1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1994, 2021, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 package java.lang; 28 29 import dalvik.annotation.optimization.FastNative; 30 import jdk.internal.vm.annotation.IntrinsicCandidate; 31 32 /** 33 * Class {@code Object} is the root of the class hierarchy. 34 * Every class has {@code Object} as a superclass. All objects, 35 * including arrays, implement the methods of this class. 36 * 37 * @see java.lang.Class 38 * @since 1.0 39 */ 40 public class Object { 41 42 // Android-removed: registerNatives() not used on Android 43 // private static native void registerNatives(); 44 // static { 45 // registerNatives(); 46 // } 47 48 // Android-added: Use Android specific fields for Class and monitor. 49 private transient Class<?> shadow$_klass_; 50 private transient int shadow$_monitor_; 51 52 53 /** 54 * Constructs a new object. 55 */ 56 @IntrinsicCandidate Object()57 public Object() {} 58 59 /** 60 * Returns the runtime class of this {@code Object}. The returned 61 * {@code Class} object is the object that is locked by {@code 62 * static synchronized} methods of the represented class. 63 * 64 * <p><b>The actual result type is {@code Class<? extends |X|>} 65 * where {@code |X|} is the erasure of the static type of the 66 * expression on which {@code getClass} is called.</b> For 67 * example, no cast is required in this code fragment:</p> 68 * 69 * <p> 70 * {@code Number n = 0; }<br> 71 * {@code Class<? extends Number> c = n.getClass(); } 72 * </p> 73 * 74 * @return The {@code Class} object that represents the runtime 75 * class of this object. 76 * @jls 15.8.2 Class Literals 77 */ 78 @IntrinsicCandidate 79 // Android-changed: Use Android specific fields for Class and monitor. 80 // public final native Class<?> getClass(); getClass()81 public final Class<?> getClass() { 82 return shadow$_klass_; 83 } 84 85 /** 86 * Returns a hash code value for the object. This method is 87 * supported for the benefit of hash tables such as those provided by 88 * {@link java.util.HashMap}. 89 * <p> 90 * The general contract of {@code hashCode} is: 91 * <ul> 92 * <li>Whenever it is invoked on the same object more than once during 93 * an execution of a Java application, the {@code hashCode} method 94 * must consistently return the same integer, provided no information 95 * used in {@code equals} comparisons on the object is modified. 96 * This integer need not remain consistent from one execution of an 97 * application to another execution of the same application. 98 * <li>If two objects are equal according to the {@link 99 * #equals(Object) equals} method, then calling the {@code 100 * hashCode} method on each of the two objects must produce the 101 * same integer result. 102 * <li>It is <em>not</em> required that if two objects are unequal 103 * according to the {@link #equals(Object) equals} method, then 104 * calling the {@code hashCode} method on each of the two objects 105 * must produce distinct integer results. However, the programmer 106 * should be aware that producing distinct integer results for 107 * unequal objects may improve the performance of hash tables. 108 * </ul> 109 * 110 * @implSpec 111 * As far as is reasonably practical, the {@code hashCode} method defined 112 * by class {@code Object} returns distinct integers for distinct objects. 113 * 114 * @return a hash code value for this object. 115 * @see java.lang.Object#equals(java.lang.Object) 116 * @see java.lang.System#identityHashCode 117 */ 118 @IntrinsicCandidate 119 // BEGIN Android-changed: Added a local helper for identityHashCode. 120 // public native int hashCode(); hashCode()121 public int hashCode() { 122 return identityHashCode(this); 123 } 124 125 // Package-private to be used by j.l.System. We do the implementation here 126 // to avoid Object.hashCode doing a clinit check on j.l.System, and also 127 // to avoid leaking shadow$_monitor_ outside of this class. identityHashCode(Object obj)128 /* package-private */ static int identityHashCode(Object obj) { 129 int lockWord = obj.shadow$_monitor_; 130 final int lockWordStateMask = 0xC0000000; // Top 2 bits. 131 final int lockWordStateHash = 0x80000000; // Top 2 bits are value 2 (kStateHash). 132 final int lockWordHashMask = 0x0FFFFFFF; // Low 28 bits. 133 if ((lockWord & lockWordStateMask) == lockWordStateHash) { 134 return lockWord & lockWordHashMask; 135 } 136 return identityHashCodeNative(obj); 137 } 138 139 /** 140 * Return the identity hash code when the information in the monitor field 141 * is not sufficient. 142 */ 143 @FastNative identityHashCodeNative(Object obj)144 private static native int identityHashCodeNative(Object obj); 145 // END Android-changed: Added a local helper for identityHashCode. 