1 /*
2 * Copyright (c) 1994, 2023, 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.event.VirtualThreadPinnedEvent;
29 import jdk.internal.misc.Blocker;
30 import jdk.internal.vm.annotation.IntrinsicCandidate;
31
32 /**
33 * Class {@code Object} is the root of the class hierarchy.
34 * Every class has {@code Object} as a superclass. All objects,
35 * including arrays, implement the methods of this class.
36 *
37 * @see java.lang.Class
38 * @since 1.0
39 */
40 public class Object {
41
42 /**
43 * Constructs a new object.
44 */
45 @IntrinsicCandidate
46 public Object() {}
47
48 /**
49 * Returns the runtime class of this {@code Object}. The returned
50 * {@code Class} object is the object that is locked by {@code
51 * static synchronized} methods of the represented class.
52 *
53 * <p><b>The actual result type is {@code Class<? extends |X|>}
54 * where {@code |X|} is the erasure of the static type of the
55 * expression on which {@code getClass} is called.</b> For
56 * example, no cast is required in this code fragment:</p>
57 *
58 * <p>
59 * {@code Number n = 0; }<br>
60 * {@code Class<? extends Number> c = n.getClass(); }
61 * </p>
62 *
63 * @return The {@code Class} object that represents the runtime
64 * class of this object.
65 * @jls 15.8.2 Class Literals
66 */
67 @IntrinsicCandidate
68 public final native Class<?> getClass();
69
70 /**
71 * {@return a hash code value for this object} This method is
72 * supported for the benefit of hash tables such as those provided by
73 * {@link java.util.HashMap}.
74 * <p>
75 * The general contract of {@code hashCode} is:
76 * <ul>
77 * <li>Whenever it is invoked on the same object more than once during
78 * an execution of a Java application, the {@code hashCode} method
79 * must consistently return the same integer, provided no information
80 * used in {@code equals} comparisons on the object is modified.
81 * This integer need not remain consistent from one execution of an
82 * application to another execution of the same application.
83 * <li>If two objects are equal according to the {@link
84 * #equals(Object) equals} method, then calling the {@code
85 * hashCode} method on each of the two objects must produce the
86 * same integer result.
87 * <li>It is <em>not</em> required that if two objects are unequal
88 * according to the {@link #equals(Object) equals} method, then
89 * calling the {@code hashCode} method on each of the two objects
90 * must produce distinct integer results. However, the programmer
91 * should be aware that producing distinct integer results for
92 * unequal objects may improve the performance of hash tables.
93 * </ul>
94 *
95 * @implSpec
96 * As far as is reasonably practical, the {@code hashCode} method defined
97 * by class {@code Object} returns distinct integers for distinct objects.
98 *
99 * @apiNote
100 * The {@link java.util.Objects#hash(Object...) hash} and {@link
101 * java.util.Objects#hashCode(Object) hashCode} methods of {@link
102 * java.util.Objects} can be used to help construct simple hash codes.
103 *
104 * @see java.lang.Object#equals(java.lang.Object)
105 * @see java.lang.System#identityHashCode
106 */
107 @IntrinsicCandidate
108 public native int hashCode();
109
110 /**
111 * Indicates whether some other object is "equal to" this one.
112 * <p>
113 * The {@code equals} method implements an equivalence relation
114 * on non-null object references:
115 * <ul>
116 * <li>It is <i>reflexive</i>: for any non-null reference value
117 * {@code x}, {@code x.equals(x)} should return
118 * {@code true}.
119 * <li>It is <i>symmetric</i>: for any non-null reference values
120 * {@code x} and {@code y}, {@code x.equals(y)}
121 * should return {@code true} if and only if
122 * {@code y.equals(x)} returns {@code true}.
123 * <li>It is <i>transitive</i>: for any non-null reference values
124 * {@code x}, {@code y}, and {@code z}, if
125 * {@code x.equals(y)} returns {@code true} and
126 * {@code y.equals(z)} returns {@code true}, then
127 * {@code x.equals(z)} should return {@code true}.
