Object源码

// 注释是我写的内容，对一些单词做了查找。

package java.lang;/*** Class {@code Object} is the root of the class hierarchy（英  [ˈhaɪərɑːki]，n. 层级；等级制度）.* Every class has {@code Object} as a superclass. All objects,* including arrays, implement the methods of this class.** @author  unascribed* @see     java.lang.Class* @since   JDK1.0*/
public class Object {private static native void registerNatives();// 当jvm加载类时，静态代码块的内容会先于其他代码块执行，且只会被执行一次static {registerNatives();}/*** Returns the runtime class of this {@code Object}. The returned* {@code Class} object is the object that is locked by {@code* static synchronized（英  ['sɪŋkrənaɪzd]，adj. 同步的；同步化的）} methods of the represented（ 英  [reprɪ'zentɪd]，v. 代表；表现；描写（represent的过去分词）） class.** <p><b>The actual result type is {@code Class<? extends |X|>}* where {@code |X|} is the erasure of the static type of the* expression on which {@code getClass} is called.</b> For* example, no cast is required in this code fragment:</p>** <p>* {@code Number n = 0;                             }<br>* {@code Class<? extends Number> c = n.getClass(); }* </p>** @return The {@code Class} object that represents the runtime*         class of this object.* @jls 15.8.2 Class Literals*/public final native Class<?> getClass();/*** Returns a hash code value for the object. This method is* supported for the benefit of hash tables such as those provided by* {@link java.util.HashMap}.* <p>* The general contract of {@code hashCode} is:* <ul>* <li>Whenever it is invoked on the same object more than once during*     an execution of a Java application, the {@code hashCode} method*     must consistently return the same integer, provided no information*     used in {@code equals} comparisons on the object is modified.*     This integer need not remain consistent from one execution of an*     application to another execution of the same application.* <li>If two objects are equal according to the {@code equals(Object)}*     method, then calling the {@code hashCode} method on each of*     the two objects must produce the same integer result.* <li>It is <em>not</em> required that if two objects are unequal*     according to the {@link java.lang.Object#equals(java.lang.Object)}*     method, then calling the {@code hashCode} method on each of the*     two objects must produce distinct integer results.  However, the*     programmer should be aware that producing distinct integer results*     for unequal objects may improve the performance of hash tables.* </ul>* <p>* As much as is reasonably practical, the hashCode method defined by* class {@code Object} does return distinct integers for distinct* objects. (This is typically implemented by converting the internal* address of the object into an integer, but this implementation* technique is not required by the* Java&trade; programming language.)** @return  a hash code value for this object.* @see     java.lang.Object#equals(java.lang.Object)* @see     java.lang.System#identityHashCode*/// 如果两个对象调equals()返回true，则他们调hashCode()应该相同// 覆盖equals()时总要覆盖hashCode()public native int hashCode();/*** Indicates（v. 表明（indicate的第三人称单数形式）；指示，显示） whether some other object is "equal to" this one.* <p>* The {@code equals} method implements an equivalence relation* on non-null object references:* <ul>* <li>It is <i>reflexive</i>: for any non-null reference value*     {@code x}, {@code x.equals(x)} should return*     {@code true}.* <li>It is <i>symmetric</i>: for any non-null reference values*     {@code x} and {@code y}, {@code x.equals(y)}*     should return {@code true} if and only if*     {@code y.equals(x)} returns {@code true}.* <li>It is <i>transitive</i>: for any non-null reference values*     {@code x}, {@code y}, and {@code z}, if*     {@code x.equals(y)} returns {@code true} and*     {@code y.equals(z)} returns {@code true}, then*     {@code x.equals(z)} should return {@code true}.* <li>It is <i>consistent</i>: for any non-null reference values*     {@code x} and {@code y}, multiple invocations of*     {@code x.equals(y)} consistently return {@code true}*     or consistently return {@code false}, provided no*     information used in {@code equals} comparisons on the*     objects is modified.* <li>For any non-null reference value {@code x},*     {@code x.equals(null)} should return {@code false}.* </ul>* <p>* The {@code equals} method for class {@code Object} implements* the most discriminating possible equivalence relation on objects;* that is, for any non-null reference values {@code x} and* {@code y}, this method returns {@code true} if and only* if {@code x} and {@code y} refer to the same object* ({@code x == y} has the value {@code true}).