//
// "closeable frame" class.
//
import java.awt.* ;
import java.awt.event.* ;

//
// a CloseableFrame object is a frame that listens for window events, 
//      and processes "close" by disposing of the frame.
// this class has a static counter variable that keeps track of the
//      number of frames created and not closed.  when all have been 
//      closed, System.exit() is called to terminate the application.
//
public class CloseableFrame extends Frame implements WindowListener {

        static int framecount = 0 ;

        // zero-argument constructor for frame without title.
        public CloseableFrame() {
                super() ;
                addWindowListener(this) ;
                framecount++ ;
        }

        // one-argument constructor for frame with title.
        public CloseableFrame(String s) {
                super(s) ;
                addWindowListener(this) ;
                framecount++ ;
        }

        // respond to window-close event.
        public void windowClosing(WindowEvent wEvt) {
                // get rid of frame and release associated resources.
                dispose() ;
                framecount-- ;
                if (framecount <= 0) System.exit(0) ;
        }

        // ignore other window events.
        public void windowClosed(WindowEvent wEvt) {} ;
        public void windowOpened(WindowEvent wEvt) {} ;
        public void windowIconified(WindowEvent wEvt) {} ;
        public void windowDeiconified(WindowEvent wEvt) {} ;
        public void windowActivated(WindowEvent wEvt) {} ;
        public void windowDeactivated(WindowEvent wEvt) {} ;
}