code: public void swap(UnorderedCollection<E> other) {
          int sizeTmp = size;
          size = other.size;
          other.size = sizeTmp;
          storage.swap(other.storage);
      }
docs: Swaps the contents of this {@link UnorderedCollection} with another one storing the same elements. This operation
  runs in constant time, by only swapping storage references.
  
  @param other
  the {@link UnorderedCollection} to swap contents with.