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 * <p>
35 * Subclasses of {@code java.lang.Object} can be either an {@linkplain Class#isIdentity identity class}
36 * or a {@linkplain Class#isValue value class}.
37 * See {@jls The Java Language Specification 8.1.1.5 Value Classes}.
38 *
39 * @see java.lang.Class
40 * @since 1.0
41 */
42 public class Object {
43
44 /**
45 * Constructs a new object.
46 */
47 @IntrinsicCandidate
48 public Object() {}
49
50 /**
51 * Returns the runtime class of this {@code Object}. The returned
52 * {@code Class} object is the object that is locked by {@code
53 * static synchronized} methods of the represented class.
54 *
55 * <p><b>The actual result type is {@code Class<? extends |X|>}
56 * where {@code |X|} is the erasure of the static type of the
57 * expression on which {@code getClass} is called.</b> For
58 * example, no cast is required in this code fragment:</p>
59 *
60 * <p>
61 * {@code Number n = 0; }<br>
62 * {@code Class<? extends Number> c = n.getClass(); }
63 * </p>
64 *
65 * @return The {@code Class} object that represents the runtime
66 * class of this object.
67 * @jls 15.8.2 Class Literals
68 */
69 @IntrinsicCandidate
70 public final native Class<?> getClass();
71
72 /**
73 * {@return a hash code value for this object} This method is
74 * supported for the benefit of hash tables such as those provided by
75 * {@link java.util.HashMap}.
76 * <p>
77 * The general contract of {@code hashCode} is:
78 * <ul>
79 * <li>Whenever it is invoked on the same object more than once during
80 * an execution of a Java application, the {@code hashCode} method
81 * must consistently return the same integer, provided no information
82 * used in {@code equals} comparisons on the object is modified.
83 * This integer need not remain consistent from one execution of an
84 * application to another execution of the same application.
85 * <li>If two objects are equal according to the {@link
86 * #equals(Object) equals} method, then calling the {@code
87 * hashCode} method on each of the two objects must produce the
88 * same integer result.
89 * <li>It is <em>not</em> required that if two objects are unequal
90 * according to the {@link #equals(Object) equals} method, then
91 * calling the {@code hashCode} method on each of the two objects
92 * must produce distinct integer results. However, the programmer
93 * should be aware that producing distinct integer results for
94 * unequal objects may improve the performance of hash tables.
95 * </ul>
96 *
97 * @implSpec
98 * As far as is reasonably practical, the {@code hashCode} method defined
99 * by class {@code Object} returns distinct integers for distinct objects.
100 *
101 * @apiNote
102 * The {@link java.util.Objects#hash(Object...) hash} and {@link
103 * java.util.Objects#hashCode(Object) hashCode} methods of {@link
104 * java.util.Objects} can be used to help construct simple hash codes.
105 *
106 * @see java.lang.Object#equals(java.lang.Object)
107 * @see java.lang.System#identityHashCode
108 */
109 @IntrinsicCandidate
110 public native int hashCode();
111
112 /**
113 * Indicates whether some other object is "equal to" this one.
114 * <p>
115 * The {@code equals} method implements an <dfn>{@index "equivalence relation"}</dfn>
116 * on non-null object references:
117 * <ul>
118 * <li>It is <i>reflexive</i>: for any non-null reference value
119 * {@code x}, {@code x.equals(x)} should return
120 * {@code true}.
121 * <li>It is <i>symmetric</i>: for any non-null reference values
122 * {@code x} and {@code y}, {@code x.equals(y)}
123 * should return {@code true} if and only if
124 * {@code y.equals(x)} returns {@code true}.
125 * <li>It is <i>transitive</i>: for any non-null reference values
126 * {@code x}, {@code y}, and {@code z}, if
127 * {@code x.equals(y)} returns {@code true} and
128 * {@code y.equals(z)} returns {@code true}, then
129 * {@code x.equals(z)} should return {@code true}.
130 * <li>It is <i>consistent</i>: for any non-null reference values
131 * {@code x} and {@code y}, multiple invocations of
132 * {@code x.equals(y)} consistently return {@code true}
133 * or consistently return {@code false}, provided no
134 * information used in {@code equals} comparisons on the
135 * objects is modified.
136 * <li>For any non-null reference value {@code x},
137 * {@code x.equals(null)} should return {@code false}.
