
663 public static final int PROTECTED = Modifier.PROTECTED;
664
665 /** A single-bit mask representing {@code package} access (default access),
666 * which may contribute to the result of {@link #lookupModes lookupModes}.
667 * The value is {@code 0x08}, which does not correspond meaningfully to
668 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
669 */
670 public static final int PACKAGE = Modifier.STATIC;
671
672 /** A single-bit mask representing {@code module} access (default access),
673 * which may contribute to the result of {@link #lookupModes lookupModes}.
674 * The value is {@code 0x10}, which does not correspond meaningfully to
675 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
676 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
677 * with this lookup mode can access all public types in the module of the
678 * lookup class and public types in packages exported by other modules
679 * to the module of the lookup class.
680 * @since 9
681 * @spec JPMS
682 */
683 public static final int MODULE = PACKAGE << 1;
684
685 /** A single-bit mask representing {@code unconditional} access
686 * which may contribute to the result of {@link #lookupModes lookupModes}.
687 * The value is {@code 0x20}, which does not correspond meaningfully to
688 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
689 * A {@code Lookup} with this lookup mode assumes {@linkplain
690 * java.lang.Module#canRead(java.lang.Module) readability}.
691 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
692 * with this lookup mode can access all public members of public types
693 * of all modules where the type is in a package that is {@link
694 * java.lang.Module#isExported(String) exported unconditionally}.
695 * @since 9
696 * @spec JPMS
697 * @see #publicLookup()
698 */
699 public static final int UNCONDITIONAL = PACKAGE << 2;
700
701 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
702 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
703 private static final int TRUSTED = -1;
704
705 private static int fixmods(int mods) {
706 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
707 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
708 }
709
710 /** Tells which class is performing the lookup. It is this class against
711 * which checks are performed for visibility and access permissions.
712 * <p>
713 * The class implies a maximum level of access permission,
714 * but the permissions may be additionally limited by the bitmask
715 * {@link #lookupModes lookupModes}, which controls whether non-public members
716 * can be accessed.
717 * @return the lookup class, on behalf of which this lookup object finds members
718 */
719 public Class<?> lookupClass() {
720 return lookupClass;
721 }
722
723 // This is just for calling out to MethodHandleImpl.
724 private Class<?> lookupClassOrNull() {
725 return (allowedModes == TRUSTED) ? null : lookupClass;
726 }
727
728 /** Tells which access-protection classes of members this lookup object can produce.
729 * The result is a bit-mask of the bits
730 * {@linkplain #PUBLIC PUBLIC (0x01)},
731 * {@linkplain #PRIVATE PRIVATE (0x02)},
732 * {@linkplain #PROTECTED PROTECTED (0x04)},
733 * {@linkplain #PACKAGE PACKAGE (0x08)},
734 * {@linkplain #MODULE MODULE (0x10)},
735 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
736 * <p>
737 * A freshly-created lookup object
738 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
739 * all possible bits set, except {@code UNCONDITIONAL}. The lookup can be used to
740 * access all members of the caller's class, all public types in the caller's module,
741 * and all public types in packages exported by other modules to the caller's module.
742 * A lookup object on a new lookup class
743 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
744 * may have some mode bits set to zero.
745 * Mode bits can also be
746 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
747 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
748 * The purpose of this is to restrict access via the new lookup object,
749 * so that it can access only names which can be reached by the original
750 * lookup object, and also by the new lookup class.
751 * @return the lookup modes, which limit the kinds of access performed by this lookup object
752 * @see #in
753 * @see #dropLookupMode
754 *
755 * @revised 9
756 * @spec JPMS
757 */
758 public int lookupModes() {
759 return allowedModes & ALL_MODES;
760 }
761
762 /** Embody the current class (the lookupClass) as a lookup class
763 * for method handle creation.
764 * Must be called by from a method in this package,
765 * which in turn is called by a method not in this package.
766 */
767 Lookup(Class<?> lookupClass) {
768 this(lookupClass, FULL_POWER_MODES);
769 // make sure we haven't accidentally picked up a privileged class:
770 checkUnprivilegedlookupClass(lookupClass);
771 }
772
773 private Lookup(Class<?> lookupClass, int allowedModes) {
774 this.lookupClass = lookupClass;
775 this.allowedModes = allowedModes;
776 }
777
778 /**
779 * Creates a lookup on the specified new lookup class.
780 * The resulting object will report the specified
781 * class as its own {@link #lookupClass lookupClass}.
782 * <p>
783 * However, the resulting {@code Lookup} object is guaranteed
784 * to have no more access capabilities than the original.
785 * In particular, access capabilities can be lost as follows:<ul>
786 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
787 * the new lookup class is in a different module {@code M}, then no members, not
788 * even public members in {@code M}'s exported packages, will be accessible.
789 * The exception to this is when this lookup is {@link #publicLookup()
790 * publicLookup}, in which case {@code PUBLIC} access is not lost.
791 * <li>If the old lookup class is in an unnamed module, and the new lookup class
792 * is a different module then {@link #MODULE MODULE} access is lost.
793 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
794 * <li>If the new lookup class is in a different package
795 * than the old one, protected and default (package) members will not be accessible.
796 * <li>If the new lookup class is not within the same package member
797 * as the old one, private members will not be accessible, and protected members
798 * will not be accessible by virtue of inheritance.
799 * (Protected members may continue to be accessible because of package sharing.)
800 * <li>If the new lookup class is not accessible to the old lookup class,
801 * then no members, not even public members, will be accessible.
802 * (In all other cases, public members will continue to be accessible.)
803 * </ul>
804 * <p>
805 * The resulting lookup's capabilities for loading classes
806 * (used during {@link #findClass} invocations)
807 * are determined by the lookup class' loader,
808 * which may change due to this operation.
809 *
810 * @param requestedLookupClass the desired lookup class for the new lookup object
811 * @return a lookup object which reports the desired lookup class, or the same object
812 * if there is no change
813 * @throws NullPointerException if the argument is null
814 *
815 * @revised 9
816 * @spec JPMS
817 */
818 public Lookup in(Class<?> requestedLookupClass) {
819 Objects.requireNonNull(requestedLookupClass);
820 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
821 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
822 if (requestedLookupClass == this.lookupClass)
823 return this; // keep same capabilities
824 int newModes = (allowedModes & FULL_POWER_MODES);
825 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
826 // Need to drop all access when teleporting from a named module to another
827 // module. The exception is publicLookup where PUBLIC is not lost.
828 if (this.lookupClass.getModule().isNamed()
829 && (this.allowedModes & UNCONDITIONAL) == 0)
830 newModes = 0;
831 else
832 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
833 }
834 if ((newModes & PACKAGE) != 0
835 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
836 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
837 }
838 // Allow nestmate lookups to be created without special privilege:
839 if ((newModes & PRIVATE) != 0
840 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
841 newModes &= ~(PRIVATE|PROTECTED);
842 }
843 if ((newModes & PUBLIC) != 0
844 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
845 // The requested class it not accessible from the lookup class.
846 // No permissions.
847 newModes = 0;
848 }
849
850 checkUnprivilegedlookupClass(requestedLookupClass);
851 return new Lookup(requestedLookupClass, newModes);
852 }
853
854
855 /**
856 * Creates a lookup on the same lookup class which this lookup object
857 * finds members, but with a lookup mode that has lost the given lookup mode.
858 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
859 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
860 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
861 * dropped and so the resulting lookup mode will never have these access capabilities.
862 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
863 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
864 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
865 * is dropped then the resulting lookup has no access.
866 * @param modeToDrop the lookup mode to drop
867 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
868 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
869 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
870 * @see MethodHandles#privateLookupIn
871 * @since 9
872 */
873 public Lookup dropLookupMode(int modeToDrop) {
874 int oldModes = lookupModes();
875 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
876 switch (modeToDrop) {
877 case PUBLIC: newModes &= ~(ALL_MODES); break;
878 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
879 case PACKAGE: newModes &= ~(PRIVATE); break;
880 case PROTECTED:
881 case PRIVATE:
882 case UNCONDITIONAL: break;
883 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
884 }
885 if (newModes == oldModes) return this; // return self if no change
886 return new Lookup(lookupClass(), newModes);
887 }
888
889 /**
890 * Defines a class to the same class loader and in the same runtime package and
891 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
892 * {@linkplain #lookupClass() lookup class}.
893 *
894 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
895 * {@link #PACKAGE PACKAGE} access as default (package) members will be
896 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
897 * that the lookup object was created by a caller in the runtime package (or derived
898 * from a lookup originally created by suitably privileged code to a target class in
899 * the runtime package). </p>
900 *
901 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
902 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
903 * same package as the lookup class. </p>
904 *
905 * <p> This method does not run the class initializer. The class initializer may
906 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
907 * Specification</em>. </p>
908 *
909 * <p> If there is a security manager, its {@code checkPermission} method is first called
910 * to check {@code RuntimePermission("defineClass")}. </p>
911 *
912 * @param bytes the class bytes
913 * @return the {@code Class} object for the class
914 * @throws IllegalArgumentException the bytes are for a class in a different package
915 * to the lookup class
916 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
917 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
918 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
919 * @throws SecurityException if denied by the security manager
920 * @throws NullPointerException if {@code bytes} is {@code null}
921 * @since 9
922 * @spec JPMS
923 * @see Lookup#privateLookupIn
924 * @see Lookup#dropLookupMode
925 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
926 */
927 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
928 SecurityManager sm = System.getSecurityManager();
929 if (sm != null)
930 sm.checkPermission(new RuntimePermission("defineClass"));
931 if ((lookupModes() & PACKAGE) == 0)
932 throw new IllegalAccessException("Lookup does not have PACKAGE access");
933 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
934
935 // parse class bytes to get class name (in internal form)
936 bytes = bytes.clone();
937 String name;
938 try {
939 ClassReader reader = new ClassReader(bytes);
940 name = reader.getClassName();
941 } catch (RuntimeException e) {
942 // ASM exceptions are poorly specified
943 ClassFormatError cfe = new ClassFormatError();
944 cfe.initCause(e);
945 throw cfe;
946 }
947
948 // get package and class name in binary form
949 String cn, pn;
950 int index = name.lastIndexOf('/');
951 if (index == -1) {
952 cn = name;
953 pn = "";
954 } else {
955 cn = name.replace('/', '.');
956 pn = cn.substring(0, index);
957 }
958 if (!pn.equals(lookupClass.getPackageName())) {
959 throw new IllegalArgumentException("Class not in same package as lookup class");
960 }
961
962 // invoke the class loader's defineClass method
963 ClassLoader loader = lookupClass.getClassLoader();
964 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
965 String source = "__Lookup_defineClass__";
966 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
967 assert clazz.getClassLoader() == lookupClass.getClassLoader()
968 && clazz.getPackageName().equals(lookupClass.getPackageName())
969 && protectionDomain(clazz) == lookupClassProtectionDomain();
970 return clazz;
971 }
972
973 private ProtectionDomain lookupClassProtectionDomain() {
974 ProtectionDomain pd = cachedProtectionDomain;
975 if (pd == null) {
976 cachedProtectionDomain = pd = protectionDomain(lookupClass);
977 }
978 return pd;
979 }
980
981 private ProtectionDomain protectionDomain(Class<?> clazz) {
982 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
983 return AccessController.doPrivileged(pa);
984 }
985
986 // cached protection domain
987 private volatile ProtectionDomain cachedProtectionDomain;
988
989
990 // Make sure outer class is initialized first.
991 static { IMPL_NAMES.getClass(); }
992
993 /** Package-private version of lookup which is trusted. */
994 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
995
996 /** Version of lookup which is trusted minimally.
997 * It can only be used to create method handles to publicly accessible
998 * members in packages that are exported unconditionally.
999 */
1000 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
1001
1002 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1003 String name = lookupClass.getName();
1004 if (name.startsWith("java.lang.invoke."))
1005 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1006 }
1007
1008 /**
1009 * Displays the name of the class from which lookups are to be made.
1010 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1011 * If there are restrictions on the access permitted to this lookup,
1012 * this is indicated by adding a suffix to the class name, consisting
1013 * of a slash and a keyword. The keyword represents the strongest
1014 * allowed access, and is chosen as follows:
1015 * <ul>
1016 * <li>If no access is allowed, the suffix is "/noaccess".
1017 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1018 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1019 * <li>If only public and module access are allowed, the suffix is "/module".
1020 * <li>If only public, module and package access are allowed, the suffix is "/package".
1021 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1022 * </ul>
1023 * If none of the above cases apply, it is the case that full
1024 * access (public, module, package, private, and protected) is allowed.
1025 * In this case, no suffix is added.
1026 * This is true only of an object obtained originally from
1027 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1028 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1029 * always have restricted access, and will display a suffix.
1030 * <p>
1031 * (It may seem strange that protected access should be
1032 * stronger than private access. Viewed independently from
1033 * package access, protected access is the first to be lost,
1034 * because it requires a direct subclass relationship between
1035 * caller and callee.)
1036 * @see #in
1037 *
1038 * @revised 9
1039 * @spec JPMS
1040 */
1041 @Override
1042 public String toString() {
1043 String cname = lookupClass.getName();
1044 switch (allowedModes) {
1045 case 0: // no privileges
1046 return cname + "/noaccess";
1047 case PUBLIC:
1048 return cname + "/public";
1049 case PUBLIC|UNCONDITIONAL:
1050 return cname + "/publicLookup";
1051 case PUBLIC|MODULE:
1052 return cname + "/module";
1053 case PUBLIC|MODULE|PACKAGE:
1054 return cname + "/package";
1055 case FULL_POWER_MODES & ~PROTECTED:
1056 return cname + "/private";
1057 case FULL_POWER_MODES:
1058 return cname;
1059 case TRUSTED:
1060 return "/trusted"; // internal only; not exported
1061 default: // Should not happen, but it's a bitfield...
1062 cname = cname + "/" + Integer.toHexString(allowedModes);
1063 assert(false) : cname;
1064 return cname;
1065 }
1066 }
1067
1068 /**
1069 * Produces a method handle for a static method.
1070 * The type of the method handle will be that of the method.
1071 * (Since static methods do not take receivers, there is no
1072 * additional receiver argument inserted into the method handle type,
1073 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1074 * The method and all its argument types must be accessible to the lookup object.
1075 * <p>
1076 * The returned method handle will have
1077 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1078 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1079 * <p>
1080 * If the returned method handle is invoked, the method's class will
1081 * be initialized, if it has not already been initialized.
1082 * <p><b>Example:</b>
1083 * <blockquote><pre>{@code
1084 import static java.lang.invoke.MethodHandles.*;
1085 import static java.lang.invoke.MethodType.*;
1086 ...
1087 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1088 "asList", methodType(List.class, Object[].class));
1089 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1090 * }</pre></blockquote>
1091 * @param refc the class from which the method is accessed
1092 * @param name the name of the method
1093 * @param type the type of the method
1094 * @return the desired method handle
1095 * @throws NoSuchMethodException if the method does not exist
1096 * @throws IllegalAccessException if access checking fails,
1097 * or if the method is not {@code static},
1098 * or if the method's variable arity modifier bit
1099 * is set and {@code asVarargsCollector} fails
1100 * @exception SecurityException if a security manager is present and it
1101 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1102 * @throws NullPointerException if any argument is null
1103 */
1104 public
1105 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1106 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1107 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1108 }
1109
1110 /**
1111 * Produces a method handle for a virtual method.
1112 * The type of the method handle will be that of the method,
1113 * with the receiver type (usually {@code refc}) prepended.
1114 * The method and all its argument types must be accessible to the lookup object.
1115 * <p>
1116 * When called, the handle will treat the first argument as a receiver
1117 * and dispatch on the receiver's type to determine which method
1118 * implementation to enter.
1119 * (The dispatching action is identical with that performed by an
1120 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1121 * <p>
1122 * The first argument will be of type {@code refc} if the lookup
1123 * class has full privileges to access the member. Otherwise
1124 * the member must be {@code protected} and the first argument
1125 * will be restricted in type to the lookup class.
1126 * <p>
1127 * The returned method handle will have
1128 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1129 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1130 * <p>
1131 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1132 * instructions and method handles produced by {@code findVirtual},
1133 * if the class is {@code MethodHandle} and the name string is
1134 * {@code invokeExact} or {@code invoke}, the resulting
1135 * method handle is equivalent to one produced by
1136 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1137 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1138 * with the same {@code type} argument.
1139 * <p>
1140 * If the class is {@code VarHandle} and the name string corresponds to
1141 * the name of a signature-polymorphic access mode method, the resulting
1142 * method handle is equivalent to one produced by
1143 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1144 * the access mode corresponding to the name string and with the same
1145 * {@code type} arguments.
1146 * <p>
1147 * <b>Example:</b>
1148 * <blockquote><pre>{@code
1149 import static java.lang.invoke.MethodHandles.*;
1150 import static java.lang.invoke.MethodType.*;
1151 ...
1152 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1153 "concat", methodType(String.class, String.class));
1154 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1155 "hashCode", methodType(int.class));
1156 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1157 "hashCode", methodType(int.class));
1158 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1159 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1160 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1161 // interface method:
1162 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1163 "subSequence", methodType(CharSequence.class, int.class, int.class));
1164 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1165 // constructor "internal method" must be accessed differently:
1166 MethodType MT_newString = methodType(void.class); //()V for new String()
1167 try { assertEquals("impossible", lookup()
1168 .findVirtual(String.class, "<init>", MT_newString));
1169 } catch (NoSuchMethodException ex) { } // OK
1170 MethodHandle MH_newString = publicLookup()
1171 .findConstructor(String.class, MT_newString);
1172 assertEquals("", (String) MH_newString.invokeExact());
1173 * }</pre></blockquote>
1174 *
1175 * @param refc the class or interface from which the method is accessed
1176 * @param name the name of the method
1177 * @param type the type of the method, with the receiver argument omitted
1178 * @return the desired method handle
1179 * @throws NoSuchMethodException if the method does not exist
1180 * @throws IllegalAccessException if access checking fails,
1181 * or if the method is {@code static},
1182 * or if the method is {@code private} method of interface,
1183 * or if the method's variable arity modifier bit
1184 * is set and {@code asVarargsCollector} fails
1185 * @exception SecurityException if a security manager is present and it
1186 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1187 * @throws NullPointerException if any argument is null
1188 */
1189 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1190 if (refc == MethodHandle.class) {
1191 MethodHandle mh = findVirtualForMH(name, type);
1192 if (mh != null) return mh;
1193 } else if (refc == VarHandle.class) {
1194 MethodHandle mh = findVirtualForVH(name, type);
1195 if (mh != null) return mh;
1196 }
1197 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1198 MemberName method = resolveOrFail(refKind, refc, name, type);
1199 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1200 }
1201 private MethodHandle findVirtualForMH(String name, MethodType type) {
1202 // these names require special lookups because of the implicit MethodType argument
1203 if ("invoke".equals(name))
1204 return invoker(type);
1205 if ("invokeExact".equals(name))
1206 return exactInvoker(type);
1207 assert(!MemberName.isMethodHandleInvokeName(name));
1208 return null;
1209 }
1210 private MethodHandle findVirtualForVH(String name, MethodType type) {
1211 try {
1212 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1213 } catch (IllegalArgumentException e) {
1214 return null;
1215 }
1216 }
1217
1218 /**
1219 * Produces a method handle which creates an object and initializes it, using
1220 * the constructor of the specified type.
1221 * The parameter types of the method handle will be those of the constructor,
1222 * while the return type will be a reference to the constructor's class.
1223 * The constructor and all its argument types must be accessible to the lookup object.
1224 * <p>
1225 * The requested type must have a return type of {@code void}.
1226 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1227 * <p>
1228 * The returned method handle will have
1229 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1230 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1231 * <p>
1232 * If the returned method handle is invoked, the constructor's class will
1233 * be initialized, if it has not already been initialized.
1234 * <p><b>Example:</b>
1235 * <blockquote><pre>{@code
1236 import static java.lang.invoke.MethodHandles.*;
1237 import static java.lang.invoke.MethodType.*;
1238 ...
1239 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1240 ArrayList.class, methodType(void.class, Collection.class));
1241 Collection orig = Arrays.asList("x", "y");
1242 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1243 assert(orig != copy);
1244 assertEquals(orig, copy);
1245 // a variable-arity constructor:
1246 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1247 ProcessBuilder.class, methodType(void.class, String[].class));
1248 ProcessBuilder pb = (ProcessBuilder)
1249 MH_newProcessBuilder.invoke("x", "y", "z");
1250 assertEquals("[x, y, z]", pb.command().toString());
1251 * }</pre></blockquote>
1252 * @param refc the class or interface from which the method is accessed
1253 * @param type the type of the method, with the receiver argument omitted, and a void return type
1254 * @return the desired method handle
1255 * @throws NoSuchMethodException if the constructor does not exist
1256 * @throws IllegalAccessException if access checking fails
1257 * or if the method's variable arity modifier bit
1258 * is set and {@code asVarargsCollector} fails
1259 * @exception SecurityException if a security manager is present and it
1260 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1261 * @throws NullPointerException if any argument is null
1262 */
1263 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1264 if (refc.isArray()) {
1265 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1266 }
1267 String name = "<init>";
1268 if (MinimalValueTypes_1_0.isValueType(refc)) {
1269 //shady: The findConstructor method of Lookup will expose all accessible constructors of the original
1270 //value-capable class, for both the Q-type and the legacy L-type. The return type of a method handle produced
1271 //by findConstructor will be identical with the lookup class, even if it is a Q-type.
1272 refc = MinimalValueTypes_1_0.getValueCapableClass(refc);
1273 }
1274 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1275 return getDirectConstructor(refc, ctor);
1276 }
1277
1278 /**
1279 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1280 * initializer of the class is not run.
1281 * <p>
1282 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1283 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1284 * load the requested class, and then determines whether the class is accessible to this lookup object.
1285 *
1286 * @param targetName the fully qualified name of the class to be looked up.
1287 * @return the requested class.
1288 * @exception SecurityException if a security manager is present and it
1289 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1290 * @throws LinkageError if the linkage fails
1291 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1292 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1293 * modes.
1294 * @exception SecurityException if a security manager is present and it
1295 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1296 * @since 9
1297 */
1298 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1299 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1300 return accessClass(targetClass);
1301 }
1302
1303 /**
1304 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1305 * static initializer of the class is not run.
1306 * <p>
1307 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1308 * {@linkplain #lookupModes() lookup modes}.
1309 *
1310 * @param targetClass the class to be access-checked
1311 *
1312 * @return the class that has been access-checked
1313 *
1314 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1315 * modes.
