Limit a TextField to Uppercase

import java.awt.*;
import java.awt.event.*;
public class UpperTF extends Frame {
public static void main(String argv[]) {
new UpperTF().setVisible(true);
}
public UpperTF() {
setLayout(new FlowLayout());
TextField tf = new TextField(10);
add(tf);
tf.addKeyListener( new KeyAdapter() {
public void keyPressed(KeyEvent e) {
if (Character.isLetter(e.getKeyChar())) e.setModifiers(Event.SHIFT_MASK); } });
pack();
addWindowListener( new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
} } ); }
public Dimension getPreferredSize() {
return new Dimension(200,200);
}}