百分相赠:helloworld问题

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class helloWorld extends MIDlet implements CommandListener
{
private Form mainForm;

private StringItem helloString;


public helloWorld(){
mainForm = new Form("Hello World Form");
mainForm.addCommand( new Command("Beenden", Command.EXIT, 0));
mainForm.setCommandListener(this);


helloString = new StringItem("Hello Label","\nHello World!");

mainForm.append(helloString);
}

public void commandAction(Command c, Displayable d) {
if (c.getCommandType() == c.EXIT ) {
destroyApp(false);
notifyDestroyed();
}
}

public void startApp() {
Display.getDisplay(this).setCurrent(mainForm);
}

public void pauseApp() {}
public void destroyApp(boolean unconditional) {}
}



上面是在网上拷来的
在Sun Java Wireless Toolkit运行时

出来以下错误 ：
Unable to create MIDlet helloWorld_MIDlet
java.lang.ClassNotFoundException: helloWorld_MIDlet
at com.sun.midp.midlet.MIDletState.createMIDlet(+29)
at com.sun.midp.midlet.Selector.run(+22)

是不是有什么问题呀？