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