138 * </ul>
139 *
140 * <p>
141 * An equivalence relation partitions the elements it operates on
142 * into <i>equivalence classes</i>; all the members of an
143 * equivalence class are equal to each other. Members of an
144 * equivalence class are substitutable for each other, at least
145 * for some purposes.
146 *
147 * @implSpec
148 * The {@code equals} method for class {@code Object} implements
149 * the most discriminating possible equivalence relation on objects;
150 * that is, for any non-null reference values {@code x} and
151 * {@code y}, this method returns {@code true} if and only
152 * if {@code x} and {@code y} refer to the same object
153 * ({@code x == y} has the value {@code true}).
154 *
155 * In other words, under the reference equality equivalence
156 * relation, each equivalence class only has a single element.
157 *
158 * @apiNote
159 * It is generally necessary to override the {@link #hashCode() hashCode}
160 * method whenever this method is overridden, so as to maintain the
161 * general contract for the {@code hashCode} method, which states
162 * that equal objects must have equal hash codes.
163 * <p>The two-argument {@link java.util.Objects#equals(Object,
164 * Object) Objects.equals} method implements an equivalence relation
165 * on two possibly-null object references.
166 *
167 * @param obj the reference object with which to compare.
168 * @return {@code true} if this object is the same as the obj
169 * argument; {@code false} otherwise.
170 * @see #hashCode()
171 * @see java.util.HashMap
172 */
173 public boolean equals(Object obj) {
174 return (this == obj);
175 }
176
177 /**
178 * Creates and returns a copy of this object. The precise meaning
179 * of "copy" may depend on the class of the object. The general
180 * intent is that, for any object {@code x}, the expression:
181 * <blockquote>
182 * <pre>
183 * x.clone() != x</pre></blockquote>
184 * will be true, and that the expression:
185 * <blockquote>
186 * <pre>
187 * x.clone().getClass() == x.getClass()</pre></blockquote>
188 * will be {@code true}, but these are not absolute requirements.
189 * While it is typically the case that:
190 * <blockquote>
191 * <pre>
192 * x.clone().equals(x)</pre></blockquote>
193 * will be {@code true}, this is not an absolute requirement.
194 * <p>
195 * By convention, the returned object should be obtained by calling
196 * {@code super.clone}. If a class and all of its superclasses (except
197 * {@code Object}) obey this convention, it will be the case that
198 * {@code x.clone().getClass() == x.getClass()}.
199 * <p>
200 * By convention, the object returned by this method should be independent
201 * of this object (which is being cloned). To achieve this independence,
202 * it may be necessary to modify one or more fields of the object returned
203 * by {@code super.clone} before returning it. Typically, this means
204 * copying any mutable objects that comprise the internal "deep structure"
205 * of the object being cloned and replacing the references to these
206 * objects with references to the copies. If a class contains only
207 * primitive fields or references to immutable objects, then it is usually
208 * the case that no fields in the object returned by {@code super.clone}
209 * need to be modified.
210 *
211 * @implSpec
212 * The method {@code clone} for class {@code Object} performs a
213 * specific cloning operation. First, if the class of this object does
214 * not implement the interface {@code Cloneable}, then a
215 * {@code CloneNotSupportedException} is thrown. Note that all arrays
216 * are considered to implement the interface {@code Cloneable} and that
217 * the return type of the {@code clone} method of an array type {@code T[]}
218 * is {@code T[]} where T is any reference or primitive type.
219 * Otherwise, this method creates a new instance of the class of this
220 * object and initializes all its fields with exactly the contents of
221 * the corresponding fields of this object, as if by assignment; the
222 * contents of the fields are not themselves cloned. Thus, this method
223 * performs a "shallow copy" of this object, not a "deep copy" operation.
224 * <p>
225 * The class {@code Object} does not itself implement the interface
226 * {@code Cloneable}, so calling the {@code clone} method on an object
227 * whose class is {@code Object} will result in throwing an
228 * exception at run time.
229 *
230 * @return a clone of this instance.
231 * @throws CloneNotSupportedException if the object's class does not
232 * support the {@code Cloneable} interface. Subclasses
233 * that override the {@code clone} method can also
234 * throw this exception to indicate that an instance cannot
235 * be cloned.
