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 *
36 * @see java.lang.Class
37 * @since 1.0
38 */
39 public class Object {
40
41 /**
42 * Constructs a new object.
43 */
44 @IntrinsicCandidate
45 public Object() {}
46
47 /**
48 * Returns the runtime class of this {@code Object}. The returned
49 * {@code Class} object is the object that is locked by {@code
50 * static synchronized} methods of the represented class.
51 *
52 * <p><b>The actual result type is {@code Class<? extends |X|>}
53 * where {@code |X|} is the erasure of the static type of the
54 * expression on which {@code getClass} is called.</b> For
55 * example, no cast is required in this code fragment:</p>
56 *
57 * <p>
58 * {@code Number n = 0; }<br>
59 * {@code Class<? extends Number> c = n.getClass(); }
60 * </p>
61 *
62 * @return The {@code Class} object that represents the runtime
63 * class of this object.
64 * @jls 15.8.2 Class Literals
65 */
66 @IntrinsicCandidate
67 public final native Class<?> getClass();
68
69 /**
70 * {@return a hash code value for this object} This method is
71 * supported for the benefit of hash tables such as those provided by
72 * {@link java.util.HashMap}.
73 * <p>
74 * The general contract of {@code hashCode} is:
75 * <ul>
76 * <li>Whenever it is invoked on the same object more than once during
77 * an execution of a Java application, the {@code hashCode} method
78 * must consistently return the same integer, provided no information
79 * used in {@code equals} comparisons on the object is modified.
80 * This integer need not remain consistent from one execution of an
81 * application to another execution of the same application.
82 * <li>If two objects are equal according to the {@link
83 * #equals(Object) equals} method, then calling the {@code
84 * hashCode} method on each of the two objects must produce the
85 * same integer result.
86 * <li>It is <em>not</em> required that if two objects are unequal
87 * according to the {@link #equals(Object) equals} method, then
88 * calling the {@code hashCode} method on each of the two objects
89 * must produce distinct integer results. However, the programmer
90 * should be aware that producing distinct integer results for
91 * unequal objects may improve the performance of hash tables.
92 * </ul>
93 *
94 * @implSpec
95 * As far as is reasonably practical, the {@code hashCode} method defined
96 * by class {@code Object} returns distinct integers for distinct objects.
97 *
98 * @apiNote
99 * The {@link java.util.Objects#hash(Object...) hash} and {@link
100 * java.util.Objects#hashCode(Object) hashCode} methods of {@link
101 * java.util.Objects} can be used to help construct simple hash codes.
102 *
103 * @see java.lang.Object#equals(java.lang.Object)
104 * @see java.lang.System#identityHashCode
105 */
106 @IntrinsicCandidate
107 public native int hashCode();
108
109 /**
110 * Indicates whether some other object is "equal to" this one.
111 * <p>
112 * The {@code equals} method implements an <dfn>{@index "equivalence relation"}</dfn>
113 * on non-null object references:
114 * <ul>
115 * <li>It is <i>reflexive</i>: for any non-null reference value
116 * {@code x}, {@code x.equals(x)} should return
117 * {@code true}.
118 * <li>It is <i>symmetric</i>: for any non-null reference values
119 * {@code x} and {@code y}, {@code x.equals(y)}
120 * should return {@code true} if and only if
121 * {@code y.equals(x)} returns {@code true}.
122 * <li>It is <i>transitive</i>: for any non-null reference values
123 * {@code x}, {@code y}, and {@code z}, if
124 * {@code x.equals(y)} returns {@code true} and
125 * {@code y.equals(z)} returns {@code true}, then
126 * {@code x.equals(z)} should return {@code true}.
127 * <li>It is <i>consistent</i>: for any non-null reference values
128 * {@code x} and {@code y}, multiple invocations of
129 * {@code x.equals(y)} consistently return {@code true}
130 * or consistently return {@code false}, provided no
131 * information used in {@code equals} comparisons on the
132 * objects is modified.
133 * <li>For any non-null reference value {@code x},
134 * {@code x.equals(null)} should return {@code false}.
135 * </ul>
136 *
137 * <p>
138 * An equivalence relation partitions the elements it operates on
139 * into <i>equivalence classes</i>; all the members of an
140 * equivalence class are equal to each other. Members of an
141 * equivalence class are substitutable for each other, at least
142 * for some purposes.