* <p>* Note that it is generally（ 英  [ˈdʒenrəli]） necessary to override the {@code hashCode}* method whenever this method is overridden, so as to maintain the* general contract for the {@code hashCode} method, which states* that equal objects must have equal hash codes.** @param   obj   the reference object with which to compare.* @return  {@code true} if this object is the same as the obj*          argument; {@code false} otherwise.* @see     #hashCode()* @see     java.util.HashMap*/// 自反性// 对称性// 传递性// 一致性// 任何非null的x，调用x.equals(null)必返回falsepublic boolean equals(Object obj) {return (this == obj);}/*** Creates and returns a copy of this object.  The precise meaning* of "copy" may depend on the class of the object. The general* intent is that, for any object {@code x}, the expression:* <blockquote>* <pre>* x.clone() != x</pre></blockquote>* will be true, and that the expression:* <blockquote>* <pre>* x.clone().getClass() == x.getClass()</pre></blockquote>* will be {@code true}, but these are not absolute requirements.* While it is typically the case that:* <blockquote>* <pre>* x.clone().equals(x)</pre></blockquote>* will be {@code true}, this is not an absolute（英  [ˈæbsəluːt]，adj. 绝对的；完全的；专制的） requirement.* <p>* By convention, the returned object should be obtained by calling* {@code super.clone}.  If a class and all of its superclasses (except* {@code Object}) obey this convention, it will be the case that* {@code x.clone().getClass() == x.getClass()}.* <p>* By convention（英  [kənˈvenʃn]，n. 大会；[法] 惯例；[计] 约定；[法] 协定；习俗）, the object returned by this method should be independent* of this object (which is being cloned).  To achieve this independence,* it may be necessary to modify one or more fields of the object returned* by {@code super.clone} before returning it.  Typically, this means* copying any mutable objects that comprise the internal "deep structure"* of the object being cloned and replacing the references（references，n. [图情] 参考文献；参照；推荐信（reference的复数）） to these* objects with references to the copies.  If a class contains only* primitive fields or references to immutable（英  [ɪˈmjuːtəbl]，adj. 不变的；不可变的；不能变的） objects, then it is usually* the case that no fields in the object returned by {@code super.clone}* need to be modified.* <p>* The method {@code clone} for class {@code Object} performs a* specific cloning operation. First, if the class of this object does* not implement the interface {@code Cloneable}, then a* {@code CloneNotSupportedException} is thrown. Note that all arrays* are considered to implement the interface {@code Cloneable} and that* the return type of the {@code clone} method of an array type {@code T[]}* is {@code T[]} where T is any reference or primitive type.* Otherwise, this method creates a new instance of the class of this* object and initializes（vt. 初始化（initialize的第三人称单数）） all its fields with exactly the contents of* the corresponding fields of this object, as if by assignment; the* contents of the fields are not themselves cloned. Thus, this method* performs a "shallow copy" of this object, not a "deep copy" operation.* <p>* The class {@code Object} does not itself implement the interface* {@code Cloneable}, so calling the {@code clone} method on an object* whose class is {@code Object} will result in throwing an* exception at run time.** @return     a clone of this instance.* @throws  CloneNotSupportedException  if the object's class does not*               support the {@code Cloneable} interface. Subclasses*               that override the {@code clone} method can also*               throw this exception to indicate that an instance cannot*               be cloned.* @see java.lang.Cloneable*/// 子类应该谨慎地覆盖clone()方法，clone()方法的通用约定较弱protected native Object clone() throws CloneNotSupportedException;/*** Returns a string representation（[,reprizen'teiʃən]，n. 代表；表现；表示法；陈述） of the object. In general, the* {@code toString} method returns a string that* "textually represents" this object. The result should* be a concise but informative representation that is easy for a* person to read.* It is recommended that all subclasses override this method.* <p>* The {@code toString} method for class {@code Object}* returns a string consisting of the name of the class of which the* object is an instance, the at-sign character `{@code @}', and* the unsigned hexadecimal representation of the hash code of the* object. In other words, this method returns a string equal to the* value of:* <blockquote>* <pre>* getClass().getName() + '@' + Integer.toHexString(hashCode())* </pre></blockquote>** @return  a string representation of the object.