1 /* 2 * Copyright (c) 2008, 2023, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang.invoke; 27 28 import jdk.internal.access.SharedSecrets; 29 import jdk.internal.foreign.Utils; 30 import jdk.internal.javac.PreviewFeature; 31 import jdk.internal.misc.Unsafe; 32 import jdk.internal.misc.VM; 33 import jdk.internal.org.objectweb.asm.ClassReader; 34 import jdk.internal.org.objectweb.asm.Opcodes; 35 import jdk.internal.org.objectweb.asm.Type; 36 import jdk.internal.reflect.CallerSensitive; 37 import jdk.internal.reflect.CallerSensitiveAdapter; 38 import jdk.internal.reflect.Reflection; 39 import jdk.internal.util.ClassFileDumper; 40 import jdk.internal.vm.annotation.ForceInline; 41 import sun.invoke.util.ValueConversions; 42 import sun.invoke.util.VerifyAccess; 43 import sun.invoke.util.Wrapper; 44 import sun.reflect.misc.ReflectUtil; 45 import sun.security.util.SecurityConstants; 46 47 import java.lang.constant.ConstantDescs; 48 import java.lang.foreign.GroupLayout; 49 import java.lang.foreign.MemoryLayout; 50 import java.lang.foreign.MemorySegment; 51 import java.lang.foreign.ValueLayout; 52 import java.lang.invoke.LambdaForm.BasicType; 53 import java.lang.reflect.Constructor; 54 import java.lang.reflect.Field; 55 import java.lang.reflect.Member; 56 import java.lang.reflect.Method; 57 import java.lang.reflect.Modifier; 58 import java.nio.ByteOrder; 59 import java.security.ProtectionDomain; 60 import java.util.ArrayList; 61 import java.util.Arrays; 62 import java.util.BitSet; 63 import java.util.Comparator; 64 import java.util.Iterator; 65 import java.util.List; 66 import java.util.Objects; 67 import java.util.Set; 68 import java.util.concurrent.ConcurrentHashMap; 69 import java.util.stream.Stream; 70 71 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE; 72 import static java.lang.invoke.MethodHandleImpl.Intrinsic; 73 import static java.lang.invoke.MethodHandleNatives.Constants.*; 74 import static java.lang.invoke.MethodHandleStatics.UNSAFE; 75 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException; 76 import static java.lang.invoke.MethodHandleStatics.newInternalError; 77 import static java.lang.invoke.MethodType.methodType; 78 79 /** 80 * This class consists exclusively of static methods that operate on or return 81 * method handles. They fall into several categories: 82 * <ul> 83 * <li>Lookup methods which help create method handles for methods and fields. 84 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones. 85 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns. 86 * </ul> 87 * A lookup, combinator, or factory method will fail and throw an 88 * {@code IllegalArgumentException} if the created method handle's type 89 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>. 90 * 91 * @author John Rose, JSR 292 EG 92 * @since 1.7 93 */ 94 public class MethodHandles { 95 96 private MethodHandles() { } // do not instantiate 97 98 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); 99 100 // See IMPL_LOOKUP below. 101 102 //// Method handle creation from ordinary methods. 103 104 /** 105 * Returns a {@link Lookup lookup object} with 106 * full capabilities to emulate all supported bytecode behaviors of the caller. 107 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller. 108 * Factory methods on the lookup object can create 109 * <a href="MethodHandleInfo.html#directmh">direct method handles</a> 110 * for any member that the caller has access to via bytecodes, 111 * including protected and private fields and methods. 112 * This lookup object is created by the original lookup class 113 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set. 114 * This lookup object is a <em>capability</em> which may be delegated to trusted agents. 115 * Do not store it in place where untrusted code can access it. 116 * <p> 117 * This method is caller sensitive, which means that it may return different 118 * values to different callers. 119 * In cases where {@code MethodHandles.lookup} is called from a context where 120 * there is no caller frame on the stack (e.g. when called directly 121 * from a JNI attached thread), {@code IllegalCallerException} is thrown. 122 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will 123 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()} 124 * to obtain a low-privileged lookup instead. 125 * @return a lookup object for the caller of this method, with 126 * {@linkplain Lookup#ORIGINAL original} and 127 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}. 128 * @throws IllegalCallerException if there is no caller frame on the stack. 129 */ 130 @CallerSensitive 131 @ForceInline // to ensure Reflection.getCallerClass optimization 132 public static Lookup lookup() { 133 final Class<?> c = Reflection.getCallerClass(); 134 if (c == null) { 135 throw new IllegalCallerException("no caller frame"); 136 } 137 return new Lookup(c); 138 } 139 140 /** 141 * This lookup method is the alternate implementation of 142 * the lookup method with a leading caller class argument which is 143 * non-caller-sensitive. This method is only invoked by reflection 144 * and method handle. 145 */ 146 @CallerSensitiveAdapter 147 private static Lookup lookup(Class<?> caller) { 148 if (caller.getClassLoader() == null) { 149 throw newInternalError("calling lookup() reflectively is not supported: "+caller); 150 } 151 return new Lookup(caller); 152 } 153 154 /** 155 * Returns a {@link Lookup lookup object} which is trusted minimally. 156 * The lookup has the {@code UNCONDITIONAL} mode. 157 * It can only be used to create method handles to public members of 158 * public classes in packages that are exported unconditionally. 159 * <p> 160 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class} 161 * of this lookup object will be {@link java.lang.Object}. 162 * 163 * @apiNote The use of Object is conventional, and because the lookup modes are 164 * limited, there is no special access provided to the internals of Object, its package 165 * or its module. This public lookup object or other lookup object with 166 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class 167 * is not used to determine the lookup context. 168 * 169 * <p style="font-size:smaller;"> 170 * <em>Discussion:</em> 171 * The lookup class can be changed to any other class {@code C} using an expression of the form 172 * {@link Lookup#in publicLookup().in(C.class)}. 173 * A public lookup object is always subject to 174 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>. 175 * Also, it cannot access 176 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>. 177 * @return a lookup object which is trusted minimally 178 * 179 * @revised 9 180 */ 181 public static Lookup publicLookup() { 182 return Lookup.PUBLIC_LOOKUP; 183 } 184 185 /** 186 * Returns a {@link Lookup lookup} object on a target class to emulate all supported 187 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>. 188 * The returned lookup object can provide access to classes in modules and packages, 189 * and members of those classes, outside the normal rules of Java access control, 190 * instead conforming to the more permissive rules for modular <em>deep reflection</em>. 191 * <p> 192 * A caller, specified as a {@code Lookup} object, in module {@code M1} is 193 * allowed to do deep reflection on module {@code M2} and package of the target class 194 * if and only if all of the following conditions are {@code true}: 195 * <ul> 196 * <li>If there is a security manager, its {@code checkPermission} method is 197 * called to check {@code ReflectPermission("suppressAccessChecks")} and 198 * that must return normally. 199 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess() 200 * full privilege access}. Specifically: 201 * <ul> 202 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode. 203 * (This is because otherwise there would be no way to ensure the original lookup 204 * creator was a member of any particular module, and so any subsequent checks 205 * for readability and qualified exports would become ineffective.) 206 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access. 207 * (This is because an application intending to share intra-module access 208 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share 209 * deep reflection to its own module.) 210 * </ul> 211 * <li>The target class must be a proper class, not a primitive or array class. 212 * (Thus, {@code M2} is well-defined.) 213 * <li>If the caller module {@code M1} differs from 214 * the target module {@code M2} then both of the following must be true: 215 * <ul> 216 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li> 217 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package 218 * containing the target class to at least {@code M1}.</li> 219 * </ul> 220 * </ul> 221 * <p> 222 * If any of the above checks is violated, this method fails with an 223 * exception. 224 * <p> 225 * Otherwise, if {@code M1} and {@code M2} are the same module, this method 226 * returns a {@code Lookup} on {@code targetClass} with 227 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} 228 * with {@code null} previous lookup class. 229 * <p> 230 * Otherwise, {@code M1} and {@code M2} are two different modules. This method 231 * returns a {@code Lookup} on {@code targetClass} that records 232 * the lookup class of the caller as the new previous lookup class with 233 * {@code PRIVATE} access but no {@code MODULE} access. 234 * <p> 235 * The resulting {@code Lookup} object has no {@code ORIGINAL} access. 236 * 237 * @apiNote The {@code Lookup} object returned by this method is allowed to 238 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package 239 * of {@code targetClass}. Extreme caution should be taken when opening a package 240 * to another module as such defined classes have the same full privilege 241 * access as other members in {@code targetClass}'s module. 242 * 243 * @param targetClass the target class 244 * @param caller the caller lookup object 245 * @return a lookup object for the target class, with private access 246 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class 247 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null} 248 * @throws SecurityException if denied by the security manager 249 * @throws IllegalAccessException if any of the other access checks specified above fails 250 * @since 9 251 * @see Lookup#dropLookupMode 252 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a> 253 */ 254 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException { 255 if (caller.allowedModes == Lookup.TRUSTED) { 256 return new Lookup(targetClass); 257 } 258 259 @SuppressWarnings("removal") 260 SecurityManager sm = System.getSecurityManager(); 261 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION); 262 if (targetClass.isPrimitive()) 263 throw new IllegalArgumentException(targetClass + " is a primitive class"); 264 if (targetClass.isArray()) 265 throw new IllegalArgumentException(targetClass + " is an array class"); 266 // Ensure that we can reason accurately about private and module access. 267 int requireAccess = Lookup.PRIVATE|Lookup.MODULE; 268 if ((caller.lookupModes() & requireAccess) != requireAccess) 269 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode"); 270 271 // previous lookup class is never set if it has MODULE access 272 assert caller.previousLookupClass() == null; 273 274 Class<?> callerClass = caller.lookupClass(); 275 Module callerModule = callerClass.getModule(); // M1 276 Module targetModule = targetClass.getModule(); // M2 277 Class<?> newPreviousClass = null; 278 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL; 279 280 if (targetModule != callerModule) { 281 if (!callerModule.canRead(targetModule)) 282 throw new IllegalAccessException(callerModule + " does not read " + targetModule); 283 if (targetModule.isNamed()) { 284 String pn = targetClass.getPackageName(); 285 assert !pn.isEmpty() : "unnamed package cannot be in named module"; 286 if (!targetModule.isOpen(pn, callerModule)) 287 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule); 288 } 289 290 // M2 != M1, set previous lookup class to M1 and drop MODULE access 291 newPreviousClass = callerClass; 292 newModes &= ~Lookup.MODULE; 293 } 294 return Lookup.newLookup(targetClass, newPreviousClass, newModes); 295 } 296 297 /** 298 * Returns the <em>class data</em> associated with the lookup class 299 * of the given {@code caller} lookup object, or {@code null}. 300 * 301 * <p> A hidden class with class data can be created by calling 302 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 303 * Lookup::defineHiddenClassWithClassData}. 304 * This method will cause the static class initializer of the lookup 305 * class of the given {@code caller} lookup object be executed if 306 * it has not been initialized. 307 * 308 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...) 309 * Lookup::defineHiddenClass} and non-hidden classes have no class data. 310 * {@code null} is returned if this method is called on the lookup object 311 * on these classes. 312 * 313 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup 314 * must have {@linkplain Lookup#ORIGINAL original access} 315 * in order to retrieve the class data. 316 * 317 * @apiNote 318 * This method can be called as a bootstrap method for a dynamically computed 319 * constant. A framework can create a hidden class with class data, for 320 * example that can be {@code Class} or {@code MethodHandle} object. 321 * The class data is accessible only to the lookup object 322 * created by the original caller but inaccessible to other members 323 * in the same nest. If a framework passes security sensitive objects 324 * to a hidden class via class data, it is recommended to load the value 325 * of class data as a dynamically computed constant instead of storing 326 * the class data in private static field(s) which are accessible to 327 * other nestmates. 328 * 329 * @param <T> the type to cast the class data object to 330 * @param caller the lookup context describing the class performing the 331 * operation (normally stacked by the JVM) 332 * @param name must be {@link ConstantDescs#DEFAULT_NAME} 333 * ({@code "_"}) 334 * @param type the type of the class data 335 * @return the value of the class data if present in the lookup class; 336 * otherwise {@code null} 337 * @throws IllegalArgumentException if name is not {@code "_"} 338 * @throws IllegalAccessException if the lookup context does not have 339 * {@linkplain Lookup#ORIGINAL original} access 340 * @throws ClassCastException if the class data cannot be converted to 341 * the given {@code type} 342 * @throws NullPointerException if {@code caller} or {@code type} argument 343 * is {@code null} 344 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 345 * @see MethodHandles#classDataAt(Lookup, String, Class, int) 346 * @since 16 347 * @jvms 5.5 Initialization 348 */ 349 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException { 350 Objects.requireNonNull(caller); 351 Objects.requireNonNull(type); 352 if (!ConstantDescs.DEFAULT_NAME.equals(name)) { 353 throw new IllegalArgumentException("name must be \"_\": " + name); 354 } 355 356 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) { 357 throw new IllegalAccessException(caller + " does not have ORIGINAL access"); 358 } 359 360 Object classdata = classData(caller.lookupClass()); 361 if (classdata == null) return null; 362 363 try { 364 return BootstrapMethodInvoker.widenAndCast(classdata, type); 365 } catch (RuntimeException|Error e) { 366 throw e; // let CCE and other runtime exceptions through 367 } catch (Throwable e) { 368 throw new InternalError(e); 369 } 370 } 371 372 /* 373 * Returns the class data set by the VM in the Class::classData field. 374 * 375 * This is also invoked by LambdaForms as it cannot use condy via 376 * MethodHandles::classData due to bootstrapping issue. 377 */ 378 static Object classData(Class<?> c) { 379 UNSAFE.ensureClassInitialized(c); 380 return SharedSecrets.getJavaLangAccess().classData(c); 381 } 382 383 /** 384 * Returns the element at the specified index in the 385 * {@linkplain #classData(Lookup, String, Class) class data}, 386 * if the class data associated with the lookup class 387 * of the given {@code caller} lookup object is a {@code List}. 388 * If the class data is not present in this lookup class, this method 389 * returns {@code null}. 390 * 391 * <p> A hidden class with class data can be created by calling 392 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 393 * Lookup::defineHiddenClassWithClassData}. 394 * This method will cause the static class initializer of the lookup 395 * class of the given {@code caller} lookup object be executed if 396 * it has not been initialized. 397 * 398 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...) 399 * Lookup::defineHiddenClass} and non-hidden classes have no class data. 400 * {@code null} is returned if this method is called on the lookup object 401 * on these classes. 402 * 403 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup 404 * must have {@linkplain Lookup#ORIGINAL original access} 405 * in order to retrieve the class data. 406 * 407 * @apiNote 408 * This method can be called as a bootstrap method for a dynamically computed 409 * constant. A framework can create a hidden class with class data, for 410 * example that can be {@code List.of(o1, o2, o3....)} containing more than 411 * one object and use this method to load one element at a specific index. 412 * The class data is accessible only to the lookup object 413 * created by the original caller but inaccessible to other members 414 * in the same nest. If a framework passes security sensitive objects 415 * to a hidden class via class data, it is recommended to load the value 416 * of class data as a dynamically computed constant instead of storing 417 * the class data in private static field(s) which are accessible to other 418 * nestmates. 419 * 420 * @param <T> the type to cast the result object to 421 * @param caller the lookup context describing the class performing the 422 * operation (normally stacked by the JVM) 423 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME} 424 * ({@code "_"}) 425 * @param type the type of the element at the given index in the class data 426 * @param index index of the element in the class data 427 * @return the element at the given index in the class data 428 * if the class data is present; otherwise {@code null} 429 * @throws IllegalArgumentException if name is not {@code "_"} 430 * @throws IllegalAccessException if the lookup context does not have 431 * {@linkplain Lookup#ORIGINAL original} access 432 * @throws ClassCastException if the class data cannot be converted to {@code List} 433 * or the element at the specified index cannot be converted to the given type 434 * @throws IndexOutOfBoundsException if the index is out of range 435 * @throws NullPointerException if {@code caller} or {@code type} argument is 436 * {@code null}; or if unboxing operation fails because 437 * the element at the given index is {@code null} 438 * 439 * @since 16 440 * @see #classData(Lookup, String, Class) 441 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 442 */ 443 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index) 444 throws IllegalAccessException 445 { 446 @SuppressWarnings("unchecked") 447 List<Object> classdata = (List<Object>)classData(caller, name, List.class); 448 if (classdata == null) return null; 449 450 try { 451 Object element = classdata.get(index); 452 return BootstrapMethodInvoker.widenAndCast(element, type); 453 } catch (RuntimeException|Error e) { 454 throw e; // let specified exceptions and other runtime exceptions/errors through 455 } catch (Throwable e) { 456 throw new InternalError(e); 457 } 458 } 459 460 /** 461 * Performs an unchecked "crack" of a 462 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>. 463 * The result is as if the user had obtained a lookup object capable enough 464 * to crack the target method handle, called 465 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} 466 * on the target to obtain its symbolic reference, and then called 467 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} 468 * to resolve the symbolic reference to a member. 469 * <p> 470 * If there is a security manager, its {@code checkPermission} method 471 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission. 472 * @param <T> the desired type of the result, either {@link Member} or a subtype 473 * @param target a direct method handle to crack into symbolic reference components 474 * @param expected a class object representing the desired result type {@code T} 475 * @return a reference to the method, constructor, or field object 476 * @throws SecurityException if the caller is not privileged to call {@code setAccessible} 477 * @throws NullPointerException if either argument is {@code null} 478 * @throws IllegalArgumentException if the target is not a direct method handle 479 * @throws ClassCastException if the member is not of the expected type 480 * @since 1.8 481 */ 482 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) { 483 @SuppressWarnings("removal") 484 SecurityManager smgr = System.getSecurityManager(); 485 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION); 486 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup 487 return lookup.revealDirect(target).reflectAs(expected, lookup); 488 } 489 490 /** 491 * A <em>lookup object</em> is a factory for creating method handles, 492 * when the creation requires access checking. 493 * Method handles do not perform 494 * access checks when they are called, but rather when they are created. 495 * Therefore, method handle access 496 * restrictions must be enforced when a method handle is created. 497 * The caller class against which those restrictions are enforced 498 * is known as the {@linkplain #lookupClass() lookup class}. 499 * <p> 500 * A lookup class which needs to create method handles will call 501 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself. 502 * When the {@code Lookup} factory object is created, the identity of the lookup class is 503 * determined, and securely stored in the {@code Lookup} object. 504 * The lookup class (or its delegates) may then use factory methods 505 * on the {@code Lookup} object to create method handles for access-checked members. 506 * This includes all methods, constructors, and fields which are allowed to the lookup class, 507 * even private ones. 508 * 509 * <h2><a id="lookups"></a>Lookup Factory Methods</h2> 510 * The factory methods on a {@code Lookup} object correspond to all major 511 * use cases for methods, constructors, and fields. 512 * Each method handle created by a factory method is the functional 513 * equivalent of a particular <em>bytecode behavior</em>. 514 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of 515 * the Java Virtual Machine Specification.) 516 * Here is a summary of the correspondence between these factory methods and 517 * the behavior of the resulting method handles: 518 * <table class="striped"> 519 * <caption style="display:none">lookup method behaviors</caption> 520 * <thead> 521 * <tr> 522 * <th scope="col"><a id="equiv"></a>lookup expression</th> 523 * <th scope="col">member</th> 524 * <th scope="col">bytecode behavior</th> 525 * </tr> 526 * </thead> 527 * <tbody> 528 * <tr> 529 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th> 530 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td> 531 * </tr> 532 * <tr> 533 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th> 534 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td> 535 * </tr> 536 * <tr> 537 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th> 538 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td> 539 * </tr> 540 * <tr> 541 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th> 542 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td> 543 * </tr> 544 * <tr> 545 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th> 546 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td> 547 * </tr> 548 * <tr> 549 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th> 550 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td> 551 * </tr> 552 * <tr> 553 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th> 554 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 555 * </tr> 556 * <tr> 557 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th> 558 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td> 559 * </tr> 560 * <tr> 561 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th> 562 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td> 563 * </tr> 564 * <tr> 565 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th> 566 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td> 567 * </tr> 568 * <tr> 569 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th> 570 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 571 * </tr> 572 * <tr> 573 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th> 574 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td> 575 * </tr> 576 * <tr> 577 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th> 578 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 579 * </tr> 580 * <tr> 581 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th> 582 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td> 583 * </tr> 584 * </tbody> 585 * </table> 586 * 587 * Here, the type {@code C} is the class or interface being searched for a member, 588 * documented as a parameter named {@code refc} in the lookup methods. 589 * The method type {@code MT} is composed from the return type {@code T} 590 * and the sequence of argument types {@code A*}. 591 * The constructor also has a sequence of argument types {@code A*} and 592 * is deemed to return the newly-created object of type {@code C}. 593 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}. 594 * The formal parameter {@code this} stands for the self-reference of type {@code C}; 595 * if it is present, it is always the leading argument to the method handle invocation. 596 * (In the case of some {@code protected} members, {@code this} may be 597 * restricted in type to the lookup class; see below.) 598 * The name {@code arg} stands for all the other method handle arguments. 599 * In the code examples for the Core Reflection API, the name {@code thisOrNull} 600 * stands for a null reference if the accessed method or field is static, 601 * and {@code this} otherwise. 602 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand 603 * for reflective objects corresponding to the given members declared in type {@code C}. 604 * <p> 605 * The bytecode behavior for a {@code findClass} operation is a load of a constant class, 606 * as if by {@code ldc CONSTANT_Class}. 607 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant. 608 * <p> 609 * In cases where the given member is of variable arity (i.e., a method or constructor) 610 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. 611 * In all other cases, the returned method handle will be of fixed arity. 612 * <p style="font-size:smaller;"> 613 * <em>Discussion:</em> 614 * The equivalence between looked-up method handles and underlying 615 * class members and bytecode behaviors 616 * can break down in a few ways: 617 * <ul style="font-size:smaller;"> 618 * <li>If {@code C} is not symbolically accessible from the lookup class's loader, 619 * the lookup can still succeed, even when there is no equivalent 620 * Java expression or bytecoded constant. 621 * <li>Likewise, if {@code T} or {@code MT} 622 * is not symbolically accessible from the lookup class's loader, 623 * the lookup can still succeed. 624 * For example, lookups for {@code MethodHandle.invokeExact} and 625 * {@code MethodHandle.invoke} will always succeed, regardless of requested type. 626 * <li>If there is a security manager installed, it can forbid the lookup 627 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>). 628 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle} 629 * constant is not subject to security manager checks. 630 * <li>If the looked-up method has a 631 * <a href="MethodHandle.html#maxarity">very large arity</a>, 632 * the method handle creation may fail with an 633 * {@code IllegalArgumentException}, due to the method handle type having 634 * <a href="MethodHandle.html#maxarity">too many parameters.</a> 635 * </ul> 636 * 637 * <h2><a id="access"></a>Access checking</h2> 638 * Access checks are applied in the factory methods of {@code Lookup}, 639 * when a method handle is created. 640 * This is a key difference from the Core Reflection API, since 641 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 642 * performs access checking against every caller, on every call. 643 * <p> 644 * All access checks start from a {@code Lookup} object, which 645 * compares its recorded lookup class against all requests to 646 * create method handles. 647 * A single {@code Lookup} object can be used to create any number 648 * of access-checked method handles, all checked against a single 649 * lookup class. 650 * <p> 651 * A {@code Lookup} object can be shared with other trusted code, 652 * such as a metaobject protocol. 653 * A shared {@code Lookup} object delegates the capability 654 * to create method handles on private members of the lookup class. 655 * Even if privileged code uses the {@code Lookup} object, 656 * the access checking is confined to the privileges of the 657 * original lookup class. 658 * <p> 659 * A lookup can fail, because 660 * the containing class is not accessible to the lookup class, or 661 * because the desired class member is missing, or because the 662 * desired class member is not accessible to the lookup class, or 663 * because the lookup object is not trusted enough to access the member. 664 * In the case of a field setter function on a {@code final} field, 665 * finality enforcement is treated as a kind of access control, 666 * and the lookup will fail, except in special cases of 667 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}. 668 * In any of these cases, a {@code ReflectiveOperationException} will be 669 * thrown from the attempted lookup. The exact class will be one of 670 * the following: 671 * <ul> 672 * <li>NoSuchMethodException — if a method is requested but does not exist 673 * <li>NoSuchFieldException — if a field is requested but does not exist 674 * <li>IllegalAccessException — if the member exists but an access check fails 675 * </ul> 676 * <p> 677 * In general, the conditions under which a method handle may be 678 * looked up for a method {@code M} are no more restrictive than the conditions 679 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}. 680 * Where the JVM would raise exceptions like {@code NoSuchMethodError}, 681 * a method handle lookup will generally raise a corresponding 682 * checked exception, such as {@code NoSuchMethodException}. 683 * And the effect of invoking the method handle resulting from the lookup 684 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a> 685 * to executing the compiled, verified, and resolved call to {@code M}. 686 * The same point is true of fields and constructors. 687 * <p style="font-size:smaller;"> 688 * <em>Discussion:</em> 689 * Access checks only apply to named and reflected methods, 690 * constructors, and fields. 691 * Other method handle creation methods, such as 692 * {@link MethodHandle#asType MethodHandle.asType}, 693 * do not require any access checks, and are used 694 * independently of any {@code Lookup} object. 695 * <p> 696 * If the desired member is {@code protected}, the usual JVM rules apply, 697 * including the requirement that the lookup class must either be in the 698 * same package as the desired member, or must inherit that member. 699 * (See the Java Virtual Machine Specification, sections {@jvms 700 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.) 701 * In addition, if the desired member is a non-static field or method 702 * in a different package, the resulting method handle may only be applied 703 * to objects of the lookup class or one of its subclasses. 704 * This requirement is enforced by narrowing the type of the leading 705 * {@code this} parameter from {@code C} 706 * (which will necessarily be a superclass of the lookup class) 707 * to the lookup class itself. 708 * <p> 709 * The JVM imposes a similar requirement on {@code invokespecial} instruction, 710 * that the receiver argument must match both the resolved method <em>and</em> 711 * the current class. Again, this requirement is enforced by narrowing the 712 * type of the leading parameter to the resulting method handle. 713 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.) 714 * <p> 715 * The JVM represents constructors and static initializer blocks as internal methods 716 * with special names ({@value ConstantDescs#INIT_NAME} and {@value 717 * ConstantDescs#CLASS_INIT_NAME}). 718 * The internal syntax of invocation instructions allows them to refer to such internal 719 * methods as if they were normal methods, but the JVM bytecode verifier rejects them. 720 * A lookup of such an internal method will produce a {@code NoSuchMethodException}. 721 * <p> 722 * If the relationship between nested types is expressed directly through the 723 * {@code NestHost} and {@code NestMembers} attributes 724 * (see the Java Virtual Machine Specification, sections {@jvms 725 * 4.7.28} and {@jvms 4.7.29}), 726 * then the associated {@code Lookup} object provides direct access to 727 * the lookup class and all of its nestmates 728 * (see {@link java.lang.Class#getNestHost Class.getNestHost}). 729 * Otherwise, access between nested classes is obtained by the Java compiler creating 730 * a wrapper method to access a private method of another class in the same nest. 731 * For example, a nested class {@code C.D} 732 * can access private members within other related classes such as 733 * {@code C}, {@code C.D.E}, or {@code C.B}, 734 * but the Java compiler may need to generate wrapper methods in 735 * those related classes. In such cases, a {@code Lookup} object on 736 * {@code C.E} would be unable to access those private members. 737 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, 738 * which can transform a lookup on {@code C.E} into one on any of those other 739 * classes, without special elevation of privilege. 740 * <p> 741 * The accesses permitted to a given lookup object may be limited, 742 * according to its set of {@link #lookupModes lookupModes}, 743 * to a subset of members normally accessible to the lookup class. 744 * For example, the {@link MethodHandles#publicLookup publicLookup} 745 * method produces a lookup object which is only allowed to access 746 * public members in public classes of exported packages. 747 * The caller sensitive method {@link MethodHandles#lookup lookup} 748 * produces a lookup object with full capabilities relative to 749 * its caller class, to emulate all supported bytecode behaviors. 750 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object 751 * with fewer access modes than the original lookup object. 752 * 753 * <p style="font-size:smaller;"> 754 * <a id="privacc"></a> 755 * <em>Discussion of private and module access:</em> 756 * We say that a lookup has <em>private access</em> 757 * if its {@linkplain #lookupModes lookup modes} 758 * include the possibility of accessing {@code private} members 759 * (which includes the private members of nestmates). 760 * As documented in the relevant methods elsewhere, 761 * only lookups with private access possess the following capabilities: 762 * <ul style="font-size:smaller;"> 763 * <li>access private fields, methods, and constructors of the lookup class and its nestmates 764 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions 765 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a> 766 * for classes accessible to the lookup class 767 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes 768 * within the same package member 769 * </ul> 770 * <p style="font-size:smaller;"> 771 * Similarly, a lookup with module access ensures that the original lookup creator was 772 * a member in the same module as the lookup class. 773 * <p style="font-size:smaller;"> 774 * Private and module access are independently determined modes; a lookup may have 775 * either or both or neither. A lookup which possesses both access modes is said to 776 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}. 777 * <p style="font-size:smaller;"> 778 * A lookup with <em>original access</em> ensures that this lookup is created by 779 * the original lookup class and the bootstrap method invoked by the VM. 780 * Such a lookup with original access also has private and module access 781 * which has the following additional capability: 782 * <ul style="font-size:smaller;"> 783 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods, 784 * such as {@code Class.forName} 785 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class) 786 * class data} associated with the lookup class</li> 787 * </ul> 788 * <p style="font-size:smaller;"> 789 * Each of these permissions is a consequence of the fact that a lookup object 790 * with private access can be securely traced back to an originating class, 791 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions 792 * can be reliably determined and emulated by method handles. 793 * 794 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2> 795 * When a lookup class in one module {@code M1} accesses a class in another module 796 * {@code M2}, extra access checking is performed beyond the access mode bits. 797 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1} 798 * can access public types in {@code M2} when {@code M2} is readable to {@code M1} 799 * and when the type is in a package of {@code M2} that is exported to 800 * at least {@code M1}. 801 * <p> 802 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class 803 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup) 804 * MethodHandles.privateLookupIn} methods. 805 * Teleporting across modules will always record the original lookup class as 806 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em> 807 * and drops {@link Lookup#MODULE MODULE} access. 808 * If the target class is in the same module as the lookup class {@code C}, 809 * then the target class becomes the new lookup class 810 * and there is no change to the previous lookup class. 811 * If the target class is in a different module from {@code M1} ({@code C}'s module), 812 * {@code C} becomes the new previous lookup class 813 * and the target class becomes the new lookup class. 814 * In that case, if there was already a previous lookup class in {@code M0}, 815 * and it differs from {@code M1} and {@code M2}, then the resulting lookup 816 * drops all privileges. 817 * For example, 818 * {@snippet lang="java" : 819 * Lookup lookup = MethodHandles.lookup(); // in class C 820 * Lookup lookup2 = lookup.in(D.class); 821 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT); 822 * } 823 * <p> 824 * The {@link #lookup()} factory method produces a {@code Lookup} object 825 * with {@code null} previous lookup class. 826 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C} 827 * to class {@code D} without elevation of privileges. 828 * If {@code C} and {@code D} are in the same module, 829 * {@code lookup2} records {@code D} as the new lookup class and keeps the 830 * same previous lookup class as the original {@code lookup}, or 831 * {@code null} if not present. 832 * <p> 833 * When a {@code Lookup} teleports from a class 834 * in one nest to another nest, {@code PRIVATE} access is dropped. 835 * When a {@code Lookup} teleports from a class in one package to 836 * another package, {@code PACKAGE} access is dropped. 837 * When a {@code Lookup} teleports from a class in one module to another module, 838 * {@code MODULE} access is dropped. 839 * Teleporting across modules drops the ability to access non-exported classes 840 * in both the module of the new lookup class and the module of the old lookup class 841 * and the resulting {@code Lookup} remains only {@code PUBLIC} access. 842 * A {@code Lookup} can teleport back and forth to a class in the module of 843 * the lookup class and the module of the previous class lookup. 844 * Teleporting across modules can only decrease access but cannot increase it. 845 * Teleporting to some third module drops all accesses. 846 * <p> 847 * In the above example, if {@code C} and {@code D} are in different modules, 848 * {@code lookup2} records {@code D} as its lookup class and 849 * {@code C} as its previous lookup class and {@code lookup2} has only 850 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in 851 * {@code C}'s module and {@code D}'s module. 852 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates 853 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup 854 * class {@code D} is recorded as its previous lookup class. 855 * <p> 856 * Teleporting across modules restricts access to the public types that 857 * both the lookup class and the previous lookup class can equally access 858 * (see below). 859 * <p> 860 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)} 861 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T} 862 * and produce a new {@code Lookup} with <a href="#privacc">private access</a> 863 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}. 864 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access 865 * to call {@code privateLookupIn}. 866 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection 867 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn} 868 * produces a new {@code Lookup} on {@code T} with full capabilities. 869 * A {@code lookup} on {@code C} is also allowed 870 * to do deep reflection on {@code T} in another module {@code M2} if 871 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens} 872 * the package containing {@code T} to at least {@code M1}. 873 * {@code T} becomes the new lookup class and {@code C} becomes the new previous 874 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}. 875 * The resulting {@code Lookup} can be used to do member lookup or teleport 876 * to another lookup class by calling {@link #in Lookup::in}. But 877 * it cannot be used to obtain another private {@code Lookup} by calling 878 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn} 879 * because it has no {@code MODULE} access. 880 * <p> 881 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to 882 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package 883 * of {@code T}. Extreme caution should be taken when opening a package 884 * to another module as such defined classes have the same full privilege 885 * access as other members in {@code M2}. 886 * 887 * <h2><a id="module-access-check"></a>Cross-module access checks</h2> 888 * 889 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode 890 * allows cross-module access. The access checking is performed with respect 891 * to both the lookup class and the previous lookup class if present. 892 * <p> 893 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type 894 * in all modules when the type is in a package that is {@linkplain Module#isExported(String) 895 * exported unconditionally}. 896 * <p> 897 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class, 898 * the lookup with {@link #PUBLIC} mode can access all public types in modules 899 * that are readable to {@code M1} and the type is in a package that is exported 900 * at least to {@code M1}. 