1 /* 2 * Copyright (c) 2008, 2022, 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.vm.annotation.ForceInline; 41 import sun.invoke.util.ValueConversions; 42 import sun.invoke.util.VerifyAccess; 43 import sun.invoke.util.Wrapper; 44 import sun.reflect.misc.ReflectUtil; 45 import sun.security.util.SecurityConstants; 46 47 import java.lang.constant.ConstantDescs; 48 import java.lang.foreign.GroupLayout; 49 import java.lang.foreign.MemoryLayout; 50 import java.lang.foreign.MemorySegment; 51 import java.lang.foreign.ValueLayout; 52 import java.lang.invoke.LambdaForm.BasicType; 53 import java.lang.reflect.Constructor; 54 import java.lang.reflect.Field; 55 import java.lang.reflect.Member; 56 import java.lang.reflect.Method; 57 import java.lang.reflect.Modifier; 58 import java.nio.ByteOrder; 59 import java.security.ProtectionDomain; 60 import java.util.ArrayList; 61 import java.util.Arrays; 62 import java.util.BitSet; 63 import java.util.Iterator; 64 import java.util.List; 65 import java.util.Objects; 66 import java.util.Set; 67 import java.util.concurrent.ConcurrentHashMap; 68 import java.util.stream.Stream; 69 70 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE; 71 import static java.lang.invoke.MethodHandleImpl.Intrinsic; 72 import static java.lang.invoke.MethodHandleNatives.Constants.*; 73 import static java.lang.invoke.MethodHandleStatics.UNSAFE; 74 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException; 75 import static java.lang.invoke.MethodHandleStatics.newInternalError; 76 import static java.lang.invoke.MethodType.methodType; 77 78 /** 79 * This class consists exclusively of static methods that operate on or return 80 * method handles. They fall into several categories: 81 * <ul> 82 * <li>Lookup methods which help create method handles for methods and fields. 83 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones. 84 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns. 85 * </ul> 86 * A lookup, combinator, or factory method will fail and throw an 87 * {@code IllegalArgumentException} if the created method handle's type 88 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>. 89 * 90 * @author John Rose, JSR 292 EG 91 * @since 1.7 92 */ 93 public class MethodHandles { 94 95 private MethodHandles() { } // do not instantiate 96 97 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); 98 99 // See IMPL_LOOKUP below. 100 101 //// Method handle creation from ordinary methods. 102 103 /** 104 * Returns a {@link Lookup lookup object} with 105 * full capabilities to emulate all supported bytecode behaviors of the caller. 106 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller. 107 * Factory methods on the lookup object can create 108 * <a href="MethodHandleInfo.html#directmh">direct method handles</a> 109 * for any member that the caller has access to via bytecodes, 110 * including protected and private fields and methods. 111 * This lookup object is created by the original lookup class 112 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set. 113 * This lookup object is a <em>capability</em> which may be delegated to trusted agents. 114 * Do not store it in place where untrusted code can access it. 115 * <p> 116 * This method is caller sensitive, which means that it may return different 117 * values to different callers. 118 * In cases where {@code MethodHandles.lookup} is called from a context where 119 * there is no caller frame on the stack (e.g. when called directly 120 * from a JNI attached thread), {@code IllegalCallerException} is thrown. 121 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will 122 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()} 123 * to obtain a low-privileged lookup instead. 124 * @return a lookup object for the caller of this method, with 125 * {@linkplain Lookup#ORIGINAL original} and 126 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}. 127 * @throws IllegalCallerException if there is no caller frame on the stack. 128 */ 129 @CallerSensitive 130 @ForceInline // to ensure Reflection.getCallerClass optimization 131 public static Lookup lookup() { 132 final Class<?> c = Reflection.getCallerClass(); 133 if (c == null) { 134 throw new IllegalCallerException("no caller frame"); 135 } 136 return new Lookup(c); 137 } 138 139 /** 140 * This lookup method is the alternate implementation of 141 * the lookup method with a leading caller class argument which is 142 * non-caller-sensitive. This method is only invoked by reflection 143 * and method handle. 144 */ 145 @CallerSensitiveAdapter 146 private static Lookup lookup(Class<?> caller) { 147 if (caller.getClassLoader() == null) { 148 throw newInternalError("calling lookup() reflectively is not supported: "+caller); 149 } 150 return new Lookup(caller); 151 } 152 153 /** 154 * Returns a {@link Lookup lookup object} which is trusted minimally. 155 * The lookup has the {@code UNCONDITIONAL} mode. 156 * It can only be used to create method handles to public members of 157 * public classes in packages that are exported unconditionally. 158 * <p> 159 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class} 160 * of this lookup object will be {@link java.lang.Object}. 161 * 162 * @apiNote The use of Object is conventional, and because the lookup modes are 163 * limited, there is no special access provided to the internals of Object, its package 164 * or its module. This public lookup object or other lookup object with 165 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class 166 * is not used to determine the lookup context. 167 * 168 * <p style="font-size:smaller;"> 169 * <em>Discussion:</em> 170 * The lookup class can be changed to any other class {@code C} using an expression of the form 171 * {@link Lookup#in publicLookup().in(C.class)}. 172 * A public lookup object is always subject to 173 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>. 174 * Also, it cannot access 175 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>. 176 * @return a lookup object which is trusted minimally 177 * 178 * @revised 9 179 */ 180 public static Lookup publicLookup() { 181 return Lookup.PUBLIC_LOOKUP; 182 } 183 184 /** 185 * Returns a {@link Lookup lookup} object on a target class to emulate all supported 186 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>. 187 * The returned lookup object can provide access to classes in modules and packages, 188 * and members of those classes, outside the normal rules of Java access control, 189 * instead conforming to the more permissive rules for modular <em>deep reflection</em>. 190 * <p> 191 * A caller, specified as a {@code Lookup} object, in module {@code M1} is 192 * allowed to do deep reflection on module {@code M2} and package of the target class 193 * if and only if all of the following conditions are {@code true}: 194 * <ul> 195 * <li>If there is a security manager, its {@code checkPermission} method is 196 * called to check {@code ReflectPermission("suppressAccessChecks")} and 197 * that must return normally. 198 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess() 199 * full privilege access}. Specifically: 200 * <ul> 201 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode. 202 * (This is because otherwise there would be no way to ensure the original lookup 203 * creator was a member of any particular module, and so any subsequent checks 204 * for readability and qualified exports would become ineffective.) 205 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access. 206 * (This is because an application intending to share intra-module access 207 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share 208 * deep reflection to its own module.) 209 * </ul> 210 * <li>The target class must be a proper class, not a primitive or array class. 211 * (Thus, {@code M2} is well-defined.) 212 * <li>If the caller module {@code M1} differs from 213 * the target module {@code M2} then both of the following must be true: 214 * <ul> 215 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li> 216 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package 217 * containing the target class to at least {@code M1}.</li> 218 * </ul> 219 * </ul> 220 * <p> 221 * If any of the above checks is violated, this method fails with an 222 * exception. 223 * <p> 224 * Otherwise, if {@code M1} and {@code M2} are the same module, this method 225 * returns a {@code Lookup} on {@code targetClass} with 226 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} 227 * with {@code null} previous lookup class. 228 * <p> 229 * Otherwise, {@code M1} and {@code M2} are two different modules. This method 230 * returns a {@code Lookup} on {@code targetClass} that records 231 * the lookup class of the caller as the new previous lookup class with 232 * {@code PRIVATE} access but no {@code MODULE} access. 233 * <p> 234 * The resulting {@code Lookup} object has no {@code ORIGINAL} access. 235 * 236 * @param targetClass the target class 237 * @param caller the caller lookup object 238 * @return a lookup object for the target class, with private access 239 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class 240 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null} 241 * @throws SecurityException if denied by the security manager 242 * @throws IllegalAccessException if any of the other access checks specified above fails 243 * @since 9 244 * @see Lookup#dropLookupMode 245 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a> 246 */ 247 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException { 248 if (caller.allowedModes == Lookup.TRUSTED) { 249 return new Lookup(targetClass); 250 } 251 252 @SuppressWarnings("removal") 253 SecurityManager sm = System.getSecurityManager(); 254 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION); 255 if (targetClass.isPrimitive()) 256 throw new IllegalArgumentException(targetClass + " is a primitive class"); 257 if (targetClass.isArray()) 258 throw new IllegalArgumentException(targetClass + " is an array class"); 259 // Ensure that we can reason accurately about private and module access. 260 int requireAccess = Lookup.PRIVATE|Lookup.MODULE; 261 if ((caller.lookupModes() & requireAccess) != requireAccess) 262 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode"); 263 264 // previous lookup class is never set if it has MODULE access 265 assert caller.previousLookupClass() == null; 266 267 Class<?> callerClass = caller.lookupClass(); 268 Module callerModule = callerClass.getModule(); // M1 269 Module targetModule = targetClass.getModule(); // M2 270 Class<?> newPreviousClass = null; 271 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL; 272 273 if (targetModule != callerModule) { 274 if (!callerModule.canRead(targetModule)) 275 throw new IllegalAccessException(callerModule + " does not read " + targetModule); 276 if (targetModule.isNamed()) { 277 String pn = targetClass.getPackageName(); 278 assert !pn.isEmpty() : "unnamed package cannot be in named module"; 279 if (!targetModule.isOpen(pn, callerModule)) 280 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule); 281 } 282 283 // M2 != M1, set previous lookup class to M1 and drop MODULE access 284 newPreviousClass = callerClass; 285 newModes &= ~Lookup.MODULE; 286 } 287 return Lookup.newLookup(targetClass, newPreviousClass, newModes); 288 } 289 290 /** 291 * Returns the <em>class data</em> associated with the lookup class 292 * of the given {@code caller} lookup object, or {@code null}. 293 * 294 * <p> A hidden class with class data can be created by calling 295 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 296 * Lookup::defineHiddenClassWithClassData}. 297 * This method will cause the static class initializer of the lookup 298 * class of the given {@code caller} lookup object be executed if 299 * it has not been initialized. 300 * 301 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...) 302 * Lookup::defineHiddenClass} and non-hidden classes have no class data. 303 * {@code null} is returned if this method is called on the lookup object 304 * on these classes. 305 * 306 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup 307 * must have {@linkplain Lookup#ORIGINAL original access} 308 * in order to retrieve the class data. 309 * 310 * @apiNote 311 * This method can be called as a bootstrap method for a dynamically computed 312 * constant. A framework can create a hidden class with class data, for 313 * example that can be {@code Class} or {@code MethodHandle} object. 314 * The class data is accessible only to the lookup object 315 * created by the original caller but inaccessible to other members 316 * in the same nest. If a framework passes security sensitive objects 317 * to a hidden class via class data, it is recommended to load the value 318 * of class data as a dynamically computed constant instead of storing 319 * the class data in private static field(s) which are accessible to 320 * other nestmates. 321 * 322 * @param <T> the type to cast the class data object to 323 * @param caller the lookup context describing the class performing the 324 * operation (normally stacked by the JVM) 325 * @param name must be {@link ConstantDescs#DEFAULT_NAME} 326 * ({@code "_"}) 327 * @param type the type of the class data 328 * @return the value of the class data if present in the lookup class; 329 * otherwise {@code null} 330 * @throws IllegalArgumentException if name is not {@code "_"} 331 * @throws IllegalAccessException if the lookup context does not have 332 * {@linkplain Lookup#ORIGINAL original} access 333 * @throws ClassCastException if the class data cannot be converted to 334 * the given {@code type} 335 * @throws NullPointerException if {@code caller} or {@code type} argument 336 * is {@code null} 337 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 338 * @see MethodHandles#classDataAt(Lookup, String, Class, int) 339 * @since 16 340 * @jvms 5.5 Initialization 341 */ 342 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException { 343 Objects.requireNonNull(caller); 344 Objects.requireNonNull(type); 345 if (!ConstantDescs.DEFAULT_NAME.equals(name)) { 346 throw new IllegalArgumentException("name must be \"_\": " + name); 347 } 348 349 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) { 350 throw new IllegalAccessException(caller + " does not have ORIGINAL access"); 351 } 352 353 Object classdata = classData(caller.lookupClass()); 354 if (classdata == null) return null; 355 356 try { 357 return BootstrapMethodInvoker.widenAndCast(classdata, type); 358 } catch (RuntimeException|Error e) { 359 throw e; // let CCE and other runtime exceptions through 360 } catch (Throwable e) { 361 throw new InternalError(e); 362 } 363 } 364 365 /* 366 * Returns the class data set by the VM in the Class::classData field. 367 * 368 * This is also invoked by LambdaForms as it cannot use condy via 369 * MethodHandles::classData due to bootstrapping issue. 370 */ 371 static Object classData(Class<?> c) { 372 UNSAFE.ensureClassInitialized(c); 373 return SharedSecrets.getJavaLangAccess().classData(c); 374 } 375 376 /** 377 * Returns the element at the specified index in the 378 * {@linkplain #classData(Lookup, String, Class) class data}, 379 * if the class data associated with the lookup class 380 * of the given {@code caller} lookup object is a {@code List}. 381 * If the class data is not present in this lookup class, this method 382 * returns {@code null}. 383 * 384 * <p> A hidden class with class data can be created by calling 385 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 386 * Lookup::defineHiddenClassWithClassData}. 387 * This method will cause the static class initializer of the lookup 388 * class of the given {@code caller} lookup object be executed if 389 * it has not been initialized. 390 * 391 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...) 392 * Lookup::defineHiddenClass} and non-hidden classes have no class data. 393 * {@code null} is returned if this method is called on the lookup object 394 * on these classes. 395 * 396 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup 397 * must have {@linkplain Lookup#ORIGINAL original access} 398 * in order to retrieve the class data. 399 * 400 * @apiNote 401 * This method can be called as a bootstrap method for a dynamically computed 402 * constant. A framework can create a hidden class with class data, for 403 * example that can be {@code List.of(o1, o2, o3....)} containing more than 404 * one object and use this method to load one element at a specific index. 405 * The class data is accessible only to the lookup object 406 * created by the original caller but inaccessible to other members 407 * in the same nest. If a framework passes security sensitive objects 408 * to a hidden class via class data, it is recommended to load the value 409 * of class data as a dynamically computed constant instead of storing 410 * the class data in private static field(s) which are accessible to other 411 * nestmates. 412 * 413 * @param <T> the type to cast the result object to 414 * @param caller the lookup context describing the class performing the 415 * operation (normally stacked by the JVM) 416 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME} 417 * ({@code "_"}) 418 * @param type the type of the element at the given index in the class data 419 * @param index index of the element in the class data 420 * @return the element at the given index in the class data 421 * if the class data is present; otherwise {@code null} 422 * @throws IllegalArgumentException if name is not {@code "_"} 423 * @throws IllegalAccessException if the lookup context does not have 424 * {@linkplain Lookup#ORIGINAL original} access 425 * @throws ClassCastException if the class data cannot be converted to {@code List} 426 * or the element at the specified index cannot be converted to the given type 427 * @throws IndexOutOfBoundsException if the index is out of range 428 * @throws NullPointerException if {@code caller} or {@code type} argument is 429 * {@code null}; or if unboxing operation fails because 430 * the element at the given index is {@code null} 431 * 432 * @since 16 433 * @see #classData(Lookup, String, Class) 434 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...) 435 */ 436 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index) 437 throws IllegalAccessException 438 { 439 @SuppressWarnings("unchecked") 440 List<Object> classdata = (List<Object>)classData(caller, name, List.class); 441 if (classdata == null) return null; 442 443 try { 444 Object element = classdata.get(index); 445 return BootstrapMethodInvoker.widenAndCast(element, type); 446 } catch (RuntimeException|Error e) { 447 throw e; // let specified exceptions and other runtime exceptions/errors through 448 } catch (Throwable e) { 449 throw new InternalError(e); 450 } 451 } 452 453 /** 454 * Performs an unchecked "crack" of a 455 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>. 456 * The result is as if the user had obtained a lookup object capable enough 457 * to crack the target method handle, called 458 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} 459 * on the target to obtain its symbolic reference, and then called 460 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} 461 * to resolve the symbolic reference to a member. 462 * <p> 463 * If there is a security manager, its {@code checkPermission} method 464 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission. 465 * @param <T> the desired type of the result, either {@link Member} or a subtype 466 * @param target a direct method handle to crack into symbolic reference components 467 * @param expected a class object representing the desired result type {@code T} 468 * @return a reference to the method, constructor, or field object 469 * @throws SecurityException if the caller is not privileged to call {@code setAccessible} 470 * @throws NullPointerException if either argument is {@code null} 471 * @throws IllegalArgumentException if the target is not a direct method handle 472 * @throws ClassCastException if the member is not of the expected type 473 * @since 1.8 474 */ 475 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) { 476 @SuppressWarnings("removal") 477 SecurityManager smgr = System.getSecurityManager(); 478 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION); 479 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup 480 return lookup.revealDirect(target).reflectAs(expected, lookup); 481 } 482 483 /** 484 * A <em>lookup object</em> is a factory for creating method handles, 485 * when the creation requires access checking. 486 * Method handles do not perform 487 * access checks when they are called, but rather when they are created. 488 * Therefore, method handle access 489 * restrictions must be enforced when a method handle is created. 490 * The caller class against which those restrictions are enforced 491 * is known as the {@linkplain #lookupClass() lookup class}. 492 * <p> 493 * A lookup class which needs to create method handles will call 494 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself. 495 * When the {@code Lookup} factory object is created, the identity of the lookup class is 496 * determined, and securely stored in the {@code Lookup} object. 497 * The lookup class (or its delegates) may then use factory methods 498 * on the {@code Lookup} object to create method handles for access-checked members. 499 * This includes all methods, constructors, and fields which are allowed to the lookup class, 500 * even private ones. 501 * 502 * <h2><a id="lookups"></a>Lookup Factory Methods</h2> 503 * The factory methods on a {@code Lookup} object correspond to all major 504 * use cases for methods, constructors, and fields. 505 * Each method handle created by a factory method is the functional 506 * equivalent of a particular <em>bytecode behavior</em>. 507 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of 508 * the Java Virtual Machine Specification.) 509 * Here is a summary of the correspondence between these factory methods and 510 * the behavior of the resulting method handles: 511 * <table class="striped"> 512 * <caption style="display:none">lookup method behaviors</caption> 513 * <thead> 514 * <tr> 515 * <th scope="col"><a id="equiv"></a>lookup expression</th> 516 * <th scope="col">member</th> 517 * <th scope="col">bytecode behavior</th> 518 * </tr> 519 * </thead> 520 * <tbody> 521 * <tr> 522 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th> 523 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td> 524 * </tr> 525 * <tr> 526 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th> 527 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td> 528 * </tr> 529 * <tr> 530 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th> 531 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td> 532 * </tr> 533 * <tr> 534 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th> 535 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td> 536 * </tr> 537 * <tr> 538 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th> 539 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td> 540 * </tr> 541 * <tr> 542 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th> 543 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td> 544 * </tr> 545 * <tr> 546 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th> 547 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 548 * </tr> 549 * <tr> 550 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th> 551 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td> 552 * </tr> 553 * <tr> 554 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th> 555 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td> 556 * </tr> 557 * <tr> 558 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th> 559 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td> 560 * </tr> 561 * <tr> 562 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th> 563 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td> 564 * </tr> 565 * <tr> 566 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th> 567 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td> 568 * </tr> 569 * <tr> 570 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th> 571 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td> 572 * </tr> 573 * <tr> 574 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th> 575 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td> 576 * </tr> 577 * </tbody> 578 * </table> 579 * 580 * Here, the type {@code C} is the class or interface being searched for a member, 581 * documented as a parameter named {@code refc} in the lookup methods. 582 * The method type {@code MT} is composed from the return type {@code T} 583 * and the sequence of argument types {@code A*}. 584 * The constructor also has a sequence of argument types {@code A*} and 585 * is deemed to return the newly-created object of type {@code C}. 586 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}. 587 * The formal parameter {@code this} stands for the self-reference of type {@code C}; 588 * if it is present, it is always the leading argument to the method handle invocation. 589 * (In the case of some {@code protected} members, {@code this} may be 590 * restricted in type to the lookup class; see below.) 591 * The name {@code arg} stands for all the other method handle arguments. 592 * In the code examples for the Core Reflection API, the name {@code thisOrNull} 593 * stands for a null reference if the accessed method or field is static, 594 * and {@code this} otherwise. 595 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand 596 * for reflective objects corresponding to the given members declared in type {@code C}. 597 * <p> 598 * The bytecode behavior for a {@code findClass} operation is a load of a constant class, 599 * as if by {@code ldc CONSTANT_Class}. 600 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant. 601 * <p> 602 * In cases where the given member is of variable arity (i.e., a method or constructor) 603 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. 604 * In all other cases, the returned method handle will be of fixed arity. 605 * <p style="font-size:smaller;"> 606 * <em>Discussion:</em> 607 * The equivalence between looked-up method handles and underlying 608 * class members and bytecode behaviors 609 * can break down in a few ways: 610 * <ul style="font-size:smaller;"> 611 * <li>If {@code C} is not symbolically accessible from the lookup class's loader, 612 * the lookup can still succeed, even when there is no equivalent 613 * Java expression or bytecoded constant. 614 * <li>Likewise, if {@code T} or {@code MT} 615 * is not symbolically accessible from the lookup class's loader, 616 * the lookup can still succeed. 617 * For example, lookups for {@code MethodHandle.invokeExact} and 618 * {@code MethodHandle.invoke} will always succeed, regardless of requested type. 619 * <li>If there is a security manager installed, it can forbid the lookup 620 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>). 621 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle} 622 * constant is not subject to security manager checks. 623 * <li>If the looked-up method has a 624 * <a href="MethodHandle.html#maxarity">very large arity</a>, 625 * the method handle creation may fail with an 626 * {@code IllegalArgumentException}, due to the method handle type having 627 * <a href="MethodHandle.html#maxarity">too many parameters.</a> 628 * </ul> 629 * 630 * <h2><a id="access"></a>Access checking</h2> 631 * Access checks are applied in the factory methods of {@code Lookup}, 632 * when a method handle is created. 633 * This is a key difference from the Core Reflection API, since 634 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 635 * performs access checking against every caller, on every call. 636 * <p> 637 * All access checks start from a {@code Lookup} object, which 638 * compares its recorded lookup class against all requests to 639 * create method handles. 640 * A single {@code Lookup} object can be used to create any number 641 * of access-checked method handles, all checked against a single 642 * lookup class. 643 * <p> 644 * A {@code Lookup} object can be shared with other trusted code, 645 * such as a metaobject protocol. 646 * A shared {@code Lookup} object delegates the capability 647 * to create method handles on private members of the lookup class. 648 * Even if privileged code uses the {@code Lookup} object, 649 * the access checking is confined to the privileges of the 650 * original lookup class. 651 * <p> 652 * A lookup can fail, because 653 * the containing class is not accessible to the lookup class, or 654 * because the desired class member is missing, or because the 655 * desired class member is not accessible to the lookup class, or 656 * because the lookup object is not trusted enough to access the member. 657 * In the case of a field setter function on a {@code final} field, 658 * finality enforcement is treated as a kind of access control, 659 * and the lookup will fail, except in special cases of 660 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}. 661 * In any of these cases, a {@code ReflectiveOperationException} will be 662 * thrown from the attempted lookup. The exact class will be one of 663 * the following: 664 * <ul> 665 * <li>NoSuchMethodException — if a method is requested but does not exist 666 * <li>NoSuchFieldException — if a field is requested but does not exist 667 * <li>IllegalAccessException — if the member exists but an access check fails 668 * </ul> 669 * <p> 670 * In general, the conditions under which a method handle may be 671 * looked up for a method {@code M} are no more restrictive than the conditions 672 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}. 673 * Where the JVM would raise exceptions like {@code NoSuchMethodError}, 674 * a method handle lookup will generally raise a corresponding 675 * checked exception, such as {@code NoSuchMethodException}. 676 * And the effect of invoking the method handle resulting from the lookup 677 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a> 678 * to executing the compiled, verified, and resolved call to {@code M}. 679 * The same point is true of fields and constructors. 680 * <p style="font-size:smaller;"> 681 * <em>Discussion:</em> 682 * Access checks only apply to named and reflected methods, 683 * constructors, and fields. 684 * Other method handle creation methods, such as 685 * {@link MethodHandle#asType MethodHandle.asType}, 686 * do not require any access checks, and are used 687 * independently of any {@code Lookup} object. 688 * <p> 689 * If the desired member is {@code protected}, the usual JVM rules apply, 690 * including the requirement that the lookup class must either be in the 691 * same package as the desired member, or must inherit that member. 692 * (See the Java Virtual Machine Specification, sections {@jvms 693 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.) 694 * In addition, if the desired member is a non-static field or method 695 * in a different package, the resulting method handle may only be applied 696 * to objects of the lookup class or one of its subclasses. 697 * This requirement is enforced by narrowing the type of the leading 698 * {@code this} parameter from {@code C} 699 * (which will necessarily be a superclass of the lookup class) 700 * to the lookup class itself. 701 * <p> 702 * The JVM imposes a similar requirement on {@code invokespecial} instruction, 703 * that the receiver argument must match both the resolved method <em>and</em> 704 * the current class. Again, this requirement is enforced by narrowing the 705 * type of the leading parameter to the resulting method handle. 706 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.) 707 * <p> 708 * The JVM represents constructors and static initializer blocks as internal methods 709 * with special names ({@code "<init>"}, {@code "<vnew>"} and {@code "<clinit>"}). 710 * The internal syntax of invocation instructions allows them to refer to such internal 711 * methods as if they were normal methods, but the JVM bytecode verifier rejects them. 712 * A lookup of such an internal method will produce a {@code NoSuchMethodException}. 713 * <p> 714 * If the relationship between nested types is expressed directly through the 715 * {@code NestHost} and {@code NestMembers} attributes 716 * (see the Java Virtual Machine Specification, sections {@jvms 717 * 4.7.28} and {@jvms 4.7.29}), 718 * then the associated {@code Lookup} object provides direct access to 719 * the lookup class and all of its nestmates 720 * (see {@link java.lang.Class#getNestHost Class.getNestHost}). 721 * Otherwise, access between nested classes is obtained by the Java compiler creating 722 * a wrapper method to access a private method of another class in the same nest. 723 * For example, a nested class {@code C.D} 724 * can access private members within other related classes such as 725 * {@code C}, {@code C.D.E}, or {@code C.B}, 726 * but the Java compiler may need to generate wrapper methods in 727 * those related classes. In such cases, a {@code Lookup} object on 728 * {@code C.E} would be unable to access those private members. 729 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, 730 * which can transform a lookup on {@code C.E} into one on any of those other 731 * classes, without special elevation of privilege. 732 * <p> 733 * The accesses permitted to a given lookup object may be limited, 734 * according to its set of {@link #lookupModes lookupModes}, 735 * to a subset of members normally accessible to the lookup class. 736 * For example, the {@link MethodHandles#publicLookup publicLookup} 737 * method produces a lookup object which is only allowed to access 738 * public members in public classes of exported packages. 739 * The caller sensitive method {@link MethodHandles#lookup lookup} 740 * produces a lookup object with full capabilities relative to 741 * its caller class, to emulate all supported bytecode behaviors. 742 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object 743 * with fewer access modes than the original lookup object. 744 * 745 * <p style="font-size:smaller;"> 746 * <a id="privacc"></a> 747 * <em>Discussion of private and module access:</em> 748 * We say that a lookup has <em>private access</em> 749 * if its {@linkplain #lookupModes lookup modes} 750 * include the possibility of accessing {@code private} members 751 * (which includes the private members of nestmates). 752 * As documented in the relevant methods elsewhere, 753 * only lookups with private access possess the following capabilities: 754 * <ul style="font-size:smaller;"> 755 * <li>access private fields, methods, and constructors of the lookup class and its nestmates 756 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions 757 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a> 758 * for classes accessible to the lookup class 759 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes 760 * within the same package member 761 * </ul> 762 * <p style="font-size:smaller;"> 763 * Similarly, a lookup with module access ensures that the original lookup creator was 764 * a member in the same module as the lookup class. 765 * <p style="font-size:smaller;"> 766 * Private and module access are independently determined modes; a lookup may have 767 * either or both or neither. A lookup which possesses both access modes is said to 768 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}. 769 * <p style="font-size:smaller;"> 770 * A lookup with <em>original access</em> ensures that this lookup is created by 771 * the original lookup class and the bootstrap method invoked by the VM. 772 * Such a lookup with original access also has private and module access 773 * which has the following additional capability: 774 * <ul style="font-size:smaller;"> 775 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods, 776 * such as {@code Class.forName} 777 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class) 778 * class data} associated with the lookup class</li> 779 * </ul> 780 * <p style="font-size:smaller;"> 781 * Each of these permissions is a consequence of the fact that a lookup object 782 * with private access can be securely traced back to an originating class, 783 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions 784 * can be reliably determined and emulated by method handles. 785 * 786 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2> 787 * When a lookup class in one module {@code M1} accesses a class in another module 788 * {@code M2}, extra access checking is performed beyond the access mode bits. 789 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1} 790 * can access public types in {@code M2} when {@code M2} is readable to {@code M1} 791 * and when the type is in a package of {@code M2} that is exported to 792 * at least {@code M1}. 793 * <p> 794 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class 795 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup) 796 * MethodHandles.privateLookupIn} methods. 797 * Teleporting across modules will always record the original lookup class as 798 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em> 799 * and drops {@link Lookup#MODULE MODULE} access. 800 * If the target class is in the same module as the lookup class {@code C}, 801 * then the target class becomes the new lookup class 802 * and there is no change to the previous lookup class. 803 * If the target class is in a different module from {@code M1} ({@code C}'s module), 804 * {@code C} becomes the new previous lookup class 805 * and the target class becomes the new lookup class. 806 * In that case, if there was already a previous lookup class in {@code M0}, 807 * and it differs from {@code M1} and {@code M2}, then the resulting lookup 808 * drops all privileges. 809 * For example, 810 * {@snippet lang="java" : 811 * Lookup lookup = MethodHandles.lookup(); // in class C 812 * Lookup lookup2 = lookup.in(D.class); 813 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT); 814 * } 815 * <p> 816 * The {@link #lookup()} factory method produces a {@code Lookup} object 817 * with {@code null} previous lookup class. 818 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C} 819 * to class {@code D} without elevation of privileges. 820 * If {@code C} and {@code D} are in the same module, 821 * {@code lookup2} records {@code D} as the new lookup class and keeps the 822 * same previous lookup class as the original {@code lookup}, or 823 * {@code null} if not present. 824 * <p> 825 * When a {@code Lookup} teleports from a class 826 * in one nest to another nest, {@code PRIVATE} access is dropped. 827 * When a {@code Lookup} teleports from a class in one package to 828 * another package, {@code PACKAGE} access is dropped. 829 * When a {@code Lookup} teleports from a class in one module to another module, 830 * {@code MODULE} access is dropped. 831 * Teleporting across modules drops the ability to access non-exported classes 832 * in both the module of the new lookup class and the module of the old lookup class 833 * and the resulting {@code Lookup} remains only {@code PUBLIC} access. 834 * A {@code Lookup} can teleport back and forth to a class in the module of 835 * the lookup class and the module of the previous class lookup. 836 * Teleporting across modules can only decrease access but cannot increase it. 837 * Teleporting to some third module drops all accesses. 838 * <p> 839 * In the above example, if {@code C} and {@code D} are in different modules, 840 * {@code lookup2} records {@code D} as its lookup class and 841 * {@code C} as its previous lookup class and {@code lookup2} has only 842 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in 843 * {@code C}'s module and {@code D}'s module. 844 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates 845 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup 846 * class {@code D} is recorded as its previous lookup class. 847 * <p> 848 * Teleporting across modules restricts access to the public types that 849 * both the lookup class and the previous lookup class can equally access 850 * (see below). 851 * <p> 852 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)} 853 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T} 854 * and create a new {@code Lookup} with <a href="#privacc">private access</a> 855 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}. 856 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access 857 * to call {@code privateLookupIn}. 858 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection 859 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn} 860 * produces a new {@code Lookup} on {@code T} with full capabilities. 861 * A {@code lookup} on {@code C} is also allowed 862 * to do deep reflection on {@code T} in another module {@code M2} if 863 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens} 864 * the package containing {@code T} to at least {@code M1}. 865 * {@code T} becomes the new lookup class and {@code C} becomes the new previous 866 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}. 867 * The resulting {@code Lookup} can be used to do member lookup or teleport 868 * to another lookup class by calling {@link #in Lookup::in}. But 869 * it cannot be used to obtain another private {@code Lookup} by calling 870 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn} 871 * because it has no {@code MODULE} access. 872 * 873 * <h2><a id="module-access-check"></a>Cross-module access checks</h2> 874 * 875 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode 876 * allows cross-module access. The access checking is performed with respect 877 * to both the lookup class and the previous lookup class if present. 878 * <p> 879 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type 880 * in all modules when the type is in a package that is {@linkplain Module#isExported(String) 881 * exported unconditionally}. 882 * <p> 883 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class, 884 * the lookup with {@link #PUBLIC} mode can access all public types in modules 885 * that are readable to {@code M1} and the type is in a package that is exported 886 * at least to {@code M1}. 