1 /* 2 * Copyright (c) 2008, 2019, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang.invoke; 27 28 import jdk.internal.access.SharedSecrets; 29 import jdk.internal.module.IllegalAccessLogger; 30 import jdk.internal.org.objectweb.asm.ClassReader; 31 import jdk.internal.reflect.CallerSensitive; 32 import jdk.internal.reflect.Reflection; 33 import jdk.internal.vm.annotation.ForceInline; 34 import sun.invoke.util.ValueConversions; 35 import sun.invoke.util.VerifyAccess; 36 import sun.invoke.util.Wrapper; 37 import sun.reflect.misc.ReflectUtil; 38 import sun.security.util.SecurityConstants; 39 40 import java.lang.invoke.LambdaForm.BasicType; 41 import java.lang.reflect.Constructor; 42 import java.lang.reflect.Field; 43 import java.lang.reflect.Member; 44 import java.lang.reflect.Method; 45 import java.lang.reflect.Modifier; 46 import java.lang.reflect.ReflectPermission; 47 import java.nio.ByteOrder; 48 import java.security.AccessController; 49 import java.security.PrivilegedAction; 50 import java.security.ProtectionDomain; 51 import java.util.ArrayList; 52 import java.util.Arrays; 53 import java.util.BitSet; 54 import java.util.Iterator; 55 import java.util.List; 56 import java.util.Objects; 57 import java.util.Set; 58 import java.util.concurrent.ConcurrentHashMap; 59 import java.util.stream.Collectors; 60 import java.util.stream.Stream; 61 62 import static java.lang.invoke.MethodHandleImpl.Intrinsic; 63 import static java.lang.invoke.MethodHandleNatives.Constants.*; 64 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException; 65 import static java.lang.invoke.MethodType.methodType; 66 67 /** 68 * This class consists exclusively of static methods that operate on or return 69 * method handles. They fall into several categories: 70 * <ul> 71 * <li>Lookup methods which help create method handles for methods and fields. 72 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones. 73 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns. 74 * </ul> 75 * A lookup, combinator, or factory method will fail and throw an 76 * {@code IllegalArgumentException} if the created method handle's type 77 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>. 78 * 79 * @author John Rose, JSR 292 EG 80 * @since 1.7 81 */ 82 public class MethodHandles { 83 84 private MethodHandles() { } // do not instantiate 85 86 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); 87 88 // See IMPL_LOOKUP below. 89 90 //// Method handle creation from ordinary methods. 91 92 /** 93 * Returns a {@link Lookup lookup object} with 94 * full capabilities to emulate all supported bytecode behaviors of the caller. 95 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller. 96 * Factory methods on the lookup object can create 97 * <a href="MethodHandleInfo.html#directmh">direct method handles</a> 98 * for any member that the caller has access to via bytecodes, 99 * including protected and private fields and methods. 100 * This lookup object is a <em>capability</em> which may be delegated to trusted agents. 101 * Do not store it in place where untrusted code can access it. 102 * <p> 103 * This method is caller sensitive, which means that it may return different 104 * values to different callers. 105 * @return a lookup object for the caller of this method, with private access 106 */ 107 @CallerSensitive 108 @ForceInline // to ensure Reflection.getCallerClass optimization 109 public static Lookup lookup() { 110 return new Lookup(Reflection.getCallerClass()); 111 } 112 113 /** 114 * This reflected$lookup method is the alternate implementation of 115 * the lookup method when being invoked by reflection. 116 */ 117 @CallerSensitive 118 private static Lookup reflected$lookup() { 119 Class<?> caller = Reflection.getCallerClass(); 120 if (caller.getClassLoader() == null) { 121 throw newIllegalArgumentException("illegal lookupClass: "+caller); 122 } 123 return new Lookup(caller); 124 } 125 126 /** 127 * Returns a {@link Lookup lookup object} which is trusted minimally. 128 * The lookup has the {@code UNCONDITIONAL} mode. 129 * It can only be used to create method handles to public members of 130 * public classes in packages that are exported unconditionally. 131 * <p> 132 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class} 133 * of this lookup object will be {@link java.lang.Object}. 134 * 135 * @apiNote The use of Object is conventional, and because the lookup modes are 136 * limited, there is no special access provided to the internals of Object, its package 137 * or its module. This public lookup object or other lookup object with 138 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class 139 * is not used to determine the lookup context. 140 * 141 * <p style="font-size:smaller;"> 142 * <em>Discussion:</em> 143 * The lookup class can be changed to any other class {@code C} using an expression of the form 144 * {@link Lookup#in publicLookup().in(C.class)}. 145 * A public lookup object is always subject to 146 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>. 147 * Also, it cannot access 148 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>. 149 * @return a lookup object which is trusted minimally 150 * 151 * @revised 9 152 * @spec JPMS 153 */ 154 public static Lookup publicLookup() { 155 return Lookup.PUBLIC_LOOKUP; 156 } 157 158 /** 159 * Returns a {@link Lookup lookup} object on a target class to emulate all supported 160 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc"> private access</a>. 161 * The returned lookup object can provide access to classes in modules and packages, 162 * and members of those classes, outside the normal rules of Java access control, 163 * instead conforming to the more permissive rules for modular <em>deep reflection</em>. 164 * <p> 165 * A caller, specified as a {@code Lookup} object, in module {@code M1} is 166 * allowed to do deep reflection on module {@code M2} and package of the target class 167 * if and only if all of the following conditions are {@code true}: 168 * <ul> 169 * <li>If there is a security manager, its {@code checkPermission} method is 170 * called to check {@code ReflectPermission("suppressAccessChecks")} and 171 * that must return normally. 172 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode. 173 * (This is because otherwise there would be no way to ensure the original lookup 174 * creator was a member of any particular module, and so any subsequent checks 175 * for readability and qualified exports would become ineffective.) 176 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access. 177 * (This is because an application intending to share intra-module access 178 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share 179 * deep reflection to its own module.) 180 * <li>The target class must be a proper class, not a primitive or array class. 181 * (Thus, {@code M2} is well-defined.) 182 * <li>If the caller module {@code M1} differs from 183 * the target module {@code M2} then both of the following must be true: 184 * <ul> 185 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li> 186 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package 187 * containing the target class to at least {@code M1}.</li> 188 * </ul> 189 * </ul> 190 * <p> 191 * If any of the above checks is violated, this method fails with an 192 * exception. 193 * <p> 194 * Otherwise, if {@code M1} and {@code M2} are the same module, this method 195 * returns a {@code Lookup} on {@code targetClass} with full capabilities and 196 * {@code null} previous lookup class. 197 * <p> 198 * Otherwise, {@code M1} and {@code M2} are two different modules. This method 199 * returns a {@code Lookup} on {@code targetClass} that records 200 * the lookup class of the caller as the new previous lookup class and 201 * drops {@code MODULE} access from the full capabilities mode. 202 * 203 * @param targetClass the target class 204 * @param caller the caller lookup object 205 * @return a lookup object for the target class, with private access 206 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or array class 207 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null} 208 * @throws SecurityException if denied by the security manager 209 * @throws IllegalAccessException if any of the other access checks specified above fails 210 * @since 9 211 * @spec JPMS 212 * @see Lookup#dropLookupMode 213 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a> 214 */ 215 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException { 216 SecurityManager sm = System.getSecurityManager(); 217 if (sm != null) sm.checkPermission(ACCESS_PERMISSION); 218 if (targetClass.isPrimitive()) 219 throw new IllegalArgumentException(targetClass + " is a primitive class"); 220 if (targetClass.isArray()) 221 throw new IllegalArgumentException(targetClass + " is an array class"); 222 // Ensure that we can reason accurately about private and module access. 223 if ((caller.lookupModes() & Lookup.PRIVATE) == 0) 224 throw new IllegalAccessException("caller does not have PRIVATE lookup mode"); 225 if ((caller.lookupModes() & Lookup.MODULE) == 0) 226 throw new IllegalAccessException("caller does not have MODULE lookup mode"); 227 228 // previous lookup class is never set if it has MODULE access 229 assert caller.previousLookupClass() == null; 230 231 Class<?> callerClass = caller.lookupClass(); 232 Module callerModule = callerClass.getModule(); // M1 233 Module targetModule = targetClass.getModule(); // M2 234 Class<?> newPreviousClass = null; 235 int newModes = Lookup.FULL_POWER_MODES; 236 237 if (targetModule != callerModule) { 238 if (!callerModule.canRead(targetModule)) 239 throw new IllegalAccessException(callerModule + " does not read " + targetModule); 240 if (targetModule.isNamed()) { 241 String pn = targetClass.getPackageName(); 242 assert !pn.isEmpty() : "unnamed package cannot be in named module"; 243 if (!targetModule.isOpen(pn, callerModule)) 244 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule); 245 } 246 247 // M2 != M1, set previous lookup class to M1 and drop MODULE access 248 newPreviousClass = callerClass; 249 newModes &= ~Lookup.MODULE; 250 } 251 252 if (!callerModule.isNamed() && targetModule.isNamed()) { 253 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger(); 254 if (logger != null) { 255 logger.logIfOpenedForIllegalAccess(caller, targetClass); 256 } 257 } 258 return Lookup.newLookup(targetClass, newPreviousClass, newModes); 259 } 260 261 /** 262 * Performs an unchecked "crack" of a 263 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>. 264 * The result is as if the user had obtained a lookup object capable enough 265 * to crack the target method handle, called 266 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} 267 * on the target to obtain its symbolic reference, and then called 268 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} 269 * to resolve the symbolic reference to a member. 270 * <p> 271 * If there is a security manager, its {@code checkPermission} method 272 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission. 273 * @param <T> the desired type of the result, either {@link Member} or a subtype 274 * @param target a direct method handle to crack into symbolic reference components 275 * @param expected a class object representing the desired result type {@code T} 276 * @return a reference to the method, constructor, or field object 277 * @exception SecurityException if the caller is not privileged to call {@code setAccessible} 278 * @exception NullPointerException if either argument is {@code null} 279 * @exception IllegalArgumentException if the target is not a direct method handle 280 * @exception ClassCastException if the member is not of the expected type 281 * @since 1.8 282 */ 283 public static <T extends Member> T 284 reflectAs(Class<T> expected, MethodHandle target) { 285 SecurityManager smgr = System.getSecurityManager(); 286 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION); 287 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup 288 return lookup.revealDirect(target).reflectAs(expected, lookup); 289 } 290 // Copied from AccessibleObject, as used by Method.setAccessible, etc.: 291 private static final java.security.Permission ACCESS_PERMISSION = 292 new ReflectPermission("suppressAccessChecks"); 293 294 /** 295 * A <em>lookup object</em> is a factory for creating method handles, 296 * when the creation requires access checking. 297 * Method handles do not perform 298 * access checks when they are called, but rather when they are created. 299 * Therefore, method handle access 300 * restrictions must be enforced when a method handle is created. 301 * The caller class against which those restrictions are enforced 302 * is known as the {@linkplain #lookupClass() lookup class}. 303 * <p> 304 * A lookup class which needs to create method handles will call 305 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself. 306 * When the {@code Lookup} factory object is created, the identity of the lookup class is 307 * determined, and securely stored in the {@code Lookup} object. 308 * The lookup class (or its delegates) may then use factory methods 309 * on the {@code Lookup} object to create method handles for access-checked members. 310 * This includes all methods, constructors, and fields which are allowed to the lookup class, 311 * even private ones. 312 * 313 * <h2><a id="lookups"></a>Lookup Factory Methods</h2> 314 * The factory methods on a {@code Lookup} object correspond to all major 315 * use cases for methods, constructors, and fields. 316 * Each method handle created by a factory method is the functional 317 * equivalent of a particular <em>bytecode behavior</em>. 318 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.) 319 * Here is a summary of the correspondence between these factory methods and 320 * the behavior of the resulting method handles: 321 * <table class="striped"> 322 * <caption style="display:none">lookup method behaviors</caption> 323 * <thead> 324 * <tr> 325 * <th scope="col"><a id="equiv"></a>lookup expression</th> 326 * <th scope="col">member</th> 327 * <th scope="col">bytecode behavior</th> 328 * </tr> 329 * </thead> 330 * <tbody> 331 * <tr> 332 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th> 333 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td> 334 * </tr> 335 * <tr> 336 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th> 337 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td> 338 * </tr> 339 * <tr> 340 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th> 341 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td> 342 * </tr> 343 * <tr> 344 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th> 345 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td> 346 * </tr> 347 * <tr> 348 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th> 349 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td> 350 * </tr> 351 * <tr> 352 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th> 353 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td> 354 * </tr> 355 * <tr> 356 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th> 357 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 358 * </tr> 359 * <tr> 360 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th> 361 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td> 362 * </tr> 363 * <tr> 364 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th> 365 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td> 366 * </tr> 367 * <tr> 368 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th> 369 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td> 370 * </tr> 371 * <tr> 372 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th> 373 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 374 * </tr> 375 * <tr> 376 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th> 377 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td> 378 * </tr> 379 * <tr> 380 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th> 381 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 382 * </tr> 383 * <tr> 384 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th> 385 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td> 386 * </tr> 387 * </tbody> 388 * </table> 389 * 390 * Here, the type {@code C} is the class or interface being searched for a member, 391 * documented as a parameter named {@code refc} in the lookup methods. 392 * The method type {@code MT} is composed from the return type {@code T} 393 * and the sequence of argument types {@code A*}. 394 * The constructor also has a sequence of argument types {@code A*} and 395 * is deemed to return the newly-created object of type {@code C}. 396 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}. 397 * The formal parameter {@code this} stands for the self-reference of type {@code C}; 398 * if it is present, it is always the leading argument to the method handle invocation. 399 * (In the case of some {@code protected} members, {@code this} may be 400 * restricted in type to the lookup class; see below.) 401 * The name {@code arg} stands for all the other method handle arguments. 402 * In the code examples for the Core Reflection API, the name {@code thisOrNull} 403 * stands for a null reference if the accessed method or field is static, 404 * and {@code this} otherwise. 405 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand 406 * for reflective objects corresponding to the given members declared in type {@code C}. 407 * <p> 408 * The bytecode behavior for a {@code findClass} operation is a load of a constant class, 409 * as if by {@code ldc CONSTANT_Class}. 410 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant. 411 * <p> 412 * In cases where the given member is of variable arity (i.e., a method or constructor) 413 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. 414 * In all other cases, the returned method handle will be of fixed arity. 415 * <p style="font-size:smaller;"> 416 * <em>Discussion:</em> 417 * The equivalence between looked-up method handles and underlying 418 * class members and bytecode behaviors 419 * can break down in a few ways: 420 * <ul style="font-size:smaller;"> 421 * <li>If {@code C} is not symbolically accessible from the lookup class's loader, 422 * the lookup can still succeed, even when there is no equivalent 423 * Java expression or bytecoded constant. 424 * <li>Likewise, if {@code T} or {@code MT} 425 * is not symbolically accessible from the lookup class's loader, 426 * the lookup can still succeed. 427 * For example, lookups for {@code MethodHandle.invokeExact} and 428 * {@code MethodHandle.invoke} will always succeed, regardless of requested type. 429 * <li>If there is a security manager installed, it can forbid the lookup 430 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>). 431 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle} 432 * constant is not subject to security manager checks. 433 * <li>If the looked-up method has a 434 * <a href="MethodHandle.html#maxarity">very large arity</a>, 435 * the method handle creation may fail with an 436 * {@code IllegalArgumentException}, due to the method handle type having 437 * <a href="MethodHandle.html#maxarity">too many parameters.</a> 438 * </ul> 439 * 440 * <h2><a id="access"></a>Access checking</h2> 441 * Access checks are applied in the factory methods of {@code Lookup}, 442 * when a method handle is created. 443 * This is a key difference from the Core Reflection API, since 444 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 445 * performs access checking against every caller, on every call. 446 * <p> 447 * All access checks start from a {@code Lookup} object, which 448 * compares its recorded lookup class against all requests to 449 * create method handles. 450 * A single {@code Lookup} object can be used to create any number 451 * of access-checked method handles, all checked against a single 452 * lookup class. 453 * <p> 454 * A {@code Lookup} object can be shared with other trusted code, 455 * such as a metaobject protocol. 456 * A shared {@code Lookup} object delegates the capability 457 * to create method handles on private members of the lookup class. 458 * Even if privileged code uses the {@code Lookup} object, 459 * the access checking is confined to the privileges of the 460 * original lookup class. 461 * <p> 462 * A lookup can fail, because 463 * the containing class is not accessible to the lookup class, or 464 * because the desired class member is missing, or because the 465 * desired class member is not accessible to the lookup class, or 466 * because the lookup object is not trusted enough to access the member. 467 * In the case of a field setter function on a {@code final} field, 468 * finality enforcement is treated as a kind of access control, 469 * and the lookup will fail, except in special cases of 470 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}. 471 * In any of these cases, a {@code ReflectiveOperationException} will be 472 * thrown from the attempted lookup. The exact class will be one of 473 * the following: 474 * <ul> 475 * <li>NoSuchMethodException — if a method is requested but does not exist 476 * <li>NoSuchFieldException — if a field is requested but does not exist 477 * <li>IllegalAccessException — if the member exists but an access check fails 478 * </ul> 479 * <p> 480 * In general, the conditions under which a method handle may be 481 * looked up for a method {@code M} are no more restrictive than the conditions 482 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}. 483 * Where the JVM would raise exceptions like {@code NoSuchMethodError}, 484 * a method handle lookup will generally raise a corresponding 485 * checked exception, such as {@code NoSuchMethodException}. 486 * And the effect of invoking the method handle resulting from the lookup 487 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a> 488 * to executing the compiled, verified, and resolved call to {@code M}. 489 * The same point is true of fields and constructors. 490 * <p style="font-size:smaller;"> 491 * <em>Discussion:</em> 492 * Access checks only apply to named and reflected methods, 493 * constructors, and fields. 494 * Other method handle creation methods, such as 495 * {@link MethodHandle#asType MethodHandle.asType}, 496 * do not require any access checks, and are used 497 * independently of any {@code Lookup} object. 498 * <p> 499 * If the desired member is {@code protected}, the usual JVM rules apply, 500 * including the requirement that the lookup class must either be in the 501 * same package as the desired member, or must inherit that member. 502 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.) 503 * In addition, if the desired member is a non-static field or method 504 * in a different package, the resulting method handle may only be applied 505 * to objects of the lookup class or one of its subclasses. 506 * This requirement is enforced by narrowing the type of the leading 507 * {@code this} parameter from {@code C} 508 * (which will necessarily be a superclass of the lookup class) 509 * to the lookup class itself. 510 * <p> 511 * The JVM imposes a similar requirement on {@code invokespecial} instruction, 512 * that the receiver argument must match both the resolved method <em>and</em> 513 * the current class. Again, this requirement is enforced by narrowing the 514 * type of the leading parameter to the resulting method handle. 515 * (See the Java Virtual Machine Specification, section 4.10.1.9.) 516 * <p> 517 * The JVM represents constructors and static initializer blocks as internal methods 518 * with special names ({@code "<init>"} and {@code "<clinit>"}). 519 * The internal syntax of invocation instructions allows them to refer to such internal 520 * methods as if they were normal methods, but the JVM bytecode verifier rejects them. 521 * A lookup of such an internal method will produce a {@code NoSuchMethodException}. 522 * <p> 523 * If the relationship between nested types is expressed directly through the 524 * {@code NestHost} and {@code NestMembers} attributes 525 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29), 526 * then the associated {@code Lookup} object provides direct access to 527 * the lookup class and all of its nestmates 528 * (see {@link java.lang.Class#getNestHost Class.getNestHost}). 529 * Otherwise, access between nested classes is obtained by the Java compiler creating 530 * a wrapper method to access a private method of another class in the same nest. 531 * For example, a nested class {@code C.D} 532 * can access private members within other related classes such as 533 * {@code C}, {@code C.D.E}, or {@code C.B}, 534 * but the Java compiler may need to generate wrapper methods in 535 * those related classes. In such cases, a {@code Lookup} object on 536 * {@code C.E} would be unable to access those private members. 537 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, 538 * which can transform a lookup on {@code C.E} into one on any of those other 539 * classes, without special elevation of privilege. 540 * <p> 541 * The accesses permitted to a given lookup object may be limited, 542 * according to its set of {@link #lookupModes lookupModes}, 543 * to a subset of members normally accessible to the lookup class. 544 * For example, the {@link MethodHandles#publicLookup publicLookup} 545 * method produces a lookup object which is only allowed to access 546 * public members in public classes of exported packages. 547 * The caller sensitive method {@link MethodHandles#lookup lookup} 548 * produces a lookup object with full capabilities relative to 549 * its caller class, to emulate all supported bytecode behaviors. 550 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object 551 * with fewer access modes than the original lookup object. 552 * 553 * <p style="font-size:smaller;"> 554 * <a id="privacc"></a> 555 * <em>Discussion of private access:</em> 556 * We say that a lookup has <em>private access</em> 557 * if its {@linkplain #lookupModes lookup modes} 558 * include the possibility of accessing {@code private} members 559 * (which includes the private members of nestmates). 560 * As documented in the relevant methods elsewhere, 561 * only lookups with private access possess the following capabilities: 562 * <ul style="font-size:smaller;"> 563 * <li>access private fields, methods, and constructors of the lookup class and its nestmates 564 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods, 565 * such as {@code Class.forName} 566 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions 567 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a> 568 * for classes accessible to the lookup class 569 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes 570 * within the same package member 571 * </ul> 572 * <p style="font-size:smaller;"> 573 * Each of these permissions is a consequence of the fact that a lookup object 574 * with private access can be securely traced back to an originating class, 575 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions 576 * can be reliably determined and emulated by method handles. 577 * 578 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2> 579 * When a lookup class in one module {@code M1} accesses a class in another module 580 * {@code M2}, extra access checking is performed beyond the access mode bits. 581 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1} 582 * can access public types in {@code M2} when {@code M2} is readable to {@code M1} 583 * and when the type is in a package of {@code M2} that is exported to 584 * at least {@code M1}. 585 * <p> 586 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class 587 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup) 588 * MethodHandles.privateLookupIn} methods. 589 * Teleporting across modules will always record the original lookup class as 590 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em> 591 * and drops {@link Lookup#MODULE MODULE} access. 592 * If the target class is in the same module as the lookup class {@code C}, 593 * then the target class becomes the new lookup class 594 * and there is no change to the previous lookup class. 595 * If the target class is in a different module from {@code M1} ({@code C}'s module), 596 * {@code C} becomes the new previous lookup class 597 * and the target class becomes the new lookup class. 598 * In that case, if there was already a previous lookup class in {@code M0}, 599 * and it differs from {@code M1} and {@code M2}, then the resulting lookup 600 * drops all privileges. 601 * For example, 602 * <blockquote><pre> 603 * {@code 604 * Lookup lookup = MethodHandles.lookup(); // in class C 605 * Lookup lookup2 = lookup.in(D.class); 606 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT); 607 * }</pre></blockquote> 608 * <p> 609 * The {@link #lookup()} factory method produces a {@code Lookup} object 610 * with {@code null} previous lookup class. 611 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C} 612 * to class {@code D} without elevation of privileges. 613 * If {@code C} and {@code D} are in the same module, 614 * {@code lookup2} records {@code D} as the new lookup class and keeps the 615 * same previous lookup class as the original {@code lookup}, or 616 * {@code null} if not present. 617 * <p> 618 * When a {@code Lookup} teleports from a class 619 * in one nest to another nest, {@code PRIVATE} access is dropped. 620 * When a {@code Lookup} teleports from a class in one package to 621 * another package, {@code PACKAGE} access is dropped. 622 * When a {@code Lookup} teleports from a class in one module to another module, 623 * {@code MODULE} access is dropped. 624 * Teleporting across modules drops the ability to access non-exported classes 625 * in both the module of the new lookup class and the module of the old lookup class 626 * and the resulting {@code Lookup} remains only {@code PUBLIC} access. 627 * A {@code Lookup} can teleport back and forth to a class in the module of 628 * the lookup class and the module of the previous class lookup. 629 * Teleporting across modules can only decrease access but cannot increase it. 630 * Teleporting to some third module drops all accesses. 631 * <p> 632 * In the above example, if {@code C} and {@code D} are in different modules, 633 * {@code lookup2} records {@code D} as its lookup class and 634 * {@code C} as its previous lookup class and {@code lookup2} has only 635 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in 636 * {@code C}'s module and {@code D}'s module. 637 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates 638 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup 639 * class {@code D} is recorded as its previous lookup class. 640 * <p> 641 * Teleporting across modules restricts access to the public types that 642 * both the lookup class and the previous lookup class can equally access 643 * (see below). 644 * <p> 645 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)} 646 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T} 647 * and create a new {@code Lookup} with <a href="#privcc">private access</a> 648 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}. 649 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access 650 * to call {@code privateLookupIn}. 651 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection 652 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn} 653 * produces a new {@code Lookup} on {@code T} with full capabilities. 654 * A {@code lookup} on {@code C} is also allowed 655 * to do deep reflection on {@code T} in another module {@code M2} if 656 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens} 657 * the package containing {@code T} to at least {@code M1}. 658 * {@code T} becomes the new lookup class and {@code C} becomes the new previous 659 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}. 660 * The resulting {@code Lookup} can be used to do member lookup or teleport 661 * to another lookup class by calling {@link #in Lookup::in}. But 662 * it cannot be used to obtain another private {@code Lookup} by calling 663 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn} 664 * because it has no {@code MODULE} access. 665 * 666 * <h2><a id="module-access-check"></a>Cross-module access checks</h2> 667 * 668 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode 669 * allows cross-module access. The access checking is performed with respect 670 * to both the lookup class and the previous lookup class if present. 671 * <p> 672 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type 673 * in all modules when the type is in a package that is {@linkplain Module#isExported(String) 674 * exported unconditionally}. 675 * <p> 676 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class, 677 * the lookup with {@link #PUBLIC} mode can access all public types in modules 678 * that are readable to {@code M1} and the type is in a package that is exported 679 * at least to {@code M1}. 680 * <p> 681 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class 682 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access 683 * the intersection of all public types that are accessible to {@code M1} 684 * with all public types that are accessible to {@code M0}. {@code M0} 685 * reads {@code M1} and hence the set of accessible types includes: 686 * 687 * <table class="striped"> 688 * <caption style="display:none"> 689 * Public types in the following packages are accessible to the 690 * lookup class and the previous lookup class. 691 * </caption> 692 * <thead> 693 * <tr> 694 * <th scope="col">Equally accessible types to {@code M0} and {@code M1}</th> 695 * </tr> 696 * </thead> 697 * <tbody> 698 * <tr> 699 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M1}</th> 700 * </tr> 701 * <tr> 702 * <th scope="row" style="text-align:left">unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</th> 703 * </tr> 704 * <tr> 705 * <th scope="row" style="text-align:left">unconditional-exported packages from a third module {@code M2} 706 * if both {@code M0} and {@code M1} read {@code M2}</th> 707 * </tr> 708 * <tr> 709 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M1} to {@code M0}</th> 710 * </tr> 711 * <tr> 712 * <th scope="row" style="text-align:left">qualified-exported packages from {@code M0} to {@code M1} 713 * if {@code M1} reads {@code M0}</th> 714 * </tr> 715 * <tr> 716 * <th scope="row" style="text-align:left">qualified-exported packages from a third module {@code M2} to 717 * both {@code M0} and {@code M1} if both {@code M0} and {@code M1} read {@code M2}</th> 718 * </tr> 719 * </tbody> 720 * </table> 721 * 722 * <h2><a id="access-modes"></a>Access modes</h2> 723 * 724 * The table below shows the access modes of a {@code Lookup} produced by 725 * any of the following factory or transformation methods: 726 * <ul> 727 * <li>{@link #lookup() MethodHandles.lookup()}</li> 728 * <li>{@link #publicLookup() MethodHandles.publicLookup()}</li> 729 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn}</li> 730 * <li>{@link Lookup#in}</li> 731 * <li>{@link Lookup#dropLookupMode(int)}</li> 732 * </ul> 733 * 734 * <table class="striped"> 735 * <caption style="display:none"> 736 * Access mode summary 737 * </caption> 738 * <thead> 739 * <tr> 740 * <th scope="col">Lookup object</th> 741 * <th style="text-align:center">protected</th> 742 * <th style="text-align:center">private</th> 743 * <th style="text-align:center">package</th> 744 * <th style="text-align:center">module</th> 745 * <th style="text-align:center">public</th> 746 * </tr> 747 * </thead> 748 * <tbody> 749 * <tr> 750 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th> 751 * <td style="text-align:center">PRO</td> 752 * <td style="text-align:center">PRI</td> 753 * <td style="text-align:center">PAC</td> 754 * <td style="text-align:center">MOD</td> 755 * <td style="text-align:center">1R</td> 756 * </tr> 757 * <tr> 758 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th> 759 * <td></td> 760 * <td></td> 761 * <td style="text-align:center">PAC</td> 762 * <td style="text-align:center">MOD</td> 763 * <td style="text-align:center">1R</td> 764 * </tr> 765 * <tr> 766 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th> 767 * <td></td> 768 * <td></td> 769 * <td></td> 770 * <td style="text-align:center">MOD</td> 771 * <td style="text-align:center">1R</td> 772 * </tr> 773 * <tr> 774 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th> 775 * <td></td> 776 * <td></td> 777 * <td></td> 778 * <td></td> 779 * <td style="text-align:center">2R</td> 780 * </tr> 781 * <tr> 782 * <td>{@code CL.in(D).in(C)} hop back to module</td> 783 * <td></td> 784 * <td></td> 785 * <td></td> 786 * <td></td> 787 * <td style="text-align:center">2R</td> 788 * </tr> 789 * <tr> 790 * <td>{@code PRI1 = privateLookupIn(C1,CL)}</td> 791 * <td style="text-align:center">PRO</td> 792 * <td style="text-align:center">PRI</td> 793 * <td style="text-align:center">PAC</td> 794 * <td style="text-align:center">MOD</td> 795 * <td style="text-align:center">1R</td> 796 * </tr> 797 * <tr> 798 * <td>{@code PRI1a = privateLookupIn(C,PRI1)}</td> 799 * <td style="text-align:center">PRO</td> 800 * <td style="text-align:center">PRI</td> 801 * <td style="text-align:center">PAC</td> 802 * <td style="text-align:center">MOD</td> 803 * <td style="text-align:center">1R</td> 804 * </tr> 805 * <tr> 806 * <td>{@code PRI1.in(C1)} same package</td> 807 * <td></td> 808 * <td></td> 809 * <td style="text-align:center">PAC</td> 810 * <td style="text-align:center">MOD</td> 811 * <td style="text-align:center">1R</td> 812 * </tr> 813 * <tr> 814 * <td>{@code PRI1.in(C1)} different package</td> 815 * <td></td> 816 * <td></td> 817 * <td></td> 818 * <td style="text-align:center">MOD</td> 819 * <td style="text-align:center">1R</td> 820 * </tr> 821 * <tr> 822 * <td>{@code PRI1.in(D)} different module</td> 823 * <td></td> 824 * <td></td> 825 * <td></td> 826 * <td></td> 827 * <td style="text-align:center">2R</td> 828 * </tr> 829 * <tr> 830 * <td>{@code PRI1.dropLookupMode(PROTECTED)}</td> 831 * <td></td> 832 * <td style="text-align:center">PRI</td> 833 * <td style="text-align:center">PAC</td> 834 * <td style="text-align:center">MOD</td> 835 * <td style="text-align:center">1R</td> 836 * </tr> 837 * <tr> 838 * <td>{@code PRI1.dropLookupMode(PRIVATE)}</td> 839 * <td></td> 840 * <td></td> 841 * <td style="text-align:center">PAC</td> 842 * <td style="text-align:center">MOD</td> 843 * <td style="text-align:center">1R</td> 844 * </tr> 845 * <tr> 846 * <td>{@code PRI1.dropLookupMode(PACKAGE)}</td> 847 * <td></td> 848 * <td></td> 849 * <td></td> 850 * <td style="text-align:center">MOD</td> 851 * <td style="text-align:center">1R</td> 852 * </tr> 853 * <tr> 854 * <td>{@code PRI1.dropLookupMode(MODULE)}</td> 855 * <td></td> 856 * <td></td> 857 * <td></td> 858 * <td></td> 859 * <td style="text-align:center">1R</td> 860 * </tr> 861 * <tr> 862 * <td>{@code PRI1.dropLookupMode(PUBLIC)}</td> 863 * <td></td> 864 * <td></td> 865 * <td></td> 866 * <td></td> 867 * <td style="text-align:center">none</td> 868 * <tr> 869 * <td>{@code PRI2 = privateLookupIn(D,CL)}</td> 870 * <td style="text-align:center">PRO</td> 871 * <td style="text-align:center">PRI</td> 872 * <td style="text-align:center">PAC</td> 873 * <td></td> 874 * <td style="text-align:center">2R</td> 875 * </tr> 876 * <tr> 877 * <td>{@code privateLookupIn(D,PRI1)}</td> 878 * <td style="text-align:center">PRO</td> 879 * <td style="text-align:center">PRI</td> 880 * <td style="text-align:center">PAC</td> 881 * <td></td> 882 * <td style="text-align:center">2R</td> 883 * </tr> 884 * <tr> 885 * <td>{@code privateLookupIn(C,PRI2)} fails</td> 886 * <td></td> 887 * <td></td> 888 * <td></td> 889 * <td></td> 890 * <td style="text-align:center">IAE</td> 891 * </tr> 892 * <tr> 893 * <td>{@code PRI2.in(D2)} same package</td> 894 * <td></td> 895 * <td></td> 896 * <td style="text-align:center">PAC</td> 897 * <td></td> 898 * <td style="text-align:center">2R</td> 899 * </tr> 900 * <tr> 901 * <td>{@code PRI2.in(D2)} different package</td> 902 * <td></td> 903 * <td></td> 904 * <td></td> 905 * <td></td> 906 * <td style="text-align:center">2R</td> 907 * </tr> 908 * <tr> 909 * <td>{@code PRI2.in(C1)} hop back to module</td> 910 * <td></td> 911 * <td></td> 912 * <td></td> 913 * <td></td> 914 * <td style="text-align:center">2R</td> 915 * </tr> 916 * <tr> 917 * <td>{@code PRI2.in(E)} hop to third module</td> 918 * <td></td> 919 * <td></td> 920 * <td></td> 921 * <td></td> 922 * <td style="text-align:center">none</td> 923 * </tr> 924 * <tr> 925 * <td>{@code PRI2.dropLookupMode(PROTECTED)}</td> 926 * <td></td> 927 * <td style="text-align:center">PRI</td> 928 * <td style="text-align:center">PAC</td> 929 * <td></td> 930 * <td style="text-align:center">2R</td> 931 * </tr> 932 * <tr> 933 * <td>{@code PRI2.dropLookupMode(PRIVATE)}</td> 934 * <td></td> 935 * <td></td> 936 * <td style="text-align:center">PAC</td> 937 * <td></td> 938 * <td style="text-align:center">2R</td> 939 * </tr> 940 * <tr> 941 * <td>{@code PRI2.dropLookupMode(PACKAGE)}</td> 942 * <td></td> 943 * <td></td> 944 * <td></td> 945 * <td></td> 946 * <td style="text-align:center">2R</td> 947 * </tr> 948 * <tr> 949 * <td>{@code PRI2.dropLookupMode(MODULE)}</td> 950 * <td></td> 951 * <td></td> 952 * <td></td> 953 * <td></td> 954 * <td style="text-align:center">2R</td> 955 * </tr> 956 * <tr> 957 * <td>{@code PRI2.dropLookupMode(PUBLIC)}</td> 958 * <td></td> 959 * <td></td> 960 * <td></td> 961 * <td></td> 962 * <td style="text-align:center">none</td> 963 * </tr> 964 * <tr> 965 * <td>{@code CL.dropLookupMode(PROTECTED)}</td> 966 * <td></td> 967 * <td style="text-align:center">PRI</td> 968 * <td style="text-align:center">PAC</td> 969 * <td style="text-align:center">MOD</td> 970 * <td style="text-align:center">1R</td> 971 * </tr> 972 * <tr> 973 * <td>{@code CL.dropLookupMode(PRIVATE)}</td> 974 * <td></td> 975 * <td></td> 976 * <td style="text-align:center">PAC</td> 977 * <td style="text-align:center">MOD</td> 978 * <td style="text-align:center">1R</td> 979 * </tr> 980 * <tr> 981 * <td>{@code CL.dropLookupMode(PACKAGE)}</td> 982 * <td></td> 983 * <td></td> 984 * <td></td> 985 * <td style="text-align:center">MOD</td> 986 * <td style="text-align:center">1R</td> 987 * </tr> 988 * <tr> 989 * <td>{@code CL.dropLookupMode(MODULE)}</td> 990 * <td></td> 991 * <td></td> 992 * <td></td> 993 * <td></td> 994 * <td style="text-align:center">1R</td> 995 * </tr> 996 * <tr> 997 * <td>{@code CL.dropLookupMode(PUBLIC)}</td> 998 * <td></td> 999 * <td></td> 1000 * <td></td> 1001 * <td></td> 1002 * <td style="text-align:center">none</td> 1003 * </tr> 1004 * <tr> 1005 * <td>{@code PUB = publicLookup()}</td> 1006 * <td></td> 1007 * <td></td> 1008 * <td></td> 1009 * <td></td> 1010 * <td style="text-align:center">U</td> 1011 * </tr> 1012 * <tr> 1013 * <td>{@code PUB.in(D)} different module</td> 1014 * <td></td> 1015 * <td></td> 1016 * <td></td> 1017 * <td></td> 1018 * <td style="text-align:center">U</td> 1019 * </tr> 1020 * <tr> 1021 * <td>{@code PUB.in(D).in(E)} third module</td> 1022 * <td></td> 1023 * <td></td> 1024 * <td></td> 1025 * <td></td> 1026 * <td style="text-align:center">U</td> 1027 * </tr> 1028 * <tr> 1029 * <td>{@code PUB.dropLookupMode(UNCONDITIONAL)}</td> 1030 * <td></td> 1031 * <td></td> 1032 * <td></td> 1033 * <td></td> 1034 * <td style="text-align:center">none</td> 1035 * </tr> 1036 * <tr> 1037 * <td>{@code privateLookupIn(C1,PUB)} fails</td> 1038 * <td></td> 1039 * <td></td> 1040 * <td></td> 1041 * <td></td> 1042 * <td style="text-align:center">IAE</td> 1043 * </tr> 1044 * <tr> 1045 * <td>{@code ANY.in(X)}, for inaccessible <code>X</code></td> 1046 * <td></td> 1047 * <td></td> 1048 * <td></td> 1049 * <td></td> 1050 * <td style="text-align:center">none</td> 1051 * </tr> 1052 * </tbody> 1053 * </table> 1054 * 1055 * <p> 1056 * Notes: 1057 * <ul> 1058 * <li>Class {@code C} and class {@code C1} are in module {@code M1}, 1059 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E} 1060 * is in module {@code M3}. {@code X} stands for class which is inaccessible 1061 * to the lookup. {@code ANY} stands for any of the example lookups.