code: public void pollAllToList(List<T> retList) {
      while (head != null) {
        retList.add(head.element);
        head = head.after;
      }
      this.clear();
    }
docs: Remove all elements from the set and return them in order. Traverse the
  link list, don't worry about hashtable - faster version of the parent
  method.
  
  @param retList put elements into the given list