Validation in JTextField

Question

Hi ,
I have a JTextField, a JComboBox , a JButton , a JList and a JTable in my Frame. I enter a value in JTextField which has to be validated with a constant. Where do u write the validation ?
i have written the validation in focus lost of JTextField.
This causes problem when i click on the jtable or jcombobox. When i click on the combobox after entering a wrong value in the textfield, cursor remains in the jtextfield but i am able selected a value from the jcombobox as well.
Following is the sample code.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.table.*;
* Title:
* Description:
* Copyright: Copyright (c) 2001
* Company:
* @author
* @version 1.0
public class EnabledTest extends JFrame implements FocusListener
JTextField jTextField1 = new JTextField();
JTextField jTextField2 = new JTextField();
JComboBox jComboBox1 = new JComboBox();
JList jList1 = new JList();
JButton jButton1 = new JButton();
JTable jTable1 = new JTable();
public EnabledTest()
try
jbInit();
addListeners();
catch(Exception e) {
e.printStackTrace();
public static void main(String[] args)
EnabledTest enabledTest1 = new EnabledTest();
enabledTest1.setVisible(true);
enabledTest1.setBounds(0,0,400,400);
public void addListeners()
jTextField1.addFocusListener(this);
jTextField2.addFocusListener(this);
jComboBox1.addFocusListener(this);
jList1.addFocusListener(this);
jButton1.addFocusListener(this);
public void focusGained(FocusEvent e)
public void focusLost(FocusEvent e)
if(e.getSource() == jTextField1)
jTextField1_validationPerformed(e);
private void jbInit() throws Exception
jTextField1.setText("jTextField1");
jTextField1.setBounds(new Rectangle(49, 39, 144, 38));
this.getContentPane().setLayout(null);
jTextField2.setBounds(new Rectangle(227, 40, 144, 38));
jTextField2.setText("jTextField1");
jComboBox1.setBounds(new Rectangle(52, 115, 141, 34));
jComboBox1.addItem("one");
jComboBox1.addItem("two");
jList1.setBounds(new Rectangle(239, 110, 135, 120));
jButton1.setText("jButton1");
jButton1.setBounds(new Rectangle(56, 187, 127, 29));
jTable1.setBounds(new Rectangle(55, 251, 330, 117));
jTable1.setModel(new DefaultTableModel(3,3));
this.getContentPane().add(jTextField1, null);
this.getContentPane().add(jTextField2, null);
this.getContentPane().add(jComboBox1, null);
this.getContentPane().add(jList1, null);
this.getContentPane().add(jButton1, null);
this.getContentPane().add(jTable1, null);
private void jTextField1_validationPerformed(FocusEvent e)
jTextField1.removeFocusListener(this);
int intValue = new Integer(jTextField1.getText()).intValue();
if (intValue > 100)
JOptionPane.showMessageDialog(this, "Should be < 100");
jTextField1.requestFocus();
jTextField1.addFocusListener(this);
}

Answer 1

It is fairly easy to validate for a range. I added this kind of validation (attached (*)). At any time you may want to set the validity range of your NumericJTextField. I did it as follows:
this.numericTextField.setValidityRange(-999, +999);
I tested and it does work nicely - couldn't fool it.
(*) Is there any holy way to post files without having to cut and paste them as a whole in this doubly holy tab-eater JTextArea :-(
package textfieldvalidator;
* Title: NumericJTextField
* Description: An example JTextFiled that accepts only digits
* Copyright: nobody - use it at will
* Company:
* @author Antonio Bigazzi - [email protected]
* @version 1.0 First and last
import javax.swing.*;
import javax.swing.text.*;
import java.awt.*;
public class ValidatorExample extends JPanel {
NumericJTextField numericTextField; // accepts only digit
JTable table;
public ValidatorExample() {
this.setLayout(new BorderLayout());
this.numericTextField = new NumericJTextField("1234X5");
this.numericTextField.setBackground(Color.black);
this.numericTextField.setForeground(Color.yellow);
this.numericTextField.setCaretColor(Color.white);
this.numericTextField.setFont(new Font("Monospaced", Font.BOLD, 16));
this.numericTextField.setValidityRange(-999, +999);
this.table = new JTable(
new String[][] { {"a1a", "b2b", "c3c"}, {"456", "777", "234"}},
new String[] {"Col 1", "Col 2", "Col 3"}
this.add(this.numericTextField, BorderLayout.NORTH);
this.add(this.table, BorderLayout.CENTER);
public static void main(String[] args) {
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setContentPane(new ValidatorExample());
f.setLocation(300, 75);
f.pack();
f.setVisible(true);
// ===================== the meat ============================
// the specialized JTextField that uses a restrictive doc model
class NumericJTextField extends JTextField {
NumericJTextField() {this("", 0);}
NumericJTextField(String text) {this(text, 0);}
NumericJTextField(int columns) {this("", columns);}
NumericJTextField(String text, int columns) {
super(new NumericDocument(), text, columns);
public void setValidityRange(int min, int max) {
((NumericDocument)this.getDocument()).setValidityRange(min, max);
// check what may have been there already (via constructor)
this.setText(this.getText());
// the restricted doc model - non-numbers make it beep
class NumericDocument extends PlainDocument {
protected int minValue = Integer.MIN_VALUE;
protected int maxValue = Integer.MAX_VALUE;
public void setValidityRange(int minValue, int maxValue) {
this.minValue = minValue;
this.maxValue = maxValue;
public void insertString(int offset, String text, AttributeSet a)
throws BadLocationException {
// digits only please (or bring your own restriction/validation)
StringBuffer buf = new StringBuffer(text.length());
for (int i = 0; i < text.length(); i++) {
     if (Character.isDigit(text.charAt(i))) {
     buf.append(text.charAt(i));
     } else {
     java.awt.Toolkit.getDefaultToolkit().beep();
super.insertString(offset, buf.toString(), a);
// get the whole "document" back for range validation
while(true) {
String num = this.getText(0, this.getLength());
     if (num.length() == 0) break;
     int value = Integer.parseInt(num);
     if (value >= this.minValue && value <= this.maxValue) {
     break;
     } else {
     // beeep and chop (or whatever reaction for out of range)
     java.awt.Toolkit.getDefaultToolkit().beep();
     this.remove(this.getLength() - 1, 1);
// Note: in insertString, length is 1 when typing, but it can be anything
// when the text comes from the constructor, when it is pasted, etc.
}