code: public static <T> Set<T> modes(Collection<T> values) {
      Counter<T> counter = new ClassicCounter<T>(values);
      List<Double> sortedCounts = CollectionUtils.sorted(counter.values());
      Double highestCount = sortedCounts.get(sortedCounts.size() - 1);
      Counters.retainAbove(counter, highestCount);
      return counter.keySet();
    }
docs: Returns a list of all modes in the Collection.  (If the Collection has multiple items with the
  highest frequency, all of them will be returned.)