Moving the ball

Question

public class Ball extends JFrame implements Runnable
     int x = 10;          
     int y = 100;     
     int radius = 20;     
     public Ballbewegung1()
          super("Ball Moving");
          setBackground (Color.blue);
          start();
          setSize(400,400);
          setVisible(true);
     public static void main(String[]args)
          Ballbewegung1 test = new Ballbewegung1();
          test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     public void start ()
          Thread th = new Thread (this);
          th.start ();
          System.out.println("Start");
     public void run ()
          Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
          while (x<=300)
               x ++;
               repaint();
               try
                    Thread.sleep (20);
               catch (InterruptedException ex)
               Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
     public void paint (Graphics g)
          g.setColor  (Color.red);
          g.fillOval (x - radius, y - radius, 2 * radius, 2 * radius);
}i not sure what wrong with my coding because it keep coming up the wrong out put.Any help will greatly appreciated. Thank you

Answer 1

Maybe this code is your desired affect. This uses active render rather than depending the OS and java to repaint the screen. I prefer active rendering when possible. You can't use it if you have menu's or some other component that comes down into the painted area (or at least I haven't figured out how to solve the problem that when your component is painted it covers the menu...something java takes care of when using repaint()).
Also, I went ahead a drew on your JFrame but as mentioned above it would be better to put a JPanel in the JFrame and draw on the JPanel. So basically create a class that extends JPanel and put this functionality in it and then add the JPanel to your top level JFrame. The flicker would go away if you drew on an off screen image and then moved it to the screen (at the end of the render method).
The Timer method is the preferred method (rather than Thread.sleep) as the action it executes is executed form the Event Dispatcher Thread.
Enjoy:
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
public class Ball extends JFrame {
     private int x = 10;
     private int y = 100;
    private int radius = 20;
    private Timer animationTimer;
     public Ball() {
          super("Ball Moving");
          this.setSize(400,400);
          this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.startAnimation();
     private void startAnimation() {
        Action animate = new AbstractAction() {
            public void actionPerformed(ActionEvent e) {
                render();
        this.animationTimer = new Timer(4, animate);
        this.animationTimer.start();
     private void render() {
        Graphics g = getGraphics();
        g.setColor(Color.blue);
        g.fillRect(0, 0, this.getSize().width, this.getSize().height);
          g.setColor(Color.red);
          g.fillOval(x - radius, y - radius, 2 * radius, 2 * radius);
        x = x + 1;
        if (x > 300) {
            this.animationTimer.stop();
    public static void main(String[]args) {
        new Ball();
}