Thread: BufferedImage create flicker in simple code

I wrote a complex program that need bufferedImage but it is very flicker, so I simplify it and show it here, but still cannot solve.

Please help. I am using java 6.0.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Main {
    Timer timer;
    Mill mill;
    JFrame frame;
    int t=0;
    public Main(){
        frame=new JFrame();
        mill=new Mill();
        frame.getContentPane().add(mill);
        frame.setSize(new java.awt.Dimension(700,700));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        mill.setPreferredSize(new java.awt.Dimension(800,700));
        frame.setVisible(true);
        frame.pack();
        timer=new Timer(100,new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                t++;
                mill.repaint();
            }
        });
        timer.start();
    }
    public static void main(String[] args) {
        new Main();
    }
    BufferedImage buff=new BufferedImage(1,1,BufferedImage.TYPE_INT_RGB);
    class Mill extends JPanel {
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g3=(Graphics2D)g;
            {//.. paint only
                if( buff==null|| buff.getWidth()!=mill.getWidth() || 
                        buff.getHeight()!=mill.getHeight()        
                ){
                    buff=new BufferedImage(mill.getWidth(),mill.getHeight(),BufferedImage.TYPE_INT_RGB);
                }
                Graphics2D g2 = (Graphics2D) buff.createGraphics();
                g2.setColor(new Color(0,0,100));
                g2.fillRect( 0,0,600,600);
                g2.setColor(new Color(0,0,200));
                g2.fillRect( 0,0,500,500);
                g2.setColor(new Color(0,0,250));
                g2.fillRect( 0,0,400,400);
            }
            g3.drawImage( buff,0,0,buff.getWidth(),buff.getHeight(),this);
        }
    }
}

result link here
img145.imageshack.us/i/eatm.jpg/