1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1994, 2017, 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 31 /** 32 * Class {@code Object} is the root of the class hierarchy. 33 * Every class has {@code Object} as a superclass. All objects, 34 * including arrays, implement the methods of this class. 35 * 36 * @author unascribed 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 * Constructs a new object. 54 */ 55 // @HotSpotIntrinsicCandidate Object()56 public Object() {} 57 58 /** 59 * Returns the runtime class of this {@code Object}. The returned 60 * {@code Class} object is the object that is locked by {@code 61 * static synchronized} methods of the represented class. 62 * 63 * <p><b>The actual result type is {@code Class<? extends |X|>} 64 * where {@code |X|} is the erasure of the static type of the 65 * expression on which {@code getClass} is called.</b> For 66 * example, no cast is required in this code fragment:</p> 67 * 68 * <p> 69 * {@code Number n = 0; }<br> 70 * {@code Class<? extends Number> c = n.getClass(); } 71 * </p> 72 * 73 * @return The {@code Class} object that represents the runtime 74 * class of this object. 75 * @jls 15.8.2 Class Literals 76 */ 77 // Android-changed: Use Android specific fields for Class and monitor. 78 // @HotSpotIntrinsicCandidate 79 // public final native Class<?> getClass(); getClass()80 public final Class<?> getClass() { 81 return shadow$_klass_; 82 } 83 84 /** 85 * Returns a hash code value for the object. This method is 86 * supported for the benefit of hash tables such as those provided by 87 * {@link java.util.HashMap}. 88 * <p> 89 * The general contract of {@code hashCode} is: 90 * <ul> 91 * <li>Whenever it is invoked on the same object more than once during 92 * an execution of a Java application, the {@code hashCode} method 93 * must consistently return the same integer, provided no information 94 * used in {@code equals} comparisons on the object is modified. 95 * This integer need not remain consistent from one execution of an 96 * application to another execution of the same application. 97 * <li>If two objects are equal according to the {@code equals(Object)} 98 * method, then calling the {@code hashCode} method on each of 99 * the two objects must produce the same integer result. 100 * <li>It is <em>not</em> required that if two objects are unequal 101 * according to the {@link java.lang.Object#equals(java.lang.Object)} 102 * method, then calling the {@code hashCode} method on each of the 103 * two objects must produce distinct integer results. However, the 104 * programmer should be aware that producing distinct integer results 105 * for unequal objects may improve the performance of hash tables. 106 * </ul> 107 * <p> 108 * As much as is reasonably practical, the hashCode method defined 109 * by class {@code Object} does return distinct integers for 110 * distinct objects. (The hashCode may or may not be implemented 111 * as some function of an object's memory address at some point 112 * in time.) 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 // BEGIN Android-changed: Added a local helper for identityHashCode. 119 // @HotSpotIntrinsicCandidate 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 * <p> 175 * The {@code equals} method for class {@code Object} implements 176 * the most discriminating possible equivalence relation on objects; 177 * that is, for any non-null reference values {@code x} and 178 * {@code y}, this method returns {@code true} if and only 179 * if {@code x} and {@code y} refer to the same object 180 * ({@code x == y} has the value {@code true}). 181 * <p> 182 * Note that it is generally necessary to override the {@code hashCode} 183 * method whenever this method is overridden, so as to maintain the 184 * general contract for the {@code hashCode} method, which states 185 * that equal objects must have equal hash codes. 186 * 187 * @param obj the reference object with which to compare. 188 * @return {@code true} if this object is the same as the obj 189 * argument; {@code false} otherwise. 190 * @see #hashCode() 191 * @see java.util.HashMap 192 */ equals(Object obj)193 public boolean equals(Object obj) { 194 return (this == obj); 195 } 196 197 /** 198 * Creates and returns a copy of this object. The precise meaning 199 * of "copy" may depend on the class of the object. The general 200 * intent is that, for any object {@code x}, the expression: 201 * <blockquote> 202 * <pre> 203 * x.clone() != x</pre></blockquote> 204 * will be true, and that the expression: 205 * <blockquote> 206 * <pre> 207 * x.clone().getClass() == x.getClass()</pre></blockquote> 208 * will be {@code true}, but these are not absolute requirements. 209 * While it is typically the case that: 210 * <blockquote> 211 * <pre> 212 * x.clone().equals(x)</pre></blockquote> 213 * will be {@code true}, this is not an absolute requirement. 