887 * <p> 888 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class 889 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access 890 * the intersection of all public types that are accessible to {@code M1} 891 * with all public types that are accessible to {@code M0}. {@code M0} 892 * reads {@code M1} and hence the set of accessible types includes: 893 * 894 * <ul> 895 * <li>unconditional-exported packages from {@code M1}</li> 896 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li> 897 * <li> 898 * unconditional-exported packages from a third module {@code M2}if both {@code M0} 899 * and {@code M1} read {@code M2} 900 * </li> 901 * <li>qualified-exported packages from {@code M1} to {@code M0}</li> 902 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li> 903 * <li> 904 * qualified-exported packages from a third module {@code M2} to both {@code M0} and 905 * {@code M1} if both {@code M0} and {@code M1} read {@code M2} 906 * </li> 907 * </ul> 908 * 909 * <h2><a id="access-modes"></a>Access modes</h2> 910 * 911 * The table below shows the access modes of a {@code Lookup} produced by 912 * any of the following factory or transformation methods: 913 * <ul> 914 * <li>{@link #lookup() MethodHandles::lookup}</li> 915 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li> 916 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li> 917 * <li>{@link Lookup#in Lookup::in}</li> 918 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li> 919 * </ul> 920 * 921 * <table class="striped"> 922 * <caption style="display:none"> 923 * Access mode summary 924 * </caption> 925 * <thead> 926 * <tr> 927 * <th scope="col">Lookup object</th> 928 * <th style="text-align:center">original</th> 929 * <th style="text-align:center">protected</th> 930 * <th style="text-align:center">private</th> 931 * <th style="text-align:center">package</th> 932 * <th style="text-align:center">module</th> 933 * <th style="text-align:center">public</th> 934 * </tr> 935 * </thead> 936 * <tbody> 937 * <tr> 938 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th> 939 * <td style="text-align:center">ORI</td> 940 * <td style="text-align:center">PRO</td> 941 * <td style="text-align:center">PRI</td> 942 * <td style="text-align:center">PAC</td> 943 * <td style="text-align:center">MOD</td> 944 * <td style="text-align:center">1R</td> 945 * </tr> 946 * <tr> 947 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th> 948 * <td></td> 949 * <td></td> 950 * <td></td> 951 * <td style="text-align:center">PAC</td> 952 * <td style="text-align:center">MOD</td> 953 * <td style="text-align:center">1R</td> 954 * </tr> 955 * <tr> 956 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th> 957 * <td></td> 958 * <td></td> 959 * <td></td> 960 * <td></td> 961 * <td style="text-align:center">MOD</td> 962 * <td style="text-align:center">1R</td> 963 * </tr> 964 * <tr> 965 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th> 966 * <td></td> 967 * <td></td> 968 * <td></td> 969 * <td></td> 970 * <td></td> 971 * <td style="text-align:center">2R</td> 972 * </tr> 973 * <tr> 974 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th> 975 * <td></td> 976 * <td></td> 977 * <td></td> 978 * <td></td> 979 * <td></td> 980 * <td style="text-align:center">2R</td> 981 * </tr> 982 * <tr> 983 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th> 984 * <td></td> 985 * <td style="text-align:center">PRO</td> 986 * <td style="text-align:center">PRI</td> 987 * <td style="text-align:center">PAC</td> 988 * <td style="text-align:center">MOD</td> 989 * <td style="text-align:center">1R</td> 990 * </tr> 991 * <tr> 992 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th> 993 * <td></td> 994 * <td style="text-align:center">PRO</td> 995 * <td style="text-align:center">PRI</td> 996 * <td style="text-align:center">PAC</td> 997 * <td style="text-align:center">MOD</td> 998 * <td style="text-align:center">1R</td> 999 * </tr> 1000 * <tr> 1001 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th> 1002 * <td></td> 1003 * <td></td> 1004 * <td></td> 1005 * <td style="text-align:center">PAC</td> 1006 * <td style="text-align:center">MOD</td> 1007 * <td style="text-align:center">1R</td> 1008 * </tr> 1009 * <tr> 1010 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th> 1011 * <td></td> 1012 * <td></td> 1013 * <td></td> 1014 * <td></td> 1015 * <td style="text-align:center">MOD</td> 1016 * <td style="text-align:center">1R</td> 1017 * </tr> 1018 * <tr> 1019 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th> 1020 * <td></td> 1021 * <td></td> 1022 * <td></td> 1023 * <td></td> 1024 * <td></td> 1025 * <td style="text-align:center">2R</td> 1026 * </tr> 1027 * <tr> 1028 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th> 1029 * <td></td> 1030 * <td></td> 1031 * <td style="text-align:center">PRI</td> 1032 * <td style="text-align:center">PAC</td> 1033 * <td style="text-align:center">MOD</td> 1034 * <td style="text-align:center">1R</td> 1035 * </tr> 1036 * <tr> 1037 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th> 1038 * <td></td> 1039 * <td></td> 1040 * <td></td> 1041 * <td style="text-align:center">PAC</td> 1042 * <td style="text-align:center">MOD</td> 1043 * <td style="text-align:center">1R</td> 1044 * </tr> 1045 * <tr> 1046 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th> 1047 * <td></td> 1048 * <td></td> 1049 * <td></td> 1050 * <td></td> 1051 * <td style="text-align:center">MOD</td> 1052 * <td style="text-align:center">1R</td> 1053 * </tr> 1054 * <tr> 1055 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th> 1056 * <td></td> 1057 * <td></td> 1058 * <td></td> 1059 * <td></td> 1060 * <td></td> 1061 * <td style="text-align:center">1R</td> 1062 * </tr> 1063 * <tr> 1064 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th> 1065 * <td></td> 1066 * <td></td> 1067 * <td></td> 1068 * <td></td> 1069 * <td></td> 1070 * <td style="text-align:center">none</td> 1071 * <tr> 1072 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th> 1073 * <td></td> 1074 * <td style="text-align:center">PRO</td> 1075 * <td style="text-align:center">PRI</td> 1076 * <td style="text-align:center">PAC</td> 1077 * <td></td> 1078 * <td style="text-align:center">2R</td> 1079 * </tr> 1080 * <tr> 1081 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th> 1082 * <td></td> 1083 * <td style="text-align:center">PRO</td> 1084 * <td style="text-align:center">PRI</td> 1085 * <td style="text-align:center">PAC</td> 1086 * <td></td> 1087 * <td style="text-align:center">2R</td> 1088 * </tr> 1089 * <tr> 1090 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th> 1091 * <td></td> 1092 * <td></td> 1093 * <td></td> 1094 * <td></td> 1095 * <td></td> 1096 * <td style="text-align:center">IAE</td> 1097 * </tr> 1098 * <tr> 1099 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th> 1100 * <td></td> 1101 * <td></td> 1102 * <td></td> 1103 * <td style="text-align:center">PAC</td> 1104 * <td></td> 1105 * <td style="text-align:center">2R</td> 1106 * </tr> 1107 * <tr> 1108 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th> 1109 * <td></td> 1110 * <td></td> 1111 * <td></td> 1112 * <td></td> 1113 * <td></td> 1114 * <td style="text-align:center">2R</td> 1115 * </tr> 1116 * <tr> 1117 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th> 1118 * <td></td> 1119 * <td></td> 1120 * <td></td> 1121 * <td></td> 1122 * <td></td> 1123 * <td style="text-align:center">2R</td> 1124 * </tr> 1125 * <tr> 1126 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th> 1127 * <td></td> 1128 * <td></td> 1129 * <td></td> 1130 * <td></td> 1131 * <td></td> 1132 * <td style="text-align:center">none</td> 1133 * </tr> 1134 * <tr> 1135 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th> 1136 * <td></td> 1137 * <td></td> 1138 * <td style="text-align:center">PRI</td> 1139 * <td style="text-align:center">PAC</td> 1140 * <td></td> 1141 * <td style="text-align:center">2R</td> 1142 * </tr> 1143 * <tr> 1144 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th> 1145 * <td></td> 1146 * <td></td> 1147 * <td></td> 1148 * <td style="text-align:center">PAC</td> 1149 * <td></td> 1150 * <td style="text-align:center">2R</td> 1151 * </tr> 1152 * <tr> 1153 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th> 1154 * <td></td> 1155 * <td></td> 1156 * <td></td> 1157 * <td></td> 1158 * <td></td> 1159 * <td style="text-align:center">2R</td> 1160 * </tr> 1161 * <tr> 1162 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th> 1163 * <td></td> 1164 * <td></td> 1165 * <td></td> 1166 * <td></td> 1167 * <td></td> 1168 * <td style="text-align:center">2R</td> 1169 * </tr> 1170 * <tr> 1171 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th> 1172 * <td></td> 1173 * <td></td> 1174 * <td></td> 1175 * <td></td> 1176 * <td></td> 1177 * <td style="text-align:center">none</td> 1178 * </tr> 1179 * <tr> 1180 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th> 1181 * <td></td> 1182 * <td></td> 1183 * <td style="text-align:center">PRI</td> 1184 * <td style="text-align:center">PAC</td> 1185 * <td style="text-align:center">MOD</td> 1186 * <td style="text-align:center">1R</td> 1187 * </tr> 1188 * <tr> 1189 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th> 1190 * <td></td> 1191 * <td></td> 1192 * <td></td> 1193 * <td style="text-align:center">PAC</td> 1194 * <td style="text-align:center">MOD</td> 1195 * <td style="text-align:center">1R</td> 1196 * </tr> 1197 * <tr> 1198 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th> 1199 * <td></td> 1200 * <td></td> 1201 * <td></td> 1202 * <td></td> 1203 * <td style="text-align:center">MOD</td> 1204 * <td style="text-align:center">1R</td> 1205 * </tr> 1206 * <tr> 1207 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th> 1208 * <td></td> 1209 * <td></td> 1210 * <td></td> 1211 * <td></td> 1212 * <td></td> 1213 * <td style="text-align:center">1R</td> 1214 * </tr> 1215 * <tr> 1216 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th> 1217 * <td></td> 1218 * <td></td> 1219 * <td></td> 1220 * <td></td> 1221 * <td></td> 1222 * <td style="text-align:center">none</td> 1223 * </tr> 1224 * <tr> 1225 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th> 1226 * <td></td> 1227 * <td></td> 1228 * <td></td> 1229 * <td></td> 1230 * <td></td> 1231 * <td style="text-align:center">U</td> 1232 * </tr> 1233 * <tr> 1234 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th> 1235 * <td></td> 1236 * <td></td> 1237 * <td></td> 1238 * <td></td> 1239 * <td></td> 1240 * <td style="text-align:center">U</td> 1241 * </tr> 1242 * <tr> 1243 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th> 1244 * <td></td> 1245 * <td></td> 1246 * <td></td> 1247 * <td></td> 1248 * <td></td> 1249 * <td style="text-align:center">U</td> 1250 * </tr> 1251 * <tr> 1252 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th> 1253 * <td></td> 1254 * <td></td> 1255 * <td></td> 1256 * <td></td> 1257 * <td></td> 1258 * <td style="text-align:center">none</td> 1259 * </tr> 1260 * <tr> 1261 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th> 1262 * <td></td> 1263 * <td></td> 1264 * <td></td> 1265 * <td></td> 1266 * <td></td> 1267 * <td style="text-align:center">IAE</td> 1268 * </tr> 1269 * <tr> 1270 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th> 1271 * <td></td> 1272 * <td></td> 1273 * <td></td> 1274 * <td></td> 1275 * <td></td> 1276 * <td style="text-align:center">none</td> 1277 * </tr> 1278 * </tbody> 1279 * </table> 1280 * 1281 * <p> 1282 * Notes: 1283 * <ul> 1284 * <li>Class {@code C} and class {@code C1} are in module {@code M1}, 1285 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E} 1286 * is in module {@code M3}. {@code X} stands for class which is inaccessible 1287 * to the lookup. {@code ANY} stands for any of the example lookups.</li> 1288 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set, 1289 * {@code PRO} indicates {@link #PROTECTED} bit set, 1290 * {@code PRI} indicates {@link #PRIVATE} bit set, 1291 * {@code PAC} indicates {@link #PACKAGE} bit set, 1292 * {@code MOD} indicates {@link #MODULE} bit set, 1293 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set, 1294 * {@code U} indicates {@link #UNCONDITIONAL} bit set, 1295 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li> 1296 * <li>Public access comes in three kinds: 1297 * <ul> 1298 * <li>unconditional ({@code U}): the lookup assumes readability. 1299 * The lookup has {@code null} previous lookup class. 1300 * <li>one-module-reads ({@code 1R}): the module access checking is 1301 * performed with respect to the lookup class. The lookup has {@code null} 1302 * previous lookup class. 1303 * <li>two-module-reads ({@code 2R}): the module access checking is 1304 * performed with respect to the lookup class and the previous lookup class. 1305 * The lookup has a non-null previous lookup class which is in a 1306 * different module from the current lookup class. 1307 * </ul> 1308 * <li>Any attempt to reach a third module loses all access.</li> 1309 * <li>If a target class {@code X} is not accessible to {@code Lookup::in} 1310 * all access modes are dropped.</li> 1311 * </ul> 1312 * 1313 * <h2><a id="secmgr"></a>Security manager interactions</h2> 1314 * Although bytecode instructions can only refer to classes in 1315 * a related class loader, this API can search for methods in any 1316 * class, as long as a reference to its {@code Class} object is 1317 * available. Such cross-loader references are also possible with the 1318 * Core Reflection API, and are impossible to bytecode instructions 1319 * such as {@code invokestatic} or {@code getfield}. 1320 * There is a {@linkplain java.lang.SecurityManager security manager API} 1321 * to allow applications to check such cross-loader references. 1322 * These checks apply to both the {@code MethodHandles.Lookup} API 1323 * and the Core Reflection API 1324 * (as found on {@link java.lang.Class Class}). 1325 * <p> 1326 * If a security manager is present, member and class lookups are subject to 1327 * additional checks. 1328 * From one to three calls are made to the security manager. 1329 * Any of these calls can refuse access by throwing a 1330 * {@link java.lang.SecurityException SecurityException}. 1331 * Define {@code smgr} as the security manager, 1332 * {@code lookc} as the lookup class of the current lookup object, 1333 * {@code refc} as the containing class in which the member 1334 * is being sought, and {@code defc} as the class in which the 1335 * member is actually defined. 1336 * (If a class or other type is being accessed, 1337 * the {@code refc} and {@code defc} values are the class itself.) 1338 * The value {@code lookc} is defined as <em>not present</em> 1339 * if the current lookup object does not have 1340 * {@linkplain #hasFullPrivilegeAccess() full privilege access}. 1341 * The calls are made according to the following rules: 1342 * <ul> 1343 * <li><b>Step 1:</b> 1344 * If {@code lookc} is not present, or if its class loader is not 1345 * the same as or an ancestor of the class loader of {@code refc}, 1346 * then {@link SecurityManager#checkPackageAccess 1347 * smgr.checkPackageAccess(refcPkg)} is called, 1348 * where {@code refcPkg} is the package of {@code refc}. 1349 * <li><b>Step 2a:</b> 1350 * If the retrieved member is not public and 1351 * {@code lookc} is not present, then 1352 * {@link SecurityManager#checkPermission smgr.checkPermission} 1353 * with {@code RuntimePermission("accessDeclaredMembers")} is called. 1354 * <li><b>Step 2b:</b> 1355 * If the retrieved class has a {@code null} class loader, 1356 * and {@code lookc} is not present, then 1357 * {@link SecurityManager#checkPermission smgr.checkPermission} 1358 * with {@code RuntimePermission("getClassLoader")} is called. 1359 * <li><b>Step 3:</b> 1360 * If the retrieved member is not public, 1361 * and if {@code lookc} is not present, 1362 * and if {@code defc} and {@code refc} are different, 1363 * then {@link SecurityManager#checkPackageAccess 1364 * smgr.checkPackageAccess(defcPkg)} is called, 1365 * where {@code defcPkg} is the package of {@code defc}. 1366 * </ul> 1367 * Security checks are performed after other access checks have passed. 1368 * Therefore, the above rules presuppose a member or class that is public, 1369 * or else that is being accessed from a lookup class that has 1370 * rights to access the member or class. 1371 * <p> 1372 * If a security manager is present and the current lookup object does not have 1373 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then 1374 * {@link #defineClass(byte[]) defineClass}, 1375 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass}, 1376 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...) 1377 * defineHiddenClassWithClassData} 1378 * calls {@link SecurityManager#checkPermission smgr.checkPermission} 1379 * with {@code RuntimePermission("defineClass")}. 1380 * 1381 * <h2><a id="callsens"></a>Caller sensitive methods</h2> 1382 * A small number of Java methods have a special property called caller sensitivity. 1383 * A <em>caller-sensitive</em> method can behave differently depending on the 1384 * identity of its immediate caller. 1385 * <p> 1386 * If a method handle for a caller-sensitive method is requested, 1387 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply, 1388 * but they take account of the lookup class in a special way. 1389 * The resulting method handle behaves as if it were called 1390 * from an instruction contained in the lookup class, 1391 * so that the caller-sensitive method detects the lookup class. 1392 * (By contrast, the invoker of the method handle is disregarded.) 1393 * Thus, in the case of caller-sensitive methods, 1394 * different lookup classes may give rise to 1395 * differently behaving method handles. 1396 * <p> 1397 * In cases where the lookup object is 1398 * {@link MethodHandles#publicLookup() publicLookup()}, 1399 * or some other lookup object without the 1400 * {@linkplain #ORIGINAL original access}, 1401 * the lookup class is disregarded. 1402 * In such cases, no caller-sensitive method handle can be created, 1403 * access is forbidden, and the lookup fails with an 1404 * {@code IllegalAccessException}. 1405 * <p style="font-size:smaller;"> 1406 * <em>Discussion:</em> 1407 * For example, the caller-sensitive method 1408 * {@link java.lang.Class#forName(String) Class.forName(x)} 1409 * can return varying classes or throw varying exceptions, 1410 * depending on the class loader of the class that calls it. 1411 * A public lookup of {@code Class.forName} will fail, because 1412 * there is no reasonable way to determine its bytecode behavior. 1413 * <p style="font-size:smaller;"> 1414 * If an application caches method handles for broad sharing, 1415 * it should use {@code publicLookup()} to create them. 1416 * If there is a lookup of {@code Class.forName}, it will fail, 1417 * and the application must take appropriate action in that case. 1418 * It may be that a later lookup, perhaps during the invocation of a 1419 * bootstrap method, can incorporate the specific identity 1420 * of the caller, making the method accessible. 1421 * <p style="font-size:smaller;"> 1422 * The function {@code MethodHandles.lookup} is caller sensitive 1423 * so that there can be a secure foundation for lookups. 1424 * Nearly all other methods in the JSR 292 API rely on lookup 1425 * objects to check access requests. 1426 * 1427 * @revised 9 1428 */ 1429 public static final 1430 class Lookup { 1431 /** The class on behalf of whom the lookup is being performed. */ 1432 private final Class<?> lookupClass; 1433 1434 /** previous lookup class */ 1435 private final Class<?> prevLookupClass; 1436 1437 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */ 1438 private final int allowedModes; 1439 1440 static { 1441 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes")); 1442 } 1443 1444 /** A single-bit mask representing {@code public} access, 1445 * which may contribute to the result of {@link #lookupModes lookupModes}. 1446 * The value, {@code 0x01}, happens to be the same as the value of the 1447 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}. 1448 * <p> 1449 * A {@code Lookup} with this lookup mode performs cross-module access check 1450 * with respect to the {@linkplain #lookupClass() lookup class} and 1451 * {@linkplain #previousLookupClass() previous lookup class} if present. 1452 */ 1453 public static final int PUBLIC = Modifier.PUBLIC; 1454 1455 /** A single-bit mask representing {@code private} access, 1456 * which may contribute to the result of {@link #lookupModes lookupModes}. 1457 * The value, {@code 0x02}, happens to be the same as the value of the 1458 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}. 1459 */ 1460 public static final int PRIVATE = Modifier.PRIVATE; 1461 1462 /** A single-bit mask representing {@code protected} access, 1463 * which may contribute to the result of {@link #lookupModes lookupModes}. 1464 * The value, {@code 0x04}, happens to be the same as the value of the 1465 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}. 1466 */ 1467 public static final int PROTECTED = Modifier.PROTECTED; 1468 1469 /** A single-bit mask representing {@code package} access (default access), 1470 * which may contribute to the result of {@link #lookupModes lookupModes}. 1471 * The value is {@code 0x08}, which does not correspond meaningfully to 1472 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1473 */ 1474 public static final int PACKAGE = Modifier.STATIC; 1475 1476 /** A single-bit mask representing {@code module} access, 1477 * which may contribute to the result of {@link #lookupModes lookupModes}. 1478 * The value is {@code 0x10}, which does not correspond meaningfully to 1479 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1480 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup} 1481 * with this lookup mode can access all public types in the module of the 1482 * lookup class and public types in packages exported by other modules 1483 * to the module of the lookup class. 1484 * <p> 1485 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1486 * previous lookup class} is always {@code null}. 1487 * 1488 * @since 9 1489 */ 1490 public static final int MODULE = PACKAGE << 1; 1491 1492 /** A single-bit mask representing {@code unconditional} access 1493 * which may contribute to the result of {@link #lookupModes lookupModes}. 1494 * The value is {@code 0x20}, which does not correspond meaningfully to 1495 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1496 * A {@code Lookup} with this lookup mode assumes {@linkplain 1497 * java.lang.Module#canRead(java.lang.Module) readability}. 1498 * This lookup mode can access all public members of public types 1499 * of all modules when the type is in a package that is {@link 1500 * java.lang.Module#isExported(String) exported unconditionally}. 1501 * 1502 * <p> 1503 * If this lookup mode is set, the {@linkplain #previousLookupClass() 1504 * previous lookup class} is always {@code null}. 1505 * 1506 * @since 9 1507 * @see #publicLookup() 1508 */ 1509 public static final int UNCONDITIONAL = PACKAGE << 2; 1510 1511 /** A single-bit mask representing {@code original} access 1512 * which may contribute to the result of {@link #lookupModes lookupModes}. 1513 * The value is {@code 0x40}, which does not correspond meaningfully to 1514 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. 1515 * 1516 * <p> 1517 * If this lookup mode is set, the {@code Lookup} object must be 1518 * created by the original lookup class by calling 1519 * {@link MethodHandles#lookup()} method or by a bootstrap method 1520 * invoked by the VM. The {@code Lookup} object with this lookup 1521 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}. 1522 * 1523 * @since 16 1524 */ 1525 public static final int ORIGINAL = PACKAGE << 3; 1526 1527 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL); 1528 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access 1529 private static final int TRUSTED = -1; 1530 1531 /* 1532 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL 1533 * Adjust 0 => PACKAGE 1534 */ 1535 private static int fixmods(int mods) { 1536 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL); 1537 if (Modifier.isPublic(mods)) 1538 mods |= UNCONDITIONAL; 1539 return (mods != 0) ? mods : PACKAGE; 1540 } 1541 1542 /** Tells which class is performing the lookup. It is this class against 1543 * which checks are performed for visibility and access permissions. 1544 * <p> 1545 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class}, 1546 * access checks are performed against both the lookup class and the previous lookup class. 1547 * <p> 1548 * The class implies a maximum level of access permission, 1549 * but the permissions may be additionally limited by the bitmask 1550 * {@link #lookupModes lookupModes}, which controls whether non-public members 1551 * can be accessed. 1552 * @return the lookup class, on behalf of which this lookup object finds members 1553 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1554 */ 1555 public Class<?> lookupClass() { 1556 return lookupClass; 1557 } 1558 1559 /** Reports a lookup class in another module that this lookup object 1560 * was previously teleported from, or {@code null}. 1561 * <p> 1562 * A {@code Lookup} object produced by the factory methods, such as the 1563 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method, 1564 * has {@code null} previous lookup class. 1565 * A {@code Lookup} object has a non-null previous lookup class 1566 * when this lookup was teleported from an old lookup class 1567 * in one module to a new lookup class in another module. 1568 * 1569 * @return the lookup class in another module that this lookup object was 1570 * previously teleported from, or {@code null} 1571 * @since 14 1572 * @see #in(Class) 1573 * @see MethodHandles#privateLookupIn(Class, Lookup) 1574 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1575 */ 1576 public Class<?> previousLookupClass() { 1577 return prevLookupClass; 1578 } 1579 1580 // This is just for calling out to MethodHandleImpl. 1581 private Class<?> lookupClassOrNull() { 1582 return (allowedModes == TRUSTED) ? null : lookupClass; 1583 } 1584 1585 /** Tells which access-protection classes of members this lookup object can produce. 1586 * The result is a bit-mask of the bits 1587 * {@linkplain #PUBLIC PUBLIC (0x01)}, 1588 * {@linkplain #PRIVATE PRIVATE (0x02)}, 1589 * {@linkplain #PROTECTED PROTECTED (0x04)}, 1590 * {@linkplain #PACKAGE PACKAGE (0x08)}, 1591 * {@linkplain #MODULE MODULE (0x10)}, 1592 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}, 1593 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}. 1594 * <p> 1595 * A freshly-created lookup object 1596 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has 1597 * all possible bits set, except {@code UNCONDITIONAL}. 1598 * A lookup object on a new lookup class 1599 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} 1600 * may have some mode bits set to zero. 1601 * Mode bits can also be 1602 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}. 1603 * Once cleared, mode bits cannot be restored from the downgraded lookup object. 1604 * The purpose of this is to restrict access via the new lookup object, 1605 * so that it can access only names which can be reached by the original 1606 * lookup object, and also by the new lookup class. 1607 * @return the lookup modes, which limit the kinds of access performed by this lookup object 1608 * @see #in 1609 * @see #dropLookupMode 1610 * 1611 * @revised 9 1612 */ 1613 public int lookupModes() { 1614 return allowedModes & ALL_MODES; 1615 } 1616 1617 /** Embody the current class (the lookupClass) as a lookup class 1618 * for method handle creation. 1619 * Must be called by from a method in this package, 1620 * which in turn is called by a method not in this package. 1621 */ 1622 Lookup(Class<?> lookupClass) { 1623 this(lookupClass, null, FULL_POWER_MODES); 1624 } 1625 1626 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1627 assert PrimitiveClass.isPrimaryType(lookupClass); 1628 assert prevLookupClass == null || ((allowedModes & MODULE) == 0 1629 && prevLookupClass.getModule() != lookupClass.getModule()); 1630 assert !lookupClass.isArray() && !lookupClass.isPrimitive(); 1631 this.lookupClass = lookupClass; 1632 this.prevLookupClass = prevLookupClass; 1633 this.allowedModes = allowedModes; 1634 } 1635 1636 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) { 1637 // make sure we haven't accidentally picked up a privileged class: 1638 checkUnprivilegedlookupClass(lookupClass); 1639 return new Lookup(lookupClass, prevLookupClass, allowedModes); 1640 } 1641 1642 /** 1643 * Creates a lookup on the specified new lookup class. 1644 * The resulting object will report the specified 1645 * class as its own {@link #lookupClass() lookupClass}. 1646 * 1647 * <p> 1648 * However, the resulting {@code Lookup} object is guaranteed 1649 * to have no more access capabilities than the original. 1650 * In particular, access capabilities can be lost as follows:<ul> 1651 * <li>If the new lookup class is different from the old lookup class, 1652 * i.e. {@link #ORIGINAL ORIGINAL} access is lost. 1653 * <li>If the new lookup class is in a different module from the old one, 1654 * i.e. {@link #MODULE MODULE} access is lost. 1655 * <li>If the new lookup class is in a different package 1656 * than the old one, protected and default (package) members will not be accessible, 1657 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost. 1658 * <li>If the new lookup class is not within the same package member 1659 * as the old one, private members will not be accessible, and protected members 1660 * will not be accessible by virtue of inheritance, 1661 * i.e. {@link #PRIVATE PRIVATE} access is lost. 1662 * (Protected members may continue to be accessible because of package sharing.) 1663 * <li>If the new lookup class is not 1664 * {@linkplain #accessClass(Class) accessible} to this lookup, 1665 * then no members, not even public members, will be accessible 1666 * i.e. all access modes are lost. 1667 * <li>If the new lookup class, the old lookup class and the previous lookup class 1668 * are all in different modules i.e. teleporting to a third module, 1669 * all access modes are lost. 1670 * </ul> 1671 * <p> 1672 * The new previous lookup class is chosen as follows: 1673 * <ul> 1674 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit, 1675 * the new previous lookup class is {@code null}. 1676 * <li>If the new lookup class is in the same module as the old lookup class, 1677 * the new previous lookup class is the old previous lookup class. 1678 * <li>If the new lookup class is in a different module from the old lookup class, 1679 * the new previous lookup class is the old lookup class. 1680 *</ul> 1681 * <p> 1682 * The resulting lookup's capabilities for loading classes 1683 * (used during {@link #findClass} invocations) 1684 * are determined by the lookup class' loader, 1685 * which may change due to this operation. 1686 * 1687 * @param requestedLookupClass the desired lookup class for the new lookup object 1688 * @return a lookup object which reports the desired lookup class, or the same object 1689 * if there is no change 1690 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class 1691 * @throws NullPointerException if the argument is null 1692 * 1693 * @revised 9 1694 * @see #accessClass(Class) 1695 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 1696 */ 1697 public Lookup in(Class<?> requestedLookupClass) { 1698 Objects.requireNonNull(requestedLookupClass); 1699 if (requestedLookupClass.isPrimitive()) 1700 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class"); 1701 if (requestedLookupClass.isArray()) 1702 throw new IllegalArgumentException(requestedLookupClass + " is an array class"); 1703 1704 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all 1705 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES); 1706 if (requestedLookupClass == this.lookupClass) 1707 return this; // keep same capabilities 1708 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL; 1709 Module fromModule = this.lookupClass.getModule(); 1710 Module targetModule = requestedLookupClass.getModule(); 1711 Class<?> plc = this.previousLookupClass(); 1712 if ((this.allowedModes & UNCONDITIONAL) != 0) { 1713 assert plc == null; 1714 newModes = UNCONDITIONAL; 1715 } else if (fromModule != targetModule) { 1716 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) { 1717 // allow hopping back and forth between fromModule and plc's module 1718 // but not the third module 1719 newModes = 0; 1720 } 1721 // drop MODULE access 1722 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED); 1723 // teleport from this lookup class 1724 plc = this.lookupClass; 1725 } 1726 if ((newModes & PACKAGE) != 0 1727 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) { 1728 newModes &= ~(PACKAGE|PRIVATE|PROTECTED); 1729 } 1730 // Allow nestmate lookups to be created without special privilege: 1731 if ((newModes & PRIVATE) != 0 1732 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) { 1733 newModes &= ~(PRIVATE|PROTECTED); 1734 } 1735 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0 1736 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) { 1737 // The requested class it not accessible from the lookup class. 1738 // No permissions. 1739 newModes = 0; 1740 } 1741 return newLookup(requestedLookupClass, plc, newModes); 1742 } 1743 1744 /** 1745 * Creates a lookup on the same lookup class which this lookup object 1746 * finds members, but with a lookup mode that has lost the given lookup mode. 1747 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE 1748 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED}, 1749 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or 1750 * {@link #UNCONDITIONAL UNCONDITIONAL}. 1751 * 1752 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup}, 1753 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set. 1754 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting 1755 * lookup has no access. 1756 * 1757 * <p> If this lookup is not a public lookup, then the following applies 1758 * regardless of its {@linkplain #lookupModes() lookup modes}. 1759 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always 1760 * dropped and so the resulting lookup mode will never have these access 1761 * capabilities. When dropping {@code PACKAGE} 1762 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE} 1763 * access. When dropping {@code MODULE} then the resulting lookup will not 1764 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. 1765 * When dropping {@code PUBLIC} then the resulting lookup has no access. 1766 * 1767 * @apiNote 1768 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely 1769 * delegate non-public access within the package of the lookup class without 1770 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>. 1771 * A lookup with {@code MODULE} but not 1772 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within 1773 * the module of the lookup class without conferring package access. 1774 * A lookup with a {@linkplain #previousLookupClass() previous lookup class} 1775 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access 1776 * to public classes accessible to both the module of the lookup class 1777 * and the module of the previous lookup class. 1778 * 1779 * @param modeToDrop the lookup mode to drop 1780 * @return a lookup object which lacks the indicated mode, or the same object if there is no change 1781 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC}, 1782 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL} 1783 * or {@code UNCONDITIONAL} 1784 * @see MethodHandles#privateLookupIn 1785 * @since 9 1786 */ 1787 public Lookup dropLookupMode(int modeToDrop) { 1788 int oldModes = lookupModes(); 1789 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL); 1790 switch (modeToDrop) { 1791 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break; 1792 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break; 1793 case PACKAGE: newModes &= ~(PRIVATE); break; 1794 case PROTECTED: 1795 case PRIVATE: 1796 case ORIGINAL: 1797 case UNCONDITIONAL: break; 1798 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop"); 1799 } 1800 if (newModes == oldModes) return this; // return self if no change 1801 return newLookup(lookupClass(), previousLookupClass(), newModes); 1802 } 1803 1804 /** 1805 * Creates and links a class or interface from {@code bytes} 1806 * with the same class loader and in the same runtime package and 1807 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's 1808 * {@linkplain #lookupClass() lookup class} as if calling 1809 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 1810 * ClassLoader::defineClass}. 1811 * 1812 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include 1813 * {@link #PACKAGE PACKAGE} access as default (package) members will be 1814 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate 1815 * that the lookup object was created by a caller in the runtime package (or derived 1816 * from a lookup originally created by suitably privileged code to a target class in 1817 * the runtime package). </p> 1818 * 1819 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined 1820 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the 1821 * same package as the lookup class. </p> 1822 * 1823 * <p> This method does not run the class initializer. The class initializer may 1824 * run at a later time, as detailed in section 12.4 of the <em>The Java Language 1825 * Specification</em>. </p> 1826 * 1827 * <p> If there is a security manager and this lookup does not have {@linkplain 1828 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method 1829 * is first called to check {@code RuntimePermission("defineClass")}. </p> 1830 * 1831 * @param bytes the class bytes 1832 * @return the {@code Class} object for the class 1833 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access 1834 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 1835 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 1836 * than the lookup class or {@code bytes} is not a class or interface 1837 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 1838 * @throws VerifyError if the newly created class cannot be verified 1839 * @throws LinkageError if the newly created class cannot be linked for any other reason 1840 * @throws SecurityException if a security manager is present and it 1841 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 1842 * @throws NullPointerException if {@code bytes} is {@code null} 1843 * @since 9 1844 * @see Lookup#privateLookupIn 1845 * @see Lookup#dropLookupMode 1846 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain) 1847 */ 1848 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException { 1849 ensureDefineClassPermission(); 1850 if ((lookupModes() & PACKAGE) == 0) 1851 throw new IllegalAccessException("Lookup does not have PACKAGE access"); 1852 return makeClassDefiner(bytes.clone()).defineClass(false); 1853 } 1854 1855 private void ensureDefineClassPermission() { 1856 if (allowedModes == TRUSTED) return; 1857 1858 if (!hasFullPrivilegeAccess()) { 1859 @SuppressWarnings("removal") 1860 SecurityManager sm = System.getSecurityManager(); 1861 if (sm != null) 1862 sm.checkPermission(new RuntimePermission("defineClass")); 1863 } 1864 } 1865 1866 /** 1867 * The set of class options that specify whether a hidden class created by 1868 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...) 1869 * Lookup::defineHiddenClass} method is dynamically added as a new member 1870 * to the nest of a lookup class and/or whether a hidden class has 1871 * a strong relationship with the class loader marked as its defining loader. 1872 * 1873 * @since 15 1874 */ 1875 public enum ClassOption { 1876 /** 1877 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest} 1878 * of a lookup class as a nestmate. 1879 * 1880 * <p> A hidden nestmate class has access to the private members of all 1881 * classes and interfaces in the same nest. 1882 * 1883 * @see Class#getNestHost() 1884 */ 1885 NESTMATE(NESTMATE_CLASS), 1886 1887 /** 1888 * Specifies that a hidden class has a <em>strong</em> 1889 * relationship with the class loader marked as its defining loader, 1890 * as a normal class or interface has with its own defining loader. 1891 * This means that the hidden class may be unloaded if and only if 1892 * its defining loader is not reachable and thus may be reclaimed 1893 * by a garbage collector (JLS {@jls 12.7}). 1894 * 1895 * <p> By default, a hidden class or interface may be unloaded 1896 * even if the class loader that is marked as its defining loader is 1897 * <a href="../ref/package-summary.html#reachability">reachable</a>. 1898 1899 * 1900 * @jls 12.7 Unloading of Classes and Interfaces 1901 */ 1902 STRONG(STRONG_LOADER_LINK); 1903 1904 /* the flag value is used by VM at define class time */ 1905 private final int flag; 1906 ClassOption(int flag) { 1907 this.flag = flag; 1908 } 1909 1910 static int optionsToFlag(Set<ClassOption> options) { 1911 int flags = 0; 1912 for (ClassOption cp : options) { 1913 flags |= cp.flag; 1914 } 1915 return flags; 1916 } 1917 } 1918 1919 /** 1920 * Creates a <em>hidden</em> class or interface from {@code bytes}, 1921 * returning a {@code Lookup} on the newly created class or interface. 1922 * 1923 * <p> Ordinarily, a class or interface {@code C} is created by a class loader, 1924 * which either defines {@code C} directly or delegates to another class loader. 1925 * A class loader defines {@code C} directly by invoking 1926 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain) 1927 * ClassLoader::defineClass}, which causes the Java Virtual Machine 1928 * to derive {@code C} from a purported representation in {@code class} file format. 1929 * In situations where use of a class loader is undesirable, a class or interface 1930 * {@code C} can be created by this method instead. This method is capable of 1931 * defining {@code C}, and thereby creating it, without invoking 1932 * {@code ClassLoader::defineClass}. 1933 * Instead, this method defines {@code C} as if by arranging for 1934 * the Java Virtual Machine to derive a nonarray class or interface {@code C} 1935 * from a purported representation in {@code class} file format 1936 * using the following rules: 1937 * 1938 * <ol> 1939 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup} 1940 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access. 1941 * This level of access is needed to create {@code C} in the module 1942 * of the lookup class of this {@code Lookup}.</li> 1943 * 1944 * <li> The purported representation in {@code bytes} must be a {@code ClassFile} 1945 * structure (JVMS {@jvms 4.1}) of a supported major and minor version. 1946 * The major and minor version may differ from the {@code class} file version 1947 * of the lookup class of this {@code Lookup}.</li> 1948 * 1949 * <li> The value of {@code this_class} must be a valid index in the 1950 * {@code constant_pool} table, and the entry at that index must be a valid 1951 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name 1952 * encoded in internal form that is specified by this structure. {@code N} must 1953 * denote a class or interface in the same package as the lookup class.</li> 1954 * 1955 * <li> Let {@code CN} be the string {@code N + "." + <suffix>}, 1956 * where {@code <suffix>} is an unqualified name. 1957 * 1958 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by 1959 * {@code bytes} with an additional entry in the {@code constant_pool} table, 1960 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and 1961 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class} 1962 * refers to the new {@code CONSTANT_Utf8_info} structure. 1963 * 1964 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}. 1965 * 1966 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and 1967 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5}, 1968 * with the following adjustments: 1969 * <ul> 1970 * <li> The constant indicated by {@code this_class} is permitted to specify a name 1971 * that includes a single {@code "."} character, even though this is not a valid 1972 * binary class or interface name in internal form.</li> 1973 * 1974 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C}, 1975 * but no class loader is recorded as an initiating class loader of {@code C}.</li> 1976 * 1977 * <li> {@code C} is considered to have the same runtime 1978 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module} 1979 * and {@linkplain java.security.ProtectionDomain protection domain} 1980 * as the lookup class of this {@code Lookup}. 1981 * <li> Let {@code GN} be the binary name obtained by taking {@code N} 1982 * (a binary name encoded in internal form) and replacing ASCII forward slashes with 1983 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}: 1984 * <ul> 1985 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>}, 1986 * even though this is not a valid binary class or interface name.</li> 1987 * <li> {@link Class#descriptorString()} returns the string 1988 * {@code "L" + N + "." + <suffix> + ";"}, 1989 * even though this is not a valid type descriptor name.</li> 1990 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C} 1991 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li> 1992 * </ul> 1993 * </ul> 1994 * </li> 1995 * </ol> 1996 * 1997 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine. 1998 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments: 1999 * <ul> 2000 * <li> During verification, whenever it is necessary to load the class named 2001 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is 2002 * made of any class loader.</li> 2003 * 2004 * <li> On any attempt to resolve the entry in the run-time constant pool indicated 2005 * by {@code this_class}, the symbolic reference is considered to be resolved to 2006 * {@code C} and resolution always succeeds immediately.</li> 2007 * </ul> 2008 * 2009 * <p> If the {@code initialize} parameter is {@code true}, 2010 * then {@code C} is initialized by the Java Virtual Machine. 2011 * 2012 * <p> The newly created class or interface {@code C} serves as the 2013 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object 2014 * returned by this method. {@code C} is <em>hidden</em> in the sense that 2015 * no other class or interface can refer to {@code C} via a constant pool entry. 2016 * That is, a hidden class or interface cannot be named as a supertype, a field type, 2017 * a method parameter type, or a method return type by any other class. 2018 * This is because a hidden class or interface does not have a binary name, so 2019 * there is no internal form available to record in any class's constant pool. 2020 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)}, 2021 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and 2022 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class) 2023 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html"> 2024 * JVM Tool Interface</a>. 2025 * 2026 * <p> A class or interface created by 2027 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain) 2028 * a class loader} has a strong relationship with that class loader. 2029 * That is, every {@code Class} object contains a reference to the {@code ClassLoader} 2030 * that {@linkplain Class#getClassLoader() defined it}. 2031 * This means that a class created by a class loader may be unloaded if and 2032 * only if its defining loader is not reachable and thus may be reclaimed 2033 * by a garbage collector (JLS {@jls 12.7}). 2034 * 2035 * By default, however, a hidden class or interface may be unloaded even if 2036 * the class loader that is marked as its defining loader is 2037 * <a href="../ref/package-summary.html#reachability">reachable</a>. 2038 * This behavior is useful when a hidden class or interface serves multiple 2039 * classes defined by arbitrary class loaders. In other cases, a hidden 2040 * class or interface may be linked to a single class (or a small number of classes) 2041 * with the same defining loader as the hidden class or interface. 2042 * In such cases, where the hidden class or interface must be coterminous 2043 * with a normal class or interface, the {@link ClassOption#STRONG STRONG} 2044 * option may be passed in {@code options}. 2045 * This arranges for a hidden class to have the same strong relationship 2046 * with the class loader marked as its defining loader, 2047 * as a normal class or interface has with its own defining loader. 2048 * 2049 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass} 2050 * may still prevent a hidden class or interface from being 2051 * unloaded by ensuring that the {@code Class} object is reachable. 2052 * 2053 * <p> The unloading characteristics are set for each hidden class when it is 2054 * defined, and cannot be changed later. An advantage of allowing hidden classes 2055 * to be unloaded independently of the class loader marked as their defining loader 2056 * is that a very large number of hidden classes may be created by an application. 2057 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory, 2058 * just as if normal classes were created by class loaders. 2059 * 2060 * <p> Classes and interfaces in a nest are allowed to have mutual access to 2061 * their private members. The nest relationship is determined by 2062 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and 2063 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file. 2064 * By default, a hidden class belongs to a nest consisting only of itself 2065 * because a hidden class has no binary name. 2066 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options} 2067 * to create a hidden class or interface {@code C} as a member of a nest. 2068 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute 2069 * in the {@code ClassFile} structure from which {@code C} was derived. 2070 * Instead, the following rules determine the nest host of {@code C}: 2071 * <ul> 2072 * <li>If the nest host of the lookup class of this {@code Lookup} has previously 2073 * been determined, then let {@code H} be the nest host of the lookup class. 2074 * Otherwise, the nest host of the lookup class is determined using the 2075 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li> 2076 * <li>The nest host of {@code C} is determined to be {@code H}, 2077 * the nest host of the lookup class.</li> 2078 * </ul> 2079 * 2080 * <p> A hidden class or interface may be serializable, but this requires a custom 2081 * serialization mechanism in order to ensure that instances are properly serialized 2082 * and deserialized. The default serialization mechanism supports only classes and 2083 * interfaces that are discoverable by their class name. 2084 * 2085 * @param bytes the bytes that make up the class data, 2086 * in the format of a valid {@code class} file as defined by 2087 * <cite>The Java Virtual Machine Specification</cite>. 2088 * @param initialize if {@code true} the class will be initialized. 2089 * @param options {@linkplain ClassOption class options} 2090 * @return the {@code Lookup} object on the hidden class, 2091 * with {@linkplain #ORIGINAL original} and 2092 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access 2093 * 2094 * @throws IllegalAccessException if this {@code Lookup} does not have 2095 * {@linkplain #hasFullPrivilegeAccess() full privilege} access 2096 * @throws SecurityException if a security manager is present and it 2097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2098 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 2099 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version 2100 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 2101 * than the lookup class or {@code bytes} is not a class or interface 2102 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 2103 * @throws IncompatibleClassChangeError if the class or interface named as 2104 * the direct superclass of {@code C} is in fact an interface, or if any of the classes 2105 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces 2106 * @throws ClassCircularityError if any of the superclasses or superinterfaces of 2107 * {@code C} is {@code C} itself 2108 * @throws VerifyError if the newly created class cannot be verified 2109 * @throws LinkageError if the newly created class cannot be linked for any other reason 2110 * @throws NullPointerException if any parameter is {@code null} 2111 * 2112 * @since 15 2113 * @see Class#isHidden() 2114 * @jvms 4.2.1 Binary Class and Interface Names 2115 * @jvms 4.2.2 Unqualified Names 2116 * @jvms 4.7.28 The {@code NestHost} Attribute 2117 * @jvms 4.7.29 The {@code NestMembers} Attribute 2118 * @jvms 5.4.3.1 Class and Interface Resolution 2119 * @jvms 5.4.4 Access Control 2120 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation 2121 * @jvms 5.4 Linking 2122 * @jvms 5.5 Initialization 2123 * @jls 12.7 Unloading of Classes and Interfaces 2124 */ 2125 @SuppressWarnings("doclint:reference") // cross-module links 2126 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options) 2127 throws IllegalAccessException 2128 { 2129 Objects.requireNonNull(bytes); 2130 Objects.requireNonNull(options); 2131 2132 ensureDefineClassPermission(); 2133 if (!hasFullPrivilegeAccess()) { 2134 throw new IllegalAccessException(this + " does not have full privilege access"); 2135 } 2136 2137 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize); 2138 } 2139 2140 /** 2141 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated 2142 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data}, 2143 * returning a {@code Lookup} on the newly created class or interface. 