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.value.PrimitiveClass; 30 import jdk.internal.foreign.Utils; 31 import jdk.internal.javac.PreviewFeature; 32 import jdk.internal.misc.Unsafe; 33 import jdk.internal.misc.VM; 34 import jdk.internal.org.objectweb.asm.ClassReader; 35 import jdk.internal.org.objectweb.asm.Opcodes; 36 import jdk.internal.org.objectweb.asm.Type; 37 import jdk.internal.reflect.CallerSensitive; 38 import jdk.internal.reflect.CallerSensitiveAdapter; 39 import jdk.internal.reflect.Reflection; 40 import jdk.internal.util.ClassFileDumper; 41 import jdk.internal.vm.annotation.ForceInline; 42 import sun.invoke.util.ValueConversions; 43 import sun.invoke.util.VerifyAccess; 44 import sun.invoke.util.Wrapper; 45 import sun.reflect.misc.ReflectUtil; 46 import sun.security.util.SecurityConstants; 47 48 import java.lang.constant.ConstantDescs; 49 import java.lang.foreign.GroupLayout; 50 import java.lang.foreign.MemoryLayout; 51 import java.lang.foreign.MemorySegment; 52 import java.lang.foreign.ValueLayout; 53 import java.lang.invoke.LambdaForm.BasicType; 54 import java.lang.reflect.Constructor; 55 import java.lang.reflect.Field; 56 import java.lang.reflect.Member; 57 import java.lang.reflect.Method; 58 import java.lang.reflect.Modifier; 59 import java.nio.ByteOrder; 60 import java.security.ProtectionDomain; 61 import java.util.ArrayList; 62 import java.util.Arrays; 63 import java.util.BitSet; 64 import java.util.Comparator; 65 import java.util.Iterator; 66 import java.util.List; 67 import java.util.Objects; 68 import java.util.Set; 69 import java.util.concurrent.ConcurrentHashMap; 70 import java.util.stream.Stream; 71 72 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE; 73 import static java.lang.invoke.MethodHandleImpl.Intrinsic; 74 import static java.lang.invoke.MethodHandleNatives.Constants.*; 75 import static java.lang.invoke.MethodHandleStatics.UNSAFE; 76 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException; 77 import static java.lang.invoke.MethodHandleStatics.newInternalError; 78 import static java.lang.invoke.MethodType.methodType; 79 80 /** 81 * This class consists exclusively of static methods that operate on or return 82 * method handles. They fall into several categories: 83 * <ul> 84 * <li>Lookup methods which help create method handles for methods and fields. 85 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones. 86 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns. 87 * </ul> 88 * A lookup, combinator, or factory method will fail and throw an 89 * {@code IllegalArgumentException} if the created method handle's type 90 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>. 91 * 92 * @author John Rose, JSR 292 EG 93 * @since 1.7 94 */ 95 public class MethodHandles { 96 97 private MethodHandles() { } // do not instantiate 98 99 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); 100 101 // See IMPL_LOOKUP below. 102 103 //// Method handle creation from ordinary methods. 104 105 /** 106 * Returns a {@link Lookup lookup object} with 107 * full capabilities to emulate all supported bytecode behaviors of the caller. 108 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller. 109 * Factory methods on the lookup object can create 110 * <a href="MethodHandleInfo.html#directmh">direct method handles</a> 111 * for any member that the caller has access to via bytecodes, 112 * including protected and private fields and methods. 113 * This lookup object is created by the original lookup class 114 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set. 115 * This lookup object is a <em>capability</em> which may be delegated to trusted agents. 116 * Do not store it in place where untrusted code can access it. 117 * <p> 118 * This method is caller sensitive, which means that it may return different 119 * values to different callers. 120 * In cases where {@code MethodHandles.lookup} is called from a context where 121 * there is no caller frame on the stack (e.g. when called directly 122 * from a JNI attached thread), {@code IllegalCallerException} is thrown. 123 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will 124 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()} 125 * to obtain a low-privileged lookup instead. 126 * @return a lookup object for the caller of this method, with 127 * {@linkplain Lookup#ORIGINAL original} and 128 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}. 129 * @throws IllegalCallerException if there is no caller frame on the stack. 130 */ 131 @CallerSensitive 132 @ForceInline // to ensure Reflection.getCallerClass optimization 133 public static Lookup lookup() { 134 final Class<?> c = Reflection.getCallerClass(); 135 if (c == null) { 136 throw new IllegalCallerException("no caller frame"); 137 } 138 return new Lookup(c); 139 } 140 141 /** 142 * This lookup method is the alternate implementation of 143 * the lookup method with a leading caller class argument which is 144 * non-caller-sensitive. This method is only invoked by reflection 145 * and method handle. 146 */ 147 @CallerSensitiveAdapter 148 private static Lookup lookup(Class<?> caller) { 149 if (caller.getClassLoader() == null) { 150 throw newInternalError("calling lookup() reflectively is not supported: "+caller); 151 } 152 return new Lookup(caller); 153 } 154 155 /** 156 * Returns a {@link Lookup lookup object} which is trusted minimally. 157 * The lookup has the {@code UNCONDITIONAL} mode. 158 * It can only be used to create method handles to public members of 159 * public classes in packages that are exported unconditionally. 160 * <p> 161 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class} 162 * of this lookup object will be {@link java.lang.Object}. 163 * 164 * @apiNote The use of Object is conventional, and because the lookup modes are 165 * limited, there is no special access provided to the internals of Object, its package 166 * or its module. This public lookup object or other lookup object with 167 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class 168 * is not used to determine the lookup context. 169 * 170 * <p style="font-size:smaller;"> 171 * <em>Discussion:</em> 172 * The lookup class can be changed to any other class {@code C} using an expression of the form 173 * {@link Lookup#in publicLookup().in(C.class)}. 174 * A public lookup object is always subject to 175 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>. 176 * Also, it cannot access 177 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>. 178 * @return a lookup object which is trusted minimally 179 * 180 * @revised 9 181 */ 182 public static Lookup publicLookup() { 183 return Lookup.PUBLIC_LOOKUP; 184 } 185 186 /** 187 * Returns a {@link Lookup lookup} object on a target class to emulate all supported 188 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>. 189 * The returned lookup object can provide access to classes in modules and packages, 190 * and members of those classes, outside the normal rules of Java access control, 191 * instead conforming to the more permissive rules for modular <em>deep reflection</em>. 192 * <p> 193 * A caller, specified as a {@code Lookup} object, in module {@code M1} is 194 * allowed to do deep reflection on module {@code M2} and package of the target class 195 * if and only if all of the following conditions are {@code true}: 196 * <ul> 197 * <li>If there is a security manager, its {@code checkPermission} method is 198 * called to check {@code ReflectPermission("suppressAccessChecks")} and 199 * that must return normally. 200 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess() 201 * full privilege access}. Specifically: 202 * <ul> 203 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode. 204 * (This is because otherwise there would be no way to ensure the original lookup 205 * creator was a member of any particular module, and so any subsequent checks 206 * for readability and qualified exports would become ineffective.) 207 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access. 208 * (This is because an application intending to share intra-module access 209 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share 210 * deep reflection to its own module.) 211 * </ul> 212 * <li>The target class must be a proper class, not a primitive or array class. 213 * (Thus, {@code M2} is well-defined.) 214 * <li>If the caller module {@code M1} differs from 215 * the target module {@code M2} then both of the following must be true: 216 * <ul> 217 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li> 218 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package 219 * containing the target class to at least {@code M1}.</li> 220 * </ul> 221 * </ul> 222 * <p> 223 * If any of the above checks is violated, this method fails with an 224 * exception. 225 * <p> 226 * Otherwise, if {@code M1} and {@code M2} are the same module, this method 227 * returns a {@code Lookup} on {@code targetClass} with 228 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} 229 * with {@code null} previous lookup class. 230 * <p> 231 * Otherwise, {@code M1} and {@code M2} are two different modules. This method 232 * returns a {@code Lookup} on {@code targetClass} that records 233 * the lookup class of the caller as the new previous lookup class with 234 * {@code PRIVATE} access but no {@code MODULE} access. 235 * <p> 236 * The resulting {@code Lookup} object has no {@code ORIGINAL} access. 237 * 238 * @apiNote The {@code Lookup} object returned by this method is allowed to 239 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package 240 * of {@code targetClass}. Extreme caution should be taken when opening a package 241 * to another module as such defined classes have the same full privilege 242 * access as other members in {@code targetClass}'s module. 243 * 244 * @param targetClass the target class 245 * @param caller the caller lookup object 246 * @return a lookup object for the target class, with private access 247 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class 248 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null} 249 * @throws SecurityException if denied by the security manager 250 * @throws IllegalAccessException if any of the other access checks specified above fails 251 * @since 9 252 * @see Lookup#dropLookupMode 253 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a> 254 */ 255 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException { 256 if (caller.allowedModes == Lookup.TRUSTED) { 257 return new Lookup(targetClass); 258 } 259 260 @SuppressWarnings("removal") 261 SecurityManager sm = System.getSecurityManager(); 262 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION); 263 if (targetClass.isPrimitive()) 264 throw new IllegalArgumentException(targetClass + " is a primitive class"); 265 if (targetClass.isArray()) 266 throw new IllegalArgumentException(targetClass + " is an array class"); 267 // Ensure that we can reason accurately about private and module access. 268 int requireAccess = Lookup.PRIVATE|Lookup.MODULE; 269 if ((caller.lookupModes() & requireAccess) != requireAccess) 270 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode"); 271 272 // previous lookup class is never set if it has MODULE access 273 assert caller.previousLookupClass() == null; 274 275 Class<?> callerClass = caller.lookupClass(); 276 Module callerModule = callerClass.getModule(); // M1 277 Module targetModule = targetClass.getModule(); // M2 278 Class<?> newPreviousClass = null; 279 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL; 280 281 if (targetModule != callerModule) { 282 if (!callerModule.canRead(targetModule)) 283 throw new IllegalAccessException(callerModule + " does not read " + targetModule); 284 if (targetModule.isNamed()) { 285 String pn = targetClass.getPackageName(); 286 assert !pn.isEmpty() : "unnamed package cannot be in named module"; 287 if (!targetModule.isOpen(pn, callerModule)) 288 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule); 289 } 290 291 // M2 != M1, set previous lookup class to M1 and drop MODULE access 292 newPreviousClass = callerClass; 293 newModes &= ~Lookup.MODULE; 294 } 295 return Lookup.newLookup(targetClass, newPreviousClass, newModes); 296 } 297 298 /** 299 * Returns the <em>class data</em> associated with the lookup class 300 * of the given {@code caller} lookup object, or {@code null}. 301 * 302 * <p> A hidden class with class data can be created by calling 303 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 304 * Lookup::defineHiddenClassWithClassData}. 305 * This method will cause the static class initializer of the lookup 306 * class of the given {@code caller} lookup object be executed if 307 * it has not been initialized. 308 * 309 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...) 310 * Lookup::defineHiddenClass} and non-hidden classes have no class data. 311 * {@code null} is returned if this method is called on the lookup object 312 * on these classes. 313 * 314 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup 315 * must have {@linkplain Lookup#ORIGINAL original access} 316 * in order to retrieve the class data. 317 * 318 * @apiNote 319 * This method can be called as a bootstrap method for a dynamically computed 320 * constant. A framework can create a hidden class with class data, for 321 * example that can be {@code Class} or {@code MethodHandle} object. 322 * The class data is accessible only to the lookup object 323 * created by the original caller but inaccessible to other members 324 * in the same nest. If a framework passes security sensitive objects 325 * to a hidden class via class data, it is recommended to load the value 326 * of class data as a dynamically computed constant instead of storing 327 * the class data in private static field(s) which are accessible to 328 * other nestmates. 329 * 330 * @param <T> the type to cast the class data object to 331 * @param caller the lookup context describing the class performing the 332 * operation (normally stacked by the JVM) 333 * @param name must be {@link ConstantDescs#DEFAULT_NAME} 334 * ({@code "_"}) 335 * @param type the type of the class data 336 * @return the value of the class data if present in the lookup class; 337 * otherwise {@code null} 338 * @throws IllegalArgumentException if name is not {@code "_"} 339 * @throws IllegalAccessException if the lookup context does not have 340 * {@linkplain Lookup#ORIGINAL original} access 341 * @throws ClassCastException if the class data cannot be converted to 342 * the given {@code type} 343 * @throws NullPointerException if {@code caller} or {@code type} argument 344 * is {@code null} 345 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 346 * @see MethodHandles#classDataAt(Lookup, String, Class, int) 347 * @since 16 348 * @jvms 5.5 Initialization 349 */ 350 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException { 351 Objects.requireNonNull(caller); 352 Objects.requireNonNull(type); 353 if (!ConstantDescs.DEFAULT_NAME.equals(name)) { 354 throw new IllegalArgumentException("name must be \"_\": " + name); 355 } 356 357 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) { 358 throw new IllegalAccessException(caller + " does not have ORIGINAL access"); 359 } 360 361 Object classdata = classData(caller.lookupClass()); 362 if (classdata == null) return null; 363 364 try { 365 return BootstrapMethodInvoker.widenAndCast(classdata, type); 366 } catch (RuntimeException|Error e) { 367 throw e; // let CCE and other runtime exceptions through 368 } catch (Throwable e) { 369 throw new InternalError(e); 370 } 371 } 372 373 /* 374 * Returns the class data set by the VM in the Class::classData field. 375 * 376 * This is also invoked by LambdaForms as it cannot use condy via 377 * MethodHandles::classData due to bootstrapping issue. 378 */ 379 static Object classData(Class<?> c) { 380 UNSAFE.ensureClassInitialized(c); 381 return SharedSecrets.getJavaLangAccess().classData(c); 382 } 383 384 /** 385 * Returns the element at the specified index in the 386 * {@linkplain #classData(Lookup, String, Class) class data}, 387 * if the class data associated with the lookup class 388 * of the given {@code caller} lookup object is a {@code List}. 389 * If the class data is not present in this lookup class, this method 390 * returns {@code null}. 391 * 392 * <p> A hidden class with class data can be created by calling 393 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 394 * Lookup::defineHiddenClassWithClassData}. 395 * This method will cause the static class initializer of the lookup 396 * class of the given {@code caller} lookup object be executed if 397 * it has not been initialized. 398 * 399 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...) 400 * Lookup::defineHiddenClass} and non-hidden classes have no class data. 401 * {@code null} is returned if this method is called on the lookup object 402 * on these classes. 403 * 404 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup 405 * must have {@linkplain Lookup#ORIGINAL original access} 406 * in order to retrieve the class data. 407 * 408 * @apiNote 409 * This method can be called as a bootstrap method for a dynamically computed 410 * constant. A framework can create a hidden class with class data, for 411 * example that can be {@code List.of(o1, o2, o3....)} containing more than 412 * one object and use this method to load one element at a specific index. 413 * The class data is accessible only to the lookup object 414 * created by the original caller but inaccessible to other members 415 * in the same nest. If a framework passes security sensitive objects 416 * to a hidden class via class data, it is recommended to load the value 417 * of class data as a dynamically computed constant instead of storing 418 * the class data in private static field(s) which are accessible to other 419 * nestmates. 420 * 421 * @param <T> the type to cast the result object to 422 * @param caller the lookup context describing the class performing the 423 * operation (normally stacked by the JVM) 424 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME} 425 * ({@code "_"}) 426 * @param type the type of the element at the given index in the class data 427 * @param index index of the element in the class data 428 * @return the element at the given index in the class data 429 * if the class data is present; otherwise {@code null} 430 * @throws IllegalArgumentException if name is not {@code "_"} 431 * @throws IllegalAccessException if the lookup context does not have 432 * {@linkplain Lookup#ORIGINAL original} access 433 * @throws ClassCastException if the class data cannot be converted to {@code List} 434 * or the element at the specified index cannot be converted to the given type 435 * @throws IndexOutOfBoundsException if the index is out of range 436 * @throws NullPointerException if {@code caller} or {@code type} argument is 437 * {@code null}; or if unboxing operation fails because 438 * the element at the given index is {@code null} 439 * 440 * @since 16 441 * @see #classData(Lookup, String, Class) 442 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 443 */ 444 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index) 445 throws IllegalAccessException 446 { 447 @SuppressWarnings("unchecked") 448 List<Object> classdata = (List<Object>)classData(caller, name, List.class); 449 if (classdata == null) return null; 450 451 try { 452 Object element = classdata.get(index); 453 return BootstrapMethodInvoker.widenAndCast(element, type); 454 } catch (RuntimeException|Error e) { 455 throw e; // let specified exceptions and other runtime exceptions/errors through 456 } catch (Throwable e) { 457 throw new InternalError(e); 458 } 459 } 460 461 /** 462 * Performs an unchecked "crack" of a 463 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>. 464 * The result is as if the user had obtained a lookup object capable enough 465 * to crack the target method handle, called 466 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} 467 * on the target to obtain its symbolic reference, and then called 468 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} 469 * to resolve the symbolic reference to a member. 470 * <p> 471 * If there is a security manager, its {@code checkPermission} method 472 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission. 473 * @param <T> the desired type of the result, either {@link Member} or a subtype 474 * @param target a direct method handle to crack into symbolic reference components 475 * @param expected a class object representing the desired result type {@code T} 476 * @return a reference to the method, constructor, or field object 477 * @throws SecurityException if the caller is not privileged to call {@code setAccessible} 478 * @throws NullPointerException if either argument is {@code null} 479 * @throws IllegalArgumentException if the target is not a direct method handle 480 * @throws ClassCastException if the member is not of the expected type 481 * @since 1.8 482 */ 483 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) { 484 @SuppressWarnings("removal") 485 SecurityManager smgr = System.getSecurityManager(); 486 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION); 487 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup 488 return lookup.revealDirect(target).reflectAs(expected, lookup); 489 } 490 491 /** 492 * A <em>lookup object</em> is a factory for creating method handles, 493 * when the creation requires access checking. 494 * Method handles do not perform 495 * access checks when they are called, but rather when they are created. 496 * Therefore, method handle access 497 * restrictions must be enforced when a method handle is created. 498 * The caller class against which those restrictions are enforced 499 * is known as the {@linkplain #lookupClass() lookup class}. 500 * <p> 501 * A lookup class which needs to create method handles will call 502 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself. 503 * When the {@code Lookup} factory object is created, the identity of the lookup class is 504 * determined, and securely stored in the {@code Lookup} object. 505 * The lookup class (or its delegates) may then use factory methods 506 * on the {@code Lookup} object to create method handles for access-checked members. 507 * This includes all methods, constructors, and fields which are allowed to the lookup class, 508 * even private ones. 509 * 510 * <h2><a id="lookups"></a>Lookup Factory Methods</h2> 511 * The factory methods on a {@code Lookup} object correspond to all major 512 * use cases for methods, constructors, and fields. 513 * Each method handle created by a factory method is the functional 514 * equivalent of a particular <em>bytecode behavior</em>. 515 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of 516 * the Java Virtual Machine Specification.) 517 * Here is a summary of the correspondence between these factory methods and 518 * the behavior of the resulting method handles: 519 * <table class="striped"> 520 * <caption style="display:none">lookup method behaviors</caption> 521 * <thead> 522 * <tr> 523 * <th scope="col"><a id="equiv"></a>lookup expression</th> 524 * <th scope="col">member</th> 525 * <th scope="col">bytecode behavior</th> 526 * </tr> 527 * </thead> 528 * <tbody> 529 * <tr> 530 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th> 531 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td> 532 * </tr> 533 * <tr> 534 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th> 535 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td> 536 * </tr> 537 * <tr> 538 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th> 539 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td> 540 * </tr> 541 * <tr> 542 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th> 543 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td> 544 * </tr> 545 * <tr> 546 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th> 547 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td> 548 * </tr> 549 * <tr> 550 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th> 551 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td> 552 * </tr> 553 * <tr> 554 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th> 555 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 556 * </tr> 557 * <tr> 558 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th> 559 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td> 560 * </tr> 561 * <tr> 562 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th> 563 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td> 564 * </tr> 565 * <tr> 566 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th> 567 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td> 568 * </tr> 569 * <tr> 570 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th> 571 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 572 * </tr> 573 * <tr> 574 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th> 575 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td> 576 * </tr> 577 * <tr> 578 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th> 579 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 580 * </tr> 581 * <tr> 582 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th> 583 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td> 584 * </tr> 585 * </tbody> 586 * </table> 587 * 588 * Here, the type {@code C} is the class or interface being searched for a member, 589 * documented as a parameter named {@code refc} in the lookup methods. 590 * The method type {@code MT} is composed from the return type {@code T} 591 * and the sequence of argument types {@code A*}. 592 * The constructor also has a sequence of argument types {@code A*} and 593 * is deemed to return the newly-created object of type {@code C}. 594 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}. 595 * The formal parameter {@code this} stands for the self-reference of type {@code C}; 596 * if it is present, it is always the leading argument to the method handle invocation. 597 * (In the case of some {@code protected} members, {@code this} may be 598 * restricted in type to the lookup class; see below.) 599 * The name {@code arg} stands for all the other method handle arguments. 600 * In the code examples for the Core Reflection API, the name {@code thisOrNull} 601 * stands for a null reference if the accessed method or field is static, 602 * and {@code this} otherwise. 603 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand 604 * for reflective objects corresponding to the given members declared in type {@code C}. 605 * <p> 606 * The bytecode behavior for a {@code findClass} operation is a load of a constant class, 607 * as if by {@code ldc CONSTANT_Class}. 608 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant. 609 * <p> 610 * In cases where the given member is of variable arity (i.e., a method or constructor) 611 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. 612 * In all other cases, the returned method handle will be of fixed arity. 613 * <p style="font-size:smaller;"> 614 * <em>Discussion:</em> 615 * The equivalence between looked-up method handles and underlying 616 * class members and bytecode behaviors 617 * can break down in a few ways: 618 * <ul style="font-size:smaller;"> 619 * <li>If {@code C} is not symbolically accessible from the lookup class's loader, 620 * the lookup can still succeed, even when there is no equivalent 621 * Java expression or bytecoded constant. 622 * <li>Likewise, if {@code T} or {@code MT} 623 * is not symbolically accessible from the lookup class's loader, 624 * the lookup can still succeed. 625 * For example, lookups for {@code MethodHandle.invokeExact} and 626 * {@code MethodHandle.invoke} will always succeed, regardless of requested type. 627 * <li>If there is a security manager installed, it can forbid the lookup 628 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>). 629 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle} 630 * constant is not subject to security manager checks. 631 * <li>If the looked-up method has a 632 * <a href="MethodHandle.html#maxarity">very large arity</a>, 633 * the method handle creation may fail with an 634 * {@code IllegalArgumentException}, due to the method handle type having 635 * <a href="MethodHandle.html#maxarity">too many parameters.</a> 636 * </ul> 637 * 638 * <h2><a id="access"></a>Access checking</h2> 639 * Access checks are applied in the factory methods of {@code Lookup}, 640 * when a method handle is created. 641 * This is a key difference from the Core Reflection API, since 642 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 643 * performs access checking against every caller, on every call. 644 * <p> 645 * All access checks start from a {@code Lookup} object, which 646 * compares its recorded lookup class against all requests to 647 * create method handles. 648 * A single {@code Lookup} object can be used to create any number 649 * of access-checked method handles, all checked against a single 650 * lookup class. 651 * <p> 652 * A {@code Lookup} object can be shared with other trusted code, 653 * such as a metaobject protocol. 654 * A shared {@code Lookup} object delegates the capability 655 * to create method handles on private members of the lookup class. 656 * Even if privileged code uses the {@code Lookup} object, 657 * the access checking is confined to the privileges of the 658 * original lookup class. 659 * <p> 660 * A lookup can fail, because 661 * the containing class is not accessible to the lookup class, or 662 * because the desired class member is missing, or because the 663 * desired class member is not accessible to the lookup class, or 664 * because the lookup object is not trusted enough to access the member. 665 * In the case of a field setter function on a {@code final} field, 666 * finality enforcement is treated as a kind of access control, 667 * and the lookup will fail, except in special cases of 668 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}. 669 * In any of these cases, a {@code ReflectiveOperationException} will be 670 * thrown from the attempted lookup. The exact class will be one of 671 * the following: 672 * <ul> 673 * <li>NoSuchMethodException — if a method is requested but does not exist 674 * <li>NoSuchFieldException — if a field is requested but does not exist 675 * <li>IllegalAccessException — if the member exists but an access check fails 676 * </ul> 677 * <p> 678 * In general, the conditions under which a method handle may be 679 * looked up for a method {@code M} are no more restrictive than the conditions 680 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}. 681 * Where the JVM would raise exceptions like {@code NoSuchMethodError}, 682 * a method handle lookup will generally raise a corresponding 683 * checked exception, such as {@code NoSuchMethodException}. 684 * And the effect of invoking the method handle resulting from the lookup 685 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a> 686 * to executing the compiled, verified, and resolved call to {@code M}. 687 * The same point is true of fields and constructors. 688 * <p style="font-size:smaller;"> 689 * <em>Discussion:</em> 690 * Access checks only apply to named and reflected methods, 691 * constructors, and fields. 692 * Other method handle creation methods, such as 693 * {@link MethodHandle#asType MethodHandle.asType}, 694 * do not require any access checks, and are used 695 * independently of any {@code Lookup} object. 696 * <p> 697 * If the desired member is {@code protected}, the usual JVM rules apply, 698 * including the requirement that the lookup class must either be in the 699 * same package as the desired member, or must inherit that member. 700 * (See the Java Virtual Machine Specification, sections {@jvms 701 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.) 702 * In addition, if the desired member is a non-static field or method 703 * in a different package, the resulting method handle may only be applied 704 * to objects of the lookup class or one of its subclasses. 705 * This requirement is enforced by narrowing the type of the leading 706 * {@code this} parameter from {@code C} 707 * (which will necessarily be a superclass of the lookup class) 708 * to the lookup class itself. 709 * <p> 710 * The JVM imposes a similar requirement on {@code invokespecial} instruction, 711 * that the receiver argument must match both the resolved method <em>and</em> 712 * the current class. Again, this requirement is enforced by narrowing the 713 * type of the leading parameter to the resulting method handle. 714 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.) 715 * <p> 716 * The JVM represents constructors and static initializer blocks as internal methods 717 * with special names ({@value ConstantDescs#INIT_NAME}, 718 * {@value ConstantDescs#VNEW_NAME} and {@value ConstantDescs#CLASS_INIT_NAME}). 719 * The internal syntax of invocation instructions allows them to refer to such internal 720 * methods as if they were normal methods, but the JVM bytecode verifier rejects them. 721 * A lookup of such an internal method will produce a {@code NoSuchMethodException}. 722 * <p> 723 * If the relationship between nested types is expressed directly through the 724 * {@code NestHost} and {@code NestMembers} attributes 725 * (see the Java Virtual Machine Specification, sections {@jvms 726 * 4.7.28} and {@jvms 4.7.29}), 727 * then the associated {@code Lookup} object provides direct access to 728 * the lookup class and all of its nestmates 729 * (see {@link java.lang.Class#getNestHost Class.getNestHost}). 730 * Otherwise, access between nested classes is obtained by the Java compiler creating 731 * a wrapper method to access a private method of another class in the same nest. 732 * For example, a nested class {@code C.D} 733 * can access private members within other related classes such as 734 * {@code C}, {@code C.D.E}, or {@code C.B}, 735 * but the Java compiler may need to generate wrapper methods in 736 * those related classes. In such cases, a {@code Lookup} object on 737 * {@code C.E} would be unable to access those private members. 738 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, 739 * which can transform a lookup on {@code C.E} into one on any of those other 740 * classes, without special elevation of privilege. 741 * <p> 742 * The accesses permitted to a given lookup object may be limited, 743 * according to its set of {@link #lookupModes lookupModes}, 744 * to a subset of members normally accessible to the lookup class. 745 * For example, the {@link MethodHandles#publicLookup publicLookup} 746 * method produces a lookup object which is only allowed to access 747 * public members in public classes of exported packages. 748 * The caller sensitive method {@link MethodHandles#lookup lookup} 749 * produces a lookup object with full capabilities relative to 750 * its caller class, to emulate all supported bytecode behaviors. 751 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object 752 * with fewer access modes than the original lookup object. 753 * 754 * <p style="font-size:smaller;"> 755 * <a id="privacc"></a> 756 * <em>Discussion of private and module access:</em> 757 * We say that a lookup has <em>private access</em> 758 * if its {@linkplain #lookupModes lookup modes} 759 * include the possibility of accessing {@code private} members 760 * (which includes the private members of nestmates). 761 * As documented in the relevant methods elsewhere, 762 * only lookups with private access possess the following capabilities: 763 * <ul style="font-size:smaller;"> 764 * <li>access private fields, methods, and constructors of the lookup class and its nestmates 765 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions 766 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a> 767 * for classes accessible to the lookup class 768 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes 769 * within the same package member 770 * </ul> 771 * <p style="font-size:smaller;"> 772 * Similarly, a lookup with module access ensures that the original lookup creator was 773 * a member in the same module as the lookup class. 774 * <p style="font-size:smaller;"> 775 * Private and module access are independently determined modes; a lookup may have 776 * either or both or neither. A lookup which possesses both access modes is said to 777 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}. 778 * <p style="font-size:smaller;"> 779 * A lookup with <em>original access</em> ensures that this lookup is created by 780 * the original lookup class and the bootstrap method invoked by the VM. 781 * Such a lookup with original access also has private and module access 782 * which has the following additional capability: 783 * <ul style="font-size:smaller;"> 784 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods, 785 * such as {@code Class.forName} 786 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class) 787 * class data} associated with the lookup class</li> 788 * </ul> 789 * <p style="font-size:smaller;"> 790 * Each of these permissions is a consequence of the fact that a lookup object 791 * with private access can be securely traced back to an originating class, 792 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions 793 * can be reliably determined and emulated by method handles. 794 * 795 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2> 796 * When a lookup class in one module {@code M1} accesses a class in another module 797 * {@code M2}, extra access checking is performed beyond the access mode bits. 798 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1} 799 * can access public types in {@code M2} when {@code M2} is readable to {@code M1} 800 * and when the type is in a package of {@code M2} that is exported to 801 * at least {@code M1}. 802 * <p> 803 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class 804 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup) 805 * MethodHandles.privateLookupIn} methods. 806 * Teleporting across modules will always record the original lookup class as 807 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em> 808 * and drops {@link Lookup#MODULE MODULE} access. 809 * If the target class is in the same module as the lookup class {@code C}, 810 * then the target class becomes the new lookup class 811 * and there is no change to the previous lookup class. 812 * If the target class is in a different module from {@code M1} ({@code C}'s module), 813 * {@code C} becomes the new previous lookup class 814 * and the target class becomes the new lookup class. 815 * In that case, if there was already a previous lookup class in {@code M0}, 816 * and it differs from {@code M1} and {@code M2}, then the resulting lookup 817 * drops all privileges. 818 * For example, 819 * {@snippet lang="java" : 820 * Lookup lookup = MethodHandles.lookup(); // in class C 821 * Lookup lookup2 = lookup.in(D.class); 822 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT); 823 * } 824 * <p> 825 * The {@link #lookup()} factory method produces a {@code Lookup} object 826 * with {@code null} previous lookup class. 827 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C} 828 * to class {@code D} without elevation of privileges. 829 * If {@code C} and {@code D} are in the same module, 830 * {@code lookup2} records {@code D} as the new lookup class and keeps the 831 * same previous lookup class as the original {@code lookup}, or 832 * {@code null} if not present. 833 * <p> 834 * When a {@code Lookup} teleports from a class 835 * in one nest to another nest, {@code PRIVATE} access is dropped. 836 * When a {@code Lookup} teleports from a class in one package to 837 * another package, {@code PACKAGE} access is dropped. 838 * When a {@code Lookup} teleports from a class in one module to another module, 839 * {@code MODULE} access is dropped. 840 * Teleporting across modules drops the ability to access non-exported classes 841 * in both the module of the new lookup class and the module of the old lookup class 842 * and the resulting {@code Lookup} remains only {@code PUBLIC} access. 843 * A {@code Lookup} can teleport back and forth to a class in the module of 844 * the lookup class and the module of the previous class lookup. 845 * Teleporting across modules can only decrease access but cannot increase it. 846 * Teleporting to some third module drops all accesses. 847 * <p> 848 * In the above example, if {@code C} and {@code D} are in different modules, 849 * {@code lookup2} records {@code D} as its lookup class and 850 * {@code C} as its previous lookup class and {@code lookup2} has only 851 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in 852 * {@code C}'s module and {@code D}'s module. 853 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates 854 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup 855 * class {@code D} is recorded as its previous lookup class. 856 * <p> 857 * Teleporting across modules restricts access to the public types that 858 * both the lookup class and the previous lookup class can equally access 859 * (see below). 860 * <p> 861 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)} 862 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T} 863 * and produce a new {@code Lookup} with <a href="#privacc">private access</a> 864 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}. 865 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access 866 * to call {@code privateLookupIn}. 867 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection 868 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn} 869 * produces a new {@code Lookup} on {@code T} with full capabilities. 870 * A {@code lookup} on {@code C} is also allowed 871 * to do deep reflection on {@code T} in another module {@code M2} if 872 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens} 873 * the package containing {@code T} to at least {@code M1}. 874 * {@code T} becomes the new lookup class and {@code C} becomes the new previous 875 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}. 876 * The resulting {@code Lookup} can be used to do member lookup or teleport 877 * to another lookup class by calling {@link #in Lookup::in}. But 878 * it cannot be used to obtain another private {@code Lookup} by calling 879 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn} 880 * because it has no {@code MODULE} access. 881 * <p> 882 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to 883 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package 884 * of {@code T}. Extreme caution should be taken when opening a package 885 * to another module as such defined classes have the same full privilege 886 * access as other members in {@code M2}. 887 * 888 * <h2><a id="module-access-check"></a>Cross-module access checks</h2> 889 * 890 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode 891 * allows cross-module access. The access checking is performed with respect 892 * to both the lookup class and the previous lookup class if present. 893 * <p> 894 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type 895 * in all modules when the type is in a package that is {@linkplain Module#isExported(String) 896 * exported unconditionally}. 897 * <p> 898 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class, 899 * the lookup with {@link #PUBLIC} mode can access all public types in modules 900 * that are readable to {@code M1} and the type is in a package that is exported 901 * at least to {@code M1}. 