Unable to create MIDlet null

A simple sample program from "Wireless java" by Jonathan knudsen. Couldn't go through.

I tried use both wireless tool kit(1.0.3 beta) and

command line, I can compile with no problem, Jar got

generated, but when I launch it from emulator, it gives

error like:

Unable to create MIDlet null

java.lang.NullPointerException

at com.sun.midp.midlet.Selector.commandAction(+47)

at javax.microedition.lcdui.Display$DisplayAccessor.commandAction(+144)

at com.sun.kvem.midp.lcdui.EmulEventHandler$EventLoop.run(+427)

I also have some samples from that book give me exactly the same messages. But still some programs from that book work fine as well as examples come with wireless tool kit.

Big confusion! Great appreciate for any help!

code:

import javax.microedition.midlet.*;

import javax.microedition.lcdui.*;

public class Commander extends MIDlet {

public void startApp() {

Displayable d = new TextBox("TextBox", "Commander", 20, 0);

Command c = new Command("Exit", Command.EXIT, 0);

d.addCommand(c);

d.setCommandListener(new CommandListener() {

public void commandAction(Command c, Displayable s) {

notifyDestroyed();

}

});

Display.getDisplay(this).setCurrent(d);

}

public void pauseApp() {}

public void destroyApp(boolean unconditional) {}

}

[1460 byte] By [raybao] at [2007-9-26 9:00:46]