Creating breakout game. Need help with thread starting.

Question

Howdy. As the title says, I've got an assignment to make a breakout game. So far it's going alright, but I've run into a rather large snag...I can't get it to animate :P I've got my main applet, then I created a class heirarchy for the paddle, ball, and brick objects. For this question, lets just focus on the ball object.
This is my applet code so far (it is not even close to being done, so don't laugh :P )
import java.awt.*;
import javax.swing.*;
import java.util.*;
* Class BreakoutApplet - Plays a simple game of Breakout.
* @author Kris Nelson
* @version November 10, 2004
public class BreakoutApplet extends JApplet implements Runnable
    protected Brick brick; // creates an object of class brick
    protected Ball ball; // creates an object of class ball
    protected Paddle paddle; // creates an object of class paddle
    protected boolean running; // tells the program whether or not the thread is running
    protected ArrayList brickArray = new ArrayList(); // stores all the bricks in the game
    protected Thread timer; // the thread which controls the animation for the applet
    * Called by the browser or applet viewer to inform this JApplet that it
    * has been loaded into the system. It is always called before the first
    * time that the start method is called.
    public void init()
        // this is a workaround for a security conflict with some browsers
        // including some versions of Netscape & Internet Explorer which do
        // not allow access to the AWT system event queue which JApplets do
        // on startup to check access. May not be necessary with your browser.
        JRootPane rootPane = this.getRootPane();   
        rootPane.putClientProperty("defeatSystemEventQueueCheck", Boolean.TRUE);
        createBricks(); // creates the games array of bricks
        ball = new Ball(400, 400, 2, 2); // sets the values for the ball
        paddle = new Paddle(300, 660, 2); // sets the values for the paddle
        // !!!!!!! have tried placing ball.start() here
    * Paint method for applet.
    * @param  g   the Graphics object for this applet
    public void paint(Graphics g)
        // draws the background, border, and all the games objects
        g.setColor(Color.lightGray); // sets the drawing color to light gray
        g.fillRect(0, 0, 600, 700); // displays the game screens background
        displayBorder(g); // displays the game screens border
        displayBricks(g); // displays the array of bricks
        ball.display(g); // displays the ball
        paddle.display(g); // displays the paddle
    * Creates the games array of bricks
    public void createBricks()
        int colorNumber = 1; // starts the color of the bricks at orange
        double yPosition = 100; // starts the bricks y screen position at 100
        for(int i = 0; i < 4; i++)
            double xPosition = 12; // starts the bricks x screen position at 12
            for(int j = 0; j < 8; j++)
                if(colorNumber == 0)
                    colorNumber = 1; // sets the color of the bricks to orange
                else
                    colorNumber = 0; // sets the color of the bricks to green
                brickArray.add(brick = new Brick(xPosition, yPosition, colorNumber)); // adds a brick to the current container in the brick array
                xPosition = xPosition + brick.getWidth(); // move the bricks x screen position to the next column
            yPosition = yPosition + brick.getHeight(); // moves the bricks y screen position to the next row
            if(colorNumber == 0)
                colorNumber = 1; // sets the color of the bricks to orange
            else
                colorNumber = 0; // sets the color of the bricks to green
    * Displays the game screens border
    * @param  g   the Graphics object for this applet
    public void displayBorder(Graphics g)
        g.setColor(Color.black); // sets the drawing color to black
        g.fillRect(0, 0, 600, 24); // draws a border on the top of the screen
        g.fillRect(0, 0, 12, 700); // draws a border on the left of the screen
        g.fillRect(588, 0, 12, 700); // draws a border on the right of the screen
    * Displays the array of bricks on the screen
    * @param  g   the Graphics object for this applet
    public void displayBricks(Graphics g)
        Brick currentBrick; // holds the brick data from the current ArrayList container
        for(int i = 0; i < 32; i++)
            currentBrick = (Brick)(brickArray.get(i)); // grabs the brick data from the current ArrayList container
            currentBrick.display(g); // displays the current brick
    * Called by the browser or applet viewer to inform this JApplet that it
    * should start its execution. It is called after the init method and
    * each time the JApplet is revisited in a Web page.
