急:为何这个程序没有用到paint方法,但又实现了他的功能!!!!

package my.first.java;import java.awt.*;public class testJava extends Frame{    public void paint(Graphics g){
    g.setColor(Color.BLUE);
    g.fillOval(30, 30, 500, 500);
    }
    public void lauchFrame(){
    this.setBounds(400,400,300,300);
    this.setVisible(true);
    }
public static void main(String[] args) {
new testJava().lauchFrame(); } }