236 * @see java.lang.Cloneable
237 */
238 @IntrinsicCandidate
239 protected native Object clone() throws CloneNotSupportedException;
240
241 /**
242 * {@return a string representation of the object}
243 *
244 * Satisfying this method's contract implies a non-{@code null}
245 * result must be returned.
246 *
247 * @apiNote
248 * In general, the
249 * {@code toString} method returns a string that
250 * "textually represents" this object. The result should
251 * be a concise but informative representation that is easy for a
252 * person to read.
253 * It is recommended that all subclasses override this method.
254 * The string output is not necessarily stable over time or across
255 * JVM invocations.
256 * @implSpec
257 * The {@code toString} method for class {@code Object}
258 * returns a string consisting of the name of the class of which the
259 * object is an instance, the at-sign character `{@code @}', and
260 * the unsigned hexadecimal representation of the hash code of the
261 * object. In other words, this method returns a string equal to the
262 * value of:
263 * {@snippet lang=java :
264 * getClass().getName() + '@' + Integer.toHexString(hashCode())
265 * }
266 * The {@link java.util.Objects#toIdentityString(Object)
267 * Objects.toIdentityString} method returns the string for an
268 * object equal to the string that would be returned if neither
269 * the {@code toString} nor {@code hashCode} methods were
270 * overridden by the object's class.
271 */
272 public String toString() {
273 return getClass().getName() + "@" + Integer.toHexString(hashCode());
274 }
275
276 /**
277 * Wakes up a single thread that is waiting on this object's
278 * monitor. If any threads are waiting on this object, one of them
279 * is chosen to be awakened. The choice is arbitrary and occurs at
280 * the discretion of the implementation. A thread waits on an object's
281 * monitor by calling one of the {@code wait} methods.
282 * <p>
283 * The awakened thread will not be able to proceed until the current
284 * thread relinquishes the lock on this object. The awakened thread will
285 * compete in the usual manner with any other threads that might be
286 * actively competing to synchronize on this object; for example, the
287 * awakened thread enjoys no reliable privilege or disadvantage in being
288 * the next thread to lock this object.
289 * <p>
290 * This method should only be called by a thread that is the owner
291 * of this object's monitor. A thread becomes the owner of the
292 * object's monitor in one of three ways:
293 * <ul>
294 * <li>By executing a synchronized instance method of that object.
295 * <li>By executing the body of a {@code synchronized} statement
296 * that synchronizes on the object.
297 * <li>For objects of type {@code Class,} by executing a
298 * static synchronized method of that class.
299 * </ul>
300 * <p>
301 * Only one thread at a time can own an object's monitor.
302 * <div class="preview-block">
303 * <div class="preview-comment">
304 * If this object is a {@linkplain Class#isValue() value object},
305 * it does does not have a monitor, an {@code IllegalMonitorStateException} is thrown.
306 * </div>
307 * </div>
308 *
309 * @throws IllegalMonitorStateException if the current thread is not
310 * the owner of this object's monitor or
311 * if this object is a {@linkplain Class#isValue() value object}.
312 * @see java.lang.Object#notifyAll()
313 * @see java.lang.Object#wait()
314 */
315 @IntrinsicCandidate
316 public final native void notify();
317
318 /**
319 * Wakes up all threads that are waiting on this object's monitor. A
320 * thread waits on an object's monitor by calling one of the
321 * {@code wait} methods.
322 * <p>
323 * The awakened threads will not be able to proceed until the current
324 * thread relinquishes the lock on this object. The awakened threads
325 * will compete in the usual manner with any other threads that might
326 * be actively competing to synchronize on this object; for example,
327 * the awakened threads enjoy no reliable privilege or disadvantage in
328 * being the next thread to lock this object.
329 * <p>
330 * This method should only be called by a thread that is the owner
331 * of this object's monitor. See the {@code notify} method for a
332 * description of the ways in which a thread can become the owner of
333 * a monitor.
334 *
335 * <div class="preview-block">
336 * <div class="preview-comment">
337 * If this object is a {@linkplain Class#isValue() value object},
338 * it does does not have a monitor, an {@code IllegalMonitorStateException} is thrown.
339 * </div>
340 * </div>
341 *
342 * @throws IllegalMonitorStateException if the current thread is not
343 * the owner of this object's monitor or
344 * if this object is a {@linkplain Class#isValue() value object}.
