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 }