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Class java.util.Observable 

java.lang.Object
   |
   +----java.util.Observable
public class Observable
extends Object
This class represents an observable object, or "data" in the model-view paradigm. It can be subclassed to represent an object that the application wants to have observed.

An observable object can have one or more observers. After an observable instance changes, an application calling the Observable's notifyObservers method causes all of its observers to be notified of the change by a call to their update method.

Since:
JDK1.0
See Also:
notifyObservers, notifyObservers, Observer, update

Constructor Index

o Observable()
Construct an Observable with zero Observers

Method Index

o addObserver(Observer)
Adds an observer to the set of observers for this object.
o clearChanged()
Indicates that this object has no longer changed, or that it has already notified all of its observers of its most recent change.
o countObservers()
Returns the number of observers of this object.
o deleteObserver(Observer)
Deletes an observer from the set of observers of this object.
o deleteObservers()
Clears the observer list so that this object no longer has any observers.
o hasChanged()
Tests if this object has changed.
o notifyObservers()
If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.
o notifyObservers(Object)
If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.
o setChanged()
Indicates that this object has changed.

Constructors

o Observable 
 public Observable()
Construct an Observable with zero Observers

Methods

o addObserver 
 public synchronized void addObserver(Observer o)
Adds an observer to the set of observers for this object.

Parameters:
o - an observer to be added.
o deleteObserver 
 public synchronized void deleteObserver(Observer o)
Deletes an observer from the set of observers of this object.

Parameters:
o - the observer to be deleted.
o notifyObservers 
 public void notifyObservers()
If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.

Each observer has its update method called with two arguments: this observable object and null.

See Also:
clearChanged, hasChanged, update
o notifyObservers 
 public void notifyObservers(Object arg)
If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.

Each observer has its update method called with two arguments: this observable object and the arg argument.

Parameters:
arg - any object.
See Also:
clearChanged, hasChanged, update
o deleteObservers 
 public synchronized void deleteObservers()
Clears the observer list so that this object no longer has any observers.

o setChanged 
 protected synchronized void setChanged()
Indicates that this object has changed.

o clearChanged 
 protected synchronized void clearChanged()
Indicates that this object has no longer changed, or that it has already notified all of its observers of its most recent change. This method is called automatically by the notifyObservers methods.

See Also:
notifyObservers, notifyObservers
o hasChanged 
 public synchronized boolean hasChanged()
Tests if this object has changed.

Returns:
true if the setChanged method has been called more recently than the clearChanged method on this object; false otherwise.
See Also:
clearChanged, setChanged
o countObservers 
 public synchronized int countObservers()
Returns the number of observers of this object.

Returns:
the number of observers of this object. 
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