214 * <p> 215 * By convention, the returned object should be obtained by calling 216 * {@code super.clone}. If a class and all of its superclasses (except 217 * {@code Object}) obey this convention, it will be the case that 218 * {@code x.clone().getClass() == x.getClass()}. 219 * <p> 220 * By convention, the object returned by this method should be independent 221 * of this object (which is being cloned). To achieve this independence, 222 * it may be necessary to modify one or more fields of the object returned 223 * by {@code super.clone} before returning it. Typically, this means 224 * copying any mutable objects that comprise the internal "deep structure" 225 * of the object being cloned and replacing the references to these 226 * objects with references to the copies. If a class contains only 227 * primitive fields or references to immutable objects, then it is usually 228 * the case that no fields in the object returned by {@code super.clone} 229 * need to be modified. 230 * <p> 231 * The method {@code clone} for class {@code Object} performs a 232 * specific cloning operation. First, if the class of this object does 233 * not implement the interface {@code Cloneable}, then a 234 * {@code CloneNotSupportedException} is thrown. Note that all arrays 235 * are considered to implement the interface {@code Cloneable} and that 236 * the return type of the {@code clone} method of an array type {@code T[]} 237 * is {@code T[]} where T is any reference or primitive type. 238 * Otherwise, this method creates a new instance of the class of this 239 * object and initializes all its fields with exactly the contents of 240 * the corresponding fields of this object, as if by assignment; the 241 * contents of the fields are not themselves cloned. Thus, this method 242 * performs a "shallow copy" of this object, not a "deep copy" operation. 243 * <p> 244 * The class {@code Object} does not itself implement the interface 245 * {@code Cloneable}, so calling the {@code clone} method on an object 246 * whose class is {@code Object} will result in throwing an 247 * exception at run time. 248 * 249 * @return a clone of this instance. 250 * @throws CloneNotSupportedException if the object's class does not 251 * support the {@code Cloneable} interface. Subclasses 252 * that override the {@code clone} method can also 253 * throw this exception to indicate that an instance cannot 254 * be cloned. 255 * @see java.lang.Cloneable 256 */ 257 // BEGIN Android-changed: Use native local helper for clone() 258 // Checks whether cloning is allowed before calling native local helper. 259 // @HotSpotIntrinsicCandidate 260 // protected native Object clone() throws CloneNotSupportedException; clone()261 protected Object clone() throws CloneNotSupportedException { 262 if (!(this instanceof Cloneable)) { 263 throw new CloneNotSupportedException("Class " + getClass().getName() + 264 " doesn't implement Cloneable"); 265 } 266 267 return internalClone(); 268 } 269 270 /* 271 * Native helper method for cloning. 272 */ 273 @FastNative internalClone()274 private native Object internalClone(); 275 // END Android-changed: Use native local helper for clone() 276 277 /** 278 * Returns a string representation of the object. In general, the 279 * {@code toString} method returns a string that 280 * "textually represents" this object. The result should 281 * be a concise but informative representation that is easy for a 282 * person to read. 283 * It is recommended that all subclasses override this method. 284 * <p> 285 * The {@code toString} method for class {@code Object} 286 * returns a string consisting of the name of the class of which the 287 * object is an instance, the at-sign character `{@code @}', and 288 * the unsigned hexadecimal representation of the hash code of the 289 * object. In other words, this method returns a string equal to the 290 * value of: 291 * <blockquote> 292 * <pre> 293 * getClass().getName() + '@' + Integer.toHexString(hashCode()) 294 * </pre></blockquote> 295 * 296 * @return a string representation of the object. 297 */ toString()298 public String toString() { 299 return getClass().getName() + "@" + Integer.toHexString(hashCode()); 300 } 301 302 /** 303 * Wakes up a single thread that is waiting on this object's 304 * monitor. If any threads are waiting on this object, one of them 305 * is chosen to be awakened. The choice is arbitrary and occurs at 306 * the discretion of the implementation. A thread waits on an object's 307 * monitor by calling one of the {@code wait} methods. 308 * <p> 309 * The awakened thread will not be able to proceed until the current 310 * thread relinquishes the lock on this object. The awakened thread will 311 * compete in the usual manner with any other threads that might be 312 * actively competing to synchronize on this object; for example, the 313 * awakened thread enjoys no reliable privilege or disadvantage in being 314 * the next thread to lock this object. 