146 147 /** 148 * Indicates whether some other object is "equal to" this one. 149 * <p> 150 * The {@code equals} method implements an equivalence relation 151 * on non-null object references: 152 * <ul> 153 * <li>It is <i>reflexive</i>: for any non-null reference value 154 * {@code x}, {@code x.equals(x)} should return 155 * {@code true}. 156 * <li>It is <i>symmetric</i>: for any non-null reference values 157 * {@code x} and {@code y}, {@code x.equals(y)} 158 * should return {@code true} if and only if 159 * {@code y.equals(x)} returns {@code true}. 160 * <li>It is <i>transitive</i>: for any non-null reference values 161 * {@code x}, {@code y}, and {@code z}, if 162 * {@code x.equals(y)} returns {@code true} and 163 * {@code y.equals(z)} returns {@code true}, then 164 * {@code x.equals(z)} should return {@code true}. 165 * <li>It is <i>consistent</i>: for any non-null reference values 166 * {@code x} and {@code y}, multiple invocations of 167 * {@code x.equals(y)} consistently return {@code true} 168 * or consistently return {@code false}, provided no 169 * information used in {@code equals} comparisons on the 170 * objects is modified. 171 * <li>For any non-null reference value {@code x}, 172 * {@code x.equals(null)} should return {@code false}. 173 * </ul> 174 * 175 * <p> 176 * An equivalence relation partitions the elements it operates on 177 * into <i>equivalence classes</i>; all the members of an 178 * equivalence class are equal to each other. Members of an 179 * equivalence class are substitutable for each other, at least 180 * for some purposes. 181 * 182 * @implSpec 183 * The {@code equals} method for class {@code Object} implements 184 * the most discriminating possible equivalence relation on objects; 185 * that is, for any non-null reference values {@code x} and 186 * {@code y}, this method returns {@code true} if and only 187 * if {@code x} and {@code y} refer to the same object 188 * ({@code x == y} has the value {@code true}). 189 * 190 * In other words, under the reference equality equivalence 191 * relation, each equivalence class only has a single element. 192 * 193 * @apiNote 194 * It is generally necessary to override the {@link #hashCode hashCode} 195 * method whenever this method is overridden, so as to maintain the 196 * general contract for the {@code hashCode} method, which states 197 * that equal objects must have equal hash codes. 198 * 199 * @param obj the reference object with which to compare. 200 * @return {@code true} if this object is the same as the obj 201 * argument; {@code false} otherwise. 202 * @see #hashCode() 203 * @see java.util.HashMap 204 */ equals(Object obj)205 public boolean equals(Object obj) { 206 return (this == obj); 207 } 208 209 /** 210 * Creates and returns a copy of this object. The precise meaning 211 * of "copy" may depend on the class of the object. The general 212 * intent is that, for any object {@code x}, the expression: 213 * <blockquote> 214 * <pre> 215 * x.clone() != x</pre></blockquote> 216 * will be true, and that the expression: 217 * <blockquote> 218 * <pre> 219 * x.clone().getClass() == x.getClass()</pre></blockquote> 220 * will be {@code true}, but these are not absolute requirements. 221 * While it is typically the case that: 222 * <blockquote> 223 * <pre> 224 * x.clone().equals(x)</pre></blockquote> 225 * will be {@code true}, this is not an absolute requirement. 226 * <p> 227 * By convention, the returned object should be obtained by calling 228 * {@code super.clone}. If a class and all of its superclasses (except 229 * {@code Object}) obey this convention, it will be the case that 230 * {@code x.clone().getClass() == x.getClass()}. 231 * <p> 232 * By convention, the object returned by this method should be independent 233 * of this object (which is being cloned). To achieve this independence, 234 * it may be necessary to modify one or more fields of the object returned 235 * by {@code super.clone} before returning it. Typically, this means 236 * copying any mutable objects that comprise the internal "deep structure" 237 * of the object being cloned and replacing the references to these 238 * objects with references to the copies. If a class contains only 239 * primitive fields or references to immutable objects, then it is usually 240 * the case that no fields in the object returned by {@code super.clone} 241 * need to be modified. 