1 /*
2 * Copyright (c) 2008, 2014, 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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23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import java.lang.reflect.*;
29 import java.util.*;
30
31 import sun.invoke.util.ValueConversions;
32 import sun.invoke.util.VerifyAccess;
33 import sun.invoke.util.Wrapper;
34 import sun.reflect.CallerSensitive;
35 import sun.reflect.Reflection;
36 import sun.reflect.misc.ReflectUtil;
37 import sun.security.util.SecurityConstants;
38 import java.lang.invoke.LambdaForm.BasicType;
39
40 import static java.lang.invoke.MethodHandleStatics.*;
41 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
42 import static java.lang.invoke.MethodHandleNatives.Constants.*;
43 import java.util.concurrent.ConcurrentHashMap;
44 import java.util.stream.Collectors;
45 import java.util.stream.Stream;
46
47 /**
48 * This class consists exclusively of static methods that operate on or return
49 * method handles. They fall into several categories:
50 * <ul>
51 * <li>Lookup methods which help create method handles for methods and fields.
52 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
53 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
54 * </ul>
55 *
56 * @author John Rose, JSR 292 EG
57 * @since 1.7
58 */
59 public class MethodHandles {
60
61 private MethodHandles() { } // do not instantiate
62
63 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
64
65 // See IMPL_LOOKUP below.
66
67 //// Method handle creation from ordinary methods.
68
69 /**
70 * Returns a {@link Lookup lookup object} with
71 * full capabilities to emulate all supported bytecode behaviors of the caller.
72 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
73 * Factory methods on the lookup object can create
74 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
75 * for any member that the caller has access to via bytecodes,
76 * including protected and private fields and methods.
77 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
78 * Do not store it in place where untrusted code can access it.
79 * <p>
80 * This method is caller sensitive, which means that it may return different
81 * values to different callers.
82 * <p>
83 * For any given caller class {@code C}, the lookup object returned by this call
84 * has equivalent capabilities to any lookup object
85 * supplied by the JVM to the bootstrap method of an
86 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
87 * executing in the same caller class {@code C}.
88 * @return a lookup object for the caller of this method, with private access
89 */
90 @CallerSensitive
91 public static Lookup lookup() {
92 return new Lookup(Reflection.getCallerClass());
93 }
94
95 /**
96 * Returns a {@link Lookup lookup object} which is trusted minimally.
97 * It can only be used to create method handles to
98 * publicly accessible fields and methods.
99 * <p>
100 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
101 * of this lookup object will be {@link java.lang.Object}.
102 *
103 * <p style="font-size:smaller;">
104 * <em>Discussion:</em>
105 * The lookup class can be changed to any other class {@code C} using an expression of the form
106 * {@link Lookup#in publicLookup().in(C.class)}.
107 * Since all classes have equal access to public names,
108 * such a change would confer no new access rights.
109 * A public lookup object is always subject to
110 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
111 * Also, it cannot access
112 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
113 * @return a lookup object which is trusted minimally
114 */
115 public static Lookup publicLookup() {
116 return Lookup.PUBLIC_LOOKUP;
117 }
118
119 /**
120 * Performs an unchecked "crack" of a
121 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
122 * The result is as if the user had obtained a lookup object capable enough
123 * to crack the target method handle, called
124 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
125 * on the target to obtain its symbolic reference, and then called
126 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
127 * to resolve the symbolic reference to a member.
128 * <p>
129 * If there is a security manager, its {@code checkPermission} method
130 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
131 * @param <T> the desired type of the result, either {@link Member} or a subtype
132 * @param target a direct method handle to crack into symbolic reference components
133 * @param expected a class object representing the desired result type {@code T}
134 * @return a reference to the method, constructor, or field object
135 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
136 * @exception NullPointerException if either argument is {@code null}
137 * @exception IllegalArgumentException if the target is not a direct method handle
138 * @exception ClassCastException if the member is not of the expected type
139 * @since 1.8
140 */
141 public static <T extends Member> T
142 reflectAs(Class<T> expected, MethodHandle target) {
143 SecurityManager smgr = System.getSecurityManager();
144 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
145 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
146 return lookup.revealDirect(target).reflectAs(expected, lookup);
147 }
148 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
149 private static final java.security.Permission ACCESS_PERMISSION =
150 new ReflectPermission("suppressAccessChecks");
151
152 /**
153 * A <em>lookup object</em> is a factory for creating method handles,
154 * when the creation requires access checking.
155 * Method handles do not perform
156 * access checks when they are called, but rather when they are created.
157 * Therefore, method handle access
158 * restrictions must be enforced when a method handle is created.
159 * The caller class against which those restrictions are enforced
160 * is known as the {@linkplain #lookupClass lookup class}.
161 * <p>
162 * A lookup class which needs to create method handles will call
163 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
164 * When the {@code Lookup} factory object is created, the identity of the lookup class is
165 * determined, and securely stored in the {@code Lookup} object.
166 * The lookup class (or its delegates) may then use factory methods
167 * on the {@code Lookup} object to create method handles for access-checked members.
168 * This includes all methods, constructors, and fields which are allowed to the lookup class,
169 * even private ones.
170 *
171 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
172 * The factory methods on a {@code Lookup} object correspond to all major
173 * use cases for methods, constructors, and fields.
174 * Each method handle created by a factory method is the functional
175 * equivalent of a particular <em>bytecode behavior</em>.
176 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
177 * Here is a summary of the correspondence between these factory methods and
178 * the behavior of the resulting method handles:
179 * <table border=1 cellpadding=5 summary="lookup method behaviors">
180 * <tr>
181 * <th><a name="equiv"></a>lookup expression</th>
182 * <th>member</th>
183 * <th>bytecode behavior</th>
184 * </tr>
185 * <tr>
186 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
187 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
188 * </tr>
189 * <tr>
190 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
191 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
192 * </tr>
193 * <tr>
194 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
195 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
196 * </tr>
197 * <tr>
198 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
199 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
200 * </tr>
201 * <tr>
202 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
203 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
204 * </tr>
205 * <tr>
206 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
207 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
208 * </tr>
209 * <tr>
210 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
211 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
212 * </tr>
213 * <tr>
214 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
215 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
216 * </tr>
217 * <tr>
218 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
219 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
220 * </tr>
221 * <tr>
222 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
223 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
224 * </tr>
225 * <tr>
226 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
227 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
228 * </tr>
229 * <tr>
230 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
231 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
232 * </tr>
233 * <tr>
234 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
235 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
236 * </tr>
237 * <tr>
238 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
239 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
240 * </tr>
241 * </table>
242 *
243 * Here, the type {@code C} is the class or interface being searched for a member,
244 * documented as a parameter named {@code refc} in the lookup methods.
245 * The method type {@code MT} is composed from the return type {@code T}
246 * and the sequence of argument types {@code A*}.
247 * The constructor also has a sequence of argument types {@code A*} and
248 * is deemed to return the newly-created object of type {@code C}.
249 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
250 * The formal parameter {@code this} stands for the self-reference of type {@code C};
251 * if it is present, it is always the leading argument to the method handle invocation.
252 * (In the case of some {@code protected} members, {@code this} may be
253 * restricted in type to the lookup class; see below.)
254 * The name {@code arg} stands for all the other method handle arguments.
255 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
256 * stands for a null reference if the accessed method or field is static,
257 * and {@code this} otherwise.
258 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
259 * for reflective objects corresponding to the given members.
260 * <p>
261 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
262 * as if by {@code ldc CONSTANT_Class}.
263 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
264 * <p>
265 * In cases where the given member is of variable arity (i.e., a method or constructor)
266 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
267 * In all other cases, the returned method handle will be of fixed arity.
268 * <p style="font-size:smaller;">
269 * <em>Discussion:</em>
270 * The equivalence between looked-up method handles and underlying
271 * class members and bytecode behaviors
272 * can break down in a few ways:
273 * <ul style="font-size:smaller;">
274 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
275 * the lookup can still succeed, even when there is no equivalent
276 * Java expression or bytecoded constant.
277 * <li>Likewise, if {@code T} or {@code MT}
278 * is not symbolically accessible from the lookup class's loader,
279 * the lookup can still succeed.
280 * For example, lookups for {@code MethodHandle.invokeExact} and
281 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
282 * <li>If there is a security manager installed, it can forbid the lookup
283 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
284 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
285 * constant is not subject to security manager checks.
286 * <li>If the looked-up method has a
287 * <a href="MethodHandle.html#maxarity">very large arity</a>,
288 * the method handle creation may fail, due to the method handle
289 * type having too many parameters.
290 * </ul>
291 *
292 * <h1><a name="access"></a>Access checking</h1>
293 * Access checks are applied in the factory methods of {@code Lookup},
294 * when a method handle is created.
295 * This is a key difference from the Core Reflection API, since
296 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
297 * performs access checking against every caller, on every call.
298 * <p>
299 * All access checks start from a {@code Lookup} object, which
300 * compares its recorded lookup class against all requests to
301 * create method handles.
302 * A single {@code Lookup} object can be used to create any number
303 * of access-checked method handles, all checked against a single
304 * lookup class.
305 * <p>
306 * A {@code Lookup} object can be shared with other trusted code,
307 * such as a metaobject protocol.
308 * A shared {@code Lookup} object delegates the capability
309 * to create method handles on private members of the lookup class.
310 * Even if privileged code uses the {@code Lookup} object,
311 * the access checking is confined to the privileges of the
312 * original lookup class.
313 * <p>
314 * A lookup can fail, because
315 * the containing class is not accessible to the lookup class, or
316 * because the desired class member is missing, or because the
317 * desired class member is not accessible to the lookup class, or
318 * because the lookup object is not trusted enough to access the member.
319 * In any of these cases, a {@code ReflectiveOperationException} will be
320 * thrown from the attempted lookup. The exact class will be one of
321 * the following:
322 * <ul>
323 * <li>NoSuchMethodException — if a method is requested but does not exist
324 * <li>NoSuchFieldException — if a field is requested but does not exist
325 * <li>IllegalAccessException — if the member exists but an access check fails
326 * </ul>
327 * <p>
328 * In general, the conditions under which a method handle may be
329 * looked up for a method {@code M} are no more restrictive than the conditions
330 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
331 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
332 * a method handle lookup will generally raise a corresponding
333 * checked exception, such as {@code NoSuchMethodException}.
334 * And the effect of invoking the method handle resulting from the lookup
335 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
336 * to executing the compiled, verified, and resolved call to {@code M}.
337 * The same point is true of fields and constructors.
338 * <p style="font-size:smaller;">
339 * <em>Discussion:</em>
340 * Access checks only apply to named and reflected methods,
341 * constructors, and fields.
342 * Other method handle creation methods, such as
343 * {@link MethodHandle#asType MethodHandle.asType},
344 * do not require any access checks, and are used
345 * independently of any {@code Lookup} object.
346 * <p>
347 * If the desired member is {@code protected}, the usual JVM rules apply,
348 * including the requirement that the lookup class must be either be in the
349 * same package as the desired member, or must inherit that member.
350 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
351 * In addition, if the desired member is a non-static field or method
352 * in a different package, the resulting method handle may only be applied
353 * to objects of the lookup class or one of its subclasses.
354 * This requirement is enforced by narrowing the type of the leading
355 * {@code this} parameter from {@code C}
356 * (which will necessarily be a superclass of the lookup class)
357 * to the lookup class itself.
358 * <p>
359 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
360 * that the receiver argument must match both the resolved method <em>and</em>
361 * the current class. Again, this requirement is enforced by narrowing the
362 * type of the leading parameter to the resulting method handle.
363 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
364 * <p>
365 * The JVM represents constructors and static initializer blocks as internal methods
366 * with special names ({@code "<init>"} and {@code "<clinit>"}).
367 * The internal syntax of invocation instructions allows them to refer to such internal
368 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
369 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
370 * <p>
371 * In some cases, access between nested classes is obtained by the Java compiler by creating
372 * an wrapper method to access a private method of another class
373 * in the same top-level declaration.
374 * For example, a nested class {@code C.D}
375 * can access private members within other related classes such as
376 * {@code C}, {@code C.D.E}, or {@code C.B},
377 * but the Java compiler may need to generate wrapper methods in
378 * those related classes. In such cases, a {@code Lookup} object on
379 * {@code C.E} would be unable to those private members.
380 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
381 * which can transform a lookup on {@code C.E} into one on any of those other
382 * classes, without special elevation of privilege.
383 * <p>
384 * The accesses permitted to a given lookup object may be limited,
385 * according to its set of {@link #lookupModes lookupModes},
386 * to a subset of members normally accessible to the lookup class.
387 * For example, the {@link MethodHandles#publicLookup publicLookup}
388 * method produces a lookup object which is only allowed to access
389 * public members in public classes.
390 * The caller sensitive method {@link MethodHandles#lookup lookup}
391 * produces a lookup object with full capabilities relative to
392 * its caller class, to emulate all supported bytecode behaviors.
393 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
394 * with fewer access modes than the original lookup object.
395 *
396 * <p style="font-size:smaller;">
397 * <a name="privacc"></a>
398 * <em>Discussion of private access:</em>
399 * We say that a lookup has <em>private access</em>
400 * if its {@linkplain #lookupModes lookup modes}
401 * include the possibility of accessing {@code private} members.
402 * As documented in the relevant methods elsewhere,
403 * only lookups with private access possess the following capabilities:
404 * <ul style="font-size:smaller;">
405 * <li>access private fields, methods, and constructors of the lookup class
406 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
407 * such as {@code Class.forName}
408 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
409 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
410 * for classes accessible to the lookup class
411 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
412 * within the same package member
413 * </ul>
414 * <p style="font-size:smaller;">
415 * Each of these permissions is a consequence of the fact that a lookup object
416 * with private access can be securely traced back to an originating class,
417 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
418 * can be reliably determined and emulated by method handles.
419 *
420 * <h1><a name="secmgr"></a>Security manager interactions</h1>
421 * Although bytecode instructions can only refer to classes in
422 * a related class loader, this API can search for methods in any
423 * class, as long as a reference to its {@code Class} object is
424 * available. Such cross-loader references are also possible with the
425 * Core Reflection API, and are impossible to bytecode instructions
426 * such as {@code invokestatic} or {@code getfield}.
427 * There is a {@linkplain java.lang.SecurityManager security manager API}
428 * to allow applications to check such cross-loader references.
429 * These checks apply to both the {@code MethodHandles.Lookup} API
430 * and the Core Reflection API
431 * (as found on {@link java.lang.Class Class}).
432 * <p>
433 * If a security manager is present, member and class lookups are subject to
434 * additional checks.
435 * From one to three calls are made to the security manager.
436 * Any of these calls can refuse access by throwing a
437 * {@link java.lang.SecurityException SecurityException}.
438 * Define {@code smgr} as the security manager,
439 * {@code lookc} as the lookup class of the current lookup object,
440 * {@code refc} as the containing class in which the member
441 * is being sought, and {@code defc} as the class in which the
442 * member is actually defined.
443 * (If a class or other type is being accessed,
444 * the {@code refc} and {@code defc} values are the class itself.)
445 * The value {@code lookc} is defined as <em>not present</em>
446 * if the current lookup object does not have
447 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
448 * The calls are made according to the following rules:
449 * <ul>
450 * <li><b>Step 1:</b>
451 * If {@code lookc} is not present, or if its class loader is not
452 * the same as or an ancestor of the class loader of {@code refc},
453 * then {@link SecurityManager#checkPackageAccess
454 * smgr.checkPackageAccess(refcPkg)} is called,
455 * where {@code refcPkg} is the package of {@code refc}.
456 * <li><b>Step 2a:</b>
457 * If the retrieved member is not public and
458 * {@code lookc} is not present, then
459 * {@link SecurityManager#checkPermission smgr.checkPermission}
460 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
461 * <li><b>Step 2b:</b>
462 * If the retrieved class has a {@code null} class loader,
463 * and {@code lookc} is not present, then
464 * {@link SecurityManager#checkPermission smgr.checkPermission}
465 * with {@code RuntimePermission("getClassLoader")} is called.
466 * <li><b>Step 3:</b>
467 * If the retrieved member is not public,
468 * and if {@code lookc} is not present,
469 * and if {@code defc} and {@code refc} are different,
470 * then {@link SecurityManager#checkPackageAccess
471 * smgr.checkPackageAccess(defcPkg)} is called,
472 * where {@code defcPkg} is the package of {@code defc}.
473 * </ul>
474 * Security checks are performed after other access checks have passed.
475 * Therefore, the above rules presuppose a member or class that is public,
476 * or else that is being accessed from a lookup class that has
477 * rights to access the member or class.
478 *
479 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
480 * A small number of Java methods have a special property called caller sensitivity.
481 * A <em>caller-sensitive</em> method can behave differently depending on the
482 * identity of its immediate caller.
483 * <p>
484 * If a method handle for a caller-sensitive method is requested,
485 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
486 * but they take account of the lookup class in a special way.
487 * The resulting method handle behaves as if it were called
488 * from an instruction contained in the lookup class,
489 * so that the caller-sensitive method detects the lookup class.
490 * (By contrast, the invoker of the method handle is disregarded.)
491 * Thus, in the case of caller-sensitive methods,
492 * different lookup classes may give rise to
493 * differently behaving method handles.
494 * <p>
495 * In cases where the lookup object is
496 * {@link MethodHandles#publicLookup() publicLookup()},
497 * or some other lookup object without
498 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
499 * the lookup class is disregarded.
500 * In such cases, no caller-sensitive method handle can be created,
501 * access is forbidden, and the lookup fails with an
502 * {@code IllegalAccessException}.
503 * <p style="font-size:smaller;">
504 * <em>Discussion:</em>
505 * For example, the caller-sensitive method
506 * {@link java.lang.Class#forName(String) Class.forName(x)}
507 * can return varying classes or throw varying exceptions,
508 * depending on the class loader of the class that calls it.
509 * A public lookup of {@code Class.forName} will fail, because
510 * there is no reasonable way to determine its bytecode behavior.
511 * <p style="font-size:smaller;">
512 * If an application caches method handles for broad sharing,
513 * it should use {@code publicLookup()} to create them.
514 * If there is a lookup of {@code Class.forName}, it will fail,
515 * and the application must take appropriate action in that case.
516 * It may be that a later lookup, perhaps during the invocation of a
517 * bootstrap method, can incorporate the specific identity
518 * of the caller, making the method accessible.
519 * <p style="font-size:smaller;">
520 * The function {@code MethodHandles.lookup} is caller sensitive
521 * so that there can be a secure foundation for lookups.
522 * Nearly all other methods in the JSR 292 API rely on lookup
523 * objects to check access requests.
