1 /* 2 * Copyright (c) 1994, 2024, 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; 27 28 import jdk.internal.misc.Blocker; 29 import jdk.internal.vm.annotation.IntrinsicCandidate; 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 * <p> 36 * Subclasses of {@code java.lang.Object} can be either an {@linkplain Class#isIdentity identity class} 37 * or a {@linkplain Class#isValue value class}. 38 * See {@jls The Java Language Specification 8.1.1.5 value Classes}. 39 * 40 * @see java.lang.Class 41 * @since 1.0 42 */ 43 public class Object { 44 45 /** 46 * Constructs a new object. 47 */ 48 @IntrinsicCandidate 49 public Object() {} 50 51 /** 52 * Returns the runtime class of this {@code Object}. The returned 53 * {@code Class} object is the object that is locked by {@code 54 * static synchronized} methods of the represented class. 55 * 56 * <p><b>The actual result type is {@code Class<? extends |X|>} 57 * where {@code |X|} is the erasure of the static type of the 58 * expression on which {@code getClass} is called.</b> For 59 * example, no cast is required in this code fragment:</p> 60 * 61 * <p> 62 * {@code Number n = 0; }<br> 63 * {@code Class<? extends Number> c = n.getClass(); } 64 * </p> 65 * 66 * @return The {@code Class} object that represents the runtime 67 * class of this object. 68 * @jls 15.8.2 Class Literals 69 */ 70 @IntrinsicCandidate 71 public final native Class<?> getClass(); 72 73 /** 74 * {@return a hash code value for this object} This method is 75 * supported for the benefit of hash tables such as those provided by 76 * {@link java.util.HashMap}. 77 * <p> 78 * The general contract of {@code hashCode} is: 79 * <ul> 80 * <li>Whenever it is invoked on the same object more than once during 81 * an execution of a Java application, the {@code hashCode} method 82 * must consistently return the same integer, provided no information 83 * used in {@code equals} comparisons on the object is modified. 84 * This integer need not remain consistent from one execution of an 85 * application to another execution of the same application. 86 * <li>If two objects are equal according to the {@link 87 * #equals(Object) equals} method, then calling the {@code 88 * hashCode} method on each of the two objects must produce the 89 * same integer result. 90 * <li>It is <em>not</em> required that if two objects are unequal 91 * according to the {@link #equals(Object) equals} method, then 92 * calling the {@code hashCode} method on each of the two objects 93 * must produce distinct integer results. However, the programmer 94 * should be aware that producing distinct integer results for 95 * unequal objects may improve the performance of hash tables. 96 * </ul> 97 * 98 * @implSpec 99 * As far as is reasonably practical, the {@code hashCode} method defined 100 * by class {@code Object} returns distinct integers for distinct objects. 101 * 102 * @apiNote 103 * The {@link java.util.Objects#hash(Object...) hash} and {@link 104 * java.util.Objects#hashCode(Object) hashCode} methods of {@link 105 * java.util.Objects} can be used to help construct simple hash codes. 106 * 107 * @see java.lang.Object#equals(java.lang.Object) 108 * @see java.lang.System#identityHashCode 109 */ 110 @IntrinsicCandidate 111 public native int hashCode(); 112 113 /** 114 * Indicates whether some other object is "equal to" this one. 115 * <p> 116 * The {@code equals} method implements an equivalence relation 117 * on non-null object references: 118 * <ul> 119 * <li>It is <i>reflexive</i>: for any non-null reference value 120 * {@code x}, {@code x.equals(x)} should return 121 * {@code true}. 122 * <li>It is <i>symmetric</i>: for any non-null reference values 123 * {@code x} and {@code y}, {@code x.equals(y)} 124 * should return {@code true} if and only if 125 * {@code y.equals(x)} returns {@code true}. 126 * <li>It is <i>transitive</i>: for any non-null reference values 127 * {@code x}, {@code y}, and {@code z}, if 128 * {@code x.equals(y)} returns {@code true} and 129 * {@code y.equals(z)} returns {@code true}, then 130 * {@code x.equals(z)} should return {@code true}. 131 * <li>It is <i>consistent</i>: for any non-null reference values 132 * {@code x} and {@code y}, multiple invocations of 133 * {@code x.equals(y)} consistently return {@code true} 134 * or consistently return {@code false}, provided no 135 * information used in {@code equals} comparisons on the 136 * objects is modified. 