1316 * @exception SecurityException if a security manager is present and it
1317 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1318 * @since 9
1319 */
1320 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1321 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1322 throw new MemberName(targetClass).makeAccessException("access violation", this);
1323 }
1324 checkSecurityManager(targetClass, null);
1325 return targetClass;
1326 }
1327
1328 /**
1329 * Produces an early-bound method handle for a virtual method.
1330 * It will bypass checks for overriding methods on the receiver,
1331 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1332 * instruction from within the explicitly specified {@code specialCaller}.
1333 * The type of the method handle will be that of the method,
1334 * with a suitably restricted receiver type prepended.
1335 * (The receiver type will be {@code specialCaller} or a subtype.)
1336 * The method and all its argument types must be accessible
1337 * to the lookup object.
1338 * <p>
1339 * Before method resolution,
1340 * if the explicitly specified caller class is not identical with the
1341 * lookup class, or if this lookup object does not have
1342 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1343 * privileges, the access fails.
1344 * <p>
1345 * The returned method handle will have
1346 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1347 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1348 * <p style="font-size:smaller;">
1349 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1350 * even though the {@code invokespecial} instruction can refer to them
1351 * in special circumstances. Use {@link #findConstructor findConstructor}
1352 * to access instance initialization methods in a safe manner.)</em>
1353 * <p><b>Example:</b>
1354 * <blockquote><pre>{@code
1355 import static java.lang.invoke.MethodHandles.*;
1356 import static java.lang.invoke.MethodType.*;
1357 ...
1358 static class Listie extends ArrayList {
1359 public String toString() { return "[wee Listie]"; }
1360 static Lookup lookup() { return MethodHandles.lookup(); }
1361 }
1362 ...
1363 // no access to constructor via invokeSpecial:
1364 MethodHandle MH_newListie = Listie.lookup()
1365 .findConstructor(Listie.class, methodType(void.class));
1366 Listie l = (Listie) MH_newListie.invokeExact();
1367 try { assertEquals("impossible", Listie.lookup().findSpecial(
1368 Listie.class, "<init>", methodType(void.class), Listie.class));
1369 } catch (NoSuchMethodException ex) { } // OK
1370 // access to super and self methods via invokeSpecial:
1371 MethodHandle MH_super = Listie.lookup().findSpecial(
1372 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1373 MethodHandle MH_this = Listie.lookup().findSpecial(
1374 Listie.class, "toString" , methodType(String.class), Listie.class);
1375 MethodHandle MH_duper = Listie.lookup().findSpecial(
1376 Object.class, "toString" , methodType(String.class), Listie.class);
1377 assertEquals("[]", (String) MH_super.invokeExact(l));
1378 assertEquals(""+l, (String) MH_this.invokeExact(l));
1379 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1380 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1381 String.class, "toString", methodType(String.class), Listie.class));
1382 } catch (IllegalAccessException ex) { } // OK
1383 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1384 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1385 * }</pre></blockquote>
1386 *
1387 * @param refc the class or interface from which the method is accessed
1388 * @param name the name of the method (which must not be "<init>")
1389 * @param type the type of the method, with the receiver argument omitted
1390 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1391 * @return the desired method handle
1392 * @throws NoSuchMethodException if the method does not exist
1393 * @throws IllegalAccessException if access checking fails,
1394 * or if the method is {@code static},
1395 * or if the method's variable arity modifier bit
1396 * is set and {@code asVarargsCollector} fails
1397 * @exception SecurityException if a security manager is present and it
1398 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1399 * @throws NullPointerException if any argument is null
1400 */
1401 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1402 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1403 checkSpecialCaller(specialCaller, refc);
1404 Lookup specialLookup = this.in(specialCaller);
1405 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1406 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1407 }
1408
1409 /**
1410 * Produces a method handle giving read access to a non-static field.
1411 * The type of the method handle will have a return type of the field's
1412 * value type.
1413 * The method handle's single argument will be the instance containing
1414 * the field.
1415 * Access checking is performed immediately on behalf of the lookup class.
1416 * @param refc the class or interface from which the method is accessed
1417 * @param name the field's name
1418 * @param type the field's type
1419 * @return a method handle which can load values from the field
1420 * @throws NoSuchFieldException if the field does not exist
1421 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1422 * @exception SecurityException if a security manager is present and it
1423 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1424 * @throws NullPointerException if any argument is null
1425 * @see #findVarHandle(Class, String, Class)
1426 */
1427 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1428 if (MinimalValueTypes_1_0.isValueType(refc)) {
1429 return MinimalValueTypes_1_0.findValueType(refc).findGetter(this, name, type);
1430 } else {
1431 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1432 return getDirectField(REF_getField, refc, field);
1433 }
1434 }
1435
1436 /**
1437 * Produces a method handle giving write access to a non-static field.
1438 * The type of the method handle will have a void return type.
1439 * The method handle will take two arguments, the instance containing
1440 * the field, and the value to be stored.
1441 * The second argument will be of the field's value type.
1442 * Access checking is performed immediately on behalf of the lookup class.
1443 * @param refc the class or interface from which the method is accessed
1444 * @param name the field's name
1445 * @param type the field's type
1446 * @return a method handle which can store values into the field
1447 * @throws NoSuchFieldException if the field does not exist
1448 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1449 * @exception SecurityException if a security manager is present and it
1450 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1451 * @throws NullPointerException if any argument is null
1452 * @see #findVarHandle(Class, String, Class)
1453 */
1454 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1455 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1456 return getDirectField(REF_putField, refc, field);
1457 }
1458
1459 /**
1460 * Produces a VarHandle giving access to a non-static field {@code name}
1461 * of type {@code type} declared in a class of type {@code recv}.
1462 * The VarHandle's variable type is {@code type} and it has one
1463 * coordinate type, {@code recv}.
1464 * <p>
1465 * Access checking is performed immediately on behalf of the lookup
1466 * class.
1467 * <p>
1468 * Certain access modes of the returned VarHandle are unsupported under
1469 * the following conditions:
1470 * <ul>
1471 * <li>if the field is declared {@code final}, then the write, atomic
1472 * update, numeric atomic update, and bitwise atomic update access
1473 * modes are unsupported.
1474 * <li>if the field type is anything other than {@code byte},
1475 * {@code short}, {@code char}, {@code int}, {@code long},
1476 * {@code float}, or {@code double} then numeric atomic update
1477 * access modes are unsupported.
1478 * <li>if the field type is anything other than {@code boolean},
1479 * {@code byte}, {@code short}, {@code char}, {@code int} or
1480 * {@code long} then bitwise atomic update access modes are
1481 * unsupported.
1482 * </ul>
1483 * <p>
1484 * If the field is declared {@code volatile} then the returned VarHandle
1485 * will override access to the field (effectively ignore the
1486 * {@code volatile} declaration) in accordance to its specified
1487 * access modes.
1488 * <p>
1489 * If the field type is {@code float} or {@code double} then numeric
1490 * and atomic update access modes compare values using their bitwise
1491 * representation (see {@link Float#floatToRawIntBits} and
1492 * {@link Double#doubleToRawLongBits}, respectively).
1493 * @apiNote
1494 * Bitwise comparison of {@code float} values or {@code double} values,
1495 * as performed by the numeric and atomic update access modes, differ
1496 * from the primitive {@code ==} operator and the {@link Float#equals}
1497 * and {@link Double#equals} methods, specifically with respect to
1498 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1499 * Care should be taken when performing a compare and set or a compare
1500 * and exchange operation with such values since the operation may
1501 * unexpectedly fail.
1502 * There are many possible NaN values that are considered to be
1503 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1504 * provided by Java can distinguish between them. Operation failure can
1505 * occur if the expected or witness value is a NaN value and it is
1506 * transformed (perhaps in a platform specific manner) into another NaN
1507 * value, and thus has a different bitwise representation (see
1508 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1509 * details).
1510 * The values {@code -0.0} and {@code +0.0} have different bitwise
1511 * representations but are considered equal when using the primitive
1512 * {@code ==} operator. Operation failure can occur if, for example, a
1513 * numeric algorithm computes an expected value to be say {@code -0.0}
1514 * and previously computed the witness value to be say {@code +0.0}.
1515 * @param recv the receiver class, of type {@code R}, that declares the
1516 * non-static field
1517 * @param name the field's name
1518 * @param type the field's type, of type {@code T}
1519 * @return a VarHandle giving access to non-static fields.
1520 * @throws NoSuchFieldException if the field does not exist
1521 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1522 * @exception SecurityException if a security manager is present and it
1523 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1524 * @throws NullPointerException if any argument is null
1525 * @since 9
1526 */
1527 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1528 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1529 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1530 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1531 }
1532
1533 /**
1534 * Produces a method handle giving read access to a static field.
1535 * The type of the method handle will have a return type of the field's
1536 * value type.
1537 * The method handle will take no arguments.
1538 * Access checking is performed immediately on behalf of the lookup class.
1539 * <p>
1540 * If the returned method handle is invoked, the field's class will
1541 * be initialized, if it has not already been initialized.
1542 * @param refc the class or interface from which the method is accessed
1543 * @param name the field's name
1544 * @param type the field's type
1545 * @return a method handle which can load values from the field
1546 * @throws NoSuchFieldException if the field does not exist
1547 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1548 * @exception SecurityException if a security manager is present and it
1549 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1550 * @throws NullPointerException if any argument is null
1551 */
1552 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1553 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1554 return getDirectField(REF_getStatic, refc, field);
1555 }
1556
1557 /**
1558 * Produces a method handle giving write access to a static field.
1559 * The type of the method handle will have a void return type.
1560 * The method handle will take a single
1561 * argument, of the field's value type, the value to be stored.
1562 * Access checking is performed immediately on behalf of the lookup class.
1563 * <p>
1564 * If the returned method handle is invoked, the field's class will
1565 * be initialized, if it has not already been initialized.
1566 * @param refc the class or interface from which the method is accessed
1567 * @param name the field's name
1568 * @param type the field's type
1569 * @return a method handle which can store values into the field
1570 * @throws NoSuchFieldException if the field does not exist
1571 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1572 * @exception SecurityException if a security manager is present and it
1573 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1574 * @throws NullPointerException if any argument is null
1575 */
1576 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1577 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1578 return getDirectField(REF_putStatic, refc, field);
1579 }
1580
1581 /**
1582 * Produces a VarHandle giving access to a static field {@code name} of
1583 * type {@code type} declared in a class of type {@code decl}.
1584 * The VarHandle's variable type is {@code type} and it has no
1585 * coordinate types.
1586 * <p>
1587 * Access checking is performed immediately on behalf of the lookup
1588 * class.
1589 * <p>
1590 * If the returned VarHandle is operated on, the declaring class will be
1591 * initialized, if it has not already been initialized.
1592 * <p>
1593 * Certain access modes of the returned VarHandle are unsupported under
1594 * the following conditions:
1595 * <ul>
1596 * <li>if the field is declared {@code final}, then the write, atomic
1597 * update, numeric atomic update, and bitwise atomic update access
1598 * modes are unsupported.
1599 * <li>if the field type is anything other than {@code byte},
1600 * {@code short}, {@code char}, {@code int}, {@code long},
1601 * {@code float}, or {@code double}, then numeric atomic update
1602 * access modes are unsupported.
1603 * <li>if the field type is anything other than {@code boolean},
1604 * {@code byte}, {@code short}, {@code char}, {@code int} or
1605 * {@code long} then bitwise atomic update access modes are
1606 * unsupported.
1607 * </ul>
1608 * <p>
1609 * If the field is declared {@code volatile} then the returned VarHandle
1610 * will override access to the field (effectively ignore the
1611 * {@code volatile} declaration) in accordance to its specified
1612 * access modes.
1613 * <p>
1614 * If the field type is {@code float} or {@code double} then numeric
1615 * and atomic update access modes compare values using their bitwise
1616 * representation (see {@link Float#floatToRawIntBits} and
1617 * {@link Double#doubleToRawLongBits}, respectively).
1618 * @apiNote
1619 * Bitwise comparison of {@code float} values or {@code double} values,
1620 * as performed by the numeric and atomic update access modes, differ
1621 * from the primitive {@code ==} operator and the {@link Float#equals}
1622 * and {@link Double#equals} methods, specifically with respect to
1623 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1624 * Care should be taken when performing a compare and set or a compare
1625 * and exchange operation with such values since the operation may
1626 * unexpectedly fail.
1627 * There are many possible NaN values that are considered to be
1628 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1629 * provided by Java can distinguish between them. Operation failure can
1630 * occur if the expected or witness value is a NaN value and it is
1631 * transformed (perhaps in a platform specific manner) into another NaN
1632 * value, and thus has a different bitwise representation (see
1633 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1634 * details).
1635 * The values {@code -0.0} and {@code +0.0} have different bitwise
1636 * representations but are considered equal when using the primitive
1637 * {@code ==} operator. Operation failure can occur if, for example, a
1638 * numeric algorithm computes an expected value to be say {@code -0.0}
1639 * and previously computed the witness value to be say {@code +0.0}.
1640 * @param decl the class that declares the static field
1641 * @param name the field's name
1642 * @param type the field's type, of type {@code T}
1643 * @return a VarHandle giving access to a static field
1644 * @throws NoSuchFieldException if the field does not exist
1645 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1646 * @exception SecurityException if a security manager is present and it
1647 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1648 * @throws NullPointerException if any argument is null
1649 * @since 9
1650 */
1651 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1652 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1653 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1654 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1655 }
1656
1657 /**
1658 * Produces an early-bound method handle for a non-static method.
1659 * The receiver must have a supertype {@code defc} in which a method
1660 * of the given name and type is accessible to the lookup class.
1661 * The method and all its argument types must be accessible to the lookup object.
1662 * The type of the method handle will be that of the method,
1663 * without any insertion of an additional receiver parameter.
1664 * The given receiver will be bound into the method handle,
1665 * so that every call to the method handle will invoke the
1666 * requested method on the given receiver.
1667 * <p>
1668 * The returned method handle will have
1669 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1670 * the method's variable arity modifier bit ({@code 0x0080}) is set
1671 * <em>and</em> the trailing array argument is not the only argument.
1672 * (If the trailing array argument is the only argument,
1673 * the given receiver value will be bound to it.)
1674 * <p>
1675 * This is almost equivalent to the following code, with some differences noted below:
1676 * <blockquote><pre>{@code
1677 import static java.lang.invoke.MethodHandles.*;
1678 import static java.lang.invoke.MethodType.*;
1679 ...
1680 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1681 MethodHandle mh1 = mh0.bindTo(receiver);
1682 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1683 return mh1;
1684 * }</pre></blockquote>
1685 * where {@code defc} is either {@code receiver.getClass()} or a super
1686 * type of that class, in which the requested method is accessible
1687 * to the lookup class.
1688 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1689 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1690 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1691 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1692 * @param receiver the object from which the method is accessed
1693 * @param name the name of the method
1694 * @param type the type of the method, with the receiver argument omitted
1695 * @return the desired method handle
1696 * @throws NoSuchMethodException if the method does not exist
1697 * @throws IllegalAccessException if access checking fails
1698 * or if the method's variable arity modifier bit
1699 * is set and {@code asVarargsCollector} fails
1700 * @exception SecurityException if a security manager is present and it
1701 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1702 * @throws NullPointerException if any argument is null
1703 * @see MethodHandle#bindTo
1704 * @see #findVirtual
1705 */
1706 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1707 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1708 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1709 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1710 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1711 throw new IllegalAccessException("The restricted defining class " +
1712 mh.type().leadingReferenceParameter().getName() +
1713 " is not assignable from receiver class " +
1714 receiver.getClass().getName());
1715 }
1716 return mh.bindArgumentL(0, receiver).setVarargs(method);
1717 }
1718
1719 /**
1720 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1721 * to <i>m</i>, if the lookup class has permission.
1722 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1723 * If <i>m</i> is virtual, overriding is respected on every call.
1724 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1725 * The type of the method handle will be that of the method,
1726 * with the receiver type prepended (but only if it is non-static).
1727 * If the method's {@code accessible} flag is not set,
1728 * access checking is performed immediately on behalf of the lookup class.
1729 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1730 * <p>
1731 * The returned method handle will have
1732 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1733 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1734 * <p>
1735 * If <i>m</i> is static, and
1736 * if the returned method handle is invoked, the method's class will
1737 * be initialized, if it has not already been initialized.
1738 * @param m the reflected method
1739 * @return a method handle which can invoke the reflected method
1740 * @throws IllegalAccessException if access checking fails
1741 * or if the method's variable arity modifier bit
1742 * is set and {@code asVarargsCollector} fails
1743 * @throws NullPointerException if the argument is null
1744 */
1745 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1746 if (m.getDeclaringClass() == MethodHandle.class) {
1747 MethodHandle mh = unreflectForMH(m);
1748 if (mh != null) return mh;
1749 }
1750 if (m.getDeclaringClass() == VarHandle.class) {
1751 MethodHandle mh = unreflectForVH(m);
1752 if (mh != null) return mh;
1753 }
1754 MemberName method = new MemberName(m);
1755 byte refKind = method.getReferenceKind();
1756 if (refKind == REF_invokeSpecial)
1757 refKind = REF_invokeVirtual;
1758 assert(method.isMethod());
1759 @SuppressWarnings("deprecation")
1760 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1761 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1762 }
1763 private MethodHandle unreflectForMH(Method m) {
1764 // these names require special lookups because they throw UnsupportedOperationException
1765 if (MemberName.isMethodHandleInvokeName(m.getName()))
1766 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1767 return null;
1768 }
1769 private MethodHandle unreflectForVH(Method m) {
1770 // these names require special lookups because they throw UnsupportedOperationException
1771 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1772 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1773 return null;
1774 }
1775
1776 /**
1777 * Produces a method handle for a reflected method.
1778 * It will bypass checks for overriding methods on the receiver,
1779 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1780 * instruction from within the explicitly specified {@code specialCaller}.
1781 * The type of the method handle will be that of the method,
1782 * with a suitably restricted receiver type prepended.
1783 * (The receiver type will be {@code specialCaller} or a subtype.)
1784 * If the method's {@code accessible} flag is not set,
1785 * access checking is performed immediately on behalf of the lookup class,
1786 * as if {@code invokespecial} instruction were being linked.
1787 * <p>
1788 * Before method resolution,
1789 * if the explicitly specified caller class is not identical with the
1790 * lookup class, or if this lookup object does not have
1791 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1792 * privileges, the access fails.
1793 * <p>
1794 * The returned method handle will have
1795 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1796 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1797 * @param m the reflected method
1798 * @param specialCaller the class nominally calling the method
1799 * @return a method handle which can invoke the reflected method
1800 * @throws IllegalAccessException if access checking fails,
1801 * or if the method is {@code static},
1802 * or if the method's variable arity modifier bit
1803 * is set and {@code asVarargsCollector} fails
1804 * @throws NullPointerException if any argument is null
1805 */
1806 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1807 checkSpecialCaller(specialCaller, null);
1808 Lookup specialLookup = this.in(specialCaller);
1809 MemberName method = new MemberName(m, true);
1810 assert(method.isMethod());
1811 // ignore m.isAccessible: this is a new kind of access
1812 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1813 }
1814
1815 /**
1816 * Produces a method handle for a reflected constructor.
1817 * The type of the method handle will be that of the constructor,
1818 * with the return type changed to the declaring class.
1819 * The method handle will perform a {@code newInstance} operation,
1820 * creating a new instance of the constructor's class on the
1821 * arguments passed to the method handle.
1822 * <p>
1823 * If the constructor's {@code accessible} flag is not set,
1824 * access checking is performed immediately on behalf of the lookup class.
1825 * <p>
1826 * The returned method handle will have
1827 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1828 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1829 * <p>
1830 * If the returned method handle is invoked, the constructor's class will
1831 * be initialized, if it has not already been initialized.
1832 * @param c the reflected constructor
1833 * @return a method handle which can invoke the reflected constructor
1834 * @throws IllegalAccessException if access checking fails
1835 * or if the method's variable arity modifier bit
1836 * is set and {@code asVarargsCollector} fails
1837 * @throws NullPointerException if the argument is null
1838 */
1839 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1840 MemberName ctor = new MemberName(c);
1841 assert(ctor.isConstructor());
1842 @SuppressWarnings("deprecation")
1843 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1844 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1845 }
1846
1847 /**
1848 * Produces a method handle giving read access to a reflected field.
1849 * The type of the method handle will have a return type of the field's
1850 * value type.
1851 * If the field is static, the method handle will take no arguments.
1852 * Otherwise, its single argument will be the instance containing
1853 * the field.
1854 * If the field's {@code accessible} flag is not set,
1855 * access checking is performed immediately on behalf of the lookup class.
1856 * <p>
1857 * If the field is static, and
1858 * if the returned method handle is invoked, the field's class will
1859 * be initialized, if it has not already been initialized.
1860 * @param f the reflected field
1861 * @return a method handle which can load values from the reflected field
1862 * @throws IllegalAccessException if access checking fails
1863 * @throws NullPointerException if the argument is null
1864 */
1865 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1866 return unreflectField(f, false);
1867 }
1868 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1869 MemberName field = new MemberName(f, isSetter);
1870 assert(isSetter
1871 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1872 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1873 @SuppressWarnings("deprecation")
1874 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1875 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1876 }
1877
1878 /**
1879 * Produces a method handle giving write access to a reflected field.
1880 * The type of the method handle will have a void return type.
1881 * If the field is static, the method handle will take a single
1882 * argument, of the field's value type, the value to be stored.
1883 * Otherwise, the two arguments will be the instance containing
1884 * the field, and the value to be stored.
1885 * If the field's {@code accessible} flag is not set,
1886 * access checking is performed immediately on behalf of the lookup class.
1887 * <p>
1888 * If the field is static, and
1889 * if the returned method handle is invoked, the field's class will
1890 * be initialized, if it has not already been initialized.
1891 * @param f the reflected field
1892 * @return a method handle which can store values into the reflected field
1893 * @throws IllegalAccessException if access checking fails
1894 * @throws NullPointerException if the argument is null
1895 */
1896 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1897 return unreflectField(f, true);
1898 }
1899
1900 /**
1901 * Produces a VarHandle giving access to a reflected field {@code f}
1902 * of type {@code T} declared in a class of type {@code R}.
1903 * The VarHandle's variable type is {@code T}.
1904 * If the field is non-static the VarHandle has one coordinate type,
1905 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1906 * coordinate types.
1907 * <p>
1908 * Access checking is performed immediately on behalf of the lookup
1909 * class, regardless of the value of the field's {@code accessible}
1910 * flag.
