//RotRing
//Demonstrates basic animation loop, primitive animation
//Andy Harris, 06/00

import java.awt.*;
import java.applet.*;

public class RotRing extends Applet implements Runnable {

  Thread looper;
  int ringSize = 10;             //height of ring
  int dSize = 10;                //difference in ring size
  int ringY;                     //placement of ring
  boolean keepGoing = true;      //sentry variable
  
  public void start(){
    if (looper == null){
      looper = new Thread(this);
      keepGoing = true;
      looper.start();
    } // end if
  } // end start

  public void stop(){
    keepGoing = false;
    looper = null;
  } // end if

  public void run(){
    while (keepGoing){
      
      try {
	looper.sleep(100);
      } catch (InterruptedException exc){
	System.out.println(exc.getMessage());
      } // end try

      ringSize += dSize;

      if (ringSize > this.getSize().height - 20){
	dSize = -10;
      } else if (ringSize < 20){
	dSize = 10;
      } // end if

      //recalculate ring height
      ringY = (this.getSize().height - ringSize) / 2;

      repaint();
    } // end while loop
  } // end run
      
  public void paint(Graphics g){
    g.drawOval(10, ringY, this.getSize().width - 20, ringSize);
  } // end paint

} // end class def