</li> 1062 * <li>{@code PRO} indicates {@link #PROTECTED} bit set, 1063 * {@code PRI} indicates {@link #PRIVATE} bit set, 1064 * {@code PAC} indicates {@link #PACKAGE} bit set, 1065 * {@code MOD} indicates {@link #MODULE} bit set, 1066 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set, 1067 * {@code U} indicates {@link #UNCONDITIONAL} bit set, 1068 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li> 1069 * <li>Public access comes in three kinds: 1070 * <ul> 1071 * <li>unconditional ({@code U}): the lookup assumes readability. 1072 * The lookup has {@code null} previous lookup class. 1073 * <li>one-module-reads ({@code 1R}): the module access checking is 1074 * performed with respect to the lookup class. The lookup has {@code null} 1075 * previous lookup class. 1076 * <li>two-module-reads ({@code 2R}): the module access checking is 1077 * performed with respect to the lookup class and the previous lookup class. 1078 * The lookup has a non-null previous lookup class which is in a 1079 * different module from the current lookup class. 1080 * </ul> 1081 * <li>Any attempt to reach a third module loses all access.</li> 1082 * <li>If a target class {@code X} is not accessible to {@code Lookup::in} 1083 * all access modes are dropped.</li> 1084 * </ul> 1085 * 1086 * <h2><a id="secmgr"></a>Security manager interactions</h2> 1087 * Although bytecode instructions can only refer to classes in 1088 * a related class loader, this API can search for methods in any 1089 * class, as long as a reference to its {@code Class} object is 1090 * available. Such cross-loader references are also possible with the 1091 * Core Reflection API, and are impossible to bytecode instructions 1092 * such as {@code invokestatic} or {@code getfield}. 1093 * There is a {@linkplain java.lang.SecurityManager security manager API} 1094 * to allow applications to check such cross-loader references. 1095 * These checks apply to both the {@code MethodHandles.Lookup} API 1096 * and the Core Reflection API 1097 * (as found on {@link java.lang.Class Class}). 1098 * <p> 1099 * If a security manager is present, member and class lookups are subject to 1100 * additional checks. 1101 * From one to three calls are made to the security manager. 1102 * Any of these calls can refuse access by throwing a 1103 * {@link java.lang.SecurityException SecurityException}. 1104 * Define {@code smgr} as the security manager, 1105 * {@code lookc} as the lookup class of the current lookup object, 1106 * {@code refc} as the containing class in which the member 1107 * is being sought, and {@code defc} as the class in which the 1108 * member is actually defined. 1109 * (If a class or other type is being accessed, 1110 * the {@code refc} and {@code defc} values are the class itself.) 1111 * The value {@code lookc} is defined as <em>not present</em> 1112 * if the current lookup object does not have 1113 * <a href="MethodHandles.Lookup.html#privacc">private access</a>. 1114 * The calls are made according to the following rules: 1115 * <ul> 1116 * <li><b>Step 1:</b> 1117 * If {@code lookc} is not present, or if its class loader is not 1118 * the same as or an ancestor of the class loader of {@code refc}, 1119 * then {@link SecurityManager#checkPackageAccess 1120 * smgr.checkPackageAccess(refcPkg)} is called, 1121 * where {@code refcPkg} is the package of {@code refc}. 1122 * <li><b>Step 2a:</b> 1123 * If the retrieved member is not public and 1124 * {@code lookc} is not present, then 1125 * {@link SecurityManager#checkPermission smgr.checkPermission} 1126 * with {@code RuntimePermission("accessDeclaredMembers")} is called. 1127 * <li><b>Step 2b:</b> 1128 * If the retrieved class has a {@code null} class loader, 1129 * and {@code lookc} is not present, then 1130 * {@link SecurityManager#checkPermission smgr.checkPermission} 1131 * with {@code RuntimePermission("getClassLoader")} is called. 1132 * <li><b>Step 3:</b> 1133 * If the retrieved member is not public, 1134 * and if {@code lookc} is not present, 1135 * and if {@code defc} and {@code refc} are different, 1136 * then {@link SecurityManager#checkPackageAccess 1137 * smgr.checkPackageAccess(defcPkg)} is called, 1138 * where {@code defcPkg} is the package of {@code defc}. 1139 * </ul> 1140 * Security checks are performed after other access checks have passed. 1141 * Therefore, the above rules presuppose a member or class that is public, 1142 * or else that is being accessed from a lookup class that has 1143 * rights to access the member or class. 1144 * 1145 * <h2><a id="callsens"></a>Caller sensitive methods</h2> 1146 * A small number of Java methods have a special property called caller sensitivity. 1147 * A <em>caller-sensitive</em> method can behave differently depending on the 1148 * identity of its immediate caller. 1149 * <p> 1150 * If a method handle for a caller-sensitive method is requested, 1151 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply, 1152 * but they take account of the lookup class in a special way. 1153 * The resulting method handle behaves as if it were called 1154 * from an instruction contained in the lookup class, 1155 * so that the caller-sensitive method detects the lookup class. 1156 * (By contrast, the invoker of the method handle is disregarded.) 1157 * Thus, in the case of caller-sensitive methods, 1158 * different lookup classes may give rise to 1159 * differently behaving method handles. 1160 * <p> 1161 * In cases where the lookup object is 1162 * {@link MethodHandles#publicLookup() publicLookup()}, 1163 * or some other lookup object without 1164 * <a href="MethodHandles.Lookup.html#privacc">private access</a>, 1165 * the lookup class is disregarded. 1166 * In such cases, no caller-sensitive method handle can be created, 1167 * access is forbidden, and the lookup fails with an 1168 * {@code IllegalAccessException}. 1169 * <p style="font-size:smaller;"> 1170 * <em>Discussion:</em> 1171 * For example, the caller-sensitive method 1172 * {@link java.lang.Class#forName(String) Class.forName(x)} 1173 * can return varying classes or throw varying exceptions, 1174 * depending on the class loader of the class that calls it. 1175 * A public lookup of {@code Class.forName} will fail, because 1176 * there is no reasonable way to determine its bytecode behavior. 1177 * <p style="font-size:smaller;"> 1178 * If an application caches method handles for broad sharing, 1179 * it should use {@code publicLookup()} to create them. 1180 * If there is a lookup of {@code Class.forName}, it will fail, 1181 * and the application must take appropriate action in that case. 1182 * It may be that a later lookup, perhaps during the invocation of a 1183 * bootstrap method, can incorporate the specific identity 1184 * of the caller, making the method accessible. 1185 * <p style="font-size:smaller;"> 1186 * The function {@code MethodHandles.lookup} is caller sensitive 1187 * so that there can be a secure foundation for lookups. 1188 * Nearly all other methods in the JSR 292 API rely on lookup 1189 * objects to check access requests. 1190 * 1191 * @revised 9 1192 */ 1193 public static final 1194 class Lookup { 1195 /** The class on behalf of whom the lookup is being performed. */ 1196 private final Class<?> lookupClass; 1197 1198 /** previous lookup class */ 1199 private final Class<?> prevLookupClass; 1200 1201 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */ 1202 private final int allowedModes; 1203 1204 static { 1205 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes")); 1206 } 1207 1208 /** A single-bit mask representing {@code public} access, 1209 * which may contribute to the result of {@link #lookupModes lookupModes}. 1210 * The value, {@code 0x01}, happens to be the same as the value of the 1211 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}. 1212 * <p> 1213 * A {@code Lookup} with this lookup mode performs cross-module access check 1214 * with respect to the {@linkplain #lookupClass() lookup class} and 1215 * {@linkplain #previousLookupClass() previous lookup class} if present. 1216 */ 1217 public static final int PUBLIC = Modifier.PUBLIC; 1218 1219 /** A single-bit mask representing {@code private} access, 1220 * which may contribute to the result of {@link #lookupModes lookupModes}. 1221 * The value, {@code 0x02}, happens to be the same as the value of the 1222 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}. 1223 */ 1224 public static final int PRIVATE = Modifier.PRIVATE; 1225 1226 /** A single-bit mask representing {@code protected} access, 1227 * which may contribute to the result of {@link #lookupModes lookupModes}. 1228 * The value, {@code 0x04}, happens to be the same as the value of the 1229 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}. 1230 */ 1231 public static final int PROTECTED = Modifier.PROTECTED; 1232 1233 /** A single-bit mask representing {@code package} access (default access), 1234 * which may contribute to the result of {@link #lookupModes lookupModes}. 1235 * The value is {@code 0x08}, which does not correspond meaningfully to 1236 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1237 */ 1238 public static final int PACKAGE = Modifier.STATIC; 1239 1240 /** A single-bit mask representing {@code module} access, 1241 * which may contribute to the result of {@link #lookupModes lookupModes}. 1242 * The value is {@code 0x10}, which does not correspond meaningfully to 1243 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1244 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup} 1245 * with this lookup mode can access all public types in the module of the 1246 * lookup class and public types in packages exported by other modules 1247 * to the module of the lookup class. 1248 * <p> 1249 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1250 * previous lookup class} is always {@code null}. 1251 * 1252 * @since 9 1253 * @spec JPMS 1254 */ 1255 public static final int MODULE = PACKAGE << 1; 1256 1257 /** A single-bit mask representing {@code unconditional} access 1258 * which may contribute to the result of {@link #lookupModes lookupModes}. 1259 * The value is {@code 0x20}, which does not correspond meaningfully to 1260 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1261 * A {@code Lookup} with this lookup mode assumes {@linkplain 1262 * java.lang.Module#canRead(java.lang.Module) readability}. 1263 * This lookup mode can access all public members of public types 1264 * of all modules when the type is in a package that is {@link 1265 * java.lang.Module#isExported(String) exported unconditionally}. 1266 * 1267 * <p> 1268 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1269 * previous lookup class} is always {@code null}. 1270 * 1271 * @since 9 1272 * @spec JPMS 1273 * @see #publicLookup() 1274 */ 1275 public static final int UNCONDITIONAL = PACKAGE << 2; 1276 1277 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL); 1278 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); 1279 private static final int TRUSTED = -1; 1280 1281 /* 1282 * Adjust PUBLIC => PUBLIC|MODULE|UNCONDITIONAL 1283 * Adjust 0 => PACKAGE 1284 */ 1285 private static int fixmods(int mods) { 1286 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL); 1287 if (Modifier.isPublic(mods)) 1288 mods |= UNCONDITIONAL; 1289 return (mods != 0) ? mods : PACKAGE; 1290 } 1291 1292 /** Tells which class is performing the lookup. It is this class against 1293 * which checks are performed for visibility and access permissions. 1294 * <p> 1295 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class}, 1296 * access checks are performed against both the lookup class and the previous lookup class. 1297 * <p> 1298 * The class implies a maximum level of access permission, 1299 * but the permissions may be additionally limited by the bitmask 1300 * {@link #lookupModes lookupModes}, which controls whether non-public members 1301 * can be accessed. 1302 * @return the lookup class, on behalf of which this lookup object finds members 1303 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1304 */ 1305 public Class<?> lookupClass() { 1306 return lookupClass; 1307 } 1308 1309 /** Reports a lookup class in another module that this lookup object 1310 * was previously teleported from, or {@code null}. 1311 * <p> 1312 * A {@code Lookup} object produced by the factory methods, such as the 1313 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method, 1314 * has {@code null} previous lookup class. 1315 * A {@code Lookup} object has a non-null previous lookup class 1316 * when this lookup was teleported from an old lookup class 1317 * in one module to a new lookup class in another module. 1318 * 1319 * @return the lookup class in another module that this lookup object was 1320 * previously teleported from, or {@code null} 1321 * @since 14 1322 * @see #in(Class) 1323 * @see MethodHandles#privateLookupIn(Class, Lookup) 1324 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1325 */ 1326 public Class<?> previousLookupClass() { 1327 return prevLookupClass; 1328 } 1329 1330 // This is just for calling out to MethodHandleImpl. 1331 private Class<?> lookupClassOrNull() { 1332 if (allowedModes == TRUSTED) { 1333 return null; 1334 } 1335 if (allowedModes == UNCONDITIONAL) { 1336 // use Object as the caller to pass to VM doing resolution 1337 return Object.class; 1338 } 1339 return lookupClass; 1340 } 1341 1342 /** Tells which access-protection classes of members this lookup object can produce. 1343 * The result is a bit-mask of the bits 1344 * {@linkplain #PUBLIC PUBLIC (0x01)}, 1345 * {@linkplain #PRIVATE PRIVATE (0x02)}, 1346 * {@linkplain #PROTECTED PROTECTED (0x04)}, 1347 * {@linkplain #PACKAGE PACKAGE (0x08)}, 1348 * {@linkplain #MODULE MODULE (0x10)}, 1349 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}. 1350 * <p> 1351 * A freshly-created lookup object 1352 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has 1353 * all possible bits set, except {@code UNCONDITIONAL}. 1354 * A lookup object on a new lookup class 1355 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} 1356 * may have some mode bits set to zero. 1357 * Mode bits can also be 1358 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}. 1359 * Once cleared, mode bits cannot be restored from the downgraded lookup object. 1360 * The purpose of this is to restrict access via the new lookup object, 1361 * so that it can access only names which can be reached by the original 1362 * lookup object, and also by the new lookup class. 1363 * @return the lookup modes, which limit the kinds of access performed by this lookup object 1364 * @see #in 1365 * @see #dropLookupMode 1366 * 1367 * @revised 9 1368 * @spec JPMS 1369 */ 1370 public int lookupModes() { 1371 return allowedModes & ALL_MODES; 1372 } 1373 1374 /** Embody the current class (the lookupClass) as a lookup class 1375 * for method handle creation. 1376 * Must be called by from a method in this package, 1377 * which in turn is called by a method not in this package. 1378 */ 1379 Lookup(Class<?> lookupClass) { 1380 this(lookupClass, null, FULL_POWER_MODES); 1381 // make sure we haven't accidentally picked up a privileged class: 1382 checkUnprivilegedlookupClass(lookupClass); 1383 } 1384 1385 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1386 assert prevLookupClass == null || ((allowedModes & MODULE) == 0 1387 && prevLookupClass.getModule() != lookupClass.getModule()); 1388 1389 this.lookupClass = lookupClass; 1390 this.prevLookupClass = prevLookupClass; 1391 this.allowedModes = allowedModes; 1392 } 1393 1394 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1395 // make sure we haven't accidentally picked up a privileged class: 1396 checkUnprivilegedlookupClass(lookupClass); 1397 return new Lookup(lookupClass, prevLookupClass, allowedModes); 1398 } 1399 1400 /** 1401 * Creates a lookup on the specified new lookup class. 1402 * The resulting object will report the specified 1403 * class as its own {@link #lookupClass() lookupClass}. 1404 * 1405 * <p> 1406 * However, the resulting {@code Lookup} object is guaranteed 1407 * to have no more access capabilities than the original. 1408 * In particular, access capabilities can be lost as follows:<ul> 1409 * <li>If the new lookup class is in a different module from the old one, 1410 * i.e. {@link #MODULE MODULE} access is lost. 1411 * <li>If the new lookup class is in a different package 1412 * than the old one, protected and default (package) members will not be accessible, 1413 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost. 1414 * <li>If the new lookup class is not within the same package member 1415 * as the old one, private members will not be accessible, and protected members 1416 * will not be accessible by virtue of inheritance, 1417 * i.e. {@link #PRIVATE PRIVATE} access is lost. 1418 * (Protected members may continue to be accessible because of package sharing.) 1419 * <li>If the new lookup class is not 1420 * {@linkplain #accessClass(Class) accessible} to this lookup, 1421 * then no members, not even public members, will be accessible 1422 * i.e. all access modes are lost. 1423 * <li>If the new lookup class, the old lookup class and the previous lookup class 1424 * are all in different modules i.e. teleporting to a third module, 1425 * all access modes are lost. 1426 * </ul> 1427 * <p> 1428 * The new previous lookup class is chosen as follows: 1429 * <ul> 1430 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit, 1431 * the new previous lookup class is {@code null}. 1432 * <li>If the new lookup class is in the same module as the old lookup class, 1433 * the new previous lookup class is the old previous lookup class. 1434 * <li>If the new lookup class is in a different module from the old lookup class, 1435 * the new previous lookup class is the the old lookup class. 1436 *</ul> 1437 * <p> 1438 * The resulting lookup's capabilities for loading classes 1439 * (used during {@link #findClass} invocations) 1440 * are determined by the lookup class' loader, 1441 * which may change due to this operation. 1442 * <p> 1443 * @param requestedLookupClass the desired lookup class for the new lookup object 1444 * @return a lookup object which reports the desired lookup class, or the same object 1445 * if there is no change 1446 * @throws NullPointerException if the argument is null 1447 * 1448 * @revised 9 1449 * @spec JPMS 1450 * @see #accessClass(Class) 1451 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1452 */ 1453 public Lookup in(Class<?> requestedLookupClass) { 1454 Objects.requireNonNull(requestedLookupClass); 1455 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all 1456 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES); 1457 if (requestedLookupClass == this.lookupClass) 1458 return this; // keep same capabilities 1459 int newModes = (allowedModes & FULL_POWER_MODES); 1460 Module fromModule = this.lookupClass.getModule(); 1461 Module targetModule = requestedLookupClass.getModule(); 1462 Class<?> plc = this.previousLookupClass(); 1463 if ((this.allowedModes & UNCONDITIONAL) != 0) { 1464 assert plc == null; 1465 newModes = UNCONDITIONAL; 1466 } else if (fromModule != targetModule) { 1467 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) { 1468 // allow hopping back and forth between fromModule and plc's module 1469 // but not the third module 1470 newModes = 0; 1471 } 1472 // drop MODULE access 1473 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED); 1474 // teleport from this lookup class 1475 plc = this.lookupClass; 1476 } 1477 if ((newModes & PACKAGE) != 0 1478 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) { 1479 newModes &= ~(PACKAGE|PRIVATE|PROTECTED); 1480 } 1481 // Allow nestmate lookups to be created without special privilege: 1482 if ((newModes & PRIVATE) != 0 1483 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) { 1484 newModes &= ~(PRIVATE|PROTECTED); 1485 } 1486 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0 1487 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) { 1488 // The requested class it not accessible from the lookup class. 1489 // No permissions. 1490 newModes = 0; 1491 } 1492 return newLookup(requestedLookupClass, plc, newModes); 1493 } 1494 1495 /** 1496 * Creates a lookup on the same lookup class which this lookup object 1497 * finds members, but with a lookup mode that has lost the given lookup mode. 1498 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE 1499 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}. 1500 * {@link #PROTECTED PROTECTED} is always 1501 * dropped and so the resulting lookup mode will never have this access capability. 1502 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE} 1503 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will 1504 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC} 1505 * is dropped then the resulting lookup has no access. If {@code UNCONDITIONAL} 1506 * is dropped then the resulting lookup has no access. 1507 * 1508 * @apiNote 1509 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely 1510 * delegate non-public access within the package of the lookup class without 1511 * conferring private access. A lookup with {@code MODULE} but not 1512 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within 1513 * the module of the lookup class without conferring package access. 1514 * A lookup with a {@linkplain #previousLookupClass() previous lookup class} 1515 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access 1516 * to public classes accessible to both the module of the lookup class 1517 * and the module of the previous lookup class. 1518 * 1519 * @param modeToDrop the lookup mode to drop 1520 * @return a lookup object which lacks the indicated mode, or the same object if there is no change 1521 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC}, 1522 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL} 1523 * @see MethodHandles#privateLookupIn 1524 * @since 9 1525 */ 1526 public Lookup dropLookupMode(int modeToDrop) { 1527 int oldModes = lookupModes(); 1528 int newModes = oldModes & ~(modeToDrop | PROTECTED); 1529 switch (modeToDrop) { 1530 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break; 1531 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break; 1532 case PACKAGE: newModes &= ~(PRIVATE); break; 1533 case PROTECTED: 1534 case PRIVATE: 1535 case UNCONDITIONAL: break; 1536 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop"); 1537 } 1538 if (newModes == oldModes) return this; // return self if no change 1539 return newLookup(lookupClass(), previousLookupClass(), newModes); 1540 } 1541 1542 /** 1543 * Defines a class to the same class loader and in the same runtime package and 1544 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's 1545 * {@linkplain #lookupClass() lookup class}. 1546 * 1547 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include 1548 * {@link #PACKAGE PACKAGE} access as default (package) members will be 1549 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate 1550 * that the lookup object was created by a caller in the runtime package (or derived 1551 * from a lookup originally created by suitably privileged code to a target class in 1552 * the runtime package). </p> 1553 * 1554 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined 1555 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the 1556 * same package as the lookup class. </p> 1557 * 1558 * <p> This method does not run the class initializer. The class initializer may 1559 * run at a later time, as detailed in section 12.4 of the <em>The Java Language 1560 * Specification</em>. </p> 1561 * 1562 * <p> If there is a security manager, its {@code checkPermission} method is first called 1563 * to check {@code RuntimePermission("defineClass")}. </p> 1564 * 1565 * @param bytes the class bytes 1566 * @return the {@code Class} object for the class 1567 * @throws IllegalArgumentException the bytes are for a class in a different package 1568 * to the lookup class 1569 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access 1570 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be 1571 * verified ({@code VerifyError}), is already defined, or another linkage error occurs 1572 * @throws SecurityException if denied by the security manager 1573 * @throws NullPointerException if {@code bytes} is {@code null} 1574 * @since 9 1575 * @spec JPMS 1576 * @see Lookup#privateLookupIn 1577 * @see Lookup#dropLookupMode 1578 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 1579 */ 1580 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException { 1581 SecurityManager sm = System.getSecurityManager(); 1582 if (sm != null) 1583 sm.checkPermission(new RuntimePermission("defineClass")); 1584 if ((lookupModes() & PACKAGE) == 0) 1585 throw new IllegalAccessException("Lookup does not have PACKAGE access"); 1586 assert (lookupModes() & (MODULE|PUBLIC)) != 0; 1587 1588 // parse class bytes to get class name (in internal form) 1589 bytes = bytes.clone(); 1590 String name; 1591 try { 1592 ClassReader reader = new ClassReader(bytes); 1593 name = reader.getClassName(); 1594 } catch (RuntimeException e) { 1595 // ASM exceptions are poorly specified 1596 ClassFormatError cfe = new ClassFormatError(); 1597 cfe.initCause(e); 1598 throw cfe; 1599 } 1600 1601 // get package and class name in binary form 1602 String cn, pn; 1603 int index = name.lastIndexOf('/'); 1604 if (index == -1) { 1605 cn = name; 1606 pn = ""; 1607 } else { 1608 cn = name.replace('/', '.'); 1609 pn = cn.substring(0, index); 1610 } 1611 if (!pn.equals(lookupClass.getPackageName())) { 1612 throw new IllegalArgumentException("Class not in same package as lookup class"); 1613 } 1614 1615 // invoke the class loader's defineClass method 1616 ClassLoader loader = lookupClass.getClassLoader(); 1617 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null; 1618 String source = "__Lookup_defineClass__"; 1619 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source); 1620 return clazz; 1621 } 1622 1623 private ProtectionDomain lookupClassProtectionDomain() { 1624 ProtectionDomain pd = cachedProtectionDomain; 1625 if (pd == null) { 1626 cachedProtectionDomain = pd = protectionDomain(lookupClass); 1627 } 1628 return pd; 1629 } 1630 1631 private ProtectionDomain protectionDomain(Class<?> clazz) { 1632 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain; 1633 return AccessController.doPrivileged(pa); 1634 } 1635 1636 // cached protection domain 1637 private volatile ProtectionDomain cachedProtectionDomain; 1638 1639 1640 // Make sure outer class is initialized first. 1641 static { IMPL_NAMES.getClass(); } 1642 1643 /** Package-private version of lookup which is trusted. */ 1644 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED); 1645 1646 /** Version of lookup which is trusted minimally. 1647 * It can only be used to create method handles to publicly accessible 1648 * members in packages that are exported unconditionally. 1649 */ 1650 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL); 1651 1652 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) { 1653 String name = lookupClass.getName(); 1654 if (name.startsWith("java.lang.invoke.")) 1655 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass); 1656 } 1657 1658 /** 1659 * Displays the name of the class from which lookups are to be made. 1660 * followed with "/" and the name of the {@linkplain #previousLookupClass() 1661 * previous lookup class} if present. 1662 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.) 1663 * If there are restrictions on the access permitted to this lookup, 1664 * this is indicated by adding a suffix to the class name, consisting 1665 * of a slash and a keyword. The keyword represents the strongest 1666 * allowed access, and is chosen as follows: 1667 * <ul> 1668 * <li>If no access is allowed, the suffix is "/noaccess". 1669 * <li>If only unconditional access is allowed, the suffix is "/publicLookup". 1670 * <li>If only public access to types in exported packages is allowed, the suffix is "/public". 1671 * <li>If only public and module access are allowed, the suffix is "/module". 1672 * <li>If public and package access are allowed, the suffix is "/package". 1673 * <li>If public, package, and private access are allowed, the suffix is "/private". 1674 * </ul> 1675 * If none of the above cases apply, it is the case that full access 1676 * (public, module, package, private, and protected) is allowed. 1677 * In this case, no suffix is added. 1678 * This is true only of an object obtained originally from 1679 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}. 1680 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in} 1681 * always have restricted access, and will display a suffix. 1682 * <p> 1683 * (It may seem strange that protected access should be 1684 * stronger than private access. Viewed independently from 1685 * package access, protected access is the first to be lost, 1686 * because it requires a direct subclass relationship between 1687 * caller and callee.) 1688 * @see #in 1689 * 1690 * @revised 9 1691 * @spec JPMS 1692 */ 1693 @Override 1694 public String toString() { 1695 String cname = lookupClass.getName(); 1696 if (prevLookupClass != null) 1697 cname += "/" + prevLookupClass.getName(); 1698 switch (allowedModes) { 1699 case 0: // no privileges 1700 return cname + "/noaccess"; 1701 case UNCONDITIONAL: 1702 return cname + "/publicLookup"; 1703 case PUBLIC: 1704 return cname + "/public"; 1705 case PUBLIC|MODULE: 1706 return cname + "/module"; 1707 case PUBLIC|PACKAGE: 1708 case PUBLIC|MODULE|PACKAGE: 1709 return cname + "/package"; 1710 case FULL_POWER_MODES & (~PROTECTED): 1711 case FULL_POWER_MODES & ~(PROTECTED|MODULE): 1712 return cname + "/private"; 1713 case FULL_POWER_MODES: 1714 case FULL_POWER_MODES & (~MODULE): 1715 return cname; 1716 case TRUSTED: 1717 return "/trusted"; // internal only; not exported 1718 default: // Should not happen, but it's a bitfield... 1719 cname = cname + "/" + Integer.toHexString(allowedModes); 1720 assert(false) : cname; 1721 return cname; 1722 } 1723 } 1724 1725 /** 1726 * Produces a method handle for a static method. 1727 * The type of the method handle will be that of the method. 1728 * (Since static methods do not take receivers, there is no 1729 * additional receiver argument inserted into the method handle type, 1730 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) 1731 * The method and all its argument types must be accessible to the lookup object. 1732 * <p> 1733 * The returned method handle will have 1734 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1735 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1736 * <p> 1737 * If the returned method handle is invoked, the method's class will 1738 * be initialized, if it has not already been initialized. 1739 * <p><b>Example:</b> 1740 * <blockquote><pre>{@code 1741 import static java.lang.invoke.MethodHandles.*; 1742 import static java.lang.invoke.MethodType.*; 1743 ... 1744 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class, 1745 "asList", methodType(List.class, Object[].class)); 1746 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString()); 1747 * }</pre></blockquote> 1748 * @param refc the class from which the method is accessed 1749 * @param name the name of the method 1750 * @param type the type of the method 1751 * @return the desired method handle 1752 * @throws NoSuchMethodException if the method does not exist 1753 * @throws IllegalAccessException if access checking fails, 1754 * or if the method is not {@code static}, 1755 * or if the method's variable arity modifier bit 1756 * is set and {@code asVarargsCollector} fails 1757 * @exception SecurityException if a security manager is present and it 1758 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1759 * @throws NullPointerException if any argument is null 1760 */ 1761 public 1762 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1763 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type); 1764 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method)); 1765 } 1766 1767 /** 1768 * Produces a method handle for a virtual method. 1769 * The type of the method handle will be that of the method, 1770 * with the receiver type (usually {@code refc}) prepended. 1771 * The method and all its argument types must be accessible to the lookup object. 1772 * <p> 1773 * When called, the handle will treat the first argument as a receiver 1774 * and, for non-private methods, dispatch on the receiver's type to determine which method 1775 * implementation to enter. 1776 * For private methods the named method in {@code refc} will be invoked on the receiver. 1777 * (The dispatching action is identical with that performed by an 1778 * {@code invokevirtual} or {@code invokeinterface} instruction.) 1779 * <p> 1780 * The first argument will be of type {@code refc} if the lookup 1781 * class has full privileges to access the member. Otherwise 1782 * the member must be {@code protected} and the first argument 1783 * will be restricted in type to the lookup class. 1784 * <p> 1785 * The returned method handle will have 1786 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1787 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1788 * <p> 1789 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual} 1790 * instructions and method handles produced by {@code findVirtual}, 1791 * if the class is {@code MethodHandle} and the name string is 1792 * {@code invokeExact} or {@code invoke}, the resulting 1793 * method handle is equivalent to one produced by 1794 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or 1795 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} 1796 * with the same {@code type} argument. 1797 * <p> 1798 * If the class is {@code VarHandle} and the name string corresponds to 1799 * the name of a signature-polymorphic access mode method, the resulting 1800 * method handle is equivalent to one produced by 1801 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with 1802 * the access mode corresponding to the name string and with the same 1803 * {@code type} arguments. 1804 * <p> 1805 * <b>Example:</b> 1806 * <blockquote><pre>{@code 1807 import static java.lang.invoke.MethodHandles.*; 1808 import static java.lang.invoke.MethodType.*; 1809 ... 