新手请问？

各位大侠：请问为什么我运行这个程序时总报这个异常：
java.lang.ClassNotFoundException: Hello
at com.sun.midp.midletsuite.MIDletSuiteImpl.loadInitialMIDlet(+18)
at com.sun.midp.dev.DevMIDletSuiteImpl.loadInitialMIDlet(+9)
at com.sun.midp.midlet.Scheduler.schedule(+31)
at com.sun.midp.dev.DevMIDletSuiteImpl.schedule(+7)
at com.sun.midp.Main.runLocalClass(+20)
at com.sun.midp.Main.main(+68)
Execution completed successfully
不知是什么原因请指教。

代码就是这样：

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


public class Hello extends MIDlet {

private Display display;

public Hello() {
display = Display.getDisplay(this);
}

public void startApp() {
TextBox t = new TextBox("Hello MIDlet", "Hello MIDP!", 256, 0);
display.setCurrent(t);
}

public void pauseApp() {
}

public void destroyApp(boolean unconditional) {
}
}