1 /*
2 * Copyright (c) 1994, 2022, 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 import jdk.internal.access.SharedSecrets;
31
32 import java.util.Objects;
33
34 /**
35 * Class {@code Object} is the root of the class hierarchy.
36 * Every class has {@code Object} as a superclass. All objects,
37 * including arrays, implement the methods of this class.
38 * <p>
39 * Subclasses of {@code java.lang.Object} can be either {@linkplain Class#isIdentity()
40 * identity classes} or {@linkplain Class#isValue value classes}.
41 * The class {@code Object} itself is neither an identity class nor a value class.
42 * See {@jls The Java Language Specification 8.1.1.5 identity and value Classes}.
43 * An instance can be created with {@code new Object()}, those instances are
44 * {@link Objects#isIdentityObject(Object) an identity object}.
45 *
46 * @see java.lang.Class
47 * @since 1.0
48 */
49 public class Object {
50
51 /**
52 * Constructs a new object.
53 */
54 @IntrinsicCandidate
55 public Object() {}
56
57 /**
58 * Returns the runtime class of this {@code Object}. The returned
59 * {@code Class} object is the object that is locked by {@code
60 * static synchronized} methods of the represented class.
61 *
62 * <p><b>The actual result type is {@code Class<? extends |X|>}
63 * where {@code |X|} is the erasure of the static type of the
64 * expression on which {@code getClass} is called.</b> For
65 * example, no cast is required in this code fragment:</p>
66 *
67 * <p>
68 * {@code Number n = 0; }<br>
69 * {@code Class<? extends Number> c = n.getClass(); }
70 * </p>
71 *
72 * @return The {@code Class} object that represents the runtime
73 * class of this object.
74 * @jls 15.8.2 Class Literals
75 */
76 @IntrinsicCandidate
77 public final native Class<?> getClass();
78
79 /**
80 * Returns a hash code value for the object. This method is
81 * supported for the benefit of hash tables such as those provided by
82 * {@link java.util.HashMap}.
83 * <p>
84 * The general contract of {@code hashCode} is:
85 * <ul>
86 * <li>Whenever it is invoked on the same object more than once during
87 * an execution of a Java application, the {@code hashCode} method
88 * must consistently return the same integer, provided no information
89 * used in {@code equals} comparisons on the object is modified.
90 * This integer need not remain consistent from one execution of an
91 * application to another execution of the same application.
92 * <li>If two objects are equal according to the {@link
93 * #equals(Object) equals} method, then calling the {@code
94 * hashCode} method on each of the two objects must produce the
95 * same integer result.
96 * <li>It is <em>not</em> required that if two objects are unequal
97 * according to the {@link #equals(Object) equals} method, then
98 * calling the {@code hashCode} method on each of the two objects
99 * must produce distinct integer results. However, the programmer
100 * should be aware that producing distinct integer results for
101 * unequal objects may improve the performance of hash tables.
102 * </ul>
103 *
104 * @implSpec
105 * As far as is reasonably practical, the {@code hashCode} method defined
106 * by class {@code Object} returns distinct integers for distinct objects.
107 *
108 * @return a hash code value for this object.
109 * @see java.lang.Object#equals(java.lang.Object)
110 * @see java.lang.System#identityHashCode
111 */
112 @IntrinsicCandidate
113 public native int hashCode();
114
115 /**
116 * Indicates whether some other object is "equal to" this one.
117 * <p>
118 * The {@code equals} method implements an equivalence relation
119 * on non-null object references:
120 * <ul>
121 * <li>It is <i>reflexive</i>: for any non-null reference value
122 * {@code x}, {@code x.equals(x)} should return
123 * {@code true}.
124 * <li>It is <i>symmetric</i>: for any non-null reference values
125 * {@code x} and {@code y}, {@code x.equals(y)}
126 * should return {@code true} if and only if
127 * {@code y.equals(x)} returns {@code true}.
