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Class java.util.Observable

java.lang.Object
    |
    +----java.util.Observable

public class Observable

extends Object

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.

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 threaads, or may guarantee that their subclass follows this order, as they choose.

Since:

JDK1.0

See Also:

notifyObservers, notifyObservers, Observer, update

Observable()

Construct an Observable with zero Observers

addObserver(Observer)

Adds an observer to the set of observers for this object.

clearChanged()

Indicates that this object has no longer changed, or that it has already notified all of its observers of its most recent change.

countObservers()

Returns the number of observers of this object.

deleteObserver(Observer)

Deletes an observer from the set of observers of this object.

deleteObservers()

Clears the observer list so that this object no longer has any observers.

hasChanged()

Tests if this object has changed.

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.

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.

setChanged()

Indicates that this object has changed.

public Observable()

Construct an Observable with zero Observers

public void addObserver(Observer o)

Adds an observer to the set of observers for this object. 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.

public void deleteObserver(Observer o)

Deletes an observer from the set of observers of this object.

Parameters:

o - the observer to be deleted.

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

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

public void deleteObservers()

Clears the observer list so that this object no longer has any observers.

protected void setChanged()

Indicates that this object has changed.

protected 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

public 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

public int countObservers()

Returns the number of observers of this object.

Returns:

the number of observers of this object.

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