901 * <p> 902 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class 903 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access 904 * the intersection of all public types that are accessible to {@code M1} 905 * with all public types that are accessible to {@code M0}. {@code M0} 906 * reads {@code M1} and hence the set of accessible types includes: 907 * 908 * <ul> 909 * <li>unconditional-exported packages from {@code M1}</li> 910 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li> 911 * <li> 912 * unconditional-exported packages from a third module {@code M2}if both {@code M0} 913 * and {@code M1} read {@code M2} 914 * </li> 915 * <li>qualified-exported packages from {@code M1} to {@code M0}</li> 916 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li> 917 * <li> 918 * qualified-exported packages from a third module {@code M2} to both {@code M0} and 919 * {@code M1} if both {@code M0} and {@code M1} read {@code M2} 920 * </li> 921 * </ul> 922 * 923 * <h2><a id="access-modes"></a>Access modes</h2> 924 * 925 * The table below shows the access modes of a {@code Lookup} produced by 926 * any of the following factory or transformation methods: 927 * <ul> 928 * <li>{@link #lookup() MethodHandles::lookup}</li> 929 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li> 930 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li> 931 * <li>{@link Lookup#in Lookup::in}</li> 932 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li> 933 * </ul> 934 * 935 * <table class="striped"> 936 * <caption style="display:none"> 937 * Access mode summary 938 * </caption> 939 * <thead> 940 * <tr> 941 * <th scope="col">Lookup object</th> 942 * <th style="text-align:center">original</th> 943 * <th style="text-align:center">protected</th> 944 * <th style="text-align:center">private</th> 945 * <th style="text-align:center">package</th> 946 * <th style="text-align:center">module</th> 947 * <th style="text-align:center">public</th> 948 * </tr> 949 * </thead> 950 * <tbody> 951 * <tr> 952 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th> 953 * <td style="text-align:center">ORI</td> 954 * <td style="text-align:center">PRO</td> 955 * <td style="text-align:center">PRI</td> 956 * <td style="text-align:center">PAC</td> 957 * <td style="text-align:center">MOD</td> 958 * <td style="text-align:center">1R</td> 959 * </tr> 960 * <tr> 961 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th> 962 * <td></td> 963 * <td></td> 964 * <td></td> 965 * <td style="text-align:center">PAC</td> 966 * <td style="text-align:center">MOD</td> 967 * <td style="text-align:center">1R</td> 968 * </tr> 969 * <tr> 970 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th> 971 * <td></td> 972 * <td></td> 973 * <td></td> 974 * <td></td> 975 * <td style="text-align:center">MOD</td> 976 * <td style="text-align:center">1R</td> 977 * </tr> 978 * <tr> 979 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th> 980 * <td></td> 981 * <td></td> 982 * <td></td> 983 * <td></td> 984 * <td></td> 985 * <td style="text-align:center">2R</td> 986 * </tr> 987 * <tr> 988 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th> 989 * <td></td> 990 * <td></td> 991 * <td></td> 992 * <td></td> 993 * <td></td> 994 * <td style="text-align:center">2R</td> 995 * </tr> 996 * <tr> 997 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th> 998 * <td></td> 999 * <td style="text-align:center">PRO</td> 1000 * <td style="text-align:center">PRI</td> 1001 * <td style="text-align:center">PAC</td> 1002 * <td style="text-align:center">MOD</td> 1003 * <td style="text-align:center">1R</td> 1004 * </tr> 1005 * <tr> 1006 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th> 1007 * <td></td> 1008 * <td style="text-align:center">PRO</td> 1009 * <td style="text-align:center">PRI</td> 1010 * <td style="text-align:center">PAC</td> 1011 * <td style="text-align:center">MOD</td> 1012 * <td style="text-align:center">1R</td> 1013 * </tr> 1014 * <tr> 1015 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th> 1016 * <td></td> 1017 * <td></td> 1018 * <td></td> 1019 * <td style="text-align:center">PAC</td> 1020 * <td style="text-align:center">MOD</td> 1021 * <td style="text-align:center">1R</td> 1022 * </tr> 1023 * <tr> 1024 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th> 1025 * <td></td> 1026 * <td></td> 1027 * <td></td> 1028 * <td></td> 1029 * <td style="text-align:center">MOD</td> 1030 * <td style="text-align:center">1R</td> 1031 * </tr> 1032 * <tr> 1033 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th> 1034 * <td></td> 1035 * <td></td> 1036 * <td></td> 1037 * <td></td> 1038 * <td></td> 1039 * <td style="text-align:center">2R</td> 1040 * </tr> 1041 * <tr> 1042 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th> 1043 * <td></td> 1044 * <td></td> 1045 * <td style="text-align:center">PRI</td> 1046 * <td style="text-align:center">PAC</td> 1047 * <td style="text-align:center">MOD</td> 1048 * <td style="text-align:center">1R</td> 1049 * </tr> 1050 * <tr> 1051 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th> 1052 * <td></td> 1053 * <td></td> 1054 * <td></td> 1055 * <td style="text-align:center">PAC</td> 1056 * <td style="text-align:center">MOD</td> 1057 * <td style="text-align:center">1R</td> 1058 * </tr> 1059 * <tr> 1060 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th> 1061 * <td></td> 1062 * <td></td> 1063 * <td></td> 1064 * <td></td> 1065 * <td style="text-align:center">MOD</td> 1066 * <td style="text-align:center">1R</td> 1067 * </tr> 1068 * <tr> 1069 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th> 1070 * <td></td> 1071 * <td></td> 1072 * <td></td> 1073 * <td></td> 1074 * <td></td> 1075 * <td style="text-align:center">1R</td> 1076 * </tr> 1077 * <tr> 1078 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th> 1079 * <td></td> 1080 * <td></td> 1081 * <td></td> 1082 * <td></td> 1083 * <td></td> 1084 * <td style="text-align:center">none</td> 1085 * <tr> 1086 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th> 1087 * <td></td> 1088 * <td style="text-align:center">PRO</td> 1089 * <td style="text-align:center">PRI</td> 1090 * <td style="text-align:center">PAC</td> 1091 * <td></td> 1092 * <td style="text-align:center">2R</td> 1093 * </tr> 1094 * <tr> 1095 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th> 1096 * <td></td> 1097 * <td style="text-align:center">PRO</td> 1098 * <td style="text-align:center">PRI</td> 1099 * <td style="text-align:center">PAC</td> 1100 * <td></td> 1101 * <td style="text-align:center">2R</td> 1102 * </tr> 1103 * <tr> 1104 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th> 1105 * <td></td> 1106 * <td></td> 1107 * <td></td> 1108 * <td></td> 1109 * <td></td> 1110 * <td style="text-align:center">IAE</td> 1111 * </tr> 1112 * <tr> 1113 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th> 1114 * <td></td> 1115 * <td></td> 1116 * <td></td> 1117 * <td style="text-align:center">PAC</td> 1118 * <td></td> 1119 * <td style="text-align:center">2R</td> 1120 * </tr> 1121 * <tr> 1122 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th> 1123 * <td></td> 1124 * <td></td> 1125 * <td></td> 1126 * <td></td> 1127 * <td></td> 1128 * <td style="text-align:center">2R</td> 1129 * </tr> 1130 * <tr> 1131 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th> 1132 * <td></td> 1133 * <td></td> 1134 * <td></td> 1135 * <td></td> 1136 * <td></td> 1137 * <td style="text-align:center">2R</td> 1138 * </tr> 1139 * <tr> 1140 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th> 1141 * <td></td> 1142 * <td></td> 1143 * <td></td> 1144 * <td></td> 1145 * <td></td> 1146 * <td style="text-align:center">none</td> 1147 * </tr> 1148 * <tr> 1149 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th> 1150 * <td></td> 1151 * <td></td> 1152 * <td style="text-align:center">PRI</td> 1153 * <td style="text-align:center">PAC</td> 1154 * <td></td> 1155 * <td style="text-align:center">2R</td> 1156 * </tr> 1157 * <tr> 1158 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th> 1159 * <td></td> 1160 * <td></td> 1161 * <td></td> 1162 * <td style="text-align:center">PAC</td> 1163 * <td></td> 1164 * <td style="text-align:center">2R</td> 1165 * </tr> 1166 * <tr> 1167 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th> 1168 * <td></td> 1169 * <td></td> 1170 * <td></td> 1171 * <td></td> 1172 * <td></td> 1173 * <td style="text-align:center">2R</td> 1174 * </tr> 1175 * <tr> 1176 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th> 1177 * <td></td> 1178 * <td></td> 1179 * <td></td> 1180 * <td></td> 1181 * <td></td> 1182 * <td style="text-align:center">2R</td> 1183 * </tr> 1184 * <tr> 1185 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th> 1186 * <td></td> 1187 * <td></td> 1188 * <td></td> 1189 * <td></td> 1190 * <td></td> 1191 * <td style="text-align:center">none</td> 1192 * </tr> 1193 * <tr> 1194 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th> 1195 * <td></td> 1196 * <td></td> 1197 * <td style="text-align:center">PRI</td> 1198 * <td style="text-align:center">PAC</td> 1199 * <td style="text-align:center">MOD</td> 1200 * <td style="text-align:center">1R</td> 1201 * </tr> 1202 * <tr> 1203 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th> 1204 * <td></td> 1205 * <td></td> 1206 * <td></td> 1207 * <td style="text-align:center">PAC</td> 1208 * <td style="text-align:center">MOD</td> 1209 * <td style="text-align:center">1R</td> 1210 * </tr> 1211 * <tr> 1212 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th> 1213 * <td></td> 1214 * <td></td> 1215 * <td></td> 1216 * <td></td> 1217 * <td style="text-align:center">MOD</td> 1218 * <td style="text-align:center">1R</td> 1219 * </tr> 1220 * <tr> 1221 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th> 1222 * <td></td> 1223 * <td></td> 1224 * <td></td> 1225 * <td></td> 1226 * <td></td> 1227 * <td style="text-align:center">1R</td> 1228 * </tr> 1229 * <tr> 1230 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th> 1231 * <td></td> 1232 * <td></td> 1233 * <td></td> 1234 * <td></td> 1235 * <td></td> 1236 * <td style="text-align:center">none</td> 1237 * </tr> 1238 * <tr> 1239 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th> 1240 * <td></td> 1241 * <td></td> 1242 * <td></td> 1243 * <td></td> 1244 * <td></td> 1245 * <td style="text-align:center">U</td> 1246 * </tr> 1247 * <tr> 1248 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th> 1249 * <td></td> 1250 * <td></td> 1251 * <td></td> 1252 * <td></td> 1253 * <td></td> 1254 * <td style="text-align:center">U</td> 1255 * </tr> 1256 * <tr> 1257 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th> 1258 * <td></td> 1259 * <td></td> 1260 * <td></td> 1261 * <td></td> 1262 * <td></td> 1263 * <td style="text-align:center">U</td> 1264 * </tr> 1265 * <tr> 1266 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th> 1267 * <td></td> 1268 * <td></td> 1269 * <td></td> 1270 * <td></td> 1271 * <td></td> 1272 * <td style="text-align:center">none</td> 1273 * </tr> 1274 * <tr> 1275 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th> 1276 * <td></td> 1277 * <td></td> 1278 * <td></td> 1279 * <td></td> 1280 * <td></td> 1281 * <td style="text-align:center">IAE</td> 1282 * </tr> 1283 * <tr> 1284 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th> 1285 * <td></td> 1286 * <td></td> 1287 * <td></td> 1288 * <td></td> 1289 * <td></td> 1290 * <td style="text-align:center">none</td> 1291 * </tr> 1292 * </tbody> 1293 * </table> 1294 * 1295 * <p> 1296 * Notes: 1297 * <ul> 1298 * <li>Class {@code C} and class {@code C1} are in module {@code M1}, 1299 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E} 1300 * is in module {@code M3}. {@code X} stands for class which is inaccessible 1301 * to the lookup. {@code ANY} stands for any of the example lookups.</li> 1302 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set, 1303 * {@code PRO} indicates {@link #PROTECTED} bit set, 1304 * {@code PRI} indicates {@link #PRIVATE} bit set, 1305 * {@code PAC} indicates {@link #PACKAGE} bit set, 1306 * {@code MOD} indicates {@link #MODULE} bit set, 1307 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set, 1308 * {@code U} indicates {@link #UNCONDITIONAL} bit set, 1309 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li> 1310 * <li>Public access comes in three kinds: 1311 * <ul> 1312 * <li>unconditional ({@code U}): the lookup assumes readability. 1313 * The lookup has {@code null} previous lookup class. 1314 * <li>one-module-reads ({@code 1R}): the module access checking is 1315 * performed with respect to the lookup class. The lookup has {@code null} 1316 * previous lookup class. 1317 * <li>two-module-reads ({@code 2R}): the module access checking is 1318 * performed with respect to the lookup class and the previous lookup class. 1319 * The lookup has a non-null previous lookup class which is in a 1320 * different module from the current lookup class. 1321 * </ul> 1322 * <li>Any attempt to reach a third module loses all access.</li> 1323 * <li>If a target class {@code X} is not accessible to {@code Lookup::in} 1324 * all access modes are dropped.</li> 1325 * </ul> 1326 * 1327 * <h2><a id="secmgr"></a>Security manager interactions</h2> 1328 * Although bytecode instructions can only refer to classes in 1329 * a related class loader, this API can search for methods in any 1330 * class, as long as a reference to its {@code Class} object is 1331 * available. Such cross-loader references are also possible with the 1332 * Core Reflection API, and are impossible to bytecode instructions 1333 * such as {@code invokestatic} or {@code getfield}. 1334 * There is a {@linkplain java.lang.SecurityManager security manager API} 1335 * to allow applications to check such cross-loader references. 1336 * These checks apply to both the {@code MethodHandles.Lookup} API 1337 * and the Core Reflection API 1338 * (as found on {@link java.lang.Class Class}). 1339 * <p> 1340 * If a security manager is present, member and class lookups are subject to 1341 * additional checks. 1342 * From one to three calls are made to the security manager. 1343 * Any of these calls can refuse access by throwing a 1344 * {@link java.lang.SecurityException SecurityException}. 1345 * Define {@code smgr} as the security manager, 1346 * {@code lookc} as the lookup class of the current lookup object, 1347 * {@code refc} as the containing class in which the member 1348 * is being sought, and {@code defc} as the class in which the 1349 * member is actually defined. 1350 * (If a class or other type is being accessed, 1351 * the {@code refc} and {@code defc} values are the class itself.) 1352 * The value {@code lookc} is defined as <em>not present</em> 1353 * if the current lookup object does not have 1354 * {@linkplain #hasFullPrivilegeAccess() full privilege access}. 1355 * The calls are made according to the following rules: 1356 * <ul> 1357 * <li><b>Step 1:</b> 1358 * If {@code lookc} is not present, or if its class loader is not 1359 * the same as or an ancestor of the class loader of {@code refc}, 1360 * then {@link SecurityManager#checkPackageAccess 1361 * smgr.checkPackageAccess(refcPkg)} is called, 1362 * where {@code refcPkg} is the package of {@code refc}. 1363 * <li><b>Step 2a:</b> 1364 * If the retrieved member is not public and 1365 * {@code lookc} is not present, then 1366 * {@link SecurityManager#checkPermission smgr.checkPermission} 1367 * with {@code RuntimePermission("accessDeclaredMembers")} is called. 1368 * <li><b>Step 2b:</b> 1369 * If the retrieved class has a {@code null} class loader, 1370 * and {@code lookc} is not present, then 1371 * {@link SecurityManager#checkPermission smgr.checkPermission} 1372 * with {@code RuntimePermission("getClassLoader")} is called. 1373 * <li><b>Step 3:</b> 1374 * If the retrieved member is not public, 1375 * and if {@code lookc} is not present, 1376 * and if {@code defc} and {@code refc} are different, 1377 * then {@link SecurityManager#checkPackageAccess 1378 * smgr.checkPackageAccess(defcPkg)} is called, 1379 * where {@code defcPkg} is the package of {@code defc}. 1380 * </ul> 1381 * Security checks are performed after other access checks have passed. 1382 * Therefore, the above rules presuppose a member or class that is public, 1383 * or else that is being accessed from a lookup class that has 1384 * rights to access the member or class. 1385 * <p> 1386 * If a security manager is present and the current lookup object does not have 1387 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then 1388 * {@link #defineClass(byte[]) defineClass}, 1389 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass}, 1390 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...) 1391 * defineHiddenClassWithClassData} 1392 * calls {@link SecurityManager#checkPermission smgr.checkPermission} 1393 * with {@code RuntimePermission("defineClass")}. 1394 * 1395 * <h2><a id="callsens"></a>Caller sensitive methods</h2> 1396 * A small number of Java methods have a special property called caller sensitivity. 1397 * A <em>caller-sensitive</em> method can behave differently depending on the 1398 * identity of its immediate caller. 1399 * <p> 1400 * If a method handle for a caller-sensitive method is requested, 1401 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply, 1402 * but they take account of the lookup class in a special way. 1403 * The resulting method handle behaves as if it were called 1404 * from an instruction contained in the lookup class, 1405 * so that the caller-sensitive method detects the lookup class. 1406 * (By contrast, the invoker of the method handle is disregarded.) 1407 * Thus, in the case of caller-sensitive methods, 1408 * different lookup classes may give rise to 1409 * differently behaving method handles. 1410 * <p> 1411 * In cases where the lookup object is 1412 * {@link MethodHandles#publicLookup() publicLookup()}, 1413 * or some other lookup object without the 1414 * {@linkplain #ORIGINAL original access}, 1415 * the lookup class is disregarded. 1416 * In such cases, no caller-sensitive method handle can be created, 1417 * access is forbidden, and the lookup fails with an 1418 * {@code IllegalAccessException}. 1419 * <p style="font-size:smaller;"> 1420 * <em>Discussion:</em> 1421 * For example, the caller-sensitive method 1422 * {@link java.lang.Class#forName(String) Class.forName(x)} 1423 * can return varying classes or throw varying exceptions, 1424 * depending on the class loader of the class that calls it. 1425 * A public lookup of {@code Class.forName} will fail, because 1426 * there is no reasonable way to determine its bytecode behavior. 1427 * <p style="font-size:smaller;"> 1428 * If an application caches method handles for broad sharing, 1429 * it should use {@code publicLookup()} to create them. 1430 * If there is a lookup of {@code Class.forName}, it will fail, 1431 * and the application must take appropriate action in that case. 1432 * It may be that a later lookup, perhaps during the invocation of a 1433 * bootstrap method, can incorporate the specific identity 1434 * of the caller, making the method accessible. 1435 * <p style="font-size:smaller;"> 1436 * The function {@code MethodHandles.lookup} is caller sensitive 1437 * so that there can be a secure foundation for lookups. 1438 * Nearly all other methods in the JSR 292 API rely on lookup 1439 * objects to check access requests. 1440 * 1441 * @revised 9 1442 */ 1443 public static final 1444 class Lookup { 1445 /** The class on behalf of whom the lookup is being performed. */ 1446 private final Class<?> lookupClass; 1447 1448 /** previous lookup class */ 1449 private final Class<?> prevLookupClass; 1450 1451 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */ 1452 private final int allowedModes; 1453 1454 static { 1455 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes")); 1456 } 1457 1458 /** A single-bit mask representing {@code public} access, 1459 * which may contribute to the result of {@link #lookupModes lookupModes}. 1460 * The value, {@code 0x01}, happens to be the same as the value of the 1461 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}. 1462 * <p> 1463 * A {@code Lookup} with this lookup mode performs cross-module access check 1464 * with respect to the {@linkplain #lookupClass() lookup class} and 1465 * {@linkplain #previousLookupClass() previous lookup class} if present. 1466 */ 1467 public static final int PUBLIC = Modifier.PUBLIC; 1468 1469 /** A single-bit mask representing {@code private} access, 1470 * which may contribute to the result of {@link #lookupModes lookupModes}. 1471 * The value, {@code 0x02}, happens to be the same as the value of the 1472 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}. 1473 */ 1474 public static final int PRIVATE = Modifier.PRIVATE; 1475 1476 /** A single-bit mask representing {@code protected} access, 1477 * which may contribute to the result of {@link #lookupModes lookupModes}. 1478 * The value, {@code 0x04}, happens to be the same as the value of the 1479 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}. 1480 */ 1481 public static final int PROTECTED = Modifier.PROTECTED; 1482 1483 /** A single-bit mask representing {@code package} access (default access), 1484 * which may contribute to the result of {@link #lookupModes lookupModes}. 1485 * The value is {@code 0x08}, which does not correspond meaningfully to 1486 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1487 */ 1488 public static final int PACKAGE = Modifier.STATIC; 1489 1490 /** A single-bit mask representing {@code module} access, 1491 * which may contribute to the result of {@link #lookupModes lookupModes}. 1492 * The value is {@code 0x10}, which does not correspond meaningfully to 1493 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1494 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup} 1495 * with this lookup mode can access all public types in the module of the 1496 * lookup class and public types in packages exported by other modules 1497 * to the module of the lookup class. 1498 * <p> 1499 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1500 * previous lookup class} is always {@code null}. 1501 * 1502 * @since 9 1503 */ 1504 public static final int MODULE = PACKAGE << 1; 1505 1506 /** A single-bit mask representing {@code unconditional} access 1507 * which may contribute to the result of {@link #lookupModes lookupModes}. 1508 * The value is {@code 0x20}, which does not correspond meaningfully to 1509 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1510 * A {@code Lookup} with this lookup mode assumes {@linkplain 1511 * java.lang.Module#canRead(java.lang.Module) readability}. 1512 * This lookup mode can access all public members of public types 1513 * of all modules when the type is in a package that is {@link 1514 * java.lang.Module#isExported(String) exported unconditionally}. 1515 * 1516 * <p> 1517 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1518 * previous lookup class} is always {@code null}. 1519 * 1520 * @since 9 1521 * @see #publicLookup() 1522 */ 1523 public static final int UNCONDITIONAL = PACKAGE << 2; 1524 1525 /** A single-bit mask representing {@code original} access 1526 * which may contribute to the result of {@link #lookupModes lookupModes}. 1527 * The value is {@code 0x40}, which does not correspond meaningfully to 1528 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1529 * 1530 * <p> 1531 * If this lookup mode is set, the {@code Lookup} object must be 1532 * created by the original lookup class by calling 1533 * {@link MethodHandles#lookup()} method or by a bootstrap method 1534 * invoked by the VM. The {@code Lookup} object with this lookup 1535 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}. 1536 * 1537 * @since 16 1538 */ 1539 public static final int ORIGINAL = PACKAGE << 3; 1540 1541 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL); 1542 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access 1543 private static final int TRUSTED = -1; 1544 1545 /* 1546 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL 1547 * Adjust 0 => PACKAGE 1548 */ 1549 private static int fixmods(int mods) { 1550 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL); 1551 if (Modifier.isPublic(mods)) 1552 mods |= UNCONDITIONAL; 1553 return (mods != 0) ? mods : PACKAGE; 1554 } 1555 1556 /** Tells which class is performing the lookup. It is this class against 1557 * which checks are performed for visibility and access permissions. 1558 * <p> 1559 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class}, 1560 * access checks are performed against both the lookup class and the previous lookup class. 1561 * <p> 1562 * The class implies a maximum level of access permission, 1563 * but the permissions may be additionally limited by the bitmask 1564 * {@link #lookupModes lookupModes}, which controls whether non-public members 1565 * can be accessed. 1566 * @return the lookup class, on behalf of which this lookup object finds members 1567 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1568 */ 1569 public Class<?> lookupClass() { 1570 return lookupClass; 1571 } 1572 1573 /** Reports a lookup class in another module that this lookup object 1574 * was previously teleported from, or {@code null}. 1575 * <p> 1576 * A {@code Lookup} object produced by the factory methods, such as the 1577 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method, 1578 * has {@code null} previous lookup class. 1579 * A {@code Lookup} object has a non-null previous lookup class 1580 * when this lookup was teleported from an old lookup class 1581 * in one module to a new lookup class in another module. 1582 * 1583 * @return the lookup class in another module that this lookup object was 1584 * previously teleported from, or {@code null} 1585 * @since 14 1586 * @see #in(Class) 1587 * @see MethodHandles#privateLookupIn(Class, Lookup) 1588 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1589 */ 1590 public Class<?> previousLookupClass() { 1591 return prevLookupClass; 1592 } 1593 1594 // This is just for calling out to MethodHandleImpl. 1595 private Class<?> lookupClassOrNull() { 1596 return (allowedModes == TRUSTED) ? null : lookupClass; 1597 } 1598 1599 /** Tells which access-protection classes of members this lookup object can produce. 1600 * The result is a bit-mask of the bits 1601 * {@linkplain #PUBLIC PUBLIC (0x01)}, 1602 * {@linkplain #PRIVATE PRIVATE (0x02)}, 1603 * {@linkplain #PROTECTED PROTECTED (0x04)}, 1604 * {@linkplain #PACKAGE PACKAGE (0x08)}, 1605 * {@linkplain #MODULE MODULE (0x10)}, 1606 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}, 1607 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}. 1608 * <p> 1609 * A freshly-created lookup object 1610 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has 1611 * all possible bits set, except {@code UNCONDITIONAL}. 1612 * A lookup object on a new lookup class 1613 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} 1614 * may have some mode bits set to zero. 1615 * Mode bits can also be 1616 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}. 1617 * Once cleared, mode bits cannot be restored from the downgraded lookup object. 1618 * The purpose of this is to restrict access via the new lookup object, 1619 * so that it can access only names which can be reached by the original 1620 * lookup object, and also by the new lookup class. 1621 * @return the lookup modes, which limit the kinds of access performed by this lookup object 1622 * @see #in 1623 * @see #dropLookupMode 1624 * 1625 * @revised 9 1626 */ 1627 public int lookupModes() { 1628 return allowedModes & ALL_MODES; 1629 } 1630 1631 /** Embody the current class (the lookupClass) as a lookup class 1632 * for method handle creation. 1633 * Must be called by from a method in this package, 1634 * which in turn is called by a method not in this package. 1635 */ 1636 Lookup(Class<?> lookupClass) { 1637 this(lookupClass, null, FULL_POWER_MODES); 1638 } 1639 1640 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1641 assert prevLookupClass == null || ((allowedModes & MODULE) == 0 1642 && prevLookupClass.getModule() != lookupClass.getModule()); 1643 assert !lookupClass.isArray() && !lookupClass.isPrimitive(); 1644 this.lookupClass = lookupClass; 1645 this.prevLookupClass = prevLookupClass; 1646 this.allowedModes = allowedModes; 1647 } 1648 1649 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1650 // make sure we haven't accidentally picked up a privileged class: 1651 checkUnprivilegedlookupClass(lookupClass); 1652 return new Lookup(lookupClass, prevLookupClass, allowedModes); 1653 } 1654 1655 /** 1656 * Creates a lookup on the specified new lookup class. 1657 * The resulting object will report the specified 1658 * class as its own {@link #lookupClass() lookupClass}. 1659 * 1660 * <p> 1661 * However, the resulting {@code Lookup} object is guaranteed 1662 * to have no more access capabilities than the original. 1663 * In particular, access capabilities can be lost as follows:<ul> 1664 * <li>If the new lookup class is different from the old lookup class, 1665 * i.e. {@link #ORIGINAL ORIGINAL} access is lost. 1666 * <li>If the new lookup class is in a different module from the old one, 1667 * i.e. {@link #MODULE MODULE} access is lost. 1668 * <li>If the new lookup class is in a different package 1669 * than the old one, protected and default (package) members will not be accessible, 1670 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost. 1671 * <li>If the new lookup class is not within the same package member 1672 * as the old one, private members will not be accessible, and protected members 1673 * will not be accessible by virtue of inheritance, 1674 * i.e. {@link #PRIVATE PRIVATE} access is lost. 1675 * (Protected members may continue to be accessible because of package sharing.) 1676 * <li>If the new lookup class is not 1677 * {@linkplain #accessClass(Class) accessible} to this lookup, 1678 * then no members, not even public members, will be accessible 1679 * i.e. all access modes are lost. 1680 * <li>If the new lookup class, the old lookup class and the previous lookup class 1681 * are all in different modules i.e. teleporting to a third module, 1682 * all access modes are lost. 1683 * </ul> 1684 * <p> 1685 * The new previous lookup class is chosen as follows: 1686 * <ul> 1687 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit, 1688 * the new previous lookup class is {@code null}. 1689 * <li>If the new lookup class is in the same module as the old lookup class, 1690 * the new previous lookup class is the old previous lookup class. 1691 * <li>If the new lookup class is in a different module from the old lookup class, 1692 * the new previous lookup class is the old lookup class. 1693 *</ul> 1694 * <p> 1695 * The resulting lookup's capabilities for loading classes 1696 * (used during {@link #findClass} invocations) 1697 * are determined by the lookup class' loader, 1698 * which may change due to this operation. 1699 * 1700 * @param requestedLookupClass the desired lookup class for the new lookup object 1701 * @return a lookup object which reports the desired lookup class, or the same object 1702 * if there is no change 1703 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class 1704 * @throws NullPointerException if the argument is null 1705 * 1706 * @revised 9 1707 * @see #accessClass(Class) 1708 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1709 */ 1710 public Lookup in(Class<?> requestedLookupClass) { 1711 Objects.requireNonNull(requestedLookupClass); 1712 if (requestedLookupClass.isPrimitive()) 1713 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class"); 1714 if (requestedLookupClass.isArray()) 1715 throw new IllegalArgumentException(requestedLookupClass + " is an array class"); 1716 1717 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all 1718 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES); 1719 if (requestedLookupClass == this.lookupClass) 1720 return this; // keep same capabilities 1721 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL; 1722 Module fromModule = this.lookupClass.getModule(); 1723 Module targetModule = requestedLookupClass.getModule(); 1724 Class<?> plc = this.previousLookupClass(); 1725 if ((this.allowedModes & UNCONDITIONAL) != 0) { 1726 assert plc == null; 1727 newModes = UNCONDITIONAL; 1728 } else if (fromModule != targetModule) { 1729 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) { 1730 // allow hopping back and forth between fromModule and plc's module 1731 // but not the third module 1732 newModes = 0; 1733 } 1734 // drop MODULE access 1735 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED); 1736 // teleport from this lookup class 1737 plc = this.lookupClass; 1738 } 1739 if ((newModes & PACKAGE) != 0 1740 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) { 1741 newModes &= ~(PACKAGE|PRIVATE|PROTECTED); 1742 } 1743 // Allow nestmate lookups to be created without special privilege: 1744 if ((newModes & PRIVATE) != 0 1745 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) { 1746 newModes &= ~(PRIVATE|PROTECTED); 1747 } 1748 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0 1749 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) { 1750 // The requested class it not accessible from the lookup class. 1751 // No permissions. 1752 newModes = 0; 1753 } 1754 return newLookup(requestedLookupClass, plc, newModes); 1755 } 1756 1757 /** 1758 * Creates a lookup on the same lookup class which this lookup object 1759 * finds members, but with a lookup mode that has lost the given lookup mode. 1760 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE 1761 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED}, 1762 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or 1763 * {@link #UNCONDITIONAL UNCONDITIONAL}. 1764 * 1765 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup}, 1766 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set. 1767 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting 1768 * lookup has no access. 1769 * 1770 * <p> If this lookup is not a public lookup, then the following applies 1771 * regardless of its {@linkplain #lookupModes() lookup modes}. 1772 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always 1773 * dropped and so the resulting lookup mode will never have these access 1774 * capabilities. When dropping {@code PACKAGE} 1775 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE} 1776 * access. When dropping {@code MODULE} then the resulting lookup will not 1777 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. 1778 * When dropping {@code PUBLIC} then the resulting lookup has no access. 1779 * 1780 * @apiNote 1781 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely 1782 * delegate non-public access within the package of the lookup class without 1783 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>. 1784 * A lookup with {@code MODULE} but not 1785 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within 1786 * the module of the lookup class without conferring package access. 1787 * A lookup with a {@linkplain #previousLookupClass() previous lookup class} 1788 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access 1789 * to public classes accessible to both the module of the lookup class 1790 * and the module of the previous lookup class. 1791 * 1792 * @param modeToDrop the lookup mode to drop 1793 * @return a lookup object which lacks the indicated mode, or the same object if there is no change 1794 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC}, 1795 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL} 1796 * or {@code UNCONDITIONAL} 1797 * @see MethodHandles#privateLookupIn 1798 * @since 9 1799 */ 1800 public Lookup dropLookupMode(int modeToDrop) { 1801 int oldModes = lookupModes(); 1802 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL); 1803 switch (modeToDrop) { 1804 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break; 1805 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break; 1806 case PACKAGE: newModes &= ~(PRIVATE); break; 1807 case PROTECTED: 1808 case PRIVATE: 1809 case ORIGINAL: 1810 case UNCONDITIONAL: break; 1811 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop"); 1812 } 1813 if (newModes == oldModes) return this; // return self if no change 1814 return newLookup(lookupClass(), previousLookupClass(), newModes); 1815 } 1816 1817 /** 1818 * Creates and links a class or interface from {@code bytes} 1819 * with the same class loader and in the same runtime package and 1820 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's 1821 * {@linkplain #lookupClass() lookup class} as if calling 1822 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 1823 * ClassLoader::defineClass}. 1824 * 1825 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include 1826 * {@link #PACKAGE PACKAGE} access as default (package) members will be 1827 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate 1828 * that the lookup object was created by a caller in the runtime package (or derived 1829 * from a lookup originally created by suitably privileged code to a target class in 1830 * the runtime package). </p> 1831 * 1832 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined 1833 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the 1834 * same package as the lookup class. </p> 1835 * 1836 * <p> This method does not run the class initializer. The class initializer may 1837 * run at a later time, as detailed in section 12.4 of the <em>The Java Language 1838 * Specification</em>. </p> 1839 * 1840 * <p> If there is a security manager and this lookup does not have {@linkplain 1841 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method 1842 * is first called to check {@code RuntimePermission("defineClass")}. </p> 1843 * 1844 * @param bytes the class bytes 1845 * @return the {@code Class} object for the class 1846 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access 1847 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 1848 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 1849 * than the lookup class or {@code bytes} is not a class or interface 1850 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 1851 * @throws VerifyError if the newly created class cannot be verified 1852 * @throws LinkageError if the newly created class cannot be linked for any other reason 1853 * @throws SecurityException if a security manager is present and it 1854 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1855 * @throws NullPointerException if {@code bytes} is {@code null} 1856 * @since 9 1857 * @see Lookup#privateLookupIn 1858 * @see Lookup#dropLookupMode 1859 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 1860 */ 1861 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException { 1862 ensureDefineClassPermission(); 1863 if ((lookupModes() & PACKAGE) == 0) 1864 throw new IllegalAccessException("Lookup does not have PACKAGE access"); 1865 return makeClassDefiner(bytes.clone()).defineClass(false); 1866 } 1867 1868 private void ensureDefineClassPermission() { 1869 if (allowedModes == TRUSTED) return; 1870 1871 if (!hasFullPrivilegeAccess()) { 1872 @SuppressWarnings("removal") 1873 SecurityManager sm = System.getSecurityManager(); 1874 if (sm != null) 1875 sm.checkPermission(new RuntimePermission("defineClass")); 1876 } 1877 } 1878 1879 /** 1880 * The set of class options that specify whether a hidden class created by 1881 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...) 1882 * Lookup::defineHiddenClass} method is dynamically added as a new member 1883 * to the nest of a lookup class and/or whether a hidden class has 1884 * a strong relationship with the class loader marked as its defining loader. 1885 * 1886 * @since 15 1887 */ 1888 public enum ClassOption { 1889 /** 1890 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest} 1891 * of a lookup class as a nestmate. 1892 * 1893 * <p> A hidden nestmate class has access to the private members of all 1894 * classes and interfaces in the same nest. 1895 * 1896 * @see Class#getNestHost() 1897 */ 1898 NESTMATE(NESTMATE_CLASS), 1899 1900 /** 1901 * Specifies that a hidden class has a <em>strong</em> 1902 * relationship with the class loader marked as its defining loader, 1903 * as a normal class or interface has with its own defining loader. 1904 * This means that the hidden class may be unloaded if and only if 1905 * its defining loader is not reachable and thus may be reclaimed 1906 * by a garbage collector (JLS {@jls 12.7}). 1907 * 1908 * <p> By default, a hidden class or interface may be unloaded 1909 * even if the class loader that is marked as its defining loader is 1910 * <a href="../ref/package-summary.html#reachability">reachable</a>. 1911 1912 * 1913 * @jls 12.7 Unloading of Classes and Interfaces 1914 */ 1915 STRONG(STRONG_LOADER_LINK); 1916 1917 /* the flag value is used by VM at define class time */ 1918 private final int flag; 1919 ClassOption(int flag) { 1920 this.flag = flag; 1921 } 1922 1923 static int optionsToFlag(Set<ClassOption> options) { 1924 int flags = 0; 1925 for (ClassOption cp : options) { 1926 flags |= cp.flag; 1927 } 1928 return flags; 1929 } 1930 } 1931 1932 /** 1933 * Creates a <em>hidden</em> class or interface from {@code bytes}, 1934 * returning a {@code Lookup} on the newly created class or interface. 1935 * 1936 * <p> Ordinarily, a class or interface {@code C} is created by a class loader, 1937 * which either defines {@code C} directly or delegates to another class loader. 1938 * A class loader defines {@code C} directly by invoking 1939 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain) 1940 * ClassLoader::defineClass}, which causes the Java Virtual Machine 1941 * to derive {@code C} from a purported representation in {@code class} file format. 1942 * In situations where use of a class loader is undesirable, a class or interface 1943 * {@code C} can be created by this method instead. This method is capable of 1944 * defining {@code C}, and thereby creating it, without invoking 1945 * {@code ClassLoader::defineClass}. 1946 * Instead, this method defines {@code C} as if by arranging for 1947 * the Java Virtual Machine to derive a nonarray class or interface {@code C} 1948 * from a purported representation in {@code class} file format 1949 * using the following rules: 1950 * 1951 * <ol> 1952 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup} 1953 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access. 1954 * This level of access is needed to create {@code C} in the module 1955 * of the lookup class of this {@code Lookup}.</li> 1956 * 1957 * <li> The purported representation in {@code bytes} must be a {@code ClassFile} 1958 * structure (JVMS {@jvms 4.1}) of a supported major and minor version. 1959 * The major and minor version may differ from the {@code class} file version 1960 * of the lookup class of this {@code Lookup}.</li> 1961 * 1962 * <li> The value of {@code this_class} must be a valid index in the 1963 * {@code constant_pool} table, and the entry at that index must be a valid 1964 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name 1965 * encoded in internal form that is specified by this structure. {@code N} must 1966 * denote a class or interface in the same package as the lookup class.</li> 1967 * 1968 * <li> Let {@code CN} be the string {@code N + "." + <suffix>}, 1969 * where {@code <suffix>} is an unqualified name. 1970 * 1971 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by 1972 * {@code bytes} with an additional entry in the {@code constant_pool} table, 1973 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and 1974 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class} 1975 * refers to the new {@code CONSTANT_Utf8_info} structure. 1976 * 1977 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}. 1978 * 1979 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and 1980 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5}, 1981 * with the following adjustments: 1982 * <ul> 1983 * <li> The constant indicated by {@code this_class} is permitted to specify a name 1984 * that includes a single {@code "."} character, even though this is not a valid 1985 * binary class or interface name in internal form.</li> 1986 * 1987 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C}, 1988 * but no class loader is recorded as an initiating class loader of {@code C}.</li> 1989 * 1990 * <li> {@code C} is considered to have the same runtime 1991 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module} 1992 * and {@linkplain java.security.ProtectionDomain protection domain} 1993 * as the lookup class of this {@code Lookup}. 1994 * <li> Let {@code GN} be the binary name obtained by taking {@code N} 1995 * (a binary name encoded in internal form) and replacing ASCII forward slashes with 1996 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}: 1997 * <ul> 1998 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>}, 1999 * even though this is not a valid binary class or interface name.</li> 2000 * <li> {@link Class#descriptorString()} returns the string 2001 * {@code "L" + N + "." + <suffix> + ";"}, 2002 * even though this is not a valid type descriptor name.</li> 2003 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C} 2004 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li> 2005 * </ul> 2006 * </ul> 2007 * </li> 2008 * </ol> 2009 * 2010 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine. 2011 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments: 2012 * <ul> 2013 * <li> During verification, whenever it is necessary to load the class named 2014 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is 2015 * made of any class loader.</li> 2016 * 2017 * <li> On any attempt to resolve the entry in the run-time constant pool indicated 2018 * by {@code this_class}, the symbolic reference is considered to be resolved to 2019 * {@code C} and resolution always succeeds immediately.</li> 2020 * </ul> 2021 * 2022 * <p> If the {@code initialize} parameter is {@code true}, 2023 * then {@code C} is initialized by the Java Virtual Machine. 2024 * 2025 * <p> The newly created class or interface {@code C} serves as the 2026 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object 2027 * returned by this method. {@code C} is <em>hidden</em> in the sense that 2028 * no other class or interface can refer to {@code C} via a constant pool entry. 2029 * That is, a hidden class or interface cannot be named as a supertype, a field type, 2030 * a method parameter type, or a method return type by any other class. 2031 * This is because a hidden class or interface does not have a binary name, so 2032 * there is no internal form available to record in any class's constant pool. 2033 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)}, 2034 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and 2035 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class) 2036 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html"> 2037 * JVM Tool Interface</a>. 2038 * 2039 * <p> A class or interface created by 2040 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain) 2041 * a class loader} has a strong relationship with that class loader. 2042 * That is, every {@code Class} object contains a reference to the {@code ClassLoader} 2043 * that {@linkplain Class#getClassLoader() defined it}. 2044 * This means that a class created by a class loader may be unloaded if and 2045 * only if its defining loader is not reachable and thus may be reclaimed 2046 * by a garbage collector (JLS {@jls 12.7}). 2047 * 2048 * By default, however, a hidden class or interface may be unloaded even if 2049 * the class loader that is marked as its defining loader is 2050 * <a href="../ref/package-summary.html#reachability">reachable</a>. 2051 * This behavior is useful when a hidden class or interface serves multiple 2052 * classes defined by arbitrary class loaders. In other cases, a hidden 2053 * class or interface may be linked to a single class (or a small number of classes) 2054 * with the same defining loader as the hidden class or interface. 2055 * In such cases, where the hidden class or interface must be coterminous 2056 * with a normal class or interface, the {@link ClassOption#STRONG STRONG} 2057 * option may be passed in {@code options}. 2058 * This arranges for a hidden class to have the same strong relationship 2059 * with the class loader marked as its defining loader, 2060 * as a normal class or interface has with its own defining loader. 2061 * 2062 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass} 2063 * may still prevent a hidden class or interface from being 2064 * unloaded by ensuring that the {@code Class} object is reachable. 2065 * 2066 * <p> The unloading characteristics are set for each hidden class when it is 2067 * defined, and cannot be changed later. An advantage of allowing hidden classes 2068 * to be unloaded independently of the class loader marked as their defining loader 2069 * is that a very large number of hidden classes may be created by an application. 2070 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory, 2071 * just as if normal classes were created by class loaders. 2072 * 2073 * <p> Classes and interfaces in a nest are allowed to have mutual access to 2074 * their private members. The nest relationship is determined by 2075 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and 2076 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file. 2077 * By default, a hidden class belongs to a nest consisting only of itself 2078 * because a hidden class has no binary name. 2079 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options} 2080 * to create a hidden class or interface {@code C} as a member of a nest. 2081 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute 2082 * in the {@code ClassFile} structure from which {@code C} was derived. 2083 * Instead, the following rules determine the nest host of {@code C}: 2084 * <ul> 2085 * <li>If the nest host of the lookup class of this {@code Lookup} has previously 2086 * been determined, then let {@code H} be the nest host of the lookup class. 2087 * Otherwise, the nest host of the lookup class is determined using the 2088 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li> 2089 * <li>The nest host of {@code C} is determined to be {@code H}, 2090 * the nest host of the lookup class.</li> 2091 * </ul> 2092 * 2093 * <p> A hidden class or interface may be serializable, but this requires a custom 2094 * serialization mechanism in order to ensure that instances are properly serialized 2095 * and deserialized. The default serialization mechanism supports only classes and 2096 * interfaces that are discoverable by their class name. 2097 * 2098 * @param bytes the bytes that make up the class data, 2099 * in the format of a valid {@code class} file as defined by 2100 * <cite>The Java Virtual Machine Specification</cite>. 2101 * @param initialize if {@code true} the class will be initialized. 