137 * <li>For any non-null reference value {@code x}, 138 * {@code x.equals(null)} should return {@code false}. 139 * </ul> 140 * 141 * <p> 142 * An equivalence relation partitions the elements it operates on 143 * into <i>equivalence classes</i>; all the members of an 144 * equivalence class are equal to each other. Members of an 145 * equivalence class are substitutable for each other, at least 146 * for some purposes. 147 * 148 * @implSpec 149 * The {@code equals} method for class {@code Object} implements 150 * the most discriminating possible equivalence relation on objects; 151 * that is, for any non-null reference values {@code x} and 152 * {@code y}, this method returns {@code true} if and only 153 * if {@code x} and {@code y} refer to the same object 154 * ({@code x == y} has the value {@code true}). 155 * 156 * In other words, under the reference equality equivalence 157 * relation, each equivalence class only has a single element. 158 * 159 * @apiNote 160 * It is generally necessary to override the {@link #hashCode() hashCode} 161 * method whenever this method is overridden, so as to maintain the 162 * general contract for the {@code hashCode} method, which states 163 * that equal objects must have equal hash codes. 164 * <p>The two-argument {@link java.util.Objects#equals(Object, 165 * Object) Objects.equals} method implements an equivalence relation 166 * on two possibly-null object references. 167 * 168 * @param obj the reference object with which to compare. 169 * @return {@code true} if this object is the same as the obj 170 * argument; {@code false} otherwise. 171 * @see #hashCode() 172 * @see java.util.HashMap 173 */ 174 public boolean equals(Object obj) { 175 return (this == obj); 176 } 177 178 /** 179 * Creates and returns a copy of this object. The precise meaning 180 * of "copy" may depend on the class of the object. The general 181 * intent is that, for any object {@code x}, the expression: 182 * <blockquote> 183 * <pre> 184 * x.clone() != x</pre></blockquote> 185 * will be true, and that the expression: 186 * <blockquote> 187 * <pre> 188 * x.clone().getClass() == x.getClass()</pre></blockquote> 189 * will be {@code true}, but these are not absolute requirements. 190 * While it is typically the case that: 191 * <blockquote> 192 * <pre> 193 * x.clone().equals(x)</pre></blockquote> 194 * will be {@code true}, this is not an absolute requirement. 195 * <p> 196 * By convention, the returned object should be obtained by calling 197 * {@code super.clone}. If a class and all of its superclasses (except 198 * {@code Object}) obey this convention, it will be the case that 199 * {@code x.clone().getClass() == x.getClass()}. 200 * <p> 201 * By convention, the object returned by this method should be independent 202 * of this object (which is being cloned). To achieve this independence, 203 * it may be necessary to modify one or more fields of the object returned 204 * by {@code super.clone} before returning it. Typically, this means 205 * copying any mutable objects that comprise the internal "deep structure" 206 * of the object being cloned and replacing the references to these 207 * objects with references to the copies. If a class contains only 208 * primitive fields or references to immutable objects, then it is usually 209 * the case that no fields in the object returned by {@code super.clone} 210 * need to be modified. 211 * 212 * @implSpec 213 * The method {@code clone} for class {@code Object} performs a 214 * specific cloning operation. First, if the class of this object does 215 * not implement the interface {@code Cloneable}, then a 216 * {@code CloneNotSupportedException} is thrown. Note that all arrays 217 * are considered to implement the interface {@code Cloneable} and that 218 * the return type of the {@code clone} method of an array type {@code T[]} 219 * is {@code T[]} where T is any reference or primitive type. 220 * Otherwise, this method creates a new instance of the class of this 221 * object and initializes all its fields with exactly the contents of 222 * the corresponding fields of this object, as if by assignment; the 223 * contents of the fields are not themselves cloned. Thus, this method 224 * performs a "shallow copy" of this object, not a "deep copy" operation. 225 * <p> 226 * The class {@code Object} does not itself implement the interface 227 * {@code Cloneable}, so calling the {@code clone} method on an object 228 * whose class is {@code Object} will result in throwing an 229 * exception at run time. 230 * 231 * @return a clone of this instance. 