a moving object in a layeredPane

Hi experts,

   I tried to put a moving object in a layeredPane which is in a Frame. It works fine if i add it to the code directly, but it doesn't work if i put it in a layeredPane first. Does anyone know what I did wrong ???

   please help ! many thanks.
--------------------------------
//  MovingFigs.java

import java.lang.* ;
import javax.swing.*;
import javax.swing.event.* ;
import java.awt.* ;
import java.awt.event.* ;
import java.awt.image.BufferedImage;


public class MovingFigs extends JFrame implements ActionListener{
    private JLayeredPane layeredPane;
    private JPanel myPanel ;

    /** Creates a new instance of Main */
    public MovingFigs() {
        layeredPane = new JLayeredPane();
        layeredPane.setPreferredSize(new Dimension(300, 310));
   
         MovingCircle myCircle = new MovingCircle() ;
         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     
          layeredPane.add( myCircle, new Integer(0)) ;
            getContentPane().setLayout(null) ;
            getContentPane().add(layeredPane) ;
          setSize(800, 600);
          show();

    }
   
   
    //-----------
    public void actionPerformed(ActionEvent e){}
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
         MovingFigs meow = new MovingFigs() ;
      //   meow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         meow.setVisible(true);
    }    
}

//---------------------------
// MovingCircle.java

import java.lang.* ;
import javax.swing.*;
import javax.swing.event.* ;
import java.awt.* ;
import java.awt.event.* ;
import java.awt.image.BufferedImage;

public class MovingCircle extends JPanel implements ActionListener{
    private int x = 30, y = 30 ;
    private final int DELTA_X = 10 ;
    /** Creates a new instance of Class */
    public MovingCircle() {
        javax.swing.Timer circleTimer = new Timer(250, this);
        circleTimer.start();}
    public void actionPerformed(ActionEvent e){ repaint() ;}
 //--------------------
    public void paintComponent(Graphics g) {
          Graphics2D g2d = (Graphics2D) g.create();
          g2d.clearRect(0, 0, getWidth(), getHeight());
          g2d.setPaint(Color.red);
          x += DELTA_X;
          g2d.fillOval(x, y, y, y);
          g2d.drawOval(x, y, y, y);
          g2d.dispose();  
     } // paintComponent
} // MovingCircle