345 * @see java.lang.Object#notify()
346 * @see java.lang.Object#wait()
347 */
348 @IntrinsicCandidate
349 public final native void notifyAll();
350
351 /**
352 * Causes the current thread to wait until it is awakened, typically
353 * by being <em>notified</em> or <em>interrupted</em>.
354 * <p>
355 * In all respects, this method behaves as if {@code wait(0L, 0)}
356 * had been called. See the specification of the {@link #wait(long, int)} method
357 * for details.
358 *
359 * <div class="preview-block">
360 * <div class="preview-comment">
361 * If this object is a {@linkplain Class#isValue() value object},
362 * it does does not have a monitor, an {@code IllegalMonitorStateException} is thrown.
363 * </div>
364 * </div>
365 *
366 * @throws IllegalMonitorStateException if the current thread is not
367 * the owner of the object's monitor or
368 * if this object is a {@linkplain Class#isValue() value object}.
369 * @throws InterruptedException if any thread interrupted the current thread before or
370 * while the current thread was waiting. The <em>interrupted status</em> of the
371 * current thread is cleared when this exception is thrown.
372 * @see #notify()
373 * @see #notifyAll()
374 * @see #wait(long)
375 * @see #wait(long, int)
376 */
377 public final void wait() throws InterruptedException {
378 wait(0L);
379 }
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 * <div class="preview-block">
391 * <div class="preview-comment">
392 * If this object is a {@linkplain Class#isValue() value object},
393 * it does does not have a monitor, an {@code IllegalMonitorStateException} is thrown.
394 * </div>
395 * </div>
396 *
397 * @param timeoutMillis the maximum time to wait, in milliseconds
398 * @throws IllegalArgumentException if {@code timeoutMillis} is negative
399 * @throws IllegalMonitorStateException if the current thread is not
400 * the owner of the object's monitor or
401 * if this object is a {@linkplain Class#isValue() value object}.
402 * @throws InterruptedException if any thread interrupted the current thread before or
403 * while the current thread was waiting. The <em>interrupted status</em> of the
404 * current thread is cleared when this exception is thrown.
405 * @see #notify()
406 * @see #notifyAll()
407 * @see #wait()
408 * @see #wait(long, int)
409 */
410 public final void wait(long timeoutMillis) throws InterruptedException {
411 if (timeoutMillis < 0) {
412 throw new IllegalArgumentException("timeout value is negative");
413 }
414
415 if (Thread.currentThread() instanceof VirtualThread vthread) {
416 try {
417 wait0(timeoutMillis);
418 } catch (InterruptedException e) {
419 // virtual thread's interrupt status needs to be cleared
420 vthread.getAndClearInterrupt();
421 throw e;
422 }
423 } else {
424 wait0(timeoutMillis);
425 }
426 }
427
428 // final modifier so method not in vtable
429 private final native void wait0(long timeoutMillis) throws InterruptedException;
430
431 /**
432 * Causes the current thread to wait until it is awakened, typically
433 * by being <em>notified</em> or <em>interrupted</em>, or until a
434 * certain amount of real time has elapsed.
435 * <p>
436 * The current thread must own this object's monitor lock. See the
437 * {@link #notify notify} method for a description of the ways in which
438 * a thread can become the owner of a monitor lock.
439 * <p>
440 * This method causes the current thread (referred to here as <var>T</var>) to
441 * place itself in the wait set for this object and then to relinquish any
442 * and all synchronization claims on this object. Note that only the locks
443 * on this object are relinquished; any other objects on which the current
444 * thread may be synchronized remain locked while the thread waits.
445 * <p>
446 * Thread <var>T</var> then becomes disabled for thread scheduling purposes
447 * and lies dormant until one of the following occurs:
448 * <ul>
449 * <li>Some other thread invokes the {@code notify} method for this
450 * object and thread <var>T</var> happens to be arbitrarily chosen as
451 * the thread to be awakened.
452 * <li>Some other thread invokes the {@code notifyAll} method for this
453 * object.
454 * <li>Some other thread {@linkplain Thread#interrupt() interrupts}
455 * thread <var>T</var>.
456 * <li>The specified amount of real time has elapsed, more or less.
