大家帮忙试下这段代码,关于TextField的,感谢

编译没问题,运行时出错,不知为什么

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

public class myTextField extends MIDlet{

private TextField aTextField;
private Display myDisplay;

public myTextField(){

myDisplay = Display.getDisplay(this);
aTextField = new TextField("info","lable",4,TextField.ANY);
}
public void startApp(){

Form aForm = new Form("form");
aForm.append(aTextField);
myDisplay.setCurrent(aForm);
}
public void pauseApp(){}
public void destroyApp(boolean unconditional){}


}