java.lang
Class Object

java.lang.Object

public class Object

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.

Since:

JDK1.0

Version:

1.54, 02/02/00

Author:

unascribed, Helge Böhme

Available on JControl Devices:

all

Constructor Summary

Object()

Method Summary

protected Object	clone() Creates and returns a copy of this object.
boolean	equals(Object obj) Indicates whether some other object is "equal to" this one.
void	notifyAll() Wakes up all threads that are waiting on this object's monitor.
void	wait() Causes current thread to wait until another thread invokes the notifyAll() method for this object.

Constructor Detail

Object

public Object()

Method Detail

clone

protected Object clone()
                throws CloneNotSupportedException

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. Copying an object will typically entail creating a new instance of its class, but it also may require copying of internal data structures as well. No constructors are called.

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. 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. The clone method is implemented by the class Object as a convenient, general utility for subclasses that implement the interface Cloneable, possibly also overriding the clone method, in which case the overriding definition can refer to this utility definition by the call:

 super.clone()

Returns:

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.

java.lang.OutOfMemoryError - if there is not enough memory.

See Also:

Cloneable

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, provided no information used in equals comparisons on the object 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 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).

Parameters:

obj - the reference object with which to compare.

Returns:

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

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.

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. 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.

See Also:

wait()

wait

public final void wait()
                throws InterruptedException

Causes current thread to wait until another thread invokes 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 through a call to 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 notifyAll 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.

InterruptedException - if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

See Also:

notifyAll()