232 * @throws CloneNotSupportedException if the object's class does not 233 * support the {@code Cloneable} interface. Subclasses 234 * that override the {@code clone} method can also 235 * throw this exception to indicate that an instance cannot 236 * be cloned. 237 * @see java.lang.Cloneable 238 */ 239 @IntrinsicCandidate 240 protected native Object clone() throws CloneNotSupportedException; 241 242 /** 243 * {@return a string representation of the object} 244 * @apiNote 245 * In general, the 246 * {@code toString} method returns a string that 247 * "textually represents" this object. The result should 248 * be a concise but informative representation that is easy for a 249 * person to read. 250 * It is recommended that all subclasses override this method. 251 * The string output is not necessarily stable over time or across 252 * JVM invocations. 253 * @implSpec 254 * The {@code toString} method for class {@code Object} 255 * returns a string consisting of the name of the class of which the 256 * object is an instance, the at-sign character `{@code @}', and 257 * the unsigned hexadecimal representation of the hash code of the 258 * object. In other words, this method returns a string equal to the 259 * value of: 260 * {@snippet lang=java : 261 * getClass().getName() + '@' + Integer.toHexString(hashCode()) 262 * } 263 * The {@link java.util.Objects#toIdentityString(Object) 264 * Objects.toIdentityString} method returns the string for an 265 * object equal to the string that would be returned if neither 266 * the {@code toString} nor {@code hashCode} methods were 267 * overridden by the object's class. 268 */ 269 public String toString() { 270 return getClass().getName() + "@" + Integer.toHexString(hashCode()); 271 } 272 273 /** 274 * Wakes up a single thread that is waiting on this object's 275 * monitor. If any threads are waiting on this object, one of them 276 * is chosen to be awakened. The choice is arbitrary and occurs at 277 * the discretion of the implementation. A thread waits on an object's 278 * monitor by calling one of the {@code wait} methods. 279 * <p> 280 * The awakened thread will not be able to proceed until the current 281 * thread relinquishes the lock on this object. The awakened thread will 282 * compete in the usual manner with any other threads that might be 283 * actively competing to synchronize on this object; for example, the 284 * awakened thread enjoys no reliable privilege or disadvantage in being 285 * the next thread to lock this object. 286 * <p> 287 * This method should only be called by a thread that is the owner 288 * of this object's monitor. A thread becomes the owner of the 289 * object's monitor in one of three ways: 290 * <ul> 291 * <li>By executing a synchronized instance method of that object. 292 * <li>By executing the body of a {@code synchronized} statement 293 * that synchronizes on the object. 294 * <li>For objects of type {@code Class,} by executing a 295 * static synchronized method of that class. 296 * </ul> 297 * <p> 298 * Only one thread at a time can own an object's monitor. 299 * 300 * @throws IllegalMonitorStateException if the current thread is not 301 * the owner of this object's monitor. 302 * @see java.lang.Object#notifyAll() 303 * @see java.lang.Object#wait() 304 */ 305 @IntrinsicCandidate 306 public final native void notify(); 307 308 /** 309 * Wakes up all threads that are waiting on this object's monitor. A 310 * thread waits on an object's monitor by calling one of the 311 * {@code wait} methods. 312 * <p> 313 * The awakened threads will not be able to proceed until the current 314 * thread relinquishes the lock on this object. The awakened threads 315 * will compete in the usual manner with any other threads that might 316 * be actively competing to synchronize on this object; for example, 317 * the awakened threads enjoy no reliable privilege or disadvantage in 318 * being the next thread to lock this object. 319 * <p> 320 * This method should only be called by a thread that is the owner 321 * of this object's monitor. See the {@code notify} method for a 322 * description of the ways in which a thread can become the owner of 323 * a monitor. 324 * 325 * @throws IllegalMonitorStateException if the current thread is not 326 * the owner of this object's monitor. 