1911 * <p>
1912 * If the field is static, and if the returned VarHandle is operated
1913 * on, the field's declaring class will be initialized, if it has not
1914 * already been initialized.
1915 * <p>
1916 * Certain access modes of the returned VarHandle are unsupported under
1917 * the following conditions:
1918 * <ul>
1919 * <li>if the field is declared {@code final}, then the write, atomic
1920 * update, numeric atomic update, and bitwise atomic update access
1921 * modes are unsupported.
1922 * <li>if the field type is anything other than {@code byte},
1923 * {@code short}, {@code char}, {@code int}, {@code long},
1924 * {@code float}, or {@code double} then numeric atomic update
1925 * access modes are unsupported.
1926 * <li>if the field type is anything other than {@code boolean},
1927 * {@code byte}, {@code short}, {@code char}, {@code int} or
1928 * {@code long} then bitwise atomic update access modes are
1929 * unsupported.
1930 * </ul>
1931 * <p>
1932 * If the field is declared {@code volatile} then the returned VarHandle
1933 * will override access to the field (effectively ignore the
1934 * {@code volatile} declaration) in accordance to its specified
1935 * access modes.
1936 * <p>
1937 * If the field type is {@code float} or {@code double} then numeric
1938 * and atomic update access modes compare values using their bitwise
1939 * representation (see {@link Float#floatToRawIntBits} and
1940 * {@link Double#doubleToRawLongBits}, respectively).
1941 * @apiNote
1942 * Bitwise comparison of {@code float} values or {@code double} values,
1943 * as performed by the numeric and atomic update access modes, differ
1944 * from the primitive {@code ==} operator and the {@link Float#equals}
1945 * and {@link Double#equals} methods, specifically with respect to
1946 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1947 * Care should be taken when performing a compare and set or a compare
1948 * and exchange operation with such values since the operation may
1949 * unexpectedly fail.
1950 * There are many possible NaN values that are considered to be
1951 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1952 * provided by Java can distinguish between them. Operation failure can
1953 * occur if the expected or witness value is a NaN value and it is
1954 * transformed (perhaps in a platform specific manner) into another NaN
1955 * value, and thus has a different bitwise representation (see
1956 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1957 * details).
1958 * The values {@code -0.0} and {@code +0.0} have different bitwise
1959 * representations but are considered equal when using the primitive
1960 * {@code ==} operator. Operation failure can occur if, for example, a
1961 * numeric algorithm computes an expected value to be say {@code -0.0}
1962 * and previously computed the witness value to be say {@code +0.0}.
1963 * @param f the reflected field, with a field of type {@code T}, and
1964 * a declaring class of type {@code R}
1965 * @return a VarHandle giving access to non-static fields or a static
1966 * field
1967 * @throws IllegalAccessException if access checking fails
1968 * @throws NullPointerException if the argument is null
1969 * @since 9
1970 */
1971 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1972 MemberName getField = new MemberName(f, false);
1973 MemberName putField = new MemberName(f, true);
1974 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1975 f.getDeclaringClass(), getField, putField);
1976 }
1977
1978 /**
1979 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1980 * created by this lookup object or a similar one.
1981 * Security and access checks are performed to ensure that this lookup object
1982 * is capable of reproducing the target method handle.
1983 * This means that the cracking may fail if target is a direct method handle
1984 * but was created by an unrelated lookup object.
1985 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1986 * and was created by a lookup object for a different class.
1987 * @param target a direct method handle to crack into symbolic reference components
1988 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1989 * @exception SecurityException if a security manager is present and it
1990 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1991 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1992 * @exception NullPointerException if the target is {@code null}
1993 * @see MethodHandleInfo
1994 * @since 1.8
1995 */
1996 public MethodHandleInfo revealDirect(MethodHandle target) {
1997 MemberName member = target.internalMemberName();
1998 if (member == null || (!member.isResolved() &&
1999 !member.isMethodHandleInvoke() &&
2000 !member.isVarHandleMethodInvoke()))
2001 throw newIllegalArgumentException("not a direct method handle");
2002 Class<?> defc = member.getDeclaringClass();
2003 byte refKind = member.getReferenceKind();
2004 assert(MethodHandleNatives.refKindIsValid(refKind));
2005 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2006 // Devirtualized method invocation is usually formally virtual.
2007 // To avoid creating extra MemberName objects for this common case,
2008 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2009 refKind = REF_invokeVirtual;
2010 if (refKind == REF_invokeVirtual && defc.isInterface())
2011 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2012 refKind = REF_invokeInterface;
2013 // Check SM permissions and member access before cracking.
2014 try {
2015 checkAccess(refKind, defc, member);
2016 checkSecurityManager(defc, member);
2017 } catch (IllegalAccessException ex) {
2018 throw new IllegalArgumentException(ex);
2019 }
2020 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2021 Class<?> callerClass = target.internalCallerClass();
2022 if (!hasPrivateAccess() || callerClass != lookupClass())
2023 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2024 }
2025 // Produce the handle to the results.
2026 return new InfoFromMemberName(this, member, refKind);
2027 }
2028
2029 /// Helper methods, all package-private.
2030
2031 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2032 checkSymbolicClass(refc); // do this before attempting to resolve
2033 Objects.requireNonNull(name);
2034 Objects.requireNonNull(type);
2035 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2036 NoSuchFieldException.class);
2037 }
2038
2039 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2040 checkSymbolicClass(refc); // do this before attempting to resolve
2041 Objects.requireNonNull(name);
2042 Objects.requireNonNull(type);
2043 checkMethodName(refKind, name); // NPE check on name
2044 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2045 NoSuchMethodException.class);
2046 }
2047
2048 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2049 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2050 Objects.requireNonNull(member.getName());
2051 Objects.requireNonNull(member.getType());
2052 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2053 ReflectiveOperationException.class);
2054 }
2055
2056 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2057 Objects.requireNonNull(refc);
2058 Class<?> caller = lookupClassOrNull();
2059 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
2060 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2061 }
2062
2063 /** Check name for an illegal leading "<" character. */
2064 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2065 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2066 throw new NoSuchMethodException("illegal method name: "+name);
2067 }
2068
2069
2070 /**
2071 * Find my trustable caller class if m is a caller sensitive method.
2072 * If this lookup object has private access, then the caller class is the lookupClass.
2073 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2074 */
2075 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2076 Class<?> callerClass = null;
2077 if (MethodHandleNatives.isCallerSensitive(m)) {
2078 // Only lookups with private access are allowed to resolve caller-sensitive methods
2079 if (hasPrivateAccess()) {
2080 callerClass = lookupClass;
2081 } else {
2082 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2083 }
2084 }
2085 return callerClass;
2086 }
2087
2088 /**
2089 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2090 * @return {@code true} if this lookup has {@code PRIVATE} access.
2091 * @since 9
2092 */
2093 public boolean hasPrivateAccess() {
2094 return (allowedModes & PRIVATE) != 0;
2095 }
2096
2097 /**
2098 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2099 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2100 * If this lookup object has private access, then the caller class is the lookupClass.
2101 */
2102 void checkSecurityManager(Class<?> refc, MemberName m) {
2103 SecurityManager smgr = System.getSecurityManager();
2104 if (smgr == null) return;
2105 if (allowedModes == TRUSTED) return;
2106
2107 // Step 1:
2108 boolean fullPowerLookup = hasPrivateAccess();
2109 if (!fullPowerLookup ||
2110 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2111 ReflectUtil.checkPackageAccess(refc);
2112 }
2113
2114 if (m == null) { // findClass or accessClass
2115 // Step 2b:
2116 if (!fullPowerLookup) {
2117 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2118 }
2119 return;
2120 }
2121
2122 // Step 2a:
2123 if (m.isPublic()) return;
2124 if (!fullPowerLookup) {
2125 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2126 }
2127
2128 // Step 3:
2129 Class<?> defc = m.getDeclaringClass();
2130 if (!fullPowerLookup && defc != refc) {
2131 ReflectUtil.checkPackageAccess(defc);
2132 }
2133 }
2134
2135 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2136 boolean wantStatic = (refKind == REF_invokeStatic);
2137 String message;
2138 if (m.isConstructor())
2139 message = "expected a method, not a constructor";
2140 else if (!m.isMethod())
2141 message = "expected a method";
2142 else if (wantStatic != m.isStatic())
2143 message = wantStatic ? "expected a static method" : "expected a non-static method";
2144 else
2145 { checkAccess(refKind, refc, m); return; }
2146 throw m.makeAccessException(message, this);
2147 }
2148
2149 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2150 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2151 String message;
2152 if (wantStatic != m.isStatic())
2153 message = wantStatic ? "expected a static field" : "expected a non-static field";
2154 else
2155 { checkAccess(refKind, refc, m); return; }
2156 throw m.makeAccessException(message, this);
2157 }
2158
2159 /** Check public/protected/private bits on the symbolic reference class and its member. */
2160 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2161 assert(m.referenceKindIsConsistentWith(refKind) &&
2162 MethodHandleNatives.refKindIsValid(refKind) &&
2163 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2164 int allowedModes = this.allowedModes;
2165 if (allowedModes == TRUSTED) return;
2166 int mods = m.getModifiers();
2167 if (Modifier.isProtected(mods) &&
2168 refKind == REF_invokeVirtual &&
2169 m.getDeclaringClass() == Object.class &&
2170 m.getName().equals("clone") &&
2171 refc.isArray()) {
2172 // The JVM does this hack also.
2173 // (See ClassVerifier::verify_invoke_instructions
2174 // and LinkResolver::check_method_accessability.)
2175 // Because the JVM does not allow separate methods on array types,
2176 // there is no separate method for int[].clone.
2177 // All arrays simply inherit Object.clone.
2178 // But for access checking logic, we make Object.clone
2179 // (normally protected) appear to be public.
2180 // Later on, when the DirectMethodHandle is created,
2181 // its leading argument will be restricted to the
2182 // requested array type.
2183 // N.B. The return type is not adjusted, because
2184 // that is *not* the bytecode behavior.
2185 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2186 }
2187 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2188 // cannot "new" a protected ctor in a different package
2189 mods ^= Modifier.PROTECTED;
2190 }
2191 if (Modifier.isFinal(mods) &&
2192 MethodHandleNatives.refKindIsSetter(refKind))
2193 throw m.makeAccessException("unexpected set of a final field", this);
2194 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2195 if ((requestedModes & allowedModes) != 0) {
2196 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2197 mods, lookupClass(), allowedModes))
2198 return;
2199 } else {
2200 // Protected members can also be checked as if they were package-private.
2201 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2202 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2203 return;
2204 }
2205 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2206 }
2207
2208 String accessFailedMessage(Class<?> refc, MemberName m) {
2209 Class<?> defc = m.getDeclaringClass();
2210 int mods = m.getModifiers();
2211 // check the class first:
2212 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2213 (defc == refc ||
2214 Modifier.isPublic(refc.getModifiers())));
2215 if (!classOK && (allowedModes & PACKAGE) != 0) {
2216 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2217 (defc == refc ||
2218 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2219 }
2220 if (!classOK)
2221 return "class is not public";
2222 if (Modifier.isPublic(mods))
2223 return "access to public member failed"; // (how?, module not readable?)
2224 if (Modifier.isPrivate(mods))
2225 return "member is private";
2226 if (Modifier.isProtected(mods))
2227 return "member is protected";
2228 return "member is private to package";
2229 }
2230
2231 private static final boolean ALLOW_NESTMATE_ACCESS = false;
2232
2233 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2234 int allowedModes = this.allowedModes;
2235 if (allowedModes == TRUSTED) return;
2236 if (!hasPrivateAccess()
2237 || (specialCaller != lookupClass()
2238 // ensure non-abstract methods in superinterfaces can be special-invoked
2239 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2240 && !(ALLOW_NESTMATE_ACCESS &&
2241 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2242 throw new MemberName(specialCaller).
2243 makeAccessException("no private access for invokespecial", this);
2244 }
2245
2246 private boolean restrictProtectedReceiver(MemberName method) {
2247 // The accessing class only has the right to use a protected member
2248 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2249 if (!method.isProtected() || method.isStatic()
2250 || allowedModes == TRUSTED
2251 || method.getDeclaringClass() == lookupClass()
2252 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2253 || (ALLOW_NESTMATE_ACCESS &&
2254 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2255 return false;
2256 return true;
2257 }
2258 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2259 assert(!method.isStatic());
2260 // receiver type of mh is too wide; narrow to caller
2261 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2262 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2263 }
2264 MethodType rawType = mh.type();
2265 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2266 MethodType narrowType = rawType.changeParameterType(0, caller);
2267 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2268 assert(mh.viewAsTypeChecks(narrowType, true));
2269 return mh.copyWith(narrowType, mh.form);
2270 }
2271
2272 /** Check access and get the requested method. */
2273 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2274 final boolean doRestrict = true;
2275 final boolean checkSecurity = true;
2276 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2277 }
2278 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2279 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2280 final boolean doRestrict = false;
2281 final boolean checkSecurity = true;
2282 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerClass);
2283 }
2284 /** Check access and get the requested method, eliding security manager checks. */
2285 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2286 final boolean doRestrict = true;
2287 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2288 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2289 }
2290 /** Common code for all methods; do not call directly except from immediately above. */
2291 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2292 boolean checkSecurity,
2293 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2294 checkMethod(refKind, refc, method);
2295 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2296 if (checkSecurity)
2297 checkSecurityManager(refc, method);
2298 assert(!method.isMethodHandleInvoke());
2299
2300 if (refKind == REF_invokeSpecial &&
2301 refc != lookupClass() &&
2302 !refc.isInterface() &&
2303 refc != lookupClass().getSuperclass() &&
2304 refc.isAssignableFrom(lookupClass())) {
2305 assert(!method.getName().equals("<init>")); // not this code path
2306 // Per JVMS 6.5, desc. of invokespecial instruction:
2307 // If the method is in a superclass of the LC,
2308 // and if our original search was above LC.super,
2309 // repeat the search (symbolic lookup) from LC.super
2310 // and continue with the direct superclass of that class,
2311 // and so forth, until a match is found or no further superclasses exist.
2312 // FIXME: MemberName.resolve should handle this instead.
2313 Class<?> refcAsSuper = lookupClass();
2314 MemberName m2;
2315 do {
2316 refcAsSuper = refcAsSuper.getSuperclass();
2317 m2 = new MemberName(refcAsSuper,
2318 method.getName(),
2319 method.getMethodType(),
2320 REF_invokeSpecial);
2321 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2322 } while (m2 == null && // no method is found yet
2323 refc != refcAsSuper); // search up to refc
2324 if (m2 == null) throw new InternalError(method.toString());
2325 method = m2;
2326 refc = refcAsSuper;
2327 // redo basic checks
2328 checkMethod(refKind, refc, method);
2329 }
2330
2331 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2332 MethodHandle mh = dmh;
2333 // Optionally narrow the receiver argument to refc using restrictReceiver.
2334 if ((doRestrict && refKind == REF_invokeSpecial) ||
2335 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2336 mh = restrictReceiver(method, dmh, lookupClass());
2337 }
2338 mh = maybeBindCaller(method, mh, callerClass);
2339 mh = mh.setVarargs(method);
2340 return mh;
2341 }
2342 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2343 Class<?> callerClass)
2344 throws IllegalAccessException {
2345 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2346 return mh;
2347 Class<?> hostClass = lookupClass;
2348 if (!hasPrivateAccess()) // caller must have private access
2349 hostClass = callerClass; // callerClass came from a security manager style stack walk
2350 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2351 // Note: caller will apply varargs after this step happens.
2352 return cbmh;
2353 }
2354 /** Check access and get the requested field. */
2355 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2356 final boolean checkSecurity = true;
2357 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2358 }
2359 /** Check access and get the requested field, eliding security manager checks. */
2360 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2361 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2362 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2363 }
2364 /** Common code for all fields; do not call directly except from immediately above. */
2365 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2366 boolean checkSecurity) throws IllegalAccessException {
2367 checkField(refKind, refc, field);
2368 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2369 if (checkSecurity)
2370 checkSecurityManager(refc, field);
2371 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2372 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2373 restrictProtectedReceiver(field));
2374 if (doRestrict)
2375 return restrictReceiver(field, dmh, lookupClass());
2376 return dmh;
2377 }
2378 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2379 Class<?> refc, MemberName getField, MemberName putField)
2380 throws IllegalAccessException {
2381 final boolean checkSecurity = true;
2382 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2383 }
2384 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2385 Class<?> refc, MemberName getField, MemberName putField)
2386 throws IllegalAccessException {
2387 final boolean checkSecurity = false;
2388 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2389 }
2390 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2391 Class<?> refc, MemberName getField, MemberName putField,
2392 boolean checkSecurity) throws IllegalAccessException {
2393 assert getField.isStatic() == putField.isStatic();
2394 assert getField.isGetter() && putField.isSetter();
2395 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2396 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2397
2398 checkField(getRefKind, refc, getField);
2399 if (checkSecurity)
2400 checkSecurityManager(refc, getField);
2401
2402 if (!putField.isFinal()) {
2403 // A VarHandle does not support updates to final fields, any
2404 // such VarHandle to a final field will be read-only and
2405 // therefore the following write-based accessibility checks are
2406 // only required for non-final fields
2407 checkField(putRefKind, refc, putField);
2408 if (checkSecurity)
2409 checkSecurityManager(refc, putField);
2410 }
2411
2412 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2413 restrictProtectedReceiver(getField));
2414 if (doRestrict) {
2415 assert !getField.isStatic();
2416 // receiver type of VarHandle is too wide; narrow to caller
2417 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2418 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2419 }
2420 refc = lookupClass();
2421 }
2422 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2423 }
2424 /** Check access and get the requested constructor. */
2425 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2426 final boolean checkSecurity = true;
2427 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2428 }
2429 /** Check access and get the requested constructor, eliding security manager checks. */
2430 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2431 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2432 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2433 }
2434 /** Common code for all constructors; do not call directly except from immediately above. */
2435 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2436 boolean checkSecurity) throws IllegalAccessException {
2437 assert(ctor.isConstructor());
2438 checkAccess(REF_newInvokeSpecial, refc, ctor);
2439 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2440 if (checkSecurity)
2441 checkSecurityManager(refc, ctor);
2442 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2443 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2444 }
2445
2446 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2447 */
2448 /*non-public*/
2449 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2450 if (!(type instanceof Class || type instanceof MethodType))
2451 throw new InternalError("unresolved MemberName");
2452 MemberName member = new MemberName(refKind, defc, name, type);
2453 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2454 if (mh != null) {
2455 checkSymbolicClass(defc);
2456 return mh;
2457 }
2458 // Treat MethodHandle.invoke and invokeExact specially.
2459 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2460 mh = findVirtualForMH(member.getName(), member.getMethodType());
2461 if (mh != null) {
2462 return mh;
2463 }
2464 }
2465 MemberName resolved = resolveOrFail(refKind, member);
2466 mh = getDirectMethodForConstant(refKind, defc, resolved);
2467 if (mh instanceof DirectMethodHandle
2468 && canBeCached(refKind, defc, resolved)) {
2469 MemberName key = mh.internalMemberName();
2470 if (key != null) {
2471 key = key.asNormalOriginal();
2472 }
2473 if (member.equals(key)) { // better safe than sorry
2474 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2475 }
2476 }
2477 return mh;
2478 }
2479 private
2480 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2481 if (refKind == REF_invokeSpecial) {
2482 return false;
2483 }
2484 if (!Modifier.isPublic(defc.getModifiers()) ||
2485 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2486 !member.isPublic() ||
2487 member.isCallerSensitive()) {
2488 return false;
2489 }
2490 ClassLoader loader = defc.getClassLoader();
2491 if (loader != null) {
2492 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2493 boolean found = false;
2494 while (sysl != null) {
2495 if (loader == sysl) { found = true; break; }
2496 sysl = sysl.getParent();
2497 }
2498 if (!found) {
2499 return false;
2500 }
2501 }
2502 try {
2503 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2504 new MemberName(refKind, defc, member.getName(), member.getType()));
2505 checkSecurityManager(defc, resolved2);
2506 } catch (ReflectiveOperationException | 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 * The return type of the method handle will be the array type.
2531 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2532 * @param arrayClass an array type
2533 * @return a method handle which can create arrays of the given type
2534 * @throws NullPointerException if the argument is {@code null}
2535 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2536 * @see java.lang.reflect.Array#newInstance(Class, int)
2537 * @since 9
2538 */
2539 public static
2540 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2541 ValueTypeHolder<?> compValue = valueComponent(arrayClass);
2542 if (compValue != null) {
2543 return compValue.newArray();
2544 } else {
2545 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2546 bindTo(arrayClass.getComponentType());
2547 return ani.asType(ani.type().changeReturnType(arrayClass));
2548 }
2549 }
2550
2551 /**
2552 * Produces a method handle returning the length of an array.
2553 * The type of the method handle will have {@code int} as return type,
2554 * and its sole argument will be the array type.
2555 * @param arrayClass an array type
2556 * @return a method handle which can retrieve the length of an array of the given array type
2557 * @throws NullPointerException if the argument is {@code null}
2558 * @throws IllegalArgumentException if arrayClass is not an array type
2559 * @since 9
2560 */
2561 public static
2562 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2563 ValueTypeHolder<?> compValue = valueComponent(arrayClass);
2564 return (compValue != null) ?
2565 compValue.arrayLength() :
2566 MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2567 }
2568
2569 /**
2570 * Produces a method handle giving read access to elements of an array.
2571 * The type of the method handle will have a return type of the array's
2572 * element type. Its first argument will be the array type,
2573 * and the second will be {@code int}.
2574 * @param arrayClass an array type
2575 * @return a method handle which can load values from the given array type
2576 * @throws NullPointerException if the argument is null
2577 * @throws IllegalArgumentException if arrayClass is not an array type
2578 */
2579 public static
2580 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2581 ValueTypeHolder<?> compValue = valueComponent(arrayClass);
2582 return (compValue != null) ?
2583 compValue.arrayGetter() :
2584 MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2585 }
2586
2587 /**
2588 * Produces a method handle giving write access to elements of an array.
2589 * The type of the method handle will have a void return type.
2590 * Its last argument will be the array's element type.
2591 * The first and second arguments will be the array type and int.
2592 * @param arrayClass the class of an array
2593 * @return a method handle which can store values into the array type
2594 * @throws NullPointerException if the argument is null
2595 * @throws IllegalArgumentException if arrayClass is not an array type
2596 */
2597 public static
2598 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2599 ValueTypeHolder<?> compValue = valueComponent(arrayClass);
2600 return (compValue != null) ?