1810 MethodHandle MH_concat = publicLookup().findVirtual(String.class, 1811 "concat", methodType(String.class, String.class)); 1812 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class, 1813 "hashCode", methodType(int.class)); 1814 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class, 1815 "hashCode", methodType(int.class)); 1816 assertEquals("xy", (String) MH_concat.invokeExact("x", "y")); 1817 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy")); 1818 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy")); 1819 // interface method: 1820 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class, 1821 "subSequence", methodType(CharSequence.class, int.class, int.class)); 1822 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString()); 1823 // constructor "internal method" must be accessed differently: 1824 MethodType MT_newString = methodType(void.class); //()V for new String() 1825 try { assertEquals("impossible", lookup() 1826 .findVirtual(String.class, "<init>", MT_newString)); 1827 } catch (NoSuchMethodException ex) { } // OK 1828 MethodHandle MH_newString = publicLookup() 1829 .findConstructor(String.class, MT_newString); 1830 assertEquals("", (String) MH_newString.invokeExact()); 1831 * }</pre></blockquote> 1832 * 1833 * @param refc the class or interface from which the method is accessed 1834 * @param name the name of the method 1835 * @param type the type of the method, with the receiver argument omitted 1836 * @return the desired method handle 1837 * @throws NoSuchMethodException if the method does not exist 1838 * @throws IllegalAccessException if access checking fails, 1839 * or if the method is {@code static}, 1840 * or if the method's variable arity modifier bit 1841 * is set and {@code asVarargsCollector} fails 1842 * @exception SecurityException if a security manager is present and it 1843 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1844 * @throws NullPointerException if any argument is null 1845 */ 1846 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1847 if (refc == MethodHandle.class) { 1848 MethodHandle mh = findVirtualForMH(name, type); 1849 if (mh != null) return mh; 1850 } else if (refc == VarHandle.class) { 1851 MethodHandle mh = findVirtualForVH(name, type); 1852 if (mh != null) return mh; 1853 } 1854 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual); 1855 MemberName method = resolveOrFail(refKind, refc, name, type); 1856 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method)); 1857 } 1858 private MethodHandle findVirtualForMH(String name, MethodType type) { 1859 // these names require special lookups because of the implicit MethodType argument 1860 if ("invoke".equals(name)) 1861 return invoker(type); 1862 if ("invokeExact".equals(name)) 1863 return exactInvoker(type); 1864 assert(!MemberName.isMethodHandleInvokeName(name)); 1865 return null; 1866 } 1867 private MethodHandle findVirtualForVH(String name, MethodType type) { 1868 try { 1869 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type); 1870 } catch (IllegalArgumentException e) { 1871 return null; 1872 } 1873 } 1874 1875 /** 1876 * Produces a method handle which creates an object and initializes it, using 1877 * the constructor of the specified type. 1878 * The parameter types of the method handle will be those of the constructor, 1879 * while the return type will be a reference to the constructor's class. 1880 * The constructor and all its argument types must be accessible to the lookup object. 1881 * <p> 1882 * The requested type must have a return type of {@code void}. 1883 * (This is consistent with the JVM's treatment of constructor type descriptors.) 1884 * <p> 1885 * The returned method handle will have 1886 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1887 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 1888 * <p> 1889 * If the returned method handle is invoked, the constructor's class will 1890 * be initialized, if it has not already been initialized. 1891 * <p><b>Example:</b> 1892 * <blockquote><pre>{@code 1893 import static java.lang.invoke.MethodHandles.*; 1894 import static java.lang.invoke.MethodType.*; 1895 ... 1896 MethodHandle MH_newArrayList = publicLookup().findConstructor( 1897 ArrayList.class, methodType(void.class, Collection.class)); 1898 Collection orig = Arrays.asList("x", "y"); 1899 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig); 1900 assert(orig != copy); 1901 assertEquals(orig, copy); 1902 // a variable-arity constructor: 1903 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor( 1904 ProcessBuilder.class, methodType(void.class, String[].class)); 1905 ProcessBuilder pb = (ProcessBuilder) 1906 MH_newProcessBuilder.invoke("x", "y", "z"); 1907 assertEquals("[x, y, z]", pb.command().toString()); 1908 * }</pre></blockquote> 1909 * @param refc the class or interface from which the method is accessed 1910 * @param type the type of the method, with the receiver argument omitted, and a void return type 1911 * @return the desired method handle 1912 * @throws NoSuchMethodException if the constructor does not exist 1913 * @throws IllegalAccessException if access checking fails 1914 * or if the method's variable arity modifier bit 1915 * is set and {@code asVarargsCollector} fails 1916 * @exception SecurityException if a security manager is present and it 1917 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1918 * @throws NullPointerException if any argument is null 1919 */ 1920 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1921 if (refc.isArray()) { 1922 throw new NoSuchMethodException("no constructor for array class: " + refc.getName()); 1923 } 1924 String name = "<init>"; 1925 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type); 1926 return getDirectConstructor(refc, ctor); 1927 } 1928 1929 /** 1930 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static 1931 * initializer of the class is not run. 1932 * <p> 1933 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class 1934 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to 1935 * load the requested class, and then determines whether the class is accessible to this lookup object. 1936 * 1937 * @param targetName the fully qualified name of the class to be looked up. 1938 * @return the requested class. 1939 * @exception SecurityException if a security manager is present and it 1940 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1941 * @throws LinkageError if the linkage fails 1942 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader. 1943 * @throws IllegalAccessException if the class is not accessible, using the allowed access 1944 * modes. 1945 * @exception SecurityException if a security manager is present and it 1946 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1947 * @since 9 1948 */ 1949 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException { 1950 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader()); 1951 return accessClass(targetClass); 1952 } 1953 1954 /** 1955 * Determines if a class can be accessed from the lookup context defined by 1956 * this {@code Lookup} object. The static initializer of the class is not run. 1957 * <p> 1958 * If the {@code targetClass} is in the same module as the lookup class, 1959 * the lookup class is {@code LC} in module {@code M1} and 1960 * the previous lookup class is in module {@code M0} or 1961 * {@code null} if not present, 1962 * {@code targetClass} is accessible if and only if one of the following is true: 1963 * <ul> 1964 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is 1965 * {@code LC} or other class in the same nest of {@code LC}.</li> 1966 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is 1967 * in the same runtime package of {@code LC}.</li> 1968 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is 1969 * a public type in {@code M1}.</li> 1970 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is 1971 * a public type in a package exported by {@code M1} to at least {@code M0} 1972 * if the previous lookup class is present; otherwise, {@code targetClass} 1973 * is a public type in a package exported by {@code M1} unconditionally.</li> 1974 * </ul> 1975 * 1976 * <p> 1977 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup 1978 * can access public types in all modules when the type is in a package 1979 * that is exported unconditionally. 1980 * <p> 1981 * Otherwise, the target class is in a different module from {@code lookupClass}, 1982 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass} 1983 * is inaccessible. 1984 * <p> 1985 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class}, 1986 * {@code M1} is the module containing {@code lookupClass} and 1987 * {@code M2} is the module containing {@code targetClass}, 1988 * then {@code targetClass} is accessible if and only if 1989 * <ul> 1990 * <li>{@code M1} reads {@code M2}, and 1991 * <li>{@code targetClass} is public and in a package exported by 1992 * {@code M2} at least to {@code M1}. 1993 * </ul> 1994 * <p> 1995 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class}, 1996 * {@code M1} and {@code M2} are as before, and {@code M0} is the module 1997 * containing the previous lookup class, then {@code targetClass} is accessible 1998 * if and only if one of the following is true: 1999 * <ul> 2000 * <li>{@code targetClass} is in {@code M0} and {@code M1} 2001 * {@linkplain Module#reads reads} {@code M0} and the type is 2002 * in a package that is exported to at least {@code M1}. 2003 * <li>{@code targetClass} is in {@code M1} and {@code M0} 2004 * {@linkplain Module#reads reads} {@code M1} and the type is 2005 * in a package that is exported to at least {@code M0}. 2006 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0} 2007 * and {@code M1} reads {@code M2} and the type is in a package 2008 * that is exported to at least both {@code M0} and {@code M2}. 2009 * </ul> 2010 * <p> 2011 * Otherwise, {@code targetClass} is not accessible. 2012 * 2013 * @param targetClass the class to be access-checked 2014 * @return the class that has been access-checked 2015 * @throws IllegalAccessException if the class is not accessible from the lookup class 2016 * and previous lookup class, if present, using the allowed access modes. 2017 * @exception SecurityException if a security manager is present and it 2018 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2019 * @since 9 2020 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 2021 */ 2022 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException { 2023 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) { 2024 throw new MemberName(targetClass).makeAccessException("access violation", this); 2025 } 2026 checkSecurityManager(targetClass, null); 2027 return targetClass; 2028 } 2029 2030 /** 2031 * Produces an early-bound method handle for a virtual method. 2032 * It will bypass checks for overriding methods on the receiver, 2033 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 2034 * instruction from within the explicitly specified {@code specialCaller}. 2035 * The type of the method handle will be that of the method, 2036 * with a suitably restricted receiver type prepended. 2037 * (The receiver type will be {@code specialCaller} or a subtype.) 2038 * The method and all its argument types must be accessible 2039 * to the lookup object. 2040 * <p> 2041 * Before method resolution, 2042 * if the explicitly specified caller class is not identical with the 2043 * lookup class, or if this lookup object does not have 2044 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 2045 * privileges, the access fails. 2046 * <p> 2047 * The returned method handle will have 2048 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2049 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2050 * <p style="font-size:smaller;"> 2051 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API, 2052 * even though the {@code invokespecial} instruction can refer to them 2053 * in special circumstances. Use {@link #findConstructor findConstructor} 2054 * to access instance initialization methods in a safe manner.)</em> 2055 * <p><b>Example:</b> 2056 * <blockquote><pre>{@code 2057 import static java.lang.invoke.MethodHandles.*; 2058 import static java.lang.invoke.MethodType.*; 2059 ... 2060 static class Listie extends ArrayList { 2061 public String toString() { return "[wee Listie]"; } 2062 static Lookup lookup() { return MethodHandles.lookup(); } 2063 } 2064 ... 2065 // no access to constructor via invokeSpecial: 2066 MethodHandle MH_newListie = Listie.lookup() 2067 .findConstructor(Listie.class, methodType(void.class)); 2068 Listie l = (Listie) MH_newListie.invokeExact(); 2069 try { assertEquals("impossible", Listie.lookup().findSpecial( 2070 Listie.class, "<init>", methodType(void.class), Listie.class)); 2071 } catch (NoSuchMethodException ex) { } // OK 2072 // access to super and self methods via invokeSpecial: 2073 MethodHandle MH_super = Listie.lookup().findSpecial( 2074 ArrayList.class, "toString" , methodType(String.class), Listie.class); 2075 MethodHandle MH_this = Listie.lookup().findSpecial( 2076 Listie.class, "toString" , methodType(String.class), Listie.class); 2077 MethodHandle MH_duper = Listie.lookup().findSpecial( 2078 Object.class, "toString" , methodType(String.class), Listie.class); 2079 assertEquals("[]", (String) MH_super.invokeExact(l)); 2080 assertEquals(""+l, (String) MH_this.invokeExact(l)); 2081 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method 2082 try { assertEquals("inaccessible", Listie.lookup().findSpecial( 2083 String.class, "toString", methodType(String.class), Listie.class)); 2084 } catch (IllegalAccessException ex) { } // OK 2085 Listie subl = new Listie() { public String toString() { return "[subclass]"; } }; 2086 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method 2087 * }</pre></blockquote> 2088 * 2089 * @param refc the class or interface from which the method is accessed 2090 * @param name the name of the method (which must not be "<init>") 2091 * @param type the type of the method, with the receiver argument omitted 2092 * @param specialCaller the proposed calling class to perform the {@code invokespecial} 2093 * @return the desired method handle 2094 * @throws NoSuchMethodException if the method does not exist 2095 * @throws IllegalAccessException if access checking fails, 2096 * or if the method is {@code static}, 2097 * or if the method's variable arity modifier bit 2098 * is set and {@code asVarargsCollector} fails 2099 * @exception SecurityException if a security manager is present and it 2100 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2101 * @throws NullPointerException if any argument is null 2102 */ 2103 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type, 2104 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException { 2105 checkSpecialCaller(specialCaller, refc); 2106 Lookup specialLookup = this.in(specialCaller); 2107 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type); 2108 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method)); 2109 } 2110 2111 /** 2112 * Produces a method handle giving read access to a non-static field. 2113 * The type of the method handle will have a return type of the field's 2114 * value type. 2115 * The method handle's single argument will be the instance containing 2116 * the field. 2117 * Access checking is performed immediately on behalf of the lookup class. 2118 * @param refc the class or interface from which the method is accessed 2119 * @param name the field's name 2120 * @param type the field's type 2121 * @return a method handle which can load values from the field 2122 * @throws NoSuchFieldException if the field does not exist 2123 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 2124 * @exception SecurityException if a security manager is present and it 2125 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2126 * @throws NullPointerException if any argument is null 2127 * @see #findVarHandle(Class, String, Class) 2128 */ 2129 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2130 MemberName field = resolveOrFail(REF_getField, refc, name, type); 2131 return getDirectField(REF_getField, refc, field); 2132 } 2133 2134 /** 2135 * Produces a method handle giving write access to a non-static field. 2136 * The type of the method handle will have a void return type. 2137 * The method handle will take two arguments, the instance containing 2138 * the field, and the value to be stored. 2139 * The second argument will be of the field's value type. 2140 * Access checking is performed immediately on behalf of the lookup class. 2141 * @param refc the class or interface from which the method is accessed 2142 * @param name the field's name 2143 * @param type the field's type 2144 * @return a method handle which can store values into the field 2145 * @throws NoSuchFieldException if the field does not exist 2146 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 2147 * or {@code final} 2148 * @exception SecurityException if a security manager is present and it 2149 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2150 * @throws NullPointerException if any argument is null 2151 * @see #findVarHandle(Class, String, Class) 2152 */ 2153 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2154 MemberName field = resolveOrFail(REF_putField, refc, name, type); 2155 return getDirectField(REF_putField, refc, field); 2156 } 2157 2158 /** 2159 * Produces a VarHandle giving access to a non-static field {@code name} 2160 * of type {@code type} declared in a class of type {@code recv}. 2161 * The VarHandle's variable type is {@code type} and it has one 2162 * coordinate type, {@code recv}. 2163 * <p> 2164 * Access checking is performed immediately on behalf of the lookup 2165 * class. 2166 * <p> 2167 * Certain access modes of the returned VarHandle are unsupported under 2168 * the following conditions: 2169 * <ul> 2170 * <li>if the field is declared {@code final}, then the write, atomic 2171 * update, numeric atomic update, and bitwise atomic update access 2172 * modes are unsupported. 2173 * <li>if the field type is anything other than {@code byte}, 2174 * {@code short}, {@code char}, {@code int}, {@code long}, 2175 * {@code float}, or {@code double} then numeric atomic update 2176 * access modes are unsupported. 2177 * <li>if the field type is anything other than {@code boolean}, 2178 * {@code byte}, {@code short}, {@code char}, {@code int} or 2179 * {@code long} then bitwise atomic update access modes are 2180 * unsupported. 2181 * </ul> 2182 * <p> 2183 * If the field is declared {@code volatile} then the returned VarHandle 2184 * will override access to the field (effectively ignore the 2185 * {@code volatile} declaration) in accordance to its specified 2186 * access modes. 2187 * <p> 2188 * If the field type is {@code float} or {@code double} then numeric 2189 * and atomic update access modes compare values using their bitwise 2190 * representation (see {@link Float#floatToRawIntBits} and 2191 * {@link Double#doubleToRawLongBits}, respectively). 2192 * @apiNote 2193 * Bitwise comparison of {@code float} values or {@code double} values, 2194 * as performed by the numeric and atomic update access modes, differ 2195 * from the primitive {@code ==} operator and the {@link Float#equals} 2196 * and {@link Double#equals} methods, specifically with respect to 2197 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 2198 * Care should be taken when performing a compare and set or a compare 2199 * and exchange operation with such values since the operation may 2200 * unexpectedly fail. 2201 * There are many possible NaN values that are considered to be 2202 * {@code NaN} in Java, although no IEEE 754 floating-point operation 2203 * provided by Java can distinguish between them. Operation failure can 2204 * occur if the expected or witness value is a NaN value and it is 2205 * transformed (perhaps in a platform specific manner) into another NaN 2206 * value, and thus has a different bitwise representation (see 2207 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 2208 * details). 2209 * The values {@code -0.0} and {@code +0.0} have different bitwise 2210 * representations but are considered equal when using the primitive 2211 * {@code ==} operator. Operation failure can occur if, for example, a 2212 * numeric algorithm computes an expected value to be say {@code -0.0} 2213 * and previously computed the witness value to be say {@code +0.0}. 2214 * @param recv the receiver class, of type {@code R}, that declares the 2215 * non-static field 2216 * @param name the field's name 2217 * @param type the field's type, of type {@code T} 2218 * @return a VarHandle giving access to non-static fields. 2219 * @throws NoSuchFieldException if the field does not exist 2220 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 2221 * @exception SecurityException if a security manager is present and it 2222 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2223 * @throws NullPointerException if any argument is null 2224 * @since 9 2225 */ 2226 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2227 MemberName getField = resolveOrFail(REF_getField, recv, name, type); 2228 MemberName putField = resolveOrFail(REF_putField, recv, name, type); 2229 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField); 2230 } 2231 2232 /** 2233 * Produces a method handle giving read access to a static field. 2234 * The type of the method handle will have a return type of the field's 2235 * value type. 2236 * The method handle will take no arguments. 2237 * Access checking is performed immediately on behalf of the lookup class. 2238 * <p> 2239 * If the returned method handle is invoked, the field's class will 2240 * be initialized, if it has not already been initialized. 2241 * @param refc the class or interface from which the method is accessed 2242 * @param name the field's name 2243 * @param type the field's type 2244 * @return a method handle which can load values from the field 2245 * @throws NoSuchFieldException if the field does not exist 2246 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 2247 * @exception SecurityException if a security manager is present and it 2248 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2249 * @throws NullPointerException if any argument is null 2250 */ 2251 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2252 MemberName field = resolveOrFail(REF_getStatic, refc, name, type); 2253 return getDirectField(REF_getStatic, refc, field); 2254 } 2255 2256 /** 2257 * Produces a method handle giving write access to a static field. 2258 * The type of the method handle will have a void return type. 2259 * The method handle will take a single 2260 * argument, of the field's value type, the value to be stored. 2261 * Access checking is performed immediately on behalf of the lookup class. 2262 * <p> 2263 * If the returned method handle is invoked, the field's class will 2264 * be initialized, if it has not already been initialized. 2265 * @param refc the class or interface from which the method is accessed 2266 * @param name the field's name 2267 * @param type the field's type 2268 * @return a method handle which can store values into the field 2269 * @throws NoSuchFieldException if the field does not exist 2270 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 2271 * or is {@code final} 2272 * @exception SecurityException if a security manager is present and it 2273 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2274 * @throws NullPointerException if any argument is null 2275 */ 2276 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2277 MemberName field = resolveOrFail(REF_putStatic, refc, name, type); 2278 return getDirectField(REF_putStatic, refc, field); 2279 } 2280 2281 /** 2282 * Produces a VarHandle giving access to a static field {@code name} of 2283 * type {@code type} declared in a class of type {@code decl}. 2284 * The VarHandle's variable type is {@code type} and it has no 2285 * coordinate types. 2286 * <p> 2287 * Access checking is performed immediately on behalf of the lookup 2288 * class. 2289 * <p> 2290 * If the returned VarHandle is operated on, the declaring class will be 2291 * initialized, if it has not already been initialized. 2292 * <p> 2293 * Certain access modes of the returned VarHandle are unsupported under 2294 * the following conditions: 2295 * <ul> 2296 * <li>if the field is declared {@code final}, then the write, atomic 2297 * update, numeric atomic update, and bitwise atomic update access 2298 * modes are unsupported. 2299 * <li>if the field type is anything other than {@code byte}, 2300 * {@code short}, {@code char}, {@code int}, {@code long}, 2301 * {@code float}, or {@code double}, then numeric atomic update 2302 * access modes are unsupported. 2303 * <li>if the field type is anything other than {@code boolean}, 2304 * {@code byte}, {@code short}, {@code char}, {@code int} or 2305 * {@code long} then bitwise atomic update access modes are 2306 * unsupported. 2307 * </ul> 2308 * <p> 2309 * If the field is declared {@code volatile} then the returned VarHandle 2310 * will override access to the field (effectively ignore the 2311 * {@code volatile} declaration) in accordance to its specified 2312 * access modes. 2313 * <p> 2314 * If the field type is {@code float} or {@code double} then numeric 2315 * and atomic update access modes compare values using their bitwise 2316 * representation (see {@link Float#floatToRawIntBits} and 2317 * {@link Double#doubleToRawLongBits}, respectively). 2318 * @apiNote 2319 * Bitwise comparison of {@code float} values or {@code double} values, 2320 * as performed by the numeric and atomic update access modes, differ 2321 * from the primitive {@code ==} operator and the {@link Float#equals} 2322 * and {@link Double#equals} methods, specifically with respect to 2323 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 2324 * Care should be taken when performing a compare and set or a compare 2325 * and exchange operation with such values since the operation may 2326 * unexpectedly fail. 2327 * There are many possible NaN values that are considered to be 2328 * {@code NaN} in Java, although no IEEE 754 floating-point operation 2329 * provided by Java can distinguish between them. Operation failure can 2330 * occur if the expected or witness value is a NaN value and it is 2331 * transformed (perhaps in a platform specific manner) into another NaN 2332 * value, and thus has a different bitwise representation (see 2333 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 2334 * details). 2335 * The values {@code -0.0} and {@code +0.0} have different bitwise 2336 * representations but are considered equal when using the primitive 2337 * {@code ==} operator. Operation failure can occur if, for example, a 2338 * numeric algorithm computes an expected value to be say {@code -0.0} 2339 * and previously computed the witness value to be say {@code +0.0}. 2340 * @param decl the class that declares the static field 2341 * @param name the field's name 2342 * @param type the field's type, of type {@code T} 2343 * @return a VarHandle giving access to a static field 2344 * @throws NoSuchFieldException if the field does not exist 2345 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 2346 * @exception SecurityException if a security manager is present and it 2347 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2348 * @throws NullPointerException if any argument is null 2349 * @since 9 2350 */ 2351 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2352 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type); 2353 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type); 2354 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField); 2355 } 2356 2357 /** 2358 * Produces an early-bound method handle for a non-static method. 2359 * The receiver must have a supertype {@code defc} in which a method 2360 * of the given name and type is accessible to the lookup class. 2361 * The method and all its argument types must be accessible to the lookup object. 2362 * The type of the method handle will be that of the method, 2363 * without any insertion of an additional receiver parameter. 2364 * The given receiver will be bound into the method handle, 2365 * so that every call to the method handle will invoke the 2366 * requested method on the given receiver. 2367 * <p> 2368 * The returned method handle will have 2369 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2370 * the method's variable arity modifier bit ({@code 0x0080}) is set 2371 * <em>and</em> the trailing array argument is not the only argument. 2372 * (If the trailing array argument is the only argument, 2373 * the given receiver value will be bound to it.) 2374 * <p> 2375 * This is almost equivalent to the following code, with some differences noted below: 2376 * <blockquote><pre>{@code 2377 import static java.lang.invoke.MethodHandles.*; 2378 import static java.lang.invoke.MethodType.*; 2379 ... 2380 MethodHandle mh0 = lookup().findVirtual(defc, name, type); 2381 MethodHandle mh1 = mh0.bindTo(receiver); 2382 mh1 = mh1.withVarargs(mh0.isVarargsCollector()); 2383 return mh1; 2384 * }</pre></blockquote> 2385 * where {@code defc} is either {@code receiver.getClass()} or a super 2386 * type of that class, in which the requested method is accessible 2387 * to the lookup class. 2388 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity. 2389 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would 2390 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and 2391 * the receiver is restricted by {@code findVirtual} to the lookup class.) 2392 * @param receiver the object from which the method is accessed 2393 * @param name the name of the method 2394 * @param type the type of the method, with the receiver argument omitted 2395 * @return the desired method handle 2396 * @throws NoSuchMethodException if the method does not exist 2397 * @throws IllegalAccessException if access checking fails 2398 * or if the method's variable arity modifier bit 2399 * is set and {@code asVarargsCollector} fails 2400 * @exception SecurityException if a security manager is present and it 2401 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2402 * @throws NullPointerException if any argument is null 2403 * @see MethodHandle#bindTo 2404 * @see #findVirtual 2405 */ 2406 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2407 Class<? extends Object> refc = receiver.getClass(); // may get NPE 2408 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type); 2409 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method)); 2410 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) { 2411 throw new IllegalAccessException("The restricted defining class " + 2412 mh.type().leadingReferenceParameter().getName() + 2413 " is not assignable from receiver class " + 2414 receiver.getClass().getName()); 2415 } 2416 return mh.bindArgumentL(0, receiver).setVarargs(method); 2417 } 2418 2419 /** 2420 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 2421 * to <i>m</i>, if the lookup class has permission. 2422 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument. 2423 * If <i>m</i> is virtual, overriding is respected on every call. 2424 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped. 2425 * The type of the method handle will be that of the method, 2426 * with the receiver type prepended (but only if it is non-static). 2427 * If the method's {@code accessible} flag is not set, 2428 * access checking is performed immediately on behalf of the lookup class. 2429 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties. 2430 * <p> 2431 * The returned method handle will have 2432 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2433 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2434 * <p> 2435 * If <i>m</i> is static, and 2436 * if the returned method handle is invoked, the method's class will 2437 * be initialized, if it has not already been initialized. 2438 * @param m the reflected method 2439 * @return a method handle which can invoke the reflected method 2440 * @throws IllegalAccessException if access checking fails 2441 * or if the method's variable arity modifier bit 2442 * is set and {@code asVarargsCollector} fails 2443 * @throws NullPointerException if the argument is null 2444 */ 2445 public MethodHandle unreflect(Method m) throws IllegalAccessException { 2446 if (m.getDeclaringClass() == MethodHandle.class) { 2447 MethodHandle mh = unreflectForMH(m); 2448 if (mh != null) return mh; 2449 } 2450 if (m.getDeclaringClass() == VarHandle.class) { 2451 MethodHandle mh = unreflectForVH(m); 2452 if (mh != null) return mh; 2453 } 2454 MemberName method = new MemberName(m); 2455 byte refKind = method.getReferenceKind(); 2456 if (refKind == REF_invokeSpecial) 2457 refKind = REF_invokeVirtual; 2458 assert(method.isMethod()); 2459 @SuppressWarnings("deprecation") 2460 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this; 2461 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method)); 2462 } 2463 private MethodHandle unreflectForMH(Method m) { 2464 // these names require special lookups because they throw UnsupportedOperationException 2465 if (MemberName.isMethodHandleInvokeName(m.getName())) 2466 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m)); 2467 return null; 2468 } 2469 private MethodHandle unreflectForVH(Method m) { 2470 // these names require special lookups because they throw UnsupportedOperationException 2471 if (MemberName.isVarHandleMethodInvokeName(m.getName())) 2472 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m)); 2473 return null; 2474 } 2475 2476 /** 2477 * Produces a method handle for a reflected method. 2478 * It will bypass checks for overriding methods on the receiver, 2479 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 2480 * instruction from within the explicitly specified {@code specialCaller}. 2481 * The type of the method handle will be that of the method, 2482 * with a suitably restricted receiver type prepended. 2483 * (The receiver type will be {@code specialCaller} or a subtype.) 2484 * If the method's {@code accessible} flag is not set, 2485 * access checking is performed immediately on behalf of the lookup class, 2486 * as if {@code invokespecial} instruction were being linked. 2487 * <p> 2488 * Before method resolution, 2489 * if the explicitly specified caller class is not identical with the 2490 * lookup class, or if this lookup object does not have 2491 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 2492 * privileges, the access fails. 2493 * <p> 2494 * The returned method handle will have 2495 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2496 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2497 * @param m the reflected method 2498 * @param specialCaller the class nominally calling the method 2499 * @return a method handle which can invoke the reflected method 2500 * @throws IllegalAccessException if access checking fails, 2501 * or if the method is {@code static}, 2502 * or if the method's variable arity modifier bit 2503 * is set and {@code asVarargsCollector} fails 2504 * @throws NullPointerException if any argument is null 2505 */ 2506 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException { 2507 checkSpecialCaller(specialCaller, m.getDeclaringClass()); 2508 Lookup specialLookup = this.in(specialCaller); 2509 MemberName method = new MemberName(m, true); 2510 assert(method.isMethod()); 2511 // ignore m.isAccessible: this is a new kind of access 2512 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method)); 2513 } 2514 2515 /** 2516 * Produces a method handle for a reflected constructor. 2517 * The type of the method handle will be that of the constructor, 2518 * with the return type changed to the declaring class. 2519 * The method handle will perform a {@code newInstance} operation, 2520 * creating a new instance of the constructor's class on the 2521 * arguments passed to the method handle. 2522 * <p> 2523 * If the constructor's {@code accessible} flag is not set, 2524 * access checking is performed immediately on behalf of the lookup class. 2525 * <p> 2526 * The returned method handle will have 2527 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2528 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 2529 * <p> 2530 * If the returned method handle is invoked, the constructor's class will 2531 * be initialized, if it has not already been initialized. 2532 * @param c the reflected constructor 2533 * @return a method handle which can invoke the reflected constructor 2534 * @throws IllegalAccessException if access checking fails 2535 * or if the method's variable arity modifier bit 2536 * is set and {@code asVarargsCollector} fails 2537 * @throws NullPointerException if the argument is null 2538 */ 2539 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException { 2540 MemberName ctor = new MemberName(c); 2541 assert(ctor.isConstructor()); 2542 @SuppressWarnings("deprecation") 2543 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this; 2544 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor); 2545 } 2546 2547 /** 2548 * Produces a method handle giving read access to a reflected field. 2549 * The type of the method handle will have a return type of the field's 2550 * value type. 2551 * If the field is {@code static}, the method handle will take no arguments. 2552 * Otherwise, its single argument will be the instance containing 2553 * the field. 2554 * If the {@code Field} object's {@code accessible} flag is not set, 2555 * access checking is performed immediately on behalf of the lookup class. 2556 * <p> 2557 * If the field is static, and 2558 * if the returned method handle is invoked, the field's class will 2559 * be initialized, if it has not already been initialized. 2560 * @param f the reflected field 2561 * @return a method handle which can load values from the reflected field 2562 * @throws IllegalAccessException if access checking fails 2563 * @throws NullPointerException if the argument is null 2564 */ 2565 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException { 2566 return unreflectField(f, false); 2567 } 2568 2569 /** 2570 * Produces a method handle giving write access to a reflected field. 2571 * The type of the method handle will have a void return type. 2572 * If the field is {@code static}, the method handle will take a single 2573 * argument, of the field's value type, the value to be stored. 2574 * Otherwise, the two arguments will be the instance containing 2575 * the field, and the value to be stored. 2576 * If the {@code Field} object's {@code accessible} flag is not set, 2577 * access checking is performed immediately on behalf of the lookup class. 2578 * <p> 2579 * If the field is {@code final}, write access will not be 2580 * allowed and access checking will fail, except under certain 2581 * narrow circumstances documented for {@link Field#set Field.set}. 2582 * A method handle is returned only if a corresponding call to 2583 * the {@code Field} object's {@code set} method could return 2584 * normally. In particular, fields which are both {@code static} 2585 * and {@code final} may never be set. 2586 * <p> 2587 * If the field is {@code static}, and 2588 * if the returned method handle is invoked, the field's class will 2589 * be initialized, if it has not already been initialized. 