2144 * 2145 * <p> This method is equivalent to calling 2146 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)} 2147 * as if the hidden class is injected with a private static final <i>unnamed</i> 2148 * field which is initialized with the given {@code classData} at 2149 * the first instruction of the class initializer. 2150 * The newly created class is linked by the Java Virtual Machine. 2151 * 2152 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData} 2153 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt} 2154 * methods can be used to retrieve the {@code classData}. 2155 * 2156 * @apiNote 2157 * A framework can create a hidden class with class data with one or more 2158 * objects and load the class data as dynamically-computed constant(s) 2159 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class) 2160 * Class data} is accessible only to the lookup object created by the newly 2161 * defined hidden class but inaccessible to other members in the same nest 2162 * (unlike private static fields that are accessible to nestmates). 2163 * Care should be taken w.r.t. mutability for example when passing 2164 * an array or other mutable structure through the class data. 2165 * Changing any value stored in the class data at runtime may lead to 2166 * unpredictable behavior. 2167 * If the class data is a {@code List}, it is good practice to make it 2168 * unmodifiable for example via {@link List#of List::of}. 2169 * 2170 * @param bytes the class bytes 2171 * @param classData pre-initialized class data 2172 * @param initialize if {@code true} the class will be initialized. 2173 * @param options {@linkplain ClassOption class options} 2174 * @return the {@code Lookup} object on the hidden class, 2175 * with {@linkplain #ORIGINAL original} and 2176 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access 2177 * 2178 * @throws IllegalAccessException if this {@code Lookup} does not have 2179 * {@linkplain #hasFullPrivilegeAccess() full privilege} access 2180 * @throws SecurityException if a security manager is present and it 2181 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2182 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure 2183 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version 2184 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package 2185 * than the lookup class or {@code bytes} is not a class or interface 2186 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item) 2187 * @throws IncompatibleClassChangeError if the class or interface named as 2188 * the direct superclass of {@code C} is in fact an interface, or if any of the classes 2189 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces 2190 * @throws ClassCircularityError if any of the superclasses or superinterfaces of 2191 * {@code C} is {@code C} itself 2192 * @throws VerifyError if the newly created class cannot be verified 2193 * @throws LinkageError if the newly created class cannot be linked for any other reason 2194 * @throws NullPointerException if any parameter is {@code null} 2195 * 2196 * @since 16 2197 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...) 2198 * @see Class#isHidden() 2199 * @see MethodHandles#classData(Lookup, String, Class) 2200 * @see MethodHandles#classDataAt(Lookup, String, Class, int) 2201 * @jvms 4.2.1 Binary Class and Interface Names 2202 * @jvms 4.2.2 Unqualified Names 2203 * @jvms 4.7.28 The {@code NestHost} Attribute 2204 * @jvms 4.7.29 The {@code NestMembers} Attribute 2205 * @jvms 5.4.3.1 Class and Interface Resolution 2206 * @jvms 5.4.4 Access Control 2207 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation 2208 * @jvms 5.4 Linking 2209 * @jvms 5.5 Initialization 2210 * @jls 12.7 Unloading of Classes and Interface 2211 */ 2212 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options) 2213 throws IllegalAccessException 2214 { 2215 Objects.requireNonNull(bytes); 2216 Objects.requireNonNull(classData); 2217 Objects.requireNonNull(options); 2218 2219 ensureDefineClassPermission(); 2220 if (!hasFullPrivilegeAccess()) { 2221 throw new IllegalAccessException(this + " does not have full privilege access"); 2222 } 2223 2224 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false) 2225 .defineClassAsLookup(initialize, classData); 2226 } 2227 2228 static class ClassFile { 2229 final String name; 2230 final int accessFlags; 2231 final byte[] bytes; 2232 ClassFile(String name, int accessFlags, byte[] bytes) { 2233 this.name = name; 2234 this.accessFlags = accessFlags; 2235 this.bytes = bytes; 2236 } 2237 2238 static ClassFile newInstanceNoCheck(String name, byte[] bytes) { 2239 return new ClassFile(name, 0, bytes); 2240 } 2241 2242 /** 2243 * This method checks the class file version and the structure of `this_class`. 2244 * and checks if the bytes is a class or interface (ACC_MODULE flag not set) 2245 * that is in the named package. 2246 * 2247 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags 2248 * or the class is not in the given package name. 2249 */ 2250 static ClassFile newInstance(byte[] bytes, String pkgName) { 2251 int magic = readInt(bytes, 0); 2252 if (magic != 0xCAFEBABE) { 2253 throw new ClassFormatError("Incompatible magic value: " + magic); 2254 } 2255 int minor = readUnsignedShort(bytes, 4); 2256 int major = readUnsignedShort(bytes, 6); 2257 if (!VM.isSupportedClassFileVersion(major, minor)) { 2258 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor); 2259 } 2260 2261 String name; 2262 int accessFlags; 2263 try { 2264 ClassReader reader = new ClassReader(bytes); 2265 // ClassReader::getClassName does not check if `this_class` is CONSTANT_Class_info 2266 // workaround to read `this_class` using readConst and validate the value 2267 int thisClass = reader.readUnsignedShort(reader.header + 2); 2268 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]); 2269 if (!(constant instanceof Type type)) { 2270 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info"); 2271 } 2272 if (!type.getDescriptor().startsWith("L")) { 2273 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info"); 2274 } 2275 name = type.getClassName(); 2276 accessFlags = reader.readUnsignedShort(reader.header); 2277 } catch (RuntimeException e) { 2278 // ASM exceptions are poorly specified 2279 ClassFormatError cfe = new ClassFormatError(); 2280 cfe.initCause(e); 2281 throw cfe; 2282 } 2283 2284 // must be a class or interface 2285 if ((accessFlags & Opcodes.ACC_MODULE) != 0) { 2286 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set"); 2287 } 2288 2289 // check if it's in the named package 2290 int index = name.lastIndexOf('.'); 2291 String pn = (index == -1) ? "" : name.substring(0, index); 2292 if (!pn.equals(pkgName)) { 2293 throw newIllegalArgumentException(name + " not in same package as lookup class"); 2294 } 2295 2296 return new ClassFile(name, accessFlags, bytes); 2297 } 2298 2299 private static int readInt(byte[] bytes, int offset) { 2300 if ((offset+4) > bytes.length) { 2301 throw new ClassFormatError("Invalid ClassFile structure"); 2302 } 2303 return ((bytes[offset] & 0xFF) << 24) 2304 | ((bytes[offset + 1] & 0xFF) << 16) 2305 | ((bytes[offset + 2] & 0xFF) << 8) 2306 | (bytes[offset + 3] & 0xFF); 2307 } 2308 2309 private static int readUnsignedShort(byte[] bytes, int offset) { 2310 if ((offset+2) > bytes.length) { 2311 throw new ClassFormatError("Invalid ClassFile structure"); 2312 } 2313 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF); 2314 } 2315 } 2316 2317 /* 2318 * Returns a ClassDefiner that creates a {@code Class} object of a normal class 2319 * from the given bytes. 2320 * 2321 * Caller should make a defensive copy of the arguments if needed 2322 * before calling this factory method. 2323 * 2324 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2325 * {@bytes} denotes a class in a different package than the lookup class 2326 */ 2327 private ClassDefiner makeClassDefiner(byte[] bytes) { 2328 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2329 return new ClassDefiner(this, cf, STRONG_LOADER_LINK); 2330 } 2331 2332 /** 2333 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2334 * from the given bytes. The name must be in the same package as the lookup class. 2335 * 2336 * Caller should make a defensive copy of the arguments if needed 2337 * before calling this factory method. 2338 * 2339 * @param bytes class bytes 2340 * @return ClassDefiner that defines a hidden class of the given bytes. 2341 * 2342 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2343 * {@bytes} denotes a class in a different package than the lookup class 2344 */ 2345 ClassDefiner makeHiddenClassDefiner(byte[] bytes) { 2346 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2347 return makeHiddenClassDefiner(cf, Set.of(), false); 2348 } 2349 2350 /** 2351 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2352 * from the given bytes and options. 2353 * The name must be in the same package as the lookup class. 2354 * 2355 * Caller should make a defensive copy of the arguments if needed 2356 * before calling this factory method. 2357 * 2358 * @param bytes class bytes 2359 * @param options class options 2360 * @param accessVmAnnotations true to give the hidden class access to VM annotations 2361 * @return ClassDefiner that defines a hidden class of the given bytes and options 2362 * 2363 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or 2364 * {@bytes} denotes a class in a different package than the lookup class 2365 */ 2366 ClassDefiner makeHiddenClassDefiner(byte[] bytes, 2367 Set<ClassOption> options, 2368 boolean accessVmAnnotations) { 2369 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName()); 2370 return makeHiddenClassDefiner(cf, options, accessVmAnnotations); 2371 } 2372 2373 /** 2374 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2375 * from the given bytes and the given options. No package name check on the given name. 2376 * 2377 * @param name fully-qualified name that specifies the prefix of the hidden class 2378 * @param bytes class bytes 2379 * @param options class options 2380 * @return ClassDefiner that defines a hidden class of the given bytes and options. 2381 */ 2382 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options) { 2383 // skip name and access flags validation 2384 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false); 2385 } 2386 2387 /** 2388 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class 2389 * from the given class file and options. 2390 * 2391 * @param cf ClassFile 2392 * @param options class options 2393 * @param accessVmAnnotations true to give the hidden class access to VM annotations 2394 */ 2395 private ClassDefiner makeHiddenClassDefiner(ClassFile cf, 2396 Set<ClassOption> options, 2397 boolean accessVmAnnotations) { 2398 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options); 2399 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) { 2400 // jdk.internal.vm.annotations are permitted for classes 2401 // defined to boot loader and platform loader 2402 flags |= ACCESS_VM_ANNOTATIONS; 2403 } 2404 2405 return new ClassDefiner(this, cf, flags); 2406 } 2407 2408 static class ClassDefiner { 2409 private final Lookup lookup; 2410 private final String name; 2411 private final byte[] bytes; 2412 private final int classFlags; 2413 2414 private ClassDefiner(Lookup lookup, ClassFile cf, int flags) { 2415 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK); 2416 this.lookup = lookup; 2417 this.bytes = cf.bytes; 2418 this.name = cf.name; 2419 this.classFlags = flags; 2420 } 2421 2422 String className() { 2423 return name; 2424 } 2425 2426 Class<?> defineClass(boolean initialize) { 2427 return defineClass(initialize, null); 2428 } 2429 2430 Lookup defineClassAsLookup(boolean initialize) { 2431 Class<?> c = defineClass(initialize, null); 2432 return new Lookup(c, null, FULL_POWER_MODES); 2433 } 2434 2435 /** 2436 * Defines the class of the given bytes and the given classData. 2437 * If {@code initialize} parameter is true, then the class will be initialized. 2438 * 2439 * @param initialize true if the class to be initialized 2440 * @param classData classData or null 2441 * @return the class 2442 * 2443 * @throws LinkageError linkage error 2444 */ 2445 Class<?> defineClass(boolean initialize, Object classData) { 2446 Class<?> lookupClass = lookup.lookupClass(); 2447 ClassLoader loader = lookupClass.getClassLoader(); 2448 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null; 2449 Class<?> c = SharedSecrets.getJavaLangAccess() 2450 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData); 2451 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost(); 2452 return c; 2453 } 2454 2455 Lookup defineClassAsLookup(boolean initialize, Object classData) { 2456 Class<?> c = defineClass(initialize, classData); 2457 return new Lookup(c, null, FULL_POWER_MODES); 2458 } 2459 2460 private boolean isNestmate() { 2461 return (classFlags & NESTMATE_CLASS) != 0; 2462 } 2463 } 2464 2465 private ProtectionDomain lookupClassProtectionDomain() { 2466 ProtectionDomain pd = cachedProtectionDomain; 2467 if (pd == null) { 2468 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass); 2469 } 2470 return pd; 2471 } 2472 2473 // cached protection domain 2474 private volatile ProtectionDomain cachedProtectionDomain; 2475 2476 // Make sure outer class is initialized first. 2477 static { IMPL_NAMES.getClass(); } 2478 2479 /** Package-private version of lookup which is trusted. */ 2480 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED); 2481 2482 /** Version of lookup which is trusted minimally. 2483 * It can only be used to create method handles to publicly accessible 2484 * members in packages that are exported unconditionally. 2485 */ 2486 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL); 2487 2488 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) { 2489 String name = lookupClass.getName(); 2490 if (name.startsWith("java.lang.invoke.")) 2491 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass); 2492 } 2493 2494 /** 2495 * Displays the name of the class from which lookups are to be made, 2496 * followed by "/" and the name of the {@linkplain #previousLookupClass() 2497 * previous lookup class} if present. 2498 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.) 2499 * If there are restrictions on the access permitted to this lookup, 2500 * this is indicated by adding a suffix to the class name, consisting 2501 * of a slash and a keyword. The keyword represents the strongest 2502 * allowed access, and is chosen as follows: 2503 * <ul> 2504 * <li>If no access is allowed, the suffix is "/noaccess". 2505 * <li>If only unconditional access is allowed, the suffix is "/publicLookup". 2506 * <li>If only public access to types in exported packages is allowed, the suffix is "/public". 2507 * <li>If only public and module access are allowed, the suffix is "/module". 2508 * <li>If public and package access are allowed, the suffix is "/package". 2509 * <li>If public, package, and private access are allowed, the suffix is "/private". 2510 * </ul> 2511 * If none of the above cases apply, it is the case that 2512 * {@linkplain #hasFullPrivilegeAccess() full privilege access} 2513 * (public, module, package, private, and protected) is allowed. 2514 * In this case, no suffix is added. 2515 * This is true only of an object obtained originally from 2516 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}. 2517 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in} 2518 * always have restricted access, and will display a suffix. 2519 * <p> 2520 * (It may seem strange that protected access should be 2521 * stronger than private access. Viewed independently from 2522 * package access, protected access is the first to be lost, 2523 * because it requires a direct subclass relationship between 2524 * caller and callee.) 2525 * @see #in 2526 * 2527 * @revised 9 2528 */ 2529 @Override 2530 public String toString() { 2531 String cname = lookupClass.getName(); 2532 if (prevLookupClass != null) 2533 cname += "/" + prevLookupClass.getName(); 2534 switch (allowedModes) { 2535 case 0: // no privileges 2536 return cname + "/noaccess"; 2537 case UNCONDITIONAL: 2538 return cname + "/publicLookup"; 2539 case PUBLIC: 2540 return cname + "/public"; 2541 case PUBLIC|MODULE: 2542 return cname + "/module"; 2543 case PUBLIC|PACKAGE: 2544 case PUBLIC|MODULE|PACKAGE: 2545 return cname + "/package"; 2546 case PUBLIC|PACKAGE|PRIVATE: 2547 case PUBLIC|MODULE|PACKAGE|PRIVATE: 2548 return cname + "/private"; 2549 case PUBLIC|PACKAGE|PRIVATE|PROTECTED: 2550 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED: 2551 case FULL_POWER_MODES: 2552 return cname; 2553 case TRUSTED: 2554 return "/trusted"; // internal only; not exported 2555 default: // Should not happen, but it's a bitfield... 2556 cname = cname + "/" + Integer.toHexString(allowedModes); 2557 assert(false) : cname; 2558 return cname; 2559 } 2560 } 2561 2562 /** 2563 * Produces a method handle for a static method. 2564 * The type of the method handle will be that of the method. 2565 * (Since static methods do not take receivers, there is no 2566 * additional receiver argument inserted into the method handle type, 2567 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) 2568 * The method and all its argument types must be accessible to the lookup object. 2569 * <p> 2570 * The returned method handle will have 2571 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2572 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2573 * <p> 2574 * If the returned method handle is invoked, the method's class will 2575 * be initialized, if it has not already been initialized. 2576 * <p><b>Example:</b> 2577 * {@snippet lang="java" : 2578 import static java.lang.invoke.MethodHandles.*; 2579 import static java.lang.invoke.MethodType.*; 2580 ... 2581 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class, 2582 "asList", methodType(List.class, Object[].class)); 2583 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString()); 2584 * } 2585 * @param refc the class from which the method is accessed 2586 * @param name the name of the method 2587 * @param type the type of the method 2588 * @return the desired method handle 2589 * @throws NoSuchMethodException if the method does not exist 2590 * @throws IllegalAccessException if access checking fails, 2591 * or if the method is not {@code static}, 2592 * or if the method's variable arity modifier bit 2593 * is set and {@code asVarargsCollector} fails 2594 * @throws SecurityException if a security manager is present and it 2595 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2596 * @throws NullPointerException if any argument is null 2597 */ 2598 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2599 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type); 2600 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method)); 2601 } 2602 2603 /** 2604 * Produces a method handle for a virtual method. 2605 * The type of the method handle will be that of the method, 2606 * with the receiver type (usually {@code refc}) prepended. 2607 * The method and all its argument types must be accessible to the lookup object. 2608 * <p> 2609 * When called, the handle will treat the first argument as a receiver 2610 * and, for non-private methods, dispatch on the receiver's type to determine which method 2611 * implementation to enter. 2612 * For private methods the named method in {@code refc} will be invoked on the receiver. 2613 * (The dispatching action is identical with that performed by an 2614 * {@code invokevirtual} or {@code invokeinterface} instruction.) 2615 * <p> 2616 * The first argument will be of type {@code refc} if the lookup 2617 * class has full privileges to access the member. Otherwise 2618 * the member must be {@code protected} and the first argument 2619 * will be restricted in type to the lookup class. 2620 * <p> 2621 * The returned method handle will have 2622 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2623 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2624 * <p> 2625 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual} 2626 * instructions and method handles produced by {@code findVirtual}, 2627 * if the class is {@code MethodHandle} and the name string is 2628 * {@code invokeExact} or {@code invoke}, the resulting 2629 * method handle is equivalent to one produced by 2630 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or 2631 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} 2632 * with the same {@code type} argument. 2633 * <p> 2634 * If the class is {@code VarHandle} and the name string corresponds to 2635 * the name of a signature-polymorphic access mode method, the resulting 2636 * method handle is equivalent to one produced by 2637 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with 2638 * the access mode corresponding to the name string and with the same 2639 * {@code type} arguments. 2640 * <p> 2641 * <b>Example:</b> 2642 * {@snippet lang="java" : 2643 import static java.lang.invoke.MethodHandles.*; 2644 import static java.lang.invoke.MethodType.*; 2645 ... 2646 MethodHandle MH_concat = publicLookup().findVirtual(String.class, 2647 "concat", methodType(String.class, String.class)); 2648 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class, 2649 "hashCode", methodType(int.class)); 2650 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class, 2651 "hashCode", methodType(int.class)); 2652 assertEquals("xy", (String) MH_concat.invokeExact("x", "y")); 2653 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy")); 2654 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy")); 2655 // interface method: 2656 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class, 2657 "subSequence", methodType(CharSequence.class, int.class, int.class)); 2658 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString()); 2659 // constructor "internal method" must be accessed differently: 2660 MethodType MT_newString = methodType(void.class); //()V for new String() 2661 try { assertEquals("impossible", lookup() 2662 .findVirtual(String.class, "<init>", MT_newString)); 2663 } catch (NoSuchMethodException ex) { } // OK 2664 MethodHandle MH_newString = publicLookup() 2665 .findConstructor(String.class, MT_newString); 2666 assertEquals("", (String) MH_newString.invokeExact()); 2667 * } 2668 * 2669 * @param refc the class or interface from which the method is accessed 2670 * @param name the name of the method 2671 * @param type the type of the method, with the receiver argument omitted 2672 * @return the desired method handle 2673 * @throws NoSuchMethodException if the method does not exist 2674 * @throws IllegalAccessException if access checking fails, 2675 * or if the method is {@code static}, 2676 * or if the method's variable arity modifier bit 2677 * is set and {@code asVarargsCollector} fails 2678 * @throws SecurityException if a security manager is present and it 2679 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2680 * @throws NullPointerException if any argument is null 2681 */ 2682 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2683 if (refc == MethodHandle.class) { 2684 MethodHandle mh = findVirtualForMH(name, type); 2685 if (mh != null) return mh; 2686 } else if (refc == VarHandle.class) { 2687 MethodHandle mh = findVirtualForVH(name, type); 2688 if (mh != null) return mh; 2689 } 2690 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual); 2691 MemberName method = resolveOrFail(refKind, refc, name, type); 2692 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method)); 2693 } 2694 private MethodHandle findVirtualForMH(String name, MethodType type) { 2695 // these names require special lookups because of the implicit MethodType argument 2696 if ("invoke".equals(name)) 2697 return invoker(type); 2698 if ("invokeExact".equals(name)) 2699 return exactInvoker(type); 2700 assert(!MemberName.isMethodHandleInvokeName(name)); 2701 return null; 2702 } 2703 private MethodHandle findVirtualForVH(String name, MethodType type) { 2704 try { 2705 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type); 2706 } catch (IllegalArgumentException e) { 2707 return null; 2708 } 2709 } 2710 2711 /** 2712 * Produces a method handle which creates an object and initializes it, using 2713 * the constructor of the specified type. 2714 * The parameter types of the method handle will be those of the constructor, 2715 * while the return type will be a reference to the constructor's class. 2716 * The constructor and all its argument types must be accessible to the lookup object. 2717 * <p> 2718 * The requested type must have a return type of {@code void}. 2719 * (This is consistent with the JVM's treatment of constructor type descriptors.) 2720 * <p> 2721 * The returned method handle will have 2722 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2723 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 2724 * <p> 2725 * If the returned method handle is invoked, the constructor's class will 2726 * be initialized, if it has not already been initialized. 2727 * <p><b>Example:</b> 2728 * {@snippet lang="java" : 2729 import static java.lang.invoke.MethodHandles.*; 2730 import static java.lang.invoke.MethodType.*; 2731 ... 2732 MethodHandle MH_newArrayList = publicLookup().findConstructor( 2733 ArrayList.class, methodType(void.class, Collection.class)); 2734 Collection orig = Arrays.asList("x", "y"); 2735 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig); 2736 assert(orig != copy); 2737 assertEquals(orig, copy); 2738 // a variable-arity constructor: 2739 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor( 2740 ProcessBuilder.class, methodType(void.class, String[].class)); 2741 ProcessBuilder pb = (ProcessBuilder) 2742 MH_newProcessBuilder.invoke("x", "y", "z"); 2743 assertEquals("[x, y, z]", pb.command().toString()); 2744 * } 2745 * 2746 * 2747 * @param refc the class or interface from which the method is accessed 2748 * @param type the type of the method, with the receiver argument omitted, and a void return type 2749 * @return the desired method handle 2750 * @throws NoSuchMethodException if the constructor does not exist 2751 * @throws IllegalAccessException if access checking fails 2752 * or if the method's variable arity modifier bit 2753 * is set and {@code asVarargsCollector} fails 2754 * @throws SecurityException if a security manager is present and it 2755 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2756 * @throws NullPointerException if any argument is null 2757 */ 2758 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException { 2759 if (refc.isArray()) { 2760 throw new NoSuchMethodException("no constructor for array class: " + refc.getName()); 2761 } 2762 if (type.returnType() != void.class) { 2763 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName()); 2764 } 2765 String name = "<init>"; 2766 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type); 2767 return getDirectConstructor(refc, ctor); 2768 } 2769 2770 /** 2771 * Looks up a class by name from the lookup context defined by this {@code Lookup} object, 2772 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction. 2773 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class, 2774 * and then determines whether the class is accessible to this lookup object. 2775 * <p> 2776 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, 2777 * its class loader, and the {@linkplain #lookupModes() lookup modes}. 2778 * 2779 * @param targetName the fully qualified name of the class to be looked up. 2780 * @return the requested class. 2781 * @throws SecurityException if a security manager is present and it 2782 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2783 * @throws LinkageError if the linkage fails 2784 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader. 2785 * @throws IllegalAccessException if the class is not accessible, using the allowed access 2786 * modes. 2787 * @throws NullPointerException if {@code targetName} is null 2788 * @since 9 2789 * @jvms 5.4.3.1 Class and Interface Resolution 2790 */ 2791 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException { 2792 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader()); 2793 return accessClass(targetClass); 2794 } 2795 2796 /** 2797 * Ensures that {@code targetClass} has been initialized. The class 2798 * to be initialized must be {@linkplain #accessClass accessible} 2799 * to this {@code Lookup} object. This method causes {@code targetClass} 2800 * to be initialized if it has not been already initialized, 2801 * as specified in JVMS {@jvms 5.5}. 2802 * 2803 * <p> 2804 * This method returns when {@code targetClass} is fully initialized, or 2805 * when {@code targetClass} is being initialized by the current thread. 2806 * 2807 * @param targetClass the class to be initialized 2808 * @return {@code targetClass} that has been initialized, or that is being 2809 * initialized by the current thread. 2810 * 2811 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void} 2812 * or array class 2813 * @throws IllegalAccessException if {@code targetClass} is not 2814 * {@linkplain #accessClass accessible} to this lookup 2815 * @throws ExceptionInInitializerError if the class initialization provoked 2816 * by this method fails 2817 * @throws SecurityException if a security manager is present and it 2818 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2819 * @since 15 2820 * @jvms 5.5 Initialization 2821 */ 2822 public Class<?> ensureInitialized(Class<?> targetClass) throws IllegalAccessException { 2823 if (targetClass.isPrimitive()) 2824 throw new IllegalArgumentException(targetClass + " is a primitive class"); 2825 if (targetClass.isArray()) 2826 throw new IllegalArgumentException(targetClass + " is an array class"); 2827 2828 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) { 2829 throw makeAccessException(targetClass); 2830 } 2831 checkSecurityManager(targetClass); 2832 2833 // ensure class initialization 2834 Unsafe.getUnsafe().ensureClassInitialized(targetClass); 2835 return targetClass; 2836 } 2837 2838 /* 2839 * Returns IllegalAccessException due to access violation to the given targetClass. 2840 * 2841 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized} 2842 * which verifies access to a class rather a member. 2843 */ 2844 private IllegalAccessException makeAccessException(Class<?> targetClass) { 2845 String message = "access violation: "+ targetClass; 2846 if (this == MethodHandles.publicLookup()) { 2847 message += ", from public Lookup"; 2848 } else { 2849 Module m = lookupClass().getModule(); 2850 message += ", from " + lookupClass() + " (" + m + ")"; 2851 if (prevLookupClass != null) { 2852 message += ", previous lookup " + 2853 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")"; 2854 } 2855 } 2856 return new IllegalAccessException(message); 2857 } 2858 2859 /** 2860 * Determines if a class can be accessed from the lookup context defined by 2861 * this {@code Lookup} object. The static initializer of the class is not run. 2862 * If {@code targetClass} is an array class, {@code targetClass} is accessible 2863 * if the element type of the array class is accessible. Otherwise, 2864 * {@code targetClass} is determined as accessible as follows. 2865 * 2866 * <p> 2867 * If {@code targetClass} is in the same module as the lookup class, 2868 * the lookup class is {@code LC} in module {@code M1} and 2869 * the previous lookup class is in module {@code M0} or 2870 * {@code null} if not present, 2871 * {@code targetClass} is accessible if and only if one of the following is true: 2872 * <ul> 2873 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is 2874 * {@code LC} or other class in the same nest of {@code LC}.</li> 2875 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is 2876 * in the same runtime package of {@code LC}.</li> 2877 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is 2878 * a public type in {@code M1}.</li> 2879 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is 2880 * a public type in a package exported by {@code M1} to at least {@code M0} 2881 * if the previous lookup class is present; otherwise, {@code targetClass} 2882 * is a public type in a package exported by {@code M1} unconditionally.</li> 2883 * </ul> 2884 * 2885 * <p> 2886 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup 2887 * can access public types in all modules when the type is in a package 2888 * that is exported unconditionally. 2889 * <p> 2890 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass}, 2891 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass} 2892 * is inaccessible. 2893 * <p> 2894 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class}, 2895 * {@code M1} is the module containing {@code lookupClass} and 2896 * {@code M2} is the module containing {@code targetClass}, 2897 * then {@code targetClass} is accessible if and only if 2898 * <ul> 2899 * <li>{@code M1} reads {@code M2}, and 2900 * <li>{@code targetClass} is public and in a package exported by 2901 * {@code M2} at least to {@code M1}. 2902 * </ul> 2903 * <p> 2904 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class}, 2905 * {@code M1} and {@code M2} are as before, and {@code M0} is the module 2906 * containing the previous lookup class, then {@code targetClass} is accessible 2907 * if and only if one of the following is true: 2908 * <ul> 2909 * <li>{@code targetClass} is in {@code M0} and {@code M1} 2910 * {@linkplain Module#reads reads} {@code M0} and the type is 2911 * in a package that is exported to at least {@code M1}. 2912 * <li>{@code targetClass} is in {@code M1} and {@code M0} 2913 * {@linkplain Module#reads reads} {@code M1} and the type is 2914 * in a package that is exported to at least {@code M0}. 2915 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0} 2916 * and {@code M1} reads {@code M2} and the type is in a package 2917 * that is exported to at least both {@code M0} and {@code M2}. 2918 * </ul> 2919 * <p> 2920 * Otherwise, {@code targetClass} is not accessible. 2921 * 2922 * @param targetClass the class to be access-checked 2923 * @return the class that has been access-checked 2924 * @throws IllegalAccessException if the class is not accessible from the lookup class 2925 * and previous lookup class, if present, using the allowed access modes. 2926 * @throws SecurityException if a security manager is present and it 2927 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 2928 * @throws NullPointerException if {@code targetClass} is {@code null} 2929 * @since 9 2930 * @see <a href="#cross-module-lookup">Cross-module lookups</a> 2931 */ 2932 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException { 2933 if (!isClassAccessible(targetClass)) { 2934 throw makeAccessException(targetClass); 2935 } 2936 checkSecurityManager(targetClass); 2937 return targetClass; 2938 } 2939 2940 /** 2941 * Produces an early-bound method handle for a virtual method. 2942 * It will bypass checks for overriding methods on the receiver, 2943 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 2944 * instruction from within the explicitly specified {@code specialCaller}. 2945 * The type of the method handle will be that of the method, 2946 * with a suitably restricted receiver type prepended. 2947 * (The receiver type will be {@code specialCaller} or a subtype.) 2948 * The method and all its argument types must be accessible 2949 * to the lookup object. 2950 * <p> 2951 * Before method resolution, 2952 * if the explicitly specified caller class is not identical with the 2953 * lookup class, or if this lookup object does not have 2954 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 2955 * privileges, the access fails. 2956 * <p> 2957 * The returned method handle will have 2958 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 2959 * the method's variable arity modifier bit ({@code 0x0080}) is set. 2960 * <p style="font-size:smaller;"> 2961 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API, 2962 * even though the {@code invokespecial} instruction can refer to them 2963 * in special circumstances. Use {@link #findConstructor findConstructor} 2964 * to access instance initialization methods in a safe manner.)</em> 2965 * <p><b>Example:</b> 2966 * {@snippet lang="java" : 2967 import static java.lang.invoke.MethodHandles.*; 2968 import static java.lang.invoke.MethodType.*; 2969 ... 2970 static class Listie extends ArrayList { 2971 public String toString() { return "[wee Listie]"; } 2972 static Lookup lookup() { return MethodHandles.lookup(); } 2973 } 2974 ... 2975 // no access to constructor via invokeSpecial: 2976 MethodHandle MH_newListie = Listie.lookup() 2977 .findConstructor(Listie.class, methodType(void.class)); 2978 Listie l = (Listie) MH_newListie.invokeExact(); 2979 try { assertEquals("impossible", Listie.lookup().findSpecial( 2980 Listie.class, "<init>", methodType(void.class), Listie.class)); 2981 } catch (NoSuchMethodException ex) { } // OK 2982 // access to super and self methods via invokeSpecial: 2983 MethodHandle MH_super = Listie.lookup().findSpecial( 2984 ArrayList.class, "toString" , methodType(String.class), Listie.class); 2985 MethodHandle MH_this = Listie.lookup().findSpecial( 2986 Listie.class, "toString" , methodType(String.class), Listie.class); 2987 MethodHandle MH_duper = Listie.lookup().findSpecial( 2988 Object.class, "toString" , methodType(String.class), Listie.class); 2989 assertEquals("[]", (String) MH_super.invokeExact(l)); 2990 assertEquals(""+l, (String) MH_this.invokeExact(l)); 2991 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method 2992 try { assertEquals("inaccessible", Listie.lookup().findSpecial( 2993 String.class, "toString", methodType(String.class), Listie.class)); 2994 } catch (IllegalAccessException ex) { } // OK 2995 Listie subl = new Listie() { public String toString() { return "[subclass]"; } }; 2996 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method 2997 * } 2998 * 2999 * @param refc the class or interface from which the method is accessed 3000 * @param name the name of the method (which must not be "<init>") 3001 * @param type the type of the method, with the receiver argument omitted 3002 * @param specialCaller the proposed calling class to perform the {@code invokespecial} 3003 * @return the desired method handle 3004 * @throws NoSuchMethodException if the method does not exist 3005 * @throws IllegalAccessException if access checking fails, 3006 * or if the method is {@code static}, 3007 * or if the method's variable arity modifier bit 3008 * is set and {@code asVarargsCollector} fails 3009 * @throws SecurityException if a security manager is present and it 3010 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3011 * @throws NullPointerException if any argument is null 3012 */ 3013 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type, 3014 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException { 3015 checkSpecialCaller(specialCaller, refc); 3016 Lookup specialLookup = this.in(specialCaller); 3017 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type); 3018 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method)); 3019 } 3020 3021 /** 3022 * Produces a method handle giving read access to a non-static field. 3023 * The type of the method handle will have a return type of the field's 3024 * value type. 3025 * The method handle's single argument will be the instance containing 3026 * the field. 3027 * Access checking is performed immediately on behalf of the lookup class. 3028 * @param refc the class or interface from which the method is accessed 3029 * @param name the field's name 3030 * @param type the field's type 3031 * @return a method handle which can load values from the field 3032 * @throws NoSuchFieldException if the field does not exist 3033 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3034 * @throws SecurityException if a security manager is present and it 3035 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3036 * @throws NullPointerException if any argument is null 3037 * @see #findVarHandle(Class, String, Class) 3038 */ 3039 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3040 MemberName field = resolveOrFail(REF_getField, refc, name, type); 3041 return getDirectField(REF_getField, refc, field); 3042 } 3043 3044 /** 3045 * Produces a method handle giving write access to a non-static field. 3046 * The type of the method handle will have a void return type. 3047 * The method handle will take two arguments, the instance containing 3048 * the field, and the value to be stored. 3049 * The second argument will be of the field's value type. 3050 * Access checking is performed immediately on behalf of the lookup class. 3051 * @param refc the class or interface from which the method is accessed 3052 * @param name the field's name 3053 * @param type the field's type 3054 * @return a method handle which can store values into the field 3055 * @throws NoSuchFieldException if the field does not exist 3056 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3057 * or {@code final} 3058 * @throws SecurityException if a security manager is present and it 3059 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3060 * @throws NullPointerException if any argument is null 3061 * @see #findVarHandle(Class, String, Class) 3062 */ 3063 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3064 MemberName field = resolveOrFail(REF_putField, refc, name, type); 3065 return getDirectField(REF_putField, refc, field); 3066 } 3067 3068 /** 3069 * Produces a VarHandle giving access to a non-static field {@code name} 3070 * of type {@code type} declared in a class of type {@code recv}. 3071 * The VarHandle's variable type is {@code type} and it has one 3072 * coordinate type, {@code recv}. 3073 * <p> 3074 * Access checking is performed immediately on behalf of the lookup 3075 * class. 3076 * <p> 3077 * Certain access modes of the returned VarHandle are unsupported under 3078 * the following conditions: 3079 * <ul> 3080 * <li>if the field is declared {@code final}, then the write, atomic 3081 * update, numeric atomic update, and bitwise atomic update access 3082 * modes are unsupported. 3083 * <li>if the field type is anything other than {@code byte}, 3084 * {@code short}, {@code char}, {@code int}, {@code long}, 3085 * {@code float}, or {@code double} then numeric atomic update 3086 * access modes are unsupported. 3087 * <li>if the field type is anything other than {@code boolean}, 3088 * {@code byte}, {@code short}, {@code char}, {@code int} or 3089 * {@code long} then bitwise atomic update access modes are 3090 * unsupported. 3091 * </ul> 3092 * <p> 3093 * If the field is declared {@code volatile} then the returned VarHandle 3094 * will override access to the field (effectively ignore the 3095 * {@code volatile} declaration) in accordance to its specified 3096 * access modes. 3097 * <p> 3098 * If the field type is {@code float} or {@code double} then numeric 3099 * and atomic update access modes compare values using their bitwise 3100 * representation (see {@link Float#floatToRawIntBits} and 3101 * {@link Double#doubleToRawLongBits}, respectively). 3102 * @apiNote 3103 * Bitwise comparison of {@code float} values or {@code double} values, 3104 * as performed by the numeric and atomic update access modes, differ 3105 * from the primitive {@code ==} operator and the {@link Float#equals} 3106 * and {@link Double#equals} methods, specifically with respect to 3107 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3108 * Care should be taken when performing a compare and set or a compare 3109 * and exchange operation with such values since the operation may 3110 * unexpectedly fail. 3111 * There are many possible NaN values that are considered to be 3112 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3113 * provided by Java can distinguish between them. Operation failure can 3114 * occur if the expected or witness value is a NaN value and it is 3115 * transformed (perhaps in a platform specific manner) into another NaN 3116 * value, and thus has a different bitwise representation (see 3117 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3118 * details). 3119 * The values {@code -0.0} and {@code +0.0} have different bitwise 3120 * representations but are considered equal when using the primitive 3121 * {@code ==} operator. Operation failure can occur if, for example, a 3122 * numeric algorithm computes an expected value to be say {@code -0.0} 3123 * and previously computed the witness value to be say {@code +0.0}. 3124 * @param recv the receiver class, of type {@code R}, that declares the 3125 * non-static field 3126 * @param name the field's name 3127 * @param type the field's type, of type {@code T} 3128 * @return a VarHandle giving access to non-static fields. 3129 * @throws NoSuchFieldException if the field does not exist 3130 * @throws IllegalAccessException if access checking fails, or if the field is {@code static} 3131 * @throws SecurityException if a security manager is present and it 3132 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3133 * @throws NullPointerException if any argument is null 3134 * @since 9 3135 */ 3136 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3137 MemberName getField = resolveOrFail(REF_getField, recv, name, type); 3138 MemberName putField = resolveOrFail(REF_putField, recv, name, type); 3139 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField); 3140 } 3141 3142 /** 3143 * Produces a method handle giving read access to a static field. 3144 * The type of the method handle will have a return type of the field's 3145 * value type. 3146 * The method handle will take no arguments. 3147 * Access checking is performed immediately on behalf of the lookup class. 3148 * <p> 3149 * If the returned method handle is invoked, the field's class will 3150 * be initialized, if it has not already been initialized. 3151 * @param refc the class or interface from which the method is accessed 3152 * @param name the field's name 3153 * @param type the field's type 3154 * @return a method handle which can load values from the field 3155 * @throws NoSuchFieldException if the field does not exist 3156 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3157 * @throws SecurityException if a security manager is present and it 3158 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3159 * @throws NullPointerException if any argument is null 3160 */ 3161 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3162 MemberName field = resolveOrFail(REF_getStatic, refc, name, type); 3163 return getDirectField(REF_getStatic, refc, field); 3164 } 3165 3166 /** 3167 * Produces a method handle giving write access to a static field. 