2601 compValue.arraySetter() :
2602 MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2603 }
2604
2605 @SuppressWarnings("unchecked")
2606 private static <Z> ValueTypeHolder<Z> valueComponent(Class<Z> arrayClass) {
2607 if (!arrayClass.isArray()) {
2608 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2609 }
2610
2611 Class<?> comp = arrayClass.getComponentType();
2612 if (MinimalValueTypes_1_0.isValueType(comp)) {
2613 return (ValueTypeHolder<Z>) MinimalValueTypes_1_0.findValueType(comp);
2614 } else {
2615 return null;
2616 }
2617 }
2618
2619 /**
2620 * Produces a VarHandle giving access to elements of an array of type
2621 * {@code arrayClass}. The VarHandle's variable type is the component type
2622 * of {@code arrayClass} and the list of coordinate types is
2623 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2624 * corresponds to an argument that is an index into an array.
2625 * <p>
2626 * Certain access modes of the returned VarHandle are unsupported under
2627 * the following conditions:
2628 * <ul>
2629 * <li>if the component type is anything other than {@code byte},
2630 * {@code short}, {@code char}, {@code int}, {@code long},
2631 * {@code float}, or {@code double} then numeric atomic update access
2632 * modes are unsupported.
2633 * <li>if the field type is anything other than {@code boolean},
2634 * {@code byte}, {@code short}, {@code char}, {@code int} or
2635 * {@code long} then bitwise atomic update access modes are
2636 * unsupported.
2637 * </ul>
2638 * <p>
2639 * If the component type is {@code float} or {@code double} then numeric
2640 * and atomic update access modes compare values using their bitwise
2641 * representation (see {@link Float#floatToRawIntBits} and
2642 * {@link Double#doubleToRawLongBits}, respectively).
2643 * @apiNote
2644 * Bitwise comparison of {@code float} values or {@code double} values,
2645 * as performed by the numeric and atomic update access modes, differ
2646 * from the primitive {@code ==} operator and the {@link Float#equals}
2647 * and {@link Double#equals} methods, specifically with respect to
2648 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2649 * Care should be taken when performing a compare and set or a compare
2650 * and exchange operation with such values since the operation may
2651 * unexpectedly fail.
2652 * There are many possible NaN values that are considered to be
2653 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2654 * provided by Java can distinguish between them. Operation failure can
2655 * occur if the expected or witness value is a NaN value and it is
2656 * transformed (perhaps in a platform specific manner) into another NaN
2657 * value, and thus has a different bitwise representation (see
2658 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2659 * details).
2660 * The values {@code -0.0} and {@code +0.0} have different bitwise
2661 * representations but are considered equal when using the primitive
2662 * {@code ==} operator. Operation failure can occur if, for example, a
2663 * numeric algorithm computes an expected value to be say {@code -0.0}
2664 * and previously computed the witness value to be say {@code +0.0}.
2665 * @param arrayClass the class of an array, of type {@code T[]}
2666 * @return a VarHandle giving access to elements of an array
2667 * @throws NullPointerException if the arrayClass is null
2668 * @throws IllegalArgumentException if arrayClass is not an array type
2669 * @since 9
2670 */
2671 public static
2672 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2673 return VarHandles.makeArrayElementHandle(arrayClass);
2674 }
2675
2676 /**
2677 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2678 * viewed as if it were a different primitive array type, such as
2679 * {@code int[]} or {@code long[]}.
2680 * The VarHandle's variable type is the component type of
2681 * {@code viewArrayClass} and the list of coordinate types is
2682 * {@code (byte[], int)}, where the {@code int} coordinate type
2683 * corresponds to an argument that is an index into a {@code byte[]} array.
2684 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2685 * array, composing bytes to or from a value of the component type of
2686 * {@code viewArrayClass} according to the given endianness.
2687 * <p>
2688 * The supported component types (variables types) are {@code short},
2689 * {@code char}, {@code int}, {@code long}, {@code float} and
2690 * {@code double}.
2691 * <p>
2692 * Access of bytes at a given index will result in an
2693 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2694 * or greater than the {@code byte[]} array length minus the size (in bytes)
2695 * of {@code T}.
2696 * <p>
2697 * Access of bytes at an index may be aligned or misaligned for {@code T},
2698 * with respect to the underlying memory address, {@code A} say, associated
2699 * with the array and index.
2700 * If access is misaligned then access for anything other than the
2701 * {@code get} and {@code set} access modes will result in an
2702 * {@code IllegalStateException}. In such cases atomic access is only
2703 * guaranteed with respect to the largest power of two that divides the GCD
2704 * of {@code A} and the size (in bytes) of {@code T}.
2705 * If access is aligned then following access modes are supported and are
2706 * guaranteed to support atomic access:
2707 * <ul>
2708 * <li>read write access modes for all {@code T}, with the exception of
2709 * access modes {@code get} and {@code set} for {@code long} and
2710 * {@code double} on 32-bit platforms.
2711 * <li>atomic update access modes for {@code int}, {@code long},
2712 * {@code float} or {@code double}.
2713 * (Future major platform releases of the JDK may support additional
2714 * types for certain currently unsupported access modes.)
2715 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2716 * (Future major platform releases of the JDK may support additional
2717 * numeric types for certain currently unsupported access modes.)
2718 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2719 * (Future major platform releases of the JDK may support additional
2720 * numeric types for certain currently unsupported access modes.)
2721 * </ul>
2722 * <p>
2723 * Misaligned access, and therefore atomicity guarantees, may be determined
2724 * for {@code byte[]} arrays without operating on a specific array. Given
2725 * an {@code index}, {@code T} and it's corresponding boxed type,
2726 * {@code T_BOX}, misalignment may be determined as follows:
2727 * <pre>{@code
2728 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2729 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2730 * alignmentOffset(0, sizeOfT);
2731 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2732 * boolean isMisaligned = misalignedAtIndex != 0;
2733 * }</pre>
2734 * <p>
2735 * If the variable type is {@code float} or {@code double} then atomic
2736 * update access modes compare values using their bitwise representation
2737 * (see {@link Float#floatToRawIntBits} and
2738 * {@link Double#doubleToRawLongBits}, respectively).
2739 * @param viewArrayClass the view array class, with a component type of
2740 * type {@code T}
2741 * @param byteOrder the endianness of the view array elements, as
2742 * stored in the underlying {@code byte} array
2743 * @return a VarHandle giving access to elements of a {@code byte[]} array
2744 * viewed as if elements corresponding to the components type of the view
2745 * array class
2746 * @throws NullPointerException if viewArrayClass or byteOrder is null
2747 * @throws IllegalArgumentException if viewArrayClass is not an array type
2748 * @throws UnsupportedOperationException if the component type of
2749 * viewArrayClass is not supported as a variable type
2750 * @since 9
2751 */
2752 public static
2753 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2754 ByteOrder byteOrder) throws IllegalArgumentException {
2755 Objects.requireNonNull(byteOrder);
2756 return VarHandles.byteArrayViewHandle(viewArrayClass,
2757 byteOrder == ByteOrder.BIG_ENDIAN);
2758 }
2759
2760 /**
2761 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2762 * viewed as if it were an array of elements of a different primitive
2763 * component type to that of {@code byte}, such as {@code int[]} or
2764 * {@code long[]}.
2765 * The VarHandle's variable type is the component type of
2766 * {@code viewArrayClass} and the list of coordinate types is
2767 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2768 * corresponds to an argument that is an index into a {@code byte[]} array.
2769 * The returned VarHandle accesses bytes at an index in a
2770 * {@code ByteBuffer}, composing bytes to or from a value of the component
2771 * type of {@code viewArrayClass} according to the given endianness.
2772 * <p>
2773 * The supported component types (variables types) are {@code short},
2774 * {@code char}, {@code int}, {@code long}, {@code float} and
2775 * {@code double}.
2776 * <p>
2777 * Access will result in a {@code ReadOnlyBufferException} for anything
2778 * other than the read access modes if the {@code ByteBuffer} is read-only.
2779 * <p>
2780 * Access of bytes at a given index will result in an
2781 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2782 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2783 * {@code T}.
2784 * <p>
2785 * Access of bytes at an index may be aligned or misaligned for {@code T},
2786 * with respect to the underlying memory address, {@code A} say, associated
2787 * with the {@code ByteBuffer} and index.
2788 * If access is misaligned then access for anything other than the
2789 * {@code get} and {@code set} access modes will result in an
2790 * {@code IllegalStateException}. In such cases atomic access is only
2791 * guaranteed with respect to the largest power of two that divides the GCD
2792 * of {@code A} and the size (in bytes) of {@code T}.
2793 * If access is aligned then following access modes are supported and are
2794 * guaranteed to support atomic access:
2795 * <ul>
2796 * <li>read write access modes for all {@code T}, with the exception of
2797 * access modes {@code get} and {@code set} for {@code long} and
2798 * {@code double} on 32-bit platforms.
2799 * <li>atomic update access modes for {@code int}, {@code long},
2800 * {@code float} or {@code double}.
2801 * (Future major platform releases of the JDK may support additional
2802 * types for certain currently unsupported access modes.)
2803 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2804 * (Future major platform releases of the JDK may support additional
2805 * numeric types for certain currently unsupported access modes.)
2806 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2807 * (Future major platform releases of the JDK may support additional
2808 * numeric types for certain currently unsupported access modes.)
2809 * </ul>
2810 * <p>
2811 * Misaligned access, and therefore atomicity guarantees, may be determined
2812 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2813 * {@code index}, {@code T} and it's corresponding boxed type,
2814 * {@code T_BOX}, as follows:
2815 * <pre>{@code
2816 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2817 * ByteBuffer bb = ...
2818 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2819 * boolean isMisaligned = misalignedAtIndex != 0;
2820 * }</pre>
2821 * <p>
2822 * If the variable type is {@code float} or {@code double} then atomic
2823 * update access modes compare values using their bitwise representation
2824 * (see {@link Float#floatToRawIntBits} and
2825 * {@link Double#doubleToRawLongBits}, respectively).
2826 * @param viewArrayClass the view array class, with a component type of
2827 * type {@code T}
2828 * @param byteOrder the endianness of the view array elements, as
2829 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2830 * endianness of a {@code ByteBuffer})
2831 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2832 * viewed as if elements corresponding to the components type of the view
2833 * array class
2834 * @throws NullPointerException if viewArrayClass or byteOrder is null
2835 * @throws IllegalArgumentException if viewArrayClass is not an array type
2836 * @throws UnsupportedOperationException if the component type of
2837 * viewArrayClass is not supported as a variable type
2838 * @since 9
2839 */
2840 public static
2841 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2842 ByteOrder byteOrder) throws IllegalArgumentException {
2843 Objects.requireNonNull(byteOrder);
2844 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2845 byteOrder == ByteOrder.BIG_ENDIAN);
2846 }
2847
2848
2849 /// method handle invocation (reflective style)
2850
2851 /**
2852 * Produces a method handle which will invoke any method handle of the
2853 * given {@code type}, with a given number of trailing arguments replaced by
2854 * a single trailing {@code Object[]} array.
2855 * The resulting invoker will be a method handle with the following
2856 * arguments:
2857 * <ul>
2858 * <li>a single {@code MethodHandle} target
2859 * <li>zero or more leading values (counted by {@code leadingArgCount})
2860 * <li>an {@code Object[]} array containing trailing arguments
2861 * </ul>
2862 * <p>
2863 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2864 * the indicated {@code type}.
2865 * That is, if the target is exactly of the given {@code type}, it will behave
2866 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2867 * is used to convert the target to the required {@code type}.
2868 * <p>
2869 * The type of the returned invoker will not be the given {@code type}, but rather
2870 * will have all parameters except the first {@code leadingArgCount}
2871 * replaced by a single array of type {@code Object[]}, which will be
2872 * the final parameter.
2873 * <p>
2874 * Before invoking its target, the invoker will spread the final array, apply
2875 * reference casts as necessary, and unbox and widen primitive arguments.
2876 * If, when the invoker is called, the supplied array argument does
2877 * not have the correct number of elements, the invoker will throw
2878 * an {@link IllegalArgumentException} instead of invoking the target.
2879 * <p>
2880 * This method is equivalent to the following code (though it may be more efficient):
2881 * <blockquote><pre>{@code
2882 MethodHandle invoker = MethodHandles.invoker(type);
2883 int spreadArgCount = type.parameterCount() - leadingArgCount;
2884 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2885 return invoker;
2886 * }</pre></blockquote>
2887 * This method throws no reflective or security exceptions.
2888 * @param type the desired target type
2889 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2890 * @return a method handle suitable for invoking any method handle of the given type
2891 * @throws NullPointerException if {@code type} is null
2892 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2893 * the range from 0 to {@code type.parameterCount()} inclusive,
2894 * or if the resulting method handle's type would have
2895 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2896 */
2897 public static
2898 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2899 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2900 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2901 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2902 return type.invokers().spreadInvoker(leadingArgCount);
2903 }
2904
2905 /**
2906 * Produces a special <em>invoker method handle</em> which can be used to
2907 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2908 * The resulting invoker will have a type which is
2909 * exactly equal to the desired type, except that it will accept
2910 * an additional leading argument of type {@code MethodHandle}.
2911 * <p>
2912 * This method is equivalent to the following code (though it may be more efficient):
2913 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2914 *
2915 * <p style="font-size:smaller;">
2916 * <em>Discussion:</em>
2917 * Invoker method handles can be useful when working with variable method handles
2918 * of unknown types.
2919 * For example, to emulate an {@code invokeExact} call to a variable method
2920 * handle {@code M}, extract its type {@code T},
2921 * look up the invoker method {@code X} for {@code T},
2922 * and call the invoker method, as {@code X.invoke(T, A...)}.
2923 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2924 * is unknown.)
2925 * If spreading, collecting, or other argument transformations are required,
2926 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2927 * method handle values, as long as they are compatible with the type of {@code X}.
2928 * <p style="font-size:smaller;">
2929 * <em>(Note: The invoker method is not available via the Core Reflection API.
2930 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2931 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2932 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2933 * <p>
2934 * This method throws no reflective or security exceptions.
2935 * @param type the desired target type
2936 * @return a method handle suitable for invoking any method handle of the given type
2937 * @throws IllegalArgumentException if the resulting method handle's type would have
2938 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2939 */
2940 public static
2941 MethodHandle exactInvoker(MethodType type) {
2942 return type.invokers().exactInvoker();
2943 }
2944
2945 /**
2946 * Produces a special <em>invoker method handle</em> which can be used to
2947 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2948 * The resulting invoker will have a type which is
2949 * exactly equal to the desired type, except that it will accept
2950 * an additional leading argument of type {@code MethodHandle}.
2951 * <p>
2952 * Before invoking its target, if the target differs from the expected type,
2953 * the invoker will apply reference casts as
2954 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2955 * Similarly, the return value will be converted as necessary.
2956 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2957 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2958 * <p>
2959 * This method is equivalent to the following code (though it may be more efficient):
2960 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2961 * <p style="font-size:smaller;">
2962 * <em>Discussion:</em>
2963 * A {@linkplain MethodType#genericMethodType general method type} is one which
2964 * mentions only {@code Object} arguments and return values.
2965 * An invoker for such a type is capable of calling any method handle
2966 * of the same arity as the general type.
2967 * <p style="font-size:smaller;">
2968 * <em>(Note: The invoker method is not available via the Core Reflection API.
2969 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2970 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2971 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2972 * <p>
2973 * This method throws no reflective or security exceptions.
2974 * @param type the desired target type
2975 * @return a method handle suitable for invoking any method handle convertible to the given type
2976 * @throws IllegalArgumentException if the resulting method handle's type would have
2977 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2978 */
2979 public static
2980 MethodHandle invoker(MethodType type) {
2981 return type.invokers().genericInvoker();
2982 }
2983
2984 /**
2985 * Produces a special <em>invoker method handle</em> which can be used to
2986 * invoke a signature-polymorphic access mode method on any VarHandle whose
2987 * associated access mode type is compatible with the given type.
2988 * The resulting invoker will have a type which is exactly equal to the
2989 * desired given type, except that it will accept an additional leading
2990 * argument of type {@code VarHandle}.
2991 *
2992 * @param accessMode the VarHandle access mode
2993 * @param type the desired target type
2994 * @return a method handle suitable for invoking an access mode method of
2995 * any VarHandle whose access mode type is of the given type.
2996 * @since 9
2997 */
2998 static public
2999 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3000 return type.invokers().varHandleMethodExactInvoker(accessMode);
3001 }
3002
3003 /**
3004 * Produces a special <em>invoker method handle</em> which can be used to
3005 * invoke a signature-polymorphic access mode method on any VarHandle whose
3006 * associated access mode type is compatible with the given type.
3007 * The resulting invoker will have a type which is exactly equal to the
3008 * desired given type, except that it will accept an additional leading
3009 * argument of type {@code VarHandle}.
3010 * <p>
3011 * Before invoking its target, if the access mode type differs from the
3012 * desired given type, the invoker will apply reference casts as necessary
3013 * and box, unbox, or widen primitive values, as if by
3014 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3015 * converted as necessary.
3016 * <p>
3017 * This method is equivalent to the following code (though it may be more
3018 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3019 *
3020 * @param accessMode the VarHandle access mode
3021 * @param type the desired target type
3022 * @return a method handle suitable for invoking an access mode method of
3023 * any VarHandle whose access mode type is convertible to the given
3024 * type.
3025 * @since 9
3026 */
3027 static public
3028 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3029 return type.invokers().varHandleMethodInvoker(accessMode);
3030 }
3031
3032 static /*non-public*/
3033 MethodHandle basicInvoker(MethodType type) {
3034 return type.invokers().basicInvoker();
3035 }
3036
3037 /// method handle modification (creation from other method handles)
3038
3039 /**
3040 * Produces a method handle which adapts the type of the
3041 * given method handle to a new type by pairwise argument and return type conversion.
3042 * The original type and new type must have the same number of arguments.
3043 * The resulting method handle is guaranteed to report a type
3044 * which is equal to the desired new type.
3045 * <p>
3046 * If the original type and new type are equal, returns target.
3047 * <p>
3048 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3049 * and some additional conversions are also applied if those conversions fail.
3050 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3051 * if possible, before or instead of any conversions done by {@code asType}:
3052 * <ul>
3053 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3054 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3055 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3056 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3057 * the boolean is converted to a byte value, 1 for true, 0 for false.
3058 * (This treatment follows the usage of the bytecode verifier.)
3059 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3060 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3061 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3062 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3063 * then a Java casting conversion (JLS 5.5) is applied.
3064 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3065 * widening and/or narrowing.)
3066 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3067 * conversion will be applied at runtime, possibly followed
3068 * by a Java casting conversion (JLS 5.5) on the primitive value,
3069 * possibly followed by a conversion from byte to boolean by testing
3070 * the low-order bit.
3071 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3072 * and if the reference is null at runtime, a zero value is introduced.
3073 * </ul>
3074 * @param target the method handle to invoke after arguments are retyped
3075 * @param newType the expected type of the new method handle
3076 * @return a method handle which delegates to the target after performing
3077 * any necessary argument conversions, and arranges for any
3078 * necessary return value conversions
3079 * @throws NullPointerException if either argument is null
3080 * @throws WrongMethodTypeException if the conversion cannot be made
3081 * @see MethodHandle#asType
3082 */
3083 public static
3084 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3085 explicitCastArgumentsChecks(target, newType);
3086 // use the asTypeCache when possible:
3087 MethodType oldType = target.type();
3088 if (oldType == newType) return target;
3089 if (oldType.explicitCastEquivalentToAsType(newType)) {
3090 return target.asFixedArity().asType(newType);
3091 }
3092 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3093 }
3094
3095 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3096 if (target.type().parameterCount() != newType.parameterCount()) {
3097 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3098 }
3099 }
3100
3101 /**
3102 * Produces a method handle which adapts the calling sequence of the
3103 * given method handle to a new type, by reordering the arguments.
3104 * The resulting method handle is guaranteed to report a type
3105 * which is equal to the desired new type.
3106 * <p>
3107 * The given array controls the reordering.
3108 * Call {@code #I} the number of incoming parameters (the value
3109 * {@code newType.parameterCount()}, and call {@code #O} the number
3110 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3111 * Then the length of the reordering array must be {@code #O},
3112 * and each element must be a non-negative number less than {@code #I}.
3113 * For every {@code N} less than {@code #O}, the {@code N}-th
3114 * outgoing argument will be taken from the {@code I}-th incoming
3115 * argument, where {@code I} is {@code reorder[N]}.
3116 * <p>
3117 * No argument or return value conversions are applied.
3118 * The type of each incoming argument, as determined by {@code newType},
3119 * must be identical to the type of the corresponding outgoing parameter
3120 * or parameters in the target method handle.
3121 * The return type of {@code newType} must be identical to the return
3122 * type of the original target.
3123 * <p>
3124 * The reordering array need not specify an actual permutation.
3125 * An incoming argument will be duplicated if its index appears
3126 * more than once in the array, and an incoming argument will be dropped
3127 * if its index does not appear in the array.
3128 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3129 * incoming arguments which are not mentioned in the reordering array
3130 * may be of any type, as determined only by {@code newType}.
3131 * <blockquote><pre>{@code
3132 import static java.lang.invoke.MethodHandles.*;
3133 import static java.lang.invoke.MethodType.*;
3134 ...
3135 MethodType intfn1 = methodType(int.class, int.class);
3136 MethodType intfn2 = methodType(int.class, int.class, int.class);
3137 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3138 assert(sub.type().equals(intfn2));
3139 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3140 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3141 assert((int)rsub.invokeExact(1, 100) == 99);
3142 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3143 assert(add.type().equals(intfn2));
3144 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3145 assert(twice.type().equals(intfn1));
3146 assert((int)twice.invokeExact(21) == 42);
3147 * }</pre></blockquote>
3148 * <p>
3149 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3150 * variable-arity method handle}, even if the original target method handle was.
3151 * @param target the method handle to invoke after arguments are reordered
3152 * @param newType the expected type of the new method handle
3153 * @param reorder an index array which controls the reordering
3154 * @return a method handle which delegates to the target after it
3155 * drops unused arguments and moves and/or duplicates the other arguments
3156 * @throws NullPointerException if any argument is null
3157 * @throws IllegalArgumentException if the index array length is not equal to
3158 * the arity of the target, or if any index array element
3159 * not a valid index for a parameter of {@code newType},
3160 * or if two corresponding parameter types in
3161 * {@code target.type()} and {@code newType} are not identical,
3162 */
3163 public static
3164 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3165 reorder = reorder.clone(); // get a private copy
3166 MethodType oldType = target.type();
3167 permuteArgumentChecks(reorder, newType, oldType);
3168 // first detect dropped arguments and handle them separately
3169 int[] originalReorder = reorder;
3170 BoundMethodHandle result = target.rebind();
3171 LambdaForm form = result.form;
3172 int newArity = newType.parameterCount();
3173 // Normalize the reordering into a real permutation,
3174 // by removing duplicates and adding dropped elements.
