1 /*
2 * Copyright (c) 2004, 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.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24 package java.lang;
25
26 import jdk.internal.misc.Blocker;
27 import nsk.jvmti.scenarios.bcinstr.BI04.bi04t002a;
28
29 /**
30 * Class <code>Object</code> is the root of the class hierarchy.
31 * Every class has <code>Object</code> as a superclass. All objects,
32 * including arrays, implement the methods of this class.
33 *
34 * @author unascribed
35 * @version 1.67, 02/03/04
36 * @see java.lang.Class
37 * @since JDK1.0
38 */
39 public class Object {
40
41 /**
42 * Returns the runtime class of an object. That <tt>Class</tt>
43 * object is the object that is locked by <tt>static synchronized</tt>
44 * methods of the represented class.
45 *
46 * @return The <code>java.lang.Class</code> object that represents
47 * the runtime class of the object. The result is of type
48 * {@code Class<? extends X>} where X is the
49 * static type of the expression on which
50 * <code>getClass</code> is called.
51 */
52 public final native Class<? extends Object> getClass();
53
54 /**
55 * Returns a hash code value for the object. This method is
56 * supported for the benefit of hashtables such as those provided by
57 * <code>java.util.Hashtable</code>.
58 * <p>
59 * The general contract of <code>hashCode</code> is:
60 * <ul>
61 * <li>Whenever it is invoked on the same object more than once during
62 * an execution of a Java application, the <tt>hashCode</tt> method
63 * must consistently return the same integer, provided no information
64 * used in <tt>equals</tt> comparisons on the object is modified.
65 * This integer need not remain consistent from one execution of an
66 * application to another execution of the same application.
67 * <li>If two objects are equal according to the <tt>equals(Object)</tt>
68 * method, then calling the <code>hashCode</code> method on each of
69 * the two objects must produce the same integer result.
70 * <li>It is <em>not</em> required that if two objects are unequal
71 * according to the {@link java.lang.Object#equals(java.lang.Object)}
72 * method, then calling the <tt>hashCode</tt> method on each of the
73 * two objects must produce distinct integer results. However, the
74 * programmer should be aware that producing distinct integer results
75 * for unequal objects may improve the performance of hashtables.
76 * </ul>
77 * <p>
78 * As much as is reasonably practical, the hashCode method defined by
79 * class <tt>Object</tt> does return distinct integers for distinct
80 * objects. (This is typically implemented by converting the internal
81 * address of the object into an integer, but this implementation
82 * technique is not required by the
83 * Java<font size="-2"><sup>TM</sup></font> programming language.)
84 *
85 * @return a hash code value for this object.
86 * @see java.lang.Object#equals(java.lang.Object)
87 * @see java.util.Hashtable
88 */
89 public native int hashCode();
90
91 /**
92 * Indicates whether some other object is "equal to" this one.
93 * <p>
94 * The <code>equals</code> method implements an equivalence relation
95 * on non-null object references:
96 * <ul>
97 * <li>It is <i>reflexive</i>: for any non-null reference value
98 * <code>x</code>, <code>x.equals(x)</code> should return
99 * <code>true</code>.
100 * <li>It is <i>symmetric</i>: for any non-null reference values
101 * <code>x</code> and <code>y</code>, <code>x.equals(y)</code>
102 * should return <code>true</code> if and only if
103 * <code>y.equals(x)</code> returns <code>true</code>.
104 * <li>It is <i>transitive</i>: for any non-null reference values
105 * <code>x</code>, <code>y</code>, and <code>z</code>, if
106 * <code>x.equals(y)</code> returns <code>true</code> and
107 * <code>y.equals(z)</code> returns <code>true</code>, then
108 * <code>x.equals(z)</code> should return <code>true</code>.
109 * <li>It is <i>consistent</i>: for any non-null reference values
110 * <code>x</code> and <code>y</code>, multiple invocations of
111 * <tt>x.equals(y)</tt> consistently return <code>true</code>
112 * or consistently return <code>false</code>, provided no
113 * information used in <code>equals</code> comparisons on the
114 * objects is modified.
