1 /* 2 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang.invoke; 27 28 import jdk.internal.misc.SharedSecrets; 29 import jdk.internal.module.IllegalAccessLogger; 30 import jdk.internal.org.objectweb.asm.ClassReader; 31 import jdk.internal.reflect.CallerSensitive; 32 import jdk.internal.reflect.Reflection; 33 import jdk.internal.vm.annotation.ForceInline; 34 import sun.invoke.util.ValueConversions; 35 import sun.invoke.util.VerifyAccess; 36 import sun.invoke.util.Wrapper; 37 import sun.reflect.misc.ReflectUtil; 38 import sun.security.util.SecurityConstants; 39 40 import java.lang.invoke.LambdaForm.BasicType; 41 import java.lang.reflect.Constructor; 42 import java.lang.reflect.Field; 43 import java.lang.reflect.Member; 44 import java.lang.reflect.Method; 45 import java.lang.reflect.Modifier; 46 import java.lang.reflect.ReflectPermission; 47 import java.nio.ByteOrder; 48 import java.security.AccessController; 49 import java.security.PrivilegedAction; 50 import java.security.ProtectionDomain; 51 import java.util.ArrayList; 52 import java.util.Arrays; 53 import java.util.BitSet; 54 import java.util.Iterator; 55 import java.util.List; 56 import java.util.Objects; 57 import java.util.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 PUBLIC} and {@code UNCONDITIONAL} modes. 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. Consequently, the lookup context of this lookup object will be the 138 * bootstrap class loader, which means it cannot find user classes. 139 * 140 * <p style="font-size:smaller;"> 141 * <em>Discussion:</em> 142 * The lookup class can be changed to any other class {@code C} using an expression of the form 143 * {@link Lookup#in publicLookup().in(C.class)}. 144 * but may change the lookup context by virtue of changing the class loader. 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} with full capabilities to emulate all 160 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc"> 161 * private access</a>, on a target class. 162 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to 163 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing 164 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing 165 * the target class, then this check ensures that 166 * <ul> 167 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li> 168 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing 169 * the target class to at least {@code m1}.</li> 170 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li> 171 * </ul> 172 * <p> 173 * If there is a security manager, its {@code checkPermission} method is called to 174 * check {@code ReflectPermission("suppressAccessChecks")}. 175 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object 176 * was created by code in the caller module (or derived from a lookup object originally 177 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be 178 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE} 179 * access to the caller. 180 * @param targetClass the target class 181 * @param lookup the caller lookup object 182 * @return a lookup object for the target class, with private access 183 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class 184 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null} 185 * @throws IllegalAccessException if the access check specified above fails 186 * @throws SecurityException if denied by the security manager 187 * @since 9 188 * @spec JPMS 189 * @see Lookup#dropLookupMode 190 */ 191 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException { 192 SecurityManager sm = System.getSecurityManager(); 193 if (sm != null) sm.checkPermission(ACCESS_PERMISSION); 194 if (targetClass.isPrimitive()) 195 throw new IllegalArgumentException(targetClass + " is a primitive class"); 196 if (targetClass.isArray()) 197 throw new IllegalArgumentException(targetClass + " is an array class"); 198 Module targetModule = targetClass.getModule(); 199 Module callerModule = lookup.lookupClass().getModule(); 200 if (!callerModule.canRead(targetModule)) 201 throw new IllegalAccessException(callerModule + " does not read " + targetModule); 202 if (targetModule.isNamed()) { 203 String pn = targetClass.getPackageName(); 204 assert pn.length() > 0 : "unnamed package cannot be in named module"; 205 if (!targetModule.isOpen(pn, callerModule)) 206 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule); 207 } 208 if ((lookup.lookupModes() & Lookup.MODULE) == 0) 209 throw new IllegalAccessException("lookup does not have MODULE lookup mode"); 210 if (!callerModule.isNamed() && targetModule.isNamed()) { 211 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger(); 212 if (logger != null) { 213 logger.logIfOpenedForIllegalAccess(lookup, targetClass); 214 } 215 } 216 return new Lookup(targetClass); 217 } 218 219 /** 220 * Performs an unchecked "crack" of a 221 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>. 222 * The result is as if the user had obtained a lookup object capable enough 223 * to crack the target method handle, called 224 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} 225 * on the target to obtain its symbolic reference, and then called 226 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} 227 * to resolve the symbolic reference to a member. 228 * <p> 229 * If there is a security manager, its {@code checkPermission} method 230 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission. 231 * @param <T> the desired type of the result, either {@link Member} or a subtype 232 * @param target a direct method handle to crack into symbolic reference components 233 * @param expected a class object representing the desired result type {@code T} 234 * @return a reference to the method, constructor, or field object 235 * @exception SecurityException if the caller is not privileged to call {@code setAccessible} 236 * @exception NullPointerException if either argument is {@code null} 237 * @exception IllegalArgumentException if the target is not a direct method handle 238 * @exception ClassCastException if the member is not of the expected type 239 * @since 1.8 240 */ 241 public static <T extends Member> T 242 reflectAs(Class<T> expected, MethodHandle target) { 243 SecurityManager smgr = System.getSecurityManager(); 244 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION); 245 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup 246 return lookup.revealDirect(target).reflectAs(expected, lookup); 247 } 248 // Copied from AccessibleObject, as used by Method.setAccessible, etc.: 249 private static final java.security.Permission ACCESS_PERMISSION = 250 new ReflectPermission("suppressAccessChecks"); 251 252 /** 253 * A <em>lookup object</em> is a factory for creating method handles, 254 * when the creation requires access checking. 255 * Method handles do not perform 256 * access checks when they are called, but rather when they are created. 257 * Therefore, method handle access 258 * restrictions must be enforced when a method handle is created. 259 * The caller class against which those restrictions are enforced 260 * is known as the {@linkplain #lookupClass() lookup class}. 261 * <p> 262 * A lookup class which needs to create method handles will call 263 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself. 264 * When the {@code Lookup} factory object is created, the identity of the lookup class is 265 * determined, and securely stored in the {@code Lookup} object. 266 * The lookup class (or its delegates) may then use factory methods 267 * on the {@code Lookup} object to create method handles for access-checked members. 268 * This includes all methods, constructors, and fields which are allowed to the lookup class, 269 * even private ones. 270 * 271 * <h1><a id="lookups"></a>Lookup Factory Methods</h1> 272 * The factory methods on a {@code Lookup} object correspond to all major 273 * use cases for methods, constructors, and fields. 274 * Each method handle created by a factory method is the functional 275 * equivalent of a particular <em>bytecode behavior</em>. 276 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.) 277 * Here is a summary of the correspondence between these factory methods and 278 * the behavior of the resulting method handles: 279 * <table class="striped"> 280 * <caption style="display:none">lookup method behaviors</caption> 281 * <thead> 282 * <tr> 283 * <th scope="col"><a id="equiv"></a>lookup expression</th> 284 * <th scope="col">member</th> 285 * <th scope="col">bytecode behavior</th> 286 * </tr> 287 * </thead> 288 * <tbody> 289 * <tr> 290 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th> 291 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td> 292 * </tr> 293 * <tr> 294 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th> 295 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td> 296 * </tr> 297 * <tr> 298 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th> 299 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td> 300 * </tr> 301 * <tr> 302 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th> 303 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td> 304 * </tr> 305 * <tr> 306 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th> 307 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td> 308 * </tr> 309 * <tr> 310 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th> 311 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td> 312 * </tr> 313 * <tr> 314 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th> 315 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 316 * </tr> 317 * <tr> 318 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th> 319 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td> 320 * </tr> 321 * <tr> 322 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th> 323 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td> 324 * </tr> 325 * <tr> 326 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th> 327 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td> 328 * </tr> 329 * <tr> 330 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th> 331 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 332 * </tr> 333 * <tr> 334 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th> 335 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td> 336 * </tr> 337 * <tr> 338 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th> 339 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 340 * </tr> 341 * <tr> 342 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th> 343 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td> 344 * </tr> 345 * </tbody> 346 * </table> 347 * 348 * Here, the type {@code C} is the class or interface being searched for a member, 349 * documented as a parameter named {@code refc} in the lookup methods. 350 * The method type {@code MT} is composed from the return type {@code T} 351 * and the sequence of argument types {@code A*}. 352 * The constructor also has a sequence of argument types {@code A*} and 353 * is deemed to return the newly-created object of type {@code C}. 354 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}. 355 * The formal parameter {@code this} stands for the self-reference of type {@code C}; 356 * if it is present, it is always the leading argument to the method handle invocation. 357 * (In the case of some {@code protected} members, {@code this} may be 358 * restricted in type to the lookup class; see below.) 359 * The name {@code arg} stands for all the other method handle arguments. 360 * In the code examples for the Core Reflection API, the name {@code thisOrNull} 361 * stands for a null reference if the accessed method or field is static, 362 * and {@code this} otherwise. 363 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand 364 * for reflective objects corresponding to the given members. 365 * <p> 366 * The bytecode behavior for a {@code findClass} operation is a load of a constant class, 367 * as if by {@code ldc CONSTANT_Class}. 368 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant. 369 * <p> 370 * In cases where the given member is of variable arity (i.e., a method or constructor) 371 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. 372 * In all other cases, the returned method handle will be of fixed arity. 373 * <p style="font-size:smaller;"> 374 * <em>Discussion:</em> 375 * The equivalence between looked-up method handles and underlying 376 * class members and bytecode behaviors 377 * can break down in a few ways: 378 * <ul style="font-size:smaller;"> 379 * <li>If {@code C} is not symbolically accessible from the lookup class's loader, 380 * the lookup can still succeed, even when there is no equivalent 381 * Java expression or bytecoded constant. 382 * <li>Likewise, if {@code T} or {@code MT} 383 * is not symbolically accessible from the lookup class's loader, 384 * the lookup can still succeed. 385 * For example, lookups for {@code MethodHandle.invokeExact} and 386 * {@code MethodHandle.invoke} will always succeed, regardless of requested type. 387 * <li>If there is a security manager installed, it can forbid the lookup 388 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>). 389 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle} 390 * constant is not subject to security manager checks. 391 * <li>If the looked-up method has a 392 * <a href="MethodHandle.html#maxarity">very large arity</a>, 393 * the method handle creation may fail with an 394 * {@code IllegalArgumentException}, due to the method handle type having 395 * <a href="MethodHandle.html#maxarity">too many parameters.</a> 396 * </ul> 397 * 398 * <h1><a id="access"></a>Access checking</h1> 399 * Access checks are applied in the factory methods of {@code Lookup}, 400 * when a method handle is created. 401 * This is a key difference from the Core Reflection API, since 402 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 403 * performs access checking against every caller, on every call. 404 * <p> 405 * All access checks start from a {@code Lookup} object, which 406 * compares its recorded lookup class against all requests to 407 * create method handles. 408 * A single {@code Lookup} object can be used to create any number 409 * of access-checked method handles, all checked against a single 410 * lookup class. 411 * <p> 412 * A {@code Lookup} object can be shared with other trusted code, 413 * such as a metaobject protocol. 414 * A shared {@code Lookup} object delegates the capability 415 * to create method handles on private members of the lookup class. 416 * Even if privileged code uses the {@code Lookup} object, 417 * the access checking is confined to the privileges of the 418 * original lookup class. 419 * <p> 420 * A lookup can fail, because 421 * the containing class is not accessible to the lookup class, or 422 * because the desired class member is missing, or because the 423 * desired class member is not accessible to the lookup class, or 424 * because the lookup object is not trusted enough to access the member. 425 * In any of these cases, a {@code ReflectiveOperationException} will be 426 * thrown from the attempted lookup. The exact class will be one of 427 * the following: 428 * <ul> 429 * <li>NoSuchMethodException — if a method is requested but does not exist 430 * <li>NoSuchFieldException — if a field is requested but does not exist 431 * <li>IllegalAccessException — if the member exists but an access check fails 432 * </ul> 433 * <p> 434 * In general, the conditions under which a method handle may be 435 * looked up for a method {@code M} are no more restrictive than the conditions 436 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}. 437 * Where the JVM would raise exceptions like {@code NoSuchMethodError}, 438 * a method handle lookup will generally raise a corresponding 439 * checked exception, such as {@code NoSuchMethodException}. 440 * And the effect of invoking the method handle resulting from the lookup 441 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a> 442 * to executing the compiled, verified, and resolved call to {@code M}. 443 * The same point is true of fields and constructors. 444 * <p style="font-size:smaller;"> 445 * <em>Discussion:</em> 446 * Access checks only apply to named and reflected methods, 447 * constructors, and fields. 448 * Other method handle creation methods, such as 449 * {@link MethodHandle#asType MethodHandle.asType}, 450 * do not require any access checks, and are used 451 * independently of any {@code Lookup} object. 452 * <p> 453 * If the desired member is {@code protected}, the usual JVM rules apply, 454 * including the requirement that the lookup class must either be in the 455 * same package as the desired member, or must inherit that member. 456 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.) 457 * In addition, if the desired member is a non-static field or method 458 * in a different package, the resulting method handle may only be applied 459 * to objects of the lookup class or one of its subclasses. 460 * This requirement is enforced by narrowing the type of the leading 461 * {@code this} parameter from {@code C} 462 * (which will necessarily be a superclass of the lookup class) 463 * to the lookup class itself. 464 * <p> 465 * The JVM imposes a similar requirement on {@code invokespecial} instruction, 466 * that the receiver argument must match both the resolved method <em>and</em> 467 * the current class. Again, this requirement is enforced by narrowing the 468 * type of the leading parameter to the resulting method handle. 469 * (See the Java Virtual Machine Specification, section 4.10.1.9.) 470 * <p> 471 * The JVM represents constructors and static initializer blocks as internal methods 472 * with special names ({@code "<init>"} and {@code "<clinit>"}). 473 * The internal syntax of invocation instructions allows them to refer to such internal 474 * methods as if they were normal methods, but the JVM bytecode verifier rejects them. 475 * A lookup of such an internal method will produce a {@code NoSuchMethodException}. 476 * <p> 477 * If the relationship between nested types is expressed directly through the 478 * {@code NestHost} and {@code NestMembers} attributes 479 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29), 480 * then the associated {@code Lookup} object provides direct access to 481 * the lookup class and all of its nestmates 482 * (see {@link java.lang.Class#getNestHost Class.getNestHost}). 483 * Otherwise, access between nested classes is obtained by the Java compiler creating 484 * a wrapper method to access a private method of another class in the same nest. 485 * For example, a nested class {@code C.D} 486 * can access private members within other related classes such as 487 * {@code C}, {@code C.D.E}, or {@code C.B}, 488 * but the Java compiler may need to generate wrapper methods in 489 * those related classes. In such cases, a {@code Lookup} object on 490 * {@code C.E} would be unable to access those private members. 491 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, 492 * which can transform a lookup on {@code C.E} into one on any of those other 493 * classes, without special elevation of privilege. 494 * <p> 495 * The accesses permitted to a given lookup object may be limited, 496 * according to its set of {@link #lookupModes lookupModes}, 497 * to a subset of members normally accessible to the lookup class. 498 * For example, the {@link MethodHandles#publicLookup publicLookup} 499 * method produces a lookup object which is only allowed to access 500 * public members in public classes of exported packages. 501 * The caller sensitive method {@link MethodHandles#lookup lookup} 502 * produces a lookup object with full capabilities relative to 503 * its caller class, to emulate all supported bytecode behaviors. 504 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object 505 * with fewer access modes than the original lookup object. 506 * 507 * <p style="font-size:smaller;"> 508 * <a id="privacc"></a> 509 * <em>Discussion of private access:</em> 510 * We say that a lookup has <em>private access</em> 511 * if its {@linkplain #lookupModes lookup modes} 512 * include the possibility of accessing {@code private} members 513 * (which includes the private members of nestmates). 514 * As documented in the relevant methods elsewhere, 515 * only lookups with private access possess the following capabilities: 516 * <ul style="font-size:smaller;"> 517 * <li>access private fields, methods, and constructors of the lookup class and its nestmates 518 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods, 519 * such as {@code Class.forName} 520 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions 521 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a> 522 * for classes accessible to the lookup class 523 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes 524 * within the same package member 525 * </ul> 526 * <p style="font-size:smaller;"> 527 * Each of these permissions is a consequence of the fact that a lookup object 528 * with private access can be securely traced back to an originating class, 529 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions 530 * can be reliably determined and emulated by method handles. 531 * 532 * <h1><a id="secmgr"></a>Security manager interactions</h1> 533 * Although bytecode instructions can only refer to classes in 534 * a related class loader, this API can search for methods in any 535 * class, as long as a reference to its {@code Class} object is 536 * available. Such cross-loader references are also possible with the 537 * Core Reflection API, and are impossible to bytecode instructions 538 * such as {@code invokestatic} or {@code getfield}. 539 * There is a {@linkplain java.lang.SecurityManager security manager API} 540 * to allow applications to check such cross-loader references. 541 * These checks apply to both the {@code MethodHandles.Lookup} API 542 * and the Core Reflection API 543 * (as found on {@link java.lang.Class Class}). 544 * <p> 545 * If a security manager is present, member and class lookups are subject to 546 * additional checks. 547 * From one to three calls are made to the security manager. 548 * Any of these calls can refuse access by throwing a 549 * {@link java.lang.SecurityException SecurityException}. 550 * Define {@code smgr} as the security manager, 551 * {@code lookc} as the lookup class of the current lookup object, 552 * {@code refc} as the containing class in which the member 553 * is being sought, and {@code defc} as the class in which the 554 * member is actually defined. 555 * (If a class or other type is being accessed, 556 * the {@code refc} and {@code defc} values are the class itself.) 557 * The value {@code lookc} is defined as <em>not present</em> 558 * if the current lookup object does not have 559 * <a href="MethodHandles.Lookup.html#privacc">private access</a>. 560 * The calls are made according to the following rules: 561 * <ul> 562 * <li><b>Step 1:</b> 563 * If {@code lookc} is not present, or if its class loader is not 564 * the same as or an ancestor of the class loader of {@code refc}, 565 * then {@link SecurityManager#checkPackageAccess 566 * smgr.checkPackageAccess(refcPkg)} is called, 567 * where {@code refcPkg} is the package of {@code refc}. 568 * <li><b>Step 2a:</b> 569 * If the retrieved member is not public and 570 * {@code lookc} is not present, then 571 * {@link SecurityManager#checkPermission smgr.checkPermission} 572 * with {@code RuntimePermission("accessDeclaredMembers")} is called. 573 * <li><b>Step 2b:</b> 574 * If the retrieved class has a {@code null} class loader, 575 * and {@code lookc} is not present, then 576 * {@link SecurityManager#checkPermission smgr.checkPermission} 577 * with {@code RuntimePermission("getClassLoader")} is called. 578 * <li><b>Step 3:</b> 579 * If the retrieved member is not public, 580 * and if {@code lookc} is not present, 581 * and if {@code defc} and {@code refc} are different, 582 * then {@link SecurityManager#checkPackageAccess 583 * smgr.checkPackageAccess(defcPkg)} is called, 584 * where {@code defcPkg} is the package of {@code defc}. 585 * </ul> 586 * Security checks are performed after other access checks have passed. 587 * Therefore, the above rules presuppose a member or class that is public, 588 * or else that is being accessed from a lookup class that has 589 * rights to access the member or class. 590 * 591 * <h1><a id="callsens"></a>Caller sensitive methods</h1> 592 * A small number of Java methods have a special property called caller sensitivity. 593 * A <em>caller-sensitive</em> method can behave differently depending on the 594 * identity of its immediate caller. 595 * <p> 596 * If a method handle for a caller-sensitive method is requested, 597 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply, 598 * but they take account of the lookup class in a special way. 599 * The resulting method handle behaves as if it were called 600 * from an instruction contained in the lookup class, 601 * so that the caller-sensitive method detects the lookup class. 602 * (By contrast, the invoker of the method handle is disregarded.) 603 * Thus, in the case of caller-sensitive methods, 604 * different lookup classes may give rise to 605 * differently behaving method handles. 606 * <p> 607 * In cases where the lookup object is 608 * {@link MethodHandles#publicLookup() publicLookup()}, 609 * or some other lookup object without 610 * <a href="MethodHandles.Lookup.html#privacc">private access</a>, 611 * the lookup class is disregarded. 612 * In such cases, no caller-sensitive method handle can be created, 613 * access is forbidden, and the lookup fails with an 614 * {@code IllegalAccessException}. 615 * <p style="font-size:smaller;"> 616 * <em>Discussion:</em> 617 * For example, the caller-sensitive method 618 * {@link java.lang.Class#forName(String) Class.forName(x)} 619 * can return varying classes or throw varying exceptions, 620 * depending on the class loader of the class that calls it. 621 * A public lookup of {@code Class.forName} will fail, because 622 * there is no reasonable way to determine its bytecode behavior. 623 * <p style="font-size:smaller;"> 624 * If an application caches method handles for broad sharing, 625 * it should use {@code publicLookup()} to create them. 626 * If there is a lookup of {@code Class.forName}, it will fail, 627 * and the application must take appropriate action in that case. 628 * It may be that a later lookup, perhaps during the invocation of a 629 * bootstrap method, can incorporate the specific identity 630 * of the caller, making the method accessible. 631 * <p style="font-size:smaller;"> 632 * The function {@code MethodHandles.lookup} is caller sensitive 633 * so that there can be a secure foundation for lookups. 634 * Nearly all other methods in the JSR 292 API rely on lookup 635 * objects to check access requests. 636 * 637 * @revised 9 638 */ 639 public static final 640 class Lookup { 641 /** The class on behalf of whom the lookup is being performed. */ 642 private final Class<?> lookupClass; 643 644 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */ 645 private final int allowedModes; 646 647 static { 648 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes")); 649 } 650 651 /** A single-bit mask representing {@code public} access, 652 * which may contribute to the result of {@link #lookupModes lookupModes}. 653 * The value, {@code 0x01}, happens to be the same as the value of the 654 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}. 655 */ 656 public static final int PUBLIC = Modifier.PUBLIC; 657 658 /** A single-bit mask representing {@code private} access, 659 * which may contribute to the result of {@link #lookupModes lookupModes}. 660 * The value, {@code 0x02}, happens to be the same as the value of the 661 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}. 662 */ 663 public static final int PRIVATE = Modifier.PRIVATE; 664 665 /** A single-bit mask representing {@code protected} access, 666 * which may contribute to the result of {@link #lookupModes lookupModes}. 667 * The value, {@code 0x04}, happens to be the same as the value of the 668 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}. 669 */ 670 public static final int PROTECTED = Modifier.PROTECTED; 671 672 /** A single-bit mask representing {@code package} access (default access), 673 * which may contribute to the result of {@link #lookupModes lookupModes}. 674 * The value is {@code 0x08}, which does not correspond meaningfully to 675 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 676 */ 677 public static final int PACKAGE = Modifier.STATIC; 678 679 /** A single-bit mask representing {@code module} access (default access), 680 * which may contribute to the result of {@link #lookupModes lookupModes}. 681 * The value is {@code 0x10}, which does not correspond meaningfully to 682 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 683 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup} 684 * with this lookup mode can access all public types in the module of the 685 * lookup class and public types in packages exported by other modules 686 * to the module of the lookup class. 687 * @since 9 688 * @spec JPMS 689 */ 690 public static final int MODULE = PACKAGE << 1; 691 692 /** A single-bit mask representing {@code unconditional} access 693 * which may contribute to the result of {@link #lookupModes lookupModes}. 694 * The value is {@code 0x20}, which does not correspond meaningfully to 695 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 696 * A {@code Lookup} with this lookup mode assumes {@linkplain 697 * java.lang.Module#canRead(java.lang.Module) readability}. 698 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup} 699 * with this lookup mode can access all public members of public types 700 * of all modules where the type is in a package that is {@link 701 * java.lang.Module#isExported(String) exported unconditionally}. 702 * @since 9 703 * @spec JPMS 704 * @see #publicLookup() 705 */ 706 public static final int UNCONDITIONAL = PACKAGE << 2; 707 708 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL); 709 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); 710 private static final int TRUSTED = -1; 711 712 private static int fixmods(int mods) { 713 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL); 714 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL); 715 } 716 717 /** Tells which class is performing the lookup. It is this class against 718 * which checks are performed for visibility and access permissions. 719 * <p> 720 * The class implies a maximum level of access permission, 721 * but the permissions may be additionally limited by the bitmask 722 * {@link #lookupModes lookupModes}, which controls whether non-public members 723 * can be accessed. 724 * @return the lookup class, on behalf of which this lookup object finds members 725 */ 726 public Class<?> lookupClass() { 727 return lookupClass; 728 } 729 730 // This is just for calling out to MethodHandleImpl. 731 private Class<?> lookupClassOrNull() { 732 return (allowedModes == TRUSTED) ? null : lookupClass; 733 } 734 735 /** Tells which access-protection classes of members this lookup object can produce. 736 * The result is a bit-mask of the bits 737 * {@linkplain #PUBLIC PUBLIC (0x01)}, 738 * {@linkplain #PRIVATE PRIVATE (0x02)}, 739 * {@linkplain #PROTECTED PROTECTED (0x04)}, 740 * {@linkplain #PACKAGE PACKAGE (0x08)}, 741 * {@linkplain #MODULE MODULE (0x10)}, 742 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}. 743 * <p> 744 * A freshly-created lookup object 745 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has 746 * all possible bits set, except {@code UNCONDITIONAL}. 747 * A lookup object on a new lookup class 748 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} 749 * may have some mode bits set to zero. 750 * Mode bits can also be 751 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}. 752 * Once cleared, mode bits cannot be restored from the downgraded lookup object. 753 * The purpose of this is to restrict access via the new lookup object, 754 * so that it can access only names which can be reached by the original 755 * lookup object, and also by the new lookup class. 756 * @return the lookup modes, which limit the kinds of access performed by this lookup object 757 * @see #in 758 * @see #dropLookupMode 759 * 760 * @revised 9 761 * @spec JPMS 762 */ 763 public int lookupModes() { 764 return allowedModes & ALL_MODES; 765 } 766 767 /** Embody the current class (the lookupClass) as a lookup class 768 * for method handle creation. 769 * Must be called by from a method in this package, 770 * which in turn is called by a method not in this package. 771 */ 772 Lookup(Class<?> lookupClass) { 773 this(lookupClass, FULL_POWER_MODES); 774 // make sure we haven't accidentally picked up a privileged class: 775 checkUnprivilegedlookupClass(lookupClass); 776 } 777 778 private Lookup(Class<?> lookupClass, int allowedModes) { 779 this.lookupClass = lookupClass; 780 this.allowedModes = allowedModes; 781 } 782 783 /** 784 * Creates a lookup on the specified new lookup class. 785 * The resulting object will report the specified 786 * class as its own {@link #lookupClass() lookupClass}. 787 * <p> 788 * However, the resulting {@code Lookup} object is guaranteed 789 * to have no more access capabilities than the original. 790 * In particular, access capabilities can be lost as follows:<ul> 791 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and 792 * the new lookup class is in a different module {@code M}, then no members, not 793 * even public members in {@code M}'s exported packages, will be accessible. 794 * The exception to this is when this lookup is {@link #publicLookup() 795 * publicLookup}, in which case {@code PUBLIC} access is not lost. 796 * <li>If the old lookup class is in an unnamed module, and the new lookup class 797 * is a different module then {@link #MODULE MODULE} access is lost. 798 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost. 799 * <li>If the new lookup class is in a different package 800 * than the old one, protected and default (package) members will not be accessible. 801 * <li>If the new lookup class is not within the same package member 802 * as the old one, private members will not be accessible, and protected members 803 * will not be accessible by virtue of inheritance. 804 * (Protected members may continue to be accessible because of package sharing.) 805 * <li>If the new lookup class is not accessible to the old lookup class, 806 * then no members, not even public members, will be accessible. 807 * (In all other cases, public members will continue to be accessible.) 