524 */
525 public static final
526 class Lookup {
527 /** The class on behalf of whom the lookup is being performed. */
528 private final Class<?> lookupClass;
529
530 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
531 private final int allowedModes;
532
533 /** A single-bit mask representing {@code public} access,
534 * which may contribute to the result of {@link #lookupModes lookupModes}.
535 * The value, {@code 0x01}, happens to be the same as the value of the
536 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
537 */
538 public static final int PUBLIC = Modifier.PUBLIC;
539
540 /** A single-bit mask representing {@code private} access,
541 * which may contribute to the result of {@link #lookupModes lookupModes}.
542 * The value, {@code 0x02}, happens to be the same as the value of the
543 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
544 */
545 public static final int PRIVATE = Modifier.PRIVATE;
546
547 /** A single-bit mask representing {@code protected} access,
548 * which may contribute to the result of {@link #lookupModes lookupModes}.
549 * The value, {@code 0x04}, happens to be the same as the value of the
550 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
551 */
552 public static final int PROTECTED = Modifier.PROTECTED;
553
554 /** A single-bit mask representing {@code package} access (default access),
555 * which may contribute to the result of {@link #lookupModes lookupModes}.
556 * The value is {@code 0x08}, which does not correspond meaningfully to
557 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
558 */
559 public static final int PACKAGE = Modifier.STATIC;
560
561 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
562 private static final int TRUSTED = -1;
563
564 private static int fixmods(int mods) {
565 mods &= (ALL_MODES - PACKAGE);
566 return (mods != 0) ? mods : PACKAGE;
567 }
568
569 /** Tells which class is performing the lookup. It is this class against
570 * which checks are performed for visibility and access permissions.
571 * <p>
572 * The class implies a maximum level of access permission,
573 * but the permissions may be additionally limited by the bitmask
574 * {@link #lookupModes lookupModes}, which controls whether non-public members
575 * can be accessed.
576 * @return the lookup class, on behalf of which this lookup object finds members
577 */
578 public Class<?> lookupClass() {
579 return lookupClass;
580 }
581
582 // This is just for calling out to MethodHandleImpl.
583 private Class<?> lookupClassOrNull() {
584 return (allowedModes == TRUSTED) ? null : lookupClass;
585 }
586
587 /** Tells which access-protection classes of members this lookup object can produce.
588 * The result is a bit-mask of the bits
589 * {@linkplain #PUBLIC PUBLIC (0x01)},
590 * {@linkplain #PRIVATE PRIVATE (0x02)},
591 * {@linkplain #PROTECTED PROTECTED (0x04)},
592 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
593 * <p>
594 * A freshly-created lookup object
595 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
596 * has all possible bits set, since the caller class can access all its own members.
597 * A lookup object on a new lookup class
598 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
599 * may have some mode bits set to zero.
600 * The purpose of this is to restrict access via the new lookup object,
601 * so that it can access only names which can be reached by the original
602 * lookup object, and also by the new lookup class.
603 * @return the lookup modes, which limit the kinds of access performed by this lookup object
604 */
605 public int lookupModes() {
606 return allowedModes & ALL_MODES;
607 }
608
609 /** Embody the current class (the lookupClass) as a lookup class
610 * for method handle creation.
611 * Must be called by from a method in this package,
612 * which in turn is called by a method not in this package.
613 */
614 Lookup(Class<?> lookupClass) {
615 this(lookupClass, ALL_MODES);
616 // make sure we haven't accidentally picked up a privileged class:
617 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
618 }
619
620 private Lookup(Class<?> lookupClass, int allowedModes) {
621 this.lookupClass = lookupClass;
622 this.allowedModes = allowedModes;
623 }
624
625 /**
626 * Creates a lookup on the specified new lookup class.
627 * The resulting object will report the specified
628 * class as its own {@link #lookupClass lookupClass}.
629 * <p>
630 * However, the resulting {@code Lookup} object is guaranteed
631 * to have no more access capabilities than the original.
632 * In particular, access capabilities can be lost as follows:<ul>
633 * <li>If the new lookup class differs from the old one,
634 * protected members will not be accessible by virtue of inheritance.
635 * (Protected members may continue to be accessible because of package sharing.)
636 * <li>If the new lookup class is in a different package
637 * than the old one, protected and default (package) members will not be accessible.
638 * <li>If the new lookup class is not within the same package member
639 * as the old one, private members will not be accessible.
640 * <li>If the new lookup class is not accessible to the old lookup class,
641 * then no members, not even public members, will be accessible.
642 * (In all other cases, public members will continue to be accessible.)
643 * </ul>
644 *
645 * @param requestedLookupClass the desired lookup class for the new lookup object
646 * @return a lookup object which reports the desired lookup class
647 * @throws NullPointerException if the argument is null
648 */
649 public Lookup in(Class<?> requestedLookupClass) {
650 Objects.requireNonNull(requestedLookupClass);
651 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
652 return new Lookup(requestedLookupClass, ALL_MODES);
653 if (requestedLookupClass == this.lookupClass)
654 return this; // keep same capabilities
655 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
656 if ((newModes & PACKAGE) != 0
657 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
658 newModes &= ~(PACKAGE|PRIVATE);
659 }
660 // Allow nestmate lookups to be created without special privilege:
661 if ((newModes & PRIVATE) != 0
662 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
663 newModes &= ~PRIVATE;
664 }
665 if ((newModes & PUBLIC) != 0
666 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
667 // The requested class it not accessible from the lookup class.
668 // No permissions.
669 newModes = 0;
670 }
671 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
672 return new Lookup(requestedLookupClass, newModes);
673 }
674
675 // Make sure outer class is initialized first.
676 static { IMPL_NAMES.getClass(); }
677
678 /** Version of lookup which is trusted minimally.
679 * It can only be used to create method handles to
680 * publicly accessible members.
681 */
682 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
683
684 /** Package-private version of lookup which is trusted. */
685 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
686
687 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
688 String name = lookupClass.getName();
689 if (name.startsWith("java.lang.invoke."))
690 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
691
692 // For caller-sensitive MethodHandles.lookup()
693 // disallow lookup more restricted packages
694 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
695 if (name.startsWith("java.") ||
696 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
697 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
698 }
699 }
700 }
701
702 /**
703 * Displays the name of the class from which lookups are to be made.
704 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
705 * If there are restrictions on the access permitted to this lookup,
706 * this is indicated by adding a suffix to the class name, consisting
707 * of a slash and a keyword. The keyword represents the strongest
708 * allowed access, and is chosen as follows:
709 * <ul>
710 * <li>If no access is allowed, the suffix is "/noaccess".
711 * <li>If only public access is allowed, the suffix is "/public".
712 * <li>If only public and package access are allowed, the suffix is "/package".
713 * <li>If only public, package, and private access are allowed, the suffix is "/private".
714 * </ul>
715 * If none of the above cases apply, it is the case that full
716 * access (public, package, private, and protected) is allowed.
717 * In this case, no suffix is added.
718 * This is true only of an object obtained originally from
719 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
720 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
721 * always have restricted access, and will display a suffix.
722 * <p>
723 * (It may seem strange that protected access should be
724 * stronger than private access. Viewed independently from
725 * package access, protected access is the first to be lost,
726 * because it requires a direct subclass relationship between
727 * caller and callee.)
728 * @see #in
729 */
730 @Override
731 public String toString() {
732 String cname = lookupClass.getName();
733 switch (allowedModes) {
734 case 0: // no privileges
735 return cname + "/noaccess";
736 case PUBLIC:
737 return cname + "/public";
738 case PUBLIC|PACKAGE:
739 return cname + "/package";
740 case ALL_MODES & ~PROTECTED:
741 return cname + "/private";
742 case ALL_MODES:
743 return cname;
744 case TRUSTED:
745 return "/trusted"; // internal only; not exported
746 default: // Should not happen, but it's a bitfield...
747 cname = cname + "/" + Integer.toHexString(allowedModes);
748 assert(false) : cname;
749 return cname;
750 }
751 }
752
753 /**
754 * Produces a method handle for a static method.
755 * The type of the method handle will be that of the method.
756 * (Since static methods do not take receivers, there is no
757 * additional receiver argument inserted into the method handle type,
758 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
759 * The method and all its argument types must be accessible to the lookup object.
760 * <p>
761 * The returned method handle will have
762 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
763 * the method's variable arity modifier bit ({@code 0x0080}) is set.
764 * <p>
765 * If the returned method handle is invoked, the method's class will
766 * be initialized, if it has not already been initialized.
767 * <p><b>Example:</b>
768 * <blockquote><pre>{@code
769 import static java.lang.invoke.MethodHandles.*;
770 import static java.lang.invoke.MethodType.*;
771 ...
772 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
773 "asList", methodType(List.class, Object[].class));
774 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
775 * }</pre></blockquote>
776 * @param refc the class from which the method is accessed
777 * @param name the name of the method
778 * @param type the type of the method
779 * @return the desired method handle
780 * @throws NoSuchMethodException if the method does not exist
781 * @throws IllegalAccessException if access checking fails,
782 * or if the method is not {@code static},
783 * or if the method's variable arity modifier bit
784 * is set and {@code asVarargsCollector} fails
785 * @exception SecurityException if a security manager is present and it
786 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
787 * @throws NullPointerException if any argument is null
788 */
789 public
790 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
791 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
792 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
793 }
794
795 /**
796 * Produces a method handle for a virtual method.
797 * The type of the method handle will be that of the method,
798 * with the receiver type (usually {@code refc}) prepended.
799 * The method and all its argument types must be accessible to the lookup object.
800 * <p>
801 * When called, the handle will treat the first argument as a receiver
802 * and dispatch on the receiver's type to determine which method
803 * implementation to enter.
804 * (The dispatching action is identical with that performed by an
805 * {@code invokevirtual} or {@code invokeinterface} instruction.)
806 * <p>
807 * The first argument will be of type {@code refc} if the lookup
808 * class has full privileges to access the member. Otherwise
809 * the member must be {@code protected} and the first argument
810 * will be restricted in type to the lookup class.
811 * <p>
812 * The returned method handle will have
813 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
814 * the method's variable arity modifier bit ({@code 0x0080}) is set.
815 * <p>
816 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
817 * instructions and method handles produced by {@code findVirtual},
818 * if the class is {@code MethodHandle} and the name string is
819 * {@code invokeExact} or {@code invoke}, the resulting
820 * method handle is equivalent to one produced by
821 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
822 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
823 * with the same {@code type} argument.
824 *
825 * <b>Example:</b>
826 * <blockquote><pre>{@code
827 import static java.lang.invoke.MethodHandles.*;
828 import static java.lang.invoke.MethodType.*;
829 ...
830 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
831 "concat", methodType(String.class, String.class));
832 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
833 "hashCode", methodType(int.class));
834 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
835 "hashCode", methodType(int.class));
836 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
837 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
838 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
839 // interface method:
840 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
841 "subSequence", methodType(CharSequence.class, int.class, int.class));
842 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
843 // constructor "internal method" must be accessed differently:
844 MethodType MT_newString = methodType(void.class); //()V for new String()
845 try { assertEquals("impossible", lookup()
846 .findVirtual(String.class, "<init>", MT_newString));
847 } catch (NoSuchMethodException ex) { } // OK
848 MethodHandle MH_newString = publicLookup()
849 .findConstructor(String.class, MT_newString);
850 assertEquals("", (String) MH_newString.invokeExact());
851 * }</pre></blockquote>
852 *
853 * @param refc the class or interface from which the method is accessed
854 * @param name the name of the method
855 * @param type the type of the method, with the receiver argument omitted
856 * @return the desired method handle
857 * @throws NoSuchMethodException if the method does not exist
858 * @throws IllegalAccessException if access checking fails,
859 * or if the method is {@code static}
860 * or if the method's variable arity modifier bit
861 * is set and {@code asVarargsCollector} fails
862 * @exception SecurityException if a security manager is present and it
863 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
864 * @throws NullPointerException if any argument is null
865 */
866 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
867 if (refc == MethodHandle.class) {
868 MethodHandle mh = findVirtualForMH(name, type);
869 if (mh != null) return mh;
870 }
871 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
872 MemberName method = resolveOrFail(refKind, refc, name, type);
873 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
874 }
875 private MethodHandle findVirtualForMH(String name, MethodType type) {
876 // these names require special lookups because of the implicit MethodType argument
877 if ("invoke".equals(name))
878 return invoker(type);
879 if ("invokeExact".equals(name))
880 return exactInvoker(type);
881 if ("invokeBasic".equals(name))
882 return basicInvoker(type);
883 assert(!MemberName.isMethodHandleInvokeName(name));
884 return null;
885 }
886
887 /**
888 * Produces a method handle which creates an object and initializes it, using
889 * the constructor of the specified type.
890 * The parameter types of the method handle will be those of the constructor,
891 * while the return type will be a reference to the constructor's class.
892 * The constructor and all its argument types must be accessible to the lookup object.
893 * <p>
894 * The requested type must have a return type of {@code void}.
895 * (This is consistent with the JVM's treatment of constructor type descriptors.)
896 * <p>
897 * The returned method handle will have
898 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
899 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
900 * <p>
901 * If the returned method handle is invoked, the constructor's class will
902 * be initialized, if it has not already been initialized.
903 * <p><b>Example:</b>
904 * <blockquote><pre>{@code
905 import static java.lang.invoke.MethodHandles.*;
906 import static java.lang.invoke.MethodType.*;
907 ...
908 MethodHandle MH_newArrayList = publicLookup().findConstructor(
909 ArrayList.class, methodType(void.class, Collection.class));
910 Collection orig = Arrays.asList("x", "y");
911 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
912 assert(orig != copy);
913 assertEquals(orig, copy);
914 // a variable-arity constructor:
915 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
916 ProcessBuilder.class, methodType(void.class, String[].class));
917 ProcessBuilder pb = (ProcessBuilder)
918 MH_newProcessBuilder.invoke("x", "y", "z");
919 assertEquals("[x, y, z]", pb.command().toString());
920 * }</pre></blockquote>
921 * @param refc the class or interface from which the method is accessed
922 * @param type the type of the method, with the receiver argument omitted, and a void return type
923 * @return the desired method handle
924 * @throws NoSuchMethodException if the constructor does not exist
925 * @throws IllegalAccessException if access checking fails
926 * or if the method's variable arity modifier bit
927 * is set and {@code asVarargsCollector} fails
928 * @exception SecurityException if a security manager is present and it
929 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
930 * @throws NullPointerException if any argument is null
931 */
932 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
933 String name = "<init>";
934 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
935 return getDirectConstructor(refc, ctor);
936 }
937
938 /**
939 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
940 * initializer of the class is not run.
941 *
942 * @param targetName the fully qualified name of the class to be looked up.
943 * @return the requested class.
944 * @exception SecurityException if a security manager is present and it
945 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
946 * @throws LinkageError if the linkage fails
947 * @throws ClassNotFoundException if the class does not exist.
948 * @throws IllegalAccessException if the class is not accessible, using the allowed access
949 * modes.
950 * @exception SecurityException if a security manager is present and it
951 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
952 * @since 9
953 */
954 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
955 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
956 return accessClass(targetClass);
957 }
958
959 /**
960 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
961 * static initializer of the class is not run.
962 *
963 * @param targetClass the class to be access-checked
964 *
965 * @return the class that has been access-checked
966 *
967 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
968 * modes.
969 * @exception SecurityException if a security manager is present and it
970 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
971 * @since 9
972 */
973 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
974 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
975 throw new MemberName(targetClass).makeAccessException("access violation", this);
976 }
977 checkSecurityManager(targetClass, null);
978 return targetClass;
979 }
980
981 /**
982 * Produces an early-bound method handle for a virtual method.
983 * It will bypass checks for overriding methods on the receiver,
984 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
985 * instruction from within the explicitly specified {@code specialCaller}.
986 * The type of the method handle will be that of the method,
987 * with a suitably restricted receiver type prepended.
988 * (The receiver type will be {@code specialCaller} or a subtype.)
989 * The method and all its argument types must be accessible
990 * to the lookup object.
991 * <p>
992 * Before method resolution,
993 * if the explicitly specified caller class is not identical with the
994 * lookup class, or if this lookup object does not have
995 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
996 * privileges, the access fails.
997 * <p>
998 * The returned method handle will have
999 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1000 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1001 * <p style="font-size:smaller;">
1002 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1003 * even though the {@code invokespecial} instruction can refer to them
1004 * in special circumstances. Use {@link #findConstructor findConstructor}
1005 * to access instance initialization methods in a safe manner.)</em>
1006 * <p><b>Example:</b>
1007 * <blockquote><pre>{@code
1008 import static java.lang.invoke.MethodHandles.*;
1009 import static java.lang.invoke.MethodType.*;
1010 ...
1011 static class Listie extends ArrayList {
1012 public String toString() { return "[wee Listie]"; }
1013 static Lookup lookup() { return MethodHandles.lookup(); }
1014 }
1015 ...
1016 // no access to constructor via invokeSpecial:
1017 MethodHandle MH_newListie = Listie.lookup()
1018 .findConstructor(Listie.class, methodType(void.class));
1019 Listie l = (Listie) MH_newListie.invokeExact();
1020 try { assertEquals("impossible", Listie.lookup().findSpecial(
1021 Listie.class, "<init>", methodType(void.class), Listie.class));
1022 } catch (NoSuchMethodException ex) { } // OK
1023 // access to super and self methods via invokeSpecial:
1024 MethodHandle MH_super = Listie.lookup().findSpecial(
1025 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1026 MethodHandle MH_this = Listie.lookup().findSpecial(
1027 Listie.class, "toString" , methodType(String.class), Listie.class);
1028 MethodHandle MH_duper = Listie.lookup().findSpecial(
1029 Object.class, "toString" , methodType(String.class), Listie.class);
1030 assertEquals("[]", (String) MH_super.invokeExact(l));
1031 assertEquals(""+l, (String) MH_this.invokeExact(l));
1032 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1033 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1034 String.class, "toString", methodType(String.class), Listie.class));
1035 } catch (IllegalAccessException ex) { } // OK
1036 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1037 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1038 * }</pre></blockquote>
1039 *
1040 * @param refc the class or interface from which the method is accessed
1041 * @param name the name of the method (which must not be "<init>")
1042 * @param type the type of the method, with the receiver argument omitted
1043 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1044 * @return the desired method handle
1045 * @throws NoSuchMethodException if the method does not exist
1046 * @throws IllegalAccessException if access checking fails
1047 * or if the method's variable arity modifier bit
1048 * is set and {@code asVarargsCollector} fails
1049 * @exception SecurityException if a security manager is present and it
1050 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1051 * @throws NullPointerException if any argument is null
1052 */
1053 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1054 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1055 checkSpecialCaller(specialCaller, refc);
1056 Lookup specialLookup = this.in(specialCaller);
1057 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1058 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1059 }
1060
1061 /**
1062 * Produces a method handle giving read access to a non-static field.
