import java.applet.*;
 import java.awt.*;
 import java.awt.event.*;
 
 public class testENTER extends Applet implements KeyListener {
 
 TextField t;
 
 public void init(){
 TextField t = new TextField("press ENTER");
 add(t);
 t.addKeyListener(this);
 }
 
 public void keyTyped(KeyEvent e) {}
 public void keyReleased(KeyEvent e) {}
 public void keyPressed(KeyEvent e) {
 
 int key = e.getKeyCode();
 
 if (key == KeyEvent.VK_ENTER) {
 Toolkit.getDefaultToolkit().beep();
 System.out.println("ENTER pressed");
 }
 }
 }

 

Or the short version using the KeyAdapter class.

 import java.applet.*;
 import java.awt.*;
 import java.awt.event.*;
 
 public class testENTER extends Applet {
 
 TextField t;
 
 public void init(){
 
 TextField t = new TextField("press ENTER");
 add(t);
 
 t.addKeyListener
 (new KeyAdapter() {
 public void keyPressed(KeyEvent e) {
 int key = e.getKeyCode();
 if (key == KeyEvent.VK_ENTER) {
 Toolkit.getDefaultToolkit().beep(); 
 System.out.println("ENTER pressed");
 }
 }
 }
 );
 }
 }