3168 * The type of the method handle will have a void return type. 3169 * The method handle will take a single 3170 * argument, of the field's value type, the value to be stored. 3171 * Access checking is performed immediately on behalf of the lookup class. 3172 * <p> 3173 * If the returned method handle is invoked, the field's class will 3174 * be initialized, if it has not already been initialized. 3175 * @param refc the class or interface from which the method is accessed 3176 * @param name the field's name 3177 * @param type the field's type 3178 * @return a method handle which can store values into the field 3179 * @throws NoSuchFieldException if the field does not exist 3180 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3181 * or is {@code final} 3182 * @throws SecurityException if a security manager is present and it 3183 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3184 * @throws NullPointerException if any argument is null 3185 */ 3186 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3187 MemberName field = resolveOrFail(REF_putStatic, refc, name, type); 3188 return getDirectField(REF_putStatic, refc, field); 3189 } 3190 3191 /** 3192 * Produces a VarHandle giving access to a static field {@code name} of 3193 * type {@code type} declared in a class of type {@code decl}. 3194 * The VarHandle's variable type is {@code type} and it has no 3195 * coordinate types. 3196 * <p> 3197 * Access checking is performed immediately on behalf of the lookup 3198 * class. 3199 * <p> 3200 * If the returned VarHandle is operated on, the declaring class will be 3201 * initialized, if it has not already been initialized. 3202 * <p> 3203 * Certain access modes of the returned VarHandle are unsupported under 3204 * the following conditions: 3205 * <ul> 3206 * <li>if the field is declared {@code final}, then the write, atomic 3207 * update, numeric atomic update, and bitwise atomic update access 3208 * modes are unsupported. 3209 * <li>if the field type is anything other than {@code byte}, 3210 * {@code short}, {@code char}, {@code int}, {@code long}, 3211 * {@code float}, or {@code double}, then numeric atomic update 3212 * access modes are unsupported. 3213 * <li>if the field type is anything other than {@code boolean}, 3214 * {@code byte}, {@code short}, {@code char}, {@code int} or 3215 * {@code long} then bitwise atomic update access modes are 3216 * unsupported. 3217 * </ul> 3218 * <p> 3219 * If the field is declared {@code volatile} then the returned VarHandle 3220 * will override access to the field (effectively ignore the 3221 * {@code volatile} declaration) in accordance to its specified 3222 * access modes. 3223 * <p> 3224 * If the field type is {@code float} or {@code double} then numeric 3225 * and atomic update access modes compare values using their bitwise 3226 * representation (see {@link Float#floatToRawIntBits} and 3227 * {@link Double#doubleToRawLongBits}, respectively). 3228 * @apiNote 3229 * Bitwise comparison of {@code float} values or {@code double} values, 3230 * as performed by the numeric and atomic update access modes, differ 3231 * from the primitive {@code ==} operator and the {@link Float#equals} 3232 * and {@link Double#equals} methods, specifically with respect to 3233 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3234 * Care should be taken when performing a compare and set or a compare 3235 * and exchange operation with such values since the operation may 3236 * unexpectedly fail. 3237 * There are many possible NaN values that are considered to be 3238 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3239 * provided by Java can distinguish between them. Operation failure can 3240 * occur if the expected or witness value is a NaN value and it is 3241 * transformed (perhaps in a platform specific manner) into another NaN 3242 * value, and thus has a different bitwise representation (see 3243 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3244 * details). 3245 * The values {@code -0.0} and {@code +0.0} have different bitwise 3246 * representations but are considered equal when using the primitive 3247 * {@code ==} operator. Operation failure can occur if, for example, a 3248 * numeric algorithm computes an expected value to be say {@code -0.0} 3249 * and previously computed the witness value to be say {@code +0.0}. 3250 * @param decl the class that declares the static field 3251 * @param name the field's name 3252 * @param type the field's type, of type {@code T} 3253 * @return a VarHandle giving access to a static field 3254 * @throws NoSuchFieldException if the field does not exist 3255 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} 3256 * @throws SecurityException if a security manager is present and it 3257 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3258 * @throws NullPointerException if any argument is null 3259 * @since 9 3260 */ 3261 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3262 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type); 3263 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type); 3264 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField); 3265 } 3266 3267 /** 3268 * Produces an early-bound method handle for a non-static method. 3269 * The receiver must have a supertype {@code defc} in which a method 3270 * of the given name and type is accessible to the lookup class. 3271 * The method and all its argument types must be accessible to the lookup object. 3272 * The type of the method handle will be that of the method, 3273 * without any insertion of an additional receiver parameter. 3274 * The given receiver will be bound into the method handle, 3275 * so that every call to the method handle will invoke the 3276 * requested method on the given receiver. 3277 * <p> 3278 * The returned method handle will have 3279 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3280 * the method's variable arity modifier bit ({@code 0x0080}) is set 3281 * <em>and</em> the trailing array argument is not the only argument. 3282 * (If the trailing array argument is the only argument, 3283 * the given receiver value will be bound to it.) 3284 * <p> 3285 * This is almost equivalent to the following code, with some differences noted below: 3286 * {@snippet lang="java" : 3287 import static java.lang.invoke.MethodHandles.*; 3288 import static java.lang.invoke.MethodType.*; 3289 ... 3290 MethodHandle mh0 = lookup().findVirtual(defc, name, type); 3291 MethodHandle mh1 = mh0.bindTo(receiver); 3292 mh1 = mh1.withVarargs(mh0.isVarargsCollector()); 3293 return mh1; 3294 * } 3295 * where {@code defc} is either {@code receiver.getClass()} or a super 3296 * type of that class, in which the requested method is accessible 3297 * to the lookup class. 3298 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity. 3299 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would 3300 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and 3301 * the receiver is restricted by {@code findVirtual} to the lookup class.) 3302 * @param receiver the object from which the method is accessed 3303 * @param name the name of the method 3304 * @param type the type of the method, with the receiver argument omitted 3305 * @return the desired method handle 3306 * @throws NoSuchMethodException if the method does not exist 3307 * @throws IllegalAccessException if access checking fails 3308 * or if the method's variable arity modifier bit 3309 * is set and {@code asVarargsCollector} fails 3310 * @throws SecurityException if a security manager is present and it 3311 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3312 * @throws NullPointerException if any argument is null 3313 * @see MethodHandle#bindTo 3314 * @see #findVirtual 3315 */ 3316 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 3317 Class<? extends Object> refc = receiver.getClass(); // may get NPE 3318 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type); 3319 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method)); 3320 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) { 3321 throw new IllegalAccessException("The restricted defining class " + 3322 mh.type().leadingReferenceParameter().getName() + 3323 " is not assignable from receiver class " + 3324 receiver.getClass().getName()); 3325 } 3326 return mh.bindArgumentL(0, receiver).setVarargs(method); 3327 } 3328 3329 /** 3330 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 3331 * to <i>m</i>, if the lookup class has permission. 3332 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument. 3333 * If <i>m</i> is virtual, overriding is respected on every call. 3334 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped. 3335 * The type of the method handle will be that of the method, 3336 * with the receiver type prepended (but only if it is non-static). 3337 * If the method's {@code accessible} flag is not set, 3338 * access checking is performed immediately on behalf of the lookup class. 3339 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties. 3340 * <p> 3341 * The returned method handle will have 3342 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3343 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3344 * <p> 3345 * If <i>m</i> is static, and 3346 * if the returned method handle is invoked, the method's class will 3347 * be initialized, if it has not already been initialized. 3348 * @param m the reflected method 3349 * @return a method handle which can invoke the reflected method 3350 * @throws IllegalAccessException if access checking fails 3351 * or if the method's variable arity modifier bit 3352 * is set and {@code asVarargsCollector} fails 3353 * @throws NullPointerException if the argument is null 3354 */ 3355 public MethodHandle unreflect(Method m) throws IllegalAccessException { 3356 if (m.getDeclaringClass() == MethodHandle.class) { 3357 MethodHandle mh = unreflectForMH(m); 3358 if (mh != null) return mh; 3359 } 3360 if (m.getDeclaringClass() == VarHandle.class) { 3361 MethodHandle mh = unreflectForVH(m); 3362 if (mh != null) return mh; 3363 } 3364 MemberName method = new MemberName(m); 3365 byte refKind = method.getReferenceKind(); 3366 if (refKind == REF_invokeSpecial) 3367 refKind = REF_invokeVirtual; 3368 assert(method.isMethod()); 3369 @SuppressWarnings("deprecation") 3370 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this; 3371 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method)); 3372 } 3373 private MethodHandle unreflectForMH(Method m) { 3374 // these names require special lookups because they throw UnsupportedOperationException 3375 if (MemberName.isMethodHandleInvokeName(m.getName())) 3376 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m)); 3377 return null; 3378 } 3379 private MethodHandle unreflectForVH(Method m) { 3380 // these names require special lookups because they throw UnsupportedOperationException 3381 if (MemberName.isVarHandleMethodInvokeName(m.getName())) 3382 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m)); 3383 return null; 3384 } 3385 3386 /** 3387 * Produces a method handle for a reflected method. 3388 * It will bypass checks for overriding methods on the receiver, 3389 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial} 3390 * instruction from within the explicitly specified {@code specialCaller}. 3391 * The type of the method handle will be that of the method, 3392 * with a suitably restricted receiver type prepended. 3393 * (The receiver type will be {@code specialCaller} or a subtype.) 3394 * If the method's {@code accessible} flag is not set, 3395 * access checking is performed immediately on behalf of the lookup class, 3396 * as if {@code invokespecial} instruction were being linked. 3397 * <p> 3398 * Before method resolution, 3399 * if the explicitly specified caller class is not identical with the 3400 * lookup class, or if this lookup object does not have 3401 * <a href="MethodHandles.Lookup.html#privacc">private access</a> 3402 * privileges, the access fails. 3403 * <p> 3404 * The returned method handle will have 3405 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3406 * the method's variable arity modifier bit ({@code 0x0080}) is set. 3407 * @param m the reflected method 3408 * @param specialCaller the class nominally calling the method 3409 * @return a method handle which can invoke the reflected method 3410 * @throws IllegalAccessException if access checking fails, 3411 * or if the method is {@code static}, 3412 * or if the method's variable arity modifier bit 3413 * is set and {@code asVarargsCollector} fails 3414 * @throws NullPointerException if any argument is null 3415 */ 3416 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException { 3417 checkSpecialCaller(specialCaller, m.getDeclaringClass()); 3418 Lookup specialLookup = this.in(specialCaller); 3419 MemberName method = new MemberName(m, true); 3420 assert(method.isMethod()); 3421 // ignore m.isAccessible: this is a new kind of access 3422 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method)); 3423 } 3424 3425 /** 3426 * Produces a method handle for a reflected constructor. 3427 * The type of the method handle will be that of the constructor, 3428 * with the return type changed to the declaring class. 3429 * The method handle will perform a {@code newInstance} operation, 3430 * creating a new instance of the constructor's class on the 3431 * arguments passed to the method handle. 3432 * <p> 3433 * If the constructor's {@code accessible} flag is not set, 3434 * access checking is performed immediately on behalf of the lookup class. 3435 * <p> 3436 * The returned method handle will have 3437 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if 3438 * the constructor's variable arity modifier bit ({@code 0x0080}) is set. 3439 * <p> 3440 * If the returned method handle is invoked, the constructor's class will 3441 * be initialized, if it has not already been initialized. 3442 * @param c the reflected constructor 3443 * @return a method handle which can invoke the reflected constructor 3444 * @throws IllegalAccessException if access checking fails 3445 * or if the method's variable arity modifier bit 3446 * is set and {@code asVarargsCollector} fails 3447 * @throws NullPointerException if the argument is null 3448 */ 3449 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException { 3450 MemberName ctor = new MemberName(c); 3451 assert(ctor.isObjectConstructor() || ctor.isStaticValueFactoryMethod()); 3452 @SuppressWarnings("deprecation") 3453 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this; 3454 Class<?> defc = c.getDeclaringClass(); 3455 if (ctor.isObjectConstructor()) { 3456 assert(ctor.getMethodType().returnType() == void.class); 3457 return lookup.getDirectConstructorNoSecurityManager(defc, ctor); 3458 } else { 3459 // static init factory is a static method 3460 assert(ctor.isMethod() && ctor.getMethodType().returnType() == defc && ctor.getReferenceKind() == REF_invokeStatic) : ctor.toString(); 3461 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // must not be caller-sensitive 3462 return lookup.getDirectMethodNoSecurityManager(ctor.getReferenceKind(), defc, ctor, lookup); 3463 } 3464 } 3465 3466 /** 3467 * Produces a method handle giving read access to a reflected field. 3468 * The type of the method handle will have a return type of the field's 3469 * value type. 3470 * If the field is {@code static}, the method handle will take no arguments. 3471 * Otherwise, its single argument will be the instance containing 3472 * the field. 3473 * If the {@code Field} object's {@code accessible} flag is not set, 3474 * access checking is performed immediately on behalf of the lookup class. 3475 * <p> 3476 * If the field is static, and 3477 * if the returned method handle is invoked, the field's class will 3478 * be initialized, if it has not already been initialized. 3479 * @param f the reflected field 3480 * @return a method handle which can load values from the reflected field 3481 * @throws IllegalAccessException if access checking fails 3482 * @throws NullPointerException if the argument is null 3483 */ 3484 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException { 3485 return unreflectField(f, false); 3486 } 3487 3488 /** 3489 * Produces a method handle giving write access to a reflected field. 3490 * The type of the method handle will have a void return type. 3491 * If the field is {@code static}, the method handle will take a single 3492 * argument, of the field's value type, the value to be stored. 3493 * Otherwise, the two arguments will be the instance containing 3494 * the field, and the value to be stored. 3495 * If the {@code Field} object's {@code accessible} flag is not set, 3496 * access checking is performed immediately on behalf of the lookup class. 3497 * <p> 3498 * If the field is {@code final}, write access will not be 3499 * allowed and access checking will fail, except under certain 3500 * narrow circumstances documented for {@link Field#set Field.set}. 3501 * A method handle is returned only if a corresponding call to 3502 * the {@code Field} object's {@code set} method could return 3503 * normally. In particular, fields which are both {@code static} 3504 * and {@code final} may never be set. 3505 * <p> 3506 * If the field is {@code static}, and 3507 * if the returned method handle is invoked, the field's class will 3508 * be initialized, if it has not already been initialized. 3509 * @param f the reflected field 3510 * @return a method handle which can store values into the reflected field 3511 * @throws IllegalAccessException if access checking fails, 3512 * or if the field is {@code final} and write access 3513 * is not enabled on the {@code Field} object 3514 * @throws NullPointerException if the argument is null 3515 */ 3516 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException { 3517 return unreflectField(f, true); 3518 } 3519 3520 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException { 3521 MemberName field = new MemberName(f, isSetter); 3522 if (isSetter && field.isFinal()) { 3523 if (field.isTrustedFinalField()) { 3524 String msg = field.isStatic() ? "static final field has no write access" 3525 : "final field has no write access"; 3526 throw field.makeAccessException(msg, this); 3527 } 3528 } 3529 assert(isSetter 3530 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind()) 3531 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind())); 3532 @SuppressWarnings("deprecation") 3533 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this; 3534 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field); 3535 } 3536 3537 /** 3538 * Produces a VarHandle giving access to a reflected field {@code f} 3539 * of type {@code T} declared in a class of type {@code R}. 3540 * The VarHandle's variable type is {@code T}. 3541 * If the field is non-static the VarHandle has one coordinate type, 3542 * {@code R}. Otherwise, the field is static, and the VarHandle has no 3543 * coordinate types. 3544 * <p> 3545 * Access checking is performed immediately on behalf of the lookup 3546 * class, regardless of the value of the field's {@code accessible} 3547 * flag. 3548 * <p> 3549 * If the field is static, and if the returned VarHandle is operated 3550 * on, the field's declaring class will be initialized, if it has not 3551 * already been initialized. 3552 * <p> 3553 * Certain access modes of the returned VarHandle are unsupported under 3554 * the following conditions: 3555 * <ul> 3556 * <li>if the field is declared {@code final}, then the write, atomic 3557 * update, numeric atomic update, and bitwise atomic update access 3558 * modes are unsupported. 3559 * <li>if the field type is anything other than {@code byte}, 3560 * {@code short}, {@code char}, {@code int}, {@code long}, 3561 * {@code float}, or {@code double} then numeric atomic update 3562 * access modes are unsupported. 3563 * <li>if the field type is anything other than {@code boolean}, 3564 * {@code byte}, {@code short}, {@code char}, {@code int} or 3565 * {@code long} then bitwise atomic update access modes are 3566 * unsupported. 3567 * </ul> 3568 * <p> 3569 * If the field is declared {@code volatile} then the returned VarHandle 3570 * will override access to the field (effectively ignore the 3571 * {@code volatile} declaration) in accordance to its specified 3572 * access modes. 3573 * <p> 3574 * If the field type is {@code float} or {@code double} then numeric 3575 * and atomic update access modes compare values using their bitwise 3576 * representation (see {@link Float#floatToRawIntBits} and 3577 * {@link Double#doubleToRawLongBits}, respectively). 3578 * @apiNote 3579 * Bitwise comparison of {@code float} values or {@code double} values, 3580 * as performed by the numeric and atomic update access modes, differ 3581 * from the primitive {@code ==} operator and the {@link Float#equals} 3582 * and {@link Double#equals} methods, specifically with respect to 3583 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 3584 * Care should be taken when performing a compare and set or a compare 3585 * and exchange operation with such values since the operation may 3586 * unexpectedly fail. 3587 * There are many possible NaN values that are considered to be 3588 * {@code NaN} in Java, although no IEEE 754 floating-point operation 3589 * provided by Java can distinguish between them. Operation failure can 3590 * occur if the expected or witness value is a NaN value and it is 3591 * transformed (perhaps in a platform specific manner) into another NaN 3592 * value, and thus has a different bitwise representation (see 3593 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 3594 * details). 3595 * The values {@code -0.0} and {@code +0.0} have different bitwise 3596 * representations but are considered equal when using the primitive 3597 * {@code ==} operator. Operation failure can occur if, for example, a 3598 * numeric algorithm computes an expected value to be say {@code -0.0} 3599 * and previously computed the witness value to be say {@code +0.0}. 3600 * @param f the reflected field, with a field of type {@code T}, and 3601 * a declaring class of type {@code R} 3602 * @return a VarHandle giving access to non-static fields or a static 3603 * field 3604 * @throws IllegalAccessException if access checking fails 3605 * @throws NullPointerException if the argument is null 3606 * @since 9 3607 */ 3608 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException { 3609 MemberName getField = new MemberName(f, false); 3610 MemberName putField = new MemberName(f, true); 3611 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(), 3612 f.getDeclaringClass(), getField, putField); 3613 } 3614 3615 /** 3616 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a> 3617 * created by this lookup object or a similar one. 3618 * Security and access checks are performed to ensure that this lookup object 3619 * is capable of reproducing the target method handle. 3620 * This means that the cracking may fail if target is a direct method handle 3621 * but was created by an unrelated lookup object. 3622 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> 3623 * and was created by a lookup object for a different class. 3624 * @param target a direct method handle to crack into symbolic reference components 3625 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object 3626 * @throws SecurityException if a security manager is present and it 3627 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a> 3628 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails 3629 * @throws NullPointerException if the target is {@code null} 3630 * @see MethodHandleInfo 3631 * @since 1.8 3632 */ 3633 public MethodHandleInfo revealDirect(MethodHandle target) { 3634 if (!target.isCrackable()) { 3635 throw newIllegalArgumentException("not a direct method handle"); 3636 } 3637 MemberName member = target.internalMemberName(); 3638 Class<?> defc = member.getDeclaringClass(); 3639 byte refKind = member.getReferenceKind(); 3640 assert(MethodHandleNatives.refKindIsValid(refKind)); 3641 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial()) 3642 // Devirtualized method invocation is usually formally virtual. 3643 // To avoid creating extra MemberName objects for this common case, 3644 // we encode this extra degree of freedom using MH.isInvokeSpecial. 3645 refKind = REF_invokeVirtual; 3646 if (refKind == REF_invokeVirtual && defc.isInterface()) 3647 // Symbolic reference is through interface but resolves to Object method (toString, etc.) 3648 refKind = REF_invokeInterface; 3649 // Check SM permissions and member access before cracking. 3650 try { 3651 checkAccess(refKind, defc, member); 3652 checkSecurityManager(defc, member); 3653 } catch (IllegalAccessException ex) { 3654 throw new IllegalArgumentException(ex); 3655 } 3656 if (allowedModes != TRUSTED && member.isCallerSensitive()) { 3657 Class<?> callerClass = target.internalCallerClass(); 3658 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass()) 3659 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass); 3660 } 3661 // Produce the handle to the results. 3662 return new InfoFromMemberName(this, member, refKind); 3663 } 3664 3665 /// Helper methods, all package-private. 3666 3667 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException { 3668 checkSymbolicClass(refc); // do this before attempting to resolve 3669 Objects.requireNonNull(name); 3670 Objects.requireNonNull(type); 3671 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes, 3672 NoSuchFieldException.class); 3673 } 3674 3675 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { 3676 checkSymbolicClass(refc); // do this before attempting to resolve 3677 Objects.requireNonNull(type); 3678 checkMethodName(refKind, name); // implicit null-check of name 3679 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes, 3680 NoSuchMethodException.class); 3681 } 3682 3683 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException { 3684 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve 3685 Objects.requireNonNull(member.getName()); 3686 Objects.requireNonNull(member.getType()); 3687 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes, 3688 ReflectiveOperationException.class); 3689 } 3690 3691 MemberName resolveOrNull(byte refKind, MemberName member) { 3692 // do this before attempting to resolve 3693 if (!isClassAccessible(member.getDeclaringClass())) { 3694 return null; 3695 } 3696 Objects.requireNonNull(member.getName()); 3697 Objects.requireNonNull(member.getType()); 3698 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes); 3699 } 3700 3701 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) { 3702 // do this before attempting to resolve 3703 if (!isClassAccessible(refc)) { 3704 return null; 3705 } 3706 Objects.requireNonNull(type); 3707 // implicit null-check of name 3708 if (isIllegalMethodName(refKind, name)) { 3709 return null; 3710 } 3711 3712 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes); 3713 } 3714 3715 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException { 3716 if (!isClassAccessible(refc)) { 3717 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this); 3718 } 3719 } 3720 3721 boolean isClassAccessible(Class<?> refc) { 3722 Objects.requireNonNull(refc); 3723 Class<?> caller = lookupClassOrNull(); 3724 Class<?> type = refc; 3725 while (type.isArray()) { 3726 type = type.getComponentType(); 3727 } 3728 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes); 3729 } 3730 3731 /* 3732 * "<init>" can only be invoked via invokespecial 3733 * "<vnew>" factory can only invoked via invokestatic 3734 */ 3735 boolean isIllegalMethodName(byte refKind, String name) { 3736 if (name.startsWith("<")) { 3737 return MemberName.VALUE_FACTORY_NAME.equals(name) ? refKind != REF_invokeStatic 3738 : refKind != REF_newInvokeSpecial; 3739 } 3740 return false; 3741 } 3742 3743 /** Check name for an illegal leading "<" character. */ 3744 void checkMethodName(byte refKind, String name) throws NoSuchMethodException { 3745 if (isIllegalMethodName(refKind, name)) { 3746 throw new NoSuchMethodException("illegal method name: " + name + " " + refKind); 3747 } 3748 } 3749 3750 /** 3751 * Find my trustable caller class if m is a caller sensitive method. 3752 * If this lookup object has original full privilege access, then the caller class is the lookupClass. 3753 * Otherwise, if m is caller-sensitive, throw IllegalAccessException. 3754 */ 3755 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException { 3756 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) { 3757 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods 3758 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 3759 } 3760 return this; 3761 } 3762 3763 /** 3764 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access. 3765 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access. 3766 * 3767 * @deprecated This method was originally designed to test {@code PRIVATE} access 3768 * that implies full privilege access but {@code MODULE} access has since become 3769 * independent of {@code PRIVATE} access. It is recommended to call 3770 * {@link #hasFullPrivilegeAccess()} instead. 3771 * @since 9 3772 */ 3773 @Deprecated(since="14") 3774 public boolean hasPrivateAccess() { 3775 return hasFullPrivilegeAccess(); 3776 } 3777 3778 /** 3779 * Returns {@code true} if this lookup has <em>full privilege access</em>, 3780 * i.e. {@code PRIVATE} and {@code MODULE} access. 3781 * A {@code Lookup} object must have full privilege access in order to 3782 * access all members that are allowed to the 3783 * {@linkplain #lookupClass() lookup class}. 3784 * 3785 * @return {@code true} if this lookup has full privilege access. 3786 * @since 14 3787 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a> 3788 */ 3789 public boolean hasFullPrivilegeAccess() { 3790 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE); 3791 } 3792 3793 /** 3794 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a> 3795 * for ensureInitialzed, findClass or accessClass. 3796 */ 3797 void checkSecurityManager(Class<?> refc) { 3798 if (allowedModes == TRUSTED) return; 3799 3800 @SuppressWarnings("removal") 3801 SecurityManager smgr = System.getSecurityManager(); 3802 if (smgr == null) return; 3803 3804 // Step 1: 3805 boolean fullPrivilegeLookup = hasFullPrivilegeAccess(); 3806 if (!fullPrivilegeLookup || 3807 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 3808 ReflectUtil.checkPackageAccess(refc); 3809 } 3810 3811 // Step 2b: 3812 if (!fullPrivilegeLookup) { 3813 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION); 3814 } 3815 } 3816 3817 /** 3818 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>. 3819 * Determines a trustable caller class to compare with refc, the symbolic reference class. 3820 * If this lookup object has full privilege access except original access, 3821 * then the caller class is the lookupClass. 3822 * 3823 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)} 3824 * from the same module skips the security permission check. 3825 */ 3826 void checkSecurityManager(Class<?> refc, MemberName m) { 3827 Objects.requireNonNull(refc); 3828 Objects.requireNonNull(m); 3829 3830 if (allowedModes == TRUSTED) return; 3831 3832 @SuppressWarnings("removal") 3833 SecurityManager smgr = System.getSecurityManager(); 3834 if (smgr == null) return; 3835 3836 // Step 1: 3837 boolean fullPrivilegeLookup = hasFullPrivilegeAccess(); 3838 if (!fullPrivilegeLookup || 3839 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { 3840 ReflectUtil.checkPackageAccess(refc); 3841 } 3842 3843 // Step 2a: 3844 if (m.isPublic()) return; 3845 if (!fullPrivilegeLookup) { 3846 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION); 3847 } 3848 3849 // Step 3: 3850 Class<?> defc = m.getDeclaringClass(); 3851 if (!fullPrivilegeLookup && PrimitiveClass.asPrimaryType(defc) != PrimitiveClass.asPrimaryType(refc)) { 3852 ReflectUtil.checkPackageAccess(defc); 3853 } 3854 } 3855 3856 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3857 boolean wantStatic = (refKind == REF_invokeStatic); 3858 String message; 3859 if (m.isObjectConstructor()) 3860 message = "expected a method, not a constructor"; 3861 else if (!m.isMethod()) 3862 message = "expected a method"; 3863 else if (wantStatic != m.isStatic()) 3864 message = wantStatic ? "expected a static method" : "expected a non-static method"; 3865 else 3866 { checkAccess(refKind, refc, m); return; } 3867 throw m.makeAccessException(message, this); 3868 } 3869 3870 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3871 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind); 3872 String message; 3873 if (wantStatic != m.isStatic()) 3874 message = wantStatic ? "expected a static field" : "expected a non-static field"; 3875 else 3876 { checkAccess(refKind, refc, m); return; } 3877 throw m.makeAccessException(message, this); 3878 } 3879 3880 /** Check public/protected/private bits on the symbolic reference class and its member. */ 3881 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException { 3882 assert(m.referenceKindIsConsistentWith(refKind) && 3883 MethodHandleNatives.refKindIsValid(refKind) && 3884 (MethodHandleNatives.refKindIsField(refKind) == m.isField())); 3885 int allowedModes = this.allowedModes; 3886 if (allowedModes == TRUSTED) return; 3887 int mods = m.getModifiers(); 3888 if (Modifier.isProtected(mods) && 3889 refKind == REF_invokeVirtual && 3890 m.getDeclaringClass() == Object.class && 3891 m.getName().equals("clone") && 3892 refc.isArray()) { 3893 // The JVM does this hack also. 3894 // (See ClassVerifier::verify_invoke_instructions 3895 // and LinkResolver::check_method_accessability.) 3896 // Because the JVM does not allow separate methods on array types, 3897 // there is no separate method for int[].clone. 3898 // All arrays simply inherit Object.clone. 3899 // But for access checking logic, we make Object.clone 3900 // (normally protected) appear to be public. 3901 // Later on, when the DirectMethodHandle is created, 3902 // its leading argument will be restricted to the 3903 // requested array type. 3904 // N.B. The return type is not adjusted, because 3905 // that is *not* the bytecode behavior. 3906 mods ^= Modifier.PROTECTED | Modifier.PUBLIC; 3907 } 3908 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) { 3909 // cannot "new" a protected ctor in a different package 3910 mods ^= Modifier.PROTECTED; 3911 } 3912 if (Modifier.isFinal(mods) && 3913 MethodHandleNatives.refKindIsSetter(refKind)) 3914 throw m.makeAccessException("unexpected set of a final field", this); 3915 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE 3916 if ((requestedModes & allowedModes) != 0) { 3917 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(), 3918 mods, lookupClass(), previousLookupClass(), allowedModes)) 3919 return; 3920 } else { 3921 // Protected members can also be checked as if they were package-private. 3922 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0 3923 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass())) 3924 return; 3925 } 3926 throw m.makeAccessException(accessFailedMessage(refc, m), this); 3927 } 3928 3929 String accessFailedMessage(Class<?> refc, MemberName m) { 3930 Class<?> defc = m.getDeclaringClass(); 3931 int mods = m.getModifiers(); 3932 // check the class first: 3933 boolean classOK = (Modifier.isPublic(defc.getModifiers()) && 3934 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) || 3935 Modifier.isPublic(refc.getModifiers()))); 3936 if (!classOK && (allowedModes & PACKAGE) != 0) { 3937 // ignore previous lookup class to check if default package access 3938 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) && 3939 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) || 3940 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES))); 3941 } 3942 if (!classOK) 3943 return "class is not public"; 3944 if (Modifier.isPublic(mods)) 3945 return "access to public member failed"; // (how?, module not readable?) 3946 if (Modifier.isPrivate(mods)) 3947 return "member is private"; 3948 if (Modifier.isProtected(mods)) 3949 return "member is protected"; 3950 return "member is private to package"; 3951 } 3952 3953 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException { 3954 int allowedModes = this.allowedModes; 3955 if (allowedModes == TRUSTED) return; 3956 if ((lookupModes() & PRIVATE) == 0 3957 || (specialCaller != lookupClass() 3958 // ensure non-abstract methods in superinterfaces can be special-invoked 3959 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller)))) 3960 throw new MemberName(specialCaller). 3961 makeAccessException("no private access for invokespecial", this); 3962 } 3963 3964 private boolean restrictProtectedReceiver(MemberName method) { 3965 // The accessing class only has the right to use a protected member 3966 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc. 3967 if (!method.isProtected() || method.isStatic() 3968 || allowedModes == TRUSTED 3969 || method.getDeclaringClass() == lookupClass() 3970 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())) 3971 return false; 3972 return true; 3973 } 3974 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException { 3975 assert(!method.isStatic()); 3976 // receiver type of mh is too wide; narrow to caller 3977 if (!method.getDeclaringClass().isAssignableFrom(caller)) { 3978 throw method.makeAccessException("caller class must be a subclass below the method", caller); 3979 } 3980 MethodType rawType = mh.type(); 3981 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow 3982 MethodType narrowType = rawType.changeParameterType(0, caller); 3983 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness 3984 assert(mh.viewAsTypeChecks(narrowType, true)); 3985 return mh.copyWith(narrowType, mh.form); 3986 } 3987 3988 /** Check access and get the requested method. */ 3989 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 3990 final boolean doRestrict = true; 3991 final boolean checkSecurity = true; 3992 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup); 3993 } 3994 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */ 3995 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 3996 final boolean doRestrict = false; 3997 final boolean checkSecurity = true; 3998 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup); 3999 } 4000 /** Check access and get the requested method, eliding security manager checks. */ 4001 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException { 4002 final boolean doRestrict = true; 4003 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4004 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup); 4005 } 4006 /** Common code for all methods; do not call directly except from immediately above. */ 4007 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method, 4008 boolean checkSecurity, 4009 boolean doRestrict, 4010 Lookup boundCaller) throws IllegalAccessException { 4011 checkMethod(refKind, refc, method); 4012 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4013 if (checkSecurity) 4014 checkSecurityManager(refc, method); 4015 assert(!method.isMethodHandleInvoke()); 4016 if (refKind == REF_invokeSpecial && 4017 refc != lookupClass() && 4018 !refc.isInterface() && 4019 refc != lookupClass().getSuperclass() && 4020 refc.isAssignableFrom(lookupClass())) { 4021 assert(!method.getName().equals("<init>")); // not this code path 4022 4023 // Per JVMS 6.5, desc. of invokespecial instruction: 4024 // If the method is in a superclass of the LC, 4025 // and if our original search was above LC.super, 4026 // repeat the search (symbolic lookup) from LC.super 4027 // and continue with the direct superclass of that class, 4028 // and so forth, until a match is found or no further superclasses exist. 4029 // FIXME: MemberName.resolve should handle this instead. 4030 Class<?> refcAsSuper = lookupClass(); 4031 MemberName m2; 4032 do { 4033 refcAsSuper = refcAsSuper.getSuperclass(); 4034 m2 = new MemberName(refcAsSuper, 4035 method.getName(), 4036 method.getMethodType(), 4037 REF_invokeSpecial); 4038 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes); 4039 } while (m2 == null && // no method is found yet 4040 refc != refcAsSuper); // search up to refc 4041 if (m2 == null) throw new InternalError(method.toString()); 4042 method = m2; 4043 refc = refcAsSuper; 4044 // redo basic checks 4045 checkMethod(refKind, refc, method); 4046 } 4047 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass()); 4048 MethodHandle mh = dmh; 4049 // Optionally narrow the receiver argument to lookupClass using restrictReceiver. 4050 if ((doRestrict && refKind == REF_invokeSpecial) || 4051 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) { 4052 mh = restrictReceiver(method, dmh, lookupClass()); 4053 } 4054 mh = maybeBindCaller(method, mh, boundCaller); 4055 mh = mh.setVarargs(method); 4056 return mh; 4057 } 4058 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller) 4059 throws IllegalAccessException { 4060 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method)) 4061 return mh; 4062 4063 // boundCaller must have full privilege access. 4064 // It should have been checked by findBoundCallerLookup. Safe to check this again. 4065 if ((boundCaller.lookupModes() & ORIGINAL) == 0) 4066 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); 4067 4068 assert boundCaller.hasFullPrivilegeAccess(); 4069 4070 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass); 4071 // Note: caller will apply varargs after this step happens. 4072 return cbmh; 4073 } 4074 4075 /** Check access and get the requested field. */ 4076 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 4077 final boolean checkSecurity = true; 4078 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 4079 } 4080 /** Check access and get the requested field, eliding security manager checks. */ 4081 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException { 4082 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4083 return getDirectFieldCommon(refKind, refc, field, checkSecurity); 4084 } 4085 /** Common code for all fields; do not call directly except from immediately above. */ 4086 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field, 4087 boolean checkSecurity) throws IllegalAccessException { 4088 checkField(refKind, refc, field); 4089 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4090 if (checkSecurity) 4091 checkSecurityManager(refc, field); 4092 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field); 4093 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) && 4094 restrictProtectedReceiver(field)); 4095 if (doRestrict) 4096 return restrictReceiver(field, dmh, lookupClass()); 4097 return dmh; 4098 } 4099 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind, 4100 Class<?> refc, MemberName getField, MemberName putField) 4101 throws IllegalAccessException { 4102 final boolean checkSecurity = true; 4103 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 4104 } 4105 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind, 4106 Class<?> refc, MemberName getField, MemberName putField) 4107 throws IllegalAccessException { 4108 final boolean checkSecurity = false; 4109 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity); 4110 } 4111 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind, 4112 Class<?> refc, MemberName getField, MemberName putField, 4113 boolean checkSecurity) throws IllegalAccessException { 4114 assert getField.isStatic() == putField.isStatic(); 4115 assert getField.isGetter() && putField.isSetter(); 4116 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind); 4117 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind); 4118 4119 checkField(getRefKind, refc, getField); 4120 if (checkSecurity) 4121 checkSecurityManager(refc, getField); 4122 4123 if (!putField.isFinal()) { 4124 // A VarHandle does not support updates to final fields, any 4125 // such VarHandle to a final field will be read-only and 4126 // therefore the following write-based accessibility checks are 4127 // only required for non-final fields 4128 checkField(putRefKind, refc, putField); 4129 if (checkSecurity) 4130 checkSecurityManager(refc, putField); 4131 } 4132 4133 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) && 4134 restrictProtectedReceiver(getField)); 4135 if (doRestrict) { 4136 assert !getField.isStatic(); 4137 // receiver type of VarHandle is too wide; narrow to caller 4138 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) { 4139 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass()); 4140 } 4141 refc = lookupClass(); 4142 } 4143 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), 4144 this.allowedModes == TRUSTED && !getField.isTrustedFinalField()); 4145 } 4146 /** Check access and get the requested constructor. */ 4147 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException { 4148 final boolean checkSecurity = true; 4149 return getDirectConstructorCommon(refc, ctor, checkSecurity); 4150 } 4151 /** Check access and get the requested constructor, eliding security manager checks. */ 4152 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException { 4153 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants 4154 return getDirectConstructorCommon(refc, ctor, checkSecurity); 4155 } 4156 /** Common code for all constructors; do not call directly except from immediately above. */ 4157 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor, 4158 boolean checkSecurity) throws IllegalAccessException { 4159 assert(ctor.isObjectConstructor()); 4160 checkAccess(REF_newInvokeSpecial, refc, ctor); 4161 // Optionally check with the security manager; this isn't needed for unreflect* calls. 4162 if (checkSecurity) 4163 checkSecurityManager(refc, ctor); 4164 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here 4165 return DirectMethodHandle.make(ctor).setVarargs(ctor); 4166 } 4167 4168 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants: 4169 */ 4170 /*non-public*/ 4171 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) 4172 throws ReflectiveOperationException { 4173 if (!(type instanceof Class || type instanceof MethodType)) 4174 throw new InternalError("unresolved MemberName"); 4175 MemberName member = new MemberName(refKind, defc, name, type); 4176 MethodHandle mh = LOOKASIDE_TABLE.get(member); 4177 if (mh != null) { 4178 checkSymbolicClass(defc); 4179 return mh; 4180 } 4181 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) { 4182 // Treat MethodHandle.invoke and invokeExact specially. 4183 mh = findVirtualForMH(member.getName(), member.getMethodType()); 4184 if (mh != null) { 4185 return mh; 4186 } 4187 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) { 4188 // Treat signature-polymorphic methods on VarHandle specially. 