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.vm.annotation.IntrinsicCandidate; 29 30 /** 31 * Class {@code Object} is the root of the class hierarchy. 32 * Every class has {@code Object} as a superclass. All objects, 33 * including arrays, implement the methods of this class. 34 * 35 * @see java.lang.Class 36 * @since 1.0 37 */ 38 public class Object { 39 40 /** 41 * Constructs a new object. 42 */ 43 @IntrinsicCandidate 44 public Object() {} 45 46 /** 47 * Returns the runtime class of this {@code Object}. The returned 48 * {@code Class} object is the object that is locked by {@code 49 * static synchronized} methods of the represented class. 50 * 51 * <p><b>The actual result type is {@code Class<? extends |X|>} 52 * where {@code |X|} is the erasure of the static type of the 53 * expression on which {@code getClass} is called.</b> For 54 * example, no cast is required in this code fragment:</p> 55 * 56 * <p> 57 * {@code Number n = 0; }<br> 58 * {@code Class<? extends Number> c = n.getClass(); } 59 * </p> 60 * 61 * @return The {@code Class} object that represents the runtime 62 * class of this object. 63 * @jls 15.8.2 Class Literals 64 */ 65 @IntrinsicCandidate 66 public final native Class<?> getClass(); 67 68 /** 69 * {@return a hash code value for this object} This method is 70 * supported for the benefit of hash tables such as those provided by 71 * {@link java.util.HashMap}. 72 * <p> 73 * The general contract of {@code hashCode} is: 74 * <ul> 75 * <li>Whenever it is invoked on the same object more than once during 76 * an execution of a Java application, the {@code hashCode} method 77 * must consistently return the same integer, provided no information 78 * used in {@code equals} comparisons on the object is modified. 79 * This integer need not remain consistent from one execution of an 80 * application to another execution of the same application. 81 * <li>If two objects are equal according to the {@link 82 * #equals(Object) equals} method, then calling the {@code 83 * hashCode} method on each of the two objects must produce the 84 * same integer result. 85 * <li>It is <em>not</em> required that if two objects are unequal 86 * according to the {@link #equals(Object) equals} method, then 87 * calling the {@code hashCode} method on each of the two objects 88 * must produce distinct integer results. However, the programmer 89 * should be aware that producing distinct integer results for 90 * unequal objects may improve the performance of hash tables. 91 * </ul> 92 * 93 * @implSpec 94 * As far as is reasonably practical, the {@code hashCode} method defined 95 * by class {@code Object} returns distinct integers for distinct objects. 96 * 97 * @apiNote 98 * The {@link java.util.Objects#hash(Object...) hash} and {@link 99 * java.util.Objects#hashCode(Object) hashCode} methods of {@link 100 * java.util.Objects} can be used to help construct simple hash codes. 101 * 102 * @see java.lang.Object#equals(java.lang.Object) 103 * @see java.lang.System#identityHashCode 104 */ 105 @IntrinsicCandidate 106 public native int hashCode(); 107 108 /** 109 * Indicates whether some other object is "equal to" this one. 110 * <p> 111 * The {@code equals} method implements an <dfn>{@index "equivalence relation"}</dfn> 112 * on non-null object references: 113 * <ul> 114 * <li>It is <i>reflexive</i>: for any non-null reference value 115 * {@code x}, {@code x.equals(x)} should return 116 * {@code true}. 117 * <li>It is <i>symmetric</i>: for any non-null reference values 118 * {@code x} and {@code y}, {@code x.equals(y)} 119 * should return {@code true} if and only if 120 * {@code y.equals(x)} returns {@code true}. 121 * <li>It is <i>transitive</i>: for any non-null reference values 122 * {@code x}, {@code y}, and {@code z}, if 123 * {@code x.equals(y)} returns {@code true} and 124 * {@code y.equals(z)} returns {@code true}, then 125 * {@code x.equals(z)} should return {@code true}. 126 * <li>It is <i>consistent</i>: for any non-null reference values 127 * {@code x} and {@code y}, multiple invocations of 128 * {@code x.equals(y)} consistently return {@code true} 129 * or consistently return {@code false}, provided no 130 * information used in {@code equals} comparisons on the 131 * objects is modified. 132 * <li>For any non-null reference value {@code x}, 133 * {@code x.equals(null)} should return {@code false}. 