902 * <p> 903 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class 904 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access 905 * the intersection of all public types that are accessible to {@code M1} 906 * with all public types that are accessible to {@code M0}. {@code M0} 907 * reads {@code M1} and hence the set of accessible types includes: 908 * 909 * <ul> 910 * <li>unconditional-exported packages from {@code M1}</li> 911 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li> 912 * <li> 913 * unconditional-exported packages from a third module {@code M2}if both {@code M0} 914 * and {@code M1} read {@code M2} 915 * </li> 916 * <li>qualified-exported packages from {@code M1} to {@code M0}</li> 917 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li> 918 * <li> 919 * qualified-exported packages from a third module {@code M2} to both {@code M0} and 920 * {@code M1} if both {@code M0} and {@code M1} read {@code M2} 921 * </li> 922 * </ul> 923 * 924 * <h2><a id="access-modes"></a>Access modes</h2> 925 * 926 * The table below shows the access modes of a {@code Lookup} produced by 927 * any of the following factory or transformation methods: 928 * <ul> 929 * <li>{@link #lookup() MethodHandles::lookup}</li> 930 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li> 931 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li> 932 * <li>{@link Lookup#in Lookup::in}</li> 933 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li> 934 * </ul> 935 * 936 * <table class="striped"> 937 * <caption style="display:none"> 938 * Access mode summary 939 * </caption> 940 * <thead> 941 * <tr> 942 * <th scope="col">Lookup object</th> 943 * <th style="text-align:center">original</th> 944 * <th style="text-align:center">protected</th> 945 * <th style="text-align:center">private</th> 946 * <th style="text-align:center">package</th> 947 * <th style="text-align:center">module</th> 948 * <th style="text-align:center">public</th> 949 * </tr> 950 * </thead> 951 * <tbody> 952 * <tr> 953 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th> 954 * <td style="text-align:center">ORI</td> 955 * <td style="text-align:center">PRO</td> 956 * <td style="text-align:center">PRI</td> 957 * <td style="text-align:center">PAC</td> 958 * <td style="text-align:center">MOD</td> 959 * <td style="text-align:center">1R</td> 960 * </tr> 961 * <tr> 962 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th> 963 * <td></td> 964 * <td></td> 965 * <td></td> 966 * <td style="text-align:center">PAC</td> 967 * <td style="text-align:center">MOD</td> 968 * <td style="text-align:center">1R</td> 969 * </tr> 970 * <tr> 971 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th> 972 * <td></td> 973 * <td></td> 974 * <td></td> 975 * <td></td> 976 * <td style="text-align:center">MOD</td> 977 * <td style="text-align:center">1R</td> 978 * </tr> 979 * <tr> 980 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th> 981 * <td></td> 982 * <td></td> 983 * <td></td> 984 * <td></td> 985 * <td></td> 986 * <td style="text-align:center">2R</td> 987 * </tr> 988 * <tr> 989 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th> 990 * <td></td> 991 * <td></td> 992 * <td></td> 993 * <td></td> 994 * <td></td> 995 * <td style="text-align:center">2R</td> 996 * </tr> 997 * <tr> 998 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th> 999 * <td></td> 1000 * <td style="text-align:center">PRO</td> 1001 * <td style="text-align:center">PRI</td> 1002 * <td style="text-align:center">PAC</td> 1003 * <td style="text-align:center">MOD</td> 1004 * <td style="text-align:center">1R</td> 1005 * </tr> 1006 * <tr> 1007 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th> 1008 * <td></td> 1009 * <td style="text-align:center">PRO</td> 1010 * <td style="text-align:center">PRI</td> 1011 * <td style="text-align:center">PAC</td> 1012 * <td style="text-align:center">MOD</td> 1013 * <td style="text-align:center">1R</td> 1014 * </tr> 1015 * <tr> 1016 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th> 1017 * <td></td> 1018 * <td></td> 1019 * <td></td> 1020 * <td style="text-align:center">PAC</td> 1021 * <td style="text-align:center">MOD</td> 1022 * <td style="text-align:center">1R</td> 1023 * </tr> 1024 * <tr> 1025 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th> 1026 * <td></td> 1027 * <td></td> 1028 * <td></td> 1029 * <td></td> 1030 * <td style="text-align:center">MOD</td> 1031 * <td style="text-align:center">1R</td> 1032 * </tr> 1033 * <tr> 1034 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th> 1035 * <td></td> 1036 * <td></td> 1037 * <td></td> 1038 * <td></td> 1039 * <td></td> 1040 * <td style="text-align:center">2R</td> 1041 * </tr> 1042 * <tr> 1043 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th> 1044 * <td></td> 1045 * <td></td> 1046 * <td style="text-align:center">PRI</td> 1047 * <td style="text-align:center">PAC</td> 1048 * <td style="text-align:center">MOD</td> 1049 * <td style="text-align:center">1R</td> 1050 * </tr> 1051 * <tr> 1052 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th> 1053 * <td></td> 1054 * <td></td> 1055 * <td></td> 1056 * <td style="text-align:center">PAC</td> 1057 * <td style="text-align:center">MOD</td> 1058 * <td style="text-align:center">1R</td> 1059 * </tr> 1060 * <tr> 1061 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th> 1062 * <td></td> 1063 * <td></td> 1064 * <td></td> 1065 * <td></td> 1066 * <td style="text-align:center">MOD</td> 1067 * <td style="text-align:center">1R</td> 1068 * </tr> 1069 * <tr> 1070 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th> 1071 * <td></td> 1072 * <td></td> 1073 * <td></td> 1074 * <td></td> 1075 * <td></td> 1076 * <td style="text-align:center">1R</td> 1077 * </tr> 1078 * <tr> 1079 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th> 1080 * <td></td> 1081 * <td></td> 1082 * <td></td> 1083 * <td></td> 1084 * <td></td> 1085 * <td style="text-align:center">none</td> 1086 * <tr> 1087 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th> 1088 * <td></td> 1089 * <td style="text-align:center">PRO</td> 1090 * <td style="text-align:center">PRI</td> 1091 * <td style="text-align:center">PAC</td> 1092 * <td></td> 1093 * <td style="text-align:center">2R</td> 1094 * </tr> 1095 * <tr> 1096 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th> 1097 * <td></td> 1098 * <td style="text-align:center">PRO</td> 1099 * <td style="text-align:center">PRI</td> 1100 * <td style="text-align:center">PAC</td> 1101 * <td></td> 1102 * <td style="text-align:center">2R</td> 1103 * </tr> 1104 * <tr> 1105 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th> 1106 * <td></td> 1107 * <td></td> 1108 * <td></td> 1109 * <td></td> 1110 * <td></td> 1111 * <td style="text-align:center">IAE</td> 1112 * </tr> 1113 * <tr> 1114 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th> 1115 * <td></td> 1116 * <td></td> 1117 * <td></td> 1118 * <td style="text-align:center">PAC</td> 1119 * <td></td> 1120 * <td style="text-align:center">2R</td> 1121 * </tr> 1122 * <tr> 1123 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th> 1124 * <td></td> 1125 * <td></td> 1126 * <td></td> 1127 * <td></td> 1128 * <td></td> 1129 * <td style="text-align:center">2R</td> 1130 * </tr> 1131 * <tr> 1132 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th> 1133 * <td></td> 1134 * <td></td> 1135 * <td></td> 1136 * <td></td> 1137 * <td></td> 1138 * <td style="text-align:center">2R</td> 1139 * </tr> 1140 * <tr> 1141 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th> 1142 * <td></td> 1143 * <td></td> 1144 * <td></td> 1145 * <td></td> 1146 * <td></td> 1147 * <td style="text-align:center">none</td> 1148 * </tr> 1149 * <tr> 1150 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th> 1151 * <td></td> 1152 * <td></td> 1153 * <td style="text-align:center">PRI</td> 1154 * <td style="text-align:center">PAC</td> 1155 * <td></td> 1156 * <td style="text-align:center">2R</td> 1157 * </tr> 1158 * <tr> 1159 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th> 1160 * <td></td> 1161 * <td></td> 1162 * <td></td> 1163 * <td style="text-align:center">PAC</td> 1164 * <td></td> 1165 * <td style="text-align:center">2R</td> 1166 * </tr> 1167 * <tr> 1168 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th> 1169 * <td></td> 1170 * <td></td> 1171 * <td></td> 1172 * <td></td> 1173 * <td></td> 1174 * <td style="text-align:center">2R</td> 1175 * </tr> 1176 * <tr> 1177 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th> 1178 * <td></td> 1179 * <td></td> 1180 * <td></td> 1181 * <td></td> 1182 * <td></td> 1183 * <td style="text-align:center">2R</td> 1184 * </tr> 1185 * <tr> 1186 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th> 1187 * <td></td> 1188 * <td></td> 1189 * <td></td> 1190 * <td></td> 1191 * <td></td> 1192 * <td style="text-align:center">none</td> 1193 * </tr> 1194 * <tr> 1195 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th> 1196 * <td></td> 1197 * <td></td> 1198 * <td style="text-align:center">PRI</td> 1199 * <td style="text-align:center">PAC</td> 1200 * <td style="text-align:center">MOD</td> 1201 * <td style="text-align:center">1R</td> 1202 * </tr> 1203 * <tr> 1204 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th> 1205 * <td></td> 1206 * <td></td> 1207 * <td></td> 1208 * <td style="text-align:center">PAC</td> 1209 * <td style="text-align:center">MOD</td> 1210 * <td style="text-align:center">1R</td> 1211 * </tr> 1212 * <tr> 1213 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th> 1214 * <td></td> 1215 * <td></td> 1216 * <td></td> 1217 * <td></td> 1218 * <td style="text-align:center">MOD</td> 1219 * <td style="text-align:center">1R</td> 1220 * </tr> 1221 * <tr> 1222 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th> 1223 * <td></td> 1224 * <td></td> 1225 * <td></td> 1226 * <td></td> 1227 * <td></td> 1228 * <td style="text-align:center">1R</td> 1229 * </tr> 1230 * <tr> 1231 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th> 1232 * <td></td> 1233 * <td></td> 1234 * <td></td> 1235 * <td></td> 1236 * <td></td> 1237 * <td style="text-align:center">none</td> 1238 * </tr> 1239 * <tr> 1240 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th> 1241 * <td></td> 1242 * <td></td> 1243 * <td></td> 1244 * <td></td> 1245 * <td></td> 1246 * <td style="text-align:center">U</td> 1247 * </tr> 1248 * <tr> 1249 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th> 1250 * <td></td> 1251 * <td></td> 1252 * <td></td> 1253 * <td></td> 1254 * <td></td> 1255 * <td style="text-align:center">U</td> 1256 * </tr> 1257 * <tr> 1258 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th> 1259 * <td></td> 1260 * <td></td> 1261 * <td></td> 1262 * <td></td> 1263 * <td></td> 1264 * <td style="text-align:center">U</td> 1265 * </tr> 1266 * <tr> 1267 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th> 1268 * <td></td> 1269 * <td></td> 1270 * <td></td> 1271 * <td></td> 1272 * <td></td> 1273 * <td style="text-align:center">none</td> 1274 * </tr> 1275 * <tr> 1276 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th> 1277 * <td></td> 1278 * <td></td> 1279 * <td></td> 1280 * <td></td> 1281 * <td></td> 1282 * <td style="text-align:center">IAE</td> 1283 * </tr> 1284 * <tr> 1285 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th> 1286 * <td></td> 1287 * <td></td> 1288 * <td></td> 1289 * <td></td> 1290 * <td></td> 1291 * <td style="text-align:center">none</td> 1292 * </tr> 1293 * </tbody> 1294 * </table> 1295 * 1296 * <p> 1297 * Notes: 1298 * <ul> 1299 * <li>Class {@code C} and class {@code C1} are in module {@code M1}, 1300 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E} 1301 * is in module {@code M3}. {@code X} stands for class which is inaccessible 1302 * to the lookup. {@code ANY} stands for any of the example lookups.</li> 1303 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set, 1304 * {@code PRO} indicates {@link #PROTECTED} bit set, 1305 * {@code PRI} indicates {@link #PRIVATE} bit set, 1306 * {@code PAC} indicates {@link #PACKAGE} bit set, 1307 * {@code MOD} indicates {@link #MODULE} bit set, 1308 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set, 1309 * {@code U} indicates {@link #UNCONDITIONAL} bit set, 1310 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li> 1311 * <li>Public access comes in three kinds: 1312 * <ul> 1313 * <li>unconditional ({@code U}): the lookup assumes readability. 1314 * The lookup has {@code null} previous lookup class. 1315 * <li>one-module-reads ({@code 1R}): the module access checking is 1316 * performed with respect to the lookup class. The lookup has {@code null} 1317 * previous lookup class. 1318 * <li>two-module-reads ({@code 2R}): the module access checking is 1319 * performed with respect to the lookup class and the previous lookup class. 1320 * The lookup has a non-null previous lookup class which is in a 1321 * different module from the current lookup class. 1322 * </ul> 1323 * <li>Any attempt to reach a third module loses all access.</li> 1324 * <li>If a target class {@code X} is not accessible to {@code Lookup::in} 1325 * all access modes are dropped.</li> 1326 * </ul> 1327 * 1328 * <h2><a id="secmgr"></a>Security manager interactions</h2> 1329 * Although bytecode instructions can only refer to classes in 1330 * a related class loader, this API can search for methods in any 1331 * class, as long as a reference to its {@code Class} object is 1332 * available. Such cross-loader references are also possible with the 1333 * Core Reflection API, and are impossible to bytecode instructions 1334 * such as {@code invokestatic} or {@code getfield}. 1335 * There is a {@linkplain java.lang.SecurityManager security manager API} 1336 * to allow applications to check such cross-loader references. 1337 * These checks apply to both the {@code MethodHandles.Lookup} API 1338 * and the Core Reflection API 1339 * (as found on {@link java.lang.Class Class}). 1340 * <p> 1341 * If a security manager is present, member and class lookups are subject to 1342 * additional checks. 1343 * From one to three calls are made to the security manager. 1344 * Any of these calls can refuse access by throwing a 1345 * {@link java.lang.SecurityException SecurityException}. 1346 * Define {@code smgr} as the security manager, 1347 * {@code lookc} as the lookup class of the current lookup object, 1348 * {@code refc} as the containing class in which the member 1349 * is being sought, and {@code defc} as the class in which the 1350 * member is actually defined. 1351 * (If a class or other type is being accessed, 1352 * the {@code refc} and {@code defc} values are the class itself.) 1353 * The value {@code lookc} is defined as <em>not present</em> 1354 * if the current lookup object does not have 1355 * {@linkplain #hasFullPrivilegeAccess() full privilege access}. 1356 * The calls are made according to the following rules: 1357 * <ul> 1358 * <li><b>Step 1:</b> 1359 * If {@code lookc} is not present, or if its class loader is not 1360 * the same as or an ancestor of the class loader of {@code refc}, 1361 * then {@link SecurityManager#checkPackageAccess 1362 * smgr.checkPackageAccess(refcPkg)} is called, 1363 * where {@code refcPkg} is the package of {@code refc}. 1364 * <li><b>Step 2a:</b> 1365 * If the retrieved member is not public and 1366 * {@code lookc} is not present, then 1367 * {@link SecurityManager#checkPermission smgr.checkPermission} 1368 * with {@code RuntimePermission("accessDeclaredMembers")} is called. 1369 * <li><b>Step 2b:</b> 1370 * If the retrieved class has a {@code null} class loader, 1371 * and {@code lookc} is not present, then 1372 * {@link SecurityManager#checkPermission smgr.checkPermission} 1373 * with {@code RuntimePermission("getClassLoader")} is called. 1374 * <li><b>Step 3:</b> 1375 * If the retrieved member is not public, 1376 * and if {@code lookc} is not present, 1377 * and if {@code defc} and {@code refc} are different, 1378 * then {@link SecurityManager#checkPackageAccess 1379 * smgr.checkPackageAccess(defcPkg)} is called, 1380 * where {@code defcPkg} is the package of {@code defc}. 1381 * </ul> 1382 * Security checks are performed after other access checks have passed. 1383 * Therefore, the above rules presuppose a member or class that is public, 1384 * or else that is being accessed from a lookup class that has 1385 * rights to access the member or class. 1386 * <p> 1387 * If a security manager is present and the current lookup object does not have 1388 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then 1389 * {@link #defineClass(byte[]) defineClass}, 1390 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass}, 1391 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...) 1392 * defineHiddenClassWithClassData} 1393 * calls {@link SecurityManager#checkPermission smgr.checkPermission} 1394 * with {@code RuntimePermission("defineClass")}. 1395 * 1396 * <h2><a id="callsens"></a>Caller sensitive methods</h2> 1397 * A small number of Java methods have a special property called caller sensitivity. 1398 * A <em>caller-sensitive</em> method can behave differently depending on the 1399 * identity of its immediate caller. 1400 * <p> 1401 * If a method handle for a caller-sensitive method is requested, 1402 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply, 1403 * but they take account of the lookup class in a special way. 1404 * The resulting method handle behaves as if it were called 1405 * from an instruction contained in the lookup class, 1406 * so that the caller-sensitive method detects the lookup class. 1407 * (By contrast, the invoker of the method handle is disregarded.) 1408 * Thus, in the case of caller-sensitive methods, 1409 * different lookup classes may give rise to 1410 * differently behaving method handles. 1411 * <p> 1412 * In cases where the lookup object is 1413 * {@link MethodHandles#publicLookup() publicLookup()}, 1414 * or some other lookup object without the 1415 * {@linkplain #ORIGINAL original access}, 1416 * the lookup class is disregarded. 1417 * In such cases, no caller-sensitive method handle can be created, 1418 * access is forbidden, and the lookup fails with an 1419 * {@code IllegalAccessException}. 1420 * <p style="font-size:smaller;"> 1421 * <em>Discussion:</em> 1422 * For example, the caller-sensitive method 1423 * {@link java.lang.Class#forName(String) Class.forName(x)} 1424 * can return varying classes or throw varying exceptions, 1425 * depending on the class loader of the class that calls it. 1426 * A public lookup of {@code Class.forName} will fail, because 1427 * there is no reasonable way to determine its bytecode behavior. 1428 * <p style="font-size:smaller;"> 1429 * If an application caches method handles for broad sharing, 1430 * it should use {@code publicLookup()} to create them. 1431 * If there is a lookup of {@code Class.forName}, it will fail, 1432 * and the application must take appropriate action in that case. 1433 * It may be that a later lookup, perhaps during the invocation of a 1434 * bootstrap method, can incorporate the specific identity 1435 * of the caller, making the method accessible. 1436 * <p style="font-size:smaller;"> 1437 * The function {@code MethodHandles.lookup} is caller sensitive 1438 * so that there can be a secure foundation for lookups. 1439 * Nearly all other methods in the JSR 292 API rely on lookup 1440 * objects to check access requests. 1441 * 1442 * @revised 9 1443 */ 1444 public static final 1445 class Lookup { 1446 /** The class on behalf of whom the lookup is being performed. */ 1447 private final Class<?> lookupClass; 1448 1449 /** previous lookup class */ 1450 private final Class<?> prevLookupClass; 1451 1452 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */ 1453 private final int allowedModes; 1454 1455 static { 1456 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes")); 1457 } 1458 1459 /** A single-bit mask representing {@code public} access, 1460 * which may contribute to the result of {@link #lookupModes lookupModes}. 1461 * The value, {@code 0x01}, happens to be the same as the value of the 1462 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}. 1463 * <p> 1464 * A {@code Lookup} with this lookup mode performs cross-module access check 1465 * with respect to the {@linkplain #lookupClass() lookup class} and 1466 * {@linkplain #previousLookupClass() previous lookup class} if present. 1467 */ 1468 public static final int PUBLIC = Modifier.PUBLIC; 1469 1470 /** A single-bit mask representing {@code private} access, 1471 * which may contribute to the result of {@link #lookupModes lookupModes}. 1472 * The value, {@code 0x02}, happens to be the same as the value of the 1473 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}. 1474 */ 1475 public static final int PRIVATE = Modifier.PRIVATE; 1476 1477 /** A single-bit mask representing {@code protected} access, 1478 * which may contribute to the result of {@link #lookupModes lookupModes}. 1479 * The value, {@code 0x04}, happens to be the same as the value of the 1480 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}. 1481 */ 1482 public static final int PROTECTED = Modifier.PROTECTED; 1483 1484 /** A single-bit mask representing {@code package} access (default access), 1485 * which may contribute to the result of {@link #lookupModes lookupModes}. 1486 * The value is {@code 0x08}, which does not correspond meaningfully to 1487 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1488 */ 1489 public static final int PACKAGE = Modifier.STATIC; 1490 1491 /** A single-bit mask representing {@code module} access, 1492 * which may contribute to the result of {@link #lookupModes lookupModes}. 1493 * The value is {@code 0x10}, which does not correspond meaningfully to 1494 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1495 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup} 1496 * with this lookup mode can access all public types in the module of the 1497 * lookup class and public types in packages exported by other modules 1498 * to the module of the lookup class. 1499 * <p> 1500 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1501 * previous lookup class} is always {@code null}. 1502 * 1503 * @since 9 1504 */ 1505 public static final int MODULE = PACKAGE << 1; 1506 1507 /** A single-bit mask representing {@code unconditional} access 1508 * which may contribute to the result of {@link #lookupModes lookupModes}. 1509 * The value is {@code 0x20}, which does not correspond meaningfully to 1510 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1511 * A {@code Lookup} with this lookup mode assumes {@linkplain 1512 * java.lang.Module#canRead(java.lang.Module) readability}. 1513 * This lookup mode can access all public members of public types 1514 * of all modules when the type is in a package that is {@link 1515 * java.lang.Module#isExported(String) exported unconditionally}. 1516 * 1517 * <p> 1518 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1519 * previous lookup class} is always {@code null}. 1520 * 1521 * @since 9 1522 * @see #publicLookup() 1523 */ 1524 public static final int UNCONDITIONAL = PACKAGE << 2; 1525 1526 /** A single-bit mask representing {@code original} access 1527 * which may contribute to the result of {@link #lookupModes lookupModes}. 1528 * The value is {@code 0x40}, which does not correspond meaningfully to 1529 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1530 * 1531 * <p> 1532 * If this lookup mode is set, the {@code Lookup} object must be 1533 * created by the original lookup class by calling 1534 * {@link MethodHandles#lookup()} method or by a bootstrap method 1535 * invoked by the VM. The {@code Lookup} object with this lookup 1536 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}. 1537 * 1538 * @since 16 1539 */ 1540 public static final int ORIGINAL = PACKAGE << 3; 1541 1542 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL); 1543 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access 1544 private static final int TRUSTED = -1; 1545 1546 /* 1547 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL 1548 * Adjust 0 => PACKAGE 1549 */ 1550 private static int fixmods(int mods) { 1551 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL); 1552 if (Modifier.isPublic(mods)) 1553 mods |= UNCONDITIONAL; 1554 return (mods != 0) ? mods : PACKAGE; 1555 } 1556 1557 /** Tells which class is performing the lookup. It is this class against 1558 * which checks are performed for visibility and access permissions. 1559 * <p> 1560 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class}, 1561 * access checks are performed against both the lookup class and the previous lookup class. 1562 * <p> 1563 * The class implies a maximum level of access permission, 1564 * but the permissions may be additionally limited by the bitmask 1565 * {@link #lookupModes lookupModes}, which controls whether non-public members 1566 * can be accessed. 1567 * @return the lookup class, on behalf of which this lookup object finds members 1568 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1569 */ 1570 public Class<?> lookupClass() { 1571 return lookupClass; 1572 } 1573 1574 /** Reports a lookup class in another module that this lookup object 1575 * was previously teleported from, or {@code null}. 1576 * <p> 1577 * A {@code Lookup} object produced by the factory methods, such as the 1578 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method, 1579 * has {@code null} previous lookup class. 1580 * A {@code Lookup} object has a non-null previous lookup class 1581 * when this lookup was teleported from an old lookup class 1582 * in one module to a new lookup class in another module. 1583 * 1584 * @return the lookup class in another module that this lookup object was 1585 * previously teleported from, or {@code null} 1586 * @since 14 1587 * @see #in(Class) 1588 * @see MethodHandles#privateLookupIn(Class, Lookup) 1589 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1590 */ 1591 public Class<?> previousLookupClass() { 1592 return prevLookupClass; 1593 } 1594 1595 // This is just for calling out to MethodHandleImpl. 1596 private Class<?> lookupClassOrNull() { 1597 return (allowedModes == TRUSTED) ? null : lookupClass; 1598 } 1599 1600 /** Tells which access-protection classes of members this lookup object can produce. 1601 * The result is a bit-mask of the bits 1602 * {@linkplain #PUBLIC PUBLIC (0x01)}, 1603 * {@linkplain #PRIVATE PRIVATE (0x02)}, 1604 * {@linkplain #PROTECTED PROTECTED (0x04)}, 1605 * {@linkplain #PACKAGE PACKAGE (0x08)}, 1606 * {@linkplain #MODULE MODULE (0x10)}, 1607 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}, 1608 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}. 1609 * <p> 1610 * A freshly-created lookup object 1611 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has 1612 * all possible bits set, except {@code UNCONDITIONAL}. 1613 * A lookup object on a new lookup class 1614 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} 1615 * may have some mode bits set to zero. 1616 * Mode bits can also be 1617 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}. 1618 * Once cleared, mode bits cannot be restored from the downgraded lookup object. 1619 * The purpose of this is to restrict access via the new lookup object, 1620 * so that it can access only names which can be reached by the original 1621 * lookup object, and also by the new lookup class. 1622 * @return the lookup modes, which limit the kinds of access performed by this lookup object 1623 * @see #in 1624 * @see #dropLookupMode 1625 * 1626 * @revised 9 1627 */ 1628 public int lookupModes() { 1629 return allowedModes & ALL_MODES; 1630 } 1631 1632 /** Embody the current class (the lookupClass) as a lookup class 1633 * for method handle creation. 1634 * Must be called by from a method in this package, 1635 * which in turn is called by a method not in this package. 1636 */ 1637 Lookup(Class<?> lookupClass) { 1638 this(lookupClass, null, FULL_POWER_MODES); 1639 } 1640 1641 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1642 assert PrimitiveClass.isPrimaryType(lookupClass); 1643 assert prevLookupClass == null || ((allowedModes & MODULE) == 0 1644 && prevLookupClass.getModule() != lookupClass.getModule()); 1645 assert !lookupClass.isArray() && !lookupClass.isPrimitive(); 1646 this.lookupClass = lookupClass; 1647 this.prevLookupClass = prevLookupClass; 1648 this.allowedModes = allowedModes; 1649 } 1650 1651 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1652 // make sure we haven't accidentally picked up a privileged class: 1653 checkUnprivilegedlookupClass(lookupClass); 1654 return new Lookup(lookupClass, prevLookupClass, allowedModes); 1655 } 1656 1657 /** 1658 * Creates a lookup on the specified new lookup class. 1659 * The resulting object will report the specified 1660 * class as its own {@link #lookupClass() lookupClass}. 1661 * 1662 * <p> 1663 * However, the resulting {@code Lookup} object is guaranteed 1664 * to have no more access capabilities than the original. 1665 * In particular, access capabilities can be lost as follows:<ul> 1666 * <li>If the new lookup class is different from the old lookup class, 1667 * i.e. {@link #ORIGINAL ORIGINAL} access is lost. 1668 * <li>If the new lookup class is in a different module from the old one, 1669 * i.e. {@link #MODULE MODULE} access is lost. 1670 * <li>If the new lookup class is in a different package 1671 * than the old one, protected and default (package) members will not be accessible, 1672 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost. 1673 * <li>If the new lookup class is not within the same package member 1674 * as the old one, private members will not be accessible, and protected members 1675 * will not be accessible by virtue of inheritance, 1676 * i.e. {@link #PRIVATE PRIVATE} access is lost. 1677 * (Protected members may continue to be accessible because of package sharing.) 1678 * <li>If the new lookup class is not 1679 * {@linkplain #accessClass(Class) accessible} to this lookup, 1680 * then no members, not even public members, will be accessible 1681 * i.e. all access modes are lost. 1682 * <li>If the new lookup class, the old lookup class and the previous lookup class 1683 * are all in different modules i.e. teleporting to a third module, 1684 * all access modes are lost. 1685 * </ul> 1686 * <p> 1687 * The new previous lookup class is chosen as follows: 1688 * <ul> 1689 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit, 1690 * the new previous lookup class is {@code null}. 1691 * <li>If the new lookup class is in the same module as the old lookup class, 1692 * the new previous lookup class is the old previous lookup class. 1693 * <li>If the new lookup class is in a different module from the old lookup class, 1694 * the new previous lookup class is the old lookup class. 1695 *</ul> 1696 * <p> 1697 * The resulting lookup's capabilities for loading classes 1698 * (used during {@link #findClass} invocations) 1699 * are determined by the lookup class' loader, 1700 * which may change due to this operation. 1701 * 1702 * @param requestedLookupClass the desired lookup class for the new lookup object 1703 * @return a lookup object which reports the desired lookup class, or the same object 1704 * if there is no change 1705 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class 1706 * @throws NullPointerException if the argument is null 1707 * 1708 * @revised 9 1709 * @see #accessClass(Class) 1710 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1711 */ 1712 public Lookup in(Class<?> requestedLookupClass) { 1713 Objects.requireNonNull(requestedLookupClass); 1714 if (requestedLookupClass.isPrimitive()) 1715 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class"); 1716 if (requestedLookupClass.isArray()) 1717 throw new IllegalArgumentException(requestedLookupClass + " is an array class"); 1718 1719 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all 1720 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES); 1721 if (requestedLookupClass == this.lookupClass) 1722 return this; // keep same capabilities 1723 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL; 1724 Module fromModule = this.lookupClass.getModule(); 1725 Module targetModule = requestedLookupClass.getModule(); 1726 Class<?> plc = this.previousLookupClass(); 1727 if ((this.allowedModes & UNCONDITIONAL) != 0) { 1728 assert plc == null; 1729 newModes = UNCONDITIONAL; 1730 } else if (fromModule != targetModule) { 1731 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) { 1732 // allow hopping back and forth between fromModule and plc's module 1733 // but not the third module 1734 newModes = 0; 1735 } 1736 // drop MODULE access 1737 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED); 1738 // teleport from this lookup class 1739 plc = this.lookupClass; 1740 } 1741 if ((newModes & PACKAGE) != 0 1742 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) { 1743 newModes &= ~(PACKAGE|PRIVATE|PROTECTED); 1744 } 1745 // Allow nestmate lookups to be created without special privilege: 1746 if ((newModes & PRIVATE) != 0 1747 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) { 1748 newModes &= ~(PRIVATE|PROTECTED); 1749 } 1750 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0 1751 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) { 1752 // The requested class it not accessible from the lookup class. 1753 // No permissions. 1754 newModes = 0; 1755 } 1756 return newLookup(requestedLookupClass, plc, newModes); 1757 } 1758 1759 /** 1760 * Creates a lookup on the same lookup class which this lookup object 1761 * finds members, but with a lookup mode that has lost the given lookup mode. 1762 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE 1763 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED}, 1764 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or 1765 * {@link #UNCONDITIONAL UNCONDITIONAL}. 1766 * 1767 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup}, 1768 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set. 1769 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting 1770 * lookup has no access. 1771 * 1772 * <p> If this lookup is not a public lookup, then the following applies 1773 * regardless of its {@linkplain #lookupModes() lookup modes}. 1774 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always 1775 * dropped and so the resulting lookup mode will never have these access 1776 * capabilities. When dropping {@code PACKAGE} 1777 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE} 1778 * access. When dropping {@code MODULE} then the resulting lookup will not 1779 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. 1780 * When dropping {@code PUBLIC} then the resulting lookup has no access. 1781 * 1782 * @apiNote 1783 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely 1784 * delegate non-public access within the package of the lookup class without 1785 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>. 1786 * A lookup with {@code MODULE} but not 1787 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within 1788 * the module of the lookup class without conferring package access. 1789 * A lookup with a {@linkplain #previousLookupClass() previous lookup class} 1790 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access 1791 * to public classes accessible to both the module of the lookup class 1792 * and the module of the previous lookup class. 1793 * 1794 * @param modeToDrop the lookup mode to drop 1795 * @return a lookup object which lacks the indicated mode, or the same object if there is no change 1796 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC}, 1797 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL} 1798 * or {@code UNCONDITIONAL} 1799 * @see MethodHandles#privateLookupIn 1800 * @since 9 1801 */ 1802 public Lookup dropLookupMode(int modeToDrop) { 1803 int oldModes = lookupModes(); 1804 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL); 1805 switch (modeToDrop) { 1806 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break; 1807 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break; 1808 case PACKAGE: newModes &= ~(PRIVATE); break; 1809 case PROTECTED: 1810 case PRIVATE: 1811 case ORIGINAL: 1812 case UNCONDITIONAL: break; 1813 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop"); 1814 } 1815 if (newModes == oldModes) return this; // return self if no change 1816 return newLookup(lookupClass(), previousLookupClass(), newModes); 1817 } 1818 1819 /** 1820 * Creates and links a class or interface from {@code bytes} 1821 * with the same class loader and in the same runtime package and 1822 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's 1823 * {@linkplain #lookupClass() lookup class} as if calling 1824 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 1825 * ClassLoader::defineClass}. 1826 * 1827 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include 1828 * {@link #PACKAGE PACKAGE} access as default (package) members will be 1829 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate 1830 * that the lookup object was created by a caller in the runtime package (or derived 1831 * from a lookup originally created by suitably privileged code to a target class in 1832 * the runtime package). </p> 1833 * 1834 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined 1835 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the 1836 * same package as the lookup class. </p> 1837 * 1838 * <p> This method does not run the class initializer. The class initializer may 1839 * run at a later time, as detailed in section 12.4 of the <em>The Java Language 1840 * Specification</em>. </p> 1841 * 1842 * <p> If there is a security manager and this lookup does not have {@linkplain 1843 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method 1844 * is first called to check {@code RuntimePermission("defineClass")}. </p> 1845 * 1846 * @param bytes the class bytes 1847 * @return the {@code Class} object for the class 1848 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access 1849 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 1850 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 1851 * than the lookup class or {@code bytes} is not a class or interface 1852 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 1853 * @throws VerifyError if the newly created class cannot be verified 1854 * @throws LinkageError if the newly created class cannot be linked for any other reason 1855 * @throws SecurityException if a security manager is present and it 1856 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1857 * @throws NullPointerException if {@code bytes} is {@code null} 1858 * @since 9 1859 * @see Lookup#privateLookupIn 1860 * @see Lookup#dropLookupMode 1861 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 1862 */ 1863 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException { 1864 ensureDefineClassPermission(); 1865 if ((lookupModes() & PACKAGE) == 0) 1866 throw new IllegalAccessException("Lookup does not have PACKAGE access"); 1867 return makeClassDefiner(bytes.clone()).defineClass(false); 1868 } 1869 1870 private void ensureDefineClassPermission() { 1871 if (allowedModes == TRUSTED) return; 1872 1873 if (!hasFullPrivilegeAccess()) { 1874 @SuppressWarnings("removal") 1875 SecurityManager sm = System.getSecurityManager(); 1876 if (sm != null) 1877 sm.checkPermission(new RuntimePermission("defineClass")); 1878 } 1879 } 1880 1881 /** 1882 * The set of class options that specify whether a hidden class created by 1883 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...) 1884 * Lookup::defineHiddenClass} method is dynamically added as a new member 1885 * to the nest of a lookup class and/or whether a hidden class has 1886 * a strong relationship with the class loader marked as its defining loader. 1887 * 1888 * @since 15 1889 */ 1890 public enum ClassOption { 1891 /** 1892 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest} 1893 * of a lookup class as a nestmate. 1894 * 1895 * <p> A hidden nestmate class has access to the private members of all 1896 * classes and interfaces in the same nest. 1897 * 1898 * @see Class#getNestHost() 1899 */ 1900 NESTMATE(NESTMATE_CLASS), 1901 1902 /** 1903 * Specifies that a hidden class has a <em>strong</em> 1904 * relationship with the class loader marked as its defining loader, 1905 * as a normal class or interface has with its own defining loader. 1906 * This means that the hidden class may be unloaded if and only if 1907 * its defining loader is not reachable and thus may be reclaimed 1908 * by a garbage collector (JLS {@jls 12.7}). 1909 * 1910 * <p> By default, a hidden class or interface may be unloaded 1911 * even if the class loader that is marked as its defining loader is 1912 * <a href="../ref/package-summary.html#reachability">reachable</a>. 1913 1914 * 1915 * @jls 12.7 Unloading of Classes and Interfaces 1916 */ 1917 STRONG(STRONG_LOADER_LINK); 1918 1919 /* the flag value is used by VM at define class time */ 1920 private final int flag; 1921 ClassOption(int flag) { 1922 this.flag = flag; 1923 } 1924 1925 static int optionsToFlag(Set<ClassOption> options) { 1926 int flags = 0; 1927 for (ClassOption cp : options) { 1928 flags |= cp.flag; 1929 } 1930 return flags; 1931 } 1932 } 1933 1934 /** 1935 * Creates a <em>hidden</em> class or interface from {@code bytes}, 1936 * returning a {@code Lookup} on the newly created class or interface. 1937 * 1938 * <p> Ordinarily, a class or interface {@code C} is created by a class loader, 1939 * which either defines {@code C} directly or delegates to another class loader. 1940 * A class loader defines {@code C} directly by invoking 1941 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain) 1942 * ClassLoader::defineClass}, which causes the Java Virtual Machine 1943 * to derive {@code C} from a purported representation in {@code class} file format. 1944 * In situations where use of a class loader is undesirable, a class or interface 1945 * {@code C} can be created by this method instead. This method is capable of 1946 * defining {@code C}, and thereby creating it, without invoking 1947 * {@code ClassLoader::defineClass}. 1948 * Instead, this method defines {@code C} as if by arranging for 1949 * the Java Virtual Machine to derive a nonarray class or interface {@code C} 1950 * from a purported representation in {@code class} file format 1951 * using the following rules: 1952 * 1953 * <ol> 1954 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup} 1955 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access. 1956 * This level of access is needed to create {@code C} in the module 1957 * of the lookup class of this {@code Lookup}.</li> 1958 * 1959 * <li> The purported representation in {@code bytes} must be a {@code ClassFile} 1960 * structure (JVMS {@jvms 4.1}) of a supported major and minor version. 1961 * The major and minor version may differ from the {@code class} file version 1962 * of the lookup class of this {@code Lookup}.</li> 1963 * 1964 * <li> The value of {@code this_class} must be a valid index in the 1965 * {@code constant_pool} table, and the entry at that index must be a valid 1966 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name 1967 * encoded in internal form that is specified by this structure. {@code N} must 1968 * denote a class or interface in the same package as the lookup class.</li> 1969 * 1970 * <li> Let {@code CN} be the string {@code N + "." + <suffix>}, 1971 * where {@code <suffix>} is an unqualified name. 1972 * 1973 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by 1974 * {@code bytes} with an additional entry in the {@code constant_pool} table, 1975 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and 1976 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class} 1977 * refers to the new {@code CONSTANT_Utf8_info} structure. 1978 * 1979 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}. 1980 * 1981 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and 1982 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5}, 1983 * with the following adjustments: 1984 * <ul> 1985 * <li> The constant indicated by {@code this_class} is permitted to specify a name 1986 * that includes a single {@code "."} character, even though this is not a valid 1987 * binary class or interface name in internal form.</li> 1988 * 1989 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C}, 1990 * but no class loader is recorded as an initiating class loader of {@code C}.</li> 1991 * 1992 * <li> {@code C} is considered to have the same runtime 1993 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module} 1994 * and {@linkplain java.security.ProtectionDomain protection domain} 1995 * as the lookup class of this {@code Lookup}. 1996 * <li> Let {@code GN} be the binary name obtained by taking {@code N} 1997 * (a binary name encoded in internal form) and replacing ASCII forward slashes with 1998 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}: 1999 * <ul> 2000 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>}, 2001 * even though this is not a valid binary class or interface name.</li> 2002 * <li> {@link Class#descriptorString()} returns the string 2003 * {@code "L" + N + "." + <suffix> + ";"}, 2004 * even though this is not a valid type descriptor name.</li> 2005 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C} 2006 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li> 2007 * </ul> 2008 * </ul> 2009 * </li> 2010 * </ol> 2011 * 2012 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine. 2013 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments: 2014 * <ul> 2015 * <li> During verification, whenever it is necessary to load the class named 2016 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is 2017 * made of any class loader.</li> 2018 * 2019 * <li> On any attempt to resolve the entry in the run-time constant pool indicated 2020 * by {@code this_class}, the symbolic reference is considered to be resolved to 2021 * {@code C} and resolution always succeeds immediately.</li> 2022 * </ul> 2023 * 2024 * <p> If the {@code initialize} parameter is {@code true}, 2025 * then {@code C} is initialized by the Java Virtual Machine. 2026 * 2027 * <p> The newly created class or interface {@code C} serves as the 2028 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object 2029 * returned by this method. {@code C} is <em>hidden</em> in the sense that 2030 * no other class or interface can refer to {@code C} via a constant pool entry. 2031 * That is, a hidden class or interface cannot be named as a supertype, a field type, 2032 * a method parameter type, or a method return type by any other class. 2033 * This is because a hidden class or interface does not have a binary name, so 2034 * there is no internal form available to record in any class's constant pool. 2035 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)}, 2036 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and 2037 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class) 2038 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html"> 2039 * JVM Tool Interface</a>. 2040 * 2041 * <p> A class or interface created by 2042 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain) 2043 * a class loader} has a strong relationship with that class loader. 2044 * That is, every {@code Class} object contains a reference to the {@code ClassLoader} 2045 * that {@linkplain Class#getClassLoader() defined it}. 2046 * This means that a class created by a class loader may be unloaded if and 2047 * only if its defining loader is not reachable and thus may be reclaimed 2048 * by a garbage collector (JLS {@jls 12.7}). 2049 * 2050 * By default, however, a hidden class or interface may be unloaded even if 2051 * the class loader that is marked as its defining loader is 2052 * <a href="../ref/package-summary.html#reachability">reachable</a>. 2053 * This behavior is useful when a hidden class or interface serves multiple 2054 * classes defined by arbitrary class loaders. In other cases, a hidden 2055 * class or interface may be linked to a single class (or a small number of classes) 2056 * with the same defining loader as the hidden class or interface. 2057 * In such cases, where the hidden class or interface must be coterminous 2058 * with a normal class or interface, the {@link ClassOption#STRONG STRONG} 2059 * option may be passed in {@code options}. 2060 * This arranges for a hidden class to have the same strong relationship 2061 * with the class loader marked as its defining loader, 2062 * as a normal class or interface has with its own defining loader. 2063 * 2064 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass} 2065 * may still prevent a hidden class or interface from being 2066 * unloaded by ensuring that the {@code Class} object is reachable. 2067 * 2068 * <p> The unloading characteristics are set for each hidden class when it is 2069 * defined, and cannot be changed later. An advantage of allowing hidden classes 2070 * to be unloaded independently of the class loader marked as their defining loader 2071 * is that a very large number of hidden classes may be created by an application. 2072 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory, 2073 * just as if normal classes were created by class loaders. 2074 * 2075 * <p> Classes and interfaces in a nest are allowed to have mutual access to 2076 * their private members. The nest relationship is determined by 2077 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and 2078 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file. 2079 * By default, a hidden class belongs to a nest consisting only of itself 2080 * because a hidden class has no binary name. 2081 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options} 2082 * to create a hidden class or interface {@code C} as a member of a nest. 2083 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute 2084 * in the {@code ClassFile} structure from which {@code C} was derived. 2085 * Instead, the following rules determine the nest host of {@code C}: 2086 * <ul> 2087 * <li>If the nest host of the lookup class of this {@code Lookup} has previously 2088 * been determined, then let {@code H} be the nest host of the lookup class. 2089 * Otherwise, the nest host of the lookup class is determined using the 2090 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li> 2091 * <li>The nest host of {@code C} is determined to be {@code H}, 2092 * the nest host of the lookup class.</li> 2093 * </ul> 2094 * 2095 * <p> A hidden class or interface may be serializable, but this requires a custom 2096 * serialization mechanism in order to ensure that instances are properly serialized 2097 * and deserialized. The default serialization mechanism supports only classes and 2098 * interfaces that are discoverable by their class name. 2099 * 2100 * @param bytes the bytes that make up the class data, 2101 * in the format of a valid {@code class} file as defined by 2102 * <cite>The Java Virtual Machine Specification</cite>. 2103 * @param initialize if {@code true} the class will be initialized. 