code: public LabelCache labels(long applicationId)
      {
          LabelCache cache = labels.get(applicationId);
          if(cache == null)
              labels.put(applicationId, cache = new LabelCache(applicationId));
          return cache;
      }
docs: Returns the cache of labels for the given application, creating one if it doesn't exist .
  @param applicationId The id of the application for the cache of labels
  @return The cache of labels for the given application