JDK 1.8中Object 的源码如下：
1 public class Object {
2
3 private static native void registerNatives();
4 static {
5 registerNatives();
6 }
7
8 /**
9 * Returns the runtime class of this {@code Object}. The returned
10 * {@code Class} object is the object that is locked by {@code
11 * static synchronized} methods of the represented class.
12 *
13 * <p><b>The actual result type is {@code Class<? extends |X|>}
14 * where {@code |X|} is the erasure of the static type of the
15 * expression on which {@code getClass} is called.</b> For
16 * example, no cast is required in this code fragment:</p>
17 *
18 * <p>
19 * {@code Number n = 0; }<br>
20 * {@code Class<? extends Number> c = n.getClass(); }
21 * </p>
22 *
23 * @return The {@code Class} object that represents the runtime
24 * class of this object.
25 * @jls 15.8.2 Class Literals
26 */
27 public final native Class<?> getClass();
28
29 /**
30 * Returns a hash code value for the object. This method is
31 * supported for the benefit of hash tables such as those provided by
32 * {@link java.util.HashMap}.
33 * <p>
34 * The general contract of {@code hashCode} is:
35 * <ul>
36 * <li>Whenever it is invoked on the same object more than once during
37 * an execution of a Java application, the {@code hashCode} method
38 * must consistently return the same integer, provided no information
39 * used in {@code equals} comparisons on the object is modified.
40 * This integer need not remain consistent from one execution of an
41 * application to another execution of the same application.
42 * <li>If two objects are equal according to the {@code equals(Object)}
43 * method, then calling the {@code hashCode} method on each of
44 * the two objects must produce the same integer result.
45 * <li>It is <em>not</em> required that if two objects are unequal
46 * according to the {@link java.lang.Object#equals(java.lang.Object)}
47 * method, then calling the {@code hashCode} method on each of the
48 * two objects must produce distinct integer results. However, the
49 * programmer should be aware that producing distinct integer results
50 * for unequal objects may improve the performance of hash tables.
51 * </ul>
52 * <p>
53 * As much as is reasonably practical, the hashCode method defined by
54 * class {@code Object} does return distinct integers for distinct
55 * objects. (This is typically implemented by converting the internal
56 * address of the object into an integer, but this implementation
57 * technique is not required by the
58 * Java™ programming language.)
59 *
60 * @return a hash code value for this object.
61 * @see java.lang.Object#equals(java.lang.Object)
62 * @see java.lang.System#identityHashCode
63 */
64 public native int hashCode();
65
66 /**
67 * Indicates whether some other object is "equal to" this one.
68 * <p>
69 * The {@code equals} method implements an equivalence relation
70 * on non-null object references:
71 * <ul>
72 * <li>It is <i>reflexive</i>: for any non-null reference value
73 * {@code x}, {@code x.equals(x)} should return
74 * {@code true}.
75 * <li>It is <i>symmetric</i>: for any non-null reference values
76 * {@code x} and {@code y}, {@code x.equals(y)}
77 * should return {@code true} if and only if
78 * {@code y.equals(x)} returns {@code true}.
79 * <li>It is <i>transitive</i>: for any non-null reference values
80 * {@code x}, {@code y}, and {@code z}, if
81 * {@code x.equals(y)} returns {@code true} and
82 * {@code y.equals(z)} returns {@code true}, then
83 * {@code x.equals(z)} should return {@code true}.
84 * <li>It is <i>consistent</i>: for any non-null reference values
85 * {@code x} and {@code y}, multiple invocations of
86 * {@code x.equals(y)} consistently return {@code true}
87 * or consistently return {@code false}, provided no
88 * information used in {@code equals} comparisons on the
89 * objects is modified.
90 * <li>For any non-null reference value {@code x},
91 * {@code x.equals(null)} should return {@code false}.
92 * </ul>
93 * <p>
94 * The {@code equals} method for class {@code Object} implements
95 * the most discriminating possible equivalence relation on objects;
96 * that is, for any non-null reference values {@code x} and
97 * {@code y}, this method returns {@code true} if and only
98 * if {@code x} and {@code y} refer to the same object
99 * ({@code x == y} has the value {@code true}).
100 * <p>
101 * Note that it is generally necessary to override the {@code hashCode}
102 * method whenever this method is overridden, so as to maintain the
103 * general contract for the {@code hashCode} method, which states
104 * that equal objects must have equal hash codes.
105 *
106 * @param obj the reference object with which to compare.
107 * @return {@code true} if this object is the same as the obj
108 * argument; {@code false} otherwise.
