[]关于JTextField限制输入的有关问题

package Test;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Demo implements MouseListener, KeyListener {

    JFrame jf;
    JPanel jp;
    JTextField text1;
    JTextField text2;

    String t2;
    
    String st = "不能为空";

    public Demo() {

        jf = new JFrame("Demo");
        jf.setSize(200, 200);

        text1 = new JTextField();
        text1.setText("text1");
        text1.setPreferredSize(new Dimension(100, 20));
        text1.addMouseListener(this);
        text1.addKeyListener(this);
        

        text2 = new JTextField();
        text2.setText("text2");
        //text2.requestFocus();
        text2.setPreferredSize(new Dimension(100, 20));
        text2.addMouseListener(this);
        text2.addKeyListener(this);
        
        jp = new JPanel();
        jp.setSize(100, 200);
        jp.add(text1);
        jp.add(text2);

        jf.getContentPane().add(jp, BorderLayout.CENTER);

        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setVisible(true);

    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Demo test = new Demo();

    }

    public void mouseClicked(MouseEvent e) {
        // TODO Auto-generated method stub
        checkValue(e);
    }

    public void mouseEntered(MouseEvent e) {
        // TODO Auto-generated method stub

    }

    public void mouseExited(MouseEvent e) {
        // TODO Auto-generated method stub

    }

    public void mousePressed(MouseEvent e) {
        // TODO Auto-generated method stub

    }

    public void mouseReleased(MouseEvent e) {
        // TODO Auto-generated method stub

    }

    public void keyPressed(KeyEvent e) {
        // TODO Auto-generated method stub
        System.out.println("keyPressed@");
        Object o = e.getSource();
        
        if(o == text2){
            String str = text1.getText();
            str = text1.getText();
            System.out.println("keyPressed"+str+e.getKeyCode());
            if(str == null || ("").equals(str.trim()) || str.equals(st)){
                System.out.println(text2.getText());
                e.setKeyCode(KeyEvent.VK_UNDEFINED);
                System.out.println("keyPressed@" + e.getKeyCode());
                System.out.println("------"+text2.getText());
            }
        }

    }

    public void keyReleased(KeyEvent e) {
        // TODO Auto-generated method stub
        System.out.println("keyReleased");
        Object o = e.getSource();
        
        if(o == text2){
            String str = text1.getText();
            str = text1.getText();
            System.out.println("keyReleased"+str+ e.getKeyCode());
            if(str == null || ("").equals(str.trim()) || str.equals(st)){
                System.out.println(text2.getText());
                e.setKeyCode(KeyEvent.VK_UNDEFINED);
                System.out.println("keyReleased@"+e.getKeyCode());
            }
        }
        
        
        System.out.println("keyReleased@");
    }

    public void keyTyped(KeyEvent e) {
        // TODO Auto-generated method stub
        System.out.println("keyTyped@");
        Object o = e.getSource();
        
        if(o == text2){
            String str = text1.getText();
            str = text1.getText();
            System.out.println("keyTyped"+str+e.getKeyCode());
            if(str == null || ("").equals(str.trim()) || str.equals(st)){
                System.out.println(text2.getText());
                e.setKeyCode(KeyEvent.VK_UNDEFINED);
                System.out.println("keyTyped@" + e.getKeyCode());
                System.out.println("++++++"+text2.getText());
            }
        }
    }

    private void checkValue(MouseEvent e) {
        Object o = null;
        o = e.getSource();
        if (o == text2) {
            t2 = text2.getText();
            String str = text1.getText();

            if (str == null || str.trim().equals("") || str.equals(st)) {
                text1.setBackground(Color.yellow);
                text1.setForeground(Color.lightGray);
                text1.setText(st);
                JOptionPane.showMessageDialog(null, "禁止", "alert", JOptionPane.ERROR_MESSAGE);
                
                text1.requestFocus();
            }
            
        }
        if (o == text1) {
            String str = text1.getText();
            if (str.equals(st)) {
                JTextField temp = (JTextField) o;
                temp.setText("");
                temp.setBackground(Color.white);
                temp.setForeground(Color.black);
            }
        }
    }
    
}