327 * @see java.lang.Object#notify() 328 * @see java.lang.Object#wait() 329 */ 330 @IntrinsicCandidate 331 public final native void notifyAll(); 332 333 /** 334 * Causes the current thread to wait until it is awakened, typically 335 * by being <em>notified</em> or <em>interrupted</em>. 336 * <p> 337 * In all respects, this method behaves as if {@code wait(0L, 0)} 338 * had been called. See the specification of the {@link #wait(long, int)} method 339 * for details. 340 * 341 * @throws IllegalMonitorStateException if the current thread is not 342 * the owner of the object's monitor 343 * @throws InterruptedException if any thread interrupted the current thread before or 344 * while the current thread was waiting. The <em>interrupted status</em> of the 345 * current thread is cleared when this exception is thrown. 346 * @see #notify() 347 * @see #notifyAll() 348 * @see #wait(long) 349 * @see #wait(long, int) 350 */ 351 public final void wait() throws InterruptedException { 352 wait(0L); 353 } 354 355 /** 356 * Causes the current thread to wait until it is awakened, typically 357 * by being <em>notified</em> or <em>interrupted</em>, or until a 358 * certain amount of real time has elapsed. 359 * <p> 360 * In all respects, this method behaves as if {@code wait(timeoutMillis, 0)} 361 * had been called. See the specification of the {@link #wait(long, int)} method 362 * for details. 363 * 364 * @param timeoutMillis the maximum time to wait, in milliseconds 365 * @throws IllegalArgumentException if {@code timeoutMillis} is negative 366 * @throws IllegalMonitorStateException if the current thread is not 367 * the owner of the object's monitor 368 * @throws InterruptedException if any thread interrupted the current thread before or 369 * while the current thread was waiting. The <em>interrupted status</em> of the 370 * current thread is cleared when this exception is thrown. 371 * @see #notify() 372 * @see #notifyAll() 373 * @see #wait() 374 * @see #wait(long, int) 375 */ 376 public final void wait(long timeoutMillis) throws InterruptedException { 377 if (!Thread.currentThread().isVirtual()) { 378 wait0(timeoutMillis); 379 return; 380 } 381 382 // virtual thread waiting 383 boolean attempted = Blocker.begin(); 384 try { 385 wait0(timeoutMillis); 386 } catch (InterruptedException e) { 387 // virtual thread's interrupt status needs to be cleared 388 Thread.currentThread().getAndClearInterrupt(); 389 throw e; 390 } finally { 391 Blocker.end(attempted); 392 } 393 } 394 395 // final modifier so method not in vtable 396 private final native void wait0(long timeoutMillis) throws InterruptedException; 397 398 /** 399 * Causes the current thread to wait until it is awakened, typically 400 * by being <em>notified</em> or <em>interrupted</em>, or until a 401 * certain amount of real time has elapsed. 402 * <p> 403 * The current thread must own this object's monitor lock. See the 404 * {@link #notify notify} method for a description of the ways in which 405 * a thread can become the owner of a monitor lock. 406 * <p> 407 * This method causes the current thread (referred to here as <var>T</var>) to 408 * place itself in the wait set for this object and then to relinquish any 409 * and all synchronization claims on this object. Note that only the locks 410 * on this object are relinquished; any other objects on which the current 411 * thread may be synchronized remain locked while the thread waits. 412 * <p> 413 * Thread <var>T</var> then becomes disabled for thread scheduling purposes 414 * and lies dormant until one of the following occurs: 415 * <ul> 416 * <li>Some other thread invokes the {@code notify} method for this 417 * object and thread <var>T</var> happens to be arbitrarily chosen as 418 * the thread to be awakened. 419 * <li>Some other thread invokes the {@code notifyAll} method for this 420 * object. 421 * <li>Some other thread {@linkplain Thread#interrupt() interrupts} 422 * thread <var>T</var>. 423 * <li>The specified amount of real time has elapsed, more or less. 424 * The amount of real time, in nanoseconds, is given by the expression 425 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos} 426 * are both zero, then real time is not taken into consideration and the 427 * thread waits until awakened by one of the other causes. 428 * <li>Thread <var>T</var> is awakened spuriously. (See below.) 