109 * @see #hashCode()
110 * @see java.util.HashMap
111 */
112 public boolean equals(Object obj) {
113 return (this == obj);
114 }
115
116 /**
117 * Creates and returns a copy of this object. The precise meaning
118 * of "copy" may depend on the class of the object. The general
119 * intent is that, for any object {@code x}, the expression:
120 * <blockquote>
121 * <pre>
122 * x.clone() != x</pre></blockquote>
123 * will be true, and that the expression:
124 * <blockquote>
125 * <pre>
126 * x.clone().getClass() == x.getClass()</pre></blockquote>
127 * will be {@code true}, but these are not absolute requirements.
128 * While it is typically the case that:
129 * <blockquote>
130 * <pre>
131 * x.clone().equals(x)</pre></blockquote>
132 * will be {@code true}, this is not an absolute requirement.
133 * <p>
134 * By convention, the returned object should be obtained by calling
135 * {@code super.clone}. If a class and all of its superclasses (except
136 * {@code Object}) obey this convention, it will be the case that
137 * {@code x.clone().getClass() == x.getClass()}.
138 * <p>
139 * By convention, the object returned by this method should be independent
140 * of this object (which is being cloned). To achieve this independence,
141 * it may be necessary to modify one or more fields of the object returned
142 * by {@code super.clone} before returning it. Typically, this means
143 * copying any mutable objects that comprise the internal "deep structure"
144 * of the object being cloned and replacing the references to these
145 * objects with references to the copies. If a class contains only
146 * primitive fields or references to immutable objects, then it is usually
147 * the case that no fields in the object returned by {@code super.clone}
148 * need to be modified.
149 * <p>
150 * The method {@code clone} for class {@code Object} performs a
151 * specific cloning operation. First, if the class of this object does
152 * not implement the interface {@code Cloneable}, then a
153 * {@code CloneNotSupportedException} is thrown. Note that all arrays
154 * are considered to implement the interface {@code Cloneable} and that
155 * the return type of the {@code clone} method of an array type {@code T[]}
156 * is {@code T[]} where T is any reference or primitive type.
157 * Otherwise, this method creates a new instance of the class of this
158 * object and initializes all its fields with exactly the contents of
159 * the corresponding fields of this object, as if by assignment; the
160 * contents of the fields are not themselves cloned. Thus, this method
161 * performs a "shallow copy" of this object, not a "deep copy" operation.
162 * <p>
163 * The class {@code Object} does not itself implement the interface
164 * {@code Cloneable}, so calling the {@code clone} method on an object
165 * whose class is {@code Object} will result in throwing an
166 * exception at run time.
167 *
168 * @return a clone of this instance.
169 * @throws CloneNotSupportedException if the object's class does not
170 * support the {@code Cloneable} interface. Subclasses
171 * that override the {@code clone} method can also
172 * throw this exception to indicate that an instance cannot
173 * be cloned.
174 * @see java.lang.Cloneable
175 */
176 protected native Object clone() throws CloneNotSupportedException;
177
178 /**
179 * Returns a string representation of the object. In general, the
180 * {@code toString} method returns a string that
181 * "textually represents" this object. The result should
182 * be a concise but informative representation that is easy for a
183 * person to read.
184 * It is recommended that all subclasses override this method.
185 * <p>
186 * The {@code toString} method for class {@code Object}
187 * returns a string consisting of the name of the class of which the
188 * object is an instance, the at-sign character `{@code @}', and
189 * the unsigned hexadecimal representation of the hash code of the
190 * object. In other words, this method returns a string equal to the
191 * value of:
192 * <blockquote>
193 * <pre>
194 * getClass().getName() + '@' + Integer.toHexString(hashCode())
195 * </pre></blockquote>
196 *
197 * @return a string representation of the object.
198 */
199 public String toString() {
200 return getClass().getName() + "@" + Integer.toHexString(hashCode());
201 }
202
203 /**
204 * Wakes up a single thread that is waiting on this object's
205 * monitor. If any threads are waiting on this object, one of them
206 * is chosen to be awakened. The choice is arbitrary and occurs at
207 * the discretion of the implementation. A thread waits on an object's
208 * monitor by calling one of the {@code wait} methods.
209 * <p>
210 * The awakened thread will not be able to proceed until the current
211 * thread relinquishes the lock on this object. The awakened thread will
212 * compete in the usual manner with any other threads that might be
213 * actively competing to synchronize on this object; for example, the
214 * awakened thread enjoys no reliable privilege or disadvantage in being
215 * the next thread to lock this object.
