to presenter

public class MainActivity extends AppCompatActivity {
    private final String TAG = this.getClass().getSimpleName();
    private CompositeDisposable mCompositeDisposable = new CompositeDisposable();
    private Presenter mPresenter;
    Button button1;
    Button button2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button1 = findViewById(R.id.btn_1);
        button2 = findViewById(R.id.btn_2);
        mPresenter = new Presenter(this);
    }

    public Observable<Integer> getObs1() {
        return RxView.clicks(button1)
                .map(view -> 1);
    }

    public Observable<Integer> getObs2() {
        return RxView.clicks(button2)
                .map(view -> 2);
    }
}

public class Presenter {
    private final String TAG = this.getClass().getSimpleName();
    MainActivity mainActivity;

    Presenter(MainActivity mainActivity) {
        this.mainActivity = mainActivity;
        Observable.merge(mainActivity.getObs1(), mainActivity.getObs2())
                .switchMap(this::getObservable)
                .subscribe(data -> Log.d(TAG, (String) data));
    }

    Observable<String> getObservable(int id) {
        return Observable.interval(1, TimeUnit.SECONDS)
                .map(data -> "Obs" + String.valueOf(id) + ":" + data);
    }
}