Hi Guys! Will you share your thoughts on a Thread issue?

Question

Hi! I am working on figuring out how to get my application to use threads to enable the simultaneous movement of (n) balls across the JFrame area. The task is to enable the user to click on the application and with each click a new ball should be created as a Thread and then it should bounce back and forth across the screen.
I have been working on this now for a couple of days. It would be really great if one of you guys could help me! :-)
Here are my specific issues:
I am using the mousePressed() method to generate the data needed to instantiate a Ball object. However, I cannot get it to work as a Thread.
I tried calling the start() method on it but all that happens is the application stays blank.
I cannot get this thing to work -and I really need to make it work today -- Please --- is there a sweetheart out there who will take a minute to help? ;-)
Jennifer
My code is below:
Balls.java
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Balls extends JFrame implements MouseListener
      private int x, y, r, g, b;//Variables to hold x,y and color values
      private Vector basketOBalls;//Hold all of the Ball objects (and Threads created)
      private Ball ballFactory;//Ball objects created here
        Method Name: Balls()
        Return Value: none
        Input Parameters: None
        Method Description: Constructor
      public Balls()
        //call to super for Title of app
        super( " Bouncing Balls " );
        //Listen for mouse events
        addMouseListener( this ); 
        //instantiate the basketOBalls object
        basketOBalls = new Vector(20);
            //Set Initial JFrame Window Size
        setSize( 400, 400 );
     //Show it!
     show();
     }//EOConstructor
        Method Name: mousePressed(MouseEvent e)
        Return Value: none
        Input Parameters: MouseEvent
        Method Description: This takes the info from the users
        mouse click and creates a new Ball Object and then adds it
        to the basketOBalls Vector. Presently, it (incorrectly?) also
        calls the repaint() method in order to draw the ball to the
        screen.
       public void mousePressed( MouseEvent e )
           x = e.getX();//set x value
           y = e.getY();//set y value
           r = 1 + (int) ( 254 * Math.random() );//set red value
           g = 1 + (int) ( 254 * Math.random() );//set green value
           b = 1 + (int) ( 254 * Math.random() );//set blue value
           Color colorin = new Color( r, g, b );
           ballFactory = new Ball( x, y, colorin );
           //new Thread(ballFactory).start(); //This is the Problem area!!!!!!!!!!!!!!!!!!!!!
           basketOBalls.addElement( ballFactory );
           repaint();
        }//EOmP
        Method Name: paint( Graphics g )
        Return Value: none
        Input Parameters: Graphics Object g
        Method Description: Walk through the Vector to
        explicitly cast each object back as a Ball and
        then calls the Ball draw() and ball move() methods
        in order to make the balls move on the screen.
    public void paint( Graphics g )
        Ball b;
        for( int i = 0; i < basketOBalls.size(); i++)
           b = (Ball) (basketOBalls.elementAt(i));
           b.draw(g);
           b.move();
        }//EOFor
      }//EOpaint
        Method Name: main()
        Return Value: none
        Input Parameters: String args[]
        Method Description: This makes it all go.
      public static void main( String args[] )
        Balls app = new Balls();
        app.addWindowListener(
          new WindowAdapter()
                 public void windowClosing( WindowEvent e )
                                System.exit(0);
                 }//EOwindowClosing Method
          }//EOWindowAdapter Method
          );//EOaddWindowListener Argument
      }//EOMain
    public void mouseClicked( MouseEvent e ) { }
    public void mouseReleased( MouseEvent e ) { }
    public void mouseEntered( MouseEvent e ) { }
    public void mouseExited( MouseEvent e ) { }
}//EOFBall.java
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Ball extends JFrame //implements Runnable
        public static final int APP_SIZE = 400;//set bounds for screen area
     public static final int RADIUS = 15;//set size of balls
        private Color bgColor = java.awt.Color.lightGray;//may be used to clear background of JFrame
     private int x, y;//x & y coordinates
     private int speedX, speedY;//distances to use to redraw the balls
        private Color color = null;//the color of a ball
        Method Name: Ball(int initX, int initY, Color colorin) 
        Return Value: none
        Input Parameters: int, int , color
        Method Description: Constructor that creates a Ball object
     public Ball(int initX, int initY, Color colorin)
          x = initX;
          y = initY;
                color = colorin;
             speedX = (int)(1 + (Math.random() * 10));
          speedY = (int)(1 + (Math.random() * 10));
        Method Name: move()
        Return Value: none
        Input Parameters: none
        Method Description: This calculates the balls position and keeps it within
        the 400 pixel size of the application frame.
     public void move()
          x += speedX;
          y += speedY;
          if ((x - RADIUS < 0) || (x + RADIUS > APP_SIZE))
               speedX = -speedX;
               x += speedX;
          if ((y - RADIUS < 0) || (y + RADIUS > APP_SIZE))
               speedY = -speedY;
               y += speedY;
     } //EOMove
        Method Name: draw(Graphics bg) 
        Return Value: none
        Input Parameters: graphics
        Method Description: This method is how the ball draws itself
        public void draw(Graphics bg)
            bg.setColor( color );
            bg.fillOval(x - RADIUS, y - RADIUS, 2 * RADIUS, 2 * RADIUS);
//PROBLEM AREA PROBLEM AREA PROBLEM AREA PROBLEM AREA PROBLEM AREA PROBLEM AREA
        Method Name: run() 
        Return Value: none
        Input Parameters: none
        Method Description: This method is called by start() in the Balls.java file
        found in the mousePressed() method. however, it does not work properly.
     public void run()
           while(true)
          try
             Thread.sleep(100);
                   move();
                   draw(g);
                   repaint();
                catch(Exception e)
                e.printStackTrace( System.out );
    }//EOF

Answer 1

There needs to be only one thread. On every mouse pressed just add a new Ball object to the vector located in Balls class. That thread need only invoke a repaint on your main class called Balls.
public class Balls extends JFrame implements Runnable,MouseListener{
Vector vector = new Vector();
public static void main(String[] args){
Balls balls = new Balls(); balls.setSize(400,400);
balls.setVisible(true);
Thread thread = new Thread(this);
thread.start();
public void run(){ 
while(true){
repaint();
try{
Thread.sleep(4000); //delay
}catch(InterruptedException e){}
public void paint(Graphics){
for(i=0; i<vector.size(); i++){
Ball b = (Ball)vector.elementAt(i);
reposition(b);
g.drawArc(b.getX(),b.getY(),0,360);
public void reposition(Ball b){
// reposition ball using balls get/set methods.
public void MouseClicked(MouseEvent e){
// add a new ball to vector.
public class Ball{
int x,y;
public int getX(){ return x; }
public int getY(){ return y; }
public int setX(int x){ this.x = x; }
public int setY(int y){ this.y = y; }
Do check the syntax and compilation errors. The code above should give you some idea for approach.