216 * <p>
217 * This method should only be called by a thread that is the owner
218 * of this object's monitor. A thread becomes the owner of the
219 * object's monitor in one of three ways:
220 * <ul>
221 * <li>By executing a synchronized instance method of that object.
222 * <li>By executing the body of a {@code synchronized} statement
223 * that synchronizes on the object.
224 * <li>For objects of type {@code Class,} by executing a
225 * synchronized static method of that class.
226 * </ul>
227 * <p>
228 * Only one thread at a time can own an object's monitor.
229 *
230 * @throws IllegalMonitorStateException if the current thread is not
231 * the owner of this object's monitor.
232 * @see java.lang.Object#notifyAll()
233 * @see java.lang.Object#wait()
234 */
235 public final native void notify();
236
237 /**
238 * Wakes up all threads that are waiting on this object's monitor. A
239 * thread waits on an object's monitor by calling one of the
240 * {@code wait} methods.
241 * <p>
242 * The awakened threads will not be able to proceed until the current
243 * thread relinquishes the lock on this object. The awakened threads
244 * will compete in the usual manner with any other threads that might
245 * be actively competing to synchronize on this object; for example,
246 * the awakened threads enjoy no reliable privilege or disadvantage in
247 * being the next thread to lock this object.
248 * <p>
249 * This method should only be called by a thread that is the owner
250 * of this object's monitor. See the {@code notify} method for a
251 * description of the ways in which a thread can become the owner of
252 * a monitor.
253 *
254 * @throws IllegalMonitorStateException if the current thread is not
255 * the owner of this object's monitor.
256 * @see java.lang.Object#notify()
257 * @see java.lang.Object#wait()
258 */
259 public final native void notifyAll();
260
261 /**
262 * Causes the current thread to wait until either another thread invokes the
263 * {@link java.lang.Object#notify()} method or the
264 * {@link java.lang.Object#notifyAll()} method for this object, or a
265 * specified amount of time has elapsed.
266 * <p>
267 * The current thread must own this object's monitor.
268 * <p>
269 * This method causes the current thread (call it <var>T</var>) to
270 * place itself in the wait set for this object and then to relinquish
271 * any and all synchronization claims on this object. Thread <var>T</var>
272 * becomes disabled for thread scheduling purposes and lies dormant
273 * until one of four things happens:
274 * <ul>
275 * <li>Some other thread invokes the {@code notify} method for this
276 * object and thread <var>T</var> happens to be arbitrarily chosen as
277 * the thread to be awakened.
278 * <li>Some other thread invokes the {@code notifyAll} method for this
279 * object.
280 * <li>Some other thread {@linkplain Thread#interrupt() interrupts}
281 * thread <var>T</var>.
282 * <li>The specified amount of real time has elapsed, more or less. If
283 * {@code timeout} is zero, however, then real time is not taken into
284 * consideration and the thread simply waits until notified.
285 * </ul>
286 * The thread <var>T</var> is then removed from the wait set for this
287 * object and re-enabled for thread scheduling. It then competes in the
288 * usual manner with other threads for the right to synchronize on the
289 * object; once it has gained control of the object, all its
290 * synchronization claims on the object are restored to the status quo
291 * ante - that is, to the situation as of the time that the {@code wait}
292 * method was invoked. Thread <var>T</var> then returns from the
293 * invocation of the {@code wait} method. Thus, on return from the
294 * {@code wait} method, the synchronization state of the object and of
295 * thread {@code T} is exactly as it was when the {@code wait} method
296 * was invoked.
297 * <p>
298 * A thread can also wake up without being notified, interrupted, or
299 * timing out, a so-called <i>spurious wakeup</i>. While this will rarely
300 * occur in practice, applications must guard against it by testing for
301 * the condition that should have caused the thread to be awakened, and
302 * continuing to wait if the condition is not satisfied. In other words,
303 * waits should always occur in loops, like this one:
304 * <pre>
305 * synchronized (obj) {
306 * while (<condition does not hold>)
307 * obj.wait(timeout);
308 * ... // Perform action appropriate to condition
309 * }
310 * </pre>
311 * (For more information on this topic, see Section 3.2.3 in Doug Lea's
312 * "Concurrent Programming in Java (Second Edition)" (Addison-Wesley,
313 * 2000), or Item 50 in Joshua Bloch's "Effective Java Programming
314 * Language Guide" (Addison-Wesley, 2001).
315 *
316 * <p>If the current thread is {@linkplain java.lang.Thread#interrupt()
317 * interrupted} by any thread before or while it is waiting, then an
318 * {@code InterruptedException} is thrown. This exception is not
319 * thrown until the lock status of this object has been restored as
320 * described above.