2104 * @param options {@linkplain ClassOption class options} 2105 * @return the {@code Lookup} object on the hidden class, 2106 * with {@linkplain #ORIGINAL original} and 2107 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access 2108 * 2109 * @throws IllegalAccessException if this {@code Lookup} does not have 2110 * {@linkplain #hasFullPrivilegeAccess() full privilege} access 2111 * @throws SecurityException if a security manager is present and it 2112 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2113 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 2114 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version 2115 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 2116 * than the lookup class or {@code bytes} is not a class or interface 2117 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 2118 * @throws IncompatibleClassChangeError if the class or interface named as 2119 * the direct superclass of {@code C} is in fact an interface, or if any of the classes 2120 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces 2121 * @throws ClassCircularityError if any of the superclasses or superinterfaces of 2122 * {@code C} is {@code C} itself 2123 * @throws VerifyError if the newly created class cannot be verified 2124 * @throws LinkageError if the newly created class cannot be linked for any other reason 2125 * @throws NullPointerException if any parameter is {@code null} 2126 * 2127 * @since 15 2128 * @see Class#isHidden() 2129 * @jvms 4.2.1 Binary Class and Interface Names 2130 * @jvms 4.2.2 Unqualified Names 2131 * @jvms 4.7.28 The {@code NestHost} Attribute 2132 * @jvms 4.7.29 The {@code NestMembers} Attribute 2133 * @jvms 5.4.3.1 Class and Interface Resolution 2134 * @jvms 5.4.4 Access Control 2135 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation 2136 * @jvms 5.4 Linking 2137 * @jvms 5.5 Initialization 2138 * @jls 12.7 Unloading of Classes and Interfaces 2139 */ 2140 @SuppressWarnings("doclint:reference") // cross-module links 2141 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options) 2142 throws IllegalAccessException 2143 { 2144 Objects.requireNonNull(bytes); 2145 Objects.requireNonNull(options); 2146 2147 ensureDefineClassPermission(); 2148 if (!hasFullPrivilegeAccess()) { 2149 throw new IllegalAccessException(this + " does not have full privilege access"); 2150 } 2151 2152 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize); 2153 } 2154 2155 /** 2156 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated 2157 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data}, 2158 * returning a {@code Lookup} on the newly created class or interface. 2159 * 2160 * <p> This method is equivalent to calling 2161 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)} 2162 * as if the hidden class is injected with a private static final <i>unnamed</i> 2163 * field which is initialized with the given {@code classData} at 2164 * the first instruction of the class initializer. 2165 * The newly created class is linked by the Java Virtual Machine. 2166 * 2167 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData} 2168 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt} 2169 * methods can be used to retrieve the {@code classData}. 2170 * 2171 * @apiNote 2172 * A framework can create a hidden class with class data with one or more 2173 * objects and load the class data as dynamically-computed constant(s) 2174 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class) 2175 * Class data} is accessible only to the lookup object created by the newly 2176 * defined hidden class but inaccessible to other members in the same nest 2177 * (unlike private static fields that are accessible to nestmates). 2178 * Care should be taken w.r.t. mutability for example when passing 2179 * an array or other mutable structure through the class data. 2180 * Changing any value stored in the class data at runtime may lead to 2181 * unpredictable behavior. 2182 * If the class data is a {@code List}, it is good practice to make it 2183 * unmodifiable for example via {@link List#of List::of}. 2184 * 2185 * @param bytes the class bytes 2186 * @param classData pre-initialized class data 2187 * @param initialize if {@code true} the class will be initialized. 2188 * @param options {@linkplain ClassOption class options} 2189 * @return the {@code Lookup} object on the hidden class, 2190 * with {@linkplain #ORIGINAL original} and 2191 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access 2192 * 2193 * @throws IllegalAccessException if this {@code Lookup} does not have 2194 * {@linkplain #hasFullPrivilegeAccess() full privilege} access 2195 * @throws SecurityException if a security manager is present and it 2196 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2197 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 2198 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version 2199 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 2200 * than the lookup class or {@code bytes} is not a class or interface 2201 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 2202 * @throws IncompatibleClassChangeError if the class or interface named as 2203 * the direct superclass of {@code C} is in fact an interface, or if any of the classes 2204 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces 2205 * @throws ClassCircularityError if any of the superclasses or superinterfaces of 2206 * {@code C} is {@code C} itself 2207 * @throws VerifyError if the newly created class cannot be verified 2208 * @throws LinkageError if the newly created class cannot be linked for any other reason 2209 * @throws NullPointerException if any parameter is {@code null} 2210 * 2211 * @since 16 2212 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...) 2213 * @see Class#isHidden() 2214 * @see MethodHandles#classData(Lookup, String, Class) 2215 * @see MethodHandles#classDataAt(Lookup, String, Class, int) 2216 * @jvms 4.2.1 Binary Class and Interface Names 2217 * @jvms 4.2.2 Unqualified Names 2218 * @jvms 4.7.28 The {@code NestHost} Attribute 2219 * @jvms 4.7.29 The {@code NestMembers} Attribute 2220 * @jvms 5.4.3.1 Class and Interface Resolution 2221 * @jvms 5.4.4 Access Control 2222 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation 2223 * @jvms 5.4 Linking 2224 * @jvms 5.5 Initialization 2225 * @jls 12.7 Unloading of Classes and Interface 2226 */ 2227 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options) 2228 throws IllegalAccessException 2229 { 2230 Objects.requireNonNull(bytes); 2231 Objects.requireNonNull(classData); 2232 Objects.requireNonNull(options); 2233 2234 ensureDefineClassPermission(); 2235 if (!hasFullPrivilegeAccess()) { 2236 throw new IllegalAccessException(this + " does not have full privilege access"); 2237 } 2238 2239 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false) 2240 .defineClassAsLookup(initialize, classData); 2241 } 2242 2243 // A default dumper for writing class files passed to Lookup::defineClass 2244 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable, 2245 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or 2246 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true 2247 // 2248 // This default dumper does not dump hidden classes defined by LambdaMetafactory 2249 // and LambdaForms and method handle internals. They are dumped via 2250 // different ClassFileDumpers. 2251 private static ClassFileDumper defaultDumper() { 2252 return DEFAULT_DUMPER; 2253 } 2254 2255 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance( 2256 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES"); 2257 2258 static class ClassFile { 2259 final String name; // internal name 2260 final int accessFlags; 2261 final byte[] bytes; 2262 ClassFile(String name, int accessFlags, byte[] bytes) { 2263 this.name = name; 2264 this.accessFlags = accessFlags; 2265 this.bytes = bytes; 2266 } 2267 2268 static ClassFile newInstanceNoCheck(String name, byte[] bytes) { 2269 return new ClassFile(name, 0, bytes); 2270 } 2271 2272 /** 2273 * This method checks the class file version and the structure of `this_class`. 2274 * and checks if the bytes is a class or interface (ACC_MODULE flag not set) 2275 * that is in the named package. 2276 * 2277 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags 2278 * or the class is not in the given package name. 2279 */ 2280 static ClassFile newInstance(byte[] bytes, String pkgName) { 2281 var cf = readClassFile(bytes); 2282 2283 // check if it's in the named package 2284 int index = cf.name.lastIndexOf('/'); 2285 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.'); 2286 if (!pn.equals(pkgName)) { 2287 throw newIllegalArgumentException(cf.name + " not in same package as lookup class"); 2288 } 2289 return cf; 2290 } 2291 2292 private static ClassFile readClassFile(byte[] bytes) { 2293 int magic = readInt(bytes, 0); 2294 if (magic != 0xCAFEBABE) { 2295 throw new ClassFormatError("Incompatible magic value: " + magic); 2296 } 2297 int minor = readUnsignedShort(bytes, 4); 2298 int major = readUnsignedShort(bytes, 6); 2299 if (!VM.isSupportedClassFileVersion(major, minor)) { 2300 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor); 2301 } 2302 2303 String name; 2304 int accessFlags; 2305 try { 2306 ClassReader reader = new ClassReader(bytes); 2307 // ClassReader does not check if `this_class` is CONSTANT_Class_info 2308 // workaround to read `this_class` using readConst and validate the value 2309 int thisClass = reader.readUnsignedShort(reader.header + 2); 2310 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]); 2311 if (!(constant instanceof Type type)) { 2312 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info"); 2313 } 2314 if (!type.getDescriptor().startsWith("L")) { 2315 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info"); 2316 } 2317 name = type.getInternalName(); 2318 accessFlags = reader.readUnsignedShort(reader.header); 2319 } catch (RuntimeException e) { 2320 // ASM exceptions are poorly specified 2321 ClassFormatError cfe = new ClassFormatError(); 2322 cfe.initCause(e); 2323 throw cfe; 2324 } 2325 // must be a class or interface 2326 if ((accessFlags & Opcodes.ACC_MODULE) != 0) { 2327 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set"); 2328 } 2329 return new ClassFile(name, accessFlags, bytes); 2330 } 2331 2332 private static int readInt(byte[] bytes, int offset) { 2333 if ((offset+4) > bytes.length) { 2334 throw new ClassFormatError("Invalid ClassFile structure"); 2335 } 2336 return ((bytes[offset] & 0xFF) << 24) 2337 | ((bytes[offset + 1] & 0xFF) << 16) 2338 | ((bytes[offset + 2] & 0xFF) << 8) 2339 | (bytes[offset + 3] & 0xFF); 2340 } 2341 2342 private static int readUnsignedShort(byte[] bytes, int offset) { 2343 if ((offset+2) > bytes.length) { 2344 throw new ClassFormatError("Invalid ClassFile structure"); 2345 } 2346 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF); 2347 } 2348 } 2349 2350 /* 2351 * Returns a ClassDefiner that creates a {@code Class} object of a normal class 2352 * from the given bytes. 2353 * 2354 * Caller should make a defensive copy of the arguments if needed 2355 * before calling this factory method. 2356 * 2357 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2358 * {@code bytes} denotes a class in a different package than the lookup class 2359 */ 2360 private ClassDefiner makeClassDefiner(byte[] bytes) { 2361 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2362 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper()); 2363 } 2364 2365 /** 2366 * Returns a ClassDefiner that creates a {@code Class} object of a normal class 2367 * from the given bytes. No package name check on the given bytes. 2368 * 2369 * @param name internal name 2370 * @param bytes class bytes 2371 * @param dumper dumper to write the given bytes to the dumper's output directory 2372 * @return ClassDefiner that defines a normal class of the given bytes. 2373 */ 2374 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) { 2375 // skip package name validation 2376 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes); 2377 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper); 2378 } 2379 2380 /** 2381 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2382 * from the given bytes. The name must be in the same package as the lookup class. 2383 * 2384 * Caller should make a defensive copy of the arguments if needed 2385 * before calling this factory method. 2386 * 2387 * @param bytes class bytes 2388 * @param dumper dumper to write the given bytes to the dumper's output directory 2389 * @return ClassDefiner that defines a hidden class of the given bytes. 2390 * 2391 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2392 * {@code bytes} denotes a class in a different package than the lookup class 2393 */ 2394 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) { 2395 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2396 return makeHiddenClassDefiner(cf, Set.of(), false, dumper); 2397 } 2398 2399 /** 2400 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2401 * from the given bytes and options. 2402 * The name must be in the same package as the lookup class. 2403 * 2404 * Caller should make a defensive copy of the arguments if needed 2405 * before calling this factory method. 2406 * 2407 * @param bytes class bytes 2408 * @param options class options 2409 * @param accessVmAnnotations true to give the hidden class access to VM annotations 2410 * @return ClassDefiner that defines a hidden class of the given bytes and options 2411 * 2412 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2413 * {@code bytes} denotes a class in a different package than the lookup class 2414 */ 2415 private ClassDefiner makeHiddenClassDefiner(byte[] bytes, 2416 Set<ClassOption> options, 2417 boolean accessVmAnnotations) { 2418 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2419 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper()); 2420 } 2421 2422 /** 2423 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2424 * from the given bytes and the given options. No package name check on the given bytes. 2425 * 2426 * @param name internal name that specifies the prefix of the hidden class 2427 * @param bytes class bytes 2428 * @param options class options 2429 * @param dumper dumper to write the given bytes to the dumper's output directory 2430 * @return ClassDefiner that defines a hidden class of the given bytes and options. 2431 */ 2432 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) { 2433 Objects.requireNonNull(dumper); 2434 // skip name and access flags validation 2435 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper); 2436 } 2437 2438 /** 2439 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2440 * from the given class file and options. 2441 * 2442 * @param cf ClassFile 2443 * @param options class options 2444 * @param accessVmAnnotations true to give the hidden class access to VM annotations 2445 * @param dumper dumper to write the given bytes to the dumper's output directory 2446 */ 2447 private ClassDefiner makeHiddenClassDefiner(ClassFile cf, 2448 Set<ClassOption> options, 2449 boolean accessVmAnnotations, 2450 ClassFileDumper dumper) { 2451 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options); 2452 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) { 2453 // jdk.internal.vm.annotations are permitted for classes 2454 // defined to boot loader and platform loader 2455 flags |= ACCESS_VM_ANNOTATIONS; 2456 } 2457 2458 return new ClassDefiner(this, cf, flags, dumper); 2459 } 2460 2461 static class ClassDefiner { 2462 private final Lookup lookup; 2463 private final String name; // internal name 2464 private final byte[] bytes; 2465 private final int classFlags; 2466 private final ClassFileDumper dumper; 2467 2468 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) { 2469 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK); 2470 this.lookup = lookup; 2471 this.bytes = cf.bytes; 2472 this.name = cf.name; 2473 this.classFlags = flags; 2474 this.dumper = dumper; 2475 } 2476 2477 String internalName() { 2478 return name; 2479 } 2480 2481 Class<?> defineClass(boolean initialize) { 2482 return defineClass(initialize, null); 2483 } 2484 2485 Lookup defineClassAsLookup(boolean initialize) { 2486 Class<?> c = defineClass(initialize, null); 2487 return new Lookup(c, null, FULL_POWER_MODES); 2488 } 2489 2490 /** 2491 * Defines the class of the given bytes and the given classData. 2492 * If {@code initialize} parameter is true, then the class will be initialized. 2493 * 2494 * @param initialize true if the class to be initialized 2495 * @param classData classData or null 2496 * @return the class 2497 * 2498 * @throws LinkageError linkage error 2499 */ 2500 Class<?> defineClass(boolean initialize, Object classData) { 2501 Class<?> lookupClass = lookup.lookupClass(); 2502 ClassLoader loader = lookupClass.getClassLoader(); 2503 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null; 2504 Class<?> c = null; 2505 try { 2506 c = SharedSecrets.getJavaLangAccess() 2507 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData); 2508 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost(); 2509 return c; 2510 } finally { 2511 // dump the classfile for debugging 2512 if (dumper.isEnabled()) { 2513 String name = internalName(); 2514 if (c != null) { 2515 dumper.dumpClass(name, c, bytes); 2516 } else { 2517 dumper.dumpFailedClass(name, bytes); 2518 } 2519 } 2520 } 2521 } 2522 2523 /** 2524 * Defines the class of the given bytes and the given classData. 2525 * If {@code initialize} parameter is true, then the class will be initialized. 2526 * 2527 * @param initialize true if the class to be initialized 2528 * @param classData classData or null 2529 * @return a Lookup for the defined class 2530 * 2531 * @throws LinkageError linkage error 2532 */ 2533 Lookup defineClassAsLookup(boolean initialize, Object classData) { 2534 Class<?> c = defineClass(initialize, classData); 2535 return new Lookup(c, null, FULL_POWER_MODES); 2536 } 2537 2538 private boolean isNestmate() { 2539 return (classFlags & NESTMATE_CLASS) != 0; 2540 } 2541 } 2542 2543 private ProtectionDomain lookupClassProtectionDomain() { 2544 ProtectionDomain pd = cachedProtectionDomain; 2545 if (pd == null) { 2546 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass); 2547 } 2548 return pd; 2549 } 2550 2551 // cached protection domain 2552 private volatile ProtectionDomain cachedProtectionDomain; 2553 2554 // Make sure outer class is initialized first. 2555 static { IMPL_NAMES.getClass(); } 2556 2557 /** Package-private version of lookup which is trusted. */ 2558 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED); 2559 2560 /** Version of lookup which is trusted minimally. 2561 * It can only be used to create method handles to publicly accessible 2562 * members in packages that are exported unconditionally. 2563 */ 2564 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL); 2565 2566 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) { 2567 String name = lookupClass.getName(); 2568 if (name.startsWith("java.lang.invoke.")) 2569 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass); 2570 } 2571 2572 /** 2573 * Displays the name of the class from which lookups are to be made, 2574 * followed by "/" and the name of the {@linkplain #previousLookupClass() 2575 * previous lookup class} if present. 2576 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.) 2577 * If there are restrictions on the access permitted to this lookup, 2578 * this is indicated by adding a suffix to the class name, consisting 2579 * of a slash and a keyword. The keyword represents the strongest 2580 * allowed access, and is chosen as follows: 2581 * <ul> 2582 * <li>If no access is allowed, the suffix is "/noaccess". 2583 * <li>If only unconditional access is allowed, the suffix is "/publicLookup". 2584 * <li>If only public access to types in exported packages is allowed, the suffix is "/public". 2585 * <li>If only public and module access are allowed, the suffix is "/module". 2586 * <li>If public and package access are allowed, the suffix is "/package". 2587 * <li>If public, package, and private access are allowed, the suffix is "/private". 2588 * </ul> 2589 * If none of the above cases apply, it is the case that 2590 * {@linkplain #hasFullPrivilegeAccess() full privilege access} 2591 * (public, module, package, private, and protected) is allowed. 2592 * In this case, no suffix is added. 2593 * This is true only of an object obtained originally from 2594 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}. 2595 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in} 2596 * always have restricted access, and will display a suffix. 2597 * <p> 2598 * (It may seem strange that protected access should be 2599 * stronger than private access. Viewed independently from 2600 * package access, protected access is the first to be lost, 2601 * because it requires a direct subclass relationship between 2602 * caller and callee.) 2603 * @see #in 2604 * 2605 * @revised 9 2606 */ 2607 @Override 2608 public String toString() { 2609 String cname = lookupClass.getName(); 2610 if (prevLookupClass != null) 2611 cname += "/" + prevLookupClass.getName(); 2612 switch (allowedModes) { 2613 case 0: // no privileges 2614 return cname + "/noaccess"; 2615 case UNCONDITIONAL: 2616 return cname + "/publicLookup"; 2617 case PUBLIC: 2618 return cname + "/public"; 2619 case PUBLIC|MODULE: 2620 return cname + "/module"; 2621 case PUBLIC|PACKAGE: 2622 case PUBLIC|MODULE|PACKAGE: 2623 return cname + "/package"; 2624 case PUBLIC|PACKAGE|PRIVATE: 2625 case PUBLIC|MODULE|PACKAGE|PRIVATE: 2626 return cname + "/private"; 2627 case PUBLIC|PACKAGE|PRIVATE|PROTECTED: 2628 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED: 2629 case FULL_POWER_MODES: 2630 return cname; 2631 case TRUSTED: 2632 return "/trusted"; // internal only; not exported 2633 default: // Should not happen, but it's a bitfield... 2634 cname = cname + "/" + Integer.toHexString(allowedModes); 2635 assert(false) : cname; 2636 return cname; 2637 } 2638 } 2639 2640 /** 2641 * Produces a method handle for a static method. 2642 * The type of the method handle will be that of the method. 2643 * (Since static methods do not take receivers, there is no 2644 * additional receiver argument inserted into the method handle type, 2645 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) 2646 * The method and all its argument types must be accessible to the lookup object. 2647 * <p> 2648 * The returned method handle will have 2649 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2650 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2651 * <p> 2652 * If the returned method handle is invoked, the method's class will 2653 * be initialized, if it has not already been initialized. 2654 * <p><b>Example:</b> 2655 * {@snippet lang="java" : 2656 import static java.lang.invoke.MethodHandles.*; 2657 import static java.lang.invoke.MethodType.*; 2658 ... 2659 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class, 2660 "asList", methodType(List.class, Object[].class)); 2661 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString()); 2662 * } 2663 * @param refc the class from which the method is accessed 2664 * @param name the name of the method 2665 * @param type the type of the method 2666 * @return the desired method handle 2667 * @throws NoSuchMethodException if the method does not exist 2668 * @throws IllegalAccessException if access checking fails, 2669 * or if the method is not {@code static}, 2670 * or if the method's variable arity modifier bit 2671 * is set and {@code asVarargsCollector} fails 2672 * @throws SecurityException if a security manager is present and it 2673 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2674 * @throws NullPointerException if any argument is null 2675 */ 2676 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2677 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type); 2678 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method)); 2679 } 2680 2681 /** 2682 * Produces a method handle for a virtual method. 2683 * The type of the method handle will be that of the method, 2684 * with the receiver type (usually {@code refc}) prepended. 2685 * The method and all its argument types must be accessible to the lookup object. 2686 * <p> 2687 * When called, the handle will treat the first argument as a receiver 2688 * and, for non-private methods, dispatch on the receiver's type to determine which method 2689 * implementation to enter. 2690 * For private methods the named method in {@code refc} will be invoked on the receiver. 2691 * (The dispatching action is identical with that performed by an 2692 * {@code invokevirtual} or {@code invokeinterface} instruction.) 2693 * <p> 2694 * The first argument will be of type {@code refc} if the lookup 2695 * class has full privileges to access the member. Otherwise 2696 * the member must be {@code protected} and the first argument 2697 * will be restricted in type to the lookup class. 2698 * <p> 2699 * The returned method handle will have 2700 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2701 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2702 * <p> 2703 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual} 2704 * instructions and method handles produced by {@code findVirtual}, 2705 * if the class is {@code MethodHandle} and the name string is 2706 * {@code invokeExact} or {@code invoke}, the resulting 2707 * method handle is equivalent to one produced by 2708 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or 2709 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} 2710 * with the same {@code type} argument. 2711 * <p> 2712 * If the class is {@code VarHandle} and the name string corresponds to 2713 * the name of a signature-polymorphic access mode method, the resulting 2714 * method handle is equivalent to one produced by 2715 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with 2716 * the access mode corresponding to the name string and with the same 2717 * {@code type} arguments. 2718 * <p> 2719 * <b>Example:</b> 2720 * {@snippet lang="java" : 2721 import static java.lang.invoke.MethodHandles.*; 2722 import static java.lang.invoke.MethodType.*; 2723 ... 2724 MethodHandle MH_concat = publicLookup().findVirtual(String.class, 2725 "concat", methodType(String.class, String.class)); 2726 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class, 2727 "hashCode", methodType(int.class)); 2728 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class, 2729 "hashCode", methodType(int.class)); 2730 assertEquals("xy", (String) MH_concat.invokeExact("x", "y")); 2731 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy")); 2732 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy")); 2733 // interface method: 2734 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class, 2735 "subSequence", methodType(CharSequence.class, int.class, int.class)); 2736 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString()); 2737 // constructor "internal method" must be accessed differently: 2738 MethodType MT_newString = methodType(void.class); //()V for new String() 2739 try { assertEquals("impossible", lookup() 2740 .findVirtual(String.class, "<init>", MT_newString)); 2741 } catch (NoSuchMethodException ex) { } // OK 2742 MethodHandle MH_newString = publicLookup() 2743 .findConstructor(String.class, MT_newString); 2744 assertEquals("", (String) MH_newString.invokeExact()); 2745 * } 2746 * 2747 * @param refc the class or interface from which the method is accessed 2748 * @param name the name of the method 2749 * @param type the type of the method, with the receiver argument omitted 2750 * @return the desired method handle 2751 * @throws NoSuchMethodException if the method does not exist 2752 * @throws IllegalAccessException if access checking fails, 2753 * or if the method is {@code static}, 2754 * or if the method's variable arity modifier bit 2755 * is set and {@code asVarargsCollector} fails 2756 * @throws SecurityException if a security manager is present and it 2757 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2758 * @throws NullPointerException if any argument is null 2759 */ 2760 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2761 if (refc == MethodHandle.class) { 2762 MethodHandle mh = findVirtualForMH(name, type); 2763 if (mh != null) return mh; 2764 } else if (refc == VarHandle.class) { 2765 MethodHandle mh = findVirtualForVH(name, type); 2766 if (mh != null) return mh; 2767 } 2768 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual); 2769 MemberName method = resolveOrFail(refKind, refc, name, type); 2770 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method)); 2771 } 2772 private MethodHandle findVirtualForMH(String name, MethodType type) { 2773 // these names require special lookups because of the implicit MethodType argument 2774 if ("invoke".equals(name)) 2775 return invoker(type); 2776 if ("invokeExact".equals(name)) 2777 return exactInvoker(type); 2778 assert(!MemberName.isMethodHandleInvokeName(name)); 2779 return null; 2780 } 2781 private MethodHandle findVirtualForVH(String name, MethodType type) { 2782 try { 2783 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type); 2784 } catch (IllegalArgumentException e) { 2785 return null; 2786 } 2787 } 2788 2789 /** 2790 * Produces a method handle which creates an object and initializes it, using 2791 * the constructor of the specified type. 2792 * The parameter types of the method handle will be those of the constructor, 2793 * while the return type will be a reference to the constructor's class. 2794 * The constructor and all its argument types must be accessible to the lookup object. 2795 * <p> 2796 * The requested type must have a return type of {@code void}. 2797 * (This is consistent with the JVM's treatment of constructor type descriptors.) 2798 * <p> 2799 * The returned method handle will have 2800 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2801 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 2802 * <p> 2803 * If the returned method handle is invoked, the constructor's class will 2804 * be initialized, if it has not already been initialized. 2805 * <p><b>Example:</b> 2806 * {@snippet lang="java" : 2807 import static java.lang.invoke.MethodHandles.*; 2808 import static java.lang.invoke.MethodType.*; 2809 ... 2810 MethodHandle MH_newArrayList = publicLookup().findConstructor( 2811 ArrayList.class, methodType(void.class, Collection.class)); 2812 Collection orig = Arrays.asList("x", "y"); 2813 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig); 2814 assert(orig != copy); 2815 assertEquals(orig, copy); 2816 // a variable-arity constructor: 2817 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor( 2818 ProcessBuilder.class, methodType(void.class, String[].class)); 2819 ProcessBuilder pb = (ProcessBuilder) 2820 MH_newProcessBuilder.invoke("x", "y", "z"); 2821 assertEquals("[x, y, z]", pb.command().toString()); 2822 * } 2823 * 2824 * 2825 * @param refc the class or interface from which the method is accessed 2826 * @param type the type of the method, with the receiver argument omitted, and a void return type 2827 * @return the desired method handle 2828 * @throws NoSuchMethodException if the constructor does not exist 2829 * @throws IllegalAccessException if access checking fails 2830 * or if the method's variable arity modifier bit 2831 * is set and {@code asVarargsCollector} fails 2832 * @throws SecurityException if a security manager is present and it 2833 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2834 * @throws NullPointerException if any argument is null 2835 */ 2836 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2837 if (refc.isArray()) { 2838 throw new NoSuchMethodException("no constructor for array class: " + refc.getName()); 2839 } 2840 if (type.returnType() != void.class) { 2841 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName()); 2842 } 2843 String name = ConstantDescs.INIT_NAME; 2844 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type); 2845 return getDirectConstructor(refc, ctor); 2846 } 2847 2848 /** 2849 * Looks up a class by name from the lookup context defined by this {@code Lookup} object, 2850 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction. 2851 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class, 2852 * and then determines whether the class is accessible to this lookup object. 2853 * <p> 2854 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}. 2855 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences 2856 * of {@code '['} and followed by the element type as encoded in the 2857 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}. 2858 * <p> 2859 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, 2860 * its class loader, and the {@linkplain #lookupModes() lookup modes}. 2861 * 2862 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class 2863 * or the string representing an array class 2864 * @return the requested class. 2865 * @throws SecurityException if a security manager is present and it 2866 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2867 * @throws LinkageError if the linkage fails 2868 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader. 2869 * @throws IllegalAccessException if the class is not accessible, using the allowed access 2870 * modes. 2871 * @throws NullPointerException if {@code targetName} is null 2872 * @since 9 2873 * @jvms 5.4.3.1 Class and Interface Resolution 2874 */ 2875 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException { 2876 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader()); 2877 return accessClass(targetClass); 2878 } 2879 2880 /** 2881 * Ensures that {@code targetClass} has been initialized. The class 2882 * to be initialized must be {@linkplain #accessClass accessible} 2883 * to this {@code Lookup} object. This method causes {@code targetClass} 2884 * to be initialized if it has not been already initialized, 2885 * as specified in JVMS {@jvms 5.5}. 2886 * 2887 * <p> 2888 * This method returns when {@code targetClass} is fully initialized, or 2889 * when {@code targetClass} is being initialized by the current thread. 2890 * 2891 * @param <T> the type of the class to be initialized 2892 * @param targetClass the class to be initialized 2893 * @return {@code targetClass} that has been initialized, or that is being 2894 * initialized by the current thread. 2895 * 2896 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void} 2897 * or array class 2898 * @throws IllegalAccessException if {@code targetClass} is not 2899 * {@linkplain #accessClass accessible} to this lookup 2900 * @throws ExceptionInInitializerError if the class initialization provoked 2901 * by this method fails 2902 * @throws SecurityException if a security manager is present and it 2903 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2904 * @since 15 2905 * @jvms 5.5 Initialization 2906 */ 2907 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException { 2908 if (targetClass.isPrimitive()) 2909 throw new IllegalArgumentException(targetClass + " is a primitive class"); 2910 if (targetClass.isArray()) 2911 throw new IllegalArgumentException(targetClass + " is an array class"); 2912 2913 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) { 2914 throw makeAccessException(targetClass); 2915 } 2916 checkSecurityManager(targetClass); 2917 2918 // ensure class initialization 2919 Unsafe.getUnsafe().ensureClassInitialized(targetClass); 2920 return targetClass; 2921 } 2922 2923 /* 2924 * Returns IllegalAccessException due to access violation to the given targetClass. 2925 * 2926 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized} 2927 * which verifies access to a class rather a member. 2928 */ 2929 private IllegalAccessException makeAccessException(Class<?> targetClass) { 2930 String message = "access violation: "+ targetClass; 2931 if (this == MethodHandles.publicLookup()) { 2932 message += ", from public Lookup"; 2933 } else { 2934 Module m = lookupClass().getModule(); 2935 message += ", from " + lookupClass() + " (" + m + ")"; 2936 if (prevLookupClass != null) { 2937 message += ", previous lookup " + 2938 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")"; 2939 } 2940 } 2941 return new IllegalAccessException(message); 2942 } 2943 2944 /** 2945 * Determines if a class can be accessed from the lookup context defined by 2946 * this {@code Lookup} object. The static initializer of the class is not run. 2947 * If {@code targetClass} is an array class, {@code targetClass} is accessible 2948 * if the element type of the array class is accessible. Otherwise, 2949 * {@code targetClass} is determined as accessible as follows. 2950 * 2951 * <p> 2952 * If {@code targetClass} is in the same module as the lookup class, 2953 * the lookup class is {@code LC} in module {@code M1} and 2954 * the previous lookup class is in module {@code M0} or 2955 * {@code null} if not present, 2956 * {@code targetClass} is accessible if and only if one of the following is true: 2957 * <ul> 2958 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is 2959 * {@code LC} or other class in the same nest of {@code LC}.</li> 2960 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is 2961 * in the same runtime package of {@code LC}.</li> 2962 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is 2963 * a public type in {@code M1}.</li> 2964 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is 2965 * a public type in a package exported by {@code M1} to at least {@code M0} 2966 * if the previous lookup class is present; otherwise, {@code targetClass} 2967 * is a public type in a package exported by {@code M1} unconditionally.</li> 2968 * </ul> 2969 * 2970 * <p> 2971 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup 2972 * can access public types in all modules when the type is in a package 2973 * that is exported unconditionally. 2974 * <p> 2975 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass}, 2976 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass} 2977 * is inaccessible. 2978 * <p> 2979 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class}, 2980 * {@code M1} is the module containing {@code lookupClass} and 2981 * {@code M2} is the module containing {@code targetClass}, 2982 * then {@code targetClass} is accessible if and only if 2983 * <ul> 2984 * <li>{@code M1} reads {@code M2}, and 2985 * <li>{@code targetClass} is public and in a package exported by 2986 * {@code M2} at least to {@code M1}. 2987 * </ul> 2988 * <p> 2989 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class}, 2990 * {@code M1} and {@code M2} are as before, and {@code M0} is the module 2991 * containing the previous lookup class, then {@code targetClass} is accessible 2992 * if and only if one of the following is true: 2993 * <ul> 2994 * <li>{@code targetClass} is in {@code M0} and {@code M1} 2995 * {@linkplain Module#reads reads} {@code M0} and the type is 2996 * in a package that is exported to at least {@code M1}. 2997 * <li>{@code targetClass} is in {@code M1} and {@code M0} 2998 * {@linkplain Module#reads reads} {@code M1} and the type is 2999 * in a package that is exported to at least {@code M0}. 3000 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0} 3001 * and {@code M1} reads {@code M2} and the type is in a package 3002 * that is exported to at least both {@code M0} and {@code M2}. 3003 * </ul> 3004 * <p> 3005 * Otherwise, {@code targetClass} is not accessible. 3006 * 3007 * @param <T> the type of the class to be access-checked 3008 * @param targetClass the class to be access-checked 3009 * @return {@code targetClass} that has been access-checked 3010 * @throws IllegalAccessException if the class is not accessible from the lookup class 3011 * and previous lookup class, if present, using the allowed access modes. 3012 * @throws SecurityException if a security manager is present and it 3013 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3014 * @throws NullPointerException if {@code targetClass} is {@code null} 3015 * @since 9 3016 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 3017 */ 3018 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException { 3019 if (!isClassAccessible(targetClass)) { 3020 throw makeAccessException(targetClass); 3021 } 3022 checkSecurityManager(targetClass); 3023 return targetClass; 3024 } 3025 3026 /** 3027 * Produces an early-bound method handle for a virtual method. 3028 * It will bypass checks for overriding methods on the receiver, 3029 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 3030 * instruction from within the explicitly specified {@code specialCaller}. 3031 * The type of the method handle will be that of the method, 3032 * with a suitably restricted receiver type prepended. 3033 * (The receiver type will be {@code specialCaller} or a subtype.) 3034 * The method and all its argument types must be accessible 3035 * to the lookup object. 3036 * <p> 3037 * Before method resolution, 3038 * if the explicitly specified caller class is not identical with the 3039 * lookup class, or if this lookup object does not have 3040 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 3041 * privileges, the access fails. 3042 * <p> 3043 * The returned method handle will have 3044 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3045 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3046 * <p style="font-size:smaller;"> 3047 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME} 3048 * are not visible to this API, 3049 * even though the {@code invokespecial} instruction can refer to them 3050 * in special circumstances. Use {@link #findConstructor findConstructor} 3051 * to access instance initialization methods in a safe manner.)</em> 3052 * <p><b>Example:</b> 3053 * {@snippet lang="java" : 3054 import static java.lang.invoke.MethodHandles.*; 3055 import static java.lang.invoke.MethodType.*; 3056 ... 3057 static class Listie extends ArrayList { 3058 public String toString() { return "[wee Listie]"; } 3059 static Lookup lookup() { return MethodHandles.lookup(); } 3060 } 3061 ... 3062 // no access to constructor via invokeSpecial: 3063 MethodHandle MH_newListie = Listie.lookup() 3064 .findConstructor(Listie.class, methodType(void.class)); 3065 Listie l = (Listie) MH_newListie.invokeExact(); 3066 try { assertEquals("impossible", Listie.lookup().findSpecial( 3067 Listie.class, "<init>", methodType(void.class), Listie.class)); 3068 } catch (NoSuchMethodException ex) { } // OK 3069 // access to super and self methods via invokeSpecial: 3070 MethodHandle MH_super = Listie.lookup().findSpecial( 3071 ArrayList.class, "toString" , methodType(String.class), Listie.class); 3072 MethodHandle MH_this = Listie.lookup().findSpecial( 3073 Listie.class, "toString" , methodType(String.class), Listie.class); 3074 MethodHandle MH_duper = Listie.lookup().findSpecial( 3075 Object.class, "toString" , methodType(String.class), Listie.class); 3076 assertEquals("[]", (String) MH_super.invokeExact(l)); 3077 assertEquals(""+l, (String) MH_this.invokeExact(l)); 3078 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method 3079 try { assertEquals("inaccessible", Listie.lookup().findSpecial( 3080 String.class, "toString", methodType(String.class), Listie.class)); 3081 } catch (IllegalAccessException ex) { } // OK 3082 Listie subl = new Listie() { public String toString() { return "[subclass]"; } }; 3083 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method 3084 * } 3085 * 3086 * @param refc the class or interface from which the method is accessed 3087 * @param name the name of the method (which must not be "<init>") 3088 * @param type the type of the method, with the receiver argument omitted 3089 * @param specialCaller the proposed calling class to perform the {@code invokespecial} 3090 * @return the desired method handle 3091 * @throws NoSuchMethodException if the method does not exist 3092 * @throws IllegalAccessException if access checking fails, 3093 * or if the method is {@code static}, 3094 * or if the method's variable arity modifier bit 3095 * is set and {@code asVarargsCollector} fails 3096 * @throws SecurityException if a security manager is present and it 3097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3098 * @throws NullPointerException if any argument is null 3099 */ 3100 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type, 3101 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException { 3102 checkSpecialCaller(specialCaller, refc); 3103 Lookup specialLookup = this.in(specialCaller); 3104 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type); 3105 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method)); 3106 } 3107 3108 /** 3109 * Produces a method handle giving read access to a non-static field. 3110 * The type of the method handle will have a return type of the field's 3111 * value type. 3112 * The method handle's single argument will be the instance containing 3113 * the field. 3114 * Access checking is performed immediately on behalf of the lookup class. 3115 * @param refc the class or interface from which the method is accessed 3116 * @param name the field's name 3117 * @param type the field's type 3118 * @return a method handle which can load values from the field 3119 * @throws NoSuchFieldException if the field does not exist 3120 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3121 * @throws SecurityException if a security manager is present and it 3122 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3123 * @throws NullPointerException if any argument is null 3124 * @see #findVarHandle(Class, String, Class) 3125 */ 3126 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3127 MemberName field = resolveOrFail(REF_getField, refc, name, type); 3128 return getDirectField(REF_getField, refc, field); 3129 } 3130 3131 /** 3132 * Produces a method handle giving write access to a non-static field. 3133 * The type of the method handle will have a void return type. 3134 * The method handle will take two arguments, the instance containing 3135 * the field, and the value to be stored. 3136 * The second argument will be of the field's value type. 3137 * Access checking is performed immediately on behalf of the lookup class. 3138 * @param refc the class or interface from which the method is accessed 3139 * @param name the field's name 3140 * @param type the field's type 3141 * @return a method handle which can store values into the field 3142 * @throws NoSuchFieldException if the field does not exist 3143 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3144 * or {@code final} 3145 * @throws SecurityException if a security manager is present and it 3146 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3147 * @throws NullPointerException if any argument is null 3148 * @see #findVarHandle(Class, String, Class) 3149 */ 3150 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3151 MemberName field = resolveOrFail(REF_putField, refc, name, type); 3152 return getDirectField(REF_putField, refc, field); 3153 } 3154 3155 /** 3156 * Produces a VarHandle giving access to a non-static field {@code name} 3157 * of type {@code type} declared in a class of type {@code recv}. 3158 * The VarHandle's variable type is {@code type} and it has one 3159 * coordinate type, {@code recv}. 3160 * <p> 3161 * Access checking is performed immediately on behalf of the lookup 3162 * class. 3163 * <p> 3164 * Certain access modes of the returned VarHandle are unsupported under 3165 * the following conditions: 3166 * <ul> 3167 * <li>if the field is declared {@code final}, then the write, atomic 3168 * update, numeric atomic update, and bitwise atomic update access 3169 * modes are unsupported. 3170 * <li>if the field type is anything other than {@code byte}, 3171 * {@code short}, {@code char}, {@code int}, {@code long}, 3172 * {@code float}, or {@code double} then numeric atomic update 3173 * access modes are unsupported. 3174 * <li>if the field type is anything other than {@code boolean}, 3175 * {@code byte}, {@code short}, {@code char}, {@code int} or 3176 * {@code long} then bitwise atomic update access modes are 3177 * unsupported. 3178 * </ul> 3179 * <p> 3180 * If the field is declared {@code volatile} then the returned VarHandle 3181 * will override access to the field (effectively ignore the 3182 * {@code volatile} declaration) in accordance to its specified 3183 * access modes. 3184 * <p> 3185 * If the field type is {@code float} or {@code double} then numeric 3186 * and atomic update access modes compare values using their bitwise 3187 * representation (see {@link Float#floatToRawIntBits} and 3188 * {@link Double#doubleToRawLongBits}, respectively). 