Jave运行窗口无法使用paint操作

加上super.paint(g);

class MyPaint extends JPanel{
    //画笔
    @Override
    public void paint(Graphics g) {
        super.paint(g);
       //画笔，设颜色，画图案
        g.setColor(Color.pink);
        g.drawOval(100,100,100,100);
        g.setColor(Color.blue);
        g.fillRect(200,200,300,300);
    }
}