RxJava vs Callback

gistfile1.txt

    /*
     * Standard way
     */
//    MarvelAndroid.getInstance().getCharacters(queryParams,
//        new ResponseCallback<com.n8.marveldroid.EntityModelObjects.Character>() {
//          @Override
//          public void onRequestComplete(List<Character> responseEntities, Throwable error) {
//            if (error != null) {
//              mResultTextView.setText(error.getLocalizedMessage());
//              return;
//            }
//
//            String msg = "";
//            for (Character character : responseEntities) {
//              msg += character.name + "\n";
//            }
//
//            mResultTextView.setText(msg);
//
//            MarvelAndroid.getInstance().getComicsForCharacterId(responseEntities.get(3).id,
//                new ComicQueryParams(), new Callback<ServiceResponse<Comic>>() {
//                  @Override
//                  public void success(ServiceResponse<Comic> comicServiceResponse,
//                      Response response) {
//                    String imagePath = comicServiceResponse.data.results.get(0).images.get(0).path;
//                    imagePath += "/portrait_xlarge.jpg";
//                    Log.d("foo", imagePath);
//                    Picasso.with(MainActivity.this).load(imagePath).into(mImageView);
//                  }
//
//                  @Override
//                  public void failure(RetrofitError error) {
//                    mResultTextView.setText(error.getLocalizedMessage());
//                    Log.d("foo", error.getLocalizedMessage());
//                  }
//                });
//          }
//        });

    /*
     * RxJava
     */
    MarvelAndroid.getInstance().getCharacters(queryParams).
        map(p1 -> new Pair<>(p1, p1.data.results.get(3).id)).
        flatMap((p1) -> {
          Observable<ServiceResponse<Character>> characterObservable = Observable.just(p1.first);
          return MarvelAndroid.getInstance().getComicsForCharacterId(p1.second, new ComicQueryParams()).
              zipWith(characterObservable, (comic, character) -> new Pair<>(character, comic));
        }).
        observeOn(AndroidSchedulers.mainThread()).
        subscribeOn(Schedulers.io()).
        subscribe(pair -> {
            String msg = "";
            for (Character character : pair.first.data.results) {
              msg += character.name + "\n";
            }

            mResultTextView.setText(msg);

            String imagePath = pair.second.data.results.get(0).images.get(0).path;
            imagePath += "/portrait_xlarge.jpg";
            Log.d("foo", imagePath);
            Picasso.with(MainActivity.this).load(imagePath).into(mImageView);
          },
          error -> mResultTextView.setText(error.getLocalizedMessage()),
          ()->{});

  }