808 * </ul> 809 * <p> 810 * The resulting lookup's capabilities for loading classes 811 * (used during {@link #findClass} invocations) 812 * are determined by the lookup class' loader, 813 * which may change due to this operation. 814 * 815 * @param requestedLookupClass the desired lookup class for the new lookup object 816 * @return a lookup object which reports the desired lookup class, or the same object 817 * if there is no change 818 * @throws NullPointerException if the argument is null 819 * 820 * @revised 9 821 * @spec JPMS 822 */ 823 public Lookup in(Class<?> requestedLookupClass) { 824 Objects.requireNonNull(requestedLookupClass); 825 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all 826 return new Lookup(requestedLookupClass, FULL_POWER_MODES); 827 if (requestedLookupClass == this.lookupClass) 828 return this; // keep same capabilities 829 int newModes = (allowedModes & FULL_POWER_MODES); 830 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) { 831 // Need to drop all access when teleporting from a named module to another 832 // module. The exception is publicLookup where PUBLIC is not lost. 833 if (this.lookupClass.getModule().isNamed() 834 && (this.allowedModes & UNCONDITIONAL) == 0) 835 newModes = 0; 836 else 837 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED); 838 } 839 if ((newModes & PACKAGE) != 0 840 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) { 841 newModes &= ~(PACKAGE|PRIVATE|PROTECTED); 842 } 843 // Allow nestmate lookups to be created without special privilege: 844 if ((newModes & PRIVATE) != 0 845 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) { 846 newModes &= ~(PRIVATE|PROTECTED); 847 } 848 if ((newModes & PUBLIC) != 0 849 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) { 850 // The requested class it not accessible from the lookup class. 851 // No permissions. 852 newModes = 0; 853 } 854 855 checkUnprivilegedlookupClass(requestedLookupClass); 856 return new Lookup(requestedLookupClass, newModes); 857 } 858 859 860 /** 861 * Creates a lookup on the same lookup class which this lookup object 862 * finds members, but with a lookup mode that has lost the given lookup mode. 863 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE 864 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}. 865 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always 866 * dropped and so the resulting lookup mode will never have these access capabilities. 867 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE} 868 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will 869 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC} 870 * is dropped then the resulting lookup has no access. 871 * @param modeToDrop the lookup mode to drop 872 * @return a lookup object which lacks the indicated mode, or the same object if there is no change 873 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC}, 874 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL} 875 * @see MethodHandles#privateLookupIn 876 * @since 9 877 */ 878 public Lookup dropLookupMode(int modeToDrop) { 879 int oldModes = lookupModes(); 880 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL); 881 switch (modeToDrop) { 882 case PUBLIC: newModes &= ~(ALL_MODES); break; 883 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break; 884 case PACKAGE: newModes &= ~(PRIVATE); break; 885 case PROTECTED: 886 case PRIVATE: 887 case UNCONDITIONAL: break; 888 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop"); 889 } 890 if (newModes == oldModes) return this; // return self if no change 891 return new Lookup(lookupClass(), newModes); 892 } 893 894 /** 895 * Defines a class to the same class loader and in the same runtime package and 896 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's 897 * {@linkplain #lookupClass() lookup class}. 898 * 899 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include 900 * {@link #PACKAGE PACKAGE} access as default (package) members will be 901 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate 902 * that the lookup object was created by a caller in the runtime package (or derived 903 * from a lookup originally created by suitably privileged code to a target class in 904 * the runtime package). </p> 905 * 906 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined 907 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the 908 * same package as the lookup class. </p> 909 * 910 * <p> This method does not run the class initializer. The class initializer may 911 * run at a later time, as detailed in section 12.4 of the <em>The Java Language 912 * Specification</em>. </p> 913 * 914 * <p> If there is a security manager, its {@code checkPermission} method is first called 915 * to check {@code RuntimePermission("defineClass")}. </p> 916 * 917 * @param bytes the class bytes 918 * @return the {@code Class} object for the class 919 * @throws IllegalArgumentException the bytes are for a class in a different package 920 * to the lookup class 921 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access 922 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be 923 * verified ({@code VerifyError}), is already defined, or another linkage error occurs 924 * @throws SecurityException if denied by the security manager 925 * @throws NullPointerException if {@code bytes} is {@code null} 926 * @since 9 927 * @spec JPMS 928 * @see Lookup#privateLookupIn 929 * @see Lookup#dropLookupMode 930 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 931 */ 932 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException { 933 SecurityManager sm = System.getSecurityManager(); 934 if (sm != null) 935 sm.checkPermission(new RuntimePermission("defineClass")); 936 if ((lookupModes() & PACKAGE) == 0) 937 throw new IllegalAccessException("Lookup does not have PACKAGE access"); 938 assert (lookupModes() & (MODULE|PUBLIC)) != 0; 939 940 // parse class bytes to get class name (in internal form) 941 bytes = bytes.clone(); 942 String name; 943 try { 944 ClassReader reader = new ClassReader(bytes); 945 name = reader.getClassName(); 946 } catch (RuntimeException e) { 947 // ASM exceptions are poorly specified 948 ClassFormatError cfe = new ClassFormatError(); 949 cfe.initCause(e); 950 throw cfe; 951 } 952 953 // get package and class name in binary form 954 String cn, pn; 955 int index = name.lastIndexOf('/'); 956 if (index == -1) { 957 cn = name; 958 pn = ""; 959 } else { 960 cn = name.replace('/', '.'); 961 pn = cn.substring(0, index); 962 } 963 if (!pn.equals(lookupClass.getPackageName())) { 964 throw new IllegalArgumentException("Class not in same package as lookup class"); 965 } 966 967 // invoke the class loader's defineClass method 968 ClassLoader loader = lookupClass.getClassLoader(); 969 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null; 970 String source = "__Lookup_defineClass__"; 971 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source); 972 return clazz; 973 } 974 975 private ProtectionDomain lookupClassProtectionDomain() { 976 ProtectionDomain pd = cachedProtectionDomain; 977 if (pd == null) { 978 cachedProtectionDomain = pd = protectionDomain(lookupClass); 979 } 980 return pd; 981 } 982 983 private ProtectionDomain protectionDomain(Class<?> clazz) { 984 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain; 985 return AccessController.doPrivileged(pa); 986 } 987 988 // cached protection domain 989 private volatile ProtectionDomain cachedProtectionDomain; 990 991 992 // Make sure outer class is initialized first. 993 static { IMPL_NAMES.getClass(); } 994 995 /** Package-private version of lookup which is trusted. */ 996 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED); 997 998 /** Version of lookup which is trusted minimally. 999 * It can only be used to create method handles to publicly accessible 1000 * members in packages that are exported unconditionally. 1001 */ 1002 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL)); 1003 1004 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) { 1005 String name = lookupClass.getName(); 1006 if (name.startsWith("java.lang.invoke.")) 1007 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass); 1008 } 1009 1010 /** 1011 * Displays the name of the class from which lookups are to be made. 1012 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.) 1013 * If there are restrictions on the access permitted to this lookup, 1014 * this is indicated by adding a suffix to the class name, consisting 1015 * of a slash and a keyword. The keyword represents the strongest 1016 * allowed access, and is chosen as follows: 1017 * <ul> 1018 * <li>If no access is allowed, the suffix is "/noaccess". 1019 * <li>If only public access to types in exported packages is allowed, the suffix is "/public". 1020 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup". 1021 * <li>If only public and module access are allowed, the suffix is "/module". 1022 * <li>If only public, module and package access are allowed, the suffix is "/package". 1023 * <li>If only public, module, package, and private access are allowed, the suffix is "/private". 1024 * </ul> 1025 * If none of the above cases apply, it is the case that full 1026 * access (public, module, package, private, and protected) is allowed. 1027 * In this case, no suffix is added. 1028 * This is true only of an object obtained originally from 1029 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}. 1030 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in} 1031 * always have restricted access, and will display a suffix. 1032 * <p> 1033 * (It may seem strange that protected access should be 1034 * stronger than private access. Viewed independently from 1035 * package access, protected access is the first to be lost, 1036 * because it requires a direct subclass relationship between 1037 * caller and callee.) 1038 * @see #in 1039 * 1040 * @revised 9 1041 * @spec JPMS 1042 */ 1043 @Override 1044 public String toString() { 1045 String cname = lookupClass.getName(); 1046 switch (allowedModes) { 1047 case 0: // no privileges 1048 return cname + "/noaccess"; 1049 case PUBLIC: 1050 return cname + "/public"; 1051 case PUBLIC|UNCONDITIONAL: 1052 return cname + "/publicLookup"; 1053 case PUBLIC|MODULE: 1054 return cname + "/module"; 1055 case PUBLIC|MODULE|PACKAGE: 1056 return cname + "/package"; 1057 case FULL_POWER_MODES & ~PROTECTED: 1058 return cname + "/private"; 1059 case FULL_POWER_MODES: 1060 return cname; 1061 case TRUSTED: 1062 return "/trusted"; // internal only; not exported 1063 default: // Should not happen, but it's a bitfield... 1064 cname = cname + "/" + Integer.toHexString(allowedModes); 1065 assert(false) : cname; 1066 return cname; 1067 } 1068 } 1069 1070 /** 1071 * Produces a method handle for a static method. 1072 * The type of the method handle will be that of the method. 1073 * (Since static methods do not take receivers, there is no 1074 * additional receiver argument inserted into the method handle type, 1075 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) 1076 * The method and all its argument types must be accessible to the lookup object. 1077 * <p> 1078 * The returned method handle will have 1079 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1080 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1081 * <p> 1082 * If the returned method handle is invoked, the method's class will 1083 * be initialized, if it has not already been initialized. 1084 * <p><b>Example:</b> 1085 * <blockquote><pre>{@code 1086 import static java.lang.invoke.MethodHandles.*; 1087 import static java.lang.invoke.MethodType.*; 1088 ... 1089 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class, 1090 "asList", methodType(List.class, Object[].class)); 1091 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString()); 1092 * }</pre></blockquote> 1093 * @param refc the class from which the method is accessed 1094 * @param name the name of the method 1095 * @param type the type of the method 1096 * @return the desired method handle 1097 * @throws NoSuchMethodException if the method does not exist 1098 * @throws IllegalAccessException if access checking fails, 1099 * or if the method is not {@code static}, 1100 * or if the method's variable arity modifier bit 1101 * is set and {@code asVarargsCollector} fails 1102 * @exception SecurityException if a security manager is present and it 1103 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1104 * @throws NullPointerException if any argument is null 1105 */ 1106 public 1107 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1108 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type); 1109 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method)); 1110 } 1111 1112 /** 1113 * Produces a method handle for a virtual method. 1114 * The type of the method handle will be that of the method, 1115 * with the receiver type (usually {@code refc}) prepended. 1116 * The method and all its argument types must be accessible to the lookup object. 1117 * <p> 1118 * When called, the handle will treat the first argument as a receiver 1119 * and, for non-private methods, dispatch on the receiver's type to determine which method 1120 * implementation to enter. 1121 * For private methods the named method in {@code refc} will be invoked on the receiver. 1122 * (The dispatching action is identical with that performed by an 1123 * {@code invokevirtual} or {@code invokeinterface} instruction.) 1124 * <p> 1125 * The first argument will be of type {@code refc} if the lookup 1126 * class has full privileges to access the member. Otherwise 1127 * the member must be {@code protected} and the first argument 1128 * will be restricted in type to the lookup class. 1129 * <p> 1130 * The returned method handle will have 1131 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1132 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1133 * <p> 1134 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual} 1135 * instructions and method handles produced by {@code findVirtual}, 1136 * if the class is {@code MethodHandle} and the name string is 1137 * {@code invokeExact} or {@code invoke}, the resulting 1138 * method handle is equivalent to one produced by 1139 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or 1140 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} 1141 * with the same {@code type} argument. 1142 * <p> 1143 * If the class is {@code VarHandle} and the name string corresponds to 1144 * the name of a signature-polymorphic access mode method, the resulting 1145 * method handle is equivalent to one produced by 1146 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with 1147 * the access mode corresponding to the name string and with the same 1148 * {@code type} arguments. 1149 * <p> 1150 * <b>Example:</b> 1151 * <blockquote><pre>{@code 1152 import static java.lang.invoke.MethodHandles.*; 1153 import static java.lang.invoke.MethodType.*; 1154 ... 1155 MethodHandle MH_concat = publicLookup().findVirtual(String.class, 1156 "concat", methodType(String.class, String.class)); 1157 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class, 1158 "hashCode", methodType(int.class)); 1159 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class, 1160 "hashCode", methodType(int.class)); 1161 assertEquals("xy", (String) MH_concat.invokeExact("x", "y")); 1162 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy")); 1163 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy")); 1164 // interface method: 1165 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class, 1166 "subSequence", methodType(CharSequence.class, int.class, int.class)); 1167 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString()); 1168 // constructor "internal method" must be accessed differently: 1169 MethodType MT_newString = methodType(void.class); //()V for new String() 1170 try { assertEquals("impossible", lookup() 1171 .findVirtual(String.class, "<init>", MT_newString)); 1172 } catch (NoSuchMethodException ex) { } // OK 1173 MethodHandle MH_newString = publicLookup() 1174 .findConstructor(String.class, MT_newString); 1175 assertEquals("", (String) MH_newString.invokeExact()); 1176 * }</pre></blockquote> 1177 * 1178 * @param refc the class or interface from which the method is accessed 1179 * @param name the name of the method 1180 * @param type the type of the method, with the receiver argument omitted 1181 * @return the desired method handle 1182 * @throws NoSuchMethodException if the method does not exist 1183 * @throws IllegalAccessException if access checking fails, 1184 * or if the method is {@code static}, 1185 * or if the method's variable arity modifier bit 1186 * is set and {@code asVarargsCollector} fails 1187 * @exception SecurityException if a security manager is present and it 1188 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1189 * @throws NullPointerException if any argument is null 1190 */ 1191 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1192 if (refc == MethodHandle.class) { 1193 MethodHandle mh = findVirtualForMH(name, type); 1194 if (mh != null) return mh; 1195 } else if (refc == VarHandle.class) { 1196 MethodHandle mh = findVirtualForVH(name, type); 1197 if (mh != null) return mh; 1198 } 1199 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual); 1200 MemberName method = resolveOrFail(refKind, refc, name, type); 1201 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method)); 1202 } 1203 private MethodHandle findVirtualForMH(String name, MethodType type) { 1204 // these names require special lookups because of the implicit MethodType argument 1205 if ("invoke".equals(name)) 1206 return invoker(type); 1207 if ("invokeExact".equals(name)) 1208 return exactInvoker(type); 1209 assert(!MemberName.isMethodHandleInvokeName(name)); 1210 return null; 1211 } 1212 private MethodHandle findVirtualForVH(String name, MethodType type) { 1213 try { 1214 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type); 1215 } catch (IllegalArgumentException e) { 1216 return null; 1217 } 1218 } 1219 1220 /** 1221 * Produces a method handle which creates an object and initializes it, using 1222 * the constructor of the specified type. 1223 * The parameter types of the method handle will be those of the constructor, 1224 * while the return type will be a reference to the constructor's class. 1225 * The constructor and all its argument types must be accessible to the lookup object. 1226 * <p> 1227 * The requested type must have a return type of {@code void}. 1228 * (This is consistent with the JVM's treatment of constructor type descriptors.) 1229 * <p> 1230 * The returned method handle will have 1231 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1232 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 1233 * <p> 1234 * If the returned method handle is invoked, the constructor's class will 1235 * be initialized, if it has not already been initialized. 1236 * <p><b>Example:</b> 1237 * <blockquote><pre>{@code 1238 import static java.lang.invoke.MethodHandles.*; 1239 import static java.lang.invoke.MethodType.*; 1240 ... 1241 MethodHandle MH_newArrayList = publicLookup().findConstructor( 1242 ArrayList.class, methodType(void.class, Collection.class)); 1243 Collection orig = Arrays.asList("x", "y"); 1244 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig); 1245 assert(orig != copy); 1246 assertEquals(orig, copy); 1247 // a variable-arity constructor: 1248 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor( 1249 ProcessBuilder.class, methodType(void.class, String[].class)); 1250 ProcessBuilder pb = (ProcessBuilder) 1251 MH_newProcessBuilder.invoke("x", "y", "z"); 1252 assertEquals("[x, y, z]", pb.command().toString()); 1253 * }</pre></blockquote> 1254 * @param refc the class or interface from which the method is accessed 1255 * @param type the type of the method, with the receiver argument omitted, and a void return type 1256 * @return the desired method handle 1257 * @throws NoSuchMethodException if the constructor does not exist 1258 * @throws IllegalAccessException if access checking fails 1259 * or if the method's variable arity modifier bit 1260 * is set and {@code asVarargsCollector} fails 1261 * @exception SecurityException if a security manager is present and it 1262 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1263 * @throws NullPointerException if any argument is null 1264 */ 1265 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1266 if (refc.isArray()) { 1267 throw new NoSuchMethodException("no constructor for array class: " + refc.getName()); 1268 } 1269 String name = "<init>"; 1270 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type); 1271 return getDirectConstructor(refc, ctor); 1272 } 1273 1274 /** 1275 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static 1276 * initializer of the class is not run. 1277 * <p> 1278 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class 1279 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to 1280 * load the requested class, and then determines whether the class is accessible to this lookup object. 1281 * 1282 * @param targetName the fully qualified name of the class to be looked up. 1283 * @return the requested class. 1284 * @exception SecurityException if a security manager is present and it 1285 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1286 * @throws LinkageError if the linkage fails 1287 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader. 1288 * @throws IllegalAccessException if the class is not accessible, using the allowed access 1289 * modes. 1290 * @exception SecurityException if a security manager is present and it 1291 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1292 * @since 9 1293 */ 1294 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException { 1295 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader()); 1296 return accessClass(targetClass); 1297 } 1298 1299 /** 1300 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The 1301 * static initializer of the class is not run. 1302 * <p> 1303 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the 1304 * {@linkplain #lookupModes() lookup modes}. 1305 * 1306 * @param targetClass the class to be access-checked 1307 * 1308 * @return the class that has been access-checked 1309 * 1310 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access 1311 * modes. 1312 * @exception SecurityException if a security manager is present and it 1313 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1314 * @since 9 1315 */ 1316 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException { 1317 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) { 1318 throw new MemberName(targetClass).makeAccessException("access violation", this); 1319 } 1320 checkSecurityManager(targetClass, null); 1321 return targetClass; 1322 } 1323 1324 /** 1325 * Produces an early-bound method handle for a virtual method. 1326 * It will bypass checks for overriding methods on the receiver, 1327 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 1328 * instruction from within the explicitly specified {@code specialCaller}. 1329 * The type of the method handle will be that of the method, 1330 * with a suitably restricted receiver type prepended. 1331 * (The receiver type will be {@code specialCaller} or a subtype.) 1332 * The method and all its argument types must be accessible 1333 * to the lookup object. 1334 * <p> 1335 * Before method resolution, 1336 * if the explicitly specified caller class is not identical with the 1337 * lookup class, or if this lookup object does not have 1338 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 1339 * privileges, the access fails. 1340 * <p> 1341 * The returned method handle will have 1342 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1343 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1344 * <p style="font-size:smaller;"> 1345 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API, 1346 * even though the {@code invokespecial} instruction can refer to them 1347 * in special circumstances. Use {@link #findConstructor findConstructor} 1348 * to access instance initialization methods in a safe manner.)</em> 1349 * <p><b>Example:</b> 1350 * <blockquote><pre>{@code 1351 import static java.lang.invoke.MethodHandles.*; 1352 import static java.lang.invoke.MethodType.*; 1353 ... 1354 static class Listie extends ArrayList { 1355 public String toString() { return "[wee Listie]"; } 1356 static Lookup lookup() { return MethodHandles.lookup(); } 1357 } 1358 ... 1359 // no access to constructor via invokeSpecial: 1360 MethodHandle MH_newListie = Listie.lookup() 1361 .findConstructor(Listie.class, methodType(void.class)); 1362 Listie l = (Listie) MH_newListie.invokeExact(); 1363 try { assertEquals("impossible", Listie.lookup().findSpecial( 1364 Listie.class, "<init>", methodType(void.class), Listie.class)); 1365 } catch (NoSuchMethodException ex) { } // OK 1366 // access to super and self methods via invokeSpecial: 1367 MethodHandle MH_super = Listie.lookup().findSpecial( 1368 ArrayList.class, "toString" , methodType(String.class), Listie.class); 1369 MethodHandle MH_this = Listie.lookup().findSpecial( 1370 Listie.class, "toString" , methodType(String.class), Listie.class); 1371 MethodHandle MH_duper = Listie.lookup().findSpecial( 1372 Object.class, "toString" , methodType(String.class), Listie.class); 1373 assertEquals("[]", (String) MH_super.invokeExact(l)); 1374 assertEquals(""+l, (String) MH_this.invokeExact(l)); 1375 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method 1376 try { assertEquals("inaccessible", Listie.lookup().findSpecial( 1377 String.class, "toString", methodType(String.class), Listie.class)); 1378 } catch (IllegalAccessException ex) { } // OK 1379 Listie subl = new Listie() { public String toString() { return "[subclass]"; } }; 1380 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method 1381 * }</pre></blockquote> 1382 * 1383 * @param refc the class or interface from which the method is accessed 1384 * @param name the name of the method (which must not be "<init>") 1385 * @param type the type of the method, with the receiver argument omitted 1386 * @param specialCaller the proposed calling class to perform the {@code invokespecial} 1387 * @return the desired method handle 1388 * @throws NoSuchMethodException if the method does not exist 1389 * @throws IllegalAccessException if access checking fails, 1390 * or if the method is {@code static}, 1391 * or if the method's variable arity modifier bit 1392 * is set and {@code asVarargsCollector} fails 1393 * @exception SecurityException if a security manager is present and it 1394 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1395 * @throws NullPointerException if any argument is null 1396 */ 1397 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type, 1398 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException { 1399 checkSpecialCaller(specialCaller, refc); 1400 Lookup specialLookup = this.in(specialCaller); 1401 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type); 1402 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method)); 1403 } 1404 1405 /** 1406 * Produces a method handle giving read access to a non-static field. 1407 * The type of the method handle will have a return type of the field's 1408 * value type. 1409 * The method handle's single argument will be the instance containing 1410 * the field. 1411 * Access checking is performed immediately on behalf of the lookup class. 1412 * @param refc the class or interface from which the method is accessed 1413 * @param name the field's name 1414 * @param type the field's type 1415 * @return a method handle which can load values from the field 1416 * @throws NoSuchFieldException if the field does not exist 1417 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 1418 * @exception SecurityException if a security manager is present and it 1419 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1420 * @throws NullPointerException if any argument is null 1421 * @see #findVarHandle(Class, String, Class) 1422 */ 1423 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1424 MemberName field = resolveOrFail(REF_getField, refc, name, type); 1425 return getDirectField(REF_getField, refc, field); 1426 } 1427 1428 /** 1429 * Produces a method handle giving write access to a non-static field. 1430 * The type of the method handle will have a void return type. 1431 * The method handle will take two arguments, the instance containing 1432 * the field, and the value to be stored. 1433 * The second argument will be of the field's value type. 1434 * Access checking is performed immediately on behalf of the lookup class. 1435 * @param refc the class or interface from which the method is accessed 1436 * @param name the field's name 1437 * @param type the field's type 1438 * @return a method handle which can store values into the field 1439 * @throws NoSuchFieldException if the field does not exist 1440 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 1441 * @exception SecurityException if a security manager is present and it 1442 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1443 * @throws NullPointerException if any argument is null 1444 * @see #findVarHandle(Class, String, Class) 1445 */ 1446 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1447 MemberName field = resolveOrFail(REF_putField, refc, name, type); 1448 return getDirectField(REF_putField, refc, field); 1449 } 1450 1451 /** 1452 * Produces a VarHandle giving access to a non-static field {@code name} 1453 * of type {@code type} declared in a class of type {@code recv}. 1454 * The VarHandle's variable type is {@code type} and it has one 1455 * coordinate type, {@code recv}. 1456 * <p> 1457 * Access checking is performed immediately on behalf of the lookup 1458 * class. 1459 * <p> 1460 * Certain access modes of the returned VarHandle are unsupported under 1461 * the following conditions: 1462 * <ul> 1463 * <li>if the field is declared {@code final}, then the write, atomic 1464 * update, numeric atomic update, and bitwise atomic update access 1465 * modes are unsupported. 1466 * <li>if the field type is anything other than {@code byte}, 1467 * {@code short}, {@code char}, {@code int}, {@code long}, 1468 * {@code float}, or {@code double} then numeric atomic update 1469 * access modes are unsupported. 1470 * <li>if the field type is anything other than {@code boolean}, 1471 * {@code byte}, {@code short}, {@code char}, {@code int} or 1472 * {@code long} then bitwise atomic update access modes are 1473 * unsupported. 1474 * </ul> 1475 * <p> 1476 * If the field is declared {@code volatile} then the returned VarHandle 1477 * will override access to the field (effectively ignore the 1478 * {@code volatile} declaration) in accordance to its specified 1479 * access modes. 1480 * <p> 1481 * If the field type is {@code float} or {@code double} then numeric 1482 * and atomic update access modes compare values using their bitwise 1483 * representation (see {@link Float#floatToRawIntBits} and 1484 * {@link Double#doubleToRawLongBits}, respectively). 1485 * @apiNote 1486 * Bitwise comparison of {@code float} values or {@code double} values, 1487 * as performed by the numeric and atomic update access modes, differ 1488 * from the primitive {@code ==} operator and the {@link Float#equals} 1489 * and {@link Double#equals} methods, specifically with respect to 1490 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 1491 * Care should be taken when performing a compare and set or a compare 1492 * and exchange operation with such values since the operation may 1493 * unexpectedly fail. 1494 * There are many possible NaN values that are considered to be 1495 * {@code NaN} in Java, although no IEEE 754 floating-point operation 1496 * provided by Java can distinguish between them. Operation failure can 1497 * occur if the expected or witness value is a NaN value and it is 1498 * transformed (perhaps in a platform specific manner) into another NaN 1499 * value, and thus has a different bitwise representation (see 1500 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 1501 * details). 1502 * The values {@code -0.0} and {@code +0.0} have different bitwise 1503 * representations but are considered equal when using the primitive 1504 * {@code ==} operator. Operation failure can occur if, for example, a 1505 * numeric algorithm computes an expected value to be say {@code -0.0} 1506 * and previously computed the witness value to be say {@code +0.0}. 1507 * @param recv the receiver class, of type {@code R}, that declares the 1508 * non-static field 1509 * @param name the field's name 1510 * @param type the field's type, of type {@code T} 1511 * @return a VarHandle giving access to non-static fields. 1512 * @throws NoSuchFieldException if the field does not exist 1513 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 1514 * @exception SecurityException if a security manager is present and it 1515 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1516 * @throws NullPointerException if any argument is null 1517 * @since 9 1518 */ 1519 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1520 MemberName getField = resolveOrFail(REF_getField, recv, name, type); 1521 MemberName putField = resolveOrFail(REF_putField, recv, name, type); 1522 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField); 1523 } 1524 1525 /** 1526 * Produces a method handle giving read access to a static field. 1527 * The type of the method handle will have a return type of the field's 1528 * value type. 1529 * The method handle will take no arguments. 1530 * Access checking is performed immediately on behalf of the lookup class. 1531 * <p> 1532 * If the returned method handle is invoked, the field's class will 1533 * be initialized, if it has not already been initialized. 1534 * @param refc the class or interface from which the method is accessed 1535 * @param name the field's name 1536 * @param type the field's type 1537 * @return a method handle which can load values from the field 1538 * @throws NoSuchFieldException if the field does not exist 1539 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 1540 * @exception SecurityException if a security manager is present and it 1541 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1542 * @throws NullPointerException if any argument is null 1543 */ 1544 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1545 MemberName field = resolveOrFail(REF_getStatic, refc, name, type); 1546 return getDirectField(REF_getStatic, refc, field); 1547 } 1548 1549 /** 1550 * Produces a method handle giving write access to a static field. 