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Java Source Code / Java Documentation » 6.0 JDK Modules » j2me » java.util

Source Cross Reference Class Diagram Java Document (Java Doc)

java.lang .Object

java.util .Observable

All known Subclasses:   sun.net .ProgressData,
Observable
public class Observable (Code)
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. An observer may be any object that implements interface Observer. 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.
The order in which notifications will be delivered is unspecified. The default implementation provided in the Observerable class will notify Observers in the order in which they registered interest, but subclasses may change this order, use no guaranteed order, deliver notifications on separate threads, or may guarantee that their subclass follows this order, as they choose.
Note that this notification mechanism is has nothing to do with threads and is completely separate from the wait and notify mechanism of class Object.
When an observable object is newly created, its set of observers is empty. Two observers are considered the same if and only if the equals method returns true for them.
author:
   Chris Warth
version:
   1.31, 02/02/00
See Also:   java.util.Observable.notifyObservers
See Also:   java.util.Observable.notifyObservers(java.lang.Object)
See Also:   java.util.Observer
See Also:   java.util.Observer.update(java.util.Observablejava.lang.Object)
since:
   JDK1.0

Constructor Summary
public Observable()
     Construct an Observable with zero Observers.

Method Summary
public synchronized void addObserver(Observer o)
     Adds an observer to the set of observers for this object, provided that it is not the same as some observer already in the set.
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, so that the hasChanged method will now return false.
public synchronized int countObservers()
     Returns the number of observers of this Observable object.
public synchronized void deleteObserver(Observer o)
     Deletes an observer from the set of observers of this object.
public synchronized void deleteObservers()
     Clears the observer list so that this object no longer has any observers.
public synchronized boolean hasChanged()
     Tests if this object has changed.
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.
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.
protected synchronized void setChanged()
     Marks this Observable object as having been changed; the hasChanged method will now return true.

Constructor Detail
Observable
public Observable()(Code)
Construct an Observable with zero Observers.

Method Detail
addObserver
public synchronized void addObserver(Observer o)(Code)
Adds an observer to the set of observers for this object, provided that it is not the same as some observer already in the set. The order in which notifications will be delivered to multiple observers is not specified. See the class comment.
Parameters:
  o - an observer to be added.
throws:
  NullPointerException - if the parameter o is null.

clearChanged
protected synchronized void clearChanged()(Code)
Indicates that this object has no longer changed, or that it has already notified all of its observers of its most recent change, so that the hasChanged method will now return false. This method is called automatically by the notifyObservers methods.
See Also:   java.util.Observable.notifyObservers
See Also:   java.util.Observable.notifyObservers(java.lang.Object)

countObservers
public synchronized int countObservers()(Code)
Returns the number of observers of this Observable object. the number of observers of this object.

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

deleteObservers
public synchronized void deleteObservers()(Code)
Clears the observer list so that this object no longer has any observers.

hasChanged
public synchronized boolean hasChanged()(Code)
Tests if this object has changed. true if and only if the setChanged method has been called more recently than the clearChanged method on this object; false otherwise.
See Also:   java.util.Observable.clearChanged
See Also:   java.util.Observable.setChanged

notifyObservers
public void notifyObservers()(Code)
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. In other words, this method is equivalent to:
notifyObservers(null)

See Also:   java.util.Observable.clearChanged
See Also:   java.util.Observable.hasChanged
See Also:   java.util.Observer.update(java.util.Observablejava.lang.Object)

notifyObservers
public void notifyObservers(Object arg)(Code)
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:   java.util.Observable.clearChanged
See Also:   java.util.Observable.hasChanged
See Also:   java.util.Observer.update(java.util.Observablejava.lang.Object)

setChanged
protected synchronized void setChanged()(Code)
Marks this Observable object as having been changed; the hasChanged method will now return true.

Methods inherited from java.lang.Object
public boolean equals(Object obj)(Code)(Java Doc)
final native public Class getClass()(Code)(Java Doc)
native public int hashCode()(Code)(Java Doc)
final native public void notify()(Code)(Java Doc)
final native public void notifyAll()(Code)(Java Doc)
public String toString()(Code)(Java Doc)
final native public void wait(long timeout) throws InterruptedException(Code)(Java Doc)
final public void wait(long timeout, int nanos) throws InterruptedException(Code)(Java Doc)
final public void wait() throws InterruptedException(Code)(Java Doc)

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