128 * <li>It is <i>transitive</i>: for any non-null reference values
129 * {@code x}, {@code y}, and {@code z}, if
130 * {@code x.equals(y)} returns {@code true} and
131 * {@code y.equals(z)} returns {@code true}, then
132 * {@code x.equals(z)} should return {@code true}.
133 * <li>It is <i>consistent</i>: for any non-null reference values
134 * {@code x} and {@code y}, multiple invocations of
135 * {@code x.equals(y)} consistently return {@code true}
136 * or consistently return {@code false}, provided no
137 * information used in {@code equals} comparisons on the
138 * objects is modified.
139 * <li>For any non-null reference value {@code x},
140 * {@code x.equals(null)} should return {@code false}.
141 * </ul>
142 *
143 * <p>
144 * An equivalence relation partitions the elements it operates on
145 * into <i>equivalence classes</i>; all the members of an
146 * equivalence class are equal to each other. Members of an
147 * equivalence class are substitutable for each other, at least
148 * for some purposes.
149 *
150 * @implSpec
151 * The {@code equals} method for class {@code Object} implements
152 * the most discriminating possible equivalence relation on objects;
153 * that is, for any non-null reference values {@code x} and
154 * {@code y}, this method returns {@code true} if and only
155 * if {@code x} and {@code y} refer to the same object
156 * ({@code x == y} has the value {@code true}).
157 *
158 * In other words, under the reference equality equivalence
159 * relation, each equivalence class only has a single element.
160 *
161 * @apiNote
162 * It is generally necessary to override the {@link #hashCode() hashCode}
163 * method whenever this method is overridden, so as to maintain the
164 * general contract for the {@code hashCode} method, which states
165 * that equal objects must have equal hash codes.
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 * Returns a string representation of the object.
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 * <blockquote>
260 * <pre>
261 * getClass().getName() + '@' + Integer.toHexString(hashCode())
262 * </pre></blockquote>
263 *
264 * @return a string representation of the object.
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 long comp = Blocker.begin();
375 try {
376 wait0(timeoutMillis);
377 } catch (InterruptedException e) {
378 Thread thread = Thread.currentThread();
379 if (thread.isVirtual())
380 thread.getAndClearInterrupt();
381 throw e;
382 } finally {
383 Blocker.end(comp);
384 }
385 }
386
387 // final modifier so method not in vtable
388 private final native void wait0(long timeoutMillis) throws InterruptedException;
389
390 /**
391 * Causes the current thread to wait until it is awakened, typically
392 * by being <em>notified</em> or <em>interrupted</em>, or until a
393 * certain amount of real time has elapsed.
394 * <p>
395 * The current thread must own this object's monitor lock. See the
396 * {@link #notify notify} method for a description of the ways in which
397 * a thread can become the owner of a monitor lock.
398 * <p>
399 * This method causes the current thread (referred to here as <var>T</var>) to
400 * place itself in the wait set for this object and then to relinquish any
401 * and all synchronization claims on this object. Note that only the locks
402 * on this object are relinquished; any other objects on which the current
403 * thread may be synchronized remain locked while the thread waits.
404 * <p>
405 * Thread <var>T</var> then becomes disabled for thread scheduling purposes
406 * and lies dormant until one of the following occurs:
407 * <ul>
408 * <li>Some other thread invokes the {@code notify} method for this
409 * object and thread <var>T</var> happens to be arbitrarily chosen as
410 * the thread to be awakened.
411 * <li>Some other thread invokes the {@code notifyAll} method for this
412 * object.
413 * <li>Some other thread {@linkplain Thread#interrupt() interrupts}
414 * thread <var>T</var>.
415 * <li>The specified amount of real time has elapsed, more or less.
416 * The amount of real time, in nanoseconds, is given by the expression
417 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos}
418 * are both zero, then real time is not taken into consideration and the
419 * thread waits until awakened by one of the other causes.
420 * <li>Thread <var>T</var> is awakened spuriously. (See below.)