115 * <li>For any non-null reference value <code>x</code>,
116 * <code>x.equals(null)</code> should return <code>false</code>.
117 * </ul>
118 * <p>
119 * The <tt>equals</tt> method for class <code>Object</code> implements
120 * the most discriminating possible equivalence relation on objects;
121 * that is, for any non-null reference values <code>x</code> and
122 * <code>y</code>, this method returns <code>true</code> if and only
123 * if <code>x</code> and <code>y</code> refer to the same object
124 * (<code>x == y</code> has the value <code>true</code>).
125 * <p>
126 * Note that it is generally necessary to override the <tt>hashCode</tt>
127 * method whenever this method is overridden, so as to maintain the
128 * general contract for the <tt>hashCode</tt> method, which states
129 * that equal objects must have equal hash codes.
130 *
131 * @param obj the reference object with which to compare.
132 * @return <code>true</code> if this object is the same as the obj
133 * argument; <code>false</code> otherwise.
134 * @see #hashCode()
135 * @see java.util.Hashtable
136 */
137 public boolean equals(Object obj) {
138 bi04t002a.instrInvoke(bi04t002a.INSTR_EQUALS);
139 return (this == obj);
140 }
141
142 /**
143 * Creates and returns a copy of this object. The precise meaning
144 * of "copy" may depend on the class of the object. The general
145 * intent is that, for any object <tt>x</tt>, the expression:
146 * <blockquote>
147 * <pre>
148 * x.clone() != x</pre></blockquote>
149 * will be true, and that the expression:
150 * <blockquote>
151 * <pre>
152 * x.clone().getClass() == x.getClass()</pre></blockquote>
153 * will be <tt>true</tt>, but these are not absolute requirements.
154 * While it is typically the case that:
155 * <blockquote>
156 * <pre>
157 * x.clone().equals(x)</pre></blockquote>
158 * will be <tt>true</tt>, this is not an absolute requirement.
159 * <p>
160 * By convention, the returned object should be obtained by calling
161 * <tt>super.clone</tt>. If a class and all of its superclasses (except
162 * <tt>Object</tt>) obey this convention, it will be the case that
163 * <tt>x.clone().getClass() == x.getClass()</tt>.
164 * <p>
165 * By convention, the object returned by this method should be independent
166 * of this object (which is being cloned). To achieve this independence,
167 * it may be necessary to modify one or more fields of the object returned
168 * by <tt>super.clone</tt> before returning it. Typically, this means
169 * copying any mutable objects that comprise the internal "deep structure"
170 * of the object being cloned and replacing the references to these
171 * objects with references to the copies. If a class contains only
172 * primitive fields or references to immutable objects, then it is usually
173 * the case that no fields in the object returned by <tt>super.clone</tt>
174 * need to be modified.
175 * <p>
176 * The method <tt>clone</tt> for class <tt>Object</tt> performs a
177 * specific cloning operation. First, if the class of this object does
178 * not implement the interface <tt>Cloneable</tt>, then a
179 * <tt>CloneNotSupportedException</tt> is thrown. Note that all arrays
180 * are considered to implement the interface <tt>Cloneable</tt>.
181 * Otherwise, this method creates a new instance of the class of this
182 * object and initializes all its fields with exactly the contents of
183 * the corresponding fields of this object, as if by assignment; the
184 * contents of the fields are not themselves cloned. Thus, this method
185 * performs a "shallow copy" of this object, not a "deep copy" operation.
186 * <p>
187 * The class <tt>Object</tt> does not itself implement the interface
188 * <tt>Cloneable</tt>, so calling the <tt>clone</tt> method on an object
189 * whose class is <tt>Object</tt> will result in throwing an
190 * exception at run time.
191 *
192 * @return a clone of this instance.
