doubly linked list

package linkedlist;

public class SortedLinkedListDouble {
    private Node first;
    private Node last;
    int size;

    public SortedLinkedListDouble() {
        first = new Node();
        last = new Node();
        first.next = last;
        last.prev = first;
        size = 0;
    }

    /**
     * Adds e to the list, so the list is still sorted by natural ordering of the
     * elements
     */
    public void addElement(String e) {
    }

    /**
     * Udskriver elementerne i listen i sorteret rækkefølge
     */
    public void udskrivElements() {
        Node temp = first;
        while (temp != null) {
            System.out.println(temp.data);
            temp = temp.next;
        }
    }

    /**
     * @return antal af elementer i listen
     */
    public int countElements() {
        int count = 0;
        Node temp = first;
        while (temp != null) {
            count++;
            temp = temp.next;
        }
        return count;
    }

    /**
     * Fjerner det sidste element i listen
     *
     * @return true hvis et element blev fjernet, ellers false
     */
    public boolean removeLast() {
        if (first != null) {
        } else if (first.next == null) {
            first = null;
            return true;
        } else {
            Node temp = first;
            while (temp.next != null) {
                if (temp.next.next == null) {
                    temp.next = null;
                } else {
                    temp = temp.next;
                }
            }
            return true;
        }
        return false;
    }

    /**
     * Fjerner første element i listen
     *
     * @param element
     * @return true hvis e blev fjernet, ellers false
     */
    public boolean removeElement(String e) {
        if (first != null) {
            if (first.data.equals(e)) {
                first = first.next;
            } else {
                Node temp = first;
                boolean found = false;
                while (!found && temp.next != null) {
                    if (temp.next.data.equals(e)) {
                        found = true;
                    } else {
                        temp = temp.next;
                    }
                }
                if (found) {
                    Node temp2 = temp.next;
                    temp.next = temp2.next;
                    temp2.next = null;
                }
            }
        }
        return false;
    }

    /**
     * Adds all the elements from list to the actual list. The list should still be
     * sorted by natural ordering of the elements
     */
    public void addAll(SortedLinkedList list) {
    }

    class Node {
        public String data;
        public Node next;
        public Node prev;
    }
}