1063 * The type of the method handle will have a return type of the field's
1064 * value type.
1065 * The method handle's single argument will be the instance containing
1066 * the field.
1067 * Access checking is performed immediately on behalf of the lookup class.
1068 * @param refc the class or interface from which the method is accessed
1069 * @param name the field's name
1070 * @param type the field's type
1071 * @return a method handle which can load values from the field
1072 * @throws NoSuchFieldException if the field does not exist
1073 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1074 * @exception SecurityException if a security manager is present and it
1075 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1076 * @throws NullPointerException if any argument is null
1077 */
1078 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1079 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1080 return getDirectField(REF_getField, refc, field);
1081 }
1082
1083 /**
1084 * Produces a method handle giving write access to a non-static field.
1085 * The type of the method handle will have a void return type.
1086 * The method handle will take two arguments, the instance containing
1087 * the field, and the value to be stored.
1088 * The second argument will be of the field's value type.
1089 * Access checking is performed immediately on behalf of the lookup class.
1090 * @param refc the class or interface from which the method is accessed
1091 * @param name the field's name
1092 * @param type the field's type
1093 * @return a method handle which can store values into the field
1094 * @throws NoSuchFieldException if the field does not exist
1095 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1096 * @exception SecurityException if a security manager is present and it
1097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1098 * @throws NullPointerException if any argument is null
1099 */
1100 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1101 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1102 return getDirectField(REF_putField, refc, field);
1103 }
1104
1105 /**
1106 * Produces a method handle giving read access to a static field.
1107 * The type of the method handle will have a return type of the field's
1108 * value type.
1109 * The method handle will take no arguments.
1110 * Access checking is performed immediately on behalf of the lookup class.
1111 * <p>
1112 * If the returned method handle is invoked, the field's class will
1113 * be initialized, if it has not already been initialized.
1114 * @param refc the class or interface from which the method is accessed
1115 * @param name the field's name
1116 * @param type the field's type
1117 * @return a method handle which can load values from the field
1118 * @throws NoSuchFieldException if the field does not exist
1119 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1120 * @exception SecurityException if a security manager is present and it
1121 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1122 * @throws NullPointerException if any argument is null
1123 */
1124 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1125 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1126 return getDirectField(REF_getStatic, refc, field);
1127 }
1128
1129 /**
1130 * Produces a method handle giving write access to a static field.
1131 * The type of the method handle will have a void return type.
1132 * The method handle will take a single
1133 * argument, of the field's value type, the value to be stored.
1134 * Access checking is performed immediately on behalf of the lookup class.
1135 * <p>
1136 * If the returned method handle is invoked, the field's class will
1137 * be initialized, if it has not already been initialized.
1138 * @param refc the class or interface from which the method is accessed
1139 * @param name the field's name
1140 * @param type the field's type
1141 * @return a method handle which can store values into the field
1142 * @throws NoSuchFieldException if the field does not exist
1143 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1144 * @exception SecurityException if a security manager is present and it
1145 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1146 * @throws NullPointerException if any argument is null
1147 */
1148 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1149 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1150 return getDirectField(REF_putStatic, refc, field);
1151 }
1152
1153 /**
1154 * Produces an early-bound method handle for a non-static method.
1155 * The receiver must have a supertype {@code defc} in which a method
1156 * of the given name and type is accessible to the lookup class.
1157 * The method and all its argument types must be accessible to the lookup object.
1158 * The type of the method handle will be that of the method,
1159 * without any insertion of an additional receiver parameter.
1160 * The given receiver will be bound into the method handle,
1161 * so that every call to the method handle will invoke the
1162 * requested method on the given receiver.
1163 * <p>
1164 * The returned method handle will have
1165 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1166 * the method's variable arity modifier bit ({@code 0x0080}) is set
1167 * <em>and</em> the trailing array argument is not the only argument.
1168 * (If the trailing array argument is the only argument,
1169 * the given receiver value will be bound to it.)
1170 * <p>
1171 * This is equivalent to the following code:
1172 * <blockquote><pre>{@code
1173 import static java.lang.invoke.MethodHandles.*;
1174 import static java.lang.invoke.MethodType.*;
1175 ...
1176 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1177 MethodHandle mh1 = mh0.bindTo(receiver);
1178 MethodType mt1 = mh1.type();
1179 if (mh0.isVarargsCollector())
1180 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1181 return mh1;
1182 * }</pre></blockquote>
1183 * where {@code defc} is either {@code receiver.getClass()} or a super
1184 * type of that class, in which the requested method is accessible
1185 * to the lookup class.
1186 * (Note that {@code bindTo} does not preserve variable arity.)
1187 * @param receiver the object from which the method is accessed
1188 * @param name the name of the method
1189 * @param type the type of the method, with the receiver argument omitted
1190 * @return the desired method handle
1191 * @throws NoSuchMethodException if the method does not exist
1192 * @throws IllegalAccessException if access checking fails
1193 * or if the method's variable arity modifier bit
1194 * is set and {@code asVarargsCollector} fails
1195 * @exception SecurityException if a security manager is present and it
1196 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1197 * @throws NullPointerException if any argument is null
1198 * @see MethodHandle#bindTo
1199 * @see #findVirtual
1200 */
1201 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1202 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1203 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1204 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1205 return mh.bindArgumentL(0, receiver).setVarargs(method);
1206 }
1207
1208 /**
1209 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1210 * to <i>m</i>, if the lookup class has permission.
1211 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1212 * If <i>m</i> is virtual, overriding is respected on every call.
1213 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1214 * The type of the method handle will be that of the method,
1215 * with the receiver type prepended (but only if it is non-static).
1216 * If the method's {@code accessible} flag is not set,
1217 * access checking is performed immediately on behalf of the lookup class.
1218 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1219 * <p>
1220 * The returned method handle will have
1221 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1222 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1223 * <p>
1224 * If <i>m</i> is static, and
1225 * if the returned method handle is invoked, the method's class will
1226 * be initialized, if it has not already been initialized.
1227 * @param m the reflected method
1228 * @return a method handle which can invoke the reflected method
1229 * @throws IllegalAccessException if access checking fails
1230 * or if the method's variable arity modifier bit
1231 * is set and {@code asVarargsCollector} fails
1232 * @throws NullPointerException if the argument is null
1233 */
1234 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1235 if (m.getDeclaringClass() == MethodHandle.class) {
1236 MethodHandle mh = unreflectForMH(m);
1237 if (mh != null) return mh;
1238 }
1239 MemberName method = new MemberName(m);
1240 byte refKind = method.getReferenceKind();
1241 if (refKind == REF_invokeSpecial)
1242 refKind = REF_invokeVirtual;
1243 assert(method.isMethod());
1244 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1245 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1246 }
1247 private MethodHandle unreflectForMH(Method m) {
1248 // these names require special lookups because they throw UnsupportedOperationException
1249 if (MemberName.isMethodHandleInvokeName(m.getName()))
1250 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1251 return null;
1252 }
1253
1254 /**
1255 * Produces a method handle for a reflected method.
1256 * It will bypass checks for overriding methods on the receiver,
1257 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1258 * instruction from within the explicitly specified {@code specialCaller}.
1259 * The type of the method handle will be that of the method,
1260 * with a suitably restricted receiver type prepended.
1261 * (The receiver type will be {@code specialCaller} or a subtype.)
1262 * If the method's {@code accessible} flag is not set,
1263 * access checking is performed immediately on behalf of the lookup class,
1264 * as if {@code invokespecial} instruction were being linked.
1265 * <p>
1266 * Before method resolution,
1267 * if the explicitly specified caller class is not identical with the
1268 * lookup class, or if this lookup object does not have
1269 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1270 * privileges, the access fails.
1271 * <p>
1272 * The returned method handle will have
1273 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1274 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1275 * @param m the reflected method
1276 * @param specialCaller the class nominally calling the method
1277 * @return a method handle which can invoke the reflected method
1278 * @throws IllegalAccessException if access checking fails
1279 * or if the method's variable arity modifier bit
1280 * is set and {@code asVarargsCollector} fails
1281 * @throws NullPointerException if any argument is null
1282 */
1283 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1284 checkSpecialCaller(specialCaller, null);
1285 Lookup specialLookup = this.in(specialCaller);
1286 MemberName method = new MemberName(m, true);
1287 assert(method.isMethod());
1288 // ignore m.isAccessible: this is a new kind of access
1289 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1290 }
1291
1292 /**
1293 * Produces a method handle for a reflected constructor.
1294 * The type of the method handle will be that of the constructor,
1295 * with the return type changed to the declaring class.
1296 * The method handle will perform a {@code newInstance} operation,
1297 * creating a new instance of the constructor's class on the
1298 * arguments passed to the method handle.
1299 * <p>
1300 * If the constructor's {@code accessible} flag is not set,
1301 * access checking is performed immediately on behalf of the lookup class.
1302 * <p>
1303 * The returned method handle will have
1304 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1305 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1306 * <p>
1307 * If the returned method handle is invoked, the constructor's class will
1308 * be initialized, if it has not already been initialized.
1309 * @param c the reflected constructor
1310 * @return a method handle which can invoke the reflected constructor
1311 * @throws IllegalAccessException if access checking fails
1312 * or if the method's variable arity modifier bit
1313 * is set and {@code asVarargsCollector} fails
1314 * @throws NullPointerException if the argument is null
1315 */
1316 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1317 MemberName ctor = new MemberName(c);
1318 assert(ctor.isConstructor());
1319 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1320 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1321 }
1322
1323 /**
1324 * Produces a method handle giving read access to a reflected field.
1325 * The type of the method handle will have a return type of the field's
1326 * value type.
1327 * If the field is static, the method handle will take no arguments.
1328 * Otherwise, its single argument will be the instance containing
1329 * the field.
1330 * If the field's {@code accessible} flag is not set,
1331 * access checking is performed immediately on behalf of the lookup class.
1332 * <p>
1333 * If the field is static, and
1334 * if the returned method handle is invoked, the field's class will
1335 * be initialized, if it has not already been initialized.
1336 * @param f the reflected field
1337 * @return a method handle which can load values from the reflected field
1338 * @throws IllegalAccessException if access checking fails
1339 * @throws NullPointerException if the argument is null
1340 */
1341 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1342 return unreflectField(f, false);
1343 }
1344 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1345 MemberName field = new MemberName(f, isSetter);
1346 assert(isSetter
1347 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1348 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1349 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1350 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1351 }
1352
1353 /**
1354 * Produces a method handle giving write access to a reflected field.
1355 * The type of the method handle will have a void return type.
1356 * If the field is static, the method handle will take a single
1357 * argument, of the field's value type, the value to be stored.
1358 * Otherwise, the two arguments will be the instance containing
1359 * the field, and the value to be stored.
1360 * If the field's {@code accessible} flag is not set,
1361 * access checking is performed immediately on behalf of the lookup class.
1362 * <p>
1363 * If the field is static, and
1364 * if the returned method handle is invoked, the field's class will
1365 * be initialized, if it has not already been initialized.
1366 * @param f the reflected field
1367 * @return a method handle which can store values into the reflected field
1368 * @throws IllegalAccessException if access checking fails
1369 * @throws NullPointerException if the argument is null
1370 */
1371 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1372 return unreflectField(f, true);
1373 }
1374
1375 /**
1376 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1377 * created by this lookup object or a similar one.
1378 * Security and access checks are performed to ensure that this lookup object
1379 * is capable of reproducing the target method handle.
1380 * This means that the cracking may fail if target is a direct method handle
1381 * but was created by an unrelated lookup object.
1382 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1383 * and was created by a lookup object for a different class.
1384 * @param target a direct method handle to crack into symbolic reference components
1385 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1386 * @exception SecurityException if a security manager is present and it
1387 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1388 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1389 * @exception NullPointerException if the target is {@code null}
1390 * @see MethodHandleInfo
1391 * @since 1.8
1392 */
1393 public MethodHandleInfo revealDirect(MethodHandle target) {
1394 MemberName member = target.internalMemberName();
1395 if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1396 throw newIllegalArgumentException("not a direct method handle");
1397 Class<?> defc = member.getDeclaringClass();
1398 byte refKind = member.getReferenceKind();
1399 assert(MethodHandleNatives.refKindIsValid(refKind));
1400 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1401 // Devirtualized method invocation is usually formally virtual.
1402 // To avoid creating extra MemberName objects for this common case,
1403 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1404 refKind = REF_invokeVirtual;
1405 if (refKind == REF_invokeVirtual && defc.isInterface())
1406 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1407 refKind = REF_invokeInterface;
1408 // Check SM permissions and member access before cracking.
1409 try {
1410 checkAccess(refKind, defc, member);
1411 checkSecurityManager(defc, member);
1412 } catch (IllegalAccessException ex) {
1413 throw new IllegalArgumentException(ex);
1414 }
1415 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1416 Class<?> callerClass = target.internalCallerClass();
1417 if (!hasPrivateAccess() || callerClass != lookupClass())
1418 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1419 }
1420 // Produce the handle to the results.
1421 return new InfoFromMemberName(this, member, refKind);
1422 }
1423
1424 /// Helper methods, all package-private.
1425
1426 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1427 checkSymbolicClass(refc); // do this before attempting to resolve
1428 Objects.requireNonNull(name);
1429 Objects.requireNonNull(type);
1430 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1431 NoSuchFieldException.class);
1432 }
1433
1434 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1435 checkSymbolicClass(refc); // do this before attempting to resolve
1436 Objects.requireNonNull(name);
1437 Objects.requireNonNull(type);
1438 checkMethodName(refKind, name); // NPE check on name
1439 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1440 NoSuchMethodException.class);
1441 }
1442
1443 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1444 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1445 Objects.requireNonNull(member.getName());
1446 Objects.requireNonNull(member.getType());
1447 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1448 ReflectiveOperationException.class);
1449 }
1450
1451 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1452 Objects.requireNonNull(refc);
1453 Class<?> caller = lookupClassOrNull();
1454 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1455 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1456 }
1457
1458 /** Check name for an illegal leading "<" character. */
1459 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1460 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1461 throw new NoSuchMethodException("illegal method name: "+name);
1462 }
1463
1464
1465 /**
1466 * Find my trustable caller class if m is a caller sensitive method.
1467 * If this lookup object has private access, then the caller class is the lookupClass.
1468 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1469 */
1470 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1471 Class<?> callerClass = null;
1472 if (MethodHandleNatives.isCallerSensitive(m)) {
1473 // Only lookups with private access are allowed to resolve caller-sensitive methods
1474 if (hasPrivateAccess()) {
1475 callerClass = lookupClass;
1476 } else {
1477 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1478 }
1479 }
1480 return callerClass;
1481 }
1482
1483 private boolean hasPrivateAccess() {
1484 return (allowedModes & PRIVATE) != 0;
1485 }
1486
1487 /**
1488 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1489 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1490 * If this lookup object has private access, then the caller class is the lookupClass.
1491 */
1492 void checkSecurityManager(Class<?> refc, MemberName m) {
1493 SecurityManager smgr = System.getSecurityManager();
1494 if (smgr == null) return;
1495 if (allowedModes == TRUSTED) return;
1496
1497 // Step 1:
1498 boolean fullPowerLookup = hasPrivateAccess();
1499 if (!fullPowerLookup ||
1500 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1501 ReflectUtil.checkPackageAccess(refc);
1502 }
1503
1504 if (m == null) { // findClass or accessClass
1505 // Step 2b:
1506 if (!fullPowerLookup) {
1507 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1508 }
1509 return;
1510 }
1511
1512 // Step 2a:
1513 if (m.isPublic()) return;
1514 if (!fullPowerLookup) {
1515 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1516 }
1517
1518 // Step 3:
1519 Class<?> defc = m.getDeclaringClass();
1520 if (!fullPowerLookup && defc != refc) {
1521 ReflectUtil.checkPackageAccess(defc);
1522 }
1523 }
1524
1525 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1526 boolean wantStatic = (refKind == REF_invokeStatic);
1527 String message;
1528 if (m.isConstructor())
1529 message = "expected a method, not a constructor";
1530 else if (!m.isMethod())
1531 message = "expected a method";
1532 else if (wantStatic != m.isStatic())
1533 message = wantStatic ? "expected a static method" : "expected a non-static method";
1534 else
1535 { checkAccess(refKind, refc, m); return; }
1536 throw m.makeAccessException(message, this);
1537 }
1538
1539 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1540 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1541 String message;
1542 if (wantStatic != m.isStatic())
1543 message = wantStatic ? "expected a static field" : "expected a non-static field";
1544 else
1545 { checkAccess(refKind, refc, m); return; }
1546 throw m.makeAccessException(message, this);
1547 }
1548
1549 /** Check public/protected/private bits on the symbolic reference class and its member. */
1550 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1551 assert(m.referenceKindIsConsistentWith(refKind) &&
1552 MethodHandleNatives.refKindIsValid(refKind) &&
1553 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1554 int allowedModes = this.allowedModes;
1555 if (allowedModes == TRUSTED) return;
1556 int mods = m.getModifiers();
1557 if (Modifier.isProtected(mods) &&
1558 refKind == REF_invokeVirtual &&
1559 m.getDeclaringClass() == Object.class &&
1560 m.getName().equals("clone") &&
1561 refc.isArray()) {
1562 // The JVM does this hack also.
1563 // (See ClassVerifier::verify_invoke_instructions
1564 // and LinkResolver::check_method_accessability.)
1565 // Because the JVM does not allow separate methods on array types,
1566 // there is no separate method for int[].clone.
1567 // All arrays simply inherit Object.clone.
1568 // But for access checking logic, we make Object.clone
1569 // (normally protected) appear to be public.
1570 // Later on, when the DirectMethodHandle is created,
1571 // its leading argument will be restricted to the
1572 // requested array type.
1573 // N.B. The return type is not adjusted, because
1574 // that is *not* the bytecode behavior.
1575 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1576 }
1577 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
1578 // cannot "new" a protected ctor in a different package
1579 mods ^= Modifier.PROTECTED;
1580 }
1581 if (Modifier.isFinal(mods) &&
1582 MethodHandleNatives.refKindIsSetter(refKind))
1583 throw m.makeAccessException("unexpected set of a final field", this);
1584 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1585 return; // common case
1586 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1587 if ((requestedModes & allowedModes) != 0) {
1588 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1589 mods, lookupClass(), allowedModes))
1590 return;
1591 } else {
1592 // Protected members can also be checked as if they were package-private.