1551 * The type of the method handle will have a void return type. 1552 * The method handle will take a single 1553 * argument, of the field's value type, the value to be stored. 1554 * Access checking is performed immediately on behalf of the lookup class. 1555 * <p> 1556 * If the returned method handle is invoked, the field's class will 1557 * be initialized, if it has not already been initialized. 1558 * @param refc the class or interface from which the method is accessed 1559 * @param name the field's name 1560 * @param type the field's type 1561 * @return a method handle which can store values into the field 1562 * @throws NoSuchFieldException if the field does not exist 1563 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 1564 * @exception SecurityException if a security manager is present and it 1565 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1566 * @throws NullPointerException if any argument is null 1567 */ 1568 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1569 MemberName field = resolveOrFail(REF_putStatic, refc, name, type); 1570 return getDirectField(REF_putStatic, refc, field); 1571 } 1572 1573 /** 1574 * Produces a VarHandle giving access to a static field {@code name} of 1575 * type {@code type} declared in a class of type {@code decl}. 1576 * The VarHandle's variable type is {@code type} and it has no 1577 * coordinate types. 1578 * <p> 1579 * Access checking is performed immediately on behalf of the lookup 1580 * class. 1581 * <p> 1582 * If the returned VarHandle is operated on, the declaring class will be 1583 * initialized, if it has not already been initialized. 1584 * <p> 1585 * Certain access modes of the returned VarHandle are unsupported under 1586 * the following conditions: 1587 * <ul> 1588 * <li>if the field is declared {@code final}, then the write, atomic 1589 * update, numeric atomic update, and bitwise atomic update access 1590 * modes are unsupported. 1591 * <li>if the field type is anything other than {@code byte}, 1592 * {@code short}, {@code char}, {@code int}, {@code long}, 1593 * {@code float}, or {@code double}, then numeric atomic update 1594 * access modes are unsupported. 1595 * <li>if the field type is anything other than {@code boolean}, 1596 * {@code byte}, {@code short}, {@code char}, {@code int} or 1597 * {@code long} then bitwise atomic update access modes are 1598 * unsupported. 1599 * </ul> 1600 * <p> 1601 * If the field is declared {@code volatile} then the returned VarHandle 1602 * will override access to the field (effectively ignore the 1603 * {@code volatile} declaration) in accordance to its specified 1604 * access modes. 1605 * <p> 1606 * If the field type is {@code float} or {@code double} then numeric 1607 * and atomic update access modes compare values using their bitwise 1608 * representation (see {@link Float#floatToRawIntBits} and 1609 * {@link Double#doubleToRawLongBits}, respectively). 1610 * @apiNote 1611 * Bitwise comparison of {@code float} values or {@code double} values, 1612 * as performed by the numeric and atomic update access modes, differ 1613 * from the primitive {@code ==} operator and the {@link Float#equals} 1614 * and {@link Double#equals} methods, specifically with respect to 1615 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 1616 * Care should be taken when performing a compare and set or a compare 1617 * and exchange operation with such values since the operation may 1618 * unexpectedly fail. 1619 * There are many possible NaN values that are considered to be 1620 * {@code NaN} in Java, although no IEEE 754 floating-point operation 1621 * provided by Java can distinguish between them. Operation failure can 1622 * occur if the expected or witness value is a NaN value and it is 1623 * transformed (perhaps in a platform specific manner) into another NaN 1624 * value, and thus has a different bitwise representation (see 1625 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 1626 * details). 1627 * The values {@code -0.0} and {@code +0.0} have different bitwise 1628 * representations but are considered equal when using the primitive 1629 * {@code ==} operator. Operation failure can occur if, for example, a 1630 * numeric algorithm computes an expected value to be say {@code -0.0} 1631 * and previously computed the witness value to be say {@code +0.0}. 1632 * @param decl the class that declares the static field 1633 * @param name the field's name 1634 * @param type the field's type, of type {@code T} 1635 * @return a VarHandle giving access to a static field 1636 * @throws NoSuchFieldException if the field does not exist 1637 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 1638 * @exception SecurityException if a security manager is present and it 1639 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1640 * @throws NullPointerException if any argument is null 1641 * @since 9 1642 */ 1643 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 1644 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type); 1645 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type); 1646 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField); 1647 } 1648 1649 /** 1650 * Produces an early-bound method handle for a non-static method. 1651 * The receiver must have a supertype {@code defc} in which a method 1652 * of the given name and type is accessible to the lookup class. 1653 * The method and all its argument types must be accessible to the lookup object. 1654 * The type of the method handle will be that of the method, 1655 * without any insertion of an additional receiver parameter. 1656 * The given receiver will be bound into the method handle, 1657 * so that every call to the method handle will invoke the 1658 * requested method on the given receiver. 1659 * <p> 1660 * The returned method handle will have 1661 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1662 * the method's variable arity modifier bit ({@code 0x0080}) is set 1663 * <em>and</em> the trailing array argument is not the only argument. 1664 * (If the trailing array argument is the only argument, 1665 * the given receiver value will be bound to it.) 1666 * <p> 1667 * This is almost equivalent to the following code, with some differences noted below: 1668 * <blockquote><pre>{@code 1669 import static java.lang.invoke.MethodHandles.*; 1670 import static java.lang.invoke.MethodType.*; 1671 ... 1672 MethodHandle mh0 = lookup().findVirtual(defc, name, type); 1673 MethodHandle mh1 = mh0.bindTo(receiver); 1674 mh1 = mh1.withVarargs(mh0.isVarargsCollector()); 1675 return mh1; 1676 * }</pre></blockquote> 1677 * where {@code defc} is either {@code receiver.getClass()} or a super 1678 * type of that class, in which the requested method is accessible 1679 * to the lookup class. 1680 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity. 1681 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would 1682 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and 1683 * the receiver is restricted by {@code findVirtual} to the lookup class.) 1684 * @param receiver the object from which the method is accessed 1685 * @param name the name of the method 1686 * @param type the type of the method, with the receiver argument omitted 1687 * @return the desired method handle 1688 * @throws NoSuchMethodException if the method does not exist 1689 * @throws IllegalAccessException if access checking fails 1690 * or if the method's variable arity modifier bit 1691 * is set and {@code asVarargsCollector} fails 1692 * @exception SecurityException if a security manager is present and it 1693 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1694 * @throws NullPointerException if any argument is null 1695 * @see MethodHandle#bindTo 1696 * @see #findVirtual 1697 */ 1698 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 1699 Class<? extends Object> refc = receiver.getClass(); // may get NPE 1700 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type); 1701 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method)); 1702 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) { 1703 throw new IllegalAccessException("The restricted defining class " + 1704 mh.type().leadingReferenceParameter().getName() + 1705 " is not assignable from receiver class " + 1706 receiver.getClass().getName()); 1707 } 1708 return mh.bindArgumentL(0, receiver).setVarargs(method); 1709 } 1710 1711 /** 1712 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 1713 * to <i>m</i>, if the lookup class has permission. 1714 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument. 1715 * If <i>m</i> is virtual, overriding is respected on every call. 1716 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped. 1717 * The type of the method handle will be that of the method, 1718 * with the receiver type prepended (but only if it is non-static). 1719 * If the method's {@code accessible} flag is not set, 1720 * access checking is performed immediately on behalf of the lookup class. 1721 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties. 1722 * <p> 1723 * The returned method handle will have 1724 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1725 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1726 * <p> 1727 * If <i>m</i> is static, and 1728 * if the returned method handle is invoked, the method's class will 1729 * be initialized, if it has not already been initialized. 1730 * @param m the reflected method 1731 * @return a method handle which can invoke the reflected method 1732 * @throws IllegalAccessException if access checking fails 1733 * or if the method's variable arity modifier bit 1734 * is set and {@code asVarargsCollector} fails 1735 * @throws NullPointerException if the argument is null 1736 */ 1737 public MethodHandle unreflect(Method m) throws IllegalAccessException { 1738 if (m.getDeclaringClass() == MethodHandle.class) { 1739 MethodHandle mh = unreflectForMH(m); 1740 if (mh != null) return mh; 1741 } 1742 if (m.getDeclaringClass() == VarHandle.class) { 1743 MethodHandle mh = unreflectForVH(m); 1744 if (mh != null) return mh; 1745 } 1746 MemberName method = new MemberName(m); 1747 byte refKind = method.getReferenceKind(); 1748 if (refKind == REF_invokeSpecial) 1749 refKind = REF_invokeVirtual; 1750 assert(method.isMethod()); 1751 @SuppressWarnings("deprecation") 1752 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this; 1753 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method)); 1754 } 1755 private MethodHandle unreflectForMH(Method m) { 1756 // these names require special lookups because they throw UnsupportedOperationException 1757 if (MemberName.isMethodHandleInvokeName(m.getName())) 1758 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m)); 1759 return null; 1760 } 1761 private MethodHandle unreflectForVH(Method m) { 1762 // these names require special lookups because they throw UnsupportedOperationException 1763 if (MemberName.isVarHandleMethodInvokeName(m.getName())) 1764 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m)); 1765 return null; 1766 } 1767 1768 /** 1769 * Produces a method handle for a reflected method. 1770 * It will bypass checks for overriding methods on the receiver, 1771 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 1772 * instruction from within the explicitly specified {@code specialCaller}. 1773 * The type of the method handle will be that of the method, 1774 * with a suitably restricted receiver type prepended. 1775 * (The receiver type will be {@code specialCaller} or a subtype.) 1776 * If the method's {@code accessible} flag is not set, 1777 * access checking is performed immediately on behalf of the lookup class, 1778 * as if {@code invokespecial} instruction were being linked. 1779 * <p> 1780 * Before method resolution, 1781 * if the explicitly specified caller class is not identical with the 1782 * lookup class, or if this lookup object does not have 1783 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 1784 * privileges, the access fails. 1785 * <p> 1786 * The returned method handle will have 1787 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1788 * the method's variable arity modifier bit ({@code 0x0080}) is set. 1789 * @param m the reflected method 1790 * @param specialCaller the class nominally calling the method 1791 * @return a method handle which can invoke the reflected method 1792 * @throws IllegalAccessException if access checking fails, 1793 * or if the method is {@code static}, 1794 * or if the method's variable arity modifier bit 1795 * is set and {@code asVarargsCollector} fails 1796 * @throws NullPointerException if any argument is null 1797 */ 1798 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException { 1799 checkSpecialCaller(specialCaller, null); 1800 Lookup specialLookup = this.in(specialCaller); 1801 MemberName method = new MemberName(m, true); 1802 assert(method.isMethod()); 1803 // ignore m.isAccessible: this is a new kind of access 1804 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method)); 1805 } 1806 1807 /** 1808 * Produces a method handle for a reflected constructor. 1809 * The type of the method handle will be that of the constructor, 1810 * with the return type changed to the declaring class. 1811 * The method handle will perform a {@code newInstance} operation, 1812 * creating a new instance of the constructor's class on the 1813 * arguments passed to the method handle. 1814 * <p> 1815 * If the constructor's {@code accessible} flag is not set, 1816 * access checking is performed immediately on behalf of the lookup class. 1817 * <p> 1818 * The returned method handle will have 1819 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 1820 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 1821 * <p> 1822 * If the returned method handle is invoked, the constructor's class will 1823 * be initialized, if it has not already been initialized. 1824 * @param c the reflected constructor 1825 * @return a method handle which can invoke the reflected constructor 1826 * @throws IllegalAccessException if access checking fails 1827 * or if the method's variable arity modifier bit 1828 * is set and {@code asVarargsCollector} fails 1829 * @throws NullPointerException if the argument is null 1830 */ 1831 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException { 1832 MemberName ctor = new MemberName(c); 1833 assert(ctor.isConstructor()); 1834 @SuppressWarnings("deprecation") 1835 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this; 1836 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor); 1837 } 1838 1839 /** 1840 * Produces a method handle giving read access to a reflected field. 1841 * The type of the method handle will have a return type of the field's 1842 * value type. 1843 * If the field is static, the method handle will take no arguments. 1844 * Otherwise, its single argument will be the instance containing 1845 * the field. 1846 * If the field's {@code accessible} flag is not set, 1847 * access checking is performed immediately on behalf of the lookup class. 1848 * <p> 1849 * If the field is static, and 1850 * if the returned method handle is invoked, the field's class will 1851 * be initialized, if it has not already been initialized. 1852 * @param f the reflected field 1853 * @return a method handle which can load values from the reflected field 1854 * @throws IllegalAccessException if access checking fails 1855 * @throws NullPointerException if the argument is null 1856 */ 1857 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException { 1858 return unreflectField(f, false); 1859 } 1860 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException { 1861 MemberName field = new MemberName(f, isSetter); 1862 assert(isSetter 1863 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind()) 1864 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind())); 1865 @SuppressWarnings("deprecation") 1866 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this; 1867 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field); 1868 } 1869 1870 /** 1871 * Produces a method handle giving write access to a reflected field. 1872 * The type of the method handle will have a void return type. 1873 * If the field is static, the method handle will take a single 1874 * argument, of the field's value type, the value to be stored. 1875 * Otherwise, the two arguments will be the instance containing 1876 * the field, and the value to be stored. 1877 * If the field's {@code accessible} flag is not set, 1878 * access checking is performed immediately on behalf of the lookup class. 1879 * <p> 1880 * If the field is static, and 1881 * if the returned method handle is invoked, the field's class will 1882 * be initialized, if it has not already been initialized. 1883 * @param f the reflected field 1884 * @return a method handle which can store values into the reflected field 1885 * @throws IllegalAccessException if access checking fails 1886 * @throws NullPointerException if the argument is null 1887 */ 1888 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException { 1889 return unreflectField(f, true); 1890 } 1891 1892 /** 1893 * Produces a VarHandle giving access to a reflected field {@code f} 1894 * of type {@code T} declared in a class of type {@code R}. 1895 * The VarHandle's variable type is {@code T}. 1896 * If the field is non-static the VarHandle has one coordinate type, 1897 * {@code R}. Otherwise, the field is static, and the VarHandle has no 1898 * coordinate types. 1899 * <p> 1900 * Access checking is performed immediately on behalf of the lookup 1901 * class, regardless of the value of the field's {@code accessible} 1902 * flag. 1903 * <p> 1904 * If the field is static, and if the returned VarHandle is operated 1905 * on, the field's declaring class will be initialized, if it has not 1906 * already been initialized. 1907 * <p> 1908 * Certain access modes of the returned VarHandle are unsupported under 1909 * the following conditions: 1910 * <ul> 1911 * <li>if the field is declared {@code final}, then the write, atomic 1912 * update, numeric atomic update, and bitwise atomic update access 1913 * modes are unsupported. 1914 * <li>if the field type is anything other than {@code byte}, 1915 * {@code short}, {@code char}, {@code int}, {@code long}, 1916 * {@code float}, or {@code double} then numeric atomic update 1917 * access modes are unsupported. 1918 * <li>if the field type is anything other than {@code boolean}, 1919 * {@code byte}, {@code short}, {@code char}, {@code int} or 1920 * {@code long} then bitwise atomic update access modes are 1921 * unsupported. 1922 * </ul> 1923 * <p> 1924 * If the field is declared {@code volatile} then the returned VarHandle 1925 * will override access to the field (effectively ignore the 1926 * {@code volatile} declaration) in accordance to its specified 1927 * access modes. 1928 * <p> 1929 * If the field type is {@code float} or {@code double} then numeric 1930 * and atomic update access modes compare values using their bitwise 1931 * representation (see {@link Float#floatToRawIntBits} and 1932 * {@link Double#doubleToRawLongBits}, respectively). 1933 * @apiNote 1934 * Bitwise comparison of {@code float} values or {@code double} values, 1935 * as performed by the numeric and atomic update access modes, differ 1936 * from the primitive {@code ==} operator and the {@link Float#equals} 1937 * and {@link Double#equals} methods, specifically with respect to 1938 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 1939 * Care should be taken when performing a compare and set or a compare 1940 * and exchange operation with such values since the operation may 1941 * unexpectedly fail. 1942 * There are many possible NaN values that are considered to be 1943 * {@code NaN} in Java, although no IEEE 754 floating-point operation 1944 * provided by Java can distinguish between them. Operation failure can 1945 * occur if the expected or witness value is a NaN value and it is 1946 * transformed (perhaps in a platform specific manner) into another NaN 1947 * value, and thus has a different bitwise representation (see 1948 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 1949 * details). 1950 * The values {@code -0.0} and {@code +0.0} have different bitwise 1951 * representations but are considered equal when using the primitive 1952 * {@code ==} operator. Operation failure can occur if, for example, a 1953 * numeric algorithm computes an expected value to be say {@code -0.0} 1954 * and previously computed the witness value to be say {@code +0.0}. 1955 * @param f the reflected field, with a field of type {@code T}, and 1956 * a declaring class of type {@code R} 1957 * @return a VarHandle giving access to non-static fields or a static 1958 * field 1959 * @throws IllegalAccessException if access checking fails 1960 * @throws NullPointerException if the argument is null 1961 * @since 9 1962 */ 1963 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException { 1964 MemberName getField = new MemberName(f, false); 1965 MemberName putField = new MemberName(f, true); 1966 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(), 1967 f.getDeclaringClass(), getField, putField); 1968 } 1969 1970 /** 1971 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 1972 * created by this lookup object or a similar one. 1973 * Security and access checks are performed to ensure that this lookup object 1974 * is capable of reproducing the target method handle. 1975 * This means that the cracking may fail if target is a direct method handle 1976 * but was created by an unrelated lookup object. 1977 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> 1978 * and was created by a lookup object for a different class. 1979 * @param target a direct method handle to crack into symbolic reference components 1980 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object 1981 * @exception SecurityException if a security manager is present and it 1982 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1983 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails 1984 * @exception NullPointerException if the target is {@code null} 1985 * @see MethodHandleInfo 1986 * @since 1.8 1987 */ 1988 public MethodHandleInfo revealDirect(MethodHandle target) { 1989 MemberName member = target.internalMemberName(); 1990 if (member == null || (!member.isResolved() && 1991 !member.isMethodHandleInvoke() && 1992 !member.isVarHandleMethodInvoke())) 1993 throw newIllegalArgumentException("not a direct method handle"); 1994 Class<?> defc = member.getDeclaringClass(); 1995 byte refKind = member.getReferenceKind(); 1996 assert(MethodHandleNatives.refKindIsValid(refKind)); 1997 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial()) 1998 // Devirtualized method invocation is usually formally virtual. 1999 // To avoid creating extra MemberName objects for this common case, 2000 // we encode this extra degree of freedom using MH.isInvokeSpecial. 2001 refKind = REF_invokeVirtual; 2002 if (refKind == REF_invokeVirtual && defc.isInterface()) 2003 // Symbolic reference is through interface but resolves to Object method (toString, etc.) 2004 refKind = REF_invokeInterface; 2005 // Check SM permissions and member access before cracking. 2006 try { 2007 checkAccess(refKind, defc, member); 2008 checkSecurityManager(defc, member); 2009 } catch (IllegalAccessException ex) { 2010 throw new IllegalArgumentException(ex); 2011 } 2012 if (allowedModes != TRUSTED && member.isCallerSensitive()) { 2013 Class<?> callerClass = target.internalCallerClass(); 2014 if (!hasPrivateAccess() || callerClass != lookupClass()) 2015 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass); 2016 } 2017 // Produce the handle to the results. 2018 return new InfoFromMemberName(this, member, refKind); 2019 } 2020 2021 /// Helper methods, all package-private. 2022 2023 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 2024 checkSymbolicClass(refc); // do this before attempting to resolve 2025 Objects.requireNonNull(name); 2026 Objects.requireNonNull(type); 2027 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), 2028 NoSuchFieldException.class); 2029 } 2030 2031 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2032 checkSymbolicClass(refc); // do this before attempting to resolve 2033 Objects.requireNonNull(name); 2034 Objects.requireNonNull(type); 2035 checkMethodName(refKind, name); // NPE check on name 2036 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), 2037 NoSuchMethodException.class); 2038 } 2039 2040 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException { 2041 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve 2042 Objects.requireNonNull(member.getName()); 2043 Objects.requireNonNull(member.getType()); 2044 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), 2045 ReflectiveOperationException.class); 2046 } 2047 2048 MemberName resolveOrNull(byte refKind, MemberName member) { 2049 // do this before attempting to resolve 2050 if (!isClassAccessible(member.getDeclaringClass())) { 2051 return null; 2052 } 2053 Objects.requireNonNull(member.getName()); 2054 Objects.requireNonNull(member.getType()); 2055 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull()); 2056 } 2057 2058 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException { 2059 if (!isClassAccessible(refc)) { 2060 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this); 2061 } 2062 } 2063 2064 boolean isClassAccessible(Class<?> refc) { 2065 Objects.requireNonNull(refc); 2066 Class<?> caller = lookupClassOrNull(); 2067 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes); 2068 } 2069 2070 /** Check name for an illegal leading "<" character. */ 2071 void checkMethodName(byte refKind, String name) throws NoSuchMethodException { 2072 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) 2073 throw new NoSuchMethodException("illegal method name: "+name); 2074 } 2075 2076 2077 /** 2078 * Find my trustable caller class if m is a caller sensitive method. 2079 * If this lookup object has private access, then the caller class is the lookupClass. 2080 * Otherwise, if m is caller-sensitive, throw IllegalAccessException. 2081 */ 2082 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException { 2083 Class<?> callerClass = null; 2084 if (MethodHandleNatives.isCallerSensitive(m)) { 2085 // Only lookups with private access are allowed to resolve caller-sensitive methods 2086 if (hasPrivateAccess()) { 2087 callerClass = lookupClass; 2088 } else { 2089 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 2090 } 2091 } 2092 return callerClass; 2093 } 2094 2095 /** 2096 * Returns {@code true} if this lookup has {@code PRIVATE} access. 2097 * @return {@code true} if this lookup has {@code PRIVATE} access. 2098 * @since 9 2099 */ 2100 public boolean hasPrivateAccess() { 2101 return (allowedModes & PRIVATE) != 0; 2102 } 2103 2104 /** 2105 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>. 2106 * Determines a trustable caller class to compare with refc, the symbolic reference class. 2107 * If this lookup object has private access, then the caller class is the lookupClass. 2108 */ 2109 void checkSecurityManager(Class<?> refc, MemberName m) { 2110 SecurityManager smgr = System.getSecurityManager(); 2111 if (smgr == null) return; 2112 if (allowedModes == TRUSTED) return; 2113 2114 // Step 1: 2115 boolean fullPowerLookup = hasPrivateAccess(); 2116 if (!fullPowerLookup || 2117 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 2118 ReflectUtil.checkPackageAccess(refc); 2119 } 2120 2121 if (m == null) { // findClass or accessClass 2122 // Step 2b: 2123 if (!fullPowerLookup) { 2124 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION); 2125 } 2126 return; 2127 } 2128 2129 // Step 2a: 2130 if (m.isPublic()) return; 2131 if (!fullPowerLookup) { 2132 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION); 2133 } 2134 2135 // Step 3: 2136 Class<?> defc = m.getDeclaringClass(); 2137 if (!fullPowerLookup && defc != refc) { 2138 ReflectUtil.checkPackageAccess(defc); 2139 } 2140 } 2141 2142 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 2143 boolean wantStatic = (refKind == REF_invokeStatic); 2144 String message; 2145 if (m.isConstructor()) 2146 message = "expected a method, not a constructor"; 2147 else if (!m.isMethod()) 2148 message = "expected a method"; 2149 else if (wantStatic != m.isStatic()) 2150 message = wantStatic ? "expected a static method" : "expected a non-static method"; 2151 else 2152 { checkAccess(refKind, refc, m); return; } 2153 throw m.makeAccessException(message, this); 2154 } 2155 2156 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 2157 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind); 2158 String message; 2159 if (wantStatic != m.isStatic()) 2160 message = wantStatic ? "expected a static field" : "expected a non-static field"; 2161 else 2162 { checkAccess(refKind, refc, m); return; } 2163 throw m.makeAccessException(message, this); 2164 } 2165 2166 /** Check public/protected/private bits on the symbolic reference class and its member. */ 2167 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 2168 assert(m.referenceKindIsConsistentWith(refKind) && 2169 MethodHandleNatives.refKindIsValid(refKind) && 2170 (MethodHandleNatives.refKindIsField(refKind) == m.isField())); 2171 int allowedModes = this.allowedModes; 2172 if (allowedModes == TRUSTED) return; 2173 int mods = m.getModifiers(); 2174 if (Modifier.isProtected(mods) && 2175 refKind == REF_invokeVirtual && 2176 m.getDeclaringClass() == Object.class && 2177 m.getName().equals("clone") && 2178 refc.isArray()) { 2179 // The JVM does this hack also. 2180 // (See ClassVerifier::verify_invoke_instructions 2181 // and LinkResolver::check_method_accessability.) 2182 // Because the JVM does not allow separate methods on array types, 2183 // there is no separate method for int[].clone. 2184 // All arrays simply inherit Object.clone. 2185 // But for access checking logic, we make Object.clone 2186 // (normally protected) appear to be public. 2187 // Later on, when the DirectMethodHandle is created, 2188 // its leading argument will be restricted to the 2189 // requested array type. 2190 // N.B. The return type is not adjusted, because 2191 // that is *not* the bytecode behavior. 2192 mods ^= Modifier.PROTECTED | Modifier.PUBLIC; 2193 } 2194 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) { 2195 // cannot "new" a protected ctor in a different package 2196 mods ^= Modifier.PROTECTED; 2197 } 2198 if (Modifier.isFinal(mods) && 2199 MethodHandleNatives.refKindIsSetter(refKind)) 2200 throw m.makeAccessException("unexpected set of a final field", this); 2201 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE 2202 if ((requestedModes & allowedModes) != 0) { 2203 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(), 2204 mods, lookupClass(), allowedModes)) 2205 return; 2206 } else { 2207 // Protected members can also be checked as if they were package-private. 2208 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0 2209 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass())) 2210 return; 2211 } 2212 throw m.makeAccessException(accessFailedMessage(refc, m), this); 2213 } 2214 2215 String accessFailedMessage(Class<?> refc, MemberName m) { 2216 Class<?> defc = m.getDeclaringClass(); 2217 int mods = m.getModifiers(); 2218 // check the class first: 2219 boolean classOK = (Modifier.isPublic(defc.getModifiers()) && 2220 (defc == refc || 2221 Modifier.isPublic(refc.getModifiers()))); 2222 if (!classOK && (allowedModes & PACKAGE) != 0) { 2223 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) && 2224 (defc == refc || 2225 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES))); 2226 } 2227 if (!classOK) 2228 return "class is not public"; 2229 if (Modifier.isPublic(mods)) 2230 return "access to public member failed"; // (how?, module not readable?) 2231 if (Modifier.isPrivate(mods)) 2232 return "member is private"; 2233 if (Modifier.isProtected(mods)) 2234 return "member is protected"; 2235 return "member is private to package"; 2236 } 2237 2238 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException { 2239 int allowedModes = this.allowedModes; 2240 if (allowedModes == TRUSTED) return; 2241 if (!hasPrivateAccess() 2242 || (specialCaller != lookupClass() 2243 // ensure non-abstract methods in superinterfaces can be special-invoked 2244 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller)))) 2245 throw new MemberName(specialCaller). 2246 makeAccessException("no private access for invokespecial", this); 2247 } 2248 2249 private boolean restrictProtectedReceiver(MemberName method) { 2250 // The accessing class only has the right to use a protected member 2251 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc. 2252 if (!method.isProtected() || method.isStatic() 2253 || allowedModes == TRUSTED 2254 || method.getDeclaringClass() == lookupClass() 2255 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())) 2256 return false; 2257 return true; 2258 } 2259 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException { 2260 assert(!method.isStatic()); 2261 // receiver type of mh is too wide; narrow to caller 2262 if (!method.getDeclaringClass().isAssignableFrom(caller)) { 2263 throw method.makeAccessException("caller class must be a subclass below the method", caller); 2264 } 2265 MethodType rawType = mh.type(); 2266 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow 2267 MethodType narrowType = rawType.changeParameterType(0, caller); 2268 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness 2269 assert(mh.viewAsTypeChecks(narrowType, true)); 2270 return mh.copyWith(narrowType, mh.form); 2271 } 2272 2273 /** Check access and get the requested method. */ 2274 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException { 2275 final boolean doRestrict = true; 2276 final boolean checkSecurity = true; 2277 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass); 2278 } 2279 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */ 2280 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException { 2281 final boolean doRestrict = false; 2282 final boolean checkSecurity = true; 2283 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass); 2284 } 2285 /** Check access and get the requested method, eliding security manager checks. */ 2286 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException { 2287 final boolean doRestrict = true; 2288 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 2289 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass); 2290 } 2291 /** Common code for all methods; do not call directly except from immediately above. */ 2292 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method, 2293 boolean checkSecurity, 2294 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException { 2295 2296 checkMethod(refKind, refc, method); 2297 // Optionally check with the security manager; this isn't needed for unreflect* calls. 