     public void start()
         if(timer == null)
             timer = new Thread(this); // creates a new object of type Thread
             timer.start(); // starts the new thread
             running = true; // tells the program that the new thread is running
    * Runs the code that controls the animation
    public void run()
        do{
            repaint(); // redraws the screen
            try{
                timer.sleep(100); // puts the thread to sleep for 100 milliseconds
            } catch(InterruptedException e) {running = false;}
            // !!!!!!! have tried placing ball.start() here
        } while(running);
        timer = null; // destroys the timer thread
    * Called by the browser or applet viewer to inform this JApplet that
    * it should stop its execution. It is called when the Web page that
    * contains this JApplet has been replaced by another page, and also
    * just before the JApplet is to be destroyed.
    public void stop()
        running = false; // tells the program that the thread is now done
}These are the bits of code for my class heirarchy, just to (hopefully) make it easier to follow.
import java.awt.*;
* The parent class of all the games objects.
* @author Kris Nelson
* @version November 9, 2004
public class Sprite
    protected double screenX, screenY; // stores the x and y location of the object
    * Constructor for objects of class Sprite
    * @param  xPosition   the initial x screen position
    * @param  yPosition   the initial y screen position
    public Sprite(double xPosition, double yPosition)
        screenX = xPosition; // sets the initial x screen position
        screenY = yPosition; // sets the initial y screen position
    * Sets new x and y screen locations for an object
    * @param  newX   the new x screen location
    * @param  newY   the new y screen location
    public void setScreenXY(double newX, double newY)
        screenX = newX; // sets the new x screen location
        screenY = newY; // sets the new y screen location
    * Sends back the current x screen location
    * @return     the current x screen location
    public double getScreenX()
        return screenX; // returns the current x screen location
    * Sends back the current y screen location
    * @return     the current y screen location
    public double getScreenY()
        return screenY; // returns the current y screen location
import java.awt.*;
* Parent class of any game object that moves.
* @author Kris Nelson
* @version November 9, 2004
public class MovingSprite extends Sprite implements Runnable
     protected double speedX, speedY; // stores the speed of an object in the x and y directions
     protected Thread timer; // the thread which controls animation for all moving objects
     protected boolean running; // tells the program whether or not the thread is running
     * Constructor for objects of class MovingSprite
     * @param  xPosition   the initial x screen position
     * @param  yPosition   the initial y screen position
     * @param  xSpeedValue   the speed in the x direction
     * @param  ySpeedValue   the speed in the y direction
     public MovingSprite(double xPosition, double yPosition, double xSpeedValue, double ySpeedValue)
          super(xPosition, yPosition); // passes the initial screen positions to Sprite
          speedX = xSpeedValue; // sets the speed in the x direction
          speedY = ySpeedValue; // sets the speed in the y direction
     * Sends back the speed in the x direction
     * @return     the speed in the x direction
     public double getSpeedX()
         return speedX; // returns the speed in the x direction
     * Sends back the speed in the y direction
     * @return     the speed in the y direction
     public double getSpeedY()
         return speedY; // returns the speed in the y direction
     * Starts the thread in order to start animation
     public void start()
         if(timer == null)
             timer = new Thread(this); // creates a new object of type Thread
             timer.start(); // starts the new thread
             running = true; // tells the program that the new thread is running
     * Empty since the child objects have their own run methods
     public void run()
     * Stops the thread from running
     public void stop()
         running = false; // tells the program that the thread is now done
import java.awt.*;
* Creates a single ball who's purpose is to bounce around and destroy the bricks.