193 * @exception CloneNotSupportedException if the object's class does not
194 * support the <code>Cloneable</code> interface. Subclasses
195 * that override the <code>clone</code> method can also
196 * throw this exception to indicate that an instance cannot
197 * be cloned.
198 * @see java.lang.Cloneable
199 */
200 protected native Object clone() throws CloneNotSupportedException;
201
202 /**
203 * Returns a string representation of the object. In general, the
204 * <code>toString</code> method returns a string that
205 * "textually represents" this object. The result should
206 * be a concise but informative representation that is easy for a
207 * person to read.
208 * It is recommended that all subclasses override this method.
209 * <p>
210 * The <code>toString</code> method for class <code>Object</code>
211 * returns a string consisting of the name of the class of which the
212 * object is an instance, the at-sign character `<code>@</code>', and
213 * the unsigned hexadecimal representation of the hash code of the
214 * object. In other words, this method returns a string equal to the
215 * value of:
216 * <blockquote>
217 * <pre>
218 * getClass().getName() + '@' + Integer.toHexString(hashCode())
219 * </pre></blockquote>
220 *
221 * @return a string representation of the object.
222 */
223 public String toString() {
224 bi04t002a.instrInvoke(bi04t002a.INSTR_TOSTRING);
225 return getClass().getName() + "@" + Integer.toHexString(hashCode());
226 }
227
228 /**
229 * Wakes up a single thread that is waiting on this object's
230 * monitor. If any threads are waiting on this object, one of them
231 * is chosen to be awakened. The choice is arbitrary and occurs at
232 * the discretion of the implementation. A thread waits on an object's
233 * monitor by calling one of the <code>wait</code> methods.
234 * <p>
235 * The awakened thread will not be able to proceed until the current
236 * thread relinquishes the lock on this object. The awakened thread will
237 * compete in the usual manner with any other threads that might be
238 * actively competing to synchronize on this object; for example, the
239 * awakened thread enjoys no reliable privilege or disadvantage in being
240 * the next thread to lock this object.
241 * <p>
242 * This method should only be called by a thread that is the owner
243 * of this object's monitor. A thread becomes the owner of the
244 * object's monitor in one of three ways:
245 * <ul>
246 * <li>By executing a synchronized instance method of that object.
247 * <li>By executing the body of a <code>synchronized</code> statement
248 * that synchronizes on the object.
249 * <li>For objects of type <code>Class,</code> by executing a
250 * synchronized static method of that class.
251 * </ul>
252 * <p>
253 * Only one thread at a time can own an object's monitor.
254 *
255 * @exception IllegalMonitorStateException if the current thread is not
256 * the owner of this object's monitor.
257 * @see java.lang.Object#notifyAll()
258 * @see java.lang.Object#wait()
259 */
260 public final native void notify();
261
262 /**
263 * Wakes up all threads that are waiting on this object's monitor. A
264 * thread waits on an object's monitor by calling one of the
265 * <code>wait</code> methods.
266 * <p>
267 * The awakened threads will not be able to proceed until the current
268 * thread relinquishes the lock on this object. The awakened threads
269 * will compete in the usual manner with any other threads that might
270 * be actively competing to synchronize on this object; for example,
271 * the awakened threads enjoy no reliable privilege or disadvantage in
272 * being the next thread to lock this object.
273 * <p>
274 * This method should only be called by a thread that is the owner
275 * of this object's monitor. See the <code>notify</code> method for a
276 * description of the ways in which a thread can become the owner of
277 * a monitor.
278 *
279 * @exception IllegalMonitorStateException if the current thread is not
280 * the owner of this object's monitor.
281 * @see java.lang.Object#notify()
282 * @see java.lang.Object#wait()
283 */
284 public final native void notifyAll();
285
286 /**
287 * Causes current thread to wait until either another thread invokes the
288 * {@link java.lang.Object#notify()} method or the
289 * {@link java.lang.Object#notifyAll()} method for this object, or a
290 * specified amount of time has elapsed.
