Java.util.Observable Class

Java.util.Observable Class

Introduction

The java.util.Observable class represents an observable object, or “data” in the model-view paradigm.Following are the important points about Observable:

  • The class can be subclassed to represent an object that the application wants to have observed.
  • An observable object can have one or more observers.

Class declaration

Following is the declaration for java.util.Observable class:

public class Observable
   extends Object

Class constructors

S.N.Constructor & Description
1Observable()

This constructs an Observable with zero Observers.

Class methods

S.N.Method & Description
1void addObserver(Observer o)

This method 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.

2protected void clearChanged()

This method 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.

3int countObservers()

This method returns the number of observers of this Observable object.

4void deleteObserver(Observer o)

This method deletes an observer from the set of observers of this object.

5void deleteObservers()

This method clears the observer list so that this object no longer has any observers.

6boolean hasChanged()

This method tests if this object has changed.

7void 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.

8void 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.

9protected void setChanged()

This method returns marks this Observable object as having been changed; the hasChanged method will now return true.

Methods inherited

This class inherits methods from the following classes:

  • java.util.Object

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