4189 mh = findVirtualForVH(member.getName(), member.getMethodType()); 4190 if (mh != null) { 4191 return mh; 4192 } 4193 } 4194 MemberName resolved = resolveOrFail(refKind, member); 4195 mh = getDirectMethodForConstant(refKind, defc, resolved); 4196 if (mh instanceof DirectMethodHandle 4197 && canBeCached(refKind, defc, resolved)) { 4198 MemberName key = mh.internalMemberName(); 4199 if (key != null) { 4200 key = key.asNormalOriginal(); 4201 } 4202 if (member.equals(key)) { // better safe than sorry 4203 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh); 4204 } 4205 } 4206 return mh; 4207 } 4208 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) { 4209 if (refKind == REF_invokeSpecial) { 4210 return false; 4211 } 4212 if (!Modifier.isPublic(defc.getModifiers()) || 4213 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) || 4214 !member.isPublic() || 4215 member.isCallerSensitive()) { 4216 return false; 4217 } 4218 ClassLoader loader = defc.getClassLoader(); 4219 if (loader != null) { 4220 ClassLoader sysl = ClassLoader.getSystemClassLoader(); 4221 boolean found = false; 4222 while (sysl != null) { 4223 if (loader == sysl) { found = true; break; } 4224 sysl = sysl.getParent(); 4225 } 4226 if (!found) { 4227 return false; 4228 } 4229 } 4230 try { 4231 MemberName resolved2 = publicLookup().resolveOrNull(refKind, 4232 new MemberName(refKind, defc, member.getName(), member.getType())); 4233 if (resolved2 == null) { 4234 return false; 4235 } 4236 checkSecurityManager(defc, resolved2); 4237 } catch (SecurityException ex) { 4238 return false; 4239 } 4240 return true; 4241 } 4242 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member) 4243 throws ReflectiveOperationException { 4244 if (MethodHandleNatives.refKindIsField(refKind)) { 4245 return getDirectFieldNoSecurityManager(refKind, defc, member); 4246 } else if (MethodHandleNatives.refKindIsMethod(refKind)) { 4247 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member)); 4248 } else if (refKind == REF_newInvokeSpecial) { 4249 return getDirectConstructorNoSecurityManager(defc, member); 4250 } 4251 // oops 4252 throw newIllegalArgumentException("bad MethodHandle constant #"+member); 4253 } 4254 4255 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>(); 4256 } 4257 4258 /** 4259 * Produces a method handle constructing arrays of a desired type, 4260 * as if by the {@code anewarray} bytecode. 4261 * The return type of the method handle will be the array type. 4262 * The type of its sole argument will be {@code int}, which specifies the size of the array. 4263 * 4264 * <p> If the returned method handle is invoked with a negative 4265 * array size, a {@code NegativeArraySizeException} will be thrown. 4266 * 4267 * @param arrayClass an array type 4268 * @return a method handle which can create arrays of the given type 4269 * @throws NullPointerException if the argument is {@code null} 4270 * @throws IllegalArgumentException if {@code arrayClass} is not an array type 4271 * @see java.lang.reflect.Array#newInstance(Class, int) 4272 * @jvms 6.5 {@code anewarray} Instruction 4273 * @since 9 4274 */ 4275 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException { 4276 if (!arrayClass.isArray()) { 4277 throw newIllegalArgumentException("not an array class: " + arrayClass.getName()); 4278 } 4279 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance). 4280 bindTo(arrayClass.getComponentType()); 4281 return ani.asType(ani.type().changeReturnType(arrayClass)); 4282 } 4283 4284 /** 4285 * Produces a method handle returning the length of an array, 4286 * as if by the {@code arraylength} bytecode. 4287 * The type of the method handle will have {@code int} as return type, 4288 * and its sole argument will be the array type. 4289 * 4290 * <p> If the returned method handle is invoked with a {@code null} 4291 * array reference, a {@code NullPointerException} will be thrown. 4292 * 4293 * @param arrayClass an array type 4294 * @return a method handle which can retrieve the length of an array of the given array type 4295 * @throws NullPointerException if the argument is {@code null} 4296 * @throws IllegalArgumentException if arrayClass is not an array type 4297 * @jvms 6.5 {@code arraylength} Instruction 4298 * @since 9 4299 */ 4300 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException { 4301 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH); 4302 } 4303 4304 /** 4305 * Produces a method handle giving read access to elements of an array, 4306 * as if by the {@code aaload} bytecode. 4307 * The type of the method handle will have a return type of the array's 4308 * element type. Its first argument will be the array type, 4309 * and the second will be {@code int}. 4310 * 4311 * <p> When the returned method handle is invoked, 4312 * the array reference and array index are checked. 4313 * A {@code NullPointerException} will be thrown if the array reference 4314 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4315 * thrown if the index is negative or if it is greater than or equal to 4316 * the length of the array. 4317 * 4318 * @param arrayClass an array type 4319 * @return a method handle which can load values from the given array type 4320 * @throws NullPointerException if the argument is null 4321 * @throws IllegalArgumentException if arrayClass is not an array type 4322 * @jvms 6.5 {@code aaload} Instruction 4323 */ 4324 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException { 4325 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET); 4326 } 4327 4328 /** 4329 * Produces a method handle giving write access to elements of an array, 4330 * as if by the {@code astore} bytecode. 4331 * The type of the method handle will have a void return type. 4332 * Its last argument will be the array's element type. 4333 * The first and second arguments will be the array type and int. 4334 * 4335 * <p> When the returned method handle is invoked, 4336 * the array reference and array index are checked. 4337 * A {@code NullPointerException} will be thrown if the array reference 4338 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4339 * thrown if the index is negative or if it is greater than or equal to 4340 * the length of the array. 4341 * 4342 * @param arrayClass the class of an array 4343 * @return a method handle which can store values into the array type 4344 * @throws NullPointerException if the argument is null 4345 * @throws IllegalArgumentException if arrayClass is not an array type 4346 * @jvms 6.5 {@code aastore} Instruction 4347 */ 4348 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException { 4349 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET); 4350 } 4351 4352 /** 4353 * Produces a VarHandle giving access to elements of an array of type 4354 * {@code arrayClass}. The VarHandle's variable type is the component type 4355 * of {@code arrayClass} and the list of coordinate types is 4356 * {@code (arrayClass, int)}, where the {@code int} coordinate type 4357 * corresponds to an argument that is an index into an array. 4358 * <p> 4359 * Certain access modes of the returned VarHandle are unsupported under 4360 * the following conditions: 4361 * <ul> 4362 * <li>if the component type is anything other than {@code byte}, 4363 * {@code short}, {@code char}, {@code int}, {@code long}, 4364 * {@code float}, or {@code double} then numeric atomic update access 4365 * modes are unsupported. 4366 * <li>if the component type is anything other than {@code boolean}, 4367 * {@code byte}, {@code short}, {@code char}, {@code int} or 4368 * {@code long} then bitwise atomic update access modes are 4369 * unsupported. 4370 * </ul> 4371 * <p> 4372 * If the component type is {@code float} or {@code double} then numeric 4373 * and atomic update access modes compare values using their bitwise 4374 * representation (see {@link Float#floatToRawIntBits} and 4375 * {@link Double#doubleToRawLongBits}, respectively). 4376 * 4377 * <p> When the returned {@code VarHandle} is invoked, 4378 * the array reference and array index are checked. 4379 * A {@code NullPointerException} will be thrown if the array reference 4380 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be 4381 * thrown if the index is negative or if it is greater than or equal to 4382 * the length of the array. 4383 * 4384 * @apiNote 4385 * Bitwise comparison of {@code float} values or {@code double} values, 4386 * as performed by the numeric and atomic update access modes, differ 4387 * from the primitive {@code ==} operator and the {@link Float#equals} 4388 * and {@link Double#equals} methods, specifically with respect to 4389 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}. 4390 * Care should be taken when performing a compare and set or a compare 4391 * and exchange operation with such values since the operation may 4392 * unexpectedly fail. 4393 * There are many possible NaN values that are considered to be 4394 * {@code NaN} in Java, although no IEEE 754 floating-point operation 4395 * provided by Java can distinguish between them. Operation failure can 4396 * occur if the expected or witness value is a NaN value and it is 4397 * transformed (perhaps in a platform specific manner) into another NaN 4398 * value, and thus has a different bitwise representation (see 4399 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more 4400 * details). 4401 * The values {@code -0.0} and {@code +0.0} have different bitwise 4402 * representations but are considered equal when using the primitive 4403 * {@code ==} operator. Operation failure can occur if, for example, a 4404 * numeric algorithm computes an expected value to be say {@code -0.0} 4405 * and previously computed the witness value to be say {@code +0.0}. 4406 * @param arrayClass the class of an array, of type {@code T[]} 4407 * @return a VarHandle giving access to elements of an array 4408 * @throws NullPointerException if the arrayClass is null 4409 * @throws IllegalArgumentException if arrayClass is not an array type 4410 * @since 9 4411 */ 4412 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException { 4413 return VarHandles.makeArrayElementHandle(arrayClass); 4414 } 4415 4416 /** 4417 * Produces a VarHandle giving access to elements of a {@code byte[]} array 4418 * viewed as if it were a different primitive array type, such as 4419 * {@code int[]} or {@code long[]}. 4420 * The VarHandle's variable type is the component type of 4421 * {@code viewArrayClass} and the list of coordinate types is 4422 * {@code (byte[], int)}, where the {@code int} coordinate type 4423 * corresponds to an argument that is an index into a {@code byte[]} array. 4424 * The returned VarHandle accesses bytes at an index in a {@code byte[]} 4425 * array, composing bytes to or from a value of the component type of 4426 * {@code viewArrayClass} according to the given endianness. 4427 * <p> 4428 * The supported component types (variables types) are {@code short}, 4429 * {@code char}, {@code int}, {@code long}, {@code float} and 4430 * {@code double}. 4431 * <p> 4432 * Access of bytes at a given index will result in an 4433 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0} 4434 * or greater than the {@code byte[]} array length minus the size (in bytes) 4435 * of {@code T}. 4436 * <p> 4437 * Access of bytes at an index may be aligned or misaligned for {@code T}, 4438 * with respect to the underlying memory address, {@code A} say, associated 4439 * with the array and index. 4440 * If access is misaligned then access for anything other than the 4441 * {@code get} and {@code set} access modes will result in an 4442 * {@code IllegalStateException}. In such cases atomic access is only 4443 * guaranteed with respect to the largest power of two that divides the GCD 4444 * of {@code A} and the size (in bytes) of {@code T}. 4445 * If access is aligned then following access modes are supported and are 4446 * guaranteed to support atomic access: 4447 * <ul> 4448 * <li>read write access modes for all {@code T}, with the exception of 4449 * access modes {@code get} and {@code set} for {@code long} and 4450 * {@code double} on 32-bit platforms. 4451 * <li>atomic update access modes for {@code int}, {@code long}, 4452 * {@code float} or {@code double}. 4453 * (Future major platform releases of the JDK may support additional 4454 * types for certain currently unsupported access modes.) 4455 * <li>numeric atomic update access modes for {@code int} and {@code long}. 4456 * (Future major platform releases of the JDK may support additional 4457 * numeric types for certain currently unsupported access modes.) 4458 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 4459 * (Future major platform releases of the JDK may support additional 4460 * numeric types for certain currently unsupported access modes.) 4461 * </ul> 4462 * <p> 4463 * Misaligned access, and therefore atomicity guarantees, may be determined 4464 * for {@code byte[]} arrays without operating on a specific array. Given 4465 * an {@code index}, {@code T} and its corresponding boxed type, 4466 * {@code T_BOX}, misalignment may be determined as follows: 4467 * <pre>{@code 4468 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 4469 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]). 4470 * alignmentOffset(0, sizeOfT); 4471 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT; 4472 * boolean isMisaligned = misalignedAtIndex != 0; 4473 * }</pre> 4474 * <p> 4475 * If the variable type is {@code float} or {@code double} then atomic 4476 * update access modes compare values using their bitwise representation 4477 * (see {@link Float#floatToRawIntBits} and 4478 * {@link Double#doubleToRawLongBits}, respectively). 4479 * @param viewArrayClass the view array class, with a component type of 4480 * type {@code T} 4481 * @param byteOrder the endianness of the view array elements, as 4482 * stored in the underlying {@code byte} array 4483 * @return a VarHandle giving access to elements of a {@code byte[]} array 4484 * viewed as if elements corresponding to the components type of the view 4485 * array class 4486 * @throws NullPointerException if viewArrayClass or byteOrder is null 4487 * @throws IllegalArgumentException if viewArrayClass is not an array type 4488 * @throws UnsupportedOperationException if the component type of 4489 * viewArrayClass is not supported as a variable type 4490 * @since 9 4491 */ 4492 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass, 4493 ByteOrder byteOrder) throws IllegalArgumentException { 4494 Objects.requireNonNull(byteOrder); 4495 return VarHandles.byteArrayViewHandle(viewArrayClass, 4496 byteOrder == ByteOrder.BIG_ENDIAN); 4497 } 4498 4499 /** 4500 * Produces a VarHandle giving access to elements of a {@code ByteBuffer} 4501 * viewed as if it were an array of elements of a different primitive 4502 * component type to that of {@code byte}, such as {@code int[]} or 4503 * {@code long[]}. 4504 * The VarHandle's variable type is the component type of 4505 * {@code viewArrayClass} and the list of coordinate types is 4506 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type 4507 * corresponds to an argument that is an index into a {@code byte[]} array. 4508 * The returned VarHandle accesses bytes at an index in a 4509 * {@code ByteBuffer}, composing bytes to or from a value of the component 4510 * type of {@code viewArrayClass} according to the given endianness. 4511 * <p> 4512 * The supported component types (variables types) are {@code short}, 4513 * {@code char}, {@code int}, {@code long}, {@code float} and 4514 * {@code double}. 4515 * <p> 4516 * Access will result in a {@code ReadOnlyBufferException} for anything 4517 * other than the read access modes if the {@code ByteBuffer} is read-only. 4518 * <p> 4519 * Access of bytes at a given index will result in an 4520 * {@code IndexOutOfBoundsException} if the index is less than {@code 0} 4521 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of 4522 * {@code T}. 4523 * <p> 4524 * Access of bytes at an index may be aligned or misaligned for {@code T}, 4525 * with respect to the underlying memory address, {@code A} say, associated 4526 * with the {@code ByteBuffer} and index. 4527 * If access is misaligned then access for anything other than the 4528 * {@code get} and {@code set} access modes will result in an 4529 * {@code IllegalStateException}. In such cases atomic access is only 4530 * guaranteed with respect to the largest power of two that divides the GCD 4531 * of {@code A} and the size (in bytes) of {@code T}. 4532 * If access is aligned then following access modes are supported and are 4533 * guaranteed to support atomic access: 4534 * <ul> 4535 * <li>read write access modes for all {@code T}, with the exception of 4536 * access modes {@code get} and {@code set} for {@code long} and 4537 * {@code double} on 32-bit platforms. 4538 * <li>atomic update access modes for {@code int}, {@code long}, 4539 * {@code float} or {@code double}. 4540 * (Future major platform releases of the JDK may support additional 4541 * types for certain currently unsupported access modes.) 4542 * <li>numeric atomic update access modes for {@code int} and {@code long}. 4543 * (Future major platform releases of the JDK may support additional 4544 * numeric types for certain currently unsupported access modes.) 4545 * <li>bitwise atomic update access modes for {@code int} and {@code long}. 4546 * (Future major platform releases of the JDK may support additional 4547 * numeric types for certain currently unsupported access modes.) 4548 * </ul> 4549 * <p> 4550 * Misaligned access, and therefore atomicity guarantees, may be determined 4551 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an 4552 * {@code index}, {@code T} and its corresponding boxed type, 4553 * {@code T_BOX}, as follows: 4554 * <pre>{@code 4555 * int sizeOfT = T_BOX.BYTES; // size in bytes of T 4556 * ByteBuffer bb = ... 4557 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT); 4558 * boolean isMisaligned = misalignedAtIndex != 0; 4559 * }</pre> 4560 * <p> 4561 * If the variable type is {@code float} or {@code double} then atomic 4562 * update access modes compare values using their bitwise representation 4563 * (see {@link Float#floatToRawIntBits} and 4564 * {@link Double#doubleToRawLongBits}, respectively). 4565 * @param viewArrayClass the view array class, with a component type of 4566 * type {@code T} 4567 * @param byteOrder the endianness of the view array elements, as 4568 * stored in the underlying {@code ByteBuffer} (Note this overrides the 4569 * endianness of a {@code ByteBuffer}) 4570 * @return a VarHandle giving access to elements of a {@code ByteBuffer} 4571 * viewed as if elements corresponding to the components type of the view 4572 * array class 4573 * @throws NullPointerException if viewArrayClass or byteOrder is null 4574 * @throws IllegalArgumentException if viewArrayClass is not an array type 4575 * @throws UnsupportedOperationException if the component type of 4576 * viewArrayClass is not supported as a variable type 4577 * @since 9 4578 */ 4579 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass, 4580 ByteOrder byteOrder) throws IllegalArgumentException { 4581 Objects.requireNonNull(byteOrder); 4582 return VarHandles.makeByteBufferViewHandle(viewArrayClass, 4583 byteOrder == ByteOrder.BIG_ENDIAN); 4584 } 4585 4586 4587 /// method handle invocation (reflective style) 4588 4589 /** 4590 * Produces a method handle which will invoke any method handle of the 4591 * given {@code type}, with a given number of trailing arguments replaced by 4592 * a single trailing {@code Object[]} array. 4593 * The resulting invoker will be a method handle with the following 4594 * arguments: 4595 * <ul> 4596 * <li>a single {@code MethodHandle} target 4597 * <li>zero or more leading values (counted by {@code leadingArgCount}) 4598 * <li>an {@code Object[]} array containing trailing arguments 4599 * </ul> 4600 * <p> 4601 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with 4602 * the indicated {@code type}. 4603 * That is, if the target is exactly of the given {@code type}, it will behave 4604 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType} 4605 * is used to convert the target to the required {@code type}. 4606 * <p> 4607 * The type of the returned invoker will not be the given {@code type}, but rather 4608 * will have all parameters except the first {@code leadingArgCount} 4609 * replaced by a single array of type {@code Object[]}, which will be 4610 * the final parameter. 4611 * <p> 4612 * Before invoking its target, the invoker will spread the final array, apply 4613 * reference casts as necessary, and unbox and widen primitive arguments. 4614 * If, when the invoker is called, the supplied array argument does 4615 * not have the correct number of elements, the invoker will throw 4616 * an {@link IllegalArgumentException} instead of invoking the target. 4617 * <p> 4618 * This method is equivalent to the following code (though it may be more efficient): 4619 * {@snippet lang="java" : 4620 MethodHandle invoker = MethodHandles.invoker(type); 4621 int spreadArgCount = type.parameterCount() - leadingArgCount; 4622 invoker = invoker.asSpreader(Object[].class, spreadArgCount); 4623 return invoker; 4624 * } 4625 * This method throws no reflective or security exceptions. 4626 * @param type the desired target type 4627 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target 4628 * @return a method handle suitable for invoking any method handle of the given type 4629 * @throws NullPointerException if {@code type} is null 4630 * @throws IllegalArgumentException if {@code leadingArgCount} is not in 4631 * the range from 0 to {@code type.parameterCount()} inclusive, 4632 * or if the resulting method handle's type would have 4633 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4634 */ 4635 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) { 4636 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) 4637 throw newIllegalArgumentException("bad argument count", leadingArgCount); 4638 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount); 4639 return type.invokers().spreadInvoker(leadingArgCount); 4640 } 4641 4642 /** 4643 * Produces a special <em>invoker method handle</em> which can be used to 4644 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. 4645 * The resulting invoker will have a type which is 4646 * exactly equal to the desired type, except that it will accept 4647 * an additional leading argument of type {@code MethodHandle}. 4648 * <p> 4649 * This method is equivalent to the following code (though it may be more efficient): 4650 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)} 4651 * 4652 * <p style="font-size:smaller;"> 4653 * <em>Discussion:</em> 4654 * Invoker method handles can be useful when working with variable method handles 4655 * of unknown types. 4656 * For example, to emulate an {@code invokeExact} call to a variable method 4657 * handle {@code M}, extract its type {@code T}, 4658 * look up the invoker method {@code X} for {@code T}, 4659 * and call the invoker method, as {@code X.invoke(T, A...)}. 4660 * (It would not work to call {@code X.invokeExact}, since the type {@code T} 4661 * is unknown.) 4662 * If spreading, collecting, or other argument transformations are required, 4663 * they can be applied once to the invoker {@code X} and reused on many {@code M} 4664 * method handle values, as long as they are compatible with the type of {@code X}. 4665 * <p style="font-size:smaller;"> 4666 * <em>(Note: The invoker method is not available via the Core Reflection API. 4667 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 4668 * on the declared {@code invokeExact} or {@code invoke} method will raise an 4669 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 4670 * <p> 4671 * This method throws no reflective or security exceptions. 4672 * @param type the desired target type 4673 * @return a method handle suitable for invoking any method handle of the given type 4674 * @throws IllegalArgumentException if the resulting method handle's type would have 4675 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4676 */ 4677 public static MethodHandle exactInvoker(MethodType type) { 4678 return type.invokers().exactInvoker(); 4679 } 4680 4681 /** 4682 * Produces a special <em>invoker method handle</em> which can be used to 4683 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}. 4684 * The resulting invoker will have a type which is 4685 * exactly equal to the desired type, except that it will accept 4686 * an additional leading argument of type {@code MethodHandle}. 4687 * <p> 4688 * Before invoking its target, if the target differs from the expected type, 4689 * the invoker will apply reference casts as 4690 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}. 4691 * Similarly, the return value will be converted as necessary. 4692 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle}, 4693 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}. 4694 * <p> 4695 * This method is equivalent to the following code (though it may be more efficient): 4696 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)} 4697 * <p style="font-size:smaller;"> 4698 * <em>Discussion:</em> 4699 * A {@linkplain MethodType#genericMethodType general method type} is one which 4700 * mentions only {@code Object} arguments and return values. 4701 * An invoker for such a type is capable of calling any method handle 4702 * of the same arity as the general type. 4703 * <p style="font-size:smaller;"> 4704 * <em>(Note: The invoker method is not available via the Core Reflection API. 4705 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} 4706 * on the declared {@code invokeExact} or {@code invoke} method will raise an 4707 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em> 4708 * <p> 4709 * This method throws no reflective or security exceptions. 4710 * @param type the desired target type 4711 * @return a method handle suitable for invoking any method handle convertible to the given type 4712 * @throws IllegalArgumentException if the resulting method handle's type would have 4713 * <a href="MethodHandle.html#maxarity">too many parameters</a> 4714 */ 4715 public static MethodHandle invoker(MethodType type) { 4716 return type.invokers().genericInvoker(); 4717 } 4718 4719 /** 4720 * Produces a special <em>invoker method handle</em> which can be used to 4721 * invoke a signature-polymorphic access mode method on any VarHandle whose 4722 * associated access mode type is compatible with the given type. 4723 * The resulting invoker will have a type which is exactly equal to the 4724 * desired given type, except that it will accept an additional leading 4725 * argument of type {@code VarHandle}. 4726 * 4727 * @param accessMode the VarHandle access mode 4728 * @param type the desired target type 4729 * @return a method handle suitable for invoking an access mode method of 4730 * any VarHandle whose access mode type is of the given type. 4731 * @since 9 4732 */ 4733 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) { 4734 return type.invokers().varHandleMethodExactInvoker(accessMode); 4735 } 4736 4737 /** 4738 * Produces a special <em>invoker method handle</em> which can be used to 4739 * invoke a signature-polymorphic access mode method on any VarHandle whose 4740 * associated access mode type is compatible with the given type. 4741 * The resulting invoker will have a type which is exactly equal to the 4742 * desired given type, except that it will accept an additional leading 4743 * argument of type {@code VarHandle}. 4744 * <p> 4745 * Before invoking its target, if the access mode type differs from the 4746 * desired given type, the invoker will apply reference casts as necessary 4747 * and box, unbox, or widen primitive values, as if by 4748 * {@link MethodHandle#asType asType}. Similarly, the return value will be 4749 * converted as necessary. 4750 * <p> 4751 * This method is equivalent to the following code (though it may be more 4752 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)} 4753 * 4754 * @param accessMode the VarHandle access mode 4755 * @param type the desired target type 4756 * @return a method handle suitable for invoking an access mode method of 4757 * any VarHandle whose access mode type is convertible to the given 4758 * type. 4759 * @since 9 4760 */ 4761 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) { 4762 return type.invokers().varHandleMethodInvoker(accessMode); 4763 } 4764 4765 /*non-public*/ 4766 static MethodHandle basicInvoker(MethodType type) { 4767 return type.invokers().basicInvoker(); 4768 } 4769 4770 /// method handle modification (creation from other method handles) 4771 4772 /** 4773 * Produces a method handle which adapts the type of the 4774 * given method handle to a new type by pairwise argument and return type conversion. 4775 * The original type and new type must have the same number of arguments. 4776 * The resulting method handle is guaranteed to report a type 4777 * which is equal to the desired new type. 4778 * <p> 4779 * If the original type and new type are equal, returns target. 4780 * <p> 4781 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType}, 4782 * and some additional conversions are also applied if those conversions fail. 4783 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied 4784 * if possible, before or instead of any conversions done by {@code asType}: 4785 * <ul> 4786 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type, 4787 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast. 4788 * (This treatment of interfaces follows the usage of the bytecode verifier.) 4789 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive, 4790 * the boolean is converted to a byte value, 1 for true, 0 for false. 4791 * (This treatment follows the usage of the bytecode verifier.) 4792 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive, 4793 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}), 4794 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}. 4795 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean, 4796 * then a Java casting conversion (JLS {@jls 5.5}) is applied. 4797 * (Specifically, <em>T0</em> will convert to <em>T1</em> by 4798 * widening and/or narrowing.) 4799 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing 4800 * conversion will be applied at runtime, possibly followed 4801 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value, 4802 * possibly followed by a conversion from byte to boolean by testing 4803 * the low-order bit. 4804 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, 4805 * and if the reference is null at runtime, a zero value is introduced. 4806 * </ul> 4807 * @param target the method handle to invoke after arguments are retyped 4808 * @param newType the expected type of the new method handle 4809 * @return a method handle which delegates to the target after performing 4810 * any necessary argument conversions, and arranges for any 4811 * necessary return value conversions 4812 * @throws NullPointerException if either argument is null 4813 * @throws WrongMethodTypeException if the conversion cannot be made 4814 * @see MethodHandle#asType 4815 */ 4816 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) { 4817 explicitCastArgumentsChecks(target, newType); 4818 // use the asTypeCache when possible: 4819 MethodType oldType = target.type(); 4820 if (oldType == newType) return target; 4821 if (oldType.explicitCastEquivalentToAsType(newType)) { 4822 return target.asFixedArity().asType(newType); 4823 } 4824 return MethodHandleImpl.makePairwiseConvert(target, newType, false); 4825 } 4826 4827 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) { 4828 if (target.type().parameterCount() != newType.parameterCount()) { 4829 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType); 4830 } 4831 } 4832 4833 /** 4834 * Produces a method handle which adapts the calling sequence of the 4835 * given method handle to a new type, by reordering the arguments. 4836 * The resulting method handle is guaranteed to report a type 4837 * which is equal to the desired new type. 4838 * <p> 4839 * The given array controls the reordering. 4840 * Call {@code #I} the number of incoming parameters (the value 4841 * {@code newType.parameterCount()}, and call {@code #O} the number 4842 * of outgoing parameters (the value {@code target.type().parameterCount()}). 4843 * Then the length of the reordering array must be {@code #O}, 4844 * and each element must be a non-negative number less than {@code #I}. 4845 * For every {@code N} less than {@code #O}, the {@code N}-th 4846 * outgoing argument will be taken from the {@code I}-th incoming 4847 * argument, where {@code I} is {@code reorder[N]}. 4848 * <p> 4849 * No argument or return value conversions are applied. 4850 * The type of each incoming argument, as determined by {@code newType}, 4851 * must be identical to the type of the corresponding outgoing parameter 4852 * or parameters in the target method handle. 4853 * The return type of {@code newType} must be identical to the return 4854 * type of the original target. 4855 * <p> 4856 * The reordering array need not specify an actual permutation. 4857 * An incoming argument will be duplicated if its index appears 4858 * more than once in the array, and an incoming argument will be dropped 4859 * if its index does not appear in the array. 4860 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments}, 4861 * incoming arguments which are not mentioned in the reordering array 4862 * may be of any type, as determined only by {@code newType}. 4863 * {@snippet lang="java" : 4864 import static java.lang.invoke.MethodHandles.*; 4865 import static java.lang.invoke.MethodType.*; 4866 ... 4867 MethodType intfn1 = methodType(int.class, int.class); 4868 MethodType intfn2 = methodType(int.class, int.class, int.class); 4869 MethodHandle sub = ... (int x, int y) -> (x-y) ...; 4870 assert(sub.type().equals(intfn2)); 4871 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1); 4872 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0); 4873 assert((int)rsub.invokeExact(1, 100) == 99); 4874 MethodHandle add = ... (int x, int y) -> (x+y) ...; 4875 assert(add.type().equals(intfn2)); 4876 MethodHandle twice = permuteArguments(add, intfn1, 0, 0); 4877 assert(twice.type().equals(intfn1)); 4878 assert((int)twice.invokeExact(21) == 42); 4879 * } 4880 * <p> 4881 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 4882 * variable-arity method handle}, even if the original target method handle was. 4883 * @param target the method handle to invoke after arguments are reordered 4884 * @param newType the expected type of the new method handle 4885 * @param reorder an index array which controls the reordering 4886 * @return a method handle which delegates to the target after it 4887 * drops unused arguments and moves and/or duplicates the other arguments 4888 * @throws NullPointerException if any argument is null 4889 * @throws IllegalArgumentException if the index array length is not equal to 4890 * the arity of the target, or if any index array element 4891 * not a valid index for a parameter of {@code newType}, 4892 * or if two corresponding parameter types in 4893 * {@code target.type()} and {@code newType} are not identical, 4894 */ 4895 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) { 4896 reorder = reorder.clone(); // get a private copy 4897 MethodType oldType = target.type(); 4898 permuteArgumentChecks(reorder, newType, oldType); 4899 // first detect dropped arguments and handle them separately 4900 int[] originalReorder = reorder; 4901 BoundMethodHandle result = target.rebind(); 4902 LambdaForm form = result.form; 4903 int newArity = newType.parameterCount(); 4904 // Normalize the reordering into a real permutation, 4905 // by removing duplicates and adding dropped elements. 4906 // This somewhat improves lambda form caching, as well 4907 // as simplifying the transform by breaking it up into steps. 4908 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) { 4909 if (ddIdx > 0) { 4910 // We found a duplicated entry at reorder[ddIdx]. 4911 // Example: (x,y,z)->asList(x,y,z) 4912 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1) 4913 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0) 4914 // The starred element corresponds to the argument 4915 // deleted by the dupArgumentForm transform. 4916 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos]; 4917 boolean killFirst = false; 4918 for (int val; (val = reorder[--dstPos]) != dupVal; ) { 4919 // Set killFirst if the dup is larger than an intervening position. 4920 // This will remove at least one inversion from the permutation. 4921 if (dupVal > val) killFirst = true; 4922 } 4923 if (!killFirst) { 4924 srcPos = dstPos; 4925 dstPos = ddIdx; 4926 } 4927 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos); 4928 assert (reorder[srcPos] == reorder[dstPos]); 4929 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1); 4930 // contract the reordering by removing the element at dstPos 4931 int tailPos = dstPos + 1; 4932 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos); 4933 reorder = Arrays.copyOf(reorder, reorder.length - 1); 4934 } else { 4935 int dropVal = ~ddIdx, insPos = 0; 4936 while (insPos < reorder.length && reorder[insPos] < dropVal) { 4937 // Find first element of reorder larger than dropVal. 4938 // This is where we will insert the dropVal. 4939 insPos += 1; 4940 } 4941 Class<?> ptype = newType.parameterType(dropVal); 4942 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype)); 4943 oldType = oldType.insertParameterTypes(insPos, ptype); 4944 // expand the reordering by inserting an element at insPos 4945 int tailPos = insPos + 1; 4946 reorder = Arrays.copyOf(reorder, reorder.length + 1); 4947 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos); 4948 reorder[insPos] = dropVal; 4949 } 4950 assert (permuteArgumentChecks(reorder, newType, oldType)); 4951 } 4952 assert (reorder.length == newArity); // a perfect permutation 4953 // Note: This may cache too many distinct LFs. Consider backing off to varargs code. 4954 form = form.editor().permuteArgumentsForm(1, reorder); 4955 if (newType == result.type() && form == result.internalForm()) 4956 return result; 4957 return result.copyWith(newType, form); 4958 } 4959 4960 /** 4961 * Return an indication of any duplicate or omission in reorder. 4962 * If the reorder contains a duplicate entry, return the index of the second occurrence. 4963 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder. 4964 * Otherwise, return zero. 4965 * If an element not in [0..newArity-1] is encountered, return reorder.length. 4966 */ 4967 private static int findFirstDupOrDrop(int[] reorder, int newArity) { 4968 final int BIT_LIMIT = 63; // max number of bits in bit mask 4969 if (newArity < BIT_LIMIT) { 4970 long mask = 0; 4971 for (int i = 0; i < reorder.length; i++) { 4972 int arg = reorder[i]; 4973 if (arg >= newArity) { 4974 return reorder.length; 4975 } 4976 long bit = 1L << arg; 4977 if ((mask & bit) != 0) { 4978 return i; // >0 indicates a dup 4979 } 4980 mask |= bit; 4981 } 4982 if (mask == (1L << newArity) - 1) { 4983 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity); 4984 return 0; 4985 } 4986 // find first zero 4987 long zeroBit = Long.lowestOneBit(~mask); 4988 int zeroPos = Long.numberOfTrailingZeros(zeroBit); 4989 assert(zeroPos <= newArity); 4990 if (zeroPos == newArity) { 4991 return 0; 4992 } 4993 return ~zeroPos; 4994 } else { 4995 // same algorithm, different bit set 4996 BitSet mask = new BitSet(newArity); 4997 for (int i = 0; i < reorder.length; i++) { 4998 int arg = reorder[i]; 4999 if (arg >= newArity) { 5000 return reorder.length; 5001 } 5002 if (mask.get(arg)) { 5003 return i; // >0 indicates a dup 5004 } 5005 mask.set(arg); 5006 } 5007 int zeroPos = mask.nextClearBit(0); 5008 assert(zeroPos <= newArity); 5009 if (zeroPos == newArity) { 5010 return 0; 5011 } 5012 return ~zeroPos; 5013 } 5014 } 5015 5016 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) { 5017 if (newType.returnType() != oldType.returnType()) 5018 throw newIllegalArgumentException("return types do not match", 5019 oldType, newType); 5020 if (reorder.length != oldType.parameterCount()) 5021 throw newIllegalArgumentException("old type parameter count and reorder array length do not match", 5022 oldType, Arrays.toString(reorder)); 5023 5024 int limit = newType.parameterCount(); 5025 for (int j = 0; j < reorder.length; j++) { 5026 int i = reorder[j]; 5027 if (i < 0 || i >= limit) { 5028 throw newIllegalArgumentException("index is out of bounds for new type", 5029 i, newType); 5030 } 5031 Class<?> src = newType.parameterType(i); 5032 Class<?> dst = oldType.parameterType(j); 5033 if (src != dst) 5034 throw newIllegalArgumentException("parameter types do not match after reorder", 5035 oldType, newType); 5036 } 5037 return true; 5038 } 5039 5040 /** 5041 * Produces a method handle of the requested return type which returns the given 5042 * constant value every time it is invoked. 5043 * <p> 5044 * Before the method handle is returned, the passed-in value is converted to the requested type. 5045 * If the requested type is primitive, widening primitive conversions are attempted, 5046 * else reference conversions are attempted. 5047 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}. 5048 * @param type the return type of the desired method handle 5049 * @param value the value to return 5050 * @return a method handle of the given return type and no arguments, which always returns the given value 5051 * @throws NullPointerException if the {@code type} argument is null 5052 * @throws ClassCastException if the value cannot be converted to the required return type 5053 * @throws IllegalArgumentException if the given type is {@code void.class} 5054 */ 5055 public static MethodHandle constant(Class<?> type, Object value) { 5056 if (type.isPrimitive()) { 5057 if (type == void.class) 5058 throw newIllegalArgumentException("void type"); 5059 Wrapper w = Wrapper.forPrimitiveType(type); 5060 value = w.convert(value, type); 5061 if (w.zero().equals(value)) 5062 return zero(w, type); 5063 return insertArguments(identity(type), 0, value); 5064 } else { 5065 if (!PrimitiveClass.isPrimitiveValueType(type) && value == null) 5066 return zero(Wrapper.OBJECT, type); 5067 return identity(type).bindTo(value); 5068 } 5069 } 5070 5071 /** 5072 * Produces a method handle which returns its sole argument when invoked. 5073 * @param type the type of the sole parameter and return value of the desired method handle 5074 * @return a unary method handle which accepts and returns the given type 5075 * @throws NullPointerException if the argument is null 5076 * @throws IllegalArgumentException if the given type is {@code void.class} 5077 */ 5078 public static MethodHandle identity(Class<?> type) { 5079 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT); 5080 int pos = btw.ordinal(); 5081 MethodHandle ident = IDENTITY_MHS[pos]; 5082 if (ident == null) { 5083 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType())); 5084 } 5085 if (ident.type().returnType() == type) 5086 return ident; 5087 // something like identity(Foo.class); do not bother to intern these 5088 assert (btw == Wrapper.OBJECT); 5089 return makeIdentity(type); 5090 } 5091 5092 /** 5093 * Produces a constant method handle of the requested return type which 5094 * returns the default value for that type every time it is invoked. 5095 * The resulting constant method handle will have no side effects. 5096 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}. 5097 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))}, 5098 * since {@code explicitCastArguments} converts {@code null} to default values. 5099 * @param type the expected return type of the desired method handle 5100 * @return a constant method handle that takes no arguments 5101 * and returns the default value of the given type (or void, if the type is void) 5102 * @throws NullPointerException if the argument is null 5103 * @see MethodHandles#constant 5104 * @see MethodHandles#empty 5105 * @see MethodHandles#explicitCastArguments 5106 * @since 9 5107 */ 5108 public static MethodHandle zero(Class<?> type) { 5109 Objects.requireNonNull(type); 5110 if (type.isPrimitive()) { 5111 return zero(Wrapper.forPrimitiveType(type), type); 5112 } else if (PrimitiveClass.isPrimitiveValueType(type)) { 5113 // singleton default value 5114 Object value = UNSAFE.uninitializedDefaultValue(type); 5115 return identity(type).bindTo(value); 5116 } else { 5117 return zero(Wrapper.OBJECT, type); 5118 } 5119 } 5120 5121 private static MethodHandle identityOrVoid(Class<?> type) { 5122 return type == void.class ? zero(type) : identity(type); 5123 } 5124 5125 /** 5126 * Produces a method handle of the requested type which ignores any arguments, does nothing, 5127 * and returns a suitable default depending on the return type. 5128 * That is, it returns a zero primitive value, a {@code null}, or {@code void}. 5129 * <p>The returned method handle is equivalent to 5130 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}. 5131 * 5132 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as 5133 * {@code guardWithTest(pred, target, empty(target.type())}. 5134 * @param type the type of the desired method handle 5135 * @return a constant method handle of the given type, which returns a default value of the given return type 5136 * @throws NullPointerException if the argument is null 5137 * @see MethodHandles#zero 5138 * @see MethodHandles#constant 5139 * @since 9 5140 */ 5141 public static MethodHandle empty(MethodType type) { 5142 Objects.requireNonNull(type); 5143 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes()); 5144 } 5145 5146 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT]; 5147 private static MethodHandle makeIdentity(Class<?> ptype) { 5148 MethodType mtype = MethodType.methodType(ptype, ptype); 5149 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype)); 5150 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY); 5151 } 5152 5153 private static MethodHandle zero(Wrapper btw, Class<?> rtype) { 5154 int pos = btw.ordinal(); 5155 MethodHandle zero = ZERO_MHS[pos]; 5156 if (zero == null) { 5157 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType())); 5158 } 5159 if (zero.type().returnType() == rtype) 5160 return zero; 5161 assert(btw == Wrapper.OBJECT); 5162 return makeZero(rtype); 5163 } 5164 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT]; 5165 private static MethodHandle makeZero(Class<?> rtype) { 5166 MethodType mtype = methodType(rtype); 5167 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype)); 5168 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO); 5169 } 5170 5171 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) { 5172 // Simulate a CAS, to avoid racy duplication of results. 5173 MethodHandle prev = cache[pos]; 5174 if (prev != null) return prev; 5175 return cache[pos] = value; 5176 } 5177 5178 /** 5179 * Provides a target method handle with one or more <em>bound arguments</em> 5180 * in advance of the method handle's invocation. 5181 * The formal parameters to the target corresponding to the bound 5182 * arguments are called <em>bound parameters</em>. 5183 * Returns a new method handle which saves away the bound arguments. 5184 * When it is invoked, it receives arguments for any non-bound parameters, 5185 * binds the saved arguments to their corresponding parameters, 5186 * and calls the original target. 5187 * <p> 5188 * The type of the new method handle will drop the types for the bound 5189 * parameters from the original target type, since the new method handle 5190 * will no longer require those arguments to be supplied by its callers. 5191 * <p> 5192 * Each given argument object must match the corresponding bound parameter type. 5193 * If a bound parameter type is a primitive, the argument object 5194 * must be a wrapper, and will be unboxed to produce the primitive value. 5195 * <p> 5196 * The {@code pos} argument selects which parameters are to be bound. 5197 * It may range between zero and <i>N-L</i> (inclusively), 5198 * where <i>N</i> is the arity of the target method handle 5199 * and <i>L</i> is the length of the values array. 