291 * <p>
292 * The current thread must own this object's monitor.
293 * <p>
294 * This method causes the current thread (call it <var>T</var>) to
295 * place itself in the wait set for this object and then to relinquish
296 * any and all synchronization claims on this object. Thread <var>T</var>
297 * becomes disabled for thread scheduling purposes and lies dormant
298 * until one of four things happens:
299 * <ul>
300 * <li>Some other thread invokes the <tt>notify</tt> method for this
301 * object and thread <var>T</var> happens to be arbitrarily chosen as
302 * the thread to be awakened.
303 * <li>Some other thread invokes the <tt>notifyAll</tt> method for this
304 * object.
305 * <li>Some other thread {@link java.lang.Thread#interrupt() interrupts}
306 * thread <var>T</var>.
307 * <li>The specified amount of real time has elapsed, more or less. If
308 * <tt>timeout</tt> is zero, however, then real time is not taken into
309 * consideration and the thread simply waits until notified.
310 * </ul>
311 * The thread <var>T</var> is then removed from the wait set for this
312 * object and re-enabled for thread scheduling. It then competes in the
313 * usual manner with other threads for the right to synchronize on the
314 * object; once it has gained control of the object, all its
315 * synchronization claims on the object are restored to the status quo
316 * ante - that is, to the situation as of the time that the <tt>wait</tt>
317 * method was invoked. Thread <var>T</var> then returns from the
318 * invocation of the <tt>wait</tt> method. Thus, on return from the
319 * <tt>wait</tt> method, the synchronization state of the object and of
320 * thread <tt>T</tt> is exactly as it was when the <tt>wait</tt> method
321 * was invoked.
322 * <p>
323 * A thread can also wake up without being notified, interrupted, or
324 * timing out, a so-called <i>spurious wakeup</i>. While this will rarely
325 * occur in practice, applications must guard against it by testing for
326 * the condition that should have caused the thread to be awakened, and
327 * continuing to wait if the condition is not satisfied. In other words,
328 * waits should always occur in loops, like this one:
329 * <pre>
330 * synchronized (obj) {
331 * while (<condition does not hold>)
332 * obj.wait(timeout);
333 * ... // Perform action appropriate to condition
334 * }
335 * </pre>
336 * (For more information on this topic, see Section 3.2.3 in Doug Lea's
337 * "Concurrent Programming in Java (Second Edition)" (Addison-Wesley,
338 * 2000), or Item 50 in Joshua Bloch's "Effective Java Programming
339 * Language Guide" (Addison-Wesley, 2001).
340 * <p>
341 * If the current thread is
342 * {@link java.lang.Thread#interrupt() interrupted} by another thread
343 * while it is waiting, then an <tt>InterruptedException</tt> is thrown.
344 * This exception is not thrown until the lock status of this object has
345 * been restored as described above.
346 * <p>
347 * Note that the <tt>wait</tt> method, as it places the current thread
348 * into the wait set for this object, unlocks only this object; any
349 * other objects on which the current thread may be synchronized remain
350 * locked while the thread waits.
351 * <p>
352 * This method should only be called by a thread that is the owner
353 * of this object's monitor. See the <code>notify</code> method for a
354 * description of the ways in which a thread can become the owner of
355 * a monitor.
356 *
357 * @param timeout the maximum time to wait in milliseconds.
358 * @exception IllegalArgumentException if the value of timeout is
359 * negative.
360 * @exception IllegalMonitorStateException if the current thread is not
361 * the owner of the object's monitor.
362 * @exception InterruptedException if another thread interrupted the
363 * current thread before or while the current thread
364 * was waiting for a notification. The <i>interrupted
365 * status</i> of the current thread is cleared when
366 * this exception is thrown.