429 * </ul> 430 * <p> 431 * The thread <var>T</var> is then removed from the wait set for this 432 * object and re-enabled for thread scheduling. It competes in the 433 * usual manner with other threads for the right to synchronize on the 434 * object; once it has regained control of the object, all its 435 * synchronization claims on the object are restored to the status quo 436 * ante - that is, to the situation as of the time that the {@code wait} 437 * method was invoked. Thread <var>T</var> then returns from the 438 * invocation of the {@code wait} method. Thus, on return from the 439 * {@code wait} method, the synchronization state of the object and of 440 * thread {@code T} is exactly as it was when the {@code wait} method 441 * was invoked. 442 * <p> 443 * A thread can wake up without being notified, interrupted, or timing out, a 444 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice, 445 * applications must guard against it by testing for the condition that should 446 * have caused the thread to be awakened, and continuing to wait if the condition 447 * is not satisfied. See the example below. 448 * <p> 449 * For more information on this topic, see section 14.2, 450 * "Condition Queues," in Brian Goetz and others' <cite>Java Concurrency 451 * in Practice</cite> (Addison-Wesley, 2006) or Item 81 in Joshua 452 * Bloch's <cite>Effective Java, Third Edition</cite> (Addison-Wesley, 453 * 2018). 454 * <p> 455 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted} 456 * by any thread before or while it is waiting, then an {@code InterruptedException} 457 * is thrown. The <em>interrupted status</em> of the current thread is cleared when 458 * this exception is thrown. This exception is not thrown until the lock status of 459 * this object has been restored as described above. 460 * 461 * @apiNote 462 * The recommended approach to waiting is to check the condition being awaited in 463 * a {@code while} loop around the call to {@code wait}, as shown in the example 464 * below. Among other things, this approach avoids problems that can be caused 465 * by spurious wakeups. 466 * 467 * {@snippet lang=java : 468 * synchronized (obj) { 469 * while ( <condition does not hold and timeout not exceeded> ) { 470 * long timeoutMillis = ... ; // recompute timeout values 471 * int nanos = ... ; 472 * obj.wait(timeoutMillis, nanos); 473 * } 474 * ... // Perform action appropriate to condition or timeout 475 * } 476 * } 477 * 478 * @param timeoutMillis the maximum time to wait, in milliseconds 479 * @param nanos additional time, in nanoseconds, in the range 0-999999 inclusive 480 * @throws IllegalArgumentException if {@code timeoutMillis} is negative, 481 * or if the value of {@code nanos} is out of range 482 * @throws IllegalMonitorStateException if the current thread is not 483 * the owner of the object's monitor 484 * @throws InterruptedException if any thread interrupted the current thread before or 485 * while the current thread was waiting. The <em>interrupted status</em> of the 486 * current thread is cleared when this exception is thrown. 487 * @see #notify() 488 * @see #notifyAll() 489 * @see #wait() 490 * @see #wait(long) 491 */ 492 public final void wait(long timeoutMillis, int nanos) throws InterruptedException { 493 if (timeoutMillis < 0) { 494 throw new IllegalArgumentException("timeoutMillis value is negative"); 495 } 496 497 if (nanos < 0 || nanos > 999999) { 498 throw new IllegalArgumentException( 499 "nanosecond timeout value out of range"); 500 } 501 502 if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) { 503 timeoutMillis++; 504 } 505 506 wait(timeoutMillis); 507 } 508 509 /** 510 * Called by the garbage collector on an object when garbage collection 511 * determines that there are no more references to the object. 512 * A subclass overrides the {@code finalize} method to dispose of 513 * system resources or to perform other cleanup. 514 * <p> 515 * <b>When running in a Java virtual machine in which finalization has been 516 * disabled or removed, the garbage collector will never call 517 * {@code finalize()}. In a Java virtual machine in which finalization is 518 * enabled, the garbage collector might call {@code finalize} only after an 519 * indefinite delay.