MainFragment.java

public class MainFragment extends Fragment {
    
    ...
    
    // ------------------
    //  RX JAVA
    // ------------------

    // 3 - Create an observable that will run a long request...
    private Observable<String> getObservable(){
        return Observable.just("Long process is ended !")
                .delay(10, TimeUnit.SECONDS)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread());
    }

    // 4 - Create a observer that will subscribe on it
    private DisposableObserver<String> getSubscriber(){
        return new DisposableObserver<String>() {
            @Override
            public void onNext(String result) {
                Log.e("TAG","On Next");
                updateUIWhenStoppingOperation(result);
            }

            @Override
            public void onError(Throwable e) {
                Log.e("TAG","On Error");
            }

            @Override
            public void onComplete() {
                Log.e("TAG","On Complete !!");
            }
        };
    }
    
    ...
        
    // ------------------
    //  UPDATE UI
    // ------------------

    // 5 - We update a TextView when observable starts
    private void updateUIWhenStartingOperation(){
        this.textView.setText("Starting long process...");
    }
    
    // 6 - We update a TextView with result of observable
    private void updateUIWhenStoppingOperation(String result){
        this.textView.setText(result);
    }
    
    ....
    
}