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