5200 * <p> 5201 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5202 * variable-arity method handle}, even if the original target method handle was. 5203 * @param target the method handle to invoke after the argument is inserted 5204 * @param pos where to insert the argument (zero for the first) 5205 * @param values the series of arguments to insert 5206 * @return a method handle which inserts an additional argument, 5207 * before calling the original method handle 5208 * @throws NullPointerException if the target or the {@code values} array is null 5209 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than 5210 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L} 5211 * is the length of the values array. 5212 * @throws ClassCastException if an argument does not match the corresponding bound parameter 5213 * type. 5214 * @see MethodHandle#bindTo 5215 */ 5216 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) { 5217 int insCount = values.length; 5218 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos); 5219 if (insCount == 0) return target; 5220 BoundMethodHandle result = target.rebind(); 5221 for (int i = 0; i < insCount; i++) { 5222 Object value = values[i]; 5223 Class<?> ptype = ptypes[pos+i]; 5224 if (ptype.isPrimitive()) { 5225 result = insertArgumentPrimitive(result, pos, ptype, value); 5226 } else { 5227 value = ptype.cast(value); // throw CCE if needed 5228 result = result.bindArgumentL(pos, value); 5229 } 5230 } 5231 return result; 5232 } 5233 5234 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos, 5235 Class<?> ptype, Object value) { 5236 Wrapper w = Wrapper.forPrimitiveType(ptype); 5237 // perform unboxing and/or primitive conversion 5238 value = w.convert(value, ptype); 5239 return switch (w) { 5240 case INT -> result.bindArgumentI(pos, (int) value); 5241 case LONG -> result.bindArgumentJ(pos, (long) value); 5242 case FLOAT -> result.bindArgumentF(pos, (float) value); 5243 case DOUBLE -> result.bindArgumentD(pos, (double) value); 5244 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value)); 5245 }; 5246 } 5247 5248 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException { 5249 MethodType oldType = target.type(); 5250 int outargs = oldType.parameterCount(); 5251 int inargs = outargs - insCount; 5252 if (inargs < 0) 5253 throw newIllegalArgumentException("too many values to insert"); 5254 if (pos < 0 || pos > inargs) 5255 throw newIllegalArgumentException("no argument type to append"); 5256 return oldType.ptypes(); 5257 } 5258 5259 /** 5260 * Produces a method handle which will discard some dummy arguments 5261 * before calling some other specified <i>target</i> method handle. 5262 * The type of the new method handle will be the same as the target's type, 5263 * except it will also include the dummy argument types, 5264 * at some given position. 5265 * <p> 5266 * The {@code pos} argument may range between zero and <i>N</i>, 5267 * where <i>N</i> is the arity of the target. 5268 * If {@code pos} is zero, the dummy arguments will precede 5269 * the target's real arguments; if {@code pos} is <i>N</i> 5270 * they will come after. 5271 * <p> 5272 * <b>Example:</b> 5273 * {@snippet lang="java" : 5274 import static java.lang.invoke.MethodHandles.*; 5275 import static java.lang.invoke.MethodType.*; 5276 ... 5277 MethodHandle cat = lookup().findVirtual(String.class, 5278 "concat", methodType(String.class, String.class)); 5279 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5280 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class); 5281 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2)); 5282 assertEquals(bigType, d0.type()); 5283 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z")); 5284 * } 5285 * <p> 5286 * This method is also equivalent to the following code: 5287 * <blockquote><pre> 5288 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))} 5289 * </pre></blockquote> 5290 * @param target the method handle to invoke after the arguments are dropped 5291 * @param pos position of first argument to drop (zero for the leftmost) 5292 * @param valueTypes the type(s) of the argument(s) to drop 5293 * @return a method handle which drops arguments of the given types, 5294 * before calling the original method handle 5295 * @throws NullPointerException if the target is null, 5296 * or if the {@code valueTypes} list or any of its elements is null 5297 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 5298 * or if {@code pos} is negative or greater than the arity of the target, 5299 * or if the new method handle's type would have too many parameters 5300 */ 5301 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) { 5302 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone()); 5303 } 5304 5305 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) { 5306 MethodType oldType = target.type(); // get NPE 5307 int dropped = dropArgumentChecks(oldType, pos, valueTypes); 5308 MethodType newType = oldType.insertParameterTypes(pos, valueTypes); 5309 if (dropped == 0) return target; 5310 BoundMethodHandle result = target.rebind(); 5311 LambdaForm lform = result.form; 5312 int insertFormArg = 1 + pos; 5313 for (Class<?> ptype : valueTypes) { 5314 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype)); 5315 } 5316 result = result.copyWith(newType, lform); 5317 return result; 5318 } 5319 5320 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) { 5321 int dropped = valueTypes.length; 5322 MethodType.checkSlotCount(dropped); 5323 int outargs = oldType.parameterCount(); 5324 int inargs = outargs + dropped; 5325 if (pos < 0 || pos > outargs) 5326 throw newIllegalArgumentException("no argument type to remove" 5327 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs) 5328 ); 5329 return dropped; 5330 } 5331 5332 /** 5333 * Produces a method handle which will discard some dummy arguments 5334 * before calling some other specified <i>target</i> method handle. 5335 * The type of the new method handle will be the same as the target's type, 5336 * except it will also include the dummy argument types, 5337 * at some given position. 5338 * <p> 5339 * The {@code pos} argument may range between zero and <i>N</i>, 5340 * where <i>N</i> is the arity of the target. 5341 * If {@code pos} is zero, the dummy arguments will precede 5342 * the target's real arguments; if {@code pos} is <i>N</i> 5343 * they will come after. 5344 * @apiNote 5345 * {@snippet lang="java" : 5346 import static java.lang.invoke.MethodHandles.*; 5347 import static java.lang.invoke.MethodType.*; 5348 ... 5349 MethodHandle cat = lookup().findVirtual(String.class, 5350 "concat", methodType(String.class, String.class)); 5351 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5352 MethodHandle d0 = dropArguments(cat, 0, String.class); 5353 assertEquals("yz", (String) d0.invokeExact("x", "y", "z")); 5354 MethodHandle d1 = dropArguments(cat, 1, String.class); 5355 assertEquals("xz", (String) d1.invokeExact("x", "y", "z")); 5356 MethodHandle d2 = dropArguments(cat, 2, String.class); 5357 assertEquals("xy", (String) d2.invokeExact("x", "y", "z")); 5358 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class); 5359 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z")); 5360 * } 5361 * <p> 5362 * This method is also equivalent to the following code: 5363 * <blockquote><pre> 5364 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))} 5365 * </pre></blockquote> 5366 * @param target the method handle to invoke after the arguments are dropped 5367 * @param pos position of first argument to drop (zero for the leftmost) 5368 * @param valueTypes the type(s) of the argument(s) to drop 5369 * @return a method handle which drops arguments of the given types, 5370 * before calling the original method handle 5371 * @throws NullPointerException if the target is null, 5372 * or if the {@code valueTypes} array or any of its elements is null 5373 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, 5374 * or if {@code pos} is negative or greater than the arity of the target, 5375 * or if the new method handle's type would have 5376 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5377 */ 5378 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) { 5379 return dropArgumentsTrusted(target, pos, valueTypes.clone()); 5380 } 5381 5382 /* Convenience overloads for trusting internal low-arity call-sites */ 5383 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) { 5384 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 }); 5385 } 5386 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) { 5387 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 }); 5388 } 5389 5390 // private version which allows caller some freedom with error handling 5391 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos, 5392 boolean nullOnFailure) { 5393 Class<?>[] oldTypes = target.type().ptypes(); 5394 int match = oldTypes.length; 5395 if (skip != 0) { 5396 if (skip < 0 || skip > match) { 5397 throw newIllegalArgumentException("illegal skip", skip, target); 5398 } 5399 oldTypes = Arrays.copyOfRange(oldTypes, skip, match); 5400 match -= skip; 5401 } 5402 Class<?>[] addTypes = newTypes; 5403 int add = addTypes.length; 5404 if (pos != 0) { 5405 if (pos < 0 || pos > add) { 5406 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes)); 5407 } 5408 addTypes = Arrays.copyOfRange(addTypes, pos, add); 5409 add -= pos; 5410 assert(addTypes.length == add); 5411 } 5412 // Do not add types which already match the existing arguments. 5413 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) { 5414 if (nullOnFailure) { 5415 return null; 5416 } 5417 throw newIllegalArgumentException("argument lists do not match", 5418 Arrays.toString(oldTypes), Arrays.toString(newTypes)); 5419 } 5420 addTypes = Arrays.copyOfRange(addTypes, match, add); 5421 add -= match; 5422 assert(addTypes.length == add); 5423 // newTypes: ( P*[pos], M*[match], A*[add] ) 5424 // target: ( S*[skip], M*[match] ) 5425 MethodHandle adapter = target; 5426 if (add > 0) { 5427 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes); 5428 } 5429 // adapter: (S*[skip], M*[match], A*[add] ) 5430 if (pos > 0) { 5431 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos)); 5432 } 5433 // adapter: (S*[skip], P*[pos], M*[match], A*[add] ) 5434 return adapter; 5435 } 5436 5437 /** 5438 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some 5439 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter 5440 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The 5441 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before 5442 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by 5443 * {@link #dropArguments(MethodHandle, int, Class[])}. 5444 * <p> 5445 * The resulting handle will have the same return type as the target handle. 5446 * <p> 5447 * In more formal terms, assume these two type lists:<ul> 5448 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as 5449 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list, 5450 * {@code newTypes}. 5451 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as 5452 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's 5453 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching 5454 * sub-list. 5455 * </ul> 5456 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type 5457 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by 5458 * {@link #dropArguments(MethodHandle, int, Class[])}. 5459 * 5460 * @apiNote 5461 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be 5462 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows: 5463 * {@snippet lang="java" : 5464 import static java.lang.invoke.MethodHandles.*; 5465 import static java.lang.invoke.MethodType.*; 5466 ... 5467 ... 5468 MethodHandle h0 = constant(boolean.class, true); 5469 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class)); 5470 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class); 5471 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList()); 5472 if (h1.type().parameterCount() < h2.type().parameterCount()) 5473 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1 5474 else 5475 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2 5476 MethodHandle h3 = guardWithTest(h0, h1, h2); 5477 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c")); 5478 * } 5479 * @param target the method handle to adapt 5480 * @param skip number of targets parameters to disregard (they will be unchanged) 5481 * @param newTypes the list of types to match {@code target}'s parameter type list to 5482 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur 5483 * @return a possibly adapted method handle 5484 * @throws NullPointerException if either argument is null 5485 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class}, 5486 * or if {@code skip} is negative or greater than the arity of the target, 5487 * or if {@code pos} is negative or greater than the newTypes list size, 5488 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position 5489 * {@code pos}. 5490 * @since 9 5491 */ 5492 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) { 5493 Objects.requireNonNull(target); 5494 Objects.requireNonNull(newTypes); 5495 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false); 5496 } 5497 5498 /** 5499 * Drop the return value of the target handle (if any). 5500 * The returned method handle will have a {@code void} return type. 5501 * 5502 * @param target the method handle to adapt 5503 * @return a possibly adapted method handle 5504 * @throws NullPointerException if {@code target} is null 5505 * @since 16 5506 */ 5507 public static MethodHandle dropReturn(MethodHandle target) { 5508 Objects.requireNonNull(target); 5509 MethodType oldType = target.type(); 5510 Class<?> oldReturnType = oldType.returnType(); 5511 if (oldReturnType == void.class) 5512 return target; 5513 MethodType newType = oldType.changeReturnType(void.class); 5514 BoundMethodHandle result = target.rebind(); 5515 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true); 5516 result = result.copyWith(newType, lform); 5517 return result; 5518 } 5519 5520 /** 5521 * Adapts a target method handle by pre-processing 5522 * one or more of its arguments, each with its own unary filter function, 5523 * and then calling the target with each pre-processed argument 5524 * replaced by the result of its corresponding filter function. 5525 * <p> 5526 * The pre-processing is performed by one or more method handles, 5527 * specified in the elements of the {@code filters} array. 5528 * The first element of the filter array corresponds to the {@code pos} 5529 * argument of the target, and so on in sequence. 5530 * The filter functions are invoked in left to right order. 5531 * <p> 5532 * Null arguments in the array are treated as identity functions, 5533 * and the corresponding arguments left unchanged. 5534 * (If there are no non-null elements in the array, the original target is returned.) 5535 * Each filter is applied to the corresponding argument of the adapter. 5536 * <p> 5537 * If a filter {@code F} applies to the {@code N}th argument of 5538 * the target, then {@code F} must be a method handle which 5539 * takes exactly one argument. The type of {@code F}'s sole argument 5540 * replaces the corresponding argument type of the target 5541 * in the resulting adapted method handle. 5542 * The return type of {@code F} must be identical to the corresponding 5543 * parameter type of the target. 5544 * <p> 5545 * It is an error if there are elements of {@code filters} 5546 * (null or not) 5547 * which do not correspond to argument positions in the target. 5548 * <p><b>Example:</b> 5549 * {@snippet lang="java" : 5550 import static java.lang.invoke.MethodHandles.*; 5551 import static java.lang.invoke.MethodType.*; 5552 ... 5553 MethodHandle cat = lookup().findVirtual(String.class, 5554 "concat", methodType(String.class, String.class)); 5555 MethodHandle upcase = lookup().findVirtual(String.class, 5556 "toUpperCase", methodType(String.class)); 5557 assertEquals("xy", (String) cat.invokeExact("x", "y")); 5558 MethodHandle f0 = filterArguments(cat, 0, upcase); 5559 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy 5560 MethodHandle f1 = filterArguments(cat, 1, upcase); 5561 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY 5562 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase); 5563 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY 5564 * } 5565 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5566 * denotes the return type of both the {@code target} and resulting adapter. 5567 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values 5568 * of the parameters and arguments that precede and follow the filter position 5569 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and 5570 * values of the filtered parameters and arguments; they also represent the 5571 * return types of the {@code filter[i]} handles. The latter accept arguments 5572 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of 5573 * the resulting adapter. 5574 * {@snippet lang="java" : 5575 * T target(P... p, A[i]... a[i], B... b); 5576 * A[i] filter[i](V[i]); 5577 * T adapter(P... p, V[i]... v[i], B... b) { 5578 * return target(p..., filter[i](v[i])..., b...); 5579 * } 5580 * } 5581 * <p> 5582 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5583 * variable-arity method handle}, even if the original target method handle was. 5584 * 5585 * @param target the method handle to invoke after arguments are filtered 5586 * @param pos the position of the first argument to filter 5587 * @param filters method handles to call initially on filtered arguments 5588 * @return method handle which incorporates the specified argument filtering logic 5589 * @throws NullPointerException if the target is null 5590 * or if the {@code filters} array is null 5591 * @throws IllegalArgumentException if a non-null element of {@code filters} 5592 * does not match a corresponding argument type of target as described above, 5593 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}, 5594 * or if the resulting method handle's type would have 5595 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5596 */ 5597 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) { 5598 // In method types arguments start at index 0, while the LF 5599 // editor have the MH receiver at position 0 - adjust appropriately. 5600 final int MH_RECEIVER_OFFSET = 1; 5601 filterArgumentsCheckArity(target, pos, filters); 5602 MethodHandle adapter = target; 5603 5604 // keep track of currently matched filters, as to optimize repeated filters 5605 int index = 0; 5606 int[] positions = new int[filters.length]; 5607 MethodHandle filter = null; 5608 5609 // process filters in reverse order so that the invocation of 5610 // the resulting adapter will invoke the filters in left-to-right order 5611 for (int i = filters.length - 1; i >= 0; --i) { 5612 MethodHandle newFilter = filters[i]; 5613 if (newFilter == null) continue; // ignore null elements of filters 5614 5615 // flush changes on update 5616 if (filter != newFilter) { 5617 if (filter != null) { 5618 if (index > 1) { 5619 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 5620 } else { 5621 adapter = filterArgument(adapter, positions[0] - 1, filter); 5622 } 5623 } 5624 filter = newFilter; 5625 index = 0; 5626 } 5627 5628 filterArgumentChecks(target, pos + i, newFilter); 5629 positions[index++] = pos + i + MH_RECEIVER_OFFSET; 5630 } 5631 if (index > 1) { 5632 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index)); 5633 } else if (index == 1) { 5634 adapter = filterArgument(adapter, positions[0] - 1, filter); 5635 } 5636 return adapter; 5637 } 5638 5639 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) { 5640 MethodType targetType = adapter.type(); 5641 MethodType filterType = filter.type(); 5642 BoundMethodHandle result = adapter.rebind(); 5643 Class<?> newParamType = filterType.parameterType(0); 5644 5645 Class<?>[] ptypes = targetType.ptypes().clone(); 5646 for (int pos : positions) { 5647 ptypes[pos - 1] = newParamType; 5648 } 5649 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true); 5650 5651 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions); 5652 return result.copyWithExtendL(newType, lform, filter); 5653 } 5654 5655 /*non-public*/ 5656 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) { 5657 filterArgumentChecks(target, pos, filter); 5658 MethodType targetType = target.type(); 5659 MethodType filterType = filter.type(); 5660 BoundMethodHandle result = target.rebind(); 5661 Class<?> newParamType = filterType.parameterType(0); 5662 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType)); 5663 MethodType newType = targetType.changeParameterType(pos, newParamType); 5664 result = result.copyWithExtendL(newType, lform, filter); 5665 return result; 5666 } 5667 5668 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) { 5669 MethodType targetType = target.type(); 5670 int maxPos = targetType.parameterCount(); 5671 if (pos + filters.length > maxPos) 5672 throw newIllegalArgumentException("too many filters"); 5673 } 5674 5675 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 5676 MethodType targetType = target.type(); 5677 MethodType filterType = filter.type(); 5678 if (filterType.parameterCount() != 1 5679 || filterType.returnType() != targetType.parameterType(pos)) 5680 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5681 } 5682 5683 /** 5684 * Adapts a target method handle by pre-processing 5685 * a sub-sequence of its arguments with a filter (another method handle). 5686 * The pre-processed arguments are replaced by the result (if any) of the 5687 * filter function. 5688 * The target is then called on the modified (usually shortened) argument list. 5689 * <p> 5690 * If the filter returns a value, the target must accept that value as 5691 * its argument in position {@code pos}, preceded and/or followed by 5692 * any arguments not passed to the filter. 5693 * If the filter returns void, the target must accept all arguments 5694 * not passed to the filter. 5695 * No arguments are reordered, and a result returned from the filter 5696 * replaces (in order) the whole subsequence of arguments originally 5697 * passed to the adapter. 5698 * <p> 5699 * The argument types (if any) of the filter 5700 * replace zero or one argument types of the target, at position {@code pos}, 5701 * in the resulting adapted method handle. 5702 * The return type of the filter (if any) must be identical to the 5703 * argument type of the target at position {@code pos}, and that target argument 5704 * is supplied by the return value of the filter. 5705 * <p> 5706 * In all cases, {@code pos} must be greater than or equal to zero, and 5707 * {@code pos} must also be less than or equal to the target's arity. 5708 * <p><b>Example:</b> 5709 * {@snippet lang="java" : 5710 import static java.lang.invoke.MethodHandles.*; 5711 import static java.lang.invoke.MethodType.*; 5712 ... 5713 MethodHandle deepToString = publicLookup() 5714 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); 5715 5716 MethodHandle ts1 = deepToString.asCollector(String[].class, 1); 5717 assertEquals("[strange]", (String) ts1.invokeExact("strange")); 5718 5719 MethodHandle ts2 = deepToString.asCollector(String[].class, 2); 5720 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down")); 5721 5722 MethodHandle ts3 = deepToString.asCollector(String[].class, 3); 5723 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2); 5724 assertEquals("[top, [up, down], strange]", 5725 (String) ts3_ts2.invokeExact("top", "up", "down", "strange")); 5726 5727 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1); 5728 assertEquals("[top, [up, down], [strange]]", 5729 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange")); 5730 5731 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3); 5732 assertEquals("[top, [[up, down, strange], charm], bottom]", 5733 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom")); 5734 * } 5735 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5736 * represents the return type of the {@code target} and resulting adapter. 5737 * {@code V}/{@code v} stand for the return type and value of the 5738 * {@code filter}, which are also found in the signature and arguments of 5739 * the {@code target}, respectively, unless {@code V} is {@code void}. 5740 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types 5741 * and values preceding and following the collection position, {@code pos}, 5742 * in the {@code target}'s signature. They also turn up in the resulting 5743 * adapter's signature and arguments, where they surround 5744 * {@code B}/{@code b}, which represent the parameter types and arguments 5745 * to the {@code filter} (if any). 5746 * {@snippet lang="java" : 5747 * T target(A...,V,C...); 5748 * V filter(B...); 5749 * T adapter(A... a,B... b,C... c) { 5750 * V v = filter(b...); 5751 * return target(a...,v,c...); 5752 * } 5753 * // and if the filter has no arguments: 5754 * T target2(A...,V,C...); 5755 * V filter2(); 5756 * T adapter2(A... a,C... c) { 5757 * V v = filter2(); 5758 * return target2(a...,v,c...); 5759 * } 5760 * // and if the filter has a void return: 5761 * T target3(A...,C...); 5762 * void filter3(B...); 5763 * T adapter3(A... a,B... b,C... c) { 5764 * filter3(b...); 5765 * return target3(a...,c...); 5766 * } 5767 * } 5768 * <p> 5769 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to 5770 * one which first "folds" the affected arguments, and then drops them, in separate 5771 * steps as follows: 5772 * {@snippet lang="java" : 5773 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2 5774 * mh = MethodHandles.foldArguments(mh, coll); //step 1 5775 * } 5776 * If the target method handle consumes no arguments besides than the result 5777 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)} 5778 * is equivalent to {@code filterReturnValue(coll, mh)}. 5779 * If the filter method handle {@code coll} consumes one argument and produces 5780 * a non-void result, then {@code collectArguments(mh, N, coll)} 5781 * is equivalent to {@code filterArguments(mh, N, coll)}. 5782 * Other equivalences are possible but would require argument permutation. 5783 * <p> 5784 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5785 * variable-arity method handle}, even if the original target method handle was. 5786 * 5787 * @param target the method handle to invoke after filtering the subsequence of arguments 5788 * @param pos the position of the first adapter argument to pass to the filter, 5789 * and/or the target argument which receives the result of the filter 5790 * @param filter method handle to call on the subsequence of arguments 5791 * @return method handle which incorporates the specified argument subsequence filtering logic 5792 * @throws NullPointerException if either argument is null 5793 * @throws IllegalArgumentException if the return type of {@code filter} 5794 * is non-void and is not the same as the {@code pos} argument of the target, 5795 * or if {@code pos} is not between 0 and the target's arity, inclusive, 5796 * or if the resulting method handle's type would have 5797 * <a href="MethodHandle.html#maxarity">too many parameters</a> 5798 * @see MethodHandles#foldArguments 5799 * @see MethodHandles#filterArguments 5800 * @see MethodHandles#filterReturnValue 5801 */ 5802 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) { 5803 MethodType newType = collectArgumentsChecks(target, pos, filter); 5804 MethodType collectorType = filter.type(); 5805 BoundMethodHandle result = target.rebind(); 5806 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType()); 5807 return result.copyWithExtendL(newType, lform, filter); 5808 } 5809 5810 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException { 5811 MethodType targetType = target.type(); 5812 MethodType filterType = filter.type(); 5813 Class<?> rtype = filterType.returnType(); 5814 Class<?>[] filterArgs = filterType.ptypes(); 5815 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) || 5816 (rtype != void.class && pos >= targetType.parameterCount())) { 5817 throw newIllegalArgumentException("position is out of range for target", target, pos); 5818 } 5819 if (rtype == void.class) { 5820 return targetType.insertParameterTypes(pos, filterArgs); 5821 } 5822 if (rtype != targetType.parameterType(pos)) { 5823 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5824 } 5825 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs); 5826 } 5827 5828 /** 5829 * Adapts a target method handle by post-processing 5830 * its return value (if any) with a filter (another method handle). 5831 * The result of the filter is returned from the adapter. 5832 * <p> 5833 * If the target returns a value, the filter must accept that value as 5834 * its only argument. 5835 * If the target returns void, the filter must accept no arguments. 5836 * <p> 5837 * The return type of the filter 5838 * replaces the return type of the target 5839 * in the resulting adapted method handle. 5840 * The argument type of the filter (if any) must be identical to the 5841 * return type of the target. 5842 * <p><b>Example:</b> 5843 * {@snippet lang="java" : 5844 import static java.lang.invoke.MethodHandles.*; 5845 import static java.lang.invoke.MethodType.*; 5846 ... 5847 MethodHandle cat = lookup().findVirtual(String.class, 5848 "concat", methodType(String.class, String.class)); 5849 MethodHandle length = lookup().findVirtual(String.class, 5850 "length", methodType(int.class)); 5851 System.out.println((String) cat.invokeExact("x", "y")); // xy 5852 MethodHandle f0 = filterReturnValue(cat, length); 5853 System.out.println((int) f0.invokeExact("x", "y")); // 2 5854 * } 5855 * <p>Here is pseudocode for the resulting adapter. In the code, 5856 * {@code T}/{@code t} represent the result type and value of the 5857 * {@code target}; {@code V}, the result type of the {@code filter}; and 5858 * {@code A}/{@code a}, the types and values of the parameters and arguments 5859 * of the {@code target} as well as the resulting adapter. 5860 * {@snippet lang="java" : 5861 * T target(A...); 5862 * V filter(T); 5863 * V adapter(A... a) { 5864 * T t = target(a...); 5865 * return filter(t); 5866 * } 5867 * // and if the target has a void return: 5868 * void target2(A...); 5869 * V filter2(); 5870 * V adapter2(A... a) { 5871 * target2(a...); 5872 * return filter2(); 5873 * } 5874 * // and if the filter has a void return: 5875 * T target3(A...); 5876 * void filter3(V); 5877 * void adapter3(A... a) { 5878 * T t = target3(a...); 5879 * filter3(t); 5880 * } 5881 * } 5882 * <p> 5883 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 5884 * variable-arity method handle}, even if the original target method handle was. 5885 * @param target the method handle to invoke before filtering the return value 5886 * @param filter method handle to call on the return value 5887 * @return method handle which incorporates the specified return value filtering logic 5888 * @throws NullPointerException if either argument is null 5889 * @throws IllegalArgumentException if the argument list of {@code filter} 5890 * does not match the return type of target as described above 5891 */ 5892 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) { 5893 MethodType targetType = target.type(); 5894 MethodType filterType = filter.type(); 5895 filterReturnValueChecks(targetType, filterType); 5896 BoundMethodHandle result = target.rebind(); 5897 BasicType rtype = BasicType.basicType(filterType.returnType()); 5898 LambdaForm lform = result.editor().filterReturnForm(rtype, false); 5899 MethodType newType = targetType.changeReturnType(filterType.returnType()); 5900 result = result.copyWithExtendL(newType, lform, filter); 5901 return result; 5902 } 5903 5904 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException { 5905 Class<?> rtype = targetType.returnType(); 5906 int filterValues = filterType.parameterCount(); 5907 if (filterValues == 0 5908 ? (rtype != void.class) 5909 : (rtype != filterType.parameterType(0) || filterValues != 1)) 5910 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); 5911 } 5912 5913 /** 5914 * Filter the return value of a target method handle with a filter function. The filter function is 5915 * applied to the return value of the original handle; if the filter specifies more than one parameters, 5916 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works 5917 * as follows: 5918 * {@snippet lang="java" : 5919 * T target(A...) 5920 * V filter(B... , T) 5921 * V adapter(A... a, B... b) { 5922 * T t = target(a...); 5923 * return filter(b..., t); 5924 * } 5925 * } 5926 * <p> 5927 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}. 5928 * 5929 * @param target the target method handle 5930 * @param filter the filter method handle 5931 * @return the adapter method handle 5932 */ 5933 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) { 5934 MethodType targetType = target.type(); 5935 MethodType filterType = filter.type(); 5936 BoundMethodHandle result = target.rebind(); 5937 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType()); 5938 MethodType newType = targetType.changeReturnType(filterType.returnType()); 5939 if (filterType.parameterCount() > 1) { 5940 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) { 5941 newType = newType.appendParameterTypes(filterType.parameterType(i)); 5942 } 5943 } 5944 result = result.copyWithExtendL(newType, lform, filter); 5945 return result; 5946 } 5947 5948 /** 5949 * Adapts a target method handle by pre-processing 5950 * some of its arguments, and then calling the target with 5951 * the result of the pre-processing, inserted into the original 5952 * sequence of arguments. 5953 * <p> 5954 * The pre-processing is performed by {@code combiner}, a second method handle. 5955 * Of the arguments passed to the adapter, the first {@code N} arguments 5956 * are copied to the combiner, which is then called. 5957 * (Here, {@code N} is defined as the parameter count of the combiner.) 5958 * After this, control passes to the target, with any result 5959 * from the combiner inserted before the original {@code N} incoming 5960 * arguments. 5961 * <p> 5962 * If the combiner returns a value, the first parameter type of the target 5963 * must be identical with the return type of the combiner, and the next 5964 * {@code N} parameter types of the target must exactly match the parameters 5965 * of the combiner. 5966 * <p> 5967 * If the combiner has a void return, no result will be inserted, 5968 * and the first {@code N} parameter types of the target 5969 * must exactly match the parameters of the combiner. 5970 * <p> 5971 * The resulting adapter is the same type as the target, except that the 5972 * first parameter type is dropped, 5973 * if it corresponds to the result of the combiner. 5974 * <p> 5975 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments 5976 * that either the combiner or the target does not wish to receive. 5977 * If some of the incoming arguments are destined only for the combiner, 5978 * consider using {@link MethodHandle#asCollector asCollector} instead, since those 5979 * arguments will not need to be live on the stack on entry to the 5980 * target.) 5981 * <p><b>Example:</b> 5982 * {@snippet lang="java" : 5983 import static java.lang.invoke.MethodHandles.*; 5984 import static java.lang.invoke.MethodType.*; 5985 ... 5986 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 5987 "println", methodType(void.class, String.class)) 5988 .bindTo(System.out); 5989 MethodHandle cat = lookup().findVirtual(String.class, 5990 "concat", methodType(String.class, String.class)); 5991 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 5992 MethodHandle catTrace = foldArguments(cat, trace); 5993 // also prints "boo": 5994 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 5995 * } 5996 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 5997 * represents the result type of the {@code target} and resulting adapter. 5998 * {@code V}/{@code v} represent the type and value of the parameter and argument 5999 * of {@code target} that precedes the folding position; {@code V} also is 6000 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 6001 * types and values of the {@code N} parameters and arguments at the folding 6002 * position. {@code B}/{@code b} represent the types and values of the 6003 * {@code target} parameters and arguments that follow the folded parameters 6004 * and arguments. 6005 * {@snippet lang="java" : 6006 * // there are N arguments in A... 6007 * T target(V, A[N]..., B...); 6008 * V combiner(A...); 6009 * T adapter(A... a, B... b) { 6010 * V v = combiner(a...); 6011 * return target(v, a..., b...); 6012 * } 6013 * // and if the combiner has a void return: 6014 * T target2(A[N]..., B...); 6015 * void combiner2(A...); 6016 * T adapter2(A... a, B... b) { 6017 * combiner2(a...); 6018 * return target2(a..., b...); 6019 * } 6020 * } 6021 * <p> 6022 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 6023 * variable-arity method handle}, even if the original target method handle was. 6024 * @param target the method handle to invoke after arguments are combined 6025 * @param combiner method handle to call initially on the incoming arguments 6026 * @return method handle which incorporates the specified argument folding logic 6027 * @throws NullPointerException if either argument is null 6028 * @throws IllegalArgumentException if {@code combiner}'s return type 6029 * is non-void and not the same as the first argument type of 6030 * the target, or if the initial {@code N} argument types 6031 * of the target 6032 * (skipping one matching the {@code combiner}'s return type) 6033 * are not identical with the argument types of {@code combiner} 6034 */ 6035 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) { 6036 return foldArguments(target, 0, combiner); 6037 } 6038 6039 /** 6040 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then 6041 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just 6042 * before the folded arguments. 6043 * <p> 6044 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the 6045 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a 6046 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position 6047 * 0. 6048 * 6049 * @apiNote Example: 6050 * {@snippet lang="java" : 6051 import static java.lang.invoke.MethodHandles.*; 6052 import static java.lang.invoke.MethodType.*; 6053 ... 6054 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class, 6055 "println", methodType(void.class, String.class)) 6056 .bindTo(System.out); 6057 MethodHandle cat = lookup().findVirtual(String.class, 6058 "concat", methodType(String.class, String.class)); 6059 assertEquals("boojum", (String) cat.invokeExact("boo", "jum")); 6060 MethodHandle catTrace = foldArguments(cat, 1, trace); 6061 // also prints "jum": 6062 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum")); 6063 * } 6064 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T} 6065 * represents the result type of the {@code target} and resulting adapter. 6066 * {@code V}/{@code v} represent the type and value of the parameter and argument 6067 * of {@code target} that precedes the folding position; {@code V} also is 6068 * the result type of the {@code combiner}. {@code A}/{@code a} denote the 6069 * types and values of the {@code N} parameters and arguments at the folding 6070 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types 6071 * and values of the {@code target} parameters and arguments that precede and 6072 * follow the folded parameters and arguments starting at {@code pos}, 6073 * respectively. 6074 * {@snippet lang="java" : 6075 * // there are N arguments in A... 6076 * T target(Z..., V, A[N]..., B...); 6077 * V combiner(A...); 6078 * T adapter(Z... z, A... a, B... b) { 6079 * V v = combiner(a...); 6080 * return target(z..., v, a..., b...); 6081 * } 6082 * // and if the combiner has a void return: 6083 * T target2(Z..., A[N]..., B...); 6084 * void combiner2(A...); 6085 * T adapter2(Z... z, A... a, B... b) { 6086 * combiner2(a...); 6087 * return target2(z..., a..., b...); 6088 * } 6089 * } 6090 * <p> 6091 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector 6092 * variable-arity method handle}, even if the original target method handle was. 6093 * 6094 * @param target the method handle to invoke after arguments are combined 6095 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code 6096 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6097 * @param combiner method handle to call initially on the incoming arguments 6098 * @return method handle which incorporates the specified argument folding logic 6099 * @throws NullPointerException if either argument is null 6100 * @throws IllegalArgumentException if either of the following two conditions holds: 6101 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 6102 * {@code pos} of the target signature; 6103 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching 6104 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}. 6105 * 6106 * @see #foldArguments(MethodHandle, MethodHandle) 6107 * @since 9 6108 */ 6109 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) { 6110 MethodType targetType = target.type(); 6111 MethodType combinerType = combiner.type(); 6112 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType); 6113 BoundMethodHandle result = target.rebind(); 6114 boolean dropResult = rtype == void.class; 6115 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType()); 6116 MethodType newType = targetType; 6117 if (!dropResult) { 6118 newType = newType.dropParameterTypes(pos, pos + 1); 6119 } 6120 result = result.copyWithExtendL(newType, lform, combiner); 6121 return result; 6122 } 6123 6124 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) { 6125 int foldArgs = combinerType.parameterCount(); 6126 Class<?> rtype = combinerType.returnType(); 6127 int foldVals = rtype == void.class ? 0 : 1; 6128 int afterInsertPos = foldPos + foldVals; 6129 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs); 6130 if (ok) { 6131 for (int i = 0; i < foldArgs; i++) { 6132 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) { 6133 ok = false; 6134 break; 6135 } 6136 } 6137 } 6138 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) 6139 ok = false; 6140 if (!ok) 6141 throw misMatchedTypes("target and combiner types", targetType, combinerType); 6142 return rtype; 6143 } 6144 6145 /** 6146 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result 6147 * of the pre-processing replacing the argument at the given position. 6148 * 6149 * @param target the method handle to invoke after arguments are combined 6150 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 6151 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6152 * @param combiner method handle to call initially on the incoming arguments 6153 * @param argPositions indexes of the target to pick arguments sent to the combiner from 6154 * @return method handle which incorporates the specified argument folding logic 6155 * @throws NullPointerException if either argument is null 6156 * @throws IllegalArgumentException if either of the following two conditions holds: 6157 * (1) {@code combiner}'s return type is not the same as the argument type at position 6158 * {@code pos} of the target signature; 6159 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are 6160 * not identical with the argument types of {@code combiner}. 6161 */ 6162 /*non-public*/ 6163 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6164 return argumentsWithCombiner(true, target, position, combiner, argPositions); 6165 } 6166 6167 /** 6168 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of 6169 * the pre-processing inserted into the original sequence of arguments at the given position. 6170 * 6171 * @param target the method handle to invoke after arguments are combined 6172 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code 6173 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}. 6174 * @param combiner method handle to call initially on the incoming arguments 6175 * @param argPositions indexes of the target to pick arguments sent to the combiner from 6176 * @return method handle which incorporates the specified argument folding logic 6177 * @throws NullPointerException if either argument is null 6178 * @throws IllegalArgumentException if either of the following two conditions holds: 6179 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position 6180 * {@code pos} of the target signature; 6181 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature 6182 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical 6183 * with the argument types of {@code combiner}. 6184 */ 6185 /*non-public*/ 6186 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6187 return argumentsWithCombiner(false, target, position, combiner, argPositions); 6188 } 6189 6190 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) { 6191 MethodType targetType = target.type(); 6192 MethodType combinerType = combiner.type(); 6193 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions); 6194 BoundMethodHandle result = target.rebind(); 6195 6196 MethodType newType = targetType; 6197 LambdaForm lform; 6198 if (filter) { 6199 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions); 6200 } else { 6201 boolean dropResult = rtype == void.class; 6202 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions); 6203 if (!dropResult) { 6204 newType = newType.dropParameterTypes(position, position + 1); 6205 } 6206 } 6207 result = result.copyWithExtendL(newType, lform, combiner); 6208 return result; 6209 } 6210 6211 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) { 6212 int combinerArgs = combinerType.parameterCount(); 6213 if (argPos.length != combinerArgs) { 6214 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length); 6215 } 6216 Class<?> rtype = combinerType.returnType(); 6217 6218 for (int i = 0; i < combinerArgs; i++) { 6219 int arg = argPos[i]; 6220 if (arg < 0 || arg > targetType.parameterCount()) { 6221 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg); 6222 } 6223 if (combinerType.parameterType(i) != targetType.parameterType(arg)) { 6224 throw newIllegalArgumentException("target argument type at position " + arg 6225 + " must match combiner argument type at index " + i + ": " + targetType 6226 + " -> " + combinerType + ", map: " + Arrays.toString(argPos)); 6227 } 6228 } 6229 if (filter && combinerType.returnType() != targetType.parameterType(position)) { 6230 throw misMatchedTypes("target and combiner types", targetType, combinerType); 6231 } 6232 return rtype; 6233 } 6234 6235 /** 6236 * Makes a method handle which adapts a target method handle, 6237 * by guarding it with a test, a boolean-valued method handle. 6238 * If the guard fails, a fallback handle is called instead. 6239 * All three method handles must have the same corresponding 6240 * argument and return types, except that the return type 6241 * of the test must be boolean, and the test is allowed 6242 * to have fewer arguments than the other two method handles. 6243 * <p> 6244 * Here is pseudocode for the resulting adapter. In the code, {@code T} 6245 * represents the uniform result type of the three involved handles; 6246 * {@code A}/{@code a}, the types and values of the {@code target} 6247 * parameters and arguments that are consumed by the {@code test}; and 6248 * {@code B}/{@code b}, those types and values of the {@code target} 6249 * parameters and arguments that are not consumed by the {@code test}. 