367 * @see java.lang.Object#notify()
368 * @see java.lang.Object#notifyAll()
369 */
370 public final void wait(long timeoutMillis) throws InterruptedException {
371 if (!Thread.currentThread().isVirtual()) {
372 wait0(timeoutMillis);
373 return;
374 }
375
376 // virtual thread waiting
377 boolean attempted = Blocker.begin();
378 try {
379 wait0(timeoutMillis);
380 } catch (InterruptedException e) {
381 // virtual thread's interrupt status needs to be cleared
382 Thread.currentThread().getAndClearInterrupt();
383 throw e;
384 } finally {
385 Blocker.end(attempted);
386 }
387 }
388
389 /**
390 * Causes current thread to wait until another thread invokes the
391 * {@link java.lang.Object#notify()} method or the
392 * {@link java.lang.Object#notifyAll()} method for this object, or
393 * some other thread interrupts the current thread, or a certain
394 * amount of real time has elapsed.
395 * <p>
396 * This method is similar to the <code>wait</code> method of one
397 * argument, but it allows finer control over the amount of time to
398 * wait for a notification before giving up. The amount of real time,
399 * measured in nanoseconds, is given by:
400 * <blockquote>
401 * <pre>
402 * 1000000*timeout+nanos</pre></blockquote>
403 * <p>
404 * In all other respects, this method does the same thing as the
405 * method {@link #wait(long)} of one argument. In particular,
406 * <tt>wait(0, 0)</tt> means the same thing as <tt>wait(0)</tt>.
407 * <p>
408 * The current thread must own this object's monitor. The thread
409 * releases ownership of this monitor and waits until either of the
410 * following two conditions has occurred:
411 * <ul>
412 * <li>Another thread notifies threads waiting on this object's monitor
413 * to wake up either through a call to the <code>notify</code> method
414 * or the <code>notifyAll</code> method.
415 * <li>The timeout period, specified by <code>timeout</code>
416 * milliseconds plus <code>nanos</code> nanoseconds arguments, has
417 * elapsed.
418 * </ul>
419 * <p>
420 * The thread then waits until it can re-obtain ownership of the
421 * monitor and resumes execution.
422 * <p>
423 * As in the one argument version, interrupts and spurious wakeups are
424 * possible, and this method should always be used in a loop:
425 * <pre>
426 * synchronized (obj) {
427 * while (<condition does not hold>)
428 * obj.wait(timeout, nanos);
429 * ... // Perform action appropriate to condition
430 * }
431 * </pre>
432 * This method should only be called by a thread that is the owner
433 * of this object's monitor. See the <code>notify</code> method for a
434 * description of the ways in which a thread can become the owner of
435 * a monitor.
436 *
437 * @param timeout the maximum time to wait in milliseconds.
438 * @param nanos additional time, in nanoseconds range
439 * 0-999999.
440 * @exception IllegalArgumentException if the value of timeout is
441 * negative or the value of nanos is
442 * not in the range 0-999999.
443 * @exception IllegalMonitorStateException if the current thread is not
444 * the owner of this object's monitor.
445 * @exception InterruptedException if another thread interrupted the
446 * current thread before or while the current thread
447 * was waiting for a notification. The <i>interrupted
448 * status</i> of the current thread is cleared when
449 * this exception is thrown.
450 */
451 public final void wait(long timeout, int nanos) throws InterruptedException {
452
453 bi04t002a.instrInvoke(bi04t002a.INSTR_WAIT_JI);
454
455 if (timeout < 0) {
456 throw new IllegalArgumentException("timeout value is negative");
457 }
458
459 if (nanos < 0 || nanos > 999999) {
460 throw new IllegalArgumentException(
461 "nanosecond timeout value out of range");
462 }
463
464 if (nanos >= 500000 || (nanos != 0 && timeout == 0)) {
465 timeout++;
466 }
467
468 wait(timeout);
469 }
470
471 // final modifier so method not in vtable
472 private final native void wait0(long timeoutMillis) throws InterruptedException;
473
474 /**
475 * Causes current thread to wait until another thread invokes the
476 * {@link java.lang.Object#notify()} method or the
477 * {@link java.lang.Object#notifyAll()} method for this object.