*/// 建议所有的子类都要覆盖此方法public String toString() {return getClass().getName() + "@" + Integer.toHexString(hashCode());}/*** Wakes up a single thread that is waiting on this object's* monitor. If any threads are waiting on this object, one of them* is chosen to be awakened. The choice is arbitrary（英  [ˈɑːbɪtrəri; ˈɑːbɪtri]，adj. [数] 任意的；武断的；专制的） and occurs at* the discretion of the implementation. A thread waits on an object's* monitor by calling one of the {@code wait} methods.* <p>* The awakened thread will not be able to proceed until the current* thread relinquishes the lock on this object. The awakened thread will* compete in the usual manner with any other threads that might be* actively competing to synchronize on this object; for example, the* awakened thread enjoys no reliable privilege or disadvantage in being* the next thread to lock this object.* <p>* This method should only be called by a thread that is the owner* of this object's monitor. A thread becomes the owner of the* object's monitor in one of three ways:* <ul>* <li>By executing a synchronized instance method of that object.* <li>By executing the body of a {@code synchronized} statement*     that synchronizes on the object.* <li>For objects of type {@code Class,} by executing a*     synchronized static method of that class.* </ul>* <p>* Only one thread at a time can own an object's monitor.** @throws  IllegalMonitorStateException  if the current thread is not*               the owner of this object's monitor.* @see        java.lang.Object#notifyAll()* @see        java.lang.Object#wait()*/public final native void notify();/*** Wakes up all threads that are waiting on this object's monitor. A* thread waits on an object's monitor by calling one of the* {@code wait} methods.* <p>* The awakened threads will not be able to proceed until the current* thread relinquishes the lock on this object. The awakened threads* will compete in the usual manner with any other threads that might* be actively competing to synchronize on this object; for example,* the awakened threads enjoy no reliable privilege or disadvantage in* being the next thread to lock this object.* <p>* This method should only be called by a thread that is the owner* of this object's monitor. See the {@code notify} method for a* description of the ways in which a thread can become the owner of* a monitor.** @throws  IllegalMonitorStateException  if the current thread is not*               the owner of this object's monitor.* @see        java.lang.Object#notify()* @see        java.lang.Object#wait()*/public final native void notifyAll();/*** Causes the current thread to wait until either another thread invokes the* {@link java.lang.Object#notify()} method or the* {@link java.lang.Object#notifyAll()} method for this object, or a* specified amount of time has elapsed.* <p>* The current thread must own this object's monitor.* <p>* This method causes the current thread (call it <var>T</var>) to* place itself in the wait set for this object and then to relinquish* any and all synchronization claims on this object. Thread <var>T</var>* becomes disabled for thread scheduling purposes and lies dormant* until one of four things happens:* <ul>* <li>Some other thread invokes the {@code notify} method for this* object and thread <var>T</var> happens to be arbitrarily chosen as* the thread to be awakened.* <li>Some other thread invokes the {@code notifyAll} method for this* object.* <li>Some other thread {@linkplain Thread#interrupt() interrupts}* thread <var>T</var>.* <li>The specified amount of real time has elapsed, more or less.  If* {@code timeout} is zero, however, then real time is not taken into* consideration and the thread simply waits until notified.* </ul>* The thread <var>T</var> is then removed from the wait set for this* object and re-enabled for thread scheduling. It then competes in the* usual manner with other threads for the right to synchronize on the* object; once it has gained control of the object, all its* synchronization claims on the object are restored to the status quo* ante - that is, to the situation as of the time that the {@code wait}* method was invoked. Thread <var>T</var> then returns from the* invocation of the {@code wait} method. Thus, on return from the* {@code wait} method, the synchronization state of the object and of* thread {@code T} is exactly as it was when the {@code wait} method* was invoked.* <p>* A thread can also wake up without being notified, interrupted, or* timing out, a so-called <i>spurious（英  [ˈspjʊəriəs]，adj. 假的；伪造的；欺骗的） wakeup</i>.  While this will rarely* occur in practice, applications must guard against（防止；提防） it by testing for* the condition that should have caused the thread to be awakened, and* continuing to wait if the condition is not satisfied.  