How to make my page can detect textbox move ment

Question

i want to create a java GUI which will do the actionPerformed after the textbox value been change after that the GUI have to set the focus back to the textbox and clear up the value inside...
this is my coding,how to modify it to let me to performed this kind of action:import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class attGUI extends JFrame implements ActionListener{
    private JTextField id;
    private JLabel label1;
    private JLabel topLabel;
    private JButton ok;
public attGUI (String title){
    buildGUI();
    setTitle(title);
    pack();
    setVisible(true);
    //JFrame.setSize(32);
private void buildGUI(){
    Container contentPane=getContentPane();
    contentPane.setLayout(new BorderLayout());
    id=new JTextField(10);
    label1=new JLabel("Student ID");
    topLabel=new JLabel("Welcome to Student Attendance System!!!");
    topLabel.setFont(new java.awt.Font("Franklin Gothic Demi", 1, 18));
    ok=new JButton("OK");
    ok.addActionListener(this);
    JPanel inputPanel=new JPanel();
    inputPanel.add(label1);
    inputPanel.add(id);
    contentPane.add("North",topLabel);
    contentPane.add("Center",inputPanel);
    contentPane.add("South",ok);
public void actionPerformed(ActionEvent e){
    if(e.getSource() == ok)
     String Stuid= id.getText();
     attend a= new attend(Stuid);
public static void main(String args[])
     new attGUI("Student Attendance System");
}

Answer 1

May I suggest you read this [url http://java.sun.com/developer/JDCTechTips/2005/tt0518.html#1]VALIDATING TEXT AND FILTERING DOCUMENTS ?