2298 if (checkSecurity) 2299 checkSecurityManager(refc, method); 2300 assert(!method.isMethodHandleInvoke()); 2301 2302 if (refKind == REF_invokeSpecial && 2303 refc != lookupClass() && 2304 !refc.isInterface() && 2305 refc != lookupClass().getSuperclass() && 2306 refc.isAssignableFrom(lookupClass())) { 2307 assert(!method.getName().equals("<init>")); // not this code path 2308 2309 // Per JVMS 6.5, desc. of invokespecial instruction: 2310 // If the method is in a superclass of the LC, 2311 // and if our original search was above LC.super, 2312 // repeat the search (symbolic lookup) from LC.super 2313 // and continue with the direct superclass of that class, 2314 // and so forth, until a match is found or no further superclasses exist. 2315 // FIXME: MemberName.resolve should handle this instead. 2316 Class<?> refcAsSuper = lookupClass(); 2317 MemberName m2; 2318 do { 2319 refcAsSuper = refcAsSuper.getSuperclass(); 2320 m2 = new MemberName(refcAsSuper, 2321 method.getName(), 2322 method.getMethodType(), 2323 REF_invokeSpecial); 2324 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull()); 2325 } while (m2 == null && // no method is found yet 2326 refc != refcAsSuper); // search up to refc 2327 if (m2 == null) throw new InternalError(method.toString()); 2328 method = m2; 2329 refc = refcAsSuper; 2330 // redo basic checks 2331 checkMethod(refKind, refc, method); 2332 } 2333 2334 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass()); 2335 MethodHandle mh = dmh; 2336 // Optionally narrow the receiver argument to lookupClass using restrictReceiver. 2337 if ((doRestrict && refKind == REF_invokeSpecial) || 2338 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) { 2339 mh = restrictReceiver(method, dmh, lookupClass()); 2340 } 2341 mh = maybeBindCaller(method, mh, boundCallerClass); 2342 mh = mh.setVarargs(method); 2343 return mh; 2344 } 2345 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, 2346 Class<?> boundCallerClass) 2347 throws IllegalAccessException { 2348 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method)) 2349 return mh; 2350 Class<?> hostClass = lookupClass; 2351 if (!hasPrivateAccess()) // caller must have private access 2352 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk 2353 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass); 2354 // Note: caller will apply varargs after this step happens. 2355 return cbmh; 2356 } 2357 /** Check access and get the requested field. */ 2358 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 2359 final boolean checkSecurity = true; 2360 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 2361 } 2362 /** Check access and get the requested field, eliding security manager checks. */ 2363 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 2364 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 2365 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 2366 } 2367 /** Common code for all fields; do not call directly except from immediately above. */ 2368 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field, 2369 boolean checkSecurity) throws IllegalAccessException { 2370 checkField(refKind, refc, field); 2371 // Optionally check with the security manager; this isn't needed for unreflect* calls. 2372 if (checkSecurity) 2373 checkSecurityManager(refc, field); 2374 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field); 2375 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) && 2376 restrictProtectedReceiver(field)); 2377 if (doRestrict) 2378 return restrictReceiver(field, dmh, lookupClass()); 2379 return dmh; 2380 } 2381 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind, 2382 Class<?> refc, MemberName getField, MemberName putField) 2383 throws IllegalAccessException { 2384 final boolean checkSecurity = true; 2385 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 2386 } 2387 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind, 2388 Class<?> refc, MemberName getField, MemberName putField) 2389 throws IllegalAccessException { 2390 final boolean checkSecurity = false; 2391 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 2392 } 2393 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind, 2394 Class<?> refc, MemberName getField, MemberName putField, 2395 boolean checkSecurity) throws IllegalAccessException { 2396 assert getField.isStatic() == putField.isStatic(); 2397 assert getField.isGetter() && putField.isSetter(); 2398 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind); 2399 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind); 2400 2401 checkField(getRefKind, refc, getField); 2402 if (checkSecurity) 2403 checkSecurityManager(refc, getField); 2404 2405 if (!putField.isFinal()) { 2406 // A VarHandle does not support updates to final fields, any 2407 // such VarHandle to a final field will be read-only and 2408 // therefore the following write-based accessibility checks are 2409 // only required for non-final fields 2410 checkField(putRefKind, refc, putField); 2411 if (checkSecurity) 2412 checkSecurityManager(refc, putField); 2413 } 2414 2415 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) && 2416 restrictProtectedReceiver(getField)); 2417 if (doRestrict) { 2418 assert !getField.isStatic(); 2419 // receiver type of VarHandle is too wide; narrow to caller 2420 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) { 2421 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass()); 2422 } 2423 refc = lookupClass(); 2424 } 2425 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED); 2426 } 2427 /** Check access and get the requested constructor. */ 2428 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException { 2429 final boolean checkSecurity = true; 2430 return getDirectConstructorCommon(refc, ctor, checkSecurity); 2431 } 2432 /** Check access and get the requested constructor, eliding security manager checks. */ 2433 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException { 2434 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 2435 return getDirectConstructorCommon(refc, ctor, checkSecurity); 2436 } 2437 /** Common code for all constructors; do not call directly except from immediately above. */ 2438 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor, 2439 boolean checkSecurity) throws IllegalAccessException { 2440 assert(ctor.isConstructor()); 2441 checkAccess(REF_newInvokeSpecial, refc, ctor); 2442 // Optionally check with the security manager; this isn't needed for unreflect* calls. 2443 if (checkSecurity) 2444 checkSecurityManager(refc, ctor); 2445 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here 2446 return DirectMethodHandle.make(ctor).setVarargs(ctor); 2447 } 2448 2449 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants: 2450 */ 2451 /*non-public*/ 2452 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException { 2453 if (!(type instanceof Class || type instanceof MethodType)) 2454 throw new InternalError("unresolved MemberName"); 2455 MemberName member = new MemberName(refKind, defc, name, type); 2456 MethodHandle mh = LOOKASIDE_TABLE.get(member); 2457 if (mh != null) { 2458 checkSymbolicClass(defc); 2459 return mh; 2460 } 2461 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) { 2462 // Treat MethodHandle.invoke and invokeExact specially. 2463 mh = findVirtualForMH(member.getName(), member.getMethodType()); 2464 if (mh != null) { 2465 return mh; 2466 } 2467 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) { 2468 // Treat signature-polymorphic methods on VarHandle specially. 2469 mh = findVirtualForVH(member.getName(), member.getMethodType()); 2470 if (mh != null) { 2471 return mh; 2472 } 2473 } 2474 MemberName resolved = resolveOrFail(refKind, member); 2475 mh = getDirectMethodForConstant(refKind, defc, resolved); 2476 if (mh instanceof DirectMethodHandle 2477 && canBeCached(refKind, defc, resolved)) { 2478 MemberName key = mh.internalMemberName(); 2479 if (key != null) { 2480 key = key.asNormalOriginal(); 2481 } 2482 if (member.equals(key)) { // better safe than sorry 2483 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh); 2484 } 2485 } 2486 return mh; 2487 } 2488 private 2489 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) { 2490 if (refKind == REF_invokeSpecial) { 2491 return false; 2492 } 2493 if (!Modifier.isPublic(defc.getModifiers()) || 2494 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) || 2495 !member.isPublic() || 2496 member.isCallerSensitive()) { 2497 return false; 2498 } 2499 ClassLoader loader = defc.getClassLoader(); 2500 if (loader != null) { 2501 ClassLoader sysl = ClassLoader.getSystemClassLoader(); 2502 boolean found = false; 2503 while (sysl != null) { 2504 if (loader == sysl) { found = true; break; } 2505 sysl = sysl.getParent(); 2506 } 2507 if (!found) { 2508 return false; 2509 } 2510 } 2511 try { 2512 MemberName resolved2 = publicLookup().resolveOrNull(refKind, 2513 new MemberName(refKind, defc, member.getName(), member.getType())); 2514 if (resolved2 == null) { 2515 return false; 2516 } 2517 checkSecurityManager(defc, resolved2); 2518 } catch (SecurityException ex) { 2519 return false; 2520 } 2521 return true; 2522 } 2523 private 2524 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member) 2525 throws ReflectiveOperationException { 2526 if (MethodHandleNatives.refKindIsField(refKind)) { 2527 return getDirectFieldNoSecurityManager(refKind, defc, member); 2528 } else if (MethodHandleNatives.refKindIsMethod(refKind)) { 2529 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass); 2530 } else if (refKind == REF_newInvokeSpecial) { 2531 return getDirectConstructorNoSecurityManager(defc, member); 2532 } 2533 // oops 2534 throw newIllegalArgumentException("bad MethodHandle constant #"+member); 2535 } 2536 2537 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>(); 2538 } 2539 2540 /** 2541 * Produces a method handle constructing arrays of a desired type, 2542 * as if by the {@code anewarray} bytecode. 2543 * The return type of the method handle will be the array type. 2544 * The type of its sole argument will be {@code int}, which specifies the size of the array. 2545 * 2546 * <p> If the returned method handle is invoked with a negative 2547 * array size, a {@code NegativeArraySizeException} will be thrown. 2548 * 2549 * @param arrayClass an array type 2550 * @return a method handle which can create arrays of the given type 2551 * @throws NullPointerException if the argument is {@code null} 2552 * @throws IllegalArgumentException if {@code arrayClass} is not an array type 2553 * @see java.lang.reflect.Array#newInstance(Class, int) 2554 * @jvms 6.5 {@code anewarray} Instruction 2555 * @since 9 2556 */ 2557 public static 2558 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException { 2559 if (!arrayClass.isArray()) { 2560 throw newIllegalArgumentException("not an array class: " + arrayClass.getName()); 2561 } 2562 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance). 2563 bindTo(arrayClass.getComponentType()); 2564 return ani.asType(ani.type().changeReturnType(arrayClass)); 2565 } 2566 2567 /** 2568 * Produces a method handle returning the length of an array, 2569 * as if by the {@code arraylength} bytecode. 2570 * The type of the method handle will have {@code int} as return type, 2571 * and its sole argument will be the array type. 2572 * 2573 * <p> If the returned method handle is invoked with a {@code null} 2574 * array reference, a {@code NullPointerException} will be thrown. 2575 * 2576 * @param arrayClass an array type 2577 * @return a method handle which can retrieve the length of an array of the given array type 2578 * @throws NullPointerException if the argument is {@code null} 2579 * @throws IllegalArgumentException if arrayClass is not an array type 2580 * @jvms 6.5 {@code arraylength} Instruction 2581 * @since 9 2582 */ 2583 public static 2584 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException { 2585 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH); 2586 } 2587 2588 /** 2589 * Produces a method handle giving read access to elements of an array, 2590 * as if by the {@code aaload} bytecode. 2591 * The type of the method handle will have a return type of the array's 2592 * element type. Its first argument will be the array type, 2593 * and the second will be {@code int}. 2594 * 2595 * <p> When the returned method handle is invoked, 2596 * the array reference and array index are checked. 2597 * A {@code NullPointerException} will be thrown if the array reference 2598 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 2599 * thrown if the index is negative or if it is greater than or equal to 2600 * the length of the array. 2601 * 2602 * @param arrayClass an array type 2603 * @return a method handle which can load values from the given array type 2604 * @throws NullPointerException if the argument is null 2605 * @throws IllegalArgumentException if arrayClass is not an array type 2606 * @jvms 6.5 {@code aaload} Instruction 2607 */ 2608 public static 2609 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException { 2610 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET); 2611 } 2612 2613 /** 2614 * Produces a method handle giving write access to elements of an array, 2615 * as if by the {@code astore} bytecode. 2616 * The type of the method handle will have a void return type. 2617 * Its last argument will be the array's element type. 2618 * The first and second arguments will be the array type and int. 2619 * 2620 * <p> When the returned method handle is invoked, 2621 * the array reference and array index are checked. 2622 * A {@code NullPointerException} will be thrown if the array reference 2623 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 2624 * thrown if the index is negative or if it is greater than or equal to 2625 * the length of the array. 2626 * 2627 * @param arrayClass the class of an array 2628 * @return a method handle which can store values into the array type 2629 * @throws NullPointerException if the argument is null 2630 * @throws IllegalArgumentException if arrayClass is not an array type 2631 * @jvms 6.5 {@code aastore} Instruction 2632 */ 2633 public static 2634 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException { 2635 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET); 2636 } 2637 2638 /** 2639 * Produces a VarHandle giving access to elements of an array of type 2640 * {@code arrayClass}. The VarHandle's variable type is the component type 2641 * of {@code arrayClass} and the list of coordinate types is 2642 * {@code (arrayClass, int)}, where the {@code int} coordinate type 2643 * corresponds to an argument that is an index into an array. 2644 * <p> 2645 * Certain access modes of the returned VarHandle are unsupported under 2646 * the following conditions: 2647 * <ul> 2648 * <li>if the component type is anything other than {@code byte}, 2649 * {@code short}, {@code char}, {@code int}, {@code long}, 2650 * {@code float}, or {@code double} then numeric atomic update access 2651 * modes are unsupported. 2652 * <li>if the field type is anything other than {@code boolean}, 2653 * {@code byte}, {@code short}, {@code char}, {@code int} or 2654 * {@code long} then bitwise atomic update access modes are 2655 * unsupported. 2656 * </ul> 2657 * <p> 2658 * If the component type is {@code float} or {@code double} then numeric 2659 * and atomic update access modes compare values using their bitwise 2660 * representation (see {@link Float#floatToRawIntBits} and 2661 * {@link Double#doubleToRawLongBits}, respectively). 2662 * 2663 * <p> When the returned {@code VarHandle} is invoked, 2664 * the array reference and array index are checked. 2665 * A {@code NullPointerException} will be thrown if the array reference 2666 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 2667 * thrown if the index is negative or if it is greater than or equal to 2668 * the length of the array. 2669 * 2670 * @apiNote 2671 * Bitwise comparison of {@code float} values or {@code double} values, 2672 * as performed by the numeric and atomic update access modes, differ 2673 * from the primitive {@code ==} operator and the {@link Float#equals} 2674 * and {@link Double#equals} methods, specifically with respect to 2675 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 2676 * Care should be taken when performing a compare and set or a compare 2677 * and exchange operation with such values since the operation may 2678 * unexpectedly fail. 2679 * There are many possible NaN values that are considered to be 2680 * {@code NaN} in Java, although no IEEE 754 floating-point operation 2681 * provided by Java can distinguish between them. Operation failure can 2682 * occur if the expected or witness value is a NaN value and it is 2683 * transformed (perhaps in a platform specific manner) into another NaN 2684 * value, and thus has a different bitwise representation (see 2685 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 2686 * details). 2687 * The values {@code -0.0} and {@code +0.0} have different bitwise 2688 * representations but are considered equal when using the primitive 2689 * {@code ==} operator. Operation failure can occur if, for example, a 2690 * numeric algorithm computes an expected value to be say {@code -0.0} 2691 * and previously computed the witness value to be say {@code +0.0}. 2692 * @param arrayClass the class of an array, of type {@code T[]} 2693 * @return a VarHandle giving access to elements of an array 2694 * @throws NullPointerException if the arrayClass is null 2695 * @throws IllegalArgumentException if arrayClass is not an array type 2696 * @since 9 2697 */ 2698 public static 2699 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException { 2700 return VarHandles.makeArrayElementHandle(arrayClass); 2701 } 2702 2703 /** 2704 * Produces a VarHandle giving access to elements of a {@code byte[]} array 2705 * viewed as if it were a different primitive array type, such as 2706 * {@code int[]} or {@code long[]}. 2707 * The VarHandle's variable type is the component type of 2708 * {@code viewArrayClass} and the list of coordinate types is 2709 * {@code (byte[], int)}, where the {@code int} coordinate type 2710 * corresponds to an argument that is an index into a {@code byte[]} array. 2711 * The returned VarHandle accesses bytes at an index in a {@code byte[]} 2712 * array, composing bytes to or from a value of the component type of 2713 * {@code viewArrayClass} according to the given endianness. 2714 * <p> 2715 * The supported component types (variables types) are {@code short}, 2716 * {@code char}, {@code int}, {@code long}, {@code float} and 2717 * {@code double}. 2718 * <p> 2719 * Access of bytes at a given index will result in an 2720 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 2721 * or greater than the {@code byte[]} array length minus the size (in bytes) 2722 * of {@code T}. 2723 * <p> 2724 * Access of bytes at an index may be aligned or misaligned for {@code T}, 2725 * with respect to the underlying memory address, {@code A} say, associated 2726 * with the array and index. 2727 * If access is misaligned then access for anything other than the 2728 * {@code get} and {@code set} access modes will result in an 2729 * {@code IllegalStateException}. In such cases atomic access is only 2730 * guaranteed with respect to the largest power of two that divides the GCD 2731 * of {@code A} and the size (in bytes) of {@code T}. 2732 * If access is aligned then following access modes are supported and are 2733 * guaranteed to support atomic access: 2734 * <ul> 2735 * <li>read write access modes for all {@code T}, with the exception of 2736 * access modes {@code get} and {@code set} for {@code long} and 2737 * {@code double} on 32-bit platforms. 2738 * <li>atomic update access modes for {@code int}, {@code long}, 2739 * {@code float} or {@code double}. 2740 * (Future major platform releases of the JDK may support additional 2741 * types for certain currently unsupported access modes.) 2742 * <li>numeric atomic update access modes for {@code int} and {@code long}. 2743 * (Future major platform releases of the JDK may support additional 2744 * numeric types for certain currently unsupported access modes.) 2745 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 2746 * (Future major platform releases of the JDK may support additional 2747 * numeric types for certain currently unsupported access modes.) 2748 * </ul> 2749 * <p> 2750 * Misaligned access, and therefore atomicity guarantees, may be determined 2751 * for {@code byte[]} arrays without operating on a specific array. Given 2752 * an {@code index}, {@code T} and it's corresponding boxed type, 2753 * {@code T_BOX}, misalignment may be determined as follows: 2754 * <pre>{@code 2755 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 2756 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]). 2757 * alignmentOffset(0, sizeOfT); 2758 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT; 2759 * boolean isMisaligned = misalignedAtIndex != 0; 2760 * }</pre> 2761 * <p> 2762 * If the variable type is {@code float} or {@code double} then atomic 2763 * update access modes compare values using their bitwise representation 2764 * (see {@link Float#floatToRawIntBits} and 2765 * {@link Double#doubleToRawLongBits}, respectively). 2766 * @param viewArrayClass the view array class, with a component type of 2767 * type {@code T} 2768 * @param byteOrder the endianness of the view array elements, as 2769 * stored in the underlying {@code byte} array 2770 * @return a VarHandle giving access to elements of a {@code byte[]} array 2771 * viewed as if elements corresponding to the components type of the view 2772 * array class 2773 * @throws NullPointerException if viewArrayClass or byteOrder is null 2774 * @throws IllegalArgumentException if viewArrayClass is not an array type 2775 * @throws UnsupportedOperationException if the component type of 2776 * viewArrayClass is not supported as a variable type 2777 * @since 9 2778 */ 2779 public static 2780 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass, 2781 ByteOrder byteOrder) throws IllegalArgumentException { 2782 Objects.requireNonNull(byteOrder); 2783 return VarHandles.byteArrayViewHandle(viewArrayClass, 2784 byteOrder == ByteOrder.BIG_ENDIAN); 2785 } 2786 2787 /** 2788 * Produces a VarHandle giving access to elements of a {@code ByteBuffer} 2789 * viewed as if it were an array of elements of a different primitive 2790 * component type to that of {@code byte}, such as {@code int[]} or 2791 * {@code long[]}. 2792 * The VarHandle's variable type is the component type of 2793 * {@code viewArrayClass} and the list of coordinate types is 2794 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type 2795 * corresponds to an argument that is an index into a {@code byte[]} array. 2796 * The returned VarHandle accesses bytes at an index in a 2797 * {@code ByteBuffer}, composing bytes to or from a value of the component 2798 * type of {@code viewArrayClass} according to the given endianness. 2799 * <p> 2800 * The supported component types (variables types) are {@code short}, 2801 * {@code char}, {@code int}, {@code long}, {@code float} and 2802 * {@code double}. 2803 * <p> 2804 * Access will result in a {@code ReadOnlyBufferException} for anything 2805 * other than the read access modes if the {@code ByteBuffer} is read-only. 2806 * <p> 2807 * Access of bytes at a given index will result in an 2808 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 2809 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of 2810 * {@code T}. 2811 * <p> 2812 * Access of bytes at an index may be aligned or misaligned for {@code T}, 2813 * with respect to the underlying memory address, {@code A} say, associated 2814 * with the {@code ByteBuffer} and index. 2815 * If access is misaligned then access for anything other than the 2816 * {@code get} and {@code set} access modes will result in an 2817 * {@code IllegalStateException}. In such cases atomic access is only 2818 * guaranteed with respect to the largest power of two that divides the GCD 2819 * of {@code A} and the size (in bytes) of {@code T}. 2820 * If access is aligned then following access modes are supported and are 2821 * guaranteed to support atomic access: 2822 * <ul> 2823 * <li>read write access modes for all {@code T}, with the exception of 2824 * access modes {@code get} and {@code set} for {@code long} and 2825 * {@code double} on 32-bit platforms. 2826 * <li>atomic update access modes for {@code int}, {@code long}, 2827 * {@code float} or {@code double}. 2828 * (Future major platform releases of the JDK may support additional 2829 * types for certain currently unsupported access modes.) 2830 * <li>numeric atomic update access modes for {@code int} and {@code long}. 2831 * (Future major platform releases of the JDK may support additional 2832 * numeric types for certain currently unsupported access modes.) 2833 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 2834 * (Future major platform releases of the JDK may support additional 2835 * numeric types for certain currently unsupported access modes.) 2836 * </ul> 2837 * <p> 2838 * Misaligned access, and therefore atomicity guarantees, may be determined 2839 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an 2840 * {@code index}, {@code T} and it's corresponding boxed type, 2841 * {@code T_BOX}, as follows: 2842 * <pre>{@code 2843 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 2844 * ByteBuffer bb = ... 2845 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT); 2846 * boolean isMisaligned = misalignedAtIndex != 0; 2847 * }</pre> 2848 * <p> 2849 * If the variable type is {@code float} or {@code double} then atomic 2850 * update access modes compare values using their bitwise representation 2851 * (see {@link Float#floatToRawIntBits} and 2852 * {@link Double#doubleToRawLongBits}, respectively). 2853 * @param viewArrayClass the view array class, with a component type of 2854 * type {@code T} 2855 * @param byteOrder the endianness of the view array elements, as 2856 * stored in the underlying {@code ByteBuffer} (Note this overrides the 2857 * endianness of a {@code ByteBuffer}) 2858 * @return a VarHandle giving access to elements of a {@code ByteBuffer} 2859 * viewed as if elements corresponding to the components type of the view 2860 * array class 2861 * @throws NullPointerException if viewArrayClass or byteOrder is null 2862 * @throws IllegalArgumentException if viewArrayClass is not an array type 2863 * @throws UnsupportedOperationException if the component type of 2864 * viewArrayClass is not supported as a variable type 2865 * @since 9 2866 */ 2867 public static 2868 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass, 2869 ByteOrder byteOrder) throws IllegalArgumentException { 2870 Objects.requireNonNull(byteOrder); 2871 return VarHandles.makeByteBufferViewHandle(viewArrayClass, 2872 byteOrder == ByteOrder.BIG_ENDIAN); 2873 } 2874 2875 2876 /// method handle invocation (reflective style) 2877 2878 /** 2879 * Produces a method handle which will invoke any method handle of the 2880 * given {@code type}, with a given number of trailing arguments replaced by 2881 * a single trailing {@code Object[]} array. 2882 * The resulting invoker will be a method handle with the following 2883 * arguments: 2884 * <ul> 2885 * <li>a single {@code MethodHandle} target 2886 * <li>zero or more leading values (counted by {@code leadingArgCount}) 2887 * <li>an {@code Object[]} array containing trailing arguments 2888 * </ul> 2889 * <p> 2890 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with 2891 * the indicated {@code type}. 2892 * That is, if the target is exactly of the given {@code type}, it will behave 2893 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType} 2894 * is used to convert the target to the required {@code type}. 2895 * <p> 2896 * The type of the returned invoker will not be the given {@code type}, but rather 2897 * will have all parameters except the first {@code leadingArgCount} 2898 * replaced by a single array of type {@code Object[]}, which will be 2899 * the final parameter. 2900 * <p> 2901 * Before invoking its target, the invoker will spread the final array, apply 2902 * reference casts as necessary, and unbox and widen primitive arguments. 2903 * If, when the invoker is called, the supplied array argument does 2904 * not have the correct number of elements, the invoker will throw 2905 * an {@link IllegalArgumentException} instead of invoking the target. 2906 * <p> 2907 * This method is equivalent to the following code (though it may be more efficient): 2908 * <blockquote><pre>{@code 2909 MethodHandle invoker = MethodHandles.invoker(type); 2910 int spreadArgCount = type.parameterCount() - leadingArgCount; 2911 invoker = invoker.asSpreader(Object[].class, spreadArgCount); 2912 return invoker; 2913 * }</pre></blockquote> 2914 * This method throws no reflective or security exceptions. 2915 * @param type the desired target type 2916 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target 2917 * @return a method handle suitable for invoking any method handle of the given type 2918 * @throws NullPointerException if {@code type} is null 2919 * @throws IllegalArgumentException if {@code leadingArgCount} is not in 2920 * the range from 0 to {@code type.parameterCount()} inclusive, 2921 * or if the resulting method handle's type would have 2922 * <a href="MethodHandle.html#maxarity">too many parameters</a> 2923 */ 2924 public static 2925 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) { 2926 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) 2927 throw newIllegalArgumentException("bad argument count", leadingArgCount); 2928 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount); 2929 return type.invokers().spreadInvoker(leadingArgCount); 2930 } 2931 2932 /** 2933 * Produces a special <em>invoker method handle</em> which can be used to 2934 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. 2935 * The resulting invoker will have a type which is 2936 * exactly equal to the desired type, except that it will accept 2937 * an additional leading argument of type {@code MethodHandle}. 2938 * <p> 2939 * This method is equivalent to the following code (though it may be more efficient): 2940 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)} 2941 * 2942 * <p style="font-size:smaller;"> 2943 * <em>Discussion:</em> 2944 * Invoker method handles can be useful when working with variable method handles 2945 * of unknown types. 2946 * For example, to emulate an {@code invokeExact} call to a variable method 2947 * handle {@code M}, extract its type {@code T}, 2948 * look up the invoker method {@code X} for {@code T}, 2949 * and call the invoker method, as {@code X.invoke(T, A...)}. 2950 * (It would not work to call {@code X.invokeExact}, since the type {@code T} 2951 * is unknown.) 2952 * If spreading, collecting, or other argument transformations are required, 2953 * they can be applied once to the invoker {@code X} and reused on many {@code M} 2954 * method handle values, as long as they are compatible with the type of {@code X}. 2955 * <p style="font-size:smaller;"> 2956 * <em>(Note: The invoker method is not available via the Core Reflection API. 2957 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 2958 * on the declared {@code invokeExact} or {@code invoke} method will raise an 2959 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 2960 * <p> 2961 * This method throws no reflective or security exceptions. 2962 * @param type the desired target type 2963 * @return a method handle suitable for invoking any method handle of the given type 2964 * @throws IllegalArgumentException if the resulting method handle's type would have 2965 * <a href="MethodHandle.html#maxarity">too many parameters</a> 2966 */ 2967 public static 2968 MethodHandle exactInvoker(MethodType type) { 2969 return type.invokers().exactInvoker(); 2970 } 2971 2972 /** 2973 * Produces a special <em>invoker method handle</em> which can be used to 2974 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}. 2975 * The resulting invoker will have a type which is 2976 * exactly equal to the desired type, except that it will accept 2977 * an additional leading argument of type {@code MethodHandle}. 2978 * <p> 2979 * Before invoking its target, if the target differs from the expected type, 2980 * the invoker will apply reference casts as 2981 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}. 2982 * Similarly, the return value will be converted as necessary. 2983 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle}, 2984 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}. 2985 * <p> 2986 * This method is equivalent to the following code (though it may be more efficient): 2987 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)} 2988 * <p style="font-size:smaller;"> 2989 * <em>Discussion:</em> 2990 * A {@linkplain MethodType#genericMethodType general method type} is one which 2991 * mentions only {@code Object} arguments and return values. 2992 * An invoker for such a type is capable of calling any method handle 2993 * of the same arity as the general type. 2994 * <p style="font-size:smaller;"> 2995 * <em>(Note: The invoker method is not available via the Core Reflection API. 2996 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 2997 * on the declared {@code invokeExact} or {@code invoke} method will raise an 2998 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 2999 * <p> 3000 * This method throws no reflective or security exceptions. 3001 * @param type the desired target type 3002 * @return a method handle suitable for invoking any method handle convertible to the given type 3003 * @throws IllegalArgumentException if the resulting method handle's type would have 3004 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3005 */ 3006 public static 3007 MethodHandle invoker(MethodType type) { 3008 return type.invokers().genericInvoker(); 3009 } 3010 3011 /** 3012 * Produces a special <em>invoker method handle</em> which can be used to 3013 * invoke a signature-polymorphic access mode method on any VarHandle whose 3014 * associated access mode type is compatible with the given type. 3015 * The resulting invoker will have a type which is exactly equal to the 3016 * desired given type, except that it will accept an additional leading 3017 * argument of type {@code VarHandle}. 