在其他类中实现的调用接口方法上的空指针异常

onSelectedListener mCallback;

永远不会初始化，或者正在使用null值初始化。

public class Common{    onSelectedListener mCallback = new onSelectedListener(){        public void getFailureDialog(){ JOptionPane.showMessageDialog(null, "An Error Has Occurred.");        }    };    public interface onSelectedListener     {        public void getFailureDialog();    }    public void myRecord(String email)    {        mCallback.getFailureDialog();  //now this works.    }}