什么功能都没有的记事本程序

/*
模拟记事本程序,里面有打开,保存,另存为,退出菜单
*/
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class NotePad
{
 private Frame f;
 private MenuBar mb;
 private Menu fileMenu;
 private MenuItem openMenuItem,saveMenuItem,saveAsMenuItem,quitMenuItem;
 private TextArea ta;
 private File file;
 NotePad()
 {
  init();
 }
 private void init()
 {
  f = new Frame("NotePad v1.0");
  mb = new MenuBar();
  fileMenu = new Menu("File");
  openMenuItem = new MenuItem("Open...");
  saveMenuItem = new MenuItem("Save");
  saveAsMenuItem = new MenuItem("Save as...");
  quitMenuItem = new MenuItem("Quit");
  ta = new TextArea("",0,0,TextArea.SCROLLBARS_VERTICAL_ONLY);
  f.setBounds(400,300,480,500);
  f.setMenuBar(mb);
  f.add(ta);
  mb.add(fileMenu);
  fileMenu.add(openMenuItem);
  fileMenu.add(saveMenuItem);
  fileMenu.add(saveAsMenuItem);
  fileMenu.add(quitMenuItem);
  frameEvent();
  menuEvent();
  
  f.setVisible(true);
 }
 private void frameEvent()
 {
  f.addWindowListener(new WindowAdapter()
  {
   public void windowClosing(WindowEvent we)
   {
    System.exit(0);
   }
  });
 }
 private void menuEvent()
 {
  saveAsMenuItem.addActionListener(new ActionListener()
  {
   public void actionPerformed(ActionEvent ae)
   {
    FileDialog saveAsDialog = new FileDialog(f,"Save file as",FileDialog.SAVE);
    saveAsDialog.setVisible(true);
    file = new File(saveAsDialog.getDirectory()+saveAsDialog.getFile());
    saveFile(file);
   }
  });
  saveMenuItem.addActionListener(new ActionListener()
  {
   public void actionPerformed(ActionEvent ae)
   {
    if (file != null)
    {
     saveFile(file);
    }
    else
    {
     FileDialog saveDialog = new FileDialog(f,"Save file",FileDialog.SAVE);
     saveDialog.setVisible(true);
     file = new File(saveDialog.getDirectory()+saveDialog.getFile());
     saveFile(file);
    }
   }
  });
  quitMenuItem.addActionListener(new ActionListener()
  {
   public void actionPerformed(ActionEvent ae)
   {
    System.exit(0);
   }
  });
  openMenuItem.addActionListener(new ActionListener()
  {
   public void actionPerformed(ActionEvent ae)
   {
    FileDialog openDialog = new FileDialog(f,"Open file",FileDialog.LOAD);
    openDialog.setVisible(true);
    try
    {
     if (openDialog.getDirectory() == null || openDialog.getFile() == null)
     {
      return;
     }
     ta.setText("");
     file = new File(openDialog.getDirectory(),openDialog.getFile());
     BufferedReader br = new BufferedReader(new FileReader(file));
     String str = null;
     while ((str = br.readLine()) != null)
     {
      ta.append(str+"\r\n");
     }
     br.close();
    }
    catch (IOException oe)
    {
     throw new RuntimeException("Open file failed.");
    }
   }
  });
 }
 private void saveFile(File file)
 {
  try
  {
   BufferedWriter bw = new BufferedWriter(new FileWriter(file));
   bw.write(ta.getText());
   bw.close();
  }
  catch (IOException se)
  {
   throw new RuntimeException("Save flie failed.");
  }
 }
 public static void main(String[] args)
 {
  new NotePad();
 }
}