test.java

class Presenter {
 Interactor interactor;
 IUiCallback uiCallback;
 public void login(String userName, String password) {
  interactor.performLogin(userName, password, new ErrorOrSuccessCallback() {
    public void onSuccess(Object obj) {
     prepareDataForUi(obj);
    }
    public void onError(String message) {}
   };
  }

 private void prepareDataForUi(Object obj) {
   uiCallback.updateUi(...);
  }
 }


 class Interactor {
  public void login(String userName, String password, ErrorOrSuccessCallback callback) {
   if (success) {
    callback.onSuccess(obj);
   } else {
    callback.onError(“Error”);
   }

  }
  interface ErrorOrSuccessCallback {
   void onSuccess(Object object);
   void onError(String message);
  }
 }