//
// simple example of threaded applet in Java.
//

public class CounterApplet extends java.applet.Applet 
implements Runnable {

	// position of leftmost end of text to write -- hardcoded to
	//   keep this example simple, and chosen to work reasonably 
	//   well with the size in CounterApplet.html.
        int messageX = 125, messageY = 95;

	// thread to repeatedly update and redisplay counter value.
        Thread countThread;
	int counter = 0;

	// ---- methods that override default applet behavior ----------

        // "paint" (called to redisplay applet):  display counter.
        public void paint(java.awt.Graphics gc) {
                gc.drawString("Count = " + getCounter(), 
			messageX, messageY);
        }

        // "start" (called when browser decides to start applet -- on
	//   initially loading the page, resizing, etc.):
	//   if there is no counter thread, create one.
        public void start() {
                if (countThread == null) {
                        System.out.println("starting counter thread");
                        countThread = new Thread(this);
			countThread.start();
                }
        }

        // "stop" (called when browser decides to stop applet -- when
	//   page is no longer being displayed, on resizing, etc.):	
	//   if there is a counter thread, interrupt and delete it.
	//   (see "run" below for how the thread deals with what is
	//   done here.)
        public void stop() {
                if (countThread != null) {
                        System.out.println("stopping counter thread");
			Thread temp = countThread;
                        countThread = null;    
			temp.interrupt();
                }
        }

	// ---- method for Runnable interface --------------------------

        // "run":  
	//   every 500 millisecs, update counter and refresh display.
        public void run() {
		// execute until stop() makes countThread null, or
		//   until interrupted.
                while (countThread != null) {
			updateCounter();
                        repaint();
                        try {
                                Thread.sleep(500);
                        } catch (InterruptedException e) {
				return;
                        }
                }
        }

        // ---- methods to update, display counter ---------------------

        //   synchronized to avoid simultaneous access to counter
        //   by getCounter (in applet display thread) and
	//   updateCounter (in counter thread).

        synchronized private int getCounter() {
		return counter;
	}

        synchronized private void updateCounter() {
		counter++;
	}
}