* @author Kris Nelson
* @version November 10, 2004
public class Ball extends MovingSprite
    protected static final double BALL_WIDTH = 15; // sets the width of the ball
    protected static final double BALL_HEIGHT = 15; // sets the height of the ball
    * Constructor for objects of class Ball
    * @param  xPosition   the initial x screen position
    * @param  yPosition   the initial y screen position
    * @param  xSpeedValue   the speed in the x direction
    * @param  ySpeedValue   the speed in the y direction
    public Ball(double xPosition, double yPosition, double xSpeedValue, double ySpeedValue)
        super(xPosition, yPosition, xSpeedValue, ySpeedValue); // passes the initial screen positions and ball speeds to MovingSprite
        // !!!!!!!! have tried placing timer.start() here
    * Displays a ball onto the screen
    * @param  g   the Graphics object for this applet
    public void display(Graphics g)
        g.setColor(Color.blue); // sets the balls color
        g.fillOval((int)(screenX), (int)(screenY), (int)(BALL_WIDTH), (int)(BALL_HEIGHT)); // displays the ball
    * Runs the code that controls the balls animation
    public void run()
        do{
            try{
                timer.sleep(100); // puts the thread to sleep for 100 milliseconds
            } catch(InterruptedException e) {running = false;}
            screenX = screenX + speedX;
            screenY = screenY + speedY;  // this is VERY SIMPLE BALL MOVEMENT FOR TESTING PURPOSES, WILL BE CHANGED LATER
        } while(running);
}Sorry if that was too much code. I'm just trying to make this easier to follow.
I placed a // !!!!!!!!!!!!! comment in the places where I have tried starting the ball thread.
So basically, everything is running fine, except that I'm not at all sure of where to start the ball Thread, and thus can't start anything moving. If someone could tell me where I should be starting the thread, I would REALLY appriciate it. Thank you :D
- Kris

Answer 1

Some advice.
1. the start method on the ball should be called from the start method on the applet and should in turn call the start method on the sprite's thread.
2. the run method of the Moveable sprite should have been declare abstract
3. don't implement borders manually. There's a java.awt.Border class for that.
4. probably, you don't want to have the game invoke each sprite by name; just make a big list of all the sprites and invoke all of them every time
5. do you really need provision for a non-circular ball? this isn't rugby.
6. I don't think you ever had a threading problem, just a display problem.
7. Don't write comments like this:     ball.display(g); // displays the ballHere's my (even more simplified version):import java.awt.*;
import javax.swing.*;
import java.util.*;
* Class BreakoutApplet - Plays a simple game of Breakout.
* @author Kris Nelson, modified by Michael Lorton
* @version November 10, 2004
public class BreakoutApplet extends JApplet implements Runnable {  
    protected Ball ball;
    protected Paddle paddle;
    public boolean running; // tells the program whether or not the thread is running
    protected Thread timer; // the thread which controls the animation for the applet
    public void init() {
        // this is a workaround for a security conflict with some browsers
        // including some versions of Netscape & Internet Explorer which do
        // not allow access to the AWT system event queue which JApplets do
        // on startup to check access. May not be necessary with your browser.
        getRootPane().putClientProperty("defeatSystemEventQueueCheck",
                                        Boolean.TRUE);
         ball = new Ball(this, GAMEWIDTH / 2, GAMEHEIGHT / 2, 5, 5);
    public final static int GAMEWIDTH = 600;
    public final static int GAMEHEIGHT = 400;
    public void paint(Graphics g) {
        g.setColor(Color.lightGray);
        g.fillRect(0, 0,
                   GAMEWIDTH, GAMEHEIGHT);
        ball.display(g); // displays the ball
    * Called by the browser or applet viewer to inform this JApplet that it
    * should start its execution. It is called after the init method and
    * each time the JApplet is revisited in a Web page.
