code: private AdView prefetchAds(int cntToPrefetch){
          AdView last = null;
          for (int i = 0; i < cntToPrefetch; i++) {
              final AdView item = AdViewHelper.getBannerAdView(mContext, adFetcher.takeNextAdPreset());
              adFetcher.setupAd(item);
              //50 ms throttling to prevent a high-load of server
              new Handler(mContext.getMainLooper()).postDelayed(new Runnable() {
                  @Override
                  public void run() {
                      adFetcher.fetchAd(item);
                  }
              }, 50 * i);
              last = item;
          }
          return last;
      }
docs: Creates N instances {@link AdView} from the next N taken instances {@link BannerAdPreset}
  Will start async prefetch of ad blocks to use its further
  @return last created banner AdView