128 * <li>It is <i>consistent</i>: for any non-null reference values
129 * {@code x} and {@code y}, multiple invocations of
130 * {@code x.equals(y)} consistently return {@code true}
131 * or consistently return {@code false}, provided no
132 * information used in {@code equals} comparisons on the
133 * objects is modified.
134 * <li>For any non-null reference value {@code x},
135 * {@code x.equals(null)} should return {@code false}.
136 * </ul>
137 *
138 * <p>
139 * An equivalence relation partitions the elements it operates on
140 * into <i>equivalence classes</i>; all the members of an
141 * equivalence class are equal to each other. Members of an
142 * equivalence class are substitutable for each other, at least
143 * for some purposes.
144 *
145 * @implSpec
146 * The {@code equals} method for class {@code Object} implements
147 * the most discriminating possible equivalence relation on objects;
148 * that is, for any non-null reference values {@code x} and
149 * {@code y}, this method returns {@code true} if and only
150 * if {@code x} and {@code y} refer to the same object
151 * ({@code x == y} has the value {@code true}).
152 *
153 * In other words, under the reference equality equivalence
154 * relation, each equivalence class only has a single element.
155 *
156 * @apiNote
157 * It is generally necessary to override the {@link #hashCode() hashCode}
158 * method whenever this method is overridden, so as to maintain the
159 * general contract for the {@code hashCode} method, which states
160 * that equal objects must have equal hash codes.
161 * <p>The two-argument {@link java.util.Objects#equals(Object,
162 * Object) Objects.equals} method implements an equivalence relation
163 * on two possibly-null object references.
164 *
165 * @param obj the reference object with which to compare.
166 * @return {@code true} if this object is the same as the obj
167 * argument; {@code false} otherwise.
168 * @see #hashCode()
169 * @see java.util.HashMap
170 */
171 public boolean equals(Object obj) {
172 return (this == obj);
173 }
174
175 /**
176 * Creates and returns a copy of this object. The precise meaning
177 * of "copy" may depend on the class of the object. The general
178 * intent is that, for any object {@code x}, the expression:
179 * <blockquote>
180 * <pre>
181 * x.clone() != x</pre></blockquote>
182 * will be true, and that the expression:
183 * <blockquote>
184 * <pre>
185 * x.clone().getClass() == x.getClass()</pre></blockquote>
186 * will be {@code true}, but these are not absolute requirements.
187 * While it is typically the case that:
188 * <blockquote>
189 * <pre>
190 * x.clone().equals(x)</pre></blockquote>
191 * will be {@code true}, this is not an absolute requirement.
192 * <p>
193 * By convention, the returned object should be obtained by calling
194 * {@code super.clone}. If a class and all of its superclasses (except
195 * {@code Object}) obey this convention, it will be the case that
196 * {@code x.clone().getClass() == x.getClass()}.
197 * <p>
198 * By convention, the object returned by this method should be independent
199 * of this object (which is being cloned). To achieve this independence,
200 * it may be necessary to modify one or more fields of the object returned
201 * by {@code super.clone} before returning it. Typically, this means
202 * copying any mutable objects that comprise the internal "deep structure"
203 * of the object being cloned and replacing the references to these
204 * objects with references to the copies. If a class contains only
205 * primitive fields or references to immutable objects, then it is usually
206 * the case that no fields in the object returned by {@code super.clone}
207 * need to be modified.
208 *
209 * @implSpec
210 * The method {@code clone} for class {@code Object} performs a
211 * specific cloning operation. First, if the class of this object does
212 * not implement the interface {@code Cloneable}, then a
213 * {@code CloneNotSupportedException} is thrown. Note that all arrays
214 * are considered to implement the interface {@code Cloneable} and that
215 * the return type of the {@code clone} method of an array type {@code T[]}
216 * is {@code T[]} where T is any reference or primitive type.
217 * Otherwise, this method creates a new instance of the class of this
218 * object and initializes all its fields with exactly the contents of
219 * the corresponding fields of this object, as if by assignment; the
220 * contents of the fields are not themselves cloned. Thus, this method
221 * performs a "shallow copy" of this object, not a "deep copy" operation.
