Restrict the input string length

Question

Hi, how do I restrict the input string length in a JTextField. Suppose if I want my text field to accept only 4 characters, the fifth character I try to enter shouldn't be accepted in the field.
Thanks,
Kalyan.

Answer 1

This is for 6 characters limit
//create a JTextField that is six characters long
JTextField textField = new JTextField(new FixedNumericDocument(5,true),"", 6);
Here boolean true means only numeric. set to false to take in alphanumeric.
import javax.swing.*;
import javax.swing.text.*;
import java.awt.*;
public class FixedNumericDocument extends PlainDocument {
private int maxLength = 9999;
private boolean numericOnly;
public FixedNumericDocument(int maxLength, boolean numericOnly) {
super();
this.maxLength = maxLength;
this.numericOnly = numericOnly;
//this is where we'll control all input to our document.
//If the text that is being entered passes our criteria, then we'll just call
//super.insertString(...)
public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException {
if (getLength() + str.length() > maxLength) {
return;
else {
try {
if (numericOnly) {
Integer.parseInt(str);
//if we get here then str contains only numbers
//so that it can be inserted
super.insertString(offset, str, attr);
catch(NumberFormatException exp) {
return;
return;