315 * <p> 316 * This method should only be called by a thread that is the owner 317 * of this object's monitor. A thread becomes the owner of the 318 * object's monitor in one of three ways: 319 * <ul> 320 * <li>By executing a synchronized instance method of that object. 321 * <li>By executing the body of a {@code synchronized} statement 322 * that synchronizes on the object. 323 * <li>For objects of type {@code Class,} by executing a 324 * synchronized static method of that class. 325 * </ul> 326 * <p> 327 * Only one thread at a time can own an object's monitor. 328 * 329 * @throws IllegalMonitorStateException if the current thread is not 330 * the owner of this object's monitor. 331 * @see java.lang.Object#notifyAll() 332 * @see java.lang.Object#wait() 333 */ 334 @FastNative notify()335 public final native void notify(); 336 337 /** 338 * Wakes up all threads that are waiting on this object's monitor. A 339 * thread waits on an object's monitor by calling one of the 340 * {@code wait} methods. 341 * <p> 342 * The awakened threads will not be able to proceed until the current 343 * thread relinquishes the lock on this object. The awakened threads 344 * will compete in the usual manner with any other threads that might 345 * be actively competing to synchronize on this object; for example, 346 * the awakened threads enjoy no reliable privilege or disadvantage in 347 * being the next thread to lock this object. 348 * <p> 349 * This method should only be called by a thread that is the owner 350 * of this object's monitor. See the {@code notify} method for a 351 * description of the ways in which a thread can become the owner of 352 * a monitor. 353 * 354 * @throws IllegalMonitorStateException if the current thread is not 355 * the owner of this object's monitor. 356 * @see java.lang.Object#notify() 357 * @see java.lang.Object#wait() 358 */ 359 @FastNative notifyAll()360 public final native void notifyAll(); 361 362 /** 363 * Causes the current thread to wait until it is awakened, typically 364 * by being <em>notified</em> or <em>interrupted</em>, or until a 365 * certain amount of real time has elapsed. 366 * <p> 367 * In all respects, this method behaves as if {@code wait(timeoutMillis, 0)} 368 * had been called. See the specification of the {@link #wait(long, int)} method 369 * for details. 370 * 371 * @param timeoutMillis the maximum time to wait, in milliseconds 372 * @throws IllegalArgumentException if {@code timeoutMillis} is negative 373 * @throws IllegalMonitorStateException if the current thread is not 374 * the owner of the object's monitor 375 * @throws InterruptedException if any thread interrupted the current thread before or 376 * while the current thread was waiting. The <em>interrupted status</em> of the 377 * current thread is cleared when this exception is thrown. 378 * @see #notify() 379 * @see #notifyAll() 380 * @see #wait() 381 * @see #wait(long, int) 382 */ 383 // Android-changed: Implement wait(long) non-natively. 384 // public final native void wait(long timeoutMillis) throws InterruptedException; wait(long timeoutMillis)385 public final void wait(long timeoutMillis) throws InterruptedException { 386 wait(timeoutMillis, 0); 387 } 388 389 /** 390 * Causes the current thread to wait until it is awakened, typically 391 * by being <em>notified</em> or <em>interrupted</em>, or until a 392 * certain amount of real time has elapsed. 393 * <p> 394 * The current thread must own this object's monitor lock. See the 395 * {@link #notify notify} method for a description of the ways in which 396 * a thread can become the owner of a monitor lock. 397 * <p> 398 * This method causes the current thread (referred to here as <var>T</var>) to 399 * place itself in the wait set for this object and then to relinquish any 400 * and all synchronization claims on this object. Note that only the locks 401 * on this object are relinquished; any other objects on which the current 402 * thread may be synchronized remain locked while the thread waits. 403 * <p> 404 * Thread <var>T</var> then becomes disabled for thread scheduling purposes 405 * and lies dormant until one of the following occurs: 406 * <ul> 407 * <li>Some other thread invokes the {@code notify} method for this 408 * object and thread <var>T</var> happens to be arbitrarily chosen as 409 * the thread to be awakened. 410 * <li>Some other thread invokes the {@code notifyAll} method for this 411 * object. 412 * <li>Some other thread {@linkplain Thread#interrupt() interrupts} 413 * thread <var>T</var>. 414 * <li>The specified amount of real time has elapsed, more or less. 415 * The amount of real time, in nanoseconds, is given by the expression 416 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos} 417 * are both zero, then real time is not taken into consideration and the 418 * thread waits until awakened by one of the other causes. 