java记事本的几个小问题

import javax.swing.*;import java.awt.*;import java.awt.event.*;import java.io.*;import javax.swing.undo.*;import javax.swing.event.*;public class NotePad extends JFrame { private UndoManager manager; private JFileChooser choose; private File selectedfile; private JTextArea text; private java.awt.Container container; private JMenuBar menuBar; private JTextField status; private boolean newPage = false; // File菜单 private JMenu menu; private JMenuItem newText; private JMenuItem open; private JCheckBoxMenuItem readOnly; private JMenuItem save; private JMenuItem saveAs; private JMenuItem exit; // Edit菜单 private JMenu edit; private JMenuItem undo; private JMenuItem redo; private JMenuItem cut; private JMenuItem copy; private JMenuItem copyAll; private JMenuItem paste; private JMenuItem delete; private JMenuItem deleteAll; private JMenuItem selectAll; private JMenuItem searchAndReplace; // 视图菜单 private JMenu view; private JCheckBoxMenuItem wrap; private JCheckBoxMenuItem onTop; private JMenuItem zoomIn; private JMenuItem zoomOut; // 工具菜单 private JMenu tool; private JMenuItem fontSum; private JMenuItem setcolor; private JMenuItem setFontColor; // 帮助菜单 private JMenu help; private JMenuItem about; // 右键菜单 private JPopupMenu pop; private JMenuItem popUndo; private JMenuItem popRedo; private JMenuItem popCut; private JMenuItem popCopy; private JMenuItem popSelectAll; private JMenuItem popCopyAll; private JMenuItem popPaste; private JMenuItem popDelete; private JMenuItem popClear; public NotePad() {  super("记事本");  try{   UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());  }catch(Exception e){}  container = getContentPane();  container.setLayout(new BorderLayout(0,-2));  manager = new UndoManager();  text = new JTextArea();  text.setFont(new Font("宋体",Font.PLAIN,14));  text.getDocument().addUndoableEditListener(manager);  text.setTabSize(2);  text.setSelectedTextColor(Color.WHITE);  text.setSelectionColor(Color.DARK_GRAY);  text.setLineWrap(true);  text.setWrapStyleWord(true);  text.setCaretColor(Color.RED);  text.setMargin(new Insets(3, 10, 3, 7));  text.setDragEnabled(true);  container.add(new JScrollPane(text,JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED));  menuBar = new JMenuBar();  // File菜单  menu = new JMenu("文件(F)");  menu.setMnemonic('F');  newText = new JMenuItem("新建(N)");  newText.setMnemonic('N');  newText.addActionListener(new ActionListener() {   public void actionPerformed(ActionEvent event) {    if(selectedfile == null && !text.getText().equals("")  &&      JOptionPane.showConfirmDialog(container, "是否保存", "是否保存", JOptionPane.YES_NO_OPTION) == JOptionPane.YES_OPTION){     choose = new JFileChooser();     int state = choose.showSaveDialog(container);     if (state == JFileChooser.APPROVE_OPTION) {      try {       File file = choose.getSelectedFile();       FileWriter os = new FileWriter(file);       os.write(text.getText(), 0, text.getText().length());       os.flush();       file.createNewFile();       os.close();      } catch (IOException e) {       JOptionPane.showMessageDialog(container, "保存文件失败","ERROR", JOptionPane.ERROR_MESSAGE);      }     }    }else if(selectedfile != null &&       JOptionPane.showConfirmDialog(container, "是否保存", "是否保存", JOptionPane.YES_NO_OPTION) == JOptionPane.YES_OPTION){    try {      FileWriter os = new FileWriter(selectedfile);      os.write(text.getText(), 0, text.getText().length());      os.flush();      os.close();    } catch (IOException e) {}   }   text.setText("");   newPage = true;    selectedfile = null;   status.setText("");   }  });  open = new JMenuItem("打开(O)");  open.setMnemonic('O');  open.addActionListener(new ActionListener() {   public void actionPerformed(ActionEvent event) {    if(selectedfile!