3018 * 3019 * @param accessMode the VarHandle access mode 3020 * @param type the desired target type 3021 * @return a method handle suitable for invoking an access mode method of 3022 * any VarHandle whose access mode type is of the given type. 3023 * @since 9 3024 */ 3025 static public 3026 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) { 3027 return type.invokers().varHandleMethodExactInvoker(accessMode); 3028 } 3029 3030 /** 3031 * Produces a special <em>invoker method handle</em> which can be used to 3032 * invoke a signature-polymorphic access mode method on any VarHandle whose 3033 * associated access mode type is compatible with the given type. 3034 * The resulting invoker will have a type which is exactly equal to the 3035 * desired given type, except that it will accept an additional leading 3036 * argument of type {@code VarHandle}. 3037 * <p> 3038 * Before invoking its target, if the access mode type differs from the 3039 * desired given type, the invoker will apply reference casts as necessary 3040 * and box, unbox, or widen primitive values, as if by 3041 * {@link MethodHandle#asType asType}. Similarly, the return value will be 3042 * converted as necessary. 3043 * <p> 3044 * This method is equivalent to the following code (though it may be more 3045 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)} 3046 * 3047 * @param accessMode the VarHandle access mode 3048 * @param type the desired target type 3049 * @return a method handle suitable for invoking an access mode method of 3050 * any VarHandle whose access mode type is convertible to the given 3051 * type. 3052 * @since 9 3053 */ 3054 static public 3055 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) { 3056 return type.invokers().varHandleMethodInvoker(accessMode); 3057 } 3058 3059 static /*non-public*/ 3060 MethodHandle basicInvoker(MethodType type) { 3061 return type.invokers().basicInvoker(); 3062 } 3063 3064 /// method handle modification (creation from other method handles) 3065 3066 /** 3067 * Produces a method handle which adapts the type of the 3068 * given method handle to a new type by pairwise argument and return type conversion. 3069 * The original type and new type must have the same number of arguments. 3070 * The resulting method handle is guaranteed to report a type 3071 * which is equal to the desired new type. 3072 * <p> 3073 * If the original type and new type are equal, returns target. 3074 * <p> 3075 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType}, 3076 * and some additional conversions are also applied if those conversions fail. 3077 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied 3078 * if possible, before or instead of any conversions done by {@code asType}: 3079 * <ul> 3080 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type, 3081 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast. 3082 * (This treatment of interfaces follows the usage of the bytecode verifier.) 3083 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive, 3084 * the boolean is converted to a byte value, 1 for true, 0 for false. 3085 * (This treatment follows the usage of the bytecode verifier.) 3086 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive, 3087 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5), 3088 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}. 3089 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean, 3090 * then a Java casting conversion (JLS 5.5) is applied. 3091 * (Specifically, <em>T0</em> will convert to <em>T1</em> by 3092 * widening and/or narrowing.) 3093 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing 3094 * conversion will be applied at runtime, possibly followed 3095 * by a Java casting conversion (JLS 5.5) on the primitive value, 3096 * possibly followed by a conversion from byte to boolean by testing 3097 * the low-order bit. 3098 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, 3099 * and if the reference is null at runtime, a zero value is introduced. 3100 * </ul> 3101 * @param target the method handle to invoke after arguments are retyped 3102 * @param newType the expected type of the new method handle 3103 * @return a method handle which delegates to the target after performing 3104 * any necessary argument conversions, and arranges for any 3105 * necessary return value conversions 3106 * @throws NullPointerException if either argument is null 3107 * @throws WrongMethodTypeException if the conversion cannot be made 3108 * @see MethodHandle#asType 3109 */ 3110 public static 3111 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) { 3112 explicitCastArgumentsChecks(target, newType); 3113 // use the asTypeCache when possible: 3114 MethodType oldType = target.type(); 3115 if (oldType == newType) return target; 3116 if (oldType.explicitCastEquivalentToAsType(newType)) { 3117 return target.asFixedArity().asType(newType); 3118 } 3119 return MethodHandleImpl.makePairwiseConvert(target, newType, false); 3120 } 3121 3122 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) { 3123 if (target.type().parameterCount() != newType.parameterCount()) { 3124 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType); 3125 } 3126 } 3127 3128 /** 3129 * Produces a method handle which adapts the calling sequence of the 3130 * given method handle to a new type, by reordering the arguments. 3131 * The resulting method handle is guaranteed to report a type 3132 * which is equal to the desired new type. 3133 * <p> 3134 * The given array controls the reordering. 3135 * Call {@code #I} the number of incoming parameters (the value 3136 * {@code newType.parameterCount()}, and call {@code #O} the number 3137 * of outgoing parameters (the value {@code target.type().parameterCount()}). 3138 * Then the length of the reordering array must be {@code #O}, 3139 * and each element must be a non-negative number less than {@code #I}. 3140 * For every {@code N} less than {@code #O}, the {@code N}-th 3141 * outgoing argument will be taken from the {@code I}-th incoming 3142 * argument, where {@code I} is {@code reorder[N]}. 3143 * <p> 3144 * No argument or return value conversions are applied. 3145 * The type of each incoming argument, as determined by {@code newType}, 3146 * must be identical to the type of the corresponding outgoing parameter 3147 * or parameters in the target method handle. 3148 * The return type of {@code newType} must be identical to the return 3149 * type of the original target. 3150 * <p> 3151 * The reordering array need not specify an actual permutation. 3152 * An incoming argument will be duplicated if its index appears 3153 * more than once in the array, and an incoming argument will be dropped 3154 * if its index does not appear in the array. 3155 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments}, 3156 * incoming arguments which are not mentioned in the reordering array 3157 * may be of any type, as determined only by {@code newType}. 3158 * <blockquote><pre>{@code 3159 import static java.lang.invoke.MethodHandles.*; 3160 import static java.lang.invoke.MethodType.*; 3161 ... 3162 MethodType intfn1 = methodType(int.class, int.class); 3163 MethodType intfn2 = methodType(int.class, int.class, int.class); 3164 MethodHandle sub = ... (int x, int y) -> (x-y) ...; 3165 assert(sub.type().equals(intfn2)); 3166 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1); 3167 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0); 3168 assert((int)rsub.invokeExact(1, 100) == 99); 3169 MethodHandle add = ... (int x, int y) -> (x+y) ...; 3170 assert(add.type().equals(intfn2)); 3171 MethodHandle twice = permuteArguments(add, intfn1, 0, 0); 3172 assert(twice.type().equals(intfn1)); 3173 assert((int)twice.invokeExact(21) == 42); 3174 * }</pre></blockquote> 3175 * <p> 3176 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 3177 * variable-arity method handle}, even if the original target method handle was. 3178 * @param target the method handle to invoke after arguments are reordered 3179 * @param newType the expected type of the new method handle 3180 * @param reorder an index array which controls the reordering 3181 * @return a method handle which delegates to the target after it 3182 * drops unused arguments and moves and/or duplicates the other arguments 3183 * @throws NullPointerException if any argument is null 3184 * @throws IllegalArgumentException if the index array length is not equal to 3185 * the arity of the target, or if any index array element 3186 * not a valid index for a parameter of {@code newType}, 3187 * or if two corresponding parameter types in 3188 * {@code target.type()} and {@code newType} are not identical, 3189 */ 3190 public static 3191 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) { 3192 reorder = reorder.clone(); // get a private copy 3193 MethodType oldType = target.type(); 3194 permuteArgumentChecks(reorder, newType, oldType); 3195 // first detect dropped arguments and handle them separately 3196 int[] originalReorder = reorder; 3197 BoundMethodHandle result = target.rebind(); 3198 LambdaForm form = result.form; 3199 int newArity = newType.parameterCount(); 3200 // Normalize the reordering into a real permutation, 3201 // by removing duplicates and adding dropped elements. 3202 // This somewhat improves lambda form caching, as well 3203 // as simplifying the transform by breaking it up into steps. 3204 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) { 3205 if (ddIdx > 0) { 3206 // We found a duplicated entry at reorder[ddIdx]. 3207 // Example: (x,y,z)->asList(x,y,z) 3208 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1) 3209 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0) 3210 // The starred element corresponds to the argument 3211 // deleted by the dupArgumentForm transform. 3212 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos]; 3213 boolean killFirst = false; 3214 for (int val; (val = reorder[--dstPos]) != dupVal; ) { 3215 // Set killFirst if the dup is larger than an intervening position. 3216 // This will remove at least one inversion from the permutation. 3217 if (dupVal > val) killFirst = true; 3218 } 3219 if (!killFirst) { 3220 srcPos = dstPos; 3221 dstPos = ddIdx; 3222 } 3223 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos); 3224 assert (reorder[srcPos] == reorder[dstPos]); 3225 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1); 3226 // contract the reordering by removing the element at dstPos 3227 int tailPos = dstPos + 1; 3228 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos); 3229 reorder = Arrays.copyOf(reorder, reorder.length - 1); 3230 } else { 3231 int dropVal = ~ddIdx, insPos = 0; 3232 while (insPos < reorder.length && reorder[insPos] < dropVal) { 3233 // Find first element of reorder larger than dropVal. 3234 // This is where we will insert the dropVal. 3235 insPos += 1; 3236 } 3237 Class<?> ptype = newType.parameterType(dropVal); 3238 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype)); 3239 oldType = oldType.insertParameterTypes(insPos, ptype); 3240 // expand the reordering by inserting an element at insPos 3241 int tailPos = insPos + 1; 3242 reorder = Arrays.copyOf(reorder, reorder.length + 1); 3243 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos); 3244 reorder[insPos] = dropVal; 3245 } 3246 assert (permuteArgumentChecks(reorder, newType, oldType)); 3247 } 3248 assert (reorder.length == newArity); // a perfect permutation 3249 // Note: This may cache too many distinct LFs. Consider backing off to varargs code. 3250 form = form.editor().permuteArgumentsForm(1, reorder); 3251 if (newType == result.type() && form == result.internalForm()) 3252 return result; 3253 return result.copyWith(newType, form); 3254 } 3255 3256 /** 3257 * Return an indication of any duplicate or omission in reorder. 3258 * If the reorder contains a duplicate entry, return the index of the second occurrence. 3259 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder. 3260 * Otherwise, return zero. 3261 * If an element not in [0..newArity-1] is encountered, return reorder.length. 3262 */ 3263 private static int findFirstDupOrDrop(int[] reorder, int newArity) { 3264 final int BIT_LIMIT = 63; // max number of bits in bit mask 3265 if (newArity < BIT_LIMIT) { 3266 long mask = 0; 3267 for (int i = 0; i < reorder.length; i++) { 3268 int arg = reorder[i]; 3269 if (arg >= newArity) { 3270 return reorder.length; 3271 } 3272 long bit = 1L << arg; 3273 if ((mask & bit) != 0) { 3274 return i; // >0 indicates a dup 3275 } 3276 mask |= bit; 3277 } 3278 if (mask == (1L << newArity) - 1) { 3279 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity); 3280 return 0; 3281 } 3282 // find first zero 3283 long zeroBit = Long.lowestOneBit(~mask); 3284 int zeroPos = Long.numberOfTrailingZeros(zeroBit); 3285 assert(zeroPos <= newArity); 3286 if (zeroPos == newArity) { 3287 return 0; 3288 } 3289 return ~zeroPos; 3290 } else { 3291 // same algorithm, different bit set 3292 BitSet mask = new BitSet(newArity); 3293 for (int i = 0; i < reorder.length; i++) { 3294 int arg = reorder[i]; 3295 if (arg >= newArity) { 3296 return reorder.length; 3297 } 3298 if (mask.get(arg)) { 3299 return i; // >0 indicates a dup 3300 } 3301 mask.set(arg); 3302 } 3303 int zeroPos = mask.nextClearBit(0); 3304 assert(zeroPos <= newArity); 3305 if (zeroPos == newArity) { 3306 return 0; 3307 } 3308 return ~zeroPos; 3309 } 3310 } 3311 3312 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) { 3313 if (newType.returnType() != oldType.returnType()) 3314 throw newIllegalArgumentException("return types do not match", 3315 oldType, newType); 3316 if (reorder.length == oldType.parameterCount()) { 3317 int limit = newType.parameterCount(); 3318 boolean bad = false; 3319 for (int j = 0; j < reorder.length; j++) { 3320 int i = reorder[j]; 3321 if (i < 0 || i >= limit) { 3322 bad = true; break; 3323 } 3324 Class<?> src = newType.parameterType(i); 3325 Class<?> dst = oldType.parameterType(j); 3326 if (src != dst) 3327 throw newIllegalArgumentException("parameter types do not match after reorder", 3328 oldType, newType); 3329 } 3330 if (!bad) return true; 3331 } 3332 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder)); 3333 } 3334 3335 /** 3336 * Produces a method handle of the requested return type which returns the given 3337 * constant value every time it is invoked. 3338 * <p> 3339 * Before the method handle is returned, the passed-in value is converted to the requested type. 3340 * If the requested type is primitive, widening primitive conversions are attempted, 3341 * else reference conversions are attempted. 3342 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}. 3343 * @param type the return type of the desired method handle 3344 * @param value the value to return 3345 * @return a method handle of the given return type and no arguments, which always returns the given value 3346 * @throws NullPointerException if the {@code type} argument is null 3347 * @throws ClassCastException if the value cannot be converted to the required return type 3348 * @throws IllegalArgumentException if the given type is {@code void.class} 3349 */ 3350 public static 3351 MethodHandle constant(Class<?> type, Object value) { 3352 if (type.isPrimitive()) { 3353 if (type == void.class) 3354 throw newIllegalArgumentException("void type"); 3355 Wrapper w = Wrapper.forPrimitiveType(type); 3356 value = w.convert(value, type); 3357 if (w.zero().equals(value)) 3358 return zero(w, type); 3359 return insertArguments(identity(type), 0, value); 3360 } else { 3361 if (value == null) 3362 return zero(Wrapper.OBJECT, type); 3363 return identity(type).bindTo(value); 3364 } 3365 } 3366 3367 /** 3368 * Produces a method handle which returns its sole argument when invoked. 3369 * @param type the type of the sole parameter and return value of the desired method handle 3370 * @return a unary method handle which accepts and returns the given type 3371 * @throws NullPointerException if the argument is null 3372 * @throws IllegalArgumentException if the given type is {@code void.class} 3373 */ 3374 public static 3375 MethodHandle identity(Class<?> type) { 3376 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT); 3377 int pos = btw.ordinal(); 3378 MethodHandle ident = IDENTITY_MHS[pos]; 3379 if (ident == null) { 3380 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType())); 3381 } 3382 if (ident.type().returnType() == type) 3383 return ident; 3384 // something like identity(Foo.class); do not bother to intern these 3385 assert (btw == Wrapper.OBJECT); 3386 return makeIdentity(type); 3387 } 3388 3389 /** 3390 * Produces a constant method handle of the requested return type which 3391 * returns the default value for that type every time it is invoked. 3392 * The resulting constant method handle will have no side effects. 3393 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}. 3394 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))}, 3395 * since {@code explicitCastArguments} converts {@code null} to default values. 3396 * @param type the expected return type of the desired method handle 3397 * @return a constant method handle that takes no arguments 3398 * and returns the default value of the given type (or void, if the type is void) 3399 * @throws NullPointerException if the argument is null 3400 * @see MethodHandles#constant 3401 * @see MethodHandles#empty 3402 * @see MethodHandles#explicitCastArguments 3403 * @since 9 3404 */ 3405 public static MethodHandle zero(Class<?> type) { 3406 Objects.requireNonNull(type); 3407 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type); 3408 } 3409 3410 private static MethodHandle identityOrVoid(Class<?> type) { 3411 return type == void.class ? zero(type) : identity(type); 3412 } 3413 3414 /** 3415 * Produces a method handle of the requested type which ignores any arguments, does nothing, 3416 * and returns a suitable default depending on the return type. 3417 * That is, it returns a zero primitive value, a {@code null}, or {@code void}. 3418 * <p>The returned method handle is equivalent to 3419 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}. 3420 * 3421 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as 3422 * {@code guardWithTest(pred, target, empty(target.type())}. 3423 * @param type the type of the desired method handle 3424 * @return a constant method handle of the given type, which returns a default value of the given return type 3425 * @throws NullPointerException if the argument is null 3426 * @see MethodHandles#zero 3427 * @see MethodHandles#constant 3428 * @since 9 3429 */ 3430 public static MethodHandle empty(MethodType type) { 3431 Objects.requireNonNull(type); 3432 return dropArguments(zero(type.returnType()), 0, type.parameterList()); 3433 } 3434 3435 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT]; 3436 private static MethodHandle makeIdentity(Class<?> ptype) { 3437 MethodType mtype = methodType(ptype, ptype); 3438 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype)); 3439 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY); 3440 } 3441 3442 private static MethodHandle zero(Wrapper btw, Class<?> rtype) { 3443 int pos = btw.ordinal(); 3444 MethodHandle zero = ZERO_MHS[pos]; 3445 if (zero == null) { 3446 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType())); 3447 } 3448 if (zero.type().returnType() == rtype) 3449 return zero; 3450 assert(btw == Wrapper.OBJECT); 3451 return makeZero(rtype); 3452 } 3453 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT]; 3454 private static MethodHandle makeZero(Class<?> rtype) { 3455 MethodType mtype = methodType(rtype); 3456 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype)); 3457 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO); 3458 } 3459 3460 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) { 3461 // Simulate a CAS, to avoid racy duplication of results. 3462 MethodHandle prev = cache[pos]; 3463 if (prev != null) return prev; 3464 return cache[pos] = value; 3465 } 3466 3467 /** 3468 * Provides a target method handle with one or more <em>bound arguments</em> 3469 * in advance of the method handle's invocation. 3470 * The formal parameters to the target corresponding to the bound 3471 * arguments are called <em>bound parameters</em>. 3472 * Returns a new method handle which saves away the bound arguments. 3473 * When it is invoked, it receives arguments for any non-bound parameters, 3474 * binds the saved arguments to their corresponding parameters, 3475 * and calls the original target. 3476 * <p> 3477 * The type of the new method handle will drop the types for the bound 3478 * parameters from the original target type, since the new method handle 3479 * will no longer require those arguments to be supplied by its callers. 3480 * <p> 3481 * Each given argument object must match the corresponding bound parameter type. 3482 * If a bound parameter type is a primitive, the argument object 3483 * must be a wrapper, and will be unboxed to produce the primitive value. 3484 * <p> 3485 * The {@code pos} argument selects which parameters are to be bound. 3486 * It may range between zero and <i>N-L</i> (inclusively), 3487 * where <i>N</i> is the arity of the target method handle 3488 * and <i>L</i> is the length of the values array. 3489 * <p> 3490 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 3491 * variable-arity method handle}, even if the original target method handle was. 3492 * @param target the method handle to invoke after the argument is inserted 3493 * @param pos where to insert the argument (zero for the first) 3494 * @param values the series of arguments to insert 3495 * @return a method handle which inserts an additional argument, 3496 * before calling the original method handle 3497 * @throws NullPointerException if the target or the {@code values} array is null 3498 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than 3499 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L} 3500 * is the length of the values array. 3501 * @throws ClassCastException if an argument does not match the corresponding bound parameter 3502 * type. 3503 * @see MethodHandle#bindTo 3504 */ 3505 public static 3506 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) { 3507 int insCount = values.length; 3508 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos); 3509 if (insCount == 0) return target; 3510 BoundMethodHandle result = target.rebind(); 3511 for (int i = 0; i < insCount; i++) { 3512 Object value = values[i]; 3513 Class<?> ptype = ptypes[pos+i]; 3514 if (ptype.isPrimitive()) { 3515 result = insertArgumentPrimitive(result, pos, ptype, value); 3516 } else { 3517 value = ptype.cast(value); // throw CCE if needed 3518 result = result.bindArgumentL(pos, value); 3519 } 3520 } 3521 return result; 3522 } 3523 3524 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos, 3525 Class<?> ptype, Object value) { 3526 Wrapper w = Wrapper.forPrimitiveType(ptype); 3527 // perform unboxing and/or primitive conversion 3528 value = w.convert(value, ptype); 3529 switch (w) { 3530 case INT: return result.bindArgumentI(pos, (int)value); 3531 case LONG: return result.bindArgumentJ(pos, (long)value); 3532 case FLOAT: return result.bindArgumentF(pos, (float)value); 3533 case DOUBLE: return result.bindArgumentD(pos, (double)value); 3534 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value)); 3535 } 3536 } 3537 3538 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException { 3539 MethodType oldType = target.type(); 3540 int outargs = oldType.parameterCount(); 3541 int inargs = outargs - insCount; 3542 if (inargs < 0) 3543 throw newIllegalArgumentException("too many values to insert"); 3544 if (pos < 0 || pos > inargs) 3545 throw newIllegalArgumentException("no argument type to append"); 3546 return oldType.ptypes(); 3547 } 3548 3549 /** 3550 * Produces a method handle which will discard some dummy arguments 3551 * before calling some other specified <i>target</i> method handle. 3552 * The type of the new method handle will be the same as the target's type, 3553 * except it will also include the dummy argument types, 3554 * at some given position. 3555 * <p> 3556 * The {@code pos} argument may range between zero and <i>N</i>, 3557 * where <i>N</i> is the arity of the target. 3558 * If {@code pos} is zero, the dummy arguments will precede 3559 * the target's real arguments; if {@code pos} is <i>N</i> 3560 * they will come after. 3561 * <p> 3562 * <b>Example:</b> 3563 * <blockquote><pre>{@code 3564 import static java.lang.invoke.MethodHandles.*; 3565 import static java.lang.invoke.MethodType.*; 3566 ... 3567 MethodHandle cat = lookup().findVirtual(String.class, 3568 "concat", methodType(String.class, String.class)); 3569 assertEquals("xy", (String) cat.invokeExact("x", "y")); 3570 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class); 3571 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2)); 3572 assertEquals(bigType, d0.type()); 3573 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z")); 3574 * }</pre></blockquote> 3575 * <p> 3576 * This method is also equivalent to the following code: 3577 * <blockquote><pre> 3578 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))} 3579 * </pre></blockquote> 3580 * @param target the method handle to invoke after the arguments are dropped 3581 * @param valueTypes the type(s) of the argument(s) to drop 3582 * @param pos position of first argument to drop (zero for the leftmost) 3583 * @return a method handle which drops arguments of the given types, 3584 * before calling the original method handle 3585 * @throws NullPointerException if the target is null, 3586 * or if the {@code valueTypes} list or any of its elements is null 3587 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 3588 * or if {@code pos} is negative or greater than the arity of the target, 3589 * or if the new method handle's type would have too many parameters 3590 */ 3591 public static 3592 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) { 3593 return dropArguments0(target, pos, copyTypes(valueTypes.toArray())); 3594 } 3595 3596 private static List<Class<?>> copyTypes(Object[] array) { 3597 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class)); 3598 } 3599 3600 private static 3601 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) { 3602 MethodType oldType = target.type(); // get NPE 3603 int dropped = dropArgumentChecks(oldType, pos, valueTypes); 3604 MethodType newType = oldType.insertParameterTypes(pos, valueTypes); 3605 if (dropped == 0) return target; 3606 BoundMethodHandle result = target.rebind(); 3607 LambdaForm lform = result.form; 3608 int insertFormArg = 1 + pos; 3609 for (Class<?> ptype : valueTypes) { 3610 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype)); 3611 } 3612 result = result.copyWith(newType, lform); 3613 return result; 3614 } 3615 3616 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) { 3617 int dropped = valueTypes.size(); 3618 MethodType.checkSlotCount(dropped); 3619 int outargs = oldType.parameterCount(); 3620 int inargs = outargs + dropped; 3621 if (pos < 0 || pos > outargs) 3622 throw newIllegalArgumentException("no argument type to remove" 3623 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs) 3624 ); 3625 return dropped; 3626 } 3627 3628 /** 3629 * Produces a method handle which will discard some dummy arguments 3630 * before calling some other specified <i>target</i> method handle. 3631 * The type of the new method handle will be the same as the target's type, 3632 * except it will also include the dummy argument types, 3633 * at some given position. 3634 * <p> 3635 * The {@code pos} argument may range between zero and <i>N</i>, 3636 * where <i>N</i> is the arity of the target. 3637 * If {@code pos} is zero, the dummy arguments will precede 3638 * the target's real arguments; if {@code pos} is <i>N</i> 3639 * they will come after. 3640 * @apiNote 3641 * <blockquote><pre>{@code 3642 import static java.lang.invoke.MethodHandles.*; 3643 import static java.lang.invoke.MethodType.*; 3644 ... 3645 MethodHandle cat = lookup().findVirtual(String.class, 3646 "concat", methodType(String.class, String.class)); 3647 assertEquals("xy", (String) cat.invokeExact("x", "y")); 3648 MethodHandle d0 = dropArguments(cat, 0, String.class); 3649 assertEquals("yz", (String) d0.invokeExact("x", "y", "z")); 3650 MethodHandle d1 = dropArguments(cat, 1, String.class); 3651 assertEquals("xz", (String) d1.invokeExact("x", "y", "z")); 3652 MethodHandle d2 = dropArguments(cat, 2, String.class); 3653 assertEquals("xy", (String) d2.invokeExact("x", "y", "z")); 3654 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class); 3655 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z")); 3656 * }</pre></blockquote> 3657 * <p> 3658 * This method is also equivalent to the following code: 3659 * <blockquote><pre> 3660 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))} 3661 * </pre></blockquote> 3662 * @param target the method handle to invoke after the arguments are dropped 3663 * @param valueTypes the type(s) of the argument(s) to drop 3664 * @param pos position of first argument to drop (zero for the leftmost) 3665 * @return a method handle which drops arguments of the given types, 3666 * before calling the original method handle 3667 * @throws NullPointerException if the target is null, 3668 * or if the {@code valueTypes} array or any of its elements is null 3669 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 3670 * or if {@code pos} is negative or greater than the arity of the target, 3671 * or if the new method handle's type would have 3672 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3673 */ 3674 public static 3675 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) { 3676 return dropArguments0(target, pos, copyTypes(valueTypes)); 3677 } 3678 3679 // private version which allows caller some freedom with error handling 3680 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos, 3681 boolean nullOnFailure) { 3682 newTypes = copyTypes(newTypes.toArray()); 3683 List<Class<?>> oldTypes = target.type().parameterList(); 3684 int match = oldTypes.size(); 3685 if (skip != 0) { 3686 if (skip < 0 || skip > match) { 3687 throw newIllegalArgumentException("illegal skip", skip, target); 3688 } 3689 oldTypes = oldTypes.subList(skip, match); 3690 match -= skip; 3691 } 3692 List<Class<?>> addTypes = newTypes; 3693 int add = addTypes.size(); 3694 if (pos != 0) { 3695 if (pos < 0 || pos > add) { 3696 throw newIllegalArgumentException("illegal pos", pos, newTypes); 3697 } 3698 addTypes = addTypes.subList(pos, add); 3699 add -= pos; 3700 assert(addTypes.size() == add); 3701 } 3702 // Do not add types which already match the existing arguments. 3703 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) { 3704 if (nullOnFailure) { 3705 return null; 3706 } 3707 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes); 3708 } 3709 addTypes = addTypes.subList(match, add); 3710 add -= match; 3711 assert(addTypes.size() == add); 3712 // newTypes: ( P*[pos], M*[match], A*[add] ) 3713 // target: ( S*[skip], M*[match] ) 3714 MethodHandle adapter = target; 3715 if (add > 0) { 3716 adapter = dropArguments0(adapter, skip+ match, addTypes); 3717 } 3718 // adapter: (S*[skip], M*[match], A*[add] ) 3719 if (pos > 0) { 3720 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos)); 3721 } 3722 // adapter: (S*[skip], P*[pos], M*[match], A*[add] ) 3723 return adapter; 3724 } 3725 3726 /** 3727 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some 3728 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter 3729 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The 3730 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before 3731 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by 3732 * {@link #dropArguments(MethodHandle, int, Class[])}. 3733 * <p> 3734 * The resulting handle will have the same return type as the target handle. 3735 * <p> 3736 * In more formal terms, assume these two type lists:<ul> 3737 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as 3738 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list, 3739 * {@code newTypes}. 3740 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as 3741 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's 3742 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching 3743 * sub-list. 3744 * </ul> 3745 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type 3746 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by 3747 * {@link #dropArguments(MethodHandle, int, Class[])}. 3748 * 3749 * @apiNote 3750 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be 3751 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows: 3752 * <blockquote><pre>{@code 3753 import static java.lang.invoke.MethodHandles.*; 3754 import static java.lang.invoke.MethodType.*; 3755 ... 3756 ... 3757 MethodHandle h0 = constant(boolean.class, true); 3758 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class)); 3759 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class); 3760 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList()); 3761 if (h1.type().parameterCount() < h2.type().parameterCount()) 3762 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1 3763 else 3764 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2 3765 MethodHandle h3 = guardWithTest(h0, h1, h2); 3766 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c")); 3767 * }</pre></blockquote> 3768 * @param target the method handle to adapt 3769 * @param skip number of targets parameters to disregard (they will be unchanged) 3770 * @param newTypes the list of types to match {@code target}'s parameter type list to 3771 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur 3772 * @return a possibly adapted method handle 3773 * @throws NullPointerException if either argument is null 3774 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class}, 3775 * or if {@code skip} is negative or greater than the arity of the target, 3776 * or if {@code pos} is negative or greater than the newTypes list size, 3777 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position 3778 * {@code pos}. 3779 * @since 9 3780 */ 3781 public static 3782 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) { 3783 Objects.requireNonNull(target); 3784 Objects.requireNonNull(newTypes); 3785 return dropArgumentsToMatch(target, skip, newTypes, pos, false); 3786 } 3787 3788 /** 3789 * Adapts a target method handle by pre-processing 3790 * one or more of its arguments, each with its own unary filter function, 3791 * and then calling the target with each pre-processed argument 3792 * replaced by the result of its corresponding filter function. 3793 * <p> 3794 * The pre-processing is performed by one or more method handles, 3795 * specified in the elements of the {@code filters} array. 