1593 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1594 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1595 return;
1596 }
1597 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1598 }
1599
1600 String accessFailedMessage(Class<?> refc, MemberName m) {
1601 Class<?> defc = m.getDeclaringClass();
1602 int mods = m.getModifiers();
1603 // check the class first:
1604 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1605 (defc == refc ||
1606 Modifier.isPublic(refc.getModifiers())));
1607 if (!classOK && (allowedModes & PACKAGE) != 0) {
1608 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1609 (defc == refc ||
1610 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1611 }
1612 if (!classOK)
1613 return "class is not public";
1614 if (Modifier.isPublic(mods))
1615 return "access to public member failed"; // (how?)
1616 if (Modifier.isPrivate(mods))
1617 return "member is private";
1618 if (Modifier.isProtected(mods))
1619 return "member is protected";
1620 return "member is private to package";
1621 }
1622
1623 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1624
1625 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
1626 int allowedModes = this.allowedModes;
1627 if (allowedModes == TRUSTED) return;
1628 if (!hasPrivateAccess()
1629 || (specialCaller != lookupClass()
1630 // ensure non-abstract methods in superinterfaces can be special-invoked
1631 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
1632 && !(ALLOW_NESTMATE_ACCESS &&
1633 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1634 throw new MemberName(specialCaller).
1635 makeAccessException("no private access for invokespecial", this);
1636 }
1637
1638 private boolean restrictProtectedReceiver(MemberName method) {
1639 // The accessing class only has the right to use a protected member
1640 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1641 if (!method.isProtected() || method.isStatic()
1642 || allowedModes == TRUSTED
1643 || method.getDeclaringClass() == lookupClass()
1644 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1645 || (ALLOW_NESTMATE_ACCESS &&
1646 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1647 return false;
1648 return true;
1649 }
1650 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
1651 assert(!method.isStatic());
1652 // receiver type of mh is too wide; narrow to caller
1653 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1654 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1655 }
1656 MethodType rawType = mh.type();
1657 if (rawType.parameterType(0) == caller) return mh;
1658 MethodType narrowType = rawType.changeParameterType(0, caller);
1659 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
1660 assert(mh.viewAsTypeChecks(narrowType, true));
1661 return mh.copyWith(narrowType, mh.form);
1662 }
1663
1664 /** Check access and get the requested method. */
1665 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1666 final boolean doRestrict = true;
1667 final boolean checkSecurity = true;
1668 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1669 }
1670 /** Check access and get the requested method, eliding receiver narrowing rules. */
1671 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1672 final boolean doRestrict = false;
1673 final boolean checkSecurity = true;
1674 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1675 }
1676 /** Check access and get the requested method, eliding security manager checks. */
1677 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1678 final boolean doRestrict = true;
1679 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1680 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1681 }
1682 /** Common code for all methods; do not call directly except from immediately above. */
1683 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1684 boolean checkSecurity,
1685 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1686 checkMethod(refKind, refc, method);
1687 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1688 if (checkSecurity)
1689 checkSecurityManager(refc, method);
1690 assert(!method.isMethodHandleInvoke());
1691
1692 if (refKind == REF_invokeSpecial &&
1693 refc != lookupClass() &&
1694 !refc.isInterface() &&
1695 refc != lookupClass().getSuperclass() &&
1696 refc.isAssignableFrom(lookupClass())) {
1697 assert(!method.getName().equals("<init>")); // not this code path
1698 // Per JVMS 6.5, desc. of invokespecial instruction:
1699 // If the method is in a superclass of the LC,
1700 // and if our original search was above LC.super,
1701 // repeat the search (symbolic lookup) from LC.super
1702 // and continue with the direct superclass of that class,
1703 // and so forth, until a match is found or no further superclasses exist.
1704 // FIXME: MemberName.resolve should handle this instead.
1705 Class<?> refcAsSuper = lookupClass();
1706 MemberName m2;
1707 do {
1708 refcAsSuper = refcAsSuper.getSuperclass();
1709 m2 = new MemberName(refcAsSuper,
1710 method.getName(),
1711 method.getMethodType(),
1712 REF_invokeSpecial);
1713 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1714 } while (m2 == null && // no method is found yet
1715 refc != refcAsSuper); // search up to refc
1716 if (m2 == null) throw new InternalError(method.toString());
1717 method = m2;
1718 refc = refcAsSuper;
1719 // redo basic checks
1720 checkMethod(refKind, refc, method);
1721 }
1722
1723 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
1724 MethodHandle mh = dmh;
1725 // Optionally narrow the receiver argument to refc using restrictReceiver.
1726 if (doRestrict &&
1727 (refKind == REF_invokeSpecial ||
1728 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1729 restrictProtectedReceiver(method)))) {
1730 mh = restrictReceiver(method, dmh, lookupClass());
1731 }
1732 mh = maybeBindCaller(method, mh, callerClass);
1733 mh = mh.setVarargs(method);
1734 return mh;
1735 }
1736 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1737 Class<?> callerClass)
1738 throws IllegalAccessException {
1739 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1740 return mh;
1741 Class<?> hostClass = lookupClass;
1742 if (!hasPrivateAccess()) // caller must have private access
1743 hostClass = callerClass; // callerClass came from a security manager style stack walk
1744 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1745 // Note: caller will apply varargs after this step happens.
1746 return cbmh;
1747 }
1748 /** Check access and get the requested field. */
1749 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1750 final boolean checkSecurity = true;
1751 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1752 }
1753 /** Check access and get the requested field, eliding security manager checks. */
1754 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1755 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1756 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1757 }
1758 /** Common code for all fields; do not call directly except from immediately above. */
1759 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1760 boolean checkSecurity) throws IllegalAccessException {
1761 checkField(refKind, refc, field);
1762 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1763 if (checkSecurity)
1764 checkSecurityManager(refc, field);
1765 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
1766 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1767 restrictProtectedReceiver(field));
1768 if (doRestrict)
1769 return restrictReceiver(field, dmh, lookupClass());
1770 return dmh;
1771 }
1772 /** Check access and get the requested constructor. */
1773 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1774 final boolean checkSecurity = true;
1775 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1776 }
1777 /** Check access and get the requested constructor, eliding security manager checks. */
1778 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1779 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1780 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1781 }
1782 /** Common code for all constructors; do not call directly except from immediately above. */
1783 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1784 boolean checkSecurity) throws IllegalAccessException {
1785 assert(ctor.isConstructor());
1786 checkAccess(REF_newInvokeSpecial, refc, ctor);
1787 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1788 if (checkSecurity)
1789 checkSecurityManager(refc, ctor);
1790 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1791 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1792 }
1793
1794 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1795 */
1796 /*non-public*/
1797 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1798 if (!(type instanceof Class || type instanceof MethodType))
1799 throw new InternalError("unresolved MemberName");
1800 MemberName member = new MemberName(refKind, defc, name, type);
1801 MethodHandle mh = LOOKASIDE_TABLE.get(member);
1802 if (mh != null) {
1803 checkSymbolicClass(defc);
1804 return mh;
1805 }
1806 // Treat MethodHandle.invoke and invokeExact specially.
1807 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1808 mh = findVirtualForMH(member.getName(), member.getMethodType());
1809 if (mh != null) {
1810 return mh;
1811 }
1812 }
1813 MemberName resolved = resolveOrFail(refKind, member);
1814 mh = getDirectMethodForConstant(refKind, defc, resolved);
1815 if (mh instanceof DirectMethodHandle
1816 && canBeCached(refKind, defc, resolved)) {
1817 MemberName key = mh.internalMemberName();
1818 if (key != null) {
1819 key = key.asNormalOriginal();
1820 }
1821 if (member.equals(key)) { // better safe than sorry
1822 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1823 }
1824 }
1825 return mh;
1826 }
1827 private
1828 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1829 if (refKind == REF_invokeSpecial) {
1830 return false;
1831 }
1832 if (!Modifier.isPublic(defc.getModifiers()) ||
1833 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1834 !member.isPublic() ||
1835 member.isCallerSensitive()) {
1836 return false;
1837 }
1838 ClassLoader loader = defc.getClassLoader();
1839 if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
1840 ClassLoader sysl = ClassLoader.getSystemClassLoader();
1841 boolean found = false;
1842 while (sysl != null) {
1843 if (loader == sysl) { found = true; break; }
1844 sysl = sysl.getParent();
1845 }
1846 if (!found) {
1847 return false;
1848 }
1849 }
1850 try {
1851 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1852 new MemberName(refKind, defc, member.getName(), member.getType()));
1853 checkSecurityManager(defc, resolved2);
1854 } catch (ReflectiveOperationException | SecurityException ex) {
1855 return false;
1856 }
1857 return true;
1858 }
1859 private
1860 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1861 throws ReflectiveOperationException {
1862 if (MethodHandleNatives.refKindIsField(refKind)) {
1863 return getDirectFieldNoSecurityManager(refKind, defc, member);
1864 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1865 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1866 } else if (refKind == REF_newInvokeSpecial) {
1867 return getDirectConstructorNoSecurityManager(defc, member);
1868 }
1869 // oops
1870 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1871 }
1872
1873 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1874 }
1875
1876 /**
1877 * Produces a method handle giving read access to elements of an array.
1878 * The type of the method handle will have a return type of the array's
1879 * element type. Its first argument will be the array type,
1880 * and the second will be {@code int}.
1881 * @param arrayClass an array type
1882 * @return a method handle which can load values from the given array type
1883 * @throws NullPointerException if the argument is null
1884 * @throws IllegalArgumentException if arrayClass is not an array type
1885 */
1886 public static
1887 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1888 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1889 }
1890
1891 /**
1892 * Produces a method handle giving write access to elements of an array.
1893 * The type of the method handle will have a void return type.
1894 * Its last argument will be the array's element type.
1895 * The first and second arguments will be the array type and int.
1896 * @param arrayClass the class of an array
1897 * @return a method handle which can store values into the array type
1898 * @throws NullPointerException if the argument is null
1899 * @throws IllegalArgumentException if arrayClass is not an array type
1900 */
1901 public static
1902 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1903 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1904 }
1905
1906 /// method handle invocation (reflective style)
1907
1908 /**
1909 * Produces a method handle which will invoke any method handle of the
1910 * given {@code type}, with a given number of trailing arguments replaced by
1911 * a single trailing {@code Object[]} array.
1912 * The resulting invoker will be a method handle with the following
1913 * arguments:
1914 * <ul>
1915 * <li>a single {@code MethodHandle} target
1916 * <li>zero or more leading values (counted by {@code leadingArgCount})
1917 * <li>an {@code Object[]} array containing trailing arguments
1918 * </ul>
1919 * <p>
1920 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1921 * the indicated {@code type}.
1922 * That is, if the target is exactly of the given {@code type}, it will behave
1923 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1924 * is used to convert the target to the required {@code type}.
1925 * <p>
1926 * The type of the returned invoker will not be the given {@code type}, but rather
1927 * will have all parameters except the first {@code leadingArgCount}
1928 * replaced by a single array of type {@code Object[]}, which will be
1929 * the final parameter.
1930 * <p>
1931 * Before invoking its target, the invoker will spread the final array, apply
1932 * reference casts as necessary, and unbox and widen primitive arguments.
1933 * If, when the invoker is called, the supplied array argument does
1934 * not have the correct number of elements, the invoker will throw
1935 * an {@link IllegalArgumentException} instead of invoking the target.
1936 * <p>
1937 * This method is equivalent to the following code (though it may be more efficient):
1938 * <blockquote><pre>{@code
1939 MethodHandle invoker = MethodHandles.invoker(type);
1940 int spreadArgCount = type.parameterCount() - leadingArgCount;
1941 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1942 return invoker;
1943 * }</pre></blockquote>
1944 * This method throws no reflective or security exceptions.
1945 * @param type the desired target type
1946 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1947 * @return a method handle suitable for invoking any method handle of the given type
1948 * @throws NullPointerException if {@code type} is null
1949 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1950 * the range from 0 to {@code type.parameterCount()} inclusive,
1951 * or if the resulting method handle's type would have
1952 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1953 */
1954 public static
1955 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1956 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1957 throw newIllegalArgumentException("bad argument count", leadingArgCount);
1958 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
1959 return type.invokers().spreadInvoker(leadingArgCount);
1960 }
1961
1962 /**
1963 * Produces a special <em>invoker method handle</em> which can be used to
1964 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1965 * The resulting invoker will have a type which is
1966 * exactly equal to the desired type, except that it will accept
1967 * an additional leading argument of type {@code MethodHandle}.
1968 * <p>
1969 * This method is equivalent to the following code (though it may be more efficient):
1970 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1971 *
1972 * <p style="font-size:smaller;">
1973 * <em>Discussion:</em>
1974 * Invoker method handles can be useful when working with variable method handles
1975 * of unknown types.
1976 * For example, to emulate an {@code invokeExact} call to a variable method
1977 * handle {@code M}, extract its type {@code T},
1978 * look up the invoker method {@code X} for {@code T},
1979 * and call the invoker method, as {@code X.invoke(T, A...)}.
1980 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1981 * is unknown.)
1982 * If spreading, collecting, or other argument transformations are required,
1983 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1984 * method handle values, as long as they are compatible with the type of {@code X}.
1985 * <p style="font-size:smaller;">
1986 * <em>(Note: The invoker method is not available via the Core Reflection API.
1987 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1988 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1989 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1990 * <p>
1991 * This method throws no reflective or security exceptions.
1992 * @param type the desired target type
1993 * @return a method handle suitable for invoking any method handle of the given type
1994 * @throws IllegalArgumentException if the resulting method handle's type would have
1995 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1996 */
1997 public static
1998 MethodHandle exactInvoker(MethodType type) {
1999 return type.invokers().exactInvoker();
2000 }
2001
2002 /**
2003 * Produces a special <em>invoker method handle</em> which can be used to
2004 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2005 * The resulting invoker will have a type which is
2006 * exactly equal to the desired type, except that it will accept
2007 * an additional leading argument of type {@code MethodHandle}.
2008 * <p>
2009 * Before invoking its target, if the target differs from the expected type,
2010 * the invoker will apply reference casts as
2011 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2012 * Similarly, the return value will be converted as necessary.
2013 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2014 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2015 * <p>
2016 * This method is equivalent to the following code (though it may be more efficient):
2017 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2018 * <p style="font-size:smaller;">
2019 * <em>Discussion:</em>
2020 * A {@linkplain MethodType#genericMethodType general method type} is one which
2021 * mentions only {@code Object} arguments and return values.
2022 * An invoker for such a type is capable of calling any method handle
2023 * of the same arity as the general type.
2024 * <p style="font-size:smaller;">
2025 * <em>(Note: The invoker method is not available via the Core Reflection API.
2026 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2027 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2028 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2029 * <p>
2030 * This method throws no reflective or security exceptions.
2031 * @param type the desired target type
2032 * @return a method handle suitable for invoking any method handle convertible to the given type
2033 * @throws IllegalArgumentException if the resulting method handle's type would have
2034 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2035 */
2036 public static
2037 MethodHandle invoker(MethodType type) {
2038 return type.invokers().genericInvoker();
2039 }
2040
2041 static /*non-public*/
2042 MethodHandle basicInvoker(MethodType type) {
2043 return type.invokers().basicInvoker();
2044 }
2045
2046 /// method handle modification (creation from other method handles)
2047
2048 /**
2049 * Produces a method handle which adapts the type of the
2050 * given method handle to a new type by pairwise argument and return type conversion.
2051 * The original type and new type must have the same number of arguments.
2052 * The resulting method handle is guaranteed to report a type
2053 * which is equal to the desired new type.
2054 * <p>
2055 * If the original type and new type are equal, returns target.
2056 * <p>
2057 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
2058 * and some additional conversions are also applied if those conversions fail.
2059 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
2060 * if possible, before or instead of any conversions done by {@code asType}:
2061 * <ul>
2062 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
2063 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
2064 * (This treatment of interfaces follows the usage of the bytecode verifier.)
2065 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
2066 * the boolean is converted to a byte value, 1 for true, 0 for false.
2067 * (This treatment follows the usage of the bytecode verifier.)
2068 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2069 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2070 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2071 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2072 * then a Java casting conversion (JLS 5.5) is applied.
2073 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2074 * widening and/or narrowing.)
2075 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2076 * conversion will be applied at runtime, possibly followed
2077 * by a Java casting conversion (JLS 5.5) on the primitive value,
2078 * possibly followed by a conversion from byte to boolean by testing
2079 * the low-order bit.
2080 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2081 * and if the reference is null at runtime, a zero value is introduced.
2082 * </ul>
2083 * @param target the method handle to invoke after arguments are retyped
2084 * @param newType the expected type of the new method handle
2085 * @return a method handle which delegates to the target after performing
2086 * any necessary argument conversions, and arranges for any
2087 * necessary return value conversions
2088 * @throws NullPointerException if either argument is null
2089 * @throws WrongMethodTypeException if the conversion cannot be made
2090 * @see MethodHandle#asType
2091 */
2092 public static
2093 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2094 explicitCastArgumentsChecks(target, newType);
2095 // use the asTypeCache when possible:
2096 MethodType oldType = target.type();
2097 if (oldType == newType) return target;
2098 if (oldType.explicitCastEquivalentToAsType(newType)) {
2099 return target.asFixedArity().asType(newType);
2100 }
2101 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2102 }
2103
2104 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2105 if (target.type().parameterCount() != newType.parameterCount()) {
2106 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2107 }
2108 }
2109
2110 /**
2111 * Produces a method handle which adapts the calling sequence of the
2112 * given method handle to a new type, by reordering the arguments.
2113 * The resulting method handle is guaranteed to report a type
2114 * which is equal to the desired new type.
2115 * <p>
2116 * The given array controls the reordering.
2117 * Call {@code #I} the number of incoming parameters (the value
2118 * {@code newType.parameterCount()}, and call {@code #O} the number
2119 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2120 * Then the length of the reordering array must be {@code #O},
2121 * and each element must be a non-negative number less than {@code #I}.
2122 * For every {@code N} less than {@code #O}, the {@code N}-th
2123 * outgoing argument will be taken from the {@code I}-th incoming
2124 * argument, where {@code I} is {@code reorder[N]}.
2125 * <p>
2126 * No argument or return value conversions are applied.
2127 * The type of each incoming argument, as determined by {@code newType},
2128 * must be identical to the type of the corresponding outgoing parameter
2129 * or parameters in the target method handle.
2130 * The return type of {@code newType} must be identical to the return
2131 * type of the original target.
