为什么我用了swing还有双缓冲闪屏

[楊uu]

package r1;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;

import javax.swing.JFrame;

public class Mian extends JFrame {
Image img=Toolkit.getDefaultToolkit().getImage("images/tank1U.png");
public void Jiemian() {
this.setLayout(null);
this.setSize(800, 600);
this.setLocationRelativeTo(null);
this.setResizable(false);
this.setBackground(Color.BLACK);
this.getContentPane().setVisible(false);//设置为不可见才能显示JFrame的颜色
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
this.setVisible(true);
}
public void paint(Graphics g) {
super.paint(g);
g.drawImage(img,400,300,30,30,null);
repaint();
}

public static void main(String[] args) {
// TODO Auto-generated method stub
Mian s=new Mian();
s.Jiemian();
}

}