求解JApplet 中的update()方法为何没有调用？

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;


public class TMouse extends JApplet implements MouseListener{
Container con;
int width,height;
int x,y;
int flag;

public void init(){
con=this.getContentPane();

x=y=0;
width=height=2;

flag=0;

con.addMouseListener(this);
}

public void update(Graphics g){
g.setColor(this.getBackground());
g.fillRect(0,0,
getWidth(),
getHeight());
paint(g);
}

public void paint(Graphics g){

g.setColor(Color.blue);
g.drawString("Click the MouseButton ....",5,20);
g.setColor(Color.red);

if(flag==1)
g.drawString("Mouse Entered Applet",5,80);

}

public void mouseEntered(MouseEvent me){
flag=1;
repaint();
}

public void mouseExited(MouseEvent me){
flag=2;
repaint();
}

public void mouseClicked(MouseEvent me){
flag=3;
x=me.getX();
y=me.getY();
repaint();
}

public void mousePressed(MouseEvent me){
flag=4;
x=me.getX();
y=me.getY();
repaint();
}

public void mouseReleased(MouseEvent me){
flag=5;
x=me.getX();
y=me.getY();
repaint();
}
}


/*
<Applet Code=TMouse width=400 height=200>
</Applet>
*/

内容没有被覆盖啊，后来在update()中 加入了打印语句，也未见执行，

repaint() ->update()->paint() 应该是这个顺序的，可是为何不见update()方法的执行呢？