3189 * @apiNote 3190 * Bitwise comparison of {@code float} values or {@code double} values, 3191 * as performed by the numeric and atomic update access modes, differ 3192 * from the primitive {@code ==} operator and the {@link Float#equals} 3193 * and {@link Double#equals} methods, specifically with respect to 3194 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3195 * Care should be taken when performing a compare and set or a compare 3196 * and exchange operation with such values since the operation may 3197 * unexpectedly fail. 3198 * There are many possible NaN values that are considered to be 3199 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3200 * provided by Java can distinguish between them. Operation failure can 3201 * occur if the expected or witness value is a NaN value and it is 3202 * transformed (perhaps in a platform specific manner) into another NaN 3203 * value, and thus has a different bitwise representation (see 3204 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3205 * details). 3206 * The values {@code -0.0} and {@code +0.0} have different bitwise 3207 * representations but are considered equal when using the primitive 3208 * {@code ==} operator. Operation failure can occur if, for example, a 3209 * numeric algorithm computes an expected value to be say {@code -0.0} 3210 * and previously computed the witness value to be say {@code +0.0}. 3211 * @param recv the receiver class, of type {@code R}, that declares the 3212 * non-static field 3213 * @param name the field's name 3214 * @param type the field's type, of type {@code T} 3215 * @return a VarHandle giving access to non-static fields. 3216 * @throws NoSuchFieldException if the field does not exist 3217 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3218 * @throws SecurityException if a security manager is present and it 3219 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3220 * @throws NullPointerException if any argument is null 3221 * @since 9 3222 */ 3223 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3224 MemberName getField = resolveOrFail(REF_getField, recv, name, type); 3225 MemberName putField = resolveOrFail(REF_putField, recv, name, type); 3226 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField); 3227 } 3228 3229 /** 3230 * Produces a method handle giving read access to a static field. 3231 * The type of the method handle will have a return type of the field's 3232 * value type. 3233 * The method handle will take no arguments. 3234 * Access checking is performed immediately on behalf of the lookup class. 3235 * <p> 3236 * If the returned method handle is invoked, the field's class will 3237 * be initialized, if it has not already been initialized. 3238 * @param refc the class or interface from which the method is accessed 3239 * @param name the field's name 3240 * @param type the field's type 3241 * @return a method handle which can load values from the field 3242 * @throws NoSuchFieldException if the field does not exist 3243 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3244 * @throws SecurityException if a security manager is present and it 3245 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3246 * @throws NullPointerException if any argument is null 3247 */ 3248 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3249 MemberName field = resolveOrFail(REF_getStatic, refc, name, type); 3250 return getDirectField(REF_getStatic, refc, field); 3251 } 3252 3253 /** 3254 * Produces a method handle giving write access to a static field. 3255 * The type of the method handle will have a void return type. 3256 * The method handle will take a single 3257 * argument, of the field's value type, the value to be stored. 3258 * Access checking is performed immediately on behalf of the lookup class. 3259 * <p> 3260 * If the returned method handle is invoked, the field's class will 3261 * be initialized, if it has not already been initialized. 3262 * @param refc the class or interface from which the method is accessed 3263 * @param name the field's name 3264 * @param type the field's type 3265 * @return a method handle which can store values into the field 3266 * @throws NoSuchFieldException if the field does not exist 3267 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3268 * or is {@code final} 3269 * @throws SecurityException if a security manager is present and it 3270 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3271 * @throws NullPointerException if any argument is null 3272 */ 3273 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3274 MemberName field = resolveOrFail(REF_putStatic, refc, name, type); 3275 return getDirectField(REF_putStatic, refc, field); 3276 } 3277 3278 /** 3279 * Produces a VarHandle giving access to a static field {@code name} of 3280 * type {@code type} declared in a class of type {@code decl}. 3281 * The VarHandle's variable type is {@code type} and it has no 3282 * coordinate types. 3283 * <p> 3284 * Access checking is performed immediately on behalf of the lookup 3285 * class. 3286 * <p> 3287 * If the returned VarHandle is operated on, the declaring class will be 3288 * initialized, if it has not already been initialized. 3289 * <p> 3290 * Certain access modes of the returned VarHandle are unsupported under 3291 * the following conditions: 3292 * <ul> 3293 * <li>if the field is declared {@code final}, then the write, atomic 3294 * update, numeric atomic update, and bitwise atomic update access 3295 * modes are unsupported. 3296 * <li>if the field type is anything other than {@code byte}, 3297 * {@code short}, {@code char}, {@code int}, {@code long}, 3298 * {@code float}, or {@code double}, then numeric atomic update 3299 * access modes are unsupported. 3300 * <li>if the field type is anything other than {@code boolean}, 3301 * {@code byte}, {@code short}, {@code char}, {@code int} or 3302 * {@code long} then bitwise atomic update access modes are 3303 * unsupported. 3304 * </ul> 3305 * <p> 3306 * If the field is declared {@code volatile} then the returned VarHandle 3307 * will override access to the field (effectively ignore the 3308 * {@code volatile} declaration) in accordance to its specified 3309 * access modes. 3310 * <p> 3311 * If the field type is {@code float} or {@code double} then numeric 3312 * and atomic update access modes compare values using their bitwise 3313 * representation (see {@link Float#floatToRawIntBits} and 3314 * {@link Double#doubleToRawLongBits}, respectively). 3315 * @apiNote 3316 * Bitwise comparison of {@code float} values or {@code double} values, 3317 * as performed by the numeric and atomic update access modes, differ 3318 * from the primitive {@code ==} operator and the {@link Float#equals} 3319 * and {@link Double#equals} methods, specifically with respect to 3320 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3321 * Care should be taken when performing a compare and set or a compare 3322 * and exchange operation with such values since the operation may 3323 * unexpectedly fail. 3324 * There are many possible NaN values that are considered to be 3325 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3326 * provided by Java can distinguish between them. Operation failure can 3327 * occur if the expected or witness value is a NaN value and it is 3328 * transformed (perhaps in a platform specific manner) into another NaN 3329 * value, and thus has a different bitwise representation (see 3330 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3331 * details). 3332 * The values {@code -0.0} and {@code +0.0} have different bitwise 3333 * representations but are considered equal when using the primitive 3334 * {@code ==} operator. Operation failure can occur if, for example, a 3335 * numeric algorithm computes an expected value to be say {@code -0.0} 3336 * and previously computed the witness value to be say {@code +0.0}. 3337 * @param decl the class that declares the static field 3338 * @param name the field's name 3339 * @param type the field's type, of type {@code T} 3340 * @return a VarHandle giving access to a static field 3341 * @throws NoSuchFieldException if the field does not exist 3342 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3343 * @throws SecurityException if a security manager is present and it 3344 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3345 * @throws NullPointerException if any argument is null 3346 * @since 9 3347 */ 3348 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3349 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type); 3350 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type); 3351 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField); 3352 } 3353 3354 /** 3355 * Produces an early-bound method handle for a non-static method. 3356 * The receiver must have a supertype {@code defc} in which a method 3357 * of the given name and type is accessible to the lookup class. 3358 * The method and all its argument types must be accessible to the lookup object. 3359 * The type of the method handle will be that of the method, 3360 * without any insertion of an additional receiver parameter. 3361 * The given receiver will be bound into the method handle, 3362 * so that every call to the method handle will invoke the 3363 * requested method on the given receiver. 3364 * <p> 3365 * The returned method handle will have 3366 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3367 * the method's variable arity modifier bit ({@code 0x0080}) is set 3368 * <em>and</em> the trailing array argument is not the only argument. 3369 * (If the trailing array argument is the only argument, 3370 * the given receiver value will be bound to it.) 3371 * <p> 3372 * This is almost equivalent to the following code, with some differences noted below: 3373 * {@snippet lang="java" : 3374 import static java.lang.invoke.MethodHandles.*; 3375 import static java.lang.invoke.MethodType.*; 3376 ... 3377 MethodHandle mh0 = lookup().findVirtual(defc, name, type); 3378 MethodHandle mh1 = mh0.bindTo(receiver); 3379 mh1 = mh1.withVarargs(mh0.isVarargsCollector()); 3380 return mh1; 3381 * } 3382 * where {@code defc} is either {@code receiver.getClass()} or a super 3383 * type of that class, in which the requested method is accessible 3384 * to the lookup class. 3385 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity. 3386 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would 3387 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and 3388 * the receiver is restricted by {@code findVirtual} to the lookup class.) 3389 * @param receiver the object from which the method is accessed 3390 * @param name the name of the method 3391 * @param type the type of the method, with the receiver argument omitted 3392 * @return the desired method handle 3393 * @throws NoSuchMethodException if the method does not exist 3394 * @throws IllegalAccessException if access checking fails 3395 * or if the method's variable arity modifier bit 3396 * is set and {@code asVarargsCollector} fails 3397 * @throws SecurityException if a security manager is present and it 3398 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3399 * @throws NullPointerException if any argument is null 3400 * @see MethodHandle#bindTo 3401 * @see #findVirtual 3402 */ 3403 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 3404 Class<? extends Object> refc = receiver.getClass(); // may get NPE 3405 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type); 3406 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method)); 3407 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) { 3408 throw new IllegalAccessException("The restricted defining class " + 3409 mh.type().leadingReferenceParameter().getName() + 3410 " is not assignable from receiver class " + 3411 receiver.getClass().getName()); 3412 } 3413 return mh.bindArgumentL(0, receiver).setVarargs(method); 3414 } 3415 3416 /** 3417 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 3418 * to <i>m</i>, if the lookup class has permission. 3419 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument. 3420 * If <i>m</i> is virtual, overriding is respected on every call. 3421 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped. 3422 * The type of the method handle will be that of the method, 3423 * with the receiver type prepended (but only if it is non-static). 3424 * If the method's {@code accessible} flag is not set, 3425 * access checking is performed immediately on behalf of the lookup class. 3426 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties. 3427 * <p> 3428 * The returned method handle will have 3429 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3430 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3431 * <p> 3432 * If <i>m</i> is static, and 3433 * if the returned method handle is invoked, the method's class will 3434 * be initialized, if it has not already been initialized. 3435 * @param m the reflected method 3436 * @return a method handle which can invoke the reflected method 3437 * @throws IllegalAccessException if access checking fails 3438 * or if the method's variable arity modifier bit 3439 * is set and {@code asVarargsCollector} fails 3440 * @throws NullPointerException if the argument is null 3441 */ 3442 public MethodHandle unreflect(Method m) throws IllegalAccessException { 3443 if (m.getDeclaringClass() == MethodHandle.class) { 3444 MethodHandle mh = unreflectForMH(m); 3445 if (mh != null) return mh; 3446 } 3447 if (m.getDeclaringClass() == VarHandle.class) { 3448 MethodHandle mh = unreflectForVH(m); 3449 if (mh != null) return mh; 3450 } 3451 MemberName method = new MemberName(m); 3452 byte refKind = method.getReferenceKind(); 3453 if (refKind == REF_invokeSpecial) 3454 refKind = REF_invokeVirtual; 3455 assert(method.isMethod()); 3456 @SuppressWarnings("deprecation") 3457 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this; 3458 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method)); 3459 } 3460 private MethodHandle unreflectForMH(Method m) { 3461 // these names require special lookups because they throw UnsupportedOperationException 3462 if (MemberName.isMethodHandleInvokeName(m.getName())) 3463 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m)); 3464 return null; 3465 } 3466 private MethodHandle unreflectForVH(Method m) { 3467 // these names require special lookups because they throw UnsupportedOperationException 3468 if (MemberName.isVarHandleMethodInvokeName(m.getName())) 3469 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m)); 3470 return null; 3471 } 3472 3473 /** 3474 * Produces a method handle for a reflected method. 3475 * It will bypass checks for overriding methods on the receiver, 3476 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 3477 * instruction from within the explicitly specified {@code specialCaller}. 3478 * The type of the method handle will be that of the method, 3479 * with a suitably restricted receiver type prepended. 3480 * (The receiver type will be {@code specialCaller} or a subtype.) 3481 * If the method's {@code accessible} flag is not set, 3482 * access checking is performed immediately on behalf of the lookup class, 3483 * as if {@code invokespecial} instruction were being linked. 3484 * <p> 3485 * Before method resolution, 3486 * if the explicitly specified caller class is not identical with the 3487 * lookup class, or if this lookup object does not have 3488 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 3489 * privileges, the access fails. 3490 * <p> 3491 * The returned method handle will have 3492 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3493 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3494 * @param m the reflected method 3495 * @param specialCaller the class nominally calling the method 3496 * @return a method handle which can invoke the reflected method 3497 * @throws IllegalAccessException if access checking fails, 3498 * or if the method is {@code static}, 3499 * or if the method's variable arity modifier bit 3500 * is set and {@code asVarargsCollector} fails 3501 * @throws NullPointerException if any argument is null 3502 */ 3503 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException { 3504 checkSpecialCaller(specialCaller, m.getDeclaringClass()); 3505 Lookup specialLookup = this.in(specialCaller); 3506 MemberName method = new MemberName(m, true); 3507 assert(method.isMethod()); 3508 // ignore m.isAccessible: this is a new kind of access 3509 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method)); 3510 } 3511 3512 /** 3513 * Produces a method handle for a reflected constructor. 3514 * The type of the method handle will be that of the constructor, 3515 * with the return type changed to the declaring class. 3516 * The method handle will perform a {@code newInstance} operation, 3517 * creating a new instance of the constructor's class on the 3518 * arguments passed to the method handle. 3519 * <p> 3520 * If the constructor's {@code accessible} flag is not set, 3521 * access checking is performed immediately on behalf of the lookup class. 3522 * <p> 3523 * The returned method handle will have 3524 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3525 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 3526 * <p> 3527 * If the returned method handle is invoked, the constructor's class will 3528 * be initialized, if it has not already been initialized. 3529 * @param c the reflected constructor 3530 * @return a method handle which can invoke the reflected constructor 3531 * @throws IllegalAccessException if access checking fails 3532 * or if the method's variable arity modifier bit 3533 * is set and {@code asVarargsCollector} fails 3534 * @throws NullPointerException if the argument is null 3535 */ 3536 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException { 3537 MemberName ctor = new MemberName(c); 3538 assert(ctor.isObjectConstructor() || ctor.isStaticValueFactoryMethod()); 3539 @SuppressWarnings("deprecation") 3540 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this; 3541 Class<?> defc = c.getDeclaringClass(); 3542 if (ctor.isObjectConstructor()) { 3543 assert(ctor.getMethodType().returnType() == void.class); 3544 return lookup.getDirectConstructorNoSecurityManager(defc, ctor); 3545 } else { 3546 // static init factory is a static method 3547 assert(ctor.isMethod() && ctor.getMethodType().returnType() == defc && ctor.getReferenceKind() == REF_invokeStatic) : ctor.toString(); 3548 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // must not be caller-sensitive 3549 return lookup.getDirectMethodNoSecurityManager(ctor.getReferenceKind(), defc, ctor, lookup); 3550 } 3551 } 3552 3553 /** 3554 * Produces a method handle giving read access to a reflected field. 3555 * The type of the method handle will have a return type of the field's 3556 * value type. 3557 * If the field is {@code static}, the method handle will take no arguments. 3558 * Otherwise, its single argument will be the instance containing 3559 * the field. 3560 * If the {@code Field} object's {@code accessible} flag is not set, 3561 * access checking is performed immediately on behalf of the lookup class. 3562 * <p> 3563 * If the field is static, and 3564 * if the returned method handle is invoked, the field's class will 3565 * be initialized, if it has not already been initialized. 3566 * @param f the reflected field 3567 * @return a method handle which can load values from the reflected field 3568 * @throws IllegalAccessException if access checking fails 3569 * @throws NullPointerException if the argument is null 3570 */ 3571 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException { 3572 return unreflectField(f, false); 3573 } 3574 3575 /** 3576 * Produces a method handle giving write access to a reflected field. 3577 * The type of the method handle will have a void return type. 3578 * If the field is {@code static}, the method handle will take a single 3579 * argument, of the field's value type, the value to be stored. 3580 * Otherwise, the two arguments will be the instance containing 3581 * the field, and the value to be stored. 3582 * If the {@code Field} object's {@code accessible} flag is not set, 3583 * access checking is performed immediately on behalf of the lookup class. 3584 * <p> 3585 * If the field is {@code final}, write access will not be 3586 * allowed and access checking will fail, except under certain 3587 * narrow circumstances documented for {@link Field#set Field.set}. 3588 * A method handle is returned only if a corresponding call to 3589 * the {@code Field} object's {@code set} method could return 3590 * normally. In particular, fields which are both {@code static} 3591 * and {@code final} may never be set. 3592 * <p> 3593 * If the field is {@code static}, and 3594 * if the returned method handle is invoked, the field's class will 3595 * be initialized, if it has not already been initialized. 3596 * @param f the reflected field 3597 * @return a method handle which can store values into the reflected field 3598 * @throws IllegalAccessException if access checking fails, 3599 * or if the field is {@code final} and write access 3600 * is not enabled on the {@code Field} object 3601 * @throws NullPointerException if the argument is null 3602 */ 3603 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException { 3604 return unreflectField(f, true); 3605 } 3606 3607 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException { 3608 MemberName field = new MemberName(f, isSetter); 3609 if (isSetter && field.isFinal()) { 3610 if (field.isTrustedFinalField()) { 3611 String msg = field.isStatic() ? "static final field has no write access" 3612 : "final field has no write access"; 3613 throw field.makeAccessException(msg, this); 3614 } 3615 } 3616 assert(isSetter 3617 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind()) 3618 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind())); 3619 @SuppressWarnings("deprecation") 3620 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this; 3621 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field); 3622 } 3623 3624 /** 3625 * Produces a VarHandle giving access to a reflected field {@code f} 3626 * of type {@code T} declared in a class of type {@code R}. 3627 * The VarHandle's variable type is {@code T}. 3628 * If the field is non-static the VarHandle has one coordinate type, 3629 * {@code R}. Otherwise, the field is static, and the VarHandle has no 3630 * coordinate types. 3631 * <p> 3632 * Access checking is performed immediately on behalf of the lookup 3633 * class, regardless of the value of the field's {@code accessible} 3634 * flag. 3635 * <p> 3636 * If the field is static, and if the returned VarHandle is operated 3637 * on, the field's declaring class will be initialized, if it has not 3638 * already been initialized. 3639 * <p> 3640 * Certain access modes of the returned VarHandle are unsupported under 3641 * the following conditions: 3642 * <ul> 3643 * <li>if the field is declared {@code final}, then the write, atomic 3644 * update, numeric atomic update, and bitwise atomic update access 3645 * modes are unsupported. 3646 * <li>if the field type is anything other than {@code byte}, 3647 * {@code short}, {@code char}, {@code int}, {@code long}, 3648 * {@code float}, or {@code double} then numeric atomic update 3649 * access modes are unsupported. 3650 * <li>if the field type is anything other than {@code boolean}, 3651 * {@code byte}, {@code short}, {@code char}, {@code int} or 3652 * {@code long} then bitwise atomic update access modes are 3653 * unsupported. 3654 * </ul> 3655 * <p> 3656 * If the field is declared {@code volatile} then the returned VarHandle 3657 * will override access to the field (effectively ignore the 3658 * {@code volatile} declaration) in accordance to its specified 3659 * access modes. 3660 * <p> 3661 * If the field type is {@code float} or {@code double} then numeric 3662 * and atomic update access modes compare values using their bitwise 3663 * representation (see {@link Float#floatToRawIntBits} and 3664 * {@link Double#doubleToRawLongBits}, respectively). 3665 * @apiNote 3666 * Bitwise comparison of {@code float} values or {@code double} values, 3667 * as performed by the numeric and atomic update access modes, differ 3668 * from the primitive {@code ==} operator and the {@link Float#equals} 3669 * and {@link Double#equals} methods, specifically with respect to 3670 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3671 * Care should be taken when performing a compare and set or a compare 3672 * and exchange operation with such values since the operation may 3673 * unexpectedly fail. 3674 * There are many possible NaN values that are considered to be 3675 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3676 * provided by Java can distinguish between them. Operation failure can 3677 * occur if the expected or witness value is a NaN value and it is 3678 * transformed (perhaps in a platform specific manner) into another NaN 3679 * value, and thus has a different bitwise representation (see 3680 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3681 * details). 3682 * The values {@code -0.0} and {@code +0.0} have different bitwise 3683 * representations but are considered equal when using the primitive 3684 * {@code ==} operator. Operation failure can occur if, for example, a 3685 * numeric algorithm computes an expected value to be say {@code -0.0} 3686 * and previously computed the witness value to be say {@code +0.0}. 3687 * @param f the reflected field, with a field of type {@code T}, and 3688 * a declaring class of type {@code R} 3689 * @return a VarHandle giving access to non-static fields or a static 3690 * field 3691 * @throws IllegalAccessException if access checking fails 3692 * @throws NullPointerException if the argument is null 3693 * @since 9 3694 */ 3695 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException { 3696 MemberName getField = new MemberName(f, false); 3697 MemberName putField = new MemberName(f, true); 3698 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(), 3699 f.getDeclaringClass(), getField, putField); 3700 } 3701 3702 /** 3703 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 3704 * created by this lookup object or a similar one. 3705 * Security and access checks are performed to ensure that this lookup object 3706 * is capable of reproducing the target method handle. 3707 * This means that the cracking may fail if target is a direct method handle 3708 * but was created by an unrelated lookup object. 3709 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> 3710 * and was created by a lookup object for a different class. 3711 * @param target a direct method handle to crack into symbolic reference components 3712 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object 3713 * @throws SecurityException if a security manager is present and it 3714 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3715 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails 3716 * @throws NullPointerException if the target is {@code null} 3717 * @see MethodHandleInfo 3718 * @since 1.8 3719 */ 3720 public MethodHandleInfo revealDirect(MethodHandle target) { 3721 if (!target.isCrackable()) { 3722 throw newIllegalArgumentException("not a direct method handle"); 3723 } 3724 MemberName member = target.internalMemberName(); 3725 Class<?> defc = member.getDeclaringClass(); 3726 byte refKind = member.getReferenceKind(); 3727 assert(MethodHandleNatives.refKindIsValid(refKind)); 3728 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial()) 3729 // Devirtualized method invocation is usually formally virtual. 3730 // To avoid creating extra MemberName objects for this common case, 3731 // we encode this extra degree of freedom using MH.isInvokeSpecial. 3732 refKind = REF_invokeVirtual; 3733 if (refKind == REF_invokeVirtual && defc.isInterface()) 3734 // Symbolic reference is through interface but resolves to Object method (toString, etc.) 3735 refKind = REF_invokeInterface; 3736 // Check SM permissions and member access before cracking. 3737 try { 3738 checkAccess(refKind, defc, member); 3739 checkSecurityManager(defc, member); 3740 } catch (IllegalAccessException ex) { 3741 throw new IllegalArgumentException(ex); 3742 } 3743 if (allowedModes != TRUSTED && member.isCallerSensitive()) { 3744 Class<?> callerClass = target.internalCallerClass(); 3745 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass()) 3746 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass); 3747 } 3748 // Produce the handle to the results. 3749 return new InfoFromMemberName(this, member, refKind); 3750 } 3751 3752 /// Helper methods, all package-private. 3753 3754 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3755 checkSymbolicClass(refc); // do this before attempting to resolve 3756 Objects.requireNonNull(name); 3757 Objects.requireNonNull(type); 3758 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes, 3759 NoSuchFieldException.class); 3760 } 3761 3762 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 3763 checkSymbolicClass(refc); // do this before attempting to resolve 3764 Objects.requireNonNull(type); 3765 checkMethodName(refKind, name); // implicit null-check of name 3766 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes, 3767 NoSuchMethodException.class); 3768 } 3769 3770 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException { 3771 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve 3772 Objects.requireNonNull(member.getName()); 3773 Objects.requireNonNull(member.getType()); 3774 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes, 3775 ReflectiveOperationException.class); 3776 } 3777 3778 MemberName resolveOrNull(byte refKind, MemberName member) { 3779 // do this before attempting to resolve 3780 if (!isClassAccessible(member.getDeclaringClass())) { 3781 return null; 3782 } 3783 Objects.requireNonNull(member.getName()); 3784 Objects.requireNonNull(member.getType()); 3785 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes); 3786 } 3787 3788 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) { 3789 // do this before attempting to resolve 3790 if (!isClassAccessible(refc)) { 3791 return null; 3792 } 3793 Objects.requireNonNull(type); 3794 // implicit null-check of name 3795 if (isIllegalMethodName(refKind, name)) { 3796 return null; 3797 } 3798 3799 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes); 3800 } 3801 3802 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException { 3803 if (!isClassAccessible(refc)) { 3804 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this); 3805 } 3806 } 3807 3808 boolean isClassAccessible(Class<?> refc) { 3809 Objects.requireNonNull(refc); 3810 Class<?> caller = lookupClassOrNull(); 3811 Class<?> type = refc; 3812 while (type.isArray()) { 3813 type = type.getComponentType(); 3814 } 3815 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes); 3816 } 3817 3818 /* 3819 * "<init>" can only be invoked via invokespecial 3820 * "<vnew>" factory can only invoked via invokestatic 3821 */ 3822 boolean isIllegalMethodName(byte refKind, String name) { 3823 if (name.startsWith("<")) { 3824 return MemberName.VALUE_FACTORY_NAME.equals(name) ? refKind != REF_invokeStatic 3825 : refKind != REF_newInvokeSpecial; 3826 } 3827 return false; 3828 } 3829 3830 /** Check name for an illegal leading "<" character. */ 3831 void checkMethodName(byte refKind, String name) throws NoSuchMethodException { 3832 if (isIllegalMethodName(refKind, name)) { 3833 throw new NoSuchMethodException("illegal method name: " + name + " " + refKind); 3834 } 3835 } 3836 3837 /** 3838 * Find my trustable caller class if m is a caller sensitive method. 3839 * If this lookup object has original full privilege access, then the caller class is the lookupClass. 3840 * Otherwise, if m is caller-sensitive, throw IllegalAccessException. 3841 */ 3842 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException { 3843 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) { 3844 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods 3845 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 3846 } 3847 return this; 3848 } 3849 3850 /** 3851 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access. 3852 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access. 3853 * 3854 * @deprecated This method was originally designed to test {@code PRIVATE} access 3855 * that implies full privilege access but {@code MODULE} access has since become 3856 * independent of {@code PRIVATE} access. It is recommended to call 3857 * {@link #hasFullPrivilegeAccess()} instead. 3858 * @since 9 3859 */ 3860 @Deprecated(since="14") 3861 public boolean hasPrivateAccess() { 3862 return hasFullPrivilegeAccess(); 3863 } 3864 3865 /** 3866 * Returns {@code true} if this lookup has <em>full privilege access</em>, 3867 * i.e. {@code PRIVATE} and {@code MODULE} access. 3868 * A {@code Lookup} object must have full privilege access in order to 3869 * access all members that are allowed to the 3870 * {@linkplain #lookupClass() lookup class}. 3871 * 3872 * @return {@code true} if this lookup has full privilege access. 3873 * @since 14 3874 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a> 3875 */ 3876 public boolean hasFullPrivilegeAccess() { 3877 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE); 3878 } 3879 3880 /** 3881 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a> 3882 * for ensureInitialized, findClass or accessClass. 3883 */ 3884 void checkSecurityManager(Class<?> refc) { 3885 if (allowedModes == TRUSTED) return; 3886 3887 @SuppressWarnings("removal") 3888 SecurityManager smgr = System.getSecurityManager(); 3889 if (smgr == null) return; 3890 3891 // Step 1: 3892 boolean fullPrivilegeLookup = hasFullPrivilegeAccess(); 3893 if (!fullPrivilegeLookup || 3894 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 3895 ReflectUtil.checkPackageAccess(refc); 3896 } 3897 3898 // Step 2b: 3899 if (!fullPrivilegeLookup) { 3900 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION); 3901 } 3902 } 3903 3904 /** 3905 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>. 3906 * Determines a trustable caller class to compare with refc, the symbolic reference class. 3907 * If this lookup object has full privilege access except original access, 3908 * then the caller class is the lookupClass. 3909 * 3910 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)} 3911 * from the same module skips the security permission check. 3912 */ 3913 void checkSecurityManager(Class<?> refc, MemberName m) { 3914 Objects.requireNonNull(refc); 3915 Objects.requireNonNull(m); 3916 3917 if (allowedModes == TRUSTED) return; 3918 3919 @SuppressWarnings("removal") 3920 SecurityManager smgr = System.getSecurityManager(); 3921 if (smgr == null) return; 3922 3923 // Step 1: 3924 boolean fullPrivilegeLookup = hasFullPrivilegeAccess(); 3925 if (!fullPrivilegeLookup || 3926 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 3927 ReflectUtil.checkPackageAccess(refc); 3928 } 3929 3930 // Step 2a: 3931 if (m.isPublic()) return; 3932 if (!fullPrivilegeLookup) { 3933 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION); 3934 } 3935 3936 // Step 3: 3937 Class<?> defc = m.getDeclaringClass(); 3938 if (!fullPrivilegeLookup && PrimitiveClass.asPrimaryType(defc) != PrimitiveClass.asPrimaryType(refc)) { 3939 ReflectUtil.checkPackageAccess(defc); 3940 } 3941 } 3942 3943 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3944 boolean wantStatic = (refKind == REF_invokeStatic); 3945 String message; 3946 if (m.isObjectConstructor()) 3947 message = "expected a method, not a constructor"; 3948 else if (!m.isMethod()) 3949 message = "expected a method"; 3950 else if (wantStatic != m.isStatic()) 3951 message = wantStatic ? "expected a static method" : "expected a non-static method"; 3952 else 3953 { checkAccess(refKind, refc, m); return; } 3954 throw m.makeAccessException(message, this); 3955 } 3956 3957 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3958 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind); 3959 String message; 3960 if (wantStatic != m.isStatic()) 3961 message = wantStatic ? "expected a static field" : "expected a non-static field"; 3962 else 3963 { checkAccess(refKind, refc, m); return; } 3964 throw m.makeAccessException(message, this); 3965 } 3966 3967 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) { 3968 return Modifier.isProtected(m.getModifiers()) && 3969 refKind == REF_invokeVirtual && 3970 m.getDeclaringClass() == Object.class && 3971 m.getName().equals("clone") && 3972 refc.isArray(); 3973 } 3974 3975 /** Check public/protected/private bits on the symbolic reference class and its member. */ 3976 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3977 assert(m.referenceKindIsConsistentWith(refKind) && 3978 MethodHandleNatives.refKindIsValid(refKind) && 3979 (MethodHandleNatives.refKindIsField(refKind) == m.isField())); 3980 int allowedModes = this.allowedModes; 3981 if (allowedModes == TRUSTED) return; 3982 int mods = m.getModifiers(); 3983 if (isArrayClone(refKind, refc, m)) { 3984 // The JVM does this hack also. 3985 // (See ClassVerifier::verify_invoke_instructions 3986 // and LinkResolver::check_method_accessability.) 3987 // Because the JVM does not allow separate methods on array types, 3988 // there is no separate method for int[].clone. 3989 // All arrays simply inherit Object.clone. 3990 // But for access checking logic, we make Object.clone 3991 // (normally protected) appear to be public. 3992 // Later on, when the DirectMethodHandle is created, 3993 // its leading argument will be restricted to the 3994 // requested array type. 3995 // N.B. The return type is not adjusted, because 3996 // that is *not* the bytecode behavior. 3997 mods ^= Modifier.PROTECTED | Modifier.PUBLIC; 3998 } 3999 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) { 4000 // cannot "new" a protected ctor in a different package 4001 mods ^= Modifier.PROTECTED; 4002 } 4003 if (Modifier.isFinal(mods) && 4004 MethodHandleNatives.refKindIsSetter(refKind)) 4005 throw m.makeAccessException("unexpected set of a final field", this); 4006 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE 4007 if ((requestedModes & allowedModes) != 0) { 4008 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(), 4009 mods, lookupClass(), previousLookupClass(), allowedModes)) 4010 return; 4011 } else { 4012 // Protected members can also be checked as if they were package-private. 4013 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0 4014 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass())) 4015 return; 4016 } 4017 throw m.makeAccessException(accessFailedMessage(refc, m), this); 4018 } 4019 4020 String accessFailedMessage(Class<?> refc, MemberName m) { 4021 Class<?> defc = m.getDeclaringClass(); 4022 int mods = m.getModifiers(); 4023 // check the class first: 4024 boolean classOK = (Modifier.isPublic(defc.getModifiers()) && 4025 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) || 4026 Modifier.isPublic(refc.getModifiers()))); 4027 if (!classOK && (allowedModes & PACKAGE) != 0) { 4028 // ignore previous lookup class to check if default package access 4029 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) && 4030 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) || 4031 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES))); 4032 } 4033 if (!classOK) 4034 return "class is not public"; 4035 if (Modifier.isPublic(mods)) 4036 return "access to public member failed"; // (how?, module not readable?) 4037 if (Modifier.isPrivate(mods)) 4038 return "member is private"; 4039 if (Modifier.isProtected(mods)) 4040 return "member is protected"; 4041 return "member is private to package"; 4042 } 4043 4044 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException { 4045 int allowedModes = this.allowedModes; 4046 if (allowedModes == TRUSTED) return; 4047 if ((lookupModes() & PRIVATE) == 0 4048 || (specialCaller != lookupClass() 4049 // ensure non-abstract methods in superinterfaces can be special-invoked 4050 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller)))) 4051 throw new MemberName(specialCaller). 4052 makeAccessException("no private access for invokespecial", this); 4053 } 4054 4055 private boolean restrictProtectedReceiver(MemberName method) { 4056 // The accessing class only has the right to use a protected member 4057 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc. 4058 if (!method.isProtected() || method.isStatic() 4059 || allowedModes == TRUSTED 4060 || method.getDeclaringClass() == lookupClass() 4061 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())) 4062 return false; 4063 return true; 4064 } 4065 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException { 4066 assert(!method.isStatic()); 4067 // receiver type of mh is too wide; narrow to caller 4068 if (!method.getDeclaringClass().isAssignableFrom(caller)) { 4069 throw method.makeAccessException("caller class must be a subclass below the method", caller); 4070 } 4071 MethodType rawType = mh.type(); 4072 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow 4073 MethodType narrowType = rawType.changeParameterType(0, caller); 4074 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness 4075 assert(mh.viewAsTypeChecks(narrowType, true)); 4076 return mh.copyWith(narrowType, mh.form); 4077 } 4078 4079 /** Check access and get the requested method. */ 4080 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 4081 final boolean doRestrict = true; 4082 final boolean checkSecurity = true; 4083 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup); 4084 } 4085 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */ 4086 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 4087 final boolean doRestrict = false; 4088 final boolean checkSecurity = true; 4089 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup); 4090 } 4091 /** Check access and get the requested method, eliding security manager checks. */ 4092 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 4093 final boolean doRestrict = true; 4094 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4095 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup); 4096 } 4097 /** Common code for all methods; do not call directly except from immediately above. */ 4098 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method, 4099 boolean checkSecurity, 4100 boolean doRestrict, 4101 Lookup boundCaller) throws IllegalAccessException { 4102 checkMethod(refKind, refc, method); 4103 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4104 if (checkSecurity) 4105 checkSecurityManager(refc, method); 4106 assert(!method.isMethodHandleInvoke()); 4107 if (refKind == REF_invokeSpecial && 4108 refc != lookupClass() && 4109 !refc.isInterface() && !lookupClass().isInterface() && 4110 refc != lookupClass().getSuperclass() && 4111 refc.isAssignableFrom(lookupClass())) { 4112 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path 4113 4114 // Per JVMS 6.5, desc. of invokespecial instruction: 4115 // If the method is in a superclass of the LC, 4116 // and if our original search was above LC.super, 4117 // repeat the search (symbolic lookup) from LC.super 4118 // and continue with the direct superclass of that class, 4119 // and so forth, until a match is found or no further superclasses exist. 4120 // FIXME: MemberName.resolve should handle this instead. 4121 Class<?> refcAsSuper = lookupClass(); 4122 MemberName m2; 4123 do { 4124 refcAsSuper = refcAsSuper.getSuperclass(); 4125 m2 = new MemberName(refcAsSuper, 4126 method.getName(), 4127 method.getMethodType(), 4128 REF_invokeSpecial); 4129 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes); 4130 } while (m2 == null && // no method is found yet 4131 refc != refcAsSuper); // search up to refc 4132 if (m2 == null) throw new InternalError(method.toString()); 4133 method = m2; 4134 refc = refcAsSuper; 4135 // redo basic checks 4136 checkMethod(refKind, refc, method); 4137 } 4138 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass()); 4139 MethodHandle mh = dmh; 4140 // Optionally narrow the receiver argument to lookupClass using restrictReceiver. 4141 if ((doRestrict && refKind == REF_invokeSpecial) || 4142 (MethodHandleNatives.refKindHasReceiver(refKind) && 4143 restrictProtectedReceiver(method) && 4144 // All arrays simply inherit the protected Object.clone method. 4145 // The leading argument is already restricted to the requested 4146 // array type (not the lookup class). 4147 !isArrayClone(refKind, refc, method))) { 4148 mh = restrictReceiver(method, dmh, lookupClass()); 4149 } 4150 mh = maybeBindCaller(method, mh, boundCaller); 4151 mh = mh.setVarargs(method); 4152 return mh; 4153 } 4154 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller) 4155 throws IllegalAccessException { 4156 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method)) 4157 return mh; 4158 4159 // boundCaller must have full privilege access. 4160 // It should have been checked by findBoundCallerLookup. Safe to check this again. 4161 if ((boundCaller.lookupModes() & ORIGINAL) == 0) 4162 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 4163 4164 assert boundCaller.hasFullPrivilegeAccess(); 4165 4166 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass); 4167 // Note: caller will apply varargs after this step happens. 4168 return cbmh; 4169 } 4170 4171 /** Check access and get the requested field. */ 4172 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 4173 final boolean checkSecurity = true; 4174 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 4175 } 4176 /** Check access and get the requested field, eliding security manager checks. */ 4177 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 4178 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4179 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 4180 } 4181 /** Common code for all fields; do not call directly except from immediately above. */ 4182 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field, 4183 boolean checkSecurity) throws IllegalAccessException { 4184 checkField(refKind, refc, field); 4185 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4186 if (checkSecurity) 4187 checkSecurityManager(refc, field); 4188 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field); 4189 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) && 4190 restrictProtectedReceiver(field)); 4191 if (doRestrict) 4192 return restrictReceiver(field, dmh, lookupClass()); 4193 return dmh; 4194 } 4195 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind, 4196 Class<?> refc, MemberName getField, MemberName putField) 4197 throws IllegalAccessException { 4198 final boolean checkSecurity = true; 4199 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 4200 } 4201 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind, 4202 Class<?> refc, MemberName getField, MemberName putField) 4203 throws IllegalAccessException { 4204 final boolean checkSecurity = false; 4205 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 4206 } 4207 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind, 4208 Class<?