Image repainting problem!! plz HELP!!

Question

I'm facing a little problem with repaint. I have a moving ball on my JPanel (canvas). Ball (which is a circle) is leaving 2 lines behind it. I don't know why it happens, the code inside my paintComponent() method is as follows:
public void paintComponent(Graphics comp)
       super.paintComponent(comp);          
       g = (Graphics2D)comp;          
       g.drawLine(0,250, 500,  500/2);      //draw horizontal line from north          
       g.drawLine(500/2, 0, 500/2, 500); //draw vertical line on the equator          
       g.setColor(Color.blue);          
       g.fillArc(width, height, ballSize, ballSize, 0, 360);
}The above "paint" event has been written for JPanel class. On fillArc() line, only width and height are changes through a thread class. Actually, my ball is bouncing against the walls (edges) of Jframe. Bouncing is fine, but it is printing 2 lines just behind the ball (arc).
Any expert commetns would be greatly appreciated.
Raheel.

Answer 1

Hi.
I think you should clean up your background at the beginnig of paintComponent:
public void paintComponent(Graphics comp) {     
  super.paintComponent(comp);
  g = (Graphics2D)comp;
  //comp cleaning
  g.setColor(Color.WHITE); //the color of your background
  comp.fillRect(0, 0, getWidth(), getHeight());
  //end of cleaning
  g.fillRect(0, 0, get
  g.drawLine(0,250, 500,  500/2); //draw horizontal line from north
  g.drawLine(500/2, 0, 500/2, 500); //draw vertical line on the equator    g.setColor(Color.blue);     
  g.fillArc(width, height, ballSize, ballSize, 0, 360);
}Hope this help.