2590 * @param f the reflected field 2591 * @return a method handle which can store values into the reflected field 2592 * @throws IllegalAccessException if access checking fails, 2593 * or if the field is {@code final} and write access 2594 * is not enabled on the {@code Field} object 2595 * @throws NullPointerException if the argument is null 2596 */ 2597 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException { 2598 return unreflectField(f, true); 2599 } 2600 2601 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException { 2602 MemberName field = new MemberName(f, isSetter); 2603 if (isSetter && field.isStatic() && field.isFinal()) 2604 throw field.makeAccessException("static final field has no write access", this); 2605 assert(isSetter 2606 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind()) 2607 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind())); 2608 @SuppressWarnings("deprecation") 2609 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this; 2610 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field); 2611 } 2612 2613 /** 2614 * Produces a VarHandle giving access to a reflected field {@code f} 2615 * of type {@code T} declared in a class of type {@code R}. 2616 * The VarHandle's variable type is {@code T}. 2617 * If the field is non-static the VarHandle has one coordinate type, 2618 * {@code R}. Otherwise, the field is static, and the VarHandle has no 2619 * coordinate types. 2620 * <p> 2621 * Access checking is performed immediately on behalf of the lookup 2622 * class, regardless of the value of the field's {@code accessible} 2623 * flag. 2624 * <p> 2625 * If the field is static, and if the returned VarHandle is operated 2626 * on, the field's declaring class will be initialized, if it has not 2627 * already been initialized. 2628 * <p> 2629 * Certain access modes of the returned VarHandle are unsupported under 2630 * the following conditions: 2631 * <ul> 2632 * <li>if the field is declared {@code final}, then the write, atomic 2633 * update, numeric atomic update, and bitwise atomic update access 2634 * modes are unsupported. 2635 * <li>if the field type is anything other than {@code byte}, 2636 * {@code short}, {@code char}, {@code int}, {@code long}, 2637 * {@code float}, or {@code double} then numeric atomic update 2638 * access modes are unsupported. 2639 * <li>if the field type is anything other than {@code boolean}, 2640 * {@code byte}, {@code short}, {@code char}, {@code int} or 2641 * {@code long} then bitwise atomic update access modes are 2642 * unsupported. 2643 * </ul> 2644 * <p> 2645 * If the field is declared {@code volatile} then the returned VarHandle 2646 * will override access to the field (effectively ignore the 2647 * {@code volatile} declaration) in accordance to its specified 2648 * access modes. 2649 * <p> 2650 * If the field type is {@code float} or {@code double} then numeric 2651 * and atomic update access modes compare values using their bitwise 2652 * representation (see {@link Float#floatToRawIntBits} and 2653 * {@link Double#doubleToRawLongBits}, respectively). 2654 * @apiNote 2655 * Bitwise comparison of {@code float} values or {@code double} values, 2656 * as performed by the numeric and atomic update access modes, differ 2657 * from the primitive {@code ==} operator and the {@link Float#equals} 2658 * and {@link Double#equals} methods, specifically with respect to 2659 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 2660 * Care should be taken when performing a compare and set or a compare 2661 * and exchange operation with such values since the operation may 2662 * unexpectedly fail. 2663 * There are many possible NaN values that are considered to be 2664 * {@code NaN} in Java, although no IEEE 754 floating-point operation 2665 * provided by Java can distinguish between them. Operation failure can 2666 * occur if the expected or witness value is a NaN value and it is 2667 * transformed (perhaps in a platform specific manner) into another NaN 2668 * value, and thus has a different bitwise representation (see 2669 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 2670 * details). 2671 * The values {@code -0.0} and {@code +0.0} have different bitwise 2672 * representations but are considered equal when using the primitive 2673 * {@code ==} operator. Operation failure can occur if, for example, a 2674 * numeric algorithm computes an expected value to be say {@code -0.0} 2675 * and previously computed the witness value to be say {@code +0.0}. 2676 * @param f the reflected field, with a field of type {@code T}, and 2677 * a declaring class of type {@code R} 2678 * @return a VarHandle giving access to non-static fields or a static 2679 * field 2680 * @throws IllegalAccessException if access checking fails 2681 * @throws NullPointerException if the argument is null 2682 * @since 9 2683 */ 2684 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException { 2685 MemberName getField = new MemberName(f, false); 2686 MemberName putField = new MemberName(f, true); 2687 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(), 2688 f.getDeclaringClass(), getField, putField); 2689 } 2690 2691 /** 2692 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 2693 * created by this lookup object or a similar one. 2694 * Security and access checks are performed to ensure that this lookup object 2695 * is capable of reproducing the target method handle. 2696 * This means that the cracking may fail if target is a direct method handle 2697 * but was created by an unrelated lookup object. 2698 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> 2699 * and was created by a lookup object for a different class. 2700 * @param target a direct method handle to crack into symbolic reference components 2701 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object 2702 * @exception SecurityException if a security manager is present and it 2703 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2704 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails 2705 * @exception NullPointerException if the target is {@code null} 2706 * @see MethodHandleInfo 2707 * @since 1.8 2708 */ 2709 public MethodHandleInfo revealDirect(MethodHandle target) { 2710 MemberName member = target.internalMemberName(); 2711 if (member == null || (!member.isResolved() && 2712 !member.isMethodHandleInvoke() && 2713 !member.isVarHandleMethodInvoke())) 2714 throw newIllegalArgumentException("not a direct method handle"); 2715 Class<?> defc = member.getDeclaringClass(); 2716 byte refKind = member.getReferenceKind(); 2717 assert(MethodHandleNatives.refKindIsValid(refKind)); 2718 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial()) 2719 // Devirtualized method invocation is usually formally virtual. 2720 // To avoid creating extra MemberName objects for this common case, 2721 // we encode this extra degree of freedom using MH.isInvokeSpecial. 2722 refKind = REF_invokeVirtual; 2723 if (refKind == REF_invokeVirtual && defc.isInterface()) 2724 // Symbolic reference is through interface but resolves to Object method (toString, etc.) 2725 refKind = REF_invokeInterface; 2726 // Check SM permissions and member access before cracking. 2727 try { 2728 checkAccess(refKind, defc, member); 2729 checkSecurityManager(defc, member); 2730 } catch (IllegalAccessException ex) { 2731 throw new IllegalArgumentException(ex); 2732 } 2733 if (allowedModes != TRUSTED && member.isCallerSensitive()) { 2734 Class<?> callerClass = target.internalCallerClass(); 2735 if (!hasPrivateAccess() || callerClass != lookupClass()) 2736 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass); 2737 } 2738 // Produce the handle to the results. 2739 return new InfoFromMemberName(this, member, refKind); 2740 } 2741 2742 /// Helper methods, all package-private. 2743 2744 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2745 checkSymbolicClass(refc); // do this before attempting to resolve 2746 Objects.requireNonNull(name); 2747 Objects.requireNonNull(type); 2748 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), 2749 NoSuchFieldException.class); 2750 } 2751 2752 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2753 checkSymbolicClass(refc); // do this before attempting to resolve 2754 Objects.requireNonNull(name); 2755 Objects.requireNonNull(type); 2756 checkMethodName(refKind, name); // NPE check on name 2757 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), 2758 NoSuchMethodException.class); 2759 } 2760 2761 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException { 2762 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve 2763 Objects.requireNonNull(member.getName()); 2764 Objects.requireNonNull(member.getType()); 2765 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), 2766 ReflectiveOperationException.class); 2767 } 2768 2769 MemberName resolveOrNull(byte refKind, MemberName member) { 2770 // do this before attempting to resolve 2771 if (!isClassAccessible(member.getDeclaringClass())) { 2772 return null; 2773 } 2774 Objects.requireNonNull(member.getName()); 2775 Objects.requireNonNull(member.getType()); 2776 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull()); 2777 } 2778 2779 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException { 2780 if (!isClassAccessible(refc)) { 2781 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this); 2782 } 2783 } 2784 2785 boolean isClassAccessible(Class<?> refc) { 2786 Objects.requireNonNull(refc); 2787 Class<?> caller = lookupClassOrNull(); 2788 return caller == null || VerifyAccess.isClassAccessible(refc, caller, prevLookupClass, allowedModes); 2789 } 2790 2791 /** Check name for an illegal leading "<" character. */ 2792 void checkMethodName(byte refKind, String name) throws NoSuchMethodException { 2793 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) 2794 throw new NoSuchMethodException("illegal method name: "+name); 2795 } 2796 2797 2798 /** 2799 * Find my trustable caller class if m is a caller sensitive method. 2800 * If this lookup object has private access, then the caller class is the lookupClass. 2801 * Otherwise, if m is caller-sensitive, throw IllegalAccessException. 2802 */ 2803 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException { 2804 Class<?> callerClass = null; 2805 if (MethodHandleNatives.isCallerSensitive(m)) { 2806 // Only lookups with private access are allowed to resolve caller-sensitive methods 2807 if (hasPrivateAccess()) { 2808 callerClass = lookupClass; 2809 } else { 2810 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 2811 } 2812 } 2813 return callerClass; 2814 } 2815 2816 /** 2817 * Returns {@code true} if this lookup has {@code PRIVATE} access. 2818 * @return {@code true} if this lookup has {@code PRIVATE} access. 2819 * @since 9 2820 */ 2821 public boolean hasPrivateAccess() { 2822 return (allowedModes & PRIVATE) != 0; 2823 } 2824 2825 /** 2826 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>. 2827 * Determines a trustable caller class to compare with refc, the symbolic reference class. 2828 * If this lookup object has private access, then the caller class is the lookupClass. 2829 */ 2830 void checkSecurityManager(Class<?> refc, MemberName m) { 2831 SecurityManager smgr = System.getSecurityManager(); 2832 if (smgr == null) return; 2833 if (allowedModes == TRUSTED) return; 2834 2835 // Step 1: 2836 boolean fullPowerLookup = hasPrivateAccess(); 2837 if (!fullPowerLookup || 2838 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 2839 ReflectUtil.checkPackageAccess(refc); 2840 } 2841 2842 if (m == null) { // findClass or accessClass 2843 // Step 2b: 2844 if (!fullPowerLookup) { 2845 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION); 2846 } 2847 return; 2848 } 2849 2850 // Step 2a: 2851 if (m.isPublic()) return; 2852 if (!fullPowerLookup) { 2853 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION); 2854 } 2855 2856 // Step 3: 2857 Class<?> defc = m.getDeclaringClass(); 2858 if (!fullPowerLookup && defc != refc) { 2859 ReflectUtil.checkPackageAccess(defc); 2860 } 2861 } 2862 2863 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 2864 boolean wantStatic = (refKind == REF_invokeStatic); 2865 String message; 2866 if (m.isConstructor()) 2867 message = "expected a method, not a constructor"; 2868 else if (!m.isMethod()) 2869 message = "expected a method"; 2870 else if (wantStatic != m.isStatic()) 2871 message = wantStatic ? "expected a static method" : "expected a non-static method"; 2872 else 2873 { checkAccess(refKind, refc, m); return; } 2874 throw m.makeAccessException(message, this); 2875 } 2876 2877 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 2878 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind); 2879 String message; 2880 if (wantStatic != m.isStatic()) 2881 message = wantStatic ? "expected a static field" : "expected a non-static field"; 2882 else 2883 { checkAccess(refKind, refc, m); return; } 2884 throw m.makeAccessException(message, this); 2885 } 2886 2887 /** Check public/protected/private bits on the symbolic reference class and its member. */ 2888 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 2889 assert(m.referenceKindIsConsistentWith(refKind) && 2890 MethodHandleNatives.refKindIsValid(refKind) && 2891 (MethodHandleNatives.refKindIsField(refKind) == m.isField())); 2892 int allowedModes = this.allowedModes; 2893 if (allowedModes == TRUSTED) return; 2894 int mods = m.getModifiers(); 2895 if (Modifier.isProtected(mods) && 2896 refKind == REF_invokeVirtual && 2897 m.getDeclaringClass() == Object.class && 2898 m.getName().equals("clone") && 2899 refc.isArray()) { 2900 // The JVM does this hack also. 2901 // (See ClassVerifier::verify_invoke_instructions 2902 // and LinkResolver::check_method_accessability.) 2903 // Because the JVM does not allow separate methods on array types, 2904 // there is no separate method for int[].clone. 2905 // All arrays simply inherit Object.clone. 2906 // But for access checking logic, we make Object.clone 2907 // (normally protected) appear to be public. 2908 // Later on, when the DirectMethodHandle is created, 2909 // its leading argument will be restricted to the 2910 // requested array type. 2911 // N.B. The return type is not adjusted, because 2912 // that is *not* the bytecode behavior. 2913 mods ^= Modifier.PROTECTED | Modifier.PUBLIC; 2914 } 2915 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) { 2916 // cannot "new" a protected ctor in a different package 2917 mods ^= Modifier.PROTECTED; 2918 } 2919 if (Modifier.isFinal(mods) && 2920 MethodHandleNatives.refKindIsSetter(refKind)) 2921 throw m.makeAccessException("unexpected set of a final field", this); 2922 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE 2923 if ((requestedModes & allowedModes) != 0) { 2924 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(), 2925 mods, lookupClass(), previousLookupClass(), allowedModes)) 2926 return; 2927 } else { 2928 // Protected members can also be checked as if they were package-private. 2929 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0 2930 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass())) 2931 return; 2932 } 2933 throw m.makeAccessException(accessFailedMessage(refc, m), this); 2934 } 2935 2936 String accessFailedMessage(Class<?> refc, MemberName m) { 2937 Class<?> defc = m.getDeclaringClass(); 2938 int mods = m.getModifiers(); 2939 // check the class first: 2940 boolean classOK = (Modifier.isPublic(defc.getModifiers()) && 2941 (defc == refc || 2942 Modifier.isPublic(refc.getModifiers()))); 2943 if (!classOK && (allowedModes & PACKAGE) != 0) { 2944 // ignore previous lookup class to check if default package access 2945 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) && 2946 (defc == refc || 2947 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES))); 2948 } 2949 if (!classOK) 2950 return "class is not public"; 2951 if (Modifier.isPublic(mods)) 2952 return "access to public member failed"; // (how?, module not readable?) 2953 if (Modifier.isPrivate(mods)) 2954 return "member is private"; 2955 if (Modifier.isProtected(mods)) 2956 return "member is protected"; 2957 return "member is private to package"; 2958 } 2959 2960 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException { 2961 int allowedModes = this.allowedModes; 2962 if (allowedModes == TRUSTED) return; 2963 if (!hasPrivateAccess() 2964 || (specialCaller != lookupClass() 2965 // ensure non-abstract methods in superinterfaces can be special-invoked 2966 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller)))) 2967 throw new MemberName(specialCaller). 2968 makeAccessException("no private access for invokespecial", this); 2969 } 2970 2971 private boolean restrictProtectedReceiver(MemberName method) { 2972 // The accessing class only has the right to use a protected member 2973 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc. 2974 if (!method.isProtected() || method.isStatic() 2975 || allowedModes == TRUSTED 2976 || method.getDeclaringClass() == lookupClass() 2977 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())) 2978 return false; 2979 return true; 2980 } 2981 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException { 2982 assert(!method.isStatic()); 2983 // receiver type of mh is too wide; narrow to caller 2984 if (!method.getDeclaringClass().isAssignableFrom(caller)) { 2985 throw method.makeAccessException("caller class must be a subclass below the method", caller); 2986 } 2987 MethodType rawType = mh.type(); 2988 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow 2989 MethodType narrowType = rawType.changeParameterType(0, caller); 2990 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness 2991 assert(mh.viewAsTypeChecks(narrowType, true)); 2992 return mh.copyWith(narrowType, mh.form); 2993 } 2994 2995 /** Check access and get the requested method. */ 2996 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException { 2997 final boolean doRestrict = true; 2998 final boolean checkSecurity = true; 2999 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass); 3000 } 3001 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */ 3002 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException { 3003 final boolean doRestrict = false; 3004 final boolean checkSecurity = true; 3005 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass); 3006 } 3007 /** Check access and get the requested method, eliding security manager checks. */ 3008 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException { 3009 final boolean doRestrict = true; 3010 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 3011 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass); 3012 } 3013 /** Common code for all methods; do not call directly except from immediately above. */ 3014 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method, 3015 boolean checkSecurity, 3016 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException { 3017 3018 checkMethod(refKind, refc, method); 3019 // Optionally check with the security manager; this isn't needed for unreflect* calls. 3020 if (checkSecurity) 3021 checkSecurityManager(refc, method); 3022 assert(!method.isMethodHandleInvoke()); 3023 3024 if (refKind == REF_invokeSpecial && 3025 refc != lookupClass() && 3026 !refc.isInterface() && 3027 refc != lookupClass().getSuperclass() && 3028 refc.isAssignableFrom(lookupClass())) { 3029 assert(!method.getName().equals("<init>")); // not this code path 3030 3031 // Per JVMS 6.5, desc. of invokespecial instruction: 3032 // If the method is in a superclass of the LC, 3033 // and if our original search was above LC.super, 3034 // repeat the search (symbolic lookup) from LC.super 3035 // and continue with the direct superclass of that class, 3036 // and so forth, until a match is found or no further superclasses exist. 3037 // FIXME: MemberName.resolve should handle this instead. 3038 Class<?> refcAsSuper = lookupClass(); 3039 MemberName m2; 3040 do { 3041 refcAsSuper = refcAsSuper.getSuperclass(); 3042 m2 = new MemberName(refcAsSuper, 3043 method.getName(), 3044 method.getMethodType(), 3045 REF_invokeSpecial); 3046 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull()); 3047 } while (m2 == null && // no method is found yet 3048 refc != refcAsSuper); // search up to refc 3049 if (m2 == null) throw new InternalError(method.toString()); 3050 method = m2; 3051 refc = refcAsSuper; 3052 // redo basic checks 3053 checkMethod(refKind, refc, method); 3054 } 3055 3056 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass()); 3057 MethodHandle mh = dmh; 3058 // Optionally narrow the receiver argument to lookupClass using restrictReceiver. 3059 if ((doRestrict && refKind == REF_invokeSpecial) || 3060 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) { 3061 mh = restrictReceiver(method, dmh, lookupClass()); 3062 } 3063 mh = maybeBindCaller(method, mh, boundCallerClass); 3064 mh = mh.setVarargs(method); 3065 return mh; 3066 } 3067 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, 3068 Class<?> boundCallerClass) 3069 throws IllegalAccessException { 3070 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method)) 3071 return mh; 3072 Class<?> hostClass = lookupClass; 3073 if (!hasPrivateAccess()) // caller must have private access 3074 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk 3075 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass); 3076 // Note: caller will apply varargs after this step happens. 3077 return cbmh; 3078 } 3079 /** Check access and get the requested field. */ 3080 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 3081 final boolean checkSecurity = true; 3082 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 3083 } 3084 /** Check access and get the requested field, eliding security manager checks. */ 3085 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 3086 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 3087 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 3088 } 3089 /** Common code for all fields; do not call directly except from immediately above. */ 3090 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field, 3091 boolean checkSecurity) throws IllegalAccessException { 3092 checkField(refKind, refc, field); 3093 // Optionally check with the security manager; this isn't needed for unreflect* calls. 3094 if (checkSecurity) 3095 checkSecurityManager(refc, field); 3096 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field); 3097 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) && 3098 restrictProtectedReceiver(field)); 3099 if (doRestrict) 3100 return restrictReceiver(field, dmh, lookupClass()); 3101 return dmh; 3102 } 3103 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind, 3104 Class<?> refc, MemberName getField, MemberName putField) 3105 throws IllegalAccessException { 3106 final boolean checkSecurity = true; 3107 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 3108 } 3109 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind, 3110 Class<?> refc, MemberName getField, MemberName putField) 3111 throws IllegalAccessException { 3112 final boolean checkSecurity = false; 3113 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 3114 } 3115 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind, 3116 Class<?> refc, MemberName getField, MemberName putField, 3117 boolean checkSecurity) throws IllegalAccessException { 3118 assert getField.isStatic() == putField.isStatic(); 3119 assert getField.isGetter() && putField.isSetter(); 3120 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind); 3121 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind); 3122 3123 checkField(getRefKind, refc, getField); 3124 if (checkSecurity) 3125 checkSecurityManager(refc, getField); 3126 3127 if (!putField.isFinal()) { 3128 // A VarHandle does not support updates to final fields, any 3129 // such VarHandle to a final field will be read-only and 3130 // therefore the following write-based accessibility checks are 3131 // only required for non-final fields 3132 checkField(putRefKind, refc, putField); 3133 if (checkSecurity) 3134 checkSecurityManager(refc, putField); 3135 } 3136 3137 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) && 3138 restrictProtectedReceiver(getField)); 3139 if (doRestrict) { 3140 assert !getField.isStatic(); 3141 // receiver type of VarHandle is too wide; narrow to caller 3142 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) { 3143 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass()); 3144 } 3145 refc = lookupClass(); 3146 } 3147 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED); 3148 } 3149 /** Check access and get the requested constructor. */ 3150 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException { 3151 final boolean checkSecurity = true; 3152 return getDirectConstructorCommon(refc, ctor, checkSecurity); 3153 } 3154 /** Check access and get the requested constructor, eliding security manager checks. */ 3155 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException { 3156 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 3157 return getDirectConstructorCommon(refc, ctor, checkSecurity); 3158 } 3159 /** Common code for all constructors; do not call directly except from immediately above. */ 3160 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor, 3161 boolean checkSecurity) throws IllegalAccessException { 3162 assert(ctor.isConstructor()); 3163 checkAccess(REF_newInvokeSpecial, refc, ctor); 3164 // Optionally check with the security manager; this isn't needed for unreflect* calls. 3165 if (checkSecurity) 3166 checkSecurityManager(refc, ctor); 3167 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here 3168 return DirectMethodHandle.make(ctor).setVarargs(ctor); 3169 } 3170 3171 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants: 3172 */ 3173 /*non-public*/ 3174 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException { 3175 if (!(type instanceof Class || type instanceof MethodType)) 3176 throw new InternalError("unresolved MemberName"); 3177 MemberName member = new MemberName(refKind, defc, name, type); 3178 MethodHandle mh = LOOKASIDE_TABLE.get(member); 3179 if (mh != null) { 3180 checkSymbolicClass(defc); 3181 return mh; 3182 } 3183 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) { 3184 // Treat MethodHandle.invoke and invokeExact specially. 3185 mh = findVirtualForMH(member.getName(), member.getMethodType()); 3186 if (mh != null) { 3187 return mh; 3188 } 3189 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) { 3190 // Treat signature-polymorphic methods on VarHandle specially. 3191 mh = findVirtualForVH(member.getName(), member.getMethodType()); 3192 if (mh != null) { 3193 return mh; 3194 } 3195 } 3196 MemberName resolved = resolveOrFail(refKind, member); 3197 mh = getDirectMethodForConstant(refKind, defc, resolved); 3198 if (mh instanceof DirectMethodHandle 3199 && canBeCached(refKind, defc, resolved)) { 3200 MemberName key = mh.internalMemberName(); 3201 if (key != null) { 3202 key = key.asNormalOriginal(); 3203 } 3204 if (member.equals(key)) { // better safe than sorry 3205 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh); 3206 } 3207 } 3208 return mh; 3209 } 3210 private 3211 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) { 3212 if (refKind == REF_invokeSpecial) { 3213 return false; 3214 } 3215 if (!Modifier.isPublic(defc.getModifiers()) || 3216 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) || 3217 !member.isPublic() || 3218 member.isCallerSensitive()) { 3219 return false; 3220 } 3221 ClassLoader loader = defc.getClassLoader(); 3222 if (loader != null) { 3223 ClassLoader sysl = ClassLoader.getSystemClassLoader(); 3224 boolean found = false; 3225 while (sysl != null) { 3226 if (loader == sysl) { found = true; break; } 3227 sysl = sysl.getParent(); 3228 } 3229 if (!found) { 3230 return false; 3231 } 3232 } 3233 try { 3234 MemberName resolved2 = publicLookup().resolveOrNull(refKind, 3235 new MemberName(refKind, defc, member.getName(), member.getType())); 3236 if (resolved2 == null) { 3237 return false; 3238 } 3239 checkSecurityManager(defc, resolved2); 3240 } catch (SecurityException ex) { 3241 return false; 3242 } 3243 return true; 3244 } 3245 private 3246 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member) 3247 throws ReflectiveOperationException { 3248 if (MethodHandleNatives.refKindIsField(refKind)) { 3249 return getDirectFieldNoSecurityManager(refKind, defc, member); 3250 } else if (MethodHandleNatives.refKindIsMethod(refKind)) { 3251 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass); 3252 } else if (refKind == REF_newInvokeSpecial) { 3253 return getDirectConstructorNoSecurityManager(defc, member); 3254 } 3255 // oops 3256 throw newIllegalArgumentException("bad MethodHandle constant #"+member); 3257 } 3258 3259 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>(); 3260 } 3261 3262 /** 3263 * Produces a method handle constructing arrays of a desired type, 3264 * as if by the {@code anewarray} bytecode. 3265 * The return type of the method handle will be the array type. 3266 * The type of its sole argument will be {@code int}, which specifies the size of the array. 3267 * 3268 * <p> If the returned method handle is invoked with a negative 3269 * array size, a {@code NegativeArraySizeException} will be thrown. 3270 * 3271 * @param arrayClass an array type 3272 * @return a method handle which can create arrays of the given type 3273 * @throws NullPointerException if the argument is {@code null} 3274 * @throws IllegalArgumentException if {@code arrayClass} is not an array type 3275 * @see java.lang.reflect.Array#newInstance(Class, int) 3276 * @jvms 6.5 {@code anewarray} Instruction 3277 * @since 9 3278 */ 3279 public static 3280 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException { 3281 if (!arrayClass.isArray()) { 3282 throw newIllegalArgumentException("not an array class: " + arrayClass.getName()); 3283 } 3284 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance). 3285 bindTo(arrayClass.getComponentType()); 3286 return ani.asType(ani.type().changeReturnType(arrayClass)); 3287 } 3288 3289 /** 3290 * Produces a method handle returning the length of an array, 3291 * as if by the {@code arraylength} bytecode. 3292 * The type of the method handle will have {@code int} as return type, 3293 * and its sole argument will be the array type. 3294 * 3295 * <p> If the returned method handle is invoked with a {@code null} 3296 * array reference, a {@code NullPointerException} will be thrown. 3297 * 3298 * @param arrayClass an array type 3299 * @return a method handle which can retrieve the length of an array of the given array type 3300 * @throws NullPointerException if the argument is {@code null} 3301 * @throws IllegalArgumentException if arrayClass is not an array type 3302 * @jvms 6.5 {@code arraylength} Instruction 3303 * @since 9 3304 */ 3305 public static 3306 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException { 3307 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH); 3308 } 3309 3310 /** 3311 * Produces a method handle giving read access to elements of an array, 3312 * as if by the {@code aaload} bytecode. 3313 * The type of the method handle will have a return type of the array's 3314 * element type. Its first argument will be the array type, 3315 * and the second will be {@code int}. 3316 * 3317 * <p> When the returned method handle is invoked, 3318 * the array reference and array index are checked. 3319 * A {@code NullPointerException} will be thrown if the array reference 3320 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 3321 * thrown if the index is negative or if it is greater than or equal to 3322 * the length of the array. 3323 * 3324 * @param arrayClass an array type 3325 * @return a method handle which can load values from the given array type 3326 * @throws NullPointerException if the argument is null 3327 * @throws IllegalArgumentException if arrayClass is not an array type 3328 * @jvms 6.5 {@code aaload} Instruction 3329 */ 3330 public static 3331 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException { 3332 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET); 3333 } 3334 3335 /** 3336 * Produces a method handle giving write access to elements of an array, 3337 * as if by the {@code astore} bytecode. 3338 * The type of the method handle will have a void return type. 3339 * Its last argument will be the array's element type. 3340 * The first and second arguments will be the array type and int. 3341 * 3342 * <p> When the returned method handle is invoked, 3343 * the array reference and array index are checked. 3344 * A {@code NullPointerException} will be thrown if the array reference 3345 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 3346 * thrown if the index is negative or if it is greater than or equal to 3347 * the length of the array. 3348 * 3349 * @param arrayClass the class of an array 3350 * @return a method handle which can store values into the array type 3351 * @throws NullPointerException if the argument is null 3352 * @throws IllegalArgumentException if arrayClass is not an array type 3353 * @jvms 6.5 {@code aastore} Instruction 3354 */ 3355 public static 3356 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException { 3357 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET); 3358 } 3359 3360 /** 3361 * Produces a VarHandle giving access to elements of an array of type 3362 * {@code arrayClass}. The VarHandle's variable type is the component type 3363 * of {@code arrayClass} and the list of coordinate types is 3364 * {@code (arrayClass, int)}, where the {@code int} coordinate type 3365 * corresponds to an argument that is an index into an array. 3366 * <p> 3367 * Certain access modes of the returned VarHandle are unsupported under 3368 * the following conditions: 3369 * <ul> 3370 * <li>if the component type is anything other than {@code byte}, 3371 * {@code short}, {@code char}, {@code int}, {@code long}, 3372 * {@code float}, or {@code double} then numeric atomic update access 3373 * modes are unsupported. 3374 * <li>if the field type is anything other than {@code boolean}, 3375 * {@code byte}, {@code short}, {@code char}, {@code int} or 3376 * {@code long} then bitwise atomic update access modes are 3377 * unsupported. 3378 * </ul> 3379 * <p> 3380 * If the component type is {@code float} or {@code double} then numeric 3381 * and atomic update access modes compare values using their bitwise 3382 * representation (see {@link Float#floatToRawIntBits} and 3383 * {@link Double#doubleToRawLongBits}, respectively). 3384 * 3385 * <p> When the returned {@code VarHandle} is invoked, 3386 * the array reference and array index are checked. 3387 * A {@code NullPointerException} will be thrown if the array reference 3388 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 3389 * thrown if the index is negative or if it is greater than or equal to 3390 * the length of the array. 3391 * 3392 * @apiNote 3393 * Bitwise comparison of {@code float} values or {@code double} values, 3394 * as performed by the numeric and atomic update access modes, differ 3395 * from the primitive {@code ==} operator and the {@link Float#equals} 3396 * and {@link Double#equals} methods, specifically with respect to 3397 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3398 * Care should be taken when performing a compare and set or a compare 3399 * and exchange operation with such values since the operation may 3400 * unexpectedly fail. 3401 * There are many possible NaN values that are considered to be 3402 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3403 * provided by Java can distinguish between them. Operation failure can 3404 * occur if the expected or witness value is a NaN value and it is 3405 * transformed (perhaps in a platform specific manner) into another NaN 3406 * value, and thus has a different bitwise representation (see 3407 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3408 * details). 3409 * The values {@code -0.0} and {@code +0.0} have different bitwise 3410 * representations but are considered equal when using the primitive 3411 * {@code ==} operator. Operation failure can occur if, for example, a 3412 * numeric algorithm computes an expected value to be say {@code -0.0} 3413 * and previously computed the witness value to be say {@code +0.0}. 3414 * @param arrayClass the class of an array, of type {@code T[]} 3415 * @return a VarHandle giving access to elements of an array 3416 * @throws NullPointerException if the arrayClass is null 3417 * @throws IllegalArgumentException if arrayClass is not an array type 3418 * @since 9 3419 */ 3420 public static 3421 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException { 3422 return VarHandles.makeArrayElementHandle(arrayClass); 3423 } 3424 3425 /** 3426 * Produces a VarHandle giving access to elements of a {@code byte[]} array 3427 * viewed as if it were a different primitive array type, such as 3428 * {@code int[]} or {@code long[]}. 3429 * The VarHandle's variable type is the component type of 3430 * {@code viewArrayClass} and the list of coordinate types is 3431 * {@code (byte[], int)}, where the {@code int} coordinate type 3432 * corresponds to an argument that is an index into a {@code byte[]} array. 3433 * The returned VarHandle accesses bytes at an index in a {@code byte[]} 3434 * array, composing bytes to or from a value of the component type of 3435 * {@code viewArrayClass} according to the given endianness. 3436 * <p> 3437 * The supported component types (variables types) are {@code short}, 3438 * {@code char}, {@code int}, {@code long}, {@code float} and 3439 * {@code double}. 3440 * <p> 3441 * Access of bytes at a given index will result in an 3442 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 3443 * or greater than the {@code byte[]} array length minus the size (in bytes) 3444 * of {@code T}. 3445 * <p> 3446 * Access of bytes at an index may be aligned or misaligned for {@code T}, 3447 * with respect to the underlying memory address, {@code A} say, associated 3448 * with the array and index. 3449 * If access is misaligned then access for anything other than the 3450 * {@code get} and {@code set} access modes will result in an 3451 * {@code IllegalStateException}. In such cases atomic access is only 3452 * guaranteed with respect to the largest power of two that divides the GCD 3453 * of {@code A} and the size (in bytes) of {@code T}. 3454 * If access is aligned then following access modes are supported and are 3455 * guaranteed to support atomic access: 3456 * <ul> 3457 * <li>read write access modes for all {@code T}, with the exception of 3458 * access modes {@code get} and {@code set} for {@code long} and 3459 * {@code double} on 32-bit platforms. 3460 * <li>atomic update access modes for {@code int}, {@code long}, 3461 * {@code float} or {@code double}. 3462 * (Future major platform releases of the JDK may support additional 3463 * types for certain currently unsupported access modes.) 3464 * <li>numeric atomic update access modes for {@code int} and {@code long}. 