code: public Observable<ArrayList<SoundCloudTrack>> getArtistTracks() {
          checkState();
          if (mCacheRam.tracks.size() != 0) {
              return Observable.create(new Observable.OnSubscribe<ArrayList<SoundCloudTrack>>() {
                  @Override
                  public void call(Subscriber<? super ArrayList<SoundCloudTrack>> subscriber) {
                      subscriber.onNext(mCacheRam.tracks);
                      subscriber.onCompleted();
                  }
              });
          } else {
              return mRetrofitService.getUserTracks(mArtistName)
                      .map(RxParser.PARSE_USER_TRACKS)
                      .map(cacheTracks());
          }
      }
docs: Retrieve the public tracks of the supported artist.
  
  @return {@link rx.Observable} on an ArrayList of the artist's tracks.