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.

See Also:
Class
Since:
JDK1.0

Constructor Summary
Object()
           
 
Method Summary
 boolean equals(Object obj)
          Indicates whether some other object is "equal to" this one.
 Class getClass()
          Returns the runtime class of an object.
 int hashCode()
          Returns a hash code value for the object.
 void notify()
          Wakes up a single thread that is waiting on this object's monitor.
 void notifyAll()
          Wakes up all threads that are waiting on this object's monitor.
 String toString()
          Returns a string representation of the object.
 void wait()
          Causes current thread to wait until another thread invokes the Object.notify() method or the Object.notifyAll() method for this object.
 void wait(long timeout)
          Causes current thread to wait until either another thread invokes the Object.notify() method or the Object.notifyAll() method for this object, or a specified amount of time has elapsed.
 void wait(long timeout, int nanos)
          Causes current thread to wait until another thread invokes the Object.notify() method or the Object.notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
 



Constructor Detail

Object

public Object()


Method Detail

getClass

public final Class getClass()
Returns the runtime class of an object. That Class object is the object that is locked by static synchronized methods of the represented class.

Returns:
the object of type Class that represents the runtime class of the object.

hashCode

public int hashCode()
Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode is:

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 JavaTM programming language.)

Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

equals

public boolean equals(Object obj)
Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation:

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.
See Also:
Boolean.hashCode(), Hashtable

toString

public String toString()
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())
 

Returns:
a string representation of the object.

notify

public final void notify()
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:

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:
Object.notifyAll(), Object.wait()

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. 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.
See Also:
Object.notify(), Object.wait()

wait

public final void wait(long timeout)
                throws InterruptedException
Causes current thread to wait until either another thread invokes the Object.notify() method or the Object.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:

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.

If the current thread is interrupted by another thread 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.

Parameters:
timeout - the maximum time to wait in milliseconds.
Throws:
IllegalArgumentException - if the value of timeout is negative.
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:
Object.notify(), Object.notifyAll()

wait

public final void wait(long timeout,
                       int nanos)
                throws InterruptedException
Causes current thread to wait until another thread invokes the Object.notify() method or the Object.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*millis+nanos

In all other respects, this method does the same thing as the method Object.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:

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.

Parameters:
timeout - the maximum time to wait in milliseconds.
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.
IllegalMonitorStateException - if the current thread is not the owner of this 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.

wait

public final void wait()
                throws InterruptedException
Causes current thread to wait until another thread invokes the Object.notify() method or the Object.notifyAll() method for this object. In other word's 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.

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.
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:
Object.notify(), Object.notifyAll()





Copyright 1999-2010 Research In Motion Limited. 295 Phillip Street, Waterloo, Ontario, Canada, N2L 3W8. All Rights Reserved.
Copyright 1993-2003 Sun Microsystems, Inc. 901 San Antonio Road, Palo Alto, California, 94303, U.S.A. All Rights Reserved.
Copyright 2002-2003 Nokia Corporation All Rights Reserved.
Java is a trademark of Sun Microsystems, Inc.