The Observer and Observable classes are superseded by a more elaborate event framework (see e333 Creating a Custom Event). However, these two classes can still be useful for implementing a simple event notifier. 
    // Declare the model
    class MyModel extends Observable {
        // The setChanged() protected method must overridden to make it public
        public synchronized void setChanged() {
            super.setChanged();
        }
    }

    // Create the model
    MyModel model = new MyModel();
    
    // Register for events
    model.addObserver(new Observer() {
        public void update(Observable o, Object arg) {
        }
    });
    
    // Indicate that the model has changed
    model.setChanged();
    
    // Fire an event to all the views
    Object arg = "some information about the event";
    model.notifyObservers(arg);