package java.lang;
/**
* Class Object is the root of the class hierarchy.
* Every class has Object as a superclass. All objects,
* including arrays, implement the methods of this class.
*/
public class Object {
private static native void registerNatives();
static {
registerNatives();
}
/**
* Returns the runtime class of this Object. The returned
* Class object is the object that is locked by
* static synchronized methods of the represented class.
*
* The actual result type is {Class<? extends |X|>}
* where {|X|} is the erasure of the static type of the
* expression on which getClass() is called.For
* example, no cast is required in this code fragment:
*
* Number n = 0;
* Class<? extends Number> c = n.getClass();
*
* @return The {Class} object that represents the runtime class of this object.
*/
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 HashMap.
*
* The general contract of hashCode is:
*
* Whenever it is invoked on the same object more than once during
* an execution of a Java application, the hashCode() method
* must consistently return the same integer, provided no information
* used in 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.
*
* If two objects are equal according to the equals(Object)
* method, then calling the hashCode() method on each of
* the two objects must produce the same integer result.
*
* It is not required that if two objects are unequal
* according to the {java.lang.Object#equals(Object)}
* method, then calling the 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.
*
* As much as is reasonably practical, the hashCode() method defined by
* class 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™ programming language.
*
* @return a hash code value for this object.
*/
public native int hashCode();
/**
* Indicates whether some other object is "equal to" this one.
*
* The equals() method implements an equivalence relation
* on non-null object references:
*
* It is reflexive: for any non-null reference value
* {x}, {x.equals(x)} should return {true}.
*
* It is symmetric: for any non-null reference values
* {x} and {y}, {x.equals(y)} should return {true} if and only if
* {y.equals(x)} returns {true}.
*
* It is transitive: for any non-null reference values
* {x}, {y}, and {z}, if {x.equals(y)} returns {true} and
* {y.equals(z)} returns {true}, then {x.equals(z)} should return {true}.
*
* It is consistent: for any non-null reference values
* {x} and {y}, multiple invocations of
* {x.equals(y)} consistently return {true}
* or consistently return {false}, provided no
* information used in {equals} comparisons on the
* objects is modified.
*
* For any non-null reference value {x},
* {x.equals(null)} should return {false}.
*
* The equals() method for class {Object} implements
* the most discriminating(区别) possible equivalence relation on objects;
* that is, for any non-null reference values {x} and
* {y}, this method returns {true} if and only
* if {x} and {y} refer to the same object
* {x == y} has the value {true}.
*
* Note that it is generally necessary to override the hashCode()
* method whenever this method is overridden, so as to maintain the
* general contract for the hashCode() method, which states
* that equal objects must have equal hash codes.
*
* @param obj the reference object with which to compare.
* @return {true} if this object is the same as the obj argument; {false} otherwise.
*/
public 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 {x}, the expression:
*
* x.clone() != x
* will be true, and that the expression:
*
* x.clone().getClass() == x.getClass()
* will be {true}, but these are not absolute requirements.
* While it is typically the case that:
*
* x.clone().equals(x)
* will be {true}, this is not an absolute requirement.
*
* By convention, the returned object should be obtained by calling
* {super.clone}. If a class and all of its superclasses (except
* {Object}) obey this convention, it will be the case that
* {x.clone().getClass() == x.getClass()}.
*
* By convention, 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 {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 to these
* objects with references to the copies. If a class contains only
* primitive fields or references to immutable objects, then it is usually
* the case that no fields in the object returned by {super.clone}
* need to be modified.
*
* The method clone() for class {Object} performs a
* specific cloning operation. First, if the class of this object does
* not implement the interface {Cloneable}, then a
* {CloneNotSupportedException} is thrown. Note that all arrays
* are considered to implement the interface {Cloneable} and that
* the return type of the clone() method of an array type {T[]}
* is {T[]} where T is any reference or primitive type.
* Otherwise, this method creates a new instance of the class of this
* object and initializes 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.
*
* The class {Object} does not itself implement the interface
* {Cloneable}, so calling the clone() method on an object
* whose class is {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 {Cloneable} interface. Subclasses
* that override the clone() method can also
* throw this exception to indicate that an instance cannot
* be cloned.
*/
protected native Object clone() throws CloneNotSupportedException;
/**
* Returns a string representation of the object. In general, the
* 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.
*
* The toString() method for class Object
* returns a string consisting of the name of the class of which the
* object is an instance, the at-sign character {@}, 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:
* getClass().getName() + ‘@‘ + Integer.toHexString(hashCode())
*
* @return a string representation of the object.
*/
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 and occurs at
* the discretion of the implementation. A thread waits on an object‘s
* monitor by calling one of the wait() methods.
*
* 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.