2102 * @param options {@linkplain ClassOption class options} 2103 * @return the {@code Lookup} object on the hidden class, 2104 * with {@linkplain #ORIGINAL original} and 2105 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access 2106 * 2107 * @throws IllegalAccessException if this {@code Lookup} does not have 2108 * {@linkplain #hasFullPrivilegeAccess() full privilege} access 2109 * @throws SecurityException if a security manager is present and it 2110 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2111 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 2112 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version 2113 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 2114 * than the lookup class or {@code bytes} is not a class or interface 2115 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 2116 * @throws IncompatibleClassChangeError if the class or interface named as 2117 * the direct superclass of {@code C} is in fact an interface, or if any of the classes 2118 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces 2119 * @throws ClassCircularityError if any of the superclasses or superinterfaces of 2120 * {@code C} is {@code C} itself 2121 * @throws VerifyError if the newly created class cannot be verified 2122 * @throws LinkageError if the newly created class cannot be linked for any other reason 2123 * @throws NullPointerException if any parameter is {@code null} 2124 * 2125 * @since 15 2126 * @see Class#isHidden() 2127 * @jvms 4.2.1 Binary Class and Interface Names 2128 * @jvms 4.2.2 Unqualified Names 2129 * @jvms 4.7.28 The {@code NestHost} Attribute 2130 * @jvms 4.7.29 The {@code NestMembers} Attribute 2131 * @jvms 5.4.3.1 Class and Interface Resolution 2132 * @jvms 5.4.4 Access Control 2133 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation 2134 * @jvms 5.4 Linking 2135 * @jvms 5.5 Initialization 2136 * @jls 12.7 Unloading of Classes and Interfaces 2137 */ 2138 @SuppressWarnings("doclint:reference") // cross-module links 2139 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options) 2140 throws IllegalAccessException 2141 { 2142 Objects.requireNonNull(bytes); 2143 Objects.requireNonNull(options); 2144 2145 ensureDefineClassPermission(); 2146 if (!hasFullPrivilegeAccess()) { 2147 throw new IllegalAccessException(this + " does not have full privilege access"); 2148 } 2149 2150 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize); 2151 } 2152 2153 /** 2154 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated 2155 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data}, 2156 * returning a {@code Lookup} on the newly created class or interface. 2157 * 2158 * <p> This method is equivalent to calling 2159 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)} 2160 * as if the hidden class is injected with a private static final <i>unnamed</i> 2161 * field which is initialized with the given {@code classData} at 2162 * the first instruction of the class initializer. 2163 * The newly created class is linked by the Java Virtual Machine. 2164 * 2165 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData} 2166 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt} 2167 * methods can be used to retrieve the {@code classData}. 2168 * 2169 * @apiNote 2170 * A framework can create a hidden class with class data with one or more 2171 * objects and load the class data as dynamically-computed constant(s) 2172 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class) 2173 * Class data} is accessible only to the lookup object created by the newly 2174 * defined hidden class but inaccessible to other members in the same nest 2175 * (unlike private static fields that are accessible to nestmates). 2176 * Care should be taken w.r.t. mutability for example when passing 2177 * an array or other mutable structure through the class data. 2178 * Changing any value stored in the class data at runtime may lead to 2179 * unpredictable behavior. 2180 * If the class data is a {@code List}, it is good practice to make it 2181 * unmodifiable for example via {@link List#of List::of}. 2182 * 2183 * @param bytes the class bytes 2184 * @param classData pre-initialized class data 2185 * @param initialize if {@code true} the class will be initialized. 2186 * @param options {@linkplain ClassOption class options} 2187 * @return the {@code Lookup} object on the hidden class, 2188 * with {@linkplain #ORIGINAL original} and 2189 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access 2190 * 2191 * @throws IllegalAccessException if this {@code Lookup} does not have 2192 * {@linkplain #hasFullPrivilegeAccess() full privilege} access 2193 * @throws SecurityException if a security manager is present and it 2194 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2195 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 2196 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version 2197 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 2198 * than the lookup class or {@code bytes} is not a class or interface 2199 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 2200 * @throws IncompatibleClassChangeError if the class or interface named as 2201 * the direct superclass of {@code C} is in fact an interface, or if any of the classes 2202 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces 2203 * @throws ClassCircularityError if any of the superclasses or superinterfaces of 2204 * {@code C} is {@code C} itself 2205 * @throws VerifyError if the newly created class cannot be verified 2206 * @throws LinkageError if the newly created class cannot be linked for any other reason 2207 * @throws NullPointerException if any parameter is {@code null} 2208 * 2209 * @since 16 2210 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...) 2211 * @see Class#isHidden() 2212 * @see MethodHandles#classData(Lookup, String, Class) 2213 * @see MethodHandles#classDataAt(Lookup, String, Class, int) 2214 * @jvms 4.2.1 Binary Class and Interface Names 2215 * @jvms 4.2.2 Unqualified Names 2216 * @jvms 4.7.28 The {@code NestHost} Attribute 2217 * @jvms 4.7.29 The {@code NestMembers} Attribute 2218 * @jvms 5.4.3.1 Class and Interface Resolution 2219 * @jvms 5.4.4 Access Control 2220 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation 2221 * @jvms 5.4 Linking 2222 * @jvms 5.5 Initialization 2223 * @jls 12.7 Unloading of Classes and Interface 2224 */ 2225 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options) 2226 throws IllegalAccessException 2227 { 2228 Objects.requireNonNull(bytes); 2229 Objects.requireNonNull(classData); 2230 Objects.requireNonNull(options); 2231 2232 ensureDefineClassPermission(); 2233 if (!hasFullPrivilegeAccess()) { 2234 throw new IllegalAccessException(this + " does not have full privilege access"); 2235 } 2236 2237 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false) 2238 .defineClassAsLookup(initialize, classData); 2239 } 2240 2241 // A default dumper for writing class files passed to Lookup::defineClass 2242 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable, 2243 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or 2244 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true 2245 // 2246 // This default dumper does not dump hidden classes defined by LambdaMetafactory 2247 // and LambdaForms and method handle internals. They are dumped via 2248 // different ClassFileDumpers. 2249 private static ClassFileDumper defaultDumper() { 2250 return DEFAULT_DUMPER; 2251 } 2252 2253 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance( 2254 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES"); 2255 2256 static class ClassFile { 2257 final String name; // internal name 2258 final int accessFlags; 2259 final byte[] bytes; 2260 ClassFile(String name, int accessFlags, byte[] bytes) { 2261 this.name = name; 2262 this.accessFlags = accessFlags; 2263 this.bytes = bytes; 2264 } 2265 2266 static ClassFile newInstanceNoCheck(String name, byte[] bytes) { 2267 return new ClassFile(name, 0, bytes); 2268 } 2269 2270 /** 2271 * This method checks the class file version and the structure of `this_class`. 2272 * and checks if the bytes is a class or interface (ACC_MODULE flag not set) 2273 * that is in the named package. 2274 * 2275 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags 2276 * or the class is not in the given package name. 2277 */ 2278 static ClassFile newInstance(byte[] bytes, String pkgName) { 2279 var cf = readClassFile(bytes); 2280 2281 // check if it's in the named package 2282 int index = cf.name.lastIndexOf('/'); 2283 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.'); 2284 if (!pn.equals(pkgName)) { 2285 throw newIllegalArgumentException(cf.name + " not in same package as lookup class"); 2286 } 2287 return cf; 2288 } 2289 2290 private static ClassFile readClassFile(byte[] bytes) { 2291 int magic = readInt(bytes, 0); 2292 if (magic != 0xCAFEBABE) { 2293 throw new ClassFormatError("Incompatible magic value: " + magic); 2294 } 2295 int minor = readUnsignedShort(bytes, 4); 2296 int major = readUnsignedShort(bytes, 6); 2297 if (!VM.isSupportedClassFileVersion(major, minor)) { 2298 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor); 2299 } 2300 2301 String name; 2302 int accessFlags; 2303 try { 2304 ClassReader reader = new ClassReader(bytes); 2305 // ClassReader does not check if `this_class` is CONSTANT_Class_info 2306 // workaround to read `this_class` using readConst and validate the value 2307 int thisClass = reader.readUnsignedShort(reader.header + 2); 2308 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]); 2309 if (!(constant instanceof Type type)) { 2310 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info"); 2311 } 2312 if (!type.getDescriptor().startsWith("L")) { 2313 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info"); 2314 } 2315 name = type.getInternalName(); 2316 accessFlags = reader.readUnsignedShort(reader.header); 2317 } catch (RuntimeException e) { 2318 // ASM exceptions are poorly specified 2319 ClassFormatError cfe = new ClassFormatError(); 2320 cfe.initCause(e); 2321 throw cfe; 2322 } 2323 // must be a class or interface 2324 if ((accessFlags & Opcodes.ACC_MODULE) != 0) { 2325 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set"); 2326 } 2327 return new ClassFile(name, accessFlags, bytes); 2328 } 2329 2330 private static int readInt(byte[] bytes, int offset) { 2331 if ((offset+4) > bytes.length) { 2332 throw new ClassFormatError("Invalid ClassFile structure"); 2333 } 2334 return ((bytes[offset] & 0xFF) << 24) 2335 | ((bytes[offset + 1] & 0xFF) << 16) 2336 | ((bytes[offset + 2] & 0xFF) << 8) 2337 | (bytes[offset + 3] & 0xFF); 2338 } 2339 2340 private static int readUnsignedShort(byte[] bytes, int offset) { 2341 if ((offset+2) > bytes.length) { 2342 throw new ClassFormatError("Invalid ClassFile structure"); 2343 } 2344 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF); 2345 } 2346 } 2347 2348 /* 2349 * Returns a ClassDefiner that creates a {@code Class} object of a normal class 2350 * from the given bytes. 2351 * 2352 * Caller should make a defensive copy of the arguments if needed 2353 * before calling this factory method. 2354 * 2355 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2356 * {@code bytes} denotes a class in a different package than the lookup class 2357 */ 2358 private ClassDefiner makeClassDefiner(byte[] bytes) { 2359 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2360 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper()); 2361 } 2362 2363 /** 2364 * Returns a ClassDefiner that creates a {@code Class} object of a normal class 2365 * from the given bytes. No package name check on the given bytes. 2366 * 2367 * @param name internal name 2368 * @param bytes class bytes 2369 * @param dumper dumper to write the given bytes to the dumper's output directory 2370 * @return ClassDefiner that defines a normal class of the given bytes. 2371 */ 2372 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) { 2373 // skip package name validation 2374 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes); 2375 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper); 2376 } 2377 2378 /** 2379 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2380 * from the given bytes. The name must be in the same package as the lookup class. 2381 * 2382 * Caller should make a defensive copy of the arguments if needed 2383 * before calling this factory method. 2384 * 2385 * @param bytes class bytes 2386 * @param dumper dumper to write the given bytes to the dumper's output directory 2387 * @return ClassDefiner that defines a hidden class of the given bytes. 2388 * 2389 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2390 * {@code bytes} denotes a class in a different package than the lookup class 2391 */ 2392 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) { 2393 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2394 return makeHiddenClassDefiner(cf, Set.of(), false, dumper); 2395 } 2396 2397 /** 2398 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2399 * from the given bytes and options. 2400 * The name must be in the same package as the lookup class. 2401 * 2402 * Caller should make a defensive copy of the arguments if needed 2403 * before calling this factory method. 2404 * 2405 * @param bytes class bytes 2406 * @param options class options 2407 * @param accessVmAnnotations true to give the hidden class access to VM annotations 2408 * @return ClassDefiner that defines a hidden class of the given bytes and options 2409 * 2410 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2411 * {@code bytes} denotes a class in a different package than the lookup class 2412 */ 2413 private ClassDefiner makeHiddenClassDefiner(byte[] bytes, 2414 Set<ClassOption> options, 2415 boolean accessVmAnnotations) { 2416 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2417 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper()); 2418 } 2419 2420 /** 2421 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2422 * from the given bytes and the given options. No package name check on the given bytes. 2423 * 2424 * @param name internal name that specifies the prefix of the hidden class 2425 * @param bytes class bytes 2426 * @param options class options 2427 * @param dumper dumper to write the given bytes to the dumper's output directory 2428 * @return ClassDefiner that defines a hidden class of the given bytes and options. 2429 */ 2430 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) { 2431 Objects.requireNonNull(dumper); 2432 // skip name and access flags validation 2433 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper); 2434 } 2435 2436 /** 2437 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2438 * from the given class file and options. 2439 * 2440 * @param cf ClassFile 2441 * @param options class options 2442 * @param accessVmAnnotations true to give the hidden class access to VM annotations 2443 * @param dumper dumper to write the given bytes to the dumper's output directory 2444 */ 2445 private ClassDefiner makeHiddenClassDefiner(ClassFile cf, 2446 Set<ClassOption> options, 2447 boolean accessVmAnnotations, 2448 ClassFileDumper dumper) { 2449 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options); 2450 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) { 2451 // jdk.internal.vm.annotations are permitted for classes 2452 // defined to boot loader and platform loader 2453 flags |= ACCESS_VM_ANNOTATIONS; 2454 } 2455 2456 return new ClassDefiner(this, cf, flags, dumper); 2457 } 2458 2459 static class ClassDefiner { 2460 private final Lookup lookup; 2461 private final String name; // internal name 2462 private final byte[] bytes; 2463 private final int classFlags; 2464 private final ClassFileDumper dumper; 2465 2466 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) { 2467 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK); 2468 this.lookup = lookup; 2469 this.bytes = cf.bytes; 2470 this.name = cf.name; 2471 this.classFlags = flags; 2472 this.dumper = dumper; 2473 } 2474 2475 String internalName() { 2476 return name; 2477 } 2478 2479 Class<?> defineClass(boolean initialize) { 2480 return defineClass(initialize, null); 2481 } 2482 2483 Lookup defineClassAsLookup(boolean initialize) { 2484 Class<?> c = defineClass(initialize, null); 2485 return new Lookup(c, null, FULL_POWER_MODES); 2486 } 2487 2488 /** 2489 * Defines the class of the given bytes and the given classData. 2490 * If {@code initialize} parameter is true, then the class will be initialized. 2491 * 2492 * @param initialize true if the class to be initialized 2493 * @param classData classData or null 2494 * @return the class 2495 * 2496 * @throws LinkageError linkage error 2497 */ 2498 Class<?> defineClass(boolean initialize, Object classData) { 2499 Class<?> lookupClass = lookup.lookupClass(); 2500 ClassLoader loader = lookupClass.getClassLoader(); 2501 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null; 2502 Class<?> c = null; 2503 try { 2504 c = SharedSecrets.getJavaLangAccess() 2505 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData); 2506 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost(); 2507 return c; 2508 } finally { 2509 // dump the classfile for debugging 2510 if (dumper.isEnabled()) { 2511 String name = internalName(); 2512 if (c != null) { 2513 dumper.dumpClass(name, c, bytes); 2514 } else { 2515 dumper.dumpFailedClass(name, bytes); 2516 } 2517 } 2518 } 2519 } 2520 2521 /** 2522 * Defines the class of the given bytes and the given classData. 2523 * If {@code initialize} parameter is true, then the class will be initialized. 2524 * 2525 * @param initialize true if the class to be initialized 2526 * @param classData classData or null 2527 * @return a Lookup for the defined class 2528 * 2529 * @throws LinkageError linkage error 2530 */ 2531 Lookup defineClassAsLookup(boolean initialize, Object classData) { 2532 Class<?> c = defineClass(initialize, classData); 2533 return new Lookup(c, null, FULL_POWER_MODES); 2534 } 2535 2536 private boolean isNestmate() { 2537 return (classFlags & NESTMATE_CLASS) != 0; 2538 } 2539 } 2540 2541 private ProtectionDomain lookupClassProtectionDomain() { 2542 ProtectionDomain pd = cachedProtectionDomain; 2543 if (pd == null) { 2544 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass); 2545 } 2546 return pd; 2547 } 2548 2549 // cached protection domain 2550 private volatile ProtectionDomain cachedProtectionDomain; 2551 2552 // Make sure outer class is initialized first. 2553 static { IMPL_NAMES.getClass(); } 2554 2555 /** Package-private version of lookup which is trusted. */ 2556 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED); 2557 2558 /** Version of lookup which is trusted minimally. 2559 * It can only be used to create method handles to publicly accessible 2560 * members in packages that are exported unconditionally. 2561 */ 2562 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL); 2563 2564 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) { 2565 String name = lookupClass.getName(); 2566 if (name.startsWith("java.lang.invoke.")) 2567 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass); 2568 } 2569 2570 /** 2571 * Displays the name of the class from which lookups are to be made, 2572 * followed by "/" and the name of the {@linkplain #previousLookupClass() 2573 * previous lookup class} if present. 2574 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.) 2575 * If there are restrictions on the access permitted to this lookup, 2576 * this is indicated by adding a suffix to the class name, consisting 2577 * of a slash and a keyword. The keyword represents the strongest 2578 * allowed access, and is chosen as follows: 2579 * <ul> 2580 * <li>If no access is allowed, the suffix is "/noaccess". 2581 * <li>If only unconditional access is allowed, the suffix is "/publicLookup". 2582 * <li>If only public access to types in exported packages is allowed, the suffix is "/public". 2583 * <li>If only public and module access are allowed, the suffix is "/module". 2584 * <li>If public and package access are allowed, the suffix is "/package". 2585 * <li>If public, package, and private access are allowed, the suffix is "/private". 2586 * </ul> 2587 * If none of the above cases apply, it is the case that 2588 * {@linkplain #hasFullPrivilegeAccess() full privilege access} 2589 * (public, module, package, private, and protected) is allowed. 2590 * In this case, no suffix is added. 2591 * This is true only of an object obtained originally from 2592 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}. 2593 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in} 2594 * always have restricted access, and will display a suffix. 2595 * <p> 2596 * (It may seem strange that protected access should be 2597 * stronger than private access. Viewed independently from 2598 * package access, protected access is the first to be lost, 2599 * because it requires a direct subclass relationship between 2600 * caller and callee.) 2601 * @see #in 2602 * 2603 * @revised 9 2604 */ 2605 @Override 2606 public String toString() { 2607 String cname = lookupClass.getName(); 2608 if (prevLookupClass != null) 2609 cname += "/" + prevLookupClass.getName(); 2610 switch (allowedModes) { 2611 case 0: // no privileges 2612 return cname + "/noaccess"; 2613 case UNCONDITIONAL: 2614 return cname + "/publicLookup"; 2615 case PUBLIC: 2616 return cname + "/public"; 2617 case PUBLIC|MODULE: 2618 return cname + "/module"; 2619 case PUBLIC|PACKAGE: 2620 case PUBLIC|MODULE|PACKAGE: 2621 return cname + "/package"; 2622 case PUBLIC|PACKAGE|PRIVATE: 2623 case PUBLIC|MODULE|PACKAGE|PRIVATE: 2624 return cname + "/private"; 2625 case PUBLIC|PACKAGE|PRIVATE|PROTECTED: 2626 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED: 2627 case FULL_POWER_MODES: 2628 return cname; 2629 case TRUSTED: 2630 return "/trusted"; // internal only; not exported 2631 default: // Should not happen, but it's a bitfield... 2632 cname = cname + "/" + Integer.toHexString(allowedModes); 2633 assert(false) : cname; 2634 return cname; 2635 } 2636 } 2637 2638 /** 2639 * Produces a method handle for a static method. 2640 * The type of the method handle will be that of the method. 2641 * (Since static methods do not take receivers, there is no 2642 * additional receiver argument inserted into the method handle type, 2643 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) 2644 * The method and all its argument types must be accessible to the lookup object. 2645 * <p> 2646 * The returned method handle will have 2647 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2648 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2649 * <p> 2650 * If the returned method handle is invoked, the method's class will 2651 * be initialized, if it has not already been initialized. 2652 * <p><b>Example:</b> 2653 * {@snippet lang="java" : 2654 import static java.lang.invoke.MethodHandles.*; 2655 import static java.lang.invoke.MethodType.*; 2656 ... 2657 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class, 2658 "asList", methodType(List.class, Object[].class)); 2659 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString()); 2660 * } 2661 * @param refc the class from which the method is accessed 2662 * @param name the name of the method 2663 * @param type the type of the method 2664 * @return the desired method handle 2665 * @throws NoSuchMethodException if the method does not exist 2666 * @throws IllegalAccessException if access checking fails, 2667 * or if the method is not {@code static}, 2668 * or if the method's variable arity modifier bit 2669 * is set and {@code asVarargsCollector} fails 2670 * @throws SecurityException if a security manager is present and it 2671 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2672 * @throws NullPointerException if any argument is null 2673 */ 2674 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2675 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type); 2676 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method)); 2677 } 2678 2679 /** 2680 * Produces a method handle for a virtual method. 2681 * The type of the method handle will be that of the method, 2682 * with the receiver type (usually {@code refc}) prepended. 2683 * The method and all its argument types must be accessible to the lookup object. 2684 * <p> 2685 * When called, the handle will treat the first argument as a receiver 2686 * and, for non-private methods, dispatch on the receiver's type to determine which method 2687 * implementation to enter. 2688 * For private methods the named method in {@code refc} will be invoked on the receiver. 2689 * (The dispatching action is identical with that performed by an 2690 * {@code invokevirtual} or {@code invokeinterface} instruction.) 2691 * <p> 2692 * The first argument will be of type {@code refc} if the lookup 2693 * class has full privileges to access the member. Otherwise 2694 * the member must be {@code protected} and the first argument 2695 * will be restricted in type to the lookup class. 2696 * <p> 2697 * The returned method handle will have 2698 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2699 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2700 * <p> 2701 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual} 2702 * instructions and method handles produced by {@code findVirtual}, 2703 * if the class is {@code MethodHandle} and the name string is 2704 * {@code invokeExact} or {@code invoke}, the resulting 2705 * method handle is equivalent to one produced by 2706 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or 2707 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} 2708 * with the same {@code type} argument. 2709 * <p> 2710 * If the class is {@code VarHandle} and the name string corresponds to 2711 * the name of a signature-polymorphic access mode method, the resulting 2712 * method handle is equivalent to one produced by 2713 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with 2714 * the access mode corresponding to the name string and with the same 2715 * {@code type} arguments. 2716 * <p> 2717 * <b>Example:</b> 2718 * {@snippet lang="java" : 2719 import static java.lang.invoke.MethodHandles.*; 2720 import static java.lang.invoke.MethodType.*; 2721 ... 2722 MethodHandle MH_concat = publicLookup().findVirtual(String.class, 2723 "concat", methodType(String.class, String.class)); 2724 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class, 2725 "hashCode", methodType(int.class)); 2726 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class, 2727 "hashCode", methodType(int.class)); 2728 assertEquals("xy", (String) MH_concat.invokeExact("x", "y")); 2729 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy")); 2730 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy")); 2731 // interface method: 2732 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class, 2733 "subSequence", methodType(CharSequence.class, int.class, int.class)); 2734 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString()); 2735 // constructor "internal method" must be accessed differently: 2736 MethodType MT_newString = methodType(void.class); //()V for new String() 2737 try { assertEquals("impossible", lookup() 2738 .findVirtual(String.class, "<init>", MT_newString)); 2739 } catch (NoSuchMethodException ex) { } // OK 2740 MethodHandle MH_newString = publicLookup() 2741 .findConstructor(String.class, MT_newString); 2742 assertEquals("", (String) MH_newString.invokeExact()); 2743 * } 2744 * 2745 * @param refc the class or interface from which the method is accessed 2746 * @param name the name of the method 2747 * @param type the type of the method, with the receiver argument omitted 2748 * @return the desired method handle 2749 * @throws NoSuchMethodException if the method does not exist 2750 * @throws IllegalAccessException if access checking fails, 2751 * or if the method is {@code static}, 2752 * or if the method's variable arity modifier bit 2753 * is set and {@code asVarargsCollector} fails 2754 * @throws SecurityException if a security manager is present and it 2755 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2756 * @throws NullPointerException if any argument is null 2757 */ 2758 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2759 if (refc == MethodHandle.class) { 2760 MethodHandle mh = findVirtualForMH(name, type); 2761 if (mh != null) return mh; 2762 } else if (refc == VarHandle.class) { 2763 MethodHandle mh = findVirtualForVH(name, type); 2764 if (mh != null) return mh; 2765 } 2766 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual); 2767 MemberName method = resolveOrFail(refKind, refc, name, type); 2768 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method)); 2769 } 2770 private MethodHandle findVirtualForMH(String name, MethodType type) { 2771 // these names require special lookups because of the implicit MethodType argument 2772 if ("invoke".equals(name)) 2773 return invoker(type); 2774 if ("invokeExact".equals(name)) 2775 return exactInvoker(type); 2776 assert(!MemberName.isMethodHandleInvokeName(name)); 2777 return null; 2778 } 2779 private MethodHandle findVirtualForVH(String name, MethodType type) { 2780 try { 2781 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type); 2782 } catch (IllegalArgumentException e) { 2783 return null; 2784 } 2785 } 2786 2787 /** 2788 * Produces a method handle which creates an object and initializes it, using 2789 * the constructor of the specified type. 2790 * The parameter types of the method handle will be those of the constructor, 2791 * while the return type will be a reference to the constructor's class. 2792 * The constructor and all its argument types must be accessible to the lookup object. 2793 * <p> 2794 * The requested type must have a return type of {@code void}. 2795 * (This is consistent with the JVM's treatment of constructor type descriptors.) 2796 * <p> 2797 * The returned method handle will have 2798 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2799 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 2800 * <p> 2801 * If the returned method handle is invoked, the constructor's class will 2802 * be initialized, if it has not already been initialized. 2803 * <p><b>Example:</b> 2804 * {@snippet lang="java" : 2805 import static java.lang.invoke.MethodHandles.*; 2806 import static java.lang.invoke.MethodType.*; 2807 ... 2808 MethodHandle MH_newArrayList = publicLookup().findConstructor( 2809 ArrayList.class, methodType(void.class, Collection.class)); 2810 Collection orig = Arrays.asList("x", "y"); 2811 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig); 2812 assert(orig != copy); 2813 assertEquals(orig, copy); 2814 // a variable-arity constructor: 2815 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor( 2816 ProcessBuilder.class, methodType(void.class, String[].class)); 2817 ProcessBuilder pb = (ProcessBuilder) 2818 MH_newProcessBuilder.invoke("x", "y", "z"); 2819 assertEquals("[x, y, z]", pb.command().toString()); 2820 * } 2821 * @param refc the class or interface from which the method is accessed 2822 * @param type the type of the method, with the receiver argument omitted, and a void return type 2823 * @return the desired method handle 2824 * @throws NoSuchMethodException if the constructor does not exist 2825 * @throws IllegalAccessException if access checking fails 2826 * or if the method's variable arity modifier bit 2827 * is set and {@code asVarargsCollector} fails 2828 * @throws SecurityException if a security manager is present and it 2829 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2830 * @throws NullPointerException if any argument is null 2831 */ 2832 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2833 if (refc.isArray()) { 2834 throw new NoSuchMethodException("no constructor for array class: " + refc.getName()); 2835 } 2836 String name = ConstantDescs.INIT_NAME; 2837 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type); 2838 return getDirectConstructor(refc, ctor); 2839 } 2840 2841 /** 2842 * Looks up a class by name from the lookup context defined by this {@code Lookup} object, 2843 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction. 2844 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class, 2845 * and then determines whether the class is accessible to this lookup object. 2846 * <p> 2847 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}. 2848 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences 2849 * of {@code '['} and followed by the element type as encoded in the 2850 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}. 2851 * <p> 2852 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, 2853 * its class loader, and the {@linkplain #lookupModes() lookup modes}. 2854 * 2855 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class 2856 * or the string representing an array class 2857 * @return the requested class. 2858 * @throws SecurityException if a security manager is present and it 2859 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2860 * @throws LinkageError if the linkage fails 2861 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader. 2862 * @throws IllegalAccessException if the class is not accessible, using the allowed access 2863 * modes. 2864 * @throws NullPointerException if {@code targetName} is null 2865 * @since 9 2866 * @jvms 5.4.3.1 Class and Interface Resolution 2867 */ 2868 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException { 2869 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader()); 2870 return accessClass(targetClass); 2871 } 2872 2873 /** 2874 * Ensures that {@code targetClass} has been initialized. The class 2875 * to be initialized must be {@linkplain #accessClass accessible} 2876 * to this {@code Lookup} object. This method causes {@code targetClass} 2877 * to be initialized if it has not been already initialized, 2878 * as specified in JVMS {@jvms 5.5}. 2879 * 2880 * <p> 2881 * This method returns when {@code targetClass} is fully initialized, or 2882 * when {@code targetClass} is being initialized by the current thread. 2883 * 2884 * @param <T> the type of the class to be initialized 2885 * @param targetClass the class to be initialized 2886 * @return {@code targetClass} that has been initialized, or that is being 2887 * initialized by the current thread. 2888 * 2889 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void} 2890 * or array class 2891 * @throws IllegalAccessException if {@code targetClass} is not 2892 * {@linkplain #accessClass accessible} to this lookup 2893 * @throws ExceptionInInitializerError if the class initialization provoked 2894 * by this method fails 2895 * @throws SecurityException if a security manager is present and it 2896 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2897 * @since 15 2898 * @jvms 5.5 Initialization 2899 */ 2900 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException { 2901 if (targetClass.isPrimitive()) 2902 throw new IllegalArgumentException(targetClass + " is a primitive class"); 2903 if (targetClass.isArray()) 2904 throw new IllegalArgumentException(targetClass + " is an array class"); 2905 2906 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) { 2907 throw makeAccessException(targetClass); 2908 } 2909 checkSecurityManager(targetClass); 2910 2911 // ensure class initialization 2912 Unsafe.getUnsafe().ensureClassInitialized(targetClass); 2913 return targetClass; 2914 } 2915 2916 /* 2917 * Returns IllegalAccessException due to access violation to the given targetClass. 2918 * 2919 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized} 2920 * which verifies access to a class rather a member. 2921 */ 2922 private IllegalAccessException makeAccessException(Class<?> targetClass) { 2923 String message = "access violation: "+ targetClass; 2924 if (this == MethodHandles.publicLookup()) { 2925 message += ", from public Lookup"; 2926 } else { 2927 Module m = lookupClass().getModule(); 2928 message += ", from " + lookupClass() + " (" + m + ")"; 2929 if (prevLookupClass != null) { 2930 message += ", previous lookup " + 2931 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")"; 2932 } 2933 } 2934 return new IllegalAccessException(message); 2935 } 2936 2937 /** 2938 * Determines if a class can be accessed from the lookup context defined by 2939 * this {@code Lookup} object. The static initializer of the class is not run. 2940 * If {@code targetClass} is an array class, {@code targetClass} is accessible 2941 * if the element type of the array class is accessible. Otherwise, 2942 * {@code targetClass} is determined as accessible as follows. 2943 * 2944 * <p> 2945 * If {@code targetClass} is in the same module as the lookup class, 2946 * the lookup class is {@code LC} in module {@code M1} and 2947 * the previous lookup class is in module {@code M0} or 2948 * {@code null} if not present, 2949 * {@code targetClass} is accessible if and only if one of the following is true: 2950 * <ul> 2951 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is 2952 * {@code LC} or other class in the same nest of {@code LC}.</li> 2953 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is 2954 * in the same runtime package of {@code LC}.</li> 2955 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is 2956 * a public type in {@code M1}.</li> 2957 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is 2958 * a public type in a package exported by {@code M1} to at least {@code M0} 2959 * if the previous lookup class is present; otherwise, {@code targetClass} 2960 * is a public type in a package exported by {@code M1} unconditionally.</li> 2961 * </ul> 2962 * 2963 * <p> 2964 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup 2965 * can access public types in all modules when the type is in a package 2966 * that is exported unconditionally. 2967 * <p> 2968 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass}, 2969 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass} 2970 * is inaccessible. 2971 * <p> 2972 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class}, 2973 * {@code M1} is the module containing {@code lookupClass} and 2974 * {@code M2} is the module containing {@code targetClass}, 2975 * then {@code targetClass} is accessible if and only if 2976 * <ul> 2977 * <li>{@code M1} reads {@code M2}, and 2978 * <li>{@code targetClass} is public and in a package exported by 2979 * {@code M2} at least to {@code M1}. 2980 * </ul> 2981 * <p> 2982 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class}, 2983 * {@code M1} and {@code M2} are as before, and {@code M0} is the module 2984 * containing the previous lookup class, then {@code targetClass} is accessible 2985 * if and only if one of the following is true: 2986 * <ul> 2987 * <li>{@code targetClass} is in {@code M0} and {@code M1} 2988 * {@linkplain Module#reads reads} {@code M0} and the type is 2989 * in a package that is exported to at least {@code M1}. 2990 * <li>{@code targetClass} is in {@code M1} and {@code M0} 2991 * {@linkplain Module#reads reads} {@code M1} and the type is 2992 * in a package that is exported to at least {@code M0}. 2993 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0} 2994 * and {@code M1} reads {@code M2} and the type is in a package 2995 * that is exported to at least both {@code M0} and {@code M2}. 2996 * </ul> 2997 * <p> 2998 * Otherwise, {@code targetClass} is not accessible. 2999 * 3000 * @param <T> the type of the class to be access-checked 3001 * @param targetClass the class to be access-checked 3002 * @return {@code targetClass} that has been access-checked 3003 * @throws IllegalAccessException if the class is not accessible from the lookup class 3004 * and previous lookup class, if present, using the allowed access modes. 3005 * @throws SecurityException if a security manager is present and it 3006 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3007 * @throws NullPointerException if {@code targetClass} is {@code null} 3008 * @since 9 3009 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 3010 */ 3011 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException { 3012 if (!isClassAccessible(targetClass)) { 3013 throw makeAccessException(targetClass); 3014 } 3015 checkSecurityManager(targetClass); 3016 return targetClass; 3017 } 3018 3019 /** 3020 * Produces an early-bound method handle for a virtual method. 3021 * It will bypass checks for overriding methods on the receiver, 3022 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 3023 * instruction from within the explicitly specified {@code specialCaller}. 3024 * The type of the method handle will be that of the method, 3025 * with a suitably restricted receiver type prepended. 3026 * (The receiver type will be {@code specialCaller} or a subtype.) 3027 * The method and all its argument types must be accessible 3028 * to the lookup object. 3029 * <p> 3030 * Before method resolution, 3031 * if the explicitly specified caller class is not identical with the 3032 * lookup class, or if this lookup object does not have 3033 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 3034 * privileges, the access fails. 3035 * <p> 3036 * The returned method handle will have 3037 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3038 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3039 * <p style="font-size:smaller;"> 3040 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME} 3041 * are not visible to this API, 3042 * even though the {@code invokespecial} instruction can refer to them 3043 * in special circumstances. Use {@link #findConstructor findConstructor} 3044 * to access instance initialization methods in a safe manner.)</em> 3045 * <p><b>Example:</b> 3046 * {@snippet lang="java" : 3047 import static java.lang.invoke.MethodHandles.*; 3048 import static java.lang.invoke.MethodType.*; 3049 ... 3050 static class Listie extends ArrayList { 3051 public String toString() { return "[wee Listie]"; } 3052 static Lookup lookup() { return MethodHandles.lookup(); } 3053 } 3054 ... 3055 // no access to constructor via invokeSpecial: 3056 MethodHandle MH_newListie = Listie.lookup() 3057 .findConstructor(Listie.class, methodType(void.class)); 3058 Listie l = (Listie) MH_newListie.invokeExact(); 3059 try { assertEquals("impossible", Listie.lookup().findSpecial( 3060 Listie.class, "<init>", methodType(void.class), Listie.class)); 3061 } catch (NoSuchMethodException ex) { } // OK 3062 // access to super and self methods via invokeSpecial: 3063 MethodHandle MH_super = Listie.lookup().findSpecial( 3064 ArrayList.class, "toString" , methodType(String.class), Listie.class); 3065 MethodHandle MH_this = Listie.lookup().findSpecial( 3066 Listie.class, "toString" , methodType(String.class), Listie.class); 3067 MethodHandle MH_duper = Listie.lookup().findSpecial( 3068 Object.class, "toString" , methodType(String.class), Listie.class); 3069 assertEquals("[]", (String) MH_super.invokeExact(l)); 3070 assertEquals(""+l, (String) MH_this.invokeExact(l)); 3071 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method 3072 try { assertEquals("inaccessible", Listie.lookup().findSpecial( 3073 String.class, "toString", methodType(String.class), Listie.class)); 3074 } catch (IllegalAccessException ex) { } // OK 3075 Listie subl = new Listie() { public String toString() { return "[subclass]"; } }; 3076 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method 3077 * } 3078 * 3079 * @param refc the class or interface from which the method is accessed 3080 * @param name the name of the method (which must not be "<init>") 3081 * @param type the type of the method, with the receiver argument omitted 3082 * @param specialCaller the proposed calling class to perform the {@code invokespecial} 3083 * @return the desired method handle 3084 * @throws NoSuchMethodException if the method does not exist 3085 * @throws IllegalAccessException if access checking fails, 3086 * or if the method is {@code static}, 3087 * or if the method's variable arity modifier bit 3088 * is set and {@code asVarargsCollector} fails 3089 * @throws SecurityException if a security manager is present and it 3090 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3091 * @throws NullPointerException if any argument is null 3092 */ 3093 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type, 3094 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException { 3095 checkSpecialCaller(specialCaller, refc); 3096 Lookup specialLookup = this.in(specialCaller); 3097 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type); 3098 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method)); 3099 } 3100 3101 /** 3102 * Produces a method handle giving read access to a non-static field. 3103 * The type of the method handle will have a return type of the field's 3104 * value type. 3105 * The method handle's single argument will be the instance containing 3106 * the field. 3107 * Access checking is performed immediately on behalf of the lookup class. 3108 * @param refc the class or interface from which the method is accessed 3109 * @param name the field's name 3110 * @param type the field's type 3111 * @return a method handle which can load values from the field 3112 * @throws NoSuchFieldException if the field does not exist 3113 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3114 * @throws SecurityException if a security manager is present and it 3115 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3116 * @throws NullPointerException if any argument is null 3117 * @see #findVarHandle(Class, String, Class) 3118 */ 3119 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3120 MemberName field = resolveOrFail(REF_getField, refc, name, type); 3121 return getDirectField(REF_getField, refc, field); 3122 } 3123 3124 /** 3125 * Produces a method handle giving write access to a non-static field. 3126 * The type of the method handle will have a void return type. 3127 * The method handle will take two arguments, the instance containing 3128 * the field, and the value to be stored. 3129 * The second argument will be of the field's value type. 3130 * Access checking is performed immediately on behalf of the lookup class. 3131 * @param refc the class or interface from which the method is accessed 3132 * @param name the field's name 3133 * @param type the field's type 3134 * @return a method handle which can store values into the field 3135 * @throws NoSuchFieldException if the field does not exist 3136 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3137 * or {@code final} 3138 * @throws SecurityException if a security manager is present and it 3139 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3140 * @throws NullPointerException if any argument is null 3141 * @see #findVarHandle(Class, String, Class) 3142 */ 3143 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3144 MemberName field = resolveOrFail(REF_putField, refc, name, type); 3145 return getDirectField(REF_putField, refc, field); 3146 } 3147 3148 /** 3149 * Produces a VarHandle giving access to a non-static field {@code name} 3150 * of type {@code type} declared in a class of type {@code recv}. 3151 * The VarHandle's variable type is {@code type} and it has one 3152 * coordinate type, {@code recv}. 3153 * <p> 3154 * Access checking is performed immediately on behalf of the lookup 3155 * class. 3156 * <p> 3157 * Certain access modes of the returned VarHandle are unsupported under 3158 * the following conditions: 3159 * <ul> 3160 * <li>if the field is declared {@code final}, then the write, atomic 3161 * update, numeric atomic update, and bitwise atomic update access 3162 * modes are unsupported. 3163 * <li>if the field type is anything other than {@code byte}, 3164 * {@code short}, {@code char}, {@code int}, {@code long}, 3165 * {@code float}, or {@code double} then numeric atomic update 3166 * access modes are unsupported. 3167 * <li>if the field type is anything other than {@code boolean}, 3168 * {@code byte}, {@code short}, {@code char}, {@code int} or 3169 * {@code long} then bitwise atomic update access modes are 3170 * unsupported. 3171 * </ul> 3172 * <p> 3173 * If the field is declared {@code volatile} then the returned VarHandle 3174 * will override access to the field (effectively ignore the 3175 * {@code volatile} declaration) in accordance to its specified 3176 * access modes. 3177 * <p> 3178 * If the field type is {@code float} or {@code double} then numeric 3179 * and atomic update access modes compare values using their bitwise 3180 * representation (see {@link Float#floatToRawIntBits} and 3181 * {@link Double#doubleToRawLongBits}, respectively). 