2132 * <p>
2133 * The reordering array need not specify an actual permutation.
2134 * An incoming argument will be duplicated if its index appears
2135 * more than once in the array, and an incoming argument will be dropped
2136 * if its index does not appear in the array.
2137 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2138 * incoming arguments which are not mentioned in the reordering array
2139 * are may be any type, as determined only by {@code newType}.
2140 * <blockquote><pre>{@code
2141 import static java.lang.invoke.MethodHandles.*;
2142 import static java.lang.invoke.MethodType.*;
2143 ...
2144 MethodType intfn1 = methodType(int.class, int.class);
2145 MethodType intfn2 = methodType(int.class, int.class, int.class);
2146 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2147 assert(sub.type().equals(intfn2));
2148 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2149 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2150 assert((int)rsub.invokeExact(1, 100) == 99);
2151 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2152 assert(add.type().equals(intfn2));
2153 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2154 assert(twice.type().equals(intfn1));
2155 assert((int)twice.invokeExact(21) == 42);
2156 * }</pre></blockquote>
2157 * @param target the method handle to invoke after arguments are reordered
2158 * @param newType the expected type of the new method handle
2159 * @param reorder an index array which controls the reordering
2160 * @return a method handle which delegates to the target after it
2161 * drops unused arguments and moves and/or duplicates the other arguments
2162 * @throws NullPointerException if any argument is null
2163 * @throws IllegalArgumentException if the index array length is not equal to
2164 * the arity of the target, or if any index array element
2165 * not a valid index for a parameter of {@code newType},
2166 * or if two corresponding parameter types in
2167 * {@code target.type()} and {@code newType} are not identical,
2168 */
2169 public static
2170 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2171 reorder = reorder.clone(); // get a private copy
2172 MethodType oldType = target.type();
2173 permuteArgumentChecks(reorder, newType, oldType);
2174 // first detect dropped arguments and handle them separately
2175 int[] originalReorder = reorder;
2176 BoundMethodHandle result = target.rebind();
2177 LambdaForm form = result.form;
2178 int newArity = newType.parameterCount();
2179 // Normalize the reordering into a real permutation,
2180 // by removing duplicates and adding dropped elements.
2181 // This somewhat improves lambda form caching, as well
2182 // as simplifying the transform by breaking it up into steps.
2183 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
2184 if (ddIdx > 0) {
2185 // We found a duplicated entry at reorder[ddIdx].
2186 // Example: (x,y,z)->asList(x,y,z)
2187 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
2188 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
2189 // The starred element corresponds to the argument
2190 // deleted by the dupArgumentForm transform.
2191 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
2192 boolean killFirst = false;
2193 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
2194 // Set killFirst if the dup is larger than an intervening position.
2195 // This will remove at least one inversion from the permutation.
2196 if (dupVal > val) killFirst = true;
2197 }
2198 if (!killFirst) {
2199 srcPos = dstPos;
2200 dstPos = ddIdx;
2201 }
2202 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
2203 assert (reorder[srcPos] == reorder[dstPos]);
2204 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
2205 // contract the reordering by removing the element at dstPos
2206 int tailPos = dstPos + 1;
2207 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
2208 reorder = Arrays.copyOf(reorder, reorder.length - 1);
2209 } else {
2210 int dropVal = ~ddIdx, insPos = 0;
2211 while (insPos < reorder.length && reorder[insPos] < dropVal) {
2212 // Find first element of reorder larger than dropVal.
2213 // This is where we will insert the dropVal.
2214 insPos += 1;
2215 }
2216 Class<?> ptype = newType.parameterType(dropVal);
2217 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
2218 oldType = oldType.insertParameterTypes(insPos, ptype);
2219 // expand the reordering by inserting an element at insPos
2220 int tailPos = insPos + 1;
2221 reorder = Arrays.copyOf(reorder, reorder.length + 1);
2222 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
2223 reorder[insPos] = dropVal;
2224 }
2225 assert (permuteArgumentChecks(reorder, newType, oldType));
2226 }
2227 assert (reorder.length == newArity); // a perfect permutation
2228 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2229 form = form.editor().permuteArgumentsForm(1, reorder);
2230 if (newType == result.type() && form == result.internalForm())
2231 return result;
2232 return result.copyWith(newType, form);
2233 }
2234
2235 /**
2236 * Return an indication of any duplicate or omission in reorder.
2237 * If the reorder contains a duplicate entry, return the index of the second occurrence.
2238 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
2239 * Otherwise, return zero.
2240 * If an element not in [0..newArity-1] is encountered, return reorder.length.
2241 */
2242 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
2243 final int BIT_LIMIT = 63; // max number of bits in bit mask
2244 if (newArity < BIT_LIMIT) {
2245 long mask = 0;
2246 for (int i = 0; i < reorder.length; i++) {
2247 int arg = reorder[i];
2248 if (arg >= newArity) {
2249 return reorder.length;
2250 }
2251 long bit = 1L << arg;
2252 if ((mask & bit) != 0) {
2253 return i; // >0 indicates a dup
2254 }
2255 mask |= bit;
2256 }
2257 if (mask == (1L << newArity) - 1) {
2258 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2259 return 0;
2260 }
2261 // find first zero
2262 long zeroBit = Long.lowestOneBit(~mask);
2263 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2264 assert(zeroPos <= newArity);
2265 if (zeroPos == newArity) {
2266 return 0;
2267 }
2268 return ~zeroPos;
2269 } else {
2270 // same algorithm, different bit set
2271 BitSet mask = new BitSet(newArity);
2272 for (int i = 0; i < reorder.length; i++) {
2273 int arg = reorder[i];
2274 if (arg >= newArity) {
2275 return reorder.length;
2276 }
2277 if (mask.get(arg)) {
2278 return i; // >0 indicates a dup
2279 }
2280 mask.set(arg);
2281 }
2282 int zeroPos = mask.nextClearBit(0);
2283 assert(zeroPos <= newArity);
2284 if (zeroPos == newArity) {
2285 return 0;
2286 }
2287 return ~zeroPos;
2288 }
2289 }
2290
2291 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
2292 if (newType.returnType() != oldType.returnType())
2293 throw newIllegalArgumentException("return types do not match",
2294 oldType, newType);
2295 if (reorder.length == oldType.parameterCount()) {
2296 int limit = newType.parameterCount();
2297 boolean bad = false;
2298 for (int j = 0; j < reorder.length; j++) {
2299 int i = reorder[j];
2300 if (i < 0 || i >= limit) {
2301 bad = true; break;
2302 }
2303 Class<?> src = newType.parameterType(i);
2304 Class<?> dst = oldType.parameterType(j);
2305 if (src != dst)
2306 throw newIllegalArgumentException("parameter types do not match after reorder",
2307 oldType, newType);
2308 }
2309 if (!bad) return true;
2310 }
2311 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2312 }
2313
2314 /**
2315 * Produces a method handle of the requested return type which returns the given
2316 * constant value every time it is invoked.
2317 * <p>
2318 * Before the method handle is returned, the passed-in value is converted to the requested type.
2319 * If the requested type is primitive, widening primitive conversions are attempted,
2320 * else reference conversions are attempted.
2321 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2322 * @param type the return type of the desired method handle
2323 * @param value the value to return
2324 * @return a method handle of the given return type and no arguments, which always returns the given value
2325 * @throws NullPointerException if the {@code type} argument is null
2326 * @throws ClassCastException if the value cannot be converted to the required return type
2327 * @throws IllegalArgumentException if the given type is {@code void.class}
2328 */
2329 public static
2330 MethodHandle constant(Class<?> type, Object value) {
2331 if (type.isPrimitive()) {
2332 if (type == void.class)
2333 throw newIllegalArgumentException("void type");
2334 Wrapper w = Wrapper.forPrimitiveType(type);
2335 value = w.convert(value, type);
2336 if (w.zero().equals(value))
2337 return zero(w, type);
2338 return insertArguments(identity(type), 0, value);
2339 } else {
2340 if (value == null)
2341 return zero(Wrapper.OBJECT, type);
2342 return identity(type).bindTo(value);
2343 }
2344 }
2345
2346 /**
2347 * Produces a method handle which returns its sole argument when invoked.
2348 * @param type the type of the sole parameter and return value of the desired method handle
2349 * @return a unary method handle which accepts and returns the given type
2350 * @throws NullPointerException if the argument is null
2351 * @throws IllegalArgumentException if the given type is {@code void.class}
2352 */
2353 public static
2354 MethodHandle identity(Class<?> type) {
2355 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
2356 int pos = btw.ordinal();
2357 MethodHandle ident = IDENTITY_MHS[pos];
2358 if (ident == null) {
2359 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
2360 }
2361 if (ident.type().returnType() == type)
2362 return ident;
2363 // something like identity(Foo.class); do not bother to intern these
2364 assert(btw == Wrapper.OBJECT);
2365 return makeIdentity(type);
2366 }
2367 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.values().length];
2368 private static MethodHandle makeIdentity(Class<?> ptype) {
2369 MethodType mtype = MethodType.methodType(ptype, ptype);
2370 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
2371 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
2372 }
2373
2374 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
2375 int pos = btw.ordinal();
2376 MethodHandle zero = ZERO_MHS[pos];
2377 if (zero == null) {
2378 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
2379 }
2380 if (zero.type().returnType() == rtype)
2381 return zero;
2382 assert(btw == Wrapper.OBJECT);
2383 return makeZero(rtype);
2384 }
2385 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.values().length];
2386 private static MethodHandle makeZero(Class<?> rtype) {
2387 MethodType mtype = MethodType.methodType(rtype);
2388 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
2389 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
2390 }
2391
2392 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
2393 // Simulate a CAS, to avoid racy duplication of results.
2394 MethodHandle prev = cache[pos];
2395 if (prev != null) return prev;
2396 return cache[pos] = value;
2397 }
2398
2399 /**
2400 * Provides a target method handle with one or more <em>bound arguments</em>
2401 * in advance of the method handle's invocation.
2402 * The formal parameters to the target corresponding to the bound
2403 * arguments are called <em>bound parameters</em>.
2404 * Returns a new method handle which saves away the bound arguments.
2405 * When it is invoked, it receives arguments for any non-bound parameters,
2406 * binds the saved arguments to their corresponding parameters,
2407 * and calls the original target.
2408 * <p>
2409 * The type of the new method handle will drop the types for the bound
2410 * parameters from the original target type, since the new method handle
2411 * will no longer require those arguments to be supplied by its callers.
2412 * <p>
2413 * Each given argument object must match the corresponding bound parameter type.
2414 * If a bound parameter type is a primitive, the argument object
2415 * must be a wrapper, and will be unboxed to produce the primitive value.
2416 * <p>
2417 * The {@code pos} argument selects which parameters are to be bound.
2418 * It may range between zero and <i>N-L</i> (inclusively),
2419 * where <i>N</i> is the arity of the target method handle
2420 * and <i>L</i> is the length of the values array.
2421 * @param target the method handle to invoke after the argument is inserted
2422 * @param pos where to insert the argument (zero for the first)
2423 * @param values the series of arguments to insert
2424 * @return a method handle which inserts an additional argument,
2425 * before calling the original method handle
2426 * @throws NullPointerException if the target or the {@code values} array is null
2427 * @see MethodHandle#bindTo
2428 */
2429 public static
2430 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2431 int insCount = values.length;
2432 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
2433 if (insCount == 0) return target;
2434 BoundMethodHandle result = target.rebind();
2435 for (int i = 0; i < insCount; i++) {
2436 Object value = values[i];
2437 Class<?> ptype = ptypes[pos+i];
2438 if (ptype.isPrimitive()) {
2439 result = insertArgumentPrimitive(result, pos, ptype, value);
2440 } else {
2441 value = ptype.cast(value); // throw CCE if needed
2442 result = result.bindArgumentL(pos, value);
2443 }
2444 }
2445 return result;
2446 }
2447
2448 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
2449 Class<?> ptype, Object value) {
2450 Wrapper w = Wrapper.forPrimitiveType(ptype);
2451 // perform unboxing and/or primitive conversion
2452 value = w.convert(value, ptype);
2453 switch (w) {
2454 case INT: return result.bindArgumentI(pos, (int)value);
2455 case LONG: return result.bindArgumentJ(pos, (long)value);
2456 case FLOAT: return result.bindArgumentF(pos, (float)value);
2457 case DOUBLE: return result.bindArgumentD(pos, (double)value);
2458 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
2459 }
2460 }
2461
2462 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
2463 MethodType oldType = target.type();
2464 int outargs = oldType.parameterCount();
2465 int inargs = outargs - insCount;
2466 if (inargs < 0)
2467 throw newIllegalArgumentException("too many values to insert");
2468 if (pos < 0 || pos > inargs)
2469 throw newIllegalArgumentException("no argument type to append");
2470 return oldType.ptypes();
2471 }
2472
2473 /**
2474 * Produces a method handle which will discard some dummy arguments
2475 * before calling some other specified <i>target</i> method handle.
2476 * The type of the new method handle will be the same as the target's type,
2477 * except it will also include the dummy argument types,
2478 * at some given position.
2479 * <p>
2480 * The {@code pos} argument may range between zero and <i>N</i>,
2481 * where <i>N</i> is the arity of the target.
2482 * If {@code pos} is zero, the dummy arguments will precede
2483 * the target's real arguments; if {@code pos} is <i>N</i>
2484 * they will come after.
2485 * <p>
2486 * <b>Example:</b>
2487 * <blockquote><pre>{@code
2488 import static java.lang.invoke.MethodHandles.*;
2489 import static java.lang.invoke.MethodType.*;
2490 ...
2491 MethodHandle cat = lookup().findVirtual(String.class,
2492 "concat", methodType(String.class, String.class));
2493 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2494 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2495 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2496 assertEquals(bigType, d0.type());
2497 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2498 * }</pre></blockquote>
2499 * <p>
2500 * This method is also equivalent to the following code:
2501 * <blockquote><pre>
2502 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2503 * </pre></blockquote>
2504 * @param target the method handle to invoke after the arguments are dropped
2505 * @param valueTypes the type(s) of the argument(s) to drop
2506 * @param pos position of first argument to drop (zero for the leftmost)
2507 * @return a method handle which drops arguments of the given types,
2508 * before calling the original method handle
2509 * @throws NullPointerException if the target is null,
2510 * or if the {@code valueTypes} list or any of its elements is null
2511 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2512 * or if {@code pos} is negative or greater than the arity of the target,
2513 * or if the new method handle's type would have too many parameters
2514 */
2515 public static
2516 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2517 MethodType oldType = target.type(); // get NPE
2518 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
2519 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
2520 if (dropped == 0) return target;
2521 BoundMethodHandle result = target.rebind();
2522 LambdaForm lform = result.form;
2523 int insertFormArg = 1 + pos;
2524 for (Class<?> ptype : valueTypes) {
2525 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
2526 }
2527 result = result.copyWith(newType, lform);
2528 return result;
2529 }
2530
2531 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
2532 int dropped = valueTypes.size();
2533 MethodType.checkSlotCount(dropped);
2534 int outargs = oldType.parameterCount();
2535 int inargs = outargs + dropped;
2536 if (pos < 0 || pos > outargs)
2537 throw newIllegalArgumentException("no argument type to remove"
2538 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
2539 );
2540 return dropped;
2541 }
2542
2543 /**
2544 * Produces a method handle which will discard some dummy arguments
2545 * before calling some other specified <i>target</i> method handle.
2546 * The type of the new method handle will be the same as the target's type,
2547 * except it will also include the dummy argument types,
2548 * at some given position.
2549 * <p>
2550 * The {@code pos} argument may range between zero and <i>N</i>,
2551 * where <i>N</i> is the arity of the target.
2552 * If {@code pos} is zero, the dummy arguments will precede
2553 * the target's real arguments; if {@code pos} is <i>N</i>
2554 * they will come after.
2555 * <p>
2556 * <b>Example:</b>
2557 * <blockquote><pre>{@code
2558 import static java.lang.invoke.MethodHandles.*;
2559 import static java.lang.invoke.MethodType.*;
2560 ...
2561 MethodHandle cat = lookup().findVirtual(String.class,
2562 "concat", methodType(String.class, String.class));
2563 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2564 MethodHandle d0 = dropArguments(cat, 0, String.class);
2565 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2566 MethodHandle d1 = dropArguments(cat, 1, String.class);
2567 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2568 MethodHandle d2 = dropArguments(cat, 2, String.class);
2569 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2570 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2571 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2572 * }</pre></blockquote>
2573 * <p>
2574 * This method is also equivalent to the following code:
2575 * <blockquote><pre>
2576 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2577 * </pre></blockquote>
2578 * @param target the method handle to invoke after the arguments are dropped
2579 * @param valueTypes the type(s) of the argument(s) to drop
2580 * @param pos position of first argument to drop (zero for the leftmost)
2581 * @return a method handle which drops arguments of the given types,
2582 * before calling the original method handle
2583 * @throws NullPointerException if the target is null,
2584 * or if the {@code valueTypes} array or any of its elements is null
2585 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2586 * or if {@code pos} is negative or greater than the arity of the target,
2587 * or if the new method handle's type would have
2588 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2589 */
2590 public static
2591 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2592 return dropArguments(target, pos, Arrays.asList(valueTypes));
2593 }
2594
2595 /**
2596 * Adapts a target method handle by pre-processing
2597 * one or more of its arguments, each with its own unary filter function,
2598 * and then calling the target with each pre-processed argument
2599 * replaced by the result of its corresponding filter function.
2600 * <p>
2601 * The pre-processing is performed by one or more method handles,
2602 * specified in the elements of the {@code filters} array.
2603 * The first element of the filter array corresponds to the {@code pos}
2604 * argument of the target, and so on in sequence.
2605 * <p>
2606 * Null arguments in the array are treated as identity functions,
2607 * and the corresponding arguments left unchanged.
2608 * (If there are no non-null elements in the array, the original target is returned.)
2609 * Each filter is applied to the corresponding argument of the adapter.
2610 * <p>
2611 * If a filter {@code F} applies to the {@code N}th argument of
2612 * the target, then {@code F} must be a method handle which
2613 * takes exactly one argument. The type of {@code F}'s sole argument
2614 * replaces the corresponding argument type of the target
2615 * in the resulting adapted method handle.
2616 * The return type of {@code F} must be identical to the corresponding
2617 * parameter type of the target.
2618 * <p>
2619 * It is an error if there are elements of {@code filters}
2620 * (null or not)
2621 * which do not correspond to argument positions in the target.
2622 * <p><b>Example:</b>
2623 * <blockquote><pre>{@code
2624 import static java.lang.invoke.MethodHandles.*;
2625 import static java.lang.invoke.MethodType.*;
2626 ...
