gistfile1.txt

        /**
         * Append a node of value val to the last element of the linked list.
         */
        public void addAtTail(int val)
        {
            Link link = new Link(val);
            //<--
            tail.prev.next = link;
            link.prev = tail.prev;
            //-->
            link.next = tail;
            tail.prev = link;
            size++;
        }