3182 * @apiNote 3183 * Bitwise comparison of {@code float} values or {@code double} values, 3184 * as performed by the numeric and atomic update access modes, differ 3185 * from the primitive {@code ==} operator and the {@link Float#equals} 3186 * and {@link Double#equals} methods, specifically with respect to 3187 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3188 * Care should be taken when performing a compare and set or a compare 3189 * and exchange operation with such values since the operation may 3190 * unexpectedly fail. 3191 * There are many possible NaN values that are considered to be 3192 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3193 * provided by Java can distinguish between them. Operation failure can 3194 * occur if the expected or witness value is a NaN value and it is 3195 * transformed (perhaps in a platform specific manner) into another NaN 3196 * value, and thus has a different bitwise representation (see 3197 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3198 * details). 3199 * The values {@code -0.0} and {@code +0.0} have different bitwise 3200 * representations but are considered equal when using the primitive 3201 * {@code ==} operator. Operation failure can occur if, for example, a 3202 * numeric algorithm computes an expected value to be say {@code -0.0} 3203 * and previously computed the witness value to be say {@code +0.0}. 3204 * @param recv the receiver class, of type {@code R}, that declares the 3205 * non-static field 3206 * @param name the field's name 3207 * @param type the field's type, of type {@code T} 3208 * @return a VarHandle giving access to non-static fields. 3209 * @throws NoSuchFieldException if the field does not exist 3210 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3211 * @throws SecurityException if a security manager is present and it 3212 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3213 * @throws NullPointerException if any argument is null 3214 * @since 9 3215 */ 3216 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3217 MemberName getField = resolveOrFail(REF_getField, recv, name, type); 3218 MemberName putField = resolveOrFail(REF_putField, recv, name, type); 3219 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField); 3220 } 3221 3222 /** 3223 * Produces a method handle giving read access to a static field. 3224 * The type of the method handle will have a return type of the field's 3225 * value type. 3226 * The method handle will take no arguments. 3227 * Access checking is performed immediately on behalf of the lookup class. 3228 * <p> 3229 * If the returned method handle is invoked, the field's class will 3230 * be initialized, if it has not already been initialized. 3231 * @param refc the class or interface from which the method is accessed 3232 * @param name the field's name 3233 * @param type the field's type 3234 * @return a method handle which can load values from the field 3235 * @throws NoSuchFieldException if the field does not exist 3236 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3237 * @throws SecurityException if a security manager is present and it 3238 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3239 * @throws NullPointerException if any argument is null 3240 */ 3241 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3242 MemberName field = resolveOrFail(REF_getStatic, refc, name, type); 3243 return getDirectField(REF_getStatic, refc, field); 3244 } 3245 3246 /** 3247 * Produces a method handle giving write access to a static field. 3248 * The type of the method handle will have a void return type. 3249 * The method handle will take a single 3250 * argument, of the field's value type, the value to be stored. 3251 * Access checking is performed immediately on behalf of the lookup class. 3252 * <p> 3253 * If the returned method handle is invoked, the field's class will 3254 * be initialized, if it has not already been initialized. 3255 * @param refc the class or interface from which the method is accessed 3256 * @param name the field's name 3257 * @param type the field's type 3258 * @return a method handle which can store values into the field 3259 * @throws NoSuchFieldException if the field does not exist 3260 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3261 * or is {@code final} 3262 * @throws SecurityException if a security manager is present and it 3263 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3264 * @throws NullPointerException if any argument is null 3265 */ 3266 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3267 MemberName field = resolveOrFail(REF_putStatic, refc, name, type); 3268 return getDirectField(REF_putStatic, refc, field); 3269 } 3270 3271 /** 3272 * Produces a VarHandle giving access to a static field {@code name} of 3273 * type {@code type} declared in a class of type {@code decl}. 3274 * The VarHandle's variable type is {@code type} and it has no 3275 * coordinate types. 3276 * <p> 3277 * Access checking is performed immediately on behalf of the lookup 3278 * class. 3279 * <p> 3280 * If the returned VarHandle is operated on, the declaring class will be 3281 * initialized, if it has not already been initialized. 3282 * <p> 3283 * Certain access modes of the returned VarHandle are unsupported under 3284 * the following conditions: 3285 * <ul> 3286 * <li>if the field is declared {@code final}, then the write, atomic 3287 * update, numeric atomic update, and bitwise atomic update access 3288 * modes are unsupported. 3289 * <li>if the field type is anything other than {@code byte}, 3290 * {@code short}, {@code char}, {@code int}, {@code long}, 3291 * {@code float}, or {@code double}, then numeric atomic update 3292 * access modes are unsupported. 3293 * <li>if the field type is anything other than {@code boolean}, 3294 * {@code byte}, {@code short}, {@code char}, {@code int} or 3295 * {@code long} then bitwise atomic update access modes are 3296 * unsupported. 3297 * </ul> 3298 * <p> 3299 * If the field is declared {@code volatile} then the returned VarHandle 3300 * will override access to the field (effectively ignore the 3301 * {@code volatile} declaration) in accordance to its specified 3302 * access modes. 3303 * <p> 3304 * If the field type is {@code float} or {@code double} then numeric 3305 * and atomic update access modes compare values using their bitwise 3306 * representation (see {@link Float#floatToRawIntBits} and 3307 * {@link Double#doubleToRawLongBits}, respectively). 3308 * @apiNote 3309 * Bitwise comparison of {@code float} values or {@code double} values, 3310 * as performed by the numeric and atomic update access modes, differ 3311 * from the primitive {@code ==} operator and the {@link Float#equals} 3312 * and {@link Double#equals} methods, specifically with respect to 3313 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3314 * Care should be taken when performing a compare and set or a compare 3315 * and exchange operation with such values since the operation may 3316 * unexpectedly fail. 3317 * There are many possible NaN values that are considered to be 3318 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3319 * provided by Java can distinguish between them. Operation failure can 3320 * occur if the expected or witness value is a NaN value and it is 3321 * transformed (perhaps in a platform specific manner) into another NaN 3322 * value, and thus has a different bitwise representation (see 3323 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3324 * details). 3325 * The values {@code -0.0} and {@code +0.0} have different bitwise 3326 * representations but are considered equal when using the primitive 3327 * {@code ==} operator. Operation failure can occur if, for example, a 3328 * numeric algorithm computes an expected value to be say {@code -0.0} 3329 * and previously computed the witness value to be say {@code +0.0}. 3330 * @param decl the class that declares the static field 3331 * @param name the field's name 3332 * @param type the field's type, of type {@code T} 3333 * @return a VarHandle giving access to a static field 3334 * @throws NoSuchFieldException if the field does not exist 3335 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3336 * @throws SecurityException if a security manager is present and it 3337 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3338 * @throws NullPointerException if any argument is null 3339 * @since 9 3340 */ 3341 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3342 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type); 3343 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type); 3344 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField); 3345 } 3346 3347 /** 3348 * Produces an early-bound method handle for a non-static method. 3349 * The receiver must have a supertype {@code defc} in which a method 3350 * of the given name and type is accessible to the lookup class. 3351 * The method and all its argument types must be accessible to the lookup object. 3352 * The type of the method handle will be that of the method, 3353 * without any insertion of an additional receiver parameter. 3354 * The given receiver will be bound into the method handle, 3355 * so that every call to the method handle will invoke the 3356 * requested method on the given receiver. 3357 * <p> 3358 * The returned method handle will have 3359 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3360 * the method's variable arity modifier bit ({@code 0x0080}) is set 3361 * <em>and</em> the trailing array argument is not the only argument. 3362 * (If the trailing array argument is the only argument, 3363 * the given receiver value will be bound to it.) 3364 * <p> 3365 * This is almost equivalent to the following code, with some differences noted below: 3366 * {@snippet lang="java" : 3367 import static java.lang.invoke.MethodHandles.*; 3368 import static java.lang.invoke.MethodType.*; 3369 ... 3370 MethodHandle mh0 = lookup().findVirtual(defc, name, type); 3371 MethodHandle mh1 = mh0.bindTo(receiver); 3372 mh1 = mh1.withVarargs(mh0.isVarargsCollector()); 3373 return mh1; 3374 * } 3375 * where {@code defc} is either {@code receiver.getClass()} or a super 3376 * type of that class, in which the requested method is accessible 3377 * to the lookup class. 3378 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity. 3379 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would 3380 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and 3381 * the receiver is restricted by {@code findVirtual} to the lookup class.) 3382 * @param receiver the object from which the method is accessed 3383 * @param name the name of the method 3384 * @param type the type of the method, with the receiver argument omitted 3385 * @return the desired method handle 3386 * @throws NoSuchMethodException if the method does not exist 3387 * @throws IllegalAccessException if access checking fails 3388 * or if the method's variable arity modifier bit 3389 * is set and {@code asVarargsCollector} fails 3390 * @throws SecurityException if a security manager is present and it 3391 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3392 * @throws NullPointerException if any argument is null 3393 * @see MethodHandle#bindTo 3394 * @see #findVirtual 3395 */ 3396 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 3397 Class<? extends Object> refc = receiver.getClass(); // may get NPE 3398 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type); 3399 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method)); 3400 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) { 3401 throw new IllegalAccessException("The restricted defining class " + 3402 mh.type().leadingReferenceParameter().getName() + 3403 " is not assignable from receiver class " + 3404 receiver.getClass().getName()); 3405 } 3406 return mh.bindArgumentL(0, receiver).setVarargs(method); 3407 } 3408 3409 /** 3410 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 3411 * to <i>m</i>, if the lookup class has permission. 3412 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument. 3413 * If <i>m</i> is virtual, overriding is respected on every call. 3414 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped. 3415 * The type of the method handle will be that of the method, 3416 * with the receiver type prepended (but only if it is non-static). 3417 * If the method's {@code accessible} flag is not set, 3418 * access checking is performed immediately on behalf of the lookup class. 3419 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties. 3420 * <p> 3421 * The returned method handle will have 3422 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3423 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3424 * <p> 3425 * If <i>m</i> is static, and 3426 * if the returned method handle is invoked, the method's class will 3427 * be initialized, if it has not already been initialized. 3428 * @param m the reflected method 3429 * @return a method handle which can invoke the reflected method 3430 * @throws IllegalAccessException if access checking fails 3431 * or if the method's variable arity modifier bit 3432 * is set and {@code asVarargsCollector} fails 3433 * @throws NullPointerException if the argument is null 3434 */ 3435 public MethodHandle unreflect(Method m) throws IllegalAccessException { 3436 if (m.getDeclaringClass() == MethodHandle.class) { 3437 MethodHandle mh = unreflectForMH(m); 3438 if (mh != null) return mh; 3439 } 3440 if (m.getDeclaringClass() == VarHandle.class) { 3441 MethodHandle mh = unreflectForVH(m); 3442 if (mh != null) return mh; 3443 } 3444 MemberName method = new MemberName(m); 3445 byte refKind = method.getReferenceKind(); 3446 if (refKind == REF_invokeSpecial) 3447 refKind = REF_invokeVirtual; 3448 assert(method.isMethod()); 3449 @SuppressWarnings("deprecation") 3450 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this; 3451 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method)); 3452 } 3453 private MethodHandle unreflectForMH(Method m) { 3454 // these names require special lookups because they throw UnsupportedOperationException 3455 if (MemberName.isMethodHandleInvokeName(m.getName())) 3456 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m)); 3457 return null; 3458 } 3459 private MethodHandle unreflectForVH(Method m) { 3460 // these names require special lookups because they throw UnsupportedOperationException 3461 if (MemberName.isVarHandleMethodInvokeName(m.getName())) 3462 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m)); 3463 return null; 3464 } 3465 3466 /** 3467 * Produces a method handle for a reflected method. 3468 * It will bypass checks for overriding methods on the receiver, 3469 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 3470 * instruction from within the explicitly specified {@code specialCaller}. 3471 * The type of the method handle will be that of the method, 3472 * with a suitably restricted receiver type prepended. 3473 * (The receiver type will be {@code specialCaller} or a subtype.) 3474 * If the method's {@code accessible} flag is not set, 3475 * access checking is performed immediately on behalf of the lookup class, 3476 * as if {@code invokespecial} instruction were being linked. 3477 * <p> 3478 * Before method resolution, 3479 * if the explicitly specified caller class is not identical with the 3480 * lookup class, or if this lookup object does not have 3481 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 3482 * privileges, the access fails. 3483 * <p> 3484 * The returned method handle will have 3485 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3486 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3487 * @param m the reflected method 3488 * @param specialCaller the class nominally calling the method 3489 * @return a method handle which can invoke the reflected method 3490 * @throws IllegalAccessException if access checking fails, 3491 * or if the method is {@code static}, 3492 * or if the method's variable arity modifier bit 3493 * is set and {@code asVarargsCollector} fails 3494 * @throws NullPointerException if any argument is null 3495 */ 3496 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException { 3497 checkSpecialCaller(specialCaller, m.getDeclaringClass()); 3498 Lookup specialLookup = this.in(specialCaller); 3499 MemberName method = new MemberName(m, true); 3500 assert(method.isMethod()); 3501 // ignore m.isAccessible: this is a new kind of access 3502 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method)); 3503 } 3504 3505 /** 3506 * Produces a method handle for a reflected constructor. 3507 * The type of the method handle will be that of the constructor, 3508 * with the return type changed to the declaring class. 3509 * The method handle will perform a {@code newInstance} operation, 3510 * creating a new instance of the constructor's class on the 3511 * arguments passed to the method handle. 3512 * <p> 3513 * If the constructor's {@code accessible} flag is not set, 3514 * access checking is performed immediately on behalf of the lookup class. 3515 * <p> 3516 * The returned method handle will have 3517 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3518 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 3519 * <p> 3520 * If the returned method handle is invoked, the constructor's class will 3521 * be initialized, if it has not already been initialized. 3522 * @param c the reflected constructor 3523 * @return a method handle which can invoke the reflected constructor 3524 * @throws IllegalAccessException if access checking fails 3525 * or if the method's variable arity modifier bit 3526 * is set and {@code asVarargsCollector} fails 3527 * @throws NullPointerException if the argument is null 3528 */ 3529 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException { 3530 MemberName ctor = new MemberName(c); 3531 assert(ctor.isConstructor()); 3532 @SuppressWarnings("deprecation") 3533 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this; 3534 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor); 3535 } 3536 3537 /** 3538 * Produces a method handle giving read access to a reflected field. 3539 * The type of the method handle will have a return type of the field's 3540 * value type. 3541 * If the field is {@code static}, the method handle will take no arguments. 3542 * Otherwise, its single argument will be the instance containing 3543 * the field. 3544 * If the {@code Field} object's {@code accessible} flag is not set, 3545 * access checking is performed immediately on behalf of the lookup class. 3546 * <p> 3547 * If the field is static, and 3548 * if the returned method handle is invoked, the field's class will 3549 * be initialized, if it has not already been initialized. 3550 * @param f the reflected field 3551 * @return a method handle which can load values from the reflected field 3552 * @throws IllegalAccessException if access checking fails 3553 * @throws NullPointerException if the argument is null 3554 */ 3555 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException { 3556 return unreflectField(f, false); 3557 } 3558 3559 /** 3560 * Produces a method handle giving write access to a reflected field. 3561 * The type of the method handle will have a void return type. 3562 * If the field is {@code static}, the method handle will take a single 3563 * argument, of the field's value type, the value to be stored. 3564 * Otherwise, the two arguments will be the instance containing 3565 * the field, and the value to be stored. 3566 * If the {@code Field} object's {@code accessible} flag is not set, 3567 * access checking is performed immediately on behalf of the lookup class. 3568 * <p> 3569 * If the field is {@code final}, write access will not be 3570 * allowed and access checking will fail, except under certain 3571 * narrow circumstances documented for {@link Field#set Field.set}. 3572 * A method handle is returned only if a corresponding call to 3573 * the {@code Field} object's {@code set} method could return 3574 * normally. In particular, fields which are both {@code static} 3575 * and {@code final} may never be set. 3576 * <p> 3577 * If the field is {@code static}, and 3578 * if the returned method handle is invoked, the field's class will 3579 * be initialized, if it has not already been initialized. 3580 * @param f the reflected field 3581 * @return a method handle which can store values into the reflected field 3582 * @throws IllegalAccessException if access checking fails, 3583 * or if the field is {@code final} and write access 3584 * is not enabled on the {@code Field} object 3585 * @throws NullPointerException if the argument is null 3586 */ 3587 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException { 3588 return unreflectField(f, true); 3589 } 3590 3591 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException { 3592 MemberName field = new MemberName(f, isSetter); 3593 if (isSetter && field.isFinal()) { 3594 if (field.isTrustedFinalField()) { 3595 String msg = field.isStatic() ? "static final field has no write access" 3596 : "final field has no write access"; 3597 throw field.makeAccessException(msg, this); 3598 } 3599 } 3600 assert(isSetter 3601 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind()) 3602 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind())); 3603 @SuppressWarnings("deprecation") 3604 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this; 3605 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field); 3606 } 3607 3608 /** 3609 * Produces a VarHandle giving access to a reflected field {@code f} 3610 * of type {@code T} declared in a class of type {@code R}. 3611 * The VarHandle's variable type is {@code T}. 3612 * If the field is non-static the VarHandle has one coordinate type, 3613 * {@code R}. Otherwise, the field is static, and the VarHandle has no 3614 * coordinate types. 3615 * <p> 3616 * Access checking is performed immediately on behalf of the lookup 3617 * class, regardless of the value of the field's {@code accessible} 3618 * flag. 3619 * <p> 3620 * If the field is static, and if the returned VarHandle is operated 3621 * on, the field's declaring class will be initialized, if it has not 3622 * already been initialized. 3623 * <p> 3624 * Certain access modes of the returned VarHandle are unsupported under 3625 * the following conditions: 3626 * <ul> 3627 * <li>if the field is declared {@code final}, then the write, atomic 3628 * update, numeric atomic update, and bitwise atomic update access 3629 * modes are unsupported. 3630 * <li>if the field type is anything other than {@code byte}, 3631 * {@code short}, {@code char}, {@code int}, {@code long}, 3632 * {@code float}, or {@code double} then numeric atomic update 3633 * access modes are unsupported. 3634 * <li>if the field type is anything other than {@code boolean}, 3635 * {@code byte}, {@code short}, {@code char}, {@code int} or 3636 * {@code long} then bitwise atomic update access modes are 3637 * unsupported. 3638 * </ul> 3639 * <p> 3640 * If the field is declared {@code volatile} then the returned VarHandle 3641 * will override access to the field (effectively ignore the 3642 * {@code volatile} declaration) in accordance to its specified 3643 * access modes. 3644 * <p> 3645 * If the field type is {@code float} or {@code double} then numeric 3646 * and atomic update access modes compare values using their bitwise 3647 * representation (see {@link Float#floatToRawIntBits} and 3648 * {@link Double#doubleToRawLongBits}, respectively). 3649 * @apiNote 3650 * Bitwise comparison of {@code float} values or {@code double} values, 3651 * as performed by the numeric and atomic update access modes, differ 3652 * from the primitive {@code ==} operator and the {@link Float#equals} 3653 * and {@link Double#equals} methods, specifically with respect to 3654 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3655 * Care should be taken when performing a compare and set or a compare 3656 * and exchange operation with such values since the operation may 3657 * unexpectedly fail. 3658 * There are many possible NaN values that are considered to be 3659 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3660 * provided by Java can distinguish between them. Operation failure can 3661 * occur if the expected or witness value is a NaN value and it is 3662 * transformed (perhaps in a platform specific manner) into another NaN 3663 * value, and thus has a different bitwise representation (see 3664 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3665 * details). 3666 * The values {@code -0.0} and {@code +0.0} have different bitwise 3667 * representations but are considered equal when using the primitive 3668 * {@code ==} operator. Operation failure can occur if, for example, a 3669 * numeric algorithm computes an expected value to be say {@code -0.0} 3670 * and previously computed the witness value to be say {@code +0.0}. 3671 * @param f the reflected field, with a field of type {@code T}, and 3672 * a declaring class of type {@code R} 3673 * @return a VarHandle giving access to non-static fields or a static 3674 * field 3675 * @throws IllegalAccessException if access checking fails 3676 * @throws NullPointerException if the argument is null 3677 * @since 9 3678 */ 3679 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException { 3680 MemberName getField = new MemberName(f, false); 3681 MemberName putField = new MemberName(f, true); 3682 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(), 3683 f.getDeclaringClass(), getField, putField); 3684 } 3685 3686 /** 3687 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 3688 * created by this lookup object or a similar one. 3689 * Security and access checks are performed to ensure that this lookup object 3690 * is capable of reproducing the target method handle. 3691 * This means that the cracking may fail if target is a direct method handle 3692 * but was created by an unrelated lookup object. 3693 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> 3694 * and was created by a lookup object for a different class. 3695 * @param target a direct method handle to crack into symbolic reference components 3696 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object 3697 * @throws SecurityException if a security manager is present and it 3698 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3699 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails 3700 * @throws NullPointerException if the target is {@code null} 3701 * @see MethodHandleInfo 3702 * @since 1.8 3703 */ 3704 public MethodHandleInfo revealDirect(MethodHandle target) { 3705 if (!target.isCrackable()) { 3706 throw newIllegalArgumentException("not a direct method handle"); 3707 } 3708 MemberName member = target.internalMemberName(); 3709 Class<?> defc = member.getDeclaringClass(); 3710 byte refKind = member.getReferenceKind(); 3711 assert(MethodHandleNatives.refKindIsValid(refKind)); 3712 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial()) 3713 // Devirtualized method invocation is usually formally virtual. 3714 // To avoid creating extra MemberName objects for this common case, 3715 // we encode this extra degree of freedom using MH.isInvokeSpecial. 3716 refKind = REF_invokeVirtual; 3717 if (refKind == REF_invokeVirtual && defc.isInterface()) 3718 // Symbolic reference is through interface but resolves to Object method (toString, etc.) 3719 refKind = REF_invokeInterface; 3720 // Check SM permissions and member access before cracking. 3721 try { 3722 checkAccess(refKind, defc, member); 3723 checkSecurityManager(defc, member); 3724 } catch (IllegalAccessException ex) { 3725 throw new IllegalArgumentException(ex); 3726 } 3727 if (allowedModes != TRUSTED && member.isCallerSensitive()) { 3728 Class<?> callerClass = target.internalCallerClass(); 3729 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass()) 3730 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass); 3731 } 3732 // Produce the handle to the results. 3733 return new InfoFromMemberName(this, member, refKind); 3734 } 3735 3736 /// Helper methods, all package-private. 3737 3738 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3739 checkSymbolicClass(refc); // do this before attempting to resolve 3740 Objects.requireNonNull(name); 3741 Objects.requireNonNull(type); 3742 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes, 3743 NoSuchFieldException.class); 3744 } 3745 3746 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 3747 checkSymbolicClass(refc); // do this before attempting to resolve 3748 Objects.requireNonNull(type); 3749 checkMethodName(refKind, name); // implicit null-check of name 3750 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes, 3751 NoSuchMethodException.class); 3752 } 3753 3754 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException { 3755 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve 3756 Objects.requireNonNull(member.getName()); 3757 Objects.requireNonNull(member.getType()); 3758 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes, 3759 ReflectiveOperationException.class); 3760 } 3761 3762 MemberName resolveOrNull(byte refKind, MemberName member) { 3763 // do this before attempting to resolve 3764 if (!isClassAccessible(member.getDeclaringClass())) { 3765 return null; 3766 } 3767 Objects.requireNonNull(member.getName()); 3768 Objects.requireNonNull(member.getType()); 3769 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes); 3770 } 3771 3772 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) { 3773 // do this before attempting to resolve 3774 if (!isClassAccessible(refc)) { 3775 return null; 3776 } 3777 Objects.requireNonNull(type); 3778 // implicit null-check of name 3779 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) { 3780 return null; 3781 } 3782 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes); 3783 } 3784 3785 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException { 3786 if (!isClassAccessible(refc)) { 3787 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this); 3788 } 3789 } 3790 3791 boolean isClassAccessible(Class<?> refc) { 3792 Objects.requireNonNull(refc); 3793 Class<?> caller = lookupClassOrNull(); 3794 Class<?> type = refc; 3795 while (type.isArray()) { 3796 type = type.getComponentType(); 3797 } 3798 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes); 3799 } 3800 3801 /** Check name for an illegal leading "<" character. */ 3802 void checkMethodName(byte refKind, String name) throws NoSuchMethodException { 3803 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) 3804 throw new NoSuchMethodException("illegal method name: "+name); 3805 } 3806 3807 /** 3808 * Find my trustable caller class if m is a caller sensitive method. 3809 * If this lookup object has original full privilege access, then the caller class is the lookupClass. 3810 * Otherwise, if m is caller-sensitive, throw IllegalAccessException. 3811 */ 3812 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException { 3813 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) { 3814 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods 3815 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 3816 } 3817 return this; 3818 } 3819 3820 /** 3821 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access. 3822 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access. 3823 * 3824 * @deprecated This method was originally designed to test {@code PRIVATE} access 3825 * that implies full privilege access but {@code MODULE} access has since become 3826 * independent of {@code PRIVATE} access. It is recommended to call 3827 * {@link #hasFullPrivilegeAccess()} instead. 3828 * @since 9 3829 */ 3830 @Deprecated(since="14") 3831 public boolean hasPrivateAccess() { 3832 return hasFullPrivilegeAccess(); 3833 } 3834 3835 /** 3836 * Returns {@code true} if this lookup has <em>full privilege access</em>, 3837 * i.e. {@code PRIVATE} and {@code MODULE} access. 3838 * A {@code Lookup} object must have full privilege access in order to 3839 * access all members that are allowed to the 3840 * {@linkplain #lookupClass() lookup class}. 3841 * 3842 * @return {@code true} if this lookup has full privilege access. 3843 * @since 14 3844 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a> 3845 */ 3846 public boolean hasFullPrivilegeAccess() { 3847 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE); 3848 } 3849 3850 /** 3851 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a> 3852 * for ensureInitialized, findClass or accessClass. 3853 */ 3854 void checkSecurityManager(Class<?> refc) { 3855 if (allowedModes == TRUSTED) return; 3856 3857 @SuppressWarnings("removal") 3858 SecurityManager smgr = System.getSecurityManager(); 3859 if (smgr == null) return; 3860 3861 // Step 1: 3862 boolean fullPrivilegeLookup = hasFullPrivilegeAccess(); 3863 if (!fullPrivilegeLookup || 3864 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 3865 ReflectUtil.checkPackageAccess(refc); 3866 } 3867 3868 // Step 2b: 3869 if (!fullPrivilegeLookup) { 3870 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION); 3871 } 3872 } 3873 3874 /** 3875 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>. 3876 * Determines a trustable caller class to compare with refc, the symbolic reference class. 3877 * If this lookup object has full privilege access except original access, 3878 * then the caller class is the lookupClass. 3879 * 3880 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)} 3881 * from the same module skips the security permission check. 3882 */ 3883 void checkSecurityManager(Class<?> refc, MemberName m) { 3884 Objects.requireNonNull(refc); 3885 Objects.requireNonNull(m); 3886 3887 if (allowedModes == TRUSTED) return; 3888 3889 @SuppressWarnings("removal") 3890 SecurityManager smgr = System.getSecurityManager(); 3891 if (smgr == null) return; 3892 3893 // Step 1: 3894 boolean fullPrivilegeLookup = hasFullPrivilegeAccess(); 3895 if (!fullPrivilegeLookup || 3896 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 3897 ReflectUtil.checkPackageAccess(refc); 3898 } 3899 3900 // Step 2a: 3901 if (m.isPublic()) return; 3902 if (!fullPrivilegeLookup) { 3903 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION); 3904 } 3905 3906 // Step 3: 3907 Class<?> defc = m.getDeclaringClass(); 3908 if (!fullPrivilegeLookup && defc != refc) { 3909 ReflectUtil.checkPackageAccess(defc); 3910 } 3911 } 3912 3913 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3914 boolean wantStatic = (refKind == REF_invokeStatic); 3915 String message; 3916 if (m.isConstructor()) 3917 message = "expected a method, not a constructor"; 3918 else if (!m.isMethod()) 3919 message = "expected a method"; 3920 else if (wantStatic != m.isStatic()) 3921 message = wantStatic ? "expected a static method" : "expected a non-static method"; 3922 else 3923 { checkAccess(refKind, refc, m); return; } 3924 throw m.makeAccessException(message, this); 3925 } 3926 3927 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3928 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind); 3929 String message; 3930 if (wantStatic != m.isStatic()) 3931 message = wantStatic ? "expected a static field" : "expected a non-static field"; 3932 else 3933 { checkAccess(refKind, refc, m); return; } 3934 throw m.makeAccessException(message, this); 3935 } 3936 3937 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) { 3938 return Modifier.isProtected(m.getModifiers()) && 3939 refKind == REF_invokeVirtual && 3940 m.getDeclaringClass() == Object.class && 3941 m.getName().equals("clone") && 3942 refc.isArray(); 3943 } 3944 3945 /** Check public/protected/private bits on the symbolic reference class and its member. */ 3946 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3947 assert(m.referenceKindIsConsistentWith(refKind) && 3948 MethodHandleNatives.refKindIsValid(refKind) && 3949 (MethodHandleNatives.refKindIsField(refKind) == m.isField())); 3950 int allowedModes = this.allowedModes; 3951 if (allowedModes == TRUSTED) return; 3952 int mods = m.getModifiers(); 3953 if (isArrayClone(refKind, refc, m)) { 3954 // The JVM does this hack also. 3955 // (See ClassVerifier::verify_invoke_instructions 3956 // and LinkResolver::check_method_accessability.) 3957 // Because the JVM does not allow separate methods on array types, 3958 // there is no separate method for int[].clone. 3959 // All arrays simply inherit Object.clone. 3960 // But for access checking logic, we make Object.clone 3961 // (normally protected) appear to be public. 3962 // Later on, when the DirectMethodHandle is created, 3963 // its leading argument will be restricted to the 3964 // requested array type. 3965 // N.B. The return type is not adjusted, because 3966 // that is *not* the bytecode behavior. 3967 mods ^= Modifier.PROTECTED | Modifier.PUBLIC; 3968 } 3969 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) { 3970 // cannot "new" a protected ctor in a different package 3971 mods ^= Modifier.PROTECTED; 3972 } 3973 if (Modifier.isFinal(mods) && 3974 MethodHandleNatives.refKindIsSetter(refKind)) 3975 throw m.makeAccessException("unexpected set of a final field", this); 3976 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE 3977 if ((requestedModes & allowedModes) != 0) { 3978 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(), 3979 mods, lookupClass(), previousLookupClass(), allowedModes)) 3980 return; 3981 } else { 3982 // Protected members can also be checked as if they were package-private. 3983 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0 3984 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass())) 3985 return; 3986 } 3987 throw m.makeAccessException(accessFailedMessage(refc, m), this); 3988 } 3989 3990 String accessFailedMessage(Class<?> refc, MemberName m) { 3991 Class<?> defc = m.getDeclaringClass(); 3992 int mods = m.getModifiers(); 3993 // check the class first: 3994 boolean classOK = (Modifier.isPublic(defc.getModifiers()) && 3995 (defc == refc || 3996 Modifier.isPublic(refc.getModifiers()))); 3997 if (!classOK && (allowedModes & PACKAGE) != 0) { 3998 // ignore previous lookup class to check if default package access 3999 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) && 4000 (defc == refc || 4001 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES))); 4002 } 4003 if (!classOK) 4004 return "class is not public"; 4005 if (Modifier.isPublic(mods)) 4006 return "access to public member failed"; // (how?, module not readable?) 4007 if (Modifier.isPrivate(mods)) 4008 return "member is private"; 4009 if (Modifier.isProtected(mods)) 4010 return "member is protected"; 4011 return "member is private to package"; 4012 } 4013 4014 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException { 4015 int allowedModes = this.allowedModes; 4016 if (allowedModes == TRUSTED) return; 4017 if ((lookupModes() & PRIVATE) == 0 4018 || (specialCaller != lookupClass() 4019 // ensure non-abstract methods in superinterfaces can be special-invoked 4020 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller)))) 4021 throw new MemberName(specialCaller). 4022 makeAccessException("no private access for invokespecial", this); 4023 } 4024 4025 private boolean restrictProtectedReceiver(MemberName method) { 4026 // The accessing class only has the right to use a protected member 4027 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc. 4028 if (!method.isProtected() || method.isStatic() 4029 || allowedModes == TRUSTED 4030 || method.getDeclaringClass() == lookupClass() 4031 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())) 4032 return false; 4033 return true; 4034 } 4035 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException { 4036 assert(!method.isStatic()); 4037 // receiver type of mh is too wide; narrow to caller 4038 if (!method.getDeclaringClass().isAssignableFrom(caller)) { 4039 throw method.makeAccessException("caller class must be a subclass below the method", caller); 4040 } 4041 MethodType rawType = mh.type(); 4042 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow 4043 MethodType narrowType = rawType.changeParameterType(0, caller); 4044 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness 4045 assert(mh.viewAsTypeChecks(narrowType, true)); 4046 return mh.copyWith(narrowType, mh.form); 4047 } 4048 4049 /** Check access and get the requested method. */ 4050 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 4051 final boolean doRestrict = true; 4052 final boolean checkSecurity = true; 4053 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup); 4054 } 4055 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */ 4056 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 4057 final boolean doRestrict = false; 4058 final boolean checkSecurity = true; 4059 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup); 4060 } 4061 /** Check access and get the requested method, eliding security manager checks. */ 4062 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 4063 final boolean doRestrict = true; 4064 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4065 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup); 4066 } 4067 /** Common code for all methods; do not call directly except from immediately above. */ 4068 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method, 4069 boolean checkSecurity, 4070 boolean doRestrict, 4071 Lookup boundCaller) throws IllegalAccessException { 4072 checkMethod(refKind, refc, method); 4073 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4074 if (checkSecurity) 4075 checkSecurityManager(refc, method); 4076 assert(!method.isMethodHandleInvoke()); 4077 4078 if (refKind == REF_invokeSpecial && 4079 refc != lookupClass() && 4080 !refc.isInterface() && !lookupClass().isInterface() && 4081 refc != lookupClass().getSuperclass() && 4082 refc.isAssignableFrom(lookupClass())) { 4083 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path 4084 4085 // Per JVMS 6.5, desc. of invokespecial instruction: 4086 // If the method is in a superclass of the LC, 4087 // and if our original search was above LC.super, 4088 // repeat the search (symbolic lookup) from LC.super 4089 // and continue with the direct superclass of that class, 4090 // and so forth, until a match is found or no further superclasses exist. 4091 // FIXME: MemberName.resolve should handle this instead. 4092 Class<?> refcAsSuper = lookupClass(); 4093 MemberName m2; 4094 do { 4095 refcAsSuper = refcAsSuper.getSuperclass(); 4096 m2 = new MemberName(refcAsSuper, 4097 method.getName(), 4098 method.getMethodType(), 4099 REF_invokeSpecial); 4100 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes); 4101 } while (m2 == null && // no method is found yet 4102 refc != refcAsSuper); // search up to refc 4103 if (m2 == null) throw new InternalError(method.toString()); 4104 method = m2; 4105 refc = refcAsSuper; 4106 // redo basic checks 4107 checkMethod(refKind, refc, method); 4108 } 4109 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass()); 4110 MethodHandle mh = dmh; 4111 // Optionally narrow the receiver argument to lookupClass using restrictReceiver. 4112 if ((doRestrict && refKind == REF_invokeSpecial) || 4113 (MethodHandleNatives.refKindHasReceiver(refKind) && 4114 restrictProtectedReceiver(method) && 4115 // All arrays simply inherit the protected Object.clone method. 4116 // The leading argument is already restricted to the requested 4117 // array type (not the lookup class). 4118 !isArrayClone(refKind, refc, method))) { 4119 mh = restrictReceiver(method, dmh, lookupClass()); 4120 } 4121 mh = maybeBindCaller(method, mh, boundCaller); 4122 mh = mh.setVarargs(method); 4123 return mh; 4124 } 4125 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller) 4126 throws IllegalAccessException { 4127 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method)) 4128 return mh; 4129 4130 // boundCaller must have full privilege access. 4131 // It should have been checked by findBoundCallerLookup. Safe to check this again. 4132 if ((boundCaller.lookupModes() & ORIGINAL) == 0) 4133 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 4134 4135 assert boundCaller.hasFullPrivilegeAccess(); 4136 4137 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass); 4138 // Note: caller will apply varargs after this step happens. 4139 return cbmh; 4140 } 4141 4142 /** Check access and get the requested field. */ 4143 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 4144 final boolean checkSecurity = true; 4145 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 4146 } 4147 /** Check access and get the requested field, eliding security manager checks. */ 4148 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 4149 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4150 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 4151 } 4152 /** Common code for all fields; do not call directly except from immediately above. */ 4153 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field, 4154 boolean checkSecurity) throws IllegalAccessException { 4155 checkField(refKind, refc, field); 4156 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4157 if (checkSecurity) 4158 checkSecurityManager(refc, field); 4159 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field); 4160 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) && 4161 restrictProtectedReceiver(field)); 4162 if (doRestrict) 4163 return restrictReceiver(field, dmh, lookupClass()); 4164 return dmh; 4165 } 4166 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind, 4167 Class<?> refc, MemberName getField, MemberName putField) 4168 throws IllegalAccessException { 4169 final boolean checkSecurity = true; 4170 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 4171 } 4172 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind, 4173 Class<?> refc, MemberName getField, MemberName putField) 4174 throws IllegalAccessException { 4175 final boolean checkSecurity = false; 4176 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 4177 } 4178 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind, 4179 Class<?> refc, MemberName getField, MemberName putField, 4180 boolean checkSecurity) throws IllegalAccessException { 4181 assert getField.isStatic() == putField.isStatic(); 4182 assert getField.isGetter() && putField.isSetter(); 4183 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind); 4184 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind); 4185 4186 checkField(getRefKind, refc, getField); 4187 if (checkSecurity) 4188 checkSecurityManager(refc, getField); 4189 4190 if (!putField.isFinal()) { 4191 // A VarHandle does not support updates to final fields, any 4192 // such VarHandle to a final field will be read-only and 4193 // therefore the following write-based accessibility checks are 4194 // only required for non-final fields 4195 checkField(putRefKind, refc, putField); 4196 if (checkSecurity) 4197 checkSecurityManager(refc, putField); 4198 } 4199 4200 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) && 4201 restrictProtectedReceiver(getField)); 4202 if (doRestrict) { 4203 assert !getField.isStatic(); 4204 // receiver type of VarHandle is too wide; narrow to caller 4205 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) { 4206 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass()); 4207 } 4208 refc = lookupClass(); 4209 } 4210 return VarHandles.makeFieldHandle(getField, refc, 4211 this.allowedModes == TRUSTED && !getField.isTrustedFinalField()); 4212 } 4213 /** Check access and get the requested constructor. */ 4214 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException { 4215 final boolean checkSecurity = true; 4216 return getDirectConstructorCommon(refc, ctor, checkSecurity); 4217 } 4218 /** Check access and get the requested constructor, eliding security manager checks. */ 4219 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException { 4220 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4221 return getDirectConstructorCommon(refc, ctor, checkSecurity); 4222 } 4223 /** Common code for all constructors; do not call directly except from immediately above. */ 4224 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor, 4225 boolean checkSecurity) throws IllegalAccessException { 4226 assert(ctor.isConstructor()); 4227 checkAccess(REF_newInvokeSpecial, refc, ctor); 4228 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4229 if (checkSecurity) 4230 checkSecurityManager(refc, ctor); 4231 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here 4232 return DirectMethodHandle.make(ctor).setVarargs(ctor); 4233 } 4234 4235 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants: 4236 */ 4237 /*non-public*/ 4238 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) 4239 throws ReflectiveOperationException { 4240 if (!