paintComponent(Graphics g)方法?

[hailun]

import javax.swing.*;
import java.awt.*;
class Mycanvas extends JPanel //并没有构造函数
{
public void paintComponent(Graphics g)//执行完哪条语句后,执行它呢?
{
super.paintComponent(g);
g.setColor(Color.red);
g.drawString("a Jpanel used as canvas",50,50);
}
}
public class Example25_6 extends JApplet
{
Mycanvas canvas;
JPanel panel;
JButton button;
public void init()
{
canvas=new Mycanvas();
panel=new JPanel();
button=new JButton("ok");
panel.add(button);
Container con=getContentPane();
con.add(panel,BorderLayout.NORTH);
con.add(canvas,BorderLayout.CENTER);
}
}

[beyondone]

对于class Mycanvas,系统为它提供了一个缺省的不带参构造函数Mycanvas().
对于所有的JComponent组件,paint()都会自动调用paintComponent()来paint这个组件.
不知道有没有将错的地方,高手指点