interface-example.java

// Create a new interface
public interface UIUpdatable {
    public void updateUI(String message);
}

// Implement the new interface on the activity
public class QuestionNew extends AppCompatActivity implements UIUpdatable {

     public TextView txtView;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
          txtView = findViewById(R.id.txt_view);

          // inject this activity to the async test
          new CCListener(this).execute(new String[]{"AnyData"}); // start your task
     }

     // method that comes from the interface
     @Override
     public void updateUI(String str) {
         txtView.setText(str);
     }

}

// Your async task
public class CCListener extends AsyncTask<Void, Void, Void> {

    UIUpdatable uiUpdatable;

    // Constructor, dependency injection
    public AsyncTest(Activity activity){
        uiUpdatable = (UIUpdatable)activity;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

        uiUpdatable.updateUI(result);
    }

}