> refc, MemberName getField, MemberName putField, 4209 boolean checkSecurity) throws IllegalAccessException { 4210 assert getField.isStatic() == putField.isStatic(); 4211 assert getField.isGetter() && putField.isSetter(); 4212 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind); 4213 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind); 4214 4215 checkField(getRefKind, refc, getField); 4216 if (checkSecurity) 4217 checkSecurityManager(refc, getField); 4218 4219 if (!putField.isFinal()) { 4220 // A VarHandle does not support updates to final fields, any 4221 // such VarHandle to a final field will be read-only and 4222 // therefore the following write-based accessibility checks are 4223 // only required for non-final fields 4224 checkField(putRefKind, refc, putField); 4225 if (checkSecurity) 4226 checkSecurityManager(refc, putField); 4227 } 4228 4229 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) && 4230 restrictProtectedReceiver(getField)); 4231 if (doRestrict) { 4232 assert !getField.isStatic(); 4233 // receiver type of VarHandle is too wide; narrow to caller 4234 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) { 4235 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass()); 4236 } 4237 refc = lookupClass(); 4238 } 4239 return VarHandles.makeFieldHandle(getField, refc, 4240 this.allowedModes == TRUSTED && !getField.isTrustedFinalField()); 4241 } 4242 /** Check access and get the requested constructor. */ 4243 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException { 4244 final boolean checkSecurity = true; 4245 return getDirectConstructorCommon(refc, ctor, checkSecurity); 4246 } 4247 /** Check access and get the requested constructor, eliding security manager checks. */ 4248 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException { 4249 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4250 return getDirectConstructorCommon(refc, ctor, checkSecurity); 4251 } 4252 /** Common code for all constructors; do not call directly except from immediately above. */ 4253 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor, 4254 boolean checkSecurity) throws IllegalAccessException { 4255 assert(ctor.isObjectConstructor()); 4256 checkAccess(REF_newInvokeSpecial, refc, ctor); 4257 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4258 if (checkSecurity) 4259 checkSecurityManager(refc, ctor); 4260 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here 4261 return DirectMethodHandle.make(ctor).setVarargs(ctor); 4262 } 4263 4264 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants: 4265 */ 4266 /*non-public*/ 4267 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) 4268 throws ReflectiveOperationException { 4269 if (!(type instanceof Class || type instanceof MethodType)) 4270 throw new InternalError("unresolved MemberName"); 4271 MemberName member = new MemberName(refKind, defc, name, type); 4272 MethodHandle mh = LOOKASIDE_TABLE.get(member); 4273 if (mh != null) { 4274 checkSymbolicClass(defc); 4275 return mh; 4276 } 4277 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) { 4278 // Treat MethodHandle.invoke and invokeExact specially. 4279 mh = findVirtualForMH(member.getName(), member.getMethodType()); 4280 if (mh != null) { 4281 return mh; 4282 } 4283 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) { 4284 // Treat signature-polymorphic methods on VarHandle specially. 4285 mh = findVirtualForVH(member.getName(), member.getMethodType()); 4286 if (mh != null) { 4287 return mh; 4288 } 4289 } 4290 MemberName resolved = resolveOrFail(refKind, member); 4291 mh = getDirectMethodForConstant(refKind, defc, resolved); 4292 if (mh instanceof DirectMethodHandle dmh 4293 && canBeCached(refKind, defc, resolved)) { 4294 MemberName key = mh.internalMemberName(); 4295 if (key != null) { 4296 key = key.asNormalOriginal(); 4297 } 4298 if (member.equals(key)) { // better safe than sorry 4299 LOOKASIDE_TABLE.put(key, dmh); 4300 } 4301 } 4302 return mh; 4303 } 4304 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) { 4305 if (refKind == REF_invokeSpecial) { 4306 return false; 4307 } 4308 if (!Modifier.isPublic(defc.getModifiers()) || 4309 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) || 4310 !member.isPublic() || 4311 member.isCallerSensitive()) { 4312 return false; 4313 } 4314 ClassLoader loader = defc.getClassLoader(); 4315 if (loader != null) { 4316 ClassLoader sysl = ClassLoader.getSystemClassLoader(); 4317 boolean found = false; 4318 while (sysl != null) { 4319 if (loader == sysl) { found = true; break; } 4320 sysl = sysl.getParent(); 4321 } 4322 if (!found) { 4323 return false; 4324 } 4325 } 4326 try { 4327 MemberName resolved2 = publicLookup().resolveOrNull(refKind, 4328 new MemberName(refKind, defc, member.getName(), member.getType())); 4329 if (resolved2 == null) { 4330 return false; 4331 } 4332 checkSecurityManager(defc, resolved2); 4333 } catch (SecurityException ex) { 4334 return false; 4335 } 4336 return true; 4337 } 4338 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member) 4339 throws ReflectiveOperationException { 4340 if (MethodHandleNatives.refKindIsField(refKind)) { 4341 return getDirectFieldNoSecurityManager(refKind, defc, member); 4342 } else if (MethodHandleNatives.refKindIsMethod(refKind)) { 4343 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member)); 4344 } else if (refKind == REF_newInvokeSpecial) { 4345 return getDirectConstructorNoSecurityManager(defc, member); 4346 } 4347 // oops 4348 throw newIllegalArgumentException("bad MethodHandle constant #"+member); 4349 } 4350 4351 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>(); 4352 } 4353 4354 /** 4355 * Produces a method handle constructing arrays of a desired type, 4356 * as if by the {@code anewarray} bytecode. 4357 * The return type of the method handle will be the array type. 4358 * The type of its sole argument will be {@code int}, which specifies the size of the array. 4359 * 4360 * <p> If the returned method handle is invoked with a negative 4361 * array size, a {@code NegativeArraySizeException} will be thrown. 4362 * 4363 * @param arrayClass an array type 4364 * @return a method handle which can create arrays of the given type 4365 * @throws NullPointerException if the argument is {@code null} 4366 * @throws IllegalArgumentException if {@code arrayClass} is not an array type 4367 * @see java.lang.reflect.Array#newInstance(Class, int) 4368 * @jvms 6.5 {@code anewarray} Instruction 4369 * @since 9 4370 */ 4371 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException { 4372 if (!arrayClass.isArray()) { 4373 throw newIllegalArgumentException("not an array class: " + arrayClass.getName()); 4374 } 4375 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance). 4376 bindTo(arrayClass.getComponentType()); 4377 return ani.asType(ani.type().changeReturnType(arrayClass)); 4378 } 4379 4380 /** 4381 * Produces a method handle returning the length of an array, 4382 * as if by the {@code arraylength} bytecode. 4383 * The type of the method handle will have {@code int} as return type, 4384 * and its sole argument will be the array type. 4385 * 4386 * <p> If the returned method handle is invoked with a {@code null} 4387 * array reference, a {@code NullPointerException} will be thrown. 4388 * 4389 * @param arrayClass an array type 4390 * @return a method handle which can retrieve the length of an array of the given array type 4391 * @throws NullPointerException if the argument is {@code null} 4392 * @throws IllegalArgumentException if arrayClass is not an array type 4393 * @jvms 6.5 {@code arraylength} Instruction 4394 * @since 9 4395 */ 4396 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException { 4397 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH); 4398 } 4399 4400 /** 4401 * Produces a method handle giving read access to elements of an array, 4402 * as if by the {@code aaload} bytecode. 4403 * The type of the method handle will have a return type of the array's 4404 * element type. Its first argument will be the array type, 4405 * and the second will be {@code int}. 4406 * 4407 * <p> When the returned method handle is invoked, 4408 * the array reference and array index are checked. 4409 * A {@code NullPointerException} will be thrown if the array reference 4410 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4411 * thrown if the index is negative or if it is greater than or equal to 4412 * the length of the array. 4413 * 4414 * @param arrayClass an array type 4415 * @return a method handle which can load values from the given array type 4416 * @throws NullPointerException if the argument is null 4417 * @throws IllegalArgumentException if arrayClass is not an array type 4418 * @jvms 6.5 {@code aaload} Instruction 4419 */ 4420 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException { 4421 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET); 4422 } 4423 4424 /** 4425 * Produces a method handle giving write access to elements of an array, 4426 * as if by the {@code astore} bytecode. 4427 * The type of the method handle will have a void return type. 4428 * Its last argument will be the array's element type. 4429 * The first and second arguments will be the array type and int. 4430 * 4431 * <p> When the returned method handle is invoked, 4432 * the array reference and array index are checked. 4433 * A {@code NullPointerException} will be thrown if the array reference 4434 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4435 * thrown if the index is negative or if it is greater than or equal to 4436 * the length of the array. 4437 * 4438 * @param arrayClass the class of an array 4439 * @return a method handle which can store values into the array type 4440 * @throws NullPointerException if the argument is null 4441 * @throws IllegalArgumentException if arrayClass is not an array type 4442 * @jvms 6.5 {@code aastore} Instruction 4443 */ 4444 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException { 4445 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET); 4446 } 4447 4448 /** 4449 * Produces a VarHandle giving access to elements of an array of type 4450 * {@code arrayClass}. The VarHandle's variable type is the component type 4451 * of {@code arrayClass} and the list of coordinate types is 4452 * {@code (arrayClass, int)}, where the {@code int} coordinate type 4453 * corresponds to an argument that is an index into an array. 4454 * <p> 4455 * Certain access modes of the returned VarHandle are unsupported under 4456 * the following conditions: 4457 * <ul> 4458 * <li>if the component type is anything other than {@code byte}, 4459 * {@code short}, {@code char}, {@code int}, {@code long}, 4460 * {@code float}, or {@code double} then numeric atomic update access 4461 * modes are unsupported. 4462 * <li>if the component type is anything other than {@code boolean}, 4463 * {@code byte}, {@code short}, {@code char}, {@code int} or 4464 * {@code long} then bitwise atomic update access modes are 4465 * unsupported. 4466 * </ul> 4467 * <p> 4468 * If the component type is {@code float} or {@code double} then numeric 4469 * and atomic update access modes compare values using their bitwise 4470 * representation (see {@link Float#floatToRawIntBits} and 4471 * {@link Double#doubleToRawLongBits}, respectively). 4472 * 4473 * <p> When the returned {@code VarHandle} is invoked, 4474 * the array reference and array index are checked. 4475 * A {@code NullPointerException} will be thrown if the array reference 4476 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4477 * thrown if the index is negative or if it is greater than or equal to 4478 * the length of the array. 4479 * 4480 * @apiNote 4481 * Bitwise comparison of {@code float} values or {@code double} values, 4482 * as performed by the numeric and atomic update access modes, differ 4483 * from the primitive {@code ==} operator and the {@link Float#equals} 4484 * and {@link Double#equals} methods, specifically with respect to 4485 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 4486 * Care should be taken when performing a compare and set or a compare 4487 * and exchange operation with such values since the operation may 4488 * unexpectedly fail. 4489 * There are many possible NaN values that are considered to be 4490 * {@code NaN} in Java, although no IEEE 754 floating-point operation 4491 * provided by Java can distinguish between them. Operation failure can 4492 * occur if the expected or witness value is a NaN value and it is 4493 * transformed (perhaps in a platform specific manner) into another NaN 4494 * value, and thus has a different bitwise representation (see 4495 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 4496 * details). 4497 * The values {@code -0.0} and {@code +0.0} have different bitwise 4498 * representations but are considered equal when using the primitive 4499 * {@code ==} operator. Operation failure can occur if, for example, a 4500 * numeric algorithm computes an expected value to be say {@code -0.0} 4501 * and previously computed the witness value to be say {@code +0.0}. 4502 * @param arrayClass the class of an array, of type {@code T[]} 4503 * @return a VarHandle giving access to elements of an array 4504 * @throws NullPointerException if the arrayClass is null 4505 * @throws IllegalArgumentException if arrayClass is not an array type 4506 * @since 9 4507 */ 4508 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException { 4509 return VarHandles.makeArrayElementHandle(arrayClass); 4510 } 4511 4512 /** 4513 * Produces a VarHandle giving access to elements of a {@code byte[]} array 4514 * viewed as if it were a different primitive array type, such as 4515 * {@code int[]} or {@code long[]}. 4516 * The VarHandle's variable type is the component type of 4517 * {@code viewArrayClass} and the list of coordinate types is 4518 * {@code (byte[], int)}, where the {@code int} coordinate type 4519 * corresponds to an argument that is an index into a {@code byte[]} array. 4520 * The returned VarHandle accesses bytes at an index in a {@code byte[]} 4521 * array, composing bytes to or from a value of the component type of 4522 * {@code viewArrayClass} according to the given endianness. 4523 * <p> 4524 * The supported component types (variables types) are {@code short}, 4525 * {@code char}, {@code int}, {@code long}, {@code float} and 4526 * {@code double}. 4527 * <p> 4528 * Access of bytes at a given index will result in an 4529 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0} 4530 * or greater than the {@code byte[]} array length minus the size (in bytes) 4531 * of {@code T}. 4532 * <p> 4533 * Access of bytes at an index may be aligned or misaligned for {@code T}, 4534 * with respect to the underlying memory address, {@code A} say, associated 4535 * with the array and index. 4536 * If access is misaligned then access for anything other than the 4537 * {@code get} and {@code set} access modes will result in an 4538 * {@code IllegalStateException}. In such cases atomic access is only 4539 * guaranteed with respect to the largest power of two that divides the GCD 4540 * of {@code A} and the size (in bytes) of {@code T}. 4541 * If access is aligned then following access modes are supported and are 4542 * guaranteed to support atomic access: 4543 * <ul> 4544 * <li>read write access modes for all {@code T}, with the exception of 4545 * access modes {@code get} and {@code set} for {@code long} and 4546 * {@code double} on 32-bit platforms. 4547 * <li>atomic update access modes for {@code int}, {@code long}, 4548 * {@code float} or {@code double}. 4549 * (Future major platform releases of the JDK may support additional 4550 * types for certain currently unsupported access modes.) 4551 * <li>numeric atomic update access modes for {@code int} and {@code long}. 4552 * (Future major platform releases of the JDK may support additional 4553 * numeric types for certain currently unsupported access modes.) 4554 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 4555 * (Future major platform releases of the JDK may support additional 4556 * numeric types for certain currently unsupported access modes.) 4557 * </ul> 4558 * <p> 4559 * Misaligned access, and therefore atomicity guarantees, may be determined 4560 * for {@code byte[]} arrays without operating on a specific array. Given 4561 * an {@code index}, {@code T} and its corresponding boxed type, 4562 * {@code T_BOX}, misalignment may be determined as follows: 4563 * <pre>{@code 4564 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 4565 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]). 4566 * alignmentOffset(0, sizeOfT); 4567 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT; 4568 * boolean isMisaligned = misalignedAtIndex != 0; 4569 * }</pre> 4570 * <p> 4571 * If the variable type is {@code float} or {@code double} then atomic 4572 * update access modes compare values using their bitwise representation 4573 * (see {@link Float#floatToRawIntBits} and 4574 * {@link Double#doubleToRawLongBits}, respectively). 4575 * @param viewArrayClass the view array class, with a component type of 4576 * type {@code T} 4577 * @param byteOrder the endianness of the view array elements, as 4578 * stored in the underlying {@code byte} array 4579 * @return a VarHandle giving access to elements of a {@code byte[]} array 4580 * viewed as if elements corresponding to the components type of the view 4581 * array class 4582 * @throws NullPointerException if viewArrayClass or byteOrder is null 4583 * @throws IllegalArgumentException if viewArrayClass is not an array type 4584 * @throws UnsupportedOperationException if the component type of 4585 * viewArrayClass is not supported as a variable type 4586 * @since 9 4587 */ 4588 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass, 4589 ByteOrder byteOrder) throws IllegalArgumentException { 4590 Objects.requireNonNull(byteOrder); 4591 return VarHandles.byteArrayViewHandle(viewArrayClass, 4592 byteOrder == ByteOrder.BIG_ENDIAN); 4593 } 4594 4595 /** 4596 * Produces a VarHandle giving access to elements of a {@code ByteBuffer} 4597 * viewed as if it were an array of elements of a different primitive 4598 * component type to that of {@code byte}, such as {@code int[]} or 4599 * {@code long[]}. 4600 * The VarHandle's variable type is the component type of 4601 * {@code viewArrayClass} and the list of coordinate types is 4602 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type 4603 * corresponds to an argument that is an index into a {@code byte[]} array. 4604 * The returned VarHandle accesses bytes at an index in a 4605 * {@code ByteBuffer}, composing bytes to or from a value of the component 4606 * type of {@code viewArrayClass} according to the given endianness. 4607 * <p> 4608 * The supported component types (variables types) are {@code short}, 4609 * {@code char}, {@code int}, {@code long}, {@code float} and 4610 * {@code double}. 4611 * <p> 4612 * Access will result in a {@code ReadOnlyBufferException} for anything 4613 * other than the read access modes if the {@code ByteBuffer} is read-only. 4614 * <p> 4615 * Access of bytes at a given index will result in an 4616 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 4617 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of 4618 * {@code T}. 4619 * <p> 4620 * Access of bytes at an index may be aligned or misaligned for {@code T}, 4621 * with respect to the underlying memory address, {@code A} say, associated 4622 * with the {@code ByteBuffer} and index. 4623 * If access is misaligned then access for anything other than the 4624 * {@code get} and {@code set} access modes will result in an 4625 * {@code IllegalStateException}. In such cases atomic access is only 4626 * guaranteed with respect to the largest power of two that divides the GCD 4627 * of {@code A} and the size (in bytes) of {@code T}. 4628 * If access is aligned then following access modes are supported and are 4629 * guaranteed to support atomic access: 4630 * <ul> 4631 * <li>read write access modes for all {@code T}, with the exception of 4632 * access modes {@code get} and {@code set} for {@code long} and 4633 * {@code double} on 32-bit platforms. 4634 * <li>atomic update access modes for {@code int}, {@code long}, 4635 * {@code float} or {@code double}. 4636 * (Future major platform releases of the JDK may support additional 4637 * types for certain currently unsupported access modes.) 4638 * <li>numeric atomic update access modes for {@code int} and {@code long}. 4639 * (Future major platform releases of the JDK may support additional 4640 * numeric types for certain currently unsupported access modes.) 4641 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 4642 * (Future major platform releases of the JDK may support additional 4643 * numeric types for certain currently unsupported access modes.) 4644 * </ul> 4645 * <p> 4646 * Misaligned access, and therefore atomicity guarantees, may be determined 4647 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an 4648 * {@code index}, {@code T} and its corresponding boxed type, 4649 * {@code T_BOX}, as follows: 4650 * <pre>{@code 4651 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 4652 * ByteBuffer bb = ... 4653 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT); 4654 * boolean isMisaligned = misalignedAtIndex != 0; 4655 * }</pre> 4656 * <p> 4657 * If the variable type is {@code float} or {@code double} then atomic 4658 * update access modes compare values using their bitwise representation 4659 * (see {@link Float#floatToRawIntBits} and 4660 * {@link Double#doubleToRawLongBits}, respectively). 4661 * @param viewArrayClass the view array class, with a component type of 4662 * type {@code T} 4663 * @param byteOrder the endianness of the view array elements, as 4664 * stored in the underlying {@code ByteBuffer} (Note this overrides the 4665 * endianness of a {@code ByteBuffer}) 4666 * @return a VarHandle giving access to elements of a {@code ByteBuffer} 4667 * viewed as if elements corresponding to the components type of the view 4668 * array class 4669 * @throws NullPointerException if viewArrayClass or byteOrder is null 4670 * @throws IllegalArgumentException if viewArrayClass is not an array type 4671 * @throws UnsupportedOperationException if the component type of 4672 * viewArrayClass is not supported as a variable type 4673 * @since 9 4674 */ 4675 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass, 4676 ByteOrder byteOrder) throws IllegalArgumentException { 4677 Objects.requireNonNull(byteOrder); 4678 return VarHandles.makeByteBufferViewHandle(viewArrayClass, 4679 byteOrder == ByteOrder.BIG_ENDIAN); 4680 } 4681 4682 4683 /// method handle invocation (reflective style) 4684 4685 /** 4686 * Produces a method handle which will invoke any method handle of the 4687 * given {@code type}, with a given number of trailing arguments replaced by 4688 * a single trailing {@code Object[]} array. 4689 * The resulting invoker will be a method handle with the following 4690 * arguments: 4691 * <ul> 4692 * <li>a single {@code MethodHandle} target 4693 * <li>zero or more leading values (counted by {@code leadingArgCount}) 4694 * <li>an {@code Object[]} array containing trailing arguments 4695 * </ul> 4696 * <p> 4697 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with 4698 * the indicated {@code type}. 4699 * That is, if the target is exactly of the given {@code type}, it will behave 4700 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType} 4701 * is used to convert the target to the required {@code type}. 4702 * <p> 4703 * The type of the returned invoker will not be the given {@code type}, but rather 4704 * will have all parameters except the first {@code leadingArgCount} 4705 * replaced by a single array of type {@code Object[]}, which will be 4706 * the final parameter. 4707 * <p> 4708 * Before invoking its target, the invoker will spread the final array, apply 4709 * reference casts as necessary, and unbox and widen primitive arguments. 4710 * If, when the invoker is called, the supplied array argument does 4711 * not have the correct number of elements, the invoker will throw 4712 * an {@link IllegalArgumentException} instead of invoking the target. 4713 * <p> 4714 * This method is equivalent to the following code (though it may be more efficient): 4715 * {@snippet lang="java" : 4716 MethodHandle invoker = MethodHandles.invoker(type); 4717 int spreadArgCount = type.parameterCount() - leadingArgCount; 4718 invoker = invoker.asSpreader(Object[].class, spreadArgCount); 4719 return invoker; 4720 * } 4721 * This method throws no reflective or security exceptions. 4722 * @param type the desired target type 4723 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target 4724 * @return a method handle suitable for invoking any method handle of the given type 4725 * @throws NullPointerException if {@code type} is null 4726 * @throws IllegalArgumentException if {@code leadingArgCount} is not in 4727 * the range from 0 to {@code type.parameterCount()} inclusive, 4728 * or if the resulting method handle's type would have 4729 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4730 */ 4731 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) { 4732 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) 4733 throw newIllegalArgumentException("bad argument count", leadingArgCount); 4734 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount); 4735 return type.invokers().spreadInvoker(leadingArgCount); 4736 } 4737 4738 /** 4739 * Produces a special <em>invoker method handle</em> which can be used to 4740 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. 4741 * The resulting invoker will have a type which is 4742 * exactly equal to the desired type, except that it will accept 4743 * an additional leading argument of type {@code MethodHandle}. 4744 * <p> 4745 * This method is equivalent to the following code (though it may be more efficient): 4746 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)} 4747 * 4748 * <p style="font-size:smaller;"> 4749 * <em>Discussion:</em> 4750 * Invoker method handles can be useful when working with variable method handles 4751 * of unknown types. 4752 * For example, to emulate an {@code invokeExact} call to a variable method 4753 * handle {@code M}, extract its type {@code T}, 4754 * look up the invoker method {@code X} for {@code T}, 4755 * and call the invoker method, as {@code X.invoke(T, A...)}. 4756 * (It would not work to call {@code X.invokeExact}, since the type {@code T} 4757 * is unknown.) 4758 * If spreading, collecting, or other argument transformations are required, 4759 * they can be applied once to the invoker {@code X} and reused on many {@code M} 4760 * method handle values, as long as they are compatible with the type of {@code X}. 4761 * <p style="font-size:smaller;"> 4762 * <em>(Note: The invoker method is not available via the Core Reflection API. 4763 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 4764 * on the declared {@code invokeExact} or {@code invoke} method will raise an 4765 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 4766 * <p> 4767 * This method throws no reflective or security exceptions. 4768 * @param type the desired target type 4769 * @return a method handle suitable for invoking any method handle of the given type 4770 * @throws IllegalArgumentException if the resulting method handle's type would have 4771 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4772 */ 4773 public static MethodHandle exactInvoker(MethodType type) { 4774 return type.invokers().exactInvoker(); 4775 } 4776 4777 /** 4778 * Produces a special <em>invoker method handle</em> which can be used to 4779 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}. 4780 * The resulting invoker will have a type which is 4781 * exactly equal to the desired type, except that it will accept 4782 * an additional leading argument of type {@code MethodHandle}. 4783 * <p> 4784 * Before invoking its target, if the target differs from the expected type, 4785 * the invoker will apply reference casts as 4786 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}. 4787 * Similarly, the return value will be converted as necessary. 4788 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle}, 4789 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}. 4790 * <p> 4791 * This method is equivalent to the following code (though it may be more efficient): 4792 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)} 4793 * <p style="font-size:smaller;"> 4794 * <em>Discussion:</em> 4795 * A {@linkplain MethodType#genericMethodType general method type} is one which 4796 * mentions only {@code Object} arguments and return values. 4797 * An invoker for such a type is capable of calling any method handle 4798 * of the same arity as the general type. 4799 * <p style="font-size:smaller;"> 4800 * <em>(Note: The invoker method is not available via the Core Reflection API. 4801 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 4802 * on the declared {@code invokeExact} or {@code invoke} method will raise an 4803 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 4804 * <p> 4805 * This method throws no reflective or security exceptions. 4806 * @param type the desired target type 4807 * @return a method handle suitable for invoking any method handle convertible to the given type 4808 * @throws IllegalArgumentException if the resulting method handle's type would have 4809 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4810 */ 4811 public static MethodHandle invoker(MethodType type) { 4812 return type.invokers().genericInvoker(); 4813 } 4814 4815 /** 4816 * Produces a special <em>invoker method handle</em> which can be used to 4817 * invoke a signature-polymorphic access mode method on any VarHandle whose 4818 * associated access mode type is compatible with the given type. 4819 * The resulting invoker will have a type which is exactly equal to the 4820 * desired given type, except that it will accept an additional leading 4821 * argument of type {@code VarHandle}. 4822 * 4823 * @param accessMode the VarHandle access mode 4824 * @param type the desired target type 4825 * @return a method handle suitable for invoking an access mode method of 4826 * any VarHandle whose access mode type is of the given type. 4827 * @since 9 4828 */ 4829 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) { 4830 return type.invokers().varHandleMethodExactInvoker(accessMode); 4831 } 4832 4833 /** 4834 * Produces a special <em>invoker method handle</em> which can be used to 4835 * invoke a signature-polymorphic access mode method on any VarHandle whose 4836 * associated access mode type is compatible with the given type. 4837 * The resulting invoker will have a type which is exactly equal to the 4838 * desired given type, except that it will accept an additional leading 4839 * argument of type {@code VarHandle}. 4840 * <p> 4841 * Before invoking its target, if the access mode type differs from the 4842 * desired given type, the invoker will apply reference casts as necessary 4843 * and box, unbox, or widen primitive values, as if by 4844 * {@link MethodHandle#asType asType}. Similarly, the return value will be 4845 * converted as necessary. 4846 * <p> 4847 * This method is equivalent to the following code (though it may be more 4848 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)} 4849 * 4850 * @param accessMode the VarHandle access mode 4851 * @param type the desired target type 4852 * @return a method handle suitable for invoking an access mode method of 4853 * any VarHandle whose access mode type is convertible to the given 4854 * type. 4855 * @since 9 4856 */ 4857 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) { 4858 return type.invokers().varHandleMethodInvoker(accessMode); 4859 } 4860 4861 /*non-public*/ 4862 static MethodHandle basicInvoker(MethodType type) { 4863 return type.invokers().basicInvoker(); 4864 } 4865 4866 /// method handle modification (creation from other method handles) 4867 4868 /** 4869 * Produces a method handle which adapts the type of the 4870 * given method handle to a new type by pairwise argument and return type conversion. 4871 * The original type and new type must have the same number of arguments. 4872 * The resulting method handle is guaranteed to report a type 4873 * which is equal to the desired new type. 4874 * <p> 4875 * If the original type and new type are equal, returns target. 4876 * <p> 4877 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType}, 4878 * and some additional conversions are also applied if those conversions fail. 4879 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied 4880 * if possible, before or instead of any conversions done by {@code asType}: 4881 * <ul> 4882 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type, 4883 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast. 4884 * (This treatment of interfaces follows the usage of the bytecode verifier.) 4885 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive, 4886 * the boolean is converted to a byte value, 1 for true, 0 for false. 4887 * (This treatment follows the usage of the bytecode verifier.) 4888 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive, 4889 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}), 4890 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}. 4891 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean, 4892 * then a Java casting conversion (JLS {@jls 5.5}) is applied. 4893 * (Specifically, <em>T0</em> will convert to <em>T1</em> by 4894 * widening and/or narrowing.) 4895 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing 4896 * conversion will be applied at runtime, possibly followed 4897 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value, 4898 * possibly followed by a conversion from byte to boolean by testing 4899 * the low-order bit. 4900 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, 4901 * and if the reference is null at runtime, a zero value is introduced. 4902 * </ul> 4903 * @param target the method handle to invoke after arguments are retyped 4904 * @param newType the expected type of the new method handle 4905 * @return a method handle which delegates to the target after performing 4906 * any necessary argument conversions, and arranges for any 4907 * necessary return value conversions 4908 * @throws NullPointerException if either argument is null 4909 * @throws WrongMethodTypeException if the conversion cannot be made 4910 * @see MethodHandle#asType 4911 */ 4912 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) { 4913 explicitCastArgumentsChecks(target, newType); 4914 // use the asTypeCache when possible: 4915 MethodType oldType = target.type(); 4916 if (oldType == newType) return target; 4917 if (oldType.explicitCastEquivalentToAsType(newType)) { 4918 return target.asFixedArity().asType(newType); 4919 } 4920 return MethodHandleImpl.makePairwiseConvert(target, newType, false); 4921 } 4922 4923 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) { 4924 if (target.type().parameterCount() != newType.parameterCount()) { 4925 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType); 4926 } 4927 } 4928 4929 /** 4930 * Produces a method handle which adapts the calling sequence of the 4931 * given method handle to a new type, by reordering the arguments. 4932 * The resulting method handle is guaranteed to report a type 4933 * which is equal to the desired new type. 4934 * <p> 4935 * The given array controls the reordering. 4936 * Call {@code #I} the number of incoming parameters (the value 4937 * {@code newType.parameterCount()}, and call {@code #O} the number 4938 * of outgoing parameters (the value {@code target.type().parameterCount()}). 4939 * Then the length of the reordering array must be {@code #O}, 4940 * and each element must be a non-negative number less than {@code #I}. 4941 * For every {@code N} less than {@code #O}, the {@code N}-th 4942 * outgoing argument will be taken from the {@code I}-th incoming 4943 * argument, where {@code I} is {@code reorder[N]}. 4944 * <p> 4945 * No argument or return value conversions are applied. 4946 * The type of each incoming argument, as determined by {@code newType}, 4947 * must be identical to the type of the corresponding outgoing parameter 4948 * or parameters in the target method handle. 4949 * The return type of {@code newType} must be identical to the return 4950 * type of the original target. 4951 * <p> 4952 * The reordering array need not specify an actual permutation. 4953 * An incoming argument will be duplicated if its index appears 4954 * more than once in the array, and an incoming argument will be dropped 4955 * if its index does not appear in the array. 4956 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments}, 4957 * incoming arguments which are not mentioned in the reordering array 4958 * may be of any type, as determined only by {@code newType}. 4959 * {@snippet lang="java" : 4960 import static java.lang.invoke.MethodHandles.*; 4961 import static java.lang.invoke.MethodType.*; 4962 ... 4963 MethodType intfn1 = methodType(int.class, int.class); 4964 MethodType intfn2 = methodType(int.class, int.class, int.class); 4965 MethodHandle sub = ... (int x, int y) -> (x-y) ...; 4966 assert(sub.type().equals(intfn2)); 4967 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1); 4968 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0); 4969 assert((int)rsub.invokeExact(1, 100) == 99); 4970 MethodHandle add = ... (int x, int y) -> (x+y) ...; 4971 assert(add.type().equals(intfn2)); 4972 MethodHandle twice = permuteArguments(add, intfn1, 0, 0); 4973 assert(twice.type().equals(intfn1)); 4974 assert((int)twice.invokeExact(21) == 42); 4975 * } 4976 * <p> 4977 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4978 * variable-arity method handle}, even if the original target method handle was. 4979 * @param target the method handle to invoke after arguments are reordered 4980 * @param newType the expected type of the new method handle 4981 * @param reorder an index array which controls the reordering 4982 * @return a method handle which delegates to the target after it 4983 * drops unused arguments and moves and/or duplicates the other arguments 4984 * @throws NullPointerException if any argument is null 4985 * @throws IllegalArgumentException if the index array length is not equal to 4986 * the arity of the target, or if any index array element 4987 * not a valid index for a parameter of {@code newType}, 4988 * or if two corresponding parameter types in 4989 * {@code target.type()} and {@code newType} are not identical, 4990 */ 4991 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) { 4992 reorder = reorder.clone(); // get a private copy 4993 MethodType oldType = target.type(); 4994 permuteArgumentChecks(reorder, newType, oldType); 4995 // first detect dropped arguments and handle them separately 4996 int[] originalReorder = reorder; 4997 BoundMethodHandle result = target.rebind(); 4998 LambdaForm form = result.form; 4999 int newArity = newType.parameterCount(); 5000 // Normalize the reordering into a real permutation, 5001 // by removing duplicates and adding dropped elements. 5002 // This somewhat improves lambda form caching, as well 5003 // as simplifying the transform by breaking it up into steps. 5004 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) { 5005 if (ddIdx > 0) { 5006 // We found a duplicated entry at reorder[ddIdx]. 5007 // Example: (x,y,z)->asList(x,y,z) 5008 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1) 5009 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0) 5010 // The starred element corresponds to the argument 5011 // deleted by the dupArgumentForm transform. 5012 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos]; 5013 boolean killFirst = false; 5014 for (int val; (val = reorder[--dstPos]) != dupVal; ) { 5015 // Set killFirst if the dup is larger than an intervening position. 5016 // This will remove at least one inversion from the permutation. 5017 if (dupVal > val) killFirst = true; 5018 } 5019 if (!killFirst) { 5020 srcPos = dstPos; 5021 dstPos = ddIdx; 5022 } 5023 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos); 5024 assert (reorder[srcPos] == reorder[dstPos]); 5025 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1); 5026 // contract the reordering by removing the element at dstPos 5027 int tailPos = dstPos + 1; 5028 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos); 5029 reorder = Arrays.copyOf(reorder, reorder.length - 1); 5030 } else { 5031 int dropVal = ~ddIdx, insPos = 0; 5032 while (insPos < reorder.length && reorder[insPos] < dropVal) { 5033 // Find first element of reorder larger than dropVal. 5034 // This is where we will insert the dropVal. 5035 insPos += 1; 5036 } 5037 Class<?> ptype = newType.parameterType(dropVal); 5038 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype)); 5039 oldType = oldType.insertParameterTypes(insPos, ptype); 5040 // expand the reordering by inserting an element at insPos 5041 int tailPos = insPos + 1; 5042 reorder = Arrays.copyOf(reorder, reorder.length + 1); 5043 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos); 5044 reorder[insPos] = dropVal; 5045 } 5046 assert (permuteArgumentChecks(reorder, newType, oldType)); 5047 } 5048 assert (reorder.length == newArity); // a perfect permutation 5049 // Note: This may cache too many distinct LFs. Consider backing off to varargs code. 5050 form = form.editor().permuteArgumentsForm(1, reorder); 5051 if (newType == result.type() && form == result.internalForm()) 5052 return result; 5053 return result.copyWith(newType, form); 5054 } 5055 5056 /** 5057 * Return an indication of any duplicate or omission in reorder. 5058 * If the reorder contains a duplicate entry, return the index of the second occurrence. 5059 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder. 5060 * Otherwise, return zero. 5061 * If an element not in [0..newArity-1] is encountered, return reorder.length. 5062 */ 5063 private static int findFirstDupOrDrop(int[] reorder, int newArity) { 5064 final int BIT_LIMIT = 63; // max number of bits in bit mask 5065 if (newArity < BIT_LIMIT) { 5066 long mask = 0; 5067 for (int i = 0; i < reorder.length; i++) { 5068 int arg = reorder[i]; 5069 if (arg >= newArity) { 5070 return reorder.length; 5071 } 5072 long bit = 1L << arg; 5073 if ((mask & bit) != 0) { 5074 return i; // >0 indicates a dup 5075 } 5076 mask |= bit; 5077 } 5078 if (mask == (1L << newArity) - 1) { 5079 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity); 5080 return 0; 5081 } 5082 // find first zero 5083 long zeroBit = Long.lowestOneBit(~mask); 5084 int zeroPos = Long.numberOfTrailingZeros(zeroBit); 5085 assert(zeroPos <= newArity); 5086 if (zeroPos == newArity) { 5087 return 0; 5088 } 5089 return ~zeroPos; 5090 } else { 5091 // same algorithm, different bit set 5092 BitSet mask = new BitSet(newArity); 5093 for (int i = 0; i < reorder.length; i++) { 5094 int arg = reorder[i]; 5095 if (arg >= newArity) { 5096 return reorder.length; 5097 } 5098 if (mask.get(arg)) { 5099 return i; // >0 indicates a dup 5100 } 5101 mask.set(arg); 5102 } 5103 int zeroPos = mask.nextClearBit(0); 5104 assert(zeroPos <= newArity); 5105 if (zeroPos == newArity) { 5106 return 0; 5107 } 5108 return ~zeroPos; 5109 } 5110 } 5111 5112 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) { 5113 if (newType.returnType() != oldType.returnType()) 5114 throw newIllegalArgumentException("return types do not match", 5115 oldType, newType); 5116 if (reorder.length != oldType.parameterCount()) 5117 throw newIllegalArgumentException("old type parameter count and reorder array length do not match", 5118 oldType, Arrays.toString(reorder)); 5119 5120 int limit = newType.parameterCount(); 5121 for (int j = 0; j < reorder.length; j++) { 5122 int i = reorder[j]; 5123 if (i < 0 || i >= limit) { 5124 throw newIllegalArgumentException("index is out of bounds for new type", 5125 i, newType); 5126 } 5127 Class<?> src = newType.parameterType(i); 5128 Class<?> dst = oldType.parameterType(j); 5129 if (src != dst) 5130 throw newIllegalArgumentException("parameter types do not match after reorder", 5131 oldType, newType); 5132 } 5133 return true; 5134 } 5135 5136 /** 5137 * Produces a method handle of the requested return type which returns the given 5138 * constant value every time it is invoked. 5139 * <p> 5140 * Before the method handle is returned, the passed-in value is converted to the requested type. 5141 * If the requested type is primitive, widening primitive conversions are attempted, 5142 * else reference conversions are attempted. 5143 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}. 5144 * @param type the return type of the desired method handle 5145 * @param value the value to return 5146 * @return a method handle of the given return type and no arguments, which always returns the given value 5147 * @throws NullPointerException if the {@code type} argument is null 5148 * @throws ClassCastException if the value cannot be converted to the required return type 5149 * @throws IllegalArgumentException if the given type is {@code void.class} 5150 */ 5151 public static MethodHandle constant(Class<?> type, Object value) { 5152 if (type.isPrimitive()) { 5153 if (type == void.class) 5154 throw newIllegalArgumentException("void type"); 5155 Wrapper w = Wrapper.forPrimitiveType(type); 5156 value = w.convert(value, type); 5157 if (w.zero().equals(value)) 5158 return zero(w, type); 5159 return insertArguments(identity(type), 0, value); 5160 } else { 5161 if (!PrimitiveClass.isPrimitiveValueType(type) && value == null) 5162 return zero(Wrapper.OBJECT, type); 5163 return identity(type).bindTo(value); 5164 } 5165 } 5166 5167 /** 5168 * Produces a method handle which returns its sole argument when invoked. 5169 * @param type the type of the sole parameter and return value of the desired method handle 5170 * @return a unary method handle which accepts and returns the given type 5171 * @throws NullPointerException if the argument is null 5172 * @throws IllegalArgumentException if the given type is {@code void.class} 5173 */ 5174 public static MethodHandle identity(Class<?> type) { 5175 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT); 5176 int pos = btw.ordinal(); 5177 MethodHandle ident = IDENTITY_MHS[pos]; 5178 if (ident == null) { 5179 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType())); 5180 } 5181 if (ident.type().returnType() == type) 5182 return ident; 5183 // something like identity(Foo.class); do not bother to intern these 5184 assert (btw == Wrapper.OBJECT); 5185 return makeIdentity(type); 5186 } 5187 5188 /** 5189 * Produces a constant method handle of the requested return type which 5190 * returns the default value for that type every time it is invoked. 5191 * The resulting constant method handle will have no side effects. 5192 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}. 5193 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))}, 5194 * since {@code explicitCastArguments} converts {@code null} to default values. 5195 * @param type the expected return type of the desired method handle 5196 * @return a constant method handle that takes no arguments 5197 * and returns the default value of the given type (or void, if the type is void) 5198 * @throws NullPointerException if the argument is null 5199 * @see MethodHandles#constant 5200 * @see MethodHandles#empty 5201 * @see MethodHandles#explicitCastArguments 5202 * @since 9 5203 */ 5204 public static MethodHandle zero(Class<?> type) { 5205 Objects.requireNonNull(type); 5206 if (type.isPrimitive()) { 5207 return zero(Wrapper.forPrimitiveType(type), type); 5208 } else if (PrimitiveClass.isPrimitiveValueType(type)) { 5209 // singleton default value 5210 Object value = UNSAFE.uninitializedDefaultValue(type); 5211 return identity(type).bindTo(value); 5212 } else { 5213 return zero(Wrapper.OBJECT, type); 5214 } 5215 } 5216 5217 private static MethodHandle identityOrVoid(Class<?> type) { 5218 return type == void.class ? zero(type) : identity(type); 5219 } 5220 5221 /** 5222 * Produces a method handle of the requested type which ignores any arguments, does nothing, 5223 * and returns a suitable default depending on the return type. 5224 * That is, it returns a zero primitive value, a {@code null}, or {@code void}. 5225 * <p>The returned method handle is equivalent to 5226 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}. 5227 * 5228 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as 5229 * {@code guardWithTest(pred, target, empty(target.type())}. 5230 * @param type the type of the desired method handle 5231 * @return a constant method handle of the given type, which returns a default value of the given return type 5232 * @throws NullPointerException if the argument is null 5233 * @see MethodHandles#zero 5234 * @see MethodHandles#constant 5235 * @since 9 5236 */ 5237 public static MethodHandle empty(MethodType type) { 5238 Objects.requireNonNull(type); 5239 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes()); 5240 } 5241 5242 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT]; 5243 private static MethodHandle makeIdentity(Class<?