421 * </ul>
422 * <p>
423 * The thread <var>T</var> is then removed from the wait set for this
424 * object and re-enabled for thread scheduling. It competes in the
425 * usual manner with other threads for the right to synchronize on the
426 * object; once it has regained control of the object, all its
427 * synchronization claims on the object are restored to the status quo
428 * ante - that is, to the situation as of the time that the {@code wait}
429 * method was invoked. Thread <var>T</var> then returns from the
430 * invocation of the {@code wait} method. Thus, on return from the
431 * {@code wait} method, the synchronization state of the object and of
432 * thread {@code T} is exactly as it was when the {@code wait} method
433 * was invoked.
434 * <p>
435 * A thread can wake up without being notified, interrupted, or timing out, a
436 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice,
437 * applications must guard against it by testing for the condition that should
438 * have caused the thread to be awakened, and continuing to wait if the condition
439 * is not satisfied. See the example below.
440 * <p>
441 * For more information on this topic, see section 14.2,
442 * "Condition Queues," in Brian Goetz and others' <cite>Java Concurrency
443 * in Practice</cite> (Addison-Wesley, 2006) or Item 81 in Joshua
444 * Bloch's <cite>Effective Java, Third Edition</cite> (Addison-Wesley,
445 * 2018).
446 * <p>
447 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted}
448 * by any thread before or while it is waiting, then an {@code InterruptedException}
449 * is thrown. The <em>interrupted status</em> of the current thread is cleared when
450 * this exception is thrown. This exception is not thrown until the lock status of
451 * this object has been restored as described above.
452 *
453 * @apiNote
454 * The recommended approach to waiting is to check the condition being awaited in
455 * a {@code while} loop around the call to {@code wait}, as shown in the example
456 * below. Among other things, this approach avoids problems that can be caused
457 * by spurious wakeups.
458 *
459 * <pre>{@code
460 * synchronized (obj) {
461 * while (<condition does not hold> and <timeout not exceeded>) {
462 * long timeoutMillis = ... ; // recompute timeout values
463 * int nanos = ... ;
464 * obj.wait(timeoutMillis, nanos);
465 * }
466 * ... // Perform action appropriate to condition or timeout
467 * }
468 * }</pre>
469 *
470 * @param timeoutMillis the maximum time to wait, in milliseconds
471 * @param nanos additional time, in nanoseconds, in the range 0-999999 inclusive
472 * @throws IllegalArgumentException if {@code timeoutMillis} is negative,
473 * or if the value of {@code nanos} is out of range
474 * @throws IllegalMonitorStateException if the current thread is not
475 * the owner of the object's monitor
476 * @throws InterruptedException if any thread interrupted the current thread before or
477 * while the current thread was waiting. The <em>interrupted status</em> of the
478 * current thread is cleared when this exception is thrown.
479 * @see #notify()
480 * @see #notifyAll()
481 * @see #wait()
482 * @see #wait(long)
483 */
484 public final void wait(long timeoutMillis, int nanos) throws InterruptedException {
485 if (timeoutMillis < 0) {
486 throw new IllegalArgumentException("timeoutMillis value is negative");
487 }
488
489 if (nanos < 0 || nanos > 999999) {
490 throw new IllegalArgumentException(
491 "nanosecond timeout value out of range");
492 }
493
494 if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) {
495 timeoutMillis++;
496 }
497
498 wait(timeoutMillis);
499 }
500
501 /**
502 * Called by the garbage collector on an object when garbage collection
503 * determines that there are no more references to the object.
504 * A subclass overrides the {@code finalize} method to dispose of
505 * system resources or to perform other cleanup.
