slider.addChangeListener(
      new ChangeListener(){
        public void stateChanged(ChangeEvent e){

          display = edgeDetector(
                      butterfly,slider.getValue());
          display.repaint();

        }//end stateChanged
      }//end new ChangeListener
    );//end addChangeListener
    //----------------------------------------------//
  }//end constructor
  //------------------------------------------------//
}//end class Prob08Runner