143 *
144 * @implSpec
145 * The {@code equals} method for class {@code Object} implements
146 * the most discriminating possible equivalence relation on objects;
147 * that is, for any non-null reference values {@code x} and
148 * {@code y}, this method returns {@code true} if and only
149 * if {@code x} and {@code y} refer to the same object
150 * ({@code x == y} has the value {@code true}).
151 *
152 * In other words, under the reference equality equivalence
153 * relation, each equivalence class only has a single element.
154 *
155 * @apiNote
156 * It is generally necessary to override the {@link #hashCode() hashCode}
157 * method whenever this method is overridden, so as to maintain the
158 * general contract for the {@code hashCode} method, which states
159 * that equal objects must have equal hash codes.
160 * <p>The two-argument {@link java.util.Objects#equals(Object,
161 * Object) Objects.equals} method implements an equivalence relation
162 * on two possibly-null object references.
163 *
164 * @param obj the reference object with which to compare.
165 * @return {@code true} if this object is the same as the obj
166 * argument; {@code false} otherwise.
167 * @see #hashCode()
168 * @see java.util.HashMap
169 */
170 public boolean equals(Object obj) {
171 return (this == obj);
172 }
173
174 /**
175 * Creates and returns a copy of this object. The precise meaning
176 * of "copy" may depend on the class of the object. The general
177 * intent is that, for any object {@code x}, the expression:
178 * <blockquote>
179 * <pre>
180 * x.clone() != x</pre></blockquote>
181 * will be true, and that the expression:
182 * <blockquote>
183 * <pre>
184 * x.clone().getClass() == x.getClass()</pre></blockquote>
185 * will be {@code true}, but these are not absolute requirements.
186 * While it is typically the case that:
187 * <blockquote>
188 * <pre>
189 * x.clone().equals(x)</pre></blockquote>
190 * will be {@code true}, this is not an absolute requirement.
191 * <p>
192 * By convention, the returned object should be obtained by calling
193 * {@code super.clone}. If a class and all of its superclasses (except
194 * {@code Object}) obey this convention, it will be the case that
195 * {@code x.clone().getClass() == x.getClass()}.
196 * <p>
197 * By convention, the object returned by this method should be independent
198 * of this object (which is being cloned). To achieve this independence,
199 * it may be necessary to modify one or more fields of the object returned
200 * by {@code super.clone} before returning it. Typically, this means
201 * copying any mutable objects that comprise the internal "deep structure"
202 * of the object being cloned and replacing the references to these
203 * objects with references to the copies. If a class contains only
204 * primitive fields or references to immutable objects, then it is usually
205 * the case that no fields in the object returned by {@code super.clone}
206 * need to be modified.
207 *
208 * @implSpec
209 * The method {@code clone} for class {@code Object} performs a
210 * specific cloning operation. First, if the class of this object does
211 * not implement the interface {@code Cloneable}, then a
212 * {@code CloneNotSupportedException} is thrown. Note that all arrays
213 * are considered to implement the interface {@code Cloneable} and that
214 * the return type of the {@code clone} method of an array type {@code T[]}
215 * is {@code T[]} where T is any reference or primitive type.
216 * Otherwise, this method creates a new instance of the class of this
217 * object and initializes all its fields with exactly the contents of
218 * the corresponding fields of this object, as if by assignment; the
219 * contents of the fields are not themselves cloned. Thus, this method
220 * performs a "shallow copy" of this object, not a "deep copy" operation.
221 * <p>
222 * The class {@code Object} does not itself implement the interface
223 * {@code Cloneable}, so calling the {@code clone} method on an object
224 * whose class is {@code Object} will result in throwing an
225 * exception at run time.
226 *
227 * @return a clone of this instance.
228 * @throws CloneNotSupportedException if the object's class does not
229 * support the {@code Cloneable} interface. Subclasses
230 * that override the {@code clone} method can also
231 * throw this exception to indicate that an instance cannot
232 * be cloned.
233 * @see java.lang.Cloneable
234 */
235 @IntrinsicCandidate
236 protected native Object clone() throws CloneNotSupportedException;
237
238 /**
239 * {@return a string representation of the object}
240 *
241 * Satisfying this method's contract implies a non-{@code null}
242 * result must be returned.
243 *
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 }