2627 MethodHandle cat = lookup().findVirtual(String.class,
2628 "concat", methodType(String.class, String.class));
2629 MethodHandle upcase = lookup().findVirtual(String.class,
2630 "toUpperCase", methodType(String.class));
2631 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2632 MethodHandle f0 = filterArguments(cat, 0, upcase);
2633 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2634 MethodHandle f1 = filterArguments(cat, 1, upcase);
2635 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2636 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2637 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2638 * }</pre></blockquote>
2639 * <p> Here is pseudocode for the resulting adapter:
2640 * <blockquote><pre>{@code
2641 * V target(P... p, A[i]... a[i], B... b);
2642 * A[i] filter[i](V[i]);
2643 * T adapter(P... p, V[i]... v[i], B... b) {
2644 * return target(p..., f[i](v[i])..., b...);
2645 * }
2646 * }</pre></blockquote>
2647 *
2648 * @param target the method handle to invoke after arguments are filtered
2649 * @param pos the position of the first argument to filter
2650 * @param filters method handles to call initially on filtered arguments
2651 * @return method handle which incorporates the specified argument filtering logic
2652 * @throws NullPointerException if the target is null
2653 * or if the {@code filters} array is null
2654 * @throws IllegalArgumentException if a non-null element of {@code filters}
2655 * does not match a corresponding argument type of target as described above,
2656 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2657 * or if the resulting method handle's type would have
2658 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2659 */
2660 public static
2661 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2662 filterArgumentsCheckArity(target, pos, filters);
2663 MethodHandle adapter = target;
2664 int curPos = pos-1; // pre-incremented
2665 for (MethodHandle filter : filters) {
2666 curPos += 1;
2667 if (filter == null) continue; // ignore null elements of filters
2668 adapter = filterArgument(adapter, curPos, filter);
2669 }
2670 return adapter;
2671 }
2672
2673 /*non-public*/ static
2674 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2675 filterArgumentChecks(target, pos, filter);
2676 MethodType targetType = target.type();
2677 MethodType filterType = filter.type();
2678 BoundMethodHandle result = target.rebind();
2679 Class<?> newParamType = filterType.parameterType(0);
2680 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
2681 MethodType newType = targetType.changeParameterType(pos, newParamType);
2682 result = result.copyWithExtendL(newType, lform, filter);
2683 return result;
2684 }
2685
2686 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
2687 MethodType targetType = target.type();
2688 int maxPos = targetType.parameterCount();
2689 if (pos + filters.length > maxPos)
2690 throw newIllegalArgumentException("too many filters");
2691 }
2692
2693 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
2694 MethodType targetType = target.type();
2695 MethodType filterType = filter.type();
2696 if (filterType.parameterCount() != 1
2697 || filterType.returnType() != targetType.parameterType(pos))
2698 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2699 }
2700
2701 /**
2702 * Adapts a target method handle by pre-processing
2703 * a sub-sequence of its arguments with a filter (another method handle).
2704 * The pre-processed arguments are replaced by the result (if any) of the
2705 * filter function.
2706 * The target is then called on the modified (usually shortened) argument list.
2707 * <p>
2708 * If the filter returns a value, the target must accept that value as
2709 * its argument in position {@code pos}, preceded and/or followed by
2710 * any arguments not passed to the filter.
2711 * If the filter returns void, the target must accept all arguments
2712 * not passed to the filter.
2713 * No arguments are reordered, and a result returned from the filter
2714 * replaces (in order) the whole subsequence of arguments originally
2715 * passed to the adapter.
2716 * <p>
2717 * The argument types (if any) of the filter
2718 * replace zero or one argument types of the target, at position {@code pos},
2719 * in the resulting adapted method handle.
2720 * The return type of the filter (if any) must be identical to the
2721 * argument type of the target at position {@code pos}, and that target argument
2722 * is supplied by the return value of the filter.
2723 * <p>
2724 * In all cases, {@code pos} must be greater than or equal to zero, and
2725 * {@code pos} must also be less than or equal to the target's arity.
2726 * <p><b>Example:</b>
2727 * <blockquote><pre>{@code
2728 import static java.lang.invoke.MethodHandles.*;
2729 import static java.lang.invoke.MethodType.*;
2730 ...
2731 MethodHandle deepToString = publicLookup()
2732 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2733
2734 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2735 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2736
2737 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2738 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2739
2740 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2741 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2742 assertEquals("[top, [up, down], strange]",
2743 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2744
2745 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2746 assertEquals("[top, [up, down], [strange]]",
2747 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2748
2749 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2750 assertEquals("[top, [[up, down, strange], charm], bottom]",
2751 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2752 * }</pre></blockquote>
2753 * <p> Here is pseudocode for the resulting adapter:
2754 * <blockquote><pre>{@code
2755 * T target(A...,V,C...);
2756 * V filter(B...);
2757 * T adapter(A... a,B... b,C... c) {
2758 * V v = filter(b...);
2759 * return target(a...,v,c...);
2760 * }
2761 * // and if the filter has no arguments:
2762 * T target2(A...,V,C...);
2763 * V filter2();
2764 * T adapter2(A... a,C... c) {
2765 * V v = filter2();
2766 * return target2(a...,v,c...);
2767 * }
2768 * // and if the filter has a void return:
2769 * T target3(A...,C...);
2770 * void filter3(B...);
2771 * void adapter3(A... a,B... b,C... c) {
2772 * filter3(b...);
2773 * return target3(a...,c...);
2774 * }
2775 * }</pre></blockquote>
2776 * <p>
2777 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2778 * one which first "folds" the affected arguments, and then drops them, in separate
2779 * steps as follows:
2780 * <blockquote><pre>{@code
2781 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2782 * mh = MethodHandles.foldArguments(mh, coll); //step 1
2783 * }</pre></blockquote>
2784 * If the target method handle consumes no arguments besides than the result
2785 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2786 * is equivalent to {@code filterReturnValue(coll, mh)}.
2787 * If the filter method handle {@code coll} consumes one argument and produces
2788 * a non-void result, then {@code collectArguments(mh, N, coll)}
2789 * is equivalent to {@code filterArguments(mh, N, coll)}.
2790 * Other equivalences are possible but would require argument permutation.
2791 *
2792 * @param target the method handle to invoke after filtering the subsequence of arguments
2793 * @param pos the position of the first adapter argument to pass to the filter,
2794 * and/or the target argument which receives the result of the filter
2795 * @param filter method handle to call on the subsequence of arguments
2796 * @return method handle which incorporates the specified argument subsequence filtering logic
2797 * @throws NullPointerException if either argument is null
2798 * @throws IllegalArgumentException if the return type of {@code filter}
2799 * is non-void and is not the same as the {@code pos} argument of the target,
2800 * or if {@code pos} is not between 0 and the target's arity, inclusive,
2801 * or if the resulting method handle's type would have
2802 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2803 * @see MethodHandles#foldArguments
2804 * @see MethodHandles#filterArguments
2805 * @see MethodHandles#filterReturnValue
2806 */
2807 public static
2808 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2809 MethodType newType = collectArgumentsChecks(target, pos, filter);
2810 MethodType collectorType = filter.type();
2811 BoundMethodHandle result = target.rebind();
2812 LambdaForm lform;
2813 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
2814 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
2815 if (lform != null) {
2816 return result.copyWith(newType, lform);
2817 }
2818 }
2819 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
2820 return result.copyWithExtendL(newType, lform, filter);
2821 }
2822
2823 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
2824 MethodType targetType = target.type();
2825 MethodType filterType = filter.type();
2826 Class<?> rtype = filterType.returnType();
2827 List<Class<?>> filterArgs = filterType.parameterList();
2828 if (rtype == void.class) {
2829 return targetType.insertParameterTypes(pos, filterArgs);
2830 }
2831 if (rtype != targetType.parameterType(pos)) {
2832 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2833 }
2834 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
2835 }
2836
2837 /**
2838 * Adapts a target method handle by post-processing
2839 * its return value (if any) with a filter (another method handle).
2840 * The result of the filter is returned from the adapter.
2841 * <p>
2842 * If the target returns a value, the filter must accept that value as
2843 * its only argument.
2844 * If the target returns void, the filter must accept no arguments.
2845 * <p>
2846 * The return type of the filter
2847 * replaces the return type of the target
2848 * in the resulting adapted method handle.
2849 * The argument type of the filter (if any) must be identical to the
2850 * return type of the target.
2851 * <p><b>Example:</b>
2852 * <blockquote><pre>{@code
2853 import static java.lang.invoke.MethodHandles.*;
2854 import static java.lang.invoke.MethodType.*;
2855 ...
2856 MethodHandle cat = lookup().findVirtual(String.class,
2857 "concat", methodType(String.class, String.class));
2858 MethodHandle length = lookup().findVirtual(String.class,
2859 "length", methodType(int.class));
2860 System.out.println((String) cat.invokeExact("x", "y")); // xy
2861 MethodHandle f0 = filterReturnValue(cat, length);
2862 System.out.println((int) f0.invokeExact("x", "y")); // 2
2863 * }</pre></blockquote>
2864 * <p> Here is pseudocode for the resulting adapter:
2865 * <blockquote><pre>{@code
2866 * V target(A...);
2867 * T filter(V);
2868 * T adapter(A... a) {
2869 * V v = target(a...);
2870 * return filter(v);
2871 * }
2872 * // and if the target has a void return:
2873 * void target2(A...);
2874 * T filter2();
2875 * T adapter2(A... a) {
2876 * target2(a...);
2877 * return filter2();
2878 * }
2879 * // and if the filter has a void return:
2880 * V target3(A...);
2881 * void filter3(V);
2882 * void adapter3(A... a) {
2883 * V v = target3(a...);
2884 * filter3(v);
2885 * }
2886 * }</pre></blockquote>
2887 * @param target the method handle to invoke before filtering the return value
2888 * @param filter method handle to call on the return value
2889 * @return method handle which incorporates the specified return value filtering logic
2890 * @throws NullPointerException if either argument is null
2891 * @throws IllegalArgumentException if the argument list of {@code filter}
2892 * does not match the return type of target as described above
2893 */
2894 public static
2895 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2896 MethodType targetType = target.type();
2897 MethodType filterType = filter.type();
2898 filterReturnValueChecks(targetType, filterType);
2899 BoundMethodHandle result = target.rebind();
2900 BasicType rtype = BasicType.basicType(filterType.returnType());
2901 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
2902 MethodType newType = targetType.changeReturnType(filterType.returnType());
2903 result = result.copyWithExtendL(newType, lform, filter);
2904 return result;
2905 }
2906
2907 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
2908 Class<?> rtype = targetType.returnType();
2909 int filterValues = filterType.parameterCount();
2910 if (filterValues == 0
2911 ? (rtype != void.class)
2912 : (rtype != filterType.parameterType(0)))
2913 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2914 }
2915
2916 /**
2917 * Adapts a target method handle by pre-processing
2918 * some of its arguments, and then calling the target with
2919 * the result of the pre-processing, inserted into the original
2920 * sequence of arguments.
2921 * <p>
2922 * The pre-processing is performed by {@code combiner}, a second method handle.
2923 * Of the arguments passed to the adapter, the first {@code N} arguments
2924 * are copied to the combiner, which is then called.
2925 * (Here, {@code N} is defined as the parameter count of the combiner.)
2926 * After this, control passes to the target, with any result
2927 * from the combiner inserted before the original {@code N} incoming
2928 * arguments.
2929 * <p>
2930 * If the combiner returns a value, the first parameter type of the target
2931 * must be identical with the return type of the combiner, and the next
2932 * {@code N} parameter types of the target must exactly match the parameters
2933 * of the combiner.
2934 * <p>
2935 * If the combiner has a void return, no result will be inserted,
2936 * and the first {@code N} parameter types of the target
2937 * must exactly match the parameters of the combiner.
2938 * <p>
2939 * The resulting adapter is the same type as the target, except that the
2940 * first parameter type is dropped,
2941 * if it corresponds to the result of the combiner.
2942 * <p>
2943 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2944 * that either the combiner or the target does not wish to receive.
2945 * If some of the incoming arguments are destined only for the combiner,
2946 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2947 * arguments will not need to be live on the stack on entry to the
2948 * target.)
2949 * <p><b>Example:</b>
2950 * <blockquote><pre>{@code
2951 import static java.lang.invoke.MethodHandles.*;
2952 import static java.lang.invoke.MethodType.*;
2953 ...
2954 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2955 "println", methodType(void.class, String.class))
2956 .bindTo(System.out);
2957 MethodHandle cat = lookup().findVirtual(String.class,
2958 "concat", methodType(String.class, String.class));
2959 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2960 MethodHandle catTrace = foldArguments(cat, trace);
2961 // also prints "boo":
2962 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2963 * }</pre></blockquote>
2964 * <p> Here is pseudocode for the resulting adapter:
2965 * <blockquote><pre>{@code
2966 * // there are N arguments in A...
2967 * T target(V, A[N]..., B...);
2968 * V combiner(A...);
2969 * T adapter(A... a, B... b) {
2970 * V v = combiner(a...);
2971 * return target(v, a..., b...);
2972 * }
2973 * // and if the combiner has a void return:
2974 * T target2(A[N]..., B...);
2975 * void combiner2(A...);
2976 * T adapter2(A... a, B... b) {
2977 * combiner2(a...);
2978 * return target2(a..., b...);
2979 * }
2980 * }</pre></blockquote>
2981 * @param target the method handle to invoke after arguments are combined
2982 * @param combiner method handle to call initially on the incoming arguments
2983 * @return method handle which incorporates the specified argument folding logic
2984 * @throws NullPointerException if either argument is null
2985 * @throws IllegalArgumentException if {@code combiner}'s return type
2986 * is non-void and not the same as the first argument type of
2987 * the target, or if the initial {@code N} argument types
2988 * of the target
2989 * (skipping one matching the {@code combiner}'s return type)
2990 * are not identical with the argument types of {@code combiner}
2991 */
2992 public static
2993 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2994 return foldArguments(target, 0, combiner);
2995 }
2996
2997 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
2998 int foldArgs = combinerType.parameterCount();
2999 Class<?> rtype = combinerType.returnType();
3000 int foldVals = rtype == void.class ? 0 : 1;
3001 int afterInsertPos = foldPos + foldVals;
3002 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
3003 if (ok && !(combinerType.parameterList()
3004 .equals(targetType.parameterList().subList(afterInsertPos,
3005 afterInsertPos + foldArgs))))
3006 ok = false;
3007 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
3008 ok = false;
3009 if (!ok)
3010 throw misMatchedTypes("target and combiner types", targetType, combinerType);
3011 return rtype;
3012 }
3013
3014 /**
3015 * Makes a method handle which adapts a target method handle,
3016 * by guarding it with a test, a boolean-valued method handle.
3017 * If the guard fails, a fallback handle is called instead.
3018 * All three method handles must have the same corresponding
3019 * argument and return types, except that the return type
3020 * of the test must be boolean, and the test is allowed
3021 * to have fewer arguments than the other two method handles.
3022 * <p> Here is pseudocode for the resulting adapter:
3023 * <blockquote><pre>{@code
3024 * boolean test(A...);
3025 * T target(A...,B...);
3026 * T fallback(A...,B...);
3027 * T adapter(A... a,B... b) {
3028 * if (test(a...))
3029 * return target(a..., b...);
3030 * else
3031 * return fallback(a..., b...);
3032 * }
3033 * }</pre></blockquote>
3034 * Note that the test arguments ({@code a...} in the pseudocode) cannot
3035 * be modified by execution of the test, and so are passed unchanged
3036 * from the caller to the target or fallback as appropriate.
3037 * @param test method handle used for test, must return boolean
3038 * @param target method handle to call if test passes
3039 * @param fallback method handle to call if test fails
3040 * @return method handle which incorporates the specified if/then/else logic
3041 * @throws NullPointerException if any argument is null
3042 * @throws IllegalArgumentException if {@code test} does not return boolean,
3043 * or if all three method types do not match (with the return
3044 * type of {@code test} changed to match that of the target).
3045 */
3046 public static
3047 MethodHandle guardWithTest(MethodHandle test,
3048 MethodHandle target,
3049 MethodHandle fallback) {
3050 MethodType gtype = test.type();
3051 MethodType ttype = target.type();
3052 MethodType ftype = fallback.type();
3053 if (!ttype.equals(ftype))
3054 throw misMatchedTypes("target and fallback types", ttype, ftype);
3055 if (gtype.returnType() != boolean.class)
3056 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
3057 List<Class<?>> targs = ttype.parameterList();
3058 List<Class<?>> gargs = gtype.parameterList();
3059 if (!targs.equals(gargs)) {
3060 int gpc = gargs.size(), tpc = targs.size();
3061 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
3062 throw misMatchedTypes("target and test types", ttype, gtype);
3063 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
3064 gtype = test.type();
3065 }
3066 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
3067 }
3068
3069 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
3070 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
3071 }
3072
3073 /**
3074 * Makes a method handle which adapts a target method handle,
3075 * by running it inside an exception handler.
3076 * If the target returns normally, the adapter returns that value.
3077 * If an exception matching the specified type is thrown, the fallback
3078 * handle is called instead on the exception, plus the original arguments.
3079 * <p>
3080 * The target and handler must have the same corresponding
3081 * argument and return types, except that handler may omit trailing arguments
3082 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
3083 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
3084 * <p> Here is pseudocode for the resulting adapter:
3085 * <blockquote><pre>{@code
3086 * T target(A..., B...);
3087 * T handler(ExType, A...);
3088 * T adapter(A... a, B... b) {
3089 * try {
3090 * return target(a..., b...);
3091 * } catch (ExType ex) {
3092 * return handler(ex, a...);
3093 * }
3094 * }
3095 * }</pre></blockquote>
3096 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
3097 * be modified by execution of the target, and so are passed unchanged
3098 * from the caller to the handler, if the handler is invoked.
3099 * <p>
3100 * The target and handler must return the same type, even if the handler
3101 * always throws. (This might happen, for instance, because the handler
3102 * is simulating a {@code finally} clause).
3103 * To create such a throwing handler, compose the handler creation logic
3104 * with {@link #throwException throwException},
3105 * in order to create a method handle of the correct return type.