> ptype) { 5244 MethodType mtype = MethodType.methodType(ptype, ptype); 5245 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype)); 5246 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY); 5247 } 5248 5249 private static MethodHandle zero(Wrapper btw, Class<?> rtype) { 5250 int pos = btw.ordinal(); 5251 MethodHandle zero = ZERO_MHS[pos]; 5252 if (zero == null) { 5253 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType())); 5254 } 5255 if (zero.type().returnType() == rtype) 5256 return zero; 5257 assert(btw == Wrapper.OBJECT); 5258 return makeZero(rtype); 5259 } 5260 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT]; 5261 private static MethodHandle makeZero(Class<?> rtype) { 5262 MethodType mtype = methodType(rtype); 5263 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype)); 5264 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO); 5265 } 5266 5267 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) { 5268 // Simulate a CAS, to avoid racy duplication of results. 5269 MethodHandle prev = cache[pos]; 5270 if (prev != null) return prev; 5271 return cache[pos] = value; 5272 } 5273 5274 /** 5275 * Provides a target method handle with one or more <em>bound arguments</em> 5276 * in advance of the method handle's invocation. 5277 * The formal parameters to the target corresponding to the bound 5278 * arguments are called <em>bound parameters</em>. 5279 * Returns a new method handle which saves away the bound arguments. 5280 * When it is invoked, it receives arguments for any non-bound parameters, 5281 * binds the saved arguments to their corresponding parameters, 5282 * and calls the original target. 5283 * <p> 5284 * The type of the new method handle will drop the types for the bound 5285 * parameters from the original target type, since the new method handle 5286 * will no longer require those arguments to be supplied by its callers. 5287 * <p> 5288 * Each given argument object must match the corresponding bound parameter type. 5289 * If a bound parameter type is a primitive, the argument object 5290 * must be a wrapper, and will be unboxed to produce the primitive value. 5291 * <p> 5292 * The {@code pos} argument selects which parameters are to be bound. 5293 * It may range between zero and <i>N-L</i> (inclusively), 5294 * where <i>N</i> is the arity of the target method handle 5295 * and <i>L</i> is the length of the values array. 5296 * <p> 5297 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5298 * variable-arity method handle}, even if the original target method handle was. 5299 * @param target the method handle to invoke after the argument is inserted 5300 * @param pos where to insert the argument (zero for the first) 5301 * @param values the series of arguments to insert 5302 * @return a method handle which inserts an additional argument, 5303 * before calling the original method handle 5304 * @throws NullPointerException if the target or the {@code values} array is null 5305 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than 5306 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L} 5307 * is the length of the values array. 5308 * @throws ClassCastException if an argument does not match the corresponding bound parameter 5309 * type. 5310 * @see MethodHandle#bindTo 5311 */ 5312 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) { 5313 int insCount = values.length; 5314 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos); 5315 if (insCount == 0) return target; 5316 BoundMethodHandle result = target.rebind(); 5317 for (int i = 0; i < insCount; i++) { 5318 Object value = values[i]; 5319 Class<?> ptype = ptypes[pos+i]; 5320 if (ptype.isPrimitive()) { 5321 result = insertArgumentPrimitive(result, pos, ptype, value); 5322 } else { 5323 value = ptype.cast(value); // throw CCE if needed 5324 result = result.bindArgumentL(pos, value); 5325 } 5326 } 5327 return result; 5328 } 5329 5330 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos, 5331 Class<?> ptype, Object value) { 5332 Wrapper w = Wrapper.forPrimitiveType(ptype); 5333 // perform unboxing and/or primitive conversion 5334 value = w.convert(value, ptype); 5335 return switch (w) { 5336 case INT -> result.bindArgumentI(pos, (int) value); 5337 case LONG -> result.bindArgumentJ(pos, (long) value); 5338 case FLOAT -> result.bindArgumentF(pos, (float) value); 5339 case DOUBLE -> result.bindArgumentD(pos, (double) value); 5340 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value)); 5341 }; 5342 } 5343 5344 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException { 5345 MethodType oldType = target.type(); 5346 int outargs = oldType.parameterCount(); 5347 int inargs = outargs - insCount; 5348 if (inargs < 0) 5349 throw newIllegalArgumentException("too many values to insert"); 5350 if (pos < 0 || pos > inargs) 5351 throw newIllegalArgumentException("no argument type to append"); 5352 return oldType.ptypes(); 5353 } 5354 5355 /** 5356 * Produces a method handle which will discard some dummy arguments 5357 * before calling some other specified <i>target</i> method handle. 5358 * The type of the new method handle will be the same as the target's type, 5359 * except it will also include the dummy argument types, 5360 * at some given position. 5361 * <p> 5362 * The {@code pos} argument may range between zero and <i>N</i>, 5363 * where <i>N</i> is the arity of the target. 5364 * If {@code pos} is zero, the dummy arguments will precede 5365 * the target's real arguments; if {@code pos} is <i>N</i> 5366 * they will come after. 5367 * <p> 5368 * <b>Example:</b> 5369 * {@snippet lang="java" : 5370 import static java.lang.invoke.MethodHandles.*; 5371 import static java.lang.invoke.MethodType.*; 5372 ... 5373 MethodHandle cat = lookup().findVirtual(String.class, 5374 "concat", methodType(String.class, String.class)); 5375 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5376 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class); 5377 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2)); 5378 assertEquals(bigType, d0.type()); 5379 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z")); 5380 * } 5381 * <p> 5382 * This method is also equivalent to the following code: 5383 * <blockquote><pre> 5384 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))} 5385 * </pre></blockquote> 5386 * @param target the method handle to invoke after the arguments are dropped 5387 * @param pos position of first argument to drop (zero for the leftmost) 5388 * @param valueTypes the type(s) of the argument(s) to drop 5389 * @return a method handle which drops arguments of the given types, 5390 * before calling the original method handle 5391 * @throws NullPointerException if the target is null, 5392 * or if the {@code valueTypes} list or any of its elements is null 5393 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 5394 * or if {@code pos} is negative or greater than the arity of the target, 5395 * or if the new method handle's type would have too many parameters 5396 */ 5397 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) { 5398 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone()); 5399 } 5400 5401 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) { 5402 MethodType oldType = target.type(); // get NPE 5403 int dropped = dropArgumentChecks(oldType, pos, valueTypes); 5404 MethodType newType = oldType.insertParameterTypes(pos, valueTypes); 5405 if (dropped == 0) return target; 5406 BoundMethodHandle result = target.rebind(); 5407 LambdaForm lform = result.form; 5408 int insertFormArg = 1 + pos; 5409 for (Class<?> ptype : valueTypes) { 5410 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype)); 5411 } 5412 result = result.copyWith(newType, lform); 5413 return result; 5414 } 5415 5416 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) { 5417 int dropped = valueTypes.length; 5418 MethodType.checkSlotCount(dropped); 5419 int outargs = oldType.parameterCount(); 5420 int inargs = outargs + dropped; 5421 if (pos < 0 || pos > outargs) 5422 throw newIllegalArgumentException("no argument type to remove" 5423 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs) 5424 ); 5425 return dropped; 5426 } 5427 5428 /** 5429 * Produces a method handle which will discard some dummy arguments 5430 * before calling some other specified <i>target</i> method handle. 5431 * The type of the new method handle will be the same as the target's type, 5432 * except it will also include the dummy argument types, 5433 * at some given position. 5434 * <p> 5435 * The {@code pos} argument may range between zero and <i>N</i>, 5436 * where <i>N</i> is the arity of the target. 5437 * If {@code pos} is zero, the dummy arguments will precede 5438 * the target's real arguments; if {@code pos} is <i>N</i> 5439 * they will come after. 5440 * @apiNote 5441 * {@snippet lang="java" : 5442 import static java.lang.invoke.MethodHandles.*; 5443 import static java.lang.invoke.MethodType.*; 5444 ... 5445 MethodHandle cat = lookup().findVirtual(String.class, 5446 "concat", methodType(String.class, String.class)); 5447 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5448 MethodHandle d0 = dropArguments(cat, 0, String.class); 5449 assertEquals("yz", (String) d0.invokeExact("x", "y", "z")); 5450 MethodHandle d1 = dropArguments(cat, 1, String.class); 5451 assertEquals("xz", (String) d1.invokeExact("x", "y", "z")); 5452 MethodHandle d2 = dropArguments(cat, 2, String.class); 5453 assertEquals("xy", (String) d2.invokeExact("x", "y", "z")); 5454 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class); 5455 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z")); 5456 * } 5457 * <p> 5458 * This method is also equivalent to the following code: 5459 * <blockquote><pre> 5460 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))} 5461 * </pre></blockquote> 5462 * @param target the method handle to invoke after the arguments are dropped 5463 * @param pos position of first argument to drop (zero for the leftmost) 5464 * @param valueTypes the type(s) of the argument(s) to drop 5465 * @return a method handle which drops arguments of the given types, 5466 * before calling the original method handle 5467 * @throws NullPointerException if the target is null, 5468 * or if the {@code valueTypes} array or any of its elements is null 5469 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 5470 * or if {@code pos} is negative or greater than the arity of the target, 5471 * or if the new method handle's type would have 5472 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5473 */ 5474 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) { 5475 return dropArgumentsTrusted(target, pos, valueTypes.clone()); 5476 } 5477 5478 /* Convenience overloads for trusting internal low-arity call-sites */ 5479 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) { 5480 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 }); 5481 } 5482 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) { 5483 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 }); 5484 } 5485 5486 // private version which allows caller some freedom with error handling 5487 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos, 5488 boolean nullOnFailure) { 5489 Class<?>[] oldTypes = target.type().ptypes(); 5490 int match = oldTypes.length; 5491 if (skip != 0) { 5492 if (skip < 0 || skip > match) { 5493 throw newIllegalArgumentException("illegal skip", skip, target); 5494 } 5495 oldTypes = Arrays.copyOfRange(oldTypes, skip, match); 5496 match -= skip; 5497 } 5498 Class<?>[] addTypes = newTypes; 5499 int add = addTypes.length; 5500 if (pos != 0) { 5501 if (pos < 0 || pos > add) { 5502 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes)); 5503 } 5504 addTypes = Arrays.copyOfRange(addTypes, pos, add); 5505 add -= pos; 5506 assert(addTypes.length == add); 5507 } 5508 // Do not add types which already match the existing arguments. 5509 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) { 5510 if (nullOnFailure) { 5511 return null; 5512 } 5513 throw newIllegalArgumentException("argument lists do not match", 5514 Arrays.toString(oldTypes), Arrays.toString(newTypes)); 5515 } 5516 addTypes = Arrays.copyOfRange(addTypes, match, add); 5517 add -= match; 5518 assert(addTypes.length == add); 5519 // newTypes: ( P*[pos], M*[match], A*[add] ) 5520 // target: ( S*[skip], M*[match] ) 5521 MethodHandle adapter = target; 5522 if (add > 0) { 5523 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes); 5524 } 5525 // adapter: (S*[skip], M*[match], A*[add] ) 5526 if (pos > 0) { 5527 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos)); 5528 } 5529 // adapter: (S*[skip], P*[pos], M*[match], A*[add] ) 5530 return adapter; 5531 } 5532 5533 /** 5534 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some 5535 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter 5536 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The 5537 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before 5538 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by 5539 * {@link #dropArguments(MethodHandle, int, Class[])}. 5540 * <p> 5541 * The resulting handle will have the same return type as the target handle. 5542 * <p> 5543 * In more formal terms, assume these two type lists:<ul> 5544 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as 5545 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list, 5546 * {@code newTypes}. 5547 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as 5548 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's 5549 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching 5550 * sub-list. 5551 * </ul> 5552 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type 5553 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by 5554 * {@link #dropArguments(MethodHandle, int, Class[])}. 5555 * 5556 * @apiNote 5557 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be 5558 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows: 5559 * {@snippet lang="java" : 5560 import static java.lang.invoke.MethodHandles.*; 5561 import static java.lang.invoke.MethodType.*; 5562 ... 5563 ... 5564 MethodHandle h0 = constant(boolean.class, true); 5565 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class)); 5566 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class); 5567 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList()); 5568 if (h1.type().parameterCount() < h2.type().parameterCount()) 5569 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1 5570 else 5571 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2 5572 MethodHandle h3 = guardWithTest(h0, h1, h2); 5573 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c")); 5574 * } 5575 * @param target the method handle to adapt 5576 * @param skip number of targets parameters to disregard (they will be unchanged) 5577 * @param newTypes the list of types to match {@code target}'s parameter type list to 5578 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur 5579 * @return a possibly adapted method handle 5580 * @throws NullPointerException if either argument is null 5581 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class}, 5582 * or if {@code skip} is negative or greater than the arity of the target, 5583 * or if {@code pos} is negative or greater than the newTypes list size, 5584 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position 5585 * {@code pos}. 5586 * @since 9 5587 */ 5588 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) { 5589 Objects.requireNonNull(target); 5590 Objects.requireNonNull(newTypes); 5591 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false); 5592 } 5593 5594 /** 5595 * Drop the return value of the target handle (if any). 5596 * The returned method handle will have a {@code void} return type. 5597 * 5598 * @param target the method handle to adapt 5599 * @return a possibly adapted method handle 5600 * @throws NullPointerException if {@code target} is null 5601 * @since 16 5602 */ 5603 public static MethodHandle dropReturn(MethodHandle target) { 5604 Objects.requireNonNull(target); 5605 MethodType oldType = target.type(); 5606 Class<?> oldReturnType = oldType.returnType(); 5607 if (oldReturnType == void.class) 5608 return target; 5609 MethodType newType = oldType.changeReturnType(void.class); 5610 BoundMethodHandle result = target.rebind(); 5611 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true); 5612 result = result.copyWith(newType, lform); 5613 return result; 5614 } 5615 5616 /** 5617 * Adapts a target method handle by pre-processing 5618 * one or more of its arguments, each with its own unary filter function, 5619 * and then calling the target with each pre-processed argument 5620 * replaced by the result of its corresponding filter function. 5621 * <p> 5622 * The pre-processing is performed by one or more method handles, 5623 * specified in the elements of the {@code filters} array. 5624 * The first element of the filter array corresponds to the {@code pos} 5625 * argument of the target, and so on in sequence. 5626 * The filter functions are invoked in left to right order. 5627 * <p> 5628 * Null arguments in the array are treated as identity functions, 5629 * and the corresponding arguments left unchanged. 5630 * (If there are no non-null elements in the array, the original target is returned.) 5631 * Each filter is applied to the corresponding argument of the adapter. 5632 * <p> 5633 * If a filter {@code F} applies to the {@code N}th argument of 5634 * the target, then {@code F} must be a method handle which 5635 * takes exactly one argument. The type of {@code F}'s sole argument 5636 * replaces the corresponding argument type of the target 5637 * in the resulting adapted method handle. 5638 * The return type of {@code F} must be identical to the corresponding 5639 * parameter type of the target. 5640 * <p> 5641 * It is an error if there are elements of {@code filters} 5642 * (null or not) 5643 * which do not correspond to argument positions in the target. 5644 * <p><b>Example:</b> 5645 * {@snippet lang="java" : 5646 import static java.lang.invoke.MethodHandles.*; 5647 import static java.lang.invoke.MethodType.*; 5648 ... 5649 MethodHandle cat = lookup().findVirtual(String.class, 5650 "concat", methodType(String.class, String.class)); 5651 MethodHandle upcase = lookup().findVirtual(String.class, 5652 "toUpperCase", methodType(String.class)); 5653 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5654 MethodHandle f0 = filterArguments(cat, 0, upcase); 5655 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy 5656 MethodHandle f1 = filterArguments(cat, 1, upcase); 5657 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY 5658 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase); 5659 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY 5660 * } 5661 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5662 * denotes the return type of both the {@code target} and resulting adapter. 5663 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values 5664 * of the parameters and arguments that precede and follow the filter position 5665 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and 5666 * values of the filtered parameters and arguments; they also represent the 5667 * return types of the {@code filter[i]} handles. The latter accept arguments 5668 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of 5669 * the resulting adapter. 5670 * {@snippet lang="java" : 5671 * T target(P... p, A[i]... a[i], B... b); 5672 * A[i] filter[i](V[i]); 5673 * T adapter(P... p, V[i]... v[i], B... b) { 5674 * return target(p..., filter[i](v[i])..., b...); 5675 * } 5676 * } 5677 * <p> 5678 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5679 * variable-arity method handle}, even if the original target method handle was. 5680 * 5681 * @param target the method handle to invoke after arguments are filtered 5682 * @param pos the position of the first argument to filter 5683 * @param filters method handles to call initially on filtered arguments 5684 * @return method handle which incorporates the specified argument filtering logic 5685 * @throws NullPointerException if the target is null 5686 * or if the {@code filters} array is null 5687 * @throws IllegalArgumentException if a non-null element of {@code filters} 5688 * does not match a corresponding argument type of target as described above, 5689 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}, 5690 * or if the resulting method handle's type would have 5691 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5692 */ 5693 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) { 5694 // In method types arguments start at index 0, while the LF 5695 // editor have the MH receiver at position 0 - adjust appropriately. 5696 final int MH_RECEIVER_OFFSET = 1; 5697 filterArgumentsCheckArity(target, pos, filters); 5698 MethodHandle adapter = target; 5699 5700 // keep track of currently matched filters, as to optimize repeated filters 5701 int index = 0; 5702 int[] positions = new int[filters.length]; 5703 MethodHandle filter = null; 5704 5705 // process filters in reverse order so that the invocation of 5706 // the resulting adapter will invoke the filters in left-to-right order 5707 for (int i = filters.length - 1; i >= 0; --i) { 5708 MethodHandle newFilter = filters[i]; 5709 if (newFilter == null) continue; // ignore null elements of filters 5710 5711 // flush changes on update 5712 if (filter != newFilter) { 5713 if (filter != null) { 5714 if (index > 1) { 5715 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 5716 } else { 5717 adapter = filterArgument(adapter, positions[0] - 1, filter); 5718 } 5719 } 5720 filter = newFilter; 5721 index = 0; 5722 } 5723 5724 filterArgumentChecks(target, pos + i, newFilter); 5725 positions[index++] = pos + i + MH_RECEIVER_OFFSET; 5726 } 5727 if (index > 1) { 5728 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 5729 } else if (index == 1) { 5730 adapter = filterArgument(adapter, positions[0] - 1, filter); 5731 } 5732 return adapter; 5733 } 5734 5735 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) { 5736 MethodType targetType = adapter.type(); 5737 MethodType filterType = filter.type(); 5738 BoundMethodHandle result = adapter.rebind(); 5739 Class<?> newParamType = filterType.parameterType(0); 5740 5741 Class<?>[] ptypes = targetType.ptypes().clone(); 5742 for (int pos : positions) { 5743 ptypes[pos - 1] = newParamType; 5744 } 5745 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true); 5746 5747 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions); 5748 return result.copyWithExtendL(newType, lform, filter); 5749 } 5750 5751 /*non-public*/ 5752 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) { 5753 filterArgumentChecks(target, pos, filter); 5754 MethodType targetType = target.type(); 5755 MethodType filterType = filter.type(); 5756 BoundMethodHandle result = target.rebind(); 5757 Class<?> newParamType = filterType.parameterType(0); 5758 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType)); 5759 MethodType newType = targetType.changeParameterType(pos, newParamType); 5760 result = result.copyWithExtendL(newType, lform, filter); 5761 return result; 5762 } 5763 5764 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) { 5765 MethodType targetType = target.type(); 5766 int maxPos = targetType.parameterCount(); 5767 if (pos + filters.length > maxPos) 5768 throw newIllegalArgumentException("too many filters"); 5769 } 5770 5771 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 5772 MethodType targetType = target.type(); 5773 MethodType filterType = filter.type(); 5774 if (filterType.parameterCount() != 1 5775 || filterType.returnType() != targetType.parameterType(pos)) 5776 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5777 } 5778 5779 /** 5780 * Adapts a target method handle by pre-processing 5781 * a sub-sequence of its arguments with a filter (another method handle). 5782 * The pre-processed arguments are replaced by the result (if any) of the 5783 * filter function. 5784 * The target is then called on the modified (usually shortened) argument list. 5785 * <p> 5786 * If the filter returns a value, the target must accept that value as 5787 * its argument in position {@code pos}, preceded and/or followed by 5788 * any arguments not passed to the filter. 5789 * If the filter returns void, the target must accept all arguments 5790 * not passed to the filter. 5791 * No arguments are reordered, and a result returned from the filter 5792 * replaces (in order) the whole subsequence of arguments originally 5793 * passed to the adapter. 5794 * <p> 5795 * The argument types (if any) of the filter 5796 * replace zero or one argument types of the target, at position {@code pos}, 5797 * in the resulting adapted method handle. 5798 * The return type of the filter (if any) must be identical to the 5799 * argument type of the target at position {@code pos}, and that target argument 5800 * is supplied by the return value of the filter. 5801 * <p> 5802 * In all cases, {@code pos} must be greater than or equal to zero, and 5803 * {@code pos} must also be less than or equal to the target's arity. 5804 * <p><b>Example:</b> 5805 * {@snippet lang="java" : 5806 import static java.lang.invoke.MethodHandles.*; 5807 import static java.lang.invoke.MethodType.*; 5808 ... 5809 MethodHandle deepToString = publicLookup() 5810 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 5811 5812 MethodHandle ts1 = deepToString.asCollector(String[].class, 1); 5813 assertEquals("[strange]", (String) ts1.invokeExact("strange")); 5814 5815 MethodHandle ts2 = deepToString.asCollector(String[].class, 2); 5816 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down")); 5817 5818 MethodHandle ts3 = deepToString.asCollector(String[].class, 3); 5819 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2); 5820 assertEquals("[top, [up, down], strange]", 5821 (String) ts3_ts2.invokeExact("top", "up", "down", "strange")); 5822 5823 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1); 5824 assertEquals("[top, [up, down], [strange]]", 5825 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange")); 5826 5827 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3); 5828 assertEquals("[top, [[up, down, strange], charm], bottom]", 5829 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom")); 5830 * } 5831 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5832 * represents the return type of the {@code target} and resulting adapter. 5833 * {@code V}/{@code v} stand for the return type and value of the 5834 * {@code filter}, which are also found in the signature and arguments of 5835 * the {@code target}, respectively, unless {@code V} is {@code void}. 5836 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types 5837 * and values preceding and following the collection position, {@code pos}, 5838 * in the {@code target}'s signature. They also turn up in the resulting 5839 * adapter's signature and arguments, where they surround 5840 * {@code B}/{@code b}, which represent the parameter types and arguments 5841 * to the {@code filter} (if any). 5842 * {@snippet lang="java" : 5843 * T target(A...,V,C...); 5844 * V filter(B...); 5845 * T adapter(A... a,B... b,C... c) { 5846 * V v = filter(b...); 5847 * return target(a...,v,c...); 5848 * } 5849 * // and if the filter has no arguments: 5850 * T target2(A...,V,C...); 5851 * V filter2(); 5852 * T adapter2(A... a,C... c) { 5853 * V v = filter2(); 5854 * return target2(a...,v,c...); 5855 * } 5856 * // and if the filter has a void return: 5857 * T target3(A...,C...); 5858 * void filter3(B...); 5859 * T adapter3(A... a,B... b,C... c) { 5860 * filter3(b...); 5861 * return target3(a...,c...); 5862 * } 5863 * } 5864 * <p> 5865 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to 5866 * one which first "folds" the affected arguments, and then drops them, in separate 5867 * steps as follows: 5868 * {@snippet lang="java" : 5869 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2 5870 * mh = MethodHandles.foldArguments(mh, coll); //step 1 5871 * } 5872 * If the target method handle consumes no arguments besides than the result 5873 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)} 5874 * is equivalent to {@code filterReturnValue(coll, mh)}. 5875 * If the filter method handle {@code coll} consumes one argument and produces 5876 * a non-void result, then {@code collectArguments(mh, N, coll)} 5877 * is equivalent to {@code filterArguments(mh, N, coll)}. 5878 * Other equivalences are possible but would require argument permutation. 5879 * <p> 5880 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5881 * variable-arity method handle}, even if the original target method handle was. 5882 * 5883 * @param target the method handle to invoke after filtering the subsequence of arguments 5884 * @param pos the position of the first adapter argument to pass to the filter, 5885 * and/or the target argument which receives the result of the filter 5886 * @param filter method handle to call on the subsequence of arguments 5887 * @return method handle which incorporates the specified argument subsequence filtering logic 5888 * @throws NullPointerException if either argument is null 5889 * @throws IllegalArgumentException if the return type of {@code filter} 5890 * is non-void and is not the same as the {@code pos} argument of the target, 5891 * or if {@code pos} is not between 0 and the target's arity, inclusive, 5892 * or if the resulting method handle's type would have 5893 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5894 * @see MethodHandles#foldArguments 5895 * @see MethodHandles#filterArguments 5896 * @see MethodHandles#filterReturnValue 5897 */ 5898 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) { 5899 MethodType newType = collectArgumentsChecks(target, pos, filter); 5900 MethodType collectorType = filter.type(); 5901 BoundMethodHandle result = target.rebind(); 5902 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType()); 5903 return result.copyWithExtendL(newType, lform, filter); 5904 } 5905 5906 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 5907 MethodType targetType = target.type(); 5908 MethodType filterType = filter.type(); 5909 Class<?> rtype = filterType.returnType(); 5910 Class<?>[] filterArgs = filterType.ptypes(); 5911 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) || 5912 (rtype != void.class && pos >= targetType.parameterCount())) { 5913 throw newIllegalArgumentException("position is out of range for target", target, pos); 5914 } 5915 if (rtype == void.class) { 5916 return targetType.insertParameterTypes(pos, filterArgs); 5917 } 5918 if (rtype != targetType.parameterType(pos)) { 5919 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5920 } 5921 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs); 5922 } 5923 5924 /** 5925 * Adapts a target method handle by post-processing 5926 * its return value (if any) with a filter (another method handle). 5927 * The result of the filter is returned from the adapter. 5928 * <p> 5929 * If the target returns a value, the filter must accept that value as 5930 * its only argument. 5931 * If the target returns void, the filter must accept no arguments. 5932 * <p> 5933 * The return type of the filter 5934 * replaces the return type of the target 5935 * in the resulting adapted method handle. 5936 * The argument type of the filter (if any) must be identical to the 5937 * return type of the target. 5938 * <p><b>Example:</b> 5939 * {@snippet lang="java" : 5940 import static java.lang.invoke.MethodHandles.*; 5941 import static java.lang.invoke.MethodType.*; 5942 ... 5943 MethodHandle cat = lookup().findVirtual(String.class, 5944 "concat", methodType(String.class, String.class)); 5945 MethodHandle length = lookup().findVirtual(String.class, 5946 "length", methodType(int.class)); 5947 System.out.println((String) cat.invokeExact("x", "y")); // xy 5948 MethodHandle f0 = filterReturnValue(cat, length); 5949 System.out.println((int) f0.invokeExact("x", "y")); // 2 5950 * } 5951 * <p>Here is pseudocode for the resulting adapter. In the code, 5952 * {@code T}/{@code t} represent the result type and value of the 5953 * {@code target}; {@code V}, the result type of the {@code filter}; and 5954 * {@code A}/{@code a}, the types and values of the parameters and arguments 5955 * of the {@code target} as well as the resulting adapter. 5956 * {@snippet lang="java" : 5957 * T target(A...); 5958 * V filter(T); 5959 * V adapter(A... a) { 5960 * T t = target(a...); 5961 * return filter(t); 5962 * } 5963 * // and if the target has a void return: 5964 * void target2(A...); 5965 * V filter2(); 5966 * V adapter2(A... a) { 5967 * target2(a...); 5968 * return filter2(); 5969 * } 5970 * // and if the filter has a void return: 5971 * T target3(A...); 5972 * void filter3(V); 5973 * void adapter3(A... a) { 5974 * T t = target3(a...); 5975 * filter3(t); 5976 * } 5977 * } 5978 * <p> 5979 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5980 * variable-arity method handle}, even if the original target method handle was. 5981 * @param target the method handle to invoke before filtering the return value 5982 * @param filter method handle to call on the return value 5983 * @return method handle which incorporates the specified return value filtering logic 5984 * @throws NullPointerException if either argument is null 5985 * @throws IllegalArgumentException if the argument list of {@code filter} 5986 * does not match the return type of target as described above 5987 */ 5988 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) { 5989 MethodType targetType = target.type(); 5990 MethodType filterType = filter.type(); 5991 filterReturnValueChecks(targetType, filterType); 5992 BoundMethodHandle result = target.rebind(); 5993 BasicType rtype = BasicType.basicType(filterType.returnType()); 5994 LambdaForm lform = result.editor().filterReturnForm(rtype, false); 5995 MethodType newType = targetType.changeReturnType(filterType.returnType()); 5996 result = result.copyWithExtendL(newType, lform, filter); 5997 return result; 5998 } 5999 6000 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException { 6001 Class<?> rtype = targetType.returnType(); 6002 int filterValues = filterType.parameterCount(); 6003 if (filterValues == 0 6004 ? (rtype != void.class) 6005 : (rtype != filterType.parameterType(0) || filterValues != 1)) 6006 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 6007 } 6008 6009 /** 6010 * Filter the return value of a target method handle with a filter function. The filter function is 6011 * applied to the return value of the original handle; if the filter specifies more than one parameters, 6012 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works 6013 * as follows: 6014 * {@snippet lang="java" : 6015 * T target(A...) 6016 * V filter(B... , T) 6017 * V adapter(A... a, B... b) { 6018 * T t = target(a...); 6019 * return filter(b..., t); 6020 * } 6021 * } 6022 * <p> 6023 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}. 6024 * 6025 * @param target the target method handle 6026 * @param filter the filter method handle 6027 * @return the adapter method handle 6028 */ 6029 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) { 6030 MethodType targetType = target.type(); 6031 MethodType filterType = filter.type(); 6032 BoundMethodHandle result = target.rebind(); 6033 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType()); 6034 MethodType newType = targetType.changeReturnType(filterType.returnType()); 6035 if (filterType.parameterCount() > 1) { 6036 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) { 6037 newType = newType.appendParameterTypes(filterType.parameterType(i)); 6038 } 6039 } 6040 result = result.copyWithExtendL(newType, lform, filter); 6041 return result; 6042 } 6043 6044 /** 6045 * Adapts a target method handle by pre-processing 6046 * some of its arguments, and then calling the target with 6047 * the result of the pre-processing, inserted into the original 6048 * sequence of arguments. 6049 * <p> 6050 * The pre-processing is performed by {@code combiner}, a second method handle. 6051 * Of the arguments passed to the adapter, the first {@code N} arguments 6052 * are copied to the combiner, which is then called. 6053 * (Here, {@code N} is defined as the parameter count of the combiner.) 6054 * After this, control passes to the target, with any result 6055 * from the combiner inserted before the original {@code N} incoming 6056 * arguments. 6057 * <p> 6058 * If the combiner returns a value, the first parameter type of the target 6059 * must be identical with the return type of the combiner, and the next 6060 * {@code N} parameter types of the target must exactly match the parameters 6061 * of the combiner. 6062 * <p> 6063 * If the combiner has a void return, no result will be inserted, 6064 * and the first {@code N} parameter types of the target 6065 * must exactly match the parameters of the combiner. 6066 * <p> 6067 * The resulting adapter is the same type as the target, except that the 6068 * first parameter type is dropped, 6069 * if it corresponds to the result of the combiner. 6070 * <p> 6071 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments 6072 * that either the combiner or the target does not wish to receive. 6073 * If some of the incoming arguments are destined only for the combiner, 6074 * consider using {@link MethodHandle#asCollector asCollector} instead, since those 6075 * arguments will not need to be live on the stack on entry to the 6076 * target.) 6077 * <p><b>Example:</b> 6078 * {@snippet lang="java" : 6079 import static java.lang.invoke.MethodHandles.*; 6080 import static java.lang.invoke.MethodType.*; 6081 ... 6082 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 6083 "println", methodType(void.class, String.class)) 6084 .bindTo(System.out); 6085 MethodHandle cat = lookup().findVirtual(String.class, 6086 "concat", methodType(String.class, String.class)); 6087 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 6088 MethodHandle catTrace = foldArguments(cat, trace); 6089 // also prints "boo": 6090 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 6091 * } 6092 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 6093 * represents the result type of the {@code target} and resulting adapter. 6094 * {@code V}/{@code v} represent the type and value of the parameter and argument 6095 * of {@code target} that precedes the folding position; {@code V} also is 6096 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 6097 * types and values of the {@code N} parameters and arguments at the folding 6098 * position. {@code B}/{@code b} represent the types and values of the 6099 * {@code target} parameters and arguments that follow the folded parameters 6100 * and arguments. 6101 * {@snippet lang="java" : 6102 * // there are N arguments in A... 6103 * T target(V, A[N]..., B...); 6104 * V combiner(A...); 6105 * T adapter(A... a, B... b) { 6106 * V v = combiner(a...); 6107 * return target(v, a..., b...); 6108 * } 6109 * // and if the combiner has a void return: 6110 * T target2(A[N]..., B...); 6111 * void combiner2(A...); 6112 * T adapter2(A... a, B... b) { 6113 * combiner2(a...); 6114 * return target2(a..., b...); 6115 * } 6116 * } 6117 * <p> 6118 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 6119 * variable-arity method handle}, even if the original target method handle was. 6120 * @param target the method handle to invoke after arguments are combined 6121 * @param combiner method handle to call initially on the incoming arguments 6122 * @return method handle which incorporates the specified argument folding logic 6123 * @throws NullPointerException if either argument is null 6124 * @throws IllegalArgumentException if {@code combiner}'s return type 6125 * is non-void and not the same as the first argument type of 6126 * the target, or if the initial {@code N} argument types 6127 * of the target 6128 * (skipping one matching the {@code combiner}'s return type) 6129 * are not identical with the argument types of {@code combiner} 6130 */ 6131 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) { 6132 return foldArguments(target, 0, combiner); 6133 } 6134 6135 /** 6136 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then 6137 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just 6138 * before the folded arguments. 6139 * <p> 6140 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the 6141 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a 6142 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position 6143 * 0. 6144 * 6145 * @apiNote Example: 6146 * {@snippet lang="java" : 6147 import static java.lang.invoke.MethodHandles.*; 6148 import static java.lang.invoke.MethodType.*; 6149 ... 6150 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 6151 "println", methodType(void.class, String.class)) 6152 .bindTo(System.out); 6153 MethodHandle cat = lookup().findVirtual(String.class, 6154 "concat", methodType(String.class, String.class)); 6155 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 6156 MethodHandle catTrace = foldArguments(cat, 1, trace); 6157 // also prints "jum": 6158 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 6159 * } 6160 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 6161 * represents the result type of the {@code target} and resulting adapter. 6162 * {@code V}/{@code v} represent the type and value of the parameter and argument 6163 * of {@code target} that precedes the folding position; {@code V} also is 6164 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 6165 * types and values of the {@code N} parameters and arguments at the folding 6166 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types 6167 * and values of the {@code target} parameters and arguments that precede and 6168 * follow the folded parameters and arguments starting at {@code pos}, 6169 * respectively. 6170 * {@snippet lang="java" : 6171 * // there are N arguments in A... 6172 * T target(Z..., V, A[N]..., B...); 6173 * V combiner(A...); 6174 * T adapter(Z... z, A... a, B... b) { 6175 * V v = combiner(a...); 6176 * return target(z..., v, a..., b...); 6177 * } 6178 * // and if the combiner has a void return: 6179 * T target2(Z..., A[N]..., B...); 6180 * void combiner2(A...); 6181 * T adapter2(Z... z, A... a, B... b) { 6182 * combiner2(a...); 6183 * return target2(z..., a..., b...); 6184 * } 6185 * } 6186 * <p> 6187 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 6188 * variable-arity method handle}, even if the original target method handle was. 6189 * 6190 * @param target the method handle to invoke after arguments are combined 6191 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code 6192 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6193 * @param combiner method handle to call initially on the incoming arguments 6194 * @return method handle which incorporates the specified argument folding logic 6195 * @throws NullPointerException if either argument is null 6196 * @throws IllegalArgumentException if either of the following two conditions holds: 6197 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 6198 * {@code pos} of the target signature; 6199 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching 6200 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}. 6201 * 6202 * @see #foldArguments(MethodHandle, MethodHandle) 6203 * @since 9 6204 */ 6205 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) { 6206 MethodType targetType = target.type(); 6207 MethodType combinerType = combiner.type(); 6208 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType); 6209 BoundMethodHandle result = target.rebind(); 6210 boolean dropResult = rtype == void.class; 6211 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType()); 6212 MethodType newType = targetType; 6213 if (!dropResult) { 6214 newType = newType.dropParameterTypes(pos, pos + 1); 6215 } 6216 result = result.copyWithExtendL(newType, lform, combiner); 6217 return result; 6218 } 6219 6220 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) { 6221 int foldArgs = combinerType.parameterCount(); 6222 Class<?> rtype = combinerType.returnType(); 6223 int foldVals = rtype == void.class ? 0 : 1; 6224 int afterInsertPos = foldPos + foldVals; 6225 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs); 6226 if (ok) { 6227 for (int i = 0; i < foldArgs; i++) { 6228 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) { 6229 ok = false; 6230 break; 6231 } 6232 } 6233 } 6234 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) 6235 ok = false; 6236 if (!ok) 6237 throw misMatchedTypes("target and combiner types", targetType, combinerType); 6238 return rtype; 6239 } 6240 6241 /** 6242 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result 6243 * of the pre-processing replacing the argument at the given position. 6244 * 6245 * @param target the method handle to invoke after arguments are combined 6246 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 6247 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6248 * @param combiner method handle to call initially on the incoming arguments 6249 * @param argPositions indexes of the target to pick arguments sent to the combiner from 6250 * @return method handle which incorporates the specified argument folding logic 6251 * @throws NullPointerException if either argument is null 6252 * @throws IllegalArgumentException if either of the following two conditions holds: 6253 * (1) {@code combiner}'s return type is not the same as the argument type at position 6254 * {@code pos} of the target signature; 6255 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are 6256 * not identical with the argument types of {@code combiner}. 6257 */ 6258 /*non-public*/ 6259 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6260 return argumentsWithCombiner(true, target, position, combiner, argPositions); 6261 } 6262 6263 /** 6264 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of 6265 * the pre-processing inserted into the original sequence of arguments at the given position. 6266 * 6267 * @param target the method handle to invoke after arguments are combined 6268 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 6269 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6270 * @param combiner method handle to call initially on the incoming arguments 6271 * @param argPositions indexes of the target to pick arguments sent to the combiner from 6272 * @return method handle which incorporates the specified argument folding logic 6273 * @throws NullPointerException if either argument is null 6274 * @throws IllegalArgumentException if either of the following two conditions holds: 6275 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 6276 * {@code pos} of the target signature; 6277 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature 6278 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical 6279 * with the argument types of {@code combiner}. 6280 */ 6281 /*non-public*/ 6282 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6283 return argumentsWithCombiner(false, target, position, combiner, argPositions); 6284 } 6285 6286 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6287 MethodType targetType = target.type(); 6288 MethodType combinerType = combiner.type(); 6289 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions); 6290 BoundMethodHandle result = target.rebind(); 6291 6292 MethodType newType = targetType; 6293 LambdaForm lform; 6294 if (filter) { 6295 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions); 6296 } else { 6297 boolean dropResult = rtype == void.class; 6298 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions); 6299 if (!dropResult) { 6300 newType = newType.dropParameterTypes(position, position + 1); 6301 } 6302 } 6303 result = result.copyWithExtendL(newType, lform, combiner); 6304 return result; 6305 } 6306 6307 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) { 6308 int combinerArgs = combinerType.parameterCount(); 6309 if (argPos.length != combinerArgs) { 6310 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length); 6311 } 6312 Class<?