Revise the class StringLinkedList in Listing 12.5 so that it can add and remove items from the end of the list.

Listing 12.5

public class StringLinkedList
{
private ListNode head;
public StringLinkedList()
{
head = null;
}
/**
Displays the data on the list.
*/
public void showList()
{
ListNode position = head;
while (position != null)
{
System.out.println(position.getData());
position = position.getLink();
}
}
/**
Returns the number of nodes on the list.
*/
public int length()
{
int count = 0.
ListNode position = head;
while (position != null)
{
count++;
position = position.getLink();
}
return count;
}
/**
Adds a node containing the data addData at the
start of the list.
*/
public void addANodeToStart(String addData)
{
head = new ListNode(addData, head);
}
/**
Deletes the first node on the list.
*/
public void deleteHeadNode()
{
if (head != null)
head = head.getLink();
else
{
System.out.println("Deleting from an empty list.");
System.exit(0);
}
}
/**
Sees whether target is on the list.
*/
public boolean onList(String target)
{
return find(target) != null;
}
//Returns a reference to the first node containing the
//target data. If target is not on the list, returns null.
private ListNode find(String target)
{
boolean found = false;
ListNode position = head;
while ((position != null) && !found)
{
String dataAtPosition = position.getData();
if (dataAtPosition.equals(target))
found = true;
else
position = position.getLink();
}
return position
}
}