242 * 243 * @implSpec 244 * The method {@code clone} for class {@code Object} performs a 245 * specific cloning operation. First, if the class of this object does 246 * not implement the interface {@code Cloneable}, then a 247 * {@code CloneNotSupportedException} is thrown. Note that all arrays 248 * are considered to implement the interface {@code Cloneable} and that 249 * the return type of the {@code clone} method of an array type {@code T[]} 250 * is {@code T[]} where T is any reference or primitive type. 251 * Otherwise, this method creates a new instance of the class of this 252 * object and initializes all its fields with exactly the contents of 253 * the corresponding fields of this object, as if by assignment; the 254 * contents of the fields are not themselves cloned. Thus, this method 255 * performs a "shallow copy" of this object, not a "deep copy" operation. 256 * <p> 257 * The class {@code Object} does not itself implement the interface 258 * {@code Cloneable}, so calling the {@code clone} method on an object 259 * whose class is {@code Object} will result in throwing an 260 * exception at run time. 261 * 262 * @return a clone of this instance. 263 * @throws CloneNotSupportedException if the object's class does not 264 * support the {@code Cloneable} interface. Subclasses 265 * that override the {@code clone} method can also 266 * throw this exception to indicate that an instance cannot 267 * be cloned. 268 * @see java.lang.Cloneable 269 */ 270 @IntrinsicCandidate 271 // BEGIN Android-changed: Use native local helper for clone() 272 // Checks whether cloning is allowed before calling native local helper. 273 // protected native Object clone() throws CloneNotSupportedException; clone()274 protected Object clone() throws CloneNotSupportedException { 275 if (!(this instanceof Cloneable)) { 276 throw new CloneNotSupportedException("Class " + getClass().getName() + 277 " doesn't implement Cloneable"); 278 } 279 280 return internalClone(); 281 } 282 283 /* 284 * Native helper method for cloning. 285 */ 286 @FastNative internalClone()287 private native Object internalClone(); 288 // END Android-changed: Use native local helper for clone() 289 290 /** 291 * Returns a string representation of the object. 292 * @apiNote 293 * In general, the 294 * {@code toString} method returns a string that 295 * "textually represents" this object. The result should 296 * be a concise but informative representation that is easy for a 297 * person to read. 298 * It is recommended that all subclasses override this method. 299 * The string output is not necessarily stable over time or across 300 * JVM invocations. 301 * @implSpec 302 * The {@code toString} method for class {@code Object} 303 * returns a string consisting of the name of the class of which the 304 * object is an instance, the at-sign character `{@code @}', and 305 * the unsigned hexadecimal representation of the hash code of the 306 * object. In other words, this method returns a string equal to the 307 * value of: 308 * <blockquote> 309 * <pre> 310 * getClass().getName() + '@' + Integer.toHexString(hashCode()) 311 * </pre></blockquote> 312 * 313 * @return a string representation of the object. 314 */ toString()315 public String toString() { 316 return getClass().getName() + "@" + Integer.toHexString(hashCode()); 317 } 318 319 /** 320 * Wakes up a single thread that is waiting on this object's 321 * monitor. If any threads are waiting on this object, one of them 322 * is chosen to be awakened. The choice is arbitrary and occurs at 323 * the discretion of the implementation. A thread waits on an object's 324 * monitor by calling one of the {@code wait} methods. 325 * <p> 326 * The awakened thread will not be able to proceed until the current 327 * thread relinquishes the lock on this object. The awakened thread will 328 * compete in the usual manner with any other threads that might be 329 * actively competing to synchronize on this object; for example, the 330 * awakened thread enjoys no reliable privilege or disadvantage in being 331 * the next thread to lock this object. 332 * <p> 333 * This method should only be called by a thread that is the owner 334 * of this object's monitor. A thread becomes the owner of the 335 * object's monitor in one of three ways: 336 * <ul> 337 * <li>By executing a synchronized instance method of that object. 338 * <li>By executing the body of a {@code synchronized} statement 339 * that synchronizes on the object. 340 * <li>For objects of type {@code Class,} by executing a 341 * synchronized static method of that class. 342 * </ul> 343 * <p> 344 * Only one thread at a time can own an object's monitor. 345 * 346 * @throws IllegalMonitorStateException if the current thread is not 347 * the owner of this object's monitor. 