134 * </ul> 135 * 136 * <p> 137 * An equivalence relation partitions the elements it operates on 138 * into <i>equivalence classes</i>; all the members of an 139 * equivalence class are equal to each other. Members of an 140 * equivalence class are substitutable for each other, at least 141 * for some purposes. 142 * 143 * @implSpec 144 * The {@code equals} method for class {@code Object} implements 145 * the most discriminating possible equivalence relation on objects; 146 * that is, for any non-null reference values {@code x} and 147 * {@code y}, this method returns {@code true} if and only 148 * if {@code x} and {@code y} refer to the same object 149 * ({@code x == y} has the value {@code true}). 150 * 151 * In other words, under the reference equality equivalence 152 * relation, each equivalence class only has a single element. 153 * 154 * @apiNote 155 * It is generally necessary to override the {@link #hashCode() hashCode} 156 * method whenever this method is overridden, so as to maintain the 157 * general contract for the {@code hashCode} method, which states 158 * that equal objects must have equal hash codes. 159 * <p>The two-argument {@link java.util.Objects#equals(Object, 160 * Object) Objects.equals} method implements an equivalence relation 161 * on two possibly-null object references. 162 * 163 * @param obj the reference object with which to compare. 164 * @return {@code true} if this object is the same as the obj 165 * argument; {@code false} otherwise. 166 * @see #hashCode() 167 * @see java.util.HashMap 168 */ 169 public boolean equals(Object obj) { 170 return (this == obj); 171 } 172 173 /** 174 * Creates and returns a copy of this object. The precise meaning 175 * of "copy" may depend on the class of the object. The general 176 * intent is that, for any object {@code x}, the expression: 177 * <blockquote> 178 * <pre> 179 * x.clone() != x</pre></blockquote> 180 * will be true, and that the expression: 181 * <blockquote> 182 * <pre> 183 * x.clone().getClass() == x.getClass()</pre></blockquote> 184 * will be {@code true}, but these are not absolute requirements. 185 * While it is typically the case that: 186 * <blockquote> 187 * <pre> 188 * x.clone().equals(x)</pre></blockquote> 189 * will be {@code true}, this is not an absolute requirement. 190 * <p> 191 * By convention, the returned object should be obtained by calling 192 * {@code super.clone}. If a class and all of its superclasses (except 193 * {@code Object}) obey this convention, it will be the case that 194 * {@code x.clone().getClass() == x.getClass()}. 195 * <p> 196 * By convention, the object returned by this method should be independent 197 * of this object (which is being cloned). To achieve this independence, 198 * it may be necessary to modify one or more fields of the object returned 199 * by {@code super.clone} before returning it. Typically, this means 200 * copying any mutable objects that comprise the internal "deep structure" 201 * of the object being cloned and replacing the references to these 202 * objects with references to the copies. If a class contains only 203 * primitive fields or references to immutable objects, then it is usually 204 * the case that no fields in the object returned by {@code super.clone} 205 * need to be modified. 206 * 207 * @implSpec 208 * The method {@code clone} for class {@code Object} performs a 209 * specific cloning operation. First, if the class of this object does 210 * not implement the interface {@code Cloneable}, then a 211 * {@code CloneNotSupportedException} is thrown. Note that all arrays 212 * are considered to implement the interface {@code Cloneable} and that 213 * the return type of the {@code clone} method of an array type {@code T[]} 214 * is {@code T[]} where T is any reference or primitive type. 215 * Otherwise, this method creates a new instance of the class of this 216 * object and initializes all its fields with exactly the contents of 217 * the corresponding fields of this object, as if by assignment; the 218 * contents of the fields are not themselves cloned. Thus, this method 219 * performs a "shallow copy" of this object, not a "deep copy" operation. 220 * <p> 221 * The class {@code Object} does not itself implement the interface 222 * {@code Cloneable}, so calling the {@code clone} method on an object 223 * whose class is {@code Object} will result in throwing an 224 * exception at run time. 225 * 226 * @return a clone of this instance. 