3796 * The first element of the filter array corresponds to the {@code pos} 3797 * argument of the target, and so on in sequence. 3798 * The filter functions are invoked in left to right order. 3799 * <p> 3800 * Null arguments in the array are treated as identity functions, 3801 * and the corresponding arguments left unchanged. 3802 * (If there are no non-null elements in the array, the original target is returned.) 3803 * Each filter is applied to the corresponding argument of the adapter. 3804 * <p> 3805 * If a filter {@code F} applies to the {@code N}th argument of 3806 * the target, then {@code F} must be a method handle which 3807 * takes exactly one argument. The type of {@code F}'s sole argument 3808 * replaces the corresponding argument type of the target 3809 * in the resulting adapted method handle. 3810 * The return type of {@code F} must be identical to the corresponding 3811 * parameter type of the target. 3812 * <p> 3813 * It is an error if there are elements of {@code filters} 3814 * (null or not) 3815 * which do not correspond to argument positions in the target. 3816 * <p><b>Example:</b> 3817 * <blockquote><pre>{@code 3818 import static java.lang.invoke.MethodHandles.*; 3819 import static java.lang.invoke.MethodType.*; 3820 ... 3821 MethodHandle cat = lookup().findVirtual(String.class, 3822 "concat", methodType(String.class, String.class)); 3823 MethodHandle upcase = lookup().findVirtual(String.class, 3824 "toUpperCase", methodType(String.class)); 3825 assertEquals("xy", (String) cat.invokeExact("x", "y")); 3826 MethodHandle f0 = filterArguments(cat, 0, upcase); 3827 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy 3828 MethodHandle f1 = filterArguments(cat, 1, upcase); 3829 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY 3830 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase); 3831 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY 3832 * }</pre></blockquote> 3833 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 3834 * denotes the return type of both the {@code target} and resulting adapter. 3835 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values 3836 * of the parameters and arguments that precede and follow the filter position 3837 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and 3838 * values of the filtered parameters and arguments; they also represent the 3839 * return types of the {@code filter[i]} handles. The latter accept arguments 3840 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of 3841 * the resulting adapter. 3842 * <blockquote><pre>{@code 3843 * T target(P... p, A[i]... a[i], B... b); 3844 * A[i] filter[i](V[i]); 3845 * T adapter(P... p, V[i]... v[i], B... b) { 3846 * return target(p..., filter[i](v[i])..., b...); 3847 * } 3848 * }</pre></blockquote> 3849 * <p> 3850 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 3851 * variable-arity method handle}, even if the original target method handle was. 3852 * 3853 * @param target the method handle to invoke after arguments are filtered 3854 * @param pos the position of the first argument to filter 3855 * @param filters method handles to call initially on filtered arguments 3856 * @return method handle which incorporates the specified argument filtering logic 3857 * @throws NullPointerException if the target is null 3858 * or if the {@code filters} array is null 3859 * @throws IllegalArgumentException if a non-null element of {@code filters} 3860 * does not match a corresponding argument type of target as described above, 3861 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}, 3862 * or if the resulting method handle's type would have 3863 * <a href="MethodHandle.html#maxarity">too many parameters</a> 3864 */ 3865 public static 3866 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) { 3867 filterArgumentsCheckArity(target, pos, filters); 3868 MethodHandle adapter = target; 3869 // process filters in reverse order so that the invocation of 3870 // the resulting adapter will invoke the filters in left-to-right order 3871 for (int i = filters.length - 1; i >= 0; --i) { 3872 MethodHandle filter = filters[i]; 3873 if (filter == null) continue; // ignore null elements of filters 3874 adapter = filterArgument(adapter, pos + i, filter); 3875 } 3876 return adapter; 3877 } 3878 3879 /*non-public*/ static 3880 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) { 3881 filterArgumentChecks(target, pos, filter); 3882 MethodType targetType = target.type(); 3883 MethodType filterType = filter.type(); 3884 BoundMethodHandle result = target.rebind(); 3885 Class<?> newParamType = filterType.parameterType(0); 3886 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType)); 3887 MethodType newType = targetType.changeParameterType(pos, newParamType); 3888 result = result.copyWithExtendL(newType, lform, filter); 3889 return result; 3890 } 3891 3892 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) { 3893 MethodType targetType = target.type(); 3894 int maxPos = targetType.parameterCount(); 3895 if (pos + filters.length > maxPos) 3896 throw newIllegalArgumentException("too many filters"); 3897 } 3898 3899 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 3900 MethodType targetType = target.type(); 3901 MethodType filterType = filter.type(); 3902 if (filterType.parameterCount() != 1 3903 || filterType.returnType() != targetType.parameterType(pos)) 3904 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 3905 } 3906 3907 /** 3908 * Adapts a target method handle by pre-processing 3909 * a sub-sequence of its arguments with a filter (another method handle). 3910 * The pre-processed arguments are replaced by the result (if any) of the 3911 * filter function. 3912 * The target is then called on the modified (usually shortened) argument list. 3913 * <p> 3914 * If the filter returns a value, the target must accept that value as 3915 * its argument in position {@code pos}, preceded and/or followed by 3916 * any arguments not passed to the filter. 3917 * If the filter returns void, the target must accept all arguments 3918 * not passed to the filter. 3919 * No arguments are reordered, and a result returned from the filter 3920 * replaces (in order) the whole subsequence of arguments originally 3921 * passed to the adapter. 3922 * <p> 3923 * The argument types (if any) of the filter 3924 * replace zero or one argument types of the target, at position {@code pos}, 3925 * in the resulting adapted method handle. 3926 * The return type of the filter (if any) must be identical to the 3927 * argument type of the target at position {@code pos}, and that target argument 3928 * is supplied by the return value of the filter. 3929 * <p> 3930 * In all cases, {@code pos} must be greater than or equal to zero, and 3931 * {@code pos} must also be less than or equal to the target's arity. 3932 * <p><b>Example:</b> 3933 * <blockquote><pre>{@code 3934 import static java.lang.invoke.MethodHandles.*; 3935 import static java.lang.invoke.MethodType.*; 3936 ... 3937 MethodHandle deepToString = publicLookup() 3938 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 3939 3940 MethodHandle ts1 = deepToString.asCollector(String[].class, 1); 3941 assertEquals("[strange]", (String) ts1.invokeExact("strange")); 3942 3943 MethodHandle ts2 = deepToString.asCollector(String[].class, 2); 3944 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down")); 3945 3946 MethodHandle ts3 = deepToString.asCollector(String[].class, 3); 3947 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2); 3948 assertEquals("[top, [up, down], strange]", 3949 (String) ts3_ts2.invokeExact("top", "up", "down", "strange")); 3950 3951 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1); 3952 assertEquals("[top, [up, down], [strange]]", 3953 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange")); 3954 3955 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3); 3956 assertEquals("[top, [[up, down, strange], charm], bottom]", 3957 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom")); 3958 * }</pre></blockquote> 3959 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 3960 * represents the return type of the {@code target} and resulting adapter. 3961 * {@code V}/{@code v} stand for the return type and value of the 3962 * {@code filter}, which are also found in the signature and arguments of 3963 * the {@code target}, respectively, unless {@code V} is {@code void}. 3964 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types 3965 * and values preceding and following the collection position, {@code pos}, 3966 * in the {@code target}'s signature. They also turn up in the resulting 3967 * adapter's signature and arguments, where they surround 3968 * {@code B}/{@code b}, which represent the parameter types and arguments 3969 * to the {@code filter} (if any). 3970 * <blockquote><pre>{@code 3971 * T target(A...,V,C...); 3972 * V filter(B...); 3973 * T adapter(A... a,B... b,C... c) { 3974 * V v = filter(b...); 3975 * return target(a...,v,c...); 3976 * } 3977 * // and if the filter has no arguments: 3978 * T target2(A...,V,C...); 3979 * V filter2(); 3980 * T adapter2(A... a,C... c) { 3981 * V v = filter2(); 3982 * return target2(a...,v,c...); 3983 * } 3984 * // and if the filter has a void return: 3985 * T target3(A...,C...); 3986 * void filter3(B...); 3987 * T adapter3(A... a,B... b,C... c) { 3988 * filter3(b...); 3989 * return target3(a...,c...); 3990 * } 3991 * }</pre></blockquote> 3992 * <p> 3993 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to 3994 * one which first "folds" the affected arguments, and then drops them, in separate 3995 * steps as follows: 3996 * <blockquote><pre>{@code 3997 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2 3998 * mh = MethodHandles.foldArguments(mh, coll); //step 1 3999 * }</pre></blockquote> 4000 * If the target method handle consumes no arguments besides than the result 4001 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)} 4002 * is equivalent to {@code filterReturnValue(coll, mh)}. 4003 * If the filter method handle {@code coll} consumes one argument and produces 4004 * a non-void result, then {@code collectArguments(mh, N, coll)} 4005 * is equivalent to {@code filterArguments(mh, N, coll)}. 4006 * Other equivalences are possible but would require argument permutation. 4007 * <p> 4008 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4009 * variable-arity method handle}, even if the original target method handle was. 4010 * 4011 * @param target the method handle to invoke after filtering the subsequence of arguments 4012 * @param pos the position of the first adapter argument to pass to the filter, 4013 * and/or the target argument which receives the result of the filter 4014 * @param filter method handle to call on the subsequence of arguments 4015 * @return method handle which incorporates the specified argument subsequence filtering logic 4016 * @throws NullPointerException if either argument is null 4017 * @throws IllegalArgumentException if the return type of {@code filter} 4018 * is non-void and is not the same as the {@code pos} argument of the target, 4019 * or if {@code pos} is not between 0 and the target's arity, inclusive, 4020 * or if the resulting method handle's type would have 4021 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4022 * @see MethodHandles#foldArguments 4023 * @see MethodHandles#filterArguments 4024 * @see MethodHandles#filterReturnValue 4025 */ 4026 public static 4027 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) { 4028 MethodType newType = collectArgumentsChecks(target, pos, filter); 4029 MethodType collectorType = filter.type(); 4030 BoundMethodHandle result = target.rebind(); 4031 LambdaForm lform; 4032 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) { 4033 lform = result.editor().collectArgumentArrayForm(1 + pos, filter); 4034 if (lform != null) { 4035 return result.copyWith(newType, lform); 4036 } 4037 } 4038 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType()); 4039 return result.copyWithExtendL(newType, lform, filter); 4040 } 4041 4042 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 4043 MethodType targetType = target.type(); 4044 MethodType filterType = filter.type(); 4045 Class<?> rtype = filterType.returnType(); 4046 List<Class<?>> filterArgs = filterType.parameterList(); 4047 if (rtype == void.class) { 4048 return targetType.insertParameterTypes(pos, filterArgs); 4049 } 4050 if (rtype != targetType.parameterType(pos)) { 4051 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 4052 } 4053 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs); 4054 } 4055 4056 /** 4057 * Adapts a target method handle by post-processing 4058 * its return value (if any) with a filter (another method handle). 4059 * The result of the filter is returned from the adapter. 4060 * <p> 4061 * If the target returns a value, the filter must accept that value as 4062 * its only argument. 4063 * If the target returns void, the filter must accept no arguments. 4064 * <p> 4065 * The return type of the filter 4066 * replaces the return type of the target 4067 * in the resulting adapted method handle. 4068 * The argument type of the filter (if any) must be identical to the 4069 * return type of the target. 4070 * <p><b>Example:</b> 4071 * <blockquote><pre>{@code 4072 import static java.lang.invoke.MethodHandles.*; 4073 import static java.lang.invoke.MethodType.*; 4074 ... 4075 MethodHandle cat = lookup().findVirtual(String.class, 4076 "concat", methodType(String.class, String.class)); 4077 MethodHandle length = lookup().findVirtual(String.class, 4078 "length", methodType(int.class)); 4079 System.out.println((String) cat.invokeExact("x", "y")); // xy 4080 MethodHandle f0 = filterReturnValue(cat, length); 4081 System.out.println((int) f0.invokeExact("x", "y")); // 2 4082 * }</pre></blockquote> 4083 * <p>Here is pseudocode for the resulting adapter. In the code, 4084 * {@code T}/{@code t} represent the result type and value of the 4085 * {@code target}; {@code V}, the result type of the {@code filter}; and 4086 * {@code A}/{@code a}, the types and values of the parameters and arguments 4087 * of the {@code target} as well as the resulting adapter. 4088 * <blockquote><pre>{@code 4089 * T target(A...); 4090 * V filter(T); 4091 * V adapter(A... a) { 4092 * T t = target(a...); 4093 * return filter(t); 4094 * } 4095 * // and if the target has a void return: 4096 * void target2(A...); 4097 * V filter2(); 4098 * V adapter2(A... a) { 4099 * target2(a...); 4100 * return filter2(); 4101 * } 4102 * // and if the filter has a void return: 4103 * T target3(A...); 4104 * void filter3(V); 4105 * void adapter3(A... a) { 4106 * T t = target3(a...); 4107 * filter3(t); 4108 * } 4109 * }</pre></blockquote> 4110 * <p> 4111 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4112 * variable-arity method handle}, even if the original target method handle was. 4113 * @param target the method handle to invoke before filtering the return value 4114 * @param filter method handle to call on the return value 4115 * @return method handle which incorporates the specified return value filtering logic 4116 * @throws NullPointerException if either argument is null 4117 * @throws IllegalArgumentException if the argument list of {@code filter} 4118 * does not match the return type of target as described above 4119 */ 4120 public static 4121 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) { 4122 MethodType targetType = target.type(); 4123 MethodType filterType = filter.type(); 4124 filterReturnValueChecks(targetType, filterType); 4125 BoundMethodHandle result = target.rebind(); 4126 BasicType rtype = BasicType.basicType(filterType.returnType()); 4127 LambdaForm lform = result.editor().filterReturnForm(rtype, false); 4128 MethodType newType = targetType.changeReturnType(filterType.returnType()); 4129 result = result.copyWithExtendL(newType, lform, filter); 4130 return result; 4131 } 4132 4133 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException { 4134 Class<?> rtype = targetType.returnType(); 4135 int filterValues = filterType.parameterCount(); 4136 if (filterValues == 0 4137 ? (rtype != void.class) 4138 : (rtype != filterType.parameterType(0) || filterValues != 1)) 4139 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 4140 } 4141 4142 /** 4143 * Adapts a target method handle by pre-processing 4144 * some of its arguments, and then calling the target with 4145 * the result of the pre-processing, inserted into the original 4146 * sequence of arguments. 4147 * <p> 4148 * The pre-processing is performed by {@code combiner}, a second method handle. 4149 * Of the arguments passed to the adapter, the first {@code N} arguments 4150 * are copied to the combiner, which is then called. 4151 * (Here, {@code N} is defined as the parameter count of the combiner.) 4152 * After this, control passes to the target, with any result 4153 * from the combiner inserted before the original {@code N} incoming 4154 * arguments. 4155 * <p> 4156 * If the combiner returns a value, the first parameter type of the target 4157 * must be identical with the return type of the combiner, and the next 4158 * {@code N} parameter types of the target must exactly match the parameters 4159 * of the combiner. 4160 * <p> 4161 * If the combiner has a void return, no result will be inserted, 4162 * and the first {@code N} parameter types of the target 4163 * must exactly match the parameters of the combiner. 4164 * <p> 4165 * The resulting adapter is the same type as the target, except that the 4166 * first parameter type is dropped, 4167 * if it corresponds to the result of the combiner. 4168 * <p> 4169 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments 4170 * that either the combiner or the target does not wish to receive. 4171 * If some of the incoming arguments are destined only for the combiner, 4172 * consider using {@link MethodHandle#asCollector asCollector} instead, since those 4173 * arguments will not need to be live on the stack on entry to the 4174 * target.) 4175 * <p><b>Example:</b> 4176 * <blockquote><pre>{@code 4177 import static java.lang.invoke.MethodHandles.*; 4178 import static java.lang.invoke.MethodType.*; 4179 ... 4180 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 4181 "println", methodType(void.class, String.class)) 4182 .bindTo(System.out); 4183 MethodHandle cat = lookup().findVirtual(String.class, 4184 "concat", methodType(String.class, String.class)); 4185 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 4186 MethodHandle catTrace = foldArguments(cat, trace); 4187 // also prints "boo": 4188 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 4189 * }</pre></blockquote> 4190 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 4191 * represents the result type of the {@code target} and resulting adapter. 4192 * {@code V}/{@code v} represent the type and value of the parameter and argument 4193 * of {@code target} that precedes the folding position; {@code V} also is 4194 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 4195 * types and values of the {@code N} parameters and arguments at the folding 4196 * position. {@code B}/{@code b} represent the types and values of the 4197 * {@code target} parameters and arguments that follow the folded parameters 4198 * and arguments. 4199 * <blockquote><pre>{@code 4200 * // there are N arguments in A... 4201 * T target(V, A[N]..., B...); 4202 * V combiner(A...); 4203 * T adapter(A... a, B... b) { 4204 * V v = combiner(a...); 4205 * return target(v, a..., b...); 4206 * } 4207 * // and if the combiner has a void return: 4208 * T target2(A[N]..., B...); 4209 * void combiner2(A...); 4210 * T adapter2(A... a, B... b) { 4211 * combiner2(a...); 4212 * return target2(a..., b...); 4213 * } 4214 * }</pre></blockquote> 4215 * <p> 4216 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4217 * variable-arity method handle}, even if the original target method handle was. 4218 * @param target the method handle to invoke after arguments are combined 4219 * @param combiner method handle to call initially on the incoming arguments 4220 * @return method handle which incorporates the specified argument folding logic 4221 * @throws NullPointerException if either argument is null 4222 * @throws IllegalArgumentException if {@code combiner}'s return type 4223 * is non-void and not the same as the first argument type of 4224 * the target, or if the initial {@code N} argument types 4225 * of the target 4226 * (skipping one matching the {@code combiner}'s return type) 4227 * are not identical with the argument types of {@code combiner} 4228 */ 4229 public static 4230 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) { 4231 return foldArguments(target, 0, combiner); 4232 } 4233 4234 /** 4235 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then 4236 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just 4237 * before the folded arguments. 4238 * <p> 4239 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the 4240 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a 4241 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position 4242 * 0. 4243 * 4244 * @apiNote Example: 4245 * <blockquote><pre>{@code 4246 import static java.lang.invoke.MethodHandles.*; 4247 import static java.lang.invoke.MethodType.*; 4248 ... 4249 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 4250 "println", methodType(void.class, String.class)) 4251 .bindTo(System.out); 4252 MethodHandle cat = lookup().findVirtual(String.class, 4253 "concat", methodType(String.class, String.class)); 4254 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 4255 MethodHandle catTrace = foldArguments(cat, 1, trace); 4256 // also prints "jum": 4257 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 4258 * }</pre></blockquote> 4259 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 4260 * represents the result type of the {@code target} and resulting adapter. 4261 * {@code V}/{@code v} represent the type and value of the parameter and argument 4262 * of {@code target} that precedes the folding position; {@code V} also is 4263 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 4264 * types and values of the {@code N} parameters and arguments at the folding 4265 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types 4266 * and values of the {@code target} parameters and arguments that precede and 4267 * follow the folded parameters and arguments starting at {@code pos}, 4268 * respectively. 4269 * <blockquote><pre>{@code 4270 * // there are N arguments in A... 4271 * T target(Z..., V, A[N]..., B...); 4272 * V combiner(A...); 4273 * T adapter(Z... z, A... a, B... b) { 4274 * V v = combiner(a...); 4275 * return target(z..., v, a..., b...); 4276 * } 4277 * // and if the combiner has a void return: 4278 * T target2(Z..., A[N]..., B...); 4279 * void combiner2(A...); 4280 * T adapter2(Z... z, A... a, B... b) { 4281 * combiner2(a...); 4282 * return target2(z..., a..., b...); 4283 * } 4284 * }</pre></blockquote> 4285 * <p> 4286 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4287 * variable-arity method handle}, even if the original target method handle was. 4288 * 4289 * @param target the method handle to invoke after arguments are combined 4290 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code 4291 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 4292 * @param combiner method handle to call initially on the incoming arguments 4293 * @return method handle which incorporates the specified argument folding logic 4294 * @throws NullPointerException if either argument is null 4295 * @throws IllegalArgumentException if either of the following two conditions holds: 4296 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 4297 * {@code pos} of the target signature; 4298 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching 4299 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}. 4300 * 4301 * @see #foldArguments(MethodHandle, MethodHandle) 4302 * @since 9 4303 */ 4304 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) { 4305 MethodType targetType = target.type(); 4306 MethodType combinerType = combiner.type(); 4307 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType); 4308 BoundMethodHandle result = target.rebind(); 4309 boolean dropResult = rtype == void.class; 4310 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType()); 4311 MethodType newType = targetType; 4312 if (!dropResult) { 4313 newType = newType.dropParameterTypes(pos, pos + 1); 4314 } 4315 result = result.copyWithExtendL(newType, lform, combiner); 4316 return result; 4317 } 4318 4319 /** 4320 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the 4321 * added capability of selecting the arguments from the targets parameters 4322 * to call the combiner with. This allows us to avoid some simple cases of 4323 * permutations and padding the combiner with dropArguments to select the 4324 * right argument, which may ultimately produce fewer intermediaries. 4325 */ 4326 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) { 4327 MethodType targetType = target.type(); 4328 MethodType combinerType = combiner.type(); 4329 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions); 4330 BoundMethodHandle result = target.rebind(); 4331 boolean dropResult = rtype == void.class; 4332 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions); 4333 MethodType newType = targetType; 4334 if (!dropResult) { 4335 newType = newType.dropParameterTypes(pos, pos + 1); 4336 } 4337 result = result.copyWithExtendL(newType, lform, combiner); 4338 return result; 4339 } 4340 4341 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) { 4342 int foldArgs = combinerType.parameterCount(); 4343 Class<?> rtype = combinerType.returnType(); 4344 int foldVals = rtype == void.class ? 0 : 1; 4345 int afterInsertPos = foldPos + foldVals; 4346 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs); 4347 if (ok) { 4348 for (int i = 0; i < foldArgs; i++) { 4349 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) { 4350 ok = false; 4351 break; 4352 } 4353 } 4354 } 4355 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) 4356 ok = false; 4357 if (!ok) 4358 throw misMatchedTypes("target and combiner types", targetType, combinerType); 4359 return rtype; 4360 } 4361 4362 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) { 4363 int foldArgs = combinerType.parameterCount(); 4364 if (argPos.length != foldArgs) { 4365 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length); 4366 } 4367 Class<?> rtype = combinerType.returnType(); 4368 int foldVals = rtype == void.class ? 0 : 1; 4369 boolean ok = true; 4370 for (int i = 0; i < foldArgs; i++) { 4371 int arg = argPos[i]; 4372 if (arg < 0 || arg > targetType.parameterCount()) { 4373 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg); 4374 } 4375 if (combinerType.parameterType(i) != targetType.parameterType(arg)) { 4376 throw newIllegalArgumentException("target argument type at position " + arg 4377 + " must match combiner argument type at index " + i + ": " + targetType 4378 + " -> " + combinerType + ", map: " + Arrays.toString(argPos)); 4379 } 4380 } 4381 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) { 4382 ok = false; 4383 } 4384 if (!ok) 4385 throw misMatchedTypes("target and combiner types", targetType, combinerType); 4386 return rtype; 4387 } 4388 4389 /** 4390 * Makes a method handle which adapts a target method handle, 4391 * by guarding it with a test, a boolean-valued method handle. 4392 * If the guard fails, a fallback handle is called instead. 4393 * All three method handles must have the same corresponding 4394 * argument and return types, except that the return type 4395 * of the test must be boolean, and the test is allowed 4396 * to have fewer arguments than the other two method handles. 4397 * <p> 4398 * Here is pseudocode for the resulting adapter. In the code, {@code T} 4399 * represents the uniform result type of the three involved handles; 4400 * {@code A}/{@code a}, the types and values of the {@code target} 4401 * parameters and arguments that are consumed by the {@code test}; and 4402 * {@code B}/{@code b}, those types and values of the {@code target} 4403 * parameters and arguments that are not consumed by the {@code test}. 4404 * <blockquote><pre>{@code 4405 * boolean test(A...); 4406 * T target(A...,B...); 4407 * T fallback(A...,B...); 4408 * T adapter(A... a,B... b) { 4409 * if (test(a...)) 4410 * return target(a..., b...); 4411 * else 4412 * return fallback(a..., b...); 4413 * } 4414 * }</pre></blockquote> 4415 * Note that the test arguments ({@code a...} in the pseudocode) cannot 4416 * be modified by execution of the test, and so are passed unchanged 4417 * from the caller to the target or fallback as appropriate. 4418 * @param test method handle used for test, must return boolean 4419 * @param target method handle to call if test passes 4420 * @param fallback method handle to call if test fails 4421 * @return method handle which incorporates the specified if/then/else logic 4422 * @throws NullPointerException if any argument is null 4423 * @throws IllegalArgumentException if {@code test} does not return boolean, 4424 * or if all three method types do not match (with the return 4425 * type of {@code test} changed to match that of the target). 4426 */ 4427 public static 4428 MethodHandle guardWithTest(MethodHandle test, 4429 MethodHandle target, 4430 MethodHandle fallback) { 4431 MethodType gtype = test.type(); 4432 MethodType ttype = target.type(); 4433 MethodType ftype = fallback.type(); 4434 if (!ttype.equals(ftype)) 4435 throw misMatchedTypes("target and fallback types", ttype, ftype); 4436 if (gtype.returnType() != boolean.class) 4437 throw newIllegalArgumentException("guard type is not a predicate "+gtype); 4438 List<Class<?>> targs = ttype.parameterList(); 4439 test = dropArgumentsToMatch(test, 0, targs, 0, true); 4440 if (test == null) { 4441 throw misMatchedTypes("target and test types", ttype, gtype); 4442 } 4443 return MethodHandleImpl.makeGuardWithTest(test, target, fallback); 4444 } 4445 4446 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) { 4447 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2); 4448 } 4449 4450 /** 4451 * Makes a method handle which adapts a target method handle, 4452 * by running it inside an exception handler. 4453 * If the target returns normally, the adapter returns that value. 4454 * If an exception matching the specified type is thrown, the fallback 4455 * handle is called instead on the exception, plus the original arguments. 4456 * <p> 4457 * The target and handler must have the same corresponding 4458 * argument and return types, except that handler may omit trailing arguments 4459 * (similarly to the predicate in {@link #guardWithTest guardWithTest}). 4460 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype. 4461 * <p> 4462 * Here is pseudocode for the resulting adapter. In the code, {@code T} 4463 * represents the return type of the {@code target} and {@code handler}, 4464 * and correspondingly that of the resulting adapter; {@code A}/{@code a}, 4465 * the types and values of arguments to the resulting handle consumed by 4466 * {@code handler}; and {@code B}/{@code b}, those of arguments to the 4467 * resulting handle discarded by {@code handler}. 4468 * <blockquote><pre>{@code 4469 * T target(A..., B...); 4470 * T handler(ExType, A...); 4471 * T adapter(A... a, B... b) { 4472 * try { 4473 * return target(a..., b...); 4474 * } catch (ExType ex) { 4475 * return handler(ex, a...); 4476 * } 4477 * } 4478 * }</pre></blockquote> 4479 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 4480 * be modified by execution of the target, and so are passed unchanged 4481 * from the caller to the handler, if the handler is invoked. 4482 * <p> 4483 * The target and handler must return the same type, even if the handler 4484 * always throws. (This might happen, for instance, because the handler 4485 * is simulating a {@code finally} clause). 4486 * To create such a throwing handler, compose the handler creation logic 4487 * with {@link #throwException throwException}, 4488 * in order to create a method handle of the correct return type. 4489 * @param target method handle to call 4490 * @param exType the type of exception which the handler will catch 4491 * @param handler method handle to call if a matching exception is thrown 4492 * @return method handle which incorporates the specified try/catch logic 4493 * @throws NullPointerException if any argument is null 4494 * @throws IllegalArgumentException if {@code handler} does not accept 4495 * the given exception type, or if the method handle types do 4496 * not match in their return types and their 4497 * corresponding parameters 4498 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle) 4499 */ 4500 public static 4501 MethodHandle catchException(MethodHandle target, 4502 Class<? extends Throwable> exType, 4503 MethodHandle handler) { 4504 MethodType ttype = target.type(); 4505 MethodType htype = handler.type(); 4506 if (!Throwable.class.isAssignableFrom(exType)) 4507 throw new ClassCastException(exType.getName()); 4508 if (htype.parameterCount() < 1 || 4509 !htype.parameterType(0).isAssignableFrom(exType)) 4510 throw newIllegalArgumentException("handler does not accept exception type "+exType); 4511 if (htype.returnType() != ttype.returnType()) 4512 throw misMatchedTypes("target and handler return types", ttype, htype); 4513 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true); 4514 if (handler == null) { 4515 throw misMatchedTypes("target and handler types", ttype, htype); 4516 } 4517 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler); 4518 } 4519 4520 /** 4521 * Produces a method handle which will throw exceptions of the given {@code exType}. 4522 * The method handle will accept a single argument of {@code exType}, 4523 * and immediately throw it as an exception. 4524 * The method type will nominally specify a return of {@code returnType}. 4525 * The return type may be anything convenient: It doesn't matter to the 4526 * method handle's behavior, since it will never return normally. 4527 * @param returnType the return type of the desired method handle 4528 * @param exType the parameter type of the desired method handle 4529 * @return method handle which can throw the given exceptions 4530 * @throws NullPointerException if either argument is null 4531 */ 4532 public static 4533 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) { 4534 if (!Throwable.class.isAssignableFrom(exType)) 4535 throw new ClassCastException(exType.getName()); 4536 return MethodHandleImpl.throwException(methodType(returnType, exType)); 4537 } 4538 4539 /** 4540 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each 4541 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and 4542 * delivers the loop's result, which is the return value of the resulting handle. 