为什么我下面程序中的"保存"功能不用实现,请指出问题所在!!
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;

class lianxi extends JFrame
{
      lianxi(String Title)
      {
              super(Title);
              LianJie();
              WenBen(); 
      }
      JMenuBar jmenubar=new JMenuBar();
      JMenu[] jmenu=new JMenu[]{new JMenu("文件"),new JMenu("编辑")};
      JMenuItem[][] jmenuitem=new JMenuItem[][]{{new JMenuItem("新建"),new JMenuItem("打开"),new JMenuItem("保存"),new JMenuItem("退出")},
                                                {new JMenuItem("剪切"),new JMenuItem("复制"),new JMenuItem("粘贴"),new JMenuItem("删除")}};                             
        final JTextArea word=new JTextArea();
        ActionListener action=new ActionListener()
                              {
                                      public void actionPerformed(ActionEvent e)
                                      {
                                            String MuLu=null;
                                            JMenuItem AnNiu=(JMenuItem)e.getSource();
                                            String str=AnNiu.getText();
                                            if(str.equals("新建"))
                                            {
                                                    word.setText(" ");
                                            }
                                            else if(str.equals("打开"))
                                            {
                                                    FileDialog DuiHuaKuang=new FileDialog(lianxi.this,"打开文件",FileDialog.LOAD);
                                                    DuiHuaKuang.setVisible(true);
                                                  MuLu=DuiHuaKuang.getDirectory()+DuiHuaKuang.getFile();
                                                    if(MuLu!=null)
                                                    {
                                                          try
                                                          {
                                                                FileInputStream FileInput=new FileInputStream(MuLu);
                                                        byte[] a=new byte[1000];
                                                            int len=FileInput.read(a);
                                                            word.append(new String(a,0,len));
                                                            FileInput.close();
                                                    }
                                                    catch(Exception ex)
                                                    {
                                                            ex.printStackTrace();
                                                    }
                                                }
                                                /*else
                                                {
                                                        
                                                }*/
                                            }
                                            else if(str.equals("保存"))
                                            {
                                                    if(MuLu!=null)
                                                    {
                                                            try
                                                            {
                                                                 FileOutputStream FileOutput=new FileOutputStream(MuLu);
                                                                 FileOutput.write(word.getText().getBytes());
                                                                 FileOutput.close();
                                                        } 
                                                        catch(Exception ex)
                                                        {
                                                                ex.printStackTrace();
                                                        }
                                                    }
                                            }
                                      }
                              };
        public void LianJie()
        {
                int i,j;
                for(i=0;i<jmenu.length;i++)
                {
                    jmenubar.add(jmenu[i]);
                  for(j=0;j<jmenuitem[i].length;j++)
                  {
                          jmenu[i].add(jmenuitem[i][j]);
                          jmenuitem[i][j].addActionListener(action);
                  }
                }
                this.setJMenuBar(jmenubar);
        }
        public void WenBen()
        {
                JScrollPane jsp = new JScrollPane(word);
                this.getContentPane().add(jsp);
        }
        public static void main(String[] args)
        {
                lianxi L=new lianxi("菜单窗口");
                L.setSize(600,400);
                L.setLocation(180,180);
                L.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                L.setVisible(true);
        }
}