227 * @throws CloneNotSupportedException if the object's class does not 228 * support the {@code Cloneable} interface. Subclasses 229 * that override the {@code clone} method can also 230 * throw this exception to indicate that an instance cannot 231 * be cloned. 232 * @see java.lang.Cloneable 233 */ 234 @IntrinsicCandidate 235 protected native Object clone() throws CloneNotSupportedException; 236 237 /** 238 * {@return a string representation of the object} 239 * 240 * Satisfying this method's contract implies a non-{@code null} 241 * result must be returned. 242 * 243 * @apiNote 244 * In general, the 245 * {@code toString} method returns a string that 246 * "textually represents" this object. The result should 247 * be a concise but informative representation that is easy for a 248 * person to read. 249 * It is recommended that all subclasses override this method. 250 * The string output is not necessarily stable over time or across 251 * JVM invocations. 252 * @implSpec 253 * The {@code toString} method for class {@code Object} 254 * returns a string consisting of the name of the class of which the 255 * object is an instance, the at-sign character `{@code @}', and 256 * the unsigned hexadecimal representation of the hash code of the 257 * object. In other words, this method returns a string equal to the 258 * value of: 259 * {@snippet lang=java : 260 * getClass().getName() + '@' + Integer.toHexString(hashCode()) 261 * } 262 * The {@link java.util.Objects#toIdentityString(Object) 263 * Objects.toIdentityString} method returns the string for an 264 * object equal to the string that would be returned if neither 265 * the {@code toString} nor {@code hashCode} methods were 266 * overridden by the object's class. 267 */ 268 public String toString() { 269 return getClass().getName() + "@" + Integer.toHexString(hashCode()); 270 } 271 272 /** 273 * Wakes up a single thread that is waiting on this object's 274 * monitor. If any threads are waiting on this object, one of them 275 * is chosen to be awakened. The choice is arbitrary and occurs at 276 * the discretion of the implementation. A thread waits on an object's 277 * monitor by calling one of the {@code wait} methods. 278 * <p> 279 * The awakened thread will not be able to proceed until the current 280 * thread relinquishes the lock on this object. The awakened thread will 281 * compete in the usual manner with any other threads that might be 282 * actively competing to synchronize on this object; for example, the 283 * awakened thread enjoys no reliable privilege or disadvantage in being 284 * the next thread to lock this object. 285 * <p> 286 * This method should only be called by a thread that is the owner 287 * of this object's monitor. A thread becomes the owner of the 288 * object's monitor in one of three ways: 289 * <ul> 290 * <li>By executing a synchronized instance method of that object. 291 * <li>By executing the body of a {@code synchronized} statement 292 * that synchronizes on the object. 293 * <li>For objects of type {@code Class,} by executing a 294 * static synchronized method of that class. 295 * </ul> 296 * <p> 297 * Only one thread at a time can own an object's monitor. 298 * 299 * @throws IllegalMonitorStateException if the current thread is not 300 * the owner of this object's monitor. 301 * @see java.lang.Object#notifyAll() 302 * @see java.lang.Object#wait() 303 */ 304 @IntrinsicCandidate 305 public final native void notify(); 306 307 /** 308 * Wakes up all threads that are waiting on this object's monitor. A 309 * thread waits on an object's monitor by calling one of the 310 * {@code wait} methods. 311 * <p> 312 * The awakened threads will not be able to proceed until the current 313 * thread relinquishes the lock on this object. The awakened threads 314 * will compete in the usual manner with any other threads that might 315 * be actively competing to synchronize on this object; for example, 316 * the awakened threads enjoy no reliable privilege or disadvantage in 317 * being the next thread to lock this object. 318 * <p> 319 * This method should only be called by a thread that is the owner 320 * of this object's monitor. See the {@code notify} method for a 321 * description of the ways in which a thread can become the owner of 322 * a monitor. 323 * 324 * @throws IllegalMonitorStateException if the current thread is not 325 * the owner of this object's monitor. 