Listeners as interfaces

Listeners are defined as interfaces and must be implemented by the application

public interface ActionListener extends EventListener {
    public void actionPerformed(ActionEvent e);
}

public interface MouseListener extends EventListener {
    public void mouseClicked(MouseEvent e);
    public void mousePressed(MouseEvent e);
    public void mouseReleased(MouseEvent e);
    public void mouseEntered(MouseEvent e);
    public void mouseExited(MouseEvent e);
}