506 * <p>
507 * <b>When running in a Java virtual machine in which finalization has been
508 * disabled or removed, the garbage collector will never call
509 * {@code finalize()}. In a Java virtual machine in which finalization is
510 * enabled, the garbage collector might call {@code finalize} only after an
511 * indefinite delay.</b>
512 * <p>
513 * The general contract of {@code finalize} is that it is invoked
514 * if and when the Java virtual
515 * machine has determined that there is no longer any
516 * means by which this object can be accessed by any thread that has
517 * not yet died, except as a result of an action taken by the
518 * finalization of some other object or class which is ready to be
519 * finalized. The {@code finalize} method may take any action, including
520 * making this object available again to other threads; the usual purpose
521 * of {@code finalize}, however, is to perform cleanup actions before
522 * the object is irrevocably discarded. For example, the finalize method
523 * for an object that represents an input/output connection might perform
524 * explicit I/O transactions to break the connection before the object is
525 * permanently discarded.
526 * <p>
527 * The {@code finalize} method of class {@code Object} performs no
528 * special action; it simply returns normally. Subclasses of
529 * {@code Object} may override this definition.
530 * <p>
531 * The Java programming language does not guarantee which thread will
532 * invoke the {@code finalize} method for any given object. It is
533 * guaranteed, however, that the thread that invokes finalize will not
534 * be holding any user-visible synchronization locks when finalize is
535 * invoked. If an uncaught exception is thrown by the finalize method,
536 * the exception is ignored and finalization of that object terminates.
537 * <p>
538 * After the {@code finalize} method has been invoked for an object, no
539 * further action is taken until the Java virtual machine has again
540 * determined that there is no longer any means by which this object can
541 * be accessed by any thread that has not yet died, including possible
542 * actions by other objects or classes which are ready to be finalized,
543 * at which point the object may be discarded.
544 * <p>
545 * The {@code finalize} method is never invoked more than once by a Java
546 * virtual machine for any given object.
547 * <p>
548 * Any exception thrown by the {@code finalize} method causes
549 * the finalization of this object to be halted, but is otherwise
550 * ignored.
551 *
552 * @apiNote
553 * Classes that embed non-heap resources have many options
554 * for cleanup of those resources. The class must ensure that the
555 * lifetime of each instance is longer than that of any resource it embeds.
556 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that
557 * objects remain reachable while resources embedded in the object are in use.
558 * <p>
559 * A subclass should avoid overriding the {@code finalize} method
560 * unless the subclass embeds non-heap resources that must be cleaned up
561 * before the instance is collected.
562 * Finalizer invocations are not automatically chained, unlike constructors.
563 * If a subclass overrides {@code finalize} it must invoke the superclass
564 * finalizer explicitly.
565 * To guard against exceptions prematurely terminating the finalize chain,
566 * the subclass should use a {@code try-finally} block to ensure
567 * {@code super.finalize()} is always invoked. For example,
568 * <pre>{@code @Override
569 * protected void finalize() throws Throwable {
570 * try {
571 * ... // cleanup subclass state
572 * } finally {
573 * super.finalize();
574 * }
575 * }
576 * }</pre>
577 *
578 * @deprecated Finalization is deprecated and subject to removal in a future
579 * release. The use of finalization can lead to problems with security,
580 * performance, and reliability.
581 * See <a href="https://openjdk.org/jeps/421">JEP 421</a> for
582 * discussion and alternatives.
583 * <p>
584 * Subclasses that override {@code finalize} to perform cleanup should use
585 * alternative cleanup mechanisms and remove the {@code finalize} method.
586 * Use {@link java.lang.ref.Cleaner} and
587 * {@link java.lang.ref.PhantomReference} as safer ways to release resources
588 * when an object becomes unreachable. Alternatively, add a {@code close}
589 * method to explicitly release resources, and implement
590 * {@code AutoCloseable} to enable use of the {@code try}-with-resources
591 * statement.
592 * <p>
593 * This method will remain in place until finalizers have been removed from
594 * most existing code.
595 *
596 * @throws Throwable the {@code Exception} raised by this method
597 * @see java.lang.ref.WeakReference
598 * @see java.lang.ref.PhantomReference
599 * @jls 12.6 Finalization of Class Instances
600 */
601 @Deprecated(since="9", forRemoval=true)
602 protected void finalize() throws Throwable { }
603 }