Method comparator

guava/src/com/google/common/graph/ElementOrder.java:152–157

Returns the {@link Comparator} used. @throws UnsupportedOperationException if comparator is not defined

()

   * @throws UnsupportedOperationException if comparator is not defined
   */
  public Comparator<T> comparator() {
    if (comparator != null) {
      return comparator;
    }
    throw new UnsupportedOperationException("This ordering does not define a comparator.");
  }

  @Override
  public boolean equals(@Nullable Object obj) {