Hi!

I have a simple animation question. I am trying to make an Oval move
from one position of a window to another.  I have managed to make the
Oval to update itself and redraw in a new position. Unfortunatly the
previous position/drawing of the Oval does not disappear.  What happens
is that the Oval moves through the window and leaves a trail after it.

I thought that the Panel (myPanel) would also redraw itself after a call
to repaint() and the previous drawing of the Oval would disappear.

My questions are:

- How do I remove the previous drawing of the Oval or make the Panel
(myPanel) update itself, so that just the Oval moves without a trail.

- Why isn't the background/Panel "black" even though I am calling the
setBackground(Color.BLACK); function ?

Thanks for any help

Alberto.V

========== Code follows below ==========

//
// Main Code
//
public class Main {
 
  public static void main(String[] args){
     JFrame gameFrame = new JFrame();    
     AVPanel p = new myPanel();
     
     gameFrame.setSize(600, 600);
     gameFrame.setLocation(150,50);
     gameFrame.getContentPane().setBackground(Color.BLACK);      
     gameFrame.getContentPane().add(p);
     
     gameFrame.setVisible(true);

  }
}

//
//  myPanel CODE
//
public class myPanel extends JPanel implements Runnable {
  Vector balls = new Vector();

  public myPanel() {
     setBackground(Color.BLACK);
     balls.add(new Ball(0, 0));
     Thread runnerThread = new Thread(this);
     runnerThread.setDaemon(true);
     runnerThread.start();
  }

  // Starts a new Thread
  public void run() {
     while (true) {
        try {
           this.updateBalls();
           this.repaint();
           Thread.sleep(9);
        } catch (InterruptedException ie) {}
     }
  }

  public void paintComponent(Graphics g) {
     int sz = balls.size();
     for (int i=0;i < sz; i++) {
        Ball b = (Ball)balls.get(i);
        b.draw(g);
     }
  }

  public void updateBalls() {
     int sz = balls.size();
     for (int i=0;i < sz; i++) {
        Ball b = (Ball)balls.get(i);
        b.updatePosition();
     }
  }
 
  public void paint(Graphics g) {
     int size = balls.size();
     super.paint(g);
     
  }
}

//
// Ball object
//
public class Ball {
  int xposition, yposition;
  int radius = 30;

  // Constructor
  public Ball(int x, int y){
     xposition = x;
     yposition = y;
  }
 
  // Draw the object
  public void draw(Graphics g) {
     g.setColor(Color.RED);
     g.fillOval(xposition, yposition, radius, radius);
  }
 
  // Update the objects position
  public void updatePosition(){
     Random r = new Random(System.currentTimeMillis() + xposition);
 
     if ((r.nextInt(10) % 2) == 0){
        xposition += 3;
     } else {
        yposition += 3;
     }
  }

}