(type instanceof Class || type instanceof MethodType)) 4241 throw new InternalError("unresolved MemberName"); 4242 MemberName member = new MemberName(refKind, defc, name, type); 4243 MethodHandle mh = LOOKASIDE_TABLE.get(member); 4244 if (mh != null) { 4245 checkSymbolicClass(defc); 4246 return mh; 4247 } 4248 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) { 4249 // Treat MethodHandle.invoke and invokeExact specially. 4250 mh = findVirtualForMH(member.getName(), member.getMethodType()); 4251 if (mh != null) { 4252 return mh; 4253 } 4254 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) { 4255 // Treat signature-polymorphic methods on VarHandle specially. 4256 mh = findVirtualForVH(member.getName(), member.getMethodType()); 4257 if (mh != null) { 4258 return mh; 4259 } 4260 } 4261 MemberName resolved = resolveOrFail(refKind, member); 4262 mh = getDirectMethodForConstant(refKind, defc, resolved); 4263 if (mh instanceof DirectMethodHandle dmh 4264 && canBeCached(refKind, defc, resolved)) { 4265 MemberName key = mh.internalMemberName(); 4266 if (key != null) { 4267 key = key.asNormalOriginal(); 4268 } 4269 if (member.equals(key)) { // better safe than sorry 4270 LOOKASIDE_TABLE.put(key, dmh); 4271 } 4272 } 4273 return mh; 4274 } 4275 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) { 4276 if (refKind == REF_invokeSpecial) { 4277 return false; 4278 } 4279 if (!Modifier.isPublic(defc.getModifiers()) || 4280 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) || 4281 !member.isPublic() || 4282 member.isCallerSensitive()) { 4283 return false; 4284 } 4285 ClassLoader loader = defc.getClassLoader(); 4286 if (loader != null) { 4287 ClassLoader sysl = ClassLoader.getSystemClassLoader(); 4288 boolean found = false; 4289 while (sysl != null) { 4290 if (loader == sysl) { found = true; break; } 4291 sysl = sysl.getParent(); 4292 } 4293 if (!found) { 4294 return false; 4295 } 4296 } 4297 try { 4298 MemberName resolved2 = publicLookup().resolveOrNull(refKind, 4299 new MemberName(refKind, defc, member.getName(), member.getType())); 4300 if (resolved2 == null) { 4301 return false; 4302 } 4303 checkSecurityManager(defc, resolved2); 4304 } catch (SecurityException ex) { 4305 return false; 4306 } 4307 return true; 4308 } 4309 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member) 4310 throws ReflectiveOperationException { 4311 if (MethodHandleNatives.refKindIsField(refKind)) { 4312 return getDirectFieldNoSecurityManager(refKind, defc, member); 4313 } else if (MethodHandleNatives.refKindIsMethod(refKind)) { 4314 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member)); 4315 } else if (refKind == REF_newInvokeSpecial) { 4316 return getDirectConstructorNoSecurityManager(defc, member); 4317 } 4318 // oops 4319 throw newIllegalArgumentException("bad MethodHandle constant #"+member); 4320 } 4321 4322 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>(); 4323 } 4324 4325 /** 4326 * Produces a method handle constructing arrays of a desired type, 4327 * as if by the {@code anewarray} bytecode. 4328 * The return type of the method handle will be the array type. 4329 * The type of its sole argument will be {@code int}, which specifies the size of the array. 4330 * 4331 * <p> If the returned method handle is invoked with a negative 4332 * array size, a {@code NegativeArraySizeException} will be thrown. 4333 * 4334 * @param arrayClass an array type 4335 * @return a method handle which can create arrays of the given type 4336 * @throws NullPointerException if the argument is {@code null} 4337 * @throws IllegalArgumentException if {@code arrayClass} is not an array type 4338 * @see java.lang.reflect.Array#newInstance(Class, int) 4339 * @jvms 6.5 {@code anewarray} Instruction 4340 * @since 9 4341 */ 4342 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException { 4343 if (!arrayClass.isArray()) { 4344 throw newIllegalArgumentException("not an array class: " + arrayClass.getName()); 4345 } 4346 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance). 4347 bindTo(arrayClass.getComponentType()); 4348 return ani.asType(ani.type().changeReturnType(arrayClass)); 4349 } 4350 4351 /** 4352 * Produces a method handle returning the length of an array, 4353 * as if by the {@code arraylength} bytecode. 4354 * The type of the method handle will have {@code int} as return type, 4355 * and its sole argument will be the array type. 4356 * 4357 * <p> If the returned method handle is invoked with a {@code null} 4358 * array reference, a {@code NullPointerException} will be thrown. 4359 * 4360 * @param arrayClass an array type 4361 * @return a method handle which can retrieve the length of an array of the given array type 4362 * @throws NullPointerException if the argument is {@code null} 4363 * @throws IllegalArgumentException if arrayClass is not an array type 4364 * @jvms 6.5 {@code arraylength} Instruction 4365 * @since 9 4366 */ 4367 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException { 4368 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH); 4369 } 4370 4371 /** 4372 * Produces a method handle giving read access to elements of an array, 4373 * as if by the {@code aaload} bytecode. 4374 * The type of the method handle will have a return type of the array's 4375 * element type. Its first argument will be the array type, 4376 * and the second will be {@code int}. 4377 * 4378 * <p> When the returned method handle is invoked, 4379 * the array reference and array index are checked. 4380 * A {@code NullPointerException} will be thrown if the array reference 4381 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4382 * thrown if the index is negative or if it is greater than or equal to 4383 * the length of the array. 4384 * 4385 * @param arrayClass an array type 4386 * @return a method handle which can load values from the given array type 4387 * @throws NullPointerException if the argument is null 4388 * @throws IllegalArgumentException if arrayClass is not an array type 4389 * @jvms 6.5 {@code aaload} Instruction 4390 */ 4391 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException { 4392 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET); 4393 } 4394 4395 /** 4396 * Produces a method handle giving write access to elements of an array, 4397 * as if by the {@code astore} bytecode. 4398 * The type of the method handle will have a void return type. 4399 * Its last argument will be the array's element type. 4400 * The first and second arguments will be the array type and int. 4401 * 4402 * <p> When the returned method handle is invoked, 4403 * the array reference and array index are checked. 4404 * A {@code NullPointerException} will be thrown if the array reference 4405 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4406 * thrown if the index is negative or if it is greater than or equal to 4407 * the length of the array. 4408 * 4409 * @param arrayClass the class of an array 4410 * @return a method handle which can store values into the array type 4411 * @throws NullPointerException if the argument is null 4412 * @throws IllegalArgumentException if arrayClass is not an array type 4413 * @jvms 6.5 {@code aastore} Instruction 4414 */ 4415 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException { 4416 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET); 4417 } 4418 4419 /** 4420 * Produces a VarHandle giving access to elements of an array of type 4421 * {@code arrayClass}. The VarHandle's variable type is the component type 4422 * of {@code arrayClass} and the list of coordinate types is 4423 * {@code (arrayClass, int)}, where the {@code int} coordinate type 4424 * corresponds to an argument that is an index into an array. 4425 * <p> 4426 * Certain access modes of the returned VarHandle are unsupported under 4427 * the following conditions: 4428 * <ul> 4429 * <li>if the component type is anything other than {@code byte}, 4430 * {@code short}, {@code char}, {@code int}, {@code long}, 4431 * {@code float}, or {@code double} then numeric atomic update access 4432 * modes are unsupported. 4433 * <li>if the component type is anything other than {@code boolean}, 4434 * {@code byte}, {@code short}, {@code char}, {@code int} or 4435 * {@code long} then bitwise atomic update access modes are 4436 * unsupported. 4437 * </ul> 4438 * <p> 4439 * If the component type is {@code float} or {@code double} then numeric 4440 * and atomic update access modes compare values using their bitwise 4441 * representation (see {@link Float#floatToRawIntBits} and 4442 * {@link Double#doubleToRawLongBits}, respectively). 4443 * 4444 * <p> When the returned {@code VarHandle} is invoked, 4445 * the array reference and array index are checked. 4446 * A {@code NullPointerException} will be thrown if the array reference 4447 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4448 * thrown if the index is negative or if it is greater than or equal to 4449 * the length of the array. 4450 * 4451 * @apiNote 4452 * Bitwise comparison of {@code float} values or {@code double} values, 4453 * as performed by the numeric and atomic update access modes, differ 4454 * from the primitive {@code ==} operator and the {@link Float#equals} 4455 * and {@link Double#equals} methods, specifically with respect to 4456 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 4457 * Care should be taken when performing a compare and set or a compare 4458 * and exchange operation with such values since the operation may 4459 * unexpectedly fail. 4460 * There are many possible NaN values that are considered to be 4461 * {@code NaN} in Java, although no IEEE 754 floating-point operation 4462 * provided by Java can distinguish between them. Operation failure can 4463 * occur if the expected or witness value is a NaN value and it is 4464 * transformed (perhaps in a platform specific manner) into another NaN 4465 * value, and thus has a different bitwise representation (see 4466 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 4467 * details). 4468 * The values {@code -0.0} and {@code +0.0} have different bitwise 4469 * representations but are considered equal when using the primitive 4470 * {@code ==} operator. Operation failure can occur if, for example, a 4471 * numeric algorithm computes an expected value to be say {@code -0.0} 4472 * and previously computed the witness value to be say {@code +0.0}. 4473 * @param arrayClass the class of an array, of type {@code T[]} 4474 * @return a VarHandle giving access to elements of an array 4475 * @throws NullPointerException if the arrayClass is null 4476 * @throws IllegalArgumentException if arrayClass is not an array type 4477 * @since 9 4478 */ 4479 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException { 4480 return VarHandles.makeArrayElementHandle(arrayClass); 4481 } 4482 4483 /** 4484 * Produces a VarHandle giving access to elements of a {@code byte[]} array 4485 * viewed as if it were a different primitive array type, such as 4486 * {@code int[]} or {@code long[]}. 4487 * The VarHandle's variable type is the component type of 4488 * {@code viewArrayClass} and the list of coordinate types is 4489 * {@code (byte[], int)}, where the {@code int} coordinate type 4490 * corresponds to an argument that is an index into a {@code byte[]} array. 4491 * The returned VarHandle accesses bytes at an index in a {@code byte[]} 4492 * array, composing bytes to or from a value of the component type of 4493 * {@code viewArrayClass} according to the given endianness. 4494 * <p> 4495 * The supported component types (variables types) are {@code short}, 4496 * {@code char}, {@code int}, {@code long}, {@code float} and 4497 * {@code double}. 4498 * <p> 4499 * Access of bytes at a given index will result in an 4500 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0} 4501 * or greater than the {@code byte[]} array length minus the size (in bytes) 4502 * of {@code T}. 4503 * <p> 4504 * Access of bytes at an index may be aligned or misaligned for {@code T}, 4505 * with respect to the underlying memory address, {@code A} say, associated 4506 * with the array and index. 4507 * If access is misaligned then access for anything other than the 4508 * {@code get} and {@code set} access modes will result in an 4509 * {@code IllegalStateException}. In such cases atomic access is only 4510 * guaranteed with respect to the largest power of two that divides the GCD 4511 * of {@code A} and the size (in bytes) of {@code T}. 4512 * If access is aligned then following access modes are supported and are 4513 * guaranteed to support atomic access: 4514 * <ul> 4515 * <li>read write access modes for all {@code T}, with the exception of 4516 * access modes {@code get} and {@code set} for {@code long} and 4517 * {@code double} on 32-bit platforms. 4518 * <li>atomic update access modes for {@code int}, {@code long}, 4519 * {@code float} or {@code double}. 4520 * (Future major platform releases of the JDK may support additional 4521 * types for certain currently unsupported access modes.) 4522 * <li>numeric atomic update access modes for {@code int} and {@code long}. 4523 * (Future major platform releases of the JDK may support additional 4524 * numeric types for certain currently unsupported access modes.) 4525 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 4526 * (Future major platform releases of the JDK may support additional 4527 * numeric types for certain currently unsupported access modes.) 4528 * </ul> 4529 * <p> 4530 * Misaligned access, and therefore atomicity guarantees, may be determined 4531 * for {@code byte[]} arrays without operating on a specific array. Given 4532 * an {@code index}, {@code T} and its corresponding boxed type, 4533 * {@code T_BOX}, misalignment may be determined as follows: 4534 * <pre>{@code 4535 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 4536 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]). 4537 * alignmentOffset(0, sizeOfT); 4538 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT; 4539 * boolean isMisaligned = misalignedAtIndex != 0; 4540 * }</pre> 4541 * <p> 4542 * If the variable type is {@code float} or {@code double} then atomic 4543 * update access modes compare values using their bitwise representation 4544 * (see {@link Float#floatToRawIntBits} and 4545 * {@link Double#doubleToRawLongBits}, respectively). 4546 * @param viewArrayClass the view array class, with a component type of 4547 * type {@code T} 4548 * @param byteOrder the endianness of the view array elements, as 4549 * stored in the underlying {@code byte} array 4550 * @return a VarHandle giving access to elements of a {@code byte[]} array 4551 * viewed as if elements corresponding to the components type of the view 4552 * array class 4553 * @throws NullPointerException if viewArrayClass or byteOrder is null 4554 * @throws IllegalArgumentException if viewArrayClass is not an array type 4555 * @throws UnsupportedOperationException if the component type of 4556 * viewArrayClass is not supported as a variable type 4557 * @since 9 4558 */ 4559 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass, 4560 ByteOrder byteOrder) throws IllegalArgumentException { 4561 Objects.requireNonNull(byteOrder); 4562 return VarHandles.byteArrayViewHandle(viewArrayClass, 4563 byteOrder == ByteOrder.BIG_ENDIAN); 4564 } 4565 4566 /** 4567 * Produces a VarHandle giving access to elements of a {@code ByteBuffer} 4568 * viewed as if it were an array of elements of a different primitive 4569 * component type to that of {@code byte}, such as {@code int[]} or 4570 * {@code long[]}. 4571 * The VarHandle's variable type is the component type of 4572 * {@code viewArrayClass} and the list of coordinate types is 4573 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type 4574 * corresponds to an argument that is an index into a {@code byte[]} array. 4575 * The returned VarHandle accesses bytes at an index in a 4576 * {@code ByteBuffer}, composing bytes to or from a value of the component 4577 * type of {@code viewArrayClass} according to the given endianness. 4578 * <p> 4579 * The supported component types (variables types) are {@code short}, 4580 * {@code char}, {@code int}, {@code long}, {@code float} and 4581 * {@code double}. 4582 * <p> 4583 * Access will result in a {@code ReadOnlyBufferException} for anything 4584 * other than the read access modes if the {@code ByteBuffer} is read-only. 4585 * <p> 4586 * Access of bytes at a given index will result in an 4587 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 4588 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of 4589 * {@code T}. 4590 * <p> 4591 * Access of bytes at an index may be aligned or misaligned for {@code T}, 4592 * with respect to the underlying memory address, {@code A} say, associated 4593 * with the {@code ByteBuffer} and index. 4594 * If access is misaligned then access for anything other than the 4595 * {@code get} and {@code set} access modes will result in an 4596 * {@code IllegalStateException}. In such cases atomic access is only 4597 * guaranteed with respect to the largest power of two that divides the GCD 4598 * of {@code A} and the size (in bytes) of {@code T}. 4599 * If access is aligned then following access modes are supported and are 4600 * guaranteed to support atomic access: 4601 * <ul> 4602 * <li>read write access modes for all {@code T}, with the exception of 4603 * access modes {@code get} and {@code set} for {@code long} and 4604 * {@code double} on 32-bit platforms. 4605 * <li>atomic update access modes for {@code int}, {@code long}, 4606 * {@code float} or {@code double}. 4607 * (Future major platform releases of the JDK may support additional 4608 * types for certain currently unsupported access modes.) 4609 * <li>numeric atomic update access modes for {@code int} and {@code long}. 4610 * (Future major platform releases of the JDK may support additional 4611 * numeric types for certain currently unsupported access modes.) 4612 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 4613 * (Future major platform releases of the JDK may support additional 4614 * numeric types for certain currently unsupported access modes.) 4615 * </ul> 4616 * <p> 4617 * Misaligned access, and therefore atomicity guarantees, may be determined 4618 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an 4619 * {@code index}, {@code T} and its corresponding boxed type, 4620 * {@code T_BOX}, as follows: 4621 * <pre>{@code 4622 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 4623 * ByteBuffer bb = ... 4624 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT); 4625 * boolean isMisaligned = misalignedAtIndex != 0; 4626 * }</pre> 4627 * <p> 4628 * If the variable type is {@code float} or {@code double} then atomic 4629 * update access modes compare values using their bitwise representation 4630 * (see {@link Float#floatToRawIntBits} and 4631 * {@link Double#doubleToRawLongBits}, respectively). 4632 * @param viewArrayClass the view array class, with a component type of 4633 * type {@code T} 4634 * @param byteOrder the endianness of the view array elements, as 4635 * stored in the underlying {@code ByteBuffer} (Note this overrides the 4636 * endianness of a {@code ByteBuffer}) 4637 * @return a VarHandle giving access to elements of a {@code ByteBuffer} 4638 * viewed as if elements corresponding to the components type of the view 4639 * array class 4640 * @throws NullPointerException if viewArrayClass or byteOrder is null 4641 * @throws IllegalArgumentException if viewArrayClass is not an array type 4642 * @throws UnsupportedOperationException if the component type of 4643 * viewArrayClass is not supported as a variable type 4644 * @since 9 4645 */ 4646 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass, 4647 ByteOrder byteOrder) throws IllegalArgumentException { 4648 Objects.requireNonNull(byteOrder); 4649 return VarHandles.makeByteBufferViewHandle(viewArrayClass, 4650 byteOrder == ByteOrder.BIG_ENDIAN); 4651 } 4652 4653 4654 /// method handle invocation (reflective style) 4655 4656 /** 4657 * Produces a method handle which will invoke any method handle of the 4658 * given {@code type}, with a given number of trailing arguments replaced by 4659 * a single trailing {@code Object[]} array. 4660 * The resulting invoker will be a method handle with the following 4661 * arguments: 4662 * <ul> 4663 * <li>a single {@code MethodHandle} target 4664 * <li>zero or more leading values (counted by {@code leadingArgCount}) 4665 * <li>an {@code Object[]} array containing trailing arguments 4666 * </ul> 4667 * <p> 4668 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with 4669 * the indicated {@code type}. 4670 * That is, if the target is exactly of the given {@code type}, it will behave 4671 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType} 4672 * is used to convert the target to the required {@code type}. 4673 * <p> 4674 * The type of the returned invoker will not be the given {@code type}, but rather 4675 * will have all parameters except the first {@code leadingArgCount} 4676 * replaced by a single array of type {@code Object[]}, which will be 4677 * the final parameter. 4678 * <p> 4679 * Before invoking its target, the invoker will spread the final array, apply 4680 * reference casts as necessary, and unbox and widen primitive arguments. 4681 * If, when the invoker is called, the supplied array argument does 4682 * not have the correct number of elements, the invoker will throw 4683 * an {@link IllegalArgumentException} instead of invoking the target. 4684 * <p> 4685 * This method is equivalent to the following code (though it may be more efficient): 4686 * {@snippet lang="java" : 4687 MethodHandle invoker = MethodHandles.invoker(type); 4688 int spreadArgCount = type.parameterCount() - leadingArgCount; 4689 invoker = invoker.asSpreader(Object[].class, spreadArgCount); 4690 return invoker; 4691 * } 4692 * This method throws no reflective or security exceptions. 4693 * @param type the desired target type 4694 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target 4695 * @return a method handle suitable for invoking any method handle of the given type 4696 * @throws NullPointerException if {@code type} is null 4697 * @throws IllegalArgumentException if {@code leadingArgCount} is not in 4698 * the range from 0 to {@code type.parameterCount()} inclusive, 4699 * or if the resulting method handle's type would have 4700 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4701 */ 4702 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) { 4703 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) 4704 throw newIllegalArgumentException("bad argument count", leadingArgCount); 4705 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount); 4706 return type.invokers().spreadInvoker(leadingArgCount); 4707 } 4708 4709 /** 4710 * Produces a special <em>invoker method handle</em> which can be used to 4711 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. 4712 * The resulting invoker will have a type which is 4713 * exactly equal to the desired type, except that it will accept 4714 * an additional leading argument of type {@code MethodHandle}. 4715 * <p> 4716 * This method is equivalent to the following code (though it may be more efficient): 4717 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)} 4718 * 4719 * <p style="font-size:smaller;"> 4720 * <em>Discussion:</em> 4721 * Invoker method handles can be useful when working with variable method handles 4722 * of unknown types. 4723 * For example, to emulate an {@code invokeExact} call to a variable method 4724 * handle {@code M}, extract its type {@code T}, 4725 * look up the invoker method {@code X} for {@code T}, 4726 * and call the invoker method, as {@code X.invoke(T, A...)}. 4727 * (It would not work to call {@code X.invokeExact}, since the type {@code T} 4728 * is unknown.) 4729 * If spreading, collecting, or other argument transformations are required, 4730 * they can be applied once to the invoker {@code X} and reused on many {@code M} 4731 * method handle values, as long as they are compatible with the type of {@code X}. 4732 * <p style="font-size:smaller;"> 4733 * <em>(Note: The invoker method is not available via the Core Reflection API. 4734 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 4735 * on the declared {@code invokeExact} or {@code invoke} method will raise an 4736 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 4737 * <p> 4738 * This method throws no reflective or security exceptions. 4739 * @param type the desired target type 4740 * @return a method handle suitable for invoking any method handle of the given type 4741 * @throws IllegalArgumentException if the resulting method handle's type would have 4742 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4743 */ 4744 public static MethodHandle exactInvoker(MethodType type) { 4745 return type.invokers().exactInvoker(); 4746 } 4747 4748 /** 4749 * Produces a special <em>invoker method handle</em> which can be used to 4750 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}. 4751 * The resulting invoker will have a type which is 4752 * exactly equal to the desired type, except that it will accept 4753 * an additional leading argument of type {@code MethodHandle}. 4754 * <p> 4755 * Before invoking its target, if the target differs from the expected type, 4756 * the invoker will apply reference casts as 4757 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}. 4758 * Similarly, the return value will be converted as necessary. 4759 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle}, 4760 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}. 4761 * <p> 4762 * This method is equivalent to the following code (though it may be more efficient): 4763 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)} 4764 * <p style="font-size:smaller;"> 4765 * <em>Discussion:</em> 4766 * A {@linkplain MethodType#genericMethodType general method type} is one which 4767 * mentions only {@code Object} arguments and return values. 4768 * An invoker for such a type is capable of calling any method handle 4769 * of the same arity as the general type. 4770 * <p style="font-size:smaller;"> 4771 * <em>(Note: The invoker method is not available via the Core Reflection API. 4772 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 4773 * on the declared {@code invokeExact} or {@code invoke} method will raise an 4774 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 4775 * <p> 4776 * This method throws no reflective or security exceptions. 4777 * @param type the desired target type 4778 * @return a method handle suitable for invoking any method handle convertible to the given type 4779 * @throws IllegalArgumentException if the resulting method handle's type would have 4780 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4781 */ 4782 public static MethodHandle invoker(MethodType type) { 4783 return type.invokers().genericInvoker(); 4784 } 4785 4786 /** 4787 * Produces a special <em>invoker method handle</em> which can be used to 4788 * invoke a signature-polymorphic access mode method on any VarHandle whose 4789 * associated access mode type is compatible with the given type. 4790 * The resulting invoker will have a type which is exactly equal to the 4791 * desired given type, except that it will accept an additional leading 4792 * argument of type {@code VarHandle}. 4793 * 4794 * @param accessMode the VarHandle access mode 4795 * @param type the desired target type 4796 * @return a method handle suitable for invoking an access mode method of 4797 * any VarHandle whose access mode type is of the given type. 4798 * @since 9 4799 */ 4800 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) { 4801 return type.invokers().varHandleMethodExactInvoker(accessMode); 4802 } 4803 4804 /** 4805 * Produces a special <em>invoker method handle</em> which can be used to 4806 * invoke a signature-polymorphic access mode method on any VarHandle whose 4807 * associated access mode type is compatible with the given type. 4808 * The resulting invoker will have a type which is exactly equal to the 4809 * desired given type, except that it will accept an additional leading 4810 * argument of type {@code VarHandle}. 4811 * <p> 4812 * Before invoking its target, if the access mode type differs from the 4813 * desired given type, the invoker will apply reference casts as necessary 4814 * and box, unbox, or widen primitive values, as if by 4815 * {@link MethodHandle#asType asType}. Similarly, the return value will be 4816 * converted as necessary. 4817 * <p> 4818 * This method is equivalent to the following code (though it may be more 4819 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)} 4820 * 4821 * @param accessMode the VarHandle access mode 4822 * @param type the desired target type 4823 * @return a method handle suitable for invoking an access mode method of 4824 * any VarHandle whose access mode type is convertible to the given 4825 * type. 4826 * @since 9 4827 */ 4828 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) { 4829 return type.invokers().varHandleMethodInvoker(accessMode); 4830 } 4831 4832 /*non-public*/ 4833 static MethodHandle basicInvoker(MethodType type) { 4834 return type.invokers().basicInvoker(); 4835 } 4836 4837 /// method handle modification (creation from other method handles) 4838 4839 /** 4840 * Produces a method handle which adapts the type of the 4841 * given method handle to a new type by pairwise argument and return type conversion. 4842 * The original type and new type must have the same number of arguments. 4843 * The resulting method handle is guaranteed to report a type 4844 * which is equal to the desired new type. 4845 * <p> 4846 * If the original type and new type are equal, returns target. 4847 * <p> 4848 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType}, 4849 * and some additional conversions are also applied if those conversions fail. 4850 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied 4851 * if possible, before or instead of any conversions done by {@code asType}: 4852 * <ul> 4853 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type, 4854 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast. 4855 * (This treatment of interfaces follows the usage of the bytecode verifier.) 4856 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive, 4857 * the boolean is converted to a byte value, 1 for true, 0 for false. 4858 * (This treatment follows the usage of the bytecode verifier.) 4859 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive, 4860 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}), 4861 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}. 4862 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean, 4863 * then a Java casting conversion (JLS {@jls 5.5}) is applied. 4864 * (Specifically, <em>T0</em> will convert to <em>T1</em> by 4865 * widening and/or narrowing.) 4866 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing 4867 * conversion will be applied at runtime, possibly followed 4868 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value, 4869 * possibly followed by a conversion from byte to boolean by testing 4870 * the low-order bit. 4871 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, 4872 * and if the reference is null at runtime, a zero value is introduced. 4873 * </ul> 4874 * @param target the method handle to invoke after arguments are retyped 4875 * @param newType the expected type of the new method handle 4876 * @return a method handle which delegates to the target after performing 4877 * any necessary argument conversions, and arranges for any 4878 * necessary return value conversions 4879 * @throws NullPointerException if either argument is null 4880 * @throws WrongMethodTypeException if the conversion cannot be made 4881 * @see MethodHandle#asType 4882 */ 4883 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) { 4884 explicitCastArgumentsChecks(target, newType); 4885 // use the asTypeCache when possible: 4886 MethodType oldType = target.type(); 4887 if (oldType == newType) return target; 4888 if (oldType.explicitCastEquivalentToAsType(newType)) { 4889 return target.asFixedArity().asType(newType); 4890 } 4891 return MethodHandleImpl.makePairwiseConvert(target, newType, false); 4892 } 4893 4894 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) { 4895 if (target.type().parameterCount() != newType.parameterCount()) { 4896 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType); 4897 } 4898 } 4899 4900 /** 4901 * Produces a method handle which adapts the calling sequence of the 4902 * given method handle to a new type, by reordering the arguments. 4903 * The resulting method handle is guaranteed to report a type 4904 * which is equal to the desired new type. 4905 * <p> 4906 * The given array controls the reordering. 4907 * Call {@code #I} the number of incoming parameters (the value 4908 * {@code newType.parameterCount()}, and call {@code #O} the number 4909 * of outgoing parameters (the value {@code target.type().parameterCount()}). 4910 * Then the length of the reordering array must be {@code #O}, 4911 * and each element must be a non-negative number less than {@code #I}. 4912 * For every {@code N} less than {@code #O}, the {@code N}-th 4913 * outgoing argument will be taken from the {@code I}-th incoming 4914 * argument, where {@code I} is {@code reorder[N]}. 4915 * <p> 4916 * No argument or return value conversions are applied. 4917 * The type of each incoming argument, as determined by {@code newType}, 4918 * must be identical to the type of the corresponding outgoing parameter 4919 * or parameters in the target method handle. 4920 * The return type of {@code newType} must be identical to the return 4921 * type of the original target. 4922 * <p> 4923 * The reordering array need not specify an actual permutation. 4924 * An incoming argument will be duplicated if its index appears 4925 * more than once in the array, and an incoming argument will be dropped 4926 * if its index does not appear in the array. 4927 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments}, 4928 * incoming arguments which are not mentioned in the reordering array 4929 * may be of any type, as determined only by {@code newType}. 4930 * {@snippet lang="java" : 4931 import static java.lang.invoke.MethodHandles.*; 4932 import static java.lang.invoke.MethodType.*; 4933 ... 4934 MethodType intfn1 = methodType(int.class, int.class); 4935 MethodType intfn2 = methodType(int.class, int.class, int.class); 4936 MethodHandle sub = ... (int x, int y) -> (x-y) ...; 4937 assert(sub.type().equals(intfn2)); 4938 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1); 4939 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0); 4940 assert((int)rsub.invokeExact(1, 100) == 99); 4941 MethodHandle add = ... (int x, int y) -> (x+y) ...; 4942 assert(add.type().equals(intfn2)); 4943 MethodHandle twice = permuteArguments(add, intfn1, 0, 0); 4944 assert(twice.type().equals(intfn1)); 4945 assert((int)twice.invokeExact(21) == 42); 4946 * } 4947 * <p> 4948 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4949 * variable-arity method handle}, even if the original target method handle was. 4950 * @param target the method handle to invoke after arguments are reordered 4951 * @param newType the expected type of the new method handle 4952 * @param reorder an index array which controls the reordering 4953 * @return a method handle which delegates to the target after it 4954 * drops unused arguments and moves and/or duplicates the other arguments 4955 * @throws NullPointerException if any argument is null 4956 * @throws IllegalArgumentException if the index array length is not equal to 4957 * the arity of the target, or if any index array element 4958 * not a valid index for a parameter of {@code newType}, 4959 * or if two corresponding parameter types in 4960 * {@code target.type()} and {@code newType} are not identical, 4961 */ 4962 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) { 4963 reorder = reorder.clone(); // get a private copy 4964 MethodType oldType = target.type(); 4965 permuteArgumentChecks(reorder, newType, oldType); 4966 // first detect dropped arguments and handle them separately 4967 int[] originalReorder = reorder; 4968 BoundMethodHandle result = target.rebind(); 4969 LambdaForm form = result.form; 4970 int newArity = newType.parameterCount(); 4971 // Normalize the reordering into a real permutation, 4972 // by removing duplicates and adding dropped elements. 4973 // This somewhat improves lambda form caching, as well 4974 // as simplifying the transform by breaking it up into steps. 4975 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) { 4976 if (ddIdx > 0) { 4977 // We found a duplicated entry at reorder[ddIdx]. 4978 // Example: (x,y,z)->asList(x,y,z) 4979 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1) 4980 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0) 4981 // The starred element corresponds to the argument 4982 // deleted by the dupArgumentForm transform. 4983 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos]; 4984 boolean killFirst = false; 4985 for (int val; (val = reorder[--dstPos]) != dupVal; ) { 4986 // Set killFirst if the dup is larger than an intervening position. 4987 // This will remove at least one inversion from the permutation. 4988 if (dupVal > val) killFirst = true; 4989 } 4990 if (!killFirst) { 4991 srcPos = dstPos; 4992 dstPos = ddIdx; 4993 } 4994 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos); 4995 assert (reorder[srcPos] == reorder[dstPos]); 4996 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1); 4997 // contract the reordering by removing the element at dstPos 4998 int tailPos = dstPos + 1; 4999 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos); 5000 reorder = Arrays.copyOf(reorder, reorder.length - 1); 5001 } else { 5002 int dropVal = ~ddIdx, insPos = 0; 5003 while (insPos < reorder.length && reorder[insPos] < dropVal) { 5004 // Find first element of reorder larger than dropVal. 5005 // This is where we will insert the dropVal. 5006 insPos += 1; 5007 } 5008 Class<?> ptype = newType.parameterType(dropVal); 5009 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype)); 5010 oldType = oldType.insertParameterTypes(insPos, ptype); 5011 // expand the reordering by inserting an element at insPos 5012 int tailPos = insPos + 1; 5013 reorder = Arrays.copyOf(reorder, reorder.length + 1); 5014 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos); 5015 reorder[insPos] = dropVal; 5016 } 5017 assert (permuteArgumentChecks(reorder, newType, oldType)); 5018 } 5019 assert (reorder.length == newArity); // a perfect permutation 5020 // Note: This may cache too many distinct LFs. Consider backing off to varargs code. 5021 form = form.editor().permuteArgumentsForm(1, reorder); 5022 if (newType == result.type() && form == result.internalForm()) 5023 return result; 5024 return result.copyWith(newType, form); 5025 } 5026 5027 /** 5028 * Return an indication of any duplicate or omission in reorder. 5029 * If the reorder contains a duplicate entry, return the index of the second occurrence. 5030 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder. 5031 * Otherwise, return zero. 5032 * If an element not in [0..newArity-1] is encountered, return reorder.length. 5033 */ 5034 private static int findFirstDupOrDrop(int[] reorder, int newArity) { 5035 final int BIT_LIMIT = 63; // max number of bits in bit mask 5036 if (newArity < BIT_LIMIT) { 5037 long mask = 0; 5038 for (int i = 0; i < reorder.length; i++) { 5039 int arg = reorder[i]; 5040 if (arg >= newArity) { 5041 return reorder.length; 5042 } 5043 long bit = 1L << arg; 5044 if ((mask & bit) != 0) { 5045 return i; // >0 indicates a dup 5046 } 5047 mask |= bit; 5048 } 5049 if (mask == (1L << newArity) - 1) { 5050 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity); 5051 return 0; 5052 } 5053 // find first zero 5054 long zeroBit = Long.lowestOneBit(~mask); 5055 int zeroPos = Long.numberOfTrailingZeros(zeroBit); 5056 assert(zeroPos <= newArity); 5057 if (zeroPos == newArity) { 5058 return 0; 5059 } 5060 return ~zeroPos; 5061 } else { 5062 // same algorithm, different bit set 5063 BitSet mask = new BitSet(newArity); 5064 for (int i = 0; i < reorder.length; i++) { 5065 int arg = reorder[i]; 5066 if (arg >= newArity) { 5067 return reorder.length; 5068 } 5069 if (mask.get(arg)) { 5070 return i; // >0 indicates a dup 5071 } 5072 mask.set(arg); 5073 } 5074 int zeroPos = mask.nextClearBit(0); 5075 assert(zeroPos <= newArity); 5076 if (zeroPos == newArity) { 5077 return 0; 5078 } 5079 return ~zeroPos; 5080 } 5081 } 5082 5083 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) { 5084 if (newType.returnType() != oldType.returnType()) 5085 throw newIllegalArgumentException("return types do not match", 5086 oldType, newType); 5087 if (reorder.length != oldType.parameterCount()) 5088 throw newIllegalArgumentException("old type parameter count and reorder array length do not match", 5089 oldType, Arrays.toString(reorder)); 5090 5091 int limit = newType.parameterCount(); 5092 for (int j = 0; j < reorder.length; j++) { 5093 int i = reorder[j]; 5094 if (i < 0 || i >= limit) { 5095 throw newIllegalArgumentException("index is out of bounds for new type", 5096 i, newType); 5097 } 5098 Class<?> src = newType.parameterType(i); 5099 Class<?> dst = oldType.parameterType(j); 5100 if (src != dst) 5101 throw newIllegalArgumentException("parameter types do not match after reorder", 5102 oldType, newType); 5103 } 5104 return true; 5105 } 5106 5107 /** 5108 * Produces a method handle of the requested return type which returns the given 5109 * constant value every time it is invoked. 5110 * <p> 5111 * Before the method handle is returned, the passed-in value is converted to the requested type. 5112 * If the requested type is primitive, widening primitive conversions are attempted, 5113 * else reference conversions are attempted. 5114 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}. 5115 * @param type the return type of the desired method handle 5116 * @param value the value to return 5117 * @return a method handle of the given return type and no arguments, which always returns the given value 5118 * @throws NullPointerException if the {@code type} argument is null 5119 * @throws ClassCastException if the value cannot be converted to the required return type 5120 * @throws IllegalArgumentException if the given type is {@code void.class} 5121 */ 5122 public static MethodHandle constant(Class<?> type, Object value) { 5123 if (type.isPrimitive()) { 5124 if (type == void.class) 5125 throw newIllegalArgumentException("void type"); 5126 Wrapper w = Wrapper.forPrimitiveType(type); 5127 value = w.convert(value, type); 5128 if (w.zero().equals(value)) 5129 return zero(w, type); 5130 return insertArguments(identity(type), 0, value); 5131 } else { 5132 if (value == null) 5133 return zero(Wrapper.OBJECT, type); 5134 return identity(type).bindTo(value); 5135 } 5136 } 5137 5138 /** 5139 * Produces a method handle which returns its sole argument when invoked. 5140 * @param type the type of the sole parameter and return value of the desired method handle 5141 * @return a unary method handle which accepts and returns the given type 5142 * @throws NullPointerException if the argument is null 5143 * @throws IllegalArgumentException if the given type is {@code void.class} 5144 */ 5145 public static MethodHandle identity(Class<?> type) { 5146 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT); 5147 int pos = btw.ordinal(); 5148 MethodHandle ident = IDENTITY_MHS[pos]; 5149 if (ident == null) { 5150 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType())); 5151 } 5152 if (ident.type().returnType() == type) 5153 return ident; 5154 // something like identity(Foo.class); do not bother to intern these 5155 assert (btw == Wrapper.OBJECT); 5156 return makeIdentity(type); 5157 } 5158 5159 /** 5160 * Produces a constant method handle of the requested return type which 5161 * returns the default value for that type every time it is invoked. 5162 * The resulting constant method handle will have no side effects. 5163 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}. 5164 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))}, 5165 * since {@code explicitCastArguments} converts {@code null} to default values. 5166 * @param type the expected return type of the desired method handle 5167 * @return a constant method handle that takes no arguments 5168 * and returns the default value of the given type (or void, if the type is void) 5169 * @throws NullPointerException if the argument is null 5170 * @see MethodHandles#constant 5171 * @see MethodHandles#empty 5172 * @see MethodHandles#explicitCastArguments 5173 * @since 9 5174 */ 5175 public static MethodHandle zero(Class<?> type) { 5176 Objects.requireNonNull(type); 5177 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type); 5178 } 5179 5180 private static MethodHandle identityOrVoid(Class<?> type) { 5181 return type == void.class ? zero(type) : identity(type); 5182 } 5183 5184 /** 5185 * Produces a method handle of the requested type which ignores any arguments, does nothing, 5186 * and returns a suitable default depending on the return type. 5187 * That is, it returns a zero primitive value, a {@code null}, or {@code void}. 5188 * <p>The returned method handle is equivalent to 5189 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}. 5190 * 5191 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as 5192 * {@code guardWithTest(pred, target, empty(target.type())}. 5193 * @param type the type of the desired method handle 5194 * @return a constant method handle of the given type, which returns a default value of the given return type 5195 * @throws NullPointerException if the argument is null 5196 * @see MethodHandles#zero 5197 * @see MethodHandles#constant 5198 * @since 9 5199 */ 5200 public static MethodHandle empty(MethodType type) { 5201 Objects.requireNonNull(type); 5202 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes()); 5203 } 5204 5205 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT]; 5206 private static MethodHandle makeIdentity(Class<?> ptype) { 5207 MethodType mtype = methodType(ptype, ptype); 5208 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype)); 5209 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY); 5210 } 5211 5212 private static MethodHandle zero(Wrapper btw, Class<?> rtype) { 5213 int pos = btw.ordinal(); 5214 MethodHandle zero = ZERO_MHS[pos]; 5215 if (zero == null) { 5216 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType())); 5217 } 5218 if (zero.type().returnType() == rtype) 5219 return zero; 5220 assert(btw == Wrapper.OBJECT); 5221 return makeZero(rtype); 5222 } 5223 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT]; 5224 private static MethodHandle makeZero(Class<?