Java: public class Casillas2 extends Applet implements ItemListener

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
/*
<APPLET
    CODE=casillas2.class
    WIDTH=200
    HEIGHT=200 >
</APPLET>
*/
public class casillas2 extends Applet implements ItemListener {
    Checkbox checkbox1, checkbox2, checkbox3, checkbox4;
    TextField text1;
    public void init()
    {
        checkbox1 = new Checkbox("1");
        add(checkbox1);
        checkbox1.addItemListener(this);
        checkbox2 = new Checkbox("2");
        add(checkbox2);
        checkbox2.addItemListener(this);
        checkbox3 = new Checkbox("3");
        add(checkbox3);
        checkbox3.addItemListener(this);
        checkbox4 = new Checkbox("4");
        add(checkbox4);
        checkbox4.addItemListener(this);
        text1 = new TextField(35);
        add(text1);
    }
    public void itemStateChanged(ItemEvent e)
    {
        text1.setText("¡Casilla de activacion " + ((Checkbox) e.getItemSelectable()).getLabel() + " pulsada!");
    }
}