> rtype = combinerType.returnType(); 6313 6314 for (int i = 0; i < combinerArgs; i++) { 6315 int arg = argPos[i]; 6316 if (arg < 0 || arg > targetType.parameterCount()) { 6317 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg); 6318 } 6319 if (combinerType.parameterType(i) != targetType.parameterType(arg)) { 6320 throw newIllegalArgumentException("target argument type at position " + arg 6321 + " must match combiner argument type at index " + i + ": " + targetType 6322 + " -> " + combinerType + ", map: " + Arrays.toString(argPos)); 6323 } 6324 } 6325 if (filter && combinerType.returnType() != targetType.parameterType(position)) { 6326 throw misMatchedTypes("target and combiner types", targetType, combinerType); 6327 } 6328 return rtype; 6329 } 6330 6331 /** 6332 * Makes a method handle which adapts a target method handle, 6333 * by guarding it with a test, a boolean-valued method handle. 6334 * If the guard fails, a fallback handle is called instead. 6335 * All three method handles must have the same corresponding 6336 * argument and return types, except that the return type 6337 * of the test must be boolean, and the test is allowed 6338 * to have fewer arguments than the other two method handles. 6339 * <p> 6340 * Here is pseudocode for the resulting adapter. In the code, {@code T} 6341 * represents the uniform result type of the three involved handles; 6342 * {@code A}/{@code a}, the types and values of the {@code target} 6343 * parameters and arguments that are consumed by the {@code test}; and 6344 * {@code B}/{@code b}, those types and values of the {@code target} 6345 * parameters and arguments that are not consumed by the {@code test}. 6346 * {@snippet lang="java" : 6347 * boolean test(A...); 6348 * T target(A...,B...); 6349 * T fallback(A...,B...); 6350 * T adapter(A... a,B... b) { 6351 * if (test(a...)) 6352 * return target(a..., b...); 6353 * else 6354 * return fallback(a..., b...); 6355 * } 6356 * } 6357 * Note that the test arguments ({@code a...} in the pseudocode) cannot 6358 * be modified by execution of the test, and so are passed unchanged 6359 * from the caller to the target or fallback as appropriate. 6360 * @param test method handle used for test, must return boolean 6361 * @param target method handle to call if test passes 6362 * @param fallback method handle to call if test fails 6363 * @return method handle which incorporates the specified if/then/else logic 6364 * @throws NullPointerException if any argument is null 6365 * @throws IllegalArgumentException if {@code test} does not return boolean, 6366 * or if all three method types do not match (with the return 6367 * type of {@code test} changed to match that of the target). 6368 */ 6369 public static MethodHandle guardWithTest(MethodHandle test, 6370 MethodHandle target, 6371 MethodHandle fallback) { 6372 MethodType gtype = test.type(); 6373 MethodType ttype = target.type(); 6374 MethodType ftype = fallback.type(); 6375 if (!ttype.equals(ftype)) 6376 throw misMatchedTypes("target and fallback types", ttype, ftype); 6377 if (gtype.returnType() != boolean.class) 6378 throw newIllegalArgumentException("guard type is not a predicate "+gtype); 6379 6380 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true); 6381 if (test == null) { 6382 throw misMatchedTypes("target and test types", ttype, gtype); 6383 } 6384 return MethodHandleImpl.makeGuardWithTest(test, target, fallback); 6385 } 6386 6387 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) { 6388 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2); 6389 } 6390 6391 /** 6392 * Makes a method handle which adapts a target method handle, 6393 * by running it inside an exception handler. 6394 * If the target returns normally, the adapter returns that value. 6395 * If an exception matching the specified type is thrown, the fallback 6396 * handle is called instead on the exception, plus the original arguments. 6397 * <p> 6398 * The target and handler must have the same corresponding 6399 * argument and return types, except that handler may omit trailing arguments 6400 * (similarly to the predicate in {@link #guardWithTest guardWithTest}). 6401 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype. 6402 * <p> 6403 * Here is pseudocode for the resulting adapter. In the code, {@code T} 6404 * represents the return type of the {@code target} and {@code handler}, 6405 * and correspondingly that of the resulting adapter; {@code A}/{@code a}, 6406 * the types and values of arguments to the resulting handle consumed by 6407 * {@code handler}; and {@code B}/{@code b}, those of arguments to the 6408 * resulting handle discarded by {@code handler}. 6409 * {@snippet lang="java" : 6410 * T target(A..., B...); 6411 * T handler(ExType, A...); 6412 * T adapter(A... a, B... b) { 6413 * try { 6414 * return target(a..., b...); 6415 * } catch (ExType ex) { 6416 * return handler(ex, a...); 6417 * } 6418 * } 6419 * } 6420 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 6421 * be modified by execution of the target, and so are passed unchanged 6422 * from the caller to the handler, if the handler is invoked. 6423 * <p> 6424 * The target and handler must return the same type, even if the handler 6425 * always throws. (This might happen, for instance, because the handler 6426 * is simulating a {@code finally} clause). 6427 * To create such a throwing handler, compose the handler creation logic 6428 * with {@link #throwException throwException}, 6429 * in order to create a method handle of the correct return type. 6430 * @param target method handle to call 6431 * @param exType the type of exception which the handler will catch 6432 * @param handler method handle to call if a matching exception is thrown 6433 * @return method handle which incorporates the specified try/catch logic 6434 * @throws NullPointerException if any argument is null 6435 * @throws IllegalArgumentException if {@code handler} does not accept 6436 * the given exception type, or if the method handle types do 6437 * not match in their return types and their 6438 * corresponding parameters 6439 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle) 6440 */ 6441 public static MethodHandle catchException(MethodHandle target, 6442 Class<? extends Throwable> exType, 6443 MethodHandle handler) { 6444 MethodType ttype = target.type(); 6445 MethodType htype = handler.type(); 6446 if (!Throwable.class.isAssignableFrom(exType)) 6447 throw new ClassCastException(exType.getName()); 6448 if (htype.parameterCount() < 1 || 6449 !htype.parameterType(0).isAssignableFrom(exType)) 6450 throw newIllegalArgumentException("handler does not accept exception type "+exType); 6451 if (htype.returnType() != ttype.returnType()) 6452 throw misMatchedTypes("target and handler return types", ttype, htype); 6453 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true); 6454 if (handler == null) { 6455 throw misMatchedTypes("target and handler types", ttype, htype); 6456 } 6457 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler); 6458 } 6459 6460 /** 6461 * Produces a method handle which will throw exceptions of the given {@code exType}. 6462 * The method handle will accept a single argument of {@code exType}, 6463 * and immediately throw it as an exception. 6464 * The method type will nominally specify a return of {@code returnType}. 6465 * The return type may be anything convenient: It doesn't matter to the 6466 * method handle's behavior, since it will never return normally. 6467 * @param returnType the return type of the desired method handle 6468 * @param exType the parameter type of the desired method handle 6469 * @return method handle which can throw the given exceptions 6470 * @throws NullPointerException if either argument is null 6471 */ 6472 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) { 6473 if (!Throwable.class.isAssignableFrom(exType)) 6474 throw new ClassCastException(exType.getName()); 6475 return MethodHandleImpl.throwException(methodType(returnType, exType)); 6476 } 6477 6478 /** 6479 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each 6480 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and 6481 * delivers the loop's result, which is the return value of the resulting handle. 6482 * <p> 6483 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop 6484 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration 6485 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in 6486 * terms of method handles, each clause will specify up to four independent actions:<ul> 6487 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}. 6488 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}. 6489 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit. 6490 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value. 6491 * </ul> 6492 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}. 6493 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually 6494 * be referring to types, but in some contexts (describing execution) the lists will be of actual values. 6495 * <p> 6496 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in 6497 * this case. See below for a detailed description. 6498 * <p> 6499 * <em>Parameters optional everywhere:</em> 6500 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}. 6501 * As an exception, the init functions cannot take any {@code v} parameters, 6502 * because those values are not yet computed when the init functions are executed. 6503 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take. 6504 * In fact, any clause function may take no arguments at all. 6505 * <p> 6506 * <em>Loop parameters:</em> 6507 * A clause function may take all the iteration variable values it is entitled to, in which case 6508 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>, 6509 * with their types and values notated as {@code (A...)} and {@code (a...)}. 6510 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed. 6511 * (Since init functions do not accept iteration variables {@code v}, any parameter to an 6512 * init function is automatically a loop parameter {@code a}.) 6513 * As with iteration variables, clause functions are allowed but not required to accept loop parameters. 6514 * These loop parameters act as loop-invariant values visible across the whole loop. 6515 * <p> 6516 * <em>Parameters visible everywhere:</em> 6517 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full 6518 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters. 6519 * The init functions can observe initial pre-loop state, in the form {@code (a...)}. 6520 * Most clause functions will not need all of this information, but they will be formally connected to it 6521 * as if by {@link #dropArguments}. 6522 * <a id="astar"></a> 6523 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full 6524 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}). 6525 * In that notation, the general form of an init function parameter list 6526 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}. 6527 * <p> 6528 * <em>Checking clause structure:</em> 6529 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the 6530 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must" 6531 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not 6532 * met by the inputs to the loop combinator. 6533 * <p> 6534 * <em>Effectively identical sequences:</em> 6535 * <a id="effid"></a> 6536 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B} 6537 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}. 6538 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical" 6539 * as a whole if the set contains a longest list, and all members of the set are effectively identical to 6540 * that longest list. 6541 * For example, any set of type sequences of the form {@code (V*)} is effectively identical, 6542 * and the same is true if more sequences of the form {@code (V... A*)} are added. 6543 * <p> 6544 * <em>Step 0: Determine clause structure.</em><ol type="a"> 6545 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element. 6546 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements. 6547 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length 6548 * four. Padding takes place by appending elements to the array. 6549 * <li>Clauses with all {@code null}s are disregarded. 6550 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini". 6551 * </ol> 6552 * <p> 6553 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a"> 6554 * <li>The iteration variable type for each clause is determined using the clause's init and step return types. 6555 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is 6556 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's 6557 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's 6558 * iteration variable type. 6559 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}. 6560 * <li>This list of types is called the "iteration variable types" ({@code (V...)}). 6561 * </ol> 6562 * <p> 6563 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul> 6564 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}). 6565 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types. 6566 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.) 6567 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types. 6568 * (These types will be checked in step 2, along with all the clause function types.) 6569 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.) 6570 * <li>All of the collected parameter lists must be effectively identical. 6571 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}). 6572 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence. 6573 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called 6574 * the "internal parameter list". 6575 * </ul> 6576 * <p> 6577 * <em>Step 1C: Determine loop return type.</em><ol type="a"> 6578 * <li>Examine fini function return types, disregarding omitted fini functions. 6579 * <li>If there are no fini functions, the loop return type is {@code void}. 6580 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return 6581 * type. 6582 * </ol> 6583 * <p> 6584 * <em>Step 1D: Check other types.</em><ol type="a"> 6585 * <li>There must be at least one non-omitted pred function. 6586 * <li>Every non-omitted pred function must have a {@code boolean} return type. 6587 * </ol> 6588 * <p> 6589 * <em>Step 2: Determine parameter lists.</em><ol type="a"> 6590 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}. 6591 * <li>The parameter list for init functions will be adjusted to the external parameter list. 6592 * (Note that their parameter lists are already effectively identical to this list.) 6593 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be 6594 * effectively identical to the internal parameter list {@code (V... A...)}. 6595 * </ol> 6596 * <p> 6597 * <em>Step 3: Fill in omitted functions.</em><ol type="a"> 6598 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable 6599 * type. 6600 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration 6601 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void} 6602 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.) 6603 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far 6604 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.) 6605 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the 6606 * loop return type. 6607 * </ol> 6608 * <p> 6609 * <em>Step 4: Fill in missing parameter types.</em><ol type="a"> 6610 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)}, 6611 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list. 6612 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter 6613 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list, 6614 * pad out the end of the list. 6615 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}. 6616 * </ol> 6617 * <p> 6618 * <em>Final observations.</em><ol type="a"> 6619 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments. 6620 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have. 6621 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have. 6622 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of 6623 * (non-{@code void}) iteration variables {@code V} followed by loop parameters. 6624 * <li>Each pair of init and step functions agrees in their return type {@code V}. 6625 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables. 6626 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters. 6627 * </ol> 6628 * <p> 6629 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property: 6630 * <ul> 6631 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}. 6632 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters. 6633 * (Only one {@code Pn} has to be non-{@code null}.) 6634 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}. 6635 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types. 6636 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}. 6637 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}. 6638 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine 6639 * the resulting loop handle's parameter types {@code (A...)}. 6640 * </ul> 6641 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions, 6642 * which is natural if most of the loop computation happens in the steps. For some loops, 6643 * the burden of computation might be heaviest in the pred functions, and so the pred functions 6644 * might need to accept the loop parameter values. For loops with complex exit logic, the fini 6645 * functions might need to accept loop parameters, and likewise for loops with complex entry logic, 6646 * where the init functions will need the extra parameters. For such reasons, the rules for 6647 * determining these parameters are as symmetric as possible, across all clause parts. 6648 * In general, the loop parameters function as common invariant values across the whole 6649 * loop, while the iteration variables function as common variant values, or (if there is 6650 * no step function) as internal loop invariant temporaries. 6651 * <p> 6652 * <em>Loop execution.</em><ol type="a"> 6653 * <li>When the loop is called, the loop input values are saved in locals, to be passed to 6654 * every clause function. These locals are loop invariant. 6655 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)}) 6656 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals. 6657 * These locals will be loop varying (unless their steps behave as identity functions, as noted above). 6658 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of 6659 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)} 6660 * (in argument order). 6661 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function 6662 * returns {@code false}. 6663 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the 6664 * sequence {@code (v...)} of loop variables. 6665 * The updated value is immediately visible to all subsequent function calls. 6666 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value 6667 * (of type {@code R}) is returned from the loop as a whole. 6668 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit 6669 * except by throwing an exception. 6670 * </ol> 6671 * <p> 6672 * <em>Usage tips.</em> 6673 * <ul> 6674 * <li>Although each step function will receive the current values of <em>all</em> the loop variables, 6675 * sometimes a step function only needs to observe the current value of its own variable. 6676 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}. 6677 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}. 6678 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create 6679 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be 6680 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable. 6681 * <li>If some of the clause functions are virtual methods on an instance, the instance 6682 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause 6683 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference 6684 * will be the first iteration variable value, and it will be easy to use virtual 6685 * methods as clause parts, since all of them will take a leading instance reference matching that value. 6686 * </ul> 6687 * <p> 6688 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types 6689 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop; 6690 * and {@code R} is the common result type of all finalizers as well as of the resulting loop. 6691 * {@snippet lang="java" : 6692 * V... init...(A...); 6693 * boolean pred...(V..., A...); 6694 * V... step...(V..., A...); 6695 * R fini...(V..., A...); 6696 * R loop(A... a) { 6697 * V... v... = init...(a...); 6698 * for (;;) { 6699 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) { 6700 * v = s(v..., a...); 6701 * if (!p(v..., a...)) { 6702 * return f(v..., a...); 6703 * } 6704 * } 6705 * } 6706 * } 6707 * } 6708 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded 6709 * to their full length, even though individual clause functions may neglect to take them all. 6710 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}. 6711 * 6712 * @apiNote Example: 6713 * {@snippet lang="java" : 6714 * // iterative implementation of the factorial function as a loop handle 6715 * static int one(int k) { return 1; } 6716 * static int inc(int i, int acc, int k) { return i + 1; } 6717 * static int mult(int i, int acc, int k) { return i * acc; } 6718 * static boolean pred(int i, int acc, int k) { return i < k; } 6719 * static int fin(int i, int acc, int k) { return acc; } 6720 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 6721 * // null initializer for counter, should initialize to 0 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(counterClause, accumulatorClause); 6725 * assertEquals(120, loop.invoke(5)); 6726 * } 6727 * The same example, dropping arguments and using combinators: 6728 * {@snippet lang="java" : 6729 * // simplified implementation of the factorial function as a loop handle 6730 * static int inc(int i) { return i + 1; } // drop acc, k 6731 * static int mult(int i, int acc) { return i * acc; } //drop k 6732 * static boolean cmp(int i, int k) { return i < k; } 6733 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods 6734 * // null initializer for counter, should initialize to 0 6735 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 6736 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc 6737 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i 6738 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6739 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6740 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 6741 * assertEquals(720, loop.invoke(6)); 6742 * } 6743 * A similar example, using a helper object to hold a loop parameter: 6744 * {@snippet lang="java" : 6745 * // instance-based implementation of the factorial function as a loop handle 6746 * static class FacLoop { 6747 * final int k; 6748 * FacLoop(int k) { this.k = k; } 6749 * int inc(int i) { return i + 1; } 6750 * int mult(int i, int acc) { return i * acc; } 6751 * boolean pred(int i) { return i < k; } 6752 * int fin(int i, int acc) { return acc; } 6753 * } 6754 * // assume MH_FacLoop is a handle to the constructor 6755 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 6756 * // null initializer for counter, should initialize to 0 6757 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 6758 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop}; 6759 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6760 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6761 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause); 6762 * assertEquals(5040, loop.invoke(7)); 6763 * } 6764 * 6765 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above. 6766 * 6767 * @return a method handle embodying the looping behavior as defined by the arguments. 6768 * 6769 * @throws IllegalArgumentException in case any of the constraints described above is violated. 6770 * 6771 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle) 6772 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 6773 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle) 6774 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle) 6775 * @since 9 6776 */ 6777 public static MethodHandle loop(MethodHandle[]... clauses) { 6778 // Step 0: determine clause structure. 6779 loopChecks0(clauses); 6780 6781 List<MethodHandle> init = new ArrayList<>(); 6782 List<MethodHandle> step = new ArrayList<>(); 6783 List<MethodHandle> pred = new ArrayList<>(); 6784 List<MethodHandle> fini = new ArrayList<>(); 6785 6786 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> { 6787 init.add(clause[0]); // all clauses have at least length 1 6788 step.add(clause.length <= 1 ? null : clause[1]); 6789 pred.add(clause.length <= 2 ? null : clause[2]); 6790 fini.add(clause.length <= 3 ? null : clause[3]); 6791 }); 6792 6793 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1; 6794 final int nclauses = init.size(); 6795 6796 // Step 1A: determine iteration variables (V...). 6797 final List<Class<?>> iterationVariableTypes = new ArrayList<>(); 6798 for (int i = 0; i < nclauses; ++i) { 6799 MethodHandle in = init.get(i); 6800 MethodHandle st = step.get(i); 6801 if (in == null && st == null) { 6802 iterationVariableTypes.add(void.class); 6803 } else if (in != null && st != null) { 6804 loopChecks1a(i, in, st); 6805 iterationVariableTypes.add(in.type().returnType()); 6806 } else { 6807 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType()); 6808 } 6809 } 6810 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList(); 6811 6812 // Step 1B: determine loop parameters (A...). 6813 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size()); 6814 loopChecks1b(init, commonSuffix); 6815 6816 // Step 1C: determine loop return type. 6817 // Step 1D: check other types. 6818 // local variable required here; see JDK-8223553 6819 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type) 6820 .map(MethodType::returnType); 6821 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class); 6822 loopChecks1cd(pred, fini, loopReturnType); 6823 6824 // Step 2: determine parameter lists. 6825 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix); 6826 commonParameterSequence.addAll(commonSuffix); 6827 loopChecks2(step, pred, fini, commonParameterSequence); 6828 // Step 3: fill in omitted functions. 6829 for (int i = 0; i < nclauses; ++i) { 6830 Class<?> t = iterationVariableTypes.get(i); 6831 if (init.get(i) == null) { 6832 init.set(i, empty(methodType(t, commonSuffix))); 6833 } 6834 if (step.get(i) == null) { 6835 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i)); 6836 } 6837 if (pred.get(i) == null) { 6838 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence)); 6839 } 6840 if (fini.get(i) == null) { 6841 fini.set(i, empty(methodType(t, commonParameterSequence))); 6842 } 6843 } 6844 6845 // Step 4: fill in missing parameter types. 6846 // Also convert all handles to fixed-arity handles. 6847 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix)); 6848 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence)); 6849 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence)); 6850 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence)); 6851 6852 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList). 6853 allMatch(pl -> pl.equals(commonSuffix)); 6854 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList). 6855 allMatch(pl -> pl.equals(commonParameterSequence)); 6856 6857 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini); 6858 } 6859 6860 private static void loopChecks0(MethodHandle[][] clauses) { 6861 if (clauses == null || clauses.length == 0) { 6862 throw newIllegalArgumentException("null or no clauses passed"); 6863 } 6864 if (Stream.of(clauses).anyMatch(Objects::isNull)) { 6865 throw newIllegalArgumentException("null clauses are not allowed"); 6866 } 6867 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) { 6868 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements."); 6869 } 6870 } 6871 6872 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) { 6873 if (in.type().returnType() != st.type().returnType()) { 6874 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(), 6875 st.type().returnType()); 6876 } 6877 } 6878 6879 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) { 6880 return mhs.filter(Objects::nonNull) 6881 // take only those that can contribute to a common suffix because they are longer than the prefix 6882 .map(MethodHandle::type) 6883 .filter(t -> t.parameterCount() > skipSize) 6884 .max(Comparator.comparingInt(MethodType::parameterCount)) 6885 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount()))) 6886 .orElse(List.of()); 6887 } 6888 6889 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) { 6890 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize); 6891 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0); 6892 return longest1.size() >= longest2.size() ? longest1 : longest2; 6893 } 6894 6895 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) { 6896 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type). 6897 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) { 6898 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init + 6899 " (common suffix: " + commonSuffix + ")"); 6900 } 6901 } 6902 6903 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) { 6904 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 6905 anyMatch(t -> t != loopReturnType)) { 6906 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " + 6907 loopReturnType + ")"); 6908 } 6909 6910 if (pred.stream().noneMatch(Objects::nonNull)) { 6911 throw newIllegalArgumentException("no predicate found", pred); 6912 } 6913 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 6914 anyMatch(t -> t != boolean.class)) { 6915 throw newIllegalArgumentException("predicates must have boolean return type", pred); 6916 } 6917 } 6918 6919 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) { 6920 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type). 6921 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) { 6922 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step + 6923 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")"); 6924 } 6925 } 6926 6927 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) { 6928 return hs.stream().map(h -> { 6929 int pc = h.type().parameterCount(); 6930 int tpsize = targetParams.size(); 6931 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h; 6932 }).toList(); 6933 } 6934 6935 private static List<MethodHandle> fixArities(List<MethodHandle> hs) { 6936 return hs.stream().map(MethodHandle::asFixedArity).toList(); 6937 } 6938 6939 /** 6940 * Constructs a {@code while} loop from an initializer, a body, and a predicate. 6941 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 6942 * <p> 6943 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 6944 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate 6945 * evaluates to {@code true}). 6946 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case). 6947 * <p> 6948 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 6949 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 6950 * and updated with the value returned from its invocation. The result of loop execution will be 6951 * the final value of the additional loop-local variable (if present). 6952 * <p> 6953 * The following rules hold for these argument handles:<ul> 6954 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 6955 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 6956 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 6957 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 6958 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 6959 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 6960 * It will constrain the parameter lists of the other loop parts. 6961 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 6962 * list {@code (A...)} is called the <em>external parameter list</em>. 6963 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 6964 * additional state variable of the loop. 6965 * The body must both accept and return a value of this type {@code V}. 6966 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 6967 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 6968 * <a href="MethodHandles.html#effid">effectively identical</a> 6969 * to the external parameter list {@code (A...)}. 6970 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 6971 * {@linkplain #empty default value}. 6972 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 6973 * Its parameter list (either empty or of the form {@code (V A*)}) must be 6974 * effectively identical to the internal parameter list. 6975 * </ul> 6976 * <p> 6977 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 6978 * <li>The loop handle's result type is the result type {@code V} of the body. 6979 * <li>The loop handle's parameter types are the types {@code (A...)}, 6980 * from the external parameter list. 6981 * </ul> 6982 * <p> 6983 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 6984 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 6985 * passed to the loop. 6986 * {@snippet lang="java" : 6987 * V init(A...); 6988 * boolean pred(V, A...); 6989 * V body(V, A...); 6990 * V whileLoop(A... a...) { 6991 * V v = init(a...); 6992 * while (pred(v, a...)) { 6993 * v = body(v, a...); 6994 * } 6995 * return v; 6996 * } 6997 * } 6998 * 6999 * @apiNote Example: 7000 * {@snippet lang="java" : 7001 * // implement the zip function for lists as a loop handle 7002 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); } 7003 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); } 7004 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) { 7005 * zip.add(a.next()); 7006 * zip.add(b.next()); 7007 * return zip; 7008 * } 7009 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods 7010 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep); 7011 * List<String> a = Arrays.asList("a", "b", "c", "d"); 7012 * List<String> b = Arrays.asList("e", "f", "g", "h"); 7013 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h"); 7014 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator())); 7015 * } 7016 * 7017 * 7018 * @apiNote The implementation of this method can be expressed as follows: 7019 * {@snippet lang="java" : 7020 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 7021 * MethodHandle fini = (body.type().returnType() == void.class 7022 * ? null : identity(body.type().returnType())); 7023 * MethodHandle[] 7024 * checkExit = { null, null, pred, fini }, 7025 * varBody = { init, body }; 7026 * return loop(checkExit, varBody); 7027 * } 7028 * } 7029 * 7030 * @param init optional initializer, providing the initial value of the loop variable. 7031 * May be {@code null}, implying a default initial value. See above for other constraints. 7032 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 7033 * above for other constraints. 7034 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 7035 * See above for other constraints. 7036 * 7037 * @return a method handle implementing the {@code while} loop as described by the arguments. 7038 * @throws IllegalArgumentException if the rules for the arguments are violated. 7039 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 7040 * 7041 * @see #loop(MethodHandle[][]) 7042 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 7043 * @since 9 7044 */ 7045 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 7046 whileLoopChecks(init, pred, body); 7047 MethodHandle fini = identityOrVoid(body.type().returnType()); 7048 MethodHandle[] checkExit = { null, null, pred, fini }; 7049 MethodHandle[] varBody = { init, body }; 7050 return loop(checkExit, varBody); 7051 } 7052 7053 /** 7054 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. 7055 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7056 * <p> 7057 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 7058 * method will, in each iteration, first execute its body and then evaluate the predicate. 7059 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body. 7060 * <p> 7061 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 7062 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 7063 * and updated with the value returned from its invocation. The result of loop execution will be 7064 * the final value of the additional loop-local variable (if present). 7065 * <p> 7066 * The following rules hold for these argument handles:<ul> 7067 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7068 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 7069 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7070 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 7071 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 7072 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 7073 * It will constrain the parameter lists of the other loop parts. 7074 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 7075 * list {@code (A...)} is called the <em>external parameter list</em>. 7076 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7077 * additional state variable of the loop. 7078 * The body must both accept and return a value of this type {@code V}. 7079 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7080 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7081 * <a href="MethodHandles.html#effid">effectively identical</a> 7082 * to the external parameter list {@code (A...)}. 7083 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7084 * {@linkplain #empty default value}. 7085 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 7086 * Its parameter list (either empty or of the form {@code (V A*)}) must be 7087 * effectively identical to the internal parameter list. 7088 * </ul> 7089 * <p> 7090 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7091 * <li>The loop handle's result type is the result type {@code V} of the body. 7092 * <li>The loop handle's parameter types are the types {@code (A...)}, 7093 * from the external parameter list. 7094 * </ul> 7095 * <p> 7096 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7097 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 7098 * passed to the loop. 7099 * {@snippet lang="java" : 7100 * V init(A...); 7101 * boolean pred(V, A...); 7102 * V body(V, A...); 7103 * V doWhileLoop(A... a...) { 7104 * V v = init(a...); 7105 * do { 7106 * v = body(v, a...); 7107 * } while (pred(v, a...)); 7108 * return v; 7109 * } 7110 * } 7111 * 7112 * @apiNote Example: 7113 * {@snippet lang="java" : 7114 * // int i = 0; while (i < limit) { ++i; } return i; => limit 7115 * static int zero(int limit) { return 0; } 7116 * static int step(int i, int limit) { return i + 1; } 7117 * static boolean pred(int i, int limit) { return i < limit; } 7118 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods 7119 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred); 7120 * assertEquals(23, loop.invoke(23)); 7121 * } 7122 * 7123 * 7124 * @apiNote The implementation of this method can be expressed as follows: 7125 * {@snippet lang="java" : 7126 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 7127 * MethodHandle fini = (body.type().returnType() == void.class 7128 * ? null : identity(body.type().returnType())); 7129 * MethodHandle[] clause = { init, body, pred, fini }; 7130 * return loop(clause); 7131 * } 7132 * } 7133 * 7134 * @param init optional initializer, providing the initial value of the loop variable. 7135 * May be {@code null}, implying a default initial value. See above for other constraints. 7136 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 7137 * See above for other constraints. 7138 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 7139 * above for other constraints. 7140 * 7141 * @return a method handle implementing the {@code while} loop as described by the arguments. 7142 * @throws IllegalArgumentException if the rules for the arguments are violated. 7143 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 7144 * 7145 * @see #loop(MethodHandle[][]) 7146 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle) 7147 * @since 9 7148 */ 7149 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 7150 whileLoopChecks(init, pred, body); 7151 MethodHandle fini = identityOrVoid(body.type().returnType()); 7152 MethodHandle[] clause = {init, body, pred, fini }; 7153 return loop(clause); 7154 } 7155 7156 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) { 7157 Objects.requireNonNull(pred); 7158 Objects.requireNonNull(body); 7159 MethodType bodyType = body.type(); 7160 Class<?> returnType = bodyType.returnType(); 7161 List<Class<?>> innerList = bodyType.parameterList(); 7162 List<Class<?>> outerList = innerList; 7163 if (returnType == void.class) { 7164 // OK 7165 } else if (innerList.isEmpty() || innerList.get(0) != returnType) { 7166 // leading V argument missing => error 7167 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7168 throw misMatchedTypes("body function", bodyType, expected); 7169 } else { 7170 outerList = innerList.subList(1, innerList.size()); 7171 } 7172 MethodType predType = pred.type(); 7173 if (predType.returnType() != boolean.class || 7174 !predType.effectivelyIdenticalParameters(0, innerList)) { 7175 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList)); 7176 } 7177 if (init != null) { 7178 MethodType initType = init.type(); 7179 if (initType.returnType() != returnType || 7180 !initType.effectivelyIdenticalParameters(0, outerList)) { 7181 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 7182 } 7183 } 7184 } 7185 7186 /** 7187 * Constructs a loop that runs a given number of iterations. 7188 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7189 * <p> 7190 * The number of iterations is determined by the {@code iterations} handle evaluation result. 7191 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}. 7192 * It will be initialized to 0 and incremented by 1 in each iteration. 7193 * <p> 7194 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7195 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7196 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7197 * <p> 7198 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7199 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7200 * iteration variable. 7201 * The result of the loop handle execution will be the final {@code V} value of that variable 7202 * (or {@code void} if there is no {@code V} variable). 7203 * <p> 7204 * The following rules hold for the argument handles:<ul> 7205 * <li>The {@code iterations} handle must not be {@code null}, and must return 7206 * the type {@code int}, referred to here as {@code I} in parameter type lists. 7207 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7208 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 7209 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7210 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 7211 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 7212 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 7213 * of types called the <em>internal parameter list</em>. 7214 * It will constrain the parameter lists of the other loop parts. 7215 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 7216 * with no additional {@code A} types, then the internal parameter list is extended by 7217 * the argument types {@code A...} of the {@code iterations} handle. 7218 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 7219 * list {@code (A...)} is called the <em>external parameter list</em>. 7220 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7221 * additional state variable of the loop. 7222 * The body must both accept a leading parameter and return a value of this type {@code V}. 7223 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7224 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7225 * <a href="MethodHandles.html#effid">effectively identical</a> 7226 * to the external parameter list {@code (A...)}. 7227 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7228 * {@linkplain #empty default value}. 7229 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be 7230 * effectively identical to the external parameter list {@code (A...)}. 7231 * </ul> 7232 * <p> 7233 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7234 * <li>The loop handle's result type is the result type {@code V} of the body. 7235 * <li>The loop handle's parameter types are the types {@code (A...)}, 7236 * from the external parameter list. 7237 * </ul> 7238 * <p> 7239 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7240 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 7241 * arguments passed to the loop. 7242 * {@snippet lang="java" : 7243 * int iterations(A...); 7244 * V init(A...); 7245 * V body(V, int, A...); 7246 * V countedLoop(A... a...) { 7247 * int end = iterations(a...); 7248 * V v = init(a...); 7249 * for (int i = 0; i < end; ++i) { 7250 * v = body(v, i, a...); 7251 * } 7252 * return v; 7253 * } 7254 * } 7255 * 7256 * @apiNote Example with a fully conformant body method: 7257 * {@snippet lang="java" : 7258 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 7259 * // => a variation on a well known theme 7260 * static String step(String v, int counter, String init) { return "na " + v; } 7261 * // assume MH_step is a handle to the method above 7262 * MethodHandle fit13 = MethodHandles.constant(int.class, 13); 7263 * MethodHandle start = MethodHandles.identity(String.class); 7264 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step); 7265 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!")); 7266 * } 7267 * 7268 * @apiNote Example with the simplest possible body method type, 7269 * and passing the number of iterations to the loop invocation: 7270 * {@snippet lang="java" : 7271 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 7272 * // => a variation on a well known theme 7273 * static String step(String v, int counter ) { return "na " + v; } 7274 * // assume MH_step is a handle to the method above 7275 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class); 7276 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class); 7277 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v 7278 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!")); 7279 * } 7280 * 7281 * @apiNote Example that treats the number of iterations, string to append to, and string to append 7282 * as loop parameters: 7283 * {@snippet lang="java" : 7284 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 7285 * // => a variation on a well known theme 7286 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; } 7287 * // assume MH_step is a handle to the method above 7288 * MethodHandle count = MethodHandles.identity(int.class); 7289 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class); 7290 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v 7291 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!")); 7292 * } 7293 * 7294 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)} 7295 * to enforce a loop type: 7296 * {@snippet lang="java" : 7297 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 7298 * // => a variation on a well known theme 7299 * static String step(String v, int counter, String pre) { return pre + " " + v; } 7300 * // assume MH_step is a handle to the method above 7301 * MethodType loopType = methodType(String.class, String.class, int.class, String.class); 7302 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1); 7303 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2); 7304 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0); 7305 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v 7306 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!")); 7307 * } 7308 * 7309 * @apiNote The implementation of this method can be expressed as follows: 7310 * {@snippet lang="java" : 7311 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 7312 * return countedLoop(empty(iterations.type()), iterations, init, body); 7313 * } 7314 * } 7315 * 7316 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's 7317 * result type must be {@code int}. See above for other constraints. 