> rtype) { 5225 MethodType mtype = methodType(rtype); 5226 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype)); 5227 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO); 5228 } 5229 5230 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) { 5231 // Simulate a CAS, to avoid racy duplication of results. 5232 MethodHandle prev = cache[pos]; 5233 if (prev != null) return prev; 5234 return cache[pos] = value; 5235 } 5236 5237 /** 5238 * Provides a target method handle with one or more <em>bound arguments</em> 5239 * in advance of the method handle's invocation. 5240 * The formal parameters to the target corresponding to the bound 5241 * arguments are called <em>bound parameters</em>. 5242 * Returns a new method handle which saves away the bound arguments. 5243 * When it is invoked, it receives arguments for any non-bound parameters, 5244 * binds the saved arguments to their corresponding parameters, 5245 * and calls the original target. 5246 * <p> 5247 * The type of the new method handle will drop the types for the bound 5248 * parameters from the original target type, since the new method handle 5249 * will no longer require those arguments to be supplied by its callers. 5250 * <p> 5251 * Each given argument object must match the corresponding bound parameter type. 5252 * If a bound parameter type is a primitive, the argument object 5253 * must be a wrapper, and will be unboxed to produce the primitive value. 5254 * <p> 5255 * The {@code pos} argument selects which parameters are to be bound. 5256 * It may range between zero and <i>N-L</i> (inclusively), 5257 * where <i>N</i> is the arity of the target method handle 5258 * and <i>L</i> is the length of the values array. 5259 * <p> 5260 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5261 * variable-arity method handle}, even if the original target method handle was. 5262 * @param target the method handle to invoke after the argument is inserted 5263 * @param pos where to insert the argument (zero for the first) 5264 * @param values the series of arguments to insert 5265 * @return a method handle which inserts an additional argument, 5266 * before calling the original method handle 5267 * @throws NullPointerException if the target or the {@code values} array is null 5268 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than 5269 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L} 5270 * is the length of the values array. 5271 * @throws ClassCastException if an argument does not match the corresponding bound parameter 5272 * type. 5273 * @see MethodHandle#bindTo 5274 */ 5275 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) { 5276 int insCount = values.length; 5277 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos); 5278 if (insCount == 0) return target; 5279 BoundMethodHandle result = target.rebind(); 5280 for (int i = 0; i < insCount; i++) { 5281 Object value = values[i]; 5282 Class<?> ptype = ptypes[pos+i]; 5283 if (ptype.isPrimitive()) { 5284 result = insertArgumentPrimitive(result, pos, ptype, value); 5285 } else { 5286 value = ptype.cast(value); // throw CCE if needed 5287 result = result.bindArgumentL(pos, value); 5288 } 5289 } 5290 return result; 5291 } 5292 5293 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos, 5294 Class<?> ptype, Object value) { 5295 Wrapper w = Wrapper.forPrimitiveType(ptype); 5296 // perform unboxing and/or primitive conversion 5297 value = w.convert(value, ptype); 5298 return switch (w) { 5299 case INT -> result.bindArgumentI(pos, (int) value); 5300 case LONG -> result.bindArgumentJ(pos, (long) value); 5301 case FLOAT -> result.bindArgumentF(pos, (float) value); 5302 case DOUBLE -> result.bindArgumentD(pos, (double) value); 5303 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value)); 5304 }; 5305 } 5306 5307 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException { 5308 MethodType oldType = target.type(); 5309 int outargs = oldType.parameterCount(); 5310 int inargs = outargs - insCount; 5311 if (inargs < 0) 5312 throw newIllegalArgumentException("too many values to insert"); 5313 if (pos < 0 || pos > inargs) 5314 throw newIllegalArgumentException("no argument type to append"); 5315 return oldType.ptypes(); 5316 } 5317 5318 /** 5319 * Produces a method handle which will discard some dummy arguments 5320 * before calling some other specified <i>target</i> method handle. 5321 * The type of the new method handle will be the same as the target's type, 5322 * except it will also include the dummy argument types, 5323 * at some given position. 5324 * <p> 5325 * The {@code pos} argument may range between zero and <i>N</i>, 5326 * where <i>N</i> is the arity of the target. 5327 * If {@code pos} is zero, the dummy arguments will precede 5328 * the target's real arguments; if {@code pos} is <i>N</i> 5329 * they will come after. 5330 * <p> 5331 * <b>Example:</b> 5332 * {@snippet lang="java" : 5333 import static java.lang.invoke.MethodHandles.*; 5334 import static java.lang.invoke.MethodType.*; 5335 ... 5336 MethodHandle cat = lookup().findVirtual(String.class, 5337 "concat", methodType(String.class, String.class)); 5338 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5339 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class); 5340 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2)); 5341 assertEquals(bigType, d0.type()); 5342 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z")); 5343 * } 5344 * <p> 5345 * This method is also equivalent to the following code: 5346 * <blockquote><pre> 5347 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))} 5348 * </pre></blockquote> 5349 * @param target the method handle to invoke after the arguments are dropped 5350 * @param pos position of first argument to drop (zero for the leftmost) 5351 * @param valueTypes the type(s) of the argument(s) to drop 5352 * @return a method handle which drops arguments of the given types, 5353 * before calling the original method handle 5354 * @throws NullPointerException if the target is null, 5355 * or if the {@code valueTypes} list or any of its elements is null 5356 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 5357 * or if {@code pos} is negative or greater than the arity of the target, 5358 * or if the new method handle's type would have too many parameters 5359 */ 5360 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) { 5361 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone()); 5362 } 5363 5364 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) { 5365 MethodType oldType = target.type(); // get NPE 5366 int dropped = dropArgumentChecks(oldType, pos, valueTypes); 5367 MethodType newType = oldType.insertParameterTypes(pos, valueTypes); 5368 if (dropped == 0) return target; 5369 BoundMethodHandle result = target.rebind(); 5370 LambdaForm lform = result.form; 5371 int insertFormArg = 1 + pos; 5372 for (Class<?> ptype : valueTypes) { 5373 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype)); 5374 } 5375 result = result.copyWith(newType, lform); 5376 return result; 5377 } 5378 5379 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) { 5380 int dropped = valueTypes.length; 5381 MethodType.checkSlotCount(dropped); 5382 int outargs = oldType.parameterCount(); 5383 int inargs = outargs + dropped; 5384 if (pos < 0 || pos > outargs) 5385 throw newIllegalArgumentException("no argument type to remove" 5386 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs) 5387 ); 5388 return dropped; 5389 } 5390 5391 /** 5392 * Produces a method handle which will discard some dummy arguments 5393 * before calling some other specified <i>target</i> method handle. 5394 * The type of the new method handle will be the same as the target's type, 5395 * except it will also include the dummy argument types, 5396 * at some given position. 5397 * <p> 5398 * The {@code pos} argument may range between zero and <i>N</i>, 5399 * where <i>N</i> is the arity of the target. 5400 * If {@code pos} is zero, the dummy arguments will precede 5401 * the target's real arguments; if {@code pos} is <i>N</i> 5402 * they will come after. 5403 * @apiNote 5404 * {@snippet lang="java" : 5405 import static java.lang.invoke.MethodHandles.*; 5406 import static java.lang.invoke.MethodType.*; 5407 ... 5408 MethodHandle cat = lookup().findVirtual(String.class, 5409 "concat", methodType(String.class, String.class)); 5410 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5411 MethodHandle d0 = dropArguments(cat, 0, String.class); 5412 assertEquals("yz", (String) d0.invokeExact("x", "y", "z")); 5413 MethodHandle d1 = dropArguments(cat, 1, String.class); 5414 assertEquals("xz", (String) d1.invokeExact("x", "y", "z")); 5415 MethodHandle d2 = dropArguments(cat, 2, String.class); 5416 assertEquals("xy", (String) d2.invokeExact("x", "y", "z")); 5417 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class); 5418 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z")); 5419 * } 5420 * <p> 5421 * This method is also equivalent to the following code: 5422 * <blockquote><pre> 5423 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))} 5424 * </pre></blockquote> 5425 * @param target the method handle to invoke after the arguments are dropped 5426 * @param pos position of first argument to drop (zero for the leftmost) 5427 * @param valueTypes the type(s) of the argument(s) to drop 5428 * @return a method handle which drops arguments of the given types, 5429 * before calling the original method handle 5430 * @throws NullPointerException if the target is null, 5431 * or if the {@code valueTypes} array or any of its elements is null 5432 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 5433 * or if {@code pos} is negative or greater than the arity of the target, 5434 * or if the new method handle's type would have 5435 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5436 */ 5437 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) { 5438 return dropArgumentsTrusted(target, pos, valueTypes.clone()); 5439 } 5440 5441 /* Convenience overloads for trusting internal low-arity call-sites */ 5442 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) { 5443 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 }); 5444 } 5445 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) { 5446 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 }); 5447 } 5448 5449 // private version which allows caller some freedom with error handling 5450 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos, 5451 boolean nullOnFailure) { 5452 Class<?>[] oldTypes = target.type().ptypes(); 5453 int match = oldTypes.length; 5454 if (skip != 0) { 5455 if (skip < 0 || skip > match) { 5456 throw newIllegalArgumentException("illegal skip", skip, target); 5457 } 5458 oldTypes = Arrays.copyOfRange(oldTypes, skip, match); 5459 match -= skip; 5460 } 5461 Class<?>[] addTypes = newTypes; 5462 int add = addTypes.length; 5463 if (pos != 0) { 5464 if (pos < 0 || pos > add) { 5465 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes)); 5466 } 5467 addTypes = Arrays.copyOfRange(addTypes, pos, add); 5468 add -= pos; 5469 assert(addTypes.length == add); 5470 } 5471 // Do not add types which already match the existing arguments. 5472 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) { 5473 if (nullOnFailure) { 5474 return null; 5475 } 5476 throw newIllegalArgumentException("argument lists do not match", 5477 Arrays.toString(oldTypes), Arrays.toString(newTypes)); 5478 } 5479 addTypes = Arrays.copyOfRange(addTypes, match, add); 5480 add -= match; 5481 assert(addTypes.length == add); 5482 // newTypes: ( P*[pos], M*[match], A*[add] ) 5483 // target: ( S*[skip], M*[match] ) 5484 MethodHandle adapter = target; 5485 if (add > 0) { 5486 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes); 5487 } 5488 // adapter: (S*[skip], M*[match], A*[add] ) 5489 if (pos > 0) { 5490 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos)); 5491 } 5492 // adapter: (S*[skip], P*[pos], M*[match], A*[add] ) 5493 return adapter; 5494 } 5495 5496 /** 5497 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some 5498 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter 5499 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The 5500 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before 5501 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by 5502 * {@link #dropArguments(MethodHandle, int, Class[])}. 5503 * <p> 5504 * The resulting handle will have the same return type as the target handle. 5505 * <p> 5506 * In more formal terms, assume these two type lists:<ul> 5507 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as 5508 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list, 5509 * {@code newTypes}. 5510 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as 5511 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's 5512 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching 5513 * sub-list. 5514 * </ul> 5515 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type 5516 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by 5517 * {@link #dropArguments(MethodHandle, int, Class[])}. 5518 * 5519 * @apiNote 5520 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be 5521 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows: 5522 * {@snippet lang="java" : 5523 import static java.lang.invoke.MethodHandles.*; 5524 import static java.lang.invoke.MethodType.*; 5525 ... 5526 ... 5527 MethodHandle h0 = constant(boolean.class, true); 5528 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class)); 5529 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class); 5530 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList()); 5531 if (h1.type().parameterCount() < h2.type().parameterCount()) 5532 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1 5533 else 5534 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2 5535 MethodHandle h3 = guardWithTest(h0, h1, h2); 5536 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c")); 5537 * } 5538 * @param target the method handle to adapt 5539 * @param skip number of targets parameters to disregard (they will be unchanged) 5540 * @param newTypes the list of types to match {@code target}'s parameter type list to 5541 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur 5542 * @return a possibly adapted method handle 5543 * @throws NullPointerException if either argument is null 5544 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class}, 5545 * or if {@code skip} is negative or greater than the arity of the target, 5546 * or if {@code pos} is negative or greater than the newTypes list size, 5547 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position 5548 * {@code pos}. 5549 * @since 9 5550 */ 5551 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) { 5552 Objects.requireNonNull(target); 5553 Objects.requireNonNull(newTypes); 5554 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false); 5555 } 5556 5557 /** 5558 * Drop the return value of the target handle (if any). 5559 * The returned method handle will have a {@code void} return type. 5560 * 5561 * @param target the method handle to adapt 5562 * @return a possibly adapted method handle 5563 * @throws NullPointerException if {@code target} is null 5564 * @since 16 5565 */ 5566 public static MethodHandle dropReturn(MethodHandle target) { 5567 Objects.requireNonNull(target); 5568 MethodType oldType = target.type(); 5569 Class<?> oldReturnType = oldType.returnType(); 5570 if (oldReturnType == void.class) 5571 return target; 5572 MethodType newType = oldType.changeReturnType(void.class); 5573 BoundMethodHandle result = target.rebind(); 5574 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true); 5575 result = result.copyWith(newType, lform); 5576 return result; 5577 } 5578 5579 /** 5580 * Adapts a target method handle by pre-processing 5581 * one or more of its arguments, each with its own unary filter function, 5582 * and then calling the target with each pre-processed argument 5583 * replaced by the result of its corresponding filter function. 5584 * <p> 5585 * The pre-processing is performed by one or more method handles, 5586 * specified in the elements of the {@code filters} array. 5587 * The first element of the filter array corresponds to the {@code pos} 5588 * argument of the target, and so on in sequence. 5589 * The filter functions are invoked in left to right order. 5590 * <p> 5591 * Null arguments in the array are treated as identity functions, 5592 * and the corresponding arguments left unchanged. 5593 * (If there are no non-null elements in the array, the original target is returned.) 5594 * Each filter is applied to the corresponding argument of the adapter. 5595 * <p> 5596 * If a filter {@code F} applies to the {@code N}th argument of 5597 * the target, then {@code F} must be a method handle which 5598 * takes exactly one argument. The type of {@code F}'s sole argument 5599 * replaces the corresponding argument type of the target 5600 * in the resulting adapted method handle. 5601 * The return type of {@code F} must be identical to the corresponding 5602 * parameter type of the target. 5603 * <p> 5604 * It is an error if there are elements of {@code filters} 5605 * (null or not) 5606 * which do not correspond to argument positions in the target. 5607 * <p><b>Example:</b> 5608 * {@snippet lang="java" : 5609 import static java.lang.invoke.MethodHandles.*; 5610 import static java.lang.invoke.MethodType.*; 5611 ... 5612 MethodHandle cat = lookup().findVirtual(String.class, 5613 "concat", methodType(String.class, String.class)); 5614 MethodHandle upcase = lookup().findVirtual(String.class, 5615 "toUpperCase", methodType(String.class)); 5616 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5617 MethodHandle f0 = filterArguments(cat, 0, upcase); 5618 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy 5619 MethodHandle f1 = filterArguments(cat, 1, upcase); 5620 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY 5621 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase); 5622 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY 5623 * } 5624 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5625 * denotes the return type of both the {@code target} and resulting adapter. 5626 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values 5627 * of the parameters and arguments that precede and follow the filter position 5628 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and 5629 * values of the filtered parameters and arguments; they also represent the 5630 * return types of the {@code filter[i]} handles. The latter accept arguments 5631 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of 5632 * the resulting adapter. 5633 * {@snippet lang="java" : 5634 * T target(P... p, A[i]... a[i], B... b); 5635 * A[i] filter[i](V[i]); 5636 * T adapter(P... p, V[i]... v[i], B... b) { 5637 * return target(p..., filter[i](v[i])..., b...); 5638 * } 5639 * } 5640 * <p> 5641 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5642 * variable-arity method handle}, even if the original target method handle was. 5643 * 5644 * @param target the method handle to invoke after arguments are filtered 5645 * @param pos the position of the first argument to filter 5646 * @param filters method handles to call initially on filtered arguments 5647 * @return method handle which incorporates the specified argument filtering logic 5648 * @throws NullPointerException if the target is null 5649 * or if the {@code filters} array is null 5650 * @throws IllegalArgumentException if a non-null element of {@code filters} 5651 * does not match a corresponding argument type of target as described above, 5652 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}, 5653 * or if the resulting method handle's type would have 5654 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5655 */ 5656 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) { 5657 // In method types arguments start at index 0, while the LF 5658 // editor have the MH receiver at position 0 - adjust appropriately. 5659 final int MH_RECEIVER_OFFSET = 1; 5660 filterArgumentsCheckArity(target, pos, filters); 5661 MethodHandle adapter = target; 5662 5663 // keep track of currently matched filters, as to optimize repeated filters 5664 int index = 0; 5665 int[] positions = new int[filters.length]; 5666 MethodHandle filter = null; 5667 5668 // process filters in reverse order so that the invocation of 5669 // the resulting adapter will invoke the filters in left-to-right order 5670 for (int i = filters.length - 1; i >= 0; --i) { 5671 MethodHandle newFilter = filters[i]; 5672 if (newFilter == null) continue; // ignore null elements of filters 5673 5674 // flush changes on update 5675 if (filter != newFilter) { 5676 if (filter != null) { 5677 if (index > 1) { 5678 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 5679 } else { 5680 adapter = filterArgument(adapter, positions[0] - 1, filter); 5681 } 5682 } 5683 filter = newFilter; 5684 index = 0; 5685 } 5686 5687 filterArgumentChecks(target, pos + i, newFilter); 5688 positions[index++] = pos + i + MH_RECEIVER_OFFSET; 5689 } 5690 if (index > 1) { 5691 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 5692 } else if (index == 1) { 5693 adapter = filterArgument(adapter, positions[0] - 1, filter); 5694 } 5695 return adapter; 5696 } 5697 5698 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) { 5699 MethodType targetType = adapter.type(); 5700 MethodType filterType = filter.type(); 5701 BoundMethodHandle result = adapter.rebind(); 5702 Class<?> newParamType = filterType.parameterType(0); 5703 5704 Class<?>[] ptypes = targetType.ptypes().clone(); 5705 for (int pos : positions) { 5706 ptypes[pos - 1] = newParamType; 5707 } 5708 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true); 5709 5710 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions); 5711 return result.copyWithExtendL(newType, lform, filter); 5712 } 5713 5714 /*non-public*/ 5715 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) { 5716 filterArgumentChecks(target, pos, filter); 5717 MethodType targetType = target.type(); 5718 MethodType filterType = filter.type(); 5719 BoundMethodHandle result = target.rebind(); 5720 Class<?> newParamType = filterType.parameterType(0); 5721 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType)); 5722 MethodType newType = targetType.changeParameterType(pos, newParamType); 5723 result = result.copyWithExtendL(newType, lform, filter); 5724 return result; 5725 } 5726 5727 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) { 5728 MethodType targetType = target.type(); 5729 int maxPos = targetType.parameterCount(); 5730 if (pos + filters.length > maxPos) 5731 throw newIllegalArgumentException("too many filters"); 5732 } 5733 5734 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 5735 MethodType targetType = target.type(); 5736 MethodType filterType = filter.type(); 5737 if (filterType.parameterCount() != 1 5738 || filterType.returnType() != targetType.parameterType(pos)) 5739 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5740 } 5741 5742 /** 5743 * Adapts a target method handle by pre-processing 5744 * a sub-sequence of its arguments with a filter (another method handle). 5745 * The pre-processed arguments are replaced by the result (if any) of the 5746 * filter function. 5747 * The target is then called on the modified (usually shortened) argument list. 5748 * <p> 5749 * If the filter returns a value, the target must accept that value as 5750 * its argument in position {@code pos}, preceded and/or followed by 5751 * any arguments not passed to the filter. 5752 * If the filter returns void, the target must accept all arguments 5753 * not passed to the filter. 5754 * No arguments are reordered, and a result returned from the filter 5755 * replaces (in order) the whole subsequence of arguments originally 5756 * passed to the adapter. 5757 * <p> 5758 * The argument types (if any) of the filter 5759 * replace zero or one argument types of the target, at position {@code pos}, 5760 * in the resulting adapted method handle. 5761 * The return type of the filter (if any) must be identical to the 5762 * argument type of the target at position {@code pos}, and that target argument 5763 * is supplied by the return value of the filter. 5764 * <p> 5765 * In all cases, {@code pos} must be greater than or equal to zero, and 5766 * {@code pos} must also be less than or equal to the target's arity. 5767 * <p><b>Example:</b> 5768 * {@snippet lang="java" : 5769 import static java.lang.invoke.MethodHandles.*; 5770 import static java.lang.invoke.MethodType.*; 5771 ... 5772 MethodHandle deepToString = publicLookup() 5773 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 5774 5775 MethodHandle ts1 = deepToString.asCollector(String[].class, 1); 5776 assertEquals("[strange]", (String) ts1.invokeExact("strange")); 5777 5778 MethodHandle ts2 = deepToString.asCollector(String[].class, 2); 5779 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down")); 5780 5781 MethodHandle ts3 = deepToString.asCollector(String[].class, 3); 5782 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2); 5783 assertEquals("[top, [up, down], strange]", 5784 (String) ts3_ts2.invokeExact("top", "up", "down", "strange")); 5785 5786 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1); 5787 assertEquals("[top, [up, down], [strange]]", 5788 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange")); 5789 5790 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3); 5791 assertEquals("[top, [[up, down, strange], charm], bottom]", 5792 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom")); 5793 * } 5794 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5795 * represents the return type of the {@code target} and resulting adapter. 5796 * {@code V}/{@code v} stand for the return type and value of the 5797 * {@code filter}, which are also found in the signature and arguments of 5798 * the {@code target}, respectively, unless {@code V} is {@code void}. 5799 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types 5800 * and values preceding and following the collection position, {@code pos}, 5801 * in the {@code target}'s signature. They also turn up in the resulting 5802 * adapter's signature and arguments, where they surround 5803 * {@code B}/{@code b}, which represent the parameter types and arguments 5804 * to the {@code filter} (if any). 5805 * {@snippet lang="java" : 5806 * T target(A...,V,C...); 5807 * V filter(B...); 5808 * T adapter(A... a,B... b,C... c) { 5809 * V v = filter(b...); 5810 * return target(a...,v,c...); 5811 * } 5812 * // and if the filter has no arguments: 5813 * T target2(A...,V,C...); 5814 * V filter2(); 5815 * T adapter2(A... a,C... c) { 5816 * V v = filter2(); 5817 * return target2(a...,v,c...); 5818 * } 5819 * // and if the filter has a void return: 5820 * T target3(A...,C...); 5821 * void filter3(B...); 5822 * T adapter3(A... a,B... b,C... c) { 5823 * filter3(b...); 5824 * return target3(a...,c...); 5825 * } 5826 * } 5827 * <p> 5828 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to 5829 * one which first "folds" the affected arguments, and then drops them, in separate 5830 * steps as follows: 5831 * {@snippet lang="java" : 5832 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2 5833 * mh = MethodHandles.foldArguments(mh, coll); //step 1 5834 * } 5835 * If the target method handle consumes no arguments besides than the result 5836 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)} 5837 * is equivalent to {@code filterReturnValue(coll, mh)}. 5838 * If the filter method handle {@code coll} consumes one argument and produces 5839 * a non-void result, then {@code collectArguments(mh, N, coll)} 5840 * is equivalent to {@code filterArguments(mh, N, coll)}. 5841 * Other equivalences are possible but would require argument permutation. 5842 * <p> 5843 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5844 * variable-arity method handle}, even if the original target method handle was. 5845 * 5846 * @param target the method handle to invoke after filtering the subsequence of arguments 5847 * @param pos the position of the first adapter argument to pass to the filter, 5848 * and/or the target argument which receives the result of the filter 5849 * @param filter method handle to call on the subsequence of arguments 5850 * @return method handle which incorporates the specified argument subsequence filtering logic 5851 * @throws NullPointerException if either argument is null 5852 * @throws IllegalArgumentException if the return type of {@code filter} 5853 * is non-void and is not the same as the {@code pos} argument of the target, 5854 * or if {@code pos} is not between 0 and the target's arity, inclusive, 5855 * or if the resulting method handle's type would have 5856 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5857 * @see MethodHandles#foldArguments 5858 * @see MethodHandles#filterArguments 5859 * @see MethodHandles#filterReturnValue 5860 */ 5861 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) { 5862 MethodType newType = collectArgumentsChecks(target, pos, filter); 5863 MethodType collectorType = filter.type(); 5864 BoundMethodHandle result = target.rebind(); 5865 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType()); 5866 return result.copyWithExtendL(newType, lform, filter); 5867 } 5868 5869 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 5870 MethodType targetType = target.type(); 5871 MethodType filterType = filter.type(); 5872 Class<?> rtype = filterType.returnType(); 5873 Class<?>[] filterArgs = filterType.ptypes(); 5874 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) || 5875 (rtype != void.class && pos >= targetType.parameterCount())) { 5876 throw newIllegalArgumentException("position is out of range for target", target, pos); 5877 } 5878 if (rtype == void.class) { 5879 return targetType.insertParameterTypes(pos, filterArgs); 5880 } 5881 if (rtype != targetType.parameterType(pos)) { 5882 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5883 } 5884 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs); 5885 } 5886 5887 /** 5888 * Adapts a target method handle by post-processing 5889 * its return value (if any) with a filter (another method handle). 5890 * The result of the filter is returned from the adapter. 5891 * <p> 5892 * If the target returns a value, the filter must accept that value as 5893 * its only argument. 5894 * If the target returns void, the filter must accept no arguments. 5895 * <p> 5896 * The return type of the filter 5897 * replaces the return type of the target 5898 * in the resulting adapted method handle. 5899 * The argument type of the filter (if any) must be identical to the 5900 * return type of the target. 5901 * <p><b>Example:</b> 5902 * {@snippet lang="java" : 5903 import static java.lang.invoke.MethodHandles.*; 5904 import static java.lang.invoke.MethodType.*; 5905 ... 5906 MethodHandle cat = lookup().findVirtual(String.class, 5907 "concat", methodType(String.class, String.class)); 5908 MethodHandle length = lookup().findVirtual(String.class, 5909 "length", methodType(int.class)); 5910 System.out.println((String) cat.invokeExact("x", "y")); // xy 5911 MethodHandle f0 = filterReturnValue(cat, length); 5912 System.out.println((int) f0.invokeExact("x", "y")); // 2 5913 * } 5914 * <p>Here is pseudocode for the resulting adapter. In the code, 5915 * {@code T}/{@code t} represent the result type and value of the 5916 * {@code target}; {@code V}, the result type of the {@code filter}; and 5917 * {@code A}/{@code a}, the types and values of the parameters and arguments 5918 * of the {@code target} as well as the resulting adapter. 5919 * {@snippet lang="java" : 5920 * T target(A...); 5921 * V filter(T); 5922 * V adapter(A... a) { 5923 * T t = target(a...); 5924 * return filter(t); 5925 * } 5926 * // and if the target has a void return: 5927 * void target2(A...); 5928 * V filter2(); 5929 * V adapter2(A... a) { 5930 * target2(a...); 5931 * return filter2(); 5932 * } 5933 * // and if the filter has a void return: 5934 * T target3(A...); 5935 * void filter3(V); 5936 * void adapter3(A... a) { 5937 * T t = target3(a...); 5938 * filter3(t); 5939 * } 5940 * } 5941 * <p> 5942 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5943 * variable-arity method handle}, even if the original target method handle was. 5944 * @param target the method handle to invoke before filtering the return value 5945 * @param filter method handle to call on the return value 5946 * @return method handle which incorporates the specified return value filtering logic 5947 * @throws NullPointerException if either argument is null 5948 * @throws IllegalArgumentException if the argument list of {@code filter} 5949 * does not match the return type of target as described above 5950 */ 5951 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) { 5952 MethodType targetType = target.type(); 5953 MethodType filterType = filter.type(); 5954 filterReturnValueChecks(targetType, filterType); 5955 BoundMethodHandle result = target.rebind(); 5956 BasicType rtype = BasicType.basicType(filterType.returnType()); 5957 LambdaForm lform = result.editor().filterReturnForm(rtype, false); 5958 MethodType newType = targetType.changeReturnType(filterType.returnType()); 5959 result = result.copyWithExtendL(newType, lform, filter); 5960 return result; 5961 } 5962 5963 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException { 5964 Class<?> rtype = targetType.returnType(); 5965 int filterValues = filterType.parameterCount(); 5966 if (filterValues == 0 5967 ? (rtype != void.class) 5968 : (rtype != filterType.parameterType(0) || filterValues != 1)) 5969 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5970 } 5971 5972 /** 5973 * Filter the return value of a target method handle with a filter function. The filter function is 5974 * applied to the return value of the original handle; if the filter specifies more than one parameters, 5975 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works 5976 * as follows: 5977 * {@snippet lang="java" : 5978 * T target(A...) 5979 * V filter(B... , T) 5980 * V adapter(A... a, B... b) { 5981 * T t = target(a...); 5982 * return filter(b..., t); 5983 * } 5984 * } 5985 * <p> 5986 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}. 5987 * 5988 * @param target the target method handle 5989 * @param filter the filter method handle 5990 * @return the adapter method handle 5991 */ 5992 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) { 5993 MethodType targetType = target.type(); 5994 MethodType filterType = filter.type(); 5995 BoundMethodHandle result = target.rebind(); 5996 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType()); 5997 MethodType newType = targetType.changeReturnType(filterType.returnType()); 5998 if (filterType.parameterCount() > 1) { 5999 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) { 6000 newType = newType.appendParameterTypes(filterType.parameterType(i)); 6001 } 6002 } 6003 result = result.copyWithExtendL(newType, lform, filter); 6004 return result; 6005 } 6006 6007 /** 6008 * Adapts a target method handle by pre-processing 6009 * some of its arguments, and then calling the target with 6010 * the result of the pre-processing, inserted into the original 6011 * sequence of arguments. 6012 * <p> 6013 * The pre-processing is performed by {@code combiner}, a second method handle. 6014 * Of the arguments passed to the adapter, the first {@code N} arguments 6015 * are copied to the combiner, which is then called. 6016 * (Here, {@code N} is defined as the parameter count of the combiner.) 6017 * After this, control passes to the target, with any result 6018 * from the combiner inserted before the original {@code N} incoming 6019 * arguments. 6020 * <p> 6021 * If the combiner returns a value, the first parameter type of the target 6022 * must be identical with the return type of the combiner, and the next 6023 * {@code N} parameter types of the target must exactly match the parameters 6024 * of the combiner. 6025 * <p> 6026 * If the combiner has a void return, no result will be inserted, 6027 * and the first {@code N} parameter types of the target 6028 * must exactly match the parameters of the combiner. 6029 * <p> 6030 * The resulting adapter is the same type as the target, except that the 6031 * first parameter type is dropped, 6032 * if it corresponds to the result of the combiner. 6033 * <p> 6034 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments 6035 * that either the combiner or the target does not wish to receive. 6036 * If some of the incoming arguments are destined only for the combiner, 6037 * consider using {@link MethodHandle#asCollector asCollector} instead, since those 6038 * arguments will not need to be live on the stack on entry to the 6039 * target.) 6040 * <p><b>Example:</b> 6041 * {@snippet lang="java" : 6042 import static java.lang.invoke.MethodHandles.*; 6043 import static java.lang.invoke.MethodType.*; 6044 ... 6045 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 6046 "println", methodType(void.class, String.class)) 6047 .bindTo(System.out); 6048 MethodHandle cat = lookup().findVirtual(String.class, 6049 "concat", methodType(String.class, String.class)); 6050 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 6051 MethodHandle catTrace = foldArguments(cat, trace); 6052 // also prints "boo": 6053 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 6054 * } 6055 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 6056 * represents the result type of the {@code target} and resulting adapter. 6057 * {@code V}/{@code v} represent the type and value of the parameter and argument 6058 * of {@code target} that precedes the folding position; {@code V} also is 6059 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 6060 * types and values of the {@code N} parameters and arguments at the folding 6061 * position. {@code B}/{@code b} represent the types and values of the 6062 * {@code target} parameters and arguments that follow the folded parameters 6063 * and arguments. 6064 * {@snippet lang="java" : 6065 * // there are N arguments in A... 6066 * T target(V, A[N]..., B...); 6067 * V combiner(A...); 6068 * T adapter(A... a, B... b) { 6069 * V v = combiner(a...); 6070 * return target(v, a..., b...); 6071 * } 6072 * // and if the combiner has a void return: 6073 * T target2(A[N]..., B...); 6074 * void combiner2(A...); 6075 * T adapter2(A... a, B... b) { 6076 * combiner2(a...); 6077 * return target2(a..., b...); 6078 * } 6079 * } 6080 * <p> 6081 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 6082 * variable-arity method handle}, even if the original target method handle was. 6083 * @param target the method handle to invoke after arguments are combined 6084 * @param combiner method handle to call initially on the incoming arguments 6085 * @return method handle which incorporates the specified argument folding logic 6086 * @throws NullPointerException if either argument is null 6087 * @throws IllegalArgumentException if {@code combiner}'s return type 6088 * is non-void and not the same as the first argument type of 6089 * the target, or if the initial {@code N} argument types 6090 * of the target 6091 * (skipping one matching the {@code combiner}'s return type) 6092 * are not identical with the argument types of {@code combiner} 6093 */ 6094 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) { 6095 return foldArguments(target, 0, combiner); 6096 } 6097 6098 /** 6099 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then 6100 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just 6101 * before the folded arguments. 6102 * <p> 6103 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the 6104 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a 6105 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position 6106 * 0. 6107 * 6108 * @apiNote Example: 6109 * {@snippet lang="java" : 6110 import static java.lang.invoke.MethodHandles.*; 6111 import static java.lang.invoke.MethodType.*; 6112 ... 6113 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 6114 "println", methodType(void.class, String.class)) 6115 .bindTo(System.out); 6116 MethodHandle cat = lookup().findVirtual(String.class, 6117 "concat", methodType(String.class, String.class)); 6118 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 6119 MethodHandle catTrace = foldArguments(cat, 1, trace); 6120 // also prints "jum": 6121 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 6122 * } 6123 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 6124 * represents the result type of the {@code target} and resulting adapter. 6125 * {@code V}/{@code v} represent the type and value of the parameter and argument 6126 * of {@code target} that precedes the folding position; {@code V} also is 6127 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 6128 * types and values of the {@code N} parameters and arguments at the folding 6129 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types 6130 * and values of the {@code target} parameters and arguments that precede and 6131 * follow the folded parameters and arguments starting at {@code pos}, 6132 * respectively. 6133 * {@snippet lang="java" : 6134 * // there are N arguments in A... 6135 * T target(Z..., V, A[N]..., B...); 6136 * V combiner(A...); 6137 * T adapter(Z... z, A... a, B... b) { 6138 * V v = combiner(a...); 6139 * return target(z..., v, a..., b...); 6140 * } 6141 * // and if the combiner has a void return: 6142 * T target2(Z..., A[N]..., B...); 6143 * void combiner2(A...); 6144 * T adapter2(Z... z, A... a, B... b) { 6145 * combiner2(a...); 6146 * return target2(z..., a..., b...); 6147 * } 6148 * } 6149 * <p> 6150 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 6151 * variable-arity method handle}, even if the original target method handle was. 6152 * 6153 * @param target the method handle to invoke after arguments are combined 6154 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code 6155 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6156 * @param combiner method handle to call initially on the incoming arguments 6157 * @return method handle which incorporates the specified argument folding logic 6158 * @throws NullPointerException if either argument is null 6159 * @throws IllegalArgumentException if either of the following two conditions holds: 6160 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 6161 * {@code pos} of the target signature; 6162 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching 6163 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}. 6164 * 6165 * @see #foldArguments(MethodHandle, MethodHandle) 6166 * @since 9 6167 */ 6168 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) { 6169 MethodType targetType = target.type(); 6170 MethodType combinerType = combiner.type(); 6171 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType); 6172 BoundMethodHandle result = target.rebind(); 6173 boolean dropResult = rtype == void.class; 6174 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType()); 6175 MethodType newType = targetType; 6176 if (!dropResult) { 6177 newType = newType.dropParameterTypes(pos, pos + 1); 6178 } 6179 result = result.copyWithExtendL(newType, lform, combiner); 6180 return result; 6181 } 6182 6183 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) { 6184 int foldArgs = combinerType.parameterCount(); 6185 Class<?> rtype = combinerType.returnType(); 6186 int foldVals = rtype == void.class ? 0 : 1; 6187 int afterInsertPos = foldPos + foldVals; 6188 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs); 6189 if (ok) { 6190 for (int i = 0; i < foldArgs; i++) { 6191 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) { 6192 ok = false; 6193 break; 6194 } 6195 } 6196 } 6197 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) 6198 ok = false; 6199 if (!ok) 6200 throw misMatchedTypes("target and combiner types", targetType, combinerType); 6201 return rtype; 6202 } 6203 6204 /** 6205 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result 6206 * of the pre-processing replacing the argument at the given position. 6207 * 6208 * @param target the method handle to invoke after arguments are combined 6209 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 6210 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6211 * @param combiner method handle to call initially on the incoming arguments 6212 * @param argPositions indexes of the target to pick arguments sent to the combiner from 6213 * @return method handle which incorporates the specified argument folding logic 6214 * @throws NullPointerException if either argument is null 6215 * @throws IllegalArgumentException if either of the following two conditions holds: 6216 * (1) {@code combiner}'s return type is not the same as the argument type at position 6217 * {@code pos} of the target signature; 6218 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are 6219 * not identical with the argument types of {@code combiner}. 6220 */ 6221 /*non-public*/ 6222 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6223 return argumentsWithCombiner(true, target, position, combiner, argPositions); 6224 } 6225 6226 /** 6227 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of 6228 * the pre-processing inserted into the original sequence of arguments at the given position. 6229 * 6230 * @param target the method handle to invoke after arguments are combined 6231 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 6232 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6233 * @param combiner method handle to call initially on the incoming arguments 6234 * @param argPositions indexes of the target to pick arguments sent to the combiner from 6235 * @return method handle which incorporates the specified argument folding logic 6236 * @throws NullPointerException if either argument is null 6237 * @throws IllegalArgumentException if either of the following two conditions holds: 6238 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 6239 * {@code pos} of the target signature; 6240 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature 6241 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical 6242 * with the argument types of {@code combiner}. 6243 */ 6244 /*non-public*/ 6245 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6246 return argumentsWithCombiner(false, target, position, combiner, argPositions); 6247 } 6248 6249 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6250 MethodType targetType = target.type(); 6251 MethodType combinerType = combiner.type(); 6252 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions); 6253 BoundMethodHandle result = target.rebind(); 6254 6255 MethodType newType = targetType; 6256 LambdaForm lform; 6257 if (filter) { 6258 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions); 6259 } else { 6260 boolean dropResult = rtype == void.class; 6261 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions); 6262 if (!dropResult) { 6263 newType = newType.dropParameterTypes(position, position + 1); 6264 } 6265 } 6266 result = result.copyWithExtendL(newType, lform, combiner); 6267 return result; 6268 } 6269 6270 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) { 6271 int combinerArgs = combinerType.parameterCount(); 6272 if (argPos.length != combinerArgs) { 6273 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length); 6274 } 6275 Class<?