3106 * @param target method handle to call
3107 * @param exType the type of exception which the handler will catch
3108 * @param handler method handle to call if a matching exception is thrown
3109 * @return method handle which incorporates the specified try/catch logic
3110 * @throws NullPointerException if any argument is null
3111 * @throws IllegalArgumentException if {@code handler} does not accept
3112 * the given exception type, or if the method handle types do
3113 * not match in their return types and their
3114 * corresponding parameters
3115 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
3116 */
3117 public static
3118 MethodHandle catchException(MethodHandle target,
3119 Class<? extends Throwable> exType,
3120 MethodHandle handler) {
3121 MethodType ttype = target.type();
3122 MethodType htype = handler.type();
3123 if (htype.parameterCount() < 1 ||
3124 !htype.parameterType(0).isAssignableFrom(exType))
3125 throw newIllegalArgumentException("handler does not accept exception type "+exType);
3126 if (htype.returnType() != ttype.returnType())
3127 throw misMatchedTypes("target and handler return types", ttype, htype);
3128 List<Class<?>> targs = ttype.parameterList();
3129 List<Class<?>> hargs = htype.parameterList();
3130 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
3131 if (!targs.equals(hargs)) {
3132 int hpc = hargs.size(), tpc = targs.size();
3133 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
3134 throw misMatchedTypes("target and handler types", ttype, htype);
3135 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
3136 htype = handler.type();
3137 }
3138 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
3139 }
3140
3141 /**
3142 * Produces a method handle which will throw exceptions of the given {@code exType}.
3143 * The method handle will accept a single argument of {@code exType},
3144 * and immediately throw it as an exception.
3145 * The method type will nominally specify a return of {@code returnType}.
3146 * The return type may be anything convenient: It doesn't matter to the
3147 * method handle's behavior, since it will never return normally.
3148 * @param returnType the return type of the desired method handle
3149 * @param exType the parameter type of the desired method handle
3150 * @return method handle which can throw the given exceptions
3151 * @throws NullPointerException if either argument is null
3152 */
3153 public static
3154 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
3155 if (!Throwable.class.isAssignableFrom(exType))
3156 throw new ClassCastException(exType.getName());
3157 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
3158 }
3159
3160 /**
3161 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
3162 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
3163 * delivers the loop's result, which is the return value of the resulting handle.
3164 * <p>
3165 * Intuitively, every loop is formed by one or more "clauses", each specifying a local iteration value and/or a loop
3166 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
3167 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
3168 * terms of method handles, each clause will determine four actions:<ul>
3169 * <li>Before the loop executes, the initialization of an iteration variable or loop invariant local.
3170 * <li>When a clause executes, an update step for the iteration variable.
3171 * <li>When a clause executes, a predicate execution to test for loop exit.
3172 * <li>If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
3173 * </ul>
3174 * <p>
3175 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
3176 * this case. See below for a detailed description.
3177 * <p>
3178 * Each clause function, with the exception of clause initializers, is able to observe the entire loop state,
3179 * because it will be passed <em>all</em> current iteration variable values, as well as all incoming loop
3180 * parameters. Most clause functions will not need all of this information, but they will be formally connected as
3181 * if by {@link #dropArguments}.
3182 * <p>
3183 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
3184 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
3185 * corresponds to a place where {@link IllegalArgumentException} may be thrown if the required constraint is not met
3186 * by the inputs to the loop combinator. The term "effectively identical", applied to parameter type lists, means
3187 * that they must be identical, or else one list must be a proper prefix of the other.
3188 * <p>
3189 * <em>Step 0: Determine clause structure.</em><ol type="a">
3190 * <li>The clause array (of type {@code MethodHandle[][]} must be non-{@code null} and contain at least one element.
3191 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
3192 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
3193 * four. Padding takes place by appending elements to the array.
3194 * <li>Clauses with all {@code null}s are disregarded.
3195 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
3196 * </ol>
3197 * <p>
3198 * <em>Step 1A: Determine iteration variables.</em><ol type="a">
3199 * <li>Examine init and step function return types, pairwise, to determine each clause's iteration variable type.
3200 * <li>If both functions are omitted, use {@code void}; else if one is omitted, use the other's return type; else
3201 * use the common return type (they must be identical).
3202 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
3203 * <li>This list of types is called the "common prefix".
3204 * </ol>
3205 * <p>
3206 * <em>Step 1B: Determine loop parameters.</em><ol type="a">
3207 * <li>Examine init function parameter lists.
3208 * <li>Omitted init functions are deemed to have {@code null} parameter lists.
3209 * <li>All init function parameter lists must be effectively identical.
3210 * <li>The longest parameter list (which is necessarily unique) is called the "common suffix".
3211 * </ol>
3212 * <p>
3213 * <em>Step 1C: Determine loop return type.</em><ol type="a">
3214 * <li>Examine fini function return types, disregarding omitted fini functions.
3215 * <li>If there are no fini functions, use {@code void} as the loop return type.
3216 * <li>Otherwise, use the common return type of the fini functions; they must all be identical.
3217 * </ol>
3218 * <p>
3219 * <em>Step 1D: Check other types.</em><ol type="a">
3220 * <li>There must be at least one non-omitted pred function.
3221 * <li>Every non-omitted pred function must have a {@code boolean} return type.
3222 * </ol>
3223 * <p>
3224 * (Implementation Note: Steps 1A, 1B, 1C, 1D are logically independent of each other, and may be performed in any
3225 * order.)
3226 * <p>
3227 * <em>Step 2: Determine parameter lists.</em><ol type="a">
3228 * <li>The parameter list for the resulting loop handle will be the "common suffix".
3229 * <li>The parameter list for init functions will be adjusted to the "common suffix". (Note that their parameter
3230 * lists are already effectively identical to the common suffix.)
3231 * <li>The parameter list for non-init (step, pred, and fini) functions will be adjusted to the common prefix
3232 * followed by the common suffix, called the "common parameter sequence".
3233 * <li>Every non-init, non-omitted function parameter list must be effectively identical to the common parameter
3234 * sequence.
3235 * </ol>
3236 * <p>
3237 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
3238 * <li>If an init function is omitted, use a {@linkplain #constant constant function} of the appropriate
3239 * {@code null}/zero/{@code false}/{@code void} type. (For this purpose, a constant {@code void} is simply a
3240 * function which does nothing and returns {@code void}; it can be obtained from another constant function by
3241 * {@linkplain MethodHandle#asType type conversion}.)
3242 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
3243 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
3244 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
3245 * <li>If a pred function is omitted, the corresponding fini function must also be omitted.
3246 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
3247 * as this clause is concerned.)
3248 * <li>If a fini function is omitted, use a constant {@code null}/zero/{@code false}/{@code void} function of the
3249 * loop return type.
3250 * </ol>
3251 * <p>
3252 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
3253 * <li>At this point, every init function parameter list is effectively identical to the common suffix, but some
3254 * lists may be shorter. For every init function with a short parameter list, pad out the end of the list by
3255 * {@linkplain #dropArguments dropping arguments}.
3256 * <li>At this point, every non-init function parameter list is effectively identical to the common parameter
3257 * sequence, but some lists may be shorter. For every non-init function with a short parameter list, pad out the end
3258 * of the list by {@linkplain #dropArguments dropping arguments}.
3259 * </ol>
3260 * <p>
3261 * <em>Final observations.</em><ol type="a">
3262 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
3263 * <li>All init functions have a common parameter type list, which the final loop handle will also have.
3264 * <li>All fini functions have a common return type, which the final loop handle will also have.
3265 * <li>All non-init functions have a common parameter type list, which is the common parameter sequence, of
3266 * (non-{@code void}) iteration variables followed by loop parameters.
3267 * <li>Each pair of init and step functions agrees in their return types.
3268 * <li>Each non-init function will be able to observe the current values of all iteration variables, by means of the
3269 * common prefix.
3270 * </ol>
3271 * <p>
3272 * <em>Loop execution.</em><ol type="a">
3273 * <li>When the loop is called, the loop input values are saved in locals, to be passed (as the common suffix) to
3274 * every clause function. These locals are loop invariant.
3275 * <li>Each init function is executed in clause order (passing the common suffix) and the non-{@code void} values
3276 * are saved (as the common prefix) into locals. These locals are loop varying (unless their steps are identity
3277 * functions, as noted above).
3278 * <li>All function executions (except init functions) will be passed the common parameter sequence, consisting of
3279 * the non-{@code void} iteration values (in clause order) and then the loop inputs (in argument order).
3280 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
3281 * returns {@code false}.
3282 * <li>The non-{@code void} result from a step function call is used to update the corresponding loop variable. The
3283 * updated value is immediately visible to all subsequent function calls.
3284 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
3285 * is returned from the loop as a whole.
3286 * </ol>
3287 * <p>
3288 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the types / values
3289 * of loop variables; {@code A}/{@code a}, those of arguments passed to the resulting loop; and {@code R}, the
3290 * result types of finalizers as well as of the resulting loop.
3291 * <blockquote><pre>{@code
3292 * V... init...(A...);
3293 * boolean pred...(V..., A...);
3294 * V... step...(V..., A...);
3295 * R fini...(V..., A...);
3296 * R loop(A... a) {
3297 * V... v... = init...(a...);
3298 * for (;;) {
3299 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
3300 * v = s(v..., a...);
3301 * if (!p(v..., a...)) {
3302 * return f(v..., a...);
3303 * }
3304 * }
3305 * }
3306 * }
3307 * }</pre></blockquote>
3308 * <p>
3309 * @apiNote Example:
3310 * <blockquote><pre>{@code
3311 * // iterative implementation of the factorial function as a loop handle
3312 * static int one(int k) { return 1; }
3313 * int inc(int i, int acc, int k) { return i + 1; }
3314 * int mult(int i, int acc, int k) { return i * acc; }
3315 * boolean pred(int i, int acc, int k) { return i < k; }
3316 * int fin(int i, int acc, int k) { return acc; }
3317 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
3318 * // null initializer for counter, should initialize to 0
3319 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
3320 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
3321 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
3322 * assertEquals(120, loop.invoke(5));
3323 * }</pre></blockquote>
3324 *
3325 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
3326 *
3327 * @return a method handle embodying the looping behavior as defined by the arguments.
3328 *
3329 * @throws IllegalArgumentException in case any of the constraints described above is violated.
3330 *
3331 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
3332 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
3333 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
3334 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
3335 * @since 9
3336 */
3337 public static MethodHandle loop(MethodHandle[]... clauses) {
3338 // Step 0: determine clause structure.
3339 checkLoop0(clauses);
3340
3341 List<MethodHandle> init = new ArrayList<>();
3342 List<MethodHandle> step = new ArrayList<>();
3343 List<MethodHandle> pred = new ArrayList<>();
3344 List<MethodHandle> fini = new ArrayList<>();
3345
3346 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
3347 init.add(clause[0]); // all clauses have at least length 1
3348 step.add(clause.length <= 1 ? null : clause[1]);
3349 pred.add(clause.length <= 2 ? null : clause[2]);
3350 fini.add(clause.length <= 3 ? null : clause[3]);
3351 });
3352
3353 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
3354 final int nclauses = init.size();
3355
3356 // Step 1A: determine iteration variables.
3357 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
3358 for (int i = 0; i < nclauses; ++i) {
3359 MethodHandle in = init.get(i);
3360 MethodHandle st = step.get(i);
3361 if (in == null && st == null) {
3362 iterationVariableTypes.add(void.class);
3363 } else if (in != null && st != null) {
3364 checkLoop1a(i, in, st);
3365 iterationVariableTypes.add(in.type().returnType());
3366 } else {
3367 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
3368 }
3369 }
3370 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
3371 collect(Collectors.toList());
3372
3373 // Step 1B: determine loop parameters.
3374 final List<Class<?>> empty = new ArrayList<>();
3375 final List<Class<?>> commonSuffix = init.stream().filter(Objects::nonNull).map(MethodHandle::type).
3376 map(MethodType::parameterList).reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
3377 checkLoop1b(init, commonSuffix);
3378
3379 // Step 1C: determine loop return type.
3380 // Step 1D: check other types.
3381 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
3382 map(MethodType::returnType).findFirst().orElse(void.class);
3383 checkLoop1cd(pred, fini, loopReturnType);
3384
3385 // Step 2: determine parameter lists.
3386 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
3387 commonParameterSequence.addAll(commonSuffix);
3388 checkLoop2(step, pred, fini, commonParameterSequence);
3389
3390 // Step 3: fill in omitted functions.
3391 for (int i = 0; i < nclauses; ++i) {
3392 Class<?> t = iterationVariableTypes.get(i);
3393 if (init.get(i) == null) {
3394 init.set(i, zeroHandle(t));
3395 }
3396 if (step.get(i) == null) {
3397 step.set(i, dropArguments(t == void.class ? zeroHandle(t) : identity(t), 0, commonPrefix.subList(0, i)));
3398 }
3399 if (pred.get(i) == null) {
3400 pred.set(i, constant(boolean.class, true));
3401 }
3402 if (fini.get(i) == null) {
3403 fini.set(i, zeroHandle(t));
3404 }
3405 }
3406
3407 // Step 4: fill in missing parameter types.
3408 List<MethodHandle> finit = fillParameterTypes(init, commonSuffix);
3409 List<MethodHandle> fstep = fillParameterTypes(step, commonParameterSequence);
3410 List<MethodHandle> fpred = fillParameterTypes(pred, commonParameterSequence);
3411 List<MethodHandle> ffini = fillParameterTypes(fini, commonParameterSequence);
3412
3413 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
3414 allMatch(pl -> pl.equals(commonSuffix));
3415 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
3416 allMatch(pl -> pl.equals(commonParameterSequence));
3417
3418 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, commonPrefix, finit, fstep, fpred, ffini);
3419 }
3420
3421 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
3422 return hs.stream().map(h -> {
3423 int pc = h.type().parameterCount();
3424 int tpsize = targetParams.size();
3425 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
3426 }).collect(Collectors.toList());
3427 }
3428
3429 /**
3430 * Constructs a {@code while} loop from an initializer, a body, and a predicate. This is a convenience wrapper for
3431 * the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
3432 * <p>
3433 * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
3434 * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
3435 * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
3436 * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
3437 * generic loop combinator}.
3438 * <p>
3439 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
3440 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
3441 * passed to the loop.
3442 * <blockquote><pre>{@code
3443 * V init(A);
3444 * boolean pred(V, A);
3445 * V body(V, A);
3446 * V whileLoop(A a) {
3447 * V v = init(a);
3448 * while (pred(v, a)) {
3449 * v = body(v, a);
3450 * }
3451 * return v;
3452 * }
3453 * }</pre></blockquote>
3454 * <p>
3455 * @apiNote Example:
3456 * <blockquote><pre>{@code
3457 * // implement the zip function for lists as a loop handle
3458 * List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
3459 * boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
3460 * List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
3461 * zip.add(a.next());
3462 * zip.add(b.next());
3463 * return zip;
3464 * }
3465 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
3466 * MethodHandle loop = MethodHandles.doWhileLoop(MH_initZip, MH_zipStep, MH_zipPred);
3467 * List<String> a = Arrays.asList("a", "b", "c", "d");
3468 * List<String> b = Arrays.asList("e", "f", "g", "h");
3469 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
3470 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
3471 * }</pre></blockquote>
3472 *
3473 * <p>
3474 * @implSpec The implementation of this method is equivalent to:
3475 * <blockquote><pre>{@code
3476 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
3477 * MethodHandle[]
3478 * checkExit = {null, null, pred, identity(init.type().returnType())},
3479 * varBody = {init, body};
3480 * return loop(checkExit, varBody);
3481 * }
3482 * }</pre></blockquote>
3483 *
3484 * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
3485 * result type. Passing {@code null} or a {@code void} init function will make the loop's result type
3486 * {@code void}.
3487 * @param pred condition for the loop, which may not be {@code null}.
3488 * @param body body of the loop, which may not be {@code null}.
3489 *
3490 * @return the value of the loop variable as the loop terminates.
3491 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
3492 *
3493 * @see MethodHandles#loop(MethodHandle[][])
3494 * @since 9
3495 */
3496 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
3497 MethodHandle fin = init == null ? zeroHandle(void.class) : identity(init.type().returnType());
3498 MethodHandle[] checkExit = {null, null, pred, fin};
3499 MethodHandle[] varBody = {init, body};
3500 return loop(checkExit, varBody);
3501 }
3502
3503 /**
3504 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. This is a convenience wrapper
3505 * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
3506 * <p>
3507 * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
3508 * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
3509 * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
3510 * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
3511 * generic loop combinator}.
3512 * <p>
3513 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
3514 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
3515 * passed to the loop.
3516 * <blockquote><pre>{@code
3517 * V init(A);
3518 * boolean pred(V, A);
3519 * V body(V, A);
3520 * V doWhileLoop(A a) {
3521 * V v = init(a);
3522 * do {
3523 * v = body(v, a);
3524 * } while (pred(v, a));
3525 * return v;
3526 * }
3527 * }</pre></blockquote>
3528 * <p>
3529 * @apiNote Example:
3530 * <blockquote><pre>{@code
3531 * // int i = 0; while (i < limit) { ++i; } return i; => limit
3532 * int zero(int limit) { return 0; }
3533 * int step(int i, int limit) { return i + 1; }
3534 * boolean pred(int i, int limit) { return i < limit; }
3535 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
3536 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
3537 * assertEquals(23, loop.invoke(23));
3538 * }</pre></blockquote>
3539 *
3540 * <p>
3541 * @implSpec The implementation of this method is equivalent to:
3542 * <blockquote><pre>{@code
3543 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
3544 * MethodHandle[] clause = { init, body, pred, identity(init.type().returnType()) };
3545 * return loop(clause);
3546 * }
3547 * }</pre></blockquote>
3548 *
3549 *
3550 * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
3551 * result type. Passing {@code null} or a {@code void} init function will make the loop's result type
3552 * {@code void}.
3553 * @param pred condition for the loop, which may not be {@code null}.
3554 * @param body body of the loop, which may not be {@code null}.
3555 *
3556 * @return the value of the loop variable as the loop terminates.
3557 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
3558 *
3559 * @see MethodHandles#loop(MethodHandle[][])
3560 * @since 9
3561 */
3562 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
3563 MethodHandle fin = init == null ? zeroHandle(void.class) : identity(init.type().returnType());
3564 MethodHandle[] clause = {init, body, pred, fin};
3565 return loop(clause);
3566 }
3567
3568 /**
3569 * Constructs a loop that runs a given number of iterations. The loop counter is an {@code int} initialized from the
3570 * {@code iterations} handle evaluation result. The counter is passed to the {@code body} function, so that must
3571 * accept an initial {@code int} argument. The result of the loop execution is the final value of the additional
3572 * local state. This is a convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop
3573 * combinator}.