326 * @see java.lang.Object#notify() 327 * @see java.lang.Object#wait() 328 */ 329 @IntrinsicCandidate 330 public final native void notifyAll(); 331 332 /** 333 * Causes the current thread to wait until it is awakened, typically 334 * by being <em>notified</em> or <em>interrupted</em>. 335 * <p> 336 * In all respects, this method behaves as if {@code wait(0L, 0)} 337 * had been called. See the specification of the {@link #wait(long, int)} method 338 * for details. 339 * 340 * @throws IllegalMonitorStateException if the current thread is not 341 * the owner of the object's monitor 342 * @throws InterruptedException if any thread interrupted the current thread before or 343 * while the current thread was waiting. The <em>interrupted status</em> of the 344 * current thread is cleared when this exception is thrown. 345 * @see #notify() 346 * @see #notifyAll() 347 * @see #wait(long) 348 * @see #wait(long, int) 349 */ 350 public final void wait() throws InterruptedException { 351 wait(0L); 352 } 353 354 /** 355 * Causes the current thread to wait until it is awakened, typically 356 * by being <em>notified</em> or <em>interrupted</em>, or until a 357 * certain amount of real time has elapsed. 358 * <p> 359 * In all respects, this method behaves as if {@code wait(timeoutMillis, 0)} 360 * had been called. See the specification of the {@link #wait(long, int)} method 361 * for details. 362 * 363 * @param timeoutMillis the maximum time to wait, in milliseconds 364 * @throws IllegalArgumentException if {@code timeoutMillis} is negative 365 * @throws IllegalMonitorStateException if the current thread is not 366 * the owner of the object's monitor 367 * @throws InterruptedException if any thread interrupted the current thread before or 368 * while the current thread was waiting. The <em>interrupted status</em> of the 369 * current thread is cleared when this exception is thrown. 370 * @see #notify() 371 * @see #notifyAll() 372 * @see #wait() 373 * @see #wait(long, int) 374 */ 375 public final void wait(long timeoutMillis) throws InterruptedException { 376 if (timeoutMillis < 0) { 377 throw new IllegalArgumentException("timeout value is negative"); 378 } 379 380 if (Thread.currentThread() instanceof VirtualThread vthread) { 381 try { 382 wait0(timeoutMillis); 383 } catch (InterruptedException e) { 384 // virtual thread's interrupt status needs to be cleared 385 vthread.getAndClearInterrupt(); 386 throw e; 387 } 388 } else { 389 wait0(timeoutMillis); 390 } 391 } 392 393 // final modifier so method not in vtable 394 private final native void wait0(long timeoutMillis) throws InterruptedException; 395 396 /** 397 * Causes the current thread to wait until it is awakened, typically 398 * by being <em>notified</em> or <em>interrupted</em>, or until a 399 * certain amount of real time has elapsed. 400 * <p> 401 * The current thread must own this object's monitor lock. See the 402 * {@link #notify notify} method for a description of the ways in which 403 * a thread can become the owner of a monitor lock. 404 * <p> 405 * This method causes the current thread (referred to here as <var>T</var>) to 406 * place itself in the wait set for this object and then to relinquish any 407 * and all synchronization claims on this object. Note that only the locks 408 * on this object are relinquished; any other objects on which the current 409 * thread may be synchronized remain locked while the thread waits. 410 * <p> 411 * Thread <var>T</var> then becomes disabled for thread scheduling purposes 412 * and lies dormant until one of the following occurs: 413 * <ul> 414 * <li>Some other thread invokes the {@code notify} method for this 415 * object and thread <var>T</var> happens to be arbitrarily chosen as 416 * the thread to be awakened. 417 * <li>Some other thread invokes the {@code notifyAll} method for this 418 * object. 419 * <li>Some other thread {@linkplain Thread#interrupt() interrupts} 420 * thread <var>T</var>. 421 * <li>The specified amount of real time has elapsed, more or less. 422 * The amount of real time, in nanoseconds, is given by the expression 423 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos} 424 * are both zero, then real time is not taken into consideration and the 425 * thread waits until awakened by one of the other causes. 426 * <li>Thread <var>T</var> is awakened spuriously. (See below.) 