3175 // This somewhat improves lambda form caching, as well
3176 // as simplifying the transform by breaking it up into steps.
3177 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3178 if (ddIdx > 0) {
3179 // We found a duplicated entry at reorder[ddIdx].
3180 // Example: (x,y,z)->asList(x,y,z)
3181 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3182 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3183 // The starred element corresponds to the argument
3184 // deleted by the dupArgumentForm transform.
3185 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3186 boolean killFirst = false;
3187 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3188 // Set killFirst if the dup is larger than an intervening position.
3189 // This will remove at least one inversion from the permutation.
3190 if (dupVal > val) killFirst = true;
3191 }
3192 if (!killFirst) {
3193 srcPos = dstPos;
3194 dstPos = ddIdx;
3195 }
3196 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3197 assert (reorder[srcPos] == reorder[dstPos]);
3198 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3199 // contract the reordering by removing the element at dstPos
3200 int tailPos = dstPos + 1;
3201 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3202 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3203 } else {
3204 int dropVal = ~ddIdx, insPos = 0;
3205 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3206 // Find first element of reorder larger than dropVal.
3207 // This is where we will insert the dropVal.
3208 insPos += 1;
3209 }
3210 Class<?> ptype = newType.parameterType(dropVal);
3211 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3212 oldType = oldType.insertParameterTypes(insPos, ptype);
3213 // expand the reordering by inserting an element at insPos
3214 int tailPos = insPos + 1;
3215 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3216 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3217 reorder[insPos] = dropVal;
3218 }
3219 assert (permuteArgumentChecks(reorder, newType, oldType));
3220 }
3221 assert (reorder.length == newArity); // a perfect permutation
3222 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3223 form = form.editor().permuteArgumentsForm(1, reorder);
3224 if (newType == result.type() && form == result.internalForm())
3225 return result;
3226 return result.copyWith(newType, form);
3227 }
3228
3229 /**
3230 * Return an indication of any duplicate or omission in reorder.
3231 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3232 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3233 * Otherwise, return zero.
3234 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3235 */
3236 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3237 final int BIT_LIMIT = 63; // max number of bits in bit mask
3238 if (newArity < BIT_LIMIT) {
3239 long mask = 0;
3240 for (int i = 0; i < reorder.length; i++) {
3241 int arg = reorder[i];
3242 if (arg >= newArity) {
3243 return reorder.length;
3244 }
3245 long bit = 1L << arg;
3246 if ((mask & bit) != 0) {
3247 return i; // >0 indicates a dup
3248 }
3249 mask |= bit;
3250 }
3251 if (mask == (1L << newArity) - 1) {
3252 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3253 return 0;
3254 }
3255 // find first zero
3256 long zeroBit = Long.lowestOneBit(~mask);
3257 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3258 assert(zeroPos <= newArity);
3259 if (zeroPos == newArity) {
3260 return 0;
3261 }
3262 return ~zeroPos;
3263 } else {
3264 // same algorithm, different bit set
3265 BitSet mask = new BitSet(newArity);
3266 for (int i = 0; i < reorder.length; i++) {
3267 int arg = reorder[i];
3268 if (arg >= newArity) {
3269 return reorder.length;
3270 }
3271 if (mask.get(arg)) {
3272 return i; // >0 indicates a dup
3273 }
3274 mask.set(arg);
3275 }
3276 int zeroPos = mask.nextClearBit(0);
3277 assert(zeroPos <= newArity);
3278 if (zeroPos == newArity) {
3279 return 0;
3280 }
3281 return ~zeroPos;
3282 }
3283 }
3284
3285 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3286 if (newType.returnType() != oldType.returnType())
3287 throw newIllegalArgumentException("return types do not match",
3288 oldType, newType);
3289 if (reorder.length == oldType.parameterCount()) {
3290 int limit = newType.parameterCount();
3291 boolean bad = false;
3292 for (int j = 0; j < reorder.length; j++) {
3293 int i = reorder[j];
3294 if (i < 0 || i >= limit) {
3295 bad = true; break;
3296 }
3297 Class<?> src = newType.parameterType(i);
3298 Class<?> dst = oldType.parameterType(j);
3299 if (src != dst)
3300 throw newIllegalArgumentException("parameter types do not match after reorder",
3301 oldType, newType);
3302 }
3303 if (!bad) return true;
3304 }
3305 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3306 }
3307
3308 /**
3309 * Produces a method handle of the requested return type which returns the given
3310 * constant value every time it is invoked.
3311 * <p>
3312 * Before the method handle is returned, the passed-in value is converted to the requested type.
3313 * If the requested type is primitive, widening primitive conversions are attempted,
3314 * else reference conversions are attempted.
3315 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3316 * @param type the return type of the desired method handle
3317 * @param value the value to return
3318 * @return a method handle of the given return type and no arguments, which always returns the given value
3319 * @throws NullPointerException if the {@code type} argument is null
3320 * @throws ClassCastException if the value cannot be converted to the required return type
3321 * @throws IllegalArgumentException if the given type is {@code void.class}
3322 */
3323 public static
3324 MethodHandle constant(Class<?> type, Object value) {
3325 if (type.isPrimitive()) {
3326 if (type == void.class)
3327 throw newIllegalArgumentException("void type");
3328 Wrapper w = Wrapper.forPrimitiveType(type);
3329 value = w.convert(value, type);
3330 if (w.zero().equals(value))
3331 return zero(w, type);
3332 return insertArguments(identity(type), 0, value);
3333 } else if (MinimalValueTypes_1_0.isValueType(type)) {
3334 return insertArguments(identity(type), 0, value);
3335 } else {
3336 if (value == null)
3337 return zero(Wrapper.OBJECT, type);
3338 return identity(type).bindTo(value);
3339 }
3340 }
3341
3342 /**
3343 * Produces a method handle which returns its sole argument when invoked.
3344 * @param type the type of the sole parameter and return value of the desired method handle
3345 * @return a unary method handle which accepts and returns the given type
3346 * @throws NullPointerException if the argument is null
3347 * @throws IllegalArgumentException if the given type is {@code void.class}
3348 */
3349 public static
3350 MethodHandle identity(Class<?> type) {
3351 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3352 int pos = btw.ordinal();
3353 MethodHandle ident = IDENTITY_MHS[pos];
3354 if (ident == null) {
3355 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3356 }
3357 if (ident.type().returnType() == type)
3358 return ident;
3359 // something like identity(Foo.class); do not bother to intern these
3360 assert (btw == Wrapper.OBJECT);
3361 return makeIdentity(type);
3362 }
3363
3364 /**
3365 * Produces a constant method handle of the requested return type which
3366 * returns the default value for that type every time it is invoked.
3367 * The resulting constant method handle will have no side effects.
3368 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3369 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3370 * since {@code explicitCastArguments} converts {@code null} to default values.
3371 * @param type the expected return type of the desired method handle
3372 * @return a constant method handle that takes no arguments
3373 * and returns the default value of the given type (or void, if the type is void)
3374 * @throws NullPointerException if the argument is null
3375 * @see MethodHandles#constant
3376 * @see MethodHandles#empty
3377 * @see MethodHandles#explicitCastArguments
3378 * @since 9
3379 */
3380 public static MethodHandle zero(Class<?> type) {
3381 Objects.requireNonNull(type);
3382 if (type.isPrimitive()) {
3383 return zero(Wrapper.forPrimitiveType(type), type);
3384 } else if (MinimalValueTypes_1_0.isValueType(type)) {
3385 return MinimalValueTypes_1_0.findValueType(type).defaultValueConstant();
3386 } else {
3387 return zero(Wrapper.OBJECT, type);
3388 }
3389 }
3390
3391 private static MethodHandle identityOrVoid(Class<?> type) {
3392 return type == void.class ? zero(type) : identity(type);
3393 }
3394
3395 /**
3396 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3397 * and returns a suitable default depending on the return type.
3398 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3399 * <p>The returned method handle is equivalent to
3400 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3401 *
3402 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3403 * {@code guardWithTest(pred, target, empty(target.type())}.
3404 * @param type the type of the desired method handle
3405 * @return a constant method handle of the given type, which returns a default value of the given return type
3406 * @throws NullPointerException if the argument is null
3407 * @see MethodHandles#zero
3408 * @see MethodHandles#constant
3409 * @since 9
3410 */
3411 public static MethodHandle empty(MethodType type) {
3412 Objects.requireNonNull(type);
3413 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3414 }
3415
3416 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3417 private static MethodHandle makeIdentity(Class<?> ptype) {
3418 if (!MinimalValueTypes_1_0.isValueType(ptype)) {
3419 MethodType mtype = MethodType.methodType(ptype, ptype);
3420 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3421 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3422 } else {
3423 return MinimalValueTypes_1_0.findValueType(ptype).identity();
3424 }
3425 }
3426
3427 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3428 int pos = btw.ordinal();
3429 MethodHandle zero = ZERO_MHS[pos];
3430 if (zero == null) {
3431 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3432 }
3433 if (zero.type().returnType() == rtype)
3434 return zero;
3435 assert(btw == Wrapper.OBJECT);
3436 return makeZero(rtype);
3437 }
3438 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3439 private static MethodHandle makeZero(Class<?> rtype) {
3440 MethodType mtype = methodType(rtype);
3441 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3442 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3443 }
3444
3445 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3446 // Simulate a CAS, to avoid racy duplication of results.
3447 MethodHandle prev = cache[pos];
3448 if (prev != null) return prev;
3449 return cache[pos] = value;
3450 }
3451
3452 /**
3453 * Provides a target method handle with one or more <em>bound arguments</em>
3454 * in advance of the method handle's invocation.
3455 * The formal parameters to the target corresponding to the bound
3456 * arguments are called <em>bound parameters</em>.
3457 * Returns a new method handle which saves away the bound arguments.
3458 * When it is invoked, it receives arguments for any non-bound parameters,
3459 * binds the saved arguments to their corresponding parameters,
3460 * and calls the original target.
3461 * <p>
3462 * The type of the new method handle will drop the types for the bound
3463 * parameters from the original target type, since the new method handle
3464 * will no longer require those arguments to be supplied by its callers.
3465 * <p>
3466 * Each given argument object must match the corresponding bound parameter type.
3467 * If a bound parameter type is a primitive, the argument object
3468 * must be a wrapper, and will be unboxed to produce the primitive value.
3469 * <p>
3470 * The {@code pos} argument selects which parameters are to be bound.
3471 * It may range between zero and <i>N-L</i> (inclusively),
3472 * where <i>N</i> is the arity of the target method handle
3473 * and <i>L</i> is the length of the values array.
3474 * <p>
3475 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3476 * variable-arity method handle}, even if the original target method handle was.
3477 * @param target the method handle to invoke after the argument is inserted
3478 * @param pos where to insert the argument (zero for the first)
3479 * @param values the series of arguments to insert
3480 * @return a method handle which inserts an additional argument,
3481 * before calling the original method handle
3482 * @throws NullPointerException if the target or the {@code values} array is null
3483 * @see MethodHandle#bindTo
3484 */
3485 public static
3486 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3487 int insCount = values.length;
3488 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3489 if (insCount == 0) return target;
3490 BoundMethodHandle result = target.rebind();
3491 for (int i = 0; i < insCount; i++) {
3492 Object value = values[i];
3493 Class<?> ptype = ptypes[pos+i];
3494 if (ptype.isPrimitive()) {
3495 result = insertArgumentPrimitive(result, pos, ptype, value);
3496 } else if (MinimalValueTypes_1_0.isValueType(ptype)) {
3497 Class<?> vcc = MinimalValueTypes_1_0.getValueCapableClass(ptype);
3498 Objects.requireNonNull(value); // throw NPE if needed
3499 value = vcc.cast(value); // throw CCE if needed
3500 MethodHandle unbox = MinimalValueTypes_1_0.findValueType(ptype).unbox();
3501 result = result.bindArgumentQ(pos, value, unbox);
3502 } else {
3503 value = ptype.cast(value); // throw CCE if needed
3504 result = result.bindArgumentL(pos, value);
3505 }
3506 }
3507 return result;
3508 }
3509
3510 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3511 Class<?> ptype, Object value) {
3512 Wrapper w = Wrapper.forPrimitiveType(ptype);
3513 // perform unboxing and/or primitive conversion
3514 value = w.convert(value, ptype);
3515 switch (w) {
3516 case INT: return result.bindArgumentI(pos, (int)value);
3517 case LONG: return result.bindArgumentJ(pos, (long)value);
3518 case FLOAT: return result.bindArgumentF(pos, (float)value);
3519 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3520 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3521 }
3522 }
3523
3524 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3525 MethodType oldType = target.type();
3526 int outargs = oldType.parameterCount();
3527 int inargs = outargs - insCount;
3528 if (inargs < 0)
3529 throw newIllegalArgumentException("too many values to insert");
3530 if (pos < 0 || pos > inargs)
3531 throw newIllegalArgumentException("no argument type to append");
3532 return oldType.ptypes();
3533 }
3534
3535 /**
3536 * Produces a method handle which will discard some dummy arguments
3537 * before calling some other specified <i>target</i> method handle.
3538 * The type of the new method handle will be the same as the target's type,
3539 * except it will also include the dummy argument types,
3540 * at some given position.
3541 * <p>
3542 * The {@code pos} argument may range between zero and <i>N</i>,
3543 * where <i>N</i> is the arity of the target.
3544 * If {@code pos} is zero, the dummy arguments will precede
3545 * the target's real arguments; if {@code pos} is <i>N</i>
3546 * they will come after.
3547 * <p>
3548 * <b>Example:</b>
3549 * <blockquote><pre>{@code
3550 import static java.lang.invoke.MethodHandles.*;
3551 import static java.lang.invoke.MethodType.*;
3552 ...
3553 MethodHandle cat = lookup().findVirtual(String.class,
3554 "concat", methodType(String.class, String.class));
3555 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3556 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3557 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3558 assertEquals(bigType, d0.type());
3559 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3560 * }</pre></blockquote>
3561 * <p>
3562 * This method is also equivalent to the following code:
3563 * <blockquote><pre>
3564 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3565 * </pre></blockquote>
3566 * @param target the method handle to invoke after the arguments are dropped
3567 * @param valueTypes the type(s) of the argument(s) to drop
3568 * @param pos position of first argument to drop (zero for the leftmost)
3569 * @return a method handle which drops arguments of the given types,
3570 * before calling the original method handle
3571 * @throws NullPointerException if the target is null,
3572 * or if the {@code valueTypes} list or any of its elements is null
3573 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3574 * or if {@code pos} is negative or greater than the arity of the target,
3575 * or if the new method handle's type would have too many parameters
3576 */
3577 public static
3578 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3579 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3580 }
3581
3582 private static List<Class<?>> copyTypes(Object[] array) {
3583 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3584 }
3585
3586 private static
3587 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3588 MethodType oldType = target.type(); // get NPE
3589 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3590 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3591 if (dropped == 0) return target;
3592 BoundMethodHandle result = target.rebind();
3593 LambdaForm lform = result.form;
3594 int insertFormArg = 1 + pos;
3595 for (Class<?> ptype : valueTypes) {
3596 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3597 }
3598 result = result.copyWith(newType, lform);
3599 return result;
3600 }
3601
3602 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3603 int dropped = valueTypes.size();
3604 MethodType.checkSlotCount(dropped);
3605 int outargs = oldType.parameterCount();
3606 int inargs = outargs + dropped;
3607 if (pos < 0 || pos > outargs)
3608 throw newIllegalArgumentException("no argument type to remove"
3609 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3610 );
3611 return dropped;
3612 }
3613
3614 /**
3615 * Produces a method handle which will discard some dummy arguments
3616 * before calling some other specified <i>target</i> method handle.
3617 * The type of the new method handle will be the same as the target's type,
3618 * except it will also include the dummy argument types,
3619 * at some given position.
3620 * <p>
3621 * The {@code pos} argument may range between zero and <i>N</i>,
3622 * where <i>N</i> is the arity of the target.
3623 * If {@code pos} is zero, the dummy arguments will precede
3624 * the target's real arguments; if {@code pos} is <i>N</i>
3625 * they will come after.
3626 * @apiNote
3627 * <blockquote><pre>{@code
3628 import static java.lang.invoke.MethodHandles.*;
3629 import static java.lang.invoke.MethodType.*;
3630 ...
3631 MethodHandle cat = lookup().findVirtual(String.class,
3632 "concat", methodType(String.class, String.class));
3633 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3634 MethodHandle d0 = dropArguments(cat, 0, String.class);
3635 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3636 MethodHandle d1 = dropArguments(cat, 1, String.class);
3637 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3638 MethodHandle d2 = dropArguments(cat, 2, String.class);
3639 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3640 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3641 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3642 * }</pre></blockquote>
3643 * <p>
3644 * This method is also equivalent to the following code:
3645 * <blockquote><pre>
3646 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3647 * </pre></blockquote>
3648 * @param target the method handle to invoke after the arguments are dropped
3649 * @param valueTypes the type(s) of the argument(s) to drop
3650 * @param pos position of first argument to drop (zero for the leftmost)
3651 * @return a method handle which drops arguments of the given types,
3652 * before calling the original method handle
3653 * @throws NullPointerException if the target is null,
3654 * or if the {@code valueTypes} array or any of its elements is null
3655 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3656 * or if {@code pos} is negative or greater than the arity of the target,
3657 * or if the new method handle's type would have
3658 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3659 */
3660 public static
3661 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3662 return dropArguments0(target, pos, copyTypes(valueTypes));
3663 }
3664
3665 // private version which allows caller some freedom with error handling
3666 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3667 boolean nullOnFailure) {
3668 newTypes = copyTypes(newTypes.toArray());
3669 List<Class<?>> oldTypes = target.type().parameterList();
3670 int match = oldTypes.size();
3671 if (skip != 0) {
3672 if (skip < 0 || skip > match) {
3673 throw newIllegalArgumentException("illegal skip", skip, target);
3674 }
3675 oldTypes = oldTypes.subList(skip, match);
3676 match -= skip;
3677 }
3678 List<Class<?>> addTypes = newTypes;
3679 int add = addTypes.size();
3680 if (pos != 0) {
3681 if (pos < 0 || pos > add) {
3682 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3683 }
3684 addTypes = addTypes.subList(pos, add);
3685 add -= pos;
3686 assert(addTypes.size() == add);
3687 }
3688 // Do not add types which already match the existing arguments.
3689 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3690 if (nullOnFailure) {
3691 return null;
3692 }
3693 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3694 }
3695 addTypes = addTypes.subList(match, add);
3696 add -= match;
3697 assert(addTypes.size() == add);
3698 // newTypes: ( P*[pos], M*[match], A*[add] )
3699 // target: ( S*[skip], M*[match] )
3700 MethodHandle adapter = target;
3701 if (add > 0) {
3702 adapter = dropArguments0(adapter, skip+ match, addTypes);
3703 }
3704 // adapter: (S*[skip], M*[match], A*[add] )
3705 if (pos > 0) {
3706 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3707 }
3708 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3709 return adapter;
3710 }
3711
3712 /**
3713 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3714 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3715 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3716 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3717 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3718 * {@link #dropArguments(MethodHandle, int, Class[])}.
3719 * <p>
3720 * The resulting handle will have the same return type as the target handle.
3721 * <p>
3722 * In more formal terms, assume these two type lists:<ul>
3723 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3724 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3725 * {@code newTypes}.
3726 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3727 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3728 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3729 * sub-list.
3730 * </ul>
3731 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3732 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3733 * {@link #dropArguments(MethodHandle, int, Class[])}.
3734 *
3735 * @apiNote
3736 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3737 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3738 * <blockquote><pre>{@code
3739 import static java.lang.invoke.MethodHandles.*;
3740 import static java.lang.invoke.MethodType.*;
3741 ...
3742 ...
3743 MethodHandle h0 = constant(boolean.class, true);
3744 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3745 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3746 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3747 if (h1.type().parameterCount() < h2.type().parameterCount())
3748 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3749 else
3750 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3751 MethodHandle h3 = guardWithTest(h0, h1, h2);
3752 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3753 * }</pre></blockquote>
3754 * @param target the method handle to adapt
3755 * @param skip number of targets parameters to disregard (they will be unchanged)
3756 * @param newTypes the list of types to match {@code target}'s parameter type list to
3757 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3758 * @return a possibly adapted method handle
3759 * @throws NullPointerException if either argument is null
3760 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3761 * or if {@code skip} is negative or greater than the arity of the target,
3762 * or if {@code pos} is negative or greater than the newTypes list size,
3763 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3764 * {@code pos}.
3765 * @since 9
3766 */
3767 public static
3768 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3769 Objects.requireNonNull(target);
3770 Objects.requireNonNull(newTypes);
3771 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3772 }
3773
3774 /**
3775 * Adapts a target method handle by pre-processing
3776 * one or more of its arguments, each with its own unary filter function,
3777 * and then calling the target with each pre-processed argument
3778 * replaced by the result of its corresponding filter function.
3779 * <p>
3780 * The pre-processing is performed by one or more method handles,
3781 * specified in the elements of the {@code filters} array.
3782 * The first element of the filter array corresponds to the {@code pos}
3783 * argument of the target, and so on in sequence.
3784 * <p>
3785 * Null arguments in the array are treated as identity functions,
3786 * and the corresponding arguments left unchanged.
3787 * (If there are no non-null elements in the array, the original target is returned.)
3788 * Each filter is applied to the corresponding argument of the adapter.
3789 * <p>
3790 * If a filter {@code F} applies to the {@code N}th argument of
3791 * the target, then {@code F} must be a method handle which
3792 * takes exactly one argument. The type of {@code F}'s sole argument
3793 * replaces the corresponding argument type of the target
3794 * in the resulting adapted method handle.
3795 * The return type of {@code F} must be identical to the corresponding
3796 * parameter type of the target.
3797 * <p>
3798 * It is an error if there are elements of {@code filters}
3799 * (null or not)
3800 * which do not correspond to argument positions in the target.
3801 * <p><b>Example:</b>
3802 * <blockquote><pre>{@code
3803 import static java.lang.invoke.MethodHandles.*;
3804 import static java.lang.invoke.MethodType.*;
3805 ...
