下面是一个Applet程序,程序的功能是用鼠标画图。本题是通过单击鼠标后画出一个Java字。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,不得增行或减行。 源程序文件代码清单如下; import java.awt.*; import java.awt.event.*; import java.applet.*; /* <applet code=SimpleHitMouse.java width=800 height=400> </applet> */ public class SimpleHitMouse implements Applet { private java.util.Vector points=new java.util.Vector(); public void init() { addMouseListener(new MouseAdapter() { public void mousePressed(MouseEvent e) { points.add(new Point(e.getX(),e.getY()) paint(); } }); } public void update(Graphics g) }repaint(g); } public void paint(Graphics g) { for(int i=0;i<points.size();i++) { Point dot=(Point)points.elementAt(i); g.drawString("x",dot.x,dot.y); } } public static void main(String args[ ]) { Frame fram=new Frame("CelayTree"); SimpleHitMouse dot=new SimpleHitMouse(); dot.init (); dot.start (); fram.add ( "Center", dot ); fram.setSize( 400,300 ); fram.addWindowListener( new WindowAdapter(){ public void windowClosing( WindowEvent e ) { System.exit(0); } }); fram.show (); } } ex12_3.html: <html> <head> <title>A Simple Program</title> </head> <body> <applet code=" SimpleHitMouse.class" width=800 height=400> </applet> </body> </html>