222 * <p>
223 * The class {@code Object} does not itself implement the interface
224 * {@code Cloneable}, so calling the {@code clone} method on an object
225 * whose class is {@code Object} will result in throwing an
226 * exception at run time.
227 *
228 * @return a clone of this instance.
229 * @throws CloneNotSupportedException if the object's class does not
230 * support the {@code Cloneable} interface. Subclasses
231 * that override the {@code clone} method can also
232 * throw this exception to indicate that an instance cannot
233 * be cloned.
234 * @see java.lang.Cloneable
235 */
236 @IntrinsicCandidate
237 protected native Object clone() throws CloneNotSupportedException;
238
239 /**
240 * {@return a string representation of the object}
241 * @apiNote
242 * In general, the
243 * {@code toString} method returns a string that
244 * "textually represents" this object. The result should
245 * be a concise but informative representation that is easy for a
246 * person to read.
247 * It is recommended that all subclasses override this method.
248 * The string output is not necessarily stable over time or across
249 * JVM invocations.
250 * @implSpec
251 * The {@code toString} method for class {@code Object}
252 * returns a string consisting of the name of the class of which the
253 * object is an instance, the at-sign character `{@code @}', and
254 * the unsigned hexadecimal representation of the hash code of the
255 * object. In other words, this method returns a string equal to the
256 * value of:
257 * {@snippet lang=java :
258 * getClass().getName() + '@' + Integer.toHexString(hashCode())
259 * }
260 * The {@link java.util.Objects#toIdentityString(Object)
261 * Objects.toIdentityString} method returns the string for an
262 * object equal to the string that would be returned if neither
263 * the {@code toString} nor {@code hashCode} methods were
264 * overridden by the object's class.
265 */
266 public String toString() {
267 return getClass().getName() + "@" + Integer.toHexString(hashCode());
268 }
269
270 /**
271 * Wakes up a single thread that is waiting on this object's
272 * monitor. If any threads are waiting on this object, one of them
273 * is chosen to be awakened. The choice is arbitrary and occurs at
274 * the discretion of the implementation. A thread waits on an object's
275 * monitor by calling one of the {@code wait} methods.
276 * <p>
277 * The awakened thread will not be able to proceed until the current
278 * thread relinquishes the lock on this object. The awakened thread will
279 * compete in the usual manner with any other threads that might be
280 * actively competing to synchronize on this object; for example, the
281 * awakened thread enjoys no reliable privilege or disadvantage in being
282 * the next thread to lock this object.
283 * <p>
284 * This method should only be called by a thread that is the owner
285 * of this object's monitor. A thread becomes the owner of the
286 * object's monitor in one of three ways:
287 * <ul>
288 * <li>By executing a synchronized instance method of that object.
289 * <li>By executing the body of a {@code synchronized} statement
290 * that synchronizes on the object.
291 * <li>For objects of type {@code Class,} by executing a
292 * static synchronized method of that class.
293 * </ul>
294 * <p>
295 * Only one thread at a time can own an object's monitor.
296 *
297 * @throws IllegalMonitorStateException if the current thread is not
298 * the owner of this object's monitor.
299 * @see java.lang.Object#notifyAll()
300 * @see java.lang.Object#wait()
301 */
302 @IntrinsicCandidate
303 public final native void notify();
304
305 /**
306 * Wakes up all threads that are waiting on this object's monitor. A
307 * thread waits on an object's monitor by calling one of the
308 * {@code wait} methods.
309 * <p>
310 * The awakened threads will not be able to proceed until the current
311 * thread relinquishes the lock on this object. The awakened threads
312 * will compete in the usual manner with any other threads that might
313 * be actively competing to synchronize on this object; for example,
314 * the awakened threads enjoy no reliable privilege or disadvantage in
315 * being the next thread to lock this object.
316 * <p>
317 * This method should only be called by a thread that is the owner
318 * of this object's monitor. See the {@code notify} method for a
319 * description of the ways in which a thread can become the owner of
320 * a monitor.
321 *
322 * @throws IllegalMonitorStateException if the current thread is not
323 * the owner of this object's monitor.