</b> 520 * <p> 521 * The general contract of {@code finalize} is that it is invoked 522 * if and when the Java virtual 523 * machine has determined that there is no longer any 524 * means by which this object can be accessed by any thread that has 525 * not yet died, except as a result of an action taken by the 526 * finalization of some other object or class which is ready to be 527 * finalized. The {@code finalize} method may take any action, including 528 * making this object available again to other threads; the usual purpose 529 * of {@code finalize}, however, is to perform cleanup actions before 530 * the object is irrevocably discarded. For example, the finalize method 531 * for an object that represents an input/output connection might perform 532 * explicit I/O transactions to break the connection before the object is 533 * permanently discarded. 534 * <p> 535 * The {@code finalize} method of class {@code Object} performs no 536 * special action; it simply returns normally. Subclasses of 537 * {@code Object} may override this definition. 538 * <p> 539 * The Java programming language does not guarantee which thread will 540 * invoke the {@code finalize} method for any given object. It is 541 * guaranteed, however, that the thread that invokes finalize will not 542 * be holding any user-visible synchronization locks when finalize is 543 * invoked. If an uncaught exception is thrown by the finalize method, 544 * the exception is ignored and finalization of that object terminates. 545 * <p> 546 * After the {@code finalize} method has been invoked for an object, no 547 * further action is taken until the Java virtual machine has again 548 * determined that there is no longer any means by which this object can 549 * be accessed by any thread that has not yet died, including possible 550 * actions by other objects or classes which are ready to be finalized, 551 * at which point the object may be discarded. 552 * <p> 553 * The {@code finalize} method is never invoked more than once by a Java 554 * virtual machine for any given object. 555 * <p> 556 * Any exception thrown by the {@code finalize} method causes 557 * the finalization of this object to be halted, but is otherwise 558 * ignored. 559 * 560 * @apiNote 561 * Classes that embed non-heap resources have many options 562 * for cleanup of those resources. The class must ensure that the 563 * lifetime of each instance is longer than that of any resource it embeds. 564 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that 565 * objects remain reachable while resources embedded in the object are in use. 566 * <p> 567 * A subclass should avoid overriding the {@code finalize} method 568 * unless the subclass embeds non-heap resources that must be cleaned up 569 * before the instance is collected. 570 * Finalizer invocations are not automatically chained, unlike constructors. 571 * If a subclass overrides {@code finalize} it must invoke the superclass 572 * finalizer explicitly. 573 * To guard against exceptions prematurely terminating the finalize chain, 574 * the subclass should use a {@code try-finally} block to ensure 575 * {@code super.finalize()} is always invoked. For example, 576 * {@snippet lang="java": 577 * @Override 578 * protected void finalize() throws Throwable { 579 * try { 580 * ... // cleanup subclass state 581 * } finally { 582 * super.finalize(); 583 * } 584 * } 585 * } 586 * 587 * @deprecated Finalization is deprecated and subject to removal in a future 588 * release. The use of finalization can lead to problems with security, 589 * performance, and reliability. 590 * See <a href="https://openjdk.org/jeps/421">JEP 421</a> for 591 * discussion and alternatives. 592 * <p> 593 * Subclasses that override {@code finalize} to perform cleanup should use 594 * alternative cleanup mechanisms and remove the {@code finalize} method. 595 * Use {@link java.lang.ref.Cleaner} and 596 * {@link java.lang.ref.PhantomReference} as safer ways to release resources 597 * when an object becomes unreachable. Alternatively, add a {@code close} 598 * method to explicitly release resources, and implement 599 * {@code AutoCloseable} to enable use of the {@code try}-with-resources 600 * statement. 601 * <p> 602 * This method will remain in place until finalizers have been removed from 603 * most existing code. 604 * 605 * @throws Throwable the {@code Exception} raised by this method 606 * @see java.lang.ref.WeakReference 607 * @see java.lang.ref.PhantomReference 608 * @jls 12.6 Finalization of Class Instances 609 */ 610 @Deprecated(since="9", forRemoval=true) 611 protected void finalize() throws Throwable { } 612 }