Probleme avec la methode repaint ()

public class Test {

	public static void main(String[] args) {

// TODO Auto-generated method stub
		new Fenetre("Mes premieres bouton");
	}

}

import java.awt.Graphics;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Fenetre extends JFrame {
	Panel panel=new Panel();
	
	public Fenetre (String titre)
	{		
		this.setSize(300,300);
		this.setLocationRelativeTo(null);
		this.setTitle(titre);
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		this.setContentPane(new Panel());
		this.setVisible(true);

go();
	}
	public void go()
	
	{
	
		for (int i=0;i<100;i++)
		{
			int x=panel.getPosx();
			int y=panel.getPosy();
			x++;
			y++;
			panel.setPosx(x);
			panel.setPosy(y);
			panel.repaint();
			
			try
			{
			Thread.sleep(1000);			
			}
			catch(InterruptedException e)
			{
			e.printStackTrace();
			}
		}
	}
}

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;

import javax.swing.JPanel;

public class Panel extends JPanel {
	int posx=0;
	int posy=0;

public void paintComponent (Graphics g){
	
	g.setColor(Color.red);
	g.fillOval(posx, posy, 50, 50);
	
 }

public int getPosx()
 	{
 		return posx;
 	}
 	public int getPosy()
 	{
 		return posy;
 	}
 	public void setPosx(int posx)
 	{
 		this.posx=posx;
 	}
	public void setPosy(int posy)
 	{
 		this.posy=posy;
 	}