=null &&       JOptionPane.showConfirmDialog(container, "是否保存", "是否保存", JOptionPane.YES_NO_OPTION) == JOptionPane.YES_NO_OPTION){     try{      FileWriter os = new FileWriter(selectedfile);      os.write(text.getText(), 0, text.getText().length());      os.flush();      os.close();      newPage = false;     }catch(IOException e){}    }else if(selectedfile==null && !text.getText().equals("") &&      JOptionPane.showConfirmDialog(container, "是否保存", "是否保存", JOptionPane.YES_NO_OPTION) == JOptionPane.YES_NO_OPTION){     choose = new JFileChooser();     int state = choose.showSaveDialog(container);     if (state == JFileChooser.APPROVE_OPTION) {      try {       File file = choose.getSelectedFile();       FileWriter os = new FileWriter(file);       os.write(text.getText(), 0, text.getText().length());       os.flush();       file.createNewFile();       os.close();       newPage = false;      } catch (IOException e) {       JOptionPane.showMessageDialog(container, "保存文件失败",         "ERROR", JOptionPane.ERROR_MESSAGE);      }     }    }    choose = new JFileChooser();    choose.setFileFilter(new filter());    int state = choose.showOpenDialog(container);    if (state == JFileChooser.APPROVE_OPTION) {     status.setText(choose.getSelectedFile().toString());     try {      selectedfile = choose.getSelectedFile();      FileReader isr = new FileReader(selectedfile);      text.read(isr, "");      isr.close();      newPage = false;     } catch (IOException e) {      JOptionPane.showMessageDialog(container, "打开文件失败",        "ERROR", JOptionPane.ERROR_MESSAGE);     }    }   }  });  readOnly = new JCheckBoxMenuItem("只读模式(R)");  readOnly.setMnemonic('R');  readOnly.addChangeListener(new ChangeListener() {   public void stateChanged(ChangeEvent event) {    if(readOnly.isSelected()){     text.setEditable(false);     cut.setEnabled(false);     paste.setEnabled(false);     delete.setEnabled(false);     deleteAll.setEnabled(false);     redo.setEnabled(false);     undo.setEnabled(false);     searchAndReplace.setEnabled(false);          popClear.setEnabled(false);     popCut.setEnabled(false);     popDelete.setEnabled(false);     popPaste.setEnabled(false);     popRedo.setEnabled(false);     popUndo.setEnabled(false);    }    else{     text.setEditable(true);     cut.setEnabled(true);     paste.setEnabled(true);     delete.setEnabled(true);     deleteAll.setEnabled(true);     redo.setEnabled(true);     undo.setEnabled(true);     searchAndReplace.setEnabled(true);          popClear.setEnabled(true);     popCut.setEnabled(true);     popDelete.setEnabled(true);     popPaste.setEnabled(true);     popRedo.setEnabled(true);     popUndo.setEnabled(true);    }   }  });  save = new JMenuItem("保存(S)");  save.setMnemonic('S');  save.addActionListener(new ActionListener() {   public void actionPerformed(ActionEvent event) {    if (newPage == true || selectedfile == null) {     choose = new JFileChooser();     int state = choose.showSaveDialog(container);     if (state == JFileChooser.APPROVE_OPTION) {      try {       File file = choose.getSelectedFile();       FileWriter os = new FileWriter(file);       os.write(text.getText(), 0, text.getText().length());       os.flush();       file.createNewFile();       os.close();       newPage = false;      } catch (IOException e) {       JOptionPane.showMessageDialog(container, "保存文件失败","ERROR", JOptionPane.ERROR_MESSAGE);      }     }    } else if(newPage == false && selectedfile != null){     try {      FileWriter os = new FileWriter(selectedfile);      os.write(text.getText(), 0, text.getText().length());      os.flush();      os.close();     } catch (IOException e) {      JOptionPane.showMessageDialog(container, "保存文件失败","ERROR", JOptionPane.ERROR_MESSAGE);     }    }   }  });  saveAs = new JMenuItem("另存为(A)");  saveAs.setMnemonic('A');  saveAs.addActionListener(new ActionListener() {   public void actionPerformed(ActionEvent event) {    choose = new JFileChooser();    int state = choose.showSaveDialog(container);    if (state == JFileChooser.APPROVE_OPTION) {     try {      File file = choose.getSelectedFile();      FileWriter os = new FileWriter(file);      os.write(text.getText(), 0, text.getText().length());      os.flush();      file.createNewFile();      os.close();      newPage = false;     } catch (IOException e) {      JOptionPane.showMessageDialog(container, "保存文件失败","ERROR", JOptionPane.ERROR_MESSAGE);     }    }   }  });  exit = new JMenuItem("退出(Q)");  exit.setMnemonic('Q');  exit.addActionListener(new ActionListener() {   public void actionPerformed(ActionEvent event) {    System.exit(0);   }  });  menu.add(newText);  menu.add(open);  menu.add(readOnly);  menu.add(save);  menu.add(saveAs);  menu.add(exit);