import java.awt.*;


public class BouncingBall extends AnimationApplet{

  protected Color color = Color.green;
  // radius of the ball
  protected int radius = 20;
  protected int x, y;
  // how much the location changes at every redraw
  protected int dx = -2, dy = -4;
  // off screen image
  protected Image image;
  // off screen graphics
  protected Graphics offscreen;
  // dimensions of the applet region
  protected Dimension d;

  public void init() {
    String att = getParameter("delay");
    if (att != null) {
      setDelay(Integer.parseInt(att));
    }
    else{
      setDelay(100); // default
    }
    
    d = getSize();
    
    // set the starting point of the ball
    x = d.width * 2 / 3;
    y = d.height - radius;
  }


  public void update(Graphics g) {
    // create the off-screen image buffer
    // if it is invoked the first time
    if (image == null) {
      image = createImage(d.width, d.height);
      offscreen = image.getGraphics();
    }

    // draw the background
    offscreen.setColor(Color.white);
    offscreen.fillRect(0,0,d.width,d.height);

    // adjust the position of the ball
    // reverse the direction if it touches
    // any of the four sides
    if (x < radius || x > d.width - radius) {
      dx  =  -dx;
    }
    if (y < radius || y > d.height - radius) {
      dy  =  -dy;
    }
    x += dx;
    y += dy;

    // draw the ball
    offscreen.setColor(color);
    offscreen.fillOval(x - radius, y - radius,
                           radius * 2, radius * 2);

    // copy the off-screen image to the screen
    g.drawImage(image, 0, 0, this);
  }

  public void paint(Graphics g) {
    update(g);
  }
}