> rtype = combinerType.returnType(); 6276 6277 for (int i = 0; i < combinerArgs; i++) { 6278 int arg = argPos[i]; 6279 if (arg < 0 || arg > targetType.parameterCount()) { 6280 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg); 6281 } 6282 if (combinerType.parameterType(i) != targetType.parameterType(arg)) { 6283 throw newIllegalArgumentException("target argument type at position " + arg 6284 + " must match combiner argument type at index " + i + ": " + targetType 6285 + " -> " + combinerType + ", map: " + Arrays.toString(argPos)); 6286 } 6287 } 6288 if (filter && combinerType.returnType() != targetType.parameterType(position)) { 6289 throw misMatchedTypes("target and combiner types", targetType, combinerType); 6290 } 6291 return rtype; 6292 } 6293 6294 /** 6295 * Makes a method handle which adapts a target method handle, 6296 * by guarding it with a test, a boolean-valued method handle. 6297 * If the guard fails, a fallback handle is called instead. 6298 * All three method handles must have the same corresponding 6299 * argument and return types, except that the return type 6300 * of the test must be boolean, and the test is allowed 6301 * to have fewer arguments than the other two method handles. 6302 * <p> 6303 * Here is pseudocode for the resulting adapter. In the code, {@code T} 6304 * represents the uniform result type of the three involved handles; 6305 * {@code A}/{@code a}, the types and values of the {@code target} 6306 * parameters and arguments that are consumed by the {@code test}; and 6307 * {@code B}/{@code b}, those types and values of the {@code target} 6308 * parameters and arguments that are not consumed by the {@code test}. 6309 * {@snippet lang="java" : 6310 * boolean test(A...); 6311 * T target(A...,B...); 6312 * T fallback(A...,B...); 6313 * T adapter(A... a,B... b) { 6314 * if (test(a...)) 6315 * return target(a..., b...); 6316 * else 6317 * return fallback(a..., b...); 6318 * } 6319 * } 6320 * Note that the test arguments ({@code a...} in the pseudocode) cannot 6321 * be modified by execution of the test, and so are passed unchanged 6322 * from the caller to the target or fallback as appropriate. 6323 * @param test method handle used for test, must return boolean 6324 * @param target method handle to call if test passes 6325 * @param fallback method handle to call if test fails 6326 * @return method handle which incorporates the specified if/then/else logic 6327 * @throws NullPointerException if any argument is null 6328 * @throws IllegalArgumentException if {@code test} does not return boolean, 6329 * or if all three method types do not match (with the return 6330 * type of {@code test} changed to match that of the target). 6331 */ 6332 public static MethodHandle guardWithTest(MethodHandle test, 6333 MethodHandle target, 6334 MethodHandle fallback) { 6335 MethodType gtype = test.type(); 6336 MethodType ttype = target.type(); 6337 MethodType ftype = fallback.type(); 6338 if (!ttype.equals(ftype)) 6339 throw misMatchedTypes("target and fallback types", ttype, ftype); 6340 if (gtype.returnType() != boolean.class) 6341 throw newIllegalArgumentException("guard type is not a predicate "+gtype); 6342 6343 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true); 6344 if (test == null) { 6345 throw misMatchedTypes("target and test types", ttype, gtype); 6346 } 6347 return MethodHandleImpl.makeGuardWithTest(test, target, fallback); 6348 } 6349 6350 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) { 6351 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2); 6352 } 6353 6354 /** 6355 * Makes a method handle which adapts a target method handle, 6356 * by running it inside an exception handler. 6357 * If the target returns normally, the adapter returns that value. 6358 * If an exception matching the specified type is thrown, the fallback 6359 * handle is called instead on the exception, plus the original arguments. 6360 * <p> 6361 * The target and handler must have the same corresponding 6362 * argument and return types, except that handler may omit trailing arguments 6363 * (similarly to the predicate in {@link #guardWithTest guardWithTest}). 6364 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype. 6365 * <p> 6366 * Here is pseudocode for the resulting adapter. In the code, {@code T} 6367 * represents the return type of the {@code target} and {@code handler}, 6368 * and correspondingly that of the resulting adapter; {@code A}/{@code a}, 6369 * the types and values of arguments to the resulting handle consumed by 6370 * {@code handler}; and {@code B}/{@code b}, those of arguments to the 6371 * resulting handle discarded by {@code handler}. 6372 * {@snippet lang="java" : 6373 * T target(A..., B...); 6374 * T handler(ExType, A...); 6375 * T adapter(A... a, B... b) { 6376 * try { 6377 * return target(a..., b...); 6378 * } catch (ExType ex) { 6379 * return handler(ex, a...); 6380 * } 6381 * } 6382 * } 6383 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 6384 * be modified by execution of the target, and so are passed unchanged 6385 * from the caller to the handler, if the handler is invoked. 6386 * <p> 6387 * The target and handler must return the same type, even if the handler 6388 * always throws. (This might happen, for instance, because the handler 6389 * is simulating a {@code finally} clause). 6390 * To create such a throwing handler, compose the handler creation logic 6391 * with {@link #throwException throwException}, 6392 * in order to create a method handle of the correct return type. 6393 * @param target method handle to call 6394 * @param exType the type of exception which the handler will catch 6395 * @param handler method handle to call if a matching exception is thrown 6396 * @return method handle which incorporates the specified try/catch logic 6397 * @throws NullPointerException if any argument is null 6398 * @throws IllegalArgumentException if {@code handler} does not accept 6399 * the given exception type, or if the method handle types do 6400 * not match in their return types and their 6401 * corresponding parameters 6402 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle) 6403 */ 6404 public static MethodHandle catchException(MethodHandle target, 6405 Class<? extends Throwable> exType, 6406 MethodHandle handler) { 6407 MethodType ttype = target.type(); 6408 MethodType htype = handler.type(); 6409 if (!Throwable.class.isAssignableFrom(exType)) 6410 throw new ClassCastException(exType.getName()); 6411 if (htype.parameterCount() < 1 || 6412 !htype.parameterType(0).isAssignableFrom(exType)) 6413 throw newIllegalArgumentException("handler does not accept exception type "+exType); 6414 if (htype.returnType() != ttype.returnType()) 6415 throw misMatchedTypes("target and handler return types", ttype, htype); 6416 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true); 6417 if (handler == null) { 6418 throw misMatchedTypes("target and handler types", ttype, htype); 6419 } 6420 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler); 6421 } 6422 6423 /** 6424 * Produces a method handle which will throw exceptions of the given {@code exType}. 6425 * The method handle will accept a single argument of {@code exType}, 6426 * and immediately throw it as an exception. 6427 * The method type will nominally specify a return of {@code returnType}. 6428 * The return type may be anything convenient: It doesn't matter to the 6429 * method handle's behavior, since it will never return normally. 6430 * @param returnType the return type of the desired method handle 6431 * @param exType the parameter type of the desired method handle 6432 * @return method handle which can throw the given exceptions 6433 * @throws NullPointerException if either argument is null 6434 */ 6435 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) { 6436 if (!Throwable.class.isAssignableFrom(exType)) 6437 throw new ClassCastException(exType.getName()); 6438 return MethodHandleImpl.throwException(methodType(returnType, exType)); 6439 } 6440 6441 /** 6442 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each 6443 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and 6444 * delivers the loop's result, which is the return value of the resulting handle. 6445 * <p> 6446 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop 6447 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration 6448 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in 6449 * terms of method handles, each clause will specify up to four independent actions:<ul> 6450 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}. 6451 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}. 6452 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit. 6453 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value. 6454 * </ul> 6455 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}. 6456 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually 6457 * be referring to types, but in some contexts (describing execution) the lists will be of actual values. 6458 * <p> 6459 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in 6460 * this case. See below for a detailed description. 6461 * <p> 6462 * <em>Parameters optional everywhere:</em> 6463 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}. 6464 * As an exception, the init functions cannot take any {@code v} parameters, 6465 * because those values are not yet computed when the init functions are executed. 6466 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take. 6467 * In fact, any clause function may take no arguments at all. 6468 * <p> 6469 * <em>Loop parameters:</em> 6470 * A clause function may take all the iteration variable values it is entitled to, in which case 6471 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>, 6472 * with their types and values notated as {@code (A...)} and {@code (a...)}. 6473 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed. 6474 * (Since init functions do not accept iteration variables {@code v}, any parameter to an 6475 * init function is automatically a loop parameter {@code a}.) 6476 * As with iteration variables, clause functions are allowed but not required to accept loop parameters. 6477 * These loop parameters act as loop-invariant values visible across the whole loop. 6478 * <p> 6479 * <em>Parameters visible everywhere:</em> 6480 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full 6481 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters. 6482 * The init functions can observe initial pre-loop state, in the form {@code (a...)}. 6483 * Most clause functions will not need all of this information, but they will be formally connected to it 6484 * as if by {@link #dropArguments}. 6485 * <a id="astar"></a> 6486 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full 6487 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}). 6488 * In that notation, the general form of an init function parameter list 6489 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}. 6490 * <p> 6491 * <em>Checking clause structure:</em> 6492 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the 6493 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must" 6494 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not 6495 * met by the inputs to the loop combinator. 6496 * <p> 6497 * <em>Effectively identical sequences:</em> 6498 * <a id="effid"></a> 6499 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B} 6500 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}. 6501 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical" 6502 * as a whole if the set contains a longest list, and all members of the set are effectively identical to 6503 * that longest list. 6504 * For example, any set of type sequences of the form {@code (V*)} is effectively identical, 6505 * and the same is true if more sequences of the form {@code (V... A*)} are added. 6506 * <p> 6507 * <em>Step 0: Determine clause structure.</em><ol type="a"> 6508 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element. 6509 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements. 6510 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length 6511 * four. Padding takes place by appending elements to the array. 6512 * <li>Clauses with all {@code null}s are disregarded. 6513 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini". 6514 * </ol> 6515 * <p> 6516 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a"> 6517 * <li>The iteration variable type for each clause is determined using the clause's init and step return types. 6518 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is 6519 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's 6520 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's 6521 * iteration variable type. 6522 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}. 6523 * <li>This list of types is called the "iteration variable types" ({@code (V...)}). 6524 * </ol> 6525 * <p> 6526 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul> 6527 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}). 6528 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types. 6529 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.) 6530 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types. 6531 * (These types will be checked in step 2, along with all the clause function types.) 6532 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.) 6533 * <li>All of the collected parameter lists must be effectively identical. 6534 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}). 6535 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence. 6536 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called 6537 * the "internal parameter list". 6538 * </ul> 6539 * <p> 6540 * <em>Step 1C: Determine loop return type.</em><ol type="a"> 6541 * <li>Examine fini function return types, disregarding omitted fini functions. 6542 * <li>If there are no fini functions, the loop return type is {@code void}. 6543 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return 6544 * type. 6545 * </ol> 6546 * <p> 6547 * <em>Step 1D: Check other types.</em><ol type="a"> 6548 * <li>There must be at least one non-omitted pred function. 6549 * <li>Every non-omitted pred function must have a {@code boolean} return type. 6550 * </ol> 6551 * <p> 6552 * <em>Step 2: Determine parameter lists.</em><ol type="a"> 6553 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}. 6554 * <li>The parameter list for init functions will be adjusted to the external parameter list. 6555 * (Note that their parameter lists are already effectively identical to this list.) 6556 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be 6557 * effectively identical to the internal parameter list {@code (V... A...)}. 6558 * </ol> 6559 * <p> 6560 * <em>Step 3: Fill in omitted functions.</em><ol type="a"> 6561 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable 6562 * type. 6563 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration 6564 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void} 6565 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.) 6566 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far 6567 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.) 6568 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the 6569 * loop return type. 6570 * </ol> 6571 * <p> 6572 * <em>Step 4: Fill in missing parameter types.</em><ol type="a"> 6573 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)}, 6574 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list. 6575 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter 6576 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list, 6577 * pad out the end of the list. 6578 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}. 6579 * </ol> 6580 * <p> 6581 * <em>Final observations.</em><ol type="a"> 6582 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments. 6583 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have. 6584 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have. 6585 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of 6586 * (non-{@code void}) iteration variables {@code V} followed by loop parameters. 6587 * <li>Each pair of init and step functions agrees in their return type {@code V}. 6588 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables. 6589 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters. 6590 * </ol> 6591 * <p> 6592 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property: 6593 * <ul> 6594 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}. 6595 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters. 6596 * (Only one {@code Pn} has to be non-{@code null}.) 6597 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}. 6598 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types. 6599 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}. 6600 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}. 6601 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine 6602 * the resulting loop handle's parameter types {@code (A...)}. 6603 * </ul> 6604 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions, 6605 * which is natural if most of the loop computation happens in the steps. For some loops, 6606 * the burden of computation might be heaviest in the pred functions, and so the pred functions 6607 * might need to accept the loop parameter values. For loops with complex exit logic, the fini 6608 * functions might need to accept loop parameters, and likewise for loops with complex entry logic, 6609 * where the init functions will need the extra parameters. For such reasons, the rules for 6610 * determining these parameters are as symmetric as possible, across all clause parts. 6611 * In general, the loop parameters function as common invariant values across the whole 6612 * loop, while the iteration variables function as common variant values, or (if there is 6613 * no step function) as internal loop invariant temporaries. 6614 * <p> 6615 * <em>Loop execution.</em><ol type="a"> 6616 * <li>When the loop is called, the loop input values are saved in locals, to be passed to 6617 * every clause function. These locals are loop invariant. 6618 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)}) 6619 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals. 6620 * These locals will be loop varying (unless their steps behave as identity functions, as noted above). 6621 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of 6622 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)} 6623 * (in argument order). 6624 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function 6625 * returns {@code false}. 6626 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the 6627 * sequence {@code (v...)} of loop variables. 6628 * The updated value is immediately visible to all subsequent function calls. 6629 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value 6630 * (of type {@code R}) is returned from the loop as a whole. 6631 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit 6632 * except by throwing an exception. 6633 * </ol> 6634 * <p> 6635 * <em>Usage tips.</em> 6636 * <ul> 6637 * <li>Although each step function will receive the current values of <em>all</em> the loop variables, 6638 * sometimes a step function only needs to observe the current value of its own variable. 6639 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}. 6640 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}. 6641 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create 6642 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be 6643 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable. 6644 * <li>If some of the clause functions are virtual methods on an instance, the instance 6645 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause 6646 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference 6647 * will be the first iteration variable value, and it will be easy to use virtual 6648 * methods as clause parts, since all of them will take a leading instance reference matching that value. 6649 * </ul> 6650 * <p> 6651 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types 6652 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop; 6653 * and {@code R} is the common result type of all finalizers as well as of the resulting loop. 6654 * {@snippet lang="java" : 6655 * V... init...(A...); 6656 * boolean pred...(V..., A...); 6657 * V... step...(V..., A...); 6658 * R fini...(V..., A...); 6659 * R loop(A... a) { 6660 * V... v... = init...(a...); 6661 * for (;;) { 6662 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) { 6663 * v = s(v..., a...); 6664 * if (!p(v..., a...)) { 6665 * return f(v..., a...); 6666 * } 6667 * } 6668 * } 6669 * } 6670 * } 6671 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded 6672 * to their full length, even though individual clause functions may neglect to take them all. 6673 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}. 6674 * 6675 * @apiNote Example: 6676 * {@snippet lang="java" : 6677 * // iterative implementation of the factorial function as a loop handle 6678 * static int one(int k) { return 1; } 6679 * static int inc(int i, int acc, int k) { return i + 1; } 6680 * static int mult(int i, int acc, int k) { return i * acc; } 6681 * static boolean pred(int i, int acc, int k) { return i < k; } 6682 * static int fin(int i, int acc, int k) { return acc; } 6683 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 6684 * // null initializer for counter, should initialize to 0 6685 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6686 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6687 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 6688 * assertEquals(120, loop.invoke(5)); 6689 * } 6690 * The same example, dropping arguments and using combinators: 6691 * {@snippet lang="java" : 6692 * // simplified implementation of the factorial function as a loop handle 6693 * static int inc(int i) { return i + 1; } // drop acc, k 6694 * static int mult(int i, int acc) { return i * acc; } //drop k 6695 * static boolean cmp(int i, int k) { return i < k; } 6696 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods 6697 * // null initializer for counter, should initialize to 0 6698 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 6699 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc 6700 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i 6701 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6702 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6703 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 6704 * assertEquals(720, loop.invoke(6)); 6705 * } 6706 * A similar example, using a helper object to hold a loop parameter: 6707 * {@snippet lang="java" : 6708 * // instance-based implementation of the factorial function as a loop handle 6709 * static class FacLoop { 6710 * final int k; 6711 * FacLoop(int k) { this.k = k; } 6712 * int inc(int i) { return i + 1; } 6713 * int mult(int i, int acc) { return i * acc; } 6714 * boolean pred(int i) { return i < k; } 6715 * int fin(int i, int acc) { return acc; } 6716 * } 6717 * // assume MH_FacLoop is a handle to the constructor 6718 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 6719 * // null initializer for counter, should initialize to 0 6720 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 6721 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop}; 6722 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6723 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6724 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause); 6725 * assertEquals(5040, loop.invoke(7)); 6726 * } 6727 * 6728 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above. 6729 * 6730 * @return a method handle embodying the looping behavior as defined by the arguments. 6731 * 6732 * @throws IllegalArgumentException in case any of the constraints described above is violated. 6733 * 6734 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle) 6735 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 6736 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle) 6737 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle) 6738 * @since 9 6739 */ 6740 public static MethodHandle loop(MethodHandle[]... clauses) { 6741 // Step 0: determine clause structure. 6742 loopChecks0(clauses); 6743 6744 List<MethodHandle> init = new ArrayList<>(); 6745 List<MethodHandle> step = new ArrayList<>(); 6746 List<MethodHandle> pred = new ArrayList<>(); 6747 List<MethodHandle> fini = new ArrayList<>(); 6748 6749 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> { 6750 init.add(clause[0]); // all clauses have at least length 1 6751 step.add(clause.length <= 1 ? null : clause[1]); 6752 pred.add(clause.length <= 2 ? null : clause[2]); 6753 fini.add(clause.length <= 3 ? null : clause[3]); 6754 }); 6755 6756 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1; 6757 final int nclauses = init.size(); 6758 6759 // Step 1A: determine iteration variables (V...). 6760 final List<Class<?>> iterationVariableTypes = new ArrayList<>(); 6761 for (int i = 0; i < nclauses; ++i) { 6762 MethodHandle in = init.get(i); 6763 MethodHandle st = step.get(i); 6764 if (in == null && st == null) { 6765 iterationVariableTypes.add(void.class); 6766 } else if (in != null && st != null) { 6767 loopChecks1a(i, in, st); 6768 iterationVariableTypes.add(in.type().returnType()); 6769 } else { 6770 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType()); 6771 } 6772 } 6773 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList(); 6774 6775 // Step 1B: determine loop parameters (A...). 6776 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size()); 6777 loopChecks1b(init, commonSuffix); 6778 6779 // Step 1C: determine loop return type. 6780 // Step 1D: check other types. 6781 // local variable required here; see JDK-8223553 6782 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type) 6783 .map(MethodType::returnType); 6784 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class); 6785 loopChecks1cd(pred, fini, loopReturnType); 6786 6787 // Step 2: determine parameter lists. 6788 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix); 6789 commonParameterSequence.addAll(commonSuffix); 6790 loopChecks2(step, pred, fini, commonParameterSequence); 6791 // Step 3: fill in omitted functions. 6792 for (int i = 0; i < nclauses; ++i) { 6793 Class<?> t = iterationVariableTypes.get(i); 6794 if (init.get(i) == null) { 6795 init.set(i, empty(methodType(t, commonSuffix))); 6796 } 6797 if (step.get(i) == null) { 6798 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i)); 6799 } 6800 if (pred.get(i) == null) { 6801 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence)); 6802 } 6803 if (fini.get(i) == null) { 6804 fini.set(i, empty(methodType(t, commonParameterSequence))); 6805 } 6806 } 6807 6808 // Step 4: fill in missing parameter types. 6809 // Also convert all handles to fixed-arity handles. 6810 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix)); 6811 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence)); 6812 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence)); 6813 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence)); 6814 6815 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList). 6816 allMatch(pl -> pl.equals(commonSuffix)); 6817 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList). 6818 allMatch(pl -> pl.equals(commonParameterSequence)); 6819 6820 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini); 6821 } 6822 6823 private static void loopChecks0(MethodHandle[][] clauses) { 6824 if (clauses == null || clauses.length == 0) { 6825 throw newIllegalArgumentException("null or no clauses passed"); 6826 } 6827 if (Stream.of(clauses).anyMatch(Objects::isNull)) { 6828 throw newIllegalArgumentException("null clauses are not allowed"); 6829 } 6830 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) { 6831 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements."); 6832 } 6833 } 6834 6835 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) { 6836 if (in.type().returnType() != st.type().returnType()) { 6837 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(), 6838 st.type().returnType()); 6839 } 6840 } 6841 6842 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) { 6843 return mhs.filter(Objects::nonNull) 6844 // take only those that can contribute to a common suffix because they are longer than the prefix 6845 .map(MethodHandle::type) 6846 .filter(t -> t.parameterCount() > skipSize) 6847 .max(Comparator.comparingInt(MethodType::parameterCount)) 6848 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount()))) 6849 .orElse(List.of()); 6850 } 6851 6852 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) { 6853 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize); 6854 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0); 6855 return longest1.size() >= longest2.size() ? longest1 : longest2; 6856 } 6857 6858 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) { 6859 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type). 6860 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) { 6861 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init + 6862 " (common suffix: " + commonSuffix + ")"); 6863 } 6864 } 6865 6866 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) { 6867 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 6868 anyMatch(t -> t != loopReturnType)) { 6869 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " + 6870 loopReturnType + ")"); 6871 } 6872 6873 if (pred.stream().noneMatch(Objects::nonNull)) { 6874 throw newIllegalArgumentException("no predicate found", pred); 6875 } 6876 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 6877 anyMatch(t -> t != boolean.class)) { 6878 throw newIllegalArgumentException("predicates must have boolean return type", pred); 6879 } 6880 } 6881 6882 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) { 6883 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type). 6884 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) { 6885 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step + 6886 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")"); 6887 } 6888 } 6889 6890 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) { 6891 return hs.stream().map(h -> { 6892 int pc = h.type().parameterCount(); 6893 int tpsize = targetParams.size(); 6894 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h; 6895 }).toList(); 6896 } 6897 6898 private static List<MethodHandle> fixArities(List<MethodHandle> hs) { 6899 return hs.stream().map(MethodHandle::asFixedArity).toList(); 6900 } 6901 6902 /** 6903 * Constructs a {@code while} loop from an initializer, a body, and a predicate. 6904 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 6905 * <p> 6906 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 6907 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate 6908 * evaluates to {@code true}). 6909 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case). 6910 * <p> 6911 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 6912 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 6913 * and updated with the value returned from its invocation. The result of loop execution will be 6914 * the final value of the additional loop-local variable (if present). 6915 * <p> 6916 * The following rules hold for these argument handles:<ul> 6917 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 6918 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 6919 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 6920 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 6921 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 6922 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 6923 * It will constrain the parameter lists of the other loop parts. 6924 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 6925 * list {@code (A...)} is called the <em>external parameter list</em>. 6926 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 6927 * additional state variable of the loop. 6928 * The body must both accept and return a value of this type {@code V}. 6929 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 6930 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 6931 * <a href="MethodHandles.html#effid">effectively identical</a> 6932 * to the external parameter list {@code (A...)}. 6933 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 6934 * {@linkplain #empty default value}. 6935 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 6936 * Its parameter list (either empty or of the form {@code (V A*)}) must be 6937 * effectively identical to the internal parameter list. 6938 * </ul> 6939 * <p> 6940 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 6941 * <li>The loop handle's result type is the result type {@code V} of the body. 6942 * <li>The loop handle's parameter types are the types {@code (A...)}, 6943 * from the external parameter list. 6944 * </ul> 6945 * <p> 6946 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 6947 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 6948 * passed to the loop. 6949 * {@snippet lang="java" : 6950 * V init(A...); 6951 * boolean pred(V, A...); 6952 * V body(V, A...); 6953 * V whileLoop(A... a...) { 6954 * V v = init(a...); 6955 * while (pred(v, a...)) { 6956 * v = body(v, a...); 6957 * } 6958 * return v; 6959 * } 6960 * } 6961 * 6962 * @apiNote Example: 6963 * {@snippet lang="java" : 6964 * // implement the zip function for lists as a loop handle 6965 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); } 6966 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); } 6967 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) { 6968 * zip.add(a.next()); 6969 * zip.add(b.next()); 6970 * return zip; 6971 * } 6972 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods 6973 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep); 6974 * List<String> a = Arrays.asList("a", "b", "c", "d"); 6975 * List<String> b = Arrays.asList("e", "f", "g", "h"); 6976 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h"); 6977 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator())); 6978 * } 6979 * 6980 * 6981 * @apiNote The implementation of this method can be expressed as follows: 6982 * {@snippet lang="java" : 6983 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 6984 * MethodHandle fini = (body.type().returnType() == void.class 6985 * ? null : identity(body.type().returnType())); 6986 * MethodHandle[] 6987 * checkExit = { null, null, pred, fini }, 6988 * varBody = { init, body }; 6989 * return loop(checkExit, varBody); 6990 * } 6991 * } 6992 * 6993 * @param init optional initializer, providing the initial value of the loop variable. 6994 * May be {@code null}, implying a default initial value. See above for other constraints. 6995 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 6996 * above for other constraints. 6997 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 6998 * See above for other constraints. 6999 * 7000 * @return a method handle implementing the {@code while} loop as described by the arguments. 7001 * @throws IllegalArgumentException if the rules for the arguments are violated. 7002 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 7003 * 7004 * @see #loop(MethodHandle[][]) 7005 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 7006 * @since 9 7007 */ 7008 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 7009 whileLoopChecks(init, pred, body); 7010 MethodHandle fini = identityOrVoid(body.type().returnType()); 7011 MethodHandle[] checkExit = { null, null, pred, fini }; 7012 MethodHandle[] varBody = { init, body }; 7013 return loop(checkExit, varBody); 7014 } 7015 7016 /** 7017 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. 7018 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7019 * <p> 7020 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 7021 * method will, in each iteration, first execute its body and then evaluate the predicate. 7022 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body. 7023 * <p> 7024 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 7025 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 7026 * and updated with the value returned from its invocation. The result of loop execution will be 7027 * the final value of the additional loop-local variable (if present). 7028 * <p> 7029 * The following rules hold for these argument handles:<ul> 7030 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7031 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 7032 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7033 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 7034 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 7035 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 7036 * It will constrain the parameter lists of the other loop parts. 7037 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 7038 * list {@code (A...)} is called the <em>external parameter list</em>. 7039 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7040 * additional state variable of the loop. 7041 * The body must both accept and return a value of this type {@code V}. 7042 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7043 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7044 * <a href="MethodHandles.html#effid">effectively identical</a> 7045 * to the external parameter list {@code (A...)}. 7046 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7047 * {@linkplain #empty default value}. 7048 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 7049 * Its parameter list (either empty or of the form {@code (V A*)}) must be 7050 * effectively identical to the internal parameter list. 7051 * </ul> 7052 * <p> 7053 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7054 * <li>The loop handle's result type is the result type {@code V} of the body. 7055 * <li>The loop handle's parameter types are the types {@code (A...)}, 7056 * from the external parameter list. 7057 * </ul> 7058 * <p> 7059 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7060 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 7061 * passed to the loop. 7062 * {@snippet lang="java" : 7063 * V init(A...); 7064 * boolean pred(V, A...); 7065 * V body(V, A...); 7066 * V doWhileLoop(A... a...) { 7067 * V v = init(a...); 7068 * do { 7069 * v = body(v, a...); 7070 * } while (pred(v, a...)); 7071 * return v; 7072 * } 7073 * } 7074 * 7075 * @apiNote Example: 7076 * {@snippet lang="java" : 7077 * // int i = 0; while (i < limit) { ++i; } return i; => limit 7078 * static int zero(int limit) { return 0; } 7079 * static int step(int i, int limit) { return i + 1; } 7080 * static boolean pred(int i, int limit) { return i < limit; } 7081 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods 7082 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred); 7083 * assertEquals(23, loop.invoke(23)); 7084 * } 7085 * 7086 * 7087 * @apiNote The implementation of this method can be expressed as follows: 7088 * {@snippet lang="java" : 7089 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 7090 * MethodHandle fini = (body.type().returnType() == void.class 7091 * ? null : identity(body.type().returnType())); 7092 * MethodHandle[] clause = { init, body, pred, fini }; 7093 * return loop(clause); 7094 * } 7095 * } 7096 * 7097 * @param init optional initializer, providing the initial value of the loop variable. 7098 * May be {@code null}, implying a default initial value. See above for other constraints. 7099 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 7100 * See above for other constraints. 7101 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 7102 * above for other constraints. 7103 * 7104 * @return a method handle implementing the {@code while} loop as described by the arguments. 7105 * @throws IllegalArgumentException if the rules for the arguments are violated. 7106 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 7107 * 7108 * @see #loop(MethodHandle[][]) 7109 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle) 7110 * @since 9 7111 */ 7112 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 7113 whileLoopChecks(init, pred, body); 7114 MethodHandle fini = identityOrVoid(body.type().returnType()); 7115 MethodHandle[] clause = {init, body, pred, fini }; 7116 return loop(clause); 7117 } 7118 7119 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) { 7120 Objects.requireNonNull(pred); 7121 Objects.requireNonNull(body); 7122 MethodType bodyType = body.type(); 7123 Class<?> returnType = bodyType.returnType(); 7124 List<Class<?>> innerList = bodyType.parameterList(); 7125 List<Class<?>> outerList = innerList; 7126 if (returnType == void.class) { 7127 // OK 7128 } else if (innerList.isEmpty() || innerList.get(0) != returnType) { 7129 // leading V argument missing => error 7130 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7131 throw misMatchedTypes("body function", bodyType, expected); 7132 } else { 7133 outerList = innerList.subList(1, innerList.size()); 7134 } 7135 MethodType predType = pred.type(); 7136 if (predType.returnType() != boolean.class || 7137 !predType.effectivelyIdenticalParameters(0, innerList)) { 7138 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList)); 7139 } 7140 if (init != null) { 7141 MethodType initType = init.type(); 7142 if (initType.returnType() != returnType || 7143 !initType.effectivelyIdenticalParameters(0, outerList)) { 7144 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 7145 } 7146 } 7147 } 7148 7149 /** 7150 * Constructs a loop that runs a given number of iterations. 7151 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7152 * <p> 7153 * The number of iterations is determined by the {@code iterations} handle evaluation result. 7154 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}. 7155 * It will be initialized to 0 and incremented by 1 in each iteration. 7156 * <p> 7157 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7158 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7159 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7160 * <p> 7161 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7162 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7163 * iteration variable. 7164 * The result of the loop handle execution will be the final {@code V} value of that variable 7165 * (or {@code void} if there is no {@code V} variable). 7166 * <p> 7167 * The following rules hold for the argument handles:<ul> 7168 * <li>The {@code iterations} handle must not be {@code null}, and must return 7169 * the type {@code int}, referred to here as {@code I} in parameter type lists. 7170 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7171 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 7172 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7173 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 7174 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 7175 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 7176 * of types called the <em>internal parameter list</em>. 7177 * It will constrain the parameter lists of the other loop parts. 7178 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 7179 * with no additional {@code A} types, then the internal parameter list is extended by 7180 * the argument types {@code A...} of the {@code iterations} handle. 7181 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 7182 * list {@code (A...)} is called the <em>external parameter list</em>. 7183 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7184 * additional state variable of the loop. 7185 * The body must both accept a leading parameter and return a value of this type {@code V}. 7186 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7187 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7188 * <a href="MethodHandles.html#effid">effectively identical</a> 7189 * to the external parameter list {@code (A...)}. 7190 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7191 * {@linkplain #empty default value}. 7192 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be 7193 * effectively identical to the external parameter list {@code (A...)}. 7194 * </ul> 7195 * <p> 7196 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7197 * <li>The loop handle's result type is the result type {@code V} of the body. 7198 * <li>The loop handle's parameter types are the types {@code (A...)}, 7199 * from the external parameter list. 7200 * </ul> 7201 * <p> 7202 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7203 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 7204 * arguments passed to the loop. 7205 * {@snippet lang="java" : 7206 * int iterations(A...); 7207 * V init(A...); 7208 * V body(V, int, A...); 7209 * V countedLoop(A... a...) { 7210 * int end = iterations(a...); 7211 * V v = init(a...); 7212 * for (int i = 0; i < end; ++i) { 7213 * v = body(v, i, a...); 7214 * } 7215 * return v; 7216 * } 7217 * } 7218 * 7219 * @apiNote Example with a fully conformant body method: 7220 * {@snippet lang="java" : 7221 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 7222 * // => a variation on a well known theme 7223 * static String step(String v, int counter, String init) { return "na " + v; } 7224 * // assume MH_step is a handle to the method above 7225 * MethodHandle fit13 = MethodHandles.constant(int.class, 13); 7226 * MethodHandle start = MethodHandles.identity(String.class); 7227 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step); 7228 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!")); 7229 * } 7230 * 7231 * @apiNote Example with the simplest possible body method type, 7232 * and passing the number of iterations to the loop invocation: 7233 * {@snippet lang="java" : 7234 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 7235 * // => a variation on a well known theme 7236 * static String step(String v, int counter ) { return "na " + v; } 7237 * // assume MH_step is a handle to the method above 7238 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class); 7239 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class); 7240 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v 7241 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!")); 7242 * } 7243 * 7244 * @apiNote Example that treats the number of iterations, string to append to, and string to append 7245 * as loop parameters: 7246 * {@snippet lang="java" : 7247 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 7248 * // => a variation on a well known theme 7249 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; } 7250 * // assume MH_step is a handle to the method above 7251 * MethodHandle count = MethodHandles.identity(int.class); 7252 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class); 7253 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v 7254 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!")); 7255 * } 7256 * 7257 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)} 7258 * to enforce a loop type: 7259 * {@snippet lang="java" : 7260 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 7261 * // => a variation on a well known theme 7262 * static String step(String v, int counter, String pre) { return pre + " " + v; } 7263 * // assume MH_step is a handle to the method above 7264 * MethodType loopType = methodType(String.class, String.class, int.class, String.class); 7265 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1); 7266 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2); 7267 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0); 7268 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v 7269 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!")); 7270 * } 7271 * 7272 * @apiNote The implementation of this method can be expressed as follows: 7273 * {@snippet lang="java" : 7274 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 7275 * return countedLoop(empty(iterations.type()), iterations, init, body); 7276 * } 7277 * } 7278 * 7279 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's 7280 * result type must be {@code int}. See above for other constraints. 