这个学期，我们学习了Java编程，期末之时老师要我们编个记事本作为这门课程的课程设计，我写了一个，大体上的功能都实现了，只有"撤销"的功能没有实现，请各位大虾指点一下，“撤销”的算法，不甚感激！
特将记事本的源码附下，请大家指点，看还有没有更简洁高效的算法，请不要吝啬，我的E-mail:yangyong@ccsu.cn,欢迎大家来信指点！
/*
*
*题目：记事本程序
*Author: Jeason
*
* 2004-12-20
*
**/
package jeason;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.io.*;
import java.util.*;
import java.text.*;
public class Jsb{
///
boolean dirty=true;
String filename="";
String strtext="";
///////////////////////////////////
////////// Menu ////////////////
///////////////////////
JFrame frame=new JFrame("我的记事本");
JPopupMenu pop=new JPopupMenu("弹出");
JTextArea text=new JTextArea();
JLabel statubar=new JLabel("状态栏");
JMenuBar Mbar=new JMenuBar();
JFileChooser jFileChooser1=new JFileChooser();
JColorChooser jColor=new JColorChooser();
JMenu jFile=new JMenu("文件");
JMenu jEdit=new JMenu("编辑");
JMenu jFormat=new JMenu("格式");
JMenu jHelp=new JMenu("帮助");
JMenuItem jnew=new JMenuItem("新建(N)");
public Jsb(){ ///无参数的构造函数
///
this.dirty=false;
/////
final BorderLayout borderLayout1=new BorderLayout();
frame.setSize(600,500);//
frame.addWindowListener(new Jsb_frame_closingAdapter(this));
JPanel panel=new JPanel();
panel.setLayout(borderLayout1);//布局
panel.add(new JScrollPane(text));//滚动条
panel.add(statubar,borderLayout1.SOUTH);
frame.getContentPane().add(panel);
//
frame.setJMenuBar(Mbar); //将主菜单添加到窗体中
/*
* jnew
**/
//jnew
jnew.addActionListener(new File_new_actionAdapter(this));
jnew.setMnemonic(´N´);//N上下划线
jnew.setAccelerator(KeyStroke.getKeyStroke(´N´,java.awt.Event.CTRL_MASK,true));
//快捷方式
/*
* jopen
**/
JMenuItem jopen=new JMenuItem("打开(O)");//jopen
jopen.addActionListener(new File_open_actionAdapter(this));
jopen.setMnemonic(´O´);
jopen.setAccelerator(KeyStroke.getKeyStroke(´O´,java.awt.Event.CTRL_MASK,true));
/*
* jsave
**/
JMenuItem jsave=new JMenuItem("保存(S)");
jsave.addActionListener(new File_save_actionAdapter(this));
jsave.setMnemonic(´S´);
jsave.setAccelerator(KeyStroke.getKeyStroke(´S´,java.awt.Event.CTRL_MASK,true));
/*
* jsave as
**/
JMenuItem jsaveas=new JMenuItem("另存为...");
jsaveas.addActionListener(new File_saveas_actionAdapter(this));
/*
* jquite
**/
JMenuItem jquite=new JMenuItem("关闭(Q)");
jquite.addActionListener(new File_quite_actionAdapter(this));
jquite.setMnemonic(´Q´);
jquite.setAccelerator(KeyStroke.getKeyStroke(´Q´,java.awt.Event.CTRL_MASK,true));
//------------------------------------
// jFile code of end
//--------------------------------------
/**
* jEdit code
*/
//jundo
JMenuItem jundo=new JMenuItem("撤销(U)");
jundo.addActionListener(new Edit_undo_actionAdapter(this));
jundo.setMnemonic(´U´);
jundo.setAccelerator(KeyStroke.getKeyStroke(´U´,java.awt.Event.CTRL_MASK,true));
/*
* jcut
**/
JMenuItem jcut=new JMenuItem("剪切(X)");
jcut.addActionListener(new Edit_cut_actionAdapter(this));
jcut.setMnemonic(´X´);
jcut.setAccelerator(KeyStroke.getKeyStroke(´X´,java.awt.Event.CTRL_MASK,true));
/*
* jcopy
**/
JMenuItem jcopy=new JMenuItem("复制(C)");
jcopy.addActionListener(new Edit_copy_actionAdapter(this));
jcopy.setMnemonic(´C´);
jcopy.setAccelerator(KeyStroke.getKeyStroke(´C´,java.awt.Event.CTRL_MASK,true));
/*
* jpaste
**/
JMenuItem jpaste=new JMenuItem("粘贴(V)");
jpaste.addActionListener(new Edit_paste_actionAdapter(this));
jpaste.setMnemonic(´V´);
jpaste.setAccelerator(KeyStroke.getKeyStroke(´V´,java.awt.Event.CTRL_MASK,true));
/*
* jdelete
**/
JMenuItem jdelete=new JMenuItem("删除(D)");
jdelete.addActionListener(new Edit_delete_actionAdapter(this));
jdelete.setMnemonic(´D´);
jdelete.setAccelerator(KeyStroke.getKeyStroke(´D´,java.awt.Event.CTRL_MASK,true));
/*
* jfind
**/
JMenuItem jfind=new JMenuItem("查找(F)");
jfind.addActionListener(new Edit_find_actionAdapter(this));
jfind.setMnemonic(´F´);
jfind.setAccelerator(KeyStroke.getKeyStroke(´F´,java.awt.Event.CTRL_MASK,true));
/*
* jreplace
**/
JMenuItem jreplace=new JMenuItem("替换(R)");
jreplace.addActionListener(new Edit_replace_actionAdapter(this));
jreplace.setMnemonic(´R´);
jreplace.setAccelerator(KeyStroke.getKeyStroke(´R´,java.awt.Event.CTRL_MASK,true));
/*
*jselectall
**/
JMenuItem jselectall=new JMenuItem("全选(A)");
jselectall.addActionListener(new Edit_selectall_actionAdapter(this));
jselectall.setMnemonic(´A´);
jselectall.setAccelerator(KeyStroke.getKeyStroke(´A´,java.awt.Event.CTRL_MASK,true));
/*
* jdate
**/
JMenuItem jdate=new JMenuItem("日期/时间(T)");
jdate.addActionListener(new Edit_timedate_actionAdapter(this));
jdate.setMnemonic(´T´);
jdate.setAccelerator(KeyStroke.getKeyStroke(´T´,java.awt.Event.CTRL_MASK,true));
//------------------------------
// jEdit code of end
//
//-----------------------------
/*
* jWord
**/
JMenuItem jword=new JMenuItem("自动换行");
jword.addActionListener(new Format_word_actionAdapter(this));
/*
* jfont
**/
JMenuItem jfont=new JMenuItem("字体..");
jfont.addActionListener(new Format_font_actionAdapter(this));
/*
* jcolor
**/
JMenuItem jcolor=new JMenuItem("颜色...");
jcolor.addActionListener(new Format_color_actionAdapter(this));
//--------------------------------------------------
// jFormat code of end
//--------------------------------------------------
/*
* jabout
**/
JMenuItem jabout=new JMenuItem("关于作者(A)");
jabout.addActionListener(new Help_about_actionAdapter(this));
jabout.setMnemonic(´A´);
jabout.setAccelerator(KeyStroke.getKeyStroke(´A´,java.awt.Event.CTRL_MASK,true));
//-------------------------------------------------
// jHelp code of end
//------------------------------------------------------
/*************************************************
*------------
