(Hãy nhớ rằng trong một chương trình nghiêm trọng sẽ được các mục dữ liệu nhiều hơn, hoặc một tham chiếu đến một đối tượng khác có chứa dữ liệu nhiều mặt hàng) Chương trình này chèn vào ba mục ở mặt trước của danh sách, chèn thêm ba ở cuối, và hiển thị các kết quả danh sách. | end main display again end class FirstLastApp For simplicity in this program we ve reduced the number of data items in each link from two to one. This makes it easier to display the link contents. Remember that in a serious program there would be many more data items or a reference to another object containing many data items. This program inserts three items at the front of the list inserts three more at the end and displays the resulting list. It then deletes the first two items and displays the list again. Here s the output List first-- last 66 44 22 11 33 55 List first-- last 22 11 33 55 Notice how repeated insertions at the front of the list reverse the order of the items while repeated insertions at the end preserve the order. The double-ended list class is called the FirstLastList. As discussed it has two data items first and last which point to the first item and the last item in the list. If there is only one item in the list then both first and last point to it and if there are no items they are both null. The class has a new method insertLast that inserts a new item at the end of the list. This involves modifying to point to the new link and then changing last to point to the new link as shown in Figure . Figure Insertion at the end of a list The insertion and deletion routines are similar to those in a single-ended list. However both insertion routines must watch out for the special case when the list is empty prior to the insertion. That is if isEmpty is true then insertFirst must set last to the new link and insertLast must set first to the new link. If inserting at the beginning with insertFirst first is set to point to the new link although when inserting at the end with insertLast last is set to point to the new link. Deleting from the start of the list is also a special case if it s the last item on the list last must be set to point to null in this case. - 160 - Unfortunately making a list double-ended doesn