419 * <li>Thread <var>T</var> is awakened spuriously. (See below.) 420 * </ul> 421 * <p> 422 * The thread <var>T</var> is then removed from the wait set for this 423 * object and re-enabled for thread scheduling. It competes in the 424 * usual manner with other threads for the right to synchronize on the 425 * object; once it has regained control of the object, all its 426 * synchronization claims on the object are restored to the status quo 427 * ante - that is, to the situation as of the time that the {@code wait} 428 * method was invoked. Thread <var>T</var> then returns from the 429 * invocation of the {@code wait} method. Thus, on return from the 430 * {@code wait} method, the synchronization state of the object and of 431 * thread {@code T} is exactly as it was when the {@code wait} method 432 * was invoked. 433 * <p> 434 * A thread can wake up without being notified, interrupted, or timing out, a 435 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice, 436 * applications must guard against it by testing for the condition that should 437 * have caused the thread to be awakened, and continuing to wait if the condition 438 * is not satisfied. See the example below. 439 * <p> 440 * For more information on this topic, see section 14.2, 441 * "Condition Queues," in Brian Goetz and others' <em>Java Concurrency 442 * in Practice</em> (Addison-Wesley, 2006) or Item 69 in Joshua 443 * Bloch's <em>Effective Java, Second Edition</em> (Addison-Wesley, 444 * 2008). 445 * <p> 446 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted} 447 * by any thread before or while it is waiting, then an {@code InterruptedException} 448 * is thrown. The <em>interrupted status</em> of the current thread is cleared when 449 * this exception is thrown. This exception is not thrown until the lock status of 450 * this object has been restored as described above. 451 * 452 * @apiNote 453 * The recommended approach to waiting is to check the condition being awaited in 454 * a {@code while} loop around the call to {@code wait}, as shown in the example 455 * below. Among other things, this approach avoids problems that can be caused 456 * by spurious wakeups. 457 * 458 * <pre>{@code 459 * synchronized (obj) { 460 * while (<condition does not hold> and <timeout not exceeded>) { 461 * long timeoutMillis = ... ; // recompute timeout values 462 * int nanos = ... ; 463 * obj.wait(timeoutMillis, nanos); 464 * } 465 * ... // Perform action appropriate to condition or timeout 466 * } 467 * }</pre> 468 * 469 * @param timeoutMillis the maximum time to wait, in milliseconds 470 * @param nanos additional time, in nanoseconds, in the range range 0-999999 inclusive 471 * @throws IllegalArgumentException if {@code timeoutMillis} is negative, 472 * or if the value of {@code nanos} is out of range 473 * @throws IllegalMonitorStateException if the current thread is not 474 * the owner of the object's monitor 475 * @throws InterruptedException if any thread interrupted the current thread before or 476 * while the current thread was waiting. The <em>interrupted status</em> of the 477 * current thread is cleared when this exception is thrown. 478 * @see #notify() 479 * @see #notifyAll() 480 * @see #wait() 481 * @see #wait(long) 482 */ 483 // Android-changed: Implement wait(long, int) natively. 484 /* 485 public final void wait(long timeoutMillis, int nanos) throws InterruptedException { 486 if (timeoutMillis < 0) { 487 throw new IllegalArgumentException("timeoutMillis value is negative"); 488 } 489 490 if (nanos < 0 || nanos > 999999) { 491 throw new IllegalArgumentException( 492 "nanosecond timeout value out of range"); 493 } 494 495 if (nanos > 0) { 496 timeoutMillis++; 497 } 498 499 wait(timeoutMillis); 500 } 501 */ 502 @FastNative wait(long timeoutMillis, int nanos)503 public final native void wait(long timeoutMillis, int nanos) throws InterruptedException; 504 505 /** 506 * Causes the current thread to wait until it is awakened, typically 507 * by being <em>notified</em> or <em>interrupted</em>. 508 * <p> 509 * In all respects, this method behaves as if {@code wait(0L, 0)} 510 * had been called. See the specification of the {@link #wait(long, int)} method 511 * for details. 512 * 513 * @throws IllegalMonitorStateException if the current thread is not 514 * the owner of the object's monitor 515 * @throws InterruptedException if any thread interrupted the current thread before or 516 * while the current thread was waiting. The <em>interrupted status</em> of the 517 * current thread is cleared when this exception is thrown. 518 * @see #notify() 519 * @see #notifyAll() 520 * @see #wait(long) 521 * @see #wait(long, int) 522 */ wait()523 public final void wait() throws InterruptedException { 524 wait(0); 525 } 526 527 /** 528 * Called by the garbage collector on an object when garbage collection 529 * determines that there are no more references to the object. 