4543 * <p> 4544 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop 4545 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration 4546 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in 4547 * terms of method handles, each clause will specify up to four independent actions:<ul> 4548 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}. 4549 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}. 4550 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit. 4551 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value. 4552 * </ul> 4553 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}. 4554 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually 4555 * be referring to types, but in some contexts (describing execution) the lists will be of actual values. 4556 * <p> 4557 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in 4558 * this case. See below for a detailed description. 4559 * <p> 4560 * <em>Parameters optional everywhere:</em> 4561 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}. 4562 * As an exception, the init functions cannot take any {@code v} parameters, 4563 * because those values are not yet computed when the init functions are executed. 4564 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take. 4565 * In fact, any clause function may take no arguments at all. 4566 * <p> 4567 * <em>Loop parameters:</em> 4568 * A clause function may take all the iteration variable values it is entitled to, in which case 4569 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>, 4570 * with their types and values notated as {@code (A...)} and {@code (a...)}. 4571 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed. 4572 * (Since init functions do not accept iteration variables {@code v}, any parameter to an 4573 * init function is automatically a loop parameter {@code a}.) 4574 * As with iteration variables, clause functions are allowed but not required to accept loop parameters. 4575 * These loop parameters act as loop-invariant values visible across the whole loop. 4576 * <p> 4577 * <em>Parameters visible everywhere:</em> 4578 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full 4579 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters. 4580 * The init functions can observe initial pre-loop state, in the form {@code (a...)}. 4581 * Most clause functions will not need all of this information, but they will be formally connected to it 4582 * as if by {@link #dropArguments}. 4583 * <a id="astar"></a> 4584 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full 4585 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}). 4586 * In that notation, the general form of an init function parameter list 4587 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}. 4588 * <p> 4589 * <em>Checking clause structure:</em> 4590 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the 4591 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must" 4592 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not 4593 * met by the inputs to the loop combinator. 4594 * <p> 4595 * <em>Effectively identical sequences:</em> 4596 * <a id="effid"></a> 4597 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B} 4598 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}. 4599 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical" 4600 * as a whole if the set contains a longest list, and all members of the set are effectively identical to 4601 * that longest list. 4602 * For example, any set of type sequences of the form {@code (V*)} is effectively identical, 4603 * and the same is true if more sequences of the form {@code (V... A*)} are added. 4604 * <p> 4605 * <em>Step 0: Determine clause structure.</em><ol type="a"> 4606 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element. 4607 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements. 4608 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length 4609 * four. Padding takes place by appending elements to the array. 4610 * <li>Clauses with all {@code null}s are disregarded. 4611 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini". 4612 * </ol> 4613 * <p> 4614 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a"> 4615 * <li>The iteration variable type for each clause is determined using the clause's init and step return types. 4616 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is 4617 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's 4618 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's 4619 * iteration variable type. 4620 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}. 4621 * <li>This list of types is called the "iteration variable types" ({@code (V...)}). 4622 * </ol> 4623 * <p> 4624 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul> 4625 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}). 4626 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types. 4627 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.) 4628 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types. 4629 * (These types will be checked in step 2, along with all the clause function types.) 4630 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.) 4631 * <li>All of the collected parameter lists must be effectively identical. 4632 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}). 4633 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence. 4634 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called 4635 * the "internal parameter list". 4636 * </ul> 4637 * <p> 4638 * <em>Step 1C: Determine loop return type.</em><ol type="a"> 4639 * <li>Examine fini function return types, disregarding omitted fini functions. 4640 * <li>If there are no fini functions, the loop return type is {@code void}. 4641 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return 4642 * type. 4643 * </ol> 4644 * <p> 4645 * <em>Step 1D: Check other types.</em><ol type="a"> 4646 * <li>There must be at least one non-omitted pred function. 4647 * <li>Every non-omitted pred function must have a {@code boolean} return type. 4648 * </ol> 4649 * <p> 4650 * <em>Step 2: Determine parameter lists.</em><ol type="a"> 4651 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}. 4652 * <li>The parameter list for init functions will be adjusted to the external parameter list. 4653 * (Note that their parameter lists are already effectively identical to this list.) 4654 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be 4655 * effectively identical to the internal parameter list {@code (V... A...)}. 4656 * </ol> 4657 * <p> 4658 * <em>Step 3: Fill in omitted functions.</em><ol type="a"> 4659 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable 4660 * type. 4661 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration 4662 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void} 4663 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.) 4664 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far 4665 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.) 4666 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the 4667 * loop return type. 4668 * </ol> 4669 * <p> 4670 * <em>Step 4: Fill in missing parameter types.</em><ol type="a"> 4671 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)}, 4672 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list. 4673 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter 4674 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list, 4675 * pad out the end of the list. 4676 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}. 4677 * </ol> 4678 * <p> 4679 * <em>Final observations.</em><ol type="a"> 4680 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments. 4681 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have. 4682 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have. 4683 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of 4684 * (non-{@code void}) iteration variables {@code V} followed by loop parameters. 4685 * <li>Each pair of init and step functions agrees in their return type {@code V}. 4686 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables. 4687 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters. 4688 * </ol> 4689 * <p> 4690 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property: 4691 * <ul> 4692 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}. 4693 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters. 4694 * (Only one {@code Pn} has to be non-{@code null}.) 4695 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}. 4696 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types. 4697 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}. 4698 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}. 4699 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine 4700 * the resulting loop handle's parameter types {@code (A...)}. 4701 * </ul> 4702 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions, 4703 * which is natural if most of the loop computation happens in the steps. For some loops, 4704 * the burden of computation might be heaviest in the pred functions, and so the pred functions 4705 * might need to accept the loop parameter values. For loops with complex exit logic, the fini 4706 * functions might need to accept loop parameters, and likewise for loops with complex entry logic, 4707 * where the init functions will need the extra parameters. For such reasons, the rules for 4708 * determining these parameters are as symmetric as possible, across all clause parts. 4709 * In general, the loop parameters function as common invariant values across the whole 4710 * loop, while the iteration variables function as common variant values, or (if there is 4711 * no step function) as internal loop invariant temporaries. 4712 * <p> 4713 * <em>Loop execution.</em><ol type="a"> 4714 * <li>When the loop is called, the loop input values are saved in locals, to be passed to 4715 * every clause function. These locals are loop invariant. 4716 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)}) 4717 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals. 4718 * These locals will be loop varying (unless their steps behave as identity functions, as noted above). 4719 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of 4720 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)} 4721 * (in argument order). 4722 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function 4723 * returns {@code false}. 4724 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the 4725 * sequence {@code (v...)} of loop variables. 4726 * The updated value is immediately visible to all subsequent function calls. 4727 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value 4728 * (of type {@code R}) is returned from the loop as a whole. 4729 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit 4730 * except by throwing an exception. 4731 * </ol> 4732 * <p> 4733 * <em>Usage tips.</em> 4734 * <ul> 4735 * <li>Although each step function will receive the current values of <em>all</em> the loop variables, 4736 * sometimes a step function only needs to observe the current value of its own variable. 4737 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}. 4738 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}. 4739 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create 4740 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be 4741 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable. 4742 * <li>If some of the clause functions are virtual methods on an instance, the instance 4743 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause 4744 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference 4745 * will be the first iteration variable value, and it will be easy to use virtual 4746 * methods as clause parts, since all of them will take a leading instance reference matching that value. 4747 * </ul> 4748 * <p> 4749 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types 4750 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop; 4751 * and {@code R} is the common result type of all finalizers as well as of the resulting loop. 4752 * <blockquote><pre>{@code 4753 * V... init...(A...); 4754 * boolean pred...(V..., A...); 4755 * V... step...(V..., A...); 4756 * R fini...(V..., A...); 4757 * R loop(A... a) { 4758 * V... v... = init...(a...); 4759 * for (;;) { 4760 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) { 4761 * v = s(v..., a...); 4762 * if (!p(v..., a...)) { 4763 * return f(v..., a...); 4764 * } 4765 * } 4766 * } 4767 * } 4768 * }</pre></blockquote> 4769 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded 4770 * to their full length, even though individual clause functions may neglect to take them all. 4771 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}. 4772 * 4773 * @apiNote Example: 4774 * <blockquote><pre>{@code 4775 * // iterative implementation of the factorial function as a loop handle 4776 * static int one(int k) { return 1; } 4777 * static int inc(int i, int acc, int k) { return i + 1; } 4778 * static int mult(int i, int acc, int k) { return i * acc; } 4779 * static boolean pred(int i, int acc, int k) { return i < k; } 4780 * static int fin(int i, int acc, int k) { return acc; } 4781 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 4782 * // null initializer for counter, should initialize to 0 4783 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 4784 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 4785 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 4786 * assertEquals(120, loop.invoke(5)); 4787 * }</pre></blockquote> 4788 * The same example, dropping arguments and using combinators: 4789 * <blockquote><pre>{@code 4790 * // simplified implementation of the factorial function as a loop handle 4791 * static int inc(int i) { return i + 1; } // drop acc, k 4792 * static int mult(int i, int acc) { return i * acc; } //drop k 4793 * static boolean cmp(int i, int k) { return i < k; } 4794 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods 4795 * // null initializer for counter, should initialize to 0 4796 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 4797 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc 4798 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i 4799 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 4800 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 4801 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 4802 * assertEquals(720, loop.invoke(6)); 4803 * }</pre></blockquote> 4804 * A similar example, using a helper object to hold a loop parameter: 4805 * <blockquote><pre>{@code 4806 * // instance-based implementation of the factorial function as a loop handle 4807 * static class FacLoop { 4808 * final int k; 4809 * FacLoop(int k) { this.k = k; } 4810 * int inc(int i) { return i + 1; } 4811 * int mult(int i, int acc) { return i * acc; } 4812 * boolean pred(int i) { return i < k; } 4813 * int fin(int i, int acc) { return acc; } 4814 * } 4815 * // assume MH_FacLoop is a handle to the constructor 4816 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 4817 * // null initializer for counter, should initialize to 0 4818 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 4819 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop}; 4820 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 4821 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 4822 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause); 4823 * assertEquals(5040, loop.invoke(7)); 4824 * }</pre></blockquote> 4825 * 4826 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above. 4827 * 4828 * @return a method handle embodying the looping behavior as defined by the arguments. 4829 * 4830 * @throws IllegalArgumentException in case any of the constraints described above is violated. 4831 * 4832 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle) 4833 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 4834 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle) 4835 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle) 4836 * @since 9 4837 */ 4838 public static MethodHandle loop(MethodHandle[]... clauses) { 4839 // Step 0: determine clause structure. 4840 loopChecks0(clauses); 4841 4842 List<MethodHandle> init = new ArrayList<>(); 4843 List<MethodHandle> step = new ArrayList<>(); 4844 List<MethodHandle> pred = new ArrayList<>(); 4845 List<MethodHandle> fini = new ArrayList<>(); 4846 4847 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> { 4848 init.add(clause[0]); // all clauses have at least length 1 4849 step.add(clause.length <= 1 ? null : clause[1]); 4850 pred.add(clause.length <= 2 ? null : clause[2]); 4851 fini.add(clause.length <= 3 ? null : clause[3]); 4852 }); 4853 4854 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1; 4855 final int nclauses = init.size(); 4856 4857 // Step 1A: determine iteration variables (V...). 4858 final List<Class<?>> iterationVariableTypes = new ArrayList<>(); 4859 for (int i = 0; i < nclauses; ++i) { 4860 MethodHandle in = init.get(i); 4861 MethodHandle st = step.get(i); 4862 if (in == null && st == null) { 4863 iterationVariableTypes.add(void.class); 4864 } else if (in != null && st != null) { 4865 loopChecks1a(i, in, st); 4866 iterationVariableTypes.add(in.type().returnType()); 4867 } else { 4868 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType()); 4869 } 4870 } 4871 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class). 4872 collect(Collectors.toList()); 4873 4874 // Step 1B: determine loop parameters (A...). 4875 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size()); 4876 loopChecks1b(init, commonSuffix); 4877 4878 // Step 1C: determine loop return type. 4879 // Step 1D: check other types. 4880 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type). 4881 map(MethodType::returnType).findFirst().orElse(void.class); 4882 loopChecks1cd(pred, fini, loopReturnType); 4883 4884 // Step 2: determine parameter lists. 4885 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix); 4886 commonParameterSequence.addAll(commonSuffix); 4887 loopChecks2(step, pred, fini, commonParameterSequence); 4888 4889 // Step 3: fill in omitted functions. 4890 for (int i = 0; i < nclauses; ++i) { 4891 Class<?> t = iterationVariableTypes.get(i); 4892 if (init.get(i) == null) { 4893 init.set(i, empty(methodType(t, commonSuffix))); 4894 } 4895 if (step.get(i) == null) { 4896 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i)); 4897 } 4898 if (pred.get(i) == null) { 4899 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence)); 4900 } 4901 if (fini.get(i) == null) { 4902 fini.set(i, empty(methodType(t, commonParameterSequence))); 4903 } 4904 } 4905 4906 // Step 4: fill in missing parameter types. 4907 // Also convert all handles to fixed-arity handles. 4908 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix)); 4909 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence)); 4910 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence)); 4911 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence)); 4912 4913 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList). 4914 allMatch(pl -> pl.equals(commonSuffix)); 4915 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList). 4916 allMatch(pl -> pl.equals(commonParameterSequence)); 4917 4918 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini); 4919 } 4920 4921 private static void loopChecks0(MethodHandle[][] clauses) { 4922 if (clauses == null || clauses.length == 0) { 4923 throw newIllegalArgumentException("null or no clauses passed"); 4924 } 4925 if (Stream.of(clauses).anyMatch(Objects::isNull)) { 4926 throw newIllegalArgumentException("null clauses are not allowed"); 4927 } 4928 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) { 4929 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements."); 4930 } 4931 } 4932 4933 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) { 4934 if (in.type().returnType() != st.type().returnType()) { 4935 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(), 4936 st.type().returnType()); 4937 } 4938 } 4939 4940 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) { 4941 final List<Class<?>> empty = List.of(); 4942 final List<Class<?>> longest = mhs.filter(Objects::nonNull). 4943 // take only those that can contribute to a common suffix because they are longer than the prefix 4944 map(MethodHandle::type). 4945 filter(t -> t.parameterCount() > skipSize). 4946 map(MethodType::parameterList). 4947 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 4948 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size()); 4949 } 4950 4951 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) { 4952 final List<Class<?>> empty = List.of(); 4953 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 4954 } 4955 4956 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) { 4957 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize); 4958 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0); 4959 return longestParameterList(Arrays.asList(longest1, longest2)); 4960 } 4961 4962 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) { 4963 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type). 4964 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) { 4965 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init + 4966 " (common suffix: " + commonSuffix + ")"); 4967 } 4968 } 4969 4970 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) { 4971 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 4972 anyMatch(t -> t != loopReturnType)) { 4973 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " + 4974 loopReturnType + ")"); 4975 } 4976 4977 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) { 4978 throw newIllegalArgumentException("no predicate found", pred); 4979 } 4980 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 4981 anyMatch(t -> t != boolean.class)) { 4982 throw newIllegalArgumentException("predicates must have boolean return type", pred); 4983 } 4984 } 4985 4986 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) { 4987 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type). 4988 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) { 4989 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step + 4990 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")"); 4991 } 4992 } 4993 4994 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) { 4995 return hs.stream().map(h -> { 4996 int pc = h.type().parameterCount(); 4997 int tpsize = targetParams.size(); 4998 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h; 4999 }).collect(Collectors.toList()); 5000 } 5001 5002 private static List<MethodHandle> fixArities(List<MethodHandle> hs) { 5003 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList()); 5004 } 5005 5006 /** 5007 * Constructs a {@code while} loop from an initializer, a body, and a predicate. 5008 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5009 * <p> 5010 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 5011 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate 5012 * evaluates to {@code true}). 5013 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case). 5014 * <p> 5015 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 5016 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 5017 * and updated with the value returned from its invocation. The result of loop execution will be 5018 * the final value of the additional loop-local variable (if present). 5019 * <p> 5020 * The following rules hold for these argument handles:<ul> 5021 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5022 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 5023 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5024 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 5025 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 5026 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 5027 * It will constrain the parameter lists of the other loop parts. 5028 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 5029 * list {@code (A...)} is called the <em>external parameter list</em>. 5030 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5031 * additional state variable of the loop. 5032 * The body must both accept and return a value of this type {@code V}. 5033 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5034 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5035 * <a href="MethodHandles.html#effid">effectively identical</a> 5036 * to the external parameter list {@code (A...)}. 5037 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5038 * {@linkplain #empty default value}. 5039 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 5040 * Its parameter list (either empty or of the form {@code (V A*)}) must be 5041 * effectively identical to the internal parameter list. 5042 * </ul> 5043 * <p> 5044 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5045 * <li>The loop handle's result type is the result type {@code V} of the body. 5046 * <li>The loop handle's parameter types are the types {@code (A...)}, 5047 * from the external parameter list. 5048 * </ul> 5049 * <p> 5050 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5051 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 5052 * passed to the loop. 5053 * <blockquote><pre>{@code 5054 * V init(A...); 5055 * boolean pred(V, A...); 5056 * V body(V, A...); 5057 * V whileLoop(A... a...) { 5058 * V v = init(a...); 5059 * while (pred(v, a...)) { 5060 * v = body(v, a...); 5061 * } 5062 * return v; 5063 * } 5064 * }</pre></blockquote> 5065 * 5066 * @apiNote Example: 5067 * <blockquote><pre>{@code 5068 * // implement the zip function for lists as a loop handle 5069 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); } 5070 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); } 5071 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) { 5072 * zip.add(a.next()); 5073 * zip.add(b.next()); 5074 * return zip; 5075 * } 5076 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods 5077 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep); 5078 * List<String> a = Arrays.asList("a", "b", "c", "d"); 5079 * List<String> b = Arrays.asList("e", "f", "g", "h"); 5080 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h"); 5081 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator())); 5082 * }</pre></blockquote> 5083 * 5084 * 5085 * @apiNote The implementation of this method can be expressed as follows: 5086 * <blockquote><pre>{@code 5087 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 5088 * MethodHandle fini = (body.type().returnType() == void.class 5089 * ? null : identity(body.type().returnType())); 5090 * MethodHandle[] 5091 * checkExit = { null, null, pred, fini }, 5092 * varBody = { init, body }; 5093 * return loop(checkExit, varBody); 5094 * } 5095 * }</pre></blockquote> 5096 * 5097 * @param init optional initializer, providing the initial value of the loop variable. 5098 * May be {@code null}, implying a default initial value. See above for other constraints. 5099 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 5100 * above for other constraints. 5101 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 5102 * See above for other constraints. 5103 * 5104 * @return a method handle implementing the {@code while} loop as described by the arguments. 5105 * @throws IllegalArgumentException if the rules for the arguments are violated. 5106 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 5107 * 5108 * @see #loop(MethodHandle[][]) 5109 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 5110 * @since 9 5111 */ 5112 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 5113 whileLoopChecks(init, pred, body); 5114 MethodHandle fini = identityOrVoid(body.type().returnType()); 5115 MethodHandle[] checkExit = { null, null, pred, fini }; 5116 MethodHandle[] varBody = { init, body }; 5117 return loop(checkExit, varBody); 5118 } 5119 5120 /** 5121 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. 5122 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5123 * <p> 5124 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 5125 * method will, in each iteration, first execute its body and then evaluate the predicate. 5126 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body. 5127 * <p> 5128 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 5129 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 5130 * and updated with the value returned from its invocation. The result of loop execution will be 5131 * the final value of the additional loop-local variable (if present). 5132 * <p> 5133 * The following rules hold for these argument handles:<ul> 5134 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5135 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 5136 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5137 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 5138 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 5139 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 5140 * It will constrain the parameter lists of the other loop parts. 5141 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 5142 * list {@code (A...)} is called the <em>external parameter list</em>. 5143 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5144 * additional state variable of the loop. 5145 * The body must both accept and return a value of this type {@code V}. 5146 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5147 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5148 * <a href="MethodHandles.html#effid">effectively identical</a> 5149 * to the external parameter list {@code (A...)}. 5150 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5151 * {@linkplain #empty default value}. 5152 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 5153 * Its parameter list (either empty or of the form {@code (V A*)}) must be 5154 * effectively identical to the internal parameter list. 5155 * </ul> 5156 * <p> 5157 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5158 * <li>The loop handle's result type is the result type {@code V} of the body. 5159 * <li>The loop handle's parameter types are the types {@code (A...)}, 5160 * from the external parameter list. 5161 * </ul> 5162 * <p> 5163 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5164 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 5165 * passed to the loop. 5166 * <blockquote><pre>{@code 5167 * V init(A...); 5168 * boolean pred(V, A...); 5169 * V body(V, A...); 5170 * V doWhileLoop(A... a...) { 5171 * V v = init(a...); 5172 * do { 5173 * v = body(v, a...); 5174 * } while (pred(v, a...)); 5175 * return v; 5176 * } 5177 * }</pre></blockquote> 5178 * 5179 * @apiNote Example: 5180 * <blockquote><pre>{@code 5181 * // int i = 0; while (i < limit) { ++i; } return i; => limit 5182 * static int zero(int limit) { return 0; } 5183 * static int step(int i, int limit) { return i + 1; } 5184 * static boolean pred(int i, int limit) { return i < limit; } 5185 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods 5186 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred); 5187 * assertEquals(23, loop.invoke(23)); 5188 * }</pre></blockquote> 5189 * 5190 * 5191 * @apiNote The implementation of this method can be expressed as follows: 5192 * <blockquote><pre>{@code 5193 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 5194 * MethodHandle fini = (body.type().returnType() == void.class 5195 * ? null : identity(body.type().returnType())); 5196 * MethodHandle[] clause = { init, body, pred, fini }; 5197 * return loop(clause); 5198 * } 5199 * }</pre></blockquote> 5200 * 5201 * @param init optional initializer, providing the initial value of the loop variable. 5202 * May be {@code null}, implying a default initial value. See above for other constraints. 5203 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 5204 * See above for other constraints. 5205 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 5206 * above for other constraints. 5207 * 5208 * @return a method handle implementing the {@code while} loop as described by the arguments. 5209 * @throws IllegalArgumentException if the rules for the arguments are violated. 5210 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 5211 * 5212 * @see #loop(MethodHandle[][]) 5213 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle) 5214 * @since 9 5215 */ 5216 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 5217 whileLoopChecks(init, pred, body); 5218 MethodHandle fini = identityOrVoid(body.type().returnType()); 5219 MethodHandle[] clause = {init, body, pred, fini }; 5220 return loop(clause); 5221 } 5222 5223 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) { 5224 Objects.requireNonNull(pred); 5225 Objects.requireNonNull(body); 5226 MethodType bodyType = body.type(); 5227 Class<?> returnType = bodyType.returnType(); 5228 List<Class<?>> innerList = bodyType.parameterList(); 5229 List<Class<?>> outerList = innerList; 5230 if (returnType == void.class) { 5231 // OK 5232 } else if (innerList.size() == 0 || innerList.get(0) != returnType) { 5233 // leading V argument missing => error 5234 MethodType expected = bodyType.insertParameterTypes(0, returnType); 5235 throw misMatchedTypes("body function", bodyType, expected); 5236 } else { 5237 outerList = innerList.subList(1, innerList.size()); 5238 } 5239 MethodType predType = pred.type(); 5240 if (predType.returnType() != boolean.class || 5241 !predType.effectivelyIdenticalParameters(0, innerList)) { 5242 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList)); 5243 } 5244 if (init != null) { 5245 MethodType initType = init.type(); 5246 if (initType.returnType() != returnType || 5247 !initType.effectivelyIdenticalParameters(0, outerList)) { 5248 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 5249 } 5250 } 5251 } 5252 5253 /** 5254 * Constructs a loop that runs a given number of iterations. 5255 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5256 * <p> 5257 * The number of iterations is determined by the {@code iterations} handle evaluation result. 5258 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}. 5259 * It will be initialized to 0 and incremented by 1 in each iteration. 5260 * <p> 5261 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 5262 * of that type is also present. This variable is initialized using the optional {@code init} handle, 5263 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 5264 * <p> 5265 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 5266 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 5267 * iteration variable. 