457 * The amount of real time, in nanoseconds, is given by the expression
458 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos}
459 * are both zero, then real time is not taken into consideration and the
460 * thread waits until awakened by one of the other causes.
461 * <li>Thread <var>T</var> is awakened spuriously. (See below.)
462 * </ul>
463 * <p>
464 * The thread <var>T</var> is then removed from the wait set for this
465 * object and re-enabled for thread scheduling. It competes in the
466 * usual manner with other threads for the right to synchronize on the
467 * object; once it has regained control of the object, all its
468 * synchronization claims on the object are restored to the status quo
469 * ante - that is, to the situation as of the time that the {@code wait}
470 * method was invoked. Thread <var>T</var> then returns from the
471 * invocation of the {@code wait} method. Thus, on return from the
472 * {@code wait} method, the synchronization state of the object and of
473 * thread {@code T} is exactly as it was when the {@code wait} method
474 * was invoked.
475 * <p>
476 * A thread can wake up without being notified, interrupted, or timing out, a
477 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice,
478 * applications must guard against it by testing for the condition that should
479 * have caused the thread to be awakened, and continuing to wait if the condition
480 * is not satisfied. See the example below.
481 * <p>
482 * For more information on this topic, see section 14.2,
483 * "Condition Queues," in Brian Goetz and others' <cite>Java Concurrency
484 * in Practice</cite> (Addison-Wesley, 2006) or Item 81 in Joshua
485 * Bloch's <cite>Effective Java, Third Edition</cite> (Addison-Wesley,
486 * 2018).
487 * <p>
488 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted}
489 * by any thread before or while it is waiting, then an {@code InterruptedException}
490 * is thrown. The <em>interrupted status</em> of the current thread is cleared when
491 * this exception is thrown. This exception is not thrown until the lock status of
492 * this object has been restored as described above.
493 *
494 * @apiNote
495 * The recommended approach to waiting is to check the condition being awaited in
496 * a {@code while} loop around the call to {@code wait}, as shown in the example
497 * below. Among other things, this approach avoids problems that can be caused
498 * by spurious wakeups.
499 *
500 * {@snippet lang=java :
501 * synchronized (obj) {
502 * while ( <condition does not hold and timeout not exceeded> ) {
503 * long timeoutMillis = ... ; // recompute timeout values
504 * int nanos = ... ;
505 * obj.wait(timeoutMillis, nanos);
506 * }
507 * ... // Perform action appropriate to condition or timeout
508 * }
509 * }
510 *
511 * <div class="preview-block">
512 * <div class="preview-comment">
513 * If this object is a {@linkplain Class#isValue() value object},
514 * it does does not have a monitor, an {@code IllegalMonitorStateException} is thrown.
515 * </div>
516 * </div>
517 * @param timeoutMillis the maximum time to wait, in milliseconds
518 * @param nanos additional time, in nanoseconds, in the range 0-999999 inclusive
519 * @throws IllegalArgumentException if {@code timeoutMillis} is negative,
520 * or if the value of {@code nanos} is out of range
521 * @throws IllegalMonitorStateException if the current thread is not
522 * the owner of the object's monitor or
523 * if this object is a {@linkplain Class#isValue() value object}.
524 * @throws InterruptedException if any thread interrupted the current thread before or
525 * while the current thread was waiting. The <em>interrupted status</em> of the
526 * current thread is cleared when this exception is thrown.
527 * @see #notify()
528 * @see #notifyAll()
529 * @see #wait()
530 * @see #wait(long)
531 */
532 public final void wait(long timeoutMillis, int nanos) throws InterruptedException {
533 if (timeoutMillis < 0) {
534 throw new IllegalArgumentException("timeoutMillis value is negative");
535 }
536
537 if (nanos < 0 || nanos > 999999) {
538 throw new IllegalArgumentException(
539 "nanosecond timeout value out of range");
540 }
541
542 if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) {
543 timeoutMillis++;
544 }
545
546 wait(timeoutMillis);
547 }
548
549 /**
550 * Called by the garbage collector on an object when garbage collection
551 * determines that there are no more references to the object.
552 * A subclass overrides the {@code finalize} method to dispose of
553 * system resources or to perform other cleanup.