324 * @see java.lang.Object#notify()
325 * @see java.lang.Object#wait()
326 */
327 @IntrinsicCandidate
328 public final native void notifyAll();
329
330 /**
331 * Causes the current thread to wait until it is awakened, typically
332 * by being <em>notified</em> or <em>interrupted</em>.
333 * <p>
334 * In all respects, this method behaves as if {@code wait(0L, 0)}
335 * had been called. See the specification of the {@link #wait(long, int)} method
336 * for details.
337 *
338 * @throws IllegalMonitorStateException if the current thread is not
339 * the owner of the object's monitor
340 * @throws InterruptedException if any thread interrupted the current thread before or
341 * while the current thread was waiting. The <em>interrupted status</em> of the
342 * current thread is cleared when this exception is thrown.
343 * @see #notify()
344 * @see #notifyAll()
345 * @see #wait(long)
346 * @see #wait(long, int)
347 */
348 public final void wait() throws InterruptedException {
349 wait(0L);
350 }
351
352 /**
353 * Causes the current thread to wait until it is awakened, typically
354 * by being <em>notified</em> or <em>interrupted</em>, or until a
355 * certain amount of real time has elapsed.
356 * <p>
357 * In all respects, this method behaves as if {@code wait(timeoutMillis, 0)}
358 * had been called. See the specification of the {@link #wait(long, int)} method
359 * for details.
360 *
361 * @param timeoutMillis the maximum time to wait, in milliseconds
362 * @throws IllegalArgumentException if {@code timeoutMillis} is negative
363 * @throws IllegalMonitorStateException if the current thread is not
364 * the owner of the object's monitor
365 * @throws InterruptedException if any thread interrupted the current thread before or
366 * while the current thread was waiting. The <em>interrupted status</em> of the
367 * current thread is cleared when this exception is thrown.
368 * @see #notify()
369 * @see #notifyAll()
370 * @see #wait()
371 * @see #wait(long, int)
372 */
373 public final void wait(long timeoutMillis) throws InterruptedException {
374 if (!Thread.currentThread().isVirtual()) {
375 wait0(timeoutMillis);
376 return;
377 }
378
379 // virtual thread waiting
380 VirtualThreadPinnedEvent event;
381 try {
382 event = new VirtualThreadPinnedEvent();
383 event.begin();
384 } catch (OutOfMemoryError e) {
385 event = null;
386 }
387 long comp = Blocker.begin();
388 try {
389 wait0(timeoutMillis);
390 } catch (InterruptedException e) {
391 // virtual thread's interrupt status needs to be cleared
392 Thread.currentThread().getAndClearInterrupt();
393 throw e;
394 } finally {
395 Blocker.end(comp);
396 if (event != null) {
397 try {
398 event.commit();
399 } catch (OutOfMemoryError e) {
400 // ignore
401 }
402 }
403 }
404 }
405
406 // final modifier so method not in vtable
407 private final native void wait0(long timeoutMillis) throws InterruptedException;
408
409 /**
410 * Causes the current thread to wait until it is awakened, typically
411 * by being <em>notified</em> or <em>interrupted</em>, or until a
412 * certain amount of real time has elapsed.
413 * <p>
414 * The current thread must own this object's monitor lock. See the
415 * {@link #notify notify} method for a description of the ways in which
416 * a thread can become the owner of a monitor lock.
417 * <p>
418 * This method causes the current thread (referred to here as <var>T</var>) to
419 * place itself in the wait set for this object and then to relinquish any
420 * and all synchronization claims on this object. Note that only the locks
421 * on this object are relinquished; any other objects on which the current
422 * thread may be synchronized remain locked while the thread waits.
423 * <p>
424 * Thread <var>T</var> then becomes disabled for thread scheduling purposes
425 * and lies dormant until one of the following occurs:
426 * <ul>
427 * <li>Some other thread invokes the {@code notify} method for this
428 * object and thread <var>T</var> happens to be arbitrarily chosen as
429 * the thread to be awakened.
430 * <li>Some other thread invokes the {@code notifyAll} method for this
431 * object.
432 * <li>Some other thread {@linkplain Thread#interrupt() interrupts}
433 * thread <var>T</var>.
434 * <li>The specified amount of real time has elapsed, more or less.
