各位大大，为啥小弟我画的圆有毛边，加了双缓冲还是看见一闪一闪的

import java.awt.*;import java.awt.event.*;public class TankClient extends Frame {    Image fim = null;    int framex =30;    int framey = 50;    public void paint(Graphics g) {        Color c = g.getColor();        g.setColor(Color.RED);        g.fillOval(framex, framey, 30, 30);        g.setColor(c);        framex+=5;        framey+=5;    }    public void update(Graphics g) {//System.out.println("调用了update");        if(fim == null){            fim = this.createImage(800, 600);        }        Graphics fimgs = fim.getGraphics();        Color c = fimgs.getColor();        fimgs.setColor(Color.GREEN);        fimgs.fillRect(0, 0, 800, 600);        paint(fimgs);        g.drawImage(fim, 0, 0, null);    }        public TankClient(String s){        super(s);    }    public void launchFrame(){                this.setBounds(250, 200, 800, 600);        this.setResizable(false);        this.setBackground(Color.green);        this.setVisible(true);                this.addWindowListener(new WindowAdapter(){            public void windowClosing(WindowEvent e) {                e.getWindow().setVisible(false);                System.exit(0);            }                        public void windowClosed(WindowEvent e) {                                            }        });                new Thread(new FrameRepaint()).start();    }        public class FrameRepaint implements Runnable{        public void run()  {            while(true){                repaint();                try {                    Thread.sleep(50);                } catch (InterruptedException e) {                    e.printStackTrace();                }            }        }            }        public static void main(String [] args){        TankClient tc = new TankClient("坦克世界");        tc.launchFrame();    }            }