code: public static int frequency(Iterator<?> iterator, @Nullable Object element) {
      int count = 0;
      while (contains(iterator, element)) {
        // Since it lives in the same class, we know contains gets to the element and then stops,
        // though that isn't currently publicly documented.
        count++;
      }
      return count;
    }
docs: Returns the number of elements in the specified iterator that equal the specified object. The
  iterator will be left exhausted: its {@code hasNext()} method will return {@code false}.
  
  @see Collections#frequency