7281 * @param init optional initializer, providing the initial value of the loop variable. 7282 * May be {@code null}, implying a default initial value. See above for other constraints. 7283 * @param body body of the loop, which may not be {@code null}. 7284 * It controls the loop parameters and result type in the standard case (see above for details). 7285 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 7286 * and may accept any number of additional types. 7287 * See above for other constraints. 7288 * 7289 * @return a method handle representing the loop. 7290 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}. 7291 * @throws IllegalArgumentException if any argument violates the rules formulated above. 7292 * 7293 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle) 7294 * @since 9 7295 */ 7296 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 7297 return countedLoop(empty(iterations.type()), iterations, init, body); 7298 } 7299 7300 /** 7301 * Constructs a loop that counts over a range of numbers. 7302 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7303 * <p> 7304 * The loop counter {@code i} is a loop iteration variable of type {@code int}. 7305 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive) 7306 * values of the loop counter. 7307 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the 7308 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1. 7309 * <p> 7310 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7311 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7312 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7313 * <p> 7314 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7315 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7316 * iteration variable. 7317 * The result of the loop handle execution will be the final {@code V} value of that variable 7318 * (or {@code void} if there is no {@code V} variable). 7319 * <p> 7320 * The following rules hold for the argument handles:<ul> 7321 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return 7322 * the common type {@code int}, referred to here as {@code I} in parameter type lists. 7323 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7324 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 7325 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7326 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 7327 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 7328 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 7329 * of types called the <em>internal parameter list</em>. 7330 * It will constrain the parameter lists of the other loop parts. 7331 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 7332 * with no additional {@code A} types, then the internal parameter list is extended by 7333 * the argument types {@code A...} of the {@code end} handle. 7334 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 7335 * list {@code (A...)} is called the <em>external parameter list</em>. 7336 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7337 * additional state variable of the loop. 7338 * The body must both accept a leading parameter and return a value of this type {@code V}. 7339 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7340 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7341 * <a href="MethodHandles.html#effid">effectively identical</a> 7342 * to the external parameter list {@code (A...)}. 7343 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7344 * {@linkplain #empty default value}. 7345 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be 7346 * effectively identical to the external parameter list {@code (A...)}. 7347 * <li>Likewise, the parameter list of {@code end} must be effectively identical 7348 * to the external parameter list. 7349 * </ul> 7350 * <p> 7351 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7352 * <li>The loop handle's result type is the result type {@code V} of the body. 7353 * <li>The loop handle's parameter types are the types {@code (A...)}, 7354 * from the external parameter list. 7355 * </ul> 7356 * <p> 7357 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7358 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 7359 * arguments passed to the loop. 7360 * {@snippet lang="java" : 7361 * int start(A...); 7362 * int end(A...); 7363 * V init(A...); 7364 * V body(V, int, A...); 7365 * V countedLoop(A... a...) { 7366 * int e = end(a...); 7367 * int s = start(a...); 7368 * V v = init(a...); 7369 * for (int i = s; i < e; ++i) { 7370 * v = body(v, i, a...); 7371 * } 7372 * return v; 7373 * } 7374 * } 7375 * 7376 * @apiNote The implementation of this method can be expressed as follows: 7377 * {@snippet lang="java" : 7378 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7379 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class); 7380 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with 7381 * // the following semantics: 7382 * // MH_increment: (int limit, int counter) -> counter + 1 7383 * // MH_predicate: (int limit, int counter) -> counter < limit 7384 * Class<?> counterType = start.type().returnType(); // int 7385 * Class<?> returnType = body.type().returnType(); 7386 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null; 7387 * if (returnType != void.class) { // ignore the V variable 7388 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 7389 * pred = dropArguments(pred, 1, returnType); // ditto 7390 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit 7391 * } 7392 * body = dropArguments(body, 0, counterType); // ignore the limit variable 7393 * MethodHandle[] 7394 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 7395 * bodyClause = { init, body }, // v = init(); v = body(v, i) 7396 * indexVar = { start, incr }; // i = start(); i = i + 1 7397 * return loop(loopLimit, bodyClause, indexVar); 7398 * } 7399 * } 7400 * 7401 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}. 7402 * See above for other constraints. 7403 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to 7404 * {@code end-1}). The result type must be {@code int}. See above for other constraints. 7405 * @param init optional initializer, providing the initial value of the loop variable. 7406 * May be {@code null}, implying a default initial value. See above for other constraints. 7407 * @param body body of the loop, which may not be {@code null}. 7408 * It controls the loop parameters and result type in the standard case (see above for details). 7409 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 7410 * and may accept any number of additional types. 7411 * See above for other constraints. 7412 * 7413 * @return a method handle representing the loop. 7414 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}. 7415 * @throws IllegalArgumentException if any argument violates the rules formulated above. 7416 * 7417 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle) 7418 * @since 9 7419 */ 7420 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7421 countedLoopChecks(start, end, init, body); 7422 Class<?> counterType = start.type().returnType(); // int, but who's counting? 7423 Class<?> limitType = end.type().returnType(); // yes, int again 7424 Class<?> returnType = body.type().returnType(); 7425 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep); 7426 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred); 7427 MethodHandle retv = null; 7428 if (returnType != void.class) { 7429 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 7430 pred = dropArguments(pred, 1, returnType); // ditto 7431 retv = dropArguments(identity(returnType), 0, counterType); 7432 } 7433 body = dropArguments(body, 0, counterType); // ignore the limit variable 7434 MethodHandle[] 7435 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 7436 bodyClause = { init, body }, // v = init(); v = body(v, i) 7437 indexVar = { start, incr }; // i = start(); i = i + 1 7438 return loop(loopLimit, bodyClause, indexVar); 7439 } 7440 7441 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7442 Objects.requireNonNull(start); 7443 Objects.requireNonNull(end); 7444 Objects.requireNonNull(body); 7445 Class<?> counterType = start.type().returnType(); 7446 if (counterType != int.class) { 7447 MethodType expected = start.type().changeReturnType(int.class); 7448 throw misMatchedTypes("start function", start.type(), expected); 7449 } else if (end.type().returnType() != counterType) { 7450 MethodType expected = end.type().changeReturnType(counterType); 7451 throw misMatchedTypes("end function", end.type(), expected); 7452 } 7453 MethodType bodyType = body.type(); 7454 Class<?> returnType = bodyType.returnType(); 7455 List<Class<?>> innerList = bodyType.parameterList(); 7456 // strip leading V value if present 7457 int vsize = (returnType == void.class ? 0 : 1); 7458 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) { 7459 // argument list has no "V" => error 7460 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7461 throw misMatchedTypes("body function", bodyType, expected); 7462 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) { 7463 // missing I type => error 7464 MethodType expected = bodyType.insertParameterTypes(vsize, counterType); 7465 throw misMatchedTypes("body function", bodyType, expected); 7466 } 7467 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size()); 7468 if (outerList.isEmpty()) { 7469 // special case; take lists from end handle 7470 outerList = end.type().parameterList(); 7471 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList(); 7472 } 7473 MethodType expected = methodType(counterType, outerList); 7474 if (!start.type().effectivelyIdenticalParameters(0, outerList)) { 7475 throw misMatchedTypes("start parameter types", start.type(), expected); 7476 } 7477 if (end.type() != start.type() && 7478 !end.type().effectivelyIdenticalParameters(0, outerList)) { 7479 throw misMatchedTypes("end parameter types", end.type(), expected); 7480 } 7481 if (init != null) { 7482 MethodType initType = init.type(); 7483 if (initType.returnType() != returnType || 7484 !initType.effectivelyIdenticalParameters(0, outerList)) { 7485 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 7486 } 7487 } 7488 } 7489 7490 /** 7491 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}. 7492 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7493 * <p> 7494 * The iterator itself will be determined by the evaluation of the {@code iterator} handle. 7495 * Each value it produces will be stored in a loop iteration variable of type {@code T}. 7496 * <p> 7497 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7498 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7499 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7500 * <p> 7501 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7502 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7503 * iteration variable. 7504 * The result of the loop handle execution will be the final {@code V} value of that variable 7505 * (or {@code void} if there is no {@code V} variable). 7506 * <p> 7507 * The following rules hold for the argument handles:<ul> 7508 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7509 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}. 7510 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7511 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V} 7512 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.) 7513 * <li>The parameter list {@code (V T A...)} of the body contributes to a list 7514 * of types called the <em>internal parameter list</em>. 7515 * It will constrain the parameter lists of the other loop parts. 7516 * <li>As a special case, if the body contributes only {@code V} and {@code T} types, 7517 * with no additional {@code A} types, then the internal parameter list is extended by 7518 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the 7519 * single type {@code Iterable} is added and constitutes the {@code A...} list. 7520 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter 7521 * list {@code (A...)} is called the <em>external parameter list</em>. 7522 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7523 * additional state variable of the loop. 7524 * The body must both accept a leading parameter and return a value of this type {@code V}. 7525 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7526 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7527 * <a href="MethodHandles.html#effid">effectively identical</a> 7528 * to the external parameter list {@code (A...)}. 7529 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7530 * {@linkplain #empty default value}. 7531 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return 7532 * type {@code java.util.Iterator} or a subtype thereof. 7533 * The iterator it produces when the loop is executed will be assumed 7534 * to yield values which can be converted to type {@code T}. 7535 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be 7536 * effectively identical to the external parameter list {@code (A...)}. 7537 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves 7538 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list 7539 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator 7540 * handle parameter is adjusted to accept the leading {@code A} type, as if by 7541 * the {@link MethodHandle#asType asType} conversion method. 7542 * The leading {@code A} type must be {@code Iterable} or a subtype thereof. 7543 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}. 7544 * </ul> 7545 * <p> 7546 * The type {@code T} may be either a primitive or reference. 7547 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator}, 7548 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object} 7549 * as if by the {@link MethodHandle#asType asType} conversion method. 7550 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur 7551 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}. 7552 * <p> 7553 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7554 * <li>The loop handle's result type is the result type {@code V} of the body. 7555 * <li>The loop handle's parameter types are the types {@code (A...)}, 7556 * from the external parameter list. 7557 * </ul> 7558 * <p> 7559 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7560 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the 7561 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop. 7562 * {@snippet lang="java" : 7563 * Iterator<T> iterator(A...); // defaults to Iterable::iterator 7564 * V init(A...); 7565 * V body(V,T,A...); 7566 * V iteratedLoop(A... a...) { 7567 * Iterator<T> it = iterator(a...); 7568 * V v = init(a...); 7569 * while (it.hasNext()) { 7570 * T t = it.next(); 7571 * v = body(v, t, a...); 7572 * } 7573 * return v; 7574 * } 7575 * } 7576 * 7577 * @apiNote Example: 7578 * {@snippet lang="java" : 7579 * // get an iterator from a list 7580 * static List<String> reverseStep(List<String> r, String e) { 7581 * r.add(0, e); 7582 * return r; 7583 * } 7584 * static List<String> newArrayList() { return new ArrayList<>(); } 7585 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods 7586 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep); 7587 * List<String> list = Arrays.asList("a", "b", "c", "d", "e"); 7588 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a"); 7589 * assertEquals(reversedList, (List<String>) loop.invoke(list)); 7590 * } 7591 * 7592 * @apiNote The implementation of this method can be expressed approximately as follows: 7593 * {@snippet lang="java" : 7594 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7595 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable 7596 * Class<?> returnType = body.type().returnType(); 7597 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 7598 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype)); 7599 * MethodHandle retv = null, step = body, startIter = iterator; 7600 * if (returnType != void.class) { 7601 * // the simple thing first: in (I V A...), drop the I to get V 7602 * retv = dropArguments(identity(returnType), 0, Iterator.class); 7603 * // body type signature (V T A...), internal loop types (I V A...) 7604 * step = swapArguments(body, 0, 1); // swap V <-> T 7605 * } 7606 * if (startIter == null) startIter = MH_getIter; 7607 * MethodHandle[] 7608 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext()) 7609 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a) 7610 * return loop(iterVar, bodyClause); 7611 * } 7612 * } 7613 * 7614 * @param iterator an optional handle to return the iterator to start the loop. 7615 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype. 7616 * See above for other constraints. 7617 * @param init optional initializer, providing the initial value of the loop variable. 7618 * May be {@code null}, implying a default initial value. See above for other constraints. 7619 * @param body body of the loop, which may not be {@code null}. 7620 * It controls the loop parameters and result type in the standard case (see above for details). 7621 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values), 7622 * and may accept any number of additional types. 7623 * See above for other constraints. 7624 * 7625 * @return a method handle embodying the iteration loop functionality. 7626 * @throws NullPointerException if the {@code body} handle is {@code null}. 7627 * @throws IllegalArgumentException if any argument violates the above requirements. 7628 * 7629 * @since 9 7630 */ 7631 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7632 Class<?> iterableType = iteratedLoopChecks(iterator, init, body); 7633 Class<?> returnType = body.type().returnType(); 7634 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred); 7635 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext); 7636 MethodHandle startIter; 7637 MethodHandle nextVal; 7638 { 7639 MethodType iteratorType; 7640 if (iterator == null) { 7641 // derive argument type from body, if available, else use Iterable 7642 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator); 7643 iteratorType = startIter.type().changeParameterType(0, iterableType); 7644 } else { 7645 // force return type to the internal iterator class 7646 iteratorType = iterator.type().changeReturnType(Iterator.class); 7647 startIter = iterator; 7648 } 7649 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 7650 MethodType nextValType = nextRaw.type().changeReturnType(ttype); 7651 7652 // perform the asType transforms under an exception transformer, as per spec.: 7653 try { 7654 startIter = startIter.asType(iteratorType); 7655 nextVal = nextRaw.asType(nextValType); 7656 } catch (WrongMethodTypeException ex) { 7657 throw new IllegalArgumentException(ex); 7658 } 7659 } 7660 7661 MethodHandle retv = null, step = body; 7662 if (returnType != void.class) { 7663 // the simple thing first: in (I V A...), drop the I to get V 7664 retv = dropArguments(identity(returnType), 0, Iterator.class); 7665 // body type signature (V T A...), internal loop types (I V A...) 7666 step = swapArguments(body, 0, 1); // swap V <-> T 7667 } 7668 7669 MethodHandle[] 7670 iterVar = { startIter, null, hasNext, retv }, 7671 bodyClause = { init, filterArgument(step, 0, nextVal) }; 7672 return loop(iterVar, bodyClause); 7673 } 7674 7675 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7676 Objects.requireNonNull(body); 7677 MethodType bodyType = body.type(); 7678 Class<?> returnType = bodyType.returnType(); 7679 List<Class<?>> internalParamList = bodyType.parameterList(); 7680 // strip leading V value if present 7681 int vsize = (returnType == void.class ? 0 : 1); 7682 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) { 7683 // argument list has no "V" => error 7684 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7685 throw misMatchedTypes("body function", bodyType, expected); 7686 } else if (internalParamList.size() <= vsize) { 7687 // missing T type => error 7688 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class); 7689 throw misMatchedTypes("body function", bodyType, expected); 7690 } 7691 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size()); 7692 Class<?> iterableType = null; 7693 if (iterator != null) { 7694 // special case; if the body handle only declares V and T then 7695 // the external parameter list is obtained from iterator handle 7696 if (externalParamList.isEmpty()) { 7697 externalParamList = iterator.type().parameterList(); 7698 } 7699 MethodType itype = iterator.type(); 7700 if (!Iterator.class.isAssignableFrom(itype.returnType())) { 7701 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type"); 7702 } 7703 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) { 7704 MethodType expected = methodType(itype.returnType(), externalParamList); 7705 throw misMatchedTypes("iterator parameters", itype, expected); 7706 } 7707 } else { 7708 if (externalParamList.isEmpty()) { 7709 // special case; if the iterator handle is null and the body handle 7710 // only declares V and T then the external parameter list consists 7711 // of Iterable 7712 externalParamList = List.of(Iterable.class); 7713 iterableType = Iterable.class; 7714 } else { 7715 // special case; if the iterator handle is null and the external 7716 // parameter list is not empty then the first parameter must be 7717 // assignable to Iterable 7718 iterableType = externalParamList.get(0); 7719 if (!Iterable.class.isAssignableFrom(iterableType)) { 7720 throw newIllegalArgumentException( 7721 "inferred first loop argument must inherit from Iterable: " + iterableType); 7722 } 7723 } 7724 } 7725 if (init != null) { 7726 MethodType initType = init.type(); 7727 if (initType.returnType() != returnType || 7728 !initType.effectivelyIdenticalParameters(0, externalParamList)) { 7729 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList)); 7730 } 7731 } 7732 return iterableType; // help the caller a bit 7733 } 7734 7735 /*non-public*/ 7736 static MethodHandle swapArguments(MethodHandle mh, int i, int j) { 7737 // there should be a better way to uncross my wires 7738 int arity = mh.type().parameterCount(); 7739 int[] order = new int[arity]; 7740 for (int k = 0; k < arity; k++) order[k] = k; 7741 order[i] = j; order[j] = i; 7742 Class<?>[] types = mh.type().parameterArray(); 7743 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti; 7744 MethodType swapType = methodType(mh.type().returnType(), types); 7745 return permuteArguments(mh, swapType, order); 7746 } 7747 7748 /** 7749 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block. 7750 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception 7751 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The 7752 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The 7753 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the 7754 * {@code try-finally} handle. 7755 * <p> 7756 * The {@code cleanup} handle will be passed one or two additional leading arguments. 7757 * The first is the exception thrown during the 7758 * execution of the {@code target} handle, or {@code null} if no exception was thrown. 7759 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception, 7760 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder. 7761 * The second argument is not present if the {@code target} handle has a {@code void} return type. 7762 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists 7763 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.) 7764 * <p> 7765 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except 7766 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or 7767 * two extra leading parameters:<ul> 7768 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and 7769 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry 7770 * the result from the execution of the {@code target} handle. 7771 * This parameter is not present if the {@code target} returns {@code void}. 7772 * </ul> 7773 * <p> 7774 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of 7775 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting 7776 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by 7777 * the cleanup. 7778 * {@snippet lang="java" : 7779 * V target(A..., B...); 7780 * V cleanup(Throwable, V, A...); 7781 * V adapter(A... a, B... b) { 7782 * V result = (zero value for V); 7783 * Throwable throwable = null; 7784 * try { 7785 * result = target(a..., b...); 7786 * } catch (Throwable t) { 7787 * throwable = t; 7788 * throw t; 7789 * } finally { 7790 * result = cleanup(throwable, result, a...); 7791 * } 7792 * return result; 7793 * } 7794 * } 7795 * <p> 7796 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 7797 * be modified by execution of the target, and so are passed unchanged 7798 * from the caller to the cleanup, if it is invoked. 7799 * <p> 7800 * The target and cleanup must return the same type, even if the cleanup 7801 * always throws. 7802 * To create such a throwing cleanup, compose the cleanup logic 7803 * with {@link #throwException throwException}, 7804 * in order to create a method handle of the correct return type. 7805 * <p> 7806 * Note that {@code tryFinally} never converts exceptions into normal returns. 7807 * In rare cases where exceptions must be converted in that way, first wrap 7808 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)} 7809 * to capture an outgoing exception, and then wrap with {@code tryFinally}. 7810 * <p> 7811 * It is recommended that the first parameter type of {@code cleanup} be 7812 * declared {@code Throwable} rather than a narrower subtype. This ensures 7813 * {@code cleanup} will always be invoked with whatever exception that 7814 * {@code target} throws. Declaring a narrower type may result in a 7815 * {@code ClassCastException} being thrown by the {@code try-finally} 7816 * handle if the type of the exception thrown by {@code target} is not 7817 * assignable to the first parameter type of {@code cleanup}. Note that 7818 * various exception types of {@code VirtualMachineError}, 7819 * {@code LinkageError}, and {@code RuntimeException} can in principle be 7820 * thrown by almost any kind of Java code, and a finally clause that 7821 * catches (say) only {@code IOException} would mask any of the others 7822 * behind a {@code ClassCastException}. 7823 * 7824 * @param target the handle whose execution is to be wrapped in a {@code try} block. 7825 * @param cleanup the handle that is invoked in the finally block. 7826 * 7827 * @return a method handle embodying the {@code try-finally} block composed of the two arguments. 7828 * @throws NullPointerException if any argument is null 7829 * @throws IllegalArgumentException if {@code cleanup} does not accept 7830 * the required leading arguments, or if the method handle types do 7831 * not match in their return types and their 7832 * corresponding trailing parameters 7833 * 7834 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle) 7835 * @since 9 7836 */ 7837 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) { 7838 Class<?>[] targetParamTypes = target.type().ptypes(); 7839 Class<?> rtype = target.type().returnType(); 7840 7841 tryFinallyChecks(target, cleanup); 7842 7843 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments. 7844 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 7845 // target parameter list. 7846 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false); 7847 7848 // Ensure that the intrinsic type checks the instance thrown by the 7849 // target against the first parameter of cleanup 7850 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class)); 7851 7852 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case. 7853 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes); 7854 } 7855 7856 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) { 7857 Class<?> rtype = target.type().returnType(); 7858 if (rtype != cleanup.type().returnType()) { 7859 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype); 7860 } 7861 MethodType cleanupType = cleanup.type(); 7862 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) { 7863 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class); 7864 } 7865 if (rtype != void.class && cleanupType.parameterType(1) != rtype) { 7866 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype); 7867 } 7868 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 7869 // target parameter list. 7870 int cleanupArgIndex = rtype == void.class ? 1 : 2; 7871 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) { 7872 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix", 7873 cleanup.type(), target.type()); 7874 } 7875 } 7876 7877 /** 7878 * Creates a table switch method handle, which can be used to switch over a set of target 7879 * method handles, based on a given target index, called selector. 7880 * <p> 7881 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)}, 7882 * and where {@code N} is the number of target method handles, the table switch method 7883 * handle will invoke the n-th target method handle from the list of target method handles. 7884 * <p> 7885 * For a selector value that does not fall in the range {@code [0, N)}, the table switch 7886 * method handle will invoke the given fallback method handle. 7887 * <p> 7888 * All method handles passed to this method must have the same type, with the additional 7889 * requirement that the leading parameter be of type {@code int}. The leading parameter 7890 * represents the selector. 7891 * <p> 7892 * Any trailing parameters present in the type will appear on the returned table switch 7893 * method handle as well. Any arguments assigned to these parameters will be forwarded, 7894 * together with the selector value, to the selected method handle when invoking it. 7895 * 7896 * @apiNote Example: 7897 * The cases each drop the {@code selector} value they are given, and take an additional 7898 * {@code String} argument, which is concatenated (using {@link String#concat(String)}) 7899 * to a specific constant label string for each case: 7900 * {@snippet lang="java" : 7901 * MethodHandles.Lookup lookup = MethodHandles.lookup(); 7902 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat", 7903 * MethodType.methodType(String.class, String.class)); 7904 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class); 7905 * 7906 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: "); 7907 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: "); 7908 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: "); 7909 * 7910 * MethodHandle mhSwitch = MethodHandles.tableSwitch( 7911 * caseDefault, 7912 * case0, 7913 * case1 7914 * ); 7915 * 7916 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data")); 7917 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data")); 7918 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data")); 7919 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data")); 7920 * } 7921 * 7922 * @param fallback the fallback method handle that is called when the selector is not 7923 * within the range {@code [0, N)}. 7924 * @param targets array of target method handles. 7925 * @return the table switch method handle. 7926 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any 7927 * any of the elements of the {@code targets} array are 7928 * {@code null}. 7929 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading 7930 * parameter of the fallback handle or any of the target 7931 * handles is not {@code int}, or if the types of 7932 * the fallback handle and all of target handles are 7933 * not the same. 7934 */ 7935 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) { 7936 Objects.requireNonNull(fallback); 7937 Objects.requireNonNull(targets); 7938 targets = targets.clone(); 7939 MethodType type = tableSwitchChecks(fallback, targets); 7940 return MethodHandleImpl.makeTableSwitch(type, fallback, targets); 7941 } 7942 7943 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) { 7944 if (caseActions.length == 0) 7945 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions)); 7946 7947 MethodType expectedType = defaultCase.type(); 7948 7949 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class) 7950 throw new IllegalArgumentException( 7951 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions)); 7952 7953 for (MethodHandle mh : caseActions) { 7954 Objects.requireNonNull(mh); 7955 if (mh.type() != expectedType) 7956 throw new IllegalArgumentException( 7957 "Case actions must have the same type: " + Arrays.toString(caseActions)); 7958 } 7959 7960 return expectedType; 7961 } 7962 7963 /** 7964 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment} 7965 * at a given byte offset, using the provided value layout. 7966 * 7967 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type}, 7968 * the {@linkplain ValueLayout#byteSize() byte size}, 7969 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order} 7970 * associated with the returned var handle. 7971 * 7972 * <p>The list of coordinate types associated with the returned var handle is {@code (MemorySegment, long)}, 7973 * where the {@code long} coordinate type corresponds to byte offset into the given memory segment coordinate. 7974 * Thus, the returned var handle accesses bytes at an offset in a given memory segment, composing bytes to or from 7975 * a value of the var handle type. Moreover, the access operation will honor the endianness and the 7976 * alignment constraints expressed in the provided layout. 7977 * 7978 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows: 7979 * {@snippet lang="java" : 7980 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout( 7981 * MemoryLayout.paddingLayout(4), 7982 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value") 7983 * ); 7984 * } 7985 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows: 7986 * {@snippet lang="java" : 7987 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int 7988 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int 7989 * } 7990 * 7991 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>, 7992 * which are common to all memory segment view var handles. A memory segment view var handle is associated 7993 * with an access size {@code S} and an alignment constraint {@code B} 7994 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs 7995 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}. 7996 * If access is fully aligned then following access modes are supported and are 7997 * guaranteed to support atomic access: 7998 * <ul> 7999 * <li>read write access modes for all {@code T}, with the exception of 8000 * access modes {@code get} and {@code set} for {@code long} and 8001 * {@code double} on 32-bit platforms. 8002 * <li>atomic update access modes for {@code int}, {@code long}, 8003 * {@code float}, {@code double} or {@link MemorySegment}. 8004 * (Future major platform releases of the JDK may support additional 8005 * types for certain currently unsupported access modes.) 8006 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}. 8007 * (Future major platform releases of the JDK may support additional 8008 * numeric types for certain currently unsupported access modes.) 8009 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}. 8010 * (Future major platform releases of the JDK may support additional 8011 * numeric types for certain currently unsupported access modes.) 8012 * </ul> 8013 * 8014 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic 8015 * update access modes compare values using their bitwise representation 8016 * (see {@link Float#floatToRawIntBits}, 8017 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively). 8018 * <p> 8019 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A} 8020 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the 8021 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned, 8022 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}. 8023 * <p> 8024 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an 8025 * {@code IllegalStateException} is thrown, irrespective of the access mode being used. 8026 * <p> 8027 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException} 8028 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment. 8029 * 8030 * @param layout the value layout for which a memory access handle is to be obtained. 8031 * @return the new memory segment view var handle. 8032 * @throws NullPointerException if {@code layout} is {@code null}. 8033 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...) 8034 * @since 19 8035 */ 8036 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8037 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) { 8038 Objects.requireNonNull(layout); 8039 return Utils.makeSegmentViewVarHandle(layout); 8040 } 8041 8042 /** 8043 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions. 8044 * <p> 8045 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where 8046 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed 8047 * to the target var handle. 8048 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from 8049 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function) 8050 * is processed using the second filter and returned to the caller. More advanced access mode types, such as 8051 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time. 8052 * <p> 8053 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and 8054 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case, 8055 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which 8056 * will be appended to the coordinates of the target var handle). 8057 * <p> 8058 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will 8059 * throw an {@link IllegalStateException}. 8060 * <p> 8061 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8062 * atomic access guarantees as those featured by the target var handle. 8063 * 8064 * @param target the target var handle 8065 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target} 8066 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S} 8067 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions. 8068 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types 8069 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle, 8070 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions. 8071 * @throws NullPointerException if any of the arguments is {@code null}. 8072 * @since 19 8073 */ 8074 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8075 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) { 8076 return VarHandles.filterValue(target, filterToTarget, filterFromTarget); 8077 } 8078 8079 /** 8080 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions. 8081 * <p> 8082 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values 8083 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types 8084 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the 8085 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered 8086 * by the adaptation) to the target var handle. 8087 * <p> 8088 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn}, 8089 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle. 8090 * <p> 8091 * If any of the filters throws a checked exception when invoked, the resulting var handle will 8092 * throw an {@link IllegalStateException}. 8093 * <p> 8094 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8095 * atomic access guarantees as those featured by the target var handle. 8096 * 8097 * @param target the target var handle 8098 * @param pos the position of the first coordinate to be transformed 8099 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos} 8100 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation 8101 * to the new coordinate values. 8102 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types 8103 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting 8104 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8105 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos}, 8106 * or if it's determined that any of the filters throws any checked exceptions. 8107 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}. 8108 * @since 19 8109 */ 8110 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8111 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) { 8112 return VarHandles.filterCoordinates(target, pos, filters); 8113 } 8114 8115 /** 8116 * Provides a target var handle with one or more <em>bound coordinates</em> 8117 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less 8118 * coordinate types than the target var handle. 8119 * <p> 8120 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values 8121 * are joined with bound coordinate values, and then passed to the target var handle. 8122 * <p> 8123 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn }, 8124 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle. 8125 * <p> 8126 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8127 * atomic access guarantees as those featured by the target var handle. 8128 * 8129 * @param target the var handle to invoke after the bound coordinates are inserted 8130 * @param pos the position of the first coordinate to be inserted 8131 * @param values the series of bound coordinates to insert 8132 * @return an adapter var handle which inserts additional coordinates, 8133 * before calling the target var handle 8134 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8135 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}. 8136 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types 8137 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} 8138 * of the target var handle. 8139 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}. 8140 * @since 19 8141 */ 8142 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8143 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) { 8144 return VarHandles.insertCoordinates(target, pos, values); 8145 } 8146 8147 /** 8148 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them 8149 * so that the new coordinates match the provided ones. 8150 * <p> 8151 * The given array controls the reordering. 8152 * Call {@code #I} the number of incoming coordinates (the value 8153 * {@code newCoordinates.size()}), and call {@code #O} the number 8154 * of outgoing coordinates (the number of coordinates associated with the target var handle). 8155 * Then the length of the reordering array must be {@code #O}, 8156 * and each element must be a non-negative number less than {@code #I}. 8157 * For every {@code N} less than {@code #O}, the {@code N}-th 8158 * outgoing coordinate will be taken from the {@code I}-th incoming 8159 * coordinate, where {@code I} is {@code reorder[N]}. 8160 * <p> 8161 * No coordinate value conversions are applied. 8162 * The type of each incoming coordinate, as determined by {@code newCoordinates}, 8163 * must be identical to the type of the corresponding outgoing coordinate 8164 * in the target var handle. 8165 * <p> 8166 * The reordering array need not specify an actual permutation. 8167 * An incoming coordinate will be duplicated if its index appears 8168 * more than once in the array, and an incoming coordinate will be dropped 8169 * if its index does not appear in the array. 8170 * <p> 8171 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8172 * atomic access guarantees as those featured by the target var handle. 8173 * @param target the var handle to invoke after the coordinates have been reordered 8174 * @param newCoordinates the new coordinate types 8175 * @param reorder an index array which controls the reordering 8176 * @return an adapter var handle which re-arranges the incoming coordinate values, 8177 * before calling the target var handle 8178 * @throws IllegalArgumentException if the index array length is not equal to 8179 * the number of coordinates of the target var handle, or if any index array element is not a valid index for 8180 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in 8181 * the target var handle and in {@code newCoordinates} are not identical. 8182 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}. 8183 * @since 19 8184 */ 8185 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8186 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) { 8187 return VarHandles.permuteCoordinates(target, newCoordinates, reorder); 8188 } 8189 8190 /** 8191 * Adapts a target var handle by pre-processing 8192 * a sub-sequence of its coordinate values with a filter (a method handle). 8193 * The pre-processed coordinates are replaced by the result (if any) of the 8194 * filter function and the target var handle is then called on the modified (usually shortened) 8195 * coordinate list. 8196 * <p> 8197 * If {@code R} is the return type of the filter, then: 8198 * <ul> 8199 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in 8200 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos} 8201 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first, 8202 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the 8203 * target var handle.</li> 8204 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the 8205 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle 8206 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a 8207 * downstream invocation of the target var handle.</li> 8208 * </ul> 8209 * <p> 8210 * If any of the filters throws a checked exception when invoked, the resulting var handle will 8211 * throw an {@link IllegalStateException}. 8212 * <p> 8213 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8214 * atomic access guarantees as those featured by the target var handle. 8215 * 8216 * @param target the var handle to invoke after the coordinates have been filtered 8217 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted 8218 * @param filter the filter method handle 8219 * @return an adapter var handle which filters the incoming coordinate values, 8220 * before calling the target var handle 8221 * @throws IllegalArgumentException if the return type of {@code filter} 8222 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle, 8223 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8224 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>, 8225 * or if it's determined that {@code filter} throws any checked exceptions. 8226 * @throws NullPointerException if any of the arguments is {@code null}. 8227 * @since 19 8228 */ 8229 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8230 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) { 8231 return VarHandles.collectCoordinates(target, pos, filter); 8232 } 8233 8234 /** 8235 * Returns a var handle which will discard some dummy coordinates before delegating to the 8236 * target var handle. As a consequence, the resulting var handle will feature more 8237 * coordinate types than the target var handle. 8238 * <p> 8239 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the 8240 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede 8241 * the target's real arguments; if {@code pos} is <i>N</i> they will come after. 8242 * <p> 8243 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8244 * atomic access guarantees as those featured by the target var handle. 8245 * 8246 * @param target the var handle to invoke after the dummy coordinates are dropped 8247 * @param pos position of the first coordinate to drop (zero for the leftmost) 8248 * @param valueTypes the type(s) of the coordinate(s) to drop 8249 * @return an adapter var handle which drops some dummy coordinates, 8250 * before calling the target var handle 8251 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive. 8252 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}. 8253 * @since 19 8254 */ 8255 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8256 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) { 8257 return VarHandles.dropCoordinates(target, pos, valueTypes); 8258 } 8259 }