427 * </ul> 428 * <p> 429 * The thread <var>T</var> is then removed from the wait set for this 430 * object and re-enabled for thread scheduling. It competes in the 431 * usual manner with other threads for the right to synchronize on the 432 * object; once it has regained control of the object, all its 433 * synchronization claims on the object are restored to the status quo 434 * ante - that is, to the situation as of the time that the {@code wait} 435 * method was invoked. Thread <var>T</var> then returns from the 436 * invocation of the {@code wait} method. Thus, on return from the 437 * {@code wait} method, the synchronization state of the object and of 438 * thread {@code T} is exactly as it was when the {@code wait} method 439 * was invoked. 440 * <p> 441 * A thread can wake up without being notified, interrupted, or timing out, a 442 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice, 443 * applications must guard against it by testing for the condition that should 444 * have caused the thread to be awakened, and continuing to wait if the condition 445 * is not satisfied. See the example below. 446 * <p> 447 * For more information on this topic, see section 14.2, 448 * "Condition Queues," in Brian Goetz and others' <cite>Java Concurrency 449 * in Practice</cite> (Addison-Wesley, 2006) or Item 81 in Joshua 450 * Bloch's <cite>Effective Java, Third Edition</cite> (Addison-Wesley, 451 * 2018). 452 * <p> 453 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted} 454 * by any thread before or while it is waiting, then an {@code InterruptedException} 455 * is thrown. The <em>interrupted status</em> of the current thread is cleared when 456 * this exception is thrown. This exception is not thrown until the lock status of 457 * this object has been restored as described above. 458 * 459 * @apiNote 460 * The recommended approach to waiting is to check the condition being awaited in 461 * a {@code while} loop around the call to {@code wait}, as shown in the example 462 * below. Among other things, this approach avoids problems that can be caused 463 * by spurious wakeups. 464 * 465 * {@snippet lang=java : 466 * synchronized (obj) { 467 * while ( <condition does not hold and timeout not exceeded> ) { 468 * long timeoutMillis = ... ; // recompute timeout values 469 * int nanos = ... ; 470 * obj.wait(timeoutMillis, nanos); 471 * } 472 * ... // Perform action appropriate to condition or timeout 473 * } 474 * } 475 * 476 * @param timeoutMillis the maximum time to wait, in milliseconds 477 * @param nanos additional time, in nanoseconds, in the range 0-999999 inclusive 478 * @throws IllegalArgumentException if {@code timeoutMillis} is negative, 479 * or if the value of {@code nanos} is out of range 480 * @throws IllegalMonitorStateException if the current thread is not 481 * the owner of the object's monitor 482 * @throws InterruptedException if any thread interrupted the current thread before or 483 * while the current thread was waiting. The <em>interrupted status</em> of the 484 * current thread is cleared when this exception is thrown. 485 * @see #notify() 486 * @see #notifyAll() 487 * @see #wait() 488 * @see #wait(long) 489 */ 490 public final void wait(long timeoutMillis, int nanos) throws InterruptedException { 491 if (timeoutMillis < 0) { 492 throw new IllegalArgumentException("timeoutMillis value is negative"); 493 } 494 495 if (nanos < 0 || nanos > 999999) { 496 throw new IllegalArgumentException( 497 "nanosecond timeout value out of range"); 498 } 499 500 if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) { 501 timeoutMillis++; 502 } 503 504 wait(timeoutMillis); 505 } 506 507 /** 508 * Called by the garbage collector on an object when garbage collection 509 * determines that there are no more references to the object. 510 * A subclass overrides the {@code finalize} method to dispose of 511 * system resources or to perform other cleanup. 512 * <p> 513 * <b>When running in a Java virtual machine in which finalization has been 514 * disabled or removed, the garbage collector will never call 515 * {@code finalize()}. In a Java virtual machine in which finalization is 516 * enabled, the garbage collector might call {@code finalize} only after an 517 * indefinite delay.