6250 * {@snippet lang="java" : 6251 * boolean test(A...); 6252 * T target(A...,B...); 6253 * T fallback(A...,B...); 6254 * T adapter(A... a,B... b) { 6255 * if (test(a...)) 6256 * return target(a..., b...); 6257 * else 6258 * return fallback(a..., b...); 6259 * } 6260 * } 6261 * Note that the test arguments ({@code a...} in the pseudocode) cannot 6262 * be modified by execution of the test, and so are passed unchanged 6263 * from the caller to the target or fallback as appropriate. 6264 * @param test method handle used for test, must return boolean 6265 * @param target method handle to call if test passes 6266 * @param fallback method handle to call if test fails 6267 * @return method handle which incorporates the specified if/then/else logic 6268 * @throws NullPointerException if any argument is null 6269 * @throws IllegalArgumentException if {@code test} does not return boolean, 6270 * or if all three method types do not match (with the return 6271 * type of {@code test} changed to match that of the target). 6272 */ 6273 public static MethodHandle guardWithTest(MethodHandle test, 6274 MethodHandle target, 6275 MethodHandle fallback) { 6276 MethodType gtype = test.type(); 6277 MethodType ttype = target.type(); 6278 MethodType ftype = fallback.type(); 6279 if (!ttype.equals(ftype)) 6280 throw misMatchedTypes("target and fallback types", ttype, ftype); 6281 if (gtype.returnType() != boolean.class) 6282 throw newIllegalArgumentException("guard type is not a predicate "+gtype); 6283 6284 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true); 6285 if (test == null) { 6286 throw misMatchedTypes("target and test types", ttype, gtype); 6287 } 6288 return MethodHandleImpl.makeGuardWithTest(test, target, fallback); 6289 } 6290 6291 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) { 6292 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2); 6293 } 6294 6295 /** 6296 * Makes a method handle which adapts a target method handle, 6297 * by running it inside an exception handler. 6298 * If the target returns normally, the adapter returns that value. 6299 * If an exception matching the specified type is thrown, the fallback 6300 * handle is called instead on the exception, plus the original arguments. 6301 * <p> 6302 * The target and handler must have the same corresponding 6303 * argument and return types, except that handler may omit trailing arguments 6304 * (similarly to the predicate in {@link #guardWithTest guardWithTest}). 6305 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype. 6306 * <p> 6307 * Here is pseudocode for the resulting adapter. In the code, {@code T} 6308 * represents the return type of the {@code target} and {@code handler}, 6309 * and correspondingly that of the resulting adapter; {@code A}/{@code a}, 6310 * the types and values of arguments to the resulting handle consumed by 6311 * {@code handler}; and {@code B}/{@code b}, those of arguments to the 6312 * resulting handle discarded by {@code handler}. 6313 * {@snippet lang="java" : 6314 * T target(A..., B...); 6315 * T handler(ExType, A...); 6316 * T adapter(A... a, B... b) { 6317 * try { 6318 * return target(a..., b...); 6319 * } catch (ExType ex) { 6320 * return handler(ex, a...); 6321 * } 6322 * } 6323 * } 6324 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 6325 * be modified by execution of the target, and so are passed unchanged 6326 * from the caller to the handler, if the handler is invoked. 6327 * <p> 6328 * The target and handler must return the same type, even if the handler 6329 * always throws. (This might happen, for instance, because the handler 6330 * is simulating a {@code finally} clause). 6331 * To create such a throwing handler, compose the handler creation logic 6332 * with {@link #throwException throwException}, 6333 * in order to create a method handle of the correct return type. 6334 * @param target method handle to call 6335 * @param exType the type of exception which the handler will catch 6336 * @param handler method handle to call if a matching exception is thrown 6337 * @return method handle which incorporates the specified try/catch logic 6338 * @throws NullPointerException if any argument is null 6339 * @throws IllegalArgumentException if {@code handler} does not accept 6340 * the given exception type, or if the method handle types do 6341 * not match in their return types and their 6342 * corresponding parameters 6343 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle) 6344 */ 6345 public static MethodHandle catchException(MethodHandle target, 6346 Class<? extends Throwable> exType, 6347 MethodHandle handler) { 6348 MethodType ttype = target.type(); 6349 MethodType htype = handler.type(); 6350 if (!Throwable.class.isAssignableFrom(exType)) 6351 throw new ClassCastException(exType.getName()); 6352 if (htype.parameterCount() < 1 || 6353 !htype.parameterType(0).isAssignableFrom(exType)) 6354 throw newIllegalArgumentException("handler does not accept exception type "+exType); 6355 if (htype.returnType() != ttype.returnType()) 6356 throw misMatchedTypes("target and handler return types", ttype, htype); 6357 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true); 6358 if (handler == null) { 6359 throw misMatchedTypes("target and handler types", ttype, htype); 6360 } 6361 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler); 6362 } 6363 6364 /** 6365 * Produces a method handle which will throw exceptions of the given {@code exType}. 6366 * The method handle will accept a single argument of {@code exType}, 6367 * and immediately throw it as an exception. 6368 * The method type will nominally specify a return of {@code returnType}. 6369 * The return type may be anything convenient: It doesn't matter to the 6370 * method handle's behavior, since it will never return normally. 6371 * @param returnType the return type of the desired method handle 6372 * @param exType the parameter type of the desired method handle 6373 * @return method handle which can throw the given exceptions 6374 * @throws NullPointerException if either argument is null 6375 */ 6376 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) { 6377 if (!Throwable.class.isAssignableFrom(exType)) 6378 throw new ClassCastException(exType.getName()); 6379 return MethodHandleImpl.throwException(methodType(returnType, exType)); 6380 } 6381 6382 /** 6383 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each 6384 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and 6385 * delivers the loop's result, which is the return value of the resulting handle. 6386 * <p> 6387 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop 6388 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration 6389 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in 6390 * terms of method handles, each clause will specify up to four independent actions:<ul> 6391 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}. 6392 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}. 6393 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit. 6394 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value. 6395 * </ul> 6396 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}. 6397 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually 6398 * be referring to types, but in some contexts (describing execution) the lists will be of actual values. 6399 * <p> 6400 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in 6401 * this case. See below for a detailed description. 6402 * <p> 6403 * <em>Parameters optional everywhere:</em> 6404 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}. 6405 * As an exception, the init functions cannot take any {@code v} parameters, 6406 * because those values are not yet computed when the init functions are executed. 6407 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take. 6408 * In fact, any clause function may take no arguments at all. 6409 * <p> 6410 * <em>Loop parameters:</em> 6411 * A clause function may take all the iteration variable values it is entitled to, in which case 6412 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>, 6413 * with their types and values notated as {@code (A...)} and {@code (a...)}. 6414 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed. 6415 * (Since init functions do not accept iteration variables {@code v}, any parameter to an 6416 * init function is automatically a loop parameter {@code a}.) 6417 * As with iteration variables, clause functions are allowed but not required to accept loop parameters. 6418 * These loop parameters act as loop-invariant values visible across the whole loop. 6419 * <p> 6420 * <em>Parameters visible everywhere:</em> 6421 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full 6422 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters. 6423 * The init functions can observe initial pre-loop state, in the form {@code (a...)}. 6424 * Most clause functions will not need all of this information, but they will be formally connected to it 6425 * as if by {@link #dropArguments}. 6426 * <a id="astar"></a> 6427 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full 6428 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}). 6429 * In that notation, the general form of an init function parameter list 6430 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}. 6431 * <p> 6432 * <em>Checking clause structure:</em> 6433 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the 6434 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must" 6435 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not 6436 * met by the inputs to the loop combinator. 6437 * <p> 6438 * <em>Effectively identical sequences:</em> 6439 * <a id="effid"></a> 6440 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B} 6441 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}. 6442 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical" 6443 * as a whole if the set contains a longest list, and all members of the set are effectively identical to 6444 * that longest list. 6445 * For example, any set of type sequences of the form {@code (V*)} is effectively identical, 6446 * and the same is true if more sequences of the form {@code (V... A*)} are added. 6447 * <p> 6448 * <em>Step 0: Determine clause structure.</em><ol type="a"> 6449 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element. 6450 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements. 6451 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length 6452 * four. Padding takes place by appending elements to the array. 6453 * <li>Clauses with all {@code null}s are disregarded. 6454 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini". 6455 * </ol> 6456 * <p> 6457 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a"> 6458 * <li>The iteration variable type for each clause is determined using the clause's init and step return types. 6459 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is 6460 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's 6461 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's 6462 * iteration variable type. 6463 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}. 6464 * <li>This list of types is called the "iteration variable types" ({@code (V...)}). 6465 * </ol> 6466 * <p> 6467 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul> 6468 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}). 6469 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types. 6470 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.) 6471 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types. 6472 * (These types will be checked in step 2, along with all the clause function types.) 6473 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.) 6474 * <li>All of the collected parameter lists must be effectively identical. 6475 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}). 6476 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence. 6477 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called 6478 * the "internal parameter list". 6479 * </ul> 6480 * <p> 6481 * <em>Step 1C: Determine loop return type.</em><ol type="a"> 6482 * <li>Examine fini function return types, disregarding omitted fini functions. 6483 * <li>If there are no fini functions, the loop return type is {@code void}. 6484 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return 6485 * type. 6486 * </ol> 6487 * <p> 6488 * <em>Step 1D: Check other types.</em><ol type="a"> 6489 * <li>There must be at least one non-omitted pred function. 6490 * <li>Every non-omitted pred function must have a {@code boolean} return type. 6491 * </ol> 6492 * <p> 6493 * <em>Step 2: Determine parameter lists.</em><ol type="a"> 6494 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}. 6495 * <li>The parameter list for init functions will be adjusted to the external parameter list. 6496 * (Note that their parameter lists are already effectively identical to this list.) 6497 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be 6498 * effectively identical to the internal parameter list {@code (V... A...)}. 6499 * </ol> 6500 * <p> 6501 * <em>Step 3: Fill in omitted functions.</em><ol type="a"> 6502 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable 6503 * type. 6504 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration 6505 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void} 6506 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.) 6507 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far 6508 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.) 6509 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the 6510 * loop return type. 6511 * </ol> 6512 * <p> 6513 * <em>Step 4: Fill in missing parameter types.</em><ol type="a"> 6514 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)}, 6515 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list. 6516 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter 6517 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list, 6518 * pad out the end of the list. 6519 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}. 6520 * </ol> 6521 * <p> 6522 * <em>Final observations.</em><ol type="a"> 6523 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments. 6524 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have. 6525 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have. 6526 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of 6527 * (non-{@code void}) iteration variables {@code V} followed by loop parameters. 6528 * <li>Each pair of init and step functions agrees in their return type {@code V}. 6529 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables. 6530 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters. 6531 * </ol> 6532 * <p> 6533 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property: 6534 * <ul> 6535 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}. 6536 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters. 6537 * (Only one {@code Pn} has to be non-{@code null}.) 6538 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}. 6539 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types. 6540 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}. 6541 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}. 6542 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine 6543 * the resulting loop handle's parameter types {@code (A...)}. 6544 * </ul> 6545 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions, 6546 * which is natural if most of the loop computation happens in the steps. For some loops, 6547 * the burden of computation might be heaviest in the pred functions, and so the pred functions 6548 * might need to accept the loop parameter values. For loops with complex exit logic, the fini 6549 * functions might need to accept loop parameters, and likewise for loops with complex entry logic, 6550 * where the init functions will need the extra parameters. For such reasons, the rules for 6551 * determining these parameters are as symmetric as possible, across all clause parts. 6552 * In general, the loop parameters function as common invariant values across the whole 6553 * loop, while the iteration variables function as common variant values, or (if there is 6554 * no step function) as internal loop invariant temporaries. 6555 * <p> 6556 * <em>Loop execution.</em><ol type="a"> 6557 * <li>When the loop is called, the loop input values are saved in locals, to be passed to 6558 * every clause function. These locals are loop invariant. 6559 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)}) 6560 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals. 6561 * These locals will be loop varying (unless their steps behave as identity functions, as noted above). 6562 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of 6563 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)} 6564 * (in argument order). 6565 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function 6566 * returns {@code false}. 6567 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the 6568 * sequence {@code (v...)} of loop variables. 6569 * The updated value is immediately visible to all subsequent function calls. 6570 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value 6571 * (of type {@code R}) is returned from the loop as a whole. 6572 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit 6573 * except by throwing an exception. 6574 * </ol> 6575 * <p> 6576 * <em>Usage tips.</em> 6577 * <ul> 6578 * <li>Although each step function will receive the current values of <em>all</em> the loop variables, 6579 * sometimes a step function only needs to observe the current value of its own variable. 6580 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}. 6581 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}. 6582 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create 6583 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be 6584 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable. 6585 * <li>If some of the clause functions are virtual methods on an instance, the instance 6586 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause 6587 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference 6588 * will be the first iteration variable value, and it will be easy to use virtual 6589 * methods as clause parts, since all of them will take a leading instance reference matching that value. 6590 * </ul> 6591 * <p> 6592 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types 6593 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop; 6594 * and {@code R} is the common result type of all finalizers as well as of the resulting loop. 6595 * {@snippet lang="java" : 6596 * V... init...(A...); 6597 * boolean pred...(V..., A...); 6598 * V... step...(V..., A...); 6599 * R fini...(V..., A...); 6600 * R loop(A... a) { 6601 * V... v... = init...(a...); 6602 * for (;;) { 6603 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) { 6604 * v = s(v..., a...); 6605 * if (!p(v..., a...)) { 6606 * return f(v..., a...); 6607 * } 6608 * } 6609 * } 6610 * } 6611 * } 6612 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded 6613 * to their full length, even though individual clause functions may neglect to take them all. 6614 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}. 6615 * 6616 * @apiNote Example: 6617 * {@snippet lang="java" : 6618 * // iterative implementation of the factorial function as a loop handle 6619 * static int one(int k) { return 1; } 6620 * static int inc(int i, int acc, int k) { return i + 1; } 6621 * static int mult(int i, int acc, int k) { return i * acc; } 6622 * static boolean pred(int i, int acc, int k) { return i < k; } 6623 * static int fin(int i, int acc, int k) { return acc; } 6624 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 6625 * // null initializer for counter, should initialize to 0 6626 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6627 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6628 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 6629 * assertEquals(120, loop.invoke(5)); 6630 * } 6631 * The same example, dropping arguments and using combinators: 6632 * {@snippet lang="java" : 6633 * // simplified implementation of the factorial function as a loop handle 6634 * static int inc(int i) { return i + 1; } // drop acc, k 6635 * static int mult(int i, int acc) { return i * acc; } //drop k 6636 * static boolean cmp(int i, int k) { return i < k; } 6637 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods 6638 * // null initializer for counter, should initialize to 0 6639 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 6640 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc 6641 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i 6642 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6643 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6644 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause); 6645 * assertEquals(720, loop.invoke(6)); 6646 * } 6647 * A similar example, using a helper object to hold a loop parameter: 6648 * {@snippet lang="java" : 6649 * // instance-based implementation of the factorial function as a loop handle 6650 * static class FacLoop { 6651 * final int k; 6652 * FacLoop(int k) { this.k = k; } 6653 * int inc(int i) { return i + 1; } 6654 * int mult(int i, int acc) { return i * acc; } 6655 * boolean pred(int i) { return i < k; } 6656 * int fin(int i, int acc) { return acc; } 6657 * } 6658 * // assume MH_FacLoop is a handle to the constructor 6659 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods 6660 * // null initializer for counter, should initialize to 0 6661 * MethodHandle MH_one = MethodHandles.constant(int.class, 1); 6662 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop}; 6663 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc}; 6664 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin}; 6665 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause); 6666 * assertEquals(5040, loop.invoke(7)); 6667 * } 6668 * 6669 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above. 6670 * 6671 * @return a method handle embodying the looping behavior as defined by the arguments. 6672 * 6673 * @throws IllegalArgumentException in case any of the constraints described above is violated. 6674 * 6675 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle) 6676 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 6677 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle) 6678 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle) 6679 * @since 9 6680 */ 6681 public static MethodHandle loop(MethodHandle[]... clauses) { 6682 // Step 0: determine clause structure. 6683 loopChecks0(clauses); 6684 6685 List<MethodHandle> init = new ArrayList<>(); 6686 List<MethodHandle> step = new ArrayList<>(); 6687 List<MethodHandle> pred = new ArrayList<>(); 6688 List<MethodHandle> fini = new ArrayList<>(); 6689 6690 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> { 6691 init.add(clause[0]); // all clauses have at least length 1 6692 step.add(clause.length <= 1 ? null : clause[1]); 6693 pred.add(clause.length <= 2 ? null : clause[2]); 6694 fini.add(clause.length <= 3 ? null : clause[3]); 6695 }); 6696 6697 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1; 6698 final int nclauses = init.size(); 6699 6700 // Step 1A: determine iteration variables (V...). 6701 final List<Class<?>> iterationVariableTypes = new ArrayList<>(); 6702 for (int i = 0; i < nclauses; ++i) { 6703 MethodHandle in = init.get(i); 6704 MethodHandle st = step.get(i); 6705 if (in == null && st == null) { 6706 iterationVariableTypes.add(void.class); 6707 } else if (in != null && st != null) { 6708 loopChecks1a(i, in, st); 6709 iterationVariableTypes.add(in.type().returnType()); 6710 } else { 6711 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType()); 6712 } 6713 } 6714 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList(); 6715 6716 // Step 1B: determine loop parameters (A...). 6717 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size()); 6718 loopChecks1b(init, commonSuffix); 6719 6720 // Step 1C: determine loop return type. 6721 // Step 1D: check other types. 6722 // local variable required here; see JDK-8223553 6723 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type) 6724 .map(MethodType::returnType); 6725 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class); 6726 loopChecks1cd(pred, fini, loopReturnType); 6727 6728 // Step 2: determine parameter lists. 6729 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix); 6730 commonParameterSequence.addAll(commonSuffix); 6731 loopChecks2(step, pred, fini, commonParameterSequence); 6732 // Step 3: fill in omitted functions. 6733 for (int i = 0; i < nclauses; ++i) { 6734 Class<?> t = iterationVariableTypes.get(i); 6735 if (init.get(i) == null) { 6736 init.set(i, empty(methodType(t, commonSuffix))); 6737 } 6738 if (step.get(i) == null) { 6739 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i)); 6740 } 6741 if (pred.get(i) == null) { 6742 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence)); 6743 } 6744 if (fini.get(i) == null) { 6745 fini.set(i, empty(methodType(t, commonParameterSequence))); 6746 } 6747 } 6748 6749 // Step 4: fill in missing parameter types. 6750 // Also convert all handles to fixed-arity handles. 6751 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix)); 6752 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence)); 6753 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence)); 6754 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence)); 6755 6756 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList). 6757 allMatch(pl -> pl.equals(commonSuffix)); 6758 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList). 6759 allMatch(pl -> pl.equals(commonParameterSequence)); 6760 6761 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini); 6762 } 6763 6764 private static void loopChecks0(MethodHandle[][] clauses) { 6765 if (clauses == null || clauses.length == 0) { 6766 throw newIllegalArgumentException("null or no clauses passed"); 6767 } 6768 if (Stream.of(clauses).anyMatch(Objects::isNull)) { 6769 throw newIllegalArgumentException("null clauses are not allowed"); 6770 } 6771 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) { 6772 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements."); 6773 } 6774 } 6775 6776 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) { 6777 if (in.type().returnType() != st.type().returnType()) { 6778 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(), 6779 st.type().returnType()); 6780 } 6781 } 6782 6783 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) { 6784 final List<Class<?>> empty = List.of(); 6785 final List<Class<?>> longest = mhs.filter(Objects::nonNull). 6786 // take only those that can contribute to a common suffix because they are longer than the prefix 6787 map(MethodHandle::type). 6788 filter(t -> t.parameterCount() > skipSize). 6789 map(MethodType::parameterList). 6790 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 6791 return longest.isEmpty() ? empty : longest.subList(skipSize, longest.size()); 6792 } 6793 6794 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) { 6795 final List<Class<?>> empty = List.of(); 6796 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty); 6797 } 6798 6799 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) { 6800 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize); 6801 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0); 6802 return longestParameterList(List.of(longest1, longest2)); 6803 } 6804 6805 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) { 6806 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type). 6807 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) { 6808 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init + 6809 " (common suffix: " + commonSuffix + ")"); 6810 } 6811 } 6812 6813 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) { 6814 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 6815 anyMatch(t -> t != loopReturnType)) { 6816 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " + 6817 loopReturnType + ")"); 6818 } 6819 6820 if (pred.stream().noneMatch(Objects::nonNull)) { 6821 throw newIllegalArgumentException("no predicate found", pred); 6822 } 6823 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType). 6824 anyMatch(t -> t != boolean.class)) { 6825 throw newIllegalArgumentException("predicates must have boolean return type", pred); 6826 } 6827 } 6828 6829 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) { 6830 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type). 6831 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) { 6832 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step + 6833 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")"); 6834 } 6835 } 6836 6837 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) { 6838 return hs.stream().map(h -> { 6839 int pc = h.type().parameterCount(); 6840 int tpsize = targetParams.size(); 6841 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h; 6842 }).toList(); 6843 } 6844 6845 private static List<MethodHandle> fixArities(List<MethodHandle> hs) { 6846 return hs.stream().map(MethodHandle::asFixedArity).toList(); 6847 } 6848 6849 /** 6850 * Constructs a {@code while} loop from an initializer, a body, and a predicate. 6851 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 6852 * <p> 6853 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 6854 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate 6855 * evaluates to {@code true}). 6856 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case). 6857 * <p> 6858 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 6859 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 6860 * and updated with the value returned from its invocation. The result of loop execution will be 6861 * the final value of the additional loop-local variable (if present). 6862 * <p> 6863 * The following rules hold for these argument handles:<ul> 6864 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 6865 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 6866 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 6867 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 6868 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 6869 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 6870 * It will constrain the parameter lists of the other loop parts. 6871 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 6872 * list {@code (A...)} is called the <em>external parameter list</em>. 6873 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 6874 * additional state variable of the loop. 6875 * The body must both accept and return a value of this type {@code V}. 6876 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 6877 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 6878 * <a href="MethodHandles.html#effid">effectively identical</a> 6879 * to the external parameter list {@code (A...)}. 6880 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 6881 * {@linkplain #empty default value}. 6882 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 6883 * Its parameter list (either empty or of the form {@code (V A*)}) must be 6884 * effectively identical to the internal parameter list. 6885 * </ul> 6886 * <p> 6887 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 6888 * <li>The loop handle's result type is the result type {@code V} of the body. 6889 * <li>The loop handle's parameter types are the types {@code (A...)}, 6890 * from the external parameter list. 6891 * </ul> 6892 * <p> 6893 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 6894 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 6895 * passed to the loop. 6896 * {@snippet lang="java" : 6897 * V init(A...); 6898 * boolean pred(V, A...); 6899 * V body(V, A...); 6900 * V whileLoop(A... a...) { 6901 * V v = init(a...); 6902 * while (pred(v, a...)) { 6903 * v = body(v, a...); 6904 * } 6905 * return v; 6906 * } 6907 * } 6908 * 6909 * @apiNote Example: 6910 * {@snippet lang="java" : 6911 * // implement the zip function for lists as a loop handle 6912 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); } 6913 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); } 6914 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) { 6915 * zip.add(a.next()); 6916 * zip.add(b.next()); 6917 * return zip; 6918 * } 6919 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods 6920 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep); 6921 * List<String> a = Arrays.asList("a", "b", "c", "d"); 6922 * List<String> b = Arrays.asList("e", "f", "g", "h"); 6923 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h"); 6924 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator())); 6925 * } 6926 * 6927 * 6928 * @apiNote The implementation of this method can be expressed as follows: 6929 * {@snippet lang="java" : 6930 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 6931 * MethodHandle fini = (body.type().returnType() == void.class 6932 * ? null : identity(body.type().returnType())); 6933 * MethodHandle[] 6934 * checkExit = { null, null, pred, fini }, 6935 * varBody = { init, body }; 6936 * return loop(checkExit, varBody); 6937 * } 6938 * } 6939 * 6940 * @param init optional initializer, providing the initial value of the loop variable. 6941 * May be {@code null}, implying a default initial value. See above for other constraints. 6942 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 6943 * above for other constraints. 6944 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 6945 * See above for other constraints. 6946 * 6947 * @return a method handle implementing the {@code while} loop as described by the arguments. 6948 * @throws IllegalArgumentException if the rules for the arguments are violated. 6949 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 6950 * 6951 * @see #loop(MethodHandle[][]) 6952 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle) 6953 * @since 9 6954 */ 6955 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) { 6956 whileLoopChecks(init, pred, body); 6957 MethodHandle fini = identityOrVoid(body.type().returnType()); 6958 MethodHandle[] checkExit = { null, null, pred, fini }; 6959 MethodHandle[] varBody = { init, body }; 6960 return loop(checkExit, varBody); 6961 } 6962 6963 /** 6964 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. 6965 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 6966 * <p> 6967 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this 6968 * method will, in each iteration, first execute its body and then evaluate the predicate. 6969 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body. 6970 * <p> 6971 * The {@code init} handle describes the initial value of an additional optional loop-local variable. 6972 * In each iteration, this loop-local variable, if present, will be passed to the {@code body} 6973 * and updated with the value returned from its invocation. The result of loop execution will be 6974 * the final value of the additional loop-local variable (if present). 6975 * <p> 6976 * The following rules hold for these argument handles:<ul> 6977 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 6978 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}. 6979 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 6980 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V} 6981 * is quietly dropped from the parameter list, leaving {@code (A...)V}.) 6982 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>. 6983 * It will constrain the parameter lists of the other loop parts. 6984 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter 6985 * list {@code (A...)} is called the <em>external parameter list</em>. 6986 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 6987 * additional state variable of the loop. 6988 * The body must both accept and return a value of this type {@code V}. 6989 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 6990 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 6991 * <a href="MethodHandles.html#effid">effectively identical</a> 6992 * to the external parameter list {@code (A...)}. 6993 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 6994 * {@linkplain #empty default value}. 6995 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type. 6996 * Its parameter list (either empty or of the form {@code (V A*)}) must be 6997 * effectively identical to the internal parameter list. 6998 * </ul> 6999 * <p> 7000 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7001 * <li>The loop handle's result type is the result type {@code V} of the body. 7002 * <li>The loop handle's parameter types are the types {@code (A...)}, 7003 * from the external parameter list. 7004 * </ul> 7005 * <p> 7006 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7007 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument 7008 * passed to the loop. 7009 * {@snippet lang="java" : 7010 * V init(A...); 7011 * boolean pred(V, A...); 7012 * V body(V, A...); 7013 * V doWhileLoop(A... a...) { 7014 * V v = init(a...); 7015 * do { 7016 * v = body(v, a...); 7017 * } while (pred(v, a...)); 7018 * return v; 7019 * } 7020 * } 7021 * 7022 * @apiNote Example: 7023 * {@snippet lang="java" : 7024 * // int i = 0; while (i < limit) { ++i; } return i; => limit 7025 * static int zero(int limit) { return 0; } 7026 * static int step(int i, int limit) { return i + 1; } 7027 * static boolean pred(int i, int limit) { return i < limit; } 7028 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods 7029 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred); 7030 * assertEquals(23, loop.invoke(23)); 7031 * } 7032 * 7033 * 7034 * @apiNote The implementation of this method can be expressed as follows: 7035 * {@snippet lang="java" : 7036 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 7037 * MethodHandle fini = (body.type().returnType() == void.class 7038 * ? null : identity(body.type().returnType())); 7039 * MethodHandle[] clause = { init, body, pred, fini }; 7040 * return loop(clause); 7041 * } 7042 * } 7043 * 7044 * @param init optional initializer, providing the initial value of the loop variable. 7045 * May be {@code null}, implying a default initial value. See above for other constraints. 7046 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type. 7047 * See above for other constraints. 7048 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See 7049 * above for other constraints. 7050 * 7051 * @return a method handle implementing the {@code while} loop as described by the arguments. 7052 * @throws IllegalArgumentException if the rules for the arguments are violated. 7053 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}. 7054 * 7055 * @see #loop(MethodHandle[][]) 7056 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle) 7057 * @since 9 7058 */ 7059 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) { 7060 whileLoopChecks(init, pred, body); 7061 MethodHandle fini = identityOrVoid(body.type().returnType()); 7062 MethodHandle[] clause = {init, body, pred, fini }; 7063 return loop(clause); 7064 } 7065 7066 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) { 7067 Objects.requireNonNull(pred); 7068 Objects.requireNonNull(body); 7069 MethodType bodyType = body.type(); 7070 Class<?> returnType = bodyType.returnType(); 7071 List<Class<?>> innerList = bodyType.parameterList(); 7072 List<Class<?>> outerList = innerList; 7073 if (returnType == void.class) { 7074 // OK 7075 } else if (innerList.isEmpty() || innerList.get(0) != returnType) { 7076 // leading V argument missing => error 7077 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7078 throw misMatchedTypes("body function", bodyType, expected); 7079 } else { 7080 outerList = innerList.subList(1, innerList.size()); 7081 } 7082 MethodType predType = pred.type(); 7083 if (predType.returnType() != boolean.class || 7084 !predType.effectivelyIdenticalParameters(0, innerList)) { 7085 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList)); 7086 } 7087 if (init != null) { 7088 MethodType initType = init.type(); 7089 if (initType.returnType() != returnType || 7090 !initType.effectivelyIdenticalParameters(0, outerList)) { 7091 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 7092 } 7093 } 7094 } 7095 7096 /** 7097 * Constructs a loop that runs a given number of iterations. 7098 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7099 * <p> 7100 * The number of iterations is determined by the {@code iterations} handle evaluation result. 7101 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}. 7102 * It will be initialized to 0 and incremented by 1 in each iteration. 7103 * <p> 7104 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7105 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7106 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7107 * <p> 7108 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7109 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7110 * iteration variable. 7111 * The result of the loop handle execution will be the final {@code V} value of that variable 7112 * (or {@code void} if there is no {@code V} variable). 7113 * <p> 7114 * The following rules hold for the argument handles:<ul> 7115 * <li>The {@code iterations} handle must not be {@code null}, and must return 7116 * the type {@code int}, referred to here as {@code I} in parameter type lists. 7117 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7118 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 7119 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7120 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 7121 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 7122 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 7123 * of types called the <em>internal parameter list</em>. 7124 * It will constrain the parameter lists of the other loop parts. 7125 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 7126 * with no additional {@code A} types, then the internal parameter list is extended by 7127 * the argument types {@code A...} of the {@code iterations} handle. 7128 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 7129 * list {@code (A...)} is called the <em>external parameter list</em>. 7130 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7131 * additional state variable of the loop. 7132 * The body must both accept a leading parameter and return a value of this type {@code V}. 7133 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7134 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7135 * <a href="MethodHandles.html#effid">effectively identical</a> 7136 * to the external parameter list {@code (A...)}. 7137 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7138 * {@linkplain #empty default value}. 7139 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be 7140 * effectively identical to the external parameter list {@code (A...)}. 7141 * </ul> 7142 * <p> 7143 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7144 * <li>The loop handle's result type is the result type {@code V} of the body. 7145 * <li>The loop handle's parameter types are the types {@code (A...)}, 7146 * from the external parameter list. 7147 * </ul> 7148 * <p> 7149 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7150 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 7151 * arguments passed to the loop. 7152 * {@snippet lang="java" : 7153 * int iterations(A...); 7154 * V init(A...); 7155 * V body(V, int, A...); 7156 * V countedLoop(A... a...) { 7157 * int end = iterations(a...); 7158 * V v = init(a...); 7159 * for (int i = 0; i < end; ++i) { 7160 * v = body(v, i, a...); 7161 * } 7162 * return v; 7163 * } 7164 * } 7165 * 7166 * @apiNote Example with a fully conformant body method: 7167 * {@snippet lang="java" : 7168 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 7169 * // => a variation on a well known theme 7170 * static String step(String v, int counter, String init) { return "na " + v; } 7171 * // assume MH_step is a handle to the method above 7172 * MethodHandle fit13 = MethodHandles.constant(int.class, 13); 7173 * MethodHandle start = MethodHandles.identity(String.class); 7174 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step); 7175 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!")); 7176 * } 7177 * 7178 * @apiNote Example with the simplest possible body method type, 7179 * and passing the number of iterations to the loop invocation: 7180 * {@snippet lang="java" : 7181 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s; 7182 * // => a variation on a well known theme 7183 * static String step(String v, int counter ) { return "na " + v; } 7184 * // assume MH_step is a handle to the method above 7185 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class); 7186 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class); 7187 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v 7188 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!")); 7189 * } 7190 * 7191 * @apiNote Example that treats the number of iterations, string to append to, and string to append 7192 * as loop parameters: 7193 * {@snippet lang="java" : 7194 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 7195 * // => a variation on a well known theme 7196 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; } 7197 * // assume MH_step is a handle to the method above 7198 * MethodHandle count = MethodHandles.identity(int.class); 7199 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class); 7200 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v 7201 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!")); 7202 * } 7203 * 7204 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)} 7205 * to enforce a loop type: 7206 * {@snippet lang="java" : 7207 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s; 7208 * // => a variation on a well known theme 7209 * static String step(String v, int counter, String pre) { return pre + " " + v; } 7210 * // assume MH_step is a handle to the method above 7211 * MethodType loopType = methodType(String.class, String.class, int.class, String.class); 7212 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1); 7213 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2); 7214 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0); 7215 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v 7216 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!")); 7217 * } 7218 * 7219 * @apiNote The implementation of this method can be expressed as follows: 7220 * {@snippet lang="java" : 7221 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 7222 * return countedLoop(empty(iterations.type()), iterations, init, body); 7223 * } 7224 * } 7225 * 7226 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's 7227 * result type must be {@code int}. See above for other constraints. 7228 * @param init optional initializer, providing the initial value of the loop variable. 7229 * May be {@code null}, implying a default initial value. See above for other constraints. 7230 * @param body body of the loop, which may not be {@code null}. 7231 * It controls the loop parameters and result type in the standard case (see above for details). 7232 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 7233 * and may accept any number of additional types. 7234 * See above for other constraints. 7235 * 7236 * @return a method handle representing the loop. 7237 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}. 7238 * @throws IllegalArgumentException if any argument violates the rules formulated above. 