3465 * (Future major platform releases of the JDK may support additional 3466 * numeric types for certain currently unsupported access modes.) 3467 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 3468 * (Future major platform releases of the JDK may support additional 3469 * numeric types for certain currently unsupported access modes.) 3470 * </ul> 3471 * <p> 3472 * Misaligned access, and therefore atomicity guarantees, may be determined 3473 * for {@code byte[]} arrays without operating on a specific array. Given 3474 * an {@code index}, {@code T} and it's corresponding boxed type, 3475 * {@code T_BOX}, misalignment may be determined as follows: 3476 * <pre>{@code 3477 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 3478 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]). 3479 * alignmentOffset(0, sizeOfT); 3480 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT; 3481 * boolean isMisaligned = misalignedAtIndex != 0; 3482 * }</pre> 3483 * <p> 3484 * If the variable type is {@code float} or {@code double} then atomic 3485 * update access modes compare values using their bitwise representation 3486 * (see {@link Float#floatToRawIntBits} and 3487 * {@link Double#doubleToRawLongBits}, respectively). 3488 * @param viewArrayClass the view array class, with a component type of 3489 * type {@code T} 3490 * @param byteOrder the endianness of the view array elements, as 3491 * stored in the underlying {@code byte} array 3492 * @return a VarHandle giving access to elements of a {@code byte[]} array 3493 * viewed as if elements corresponding to the components type of the view 3494 * array class 3495 * @throws NullPointerException if viewArrayClass or byteOrder is null 3496 * @throws IllegalArgumentException if viewArrayClass is not an array type 3497 * @throws UnsupportedOperationException if the component type of 3498 * viewArrayClass is not supported as a variable type 3499 * @since 9 3500 */ 3501 public static 3502 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass, 3503 ByteOrder byteOrder) throws IllegalArgumentException { 3504 Objects.requireNonNull(byteOrder); 3505 return VarHandles.byteArrayViewHandle(viewArrayClass, 3506 byteOrder == ByteOrder.BIG_ENDIAN); 3507 } 3508 3509 /** 3510 * Produces a VarHandle giving access to elements of a {@code ByteBuffer} 3511 * viewed as if it were an array of elements of a different primitive 3512 * component type to that of {@code byte}, such as {@code int[]} or 3513 * {@code long[]}. 3514 * The VarHandle's variable type is the component type of 3515 * {@code viewArrayClass} and the list of coordinate types is 3516 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type 3517 * corresponds to an argument that is an index into a {@code byte[]} array. 3518 * The returned VarHandle accesses bytes at an index in a 3519 * {@code ByteBuffer}, composing bytes to or from a value of the component 3520 * type of {@code viewArrayClass} according to the given endianness. 3521 * <p> 3522 * The supported component types (variables types) are {@code short}, 3523 * {@code char}, {@code int}, {@code long}, {@code float} and 3524 * {@code double}. 3525 * <p> 3526 * Access will result in a {@code ReadOnlyBufferException} for anything 3527 * other than the read access modes if the {@code ByteBuffer} is read-only. 3528 * <p> 3529 * Access of bytes at a given index will result in an 3530 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 3531 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of 3532 * {@code T}. 3533 * <p> 3534 * Access of bytes at an index may be aligned or misaligned for {@code T}, 3535 * with respect to the underlying memory address, {@code A} say, associated 3536 * with the {@code ByteBuffer} and index. 3537 * If access is misaligned then access for anything other than the 3538 * {@code get} and {@code set} access modes will result in an 3539 * {@code IllegalStateException}. In such cases atomic access is only 3540 * guaranteed with respect to the largest power of two that divides the GCD 3541 * of {@code A} and the size (in bytes) of {@code T}. 3542 * If access is aligned then following access modes are supported and are 3543 * guaranteed to support atomic access: 3544 * <ul> 3545 * <li>read write access modes for all {@code T}, with the exception of 3546 * access modes {@code get} and {@code set} for {@code long} and 3547 * {@code double} on 32-bit platforms. 3548 * <li>atomic update access modes for {@code int}, {@code long}, 3549 * {@code float} or {@code double}. 3550 * (Future major platform releases of the JDK may support additional 3551 * types for certain currently unsupported access modes.) 3552 * <li>numeric atomic update access modes for {@code int} and {@code long}. 3553 * (Future major platform releases of the JDK may support additional 3554 * numeric types for certain currently unsupported access modes.) 3555 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 3556 * (Future major platform releases of the JDK may support additional 3557 * numeric types for certain currently unsupported access modes.) 3558 * </ul> 3559 * <p> 3560 * Misaligned access, and therefore atomicity guarantees, may be determined 3561 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an 3562 * {@code index}, {@code T} and it's corresponding boxed type, 3563 * {@code T_BOX}, as follows: 3564 * <pre>{@code 3565 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 3566 * ByteBuffer bb = ... 3567 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT); 3568 * boolean isMisaligned = misalignedAtIndex != 0; 3569 * }</pre> 3570 * <p> 3571 * If the variable type is {@code float} or {@code double} then atomic 3572 * update access modes compare values using their bitwise representation 3573 * (see {@link Float#floatToRawIntBits} and 3574 * {@link Double#doubleToRawLongBits}, respectively). 3575 * @param viewArrayClass the view array class, with a component type of 3576 * type {@code T} 3577 * @param byteOrder the endianness of the view array elements, as 3578 * stored in the underlying {@code ByteBuffer} (Note this overrides the 3579 * endianness of a {@code ByteBuffer}) 3580 * @return a VarHandle giving access to elements of a {@code ByteBuffer} 3581 * viewed as if elements corresponding to the components type of the view 3582 * array class 3583 * @throws NullPointerException if viewArrayClass or byteOrder is null 3584 * @throws IllegalArgumentException if viewArrayClass is not an array type 3585 * @throws UnsupportedOperationException if the component type of 3586 * viewArrayClass is not supported as a variable type 3587 * @since 9 3588 */ 3589 public static 3590 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass, 3591 ByteOrder byteOrder) throws IllegalArgumentException { 3592 Objects.requireNonNull(byteOrder); 3593 return VarHandles.makeByteBufferViewHandle(viewArrayClass, 3594 byteOrder == ByteOrder.BIG_ENDIAN); 3595 } 3596 3597 3598 /// method handle invocation (reflective style) 3599 3600 /** 3601 * Produces a method handle which will invoke any method handle of the 3602 * given {@code type}, with a given number of trailing arguments replaced by 3603 * a single trailing {@code Object[]} array. 3604 * The resulting invoker will be a method handle with the following 3605 * arguments: 3606 * <ul> 3607 * <li>a single {@code MethodHandle} target 3608 * <li>zero or more leading values (counted by {@code leadingArgCount}) 3609 * <li>an {@code Object[]} array containing trailing arguments 3610 * </ul> 3611 * <p> 3612 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with 3613 * the indicated {@code type}. 3614 * That is, if the target is exactly of the given {@code type}, it will behave 3615 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType} 3616 * is used to convert the target to the required {@code type}. 3617 * <p> 3618 * The type of the returned invoker will not be the given {@code type}, but rather 3619 * will have all parameters except the first {@code leadingArgCount} 3620 * replaced by a single array of type {@code Object[]}, which will be 3621 * the final parameter. 3622 * <p> 3623 * Before invoking its target, the invoker will spread the final array, apply 3624 * reference casts as necessary, and unbox and widen primitive arguments. 3625 * If, when the invoker is called, the supplied array argument does 3626 * not have the correct number of elements, the invoker will throw 3627 * an {@link IllegalArgumentException} instead of invoking the target. 3628 * <p> 3629 * This method is equivalent to the following code (though it may be more efficient): 3630 * <blockquote><pre>{@code 3631 MethodHandle invoker = MethodHandles.invoker(type); 3632 int spreadArgCount = type.parameterCount() - leadingArgCount; 3633 invoker = invoker.asSpreader(Object[].class, spreadArgCount); 3634 return invoker; 3635 * }</pre></blockquote> 3636 * This method throws no reflective or security exceptions. 3637 * @param type the desired target type 3638 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target 3639 * @return a method handle suitable for invoking any method handle of the given type 3640 * @throws NullPointerException if {@code type} is null 3641 * @throws IllegalArgumentException if {@code leadingArgCount} is not in 3642 * the range from 0 to {@code type.parameterCount()} inclusive, 3643 * or if the resulting method handle's type would have 3644 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3645 */ 3646 public static 3647 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) { 3648 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) 3649 throw newIllegalArgumentException("bad argument count", leadingArgCount); 3650 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount); 3651 return type.invokers().spreadInvoker(leadingArgCount); 3652 } 3653 3654 /** 3655 * Produces a special <em>invoker method handle</em> which can be used to 3656 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. 3657 * The resulting invoker will have a type which is 3658 * exactly equal to the desired type, except that it will accept 3659 * an additional leading argument of type {@code MethodHandle}. 3660 * <p> 3661 * This method is equivalent to the following code (though it may be more efficient): 3662 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)} 3663 * 3664 * <p style="font-size:smaller;"> 3665 * <em>Discussion:</em> 3666 * Invoker method handles can be useful when working with variable method handles 3667 * of unknown types. 3668 * For example, to emulate an {@code invokeExact} call to a variable method 3669 * handle {@code M}, extract its type {@code T}, 3670 * look up the invoker method {@code X} for {@code T}, 3671 * and call the invoker method, as {@code X.invoke(T, A...)}. 3672 * (It would not work to call {@code X.invokeExact}, since the type {@code T} 3673 * is unknown.) 3674 * If spreading, collecting, or other argument transformations are required, 3675 * they can be applied once to the invoker {@code X} and reused on many {@code M} 3676 * method handle values, as long as they are compatible with the type of {@code X}. 3677 * <p style="font-size:smaller;"> 3678 * <em>(Note: The invoker method is not available via the Core Reflection API. 3679 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 3680 * on the declared {@code invokeExact} or {@code invoke} method will raise an 3681 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 3682 * <p> 3683 * This method throws no reflective or security exceptions. 3684 * @param type the desired target type 3685 * @return a method handle suitable for invoking any method handle of the given type 3686 * @throws IllegalArgumentException if the resulting method handle's type would have 3687 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3688 */ 3689 public static 3690 MethodHandle exactInvoker(MethodType type) { 3691 return type.invokers().exactInvoker(); 3692 } 3693 3694 /** 3695 * Produces a special <em>invoker method handle</em> which can be used to 3696 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}. 3697 * The resulting invoker will have a type which is 3698 * exactly equal to the desired type, except that it will accept 3699 * an additional leading argument of type {@code MethodHandle}. 3700 * <p> 3701 * Before invoking its target, if the target differs from the expected type, 3702 * the invoker will apply reference casts as 3703 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}. 3704 * Similarly, the return value will be converted as necessary. 3705 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle}, 3706 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}. 3707 * <p> 3708 * This method is equivalent to the following code (though it may be more efficient): 3709 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)} 3710 * <p style="font-size:smaller;"> 3711 * <em>Discussion:</em> 3712 * A {@linkplain MethodType#genericMethodType general method type} is one which 3713 * mentions only {@code Object} arguments and return values. 3714 * An invoker for such a type is capable of calling any method handle 3715 * of the same arity as the general type. 3716 * <p style="font-size:smaller;"> 3717 * <em>(Note: The invoker method is not available via the Core Reflection API. 3718 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 3719 * on the declared {@code invokeExact} or {@code invoke} method will raise an 3720 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 3721 * <p> 3722 * This method throws no reflective or security exceptions. 3723 * @param type the desired target type 3724 * @return a method handle suitable for invoking any method handle convertible to the given type 3725 * @throws IllegalArgumentException if the resulting method handle's type would have 3726 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3727 */ 3728 public static 3729 MethodHandle invoker(MethodType type) { 3730 return type.invokers().genericInvoker(); 3731 } 3732 3733 /** 3734 * Produces a special <em>invoker method handle</em> which can be used to 3735 * invoke a signature-polymorphic access mode method on any VarHandle whose 3736 * associated access mode type is compatible with the given type. 3737 * The resulting invoker will have a type which is exactly equal to the 3738 * desired given type, except that it will accept an additional leading 3739 * argument of type {@code VarHandle}. 3740 * 3741 * @param accessMode the VarHandle access mode 3742 * @param type the desired target type 3743 * @return a method handle suitable for invoking an access mode method of 3744 * any VarHandle whose access mode type is of the given type. 3745 * @since 9 3746 */ 3747 static public 3748 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) { 3749 return type.invokers().varHandleMethodExactInvoker(accessMode); 3750 } 3751 3752 /** 3753 * Produces a special <em>invoker method handle</em> which can be used to 3754 * invoke a signature-polymorphic access mode method on any VarHandle whose 3755 * associated access mode type is compatible with the given type. 3756 * The resulting invoker will have a type which is exactly equal to the 3757 * desired given type, except that it will accept an additional leading 3758 * argument of type {@code VarHandle}. 3759 * <p> 3760 * Before invoking its target, if the access mode type differs from the 3761 * desired given type, the invoker will apply reference casts as necessary 3762 * and box, unbox, or widen primitive values, as if by 3763 * {@link MethodHandle#asType asType}. Similarly, the return value will be 3764 * converted as necessary. 3765 * <p> 3766 * This method is equivalent to the following code (though it may be more 3767 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)} 3768 * 3769 * @param accessMode the VarHandle access mode 3770 * @param type the desired target type 3771 * @return a method handle suitable for invoking an access mode method of 3772 * any VarHandle whose access mode type is convertible to the given 3773 * type. 3774 * @since 9 3775 */ 3776 static public 3777 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) { 3778 return type.invokers().varHandleMethodInvoker(accessMode); 3779 } 3780 3781 static /*non-public*/ 3782 MethodHandle basicInvoker(MethodType type) { 3783 return type.invokers().basicInvoker(); 3784 } 3785 3786 /// method handle modification (creation from other method handles) 3787 3788 /** 3789 * Produces a method handle which adapts the type of the 3790 * given method handle to a new type by pairwise argument and return type conversion. 3791 * The original type and new type must have the same number of arguments. 3792 * The resulting method handle is guaranteed to report a type 3793 * which is equal to the desired new type. 3794 * <p> 3795 * If the original type and new type are equal, returns target. 3796 * <p> 3797 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType}, 3798 * and some additional conversions are also applied if those conversions fail. 3799 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied 3800 * if possible, before or instead of any conversions done by {@code asType}: 3801 * <ul> 3802 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type, 3803 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast. 3804 * (This treatment of interfaces follows the usage of the bytecode verifier.) 3805 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive, 3806 * the boolean is converted to a byte value, 1 for true, 0 for false. 3807 * (This treatment follows the usage of the bytecode verifier.) 3808 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive, 3809 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5), 3810 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}. 3811 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean, 3812 * then a Java casting conversion (JLS 5.5) is applied. 3813 * (Specifically, <em>T0</em> will convert to <em>T1</em> by 3814 * widening and/or narrowing.) 3815 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing 3816 * conversion will be applied at runtime, possibly followed 3817 * by a Java casting conversion (JLS 5.5) on the primitive value, 3818 * possibly followed by a conversion from byte to boolean by testing 3819 * the low-order bit. 3820 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, 3821 * and if the reference is null at runtime, a zero value is introduced. 3822 * </ul> 3823 * @param target the method handle to invoke after arguments are retyped 3824 * @param newType the expected type of the new method handle 3825 * @return a method handle which delegates to the target after performing 3826 * any necessary argument conversions, and arranges for any 3827 * necessary return value conversions 3828 * @throws NullPointerException if either argument is null 3829 * @throws WrongMethodTypeException if the conversion cannot be made 3830 * @see MethodHandle#asType 3831 */ 3832 public static 3833 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) { 3834 explicitCastArgumentsChecks(target, newType); 3835 // use the asTypeCache when possible: 3836 MethodType oldType = target.type(); 3837 if (oldType == newType) return target; 3838 if (oldType.explicitCastEquivalentToAsType(newType)) { 3839 return target.asFixedArity().asType(newType); 3840 } 3841 return MethodHandleImpl.makePairwiseConvert(target, newType, false); 3842 } 3843 3844 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) { 3845 if (target.type().parameterCount() != newType.parameterCount()) { 3846 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType); 3847 } 3848 } 3849 3850 /** 3851 * Produces a method handle which adapts the calling sequence of the 3852 * given method handle to a new type, by reordering the arguments. 3853 * The resulting method handle is guaranteed to report a type 3854 * which is equal to the desired new type. 3855 * <p> 3856 * The given array controls the reordering. 3857 * Call {@code #I} the number of incoming parameters (the value 3858 * {@code newType.parameterCount()}, and call {@code #O} the number 3859 * of outgoing parameters (the value {@code target.type().parameterCount()}). 3860 * Then the length of the reordering array must be {@code #O}, 3861 * and each element must be a non-negative number less than {@code #I}. 3862 * For every {@code N} less than {@code #O}, the {@code N}-th 3863 * outgoing argument will be taken from the {@code I}-th incoming 3864 * argument, where {@code I} is {@code reorder[N]}. 3865 * <p> 3866 * No argument or return value conversions are applied. 3867 * The type of each incoming argument, as determined by {@code newType}, 3868 * must be identical to the type of the corresponding outgoing parameter 3869 * or parameters in the target method handle. 3870 * The return type of {@code newType} must be identical to the return 3871 * type of the original target. 3872 * <p> 3873 * The reordering array need not specify an actual permutation. 3874 * An incoming argument will be duplicated if its index appears 3875 * more than once in the array, and an incoming argument will be dropped 3876 * if its index does not appear in the array. 3877 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments}, 3878 * incoming arguments which are not mentioned in the reordering array 3879 * may be of any type, as determined only by {@code newType}. 3880 * <blockquote><pre>{@code 3881 import static java.lang.invoke.MethodHandles.*; 3882 import static java.lang.invoke.MethodType.*; 3883 ... 3884 MethodType intfn1 = methodType(int.class, int.class); 3885 MethodType intfn2 = methodType(int.class, int.class, int.class); 3886 MethodHandle sub = ... (int x, int y) -> (x-y) ...; 3887 assert(sub.type().equals(intfn2)); 3888 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1); 3889 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0); 3890 assert((int)rsub.invokeExact(1, 100) == 99); 3891 MethodHandle add = ... (int x, int y) -> (x+y) ...; 3892 assert(add.type().equals(intfn2)); 3893 MethodHandle twice = permuteArguments(add, intfn1, 0, 0); 3894 assert(twice.type().equals(intfn1)); 3895 assert((int)twice.invokeExact(21) == 42); 3896 * }</pre></blockquote> 3897 * <p> 3898 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 3899 * variable-arity method handle}, even if the original target method handle was. 3900 * @param target the method handle to invoke after arguments are reordered 3901 * @param newType the expected type of the new method handle 3902 * @param reorder an index array which controls the reordering 3903 * @return a method handle which delegates to the target after it 3904 * drops unused arguments and moves and/or duplicates the other arguments 3905 * @throws NullPointerException if any argument is null 3906 * @throws IllegalArgumentException if the index array length is not equal to 3907 * the arity of the target, or if any index array element 3908 * not a valid index for a parameter of {@code newType}, 3909 * or if two corresponding parameter types in 3910 * {@code target.type()} and {@code newType} are not identical, 3911 */ 3912 public static 3913 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) { 3914 reorder = reorder.clone(); // get a private copy 3915 MethodType oldType = target.type(); 3916 permuteArgumentChecks(reorder, newType, oldType); 3917 // first detect dropped arguments and handle them separately 3918 int[] originalReorder = reorder; 3919 BoundMethodHandle result = target.rebind(); 3920 LambdaForm form = result.form; 3921 int newArity = newType.parameterCount(); 3922 // Normalize the reordering into a real permutation, 3923 // by removing duplicates and adding dropped elements. 3924 // This somewhat improves lambda form caching, as well 3925 // as simplifying the transform by breaking it up into steps. 3926 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) { 3927 if (ddIdx > 0) { 3928 // We found a duplicated entry at reorder[ddIdx]. 3929 // Example: (x,y,z)->asList(x,y,z) 3930 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1) 3931 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0) 3932 // The starred element corresponds to the argument 3933 // deleted by the dupArgumentForm transform. 3934 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos]; 3935 boolean killFirst = false; 3936 for (int val; (val = reorder[--dstPos]) != dupVal; ) { 3937 // Set killFirst if the dup is larger than an intervening position. 3938 // This will remove at least one inversion from the permutation. 3939 if (dupVal > val) killFirst = true; 3940 } 3941 if (!killFirst) { 3942 srcPos = dstPos; 3943 dstPos = ddIdx; 3944 } 3945 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos); 3946 assert (reorder[srcPos] == reorder[dstPos]); 3947 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1); 3948 // contract the reordering by removing the element at dstPos 3949 int tailPos = dstPos + 1; 3950 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos); 3951 reorder = Arrays.copyOf(reorder, reorder.length - 1); 3952 } else { 3953 int dropVal = ~ddIdx, insPos = 0; 3954 while (insPos < reorder.length && reorder[insPos] < dropVal) { 3955 // Find first element of reorder larger than dropVal. 3956 // This is where we will insert the dropVal. 3957 insPos += 1; 3958 } 3959 Class<?> ptype = newType.parameterType(dropVal); 3960 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype)); 3961 oldType = oldType.insertParameterTypes(insPos, ptype); 3962 // expand the reordering by inserting an element at insPos 3963 int tailPos = insPos + 1; 3964 reorder = Arrays.copyOf(reorder, reorder.length + 1); 3965 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos); 3966 reorder[insPos] = dropVal; 3967 } 3968 assert (permuteArgumentChecks(reorder, newType, oldType)); 3969 } 3970 assert (reorder.length == newArity); // a perfect permutation 3971 // Note: This may cache too many distinct LFs. Consider backing off to varargs code. 3972 form = form.editor().permuteArgumentsForm(1, reorder); 3973 if (newType == result.type() && form == result.internalForm()) 3974 return result; 3975 return result.copyWith(newType, form); 3976 } 3977 3978 /** 3979 * Return an indication of any duplicate or omission in reorder. 3980 * If the reorder contains a duplicate entry, return the index of the second occurrence. 3981 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder. 3982 * Otherwise, return zero. 3983 * If an element not in [0..newArity-1] is encountered, return reorder.length. 3984 */ 3985 private static int findFirstDupOrDrop(int[] reorder, int newArity) { 3986 final int BIT_LIMIT = 63; // max number of bits in bit mask 3987 if (newArity < BIT_LIMIT) { 3988 long mask = 0; 3989 for (int i = 0; i < reorder.length; i++) { 3990 int arg = reorder[i]; 3991 if (arg >= newArity) { 3992 return reorder.length; 3993 } 3994 long bit = 1L << arg; 3995 if ((mask & bit) != 0) { 3996 return i; // >0 indicates a dup 3997 } 3998 mask |= bit; 3999 } 4000 if (mask == (1L << newArity) - 1) { 4001 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity); 4002 return 0; 4003 } 4004 // find first zero 4005 long zeroBit = Long.lowestOneBit(~mask); 4006 int zeroPos = Long.numberOfTrailingZeros(zeroBit); 4007 assert(zeroPos <= newArity); 4008 if (zeroPos == newArity) { 4009 return 0; 4010 } 4011 return ~zeroPos; 4012 } else { 4013 // same algorithm, different bit set 4014 BitSet mask = new BitSet(newArity); 4015 for (int i = 0; i < reorder.length; i++) { 4016 int arg = reorder[i]; 4017 if (arg >= newArity) { 4018 return reorder.length; 4019 } 4020 if (mask.get(arg)) { 4021 return i; // >0 indicates a dup 4022 } 4023 mask.set(arg); 4024 } 4025 int zeroPos = mask.nextClearBit(0); 4026 assert(zeroPos <= newArity); 4027 if (zeroPos == newArity) { 4028 return 0; 4029 } 4030 return ~zeroPos; 4031 } 4032 } 4033 4034 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) { 4035 if (newType.returnType() != oldType.returnType()) 4036 throw newIllegalArgumentException("return types do not match", 4037 oldType, newType); 4038 if (reorder.length == oldType.parameterCount()) { 4039 int limit = newType.parameterCount(); 4040 boolean bad = false; 4041 for (int j = 0; j < reorder.length; j++) { 4042 int i = reorder[j]; 4043 if (i < 0 || i >= limit) { 4044 bad = true; break; 4045 } 4046 Class<?> src = newType.parameterType(i); 4047 Class<?> dst = oldType.parameterType(j); 4048 if (src != dst) 4049 throw newIllegalArgumentException("parameter types do not match after reorder", 4050 oldType, newType); 4051 } 4052 if (!bad) return true; 4053 } 4054 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder)); 4055 } 4056 4057 /** 4058 * Produces a method handle of the requested return type which returns the given 4059 * constant value every time it is invoked. 4060 * <p> 4061 * Before the method handle is returned, the passed-in value is converted to the requested type. 4062 * If the requested type is primitive, widening primitive conversions are attempted, 4063 * else reference conversions are attempted. 4064 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}. 4065 * @param type the return type of the desired method handle 4066 * @param value the value to return 4067 * @return a method handle of the given return type and no arguments, which always returns the given value 4068 * @throws NullPointerException if the {@code type} argument is null 4069 * @throws ClassCastException if the value cannot be converted to the required return type 4070 * @throws IllegalArgumentException if the given type is {@code void.class} 4071 */ 4072 public static 4073 MethodHandle constant(Class<?> type, Object value) { 4074 if (type.isPrimitive()) { 4075 if (type == void.class) 4076 throw newIllegalArgumentException("void type"); 4077 Wrapper w = Wrapper.forPrimitiveType(type); 4078 value = w.convert(value, type); 4079 if (w.zero().equals(value)) 4080 return zero(w, type); 4081 return insertArguments(identity(type), 0, value); 4082 } else { 4083 if (value == null) 4084 return zero(Wrapper.OBJECT, type); 4085 return identity(type).bindTo(value); 4086 } 4087 } 4088 4089 /** 4090 * Produces a method handle which returns its sole argument when invoked. 4091 * @param type the type of the sole parameter and return value of the desired method handle 4092 * @return a unary method handle which accepts and returns the given type 4093 * @throws NullPointerException if the argument is null 4094 * @throws IllegalArgumentException if the given type is {@code void.class} 4095 */ 4096 public static 4097 MethodHandle identity(Class<?> type) { 4098 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT); 4099 int pos = btw.ordinal(); 4100 MethodHandle ident = IDENTITY_MHS[pos]; 4101 if (ident == null) { 4102 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType())); 4103 } 4104 if (ident.type().returnType() == type) 4105 return ident; 4106 // something like identity(Foo.class); do not bother to intern these 4107 assert (btw == Wrapper.OBJECT); 4108 return makeIdentity(type); 4109 } 4110 4111 /** 4112 * Produces a constant method handle of the requested return type which 4113 * returns the default value for that type every time it is invoked. 4114 * The resulting constant method handle will have no side effects. 4115 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}. 4116 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))}, 4117 * since {@code explicitCastArguments} converts {@code null} to default values. 4118 * @param type the expected return type of the desired method handle 4119 * @return a constant method handle that takes no arguments 4120 * and returns the default value of the given type (or void, if the type is void) 4121 * @throws NullPointerException if the argument is null 4122 * @see MethodHandles#constant 4123 * @see MethodHandles#empty 4124 * @see MethodHandles#explicitCastArguments 4125 * @since 9 4126 */ 4127 public static MethodHandle zero(Class<?> type) { 4128 Objects.requireNonNull(type); 4129 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type); 4130 } 4131 4132 private static MethodHandle identityOrVoid(Class<?> type) { 4133 return type == void.class ? zero(type) : identity(type); 4134 } 4135 4136 /** 4137 * Produces a method handle of the requested type which ignores any arguments, does nothing, 4138 * and returns a suitable default depending on the return type. 4139 * That is, it returns a zero primitive value, a {@code null}, or {@code void}. 4140 * <p>The returned method handle is equivalent to 4141 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}. 4142 * 4143 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as 4144 * {@code guardWithTest(pred, target, empty(target.type())}. 4145 * @param type the type of the desired method handle 4146 * @return a constant method handle of the given type, which returns a default value of the given return type 4147 * @throws NullPointerException if the argument is null 4148 * @see MethodHandles#zero 4149 * @see MethodHandles#constant 4150 * @since 9 4151 */ 4152 public static MethodHandle empty(MethodType type) { 4153 Objects.requireNonNull(type); 4154 return dropArguments(zero(type.returnType()), 0, type.parameterList()); 4155 } 4156 4157 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT]; 4158 private static MethodHandle makeIdentity(Class<?> ptype) { 4159 MethodType mtype = methodType(ptype, ptype); 4160 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype)); 4161 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY); 4162 } 4163 4164 private static MethodHandle zero(Wrapper btw, Class<?> rtype) { 4165 int pos = btw.ordinal(); 4166 MethodHandle zero = ZERO_MHS[pos]; 4167 if (zero == null) { 4168 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType())); 4169 } 4170 if (zero.type().returnType() == rtype) 4171 return zero; 4172 assert(btw == Wrapper.OBJECT); 4173 return makeZero(rtype); 4174 } 4175 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT]; 4176 private static MethodHandle makeZero(Class<?> rtype) { 4177 MethodType mtype = methodType(rtype); 4178 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype)); 4179 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO); 4180 } 4181 4182 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) { 4183 // Simulate a CAS, to avoid racy duplication of results. 4184 MethodHandle prev = cache[pos]; 4185 if (prev != null) return prev; 4186 return cache[pos] = value; 4187 } 4188 4189 /** 4190 * Provides a target method handle with one or more <em>bound arguments</em> 4191 * in advance of the method handle's invocation. 4192 * The formal parameters to the target corresponding to the bound 4193 * arguments are called <em>bound parameters</em>. 4194 * Returns a new method handle which saves away the bound arguments. 4195 * When it is invoked, it receives arguments for any non-bound parameters, 4196 * binds the saved arguments to their corresponding parameters, 4197 * and calls the original target. 4198 * <p> 4199 * The type of the new method handle will drop the types for the bound 4200 * parameters from the original target type, since the new method handle 4201 * will no longer require those arguments to be supplied by its callers. 4202 * <p> 4203 * Each given argument object must match the corresponding bound parameter type. 4204 * If a bound parameter type is a primitive, the argument object 4205 * must be a wrapper, and will be unboxed to produce the primitive value. 4206 * <p> 4207 * The {@code pos} argument selects which parameters are to be bound. 4208 * It may range between zero and <i>N-L</i> (inclusively), 4209 * where <i>N</i> is the arity of the target method handle 4210 * and <i>L</i> is the length of the values array. 4211 * <p> 4212 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4213 * variable-arity method handle}, even if the original target method handle was. 4214 * @param target the method handle to invoke after the argument is inserted 4215 * @param pos where to insert the argument (zero for the first) 4216 * @param values the series of arguments to insert 4217 * @return a method handle which inserts an additional argument, 4218 * before calling the original method handle 4219 * @throws NullPointerException if the target or the {@code values} array is null 4220 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than 4221 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L} 4222 * is the length of the values array. 4223 * @throws ClassCastException if an argument does not match the corresponding bound parameter 4224 * type. 4225 * @see MethodHandle#bindTo 4226 */ 4227 public static 4228 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) { 4229 int insCount = values.length; 4230 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos); 4231 if (insCount == 0) return target; 4232 BoundMethodHandle result = target.rebind(); 4233 for (int i = 0; i < insCount; i++) { 4234 Object value = values[i]; 4235 Class<?> ptype = ptypes[pos+i]; 4236 if (ptype.isPrimitive()) { 4237 result = insertArgumentPrimitive(result, pos, ptype, value); 4238 } else { 4239 value = ptype.cast(value); // throw CCE if needed 4240 result = result.bindArgumentL(pos, value); 4241 } 4242 } 4243 return result; 4244 } 4245 4246 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos, 4247 Class<?> ptype, Object value) { 4248 Wrapper w = Wrapper.forPrimitiveType(ptype); 4249 // perform unboxing and/or primitive conversion 4250 value = w.convert(value, ptype); 4251 switch (w) { 4252 case INT: return result.bindArgumentI(pos, (int)value); 4253 case LONG: return result.bindArgumentJ(pos, (long)value); 4254 case FLOAT: return result.bindArgumentF(pos, (float)value); 4255 case DOUBLE: return result.bindArgumentD(pos, (double)value); 4256 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value)); 4257 } 4258 } 4259 4260 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException { 4261 MethodType oldType = target.type(); 4262 int outargs = oldType.parameterCount(); 4263 int inargs = outargs - insCount; 4264 if (inargs < 0) 4265 throw newIllegalArgumentException("too many values to insert"); 4266 if (pos < 0 || pos > inargs) 4267 throw newIllegalArgumentException("no argument type to append"); 4268 return oldType.ptypes(); 4269 } 4270 4271 /** 4272 * Produces a method handle which will discard some dummy arguments 4273 * before calling some other specified <i>target</i> method handle. 4274 * The type of the new method handle will be the same as the target's type, 4275 * except it will also include the dummy argument types, 4276 * at some given position. 4277 * <p> 4278 * The {@code pos} argument may range between zero and <i>N</i>, 4279 * where <i>N</i> is the arity of the target. 4280 * If {@code pos} is zero, the dummy arguments will precede 4281 * the target's real arguments; if {@code pos} is <i>N</i> 4282 * they will come after. 4283 * <p> 4284 * <b>Example:</b> 4285 * <blockquote><pre>{@code 4286 import static java.lang.invoke.MethodHandles.*; 4287 import static java.lang.invoke.MethodType.*; 4288 ... 