348 * @see java.lang.Object#notifyAll() 349 * @see java.lang.Object#wait() 350 */ 351 @FastNative 352 @IntrinsicCandidate notify()353 public final native void notify(); 354 355 /** 356 * Wakes up all threads that are waiting on this object's monitor. A 357 * thread waits on an object's monitor by calling one of the 358 * {@code wait} methods. 359 * <p> 360 * The awakened threads will not be able to proceed until the current 361 * thread relinquishes the lock on this object. The awakened threads 362 * will compete in the usual manner with any other threads that might 363 * be actively competing to synchronize on this object; for example, 364 * the awakened threads enjoy no reliable privilege or disadvantage in 365 * being the next thread to lock this object. 366 * <p> 367 * This method should only be called by a thread that is the owner 368 * of this object's monitor. See the {@code notify} method for a 369 * description of the ways in which a thread can become the owner of 370 * a monitor. 371 * 372 * @throws IllegalMonitorStateException if the current thread is not 373 * the owner of this object's monitor. 374 * @see java.lang.Object#notify() 375 * @see java.lang.Object#wait() 376 */ 377 @FastNative 378 @IntrinsicCandidate notifyAll()379 public final native void notifyAll(); 380 381 /** 382 * Causes the current thread to wait until it is awakened, typically 383 * by being <em>notified</em> or <em>interrupted</em>, or until a 384 * certain amount of real time has elapsed. 385 * <p> 386 * In all respects, this method behaves as if {@code wait(timeoutMillis, 0)} 387 * had been called. See the specification of the {@link #wait(long, int)} method 388 * for details. 389 * 390 * @param timeoutMillis the maximum time to wait, in milliseconds 391 * @throws IllegalArgumentException if {@code timeoutMillis} is negative 392 * @throws IllegalMonitorStateException if the current thread is not 393 * the owner of the object's monitor 394 * @throws InterruptedException if any thread interrupted the current thread before or 395 * while the current thread was waiting. The <em>interrupted status</em> of the 396 * current thread is cleared when this exception is thrown. 397 * @see #notify() 398 * @see #notifyAll() 399 * @see #wait() 400 * @see #wait(long, int) 401 */ 402 // Android-changed: Implement wait(long) non-natively. 403 // public final native void wait(long timeoutMillis) throws InterruptedException; wait(long timeoutMillis)404 public final void wait(long timeoutMillis) throws InterruptedException { 405 wait(timeoutMillis, 0); 406 } 407 408 /** 409 * Causes the current thread to wait until it is awakened, typically 410 * by being <em>notified</em> or <em>interrupted</em>, or until a 411 * certain amount of real time has elapsed. 412 * <p> 413 * The current thread must own this object's monitor lock. See the 414 * {@link #notify notify} method for a description of the ways in which 415 * a thread can become the owner of a monitor lock. 416 * <p> 417 * This method causes the current thread (referred to here as <var>T</var>) to 418 * place itself in the wait set for this object and then to relinquish any 419 * and all synchronization claims on this object. Note that only the locks 420 * on this object are relinquished; any other objects on which the current 421 * thread may be synchronized remain locked while the thread waits. 422 * <p> 423 * Thread <var>T</var> then becomes disabled for thread scheduling purposes 424 * and lies dormant until one of the following occurs: 425 * <ul> 426 * <li>Some other thread invokes the {@code notify} method for this 427 * object and thread <var>T</var> happens to be arbitrarily chosen as 428 * the thread to be awakened. 429 * <li>Some other thread invokes the {@code notifyAll} method for this 430 * object. 431 * <li>Some other thread {@linkplain Thread#interrupt() interrupts} 432 * thread <var>T</var>. 433 * <li>The specified amount of real time has elapsed, more or less. 434 * The amount of real time, in nanoseconds, is given by the expression 435 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos} 436 * are both zero, then real time is not taken into consideration and the 437 * thread waits until awakened by one of the other causes. 438 * <li>Thread <var>T</var> is awakened spuriously. (See below.) 439 * </ul> 440 * <p> 441 * The thread <var>T</var> is then removed from the wait set for this 442 * object and re-enabled for thread scheduling. It competes in the 443 * usual manner with other threads for the right to synchronize on the 444 * object; once it has regained control of the object, all its 445 * synchronization claims on the object are restored to the status quo 446 * ante - that is, to the situation as of the time that the {@code wait} 447 * method was invoked. Thread <var>T</var> then returns from the 448 * invocation of the {@code wait} method. Thus, on return from the 449 * {@code wait} method, the synchronization state of the object and of 450 * thread {@code T} is exactly as it was when the {@code wait} method 451 * was invoked. 