public void addActionListener(ActionListener al){
  if (backButton != null && forwardButton != null) {
    backButton.addActionListener(al);
    forwardButton.addActionListener(al);
  }
 else {
    if (listeners == null) {
      listeners=new Vector();
    }
    listeners.add(al);
  }
}

public void addActionListener ( ActionListener al ) { if ( backButton != null && forwardButton != null ) { backButton . addActionListener ( al ) ; forwardButton . addActionListener ( al ) ; } else { if ( listeners == null ) { listeners = new Vector ( ) ; } listeners . add ( al ) ; } }
add an actionlistener for events that trigger events to shift the projection stack . if you are hooking up a projectionstack , you don ' t need to call this . the projectionstack will call this when you can addprojectionstacktrigger on it .
