code: public static function reverseOrder(Comparator $comparator = null) : Comparator
      {
          if ($comparator === null) {
              $comparator = ComparableComparator::instance();
          }
          return new ReverseComparator($comparator);
      }
docs: Returns a comparator that imposes the reverse ordering of the specified comparator.
  
  <p>
  If the specified comparator is null, it returns a comparator that imposes the reverse of the natural ordering
  on a collection of objects that implement the {@link Comparable} interface.
  (The natural ordering is the ordering imposed by the objects' own compareTo method.)
  
  <p>
  This enables a simple idiom for sorting (or maintaining) collections (or arrays) of objects
  that implement the {@link Comparable} interface in reverse-natural-order.
  For example, suppose a is an array. Then:
  
  <pre>
  Arrays::sortWith(a, Collections::reverseOrder());
  </pre>
  
  sorts the array in reverse order.
  
  @param Comparator $comparator
  @return Comparator