7239 * 7240 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle) 7241 * @since 9 7242 */ 7243 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) { 7244 return countedLoop(empty(iterations.type()), iterations, init, body); 7245 } 7246 7247 /** 7248 * Constructs a loop that counts over a range of numbers. 7249 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7250 * <p> 7251 * The loop counter {@code i} is a loop iteration variable of type {@code int}. 7252 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive) 7253 * values of the loop counter. 7254 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the 7255 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1. 7256 * <p> 7257 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7258 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7259 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7260 * <p> 7261 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7262 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7263 * iteration variable. 7264 * The result of the loop handle execution will be the final {@code V} value of that variable 7265 * (or {@code void} if there is no {@code V} variable). 7266 * <p> 7267 * The following rules hold for the argument handles:<ul> 7268 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return 7269 * the common type {@code int}, referred to here as {@code I} in parameter type lists. 7270 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7271 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}. 7272 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7273 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V} 7274 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.) 7275 * <li>The parameter list {@code (V I A...)} of the body contributes to a list 7276 * of types called the <em>internal parameter list</em>. 7277 * It will constrain the parameter lists of the other loop parts. 7278 * <li>As a special case, if the body contributes only {@code V} and {@code I} types, 7279 * with no additional {@code A} types, then the internal parameter list is extended by 7280 * the argument types {@code A...} of the {@code end} handle. 7281 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter 7282 * list {@code (A...)} is called the <em>external parameter list</em>. 7283 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7284 * additional state variable of the loop. 7285 * The body must both accept a leading parameter and return a value of this type {@code V}. 7286 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7287 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7288 * <a href="MethodHandles.html#effid">effectively identical</a> 7289 * to the external parameter list {@code (A...)}. 7290 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7291 * {@linkplain #empty default value}. 7292 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be 7293 * effectively identical to the external parameter list {@code (A...)}. 7294 * <li>Likewise, the parameter list of {@code end} must be effectively identical 7295 * to the external parameter list. 7296 * </ul> 7297 * <p> 7298 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7299 * <li>The loop handle's result type is the result type {@code V} of the body. 7300 * <li>The loop handle's parameter types are the types {@code (A...)}, 7301 * from the external parameter list. 7302 * </ul> 7303 * <p> 7304 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7305 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent 7306 * arguments passed to the loop. 7307 * {@snippet lang="java" : 7308 * int start(A...); 7309 * int end(A...); 7310 * V init(A...); 7311 * V body(V, int, A...); 7312 * V countedLoop(A... a...) { 7313 * int e = end(a...); 7314 * int s = start(a...); 7315 * V v = init(a...); 7316 * for (int i = s; i < e; ++i) { 7317 * v = body(v, i, a...); 7318 * } 7319 * return v; 7320 * } 7321 * } 7322 * 7323 * @apiNote The implementation of this method can be expressed as follows: 7324 * {@snippet lang="java" : 7325 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7326 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class); 7327 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with 7328 * // the following semantics: 7329 * // MH_increment: (int limit, int counter) -> counter + 1 7330 * // MH_predicate: (int limit, int counter) -> counter < limit 7331 * Class<?> counterType = start.type().returnType(); // int 7332 * Class<?> returnType = body.type().returnType(); 7333 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null; 7334 * if (returnType != void.class) { // ignore the V variable 7335 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 7336 * pred = dropArguments(pred, 1, returnType); // ditto 7337 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit 7338 * } 7339 * body = dropArguments(body, 0, counterType); // ignore the limit variable 7340 * MethodHandle[] 7341 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 7342 * bodyClause = { init, body }, // v = init(); v = body(v, i) 7343 * indexVar = { start, incr }; // i = start(); i = i + 1 7344 * return loop(loopLimit, bodyClause, indexVar); 7345 * } 7346 * } 7347 * 7348 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}. 7349 * See above for other constraints. 7350 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to 7351 * {@code end-1}). The result type must be {@code int}. See above for other constraints. 7352 * @param init optional initializer, providing the initial value of the loop variable. 7353 * May be {@code null}, implying a default initial value. See above for other constraints. 7354 * @param body body of the loop, which may not be {@code null}. 7355 * It controls the loop parameters and result type in the standard case (see above for details). 7356 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter), 7357 * and may accept any number of additional types. 7358 * See above for other constraints. 7359 * 7360 * @return a method handle representing the loop. 7361 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}. 7362 * @throws IllegalArgumentException if any argument violates the rules formulated above. 7363 * 7364 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle) 7365 * @since 9 7366 */ 7367 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7368 countedLoopChecks(start, end, init, body); 7369 Class<?> counterType = start.type().returnType(); // int, but who's counting? 7370 Class<?> limitType = end.type().returnType(); // yes, int again 7371 Class<?> returnType = body.type().returnType(); 7372 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep); 7373 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred); 7374 MethodHandle retv = null; 7375 if (returnType != void.class) { 7376 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i) 7377 pred = dropArguments(pred, 1, returnType); // ditto 7378 retv = dropArguments(identity(returnType), 0, counterType); 7379 } 7380 body = dropArguments(body, 0, counterType); // ignore the limit variable 7381 MethodHandle[] 7382 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v 7383 bodyClause = { init, body }, // v = init(); v = body(v, i) 7384 indexVar = { start, incr }; // i = start(); i = i + 1 7385 return loop(loopLimit, bodyClause, indexVar); 7386 } 7387 7388 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) { 7389 Objects.requireNonNull(start); 7390 Objects.requireNonNull(end); 7391 Objects.requireNonNull(body); 7392 Class<?> counterType = start.type().returnType(); 7393 if (counterType != int.class) { 7394 MethodType expected = start.type().changeReturnType(int.class); 7395 throw misMatchedTypes("start function", start.type(), expected); 7396 } else if (end.type().returnType() != counterType) { 7397 MethodType expected = end.type().changeReturnType(counterType); 7398 throw misMatchedTypes("end function", end.type(), expected); 7399 } 7400 MethodType bodyType = body.type(); 7401 Class<?> returnType = bodyType.returnType(); 7402 List<Class<?>> innerList = bodyType.parameterList(); 7403 // strip leading V value if present 7404 int vsize = (returnType == void.class ? 0 : 1); 7405 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) { 7406 // argument list has no "V" => error 7407 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7408 throw misMatchedTypes("body function", bodyType, expected); 7409 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) { 7410 // missing I type => error 7411 MethodType expected = bodyType.insertParameterTypes(vsize, counterType); 7412 throw misMatchedTypes("body function", bodyType, expected); 7413 } 7414 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size()); 7415 if (outerList.isEmpty()) { 7416 // special case; take lists from end handle 7417 outerList = end.type().parameterList(); 7418 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList(); 7419 } 7420 MethodType expected = methodType(counterType, outerList); 7421 if (!start.type().effectivelyIdenticalParameters(0, outerList)) { 7422 throw misMatchedTypes("start parameter types", start.type(), expected); 7423 } 7424 if (end.type() != start.type() && 7425 !end.type().effectivelyIdenticalParameters(0, outerList)) { 7426 throw misMatchedTypes("end parameter types", end.type(), expected); 7427 } 7428 if (init != null) { 7429 MethodType initType = init.type(); 7430 if (initType.returnType() != returnType || 7431 !initType.effectivelyIdenticalParameters(0, outerList)) { 7432 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList)); 7433 } 7434 } 7435 } 7436 7437 /** 7438 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}. 7439 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}. 7440 * <p> 7441 * The iterator itself will be determined by the evaluation of the {@code iterator} handle. 7442 * Each value it produces will be stored in a loop iteration variable of type {@code T}. 7443 * <p> 7444 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable 7445 * of that type is also present. This variable is initialized using the optional {@code init} handle, 7446 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}. 7447 * <p> 7448 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle. 7449 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading 7450 * iteration variable. 7451 * The result of the loop handle execution will be the final {@code V} value of that variable 7452 * (or {@code void} if there is no {@code V} variable). 7453 * <p> 7454 * The following rules hold for the argument handles:<ul> 7455 * <li>The {@code body} handle must not be {@code null}; its type must be of the form 7456 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}. 7457 * (In the {@code void} case, we assign the type {@code void} to the name {@code V}, 7458 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V} 7459 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.) 7460 * <li>The parameter list {@code (V T A...)} of the body contributes to a list 7461 * of types called the <em>internal parameter list</em>. 7462 * It will constrain the parameter lists of the other loop parts. 7463 * <li>As a special case, if the body contributes only {@code V} and {@code T} types, 7464 * with no additional {@code A} types, then the internal parameter list is extended by 7465 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the 7466 * single type {@code Iterable} is added and constitutes the {@code A...} list. 7467 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter 7468 * list {@code (A...)} is called the <em>external parameter list</em>. 7469 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an 7470 * additional state variable of the loop. 7471 * The body must both accept a leading parameter and return a value of this type {@code V}. 7472 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}. 7473 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be 7474 * <a href="MethodHandles.html#effid">effectively identical</a> 7475 * to the external parameter list {@code (A...)}. 7476 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its 7477 * {@linkplain #empty default value}. 7478 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return 7479 * type {@code java.util.Iterator} or a subtype thereof. 7480 * The iterator it produces when the loop is executed will be assumed 7481 * to yield values which can be converted to type {@code T}. 7482 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be 7483 * effectively identical to the external parameter list {@code (A...)}. 7484 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves 7485 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list 7486 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator 7487 * handle parameter is adjusted to accept the leading {@code A} type, as if by 7488 * the {@link MethodHandle#asType asType} conversion method. 7489 * The leading {@code A} type must be {@code Iterable} or a subtype thereof. 7490 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}. 7491 * </ul> 7492 * <p> 7493 * The type {@code T} may be either a primitive or reference. 7494 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator}, 7495 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object} 7496 * as if by the {@link MethodHandle#asType asType} conversion method. 7497 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur 7498 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}. 7499 * <p> 7500 * The resulting loop handle's result type and parameter signature are determined as follows:<ul> 7501 * <li>The loop handle's result type is the result type {@code V} of the body. 7502 * <li>The loop handle's parameter types are the types {@code (A...)}, 7503 * from the external parameter list. 7504 * </ul> 7505 * <p> 7506 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of 7507 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the 7508 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop. 7509 * {@snippet lang="java" : 7510 * Iterator<T> iterator(A...); // defaults to Iterable::iterator 7511 * V init(A...); 7512 * V body(V,T,A...); 7513 * V iteratedLoop(A... a...) { 7514 * Iterator<T> it = iterator(a...); 7515 * V v = init(a...); 7516 * while (it.hasNext()) { 7517 * T t = it.next(); 7518 * v = body(v, t, a...); 7519 * } 7520 * return v; 7521 * } 7522 * } 7523 * 7524 * @apiNote Example: 7525 * {@snippet lang="java" : 7526 * // get an iterator from a list 7527 * static List<String> reverseStep(List<String> r, String e) { 7528 * r.add(0, e); 7529 * return r; 7530 * } 7531 * static List<String> newArrayList() { return new ArrayList<>(); } 7532 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods 7533 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep); 7534 * List<String> list = Arrays.asList("a", "b", "c", "d", "e"); 7535 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a"); 7536 * assertEquals(reversedList, (List<String>) loop.invoke(list)); 7537 * } 7538 * 7539 * @apiNote The implementation of this method can be expressed approximately as follows: 7540 * {@snippet lang="java" : 7541 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7542 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable 7543 * Class<?> returnType = body.type().returnType(); 7544 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 7545 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype)); 7546 * MethodHandle retv = null, step = body, startIter = iterator; 7547 * if (returnType != void.class) { 7548 * // the simple thing first: in (I V A...), drop the I to get V 7549 * retv = dropArguments(identity(returnType), 0, Iterator.class); 7550 * // body type signature (V T A...), internal loop types (I V A...) 7551 * step = swapArguments(body, 0, 1); // swap V <-> T 7552 * } 7553 * if (startIter == null) startIter = MH_getIter; 7554 * MethodHandle[] 7555 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext()) 7556 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a) 7557 * return loop(iterVar, bodyClause); 7558 * } 7559 * } 7560 * 7561 * @param iterator an optional handle to return the iterator to start the loop. 7562 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype. 7563 * See above for other constraints. 7564 * @param init optional initializer, providing the initial value of the loop variable. 7565 * May be {@code null}, implying a default initial value. See above for other constraints. 7566 * @param body body of the loop, which may not be {@code null}. 7567 * It controls the loop parameters and result type in the standard case (see above for details). 7568 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values), 7569 * and may accept any number of additional types. 7570 * See above for other constraints. 7571 * 7572 * @return a method handle embodying the iteration loop functionality. 7573 * @throws NullPointerException if the {@code body} handle is {@code null}. 7574 * @throws IllegalArgumentException if any argument violates the above requirements. 7575 * 7576 * @since 9 7577 */ 7578 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7579 Class<?> iterableType = iteratedLoopChecks(iterator, init, body); 7580 Class<?> returnType = body.type().returnType(); 7581 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred); 7582 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext); 7583 MethodHandle startIter; 7584 MethodHandle nextVal; 7585 { 7586 MethodType iteratorType; 7587 if (iterator == null) { 7588 // derive argument type from body, if available, else use Iterable 7589 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator); 7590 iteratorType = startIter.type().changeParameterType(0, iterableType); 7591 } else { 7592 // force return type to the internal iterator class 7593 iteratorType = iterator.type().changeReturnType(Iterator.class); 7594 startIter = iterator; 7595 } 7596 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1); 7597 MethodType nextValType = nextRaw.type().changeReturnType(ttype); 7598 7599 // perform the asType transforms under an exception transformer, as per spec.: 7600 try { 7601 startIter = startIter.asType(iteratorType); 7602 nextVal = nextRaw.asType(nextValType); 7603 } catch (WrongMethodTypeException ex) { 7604 throw new IllegalArgumentException(ex); 7605 } 7606 } 7607 7608 MethodHandle retv = null, step = body; 7609 if (returnType != void.class) { 7610 // the simple thing first: in (I V A...), drop the I to get V 7611 retv = dropArguments(identity(returnType), 0, Iterator.class); 7612 // body type signature (V T A...), internal loop types (I V A...) 7613 step = swapArguments(body, 0, 1); // swap V <-> T 7614 } 7615 7616 MethodHandle[] 7617 iterVar = { startIter, null, hasNext, retv }, 7618 bodyClause = { init, filterArgument(step, 0, nextVal) }; 7619 return loop(iterVar, bodyClause); 7620 } 7621 7622 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) { 7623 Objects.requireNonNull(body); 7624 MethodType bodyType = body.type(); 7625 Class<?> returnType = bodyType.returnType(); 7626 List<Class<?>> internalParamList = bodyType.parameterList(); 7627 // strip leading V value if present 7628 int vsize = (returnType == void.class ? 0 : 1); 7629 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) { 7630 // argument list has no "V" => error 7631 MethodType expected = bodyType.insertParameterTypes(0, returnType); 7632 throw misMatchedTypes("body function", bodyType, expected); 7633 } else if (internalParamList.size() <= vsize) { 7634 // missing T type => error 7635 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class); 7636 throw misMatchedTypes("body function", bodyType, expected); 7637 } 7638 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size()); 7639 Class<?> iterableType = null; 7640 if (iterator != null) { 7641 // special case; if the body handle only declares V and T then 7642 // the external parameter list is obtained from iterator handle 7643 if (externalParamList.isEmpty()) { 7644 externalParamList = iterator.type().parameterList(); 7645 } 7646 MethodType itype = iterator.type(); 7647 if (!Iterator.class.isAssignableFrom(itype.returnType())) { 7648 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type"); 7649 } 7650 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) { 7651 MethodType expected = methodType(itype.returnType(), externalParamList); 7652 throw misMatchedTypes("iterator parameters", itype, expected); 7653 } 7654 } else { 7655 if (externalParamList.isEmpty()) { 7656 // special case; if the iterator handle is null and the body handle 7657 // only declares V and T then the external parameter list consists 7658 // of Iterable 7659 externalParamList = List.of(Iterable.class); 7660 iterableType = Iterable.class; 7661 } else { 7662 // special case; if the iterator handle is null and the external 7663 // parameter list is not empty then the first parameter must be 7664 // assignable to Iterable 7665 iterableType = externalParamList.get(0); 7666 if (!Iterable.class.isAssignableFrom(iterableType)) { 7667 throw newIllegalArgumentException( 7668 "inferred first loop argument must inherit from Iterable: " + iterableType); 7669 } 7670 } 7671 } 7672 if (init != null) { 7673 MethodType initType = init.type(); 7674 if (initType.returnType() != returnType || 7675 !initType.effectivelyIdenticalParameters(0, externalParamList)) { 7676 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList)); 7677 } 7678 } 7679 return iterableType; // help the caller a bit 7680 } 7681 7682 /*non-public*/ 7683 static MethodHandle swapArguments(MethodHandle mh, int i, int j) { 7684 // there should be a better way to uncross my wires 7685 int arity = mh.type().parameterCount(); 7686 int[] order = new int[arity]; 7687 for (int k = 0; k < arity; k++) order[k] = k; 7688 order[i] = j; order[j] = i; 7689 Class<?>[] types = mh.type().parameterArray(); 7690 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti; 7691 MethodType swapType = methodType(mh.type().returnType(), types); 7692 return permuteArguments(mh, swapType, order); 7693 } 7694 7695 /** 7696 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block. 7697 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception 7698 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The 7699 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The 7700 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the 7701 * {@code try-finally} handle. 7702 * <p> 7703 * The {@code cleanup} handle will be passed one or two additional leading arguments. 7704 * The first is the exception thrown during the 7705 * execution of the {@code target} handle, or {@code null} if no exception was thrown. 7706 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception, 7707 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder. 7708 * The second argument is not present if the {@code target} handle has a {@code void} return type. 7709 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists 7710 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.) 7711 * <p> 7712 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except 7713 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or 7714 * two extra leading parameters:<ul> 7715 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and 7716 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry 7717 * the result from the execution of the {@code target} handle. 7718 * This parameter is not present if the {@code target} returns {@code void}. 7719 * </ul> 7720 * <p> 7721 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of 7722 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting 7723 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by 7724 * the cleanup. 7725 * {@snippet lang="java" : 7726 * V target(A..., B...); 7727 * V cleanup(Throwable, V, A...); 7728 * V adapter(A... a, B... b) { 7729 * V result = (zero value for V); 7730 * Throwable throwable = null; 7731 * try { 7732 * result = target(a..., b...); 7733 * } catch (Throwable t) { 7734 * throwable = t; 7735 * throw t; 7736 * } finally { 7737 * result = cleanup(throwable, result, a...); 7738 * } 7739 * return result; 7740 * } 7741 * } 7742 * <p> 7743 * Note that the saved arguments ({@code a...} in the pseudocode) cannot 7744 * be modified by execution of the target, and so are passed unchanged 7745 * from the caller to the cleanup, if it is invoked. 7746 * <p> 7747 * The target and cleanup must return the same type, even if the cleanup 7748 * always throws. 7749 * To create such a throwing cleanup, compose the cleanup logic 7750 * with {@link #throwException throwException}, 7751 * in order to create a method handle of the correct return type. 7752 * <p> 7753 * Note that {@code tryFinally} never converts exceptions into normal returns. 7754 * In rare cases where exceptions must be converted in that way, first wrap 7755 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)} 7756 * to capture an outgoing exception, and then wrap with {@code tryFinally}. 7757 * <p> 7758 * It is recommended that the first parameter type of {@code cleanup} be 7759 * declared {@code Throwable} rather than a narrower subtype. This ensures 7760 * {@code cleanup} will always be invoked with whatever exception that 7761 * {@code target} throws. Declaring a narrower type may result in a 7762 * {@code ClassCastException} being thrown by the {@code try-finally} 7763 * handle if the type of the exception thrown by {@code target} is not 7764 * assignable to the first parameter type of {@code cleanup}. Note that 7765 * various exception types of {@code VirtualMachineError}, 7766 * {@code LinkageError}, and {@code RuntimeException} can in principle be 7767 * thrown by almost any kind of Java code, and a finally clause that 7768 * catches (say) only {@code IOException} would mask any of the others 7769 * behind a {@code ClassCastException}. 7770 * 7771 * @param target the handle whose execution is to be wrapped in a {@code try} block. 7772 * @param cleanup the handle that is invoked in the finally block. 7773 * 7774 * @return a method handle embodying the {@code try-finally} block composed of the two arguments. 7775 * @throws NullPointerException if any argument is null 7776 * @throws IllegalArgumentException if {@code cleanup} does not accept 7777 * the required leading arguments, or if the method handle types do 7778 * not match in their return types and their 7779 * corresponding trailing parameters 7780 * 7781 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle) 7782 * @since 9 7783 */ 7784 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) { 7785 Class<?>[] targetParamTypes = target.type().ptypes(); 7786 Class<?> rtype = target.type().returnType(); 7787 7788 tryFinallyChecks(target, cleanup); 7789 7790 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments. 7791 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 7792 // target parameter list. 7793 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false); 7794 7795 // Ensure that the intrinsic type checks the instance thrown by the 7796 // target against the first parameter of cleanup 7797 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class)); 7798 7799 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case. 7800 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes); 7801 } 7802 7803 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) { 7804 Class<?> rtype = target.type().returnType(); 7805 if (rtype != cleanup.type().returnType()) { 7806 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype); 7807 } 7808 MethodType cleanupType = cleanup.type(); 7809 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) { 7810 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class); 7811 } 7812 if (rtype != void.class && cleanupType.parameterType(1) != rtype) { 7813 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype); 7814 } 7815 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the 7816 // target parameter list. 7817 int cleanupArgIndex = rtype == void.class ? 1 : 2; 7818 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) { 7819 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix", 7820 cleanup.type(), target.type()); 7821 } 7822 } 7823 7824 /** 7825 * Creates a table switch method handle, which can be used to switch over a set of target 7826 * method handles, based on a given target index, called selector. 7827 * <p> 7828 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)}, 7829 * and where {@code N} is the number of target method handles, the table switch method 7830 * handle will invoke the n-th target method handle from the list of target method handles. 7831 * <p> 7832 * For a selector value that does not fall in the range {@code [0, N)}, the table switch 7833 * method handle will invoke the given fallback method handle. 7834 * <p> 7835 * All method handles passed to this method must have the same type, with the additional 7836 * requirement that the leading parameter be of type {@code int}. The leading parameter 7837 * represents the selector. 7838 * <p> 7839 * Any trailing parameters present in the type will appear on the returned table switch 7840 * method handle as well. Any arguments assigned to these parameters will be forwarded, 7841 * together with the selector value, to the selected method handle when invoking it. 7842 * 7843 * @apiNote Example: 7844 * The cases each drop the {@code selector} value they are given, and take an additional 7845 * {@code String} argument, which is concatenated (using {@link String#concat(String)}) 7846 * to a specific constant label string for each case: 7847 * {@snippet lang="java" : 7848 * MethodHandles.Lookup lookup = MethodHandles.lookup(); 7849 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat", 7850 * MethodType.methodType(String.class, String.class)); 7851 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class); 7852 * 7853 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: "); 7854 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: "); 7855 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: "); 7856 * 7857 * MethodHandle mhSwitch = MethodHandles.tableSwitch( 7858 * caseDefault, 7859 * case0, 7860 * case1 7861 * ); 7862 * 7863 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data")); 7864 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data")); 7865 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data")); 7866 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data")); 7867 * } 7868 * 7869 * @param fallback the fallback method handle that is called when the selector is not 7870 * within the range {@code [0, N)}. 7871 * @param targets array of target method handles. 7872 * @return the table switch method handle. 7873 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any 7874 * any of the elements of the {@code targets} array are 7875 * {@code null}. 7876 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading 7877 * parameter of the fallback handle or any of the target 7878 * handles is not {@code int}, or if the types of 7879 * the fallback handle and all of target handles are 7880 * not the same. 7881 */ 7882 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) { 7883 Objects.requireNonNull(fallback); 7884 Objects.requireNonNull(targets); 7885 targets = targets.clone(); 7886 MethodType type = tableSwitchChecks(fallback, targets); 7887 return MethodHandleImpl.makeTableSwitch(type, fallback, targets); 7888 } 7889 7890 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) { 7891 if (caseActions.length == 0) 7892 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions)); 7893 7894 MethodType expectedType = defaultCase.type(); 7895 7896 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class) 7897 throw new IllegalArgumentException( 7898 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions)); 7899 7900 for (MethodHandle mh : caseActions) { 7901 Objects.requireNonNull(mh); 7902 if (mh.type() != expectedType) 7903 throw new IllegalArgumentException( 7904 "Case actions must have the same type: " + Arrays.toString(caseActions)); 7905 } 7906 7907 return expectedType; 7908 } 7909 7910 /** 7911 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment} 7912 * by viewing its contents as a sequence of the provided value layout. 7913 * 7914 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type}, 7915 * the {@linkplain ValueLayout#byteSize() byte size}, 7916 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order} 7917 * associated with the returned var handle. 7918 * 7919 * <p>The returned var handle's type is {@code carrier} and the list of coordinate types is 7920 * {@code (MemorySegment, long)}, where the {@code long} coordinate type corresponds to byte offset into 7921 * a given memory segment. The returned var handle accesses bytes at an offset in a given 7922 * memory segment, composing bytes to or from a value of the type {@code carrier} according to the given endianness; 7923 * the alignment constraint (in bytes) for the resulting var handle is given by {@code alignmentBytes}. 7924 * 7925 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows: 7926 * {@snippet lang="java" : 7927 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout( 7928 * MemoryLayout.paddingLayout(32), 7929 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value") 7930 * ); 7931 * } 7932 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows: 7933 * {@snippet lang="java" : 7934 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int 7935 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int 7936 * } 7937 * 7938 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>, 7939 * which are common to all memory segment view var handles. A memory segment view var handle is associated 7940 * with an access size {@code S} and an alignment constraint {@code B} 7941 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs 7942 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}. 7943 * If access is fully aligned then following access modes are supported and are 7944 * guaranteed to support atomic access: 7945 * <ul> 7946 * <li>read write access modes for all {@code T}, with the exception of 7947 * access modes {@code get} and {@code set} for {@code long} and 7948 * {@code double} on 32-bit platforms. 7949 * <li>atomic update access modes for {@code int}, {@code long}, 7950 * {@code float}, {@code double} or {@link MemorySegment}. 7951 * (Future major platform releases of the JDK may support additional 7952 * types for certain currently unsupported access modes.) 7953 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}. 7954 * (Future major platform releases of the JDK may support additional 7955 * numeric types for certain currently unsupported access modes.) 7956 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}. 7957 * (Future major platform releases of the JDK may support additional 7958 * numeric types for certain currently unsupported access modes.) 7959 * </ul> 7960 * 7961 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic 7962 * update access modes compare values using their bitwise representation 7963 * (see {@link Float#floatToRawIntBits}, 7964 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively). 7965 * <p> 7966 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A} 7967 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the 7968 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned, 7969 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}. 7970 * <p> 7971 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an 7972 * {@code IllegalStateException} is thrown, irrespective of the access mode being used. 7973 * <p> 7974 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException} 7975 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment. 7976 * 7977 * @param layout the value layout for which a memory access handle is to be obtained. 7978 * @return the new memory segment view var handle. 7979 * @throws IllegalArgumentException if an illegal carrier type is used, or if {@code alignmentBytes} is not a power of two. 7980 * @throws NullPointerException if {@code layout} is {@code null}. 7981 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...) 7982 * @since 19 7983 */ 7984 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 7985 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) { 7986 Objects.requireNonNull(layout); 7987 return Utils.makeSegmentViewVarHandle(layout); 7988 } 7989 7990 /** 7991 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions. 7992 * <p> 7993 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where 7994 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed 7995 * to the target var handle. 7996 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from 7997 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function) 7998 * is processed using the second filter and returned to the caller. More advanced access mode types, such as 7999 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time. 8000 * <p> 8001 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and 8002 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case, 8003 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which 8004 * will be appended to the coordinates of the target var handle). 8005 * <p> 8006 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will 8007 * throw an {@link IllegalStateException}. 8008 * <p> 8009 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8010 * atomic access guarantees as those featured by the target var handle. 8011 * 8012 * @param target the target var handle 8013 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target} 8014 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S} 8015 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions. 8016 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types 8017 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle, 8018 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions. 8019 * @throws NullPointerException if any of the arguments is {@code null}. 8020 * @since 19 8021 */ 8022 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8023 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) { 8024 return VarHandles.filterValue(target, filterToTarget, filterFromTarget); 8025 } 8026 8027 /** 8028 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions. 8029 * <p> 8030 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values 8031 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types 8032 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the 8033 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered 8034 * by the adaptation) to the target var handle. 8035 * <p> 8036 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn}, 8037 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle. 8038 * <p> 8039 * If any of the filters throws a checked exception when invoked, the resulting var handle will 8040 * throw an {@link IllegalStateException}. 8041 * <p> 8042 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8043 * atomic access guarantees as those featured by the target var handle. 8044 * 8045 * @param target the target var handle 8046 * @param pos the position of the first coordinate to be transformed 8047 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos} 8048 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation 8049 * to the new coordinate values. 8050 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types 8051 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting 8052 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8053 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos}, 8054 * or if it's determined that any of the filters throws any checked exceptions. 8055 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}. 8056 * @since 19 8057 */ 8058 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8059 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) { 8060 return VarHandles.filterCoordinates(target, pos, filters); 8061 } 8062 8063 /** 8064 * Provides a target var handle with one or more <em>bound coordinates</em> 8065 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less 8066 * coordinate types than the target var handle. 8067 * <p> 8068 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values 8069 * are joined with bound coordinate values, and then passed to the target var handle. 8070 * <p> 8071 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn }, 8072 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle. 8073 * <p> 8074 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8075 * atomic access guarantees as those featured by the target var handle. 8076 * 8077 * @param target the var handle to invoke after the bound coordinates are inserted 8078 * @param pos the position of the first coordinate to be inserted 8079 * @param values the series of bound coordinates to insert 8080 * @return an adapter var handle which inserts additional coordinates, 8081 * before calling the target var handle 8082 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8083 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}. 8084 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types 8085 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} 8086 * of the target var handle. 8087 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}. 8088 * @since 19 8089 */ 8090 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8091 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) { 8092 return VarHandles.insertCoordinates(target, pos, values); 8093 } 8094 8095 /** 8096 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them 8097 * so that the new coordinates match the provided ones. 8098 * <p> 8099 * The given array controls the reordering. 8100 * Call {@code #I} the number of incoming coordinates (the value 8101 * {@code newCoordinates.size()}), and call {@code #O} the number 8102 * of outgoing coordinates (the number of coordinates associated with the target var handle). 8103 * Then the length of the reordering array must be {@code #O}, 8104 * and each element must be a non-negative number less than {@code #I}. 8105 * For every {@code N} less than {@code #O}, the {@code N}-th 8106 * outgoing coordinate will be taken from the {@code I}-th incoming 8107 * coordinate, where {@code I} is {@code reorder[N]}. 8108 * <p> 8109 * No coordinate value conversions are applied. 8110 * The type of each incoming coordinate, as determined by {@code newCoordinates}, 8111 * must be identical to the type of the corresponding outgoing coordinate 8112 * in the target var handle. 8113 * <p> 8114 * The reordering array need not specify an actual permutation. 8115 * An incoming coordinate will be duplicated if its index appears 8116 * more than once in the array, and an incoming coordinate will be dropped 8117 * if its index does not appear in the array. 8118 * <p> 8119 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8120 * atomic access guarantees as those featured by the target var handle. 8121 * @param target the var handle to invoke after the coordinates have been reordered 8122 * @param newCoordinates the new coordinate types 8123 * @param reorder an index array which controls the reordering 8124 * @return an adapter var handle which re-arranges the incoming coordinate values, 8125 * before calling the target var handle 8126 * @throws IllegalArgumentException if the index array length is not equal to 8127 * the number of coordinates of the target var handle, or if any index array element is not a valid index for 8128 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in 8129 * the target var handle and in {@code newCoordinates} are not identical. 8130 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}. 8131 * @since 19 8132 */ 8133 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8134 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) { 8135 return VarHandles.permuteCoordinates(target, newCoordinates, reorder); 8136 } 8137 8138 /** 8139 * Adapts a target var handle by pre-processing 8140 * a sub-sequence of its coordinate values with a filter (a method handle). 8141 * The pre-processed coordinates are replaced by the result (if any) of the 8142 * filter function and the target var handle is then called on the modified (usually shortened) 8143 * coordinate list. 8144 * <p> 8145 * If {@code R} is the return type of the filter (which cannot be void), the target var handle must accept a value of 8146 * type {@code R} as its coordinate in position {@code pos}, preceded and/or followed by 8147 * any coordinate not passed to the filter. 8148 * No coordinates are reordered, and the result returned from the filter 8149 * replaces (in order) the whole subsequence of coordinates originally 8150 * passed to the adapter. 8151 * <p> 8152 * The argument types (if any) of the filter 8153 * replace zero or one coordinate types of the target var handle, at position {@code pos}, 8154 * in the resulting adapted var handle. 8155 * The return type of the filter must be identical to the 8156 * coordinate type of the target var handle at position {@code pos}, and that target var handle 8157 * coordinate is supplied by the return value of the filter. 8158 * <p> 8159 * If any of the filters throws a checked exception when invoked, the resulting var handle will 8160 * throw an {@link IllegalStateException}. 8161 * <p> 8162 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8163 * atomic access guarantees as those featured by the target var handle. 8164 * 8165 * @param target the var handle to invoke after the coordinates have been filtered 8166 * @param pos the position of the coordinate to be filtered 8167 * @param filter the filter method handle 8168 * @return an adapter var handle which filters the incoming coordinate values, 8169 * before calling the target var handle 8170 * @throws IllegalArgumentException if the return type of {@code filter} 8171 * is void, or it is not the same as the {@code pos} coordinate of the target var handle, 8172 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive, 8173 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>, 8174 * or if it's determined that {@code filter} throws any checked exceptions. 8175 * @throws NullPointerException if any of the arguments is {@code null}. 8176 * @since 19 8177 */ 8178 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8179 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) { 8180 return VarHandles.collectCoordinates(target, pos, filter); 8181 } 8182 8183 /** 8184 * Returns a var handle which will discard some dummy coordinates before delegating to the 8185 * target var handle. As a consequence, the resulting var handle will feature more 8186 * coordinate types than the target var handle. 8187 * <p> 8188 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the 8189 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede 8190 * the target's real arguments; if {@code pos} is <i>N</i> they will come after. 8191 * <p> 8192 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and 8193 * atomic access guarantees as those featured by the target var handle. 8194 * 8195 * @param target the var handle to invoke after the dummy coordinates are dropped 8196 * @param pos position of the first coordinate to drop (zero for the leftmost) 8197 * @param valueTypes the type(s) of the coordinate(s) to drop 8198 * @return an adapter var handle which drops some dummy coordinates, 8199 * before calling the target var handle 8200 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive. 8201 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}. 8202 * @since 19 8203 */ 8204 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN) 8205 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) { 8206 return VarHandles.dropCoordinates(target, pos, valueTypes); 8207 } 8208 }