Java实现简易记事本程序

package vacc;
import java.awt.BorderLayout;  
import java.awt.event.ActionEvent;  
import java.awt.event.ActionListener;  
import java.awt.event.InputEvent;  
import java.awt.event.KeyEvent;  
import java.io.BufferedReader;  
import java.io.File;  
import java.io.FileNotFoundException;  
import java.io.FileReader;  
import java.io.IOException;  
import java.io.PrintWriter;  
  
import javax.swing.JFileChooser;  
import javax.swing.JFrame;  
import javax.swing.JMenu;  
import javax.swing.JMenuBar;  
import javax.swing.JMenuItem;  
import javax.swing.JPanel;  
import javax.swing.JScrollPane;  
import javax.swing.JTextArea;  
import javax.swing.KeyStroke;  
import javax.swing.filechooser.FileNameExtensionFilter;  
  
 
public class TestNotepad {  
  
    private JFrame jframe;// 主窗体  
    JPanel jpanel;// 面板  
    JMenuBar jmenuBar = new JMenuBar();// 菜单面板  

    JMenu jmenuFile, jmenuEdit;// 主菜单  
    JMenuItem jmenuItemOpen, jmenuItemNew, jmenuItemSave, jmenuItemSaveAs,  
            jmenuItemExit;// 菜单中的子菜单  
    JTextArea jtextArea;// 文本框  
    JScrollPane jscrollPane;// 带滑动条的  
    JFileChooser jfileChooser;//文件选择器  
    File currentFile;  
  
    public TestNotepad() {  
        // TODO Auto-generated constructor stub  
        jframe = new JFrame("我的记事本");  
        jpanel = new JPanel();  
        jmenuBar = new JMenuBar();  
        jtextArea = new JTextArea();  
        jtextArea.setLineWrap(true);//设置自动换行  
        jscrollPane = new JScrollPane(jtextArea);  
        jfileChooser = new JFileChooser();  
        jfileChooser.setFileFilter(new FileNameExtensionFilter("文本文件(*.txt)", "txt"));  
          
        jmenuFile = new JMenu("文件(F)");  
        jmenuFile.setMnemonic('F');  
        jmenuEdit = new JMenu("编辑(E)");  
        jmenuEdit.setMnemonic('E');  
        jmenuItemNew = new JMenuItem("新建(N)", 'N');  
        jmenuItemNew.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_N, InputEvent.CTRL_DOWN_MASK));  
          
        jmenuItemOpen = new JMenuItem("打开(O)", 'O');  
        jmenuItemOpen.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_O, InputEvent.CTRL_DOWN_MASK));  
        jmenuItemOpen.addActionListener(new ActionListener() {