554 * <p>
555 * <b>When running in a Java virtual machine in which finalization has been
556 * disabled or removed, the garbage collector will never call
557 * {@code finalize()}. In a Java virtual machine in which finalization is
558 * enabled, the garbage collector might call {@code finalize} only after an
559 * indefinite delay.</b>
560 * <p>
561 * The general contract of {@code finalize} is that it is invoked
562 * if and when the Java virtual
563 * machine has determined that there is no longer any
564 * means by which this object can be accessed by any thread that has
565 * not yet died, except as a result of an action taken by the
566 * finalization of some other object or class which is ready to be
567 * finalized. The {@code finalize} method may take any action, including
568 * making this object available again to other threads; the usual purpose
569 * of {@code finalize}, however, is to perform cleanup actions before
570 * the object is irrevocably discarded. For example, the finalize method
571 * for an object that represents an input/output connection might perform
572 * explicit I/O transactions to break the connection before the object is
573 * permanently discarded.
574 * <p>
575 * The {@code finalize} method of class {@code Object} performs no
576 * special action; it simply returns normally. Subclasses of
577 * {@code Object} may override this definition.
578 * <p>
579 * The Java programming language does not guarantee which thread will
580 * invoke the {@code finalize} method for any given object. It is
581 * guaranteed, however, that the thread that invokes finalize will not
582 * be holding any user-visible synchronization locks when finalize is
583 * invoked. If an uncaught exception is thrown by the finalize method,
584 * the exception is ignored and finalization of that object terminates.
585 * <p>
586 * After the {@code finalize} method has been invoked for an object, no
587 * further action is taken until the Java virtual machine has again
588 * determined that there is no longer any means by which this object can
589 * be accessed by any thread that has not yet died, including possible
590 * actions by other objects or classes which are ready to be finalized,
591 * at which point the object may be discarded.
592 * <p>
593 * The {@code finalize} method is never invoked more than once by a Java
594 * virtual machine for any given object.
595 * <p>
596 * Any exception thrown by the {@code finalize} method causes
597 * the finalization of this object to be halted, but is otherwise
598 * ignored.
599 *
600 * @apiNote
601 * Classes that embed non-heap resources have many options
602 * for cleanup of those resources. The class must ensure that the
603 * lifetime of each instance is longer than that of any resource it embeds.
604 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that
605 * objects remain reachable while resources embedded in the object are in use.
606 * <p>
607 * A subclass should avoid overriding the {@code finalize} method
608 * unless the subclass embeds non-heap resources that must be cleaned up
609 * before the instance is collected.
610 * Finalizer invocations are not automatically chained, unlike constructors.
611 * If a subclass overrides {@code finalize} it must invoke the superclass
612 * finalizer explicitly.
613 * To guard against exceptions prematurely terminating the finalize chain,
614 * the subclass should use a {@code try-finally} block to ensure
615 * {@code super.finalize()} is always invoked. For example,
616 * {@snippet lang="java":
617 * @Override
618 * protected void finalize() throws Throwable {
619 * try {
620 * ... // cleanup subclass state
621 * } finally {
622 * super.finalize();
623 * }
624 * }
625 * }
626 *
627 * @deprecated Finalization is deprecated and subject to removal in a future
628 * release. The use of finalization can lead to problems with security,
629 * performance, and reliability.
630 * See <a href="https://openjdk.org/jeps/421">JEP 421</a> for
631 * discussion and alternatives.
632 * <p>
633 * Subclasses that override {@code finalize} to perform cleanup should use
634 * alternative cleanup mechanisms and remove the {@code finalize} method.
635 * Use {@link java.lang.ref.Cleaner} and
636 * {@link java.lang.ref.PhantomReference} as safer ways to release resources
637 * when an object becomes unreachable. Alternatively, add a {@code close}
638 * method to explicitly release resources, and implement
639 * {@code AutoCloseable} to enable use of the {@code try}-with-resources
640 * statement.
641 * <p>
642 * This method will remain in place until finalizers have been removed from
643 * most existing code.
644 *
645 * @throws Throwable the {@code Exception} raised by this method
646 * @see java.lang.ref.WeakReference
647 * @see java.lang.ref.PhantomReference
648 * @jls 12.6 Finalization of Class Instances
649 */
650 @Deprecated(since="9", forRemoval=true)
651 protected void finalize() throws Throwable { }
652 }