Linked List trouble

Question

//I need to add a header node into this Linked list class and
// i dont understand it. can anyone give me a few pointers.
// This is the orginal code. What im trying to figure out is below.
public abstract class LinkedList implements ListInterface
protected class ListNode
// Used to hold references tolist nodes for the linked list implementation
protected Listable info; // the info in a list node
protected ListNode next; // a link to the next node on the list
protected ListNode list; // reference to the first node on the list
protected int numItems; // Number of elements in the list
protected ListNode currentPos; // Current position for iteration
public LinkedList()
// Creates an empty list object.
numItems = 0;
list = null;
currentPos = null;
public boolean isFull()
// Determines whether this list is full.
return false;
public int lengthIs()
// Determines the number of elements on this list.
return numItems;
public abstract boolean isThere (Listable item);
// Determines if element matching item is on this list.
public Listable retrieve (Listable item)
// Returns a copy of the list element with the same key as item.
ListNode location = list;
boolean found = false;
while (!found)
if (item.compareTo(location.info) == 0) // if they match
found = true;
else
location = location.next;
return location.info.copy();
public abstract void insert (Listable item);
// Adds a copy of item to this list.
public void delete (Listable item)
// Deletes the element of this list whose key matches item�s key.
ListNode location = list;
// Locate node to be deleted.
if (item.compareTo(location.info) == 0)
list = list.next; // Delete first node.
else
while (item.compareTo(location.next.info) != 0)
location = location.next;
// Delete node at location.next.
location.next = location.next.next;
numItems--;
public void reset()
// Initializes current position for an iteration through this list.
currentPos = list;
public Listable getNextItem ()
// Returns copy of the next element in list.
Listable nextItemInfo = currentPos.info.copy();
if (currentPos.next == null)
currentPos = list;
else
currentPos = currentPos.next;
return nextItemInfo;
//now heres the part i dont get i need to make list point to a new
// node say HeaderNode. Now wouldnt just...
public LinkedList()
// Creates an empty list object.
numItems = 0;
list.next = HeaderNode; //....this line do the trick???
currentPos = null;
I know that i cant use any insert methods to put it in, so what else could i possibly do?

Answer 1

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