Java Reference
In-Depth Information
(a)
firstNode
lastNode
12
7
11
5
(b)
firstNode
lastNode
12
7
11
5
removeItem
Fig. 21.8
|
Graphical representation of operation
removeFromFront
.
Method
removeFromBack
(lines 95-118 of Fig. 21.3) removes the last node of a list and
returns a reference to the removed data. The method throws an
EmptyListException
(lines 97-98) if the list is empty when the program calls this method. The steps are:
1.
Assign
lastNode.data
(the data being removed) to
removedItem
(line 100).
2.
If the
firstNode
and
lastNode
refer to the same object (line 103), the list has
only one element at this time. So, line 104 sets
firstNode
and
lastNode
to
null
to remove that node from the list (leaving the list empty).
3.
If the list has more than one node, create the
ListNode
reference
current
and as-
sign it
firstNode
(line 107).
4.
Now “walk the list” with
current
until it references the node before the last node.
The
while
loop (lines 110-111) assigns
current.nextNode
to
current
as long as
current.nextNode
(the next node in the list) is not
lastNode
.
5.
After locating the second-to-last node, assign
current
to
lastNode
(line 113) to
update which node is last in the list.
6.
Set the
current.nextNode
to
null
(line 114) to remove the last node from the
list and terminate the list at the current node.
7.
Return the
removedItem
reference (line 117).
In Fig. 21.9, part (a) illustrates the list before the removal operation. The dashed lines
and arrows in part (b) show the reference manipulations. [We limited the
List
insertion