In other words,* waits should always occur in loops, like this one:* <pre>*     synchronized (obj) {*         while (&lt;condition does not hold&gt;)*             obj.wait(timeout);*         ... // Perform action appropriate to condition*     }* </pre>* (For more information on this topic, see Section 3.2.3 in Doug Lea's* "Concurrent Programming in Java (Second Edition)" (Addison-Wesley,* 2000), or Item 50 in Joshua Bloch's "Effective Java Programming* Language Guide" (Addison-Wesley, 2001).** <p>If the current thread is {@linkplain java.lang.Thread#interrupt()* interrupted} by any thread before or while it is waiting, then an* {@code InterruptedException} is thrown.  This exception is not* thrown until the lock status of this object has been restored as* described above.** <p>* Note that the {@code wait} method, as it places the current thread* into the wait set for this object, unlocks only this object; any* other objects on which the current thread may be synchronized remain* locked while the thread waits.* <p>* This method should only be called by a thread that is the owner* of this object's monitor. See the {@code notify} method for a* description of the ways in which a thread can become the owner of* a monitor.** @param      timeout   the maximum time to wait in milliseconds.* @throws  IllegalArgumentException      if the value of timeout is*               negative.* @throws  IllegalMonitorStateException  if the current thread is not*               the owner of the object's monitor.* @throws  InterruptedException if any thread interrupted the*             current thread before or while the current thread*             was waiting for a notification.  The <i>interrupted*             status</i> of the current thread is cleared when*             this exception is thrown.* @see        java.lang.Object#notify()* @see        java.lang.Object#notifyAll()*/public final native void wait(long timeout) throws InterruptedException;/*** Causes the current thread to wait until another thread invokes the* {@link java.lang.Object#notify()} method or the* {@link java.lang.Object#notifyAll()} method for this object, or* some other thread interrupts the current thread, or a certain* amount of real time has elapsed.* <p>* This method is similar to the {@code wait} method of one* argument, but it allows finer control over the amount of time to* wait for a notification before giving up. The amount of real time,* measured in nanoseconds, is given by:* <blockquote>* <pre>* 1000000*timeout+nanos</pre></blockquote>* <p>* In all other respects, this method does the same thing as the* method {@link #wait(long)} of one argument. In particular,* {@code wait(0, 0)} means the same thing as {@code wait(0)}.* <p>* The current thread must own this object's monitor. The thread* releases ownership of this monitor and waits until either of the* following two conditions has occurred:* <ul>* <li>Another thread notifies threads waiting on this object's monitor*     to wake up either through a call to the {@code notify} method*     or the {@code notifyAll} method.* <li>The timeout period, specified by {@code timeout}*     milliseconds plus {@code nanos} nanoseconds arguments, has*     elapsed.* </ul>* <p>* The thread then waits until it can re-obtain ownership of the* monitor and resumes execution.* <p>* As in the one argument version, interrupts and spurious wakeups are* possible, and this method should always be used in a loop:* <pre>*     synchronized (obj) {*         while (&lt;condition does not hold&gt;)*             obj.wait(timeout, nanos);*         ... // Perform action appropriate to condition*     }* </pre>* This method should only be called by a thread that is the owner* of this object's monitor. See the {@code notify} method for a* description of the ways in which a thread can become the owner of* a monitor.** @param      timeout   the maximum time to wait in milliseconds.* @param      nanos      additional time, in nanoseconds range*                       0-999999.* @throws  IllegalArgumentException      if the value of timeout is*                      negative or the value of nanos is*                      not in the range 0-999999.* @throws  IllegalMonitorStateException  if the current thread is not*               the owner of this object's monitor.* @throws  InterruptedException if any thread interrupted the*             current thread before or while the current thread*             was waiting for a notification.  The <i>interrupted*             status</i> of the current thread is cleared when*             this exception is thrown.