5268 * The result of the loop handle execution will be the final {@code V} value of that variable 5269 * (or {@code void} if there is no {@code V} variable). 5270 * <p> 5271 * The following rules hold for the argument handles:<ul> 5272 * <li>The {@code iterations} handle must not be {@code null}, and must return 5273 * the type {@code int}, referred to here as {@code I} in parameter type lists. 5274 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5275 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 5276 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5277 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 5278 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 5279 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 5280 * of types called the <em>internal parameter list</em>. 5281 * It will constrain the parameter lists of the other loop parts. 5282 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 5283 * with no additional {@code A} types, then the internal parameter list is extended by 5284 * the argument types {@code A...} of the {@code iterations} handle. 5285 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 5286 * list {@code (A...)} is called the <em>external parameter list</em>. 5287 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5288 * additional state variable of the loop. 5289 * The body must both accept a leading parameter and return a value of this type {@code V}. 5290 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5291 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5292 * <a href="MethodHandles.html#effid">effectively identical</a> 5293 * to the external parameter list {@code (A...)}. 5294 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5295 * {@linkplain #empty default value}. 5296 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be 5297 * effectively identical to the external parameter list {@code (A...)}. 5298 * </ul> 5299 * <p> 5300 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5301 * <li>The loop handle's result type is the result type {@code V} of the body. 5302 * <li>The loop handle's parameter types are the types {@code (A...)}, 5303 * from the external parameter list. 5304 * </ul> 5305 * <p> 5306 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5307 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 5308 * arguments passed to the loop. 5309 * <blockquote><pre>{@code 5310 * int iterations(A...); 5311 * V init(A...); 5312 * V body(V, int, A...); 5313 * V countedLoop(A... a...) { 5314 * int end = iterations(a...); 5315 * V v = init(a...); 5316 * for (int i = 0; i < end; ++i) { 5317 * v = body(v, i, a...); 5318 * } 5319 * return v; 5320 * } 5321 * }</pre></blockquote> 5322 * 5323 * @apiNote Example with a fully conformant body method: 5324 * <blockquote><pre>{@code 5325 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 5326 * // => a variation on a well known theme 5327 * static String step(String v, int counter, String init) { return "na " + v; } 5328 * // assume MH_step is a handle to the method above 5329 * MethodHandle fit13 = MethodHandles.constant(int.class, 13); 5330 * MethodHandle start = MethodHandles.identity(String.class); 5331 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step); 5332 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!")); 5333 * }</pre></blockquote> 5334 * 5335 * @apiNote Example with the simplest possible body method type, 5336 * and passing the number of iterations to the loop invocation: 5337 * <blockquote><pre>{@code 5338 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 5339 * // => a variation on a well known theme 5340 * static String step(String v, int counter ) { return "na " + v; } 5341 * // assume MH_step is a handle to the method above 5342 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class); 5343 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class); 5344 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v 5345 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!")); 5346 * }</pre></blockquote> 5347 * 5348 * @apiNote Example that treats the number of iterations, string to append to, and string to append 5349 * as loop parameters: 5350 * <blockquote><pre>{@code 5351 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 5352 * // => a variation on a well known theme 5353 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; } 5354 * // assume MH_step is a handle to the method above 5355 * MethodHandle count = MethodHandles.identity(int.class); 5356 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class); 5357 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v 5358 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!")); 5359 * }</pre></blockquote> 5360 * 5361 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)} 5362 * to enforce a loop type: 5363 * <blockquote><pre>{@code 5364 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 5365 * // => a variation on a well known theme 5366 * static String step(String v, int counter, String pre) { return pre + " " + v; } 5367 * // assume MH_step is a handle to the method above 5368 * MethodType loopType = methodType(String.class, String.class, int.class, String.class); 5369 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1); 5370 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2); 5371 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0); 5372 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v 5373 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!")); 5374 * }</pre></blockquote> 5375 * 5376 * @apiNote The implementation of this method can be expressed as follows: 5377 * <blockquote><pre>{@code 5378 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 5379 * return countedLoop(empty(iterations.type()), iterations, init, body); 5380 * } 5381 * }</pre></blockquote> 5382 * 5383 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's 5384 * result type must be {@code int}. See above for other constraints. 5385 * @param init optional initializer, providing the initial value of the loop variable. 5386 * May be {@code null}, implying a default initial value. See above for other constraints. 5387 * @param body body of the loop, which may not be {@code null}. 5388 * It controls the loop parameters and result type in the standard case (see above for details). 5389 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 5390 * and may accept any number of additional types. 5391 * See above for other constraints. 5392 * 5393 * @return a method handle representing the loop. 5394 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}. 5395 * @throws IllegalArgumentException if any argument violates the rules formulated above. 5396 * 5397 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle) 5398 * @since 9 5399 */ 5400 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 5401 return countedLoop(empty(iterations.type()), iterations, init, body); 5402 } 5403 5404 /** 5405 * Constructs a loop that counts over a range of numbers. 5406 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5407 * <p> 5408 * The loop counter {@code i} is a loop iteration variable of type {@code int}. 5409 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive) 5410 * values of the loop counter. 5411 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the 5412 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1. 5413 * <p> 5414 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 5415 * of that type is also present. This variable is initialized using the optional {@code init} handle, 5416 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 5417 * <p> 5418 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 5419 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 5420 * iteration variable. 5421 * The result of the loop handle execution will be the final {@code V} value of that variable 5422 * (or {@code void} if there is no {@code V} variable). 5423 * <p> 5424 * The following rules hold for the argument handles:<ul> 5425 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return 5426 * the common type {@code int}, referred to here as {@code I} in parameter type lists. 5427 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5428 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 5429 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5430 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 5431 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 5432 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 5433 * of types called the <em>internal parameter list</em>. 5434 * It will constrain the parameter lists of the other loop parts. 5435 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 5436 * with no additional {@code A} types, then the internal parameter list is extended by 5437 * the argument types {@code A...} of the {@code end} handle. 5438 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 5439 * list {@code (A...)} is called the <em>external parameter list</em>. 5440 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5441 * additional state variable of the loop. 5442 * The body must both accept a leading parameter and return a value of this type {@code V}. 5443 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5444 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5445 * <a href="MethodHandles.html#effid">effectively identical</a> 5446 * to the external parameter list {@code (A...)}. 5447 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5448 * {@linkplain #empty default value}. 5449 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be 5450 * effectively identical to the external parameter list {@code (A...)}. 5451 * <li>Likewise, the parameter list of {@code end} must be effectively identical 5452 * to the external parameter list. 5453 * </ul> 5454 * <p> 5455 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5456 * <li>The loop handle's result type is the result type {@code V} of the body. 5457 * <li>The loop handle's parameter types are the types {@code (A...)}, 5458 * from the external parameter list. 5459 * </ul> 5460 * <p> 5461 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5462 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 5463 * arguments passed to the loop. 5464 * <blockquote><pre>{@code 5465 * int start(A...); 5466 * int end(A...); 5467 * V init(A...); 5468 * V body(V, int, A...); 5469 * V countedLoop(A... a...) { 5470 * int e = end(a...); 5471 * int s = start(a...); 5472 * V v = init(a...); 5473 * for (int i = s; i < e; ++i) { 5474 * v = body(v, i, a...); 5475 * } 5476 * return v; 5477 * } 5478 * }</pre></blockquote> 5479 * 5480 * @apiNote The implementation of this method can be expressed as follows: 5481 * <blockquote><pre>{@code 5482 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 5483 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class); 5484 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with 5485 * // the following semantics: 5486 * // MH_increment: (int limit, int counter) -> counter + 1 5487 * // MH_predicate: (int limit, int counter) -> counter < limit 5488 * Class<?> counterType = start.type().returnType(); // int 5489 * Class<?> returnType = body.type().returnType(); 5490 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null; 5491 * if (returnType != void.class) { // ignore the V variable 5492 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 5493 * pred = dropArguments(pred, 1, returnType); // ditto 5494 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit 5495 * } 5496 * body = dropArguments(body, 0, counterType); // ignore the limit variable 5497 * MethodHandle[] 5498 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 5499 * bodyClause = { init, body }, // v = init(); v = body(v, i) 5500 * indexVar = { start, incr }; // i = start(); i = i + 1 5501 * return loop(loopLimit, bodyClause, indexVar); 5502 * } 5503 * }</pre></blockquote> 5504 * 5505 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}. 5506 * See above for other constraints. 5507 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to 5508 * {@code end-1}). The result type must be {@code int}. See above for other constraints. 5509 * @param init optional initializer, providing the initial value of the loop variable. 5510 * May be {@code null}, implying a default initial value. See above for other constraints. 5511 * @param body body of the loop, which may not be {@code null}. 5512 * It controls the loop parameters and result type in the standard case (see above for details). 5513 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 5514 * and may accept any number of additional types. 5515 * See above for other constraints. 5516 * 5517 * @return a method handle representing the loop. 5518 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}. 5519 * @throws IllegalArgumentException if any argument violates the rules formulated above. 5520 * 5521 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle) 5522 * @since 9 5523 */ 5524 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 5525 countedLoopChecks(start, end, init, body); 5526 Class<?> counterType = start.type().returnType(); // int, but who's counting? 5527 Class<?> limitType = end.type().returnType(); // yes, int again 5528 Class<?> returnType = body.type().returnType(); 5529 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep); 5530 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred); 5531 MethodHandle retv = null; 5532 if (returnType != void.class) { 5533 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 5534 pred = dropArguments(pred, 1, returnType); // ditto 5535 retv = dropArguments(identity(returnType), 0, counterType); 5536 } 5537 body = dropArguments(body, 0, counterType); // ignore the limit variable 5538 MethodHandle[] 5539 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 5540 bodyClause = { init, body }, // v = init(); v = body(v, i) 5541 indexVar = { start, incr }; // i = start(); i = i + 1 5542 return loop(loopLimit, bodyClause, indexVar); 5543 } 5544 5545 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 5546 Objects.requireNonNull(start); 5547 Objects.requireNonNull(end); 5548 Objects.requireNonNull(body); 5549 Class<?> counterType = start.type().returnType(); 5550 if (counterType != int.class) { 5551 MethodType expected = start.type().changeReturnType(int.class); 5552 throw misMatchedTypes("start function", start.type(), expected); 5553 } else if (end.type().returnType() != counterType) { 5554 MethodType expected = end.type().changeReturnType(counterType); 5555 throw misMatchedTypes("end function", end.type(), expected); 5556 } 5557 MethodType bodyType = body.type(); 5558 Class<?> returnType = bodyType.returnType(); 5559 List<Class<?>> innerList = bodyType.parameterList(); 5560 // strip leading V value if present 5561 int vsize = (returnType == void.class ? 0 : 1); 5562 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) { 5563 // argument list has no "V" => error 5564 MethodType expected = bodyType.insertParameterTypes(0, returnType); 5565 throw misMatchedTypes("body function", bodyType, expected); 5566 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) { 5567 // missing I type => error 5568 MethodType expected = bodyType.insertParameterTypes(vsize, counterType); 5569 throw misMatchedTypes("body function", bodyType, expected); 5570 } 5571 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size()); 5572 if (outerList.isEmpty()) { 5573 // special case; take lists from end handle 5574 outerList = end.type().parameterList(); 5575 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList(); 5576 } 5577 MethodType expected = methodType(counterType, outerList); 5578 if (!start.type().effectivelyIdenticalParameters(0, outerList)) { 5579 throw misMatchedTypes("start parameter types", start.type(), expected); 5580 } 5581 if (end.type() != start.type() && 5582 !end.type().effectivelyIdenticalParameters(0, outerList)) { 5583 throw misMatchedTypes("end parameter types", end.type(), expected); 5584 } 5585 if (init != null) { 5586 MethodType initType = init.type(); 5587 if (initType.returnType() != returnType || 5588 !initType.effectivelyIdenticalParameters(0, outerList)) { 5589 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 5590 } 5591 } 5592 } 5593 5594 /** 5595 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}. 5596 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 5597 * <p> 5598 * The iterator itself will be determined by the evaluation of the {@code iterator} handle. 5599 * Each value it produces will be stored in a loop iteration variable of type {@code T}. 5600 * <p> 5601 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 5602 * of that type is also present. This variable is initialized using the optional {@code init} handle, 5603 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 5604 * <p> 5605 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 5606 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 5607 * iteration variable. 5608 * The result of the loop handle execution will be the final {@code V} value of that variable 5609 * (or {@code void} if there is no {@code V} variable). 5610 * <p> 5611 * The following rules hold for the argument handles:<ul> 5612 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 5613 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}. 5614 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 5615 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V} 5616 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.) 5617 * <li>The parameter list {@code (V T A...)} of the body contributes to a list 5618 * of types called the <em>internal parameter list</em>. 5619 * It will constrain the parameter lists of the other loop parts. 5620 * <li>As a special case, if the body contributes only {@code V} and {@code T} types, 5621 * with no additional {@code A} types, then the internal parameter list is extended by 5622 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the 5623 * single type {@code Iterable} is added and constitutes the {@code A...} list. 5624 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter 5625 * list {@code (A...)} is called the <em>external parameter list</em>. 5626 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 5627 * additional state variable of the loop. 5628 * The body must both accept a leading parameter and return a value of this type {@code V}. 5629 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 5630 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 5631 * <a href="MethodHandles.html#effid">effectively identical</a> 5632 * to the external parameter list {@code (A...)}. 5633 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 5634 * {@linkplain #empty default value}. 5635 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return 5636 * type {@code java.util.Iterator} or a subtype thereof. 5637 * The iterator it produces when the loop is executed will be assumed 5638 * to yield values which can be converted to type {@code T}. 5639 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be 5640 * effectively identical to the external parameter list {@code (A...)}. 5641 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves 5642 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list 5643 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator 5644 * handle parameter is adjusted to accept the leading {@code A} type, as if by 5645 * the {@link MethodHandle#asType asType} conversion method. 5646 * The leading {@code A} type must be {@code Iterable} or a subtype thereof. 5647 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}. 5648 * </ul> 5649 * <p> 5650 * The type {@code T} may be either a primitive or reference. 5651 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator}, 5652 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object} 5653 * as if by the {@link MethodHandle#asType asType} conversion method. 5654 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur 5655 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}. 5656 * <p> 5657 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 5658 * <li>The loop handle's result type is the result type {@code V} of the body. 5659 * <li>The loop handle's parameter types are the types {@code (A...)}, 5660 * from the external parameter list. 5661 * </ul> 5662 * <p> 5663 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 5664 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the 5665 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop. 5666 * <blockquote><pre>{@code 5667 * Iterator<T> iterator(A...); // defaults to Iterable::iterator 5668 * V init(A...); 5669 * V body(V,T,A...); 5670 * V iteratedLoop(A... a...) { 5671 * Iterator<T> it = iterator(a...); 5672 * V v = init(a...); 5673 * while (it.hasNext()) { 5674 * T t = it.next(); 5675 * v = body(v, t, a...); 5676 * } 5677 * return v; 5678 * } 5679 * }</pre></blockquote> 5680 * 5681 * @apiNote Example: 5682 * <blockquote><pre>{@code 5683 * // get an iterator from a list 5684 * static List<String> reverseStep(List<String> r, String e) { 5685 * r.add(0, e); 5686 * return r; 5687 * } 5688 * static List<String> newArrayList() { return new ArrayList<>(); } 5689 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods 5690 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep); 5691 * List<String> list = Arrays.asList("a", "b", "c", "d", "e"); 5692 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a"); 5693 * assertEquals(reversedList, (List<String>) loop.invoke(list)); 5694 * }</pre></blockquote> 5695 * 5696 * @apiNote The implementation of this method can be expressed approximately as follows: 5697 * <blockquote><pre>{@code 5698 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 5699 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable 5700 * Class<?> returnType = body.type().returnType(); 5701 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 5702 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype)); 5703 * MethodHandle retv = null, step = body, startIter = iterator; 5704 * if (returnType != void.class) { 5705 * // the simple thing first: in (I V A...), drop the I to get V 5706 * retv = dropArguments(identity(returnType), 0, Iterator.class); 5707 * // body type signature (V T A...), internal loop types (I V A...) 5708 * step = swapArguments(body, 0, 1); // swap V <-> T 5709 * } 5710 * if (startIter == null) startIter = MH_getIter; 5711 * MethodHandle[] 5712 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext()) 5713 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a) 5714 * return loop(iterVar, bodyClause); 5715 * } 5716 * }</pre></blockquote> 5717 * 5718 * @param iterator an optional handle to return the iterator to start the loop. 5719 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype. 5720 * See above for other constraints. 5721 * @param init optional initializer, providing the initial value of the loop variable. 5722 * May be {@code null}, implying a default initial value. See above for other constraints. 5723 * @param body body of the loop, which may not be {@code null}. 5724 * It controls the loop parameters and result type in the standard case (see above for details). 5725 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values), 5726 * and may accept any number of additional types. 5727 * See above for other constraints. 5728 * 5729 * @return a method handle embodying the iteration loop functionality. 5730 * @throws NullPointerException if the {@code body} handle is {@code null}. 5731 * @throws IllegalArgumentException if any argument violates the above requirements. 5732 * 5733 * @since 9 5734 */ 5735 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 5736 Class<?> iterableType = iteratedLoopChecks(iterator, init, body); 5737 Class<?> returnType = body.type().returnType(); 5738 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred); 5739 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext); 5740 MethodHandle startIter; 5741 MethodHandle nextVal; 5742 { 5743 MethodType iteratorType; 5744 if (iterator == null) { 5745 // derive argument type from body, if available, else use Iterable 5746 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator); 5747 iteratorType = startIter.type().changeParameterType(0, iterableType); 5748 } else { 5749 // force return type to the internal iterator class 5750 iteratorType = iterator.type().changeReturnType(Iterator.class); 5751 startIter = iterator; 5752 } 5753 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 5754 MethodType nextValType = nextRaw.type().changeReturnType(ttype); 5755 5756 // perform the asType transforms under an exception transformer, as per spec.: 5757 try { 5758 startIter = startIter.asType(iteratorType); 5759 nextVal = nextRaw.asType(nextValType); 5760 } catch (WrongMethodTypeException ex) { 5761 throw new IllegalArgumentException(ex); 5762 } 5763 } 5764 5765 MethodHandle retv = null, step = body; 5766 if (returnType != void.class) { 5767 // the simple thing first: in (I V A...), drop the I to get V 5768 retv = dropArguments(identity(returnType), 0, Iterator.class); 5769 // body type signature (V T A...), internal loop types (I V A...) 5770 step = swapArguments(body, 0, 1); // swap V <-> T 5771 } 5772 5773 MethodHandle[] 5774 iterVar = { startIter, null, hasNext, retv }, 5775 bodyClause = { init, filterArgument(step, 0, nextVal) }; 5776 return loop(iterVar, bodyClause); 5777 } 5778 5779 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) { 5780 Objects.requireNonNull(body); 5781 MethodType bodyType = body.type(); 5782 Class<?> returnType = bodyType.returnType(); 5783 List<Class<?>> internalParamList = bodyType.parameterList(); 5784 // strip leading V value if present 5785 int vsize = (returnType == void.class ? 0 : 1); 5786 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) { 5787 // argument list has no "V" => error 5788 MethodType expected = bodyType.insertParameterTypes(0, returnType); 5789 throw misMatchedTypes("body function", bodyType, expected); 5790 } else if (internalParamList.size() <= vsize) { 5791 // missing T type => error 5792 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class); 5793 throw misMatchedTypes("body function", bodyType, expected); 5794 } 5795 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size()); 5796 Class<?> iterableType = null; 5797 if (iterator != null) { 5798 // special case; if the body handle only declares V and T then 5799 // the external parameter list is obtained from iterator handle 5800 if (externalParamList.isEmpty()) { 5801 externalParamList = iterator.type().parameterList(); 5802 } 5803 MethodType itype = iterator.type(); 5804 if (!Iterator.class.isAssignableFrom(itype.returnType())) { 5805 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type"); 5806 } 5807 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) { 5808 MethodType expected = methodType(itype.returnType(), externalParamList); 5809 throw misMatchedTypes("iterator parameters", itype, expected); 5810 } 5811 } else { 5812 if (externalParamList.isEmpty()) { 5813 // special case; if the iterator handle is null and the body handle 5814 // only declares V and T then the external parameter list consists 5815 // of Iterable 5816 externalParamList = Arrays.asList(Iterable.class); 5817 iterableType = Iterable.class; 5818 } else { 5819 // special case; if the iterator handle is null and the external 5820 // parameter list is not empty then the first parameter must be 5821 // assignable to Iterable 5822 iterableType = externalParamList.get(0); 5823 if (!Iterable.class.isAssignableFrom(iterableType)) { 5824 throw newIllegalArgumentException( 5825 "inferred first loop argument must inherit from Iterable: " + iterableType); 5826 } 5827 } 5828 } 5829 if (init != null) { 5830 MethodType initType = init.type(); 5831 if (initType.returnType() != returnType || 5832 !initType.effectivelyIdenticalParameters(0, externalParamList)) { 5833 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList)); 5834 } 5835 } 5836 return iterableType; // help the caller a bit 5837 } 5838 5839 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) { 5840 // there should be a better way to uncross my wires 5841 int arity = mh.type().parameterCount(); 5842 int[] order = new int[arity]; 5843 for (int k = 0; k < arity; k++) order[k] = k; 5844 order[i] = j; order[j] = i; 5845 Class<?>[] types = mh.type().parameterArray(); 5846 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti; 5847 MethodType swapType = methodType(mh.type().returnType(), types); 5848 return permuteArguments(mh, swapType, order); 5849 } 5850 5851 /** 5852 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block. 5853 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception 5854 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The 5855 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The 5856 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the 5857 * {@code try-finally} handle. 5858 * <p> 5859 * The {@code cleanup} handle will be passed one or two additional leading arguments. 5860 * The first is the exception thrown during the 5861 * execution of the {@code target} handle, or {@code null} if no exception was thrown. 5862 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception, 5863 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder. 5864 * The second argument is not present if the {@code target} handle has a {@code void} return type. 5865 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists 5866 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.) 5867 * <p> 5868 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except 5869 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or 5870 * two extra leading parameters:<ul> 5871 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and 5872 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry 5873 * the result from the execution of the {@code target} handle. 5874 * This parameter is not present if the {@code target} returns {@code void}. 5875 * </ul> 5876 * <p> 5877 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of 5878 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting 5879 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by 5880 * the cleanup. 5881 * <blockquote><pre>{@code 5882 * V target(A..., B...); 5883 * V cleanup(Throwable, V, A...); 5884 * V adapter(A... a, B... b) { 5885 * V result = (zero value for V); 5886 * Throwable throwable = null; 5887 * try { 5888 * result = target(a..., b...); 5889 * } catch (Throwable t) { 5890 * throwable = t; 5891 * throw t; 5892 * } finally { 5893 * result = cleanup(throwable, result, a...); 5894 * } 5895 * return result; 5896 * } 5897 * }</pre></blockquote> 5898 * <p> 5899 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 5900 * be modified by execution of the target, and so are passed unchanged 5901 * from the caller to the cleanup, if it is invoked. 5902 * <p> 5903 * The target and cleanup must return the same type, even if the cleanup 5904 * always throws. 5905 * To create such a throwing cleanup, compose the cleanup logic 5906 * with {@link #throwException throwException}, 5907 * in order to create a method handle of the correct return type. 5908 * <p> 5909 * Note that {@code tryFinally} never converts exceptions into normal returns. 5910 * In rare cases where exceptions must be converted in that way, first wrap 5911 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)} 5912 * to capture an outgoing exception, and then wrap with {@code tryFinally}. 5913 * <p> 5914 * It is recommended that the first parameter type of {@code cleanup} be 5915 * declared {@code Throwable} rather than a narrower subtype. This ensures 5916 * {@code cleanup} will always be invoked with whatever exception that 5917 * {@code target} throws. Declaring a narrower type may result in a 5918 * {@code ClassCastException} being thrown by the {@code try-finally} 5919 * handle if the type of the exception thrown by {@code target} is not 5920 * assignable to the first parameter type of {@code cleanup}. Note that 5921 * various exception types of {@code VirtualMachineError}, 5922 * {@code LinkageError}, and {@code RuntimeException} can in principle be 5923 * thrown by almost any kind of Java code, and a finally clause that 5924 * catches (say) only {@code IOException} would mask any of the others 5925 * behind a {@code ClassCastException}. 5926 * 5927 * @param target the handle whose execution is to be wrapped in a {@code try} block. 5928 * @param cleanup the handle that is invoked in the finally block. 5929 * 5930 * @return a method handle embodying the {@code try-finally} block composed of the two arguments. 5931 * @throws NullPointerException if any argument is null 5932 * @throws IllegalArgumentException if {@code cleanup} does not accept 5933 * the required leading arguments, or if the method handle types do 5934 * not match in their return types and their 5935 * corresponding trailing parameters 5936 * 5937 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle) 5938 * @since 9 5939 */ 5940 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) { 5941 List<Class<?>> targetParamTypes = target.type().parameterList(); 5942 Class<?> rtype = target.type().returnType(); 5943 5944 tryFinallyChecks(target, cleanup); 5945 5946 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments. 5947 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 5948 // target parameter list. 5949 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0); 5950 5951 // Ensure that the intrinsic type checks the instance thrown by the 5952 // target against the first parameter of cleanup 5953 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class)); 5954 5955 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case. 5956 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes); 5957 } 5958 5959 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) { 5960 Class<?> rtype = target.type().returnType(); 5961 if (rtype != cleanup.type().returnType()) { 5962 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype); 5963 } 5964 MethodType cleanupType = cleanup.type(); 5965 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) { 5966 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class); 5967 } 5968 if (rtype != void.class && cleanupType.parameterType(1) != rtype) { 5969 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype); 5970 } 5971 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 5972 // target parameter list. 5973 int cleanupArgIndex = rtype == void.class ? 1 : 2; 5974 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) { 5975 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix", 5976 cleanup.type(), target.type()); 5977 } 5978 } 5979 5980 }