code: public boolean addAll(Collection<E> items){
          boolean modified = false;
          for(E e : items){
              modified = add(e) || modified;
          }
          return modified;
      }
docs: Add the given collection of items. Only those items which are not yet contained in the queue are added, in the
  order of iteration through the given collection. Runs in linear time, assuming the hash function disperses the
  elements properly among the buckets of the underlying hash set.
  
  @param items items to add to the queue
  @return <code>true</code> if the queue is modified, i.e. if at least one new item has been added