*
* 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:
*
* By executing a synchronized instance method of that object.
* By executing the body of a synchronized statement
* that synchronizes on the object.
* For objects of type Class by executing a
* synchronized static method of that class.
*
* 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.
*/
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 wait() methods.
*
* 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.
*
* This method should only be called by a thread that is the owner
* of this object‘s monitor. See the 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.
*/
public final native void notifyAll();
/**
* Causes the current thread to wait until either another thread invokes the
* notify() method or the notifyAll() method for this object, or a
* specified amount of time has elapsed.
*
* The current thread must own this object‘s monitor.
*
* This method causes the current thread (call it T) to
* place itself in the wait set for this object and then to relinquish
* any and all synchronization claims on this object. Thread T
* becomes disabled for thread scheduling purposes and lies dormant
* until one of four things happens:
*
* Some other thread invokes the notify() method for this
* object and thread T happens to be arbitrarily chosen as
* the thread to be awakened.
* Some other thread invokes the notifyAll() method for this
* object.
* Some other thread Thread#interrupt() interrupts
* thread T.
* The specified amount of real time has elapsed, more or less. If
* timeout is zero, however, then real time is not taken into
* consideration and the thread simply waits until notified.
*
* The thread T 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 wait()
* method was invoked. Thread T then returns from the
* invocation of the wait() method. Thus, on return from the
* wait() method, the synchronization state of the object and of
* thread T is exactly as it was when the wait() method
* was invoked.
*
* A thread can also wake up without being notified, interrupted, or
* timing out, a so-called spurious wakeup. While this will rarely
* occur in practice, applications must guard against 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:
*
* synchronized (obj) {
* while (<condition does not hold>)
* obj.wait(timeout);
* ... // Perform action appropriate to condition
* }
*
* If the current thread is interrupted
* by any thread before or while it is waiting, then an
* InterruptedException is thrown. This exception is not
* thrown until the lock status of this object has been restored as
* described above.
*
* Note that the 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.
*
* This method should only be called by a thread that is the owner
* of this object‘s monitor. See the 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 interrupted
* status of the current thread is cleared when
* this exception is thrown.
*/
public final native void wait(long timeout) throws InterruptedException;
/**
* Causes the current thread to wait until another thread invokes the
* notify()method or the notifyAll() method for this object, or
* some other thread interrupts the current thread, or a certain
* amount of real time has elapsed.
*
* This method is similar to the 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:
* 1000000*timeout+nanos
*
* In all other respects, this method does the same thing as the
* method wait(long) of one argument. In particular,
* wait(0, 0) means the same thing as wait(0).
*
* 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:
*
* 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 timeout period, specified by timeout
* milliseconds plus {@code nanos} nanoseconds arguments, has
* elapsed.
*
* The thread then waits until it can re-obtain ownership of the
* monitor and resumes execution.
*
* As in the one argument version, interrupts and spurious wakeups are
* possible, and this method should always be used in a loop:
*
* synchronized (obj) {
* while (<condition does not hold>)
* obj.wait(timeout, nanos);
* ... // Perform action appropriate to condition
* }
*
* This method should only be called by a thread that is the owner
* of this object‘s monitor. See the 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 interrupted
* status 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
* notify() method or the notifyAll() method for this object.
* In other words, this method behaves exactly as if it simply
* performs the call wait(0).
*
* 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 notify() method or the
* notifyAll() method. The thread then waits until it can
* re-obtain ownership of the monitor and resumes execution.
*
* As in the one argument version, interrupts and spurious wakeups are
* possible, and this method should always be used in a loop:
*
* synchronized (obj) {
* while (condition does not hold)
* obj.wait();
* ... // Perform action appropriate to condition
* }
*
* This method should only be called by a thread that is the owner
* of this object‘s monitor. See the 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 interrupted
* status of the current thread is cleared when
* this exception is thrown.
*/
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 finalize() method to dispose of
* system resources or to perform other cleanup.
*
* The general contract of finalize is that it is invoked
* if and when the Java™ 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 finalize method() may take any action, including
* making this object available again to other threads; the usual purpose
* of 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.
*
* The finalize() method of class Object performs no
* special action; it simply returns normally. Subclasses of
* Object may override this definition.
*
* The Java programming language does not guarantee which thread will
* invoke the 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.
*
* After the 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.
*
* The finalize() method is never invoked more than once by a Java
* virtual machine for any given object.
*
* Any exception thrown by the finalize() method causes
* the finalization of this object to be halted, but is otherwise
* ignored.
*
* @throws Throwable the Exception raised by this method.
*/
protected void finalize() throws Throwable { }
}
原文：https://www.cnblogs.com/feiqiangsheng/p/15220234.html