4289 MethodHandle cat = lookup().findVirtual(String.class, 4290 "concat", methodType(String.class, String.class)); 4291 assertEquals("xy", (String) cat.invokeExact("x", "y")); 4292 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class); 4293 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2)); 4294 assertEquals(bigType, d0.type()); 4295 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z")); 4296 * }</pre></blockquote> 4297 * <p> 4298 * This method is also equivalent to the following code: 4299 * <blockquote><pre> 4300 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))} 4301 * </pre></blockquote> 4302 * @param target the method handle to invoke after the arguments are dropped 4303 * @param valueTypes the type(s) of the argument(s) to drop 4304 * @param pos position of first argument to drop (zero for the leftmost) 4305 * @return a method handle which drops arguments of the given types, 4306 * before calling the original method handle 4307 * @throws NullPointerException if the target is null, 4308 * or if the {@code valueTypes} list or any of its elements is null 4309 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 4310 * or if {@code pos} is negative or greater than the arity of the target, 4311 * or if the new method handle's type would have too many parameters 4312 */ 4313 public static 4314 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) { 4315 return dropArguments0(target, pos, copyTypes(valueTypes.toArray())); 4316 } 4317 4318 private static List<Class<?>> copyTypes(Object[] array) { 4319 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class)); 4320 } 4321 4322 private static 4323 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) { 4324 MethodType oldType = target.type(); // get NPE 4325 int dropped = dropArgumentChecks(oldType, pos, valueTypes); 4326 MethodType newType = oldType.insertParameterTypes(pos, valueTypes); 4327 if (dropped == 0) return target; 4328 BoundMethodHandle result = target.rebind(); 4329 LambdaForm lform = result.form; 4330 int insertFormArg = 1 + pos; 4331 for (Class<?> ptype : valueTypes) { 4332 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype)); 4333 } 4334 result = result.copyWith(newType, lform); 4335 return result; 4336 } 4337 4338 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) { 4339 int dropped = valueTypes.size(); 4340 MethodType.checkSlotCount(dropped); 4341 int outargs = oldType.parameterCount(); 4342 int inargs = outargs + dropped; 4343 if (pos < 0 || pos > outargs) 4344 throw newIllegalArgumentException("no argument type to remove" 4345 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs) 4346 ); 4347 return dropped; 4348 } 4349 4350 /** 4351 * Produces a method handle which will discard some dummy arguments 4352 * before calling some other specified <i>target</i> method handle. 4353 * The type of the new method handle will be the same as the target's type, 4354 * except it will also include the dummy argument types, 4355 * at some given position. 4356 * <p> 4357 * The {@code pos} argument may range between zero and <i>N</i>, 4358 * where <i>N</i> is the arity of the target. 4359 * If {@code pos} is zero, the dummy arguments will precede 4360 * the target's real arguments; if {@code pos} is <i>N</i> 4361 * they will come after. 4362 * @apiNote 4363 * <blockquote><pre>{@code 4364 import static java.lang.invoke.MethodHandles.*; 4365 import static java.lang.invoke.MethodType.*; 4366 ... 4367 MethodHandle cat = lookup().findVirtual(String.class, 4368 "concat", methodType(String.class, String.class)); 4369 assertEquals("xy", (String) cat.invokeExact("x", "y")); 4370 MethodHandle d0 = dropArguments(cat, 0, String.class); 4371 assertEquals("yz", (String) d0.invokeExact("x", "y", "z")); 4372 MethodHandle d1 = dropArguments(cat, 1, String.class); 4373 assertEquals("xz", (String) d1.invokeExact("x", "y", "z")); 4374 MethodHandle d2 = dropArguments(cat, 2, String.class); 4375 assertEquals("xy", (String) d2.invokeExact("x", "y", "z")); 4376 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class); 4377 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z")); 4378 * }</pre></blockquote> 4379 * <p> 4380 * This method is also equivalent to the following code: 4381 * <blockquote><pre> 4382 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))} 4383 * </pre></blockquote> 4384 * @param target the method handle to invoke after the arguments are dropped 4385 * @param valueTypes the type(s) of the argument(s) to drop 4386 * @param pos position of first argument to drop (zero for the leftmost) 4387 * @return a method handle which drops arguments of the given types, 4388 * before calling the original method handle 4389 * @throws NullPointerException if the target is null, 4390 * or if the {@code valueTypes} array or any of its elements is null 4391 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 4392 * or if {@code pos} is negative or greater than the arity of the target, 4393 * or if the new method handle's type would have 4394 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4395 */ 4396 public static 4397 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) { 4398 return dropArguments0(target, pos, copyTypes(valueTypes)); 4399 } 4400 4401 // private version which allows caller some freedom with error handling 4402 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos, 4403 boolean nullOnFailure) { 4404 newTypes = copyTypes(newTypes.toArray()); 4405 List<Class<?>> oldTypes = target.type().parameterList(); 4406 int match = oldTypes.size(); 4407 if (skip != 0) { 4408 if (skip < 0 || skip > match) { 4409 throw newIllegalArgumentException("illegal skip", skip, target); 4410 } 4411 oldTypes = oldTypes.subList(skip, match); 4412 match -= skip; 4413 } 4414 List<Class<?>> addTypes = newTypes; 4415 int add = addTypes.size(); 4416 if (pos != 0) { 4417 if (pos < 0 || pos > add) { 4418 throw newIllegalArgumentException("illegal pos", pos, newTypes); 4419 } 4420 addTypes = addTypes.subList(pos, add); 4421 add -= pos; 4422 assert(addTypes.size() == add); 4423 } 4424 // Do not add types which already match the existing arguments. 4425 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) { 4426 if (nullOnFailure) { 4427 return null; 4428 } 4429 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes); 4430 } 4431 addTypes = addTypes.subList(match, add); 4432 add -= match; 4433 assert(addTypes.size() == add); 4434 // newTypes: ( P*[pos], M*[match], A*[add] ) 4435 // target: ( S*[skip], M*[match] ) 4436 MethodHandle adapter = target; 4437 if (add > 0) { 4438 adapter = dropArguments0(adapter, skip+ match, addTypes); 4439 } 4440 // adapter: (S*[skip], M*[match], A*[add] ) 4441 if (pos > 0) { 4442 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos)); 4443 } 4444 // adapter: (S*[skip], P*[pos], M*[match], A*[add] ) 4445 return adapter; 4446 } 4447 4448 /** 4449 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some 4450 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter 4451 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The 4452 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before 4453 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by 4454 * {@link #dropArguments(MethodHandle, int, Class[])}. 4455 * <p> 4456 * The resulting handle will have the same return type as the target handle. 4457 * <p> 4458 * In more formal terms, assume these two type lists:<ul> 4459 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as 4460 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list, 4461 * {@code newTypes}. 4462 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as 4463 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's 4464 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching 4465 * sub-list. 4466 * </ul> 4467 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type 4468 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by 4469 * {@link #dropArguments(MethodHandle, int, Class[])}. 4470 * 4471 * @apiNote 4472 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be 4473 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows: 4474 * <blockquote><pre>{@code 4475 import static java.lang.invoke.MethodHandles.*; 4476 import static java.lang.invoke.MethodType.*; 4477 ... 4478 ... 4479 MethodHandle h0 = constant(boolean.class, true); 4480 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class)); 4481 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class); 4482 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList()); 4483 if (h1.type().parameterCount() < h2.type().parameterCount()) 4484 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1 4485 else 4486 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2 4487 MethodHandle h3 = guardWithTest(h0, h1, h2); 4488 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c")); 4489 * }</pre></blockquote> 4490 * @param target the method handle to adapt 4491 * @param skip number of targets parameters to disregard (they will be unchanged) 4492 * @param newTypes the list of types to match {@code target}'s parameter type list to 4493 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur 4494 * @return a possibly adapted method handle 4495 * @throws NullPointerException if either argument is null 4496 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class}, 4497 * or if {@code skip} is negative or greater than the arity of the target, 4498 * or if {@code pos} is negative or greater than the newTypes list size, 4499 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position 4500 * {@code pos}. 4501 * @since 9 4502 */ 4503 public static 4504 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) { 4505 Objects.requireNonNull(target); 4506 Objects.requireNonNull(newTypes); 4507 return dropArgumentsToMatch(target, skip, newTypes, pos, false); 4508 } 4509 4510 /** 4511 * Adapts a target method handle by pre-processing 4512 * one or more of its arguments, each with its own unary filter function, 4513 * and then calling the target with each pre-processed argument 4514 * replaced by the result of its corresponding filter function. 4515 * <p> 4516 * The pre-processing is performed by one or more method handles, 4517 * specified in the elements of the {@code filters} array. 4518 * The first element of the filter array corresponds to the {@code pos} 4519 * argument of the target, and so on in sequence. 4520 * The filter functions are invoked in left to right order. 4521 * <p> 4522 * Null arguments in the array are treated as identity functions, 4523 * and the corresponding arguments left unchanged. 4524 * (If there are no non-null elements in the array, the original target is returned.) 4525 * Each filter is applied to the corresponding argument of the adapter. 4526 * <p> 4527 * If a filter {@code F} applies to the {@code N}th argument of 4528 * the target, then {@code F} must be a method handle which 4529 * takes exactly one argument. The type of {@code F}'s sole argument 4530 * replaces the corresponding argument type of the target 4531 * in the resulting adapted method handle. 4532 * The return type of {@code F} must be identical to the corresponding 4533 * parameter type of the target. 4534 * <p> 4535 * It is an error if there are elements of {@code filters} 4536 * (null or not) 4537 * which do not correspond to argument positions in the target. 4538 * <p><b>Example:</b> 4539 * <blockquote><pre>{@code 4540 import static java.lang.invoke.MethodHandles.*; 4541 import static java.lang.invoke.MethodType.*; 4542 ... 4543 MethodHandle cat = lookup().findVirtual(String.class, 4544 "concat", methodType(String.class, String.class)); 4545 MethodHandle upcase = lookup().findVirtual(String.class, 4546 "toUpperCase", methodType(String.class)); 4547 assertEquals("xy", (String) cat.invokeExact("x", "y")); 4548 MethodHandle f0 = filterArguments(cat, 0, upcase); 4549 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy 4550 MethodHandle f1 = filterArguments(cat, 1, upcase); 4551 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY 4552 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase); 4553 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY 4554 * }</pre></blockquote> 4555 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 4556 * denotes the return type of both the {@code target} and resulting adapter. 4557 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values 4558 * of the parameters and arguments that precede and follow the filter position 4559 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and 4560 * values of the filtered parameters and arguments; they also represent the 4561 * return types of the {@code filter[i]} handles. The latter accept arguments 4562 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of 4563 * the resulting adapter. 4564 * <blockquote><pre>{@code 4565 * T target(P... p, A[i]... a[i], B... b); 4566 * A[i] filter[i](V[i]); 4567 * T adapter(P... p, V[i]... v[i], B... b) { 4568 * return target(p..., filter[i](v[i])..., b...); 4569 * } 4570 * }</pre></blockquote> 4571 * <p> 4572 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4573 * variable-arity method handle}, even if the original target method handle was. 4574 * 4575 * @param target the method handle to invoke after arguments are filtered 4576 * @param pos the position of the first argument to filter 4577 * @param filters method handles to call initially on filtered arguments 4578 * @return method handle which incorporates the specified argument filtering logic 4579 * @throws NullPointerException if the target is null 4580 * or if the {@code filters} array is null 4581 * @throws IllegalArgumentException if a non-null element of {@code filters} 4582 * does not match a corresponding argument type of target as described above, 4583 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}, 4584 * or if the resulting method handle's type would have 4585 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4586 */ 4587 public static 4588 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) { 4589 // In method types arguments start at index 0, while the LF 4590 // editor have the MH receiver at position 0 - adjust appropriately. 4591 final int MH_RECEIVER_OFFSET = 1; 4592 filterArgumentsCheckArity(target, pos, filters); 4593 MethodHandle adapter = target; 4594 4595 // keep track of currently matched filters, as to optimize repeated filters 4596 int index = 0; 4597 int[] positions = new int[filters.length]; 4598 MethodHandle filter = null; 4599 4600 // process filters in reverse order so that the invocation of 4601 // the resulting adapter will invoke the filters in left-to-right order 4602 for (int i = filters.length - 1; i >= 0; --i) { 4603 MethodHandle newFilter = filters[i]; 4604 if (newFilter == null) continue; // ignore null elements of filters 4605 4606 // flush changes on update 4607 if (filter != newFilter) { 4608 if (filter != null) { 4609 if (index > 1) { 4610 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 4611 } else { 4612 adapter = filterArgument(adapter, positions[0] - 1, filter); 4613 } 4614 } 4615 filter = newFilter; 4616 index = 0; 4617 } 4618 4619 filterArgumentChecks(target, pos + i, newFilter); 4620 positions[index++] = pos + i + MH_RECEIVER_OFFSET; 4621 } 4622 if (index > 1) { 4623 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 4624 } else if (index == 1) { 4625 adapter = filterArgument(adapter, positions[0] - 1, filter); 4626 } 4627 return adapter; 4628 } 4629 4630 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) { 4631 MethodType targetType = adapter.type(); 4632 MethodType filterType = filter.type(); 4633 BoundMethodHandle result = adapter.rebind(); 4634 Class<?> newParamType = filterType.parameterType(0); 4635 4636 Class<?>[] ptypes = targetType.ptypes().clone(); 4637 for (int pos : positions) { 4638 ptypes[pos - 1] = newParamType; 4639 } 4640 MethodType newType = MethodType.makeImpl(targetType.rtype(), ptypes, true); 4641 4642 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions); 4643 return result.copyWithExtendL(newType, lform, filter); 4644 } 4645 4646 /*non-public*/ static 4647 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) { 4648 filterArgumentChecks(target, pos, filter); 4649 MethodType targetType = target.type(); 4650 MethodType filterType = filter.type(); 4651 BoundMethodHandle result = target.rebind(); 4652 Class<?> newParamType = filterType.parameterType(0); 4653 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType)); 4654 MethodType newType = targetType.changeParameterType(pos, newParamType); 4655 result = result.copyWithExtendL(newType, lform, filter); 4656 return result; 4657 } 4658 4659 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) { 4660 MethodType targetType = target.type(); 4661 int maxPos = targetType.parameterCount(); 4662 if (pos + filters.length > maxPos) 4663 throw newIllegalArgumentException("too many filters"); 4664 } 4665 4666 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 4667 MethodType targetType = target.type(); 4668 MethodType filterType = filter.type(); 4669 if (filterType.parameterCount() != 1 4670 || filterType.returnType() != targetType.parameterType(pos)) 4671 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 4672 } 4673 4674 /** 4675 * Adapts a target method handle by pre-processing 4676 * a sub-sequence of its arguments with a filter (another method handle). 4677 * The pre-processed arguments are replaced by the result (if any) of the 4678 * filter function. 4679 * The target is then called on the modified (usually shortened) argument list. 4680 * <p> 4681 * If the filter returns a value, the target must accept that value as 4682 * its argument in position {@code pos}, preceded and/or followed by 4683 * any arguments not passed to the filter. 4684 * If the filter returns void, the target must accept all arguments 4685 * not passed to the filter. 4686 * No arguments are reordered, and a result returned from the filter 4687 * replaces (in order) the whole subsequence of arguments originally 4688 * passed to the adapter. 4689 * <p> 4690 * The argument types (if any) of the filter 4691 * replace zero or one argument types of the target, at position {@code pos}, 4692 * in the resulting adapted method handle. 4693 * The return type of the filter (if any) must be identical to the 4694 * argument type of the target at position {@code pos}, and that target argument 4695 * is supplied by the return value of the filter. 4696 * <p> 4697 * In all cases, {@code pos} must be greater than or equal to zero, and 4698 * {@code pos} must also be less than or equal to the target's arity. 4699 * <p><b>Example:</b> 4700 * <blockquote><pre>{@code 4701 import static java.lang.invoke.MethodHandles.*; 4702 import static java.lang.invoke.MethodType.*; 4703 ... 4704 MethodHandle deepToString = publicLookup() 4705 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 4706 4707 MethodHandle ts1 = deepToString.asCollector(String[].class, 1); 4708 assertEquals("[strange]", (String) ts1.invokeExact("strange")); 4709 4710 MethodHandle ts2 = deepToString.asCollector(String[].class, 2); 4711 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down")); 4712 4713 MethodHandle ts3 = deepToString.asCollector(String[].class, 3); 4714 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2); 4715 assertEquals("[top, [up, down], strange]", 4716 (String) ts3_ts2.invokeExact("top", "up", "down", "strange")); 4717 4718 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1); 4719 assertEquals("[top, [up, down], [strange]]", 4720 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange")); 4721 4722 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3); 4723 assertEquals("[top, [[up, down, strange], charm], bottom]", 4724 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom")); 4725 * }</pre></blockquote> 4726 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 4727 * represents the return type of the {@code target} and resulting adapter. 4728 * {@code V}/{@code v} stand for the return type and value of the 4729 * {@code filter}, which are also found in the signature and arguments of 4730 * the {@code target}, respectively, unless {@code V} is {@code void}. 4731 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types 4732 * and values preceding and following the collection position, {@code pos}, 4733 * in the {@code target}'s signature. They also turn up in the resulting 4734 * adapter's signature and arguments, where they surround 4735 * {@code B}/{@code b}, which represent the parameter types and arguments 4736 * to the {@code filter} (if any). 4737 * <blockquote><pre>{@code 4738 * T target(A...,V,C...); 4739 * V filter(B...); 4740 * T adapter(A... a,B... b,C... c) { 4741 * V v = filter(b...); 4742 * return target(a...,v,c...); 4743 * } 4744 * // and if the filter has no arguments: 4745 * T target2(A...,V,C...); 4746 * V filter2(); 4747 * T adapter2(A... a,C... c) { 4748 * V v = filter2(); 4749 * return target2(a...,v,c...); 4750 * } 4751 * // and if the filter has a void return: 4752 * T target3(A...,C...); 4753 * void filter3(B...); 4754 * T adapter3(A... a,B... b,C... c) { 4755 * filter3(b...); 4756 * return target3(a...,c...); 4757 * } 4758 * }</pre></blockquote> 4759 * <p> 4760 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to 4761 * one which first "folds" the affected arguments, and then drops them, in separate 4762 * steps as follows: 4763 * <blockquote><pre>{@code 4764 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2 4765 * mh = MethodHandles.foldArguments(mh, coll); //step 1 4766 * }</pre></blockquote> 4767 * If the target method handle consumes no arguments besides than the result 4768 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)} 4769 * is equivalent to {@code filterReturnValue(coll, mh)}. 4770 * If the filter method handle {@code coll} consumes one argument and produces 4771 * a non-void result, then {@code collectArguments(mh, N, coll)} 4772 * is equivalent to {@code filterArguments(mh, N, coll)}. 4773 * Other equivalences are possible but would require argument permutation. 4774 * <p> 4775 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4776 * variable-arity method handle}, even if the original target method handle was. 4777 * 4778 * @param target the method handle to invoke after filtering the subsequence of arguments 4779 * @param pos the position of the first adapter argument to pass to the filter, 4780 * and/or the target argument which receives the result of the filter 4781 * @param filter method handle to call on the subsequence of arguments 4782 * @return method handle which incorporates the specified argument subsequence filtering logic 4783 * @throws NullPointerException if either argument is null 4784 * @throws IllegalArgumentException if the return type of {@code filter} 4785 * is non-void and is not the same as the {@code pos} argument of the target, 4786 * or if {@code pos} is not between 0 and the target's arity, inclusive, 4787 * or if the resulting method handle's type would have 4788 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4789 * @see MethodHandles#foldArguments 4790 * @see MethodHandles#filterArguments 4791 * @see MethodHandles#filterReturnValue 4792 */ 4793 public static 4794 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) { 4795 MethodType newType = collectArgumentsChecks(target, pos, filter); 4796 MethodType collectorType = filter.type(); 4797 BoundMethodHandle result = target.rebind(); 4798 LambdaForm lform; 4799 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) { 4800 lform = result.editor().collectArgumentArrayForm(1 + pos, filter); 4801 if (lform != null) { 4802 return result.copyWith(newType, lform); 4803 } 4804 } 4805 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType()); 4806 return result.copyWithExtendL(newType, lform, filter); 4807 } 4808 4809 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 4810 MethodType targetType = target.type(); 4811 MethodType filterType = filter.type(); 4812 Class<?> rtype = filterType.returnType(); 4813 List<Class<?>> filterArgs = filterType.parameterList(); 4814 if (rtype == void.class) { 4815 return targetType.insertParameterTypes(pos, filterArgs); 4816 } 4817 if (rtype != targetType.parameterType(pos)) { 4818 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 4819 } 4820 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs); 4821 } 4822 4823 /** 4824 * Adapts a target method handle by post-processing 4825 * its return value (if any) with a filter (another method handle). 4826 * The result of the filter is returned from the adapter. 4827 * <p> 4828 * If the target returns a value, the filter must accept that value as 4829 * its only argument. 4830 * If the target returns void, the filter must accept no arguments. 4831 * <p> 4832 * The return type of the filter 4833 * replaces the return type of the target 4834 * in the resulting adapted method handle. 4835 * The argument type of the filter (if any) must be identical to the 4836 * return type of the target. 4837 * <p><b>Example:</b> 4838 * <blockquote><pre>{@code 4839 import static java.lang.invoke.MethodHandles.*; 4840 import static java.lang.invoke.MethodType.*; 4841 ... 4842 MethodHandle cat = lookup().findVirtual(String.class, 4843 "concat", methodType(String.class, String.class)); 4844 MethodHandle length = lookup().findVirtual(String.class, 4845 "length", methodType(int.class)); 4846 System.out.println((String) cat.invokeExact("x", "y")); // xy 4847 MethodHandle f0 = filterReturnValue(cat, length); 4848 System.out.println((int) f0.invokeExact("x", "y")); // 2 4849 * }</pre></blockquote> 4850 * <p>Here is pseudocode for the resulting adapter. In the code, 4851 * {@code T}/{@code t} represent the result type and value of the 4852 * {@code target}; {@code V}, the result type of the {@code filter}; and 4853 * {@code A}/{@code a}, the types and values of the parameters and arguments 4854 * of the {@code target} as well as the resulting adapter. 4855 * <blockquote><pre>{@code 4856 * T target(A...); 4857 * V filter(T); 4858 * V adapter(A... a) { 4859 * T t = target(a...); 4860 * return filter(t); 4861 * } 4862 * // and if the target has a void return: 4863 * void target2(A...); 4864 * V filter2(); 4865 * V adapter2(A... a) { 4866 * target2(a...); 4867 * return filter2(); 4868 * } 4869 * // and if the filter has a void return: 4870 * T target3(A...); 4871 * void filter3(V); 4872 * void adapter3(A... a) { 4873 * T t = target3(a...); 4874 * filter3(t); 4875 * } 4876 * }</pre></blockquote> 4877 * <p> 4878 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4879 * variable-arity method handle}, even if the original target method handle was. 4880 * @param target the method handle to invoke before filtering the return value 4881 * @param filter method handle to call on the return value 4882 * @return method handle which incorporates the specified return value filtering logic 4883 * @throws NullPointerException if either argument is null 4884 * @throws IllegalArgumentException if the argument list of {@code filter} 4885 * does not match the return type of target as described above 4886 */ 4887 public static 4888 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) { 4889 MethodType targetType = target.type(); 4890 MethodType filterType = filter.type(); 4891 filterReturnValueChecks(targetType, filterType); 4892 BoundMethodHandle result = target.rebind(); 4893 BasicType rtype = BasicType.basicType(filterType.returnType()); 4894 LambdaForm lform = result.editor().filterReturnForm(rtype, false); 4895 MethodType newType = targetType.changeReturnType(filterType.returnType()); 4896 result = result.copyWithExtendL(newType, lform, filter); 4897 return result; 4898 } 4899 4900 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException { 4901 Class<?> rtype = targetType.returnType(); 4902 int filterValues = filterType.parameterCount(); 4903 if (filterValues == 0 4904 ? (rtype != void.class) 4905 : (rtype != filterType.parameterType(0) || filterValues != 1)) 4906 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 4907 } 4908 4909 /** 4910 * Adapts a target method handle by pre-processing 4911 * some of its arguments, and then calling the target with 4912 * the result of the pre-processing, inserted into the original 4913 * sequence of arguments. 4914 * <p> 4915 * The pre-processing is performed by {@code combiner}, a second method handle. 4916 * Of the arguments passed to the adapter, the first {@code N} arguments 4917 * are copied to the combiner, which is then called. 4918 * (Here, {@code N} is defined as the parameter count of the combiner.) 4919 * After this, control passes to the target, with any result 4920 * from the combiner inserted before the original {@code N} incoming 4921 * arguments. 4922 * <p> 4923 * If the combiner returns a value, the first parameter type of the target 4924 * must be identical with the return type of the combiner, and the next 4925 * {@code N} parameter types of the target must exactly match the parameters 4926 * of the combiner. 4927 * <p> 4928 * If the combiner has a void return, no result will be inserted, 4929 * and the first {@code N} parameter types of the target 4930 * must exactly match the parameters of the combiner. 4931 * <p> 4932 * The resulting adapter is the same type as the target, except that the 4933 * first parameter type is dropped, 4934 * if it corresponds to the result of the combiner. 4935 * <p> 4936 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments 4937 * that either the combiner or the target does not wish to receive. 4938 * If some of the incoming arguments are destined only for the combiner, 4939 * consider using {@link MethodHandle#asCollector asCollector} instead, since those 4940 * arguments will not need to be live on the stack on entry to the 4941 * target.) 4942 * <p><b>Example:</b> 4943 * <blockquote><pre>{@code 4944 import static java.lang.invoke.MethodHandles.*; 4945 import static java.lang.invoke.MethodType.*; 4946 ... 4947 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 4948 "println", methodType(void.class, String.class)) 4949 .bindTo(System.out); 4950 MethodHandle cat = lookup().findVirtual(String.class, 4951 "concat", methodType(String.class, String.class)); 4952 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 4953 MethodHandle catTrace = foldArguments(cat, trace); 4954 // also prints "boo": 4955 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 4956 * }</pre></blockquote> 4957 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 4958 * represents the result type of the {@code target} and resulting adapter. 4959 * {@code V}/{@code v} represent the type and value of the parameter and argument 4960 * of {@code target} that precedes the folding position; {@code V} also is 4961 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 4962 * types and values of the {@code N} parameters and arguments at the folding 4963 * position. {@code B}/{@code b} represent the types and values of the 4964 * {@code target} parameters and arguments that follow the folded parameters 4965 * and arguments. 4966 * <blockquote><pre>{@code 4967 * // there are N arguments in A... 4968 * T target(V, A[N]..., B...); 4969 * V combiner(A...); 4970 * T adapter(A... a, B... b) { 4971 * V v = combiner(a...); 4972 * return target(v, a..., b...); 4973 * } 4974 * // and if the combiner has a void return: 4975 * T target2(A[N]..., B...); 4976 * void combiner2(A...); 4977 * T adapter2(A... a, B... b) { 4978 * combiner2(a...); 4979 * return target2(a..., b...); 4980 * } 4981 * }</pre></blockquote> 4982 * <p> 4983 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4984 * variable-arity method handle}, even if the original target method handle was. 4985 * @param target the method handle to invoke after arguments are combined 4986 * @param combiner method handle to call initially on the incoming arguments 4987 * @return method handle which incorporates the specified argument folding logic 4988 * @throws NullPointerException if either argument is null 4989 * @throws IllegalArgumentException if {@code combiner}'s return type 4990 * is non-void and not the same as the first argument type of 4991 * the target, or if the initial {@code N} argument types 4992 * of the target 4993 * (skipping one matching the {@code combiner}'s return type) 4994 * are not identical with the argument types of {@code combiner} 4995 */ 4996 public static 4997 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) { 4998 return foldArguments(target, 0, combiner); 4999 } 5000 5001 /** 5002 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then 5003 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just 5004 * before the folded arguments. 5005 * <p> 5006 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the 5007 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a 5008 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position 5009 * 0. 5010 * 5011 * @apiNote Example: 5012 * <blockquote><pre>{@code 5013 import static java.lang.invoke.MethodHandles.*; 5014 import static java.lang.invoke.MethodType.*; 5015 ... 5016 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 5017 "println", methodType(void.class, String.class)) 5018 .bindTo(System.out); 5019 MethodHandle cat = lookup().findVirtual(String.class, 5020 "concat", methodType(String.class, String.class)); 5021 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 5022 MethodHandle catTrace = foldArguments(cat, 1, trace); 5023 // also prints "jum": 5024 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 5025 * }</pre></blockquote> 5026 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5027 * represents the result type of the {@code target} and resulting adapter. 5028 * {@code V}/{@code v} represent the type and value of the parameter and argument 5029 * of {@code target} that precedes the folding position; {@code V} also is 5030 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 5031 * types and values of the {@code N} parameters and arguments at the folding 5032 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types 5033 * and values of the {@code target} parameters and arguments that precede and 5034 * follow the folded parameters and arguments starting at {@code pos}, 5035 * respectively. 5036 * <blockquote><pre>{@code 5037 * // there are N arguments in A... 5038 * T target(Z..., V, A[N]..., B...); 5039 * V combiner(A...); 5040 * T adapter(Z... z, A... a, B... b) { 5041 * V v = combiner(a...); 5042 * return target(z..., v, a..., b...); 5043 * } 5044 * // and if the combiner has a void return: 5045 * T target2(Z..., A[N]..., B...); 5046 * void combiner2(A...); 5047 * T adapter2(Z... z, A... a, B... b) { 5048 * combiner2(a...); 5049 * return target2(z..., a..., b...); 5050 * } 5051 * }</pre></blockquote> 5052 * <p> 5053 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5054 * variable-arity method handle}, even if the original target method handle was. 5055 * 5056 * @param target the method handle to invoke after arguments are combined 5057 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code 5058 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 5059 * @param combiner method handle to call initially on the incoming arguments 5060 * @return method handle which incorporates the specified argument folding logic 5061 * @throws NullPointerException if either argument is null 5062 * @throws IllegalArgumentException if either of the following two conditions holds: 5063 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 5064 * {@code pos} of the target signature; 5065 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching 5066 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}. 5067 * 5068 * @see #foldArguments(MethodHandle, MethodHandle) 5069 * @since 9 5070 */ 5071 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) { 5072 MethodType targetType = target.type(); 5073 MethodType combinerType = combiner.type(); 5074 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType); 5075 BoundMethodHandle result = target.rebind(); 5076 boolean dropResult = rtype == void.class; 5077 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType()); 5078 MethodType newType = targetType; 5079 if (!dropResult) { 5080 newType = newType.dropParameterTypes(pos, pos + 1); 5081 } 5082 result = result.copyWithExtendL(newType, lform, combiner); 5083 return result; 5084 } 5085 5086 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) { 5087 int foldArgs = combinerType.parameterCount(); 5088 Class<?> rtype = combinerType.returnType(); 5089 int foldVals = rtype == void.class ? 0 : 1; 5090 int afterInsertPos = foldPos + foldVals; 5091 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs); 5092 if (ok) { 5093 for (int i = 0; i < foldArgs; i++) { 5094 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) { 5095 ok = false; 5096 break; 5097 } 5098 } 5099 } 5100 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) 5101 ok = false; 5102 if (!ok) 5103 throw misMatchedTypes("target and combiner types", targetType, combinerType); 5104 return rtype; 5105 } 5106 5107 /** 5108 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result 5109 * of the pre-processing replacing the argument at the given position. 5110 * 5111 * @param target the method handle to invoke after arguments are combined 5112 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 5113 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 5114 * @param combiner method handle to call initially on the incoming arguments 5115 * @param argPositions indexes of the target to pick arguments sent to the combiner from 5116 * @return method handle which incorporates the specified argument folding logic 5117 * @throws NullPointerException if either argument is null 5118 * @throws IllegalArgumentException if either of the following two conditions holds: 5119 * (1) {@code combiner}'s return type is not the same as the argument type at position 5120 * {@code pos} of the target signature; 5121 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are 5122 * not identical with the argument types of {@code combiner}. 5123 */ 5124 /*non-public*/ static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 5125 return argumentsWithCombiner(true, target, position, combiner, argPositions); 5126 } 5127 5128 /** 5129 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of 5130 * the pre-processing inserted into the original sequence of arguments at the given position. 5131 * 5132 * @param target the method handle to invoke after arguments are combined 5133 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 5134 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 5135 * @param combiner method handle to call initially on the incoming arguments 5136 * @param argPositions indexes of the target to pick arguments sent to the combiner from 5137 * @return method handle which incorporates the specified argument folding logic 5138 * @throws NullPointerException if either argument is null 5139 * @throws IllegalArgumentException if either of the following two conditions holds: 5140 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 5141 * {@code pos} of the target signature; 5142 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature 5143 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical 5144 * with the argument types of {@code combiner}. 