Format JTextField

Question

How can I format the JTextField to receive a certain input String like currency or decimal point. I know that I can write a function to validate those strings but it is more convinient to user if the text field just let them replace string of zero like Visual Basic.

Answer 1

Use this class..
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusListener;
import java.text.NumberFormat;
import java.text.ParseException;
import javax.swing.JTextField;
import javax.swing.text.Document;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;
public class JFormattedField extends JTextField implements ActionListener, FocusListener {
private NumberFormat format;
public JFormattedField() {
     this(0.0, 8, new java.text.DecimalFormat("0.00000"));
public JFormattedField(String value, int columns) {
     this(value, columns, new java.text.DecimalFormat("0.00000"));
public JFormattedField(String value, int columns, NumberFormat f) {
     this(Double.parseDouble(value), columns, f);
public JFormattedField(double value, int columns, NumberFormat f) {
super(columns);
format = f;
     setHorizontalAlignment(JTextField.RIGHT);
     addActionListener(this);
     addFocusListener(this);
setValue(value);
public void focusGained(java.awt.event.FocusEvent f) { }
public void focusLost(java.awt.event.FocusEvent f) {
     try {
     if (!f.isTemporary())
          setValue(Double.parseDouble(getText()));
     } catch (NumberFormatException ne) {
          Toolkit.getDefaultToolkit().beep();
public void actionPerformed(ActionEvent a) {
     try {
     setValue(Double.parseDouble(a.getActionCommand()));
     } catch (NumberFormatException ne) {
     Toolkit.getDefaultToolkit().beep();
public double getValue() {
double retVal = 0.0;
try {
retVal = format.parse(getText()).doubleValue();
} catch (ParseException e) {
Toolkit.getDefaultToolkit().beep();
return retVal;
public void setValue(double value) {
setText(format.format(value));
public void setValue(String value) {
setText(value);
protected Document createDefaultModel() {
return new NumberDocument(format);
private class NumberDocument extends PlainDocument {
     NumberFormat format;
     NumberDocument(NumberFormat f) {
     this.format = f;
public void insertString(int offset, String string, AttributeSet as) throws BadLocationException {
     final String NUMBERS = "-.,0123456789";
     try {
          char [] src = string.toCharArray();
          char [] dest = new char[src.length];
          int count=0;
          for (int i=0; i<src.length; i++)
          if (NUMBERS.indexOf(src) != -1)
               dest[count++] = src[i];
          super.insertString(offset, new String(dest, 0, count), as);
     } catch (Exception e) {
          e.printStackTrace(System.err);
Sample test program...
import javax.swing.text.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
import java.awt.*;
import tools.*;
public class Field extends JFrame {
public Field() {
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(2, 1));
panel.add(new JFormattedField(0.0,11,new java.text.DecimalFormat("0.00000")));
panel.add(new JFormattedField(0.0,11,new java.text.DecimalFormat("0.00")));
panel.add(new JFormattedField("1",11,new java.text.DecimalFormat("0.00")));
getContentPane().add(panel);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent event) {
System.exit(0);
pack();
public static void main(String[] args) {
(new Field()).show();
Hope it helps..
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