*/public final void wait(long timeout, int nanos) throws InterruptedException {if (timeout < 0) {throw new IllegalArgumentException("timeout value is negative");}if (nanos < 0 || nanos > 999999) {throw new IllegalArgumentException("nanosecond timeout value out of range");}if (nanos > 0) {timeout++;}wait(timeout);}/*** Causes the current thread to wait until another thread invokes the* {@link java.lang.Object#notify()} method or the* {@link java.lang.Object#notifyAll()} method for this object.* In other words, this method behaves exactly as if it simply* performs the call {@code wait(0)}.* <p>* The current thread must own this object's monitor. The thread* releases ownership of this monitor and waits until another thread* notifies threads waiting on this object's monitor to wake up* either through a call to the {@code notify} method or the* {@code notifyAll} method. The thread then waits until it can* re-obtain ownership of the monitor and resumes execution.* <p>* As in the one argument version, interrupts and spurious wakeups are* possible, and this method should always be used in a loop:* <pre>*     synchronized (obj) {*         while (&lt;condition does not hold&gt;)*             obj.wait();*         ... // Perform action appropriate to condition*     }* </pre>* This method should only be called by a thread that is the owner* of this object's monitor. See the {@code notify} method for a* description of the ways in which a thread can become the owner of* a monitor.** @throws  IllegalMonitorStateException  if the current thread is not*               the owner of the object's monitor.* @throws  InterruptedException if any thread interrupted the*             current thread before or while the current thread*             was waiting for a notification.  The <i>interrupted*             status</i> of the current thread is cleared when*             this exception is thrown.* @see        java.lang.Object#notify()* @see        java.lang.Object#notifyAll()*/public final void wait() throws InterruptedException {wait(0);}/*** Called by the garbage collector on an object when garbage collection* determines that there are no more references to the object.* A subclass overrides the {@code finalize} method to dispose of* system resources or to perform other cleanup.* <p>* The general contract of {@code finalize} is that it is invoked* if and when the Java&trade; virtual* machine has determined that there is no longer any* means by which this object can be accessed by any thread that has* not yet died, except as a result of an action taken by the* finalization of some other object or class which is ready to be* finalized. The {@code finalize} method may take any action, including* making this object available again to other threads; the usual purpose* of {@code finalize}, however, is to perform cleanup actions before* the object is irrevocably discarded. For example, the finalize method* for an object that represents an input/output connection might perform* explicit I/O transactions to break the connection before the object is* permanently discarded.* <p>* The {@code finalize} method of class {@code Object} performs no* special action; it simply returns normally. Subclasses of* {@code Object} may override this definition.* <p>* The Java programming language does not guarantee which thread will* invoke the {@code finalize} method for any given object. It is* guaranteed, however, that the thread that invokes finalize will not* be holding any user-visible synchronization locks when finalize is* invoked. If an uncaught exception is thrown by the finalize method,* the exception is ignored and finalization of that object terminates.* <p>* After the {@code finalize} method has been invoked for an object, no* further action is taken until the Java virtual machine has again* determined that there is no longer any means by which this object can* be accessed by any thread that has not yet died, including possible* actions by other objects or classes which are ready to be finalized,* at which point the object may be discarded.* <p>* The {@code finalize} method is never invoked more than once by a Java* virtual machine for any given object.* <p>* Any exception thrown by the {@code finalize} method causes* the finalization of this object to be halted, but is otherwise* ignored.** @throws Throwable the {@code Exception} raised by this method* @see java.lang.ref.WeakReference* @see java.lang.ref.PhantomReference* @jls 12.6 Finalization of Class Instances*/// 与JVM垃圾回收机制有关protected void finalize() throws Throwable { }
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