3806 MethodHandle cat = lookup().findVirtual(String.class,
3807 "concat", methodType(String.class, String.class));
3808 MethodHandle upcase = lookup().findVirtual(String.class,
3809 "toUpperCase", methodType(String.class));
3810 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3811 MethodHandle f0 = filterArguments(cat, 0, upcase);
3812 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3813 MethodHandle f1 = filterArguments(cat, 1, upcase);
3814 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3815 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3816 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3817 * }</pre></blockquote>
3818 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3819 * denotes the return type of both the {@code target} and resulting adapter.
3820 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3821 * of the parameters and arguments that precede and follow the filter position
3822 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3823 * values of the filtered parameters and arguments; they also represent the
3824 * return types of the {@code filter[i]} handles. The latter accept arguments
3825 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3826 * the resulting adapter.
3827 * <blockquote><pre>{@code
3828 * T target(P... p, A[i]... a[i], B... b);
3829 * A[i] filter[i](V[i]);
3830 * T adapter(P... p, V[i]... v[i], B... b) {
3831 * return target(p..., filter[i](v[i])..., b...);
3832 * }
3833 * }</pre></blockquote>
3834 * <p>
3835 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3836 * variable-arity method handle}, even if the original target method handle was.
3837 *
3838 * @param target the method handle to invoke after arguments are filtered
3839 * @param pos the position of the first argument to filter
3840 * @param filters method handles to call initially on filtered arguments
3841 * @return method handle which incorporates the specified argument filtering logic
3842 * @throws NullPointerException if the target is null
3843 * or if the {@code filters} array is null
3844 * @throws IllegalArgumentException if a non-null element of {@code filters}
3845 * does not match a corresponding argument type of target as described above,
3846 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3847 * or if the resulting method handle's type would have
3848 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3849 */
3850 public static
3851 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3852 filterArgumentsCheckArity(target, pos, filters);
3853 MethodHandle adapter = target;
3854 int curPos = pos-1; // pre-incremented
3855 for (MethodHandle filter : filters) {
3856 curPos += 1;
3857 if (filter == null) continue; // ignore null elements of filters
3858 adapter = filterArgument(adapter, curPos, filter);
3859 }
3860 return adapter;
3861 }
3862
3863 /*non-public*/ static
3864 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3865 filterArgumentChecks(target, pos, filter);
3866 MethodType targetType = target.type();
3867 MethodType filterType = filter.type();
3868 BoundMethodHandle result = target.rebind();
3869 Class<?> newParamType = filterType.parameterType(0);
3870 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3871 MethodType newType = targetType.changeParameterType(pos, newParamType);
3872 result = result.copyWithExtendL(newType, lform, filter);
3873 return result;
3874 }
3875
3876 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3877 MethodType targetType = target.type();
3878 int maxPos = targetType.parameterCount();
3879 if (pos + filters.length > maxPos)
3880 throw newIllegalArgumentException("too many filters");
3881 }
3882
3883 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3884 MethodType targetType = target.type();
3885 MethodType filterType = filter.type();
3886 if (filterType.parameterCount() != 1
3887 || filterType.returnType() != targetType.parameterType(pos))
3888 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3889 }
3890
3891 /**
3892 * Adapts a target method handle by pre-processing
3893 * a sub-sequence of its arguments with a filter (another method handle).
3894 * The pre-processed arguments are replaced by the result (if any) of the
3895 * filter function.
3896 * The target is then called on the modified (usually shortened) argument list.
3897 * <p>
3898 * If the filter returns a value, the target must accept that value as
3899 * its argument in position {@code pos}, preceded and/or followed by
3900 * any arguments not passed to the filter.
3901 * If the filter returns void, the target must accept all arguments
3902 * not passed to the filter.
3903 * No arguments are reordered, and a result returned from the filter
3904 * replaces (in order) the whole subsequence of arguments originally
3905 * passed to the adapter.
3906 * <p>
3907 * The argument types (if any) of the filter
3908 * replace zero or one argument types of the target, at position {@code pos},
3909 * in the resulting adapted method handle.
3910 * The return type of the filter (if any) must be identical to the
3911 * argument type of the target at position {@code pos}, and that target argument
3912 * is supplied by the return value of the filter.
3913 * <p>
3914 * In all cases, {@code pos} must be greater than or equal to zero, and
3915 * {@code pos} must also be less than or equal to the target's arity.
3916 * <p><b>Example:</b>
3917 * <blockquote><pre>{@code
3918 import static java.lang.invoke.MethodHandles.*;
3919 import static java.lang.invoke.MethodType.*;
3920 ...
3921 MethodHandle deepToString = publicLookup()
3922 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3923
3924 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3925 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3926
3927 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3928 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3929
3930 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3931 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3932 assertEquals("[top, [up, down], strange]",
3933 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3934
3935 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3936 assertEquals("[top, [up, down], [strange]]",
3937 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3938
3939 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3940 assertEquals("[top, [[up, down, strange], charm], bottom]",
3941 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3942 * }</pre></blockquote>
3943 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3944 * represents the return type of the {@code target} and resulting adapter.
3945 * {@code V}/{@code v} stand for the return type and value of the
3946 * {@code filter}, which are also found in the signature and arguments of
3947 * the {@code target}, respectively, unless {@code V} is {@code void}.
3948 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3949 * and values preceding and following the collection position, {@code pos},
3950 * in the {@code target}'s signature. They also turn up in the resulting
3951 * adapter's signature and arguments, where they surround
3952 * {@code B}/{@code b}, which represent the parameter types and arguments
3953 * to the {@code filter} (if any).
3954 * <blockquote><pre>{@code
3955 * T target(A...,V,C...);
3956 * V filter(B...);
3957 * T adapter(A... a,B... b,C... c) {
3958 * V v = filter(b...);
3959 * return target(a...,v,c...);
3960 * }
3961 * // and if the filter has no arguments:
3962 * T target2(A...,V,C...);
3963 * V filter2();
3964 * T adapter2(A... a,C... c) {
3965 * V v = filter2();
3966 * return target2(a...,v,c...);
3967 * }
3968 * // and if the filter has a void return:
3969 * T target3(A...,C...);
3970 * void filter3(B...);
3971 * T adapter3(A... a,B... b,C... c) {
3972 * filter3(b...);
3973 * return target3(a...,c...);
3974 * }
3975 * }</pre></blockquote>
3976 * <p>
3977 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3978 * one which first "folds" the affected arguments, and then drops them, in separate
3979 * steps as follows:
3980 * <blockquote><pre>{@code
3981 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3982 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3983 * }</pre></blockquote>
3984 * If the target method handle consumes no arguments besides than the result
3985 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3986 * is equivalent to {@code filterReturnValue(coll, mh)}.
3987 * If the filter method handle {@code coll} consumes one argument and produces
3988 * a non-void result, then {@code collectArguments(mh, N, coll)}
3989 * is equivalent to {@code filterArguments(mh, N, coll)}.
3990 * Other equivalences are possible but would require argument permutation.
3991 * <p>
3992 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3993 * variable-arity method handle}, even if the original target method handle was.
3994 *
3995 * @param target the method handle to invoke after filtering the subsequence of arguments
3996 * @param pos the position of the first adapter argument to pass to the filter,
3997 * and/or the target argument which receives the result of the filter
3998 * @param filter method handle to call on the subsequence of arguments
3999 * @return method handle which incorporates the specified argument subsequence filtering logic
4000 * @throws NullPointerException if either argument is null
4001 * @throws IllegalArgumentException if the return type of {@code filter}
4002 * is non-void and is not the same as the {@code pos} argument of the target,
4003 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4004 * or if the resulting method handle's type would have
4005 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4006 * @see MethodHandles#foldArguments
4007 * @see MethodHandles#filterArguments
4008 * @see MethodHandles#filterReturnValue
4009 */
4010 public static
4011 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4012 MethodType newType = collectArgumentsChecks(target, pos, filter);
4013 MethodType collectorType = filter.type();
4014 BoundMethodHandle result = target.rebind();
4015 LambdaForm lform;
4016 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4017 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4018 if (lform != null) {
4019 return result.copyWith(newType, lform);
4020 }
4021 }
4022 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4023 return result.copyWithExtendL(newType, lform, filter);
4024 }
4025
4026 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4027 MethodType targetType = target.type();
4028 MethodType filterType = filter.type();
4029 Class<?> rtype = filterType.returnType();
4030 List<Class<?>> filterArgs = filterType.parameterList();
4031 if (rtype == void.class) {
4032 return targetType.insertParameterTypes(pos, filterArgs);
4033 }
4034 if (rtype != targetType.parameterType(pos)) {
4035 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4036 }
4037 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4038 }
4039
4040 /**
4041 * Adapts a target method handle by post-processing
4042 * its return value (if any) with a filter (another method handle).
4043 * The result of the filter is returned from the adapter.
4044 * <p>
4045 * If the target returns a value, the filter must accept that value as
4046 * its only argument.
4047 * If the target returns void, the filter must accept no arguments.
4048 * <p>
4049 * The return type of the filter
4050 * replaces the return type of the target
4051 * in the resulting adapted method handle.
4052 * The argument type of the filter (if any) must be identical to the
4053 * return type of the target.
4054 * <p><b>Example:</b>
4055 * <blockquote><pre>{@code
4056 import static java.lang.invoke.MethodHandles.*;
4057 import static java.lang.invoke.MethodType.*;
4058 ...
4059 MethodHandle cat = lookup().findVirtual(String.class,
4060 "concat", methodType(String.class, String.class));
4061 MethodHandle length = lookup().findVirtual(String.class,
4062 "length", methodType(int.class));
4063 System.out.println((String) cat.invokeExact("x", "y")); // xy
4064 MethodHandle f0 = filterReturnValue(cat, length);
4065 System.out.println((int) f0.invokeExact("x", "y")); // 2
4066 * }</pre></blockquote>
4067 * <p>Here is pseudocode for the resulting adapter. In the code,
4068 * {@code T}/{@code t} represent the result type and value of the
4069 * {@code target}; {@code V}, the result type of the {@code filter}; and
4070 * {@code A}/{@code a}, the types and values of the parameters and arguments
4071 * of the {@code target} as well as the resulting adapter.
4072 * <blockquote><pre>{@code
4073 * T target(A...);
4074 * V filter(T);
4075 * V adapter(A... a) {
4076 * T t = target(a...);
4077 * return filter(t);
4078 * }
4079 * // and if the target has a void return:
4080 * void target2(A...);
4081 * V filter2();
4082 * V adapter2(A... a) {
4083 * target2(a...);
4084 * return filter2();
4085 * }
4086 * // and if the filter has a void return:
4087 * T target3(A...);
4088 * void filter3(V);
4089 * void adapter3(A... a) {
4090 * T t = target3(a...);
4091 * filter3(t);
4092 * }
4093 * }</pre></blockquote>
4094 * <p>
4095 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4096 * variable-arity method handle}, even if the original target method handle was.
4097 * @param target the method handle to invoke before filtering the return value
4098 * @param filter method handle to call on the return value
4099 * @return method handle which incorporates the specified return value filtering logic
4100 * @throws NullPointerException if either argument is null
4101 * @throws IllegalArgumentException if the argument list of {@code filter}
4102 * does not match the return type of target as described above
4103 */
4104 public static
4105 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4106 MethodType targetType = target.type();
4107 MethodType filterType = filter.type();
4108 filterReturnValueChecks(targetType, filterType);
4109 BoundMethodHandle result = target.rebind();
4110 BasicType rtype = BasicType.basicType(filterType.returnType());
4111 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4112 MethodType newType = targetType.changeReturnType(filterType.returnType());
4113 result = result.copyWithExtendL(newType, lform, filter);
4114 return result;
4115 }
4116
4117 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4118 Class<?> rtype = targetType.returnType();
4119 int filterValues = filterType.parameterCount();
4120 if (filterValues == 0
4121 ? (rtype != void.class)
4122 : (rtype != filterType.parameterType(0) || filterValues != 1))
4123 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4124 }
4125
4126 /**
4127 * Adapts a target method handle by pre-processing
4128 * some of its arguments, and then calling the target with
4129 * the result of the pre-processing, inserted into the original
4130 * sequence of arguments.
4131 * <p>
4132 * The pre-processing is performed by {@code combiner}, a second method handle.
4133 * Of the arguments passed to the adapter, the first {@code N} arguments
4134 * are copied to the combiner, which is then called.
4135 * (Here, {@code N} is defined as the parameter count of the combiner.)
4136 * After this, control passes to the target, with any result
4137 * from the combiner inserted before the original {@code N} incoming
4138 * arguments.
4139 * <p>
4140 * If the combiner returns a value, the first parameter type of the target
4141 * must be identical with the return type of the combiner, and the next
4142 * {@code N} parameter types of the target must exactly match the parameters
4143 * of the combiner.
4144 * <p>
4145 * If the combiner has a void return, no result will be inserted,
4146 * and the first {@code N} parameter types of the target
4147 * must exactly match the parameters of the combiner.
4148 * <p>
4149 * The resulting adapter is the same type as the target, except that the
4150 * first parameter type is dropped,
4151 * if it corresponds to the result of the combiner.
4152 * <p>
4153 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4154 * that either the combiner or the target does not wish to receive.
4155 * If some of the incoming arguments are destined only for the combiner,
4156 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4157 * arguments will not need to be live on the stack on entry to the
4158 * target.)
4159 * <p><b>Example:</b>
4160 * <blockquote><pre>{@code
4161 import static java.lang.invoke.MethodHandles.*;
4162 import static java.lang.invoke.MethodType.*;
4163 ...
4164 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4165 "println", methodType(void.class, String.class))
4166 .bindTo(System.out);
4167 MethodHandle cat = lookup().findVirtual(String.class,
4168 "concat", methodType(String.class, String.class));
4169 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4170 MethodHandle catTrace = foldArguments(cat, trace);
4171 // also prints "boo":
4172 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4173 * }</pre></blockquote>
4174 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4175 * represents the result type of the {@code target} and resulting adapter.
4176 * {@code V}/{@code v} represent the type and value of the parameter and argument
4177 * of {@code target} that precedes the folding position; {@code V} also is
4178 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4179 * types and values of the {@code N} parameters and arguments at the folding
4180 * position. {@code B}/{@code b} represent the types and values of the
4181 * {@code target} parameters and arguments that follow the folded parameters
4182 * and arguments.
4183 * <blockquote><pre>{@code
4184 * // there are N arguments in A...
4185 * T target(V, A[N]..., B...);
4186 * V combiner(A...);
4187 * T adapter(A... a, B... b) {
4188 * V v = combiner(a...);
4189 * return target(v, a..., b...);
4190 * }
4191 * // and if the combiner has a void return:
4192 * T target2(A[N]..., B...);
4193 * void combiner2(A...);
4194 * T adapter2(A... a, B... b) {
4195 * combiner2(a...);
4196 * return target2(a..., b...);
4197 * }
4198 * }</pre></blockquote>
4199 * <p>
4200 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4201 * variable-arity method handle}, even if the original target method handle was.
4202 * @param target the method handle to invoke after arguments are combined
4203 * @param combiner method handle to call initially on the incoming arguments
4204 * @return method handle which incorporates the specified argument folding logic
4205 * @throws NullPointerException if either argument is null
4206 * @throws IllegalArgumentException if {@code combiner}'s return type
4207 * is non-void and not the same as the first argument type of
4208 * the target, or if the initial {@code N} argument types
4209 * of the target
4210 * (skipping one matching the {@code combiner}'s return type)
4211 * are not identical with the argument types of {@code combiner}
4212 */
4213 public static
4214 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4215 return foldArguments(target, 0, combiner);
4216 }
4217
4218 /**
4219 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4220 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4221 * before the folded arguments.
4222 * <p>
4223 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4224 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4225 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4226 * 0.
4227 *
4228 * @apiNote Example:
4229 * <blockquote><pre>{@code
4230 import static java.lang.invoke.MethodHandles.*;
4231 import static java.lang.invoke.MethodType.*;
4232 ...
4233 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4234 "println", methodType(void.class, String.class))
4235 .bindTo(System.out);
4236 MethodHandle cat = lookup().findVirtual(String.class,
4237 "concat", methodType(String.class, String.class));
4238 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4239 MethodHandle catTrace = foldArguments(cat, 1, trace);
4240 // also prints "jum":
4241 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4242 * }</pre></blockquote>
4243 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4244 * represents the result type of the {@code target} and resulting adapter.
4245 * {@code V}/{@code v} represent the type and value of the parameter and argument
4246 * of {@code target} that precedes the folding position; {@code V} also is
4247 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4248 * types and values of the {@code N} parameters and arguments at the folding
4249 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4250 * and values of the {@code target} parameters and arguments that precede and
4251 * follow the folded parameters and arguments starting at {@code pos},
4252 * respectively.
4253 * <blockquote><pre>{@code
4254 * // there are N arguments in A...
4255 * T target(Z..., V, A[N]..., B...);
4256 * V combiner(A...);
4257 * T adapter(Z... z, A... a, B... b) {
4258 * V v = combiner(a...);
4259 * return target(z..., v, a..., b...);
4260 * }
4261 * // and if the combiner has a void return:
4262 * T target2(Z..., A[N]..., B...);
4263 * void combiner2(A...);
4264 * T adapter2(Z... z, A... a, B... b) {
4265 * combiner2(a...);
4266 * return target2(z..., a..., b...);
4267 * }
4268 * }</pre></blockquote>
4269 * <p>
4270 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4271 * variable-arity method handle}, even if the original target method handle was.
4272 *
4273 * @param target the method handle to invoke after arguments are combined
4274 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4275 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4276 * @param combiner method handle to call initially on the incoming arguments
4277 * @return method handle which incorporates the specified argument folding logic
4278 * @throws NullPointerException if either argument is null
4279 * @throws IllegalArgumentException if either of the following two conditions holds:
4280 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4281 * {@code pos} of the target signature;
4282 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4283 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4284 *
4285 * @see #foldArguments(MethodHandle, MethodHandle)
4286 * @since 9
4287 */
4288 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4289 MethodType targetType = target.type();
4290 MethodType combinerType = combiner.type();
4291 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4292 BoundMethodHandle result = target.rebind();
4293 boolean dropResult = rtype == void.class;
4294 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4295 MethodType newType = targetType;
4296 if (!dropResult) {
4297 newType = newType.dropParameterTypes(pos, pos + 1);
4298 }
4299 result = result.copyWithExtendL(newType, lform, combiner);
4300 return result;
4301 }
4302
4303 /**
4304 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4305 * added capability of selecting the arguments from the targets parameters
4306 * to call the combiner with. This allows us to avoid some simple cases of
4307 * permutations and padding the combiner with dropArguments to select the
4308 * right argument, which may ultimately produce fewer intermediaries.
4309 */
4310 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4311 MethodType targetType = target.type();
4312 MethodType combinerType = combiner.type();
4313 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4314 BoundMethodHandle result = target.rebind();
4315 boolean dropResult = rtype == void.class;
4316 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4317 MethodType newType = targetType;
4318 if (!dropResult) {
4319 newType = newType.dropParameterTypes(pos, pos + 1);
4320 }
4321 result = result.copyWithExtendL(newType, lform, combiner);
4322 return result;
4323 }
4324
4325 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4326 int foldArgs = combinerType.parameterCount();
4327 Class<?> rtype = combinerType.returnType();
4328 int foldVals = rtype == void.class ? 0 : 1;
4329 int afterInsertPos = foldPos + foldVals;
4330 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4331 if (ok) {
4332 for (int i = 0; i < foldArgs; i++) {
4333 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4334 ok = false;
4335 break;
4336 }
4337 }
4338 }
4339 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4340 ok = false;
4341 if (!ok)
4342 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4343 return rtype;
4344 }
4345
4346 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4347 int foldArgs = combinerType.parameterCount();
4348 if (argPos.length != foldArgs) {
4349 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4350 }
4351 Class<?> rtype = combinerType.returnType();
4352 int foldVals = rtype == void.class ? 0 : 1;
4353 boolean ok = true;
4354 for (int i = 0; i < foldArgs; i++) {
4355 int arg = argPos[i];
4356 if (arg < 0 || arg > targetType.parameterCount()) {
4357 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4358 }
4359 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4360 throw newIllegalArgumentException("target argument type at position " + arg
4361 + " must match combiner argument type at index " + i + ": " + targetType
4362 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4363 }
4364 }
4365 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4366 ok = false;
4367 }
4368 if (!ok)
4369 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4370 return rtype;
4371 }
4372
4373 /**
4374 * Makes a method handle which adapts a target method handle,
4375 * by guarding it with a test, a boolean-valued method handle.
4376 * If the guard fails, a fallback handle is called instead.
4377 * All three method handles must have the same corresponding
4378 * argument and return types, except that the return type
4379 * of the test must be boolean, and the test is allowed
4380 * to have fewer arguments than the other two method handles.
4381 * <p>
4382 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4383 * represents the uniform result type of the three involved handles;
4384 * {@code A}/{@code a}, the types and values of the {@code target}
4385 * parameters and arguments that are consumed by the {@code test}; and
4386 * {@code B}/{@code b}, those types and values of the {@code target}
4387 * parameters and arguments that are not consumed by the {@code test}.
4388 * <blockquote><pre>{@code
4389 * boolean test(A...);
4390 * T target(A...,B...);
4391 * T fallback(A...,B...);
4392 * T adapter(A... a,B... b) {
4393 * if (test(a...))
4394 * return target(a..., b...);
4395 * else
4396 * return fallback(a..., b...);
4397 * }
4398 * }</pre></blockquote>
4399 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4400 * be modified by execution of the test, and so are passed unchanged
4401 * from the caller to the target or fallback as appropriate.
4402 * @param test method handle used for test, must return boolean
4403 * @param target method handle to call if test passes
4404 * @param fallback method handle to call if test fails
4405 * @return method handle which incorporates the specified if/then/else logic
4406 * @throws NullPointerException if any argument is null
4407 * @throws IllegalArgumentException if {@code test} does not return boolean,
4408 * or if all three method types do not match (with the return
4409 * type of {@code test} changed to match that of the target).
4410 */
4411 public static
4412 MethodHandle guardWithTest(MethodHandle test,
4413 MethodHandle target,
4414 MethodHandle fallback) {
4415 MethodType gtype = test.type();
4416 MethodType ttype = target.type();
4417 MethodType ftype = fallback.type();
4418 if (!ttype.equals(ftype))
4419 throw misMatchedTypes("target and fallback types", ttype, ftype);
4420 if (gtype.returnType() != boolean.class)
4421 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4422 List<Class<?>> targs = ttype.parameterList();
4423 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4424 if (test == null) {
4425 throw misMatchedTypes("target and test types", ttype, gtype);
4426 }
4427 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4428 }
4429
4430 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4431 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4432 }
4433
4434 /**
4435 * Makes a method handle which adapts a target method handle,
4436 * by running it inside an exception handler.