</b> 518 * <p> 519 * The general contract of {@code finalize} is that it is invoked 520 * if and when the Java virtual 521 * machine has determined that there is no longer any 522 * means by which this object can be accessed by any thread that has 523 * not yet died, except as a result of an action taken by the 524 * finalization of some other object or class which is ready to be 525 * finalized. The {@code finalize} method may take any action, including 526 * making this object available again to other threads; the usual purpose 527 * of {@code finalize}, however, is to perform cleanup actions before 528 * the object is irrevocably discarded. For example, the finalize method 529 * for an object that represents an input/output connection might perform 530 * explicit I/O transactions to break the connection before the object is 531 * permanently discarded. 532 * <p> 533 * The {@code finalize} method of class {@code Object} performs no 534 * special action; it simply returns normally. Subclasses of 535 * {@code Object} may override this definition. 536 * <p> 537 * The Java programming language does not guarantee which thread will 538 * invoke the {@code finalize} method for any given object. It is 539 * guaranteed, however, that the thread that invokes finalize will not 540 * be holding any user-visible synchronization locks when finalize is 541 * invoked. If an uncaught exception is thrown by the finalize method, 542 * the exception is ignored and finalization of that object terminates. 543 * <p> 544 * After the {@code finalize} method has been invoked for an object, no 545 * further action is taken until the Java virtual machine has again 546 * determined that there is no longer any means by which this object can 547 * be accessed by any thread that has not yet died, including possible 548 * actions by other objects or classes which are ready to be finalized, 549 * at which point the object may be discarded. 550 * <p> 551 * The {@code finalize} method is never invoked more than once by a Java 552 * virtual machine for any given object. 553 * <p> 554 * Any exception thrown by the {@code finalize} method causes 555 * the finalization of this object to be halted, but is otherwise 556 * ignored. 557 * 558 * @apiNote 559 * Classes that embed non-heap resources have many options 560 * for cleanup of those resources. The class must ensure that the 561 * lifetime of each instance is longer than that of any resource it embeds. 562 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that 563 * objects remain reachable while resources embedded in the object are in use. 564 * <p> 565 * A subclass should avoid overriding the {@code finalize} method 566 * unless the subclass embeds non-heap resources that must be cleaned up 567 * before the instance is collected. 568 * Finalizer invocations are not automatically chained, unlike constructors. 569 * If a subclass overrides {@code finalize} it must invoke the superclass 570 * finalizer explicitly. 571 * To guard against exceptions prematurely terminating the finalize chain, 572 * the subclass should use a {@code try-finally} block to ensure 573 * {@code super.finalize()} is always invoked. For example, 574 * {@snippet lang="java": 575 * @Override 576 * protected void finalize() throws Throwable { 577 * try { 578 * ... // cleanup subclass state 579 * } finally { 580 * super.finalize(); 581 * } 582 * } 583 * } 584 * 585 * @deprecated Finalization is deprecated and subject to removal in a future 586 * release. The use of finalization can lead to problems with security, 587 * performance, and reliability. 588 * See <a href="https://openjdk.org/jeps/421">JEP 421</a> for 589 * discussion and alternatives. 590 * <p> 591 * Subclasses that override {@code finalize} to perform cleanup should use 592 * alternative cleanup mechanisms and remove the {@code finalize} method. 593 * Use {@link java.lang.ref.Cleaner} and 594 * {@link java.lang.ref.PhantomReference} as safer ways to release resources 595 * when an object becomes unreachable. Alternatively, add a {@code close} 596 * method to explicitly release resources, and implement 597 * {@code AutoCloseable} to enable use of the {@code try}-with-resources 598 * statement. 599 * <p> 600 * This method will remain in place until finalizers have been removed from 601 * most existing code. 602 * 603 * @throws Throwable the {@code Exception} raised by this method 604 * @see java.lang.ref.WeakReference 605 * @see java.lang.ref.PhantomReference 606 * @jls 12.6 Finalization of Class Instances 607 */ 608 @Deprecated(since="9", forRemoval=true) 609 protected void finalize() throws Throwable { } 610 }