Package java.lang

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Class Object

public  class  java.lang.Object
{
        // Constructors
    public Object();	

        // Methods
    protected Object clone();	
    public boolean equals(Object  obj);	
    protected void finalize();	
    public final Class getClass();	
    public int hashCode();	
    public final void notify();	
    public final void notifyAll();	
    public String toString();	
    public final void wait();	
    public final void wait(long  timeout);	
    public final void wait(long  timeout, int  nanos);	
}

Class Object is the root of the class hierarchy. Every class has Object as a superclass. parent. All objects, including arrays, implement the methods of this class.

Constructors

Object

public Object() 

Allocates a new instance of class Object.

Methods

clone

protected Object clone() 

throws CloneNotSupportedException 

The clone method of class Object creates a new object of the same class as this object. It then initializes each of the new object's fields by assigning it the same value as the corresponding field in this object. No constructor is called.

The clone method of class Object will only clone an object whose class indicates that it is willing for its instances to be cloned. A class indicates that its instances can be cloned by declaring that it implements the Cloneable interface.

Return Value:

Returns a clone of this instance.

Throw:

OutOfMemoryError

If there is not enough memory.

Throw:

CloneNotSupportedException

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.

equals

public boolean equals(Object  obj) 

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation:

• It is reflexive: for any reference value x, x.equals(x) should return true.

• It is symmetric: for any 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 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 reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false.
• For any reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any 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).

Return Value:

Returns true if this object is the same as the obj argument; false otherwise.

Parameter	Description
obj	the reference object with which to compare

See Also: Hashtable

hashCode (hashCode).

finalize

protected void finalize() 

throws Throwable 

The finalize method is 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 in order to dispose of system resources or to perform other cleanup.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

The finalize method in Object does nothing.

getClass

public final Class getClass() 

Determines the run-time class of an object.

Return Value:

Returns the object of type Class that represents the run-time class of the object.

hashCode

public int hashCode() 

Calculates a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by java.util.Hashtable .

The general contract of hashCode is:

• Whenever invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer. 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 method , then calling the hashCode method on each of the two objects must produce the same integer result.

Return Value:

Returns a hash code value for this object.

notify

public final void notify() 

Wakes up a single thread that is waiting on this object's monitor. A thread waits on an object's monitor by calling one of the wait methods .

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 only an object's monitor.

Throw:

IllegalMonitorStateException

If the current thread is not the owner of this object's monitor.

See Also: notifyAll .

notifyAll

public final void notifyAll() 

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 .

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.

Throw:

IllegalMonitorStateException

If the current thread is not the owner of this object's monitor.

toString

public String toString() 

Creates 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.

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(1).

Return Value:

Returns A string representation of the object.

wait

public final void wait() 

throws InterruptedException 

Waits to be notified by another thread of a change in this object.

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.

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.

Throw:

IllegalMonitorStateException

If the current thread is not the owner of the object's monitor.

Throw:

InterruptedException

Another thread has interrupted this thread.

wait

public final void wait(long  timeout) 

throws InterruptedException 

Waits to be notified by another thread of a change in this object.

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 notify method or the notifyAll method.

• The timeout period, specified by the timeout argument is milliseconds, has elapsed.

The thread then waits until it can re-obtain ownership of the monitor and resumes execution

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.

Parameter	Description
timeout	the maximum time to wait in milliseconds

Throw:

IllegalMonitorStateException

If the current thread is not the owner of the object's monitor.

Throw:

InterruptedException Another thread has interrupted this thread.

wait

public final void wait(long  timeout, int  nanos) 

throws InterruptedException 

Waits to be notified by another thread of a change in this object.

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 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 notify method or the notifyAll method.

• The timeout period, specified by timeout milliseconds plus nanos nanoseconds arguments has elapsed.

The thread then waits until it can re-obtain ownership of the monitor and resumes execution

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.

Parameter	Description
timeout	the maximum time to wait in milliseconds
nano	additional time, in nanoseconds range 0-999999

Throw:

IllegalMonitorStateException

If the current thread is not the owner of this object's monitor.

Throw:

InterruptedException

Another thread has interrupted this thread.

Footnotes

(1)In Java 1.0, the hexidecimal string printed after the `@' is based on the hash code value, but may not be the actual hash code value.