我正在编写一个小型演示程序来显示一个消息框以在黑莓中运行。当我单击对话框上的确定按钮时，它会抛出一个 JVM 错误 104，未捕获：运行时异常。请问有什么帮助吗？这是代码：
import net.rim.device.api.ui.FieldChangeListener;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.*;
import net.rim.device.api.ui.container.HorizontalFieldManager;
import net.rim.device.api.ui.container.MainScreen;
import net.rim.device.api.ui.container.VerticalFieldManager;
import net.rim.device.api.ui.*;
import net.rim.device.api.ui.container.*;
public class My_First_App extends UiApplication
{
public static void main(String[] args)
{
My_First_App theApp = new My_First_App();
theApp.enterEventDispatcher();
}
public My_First_App()
{
pushScreen(new My_First_AppScreen());
}
}
final class My_First_AppScreen extends MainScreen
{
public My_First_AppScreen()
{
super();
HorizontalFieldManager _fieldmanager;
_fieldmanager = new HorizontalFieldManager();
/* declare one label to how the application title */
LabelField applicationtitle = new LabelField("Demo",LabelField.ELLIPSIS | LabelField.USE_ALL_WIDTH);
ButtonField _pairMe = new ButtonField("PairMe");
FieldChangeListener listenerPairMe = new FieldChangeListener() {
public void fieldChanged(Field field, int context){
Dialog.alert("You clicked the button!");
}
};
/*set the title*/
add(_fieldmanager);
setTitle(applicationtitle);
_fieldmanager.add(_pairMe);
_pairMe.setChangeListener(listenerPairMe);
}
public boolean onClose()
{
Dialog.alert("Goodbye!");
System.exit(0);
return true;
}
}