5145 */ 5146 /*non-public*/ static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 5147 return argumentsWithCombiner(false, target, position, combiner, argPositions); 5148 } 5149 5150 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 5151 MethodType targetType = target.type(); 5152 MethodType combinerType = combiner.type(); 5153 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions); 5154 BoundMethodHandle result = target.rebind(); 5155 5156 MethodType newType = targetType; 5157 LambdaForm lform; 5158 if (filter) { 5159 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions); 5160 } else { 5161 boolean dropResult = rtype == void.class; 5162 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions); 5163 if (!dropResult) { 5164 newType = newType.dropParameterTypes(position, position + 1); 5165 } 5166 } 5167 result = result.copyWithExtendL(newType, lform, combiner); 5168 return result; 5169 } 5170 5171 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) { 5172 int combinerArgs = combinerType.parameterCount(); 5173 if (argPos.length != combinerArgs) { 5174 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length); 5175 } 5176 Class<?> rtype = combinerType.returnType(); 5177 5178 for (int i = 0; i < combinerArgs; i++) { 5179 int arg = argPos[i]; 5180 if (arg < 0 || arg > targetType.parameterCount()) { 5181 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg); 5182 } 5183 if (combinerType.parameterType(i) != targetType.parameterType(arg)) { 5184 throw newIllegalArgumentException("target argument type at position " + arg 5185 + " must match combiner argument type at index " + i + ": " + targetType 5186 + " -> " + combinerType + ", map: " + Arrays.toString(argPos)); 5187 } 5188 } 5189 if (filter && combinerType.returnType() != targetType.parameterType(position)) { 5190 throw misMatchedTypes("target and combiner types", targetType, combinerType); 5191 } 5192 return rtype; 5193 } 5194 5195 /** 5196 * Makes a method handle which adapts a target method handle, 5197 * by guarding it with a test, a boolean-valued method handle. 5198 * If the guard fails, a fallback handle is called instead. 5199 * All three method handles must have the same corresponding 5200 * argument and return types, except that the return type 5201 * of the test must be boolean, and the test is allowed 5202 * to have fewer arguments than the other two method handles. 5203 * <p> 5204 * Here is pseudocode for the resulting adapter. In the code, {@code T} 5205 * represents the uniform result type of the three involved handles; 5206 * {@code A}/{@code a}, the types and values of the {@code target} 5207 * parameters and arguments that are consumed by the {@code test}; and 5208 * {@code B}/{@code b}, those types and values of the {@code target} 5209 * parameters and arguments that are not consumed by the {@code test}. 5210 * <blockquote><pre>{@code 5211 * boolean test(A...); 5212 * T target(A...,B...); 5213 * T fallback(A...,B...); 5214 * T adapter(A... a,B... b) { 5215 * if (test(a...)) 5216 * return target(a..., b...); 5217 * else 5218 * return fallback(a..., b...); 5219 * } 5220 * }</pre></blockquote> 5221 * Note that the test arguments ({@code a...} in the pseudocode) cannot 5222 * be modified by execution of the test, and so are passed unchanged 5223 * from the caller to the target or fallback as appropriate. 5224 * @param test method handle used for test, must return boolean 5225 * @param target method handle to call if test passes 5226 * @param fallback method handle to call if test fails 5227 * @return method handle which incorporates the specified if/then/else logic 5228 * @throws NullPointerException if any argument is null 5229 * @throws IllegalArgumentException if {@code test} does not return boolean, 5230 * or if all three method types do not match (with the return 5231 * type of {@code test} changed to match that of the target). 5232 */ 5233 public static 5234 MethodHandle guardWithTest(MethodHandle test, 5235 MethodHandle target, 5236 MethodHandle fallback) { 5237 MethodType gtype = test.type(); 5238 MethodType ttype = target.type(); 5239 MethodType ftype = fallback.type(); 5240 if (!ttype.equals(ftype)) 5241 throw misMatchedTypes("target and fallback types", ttype, ftype); 5242 if (gtype.returnType() != boolean.class) 5243 throw newIllegalArgumentException("guard type is not a predicate "+gtype); 5244 List<Class<?>> targs = ttype.parameterList(); 5245 test = dropArgumentsToMatch(test, 0, targs, 0, true); 5246 if (test == null) { 5247 throw misMatchedTypes("target and test types", ttype, gtype); 5248 } 5249 return MethodHandleImpl.makeGuardWithTest(test, target, fallback); 5250 } 5251 5252 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) { 5253 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2); 5254 } 5255 5256 /** 5257 * Makes a method handle which adapts a target method handle, 5258 * by running it inside an exception handler. 5259 * If the target returns normally, the adapter returns that value. 5260 * If an exception matching the specified type is thrown, the fallback 5261 * handle is called instead on the exception, plus the original arguments. 5262 * <p> 5263 * The target and handler must have the same corresponding 5264 * argument and return types, except that handler may omit trailing arguments 5265 * (similarly to the predicate in {@link #guardWithTest guardWithTest}). 5266 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype. 5267 * <p> 5268 * Here is pseudocode for the resulting adapter. In the code, {@code T} 5269 * represents the return type of the {@code target} and {@code handler}, 5270 * and correspondingly that of the resulting adapter; {@code A}/{@code a}, 5271 * the types and values of arguments to the resulting handle consumed by 5272 * {@code handler}; and {@code B}/{@code b}, those of arguments to the 5273 * resulting handle discarded by {@code handler}. 5274 * <blockquote><pre>{@code 5275 * T target(A..., B...); 5276 * T handler(ExType, A...); 5277 * T adapter(A... a, B... b) { 5278 * try { 5279 * return target(a..., b...); 5280 * } catch (ExType ex) { 5281 * return handler(ex, a...); 5282 * } 5283 * } 5284 * }</pre></blockquote> 5285 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 5286 * be modified by execution of the target, and so are passed unchanged 5287 * from the caller to the handler, if the handler is invoked. 5288 * <p> 5289 * The target and handler must return the same type, even if the handler 5290 * always throws. (This might happen, for instance, because the handler 5291 * is simulating a {@code finally} clause). 5292 * To create such a throwing handler, compose the handler creation logic 5293 * with {@link #throwException throwException}, 5294 * in order to create a method handle of the correct return type. 5295 * @param target method handle to call 5296 * @param exType the type of exception which the handler will catch 5297 * @param handler method handle to call if a matching exception is thrown 5298 * @return method handle which incorporates the specified try/catch logic 5299 * @throws NullPointerException if any argument is null 5300 * @throws IllegalArgumentException if {@code handler} does not accept 5301 * the given exception type, or if the method handle types do 5302 * not match in their return types and their 5303 * corresponding parameters 5304 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle) 5305 */ 5306 public static 5307 MethodHandle catchException(MethodHandle target, 5308 Class<? extends Throwable> exType, 5309 MethodHandle handler) { 5310 MethodType ttype = target.type(); 5311 MethodType htype = handler.type(); 5312 if (!Throwable.class.isAssignableFrom(exType)) 5313 throw new ClassCastException(exType.getName()); 5314 if (htype.parameterCount() < 1 || 5315 !htype.parameterType(0).isAssignableFrom(exType)) 5316 throw newIllegalArgumentException("handler does not accept exception type "+exType); 5317 if (htype.returnType() != ttype.returnType()) 5318 throw misMatchedTypes("target and handler return types", ttype, htype); 5319 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true); 5320 if (handler == null) { 5321 throw misMatchedTypes("target and handler types", ttype, htype); 5322 } 5323 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler); 5324 } 5325 5326 /** 5327 * Produces a method handle which will throw exceptions of the given {@code exType}. 5328 * The method handle will accept a single argument of {@code exType}, 5329 * and immediately throw it as an exception. 5330 * The method type will nominally specify a return of {@code returnType}. 5331 * The return type may be anything convenient: It doesn't matter to the 5332 * method handle's behavior, since it will never return normally. 5333 * @param returnType the return type of the desired method handle 5334 * @param exType the parameter type of the desired method handle 5335 * @return method handle which can throw the given exceptions 5336 * @throws NullPointerException if either argument is null 5337 */ 5338 public static 5339 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) { 5340 if (!Throwable.class.isAssignableFrom(exType)) 5341 throw new ClassCastException(exType.getName()); 5342 return MethodHandleImpl.throwException(methodType(returnType, exType)); 5343 } 5344 5345 /** 5346 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each 5347 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and 5348 * delivers the loop's result, which is the return value of the resulting handle. 5349 * <p> 5350 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop 5351 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration 5352 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in 5353 * terms of method handles, each clause will specify up to four independent actions:<ul> 5354 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}. 5355 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}. 5356 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit. 5357 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value. 5358 * </ul> 5359 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}. 5360 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually 5361 * be referring to types, but in some contexts (describing execution) the lists will be of actual values. 5362 * <p> 5363 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in 5364 * this case. See below for a detailed description. 5365 * <p> 5366 * <em>Parameters optional everywhere:</em> 5367 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}. 5368 * As an exception, the init functions cannot take any {@code v} parameters, 5369 * because those values are not yet computed when the init functions are executed. 5370 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take. 5371 * In fact, any clause function may take no arguments at all. 5372 * <p> 5373 * <em>Loop parameters:</em> 5374 * A clause function may take all the iteration variable values it is entitled to, in which case 5375 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>, 5376 * with their types and values notated as {@code (A...)} and {@code (a...)}. 5377 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed. 5378 * (Since init functions do not accept iteration variables {@code v}, any parameter to an 5379 * init function is automatically a loop parameter {@code a}.) 5380 * As with iteration variables, clause functions are allowed but not required to accept loop parameters. 5381 * These loop parameters act as loop-invariant values visible across the whole loop. 5382 * <p> 5383 * <em>Parameters visible everywhere:</em> 5384 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full 5385 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters. 5386 * The init functions can observe initial pre-loop state, in the form {@code (a...)}. 5387 * Most clause functions will not need all of this information, but they will be formally connected to it 5388 * as if by {@link #dropArguments}. 5389 * <a id="astar"></a> 5390 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full 5391 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}). 5392 * In that notation, the general form of an init function parameter list 5393 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}. 5394 * <p> 5395 * <em>Checking clause structure:</em> 5396 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the 5397 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must" 5398 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not 5399 * met by the inputs to the loop combinator. 5400 * <p> 5401 * <em>Effectively identical sequences:</em> 5402 * <a id="effid"></a> 5403 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B} 5404 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}. 5405 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical" 5406 * as a whole if the set contains a longest list, and all members of the set are effectively identical to 5407 * that longest list. 5408 * For example, any set of type sequences of the form {@code (V*)} is effectively identical, 5409 * and the same is true if more sequences of the form {@code (V... A*)} are added. 5410 * <p> 5411 * <em>Step 0: Determine clause structure.</em><ol type="a"> 5412 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element. 5413 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements. 5414 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length 5415 * four. Padding takes place by appending elements to the array. 5416 * <li>Clauses with all {@code null}s are disregarded. 5417 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini". 5418 * </ol> 5419 * <p> 5420 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a"> 5421 * <li>The iteration variable type for each clause is determined using the clause's init and step return types. 5422 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is 5423 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's 5424 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's 5425 * iteration variable type. 5426 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}. 5427 * <li>This list of types is called the "iteration variable types" ({@code (V...)}). 5428 * </ol> 5429 * <p> 5430 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul> 5431 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}). 5432 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types. 5433 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.) 5434 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types. 5435 * (These types will be checked in step 2, along with all the clause function types.) 5436 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.) 5437 * <li>All of the collected parameter lists must be effectively identical. 5438 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}). 5439 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence. 5440 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called 5441 * the "internal parameter list". 5442 * </ul> 5443 * <p> 5444 * <em>Step 1C: Determine loop return type.</em><ol type="a"> 5445 * <li>Examine fini function return types, disregarding omitted fini functions. 5446 * <li>If there are no fini functions, the loop return type is {@code void}. 5447 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return 5448 * type. 5449 * </ol> 5450 * <p> 5451 * <em>Step 1D: Check other types.</em><ol type="a"> 5452 * <li>There must be at least one non-omitted pred function. 5453 * <li>Every non-omitted pred function must have a {@code boolean} return type. 5454 * </ol> 5455 * <p> 5456 * <em>Step 2: Determine parameter lists.</em><ol type="a"> 5457 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}. 5458 * <li>The parameter list for init functions will be adjusted to the external parameter list. 5459 * (Note that their parameter lists are already effectively identical to this list.) 5460 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be 5461 * effectively identical to the internal parameter list {@code (V... A...)}. 5462 * </ol> 5463 * <p> 5464 * <em>Step 3: Fill in omitted functions.</em><ol type="a"> 5465 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable 5466 * type. 5467 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration 5468 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void} 5469 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.) 5470 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far 5471 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.) 5472 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the 5473 * loop return type. 5474 * </ol> 5475 * <p> 5476 * <em>Step 4: Fill in missing parameter types.</em><ol type="a"> 5477 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)}, 5478 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list. 5479 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter 5480 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list, 5481 * pad out the end of the list. 5482 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}. 5483 * </ol> 5484 * <p> 5485 * <em>Final observations.</em><ol type="a"> 5486 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments. 5487 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have. 5488 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have. 5489 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of 5490 * (non-{@code void}) iteration variables {@code V} followed by loop parameters. 5491 * <li>Each pair of init and step functions agrees in their return type {@code V}. 5492 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables. 5493 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters. 5494 * </ol> 5495 * <p> 5496 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property: 5497 * <ul> 5498 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}. 5499 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters. 5500 * (Only one {@code Pn} has to be non-{@code null}.) 5501 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}. 5502 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types. 5503 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}. 5504 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}. 5505 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine 5506 * the resulting loop handle's parameter types {@code (A...)}. 5507 * </ul> 5508 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions, 5509 * which is natural if most of the loop computation happens in the steps. For some loops, 5510 * the burden of computation might be heaviest in the pred functions, and so the pred functions 5511 * might need to accept the loop parameter values. For loops with complex exit logic, the fini 5512 * functions might need to accept loop parameters, and likewise for loops with complex entry logic, 5513 * where the init functions will need the extra parameters. For such reasons, the rules for 5514 * determining these parameters are as symmetric as possible, across all clause parts. 5515 * In general, the loop parameters function as common invariant values across the whole 5516 * loop, while the iteration variables function as common variant values, or (if there is 5517 * no step function) as internal loop invariant temporaries. 5518 * <p> 5519 * <em>Loop execution.</em><ol type="a"> 5520 * <li>When the loop is called, the loop input values are saved in locals, to be passed to 5521 * every clause function. These locals are loop invariant. 5522 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)}) 5523 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals. 5524 * These locals will be loop varying (unless their steps behave as identity functions, as noted above). 5525 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of 5526 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)} 5527 * (in argument order). 5528 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function 5529 * returns {@code false}. 5530 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the 5531 * sequence {@code (v...)} of loop variables. 5532 * The updated value is immediately visible to all subsequent function calls. 5533 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value 5534 * (of type {@code R}) is returned from the loop as a whole. 5535 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit 5536 * except by throwing an exception. 5537 * </ol> 5538 * <p> 5539 * <em>Usage tips.</em> 5540 * <ul> 5541 * <li>Although each step function will receive the current values of <em>all</em> the loop variables, 5542 * sometimes a step function only needs to observe the current value of its own variable. 5543 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}. 5544 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}. 5545 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create 5546 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be 5547 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable. 5548 * <li>If some of the clause functions are virtual methods on an instance, the instance 5549 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause 5550 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference 5551 * will be the first iteration variable value, and it will be easy to use virtual 5552 * methods as clause parts, since all of them will take a leading instance reference matching that value. 5553 * </ul> 5554 * <p> 5555 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types 5556 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop; 5557 * and {@code R} is the common result type of all finalizers as well as of the resulting loop. 5558 * <blockquote><pre>{@code 5559 * V... init...(A...); 5560 * boolean pred...(V..., A...); 5561 * V... step...(V..., A...); 5562 * R fini...(V..., A...); 5563 * R loop(A... a) { 5564 * V... v... = init...(a...); 5565 * for (;;) { 5566 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) { 5567 * v = s(v..., a...); 5568 * if (!p(v..., a...)) { 5569 * return f(v..., a...); 5570 * } 5571 * } 5572 * } 5573 * } 5574 * }</pre></blockquote> 5575 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded 5576 * to their full length, even though individual clause functions may neglect to take them all. 5577 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}. 5578 * 5579 * @apiNote Example: 5580 * <blockquote><pre>{@code 5581 * // iterative implementation of the factorial function as a loop handle 5582 * static int one(int k) { return 1; } 5583 * static int inc(int i, int acc, int k) { return i + 1; } 5584 * static int mult(int i, int acc, int k) { return i * acc; } 5585 * static boolean pred(int i, int acc, int k) { return i < k; } 5586 * static int fin(int i, int acc, int k) { return acc; } 5587 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 5588 * // null initializer for counter, should initialize to 0 5589 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 5590 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 5591 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 5592 * assertEquals(120, loop.invoke(5)); 5593 * }</pre></blockquote> 5594 * The same example, dropping arguments and using combinators: 5595 * <blockquote><pre>{@code 5596 * // simplified implementation of the factorial function as a loop handle 5597 * static int inc(int i) { return i + 1; } // drop acc, k 5598 * static int mult(int i, int acc) { return i * acc; } //drop k 5599 * static boolean cmp(int i, int k) { return i < k; } 5600 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods 5601 * // null initializer for counter, should initialize to 0 5602 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 5603 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc 5604 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i 5605 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 5606 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 5607 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 5608 * assertEquals(720, loop.invoke(6)); 5609 * }</pre></blockquote> 5610 * A similar example, using a helper object to hold a loop parameter: 5611 * <blockquote><pre>{@code 5612 * // instance-based implementation of the factorial function as a loop handle 5613 * static class FacLoop { 5614 * final int k; 5615 * FacLoop(int k) { this.k = k; } 5616 * int inc(int i) { return i + 1; } 5617 * int mult(int i, int acc) { return i * acc; } 5618 * boolean pred(int i) { return i < k; } 5619 * int fin(int i, int acc) { return acc; } 5620 * } 5621 * // assume MH_FacLoop is a handle to the constructor 5622 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 5623 * // null initializer for counter, should initialize to 0 5624 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 5625 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop}; 5626 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 5627 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 5628 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause); 5629 * assertEquals(5040, loop.invoke(7)); 5630 * }</pre></blockquote> 5631 * 5632 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above. 5633 * 5634 * @return a method handle embodying the looping behavior as defined by the arguments. 5635 * 5636 * @throws IllegalArgumentException in case any of the constraints described above is violated. 5637 * 5638 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle) 5639 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 5640 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle) 5641 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle) 5642 * @since 9 5643 */ 5644 public static MethodHandle loop(MethodHandle[]... clauses) { 5645 // Step 0: determine clause structure. 5646 loopChecks0(clauses); 5647 5648 List<MethodHandle> init = new ArrayList<>(); 5649 List<MethodHandle> step = new ArrayList<>(); 5650 List<MethodHandle> pred = new ArrayList<>(); 5651 List<MethodHandle> fini = new ArrayList<>(); 5652 5653 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> { 5654 init.add(clause[0]); // all clauses have at least length 1 5655 step.add(clause.length <= 1 ? null : clause[1]); 5656 pred.add(clause.length <= 2 ? null : clause[2]); 5657 fini.add(clause.length <= 3 ? null : clause[3]); 5658 }); 5659 5660 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1; 5661 final int nclauses = init.size(); 5662 5663 // Step 1A: determine iteration variables (V...). 5664 final List<Class<?>> iterationVariableTypes = new ArrayList<>(); 5665 for (int i = 0; i < nclauses; ++i) { 5666 MethodHandle in = init.get(i); 5667 MethodHandle st = step.get(i); 5668 if (in == null && st == null) { 5669 iterationVariableTypes.add(void.class); 5670 } else if (in != null && st != null) { 5671 loopChecks1a(i, in, st); 5672 iterationVariableTypes.add(in.type().returnType()); 5673 } else { 5674 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType()); 5675 } 5676 } 5677 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class). 5678 collect(Collectors.toList()); 5679 5680 // Step 1B: determine loop parameters (A...). 5681 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size()); 5682 loopChecks1b(init, commonSuffix); 5683 5684 // Step 1C: determine loop return type. 5685 // Step 1D: check other types. 5686 // local variable required here; see JDK-8223553 5687 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type) 5688 .map(MethodType::returnType); 5689 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class); 5690 loopChecks1cd(pred, fini, loopReturnType); 5691 5692 // Step 2: determine parameter lists. 5693 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix); 5694 commonParameterSequence.addAll(commonSuffix); 5695 loopChecks2(step, pred, fini, commonParameterSequence); 5696 5697 // Step 3: fill in omitted functions. 5698 for (int i = 0; i < nclauses; ++i) { 5699 Class<?> t = iterationVariableTypes.get(i); 5700 if (init.get(i) == null) { 5701 init.set(i, empty(methodType(t, commonSuffix))); 5702 } 5703 if (step.get(i) == null) { 5704 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i)); 5705 } 5706 if (pred.get(i) == null) { 5707 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence)); 5708 } 5709 if (fini.get(i) == null) { 5710 fini.set(i, empty(methodType(t, commonParameterSequence))); 5711 } 5712 } 5713 5714 // Step 4: fill in missing parameter types. 5715 // Also convert all handles to fixed-arity handles. 5716 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix)); 5717 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence)); 5718 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence)); 5719 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence)); 5720 5721 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList). 5722 allMatch(pl -> pl.equals(commonSuffix)); 5723 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList). 5724 allMatch(pl -> pl.equals(commonParameterSequence)); 5725 5726 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini); 5727 } 5728 5729 private static void loopChecks0(MethodHandle[][] clauses) { 5730 if (clauses == null || clauses.length == 0) { 5731 throw newIllegalArgumentException("null or no clauses passed"); 5732 } 5733 if (Stream.of(clauses).anyMatch(Objects::isNull)) { 5734 throw newIllegalArgumentException("null clauses are not allowed"); 5735 } 5736 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) { 5737 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements."); 5738 } 5739 } 5740 5741 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) { 5742 if (in.type().returnType() != st.type().returnType()) { 5743 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(), 5744 st.type().returnType()); 5745 } 5746 } 5747 5748 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) { 5749 final List<Class<?>> empty = List.of(); 5750 final List<Class<?>> longest = mhs.filter(Objects::nonNull). 5751 // take only those that can contribute to a common suffix because they are longer than the prefix 5752 map(MethodHandle::type). 5753 filter(t -> t.parameterCount() > skipSize). 5754 map(MethodType::parameterList). 5755 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 5756 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size()); 5757 } 5758 5759 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) { 5760 final List<Class<?>> empty = List.of(); 5761 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 5762 } 5763 5764 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) { 5765 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize); 5766 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0); 5767 return longestParameterList(Arrays.asList(longest1, longest2)); 5768 } 5769 5770 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) { 5771 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type). 5772 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) { 5773 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init + 5774 " (common suffix: " + commonSuffix + ")"); 5775 } 5776 } 5777 5778 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) { 5779 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 5780 anyMatch(t -> t != loopReturnType)) { 5781 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " + 5782 loopReturnType + ")"); 5783 } 5784 5785 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) { 5786 throw newIllegalArgumentException("no predicate found", pred); 5787 } 5788 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 5789 anyMatch(t -> t != boolean.class)) { 5790 throw newIllegalArgumentException("predicates must have boolean return type", pred); 5791 } 5792 } 5793 5794 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) { 5795 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type). 5796 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) { 5797 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step + 5798 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")"); 5799 } 5800 } 5801 5802 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) { 5803 return hs.stream().map(h -> { 5804 int pc = h.type().parameterCount(); 5805 int tpsize = targetParams.size(); 5806 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h; 5807 }).collect(Collectors.toList()); 5808 } 5809 5810 private static List<MethodHandle> fixArities(List<MethodHandle> hs) { 5811 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList()); 5812 } 5813 5814 /** 5815 * Constructs a {@code while} loop from an initializer, a body, and a predicate. 5816 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5817 * <p> 5818 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 5819 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate 5820 * evaluates to {@code true}). 5821 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case). 5822 * <p> 5823 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 5824 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 5825 * and updated with the value returned from its invocation. The result of loop execution will be 5826 * the final value of the additional loop-local variable (if present). 5827 * <p> 5828 * The following rules hold for these argument handles:<ul> 5829 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5830 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 5831 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5832 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 5833 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 5834 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 5835 * It will constrain the parameter lists of the other loop parts. 5836 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 5837 * list {@code (A...)} is called the <em>external parameter list</em>. 5838 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5839 * additional state variable of the loop. 5840 * The body must both accept and return a value of this type {@code V}. 5841 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5842 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5843 * <a href="MethodHandles.html#effid">effectively identical</a> 5844 * to the external parameter list {@code (A...)}. 5845 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5846 * {@linkplain #empty default value}. 5847 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 5848 * Its parameter list (either empty or of the form {@code (V A*)}) must be 5849 * effectively identical to the internal parameter list. 5850 * </ul> 5851 * <p> 5852 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5853 * <li>The loop handle's result type is the result type {@code V} of the body. 5854 * <li>The loop handle's parameter types are the types {@code (A...)}, 5855 * from the external parameter list. 5856 * </ul> 5857 * <p> 5858 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5859 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 5860 * passed to the loop. 5861 * <blockquote><pre>{@code 5862 * V init(A...); 5863 * boolean pred(V, A...); 5864 * V body(V, A...); 5865 * V whileLoop(A... a...) { 5866 * V v = init(a...); 5867 * while (pred(v, a...)) { 5868 * v = body(v, a...); 5869 * } 5870 * return v; 5871 * } 5872 * }</pre></blockquote> 5873 * 5874 * @apiNote Example: 5875 * <blockquote><pre>{@code 5876 * // implement the zip function for lists as a loop handle 5877 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); } 5878 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); } 5879 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) { 5880 * zip.add(a.next()); 5881 * zip.add(b.next()); 5882 * return zip; 5883 * } 5884 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods 5885 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep); 5886 * List<String> a = Arrays.asList("a", "b", "c", "d"); 5887 * List<String> b = Arrays.asList("e", "f", "g", "h"); 5888 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h"); 5889 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator())); 5890 * }</pre></blockquote> 5891 * 5892 * 5893 * @apiNote The implementation of this method can be expressed as follows: 5894 * <blockquote><pre>{@code 5895 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 5896 * MethodHandle fini = (body.type().returnType() == void.class 5897 * ? null : identity(body.type().returnType())); 5898 * MethodHandle[] 5899 * checkExit = { null, null, pred, fini }, 5900 * varBody = { init, body }; 5901 * return loop(checkExit, varBody); 5902 * } 5903 * }</pre></blockquote> 5904 * 5905 * @param init optional initializer, providing the initial value of the loop variable. 5906 * May be {@code null}, implying a default initial value. See above for other constraints. 5907 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 5908 * above for other constraints. 5909 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 5910 * See above for other constraints. 5911 * 5912 * @return a method handle implementing the {@code while} loop as described by the arguments. 5913 * @throws IllegalArgumentException if the rules for the arguments are violated. 5914 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 5915 * 5916 * @see #loop(MethodHandle[][]) 5917 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 5918 * @since 9 5919 */ 5920 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 5921 whileLoopChecks(init, pred, body); 5922 MethodHandle fini = identityOrVoid(body.type().returnType()); 5923 MethodHandle[] checkExit = { null, null, pred, fini }; 5924 MethodHandle[] varBody = { init, body }; 5925 return loop(checkExit, varBody); 5926 } 5927 5928 /** 5929 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. 5930 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5931 * <p> 5932 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 5933 * method will, in each iteration, first execute its body and then evaluate the predicate. 5934 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body. 5935 * <p> 5936 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 5937 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 5938 * and updated with the value returned from its invocation. The result of loop execution will be 5939 * the final value of the additional loop-local variable (if present). 5940 * <p> 5941 * The following rules hold for these argument handles:<ul> 5942 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5943 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 5944 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5945 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 5946 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 5947 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 5948 * It will constrain the parameter lists of the other loop parts. 5949 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 5950 * list {@code (A...)} is called the <em>external parameter list</em>. 5951 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5952 * additional state variable of the loop. 5953 * The body must both accept and return a value of this type {@code V}. 5954 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5955 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5956 * <a href="MethodHandles.html#effid">effectively identical</a> 5957 * to the external parameter list {@code (A...)}. 5958 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5959 * {@linkplain #empty default value}. 5960 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 5961 * Its parameter list (either empty or of the form {@code (V A*)}) must be 5962 * effectively identical to the internal parameter list. 5963 * </ul> 5964 * <p> 5965 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5966 * <li>The loop handle's result type is the result type {@code V} of the body. 5967 * <li>The loop handle's parameter types are the types {@code (A...)