30.16 java.util.Observer (JDK 1.0)

This interface defines the update() method required for an object to "observe" subclasses of Observable. An Observer registers interest in an Observable() by calling the Observable.addObserver() method. Observer objects that have been registered in this way will have their update() method invoked by the Observable when that object has changed.

public abstract interface Observer {
    // Public Instance Methods
            public abstract void update(Observable o, Object arg);
}

Passed To:

Observable.addObserver(), Observable.deleteObserver()