Thread: Simple animation. Strange behavior

When I run the code below with the "thread.sleep", the ball runs from left corner to right corner, leaving a trail behind it as expected.

but when I remove the thread.sleep part, the balls appears directly at the right side corner, without a trail (similar to the behavior after adding a "fill.rec", but there is no such thing is this code".)

So I ran the code without "thread.sleep" in DEBUG mode. Then it left a trail as expected. The same code, but in debug mode. What is going on here?

package mypong;
 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 
/**
 *
 * @author Administrator
 */
 
 
public class MyPong extends JFrame
{
    int x=0; //ball X coordinate at the beginning
    int y=0; //ball's Y coordinate at the beginning
    int xPos=100;
    int yPos=100;
    int circ=20; //width height of the ball
 
     //initialize the frame
 
     public void go() 
     {          
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        MyDrawPanel drawPanel = new MyDrawPanel();     
 
        frame.getContentPane().add(drawPanel);
        frame.setSize(480,500);
        frame.setVisible(true);                
 
 
 
        while (true)
        {     
 
           if (x<440) 
           { 
 
                x+=1;
                y+=1; 
           }
 
             drawPanel.repaint();
 
//        try
//        {
//            Thread.sleep(10);
//        }
//        catch(Exception x)
//        {
//           x.printStackTrace();
//        }
        }//end for
 
     }//end go
 
     public static void main(String[] args)
     {
         MyPong mypong=new MyPong();
         mypong.go();
     }
 
    //inner class drawpanel
 
    class MyDrawPanel extends JPanel
    {
        @Override
        public void  paintComponent(Graphics g)
        {
 
            g.setColor(Color.black);
            g.fillOval(x, y, circ, circ);
 
 
        }
    }
}

The first call in a paintComponent() method should be:

super.paintComponent( g );

That will correctly remove the trail. If you want to include a trail effect, then you should do as KW suggested and add the last (some number) of balls to a data structure, perhaps with decreasing opacity, perhaps only saving every Xth ball depending on the ball's velocity, and print the trail or history in the paintComponent() method.