452 * <p> 453 * A thread can wake up without being notified, interrupted, or timing out, a 454 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice, 455 * applications must guard against it by testing for the condition that should 456 * have caused the thread to be awakened, and continuing to wait if the condition 457 * is not satisfied. See the example below. 458 * <p> 459 * For more information on this topic, see section 14.2, 460 * "Condition Queues," in Brian Goetz and others' <em>Java Concurrency 461 * in Practice</em> (Addison-Wesley, 2006) or Item 69 in Joshua 462 * Bloch's <em>Effective Java, Second Edition</em> (Addison-Wesley, 463 * 2008). 464 * <p> 465 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted} 466 * by any thread before or while it is waiting, then an {@code InterruptedException} 467 * is thrown. The <em>interrupted status</em> of the current thread is cleared when 468 * this exception is thrown. This exception is not thrown until the lock status of 469 * this object has been restored as described above. 470 * 471 * @apiNote 472 * The recommended approach to waiting is to check the condition being awaited in 473 * a {@code while} loop around the call to {@code wait}, as shown in the example 474 * below. Among other things, this approach avoids problems that can be caused 475 * by spurious wakeups. 476 * 477 * <pre>{@code 478 * synchronized (obj) { 479 * while (<condition does not hold> and <timeout not exceeded>) { 480 * long timeoutMillis = ... ; // recompute timeout values 481 * int nanos = ... ; 482 * obj.wait(timeoutMillis, nanos); 483 * } 484 * ... // Perform action appropriate to condition or timeout 485 * } 486 * }</pre> 487 * 488 * @param timeoutMillis the maximum time to wait, in milliseconds 489 * @param nanos additional time, in nanoseconds, in the range 0-999999 inclusive 490 * @throws IllegalArgumentException if {@code timeoutMillis} is negative, 491 * or if the value of {@code nanos} is out of range 492 * @throws IllegalMonitorStateException if the current thread is not 493 * the owner of the object's monitor 494 * @throws InterruptedException if any thread interrupted the current thread before or 495 * while the current thread was waiting. The <em>interrupted status</em> of the 496 * current thread is cleared when this exception is thrown. 497 * @see #notify() 498 * @see #notifyAll() 499 * @see #wait() 500 * @see #wait(long) 501 */ 502 // Android-changed: Implement wait(long, int) natively. 503 /* 504 public final void wait(long timeoutMillis, int nanos) throws InterruptedException { 505 if (timeoutMillis < 0) { 506 throw new IllegalArgumentException("timeoutMillis value is negative"); 507 } 508 509 if (nanos < 0 || nanos > 999999) { 510 throw new IllegalArgumentException( 511 "nanosecond timeout value out of range"); 512 } 513 514 if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) { 515 timeoutMillis++; 516 } 517 518 wait(timeoutMillis); 519 } 520 */ 521 @FastNative wait(long timeoutMillis, int nanos)522 public final native void wait(long timeoutMillis, int nanos) throws InterruptedException; 523 524 /** 525 * Causes the current thread to wait until it is awakened, typically 526 * by being <em>notified</em> or <em>interrupted</em>. 527 * <p> 528 * In all respects, this method behaves as if {@code wait(0L, 0)} 529 * had been called. See the specification of the {@link #wait(long, int)} method 530 * for details. 531 * 532 * @throws IllegalMonitorStateException if the current thread is not 533 * the owner of the object's monitor 534 * @throws InterruptedException if any thread interrupted the current thread before or 535 * while the current thread was waiting. The <em>interrupted status</em> of the 536 * current thread is cleared when this exception is thrown. 537 * @see #notify() 538 * @see #notifyAll() 539 * @see #wait(long) 540 * @see #wait(long, int) 541 */ wait()542 public final void wait() throws InterruptedException { 543 wait(0); 544 } 545 546 /** 547 * Called by the garbage collector on an object when garbage collection 548 * determines that there are no more references to the object. 549 * A subclass overrides the {@code finalize} method to dispose of 550 * system resources or to perform other cleanup. 