    public void start() {
        if(timer == null) {
            timer = new Thread(this); // creates a new object of type Thread
            timer.start(); // starts the new thread
            running = true; // tells the program that the new thread is running
        ball.start();
    * Runs the code that controls the animation
    public void run() {
        do{
            repaint(); // redraws the screen
            try{
                Thread.sleep(100);
            } catch(InterruptedException e) {running = false;}
        } while(running);
    public void stop() {
        running = false;
abstract class Sprite {
    protected double screenX, screenY; // stores the x and y location of the object
    protected final BreakoutApplet parent;
    * Constructor for objects of class Sprite
    * @param  xPosition   the initial x screen position
    * @param  yPosition   the initial y screen position
    public Sprite(BreakoutApplet parent, double xPosition, double yPosition) {
        this.parent = parent;
        screenX = xPosition; // sets the initial x screen position
        screenY = yPosition; // sets the initial y screen position
    * Sets new x and y screen locations for an object
    * @param  newX   the new x screen location
    * @param  newY   the new y screen location
    public void setScreenXY(double newX, double newY) {
        screenX = newX; // sets the new x screen location
        screenY = newY; // sets the new y screen location
    * Sends back the current x screen location
    * @return     the current x screen location
    public double getScreenX() {
        return screenX; // returns the current x screen location
    * Sends back the current y screen location
    * @return     the current y screen location
    public double getScreenY() {
        return screenY; // returns the current y screen location
    abstract public void display(Graphics g);
* Parent class of any game object that moves.
* @author Kris Nelson
* @version November 9, 2004
abstract class MovingSprite extends Sprite implements Runnable {
    protected double speedX, speedY; // stores the speed of an object in the x and y directions
    protected Thread timer; // the thread which controls animation for all moving objects
    protected boolean running; // tells the program whether or not the thread is running
    * Constructor for objects of class MovingSprite
    * @param  xPosition   the initial x screen position
    * @param  yPosition   the initial y screen position
    * @param  xSpeedValue   the speed in the x direction
    * @param  ySpeedValue   the speed in the y direction
    public MovingSprite(BreakoutApplet parent,
                        double xPosition, double yPosition,
                        double xSpeedValue, double ySpeedValue) {
        super(parent, xPosition, yPosition);
        speedX = xSpeedValue; // sets the speed in the x direction
        speedY = ySpeedValue; // sets the speed in the y direction
    * Starts the thread in order to start animation
    public void start() {
        if(timer == null) {
            timer = new Thread(this); // creates a new object of type Thread
            timer.start(); // starts the new thread
            running = true; // tells the program that the new thread is running
    * Runs the code that controls the balls animation
    public void run() {
        while (parent.running) {
            try{
                Thread.sleep(100);
            } catch(InterruptedException e) {
                System.err.println(e);
            step();
    abstract protected void step();
* Creates a single ball whose purpose is to bounce around and destroy the bricks.
* @author Kris Nelson
* @version November 10, 2004
class Ball extends MovingSprite {
    protected static final int BALL_DIAMETER = 15;
    * Constructor for objects of class Ball
    * @param  xPosition   the initial x screen position
    * @param  yPosition   the initial y screen position
    * @param  xSpeedValue   the speed in the x direction
    * @param  ySpeedValue   the speed in the y direction
    public Ball(BreakoutApplet parent,
                double xPosition, double yPosition,
                double xSpeedValue, double ySpeedValue) {
        super(parent, xPosition, yPosition, xSpeedValue, ySpeedValue);
    * Displays a ball onto the screen
    * @param  g   the Graphics object for this applet
    public void display(Graphics g) {
        g.setColor(Color.blue);
        g.fillOval((int)(screenX),
                   (int)(screenY),
                   BALL_DIAMETER, BALL_DIAMETER);
    protected void step() {
            screenX = screenX + speedX;
            if (screenX < 0) {
                screenX = -screenX;
                speedX = -speedX;
            else if ((screenX + BALL_DIAMETER)> BreakoutApplet.GAMEWIDTH) {
                screenX = 2*(BreakoutApplet.GAMEWIDTH  - BALL_DIAMETER) - screenX;
                speedX = -speedX;
            screenY = screenY + speedY;
            if (screenY < 0) {
                screenY = -screenY;
                speedY = -speedY;
            else if ((screenY  + BALL_DIAMETER) > BreakoutApplet.GAMEHEIGHT) {
                screenY = 2*(BreakoutApplet.GAMEHEIGHT - BALL_DIAMETER) - screenY;
                speedY = -speedY;
}