code: @NotNull
      public static <T> ComparatorCompat<T> comparingInt(
              @NotNull final ToIntFunction<? super T> keyExtractor) {
          Objects.requireNonNull(keyExtractor);
          return new ComparatorCompat<T>(new Comparator<T>() {
  
              @Override
              public int compare(T t1, T t2) {
                  final int i1 = keyExtractor.applyAsInt(t1);
                  final int i2 = keyExtractor.applyAsInt(t2);
                  return Objects.compareInt(i1, i2);
              }
          });
      }
docs: Returns a comparator that uses a function that extracts
  an {@code int} sort key to be compared.
  
  @param <T> the type of the objects compared by the comparator
  @param keyExtractor  the function that extracts the sort key
  @return a comparator
  @throws NullPointerException if {@code keyExtractor} is null