551 * <p> 552 * The general contract of {@code finalize} is that it is invoked 553 * if and when the Java virtual 554 * machine has determined that there is no longer any 555 * means by which this object can be accessed by any thread that has 556 * not yet died, except as a result of an action taken by the 557 * finalization of some other object or class which is ready to be 558 * finalized. The {@code finalize} method may take any action, including 559 * making this object available again to other threads; the usual purpose 560 * of {@code finalize}, however, is to perform cleanup actions before 561 * the object is irrevocably discarded. For example, the finalize method 562 * for an object that represents an input/output connection might perform 563 * explicit I/O transactions to break the connection before the object is 564 * permanently discarded. 565 * <p> 566 * The {@code finalize} method of class {@code Object} performs no 567 * special action; it simply returns normally. Subclasses of 568 * {@code Object} may override this definition. 569 * <p> 570 * The Java programming language does not guarantee which thread will 571 * invoke the {@code finalize} method for any given object. It is 572 * guaranteed, however, that the thread that invokes finalize will not 573 * be holding any user-visible synchronization locks when finalize is 574 * invoked. If an uncaught exception is thrown by the finalize method, 575 * the exception is ignored and finalization of that object terminates. 576 * <p> 577 * After the {@code finalize} method has been invoked for an object, no 578 * further action is taken until the Java virtual machine has again 579 * determined that there is no longer any means by which this object can 580 * be accessed by any thread that has not yet died, including possible 581 * actions by other objects or classes which are ready to be finalized, 582 * at which point the object may be discarded. 583 * <p> 584 * The {@code finalize} method is never invoked more than once by a Java 585 * virtual machine for any given object. 586 * <p> 587 * Any exception thrown by the {@code finalize} method causes 588 * the finalization of this object to be halted, but is otherwise 589 * ignored. 590 * 591 * @apiNote 592 * Classes that embed non-heap resources have many options 593 * for cleanup of those resources. The class must ensure that the 594 * lifetime of each instance is longer than that of any resource it embeds. 595 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that 596 * objects remain reachable while resources embedded in the object are in use. 597 * <p> 598 * A subclass should avoid overriding the {@code finalize} method 599 * unless the subclass embeds non-heap resources that must be cleaned up 600 * before the instance is collected. 601 * Finalizer invocations are not automatically chained, unlike constructors. 602 * If a subclass overrides {@code finalize} it must invoke the superclass 603 * finalizer explicitly. 604 * To guard against exceptions prematurely terminating the finalize chain, 605 * the subclass should use a {@code try-finally} block to ensure 606 * {@code super.finalize()} is always invoked. For example, 607 * <pre>{@code @Override 608 * protected void finalize() throws Throwable { 609 * try { 610 * ... // cleanup subclass state 611 * } finally { 612 * super.finalize(); 613 * } 614 * } 615 * }</pre> 616 * 617 * Deprecation: The finalization mechanism is inherently problematic. 618 * Finalization can lead to performance issues, deadlocks, and hangs. 619 * Errors in finalizers can lead to resource leaks; there is no way to cancel 620 * finalization if it is no longer necessary; and no ordering is specified 621 * among calls to {@code finalize} methods of different objects. 622 * Furthermore, there are no guarantees regarding the timing of finalization. 623 * The {@code finalize} method might be called on a finalizable object 624 * only after an indefinite delay, if at all. 625 * 626 * Classes whose instances hold non-heap resources should provide a method 627 * to enable explicit release of those resources, and they should also 628 * implement {@link AutoCloseable} if appropriate. 629 * The {@link java.lang.ref.Cleaner} and {@link java.lang.ref.PhantomReference} 630 * provide more flexible and efficient ways to release resources when an object 631 * becomes unreachable. 632 * 633 * @throws Throwable the {@code Exception} raised by this method 634 * @see java.lang.ref.WeakReference 635 * @see java.lang.ref.PhantomReference 636 * @jls 12.6 Finalization of Class Instances 637 */ 638 // Android-changed: Avoid deprecating finalize() causing deprecation of the overridden methods. 639 // @Deprecated(since="9") finalize()640 protected void finalize() throws Throwable { } 641 } 642