3574 * <p>
3575 * The result type and parameter type list of {@code init} determine those of the resulting handle. The {@code
3576 * iterations} handle must accept the same parameter types as {@code init} but return an {@code int}. The {@code
3577 * body} handle must accept the same parameter types as well, preceded by an {@code int} parameter for the counter,
3578 * and a parameter of the same type as {@code init}'s result. These constraints follow directly from those described
3579 * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
3580 * <p>
3581 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
3582 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
3583 * passed to the loop.
3584 * <blockquote><pre>{@code
3585 * int iterations(A);
3586 * V init(A);
3587 * V body(int, V, A);
3588 * V countedLoop(A a) {
3589 * int end = iterations(a);
3590 * V v = init(a);
3591 * for (int i = 0; i < end; ++i) {
3592 * v = body(i, v, a);
3593 * }
3594 * return v;
3595 * }
3596 * }</pre></blockquote>
3597 * <p>
3598 * @apiNote Example:
3599 * <blockquote><pre>{@code
3600 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
3601 * // => a variation on a well known theme
3602 * String start(String arg) { return arg; }
3603 * String step(int counter, String v, String arg) { return "na " + v; }
3604 * // assume MH_start and MH_step are handles to the two methods above
3605 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
3606 * MethodHandle loop = MethodHandles.countedLoop(fit13, MH_start, MH_step);
3607 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
3608 * }</pre></blockquote>
3609 *
3610 * <p>
3611 * @implSpec The implementation of this method is equivalent to:
3612 * <blockquote><pre>{@code
3613 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
3614 * return countedLoop(null, iterations, init, body); // null => constant zero
3615 * }
3616 * }</pre></blockquote>
3617 *
3618 * @param iterations a handle to return the number of iterations this loop should run.
3619 * @param init initializer for additional loop state. This determines the loop's result type.
3620 * Passing {@code null} or a {@code void} init function will make the loop's result type
3621 * {@code void}.
3622 * @param body the body of the loop, which must not be {@code null}.
3623 * It must accept an initial {@code int} parameter (for the counter), and then any
3624 * additional loop-local variable plus loop parameters.
3625 *
3626 * @return a method handle representing the loop.
3627 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
3628 *
3629 * @since 9
3630 */
3631 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
3632 return countedLoop(null, iterations, init, body);
3633 }
3634
3635 /**
3636 * Constructs a loop that counts over a range of numbers. The loop counter is an {@code int} that will be
3637 * initialized to the {@code int} value returned from the evaluation of the {@code start} handle and run to the
3638 * value returned from {@code end} (exclusively) with a step width of 1. The counter value is passed to the {@code
3639 * body} function in each iteration; it has to accept an initial {@code int} parameter
3640 * for that. The result of the loop execution is the final value of the additional local state
3641 * obtained by running {@code init}.
3642 * This is a
3643 * convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
3644 * <p>
3645 * The constraints for the {@code init} and {@code body} handles are the same as for {@link
3646 * #countedLoop(MethodHandle, MethodHandle, MethodHandle)}. Additionally, the {@code start} and {@code end} handles
3647 * must return an {@code int} and accept the same parameters as {@code init}.
3648 * <p>
3649 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
3650 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
3651 * passed to the loop.
3652 * <blockquote><pre>{@code
3653 * int start(A);
3654 * int end(A);
3655 * V init(A);
3656 * V body(int, V, A);
3657 * V countedLoop(A a) {
3658 * int s = start(a);
3659 * int e = end(a);
3660 * V v = init(a);
3661 * for (int i = s; i < e; ++i) {
3662 * v = body(i, v, a);
3663 * }
3664 * return v;
3665 * }
3666 * }</pre></blockquote>
3667 *
3668 * <p>
3669 * @implSpec The implementation of this method is equivalent to:
3670 * <blockquote><pre>{@code
3671 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
3672 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
3673 * // assume MH_increment and MH_lessThan are handles to x+1 and x<y of type int
3674 * MethodHandle[]
3675 * indexVar = {start, MH_increment}, // i = start; i = i+1
3676 * loopLimit = {end, null, MH_lessThan, returnVar }, // i<end
3677 * bodyClause = {init, dropArguments(body, 1, int.class)}; // v = body(i, v);
3678 * return loop(indexVar, loopLimit, bodyClause);
3679 * }
3680 * }</pre></blockquote>
3681 *
3682 * @param start a handle to return the start value of the loop counter.
3683 * If it is {@code null}, a constant zero is assumed.
3684 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to {@code end-1}).
3685 * @param init initializer for additional loop state. This determines the loop's result type.
3686 * Passing {@code null} or a {@code void} init function will make the loop's result type
3687 * {@code void}.
3688 * @param body the body of the loop, which must not be {@code null}.
3689 * It must accept an initial {@code int} parameter (for the counter), and then any
3690 * additional loop-local variable plus loop parameters.
3691 *
3692 * @return a method handle representing the loop.
3693 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
3694 *
3695 * @since 9
3696 */
3697 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
3698 MethodHandle returnVar = dropArguments(init == null ? zeroHandle(void.class) : identity(init.type().returnType()),
3699 0, int.class, int.class);
3700 MethodHandle[] indexVar = {start, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep)};
3701 MethodHandle[] loopLimit = {end, null, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred), returnVar};
3702 MethodHandle[] bodyClause = {init, dropArguments(body, 1, int.class)};
3703 return loop(indexVar, loopLimit, bodyClause);
3704 }
3705
3706 /**
3707 * Constructs a loop that ranges over the elements produced by an {@code Iterator<T>}.
3708 * The iterator will be produced by the evaluation of the {@code iterator} handle.
3709 * If this handle is passed as {@code null} the method {@link Iterable#iterator} will be used instead,
3710 * and will be applied to a leading argument of the loop handle.
3711 * Each value produced by the iterator is passed to the {@code body}, which must accept an initial {@code T} parameter.
3712 * The result of the loop execution is the final value of the additional local state
3713 * obtained by running {@code init}.
3714 * <p>
3715 * This is a convenience wrapper for the
3716 * {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}, and the constraints imposed on the {@code body}
3717 * handle follow directly from those described for the latter.
3718 * <p>
3719 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
3720 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
3721 * structure the loop iterates over, and {@code A}/{@code a}, that of the argument passed to the loop.
3722 * <blockquote><pre>{@code
3723 * Iterator<T> iterator(A); // defaults to Iterable::iterator
3724 * V init(A);
3725 * V body(T,V,A);
3726 * V iteratedLoop(A a) {
3727 * Iterator<T> it = iterator(a);
3728 * V v = init(a);
3729 * for (T t : it) {
3730 * v = body(t, v, a);
3731 * }
3732 * return v;
3733 * }
3734 * }</pre></blockquote>
3735 * <p>
3736 * The type {@code T} may be either a primitive or reference.
3737 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type
3738 * {@code Iterator}, the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body}
3739 * to {@code Object} as if by the {@link MethodHandle#asType asType} conversion method.
3740 * Therefore, if an iterator of the wrong type appears as the loop is executed,
3741 * runtime exceptions may occur as the result of dynamic conversions performed by {@code asType}.
3742 * <p>
3743 * @apiNote Example:
3744 * <blockquote><pre>{@code
3745 * // reverse a list
3746 * List<String> reverseStep(String e, List<String> r, List<String> l) {
3747 * r.add(0, e);
3748 * return r;
3749 * }
3750 * List<String> newArrayList(List<String> l) { return new ArrayList<>(); }
3751 * // assume MH_reverseStep, MH_newArrayList are handles to the above methods
3752 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
3753 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
3754 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
3755 * assertEquals(reversedList, (List<String>) loop.invoke(list));
3756 * }</pre></blockquote>
3757 * <p>
3758 * @implSpec The implementation of this method is equivalent to:
3759 * <blockquote><pre>{@code
3760 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
3761 * // assume MH_next and MH_hasNext are handles to methods of Iterator
3762 * Class<?> itype = iterator.type().returnType();
3763 * Class<?> ttype = body.type().parameterType(0);
3764 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, itype);
3765 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
3766 * MethodHandle[]
3767 * iterVar = {iterator, null, MH_hasNext, returnVar}, // it = iterator(); while (it.hasNext)
3768 * bodyClause = {init, filterArgument(body, 0, nextVal)}; // v = body(t, v, a);
3769 * return loop(iterVar, bodyClause);
3770 * }
3771 * }</pre></blockquote>
3772 *
3773 * @param iterator a handle to return the iterator to start the loop.
3774 * Passing {@code null} will make the loop call {@link Iterable#iterator()} on the first
3775 * incoming value.
3776 * @param init initializer for additional loop state. This determines the loop's result type.
3777 * Passing {@code null} or a {@code void} init function will make the loop's result type
3778 * {@code void}.
3779 * @param body the body of the loop, which must not be {@code null}.
3780 * It must accept an initial {@code T} parameter (for the iterated values), and then any
3781 * additional loop-local variable plus loop parameters.
3782 *
3783 * @return a method handle embodying the iteration loop functionality.
3784 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
3785 *
3786 * @since 9
3787 */
3788 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
3789 checkIteratedLoop(body);
3790
3791 MethodHandle initit = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
3792 MethodHandle initIterator = iterator == null ?
3793 initit.asType(initit.type().changeParameterType(0, body.type().parameterType(init == null ? 1 : 2))) :
3794 iterator;
3795 Class<?> itype = initIterator.type().returnType();
3796 Class<?> ttype = body.type().parameterType(0);
3797
3798 MethodHandle returnVar =
3799 dropArguments(init == null ? zeroHandle(void.class) : identity(init.type().returnType()), 0, itype);
3800 MethodHandle initnx = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
3801 MethodHandle nextVal = initnx.asType(initnx.type().changeReturnType(ttype));
3802
3803 MethodHandle[] iterVar = {initIterator, null, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred), returnVar};
3804 MethodHandle[] bodyClause = {init, filterArgument(body, 0, nextVal)};
3805
3806 return loop(iterVar, bodyClause);
3807 }
3808
3809 /**
3810 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
3811 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
3812 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
3813 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
3814 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
3815 * {@code try-finally} handle.
3816 * <p>
3817 * The {@code cleanup} handle will be passed one or two additional leading arguments.
3818 * The first is the exception thrown during the
3819 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
3820 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
3821 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
3822 * The second argument is not present if the {@code target} handle has a {@code void} return type.
3823 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
3824 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
3825 * <p>
3826 * The {@code target} and {@code cleanup} handles' return types must be the same. Their parameter type lists also
3827 * must be the same, but the {@code cleanup} handle must accept one or two more leading parameters:<ul>
3828 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
3829 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
3830 * the result from the execution of the {@code target} handle.
3831 * This parameter is not present if the {@code target} returns {@code void}.
3832 * </ul>
3833 * <p>
3834 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
3835 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
3836 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
3837 * the cleanup.
3838 * <blockquote><pre>{@code
3839 * V target(A..., B...);
3840 * V cleanup(Throwable, V, A...);
3841 * V adapter(A... a, B... b) {
3842 * V result = (zero value for V);
3843 * Throwable throwable = null;
3844 * try {
3845 * result = target(a..., b...);
3846 * } catch (Throwable t) {
3847 * throwable = t;
3848 * throw t;
3849 * } finally {
3850 * result = cleanup(throwable, result, a...);
3851 * }
3852 * return result;
3853 * }
3854 * }</pre></blockquote>
3855 * <p>
3856 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
3857 * be modified by execution of the target, and so are passed unchanged
3858 * from the caller to the cleanup, if it is invoked.
3859 * <p>
3860 * The target and cleanup must return the same type, even if the cleanup
3861 * always throws.
3862 * To create such a throwing cleanup, compose the cleanup logic
3863 * with {@link #throwException throwException},
3864 * in order to create a method handle of the correct return type.
3865 * <p>
3866 * Note that {@code tryFinally} never converts exceptions into normal returns.
3867 * In rare cases where exceptions must be converted in that way, first wrap
3868 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
3869 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
3870 *
3871 * @param target the handle whose execution is to be wrapped in a {@code try} block.
3872 * @param cleanup the handle that is invoked in the finally block.
3873 *
3874 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
3875 * @throws NullPointerException if any argument is null
3876 * @throws IllegalArgumentException if {@code cleanup} does not accept
3877 * the required leading arguments, or if the method handle types do
3878 * not match in their return types and their
3879 * corresponding trailing parameters
3880 *
3881 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
3882 * @since 9
3883 */
3884 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
3885 List<Class<?>> targetParamTypes = target.type().parameterList();
3886 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
3887 Class<?> rtype = target.type().returnType();
3888
3889 checkTryFinally(target, cleanup);
3890
3891 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
3892 int tpSize = targetParamTypes.size();
3893 int cpPrefixLength = rtype == void.class ? 1 : 2;
3894 int cpSize = cleanupParamTypes.size();
3895 MethodHandle aCleanup = cpSize - cpPrefixLength < tpSize ?
3896 dropArguments(cleanup, cpSize, targetParamTypes.subList(tpSize - (cpSize - cpPrefixLength), tpSize)) :
3897 cleanup;
3898
3899 MethodHandle aTarget = target.asSpreader(Object[].class, target.type().parameterCount());
3900 aCleanup = aCleanup.asSpreader(Object[].class, tpSize);
3901
3902 return MethodHandleImpl.makeTryFinally(aTarget, aCleanup, rtype, targetParamTypes);
3903 }
3904
3905 /**
3906 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
3907 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
3908 * before the folded arguments.
3909 * <p>
3910 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
3911 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
3912 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
3913 * 0.
3914 * <p>
3915 * @apiNote Example:
3916 * <blockquote><pre>{@code
3917 import static java.lang.invoke.MethodHandles.*;
3918 import static java.lang.invoke.MethodType.*;
3919 ...
3920 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
3921 "println", methodType(void.class, String.class))
3922 .bindTo(System.out);
3923 MethodHandle cat = lookup().findVirtual(String.class,
3924 "concat", methodType(String.class, String.class));
3925 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
3926 MethodHandle catTrace = foldArguments(cat, 1, trace);
3927 // also prints "jum":
3928 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
3929 * }</pre></blockquote>
3930 * <p> Here is pseudocode for the resulting adapter:
3931 * <blockquote><pre>{@code
3932 * // there are N arguments in A...
3933 * T target(Z..., V, A[N]..., B...);
3934 * V combiner(A...);
3935 * T adapter(Z... z, A... a, B... b) {
3936 * V v = combiner(a...);
3937 * return target(z..., v, a..., b...);
3938 * }
3939 * // and if the combiner has a void return:
3940 * T target2(Z..., A[N]..., B...);
3941 * void combiner2(A...);
3942 * T adapter2(Z... z, A... a, B... b) {
3943 * combiner2(a...);
3944 * return target2(z..., a..., b...);
3945 * }
3946 * }</pre></blockquote>
3947 *
3948 * @param target the method handle to invoke after arguments are combined
3949 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
3950 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
3951 * @param combiner method handle to call initially on the incoming arguments
3952 * @return method handle which incorporates the specified argument folding logic
3953 * @throws NullPointerException if either argument is null
3954 * @throws IllegalArgumentException if {@code combiner}'s return type
3955 * is non-void and not the same as the argument type at position {@code pos} of
3956 * the target signature, or if the {@code N} argument types at position {@code pos}
3957 * of the target signature
3958 * (skipping one matching the {@code combiner}'s return type)
3959 * are not identical with the argument types of {@code combiner}
3960 *
3961 * @see #foldArguments(MethodHandle, MethodHandle)
3962 * @since 9
3963 */
3964 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
3965 MethodType targetType = target.type();
3966 MethodType combinerType = combiner.type();
3967 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
3968 BoundMethodHandle result = target.rebind();
3969 boolean dropResult = rtype == void.class;
3970 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
3971 MethodType newType = targetType;
3972 if (!dropResult) {
3973 newType = newType.dropParameterTypes(pos, pos + 1);
3974 }
3975 result = result.copyWithExtendL(newType, lform, combiner);
3976 return result;
3977 }
3978
3979 /**
3980 * Wrap creation of a proper zero handle for a given type.
3981 *
3982 * @param type the type.
3983 *
3984 * @return a zero value for the given type.
3985 */
3986 static MethodHandle zeroHandle(Class<?> type) {
3987 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3988 }
3989
3990 private static void checkLoop0(MethodHandle[][] clauses) {
3991 if (clauses == null || clauses.length == 0) {
3992 throw newIllegalArgumentException("null or no clauses passed");
3993 }
3994 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
3995 throw newIllegalArgumentException("null clauses are not allowed");
3996 }
3997 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
3998 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
3999 }
4000 }
4001
4002 private static void checkLoop1a(int i, MethodHandle in, MethodHandle st) {
4003 if (in.type().returnType() != st.type().returnType()) {
4004 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4005 st.type().returnType());
4006 }
4007 }
4008
4009 private static void checkLoop1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4010 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::parameterList).
4011 anyMatch(pl -> !pl.equals(commonSuffix.subList(0, pl.size())))) {
4012 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4013 " (common suffix: " + commonSuffix + ")");
4014 }
4015 }
4016
4017 private static void checkLoop1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4018 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4019 anyMatch(t -> t != loopReturnType)) {
4020 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4021 loopReturnType + ")");
4022 }
4023
4024 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4025 throw newIllegalArgumentException("no predicate found", pred);
4026 }
4027 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4028 anyMatch(t -> t != boolean.class)) {
4029 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4030 }
4031 }
4032
4033 private static void checkLoop2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4034 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4035 map(MethodType::parameterList).anyMatch(pl -> !pl.equals(commonParameterSequence.subList(0, pl.size())))) {
4036 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4037 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4038 }
4039 }
4040
4041 private static void checkIteratedLoop(MethodHandle body) {
4042 if (null == body) {
4043 throw newIllegalArgumentException("iterated loop body must not be null");
4044 }
4045 }
4046
4047 private static void checkTryFinally(MethodHandle target, MethodHandle cleanup) {
4048 Class<?> rtype = target.type().returnType();
4049 if (rtype != cleanup.type().returnType()) {
4050 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
4051 }
4052 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
4053 if (!Throwable.class.isAssignableFrom(cleanupParamTypes.get(0))) {
4054 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
4055 }
4056 if (rtype != void.class && cleanupParamTypes.get(1) != rtype) {
4057 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
4058 }
4059 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
4060 // target parameter list.
4061 int cleanupArgIndex = rtype == void.class ? 1 : 2;
4062 if (!cleanupParamTypes.subList(cleanupArgIndex, cleanupParamTypes.size()).
4063 equals(target.type().parameterList().subList(0, cleanupParamTypes.size() - cleanupArgIndex))) {
4064 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
4065 cleanup.type(), target.type());
4066 }
4067 }
4068
4069 }