530 * A subclass overrides the {@code finalize} method to dispose of 531 * system resources or to perform other cleanup. 532 * <p> 533 * The general contract of {@code finalize} is that it is invoked 534 * if and when the Java™ virtual 535 * machine has determined that there is no longer any 536 * means by which this object can be accessed by any thread that has 537 * not yet died, except as a result of an action taken by the 538 * finalization of some other object or class which is ready to be 539 * finalized. The {@code finalize} method may take any action, including 540 * making this object available again to other threads; the usual purpose 541 * of {@code finalize}, however, is to perform cleanup actions before 542 * the object is irrevocably discarded. For example, the finalize method 543 * for an object that represents an input/output connection might perform 544 * explicit I/O transactions to break the connection before the object is 545 * permanently discarded. 546 * <p> 547 * The {@code finalize} method of class {@code Object} performs no 548 * special action; it simply returns normally. Subclasses of 549 * {@code Object} may override this definition. 550 * <p> 551 * The Java programming language does not guarantee which thread will 552 * invoke the {@code finalize} method for any given object. It is 553 * guaranteed, however, that the thread that invokes finalize will not 554 * be holding any user-visible synchronization locks when finalize is 555 * invoked. If an uncaught exception is thrown by the finalize method, 556 * the exception is ignored and finalization of that object terminates. 557 * <p> 558 * After the {@code finalize} method has been invoked for an object, no 559 * further action is taken until the Java virtual machine has again 560 * determined that there is no longer any means by which this object can 561 * be accessed by any thread that has not yet died, including possible 562 * actions by other objects or classes which are ready to be finalized, 563 * at which point the object may be discarded. 564 * <p> 565 * The {@code finalize} method is never invoked more than once by a Java 566 * virtual machine for any given object. 567 * <p> 568 * Any exception thrown by the {@code finalize} method causes 569 * the finalization of this object to be halted, but is otherwise 570 * ignored. 571 * 572 * @apiNote 573 * Classes that embed non-heap resources have many options 574 * for cleanup of those resources. The class must ensure that the 575 * lifetime of each instance is longer than that of any resource it embeds. 576 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that 577 * objects remain reachable while resources embedded in the object are in use. 578 * <p> 579 * A subclass should avoid overriding the {@code finalize} method 580 * unless the subclass embeds non-heap resources that must be cleaned up 581 * before the instance is collected. 582 * Finalizer invocations are not automatically chained, unlike constructors. 583 * If a subclass overrides {@code finalize} it must invoke the superclass 584 * finalizer explicitly. 585 * To guard against exceptions prematurely terminating the finalize chain, 586 * the subclass should use a {@code try-finally} block to ensure 587 * {@code super.finalize()} is always invoked. For example, 588 * <pre>{@code @Override 589 * protected void finalize() throws Throwable { 590 * try { 591 * ... // cleanup subclass state 592 * } finally { 593 * super.finalize(); 594 * } 595 * } 596 * }</pre> 597 * 598 * Deprecation: The finalization mechanism is inherently problematic. 599 * Finalization can lead to performance issues, deadlocks, and hangs. 600 * Errors in finalizers can lead to resource leaks; there is no way to cancel 601 * finalization if it is no longer necessary; and no ordering is specified 602 * among calls to {@code finalize} methods of different objects. 603 * Furthermore, there are no guarantees regarding the timing of finalization. 604 * The {@code finalize} method might be called on a finalizable object 605 * only after an indefinite delay, if at all. 606 * 607 * Classes whose instances hold non-heap resources should provide a method 608 * to enable explicit release of those resources, and they should also 609 * implement {@link AutoCloseable} if appropriate. 610 * The {@link java.lang.ref.Cleaner} and {@link java.lang.ref.PhantomReference} 611 * provide more flexible and efficient ways to release resources when an object 612 * becomes unreachable. 613 * 614 * @throws Throwable the {@code Exception} raised by this method 615 * @see java.lang.ref.WeakReference 616 * @see java.lang.ref.PhantomReference 617 * @jls 12.6 Finalization of Class Instances 618 */ 619 // Android-changed: Avoid deprecating finalize() causing deprecation of the overridden methods. 620 // @Deprecated(since="9") finalize()621 protected void finalize() throws Throwable { } 622 } 623