Membuat interface ItemStateListener pada JAVA (J2ME)

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.Calendar;
import java.util.TimeZone;
import java.util.Date;

public class DemoItemStateListener extends MIDlet
  implements CommandListener {
   
  private Display display;
  private Form form;

  private final Command cmdKeluar =
    new Command("Keluar", Command.EXIT, 1);
 
  public DemoItemStateListener() {
    display = Display.getDisplay(this);        
    form = new Form("Demo ItemStateListener");
    form.addCommand(cmdKeluar);
    form.setCommandListener(this);
  }
   
  public void startApp() {
    ItemStateListener listener = new ItemStateListener() {
      Calendar cal =
        Calendar.getInstance(TimeZone.getDefault()); 
       
      public void itemStateChanged(Item item) {
        cal.setTime(((DateField) item).getDate());
        Alert alert = new Alert("Informasi", null, null,
                        AlertType.INFO);
        alert.setTimeout(3000);
        alert.setString("Tanggal telah berhasil diubah.");
        display.setCurrent(alert, form);
      }     
    };
   
    form.setItemStateListener(listener);
    Date now = new Date();
    DateField dateItem = new DateField("Hari ini tanggal: ",
                           DateField.DATE);
    dateItem.setDate(now);
    form.append(dateItem);
    display.setCurrent(form);     
  }
   
  public void pauseApp() {
  }
   
  public void destroyApp(boolean unconditional) {
  }
   
  public void commandAction(Command c, Displayable s) {
    if (c == cmdKeluar) {
      destroyApp(false);
      notifyDestroyed();
    }
  }  
 
}