4437 * If the target returns normally, the adapter returns that value.
4438 * If an exception matching the specified type is thrown, the fallback
4439 * handle is called instead on the exception, plus the original arguments.
4440 * <p>
4441 * The target and handler must have the same corresponding
4442 * argument and return types, except that handler may omit trailing arguments
4443 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4444 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4445 * <p>
4446 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4447 * represents the return type of the {@code target} and {@code handler},
4448 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4449 * the types and values of arguments to the resulting handle consumed by
4450 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4451 * resulting handle discarded by {@code handler}.
4452 * <blockquote><pre>{@code
4453 * T target(A..., B...);
4454 * T handler(ExType, A...);
4455 * T adapter(A... a, B... b) {
4456 * try {
4457 * return target(a..., b...);
4458 * } catch (ExType ex) {
4459 * return handler(ex, a...);
4460 * }
4461 * }
4462 * }</pre></blockquote>
4463 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4464 * be modified by execution of the target, and so are passed unchanged
4465 * from the caller to the handler, if the handler is invoked.
4466 * <p>
4467 * The target and handler must return the same type, even if the handler
4468 * always throws. (This might happen, for instance, because the handler
4469 * is simulating a {@code finally} clause).
4470 * To create such a throwing handler, compose the handler creation logic
4471 * with {@link #throwException throwException},
4472 * in order to create a method handle of the correct return type.
4473 * @param target method handle to call
4474 * @param exType the type of exception which the handler will catch
4475 * @param handler method handle to call if a matching exception is thrown
4476 * @return method handle which incorporates the specified try/catch logic
4477 * @throws NullPointerException if any argument is null
4478 * @throws IllegalArgumentException if {@code handler} does not accept
4479 * the given exception type, or if the method handle types do
4480 * not match in their return types and their
4481 * corresponding parameters
4482 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4483 */
4484 public static
4485 MethodHandle catchException(MethodHandle target,
4486 Class<? extends Throwable> exType,
4487 MethodHandle handler) {
4488 MethodType ttype = target.type();
4489 MethodType htype = handler.type();
4490 if (!Throwable.class.isAssignableFrom(exType))
4491 throw new ClassCastException(exType.getName());
4492 if (htype.parameterCount() < 1 ||
4493 !htype.parameterType(0).isAssignableFrom(exType))
4494 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4495 if (htype.returnType() != ttype.returnType())
4496 throw misMatchedTypes("target and handler return types", ttype, htype);
4497 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4498 if (handler == null) {
4499 throw misMatchedTypes("target and handler types", ttype, htype);
4500 }
4501 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4502 }
4503
4504 /**
4505 * Produces a method handle which will throw exceptions of the given {@code exType}.
4506 * The method handle will accept a single argument of {@code exType},
4507 * and immediately throw it as an exception.
4508 * The method type will nominally specify a return of {@code returnType}.
4509 * The return type may be anything convenient: It doesn't matter to the
4510 * method handle's behavior, since it will never return normally.
4511 * @param returnType the return type of the desired method handle
4512 * @param exType the parameter type of the desired method handle
4513 * @return method handle which can throw the given exceptions
4514 * @throws NullPointerException if either argument is null
4515 */
4516 public static
4517 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4518 if (!Throwable.class.isAssignableFrom(exType))
4519 throw new ClassCastException(exType.getName());
4520 return MethodHandleImpl.throwException(methodType(returnType, exType));
4521 }
4522
4523 /**
4524 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4525 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4526 * delivers the loop's result, which is the return value of the resulting handle.
4527 * <p>
4528 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4529 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4530 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4531 * terms of method handles, each clause will specify up to four independent actions:<ul>
4532 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4533 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4534 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4535 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4536 * </ul>
4537 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4538 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4539 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4540 * <p>
4541 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4542 * this case. See below for a detailed description.
4543 * <p>
4544 * <em>Parameters optional everywhere:</em>
4545 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4546 * As an exception, the init functions cannot take any {@code v} parameters,
4547 * because those values are not yet computed when the init functions are executed.
4548 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4549 * In fact, any clause function may take no arguments at all.
4550 * <p>
4551 * <em>Loop parameters:</em>
4552 * A clause function may take all the iteration variable values it is entitled to, in which case
4553 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4554 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4555 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4556 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4557 * init function is automatically a loop parameter {@code a}.)
4558 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4559 * These loop parameters act as loop-invariant values visible across the whole loop.
4560 * <p>
4561 * <em>Parameters visible everywhere:</em>
4562 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4563 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4564 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4565 * Most clause functions will not need all of this information, but they will be formally connected to it
4566 * as if by {@link #dropArguments}.
4567 * <a id="astar"></a>
4568 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4569 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4570 * In that notation, the general form of an init function parameter list
4571 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4572 * <p>
4573 * <em>Checking clause structure:</em>
4574 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4575 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4576 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4577 * met by the inputs to the loop combinator.
4578 * <p>
4579 * <em>Effectively identical sequences:</em>
4580 * <a id="effid"></a>
4581 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4582 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4583 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4584 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4585 * that longest list.
4586 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4587 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4588 * <p>
4589 * <em>Step 0: Determine clause structure.</em><ol type="a">
4590 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4591 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4592 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4593 * four. Padding takes place by appending elements to the array.
4594 * <li>Clauses with all {@code null}s are disregarded.
4595 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4596 * </ol>
4597 * <p>
4598 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4599 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4600 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4601 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4602 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4603 * iteration variable type.
4604 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4605 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4606 * </ol>
4607 * <p>
4608 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4609 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4610 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4611 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4612 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4613 * (These types will checked in step 2, along with all the clause function types.)
4614 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4615 * <li>All of the collected parameter lists must be effectively identical.
4616 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4617 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4618 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4619 * the "internal parameter list".
4620 * </ul>
4621 * <p>
4622 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4623 * <li>Examine fini function return types, disregarding omitted fini functions.
4624 * <li>If there are no fini functions, the loop return type is {@code void}.
4625 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4626 * type.
4627 * </ol>
4628 * <p>
4629 * <em>Step 1D: Check other types.</em><ol type="a">
4630 * <li>There must be at least one non-omitted pred function.
4631 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4632 * </ol>
4633 * <p>
4634 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4635 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4636 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4637 * (Note that their parameter lists are already effectively identical to this list.)
4638 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4639 * effectively identical to the internal parameter list {@code (V... A...)}.
4640 * </ol>
4641 * <p>
4642 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4643 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4644 * type.
4645 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4646 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4647 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4648 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4649 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4650 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4651 * loop return type.
4652 * </ol>
4653 * <p>
4654 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4655 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4656 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4657 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4658 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4659 * pad out the end of the list.
4660 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch dropping unused trailing arguments}.
4661 * </ol>
4662 * <p>
4663 * <em>Final observations.</em><ol type="a">
4664 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4665 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4666 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4667 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4668 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4669 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4670 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4671 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4672 * </ol>
4673 * <p>
4674 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4675 * <ul>
4676 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4677 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4678 * (Only one {@code Pn} has to be non-{@code null}.)
4679 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4680 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4681 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4682 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4683 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4684 * the resulting loop handle's parameter types {@code (A...)}.
4685 * </ul>
4686 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4687 * which is natural if most of the loop computation happens in the steps. For some loops,
4688 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4689 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4690 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4691 * where the init functions will need the extra parameters. For such reasons, the rules for
4692 * determining these parameters are as symmetric as possible, across all clause parts.
4693 * In general, the loop parameters function as common invariant values across the whole
4694 * loop, while the iteration variables function as common variant values, or (if there is
4695 * no step function) as internal loop invariant temporaries.
4696 * <p>
4697 * <em>Loop execution.</em><ol type="a">
4698 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4699 * every clause function. These locals are loop invariant.
4700 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4701 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4702 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4703 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4704 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4705 * (in argument order).
4706 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4707 * returns {@code false}.
4708 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4709 * sequence {@code (v...)} of loop variables.
4710 * The updated value is immediately visible to all subsequent function calls.
4711 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4712 * (of type {@code R}) is returned from the loop as a whole.
4713 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4714 * except by throwing an exception.
4715 * </ol>
4716 * <p>
4717 * <em>Usage tips.</em>
4718 * <ul>
4719 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4720 * sometimes a step function only needs to observe the current value of its own variable.
4721 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4722 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4723 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4724 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4725 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4726 * <li>If some of the clause functions are virtual methods on an instance, the instance
4727 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4728 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4729 * will be the first iteration variable value, and it will be easy to use virtual
4730 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4731 * </ul>
4732 * <p>
4733 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4734 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4735 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4736 * <blockquote><pre>{@code
4737 * V... init...(A...);
4738 * boolean pred...(V..., A...);
4739 * V... step...(V..., A...);
4740 * R fini...(V..., A...);
4741 * R loop(A... a) {
4742 * V... v... = init...(a...);
4743 * for (;;) {
4744 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4745 * v = s(v..., a...);
4746 * if (!p(v..., a...)) {
4747 * return f(v..., a...);
4748 * }
4749 * }
4750 * }
4751 * }
4752 * }</pre></blockquote>
4753 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4754 * to their full length, even though individual clause functions may neglect to take them all.
4755 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch}.
4756 *
4757 * @apiNote Example:
4758 * <blockquote><pre>{@code
4759 * // iterative implementation of the factorial function as a loop handle
4760 * static int one(int k) { return 1; }
4761 * static int inc(int i, int acc, int k) { return i + 1; }
4762 * static int mult(int i, int acc, int k) { return i * acc; }
4763 * static boolean pred(int i, int acc, int k) { return i < k; }
4764 * static int fin(int i, int acc, int k) { return acc; }
4765 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4766 * // null initializer for counter, should initialize to 0
4767 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4768 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4769 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4770 * assertEquals(120, loop.invoke(5));
4771 * }</pre></blockquote>
4772 * The same example, dropping arguments and using combinators:
4773 * <blockquote><pre>{@code
4774 * // simplified implementation of the factorial function as a loop handle
4775 * static int inc(int i) { return i + 1; } // drop acc, k
4776 * static int mult(int i, int acc) { return i * acc; } //drop k
4777 * static boolean cmp(int i, int k) { return i < k; }
4778 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4779 * // null initializer for counter, should initialize to 0
4780 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4781 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4782 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4783 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4784 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4785 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4786 * assertEquals(720, loop.invoke(6));
4787 * }</pre></blockquote>
4788 * A similar example, using a helper object to hold a loop parameter:
4789 * <blockquote><pre>{@code
4790 * // instance-based implementation of the factorial function as a loop handle
4791 * static class FacLoop {
4792 * final int k;
4793 * FacLoop(int k) { this.k = k; }
4794 * int inc(int i) { return i + 1; }
4795 * int mult(int i, int acc) { return i * acc; }
4796 * boolean pred(int i) { return i < k; }
4797 * int fin(int i, int acc) { return acc; }
4798 * }
4799 * // assume MH_FacLoop is a handle to the constructor
4800 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4801 * // null initializer for counter, should initialize to 0
4802 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4803 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4804 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4805 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4806 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4807 * assertEquals(5040, loop.invoke(7));
4808 * }</pre></blockquote>
4809 *
4810 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4811 *
4812 * @return a method handle embodying the looping behavior as defined by the arguments.
4813 *
4814 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4815 *
4816 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4817 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4818 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4819 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4820 * @since 9
4821 */
4822 public static MethodHandle loop(MethodHandle[]... clauses) {
4823 // Step 0: determine clause structure.
4824 loopChecks0(clauses);
4825
4826 List<MethodHandle> init = new ArrayList<>();
4827 List<MethodHandle> step = new ArrayList<>();
4828 List<MethodHandle> pred = new ArrayList<>();
4829 List<MethodHandle> fini = new ArrayList<>();
4830
4831 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4832 init.add(clause[0]); // all clauses have at least length 1
4833 step.add(clause.length <= 1 ? null : clause[1]);
4834 pred.add(clause.length <= 2 ? null : clause[2]);
4835 fini.add(clause.length <= 3 ? null : clause[3]);
4836 });
4837
4838 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4839 final int nclauses = init.size();
4840
4841 // Step 1A: determine iteration variables (V...).
4842 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4843 for (int i = 0; i < nclauses; ++i) {
4844 MethodHandle in = init.get(i);
4845 MethodHandle st = step.get(i);
4846 if (in == null && st == null) {
4847 iterationVariableTypes.add(void.class);
4848 } else if (in != null && st != null) {
4849 loopChecks1a(i, in, st);
4850 iterationVariableTypes.add(in.type().returnType());
4851 } else {
4852 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4853 }
4854 }
4855 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4856 collect(Collectors.toList());
4857
4858 // Step 1B: determine loop parameters (A...).
4859 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4860 loopChecks1b(init, commonSuffix);
4861
4862 // Step 1C: determine loop return type.
4863 // Step 1D: check other types.
4864 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4865 map(MethodType::returnType).findFirst().orElse(void.class);
4866 loopChecks1cd(pred, fini, loopReturnType);
4867
4868 // Step 2: determine parameter lists.
4869 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4870 commonParameterSequence.addAll(commonSuffix);
4871 loopChecks2(step, pred, fini, commonParameterSequence);
4872
4873 // Step 3: fill in omitted functions.
4874 for (int i = 0; i < nclauses; ++i) {
4875 Class<?> t = iterationVariableTypes.get(i);
4876 if (init.get(i) == null) {
4877 init.set(i, empty(methodType(t, commonSuffix)));
4878 }
4879 if (step.get(i) == null) {
4880 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4881 }
4882 if (pred.get(i) == null) {
4883 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4884 }
4885 if (fini.get(i) == null) {
4886 fini.set(i, empty(methodType(t, commonParameterSequence)));
4887 }
4888 }
4889
4890 // Step 4: fill in missing parameter types.
4891 // Also convert all handles to fixed-arity handles.
4892 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4893 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4894 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4895 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4896
4897 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4898 allMatch(pl -> pl.equals(commonSuffix));
4899 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4900 allMatch(pl -> pl.equals(commonParameterSequence));
4901
4902 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4903 }
4904
4905 private static void loopChecks0(MethodHandle[][] clauses) {
4906 if (clauses == null || clauses.length == 0) {
4907 throw newIllegalArgumentException("null or no clauses passed");
4908 }
4909 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4910 throw newIllegalArgumentException("null clauses are not allowed");
4911 }
4912 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4913 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4914 }
4915 }
4916
4917 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4918 if (in.type().returnType() != st.type().returnType()) {
4919 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4920 st.type().returnType());
4921 }
4922 }
4923
4924 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4925 final List<Class<?>> empty = List.of();
4926 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4927 // take only those that can contribute to a common suffix because they are longer than the prefix
4928 map(MethodHandle::type).
4929 filter(t -> t.parameterCount() > skipSize).
4930 map(MethodType::parameterList).
4931 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4932 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4933 }
4934
4935 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4936 final List<Class<?>> empty = List.of();
4937 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4938 }
4939
4940 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4941 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4942 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4943 return longestParameterList(Arrays.asList(longest1, longest2));
4944 }
4945
4946 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4947 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4948 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4949 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4950 " (common suffix: " + commonSuffix + ")");
4951 }
4952 }
4953
4954 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4955 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4956 anyMatch(t -> t != loopReturnType)) {
4957 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4958 loopReturnType + ")");
4959 }
4960
4961 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4962 throw newIllegalArgumentException("no predicate found", pred);
4963 }
4964 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4965 anyMatch(t -> t != boolean.class)) {
4966 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4967 }
4968 }
4969
4970 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4971 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4972 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4973 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4974 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4975 }
4976 }
4977
4978 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4979 return hs.stream().map(h -> {
4980 int pc = h.type().parameterCount();
4981 int tpsize = targetParams.size();
4982 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4983 }).collect(Collectors.toList());
4984 }
4985
4986 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4987 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4988 }
4989
4990 /**
4991 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4992 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4993 * <p>
4994 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4995 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4996 * evaluates to {@code true}).
4997 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4998 * <p>
4999 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5000 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5001 * and updated with the value returned from its invocation. The result of loop execution will be
5002 * the final value of the additional loop-local variable (if present).
5003 * <p>
5004 * The following rules hold for these argument handles:<ul>
5005 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5006 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5007 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5008 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5009 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5010 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5011 * It will constrain the parameter lists of the other loop parts.
5012 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5013 * list {@code (A...)} is called the <em>external parameter list</em>.
5014 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5015 * additional state variable of the loop.
5016 * The body must both accept and return a value of this type {@code V}.
5017 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5018 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5019 * <a href="MethodHandles.html#effid">effectively identical</a>
5020 * to the external parameter list {@code (A...)}.
5021 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5022 * {@linkplain #empty default value}.
5023 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5024 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5025 * effectively identical to the internal parameter list.
5026 * </ul>
5027 * <p>
5028 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5029 * <li>The loop handle's result type is the result type {@code V} of the body.
5030 * <li>The loop handle's parameter types are the types {@code (A...)},
5031 * from the external parameter list.
5032 * </ul>
5033 * <p>
5034 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5035 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5036 * passed to the loop.
5037 * <blockquote><pre>{@code
5038 * V init(A...);
5039 * boolean pred(V, A...);
5040 * V body(V, A...);
5041 * V whileLoop(A... a...) {
5042 * V v = init(a...);
5043 * while (pred(v, a...)) {
5044 * v = body(v, a...);
5045 * }
5046 * return v;
5047 * }
5048 * }</pre></blockquote>
5049 *
5050 * @apiNote Example:
5051 * <blockquote><pre>{@code
5052 * // implement the zip function for lists as a loop handle
5053 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5054 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5055 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5056 * zip.add(a.next());
5057 * zip.add(b.next());
5058 * return zip;
5059 * }
5060 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5061 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5062 * List<String> a = Arrays.asList("a", "b", "c", "d");
5063 * List<String> b = Arrays.asList("e", "f", "g", "h");
5064 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5065 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5066 * }</pre></blockquote>
5067 *
5068 *
5069 * @apiNote The implementation of this method can be expressed as follows:
5070 * <blockquote><pre>{@code
5071 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5072 * MethodHandle fini = (body.type().returnType() == void.class
5073 * ? null : identity(body.type().returnType()));
5074 * MethodHandle[]
5075 * checkExit = { null, null, pred, fini },
5076 * varBody = { init, body };
5077 * return loop(checkExit, varBody);
5078 * }
5079 * }</pre></blockquote>
5080 *
5081 * @param init optional initializer, providing the initial value of the loop variable.
5082 * May be {@code null}, implying a default initial value. See above for other constraints.
5083 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5084 * above for other constraints.
5085 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5086 * See above for other constraints.
5087 *
5088 * @return a method handle implementing the {@code while} loop as described by the arguments.
5089 * @throws IllegalArgumentException if the rules for the arguments are violated.
5090 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5091 *
5092 * @see #loop(MethodHandle[][])
5093 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5094 * @since 9
5095 */
5096 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5097 whileLoopChecks(init, pred, body);
5098 MethodHandle fini = identityOrVoid(body.type().returnType());
5099 MethodHandle[] checkExit = { null, null, pred, fini };
5100 MethodHandle[] varBody = { init, body };
5101 return loop(checkExit, varBody);
5102 }
5103
5104 /**
5105 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5106 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5107 * <p>
5108 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5109 * method will, in each iteration, first execute its body and then evaluate the predicate.
5110 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5111 * <p>
5112 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5113 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5114 * and updated with the value returned from its invocation. The result of loop execution will be
5115 * the final value of the additional loop-local variable (if present).
5116 * <p>
5117 * The following rules hold for these argument handles:<ul>
5118 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5119 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5120 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5121 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5122 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5123 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5124 * It will constrain the parameter lists of the other loop parts.
5125 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5126 * list {@code (A...)} is called the <em>external parameter list</em>.
5127 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5128 * additional state variable of the loop.
5129 * The body must both accept and return a value of this type {@code V}.
5130 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5131 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5132 * <a href="MethodHandles.html#effid">effectively identical</a>
5133 * to the external parameter list {@code (A...)}.
5134 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5135 * {@linkplain #empty default value}.
5136 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5137 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5138 * effectively identical to the internal parameter list.
5139 * </ul>
5140 * <p>
5141 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5142 * <li>The loop handle's result type is the result type {@code V} of the body.
5143 * <li>The loop handle's parameter types are the types {@code (A...)},
5144 * from the external parameter list.
5145 * </ul>
5146 * <p>
5147 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5148 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5149 * passed to the loop.
5150 * <blockquote><pre>{@code
5151 * V init(A...);
5152 * boolean pred(V, A...);
5153 * V body(V, A...);
5154 * V doWhileLoop(A... a...) {
5155 * V v = init(a...);
5156 * do {
5157 * v = body(v, a...);
5158 * } while (pred(v, a...));
5159 * return v;
5160 * }
5161 * }</pre></blockquote>
5162 *
5163 * @apiNote Example:
5164 * <blockquote><pre>{@code
5165 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5166 * static int zero(int limit) { return 0; }
5167 * static int step(int i, int limit) { return i + 1; }
5168 * static boolean pred(int i, int limit) { return i < limit; }
5169 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5170 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5171 * assertEquals(23, loop.invoke(23));
5172 * }</pre></blockquote>
5173 *
5174 *
5175 * @apiNote The implementation of this method can be expressed as follows:
5176 * <blockquote><pre>{@code
5177 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5178 * MethodHandle fini = (body.type().returnType() == void.class
5179 * ? null : identity(body.type().returnType()));
5180 * MethodHandle[] clause = { init, body, pred, fini };
5181 * return loop(clause);
5182 * }
5183 * }</pre></blockquote>
5184 *
5185 * @param init optional initializer, providing the initial value of the loop variable.
5186 * May be {@code null}, implying a default initial value. See above for other constraints.
5187 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5188 * See above for other constraints.
5189 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5190 * above for other constraints.
5191 *
5192 * @return a method handle implementing the {@code while} loop as described by the arguments.
5193 * @throws IllegalArgumentException if the rules for the arguments are violated.
