Java开发网 - 请帮我看一看这段代码! (可以不理，已解决)

Topic: 请帮我看一看这段代码! (可以不理，已解决)

1.请帮我看一看这段代码! (可以不理，已解决)

Posted by: q_yuan
Posted on: 2004-11-09 10:35

import java.awt.*;
import java.awt.event.*;
public class TesttingMenu implements WindowListener{
  private Frame f;
  private MenuBar mb;
  private Menu m1,m2,mhelp;
  private MenuItem mi11,mi12,mi13,mi21,mi22,mihelp;
  public TesttingMenu(){
   f.addWindowListener(this);
   f= new Frame("Testing Menu");
    mb = new MenuBar();
    m1 = new Menu("文件");
    m2 = new Menu("编辑");
    mhelp = new Menu("帮助");
    mi11 = new MenuItem("新建");
    mi12 = new MenuItem("打开");
    mi13 = new MenuItem("保存");
    mi21 = new MenuItem("查找");
    mi22 = new MenuItem("工具");
    mihelp = new MenuItem("帮助文件");
    m1.add(mi11);
    m1.add(mi12);
    m1.add(mi13);
    m2.add(mi21);
    m2.add(mi22);
    mhelp.add(mihelp);
    m1.add(m2);
    mb.add(m1);
    mb.setHelpMenu(mhelp);
    f.setMenuBar(mb);
    f.setSize(200,200);
    f.setVisible(true);
    }
    public static void main(String[] args){
      TesttingMenu tm = new TesttingMenu();
            }
  public void windowActivated(WindowEvent e){};
  public void windowClosed(WindowEvent e){};
  public void windowClosing(WindowEvent e){System.exit(1);};
  public void windowDeactivated(WindowEvent e){};
  public void windowDeiconified(WindowEvent e){};
  public void windowIconified(WindowEvent e){};
  public void windowOpened(WindowEvent e){};
  }

这段代码可以编译过去，为什么执行起来就有问题？提示说是:
Exception in thread "main" java.lang.NullPointerException
at TesttingMenu.<init><TesttingMenu.java:9>
at TesttingMenu.main<TesttingMenu.java:35>

请问这是什么原因？要怎么解决？谢了!

2.Re:请帮我看一看这段代码! [Re: q_yuan]	Copy to clipboard
Posted by: nothing Posted on: 2004-11-09 10:40

3.Re:请帮我看一看这段代码! [Re: q_yuan]	Copy to clipboard
Posted by: q_yuan Posted on: 2004-11-09 10:43 谢谢上面的兄弟了! 我改过来了!

4.Re:请帮我看一看这段代码!了 (可以不理，已解决) [Re: q_yuan]	Copy to clipboard
Posted by: why Posted on: 2004-11-10 08:53 NullPointerException！！很直接地说：这样的问题，自己也不能解决的话，请好好从头学起。不要浪费版面和大家的时间。请尽量用准确的文字描述作为标题否则这样的标题，见即删！