321 *
322 * <p>
323 * Note that the {@code wait} method, as it places the current thread
324 * into the wait set for this object, unlocks only this object; any
325 * other objects on which the current thread may be synchronized remain
326 * locked while the thread waits.
327 * <p>
328 * This method should only be called by a thread that is the owner
329 * of this object's monitor. See the {@code notify} method for a
330 * description of the ways in which a thread can become the owner of
331 * a monitor.
332 *
333 * @param timeout the maximum time to wait in milliseconds.
334 * @throws IllegalArgumentException if the value of timeout is
335 * negative.
336 * @throws IllegalMonitorStateException if the current thread is not
337 * the owner of the object's monitor.
338 * @throws InterruptedException if any thread interrupted the
339 * current thread before or while the current thread
340 * was waiting for a notification. The <i>interrupted
341 * status</i> of the current thread is cleared when
342 * this exception is thrown.
343 * @see java.lang.Object#notify()
344 * @see java.lang.Object#notifyAll()
345 */
346 public final native void wait(long timeout) throws InterruptedException;
347
348 /**
349 * Causes the current thread to wait until another thread invokes the
350 * {@link java.lang.Object#notify()} method or the
351 * {@link java.lang.Object#notifyAll()} method for this object, or
352 * some other thread interrupts the current thread, or a certain
353 * amount of real time has elapsed.
354 * <p>
355 * This method is similar to the {@code wait} method of one
356 * argument, but it allows finer control over the amount of time to
357 * wait for a notification before giving up. The amount of real time,
358 * measured in nanoseconds, is given by:
359 * <blockquote>
360 * <pre>
361 * 1000000*timeout+nanos</pre></blockquote>
362 * <p>
363 * In all other respects, this method does the same thing as the
364 * method {@link #wait(long)} of one argument. In particular,
365 * {@code wait(0, 0)} means the same thing as {@code wait(0)}.
366 * <p>
367 * The current thread must own this object's monitor. The thread
368 * releases ownership of this monitor and waits until either of the
369 * following two conditions has occurred:
370 * <ul>
371 * <li>Another thread notifies threads waiting on this object's monitor
372 * to wake up either through a call to the {@code notify} method
373 * or the {@code notifyAll} method.
374 * <li>The timeout period, specified by {@code timeout}
375 * milliseconds plus {@code nanos} nanoseconds arguments, has
376 * elapsed.
377 * </ul>
378 * <p>
379 * The thread then waits until it can re-obtain ownership of the
380 * monitor and resumes execution.
381 * <p>
382 * As in the one argument version, interrupts and spurious wakeups are
383 * possible, and this method should always be used in a loop:
384 * <pre>
385 * synchronized (obj) {
386 * while (<condition does not hold>)
387 * obj.wait(timeout, nanos);
388 * ... // Perform action appropriate to condition
389 * }
390 * </pre>
391 * This method should only be called by a thread that is the owner
392 * of this object's monitor. See the {@code notify} method for a
393 * description of the ways in which a thread can become the owner of
394 * a monitor.
395 *
396 * @param timeout the maximum time to wait in milliseconds.
397 * @param nanos additional time, in nanoseconds range
398 * 0-999999.
399 * @throws IllegalArgumentException if the value of timeout is
400 * negative or the value of nanos is
401 * not in the range 0-999999.
402 * @throws IllegalMonitorStateException if the current thread is not
403 * the owner of this object's monitor.
404 * @throws InterruptedException if any thread interrupted the
405 * current thread before or while the current thread
406 * was waiting for a notification. The <i>interrupted
407 * status</i> of the current thread is cleared when
408 * this exception is thrown.
409 */
410 public final void wait(long timeout, int nanos) throws InterruptedException {
411 if (timeout < 0) {
412 throw new IllegalArgumentException("timeout value is negative");
413 }
414
415 if (nanos < 0 || nanos > 999999) {
416 throw new IllegalArgumentException(
417 "nanosecond timeout value out of range");
418 }
419
420 if (nanos > 0) {
421 timeout++;
422 }
423
424 wait(timeout);
425 }
426
427 /**
428 * Causes the current thread to wait until another thread invokes the
429 * {@link java.lang.Object#notify()} method or the
430 * {@link java.lang.Object#notifyAll()} method for this object.
431 * In other words, this method behaves exactly as if it simply
432 * performs the call {@code wait(0)}.
433 * <p>
434 * The current thread must own this object's monitor. The thread
435 * releases ownership of this monitor and waits until another thread
436 * notifies threads waiting on this object's monitor to wake up
437 * either through a call to the {@code notify} method or the
438 * {@code notifyAll} method. The thread then waits until it can
439 * re-obtain ownership of the monitor and resumes execution.