7318 * @param init optional initializer, providing the initial value of the loop variable. 7319 * May be {@code null}, implying a default initial value. See above for other constraints. 7320 * @param body body of the loop, which may not be {@code null}. 7321 * It controls the loop parameters and result type in the standard case (see above for details). 7322 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 7323 * and may accept any number of additional types. 7324 * See above for other constraints. 7325 * 7326 * @return a method handle representing the loop. 7327 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}. 7328 * @throws IllegalArgumentException if any argument violates the rules formulated above. 7329 * 7330 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle) 7331 * @since 9 7332 */ 7333 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 7334 return countedLoop(empty(iterations.type()), iterations, init, body); 7335 } 7336 7337 /** 7338 * Constructs a loop that counts over a range of numbers. 7339 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7340 * <p> 7341 * The loop counter {@code i} is a loop iteration variable of type {@code int}. 7342 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive) 7343 * values of the loop counter. 7344 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the 7345 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1. 7346 * <p> 7347 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7348 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7349 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7350 * <p> 7351 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7352 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7353 * iteration variable. 7354 * The result of the loop handle execution will be the final {@code V} value of that variable 7355 * (or {@code void} if there is no {@code V} variable). 7356 * <p> 7357 * The following rules hold for the argument handles:<ul> 7358 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return 7359 * the common type {@code int}, referred to here as {@code I} in parameter type lists. 7360 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7361 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 7362 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7363 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 7364 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 7365 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 7366 * of types called the <em>internal parameter list</em>. 7367 * It will constrain the parameter lists of the other loop parts. 7368 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 7369 * with no additional {@code A} types, then the internal parameter list is extended by 7370 * the argument types {@code A...} of the {@code end} handle. 7371 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 7372 * list {@code (A...)} is called the <em>external parameter list</em>. 7373 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7374 * additional state variable of the loop. 7375 * The body must both accept a leading parameter and return a value of this type {@code V}. 7376 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7377 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7378 * <a href="MethodHandles.html#effid">effectively identical</a> 7379 * to the external parameter list {@code (A...)}. 7380 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7381 * {@linkplain #empty default value}. 7382 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be 7383 * effectively identical to the external parameter list {@code (A...)}. 7384 * <li>Likewise, the parameter list of {@code end} must be effectively identical 7385 * to the external parameter list. 7386 * </ul> 7387 * <p> 7388 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7389 * <li>The loop handle's result type is the result type {@code V} of the body. 7390 * <li>The loop handle's parameter types are the types {@code (A...)}, 7391 * from the external parameter list. 7392 * </ul> 7393 * <p> 7394 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7395 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 7396 * arguments passed to the loop. 7397 * {@snippet lang="java" : 7398 * int start(A...); 7399 * int end(A...); 7400 * V init(A...); 7401 * V body(V, int, A...); 7402 * V countedLoop(A... a...) { 7403 * int e = end(a...); 7404 * int s = start(a...); 7405 * V v = init(a...); 7406 * for (int i = s; i < e; ++i) { 7407 * v = body(v, i, a...); 7408 * } 7409 * return v; 7410 * } 7411 * } 7412 * 7413 * @apiNote The implementation of this method can be expressed as follows: 7414 * {@snippet lang="java" : 7415 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7416 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class); 7417 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with 7418 * // the following semantics: 7419 * // MH_increment: (int limit, int counter) -> counter + 1 7420 * // MH_predicate: (int limit, int counter) -> counter < limit 7421 * Class<?> counterType = start.type().returnType(); // int 7422 * Class<?> returnType = body.type().returnType(); 7423 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null; 7424 * if (returnType != void.class) { // ignore the V variable 7425 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 7426 * pred = dropArguments(pred, 1, returnType); // ditto 7427 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit 7428 * } 7429 * body = dropArguments(body, 0, counterType); // ignore the limit variable 7430 * MethodHandle[] 7431 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 7432 * bodyClause = { init, body }, // v = init(); v = body(v, i) 7433 * indexVar = { start, incr }; // i = start(); i = i + 1 7434 * return loop(loopLimit, bodyClause, indexVar); 7435 * } 7436 * } 7437 * 7438 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}. 7439 * See above for other constraints. 7440 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to 7441 * {@code end-1}). The result type must be {@code int}. See above for other constraints. 7442 * @param init optional initializer, providing the initial value of the loop variable. 7443 * May be {@code null}, implying a default initial value. See above for other constraints. 7444 * @param body body of the loop, which may not be {@code null}. 7445 * It controls the loop parameters and result type in the standard case (see above for details). 7446 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 7447 * and may accept any number of additional types. 7448 * See above for other constraints. 7449 * 7450 * @return a method handle representing the loop. 7451 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}. 7452 * @throws IllegalArgumentException if any argument violates the rules formulated above. 7453 * 7454 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle) 7455 * @since 9 7456 */ 7457 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7458 countedLoopChecks(start, end, init, body); 7459 Class<?> counterType = start.type().returnType(); // int, but who's counting? 7460 Class<?> limitType = end.type().returnType(); // yes, int again 7461 Class<?> returnType = body.type().returnType(); 7462 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep); 7463 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred); 7464 MethodHandle retv = null; 7465 if (returnType != void.class) { 7466 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 7467 pred = dropArguments(pred, 1, returnType); // ditto 7468 retv = dropArguments(identity(returnType), 0, counterType); 7469 } 7470 body = dropArguments(body, 0, counterType); // ignore the limit variable 7471 MethodHandle[] 7472 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 7473 bodyClause = { init, body }, // v = init(); v = body(v, i) 7474 indexVar = { start, incr }; // i = start(); i = i + 1 7475 return loop(loopLimit, bodyClause, indexVar); 7476 } 7477 7478 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7479 Objects.requireNonNull(start); 7480 Objects.requireNonNull(end); 7481 Objects.requireNonNull(body); 7482 Class<?> counterType = start.type().returnType(); 7483 if (counterType != int.class) { 7484 MethodType expected = start.type().changeReturnType(int.class); 7485 throw misMatchedTypes("start function", start.type(), expected); 7486 } else if (end.type().returnType() != counterType) { 7487 MethodType expected = end.type().changeReturnType(counterType); 7488 throw misMatchedTypes("end function", end.type(), expected); 7489 } 7490 MethodType bodyType = body.type(); 7491 Class<?> returnType = bodyType.returnType(); 7492 List<Class<?>> innerList = bodyType.parameterList(); 7493 // strip leading V value if present 7494 int vsize = (returnType == void.class ? 0 : 1); 7495 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) { 7496 // argument list has no "V" => error 7497 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7498 throw misMatchedTypes("body function", bodyType, expected); 7499 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) { 7500 // missing I type => error 7501 MethodType expected = bodyType.insertParameterTypes(vsize, counterType); 7502 throw misMatchedTypes("body function", bodyType, expected); 7503 } 7504 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size()); 7505 if (outerList.isEmpty()) { 7506 // special case; take lists from end handle 7507 outerList = end.type().parameterList(); 7508 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList(); 7509 } 7510 MethodType expected = methodType(counterType, outerList); 7511 if (!start.type().effectivelyIdenticalParameters(0, outerList)) { 7512 throw misMatchedTypes("start parameter types", start.type(), expected); 7513 } 7514 if (end.type() != start.type() && 7515 !end.type().effectivelyIdenticalParameters(0, outerList)) { 7516 throw misMatchedTypes("end parameter types", end.type(), expected); 7517 } 7518 if (init != null) { 7519 MethodType initType = init.type(); 7520 if (initType.returnType() != returnType || 7521 !initType.effectivelyIdenticalParameters(0, outerList)) { 7522 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 7523 } 7524 } 7525 } 7526 7527 /** 7528 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}. 7529 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7530 * <p> 7531 * The iterator itself will be determined by the evaluation of the {@code iterator} handle. 7532 * Each value it produces will be stored in a loop iteration variable of type {@code T}. 7533 * <p> 7534 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7535 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7536 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7537 * <p> 7538 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7539 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7540 * iteration variable. 7541 * The result of the loop handle execution will be the final {@code V} value of that variable 7542 * (or {@code void} if there is no {@code V} variable). 7543 * <p> 7544 * The following rules hold for the argument handles:<ul> 7545 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7546 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}. 7547 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7548 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V} 7549 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.) 7550 * <li>The parameter list {@code (V T A...)} of the body contributes to a list 7551 * of types called the <em>internal parameter list</em>. 7552 * It will constrain the parameter lists of the other loop parts. 7553 * <li>As a special case, if the body contributes only {@code V} and {@code T} types, 7554 * with no additional {@code A} types, then the internal parameter list is extended by 7555 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the 7556 * single type {@code Iterable} is added and constitutes the {@code A...} list. 7557 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter 7558 * list {@code (A...)} is called the <em>external parameter list</em>. 7559 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7560 * additional state variable of the loop. 7561 * The body must both accept a leading parameter and return a value of this type {@code V}. 7562 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7563 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7564 * <a href="MethodHandles.html#effid">effectively identical</a> 7565 * to the external parameter list {@code (A...)}. 7566 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7567 * {@linkplain #empty default value}. 7568 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return 7569 * type {@code java.util.Iterator} or a subtype thereof. 7570 * The iterator it produces when the loop is executed will be assumed 7571 * to yield values which can be converted to type {@code T}. 7572 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be 7573 * effectively identical to the external parameter list {@code (A...)}. 7574 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves 7575 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list 7576 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator 7577 * handle parameter is adjusted to accept the leading {@code A} type, as if by 7578 * the {@link MethodHandle#asType asType} conversion method. 7579 * The leading {@code A} type must be {@code Iterable} or a subtype thereof. 7580 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}. 7581 * </ul> 7582 * <p> 7583 * The type {@code T} may be either a primitive or reference. 7584 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator}, 7585 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object} 7586 * as if by the {@link MethodHandle#asType asType} conversion method. 7587 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur 7588 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}. 7589 * <p> 7590 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7591 * <li>The loop handle's result type is the result type {@code V} of the body. 7592 * <li>The loop handle's parameter types are the types {@code (A...)}, 7593 * from the external parameter list. 7594 * </ul> 7595 * <p> 7596 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7597 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the 7598 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop. 7599 * {@snippet lang="java" : 7600 * Iterator<T> iterator(A...); // defaults to Iterable::iterator 7601 * V init(A...); 7602 * V body(V,T,A...); 7603 * V iteratedLoop(A... a...) { 7604 * Iterator<T> it = iterator(a...); 7605 * V v = init(a...); 7606 * while (it.hasNext()) { 7607 * T t = it.next(); 7608 * v = body(v, t, a...); 7609 * } 7610 * return v; 7611 * } 7612 * } 7613 * 7614 * @apiNote Example: 7615 * {@snippet lang="java" : 7616 * // get an iterator from a list 7617 * static List<String> reverseStep(List<String> r, String e) { 7618 * r.add(0, e); 7619 * return r; 7620 * } 7621 * static List<String> newArrayList() { return new ArrayList<>(); } 7622 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods 7623 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep); 7624 * List<String> list = Arrays.asList("a", "b", "c", "d", "e"); 7625 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a"); 7626 * assertEquals(reversedList, (List<String>) loop.invoke(list)); 7627 * } 7628 * 7629 * @apiNote The implementation of this method can be expressed approximately as follows: 7630 * {@snippet lang="java" : 7631 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7632 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable 7633 * Class<?> returnType = body.type().returnType(); 7634 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 7635 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype)); 7636 * MethodHandle retv = null, step = body, startIter = iterator; 7637 * if (returnType != void.class) { 7638 * // the simple thing first: in (I V A...), drop the I to get V 7639 * retv = dropArguments(identity(returnType), 0, Iterator.class); 7640 * // body type signature (V T A...), internal loop types (I V A...) 7641 * step = swapArguments(body, 0, 1); // swap V <-> T 7642 * } 7643 * if (startIter == null) startIter = MH_getIter; 7644 * MethodHandle[] 7645 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext()) 7646 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a) 7647 * return loop(iterVar, bodyClause); 7648 * } 7649 * } 7650 * 7651 * @param iterator an optional handle to return the iterator to start the loop. 7652 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype. 7653 * See above for other constraints. 7654 * @param init optional initializer, providing the initial value of the loop variable. 7655 * May be {@code null}, implying a default initial value. See above for other constraints. 7656 * @param body body of the loop, which may not be {@code null}. 7657 * It controls the loop parameters and result type in the standard case (see above for details). 7658 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values), 7659 * and may accept any number of additional types. 7660 * See above for other constraints. 7661 * 7662 * @return a method handle embodying the iteration loop functionality. 7663 * @throws NullPointerException if the {@code body} handle is {@code null}. 7664 * @throws IllegalArgumentException if any argument violates the above requirements. 7665 * 7666 * @since 9 7667 */ 7668 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7669 Class<?> iterableType = iteratedLoopChecks(iterator, init, body); 7670 Class<?> returnType = body.type().returnType(); 7671 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred); 7672 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext); 7673 MethodHandle startIter; 7674 MethodHandle nextVal; 7675 { 7676 MethodType iteratorType; 7677 if (iterator == null) { 7678 // derive argument type from body, if available, else use Iterable 7679 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator); 7680 iteratorType = startIter.type().changeParameterType(0, iterableType); 7681 } else { 7682 // force return type to the internal iterator class 7683 iteratorType = iterator.type().changeReturnType(Iterator.class); 7684 startIter = iterator; 7685 } 7686 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 7687 MethodType nextValType = nextRaw.type().changeReturnType(ttype); 7688 7689 // perform the asType transforms under an exception transformer, as per spec.: 7690 try { 7691 startIter = startIter.asType(iteratorType); 7692 nextVal = nextRaw.asType(nextValType); 7693 } catch (WrongMethodTypeException ex) { 7694 throw new IllegalArgumentException(ex); 7695 } 7696 } 7697 7698 MethodHandle retv = null, step = body; 7699 if (returnType != void.class) { 7700 // the simple thing first: in (I V A...), drop the I to get V 7701 retv = dropArguments(identity(returnType), 0, Iterator.class); 7702 // body type signature (V T A...), internal loop types (I V A...) 7703 step = swapArguments(body, 0, 1); // swap V <-> T 7704 } 7705 7706 MethodHandle[] 7707 iterVar = { startIter, null, hasNext, retv }, 7708 bodyClause = { init, filterArgument(step, 0, nextVal) }; 7709 return loop(iterVar, bodyClause); 7710 } 7711 7712 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7713 Objects.requireNonNull(body); 7714 MethodType bodyType = body.type(); 7715 Class<?> returnType = bodyType.returnType(); 7716 List<Class<?>> internalParamList = bodyType.parameterList(); 7717 // strip leading V value if present 7718 int vsize = (returnType == void.class ? 0 : 1); 7719 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) { 7720 // argument list has no "V" => error 7721 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7722 throw misMatchedTypes("body function", bodyType, expected); 7723 } else if (internalParamList.size() <= vsize) { 7724 // missing T type => error 7725 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class); 7726 throw misMatchedTypes("body function", bodyType, expected); 7727 } 7728 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size()); 7729 Class<?> iterableType = null; 7730 if (iterator != null) { 7731 // special case; if the body handle only declares V and T then 7732 // the external parameter list is obtained from iterator handle 7733 if (externalParamList.isEmpty()) { 7734 externalParamList = iterator.type().parameterList(); 7735 } 7736 MethodType itype = iterator.type(); 7737 if (!Iterator.class.isAssignableFrom(itype.returnType())) { 7738 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type"); 7739 } 7740 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) { 7741 MethodType expected = methodType(itype.returnType(), externalParamList); 7742 throw misMatchedTypes("iterator parameters", itype, expected); 7743 } 7744 } else { 7745 if (externalParamList.isEmpty()) { 7746 // special case; if the iterator handle is null and the body handle 7747 // only declares V and T then the external parameter list consists 7748 // of Iterable 7749 externalParamList = List.of(Iterable.class); 7750 iterableType = Iterable.class; 7751 } else { 7752 // special case; if the iterator handle is null and the external 7753 // parameter list is not empty then the first parameter must be 7754 // assignable to Iterable 7755 iterableType = externalParamList.get(0); 7756 if (!Iterable.class.isAssignableFrom(iterableType)) { 7757 throw newIllegalArgumentException( 7758 "inferred first loop argument must inherit from Iterable: " + iterableType); 7759 } 7760 } 7761 } 7762 if (init != null) { 7763 MethodType initType = init.type(); 7764 if (initType.returnType() != returnType || 7765 !initType.effectivelyIdenticalParameters(0, externalParamList)) { 7766 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList)); 7767 } 7768 } 7769 return iterableType; // help the caller a bit 7770 } 7771 7772 /*non-public*/ 7773 static MethodHandle swapArguments(MethodHandle mh, int i, int j) { 7774 // there should be a better way to uncross my wires 7775 int arity = mh.type().parameterCount(); 7776 int[] order = new int[arity]; 7777 for (int k = 0; k < arity; k++) order[k] = k; 7778 order[i] = j; order[j] = i; 7779 Class<?>[] types = mh.type().parameterArray(); 7780 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti; 7781 MethodType swapType = methodType(mh.type().returnType(), types); 7782 return permuteArguments(mh, swapType, order); 7783 } 7784 7785 /** 7786 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block. 7787 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception 7788 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The 7789 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The 7790 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the 7791 * {@code try-finally} handle. 7792 * <p> 7793 * The {@code cleanup} handle will be passed one or two additional leading arguments. 7794 * The first is the exception thrown during the 7795 * execution of the {@code target} handle, or {@code null} if no exception was thrown. 7796 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception, 7797 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder. 7798 * The second argument is not present if the {@code target} handle has a {@code void} return type. 7799 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists 7800 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.) 7801 * <p> 7802 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except 7803 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or 7804 * two extra leading parameters:<ul> 7805 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and 7806 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry 7807 * the result from the execution of the {@code target} handle. 7808 * This parameter is not present if the {@code target} returns {@code void}. 7809 * </ul> 7810 * <p> 7811 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of 7812 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting 7813 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by 7814 * the cleanup. 7815 * {@snippet lang="java" : 7816 * V target(A..., B...); 7817 * V cleanup(Throwable, V, A...); 7818 * V adapter(A... a, B... b) { 7819 * V result = (zero value for V); 7820 * Throwable throwable = null; 7821 * try { 7822 * result = target(a..., b...); 7823 * } catch (Throwable t) { 7824 * throwable = t; 7825 * throw t; 7826 * } finally { 7827 * result = cleanup(throwable, result, a...); 7828 * } 7829 * return result; 7830 * } 7831 * } 7832 * <p> 7833 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 7834 * be modified by execution of the target, and so are passed unchanged 7835 * from the caller to the cleanup, if it is invoked. 7836 * <p> 7837 * The target and cleanup must return the same type, even if the cleanup 7838 * always throws. 7839 * To create such a throwing cleanup, compose the cleanup logic 7840 * with {@link #throwException throwException}, 7841 * in order to create a method handle of the correct return type. 7842 * <p> 7843 * Note that {@code tryFinally} never converts exceptions into normal returns. 7844 * In rare cases where exceptions must be converted in that way, first wrap 7845 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)} 7846 * to capture an outgoing exception, and then wrap with {@code tryFinally}. 7847 * <p> 7848 * It is recommended that the first parameter type of {@code cleanup} be 7849 * declared {@code Throwable} rather than a narrower subtype. This ensures 7850 * {@code cleanup} will always be invoked with whatever exception that 7851 * {@code target} throws. Declaring a narrower type may result in a 7852 * {@code ClassCastException} being thrown by the {@code try-finally} 7853 * handle if the type of the exception thrown by {@code target} is not 7854 * assignable to the first parameter type of {@code cleanup}. Note that 7855 * various exception types of {@code VirtualMachineError}, 7856 * {@code LinkageError}, and {@code RuntimeException} can in principle be 7857 * thrown by almost any kind of Java code, and a finally clause that 7858 * catches (say) only {@code IOException} would mask any of the others 7859 * behind a {@code ClassCastException}. 7860 * 7861 * @param target the handle whose execution is to be wrapped in a {@code try} block. 7862 * @param cleanup the handle that is invoked in the finally block. 7863 * 7864 * @return a method handle embodying the {@code try-finally} block composed of the two arguments. 7865 * @throws NullPointerException if any argument is null 7866 * @throws IllegalArgumentException if {@code cleanup} does not accept 7867 * the required leading arguments, or if the method handle types do 7868 * not match in their return types and their 7869 * corresponding trailing parameters 7870 * 7871 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle) 7872 * @since 9 7873 */ 7874 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) { 7875 Class<?>[] targetParamTypes = target.type().ptypes(); 7876 Class<?> rtype = target.type().returnType(); 7877 7878 tryFinallyChecks(target, cleanup); 7879 7880 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments. 7881 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 7882 // target parameter list. 7883 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false); 7884 7885 // Ensure that the intrinsic type checks the instance thrown by the 7886 // target against the first parameter of cleanup 7887 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class)); 7888 7889 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case. 7890 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes); 7891 } 7892 7893 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) { 7894 Class<?> rtype = target.type().returnType(); 7895 if (rtype != cleanup.type().returnType()) { 7896 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype); 7897 } 7898 MethodType cleanupType = cleanup.type(); 7899 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) { 7900 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class); 7901 } 7902 if (rtype != void.class && cleanupType.parameterType(1) != rtype) { 7903 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype); 7904 } 7905 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 7906 // target parameter list. 7907 int cleanupArgIndex = rtype == void.class ? 1 : 2; 7908 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) { 7909 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix", 7910 cleanup.type(), target.type()); 7911 } 7912 } 7913 7914 /** 7915 * Creates a table switch method handle, which can be used to switch over a set of target 7916 * method handles, based on a given target index, called selector. 7917 * <p> 7918 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)}, 7919 * and where {@code N} is the number of target method handles, the table switch method 7920 * handle will invoke the n-th target method handle from the list of target method handles. 7921 * <p> 7922 * For a selector value that does not fall in the range {@code [0, N)}, the table switch 7923 * method handle will invoke the given fallback method handle. 7924 * <p> 7925 * All method handles passed to this method must have the same type, with the additional 7926 * requirement that the leading parameter be of type {@code int}. The leading parameter 7927 * represents the selector. 7928 * <p> 7929 * Any trailing parameters present in the type will appear on the returned table switch 7930 * method handle as well. Any arguments assigned to these parameters will be forwarded, 7931 * together with the selector value, to the selected method handle when invoking it. 7932 * 7933 * @apiNote Example: 7934 * The cases each drop the {@code selector} value they are given, and take an additional 7935 * {@code String} argument, which is concatenated (using {@link String#concat(String)}) 7936 * to a specific constant label string for each case: 7937 * {@snippet lang="java" : 7938 * MethodHandles.Lookup lookup = MethodHandles.lookup(); 7939 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat", 7940 * MethodType.methodType(String.class, String.class)); 7941 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class); 7942 * 7943 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: "); 7944 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: "); 7945 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: "); 7946 * 7947 * MethodHandle mhSwitch = MethodHandles.tableSwitch( 7948 * caseDefault, 7949 * case0, 7950 * case1 7951 * ); 7952 * 7953 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data")); 7954 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data")); 7955 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data")); 7956 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data")); 7957 * } 7958 * 7959 * @param fallback the fallback method handle that is called when the selector is not 7960 * within the range {@code [0, N)}. 7961 * @param targets array of target method handles. 7962 * @return the table switch method handle. 7963 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any 7964 * any of the elements of the {@code targets} array are 7965 * {@code null}. 7966 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading 7967 * parameter of the fallback handle or any of the target 7968 * handles is not {@code int}, or if the types of 7969 * the fallback handle and all of target handles are 7970 * not the same. 7971 */ 7972 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) { 7973 Objects.requireNonNull(fallback); 7974 Objects.requireNonNull(targets); 7975 targets = targets.clone(); 7976 MethodType type = tableSwitchChecks(fallback, targets); 7977 return MethodHandleImpl.makeTableSwitch(type, fallback, targets); 7978 } 7979 7980 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) { 7981 if (caseActions.length == 0) 7982 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions)); 7983 7984 MethodType expectedType = defaultCase.type(); 7985 7986 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class) 7987 throw new IllegalArgumentException( 7988 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions)); 7989 7990 for (MethodHandle mh : caseActions) { 7991 Objects.requireNonNull(mh); 7992 if (mh.type() != expectedType) 7993 throw new IllegalArgumentException( 7994 "Case actions must have the same type: " + Arrays.toString(caseActions)); 7995 } 7996 7997 return expectedType; 7998 } 7999 8000 /** 8001 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment} 8002 * at a given byte offset, using the provided value layout. 8003 * 8004 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type}, 8005 * the {@linkplain ValueLayout#byteSize() byte size}, 8006 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order} 8007 * associated with the returned var handle. 8008 * 8009 * <p>The list of coordinate types associated with the returned var handle is {@code (MemorySegment, long)}, 8010 * where the {@code long} coordinate type corresponds to byte offset into the given memory segment coordinate. 8011 * Thus, the returned var handle accesses bytes at an offset in a given memory segment, composing bytes to or from 8012 * a value of the var handle type. Moreover, the access operation will honor the endianness and the 8013 * alignment constraints expressed in the provided layout. 8014 * 8015 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows: 8016 * {@snippet lang="java" : 8017 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout( 8018 * MemoryLayout.paddingLayout(4), 8019 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value") 8020 * ); 8021 * } 8022 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows: 8023 * {@snippet lang="java" : 8024 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int 8025 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int 8026 * } 8027 * 8028 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>, 8029 * which are common to all memory segment view var handles. A memory segment view var handle is associated 8030 * with an access size {@code S} and an alignment constraint {@code B} 8031 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs 8032 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}. 8033 * If access is fully aligned then following access modes are supported and are 8034 * guaranteed to support atomic access: 8035 * <ul> 8036 * <li>read write access modes for all {@code T}, with the exception of 8037 * access modes {@code get} and {@code set} for {@code long} and 8038 * {@code double} on 32-bit platforms. 8039 * <li>atomic update access modes for {@code int}, {@code long}, 8040 * {@code float}, {@code double} or {@link MemorySegment}. 8041 * (Future major platform releases of the JDK may support additional 8042 * types for certain currently unsupported access modes.) 8043 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}. 8044 * (Future major platform releases of the JDK may support additional 8045 * numeric types for certain currently unsupported access modes.) 8046 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}. 8047 * (Future major platform releases of the JDK may support additional 8048 * numeric types for certain currently unsupported access modes.) 8049 * </ul> 8050 * 8051 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic 8052 * update access modes compare values using their bitwise representation 8053 * (see {@link Float#floatToRawIntBits}, 8054 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively). 8055 * <p> 8056 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A} 8057 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the 8058 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned, 8059 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}. 8060 * <p> 8061 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an 8062 * {@code IllegalStateException} is thrown, irrespective of the access mode being used. 8063 * <p> 8064 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException} 8065 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment. 8066 * 8067 * @param layout the value layout for which a memory access handle is to be obtained. 8068 * @return the new memory segment view var handle. 8069 * @throws NullPointerException if {@code layout} is {@code null}. 8070 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...) 8071 * @since 19 8072 */ 8073 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8074 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) { 8075 Objects.requireNonNull(layout); 8076 return Utils.makeSegmentViewVarHandle(layout); 8077 } 8078 8079 /** 8080 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions. 8081 * <p> 8082 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where 8083 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed 8084 * to the target var handle. 8085 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from 8086 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function) 8087 * is processed using the second filter and returned to the caller. More advanced access mode types, such as 8088 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time. 8089 * <p> 8090 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and 8091 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case, 8092 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which 8093 * will be appended to the coordinates of the target var handle). 8094 * <p> 8095 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will 8096 * throw an {@link IllegalStateException}. 8097 * <p> 8098 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8099 * atomic access guarantees as those featured by the target var handle. 8100 * 8101 * @param target the target var handle 8102 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target} 8103 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S} 8104 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions. 8105 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types 8106 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle, 8107 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions. 8108 * @throws NullPointerException if any of the arguments is {@code null}. 8109 * @since 19 8110 */ 8111 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8112 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) { 8113 return VarHandles.filterValue(target, filterToTarget, filterFromTarget); 8114 } 8115 8116 /** 8117 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions. 8118 * <p> 8119 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values 8120 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types 8121 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the 8122 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered 8123 * by the adaptation) to the target var handle. 8124 * <p> 8125 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn}, 8126 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle. 8127 * <p> 8128 * If any of the filters throws a checked exception when invoked, the resulting var handle will 8129 * throw an {@link IllegalStateException}. 8130 * <p> 8131 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8132 * atomic access guarantees as those featured by the target var handle. 8133 * 8134 * @param target the target var handle 8135 * @param pos the position of the first coordinate to be transformed 8136 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos} 8137 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation 8138 * to the new coordinate values. 8139 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types 8140 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting 8141 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8142 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos}, 8143 * or if it's determined that any of the filters throws any checked exceptions. 8144 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}. 8145 * @since 19 8146 */ 8147 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8148 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) { 8149 return VarHandles.filterCoordinates(target, pos, filters); 8150 } 8151 8152 /** 8153 * Provides a target var handle with one or more <em>bound coordinates</em> 8154 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less 8155 * coordinate types than the target var handle. 8156 * <p> 8157 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values 8158 * are joined with bound coordinate values, and then passed to the target var handle. 8159 * <p> 8160 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn }, 8161 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle. 8162 * <p> 8163 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8164 * atomic access guarantees as those featured by the target var handle. 8165 * 8166 * @param target the var handle to invoke after the bound coordinates are inserted 8167 * @param pos the position of the first coordinate to be inserted 8168 * @param values the series of bound coordinates to insert 8169 * @return an adapter var handle which inserts additional coordinates, 8170 * before calling the target var handle 8171 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8172 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}. 8173 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types 8174 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} 8175 * of the target var handle. 8176 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}. 8177 * @since 19 8178 */ 8179 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8180 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) { 8181 return VarHandles.insertCoordinates(target, pos, values); 8182 } 8183 8184 /** 8185 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them 8186 * so that the new coordinates match the provided ones. 8187 * <p> 8188 * The given array controls the reordering. 8189 * Call {@code #I} the number of incoming coordinates (the value 8190 * {@code newCoordinates.size()}), and call {@code #O} the number 8191 * of outgoing coordinates (the number of coordinates associated with the target var handle). 8192 * Then the length of the reordering array must be {@code #O}, 8193 * and each element must be a non-negative number less than {@code #I}. 8194 * For every {@code N} less than {@code #O}, the {@code N}-th 8195 * outgoing coordinate will be taken from the {@code I}-th incoming 8196 * coordinate, where {@code I} is {@code reorder[N]}. 8197 * <p> 8198 * No coordinate value conversions are applied. 8199 * The type of each incoming coordinate, as determined by {@code newCoordinates}, 8200 * must be identical to the type of the corresponding outgoing coordinate 8201 * in the target var handle. 8202 * <p> 8203 * The reordering array need not specify an actual permutation. 8204 * An incoming coordinate will be duplicated if its index appears 8205 * more than once in the array, and an incoming coordinate will be dropped 8206 * if its index does not appear in the array. 8207 * <p> 8208 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8209 * atomic access guarantees as those featured by the target var handle. 8210 * @param target the var handle to invoke after the coordinates have been reordered 8211 * @param newCoordinates the new coordinate types 8212 * @param reorder an index array which controls the reordering 8213 * @return an adapter var handle which re-arranges the incoming coordinate values, 8214 * before calling the target var handle 8215 * @throws IllegalArgumentException if the index array length is not equal to 8216 * the number of coordinates of the target var handle, or if any index array element is not a valid index for 8217 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in 8218 * the target var handle and in {@code newCoordinates} are not identical. 8219 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}. 8220 * @since 19 8221 */ 8222 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8223 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) { 8224 return VarHandles.permuteCoordinates(target, newCoordinates, reorder); 8225 } 8226 8227 /** 8228 * Adapts a target var handle by pre-processing 8229 * a sub-sequence of its coordinate values with a filter (a method handle). 8230 * The pre-processed coordinates are replaced by the result (if any) of the 8231 * filter function and the target var handle is then called on the modified (usually shortened) 8232 * coordinate list. 8233 * <p> 8234 * If {@code R} is the return type of the filter, then: 8235 * <ul> 8236 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in 8237 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos} 8238 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first, 8239 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the 8240 * target var handle.</li> 8241 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the 8242 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle 8243 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a 8244 * downstream invocation of the target var handle.</li> 8245 * </ul> 8246 * <p> 8247 * If any of the filters throws a checked exception when invoked, the resulting var handle will 8248 * throw an {@link IllegalStateException}. 8249 * <p> 8250 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8251 * atomic access guarantees as those featured by the target var handle. 8252 * 8253 * @param target the var handle to invoke after the coordinates have been filtered 8254 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted 8255 * @param filter the filter method handle 8256 * @return an adapter var handle which filters the incoming coordinate values, 8257 * before calling the target var handle 8258 * @throws IllegalArgumentException if the return type of {@code filter} 8259 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle, 8260 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8261 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>, 8262 * or if it's determined that {@code filter} throws any checked exceptions. 8263 * @throws NullPointerException if any of the arguments is {@code null}. 8264 * @since 19 8265 */ 8266 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8267 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) { 8268 return VarHandles.collectCoordinates(target, pos, filter); 8269 } 8270 8271 /** 8272 * Returns a var handle which will discard some dummy coordinates before delegating to the 8273 * target var handle. As a consequence, the resulting var handle will feature more 8274 * coordinate types than the target var handle. 8275 * <p> 8276 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the 8277 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede 8278 * the target's real arguments; if {@code pos} is <i>N</i> they will come after. 8279 * <p> 8280 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8281 * atomic access guarantees as those featured by the target var handle. 8282 * 8283 * @param target the var handle to invoke after the dummy coordinates are dropped 8284 * @param pos position of the first coordinate to drop (zero for the leftmost) 8285 * @param valueTypes the type(s) of the coordinate(s) to drop 8286 * @return an adapter var handle which drops some dummy coordinates, 8287 * before calling the target var handle 8288 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive. 8289 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}. 8290 * @since 19 8291 */ 8292 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8293 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) { 8294 return VarHandles.dropCoordinates(target, pos, valueTypes); 8295 } 8296 }