/* * 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 http://www.davidflanagan.com/javaexamples2. */package com.davidflanagan.examples.graphics;import java.applet.*;import java.awt.*;/** 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.setColor(Color.red);	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.	repaint();    }        /**     * 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 { Thread.sleep(100); }       // 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;    }}