435 * The amount of real time, in nanoseconds, is given by the expression
436 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos}
437 * are both zero, then real time is not taken into consideration and the
438 * thread waits until awakened by one of the other causes.
439 * <li>Thread <var>T</var> is awakened spuriously. (See below.)
440 * </ul>
441 * <p>
442 * The thread <var>T</var> is then removed from the wait set for this
443 * object and re-enabled for thread scheduling. It competes in the
444 * usual manner with other threads for the right to synchronize on the
445 * object; once it has regained control of the object, all its
446 * synchronization claims on the object are restored to the status quo
447 * ante - that is, to the situation as of the time that the {@code wait}
448 * method was invoked. Thread <var>T</var> then returns from the
449 * invocation of the {@code wait} method. Thus, on return from the
450 * {@code wait} method, the synchronization state of the object and of
451 * thread {@code T} is exactly as it was when the {@code wait} method
452 * was invoked.
453 * <p>
454 * A thread can wake up without being notified, interrupted, or timing out, a
455 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice,
456 * applications must guard against it by testing for the condition that should
457 * have caused the thread to be awakened, and continuing to wait if the condition
458 * is not satisfied. See the example below.
459 * <p>
460 * For more information on this topic, see section 14.2,
461 * "Condition Queues," in Brian Goetz and others' <cite>Java Concurrency
462 * in Practice</cite> (Addison-Wesley, 2006) or Item 81 in Joshua
463 * Bloch's <cite>Effective Java, Third Edition</cite> (Addison-Wesley,
464 * 2018).
465 * <p>
466 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted}
467 * by any thread before or while it is waiting, then an {@code InterruptedException}
468 * is thrown. The <em>interrupted status</em> of the current thread is cleared when
469 * this exception is thrown. This exception is not thrown until the lock status of
470 * this object has been restored as described above.
471 *
472 * @apiNote
473 * The recommended approach to waiting is to check the condition being awaited in
474 * a {@code while} loop around the call to {@code wait}, as shown in the example
475 * below. Among other things, this approach avoids problems that can be caused
476 * by spurious wakeups.
477 *
478 * {@snippet lang=java :
479 * synchronized (obj) {
480 * while ( <condition does not hold and timeout not exceeded> ) {
481 * long timeoutMillis = ... ; // recompute timeout values
482 * int nanos = ... ;
483 * obj.wait(timeoutMillis, nanos);
484 * }
485 * ... // Perform action appropriate to condition or timeout
486 * }
487 * }
488 *
489 * @param timeoutMillis the maximum time to wait, in milliseconds
490 * @param nanos additional time, in nanoseconds, in the range 0-999999 inclusive
491 * @throws IllegalArgumentException if {@code timeoutMillis} is negative,
492 * or if the value of {@code nanos} is out of range
493 * @throws IllegalMonitorStateException if the current thread is not
494 * the owner of the object's monitor
495 * @throws InterruptedException if any thread interrupted the current thread before or
496 * while the current thread was waiting. The <em>interrupted status</em> of the
497 * current thread is cleared when this exception is thrown.
498 * @see #notify()
499 * @see #notifyAll()
500 * @see #wait()
501 * @see #wait(long)
502 */
503 public final void wait(long timeoutMillis, int nanos) throws InterruptedException {
504 if (timeoutMillis < 0) {
505 throw new IllegalArgumentException("timeoutMillis value is negative");
506 }
507
508 if (nanos < 0 || nanos > 999999) {
509 throw new IllegalArgumentException(
510 "nanosecond timeout value out of range");
511 }
512
513 if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) {
514 timeoutMillis++;
515 }
516
517 wait(timeoutMillis);
518 }
519
520 /**
521 * Called by the garbage collector on an object when garbage collection
522 * determines that there are no more references to the object.
523 * A subclass overrides the {@code finalize} method to dispose of
524 * system resources or to perform other cleanup.
