Insert & Delete Methods

public void insertNode(T insertItem){

        boolean found;

        DoubleLinkedListNode<T> current;//moving reference 

        DoubleLinkedListNode<T> trailCurrent = null; //just before current

        // Set up node to be inserted

        DoubleLinkedListNode<T> newNode = new DoubleLinkedListNode<T>();

        newNode.info = insertItem;

        newNode.next = null;

        newNode.back = null;

        //if the list is empty, newNode is the only node

        if (first == null) {

            first = newNode;

            last = newNode;

            count++;

        }

        else {

            found = false;

            current = first;

            //search the list

            while (current != null && !found) {

                Comparable<T> temp = (Comparable<T>) current.info;

                if (temp.compareTo(insertItem) >= 0)

                    found = true;

                else {

                    trailCurrent = current;

                    current = current.next;

                }

            } 

            //insert new node before first

            if (current == first) {

                first.back = newNode;

                newNode.next = first;

                first = newNode;

                count++;

            }

            else {

                //insert newNode between trailCurrent and current

                if (current != null) {

                    trailCurrent.next = newNode;

                    newNode.back = trailCurrent;

                    newNode.next = current;

                    current.back = newNode;

                }

                else {

                    //insert new node after last

                    trailCurrent.next = newNode;

                    newNode.back = trailCurrent;

                    last = newNode;

                }

                count++;

            }

        }

    }

     

    public void deleteNode(T deleteItem) {

        DoubleLinkedListNode<T> current; //moving reference 

        DoubleLinkedListNode<T> trailCurrent;//just before current 

        boolean found;

        if (first == null)

            System.err.println("Cannot delete from an empty list.");

        //if node to be deleted is the first node

        else if (first.info.equals(deleteItem)) {

            current = first;

            first = first.next;

            if (first != null)

                first.back = null;

            else

                last = null;

            count--;

        }

        else {

            found = false;

            current = first;

            //search the list

            while (current != null && !found) {

                Comparable<T> temp = (Comparable<T>) current.info;

                if (temp.compareTo(deleteItem) >= 0)

                    found = true;

                else

                    current = current.next;

            }

            if (current == null)

                System.out.println("The item to be deleted is not in the list.");

            else if (current.info.equals(deleteItem)) {

                trailCurrent = current.back;

                trailCurrent.next = current.next;

                if (current.next != null)

                    current.next.back = trailCurrent;

                if (current == last)

                    last = trailCurrent;

                count--;

            }

            else

                System.out.println("The item to be deleted is not in list.");

        }

    }