Bouncing Circle : Animation « 2D Graphics GUI « Java

Bouncing Circle

Bouncing Circle
 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit

import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;

/** An applet that displays a simple animation */
public class BouncingCircle extends Applet implements Runnable {
  int x = 150, y = 50, r = 50; // Position and radius of the circle

  int dx = 11, dy = 7; // Trajectory of circle

  Thread animator; // The thread that performs the animation

  volatile boolean pleaseStop; // A flag to ask the thread to stop

  /** This method simply draws the circle at its current position */
  public void paint(Graphics g) {
    g.fillOval(x - r, y - r, r * 2, r * 2);

   * This method moves (and bounces) the circle and then requests a redraw.
   * The animator thread calls this method periodically.
  public void animate() {
    // Bounce if we've hit an edge.
    Rectangle bounds = getBounds();
    if ((x - r + dx < 0) || (x + r + dx > bounds.width))
      dx = -dx;
    if ((y - r + dy < 0) || (y + r + dy > bounds.height))
      dy = -dy;

    // Move the circle.
    x += dx;
    y += dy;

    // Ask the browser to call our paint() method to draw the circle
    // at its new position.

   * This method is from the Runnable interface. It is the body of the thread
   * that performs the animation. The thread itself is created and started in
   * the start() method.
  public void run() {
    while (!pleaseStop) { // Loop until we're asked to stop
      animate(); // Update and request redraw
      try {
      } // Wait 100 milliseconds
      catch (InterruptedException e) {
      } // Ignore interruptions

  /** Start animating when the browser starts the applet */
  public void start() {
    animator = new Thread(this); // Create a thread
    pleaseStop = false; // Don't ask it to stop now
    animator.start(); // Start the thread.
    // The thread that called start now returns to its caller.
    // Meanwhile, the new animator thread has called the run() method

  /** Stop animating when the browser stops the applet */
  public void stop() {
    // Set the flag that causes the run() method to end
    pleaseStop = true;


Related examples in the same category

1.Is Event Dispatcher ThreadIs Event Dispatcher Thread
2.Timer based animation
3.A rotating and scaling rectangle.
4.Fade out an image: image gradually get more transparent until it is completely invisible.
5.Font size animation
6.Hypnosis animationHypnosis animation
7.Noise ImageNoise Image
8.How to create Animation: Paint and threadHow to create Animation: Paint and thread
9.How to create animationHow to create animation
10.Animation: bounce
11.Image BouncerImage Bouncer
12.Text animationText animation
13.Buffered Animation DemoBuffered Animation Demo
14.Hypnosis SpiralHypnosis Spiral
15.Animator DemoAnimator Demo
16.Towers of Hanoi
17.Make your own animation from a series of images
18.Composition technique in this animation.
19.Animated Button
20.Animated Message Panel
21.Animated PasswordField
22.Animated TextField
23.A simple spring simulation in one dimension
24.Shows an animated bouncing ball
25.Shows animated bouncing ballsShows animated bouncing balls