478 * In other words, this method behaves exactly as if it simply
479 * performs the call <tt>wait(0)</tt>.
480 * <p>
481 * The current thread must own this object's monitor. The thread
482 * releases ownership of this monitor and waits until another thread
483 * notifies threads waiting on this object's monitor to wake up
484 * either through a call to the <code>notify</code> method or the
485 * <code>notifyAll</code> method. The thread then waits until it can
486 * re-obtain ownership of the monitor and resumes execution.
487 * <p>
488 * As in the one argument version, interrupts and spurious wakeups are
489 * possible, and this method should always be used in a loop:
490 * <pre>
491 * synchronized (obj) {
492 * while (<condition does not hold>)
493 * obj.wait();
494 * ... // Perform action appropriate to condition
495 * }
496 * </pre>
497 * This method should only be called by a thread that is the owner
498 * of this object's monitor. See the <code>notify</code> method for a
499 * description of the ways in which a thread can become the owner of
500 * a monitor.
501 *
502 * @exception IllegalMonitorStateException if the current thread is not
503 * the owner of the object's monitor.
504 * @exception InterruptedException if another thread interrupted the
505 * current thread before or while the current thread
506 * was waiting for a notification. The <i>interrupted
507 * status</i> of the current thread is cleared when
508 * this exception is thrown.
509 * @see java.lang.Object#notify()
510 * @see java.lang.Object#notifyAll()
511 */
512 public final void wait() throws InterruptedException {
513 bi04t002a.instrInvoke(bi04t002a.INSTR_WAIT);
514 wait(0);
515 }
516
517 /**
518 * Called by the garbage collector on an object when garbage collection
519 * determines that there are no more references to the object.
520 * A subclass overrides the <code>finalize</code> method to dispose of
521 * system resources or to perform other cleanup.
522 * <p>
523 * The general contract of <tt>finalize</tt> is that it is invoked
524 * if and when the Java<font size="-2"><sup>TM</sup></font> virtual
525 * machine has determined that there is no longer any
526 * means by which this object can be accessed by any thread that has
527 * not yet died, except as a result of an action taken by the
528 * finalization of some other object or class which is ready to be
529 * finalized. The <tt>finalize</tt> method may take any action, including
530 * making this object available again to other threads; the usual purpose
531 * of <tt>finalize</tt>, however, is to perform cleanup actions before
532 * the object is irrevocably discarded. For example, the finalize method
533 * for an object that represents an input/output connection might perform
534 * explicit I/O transactions to break the connection before the object is
535 * permanently discarded.
536 * <p>
537 * The <tt>finalize</tt> method of class <tt>Object</tt> performs no
538 * special action; it simply returns normally. Subclasses of
539 * <tt>Object</tt> may override this definition.
540 * <p>
541 * The Java programming language does not guarantee which thread will
542 * invoke the <tt>finalize</tt> method for any given object. It is
543 * guaranteed, however, that the thread that invokes finalize will not
544 * be holding any user-visible synchronization locks when finalize is
545 * invoked. If an uncaught exception is thrown by the finalize method,
546 * the exception is ignored and finalization of that object terminates.
547 * <p>
548 * After the <tt>finalize</tt> method has been invoked for an object, no
549 * further action is taken until the Java virtual machine has again
550 * determined that there is no longer any means by which this object can
551 * be accessed by any thread that has not yet died, including possible
552 * actions by other objects or classes which are ready to be finalized,
553 * at which point the object may be discarded.
554 * <p>
555 * The <tt>finalize</tt> method is never invoked more than once by a Java
556 * virtual machine for any given object.
557 * <p>
558 * Any exception thrown by the <code>finalize</code> method causes
559 * the finalization of this object to be halted, but is otherwise
560 * ignored.
561 *
562 * @throws Throwable the <code>Exception</code> raised by this method
563 */
564 protected void finalize() throws Throwable { }
565
566 }