Java GUI之JTextArea

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public class JTextAreaDemo {   public static void main(String[] args) {      JFrame f = new JFrame("留言板");      JTextArea message = new JTextArea(20, 20);      f.add(new JLabel("请您留言"), "North");      f.add(message, "Center");      JPanel p = new JPanel();      p.setLayout(new GridLayout(1, 6));      String[] string = { "剪切", "复制", "粘贴", "删除", "提交", "清除" };      String[] buttonActionCommands = { "CUT", "COPY", "PASTE", "DELETE",            "SUBMIT", "RESET" };      JButton button[] = new JButton[6];      OuterMonitor om = new OuterMonitor(message, button);      for (int i = 0; i < string.length; i++) {         button[i] = new JButton(string[i]);         button[i].setActionCommand(buttonActionCommands[i]);         if (i < 4) {            button[i].setEnabled(false);         }         button[i].addActionListener(om);         p.add(button[i]);      }      message.addMouseMotionListener(om);      f.add(p, "North");      f.setSize(400, 150);      f.setLocation(300, 100);      f.setVisible(true);      f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   }}class OuterMonitor extends MouseMotionAdapter implements ActionListener {   private JTextArea msg;   private JButton buttons[];   private String clipBoard = "";   public OuterMonitor(JTextArea msg, JButton buttons[]) {      this.msg = msg;      this.buttons = buttons;   }   public void setClipBoard(String text) {      this.clipBoard = text;   }   public void actionPerformed(ActionEvent e) {      int position = msg.getSelectionStart();      String s = e.getActionCommand();      if (s.equals("RESET")) {         msg.setText("");      } else if (s.equals("SUBMIT")) {         System.out.println("你的留言为:\n" + msg.getText());      } else if (s.equals("COPY")) {         clipBoard = msg.getSelectedText();         msg.setSelectionStart(msg.getSelectionEnd());      } else if (s.equals("CUT")) {         clipBoard = msg.getSelectedText();         this.delete();      } else if (s.equals("PASTE")) {         String content = msg.getText();         String alter = content.substring(0, position) + clipBoard               + content.substring(position);         msg.setText(alter);      } else if (s.equals("DELETE")) {         this.delete();      }      this.switchButtons();   }   public void delete() {      int start = msg.getSelectionStart();      int end = msg.getSelectionEnd();      String content = msg.getText();      String alter = content.substring(0, start) + content.substring(end);      msg.setText(alter);   }   public void switchButtons() {      boolean cliped = (clipBoard != null) && (clipBoard.length() > 0);      buttons[2].setEnabled(cliped);      boolean selected = msg.getSelectionEnd() != msg.getSelectionStart();      buttons[0].setEnabled(selected);      buttons[1].setEnabled(selected);      buttons[3].setEnabled(selected);   }   public void mouseDragged(MouseEvent m) {      this.switchButtons();   }}
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