code: public void run() {
          // TODO: if we had a way to check for in-memory hits, we could improve performance by
          // fetching an image from the in-memory cache on the main thread
          Bitmap bitmap = imageCache.getBitmap(imageUrl);
  
          if (bitmap == null) {
              bitmap = downloadImage();
          }
  
          // TODO: gracefully handle this case.
          notifyImageLoaded(imageUrl, bitmap);
  
      }
docs: The job method run on a worker thread. It will first query the image cache, and on a miss,
  download the image from the Web.