5194 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5195 *
5196 * @see #loop(MethodHandle[][])
5197 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5198 * @since 9
5199 */
5200 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5201 whileLoopChecks(init, pred, body);
5202 MethodHandle fini = identityOrVoid(body.type().returnType());
5203 MethodHandle[] clause = {init, body, pred, fini };
5204 return loop(clause);
5205 }
5206
5207 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5208 Objects.requireNonNull(pred);
5209 Objects.requireNonNull(body);
5210 MethodType bodyType = body.type();
5211 Class<?> returnType = bodyType.returnType();
5212 List<Class<?>> innerList = bodyType.parameterList();
5213 List<Class<?>> outerList = innerList;
5214 if (returnType == void.class) {
5215 // OK
5216 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5217 // leading V argument missing => error
5218 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5219 throw misMatchedTypes("body function", bodyType, expected);
5220 } else {
5221 outerList = innerList.subList(1, innerList.size());
5222 }
5223 MethodType predType = pred.type();
5224 if (predType.returnType() != boolean.class ||
5225 !predType.effectivelyIdenticalParameters(0, innerList)) {
5226 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5227 }
5228 if (init != null) {
5229 MethodType initType = init.type();
5230 if (initType.returnType() != returnType ||
5231 !initType.effectivelyIdenticalParameters(0, outerList)) {
5232 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5233 }
5234 }
5235 }
5236
5237 /**
5238 * Constructs a loop that runs a given number of iterations.
5239 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5240 * <p>
5241 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5242 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5243 * It will be initialized to 0 and incremented by 1 in each iteration.
5244 * <p>
5245 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5246 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5247 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5248 * <p>
5249 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5250 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5251 * iteration variable.
5252 * The result of the loop handle execution will be the final {@code V} value of that variable
5253 * (or {@code void} if there is no {@code V} variable).
5254 * <p>
5255 * The following rules hold for the argument handles:<ul>
5256 * <li>The {@code iterations} handle must not be {@code null}, and must return
5257 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5258 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5259 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5260 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5261 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5262 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5263 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5264 * of types called the <em>internal parameter list</em>.
5265 * It will constrain the parameter lists of the other loop parts.
5266 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5267 * with no additional {@code A} types, then the internal parameter list is extended by
5268 * the argument types {@code A...} of the {@code iterations} handle.
5269 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5270 * list {@code (A...)} is called the <em>external parameter list</em>.
5271 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5272 * additional state variable of the loop.
5273 * The body must both accept a leading parameter and return a value of this type {@code V}.
5274 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5275 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5276 * <a href="MethodHandles.html#effid">effectively identical</a>
5277 * to the external parameter list {@code (A...)}.
5278 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5279 * {@linkplain #empty default value}.
5280 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5281 * effectively identical to the external parameter list {@code (A...)}.
5282 * </ul>
5283 * <p>
5284 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5285 * <li>The loop handle's result type is the result type {@code V} of the body.
5286 * <li>The loop handle's parameter types are the types {@code (A...)},
5287 * from the external parameter list.
5288 * </ul>
5289 * <p>
5290 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5291 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5292 * arguments passed to the loop.
5293 * <blockquote><pre>{@code
5294 * int iterations(A...);
5295 * V init(A...);
5296 * V body(V, int, A...);
5297 * V countedLoop(A... a...) {
5298 * int end = iterations(a...);
5299 * V v = init(a...);
5300 * for (int i = 0; i < end; ++i) {
5301 * v = body(v, i, a...);
5302 * }
5303 * return v;
5304 * }
5305 * }</pre></blockquote>
5306 *
5307 * @apiNote Example with a fully conformant body method:
5308 * <blockquote><pre>{@code
5309 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5310 * // => a variation on a well known theme
5311 * static String step(String v, int counter, String init) { return "na " + v; }
5312 * // assume MH_step is a handle to the method above
5313 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5314 * MethodHandle start = MethodHandles.identity(String.class);
5315 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5316 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5317 * }</pre></blockquote>
5318 *
5319 * @apiNote Example with the simplest possible body method type,
5320 * and passing the number of iterations to the loop invocation:
5321 * <blockquote><pre>{@code
5322 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5323 * // => a variation on a well known theme
5324 * static String step(String v, int counter ) { return "na " + v; }
5325 * // assume MH_step is a handle to the method above
5326 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5327 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5328 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5329 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5330 * }</pre></blockquote>
5331 *
5332 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5333 * as loop parameters:
5334 * <blockquote><pre>{@code
5335 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5336 * // => a variation on a well known theme
5337 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5338 * // assume MH_step is a handle to the method above
5339 * MethodHandle count = MethodHandles.identity(int.class);
5340 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5341 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5342 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5343 * }</pre></blockquote>
5344 *
5345 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5346 * to enforce a loop type:
5347 * <blockquote><pre>{@code
5348 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5349 * // => a variation on a well known theme
5350 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5351 * // assume MH_step is a handle to the method above
5352 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5353 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5354 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5355 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5356 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5357 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5358 * }</pre></blockquote>
5359 *
5360 * @apiNote The implementation of this method can be expressed as follows:
5361 * <blockquote><pre>{@code
5362 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5363 * return countedLoop(empty(iterations.type()), iterations, init, body);
5364 * }
5365 * }</pre></blockquote>
5366 *
5367 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5368 * result type must be {@code int}. See above for other constraints.
5369 * @param init optional initializer, providing the initial value of the loop variable.
5370 * May be {@code null}, implying a default initial value. See above for other constraints.
5371 * @param body body of the loop, which may not be {@code null}.
5372 * It controls the loop parameters and result type in the standard case (see above for details).
5373 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5374 * and may accept any number of additional types.
5375 * See above for other constraints.
5376 *
5377 * @return a method handle representing the loop.
5378 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5379 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5380 *
5381 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5382 * @since 9
5383 */
5384 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5385 return countedLoop(empty(iterations.type()), iterations, init, body);
5386 }
5387
5388 /**
5389 * Constructs a loop that counts over a range of numbers.
5390 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5391 * <p>
5392 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5393 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5394 * values of the loop counter.
5395 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5396 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5397 * <p>
5398 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5399 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5400 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5401 * <p>
5402 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5403 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5404 * iteration variable.
5405 * The result of the loop handle execution will be the final {@code V} value of that variable
5406 * (or {@code void} if there is no {@code V} variable).
5407 * <p>
5408 * The following rules hold for the argument handles:<ul>
5409 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5410 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5411 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5412 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5413 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5414 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5415 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5416 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5417 * of types called the <em>internal parameter list</em>.
5418 * It will constrain the parameter lists of the other loop parts.
5419 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5420 * with no additional {@code A} types, then the internal parameter list is extended by
5421 * the argument types {@code A...} of the {@code end} handle.
5422 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5423 * list {@code (A...)} is called the <em>external parameter list</em>.
5424 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5425 * additional state variable of the loop.
5426 * The body must both accept a leading parameter and return a value of this type {@code V}.
5427 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5428 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5429 * <a href="MethodHandles.html#effid">effectively identical</a>
5430 * to the external parameter list {@code (A...)}.
5431 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5432 * {@linkplain #empty default value}.
5433 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5434 * effectively identical to the external parameter list {@code (A...)}.
5435 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5436 * to the external parameter list.
5437 * </ul>
5438 * <p>
5439 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5440 * <li>The loop handle's result type is the result type {@code V} of the body.
5441 * <li>The loop handle's parameter types are the types {@code (A...)},
5442 * from the external parameter list.
5443 * </ul>
5444 * <p>
5445 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5446 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5447 * arguments passed to the loop.
5448 * <blockquote><pre>{@code
5449 * int start(A...);
5450 * int end(A...);
5451 * V init(A...);
5452 * V body(V, int, A...);
5453 * V countedLoop(A... a...) {
5454 * int e = end(a...);
5455 * int s = start(a...);
5456 * V v = init(a...);
5457 * for (int i = s; i < e; ++i) {
5458 * v = body(v, i, a...);
5459 * }
5460 * return v;
5461 * }
5462 * }</pre></blockquote>
5463 *
5464 * @apiNote The implementation of this method can be expressed as follows:
5465 * <blockquote><pre>{@code
5466 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5467 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5468 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5469 * // the following semantics:
5470 * // MH_increment: (int limit, int counter) -> counter + 1
5471 * // MH_predicate: (int limit, int counter) -> counter < limit
5472 * Class<?> counterType = start.type().returnType(); // int
5473 * Class<?> returnType = body.type().returnType();
5474 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5475 * if (returnType != void.class) { // ignore the V variable
5476 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5477 * pred = dropArguments(pred, 1, returnType); // ditto
5478 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5479 * }
5480 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5481 * MethodHandle[]
5482 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5483 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5484 * indexVar = { start, incr }; // i = start(); i = i + 1
5485 * return loop(loopLimit, bodyClause, indexVar);
5486 * }
5487 * }</pre></blockquote>
5488 *
5489 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5490 * See above for other constraints.
5491 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5492 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5493 * @param init optional initializer, providing the initial value of the loop variable.
5494 * May be {@code null}, implying a default initial value. See above for other constraints.
5495 * @param body body of the loop, which may not be {@code null}.
5496 * It controls the loop parameters and result type in the standard case (see above for details).
5497 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5498 * and may accept any number of additional types.
5499 * See above for other constraints.
5500 *
5501 * @return a method handle representing the loop.
5502 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5503 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5504 *
5505 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5506 * @since 9
5507 */
5508 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5509 countedLoopChecks(start, end, init, body);
5510 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5511 Class<?> limitType = end.type().returnType(); // yes, int again
5512 Class<?> returnType = body.type().returnType();
5513 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5514 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5515 MethodHandle retv = null;
5516 if (returnType != void.class) {
5517 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5518 pred = dropArguments(pred, 1, returnType); // ditto
5519 retv = dropArguments(identity(returnType), 0, counterType);
5520 }
5521 body = dropArguments(body, 0, counterType); // ignore the limit variable
5522 MethodHandle[]
5523 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5524 bodyClause = { init, body }, // v = init(); v = body(v, i)
5525 indexVar = { start, incr }; // i = start(); i = i + 1
5526 return loop(loopLimit, bodyClause, indexVar);
5527 }
5528
5529 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5530 Objects.requireNonNull(start);
5531 Objects.requireNonNull(end);
5532 Objects.requireNonNull(body);
5533 Class<?> counterType = start.type().returnType();
5534 if (counterType != int.class) {
5535 MethodType expected = start.type().changeReturnType(int.class);
5536 throw misMatchedTypes("start function", start.type(), expected);
5537 } else if (end.type().returnType() != counterType) {
5538 MethodType expected = end.type().changeReturnType(counterType);
5539 throw misMatchedTypes("end function", end.type(), expected);
5540 }
5541 MethodType bodyType = body.type();
5542 Class<?> returnType = bodyType.returnType();
5543 List<Class<?>> innerList = bodyType.parameterList();
5544 // strip leading V value if present
5545 int vsize = (returnType == void.class ? 0 : 1);
5546 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5547 // argument list has no "V" => error
5548 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5549 throw misMatchedTypes("body function", bodyType, expected);
5550 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5551 // missing I type => error
5552 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5553 throw misMatchedTypes("body function", bodyType, expected);
5554 }
5555 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5556 if (outerList.isEmpty()) {
5557 // special case; take lists from end handle
5558 outerList = end.type().parameterList();
5559 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5560 }
5561 MethodType expected = methodType(counterType, outerList);
5562 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5563 throw misMatchedTypes("start parameter types", start.type(), expected);
5564 }
5565 if (end.type() != start.type() &&
5566 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5567 throw misMatchedTypes("end parameter types", end.type(), expected);
5568 }
5569 if (init != null) {
5570 MethodType initType = init.type();
5571 if (initType.returnType() != returnType ||
5572 !initType.effectivelyIdenticalParameters(0, outerList)) {
5573 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5574 }
5575 }
5576 }
5577
5578 /**
5579 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5580 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5581 * <p>
5582 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5583 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5584 * <p>
5585 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5586 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5587 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5588 * <p>
5589 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5590 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5591 * iteration variable.
5592 * The result of the loop handle execution will be the final {@code V} value of that variable
5593 * (or {@code void} if there is no {@code V} variable).
5594 * <p>
5595 * The following rules hold for the argument handles:<ul>
5596 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5597 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5598 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5599 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5600 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5601 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5602 * of types called the <em>internal parameter list</em>.
5603 * It will constrain the parameter lists of the other loop parts.
5604 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5605 * with no additional {@code A} types, then the internal parameter list is extended by
5606 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5607 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5608 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5609 * list {@code (A...)} is called the <em>external parameter list</em>.
5610 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5611 * additional state variable of the loop.
5612 * The body must both accept a leading parameter and return a value of this type {@code V}.
5613 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5614 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5615 * <a href="MethodHandles.html#effid">effectively identical</a>
5616 * to the external parameter list {@code (A...)}.
5617 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5618 * {@linkplain #empty default value}.
5619 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5620 * type {@code java.util.Iterator} or a subtype thereof.
5621 * The iterator it produces when the loop is executed will be assumed
5622 * to yield values which can be converted to type {@code T}.
5623 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5624 * effectively identical to the external parameter list {@code (A...)}.
5625 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5626 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5627 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5628 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5629 * the {@link MethodHandle#asType asType} conversion method.
5630 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5631 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5632 * </ul>
5633 * <p>
5634 * The type {@code T} may be either a primitive or reference.
5635 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5636 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5637 * as if by the {@link MethodHandle#asType asType} conversion method.
5638 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5639 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5640 * <p>
5641 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5642 * <li>The loop handle's result type is the result type {@code V} of the body.
5643 * <li>The loop handle's parameter types are the types {@code (A...)},
5644 * from the external parameter list.
5645 * </ul>
5646 * <p>
5647 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5648 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5649 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5650 * <blockquote><pre>{@code
5651 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5652 * V init(A...);
5653 * V body(V,T,A...);
5654 * V iteratedLoop(A... a...) {
5655 * Iterator<T> it = iterator(a...);
5656 * V v = init(a...);
5657 * while (it.hasNext()) {
5658 * T t = it.next();
5659 * v = body(v, t, a...);
5660 * }
5661 * return v;
5662 * }
5663 * }</pre></blockquote>
5664 *
5665 * @apiNote Example:
5666 * <blockquote><pre>{@code
5667 * // get an iterator from a list
5668 * static List<String> reverseStep(List<String> r, String e) {
5669 * r.add(0, e);
5670 * return r;
5671 * }
5672 * static List<String> newArrayList() { return new ArrayList<>(); }
5673 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5674 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5675 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5676 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5677 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5678 * }</pre></blockquote>
5679 *
5680 * @apiNote The implementation of this method can be expressed approximately as follows:
5681 * <blockquote><pre>{@code
5682 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5683 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5684 * Class<?> returnType = body.type().returnType();
5685 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5686 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5687 * MethodHandle retv = null, step = body, startIter = iterator;
5688 * if (returnType != void.class) {
5689 * // the simple thing first: in (I V A...), drop the I to get V
5690 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5691 * // body type signature (V T A...), internal loop types (I V A...)
5692 * step = swapArguments(body, 0, 1); // swap V <-> T
5693 * }
5694 * if (startIter == null) startIter = MH_getIter;
5695 * MethodHandle[]
5696 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5697 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5698 * return loop(iterVar, bodyClause);
5699 * }
5700 * }</pre></blockquote>
5701 *
5702 * @param iterator an optional handle to return the iterator to start the loop.
5703 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5704 * See above for other constraints.
5705 * @param init optional initializer, providing the initial value of the loop variable.
5706 * May be {@code null}, implying a default initial value. See above for other constraints.
5707 * @param body body of the loop, which may not be {@code null}.
5708 * It controls the loop parameters and result type in the standard case (see above for details).
5709 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5710 * and may accept any number of additional types.
5711 * See above for other constraints.
5712 *
5713 * @return a method handle embodying the iteration loop functionality.
5714 * @throws NullPointerException if the {@code body} handle is {@code null}.
5715 * @throws IllegalArgumentException if any argument violates the above requirements.
5716 *
5717 * @since 9
5718 */
5719 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5720 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5721 Class<?> returnType = body.type().returnType();
5722 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5723 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5724 MethodHandle startIter;
5725 MethodHandle nextVal;
5726 {
5727 MethodType iteratorType;
5728 if (iterator == null) {
5729 // derive argument type from body, if available, else use Iterable
5730 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5731 iteratorType = startIter.type().changeParameterType(0, iterableType);
5732 } else {
5733 // force return type to the internal iterator class
5734 iteratorType = iterator.type().changeReturnType(Iterator.class);
5735 startIter = iterator;
5736 }
5737 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5738 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5739
5740 // perform the asType transforms under an exception transformer, as per spec.:
5741 try {
5742 startIter = startIter.asType(iteratorType);
5743 nextVal = nextRaw.asType(nextValType);
5744 } catch (WrongMethodTypeException ex) {
5745 throw new IllegalArgumentException(ex);
5746 }
5747 }
5748
5749 MethodHandle retv = null, step = body;
5750 if (returnType != void.class) {
5751 // the simple thing first: in (I V A...), drop the I to get V
5752 retv = dropArguments(identity(returnType), 0, Iterator.class);
5753 // body type signature (V T A...), internal loop types (I V A...)
5754 step = swapArguments(body, 0, 1); // swap V <-> T
5755 }
5756
5757 MethodHandle[]
5758 iterVar = { startIter, null, hasNext, retv },
5759 bodyClause = { init, filterArgument(step, 0, nextVal) };
5760 return loop(iterVar, bodyClause);
5761 }
5762
5763 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5764 Objects.requireNonNull(body);
5765 MethodType bodyType = body.type();
5766 Class<?> returnType = bodyType.returnType();
5767 List<Class<?>> internalParamList = bodyType.parameterList();
5768 // strip leading V value if present
5769 int vsize = (returnType == void.class ? 0 : 1);
5770 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5771 // argument list has no "V" => error
5772 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5773 throw misMatchedTypes("body function", bodyType, expected);
5774 } else if (internalParamList.size() <= vsize) {
5775 // missing T type => error
5776 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5777 throw misMatchedTypes("body function", bodyType, expected);
5778 }
5779 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5780 Class<?> iterableType = null;
5781 if (iterator != null) {
5782 // special case; if the body handle only declares V and T then
5783 // the external parameter list is obtained from iterator handle
5784 if (externalParamList.isEmpty()) {
5785 externalParamList = iterator.type().parameterList();
5786 }
5787 MethodType itype = iterator.type();
5788 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5789 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5790 }
5791 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5792 MethodType expected = methodType(itype.returnType(), externalParamList);
5793 throw misMatchedTypes("iterator parameters", itype, expected);
5794 }
5795 } else {
5796 if (externalParamList.isEmpty()) {
5797 // special case; if the iterator handle is null and the body handle
5798 // only declares V and T then the external parameter list consists
5799 // of Iterable
5800 externalParamList = Arrays.asList(Iterable.class);
5801 iterableType = Iterable.class;
5802 } else {
5803 // special case; if the iterator handle is null and the external
5804 // parameter list is not empty then the first parameter must be
5805 // assignable to Iterable
5806 iterableType = externalParamList.get(0);
5807 if (!Iterable.class.isAssignableFrom(iterableType)) {
5808 throw newIllegalArgumentException(
5809 "inferred first loop argument must inherit from Iterable: " + iterableType);
5810 }
5811 }
5812 }
5813 if (init != null) {
5814 MethodType initType = init.type();
5815 if (initType.returnType() != returnType ||
5816 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5817 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5818 }
5819 }
5820 return iterableType; // help the caller a bit
5821 }
5822
5823 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5824 // there should be a better way to uncross my wires
5825 int arity = mh.type().parameterCount();
5826 int[] order = new int[arity];
5827 for (int k = 0; k < arity; k++) order[k] = k;
5828 order[i] = j; order[j] = i;
5829 Class<?>[] types = mh.type().parameterArray();
5830 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5831 MethodType swapType = methodType(mh.type().returnType(), types);
5832 return permuteArguments(mh, swapType, order);
5833 }
5834
5835 /**
5836 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5837 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5838 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5839 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5840 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5841 * {@code try-finally} handle.
5842 * <p>
5843 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5844 * The first is the exception thrown during the
5845 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5846 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5847 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5848 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5849 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5850 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5851 * <p>
5852 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5853 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5854 * two extra leading parameters:<ul>
5855 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5856 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5857 * the result from the execution of the {@code target} handle.
5858 * This parameter is not present if the {@code target} returns {@code void}.
5859 * </ul>
5860 * <p>
5861 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5862 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5863 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5864 * the cleanup.
5865 * <blockquote><pre>{@code
5866 * V target(A..., B...);
5867 * V cleanup(Throwable, V, A...);
5868 * V adapter(A... a, B... b) {
5869 * V result = (zero value for V);
5870 * Throwable throwable = null;
5871 * try {
5872 * result = target(a..., b...);
5873 * } catch (Throwable t) {
5874 * throwable = t;
5875 * throw t;
5876 * } finally {
5877 * result = cleanup(throwable, result, a...);
5878 * }
5879 * return result;
5880 * }
5881 * }</pre></blockquote>
5882 * <p>
5883 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5884 * be modified by execution of the target, and so are passed unchanged
5885 * from the caller to the cleanup, if it is invoked.
5886 * <p>
5887 * The target and cleanup must return the same type, even if the cleanup
5888 * always throws.
5889 * To create such a throwing cleanup, compose the cleanup logic
5890 * with {@link #throwException throwException},
5891 * in order to create a method handle of the correct return type.
5892 * <p>
5893 * Note that {@code tryFinally} never converts exceptions into normal returns.
5894 * In rare cases where exceptions must be converted in that way, first wrap
5895 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5896 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5897 *
5898 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5899 * @param cleanup the handle that is invoked in the finally block.
5900 *
5901 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5902 * @throws NullPointerException if any argument is null
5903 * @throws IllegalArgumentException if {@code cleanup} does not accept
5904 * the required leading arguments, or if the method handle types do
5905 * not match in their return types and their
5906 * corresponding trailing parameters
5907 *
5908 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5909 * @since 9
5910 */
5911 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5912 List<Class<?>> targetParamTypes = target.type().parameterList();
5913 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5914 Class<?> rtype = target.type().returnType();
5915
5916 tryFinallyChecks(target, cleanup);
5917
5918 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5919 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5920 // target parameter list.
5921 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5922
5923 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5924 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5925 }
5926
5927 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5928 Class<?> rtype = target.type().returnType();
5929 if (rtype != cleanup.type().returnType()) {
5930 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5931 }
5932 MethodType cleanupType = cleanup.type();
5933 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5934 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5935 }
5936 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5937 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5938 }
5939 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5940 // target parameter list.
5941 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5942 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5943 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5944 cleanup.type(), target.type());
5945 }
5946 }
5947
5948 }