/* pre: Have object to be added to calling doubly linked list object, and a link in the doubly linked list AFTER
* which the newItem's node must be added.
* post: newItem is the element of the added node of the doubly linked list. All other existing nodes of the
* doubly linked list retain their ordering relevant to the position of the newly added node.
* The counter is modified to reflect the addition of a new node to the doubly linked list. */
public void addAfter(Object newItem, DLLNode link)
{
// ADD CODE FOR METHOD addAfter BELOW
if (link == null)
{
this.addLast(newItem);
return;
}
DLLNode newNode = new DLLNode(newItem);
newNode.setNext(link.next());
if ((DLLNode)(link.next()) != null)
((DLLNode)(link.next())).setPrevious(newNode);
newNode.setPrevious(link);
link.setNext(newNode);
counter++;
}
/* pre: Have object to be added to calling doubly linked list object, and a link in the doubly linked list BEFORE
* which the newItem's node must be added.
* post: newItem is the element of the added node of the doubly linked list. All other existing nodes of the
* doubly linked list retain their ordering relevant to the position of the newly added node.
* The counter is modified to reflect the addition of a new node to the doubly linked list. */
public void addBefore(Object newItem, DLLNode link)
{
// ADD CODE FOR METHOD addBefore BELOW
if (link == null) // list either empty or must be added at end of list
{
this.addLast(newItem);
return;
}
DLLNode newNode = new DLLNode(newItem);
if (head == link) // must be added as first node
{
this.addFirst(newItem);
return;
}
newNode.setPrevious(link.previous());
newNode.setNext(link);
link.previous().setNext(newNode);
link.setPrevious(newNode);
counter++;
}
/* pre: Have object to be added to calling doubly linked list object, which may be empty.
* post: newItem is the element of the FIRST node of the doubly linked list. All other existing nodes of the
* doubly linked list retain their ordering AFTER the new first node.
* The counter is modified to reflect the addition of a new node to the doubly linked list. */
public void addFirst(Object newItem)
{
// ADD CODE FOR METHOD addFirst BELOW
DLLNode newNode = new DLLNode(newItem);
newNode.setNext(head);
if (head != null) // already has at least 1 node
head.setPrevious(newNode);
else // the new node is also the tail node
tail = newNode;
head = newNode;
counter++;
}
/* pre: Have at least one node in calling doubly linked list object.
* post: Return the node removed, which is the last node in the list.
* The counter is modified to reflect the removal of the last node from the doubly linked list. */
public DLLNode removeLast()
{
// ADD CODE FOR METHOD removeLast BELOW
DLLNode cur = tail;
if (cur.previous() == null) // then only one node in DLL
{
head = null;
tail = null;
}
else
{
tail = cur.previous();
tail.setNext(null);
cur.setPrevious(null);
}
counter--;
return cur;
}
protected DLLNode tail; // points to last node in the list
#endregion Fields
#region Constructors
public DoublyLinkedList()
{
counter = 0;
head = null;
tail = null;
}
/* pre: Have calling doubly linked list object.
* post: Empty the list. */
public void Clear()
{
// ADD CODE FOR METHOD Clear BELOW
this.head = null;
this.tail = null;
this.counter = 0;
}
/* pre: Have at least one node in calling doubly linked list object.
* post: Return the node removed, which is the first node in the list.
* The counter is modified to reflect the removal of the first node from the doubly linked list. */
public DLLNode removeFirst()
{
// ADD CODE FOR METHOD removeFirst BELOW
DLLNode cur = head;
head = (DLLNode)cur.next();
if (cur.next() != null)
{
((DLLNode)cur.next()).setPrevious(null);
cur.setNext(null);
}
else // only one node in list
tail = null;
counter--;
return cur;
}
/* pre: Have object to be added to calling doubly linked list object, which may be empty.
* post: newItem is the element of the LAST node of the doubly linked list. All other existing nodes of the
* doubly linked list retain their ordering BEFORE the new last node.
* The counter is modified to reflect the addition of a new node to the doubly linked list. */
public void addLast(Object newItem)
{
// ADD CODE FOR METHOD addLast BELOW
if (tail == null)
{
addFirst(newItem);
return;
}
DLLNode newNode = new DLLNode(newItem);
newNode.setPrevious(tail);
tail.setNext(newNode);
tail = newNode;
counter++;
}
public void setPrevious(DLLNode theLink)
{
BackLink = theLink;
}
public DLLNode()
: base()
{
BackLink = null;
}
public DLLNode(Object theElement)
: base(theElement)
{
BackLink = null;
}
public DLLNode(Object theElement, DLLNode theLink, DLLNode theBackLink)
: base(theElement, theLink)
{
BackLink = theBackLink;
}