525 * <p>
526 * <b>When running in a Java virtual machine in which finalization has been
527 * disabled or removed, the garbage collector will never call
528 * {@code finalize()}. In a Java virtual machine in which finalization is
529 * enabled, the garbage collector might call {@code finalize} only after an
530 * indefinite delay.</b>
531 * <p>
532 * The general contract of {@code finalize} is that it is invoked
533 * if and when the Java virtual
534 * machine has determined that there is no longer any
535 * means by which this object can be accessed by any thread that has
536 * not yet died, except as a result of an action taken by the
537 * finalization of some other object or class which is ready to be
538 * finalized. The {@code finalize} method may take any action, including
539 * making this object available again to other threads; the usual purpose
540 * of {@code finalize}, however, is to perform cleanup actions before
541 * the object is irrevocably discarded. For example, the finalize method
542 * for an object that represents an input/output connection might perform
543 * explicit I/O transactions to break the connection before the object is
544 * permanently discarded.
545 * <p>
546 * The {@code finalize} method of class {@code Object} performs no
547 * special action; it simply returns normally. Subclasses of
548 * {@code Object} may override this definition.
549 * <p>
550 * The Java programming language does not guarantee which thread will
551 * invoke the {@code finalize} method for any given object. It is
552 * guaranteed, however, that the thread that invokes finalize will not
553 * be holding any user-visible synchronization locks when finalize is
554 * invoked. If an uncaught exception is thrown by the finalize method,
555 * the exception is ignored and finalization of that object terminates.
556 * <p>
557 * After the {@code finalize} method has been invoked for an object, no
558 * further action is taken until the Java virtual machine has again
559 * determined that there is no longer any means by which this object can
560 * be accessed by any thread that has not yet died, including possible
561 * actions by other objects or classes which are ready to be finalized,
562 * at which point the object may be discarded.
563 * <p>
564 * The {@code finalize} method is never invoked more than once by a Java
565 * virtual machine for any given object.
566 * <p>
567 * Any exception thrown by the {@code finalize} method causes
568 * the finalization of this object to be halted, but is otherwise
569 * ignored.
570 *
571 * @apiNote
572 * Classes that embed non-heap resources have many options
573 * for cleanup of those resources. The class must ensure that the
574 * lifetime of each instance is longer than that of any resource it embeds.
575 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that
576 * objects remain reachable while resources embedded in the object are in use.
577 * <p>
578 * A subclass should avoid overriding the {@code finalize} method
579 * unless the subclass embeds non-heap resources that must be cleaned up
580 * before the instance is collected.
581 * Finalizer invocations are not automatically chained, unlike constructors.
582 * If a subclass overrides {@code finalize} it must invoke the superclass
583 * finalizer explicitly.
584 * To guard against exceptions prematurely terminating the finalize chain,
585 * the subclass should use a {@code try-finally} block to ensure
586 * {@code super.finalize()} is always invoked. For example,
587 * {@snippet lang="java":
588 * @Override
589 * protected void finalize() throws Throwable {
590 * try {
591 * ... // cleanup subclass state
592 * } finally {
593 * super.finalize();
594 * }
595 * }
596 * }
597 *
598 * @deprecated Finalization is deprecated and subject to removal in a future
599 * release. The use of finalization can lead to problems with security,
600 * performance, and reliability.
601 * See <a href="https://openjdk.org/jeps/421">JEP 421</a> for
602 * discussion and alternatives.
603 * <p>
604 * Subclasses that override {@code finalize} to perform cleanup should use
605 * alternative cleanup mechanisms and remove the {@code finalize} method.
606 * Use {@link java.lang.ref.Cleaner} and
607 * {@link java.lang.ref.PhantomReference} as safer ways to release resources
608 * when an object becomes unreachable. Alternatively, add a {@code close}
609 * method to explicitly release resources, and implement
610 * {@code AutoCloseable} to enable use of the {@code try}-with-resources
611 * statement.
612 * <p>
613 * This method will remain in place until finalizers have been removed from
614 * most existing code.
615 *
616 * @throws Throwable the {@code Exception} raised by this method
617 * @see java.lang.ref.WeakReference
618 * @see java.lang.ref.PhantomReference
619 * @jls 12.6 Finalization of Class Instances
620 */
621 @Deprecated(since="9", forRemoval=true)
622 protected void finalize() throws Throwable { }
623 }