}, 5968 * from the external parameter list. 5969 * </ul> 5970 * <p> 5971 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5972 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 5973 * passed to the loop. 5974 * <blockquote><pre>{@code 5975 * V init(A...); 5976 * boolean pred(V, A...); 5977 * V body(V, A...); 5978 * V doWhileLoop(A... a...) { 5979 * V v = init(a...); 5980 * do { 5981 * v = body(v, a...); 5982 * } while (pred(v, a...)); 5983 * return v; 5984 * } 5985 * }</pre></blockquote> 5986 * 5987 * @apiNote Example: 5988 * <blockquote><pre>{@code 5989 * // int i = 0; while (i < limit) { ++i; } return i; => limit 5990 * static int zero(int limit) { return 0; } 5991 * static int step(int i, int limit) { return i + 1; } 5992 * static boolean pred(int i, int limit) { return i < limit; } 5993 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods 5994 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred); 5995 * assertEquals(23, loop.invoke(23)); 5996 * }</pre></blockquote> 5997 * 5998 * 5999 * @apiNote The implementation of this method can be expressed as follows: 6000 * <blockquote><pre>{@code 6001 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 6002 * MethodHandle fini = (body.type().returnType() == void.class 6003 * ? null : identity(body.type().returnType())); 6004 * MethodHandle[] clause = { init, body, pred, fini }; 6005 * return loop(clause); 6006 * } 6007 * }</pre></blockquote> 6008 * 6009 * @param init optional initializer, providing the initial value of the loop variable. 6010 * May be {@code null}, implying a default initial value. See above for other constraints. 6011 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 6012 * See above for other constraints. 6013 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 6014 * above for other constraints. 6015 * 6016 * @return a method handle implementing the {@code while} loop as described by the arguments. 6017 * @throws IllegalArgumentException if the rules for the arguments are violated. 6018 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 6019 * 6020 * @see #loop(MethodHandle[][]) 6021 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle) 6022 * @since 9 6023 */ 6024 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 6025 whileLoopChecks(init, pred, body); 6026 MethodHandle fini = identityOrVoid(body.type().returnType()); 6027 MethodHandle[] clause = {init, body, pred, fini }; 6028 return loop(clause); 6029 } 6030 6031 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) { 6032 Objects.requireNonNull(pred); 6033 Objects.requireNonNull(body); 6034 MethodType bodyType = body.type(); 6035 Class<?> returnType = bodyType.returnType(); 6036 List<Class<?>> innerList = bodyType.parameterList(); 6037 List<Class<?>> outerList = innerList; 6038 if (returnType == void.class) { 6039 // OK 6040 } else if (innerList.size() == 0 || innerList.get(0) != returnType) { 6041 // leading V argument missing => error 6042 MethodType expected = bodyType.insertParameterTypes(0, returnType); 6043 throw misMatchedTypes("body function", bodyType, expected); 6044 } else { 6045 outerList = innerList.subList(1, innerList.size()); 6046 } 6047 MethodType predType = pred.type(); 6048 if (predType.returnType() != boolean.class || 6049 !predType.effectivelyIdenticalParameters(0, innerList)) { 6050 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList)); 6051 } 6052 if (init != null) { 6053 MethodType initType = init.type(); 6054 if (initType.returnType() != returnType || 6055 !initType.effectivelyIdenticalParameters(0, outerList)) { 6056 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 6057 } 6058 } 6059 } 6060 6061 /** 6062 * Constructs a loop that runs a given number of iterations. 6063 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 6064 * <p> 6065 * The number of iterations is determined by the {@code iterations} handle evaluation result. 6066 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}. 6067 * It will be initialized to 0 and incremented by 1 in each iteration. 6068 * <p> 6069 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 6070 * of that type is also present. This variable is initialized using the optional {@code init} handle, 6071 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 6072 * <p> 6073 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 6074 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 6075 * iteration variable. 6076 * The result of the loop handle execution will be the final {@code V} value of that variable 6077 * (or {@code void} if there is no {@code V} variable). 6078 * <p> 6079 * The following rules hold for the argument handles:<ul> 6080 * <li>The {@code iterations} handle must not be {@code null}, and must return 6081 * the type {@code int}, referred to here as {@code I} in parameter type lists. 6082 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 6083 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 6084 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 6085 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 6086 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 6087 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 6088 * of types called the <em>internal parameter list</em>. 6089 * It will constrain the parameter lists of the other loop parts. 6090 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 6091 * with no additional {@code A} types, then the internal parameter list is extended by 6092 * the argument types {@code A...} of the {@code iterations} handle. 6093 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 6094 * list {@code (A...)} is called the <em>external parameter list</em>. 6095 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 6096 * additional state variable of the loop. 6097 * The body must both accept a leading parameter and return a value of this type {@code V}. 6098 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 6099 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 6100 * <a href="MethodHandles.html#effid">effectively identical</a> 6101 * to the external parameter list {@code (A...)}. 6102 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 6103 * {@linkplain #empty default value}. 6104 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be 6105 * effectively identical to the external parameter list {@code (A...)}. 6106 * </ul> 6107 * <p> 6108 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 6109 * <li>The loop handle's result type is the result type {@code V} of the body. 6110 * <li>The loop handle's parameter types are the types {@code (A...)}, 6111 * from the external parameter list. 6112 * </ul> 6113 * <p> 6114 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 6115 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 6116 * arguments passed to the loop. 6117 * <blockquote><pre>{@code 6118 * int iterations(A...); 6119 * V init(A...); 6120 * V body(V, int, A...); 6121 * V countedLoop(A... a...) { 6122 * int end = iterations(a...); 6123 * V v = init(a...); 6124 * for (int i = 0; i < end; ++i) { 6125 * v = body(v, i, a...); 6126 * } 6127 * return v; 6128 * } 6129 * }</pre></blockquote> 6130 * 6131 * @apiNote Example with a fully conformant body method: 6132 * <blockquote><pre>{@code 6133 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 6134 * // => a variation on a well known theme 6135 * static String step(String v, int counter, String init) { return "na " + v; } 6136 * // assume MH_step is a handle to the method above 6137 * MethodHandle fit13 = MethodHandles.constant(int.class, 13); 6138 * MethodHandle start = MethodHandles.identity(String.class); 6139 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step); 6140 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!")); 6141 * }</pre></blockquote> 6142 * 6143 * @apiNote Example with the simplest possible body method type, 6144 * and passing the number of iterations to the loop invocation: 6145 * <blockquote><pre>{@code 6146 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 6147 * // => a variation on a well known theme 6148 * static String step(String v, int counter ) { return "na " + v; } 6149 * // assume MH_step is a handle to the method above 6150 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class); 6151 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class); 6152 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v 6153 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!")); 6154 * }</pre></blockquote> 6155 * 6156 * @apiNote Example that treats the number of iterations, string to append to, and string to append 6157 * as loop parameters: 6158 * <blockquote><pre>{@code 6159 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 6160 * // => a variation on a well known theme 6161 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; } 6162 * // assume MH_step is a handle to the method above 6163 * MethodHandle count = MethodHandles.identity(int.class); 6164 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class); 6165 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v 6166 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!")); 6167 * }</pre></blockquote> 6168 * 6169 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)} 6170 * to enforce a loop type: 6171 * <blockquote><pre>{@code 6172 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 6173 * // => a variation on a well known theme 6174 * static String step(String v, int counter, String pre) { return pre + " " + v; } 6175 * // assume MH_step is a handle to the method above 6176 * MethodType loopType = methodType(String.class, String.class, int.class, String.class); 6177 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1); 6178 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2); 6179 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0); 6180 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v 6181 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!")); 6182 * }</pre></blockquote> 6183 * 6184 * @apiNote The implementation of this method can be expressed as follows: 6185 * <blockquote><pre>{@code 6186 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 6187 * return countedLoop(empty(iterations.type()), iterations, init, body); 6188 * } 6189 * }</pre></blockquote> 6190 * 6191 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's 6192 * result type must be {@code int}. See above for other constraints. 6193 * @param init optional initializer, providing the initial value of the loop variable. 6194 * May be {@code null}, implying a default initial value. See above for other constraints. 6195 * @param body body of the loop, which may not be {@code null}. 6196 * It controls the loop parameters and result type in the standard case (see above for details). 6197 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 6198 * and may accept any number of additional types. 6199 * See above for other constraints. 6200 * 6201 * @return a method handle representing the loop. 6202 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}. 6203 * @throws IllegalArgumentException if any argument violates the rules formulated above. 6204 * 6205 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle) 6206 * @since 9 6207 */ 6208 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 6209 return countedLoop(empty(iterations.type()), iterations, init, body); 6210 } 6211 6212 /** 6213 * Constructs a loop that counts over a range of numbers. 6214 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 6215 * <p> 6216 * The loop counter {@code i} is a loop iteration variable of type {@code int}. 6217 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive) 6218 * values of the loop counter. 6219 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the 6220 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1. 6221 * <p> 6222 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 6223 * of that type is also present. This variable is initialized using the optional {@code init} handle, 6224 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 6225 * <p> 6226 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 6227 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 6228 * iteration variable. 6229 * The result of the loop handle execution will be the final {@code V} value of that variable 6230 * (or {@code void} if there is no {@code V} variable). 6231 * <p> 6232 * The following rules hold for the argument handles:<ul> 6233 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return 6234 * the common type {@code int}, referred to here as {@code I} in parameter type lists. 6235 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 6236 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 6237 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 6238 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 6239 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 6240 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 6241 * of types called the <em>internal parameter list</em>. 6242 * It will constrain the parameter lists of the other loop parts. 6243 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 6244 * with no additional {@code A} types, then the internal parameter list is extended by 6245 * the argument types {@code A...} of the {@code end} handle. 6246 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 6247 * list {@code (A...)} is called the <em>external parameter list</em>. 6248 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 6249 * additional state variable of the loop. 6250 * The body must both accept a leading parameter and return a value of this type {@code V}. 6251 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 6252 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 6253 * <a href="MethodHandles.html#effid">effectively identical</a> 6254 * to the external parameter list {@code (A...)}. 6255 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 6256 * {@linkplain #empty default value}. 6257 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be 6258 * effectively identical to the external parameter list {@code (A...)}. 6259 * <li>Likewise, the parameter list of {@code end} must be effectively identical 6260 * to the external parameter list. 6261 * </ul> 6262 * <p> 6263 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 6264 * <li>The loop handle's result type is the result type {@code V} of the body. 6265 * <li>The loop handle's parameter types are the types {@code (A...)}, 6266 * from the external parameter list. 6267 * </ul> 6268 * <p> 6269 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 6270 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 6271 * arguments passed to the loop. 6272 * <blockquote><pre>{@code 6273 * int start(A...); 6274 * int end(A...); 6275 * V init(A...); 6276 * V body(V, int, A...); 6277 * V countedLoop(A... a...) { 6278 * int e = end(a...); 6279 * int s = start(a...); 6280 * V v = init(a...); 6281 * for (int i = s; i < e; ++i) { 6282 * v = body(v, i, a...); 6283 * } 6284 * return v; 6285 * } 6286 * }</pre></blockquote> 6287 * 6288 * @apiNote The implementation of this method can be expressed as follows: 6289 * <blockquote><pre>{@code 6290 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 6291 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class); 6292 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with 6293 * // the following semantics: 6294 * // MH_increment: (int limit, int counter) -> counter + 1 6295 * // MH_predicate: (int limit, int counter) -> counter < limit 6296 * Class<?> counterType = start.type().returnType(); // int 6297 * Class<?> returnType = body.type().returnType(); 6298 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null; 6299 * if (returnType != void.class) { // ignore the V variable 6300 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 6301 * pred = dropArguments(pred, 1, returnType); // ditto 6302 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit 6303 * } 6304 * body = dropArguments(body, 0, counterType); // ignore the limit variable 6305 * MethodHandle[] 6306 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 6307 * bodyClause = { init, body }, // v = init(); v = body(v, i) 6308 * indexVar = { start, incr }; // i = start(); i = i + 1 6309 * return loop(loopLimit, bodyClause, indexVar); 6310 * } 6311 * }</pre></blockquote> 6312 * 6313 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}. 6314 * See above for other constraints. 6315 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to 6316 * {@code end-1}). The result type must be {@code int}. See above for other constraints. 6317 * @param init optional initializer, providing the initial value of the loop variable. 6318 * May be {@code null}, implying a default initial value. See above for other constraints. 6319 * @param body body of the loop, which may not be {@code null}. 6320 * It controls the loop parameters and result type in the standard case (see above for details). 6321 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 6322 * and may accept any number of additional types. 6323 * See above for other constraints. 6324 * 6325 * @return a method handle representing the loop. 6326 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}. 6327 * @throws IllegalArgumentException if any argument violates the rules formulated above. 6328 * 6329 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle) 6330 * @since 9 6331 */ 6332 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 6333 countedLoopChecks(start, end, init, body); 6334 Class<?> counterType = start.type().returnType(); // int, but who's counting? 6335 Class<?> limitType = end.type().returnType(); // yes, int again 6336 Class<?> returnType = body.type().returnType(); 6337 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep); 6338 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred); 6339 MethodHandle retv = null; 6340 if (returnType != void.class) { 6341 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 6342 pred = dropArguments(pred, 1, returnType); // ditto 6343 retv = dropArguments(identity(returnType), 0, counterType); 6344 } 6345 body = dropArguments(body, 0, counterType); // ignore the limit variable 6346 MethodHandle[] 6347 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 6348 bodyClause = { init, body }, // v = init(); v = body(v, i) 6349 indexVar = { start, incr }; // i = start(); i = i + 1 6350 return loop(loopLimit, bodyClause, indexVar); 6351 } 6352 6353 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 6354 Objects.requireNonNull(start); 6355 Objects.requireNonNull(end); 6356 Objects.requireNonNull(body); 6357 Class<?> counterType = start.type().returnType(); 6358 if (counterType != int.class) { 6359 MethodType expected = start.type().changeReturnType(int.class); 6360 throw misMatchedTypes("start function", start.type(), expected); 6361 } else if (end.type().returnType() != counterType) { 6362 MethodType expected = end.type().changeReturnType(counterType); 6363 throw misMatchedTypes("end function", end.type(), expected); 6364 } 6365 MethodType bodyType = body.type(); 6366 Class<?> returnType = bodyType.returnType(); 6367 List<Class<?>> innerList = bodyType.parameterList(); 6368 // strip leading V value if present 6369 int vsize = (returnType == void.class ? 0 : 1); 6370 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) { 6371 // argument list has no "V" => error 6372 MethodType expected = bodyType.insertParameterTypes(0, returnType); 6373 throw misMatchedTypes("body function", bodyType, expected); 6374 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) { 6375 // missing I type => error 6376 MethodType expected = bodyType.insertParameterTypes(vsize, counterType); 6377 throw misMatchedTypes("body function", bodyType, expected); 6378 } 6379 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size()); 6380 if (outerList.isEmpty()) { 6381 // special case; take lists from end handle 6382 outerList = end.type().parameterList(); 6383 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList(); 6384 } 6385 MethodType expected = methodType(counterType, outerList); 6386 if (!start.type().effectivelyIdenticalParameters(0, outerList)) { 6387 throw misMatchedTypes("start parameter types", start.type(), expected); 6388 } 6389 if (end.type() != start.type() && 6390 !end.type().effectivelyIdenticalParameters(0, outerList)) { 6391 throw misMatchedTypes("end parameter types", end.type(), expected); 6392 } 6393 if (init != null) { 6394 MethodType initType = init.type(); 6395 if (initType.returnType() != returnType || 6396 !initType.effectivelyIdenticalParameters(0, outerList)) { 6397 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 6398 } 6399 } 6400 } 6401 6402 /** 6403 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}. 6404 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 6405 * <p> 6406 * The iterator itself will be determined by the evaluation of the {@code iterator} handle. 6407 * Each value it produces will be stored in a loop iteration variable of type {@code T}. 6408 * <p> 6409 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 6410 * of that type is also present. This variable is initialized using the optional {@code init} handle, 6411 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 6412 * <p> 6413 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 6414 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 6415 * iteration variable. 6416 * The result of the loop handle execution will be the final {@code V} value of that variable 6417 * (or {@code void} if there is no {@code V} variable). 6418 * <p> 6419 * The following rules hold for the argument handles:<ul> 6420 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 6421 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}. 6422 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 6423 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V} 6424 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.) 6425 * <li>The parameter list {@code (V T A...)} of the body contributes to a list 6426 * of types called the <em>internal parameter list</em>. 6427 * It will constrain the parameter lists of the other loop parts. 6428 * <li>As a special case, if the body contributes only {@code V} and {@code T} types, 6429 * with no additional {@code A} types, then the internal parameter list is extended by 6430 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the 6431 * single type {@code Iterable} is added and constitutes the {@code A...} list. 6432 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter 6433 * list {@code (A...)} is called the <em>external parameter list</em>. 6434 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 6435 * additional state variable of the loop. 6436 * The body must both accept a leading parameter and return a value of this type {@code V}. 6437 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 6438 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 6439 * <a href="MethodHandles.html#effid">effectively identical</a> 6440 * to the external parameter list {@code (A...)}. 6441 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 6442 * {@linkplain #empty default value}. 6443 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return 6444 * type {@code java.util.Iterator} or a subtype thereof. 6445 * The iterator it produces when the loop is executed will be assumed 6446 * to yield values which can be converted to type {@code T}. 6447 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be 6448 * effectively identical to the external parameter list {@code (A...)}. 6449 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves 6450 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list 6451 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator 6452 * handle parameter is adjusted to accept the leading {@code A} type, as if by 6453 * the {@link MethodHandle#asType asType} conversion method. 6454 * The leading {@code A} type must be {@code Iterable} or a subtype thereof. 6455 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}. 6456 * </ul> 6457 * <p> 6458 * The type {@code T} may be either a primitive or reference. 6459 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator}, 6460 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object} 6461 * as if by the {@link MethodHandle#asType asType} conversion method. 6462 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur 6463 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}. 6464 * <p> 6465 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 6466 * <li>The loop handle's result type is the result type {@code V} of the body. 6467 * <li>The loop handle's parameter types are the types {@code (A...)}, 6468 * from the external parameter list. 6469 * </ul> 6470 * <p> 6471 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 6472 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the 6473 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop. 6474 * <blockquote><pre>{@code 6475 * Iterator<T> iterator(A...); // defaults to Iterable::iterator 6476 * V init(A...); 6477 * V body(V,T,A...); 6478 * V iteratedLoop(A... a...) { 6479 * Iterator<T> it = iterator(a...); 6480 * V v = init(a...); 6481 * while (it.hasNext()) { 6482 * T t = it.next(); 6483 * v = body(v, t, a...); 6484 * } 6485 * return v; 6486 * } 6487 * }</pre></blockquote> 6488 * 6489 * @apiNote Example: 6490 * <blockquote><pre>{@code 6491 * // get an iterator from a list 6492 * static List<String> reverseStep(List<String> r, String e) { 6493 * r.add(0, e); 6494 * return r; 6495 * } 6496 * static List<String> newArrayList() { return new ArrayList<>(); } 6497 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods 6498 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep); 6499 * List<String> list = Arrays.asList("a", "b", "c", "d", "e"); 6500 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a"); 6501 * assertEquals(reversedList, (List<String>) loop.invoke(list)); 6502 * }</pre></blockquote> 6503 * 6504 * @apiNote The implementation of this method can be expressed approximately as follows: 6505 * <blockquote><pre>{@code 6506 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 6507 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable 6508 * Class<?> returnType = body.type().returnType(); 6509 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 6510 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype)); 6511 * MethodHandle retv = null, step = body, startIter = iterator; 6512 * if (returnType != void.class) { 6513 * // the simple thing first: in (I V A...), drop the I to get V 6514 * retv = dropArguments(identity(returnType), 0, Iterator.class); 6515 * // body type signature (V T A...), internal loop types (I V A...) 6516 * step = swapArguments(body, 0, 1); // swap V <-> T 6517 * } 6518 * if (startIter == null) startIter = MH_getIter; 6519 * MethodHandle[] 6520 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext()) 6521 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a) 6522 * return loop(iterVar, bodyClause); 6523 * } 6524 * }</pre></blockquote> 6525 * 6526 * @param iterator an optional handle to return the iterator to start the loop. 6527 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype. 6528 * See above for other constraints. 6529 * @param init optional initializer, providing the initial value of the loop variable. 6530 * May be {@code null}, implying a default initial value. See above for other constraints. 6531 * @param body body of the loop, which may not be {@code null}. 6532 * It controls the loop parameters and result type in the standard case (see above for details). 6533 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values), 6534 * and may accept any number of additional types. 6535 * See above for other constraints. 6536 * 6537 * @return a method handle embodying the iteration loop functionality. 6538 * @throws NullPointerException if the {@code body} handle is {@code null}. 6539 * @throws IllegalArgumentException if any argument violates the above requirements. 6540 * 6541 * @since 9 6542 */ 6543 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 6544 Class<?> iterableType = iteratedLoopChecks(iterator, init, body); 6545 Class<?> returnType = body.type().returnType(); 6546 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred); 6547 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext); 6548 MethodHandle startIter; 6549 MethodHandle nextVal; 6550 { 6551 MethodType iteratorType; 6552 if (iterator == null) { 6553 // derive argument type from body, if available, else use Iterable 6554 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator); 6555 iteratorType = startIter.type().changeParameterType(0, iterableType); 6556 } else { 6557 // force return type to the internal iterator class 6558 iteratorType = iterator.type().changeReturnType(Iterator.class); 6559 startIter = iterator; 6560 } 6561 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 6562 MethodType nextValType = nextRaw.type().changeReturnType(ttype); 6563 6564 // perform the asType transforms under an exception transformer, as per spec.: 6565 try { 6566 startIter = startIter.asType(iteratorType); 6567 nextVal = nextRaw.asType(nextValType); 6568 } catch (WrongMethodTypeException ex) { 6569 throw new IllegalArgumentException(ex); 6570 } 6571 } 6572 6573 MethodHandle retv = null, step = body; 6574 if (returnType != void.class) { 6575 // the simple thing first: in (I V A...), drop the I to get V 6576 retv = dropArguments(identity(returnType), 0, Iterator.class); 6577 // body type signature (V T A...), internal loop types (I V A...) 6578 step = swapArguments(body, 0, 1); // swap V <-> T 6579 } 6580 6581 MethodHandle[] 6582 iterVar = { startIter, null, hasNext, retv }, 6583 bodyClause = { init, filterArgument(step, 0, nextVal) }; 6584 return loop(iterVar, bodyClause); 6585 } 6586 6587 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) { 6588 Objects.requireNonNull(body); 6589 MethodType bodyType = body.type(); 6590 Class<?> returnType = bodyType.returnType(); 6591 List<Class<?>> internalParamList = bodyType.parameterList(); 6592 // strip leading V value if present 6593 int vsize = (returnType == void.class ? 0 : 1); 6594 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) { 6595 // argument list has no "V" => error 6596 MethodType expected = bodyType.insertParameterTypes(0, returnType); 6597 throw misMatchedTypes("body function", bodyType, expected); 6598 } else if (internalParamList.size() <= vsize) { 6599 // missing T type => error 6600 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class); 6601 throw misMatchedTypes("body function", bodyType, expected); 6602 } 6603 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size()); 6604 Class<?> iterableType = null; 6605 if (iterator != null) { 6606 // special case; if the body handle only declares V and T then 6607 // the external parameter list is obtained from iterator handle 6608 if (externalParamList.isEmpty()) { 6609 externalParamList = iterator.type().parameterList(); 6610 } 6611 MethodType itype = iterator.type(); 6612 if (!Iterator.class.isAssignableFrom(itype.returnType())) { 6613 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type"); 6614 } 6615 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) { 6616 MethodType expected = methodType(itype.returnType(), externalParamList); 6617 throw misMatchedTypes("iterator parameters", itype, expected); 6618 } 6619 } else { 6620 if (externalParamList.isEmpty()) { 6621 // special case; if the iterator handle is null and the body handle 6622 // only declares V and T then the external parameter list consists 6623 // of Iterable 6624 externalParamList = Arrays.asList(Iterable.class); 6625 iterableType = Iterable.class; 6626 } else { 6627 // special case; if the iterator handle is null and the external 6628 // parameter list is not empty then the first parameter must be 6629 // assignable to Iterable 6630 iterableType = externalParamList.get(0); 6631 if (!Iterable.class.isAssignableFrom(iterableType)) { 6632 throw newIllegalArgumentException( 6633 "inferred first loop argument must inherit from Iterable: " + iterableType); 6634 } 6635 } 6636 } 6637 if (init != null) { 6638 MethodType initType = init.type(); 6639 if (initType.returnType() != returnType || 6640 !initType.effectivelyIdenticalParameters(0, externalParamList)) { 6641 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList)); 6642 } 6643 } 6644 return iterableType; // help the caller a bit 6645 } 6646 6647 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) { 6648 // there should be a better way to uncross my wires 6649 int arity = mh.type().parameterCount(); 6650 int[] order = new int[arity]; 6651 for (int k = 0; k < arity; k++) order[k] = k; 6652 order[i] = j; order[j] = i; 6653 Class<?>[] types = mh.type().parameterArray(); 6654 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti; 6655 MethodType swapType = methodType(mh.type().returnType(), types); 6656 return permuteArguments(mh, swapType, order); 6657 } 6658 6659 /** 6660 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block. 6661 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception 6662 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The 6663 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The 6664 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the 6665 * {@code try-finally} handle. 6666 * <p> 6667 * The {@code cleanup} handle will be passed one or two additional leading arguments. 6668 * The first is the exception thrown during the 6669 * execution of the {@code target} handle, or {@code null} if no exception was thrown. 6670 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception, 6671 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder. 6672 * The second argument is not present if the {@code target} handle has a {@code void} return type. 6673 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists 6674 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.) 6675 * <p> 6676 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except 6677 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or 6678 * two extra leading parameters:<ul> 6679 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and 6680 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry 6681 * the result from the execution of the {@code target} handle. 6682 * This parameter is not present if the {@code target} returns {@code void}. 6683 * </ul> 6684 * <p> 6685 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of 6686 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting 6687 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by 6688 * the cleanup. 6689 * <blockquote><pre>{@code 6690 * V target(A..., B...); 6691 * V cleanup(Throwable, V, A...); 6692 * V adapter(A... a, B... b) { 6693 * V result = (zero value for V); 6694 * Throwable throwable = null; 6695 * try { 6696 * result = target(a..., b...); 6697 * } catch (Throwable t) { 6698 * throwable = t; 6699 * throw t; 6700 * } finally { 6701 * result = cleanup(throwable, result, a...); 6702 * } 6703 * return result; 6704 * } 6705 * }</pre></blockquote> 6706 * <p> 6707 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 6708 * be modified by execution of the target, and so are passed unchanged 6709 * from the caller to the cleanup, if it is invoked. 6710 * <p> 6711 * The target and cleanup must return the same type, even if the cleanup 6712 * always throws. 6713 * To create such a throwing cleanup, compose the cleanup logic 6714 * with {@link #throwException throwException}, 6715 * in order to create a method handle of the correct return type. 6716 * <p> 6717 * Note that {@code tryFinally} never converts exceptions into normal returns. 6718 * In rare cases where exceptions must be converted in that way, first wrap 6719 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)} 6720 * to capture an outgoing exception, and then wrap with {@code tryFinally}. 6721 * <p> 6722 * It is recommended that the first parameter type of {@code cleanup} be 6723 * declared {@code Throwable} rather than a narrower subtype. This ensures 6724 * {@code cleanup} will always be invoked with whatever exception that 6725 * {@code target} throws. Declaring a narrower type may result in a 6726 * {@code ClassCastException} being thrown by the {@code try-finally} 6727 * handle if the type of the exception thrown by {@code target} is not 6728 * assignable to the first parameter type of {@code cleanup}. Note that 6729 * various exception types of {@code VirtualMachineError}, 6730 * {@code LinkageError}, and {@code RuntimeException} can in principle be 6731 * thrown by almost any kind of Java code, and a finally clause that 6732 * catches (say) only {@code IOException} would mask any of the others 6733 * behind a {@code ClassCastException}. 6734 * 6735 * @param target the handle whose execution is to be wrapped in a {@code try} block. 6736 * @param cleanup the handle that is invoked in the finally block. 6737 * 6738 * @return a method handle embodying the {@code try-finally} block composed of the two arguments. 6739 * @throws NullPointerException if any argument is null 6740 * @throws IllegalArgumentException if {@code cleanup} does not accept 6741 * the required leading arguments, or if the method handle types do 6742 * not match in their return types and their 6743 * corresponding trailing parameters 6744 * 6745 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle) 6746 * @since 9 6747 */ 6748 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) { 6749 List<Class<?>> targetParamTypes = target.type().parameterList(); 6750 Class<?> rtype = target.type().returnType(); 6751 6752 tryFinallyChecks(target, cleanup); 6753 6754 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments. 6755 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 6756 // target parameter list. 6757 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0); 6758 6759 // Ensure that the intrinsic type checks the instance thrown by the 6760 // target against the first parameter of cleanup 6761 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class)); 6762 6763 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case. 6764 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes); 6765 } 6766 6767 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) { 6768 Class<?> rtype = target.type().returnType(); 6769 if (rtype != cleanup.type().returnType()) { 6770 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype); 6771 } 6772 MethodType cleanupType = cleanup.type(); 6773 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) { 6774 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class); 6775 } 6776 if (rtype != void.class && cleanupType.parameterType(1) != rtype) { 6777 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype); 6778 } 6779 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 6780 // target parameter list. 6781 int cleanupArgIndex = rtype == void.class ? 1 : 2; 6782 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) { 6783 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix", 6784 cleanup.type(), target.type()); 6785 } 6786 } 6787 6788 }