440 * <p>
441 * As in the one argument version, interrupts and spurious wakeups are
442 * possible, and this method should always be used in a loop:
443 * <pre>
444 * synchronized (obj) {
445 * while (<condition does not hold>)
446 * obj.wait();
447 * ... // Perform action appropriate to condition
448 * }
449 * </pre>
450 * This method should only be called by a thread that is the owner
451 * of this object's monitor. See the {@code notify} method for a
452 * description of the ways in which a thread can become the owner of
453 * a monitor.
454 *
455 * @throws IllegalMonitorStateException if the current thread is not
456 * the owner of the object's monitor.
457 * @throws InterruptedException if any thread interrupted the
458 * current thread before or while the current thread
459 * was waiting for a notification. The <i>interrupted
460 * status</i> of the current thread is cleared when
461 * this exception is thrown.
462 * @see java.lang.Object#notify()
463 * @see java.lang.Object#notifyAll()
464 */
465 public final void wait() throws InterruptedException {
466 wait(0);
467 }
468
469 /**
470 * Called by the garbage collector on an object when garbage collection
471 * determines that there are no more references to the object.
472 * A subclass overrides the {@code finalize} method to dispose of
473 * system resources or to perform other cleanup.
474 * <p>
475 * The general contract of {@code finalize} is that it is invoked
476 * if and when the Java™ virtual
477 * machine has determined that there is no longer any
478 * means by which this object can be accessed by any thread that has
479 * not yet died, except as a result of an action taken by the
480 * finalization of some other object or class which is ready to be
481 * finalized. The {@code finalize} method may take any action, including
482 * making this object available again to other threads; the usual purpose
483 * of {@code finalize}, however, is to perform cleanup actions before
484 * the object is irrevocably discarded. For example, the finalize method
485 * for an object that represents an input/output connection might perform
486 * explicit I/O transactions to break the connection before the object is
487 * permanently discarded.
488 * <p>
489 * The {@code finalize} method of class {@code Object} performs no
490 * special action; it simply returns normally. Subclasses of
491 * {@code Object} may override this definition.
492 * <p>
493 * The Java programming language does not guarantee which thread will
494 * invoke the {@code finalize} method for any given object. It is
495 * guaranteed, however, that the thread that invokes finalize will not
496 * be holding any user-visible synchronization locks when finalize is
497 * invoked. If an uncaught exception is thrown by the finalize method,
498 * the exception is ignored and finalization of that object terminates.
499 * <p>
500 * After the {@code finalize} method has been invoked for an object, no
501 * further action is taken until the Java virtual machine has again
502 * determined that there is no longer any means by which this object can
503 * be accessed by any thread that has not yet died, including possible
504 * actions by other objects or classes which are ready to be finalized,
505 * at which point the object may be discarded.
506 * <p>
507 * The {@code finalize} method is never invoked more than once by a Java
508 * virtual machine for any given object.
509 * <p>
510 * Any exception thrown by the {@code finalize} method causes
511 * the finalization of this object to be halted, but is otherwise
512 * ignored.
513 *
514 * @throws Throwable the {@code Exception} raised by this method
515 * @see java.lang.ref.WeakReference
516 * @see java.lang.ref.PhantomReference
517 * @jls 12.6 Finalization of Class Instances
518 */
519 protected void finalize() throws Throwable { }
520 }
所以Object的所有方法如下：
需要注意的是：其中：这些方法是 被 native 关键字修饰的
1 registerNatives();
2 getClass();
3 hashCode();
4 clone();
5 notify();
6 notifyAll();
7 wait(long timeout)
备注下：native 关键字主要是说明，这是java对外的方法定义，是与其他语言(C语言)的沟通
官方的解释如下：
native关键字说明其修饰的方法是一个原生态方法，方法对应的实现不是在当前文件，而是在用其他语言（如C和C++）实现的文件中。Java语言本身不能对操作系统底层进行访问和操作，但是可以通过JNI接口调用其他语言来实现对底层的访问。
JNI是Java本机接口（Java Native Interface），是一个本机编程接口，它是Java软件开发工具箱（Java Software Development Kit，SDK）的一部分。JNI允许Java代码使用以其他语言编写的代码和代码库。Invocation API（JNI的一部分）可以用来将Java虚拟机（JVM）嵌入到本机应用程序中，从而允许程序员从本机代码内部调用Java代码。
参考文章：http://www.cnblogs.com/huzi007/p/3982026.html
深入了解每个方法的解释可以参考这篇文章