code: public String[] getLocations() throws IOException {
      HashSet<String> hosts = new HashSet<String>();
      for (InputSplit s : splits) {
        String[] hints = s.getLocations();
        if (hints != null && hints.length > 0) {
          for (String host : hints) {
            hosts.add(host);
          }
        }
      }
      return hosts.toArray(new String[hosts.size()]);
    }
docs: Collect a set of hosts from all child InputSplits.