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How to add key listener event handler to JTextField?

In this small swing example we demonstrate how to use KeyAdapter class to handle keyboard event for the text field component to change the text-field's text to uppercase.

package com.javacoderanch.example.swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

public class UppercaseTextFieldDemo extends JFrame {
    public UppercaseTextFieldDemo() throws HeadlessException {

    protected void initComponents() {
        // Set default form size, closing event and layout manager
        setSize(200, 200);
        getContentPane().setLayout(new FlowLayout(FlowLayout.LEFT));

        // Create a label and text field for our demo application and add the
        // component to the frame content pane object.
        JLabel usernameLabel = new JLabel("Username: ");
        JTextField usernameTextField = new JTextField();
        usernameTextField.setPreferredSize(new Dimension(100, 20));

        // Register a KeyListener for the text field. Using the KeyAdapter class
        // allow us implement the only key listener event that we want to listen,
        // in this example we use the keyReleased event.
        usernameTextField.addKeyListener(new KeyAdapter() {
            public void keyReleased(KeyEvent e) {
                JTextField textField = (JTextField) e.getSource();
                String text = textField.getText();

            public void keyTyped(KeyEvent e) {
                // TODO: Do something for the keyTyped event

            public void keyPressed(KeyEvent e) {
                // TODO: Do something for the keyPressed event

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                // Create a new instance of our application and display it.
                new UppercaseTextFieldDemo().setVisible(true);