在以下程序中，鼠标单击小应用程序的某一点，则会在该点显示一个图标，如果双击，则会清除该图标。且在浏览器的状态栏上会显示鼠标单击位置的坐标。运行结果如下图所示。请改正程序中的错误(有下划线的语句)，使程序能输出正确的结果。

注意：不改动程序的结构，不是增行或删行。

import java.applet.*;

import java.awt.*;

import java.awt.event.*;

public class Example3_1 extends Applet

{

int xPoint, yPoint;

int sum;

Image displayIm;

public void init()

{

displayIm = getImage("ms.jpg");

addMouseListener(new SClickMouse()) ;

sum = 2;

}

public void paint(Graphics g)

{

if(sum == 1)

g.drawImage(displayIm, xPoint, yPoint, this);

else

g.fillRect(xPoint, yPoint, 60, 60);

}

public class SClickMouse implements MouseListener

{

public void mouseClicked(MouseEvent mouse)

{

sum = mouse.getClickCount();

xPoint = mouse.getX();

yPoint = mouse.getY();

paint();

}

public void mouseEntered(MouseEvent mouse)

{

}

public void mouseExited(MouseEvent mouse)

{}

public void mousePressed(MouseEvent mouse)

{

xPoint = mouse.getX();

yPoint = mouse.getY();

showStatus("x="+xPoint+",y-"+yPoint);

}

public void mouseReleased(MouseEvent mouse)

}

}

}

}

Exampie3_1.html:

＜html＞

＜head＞＜title＞Example3_1＜/title＞＜/head＞

＜body＞

＜applet code="Example3_1.class" width="400" height="500"＞

＜/applet＞

＜/body＞

＜/html＞