public class DoublyLinkedList<E> {
    protected int count; // list size 
    protected Node<E> head; // ref. to first element
    // The tail element will be accessible as head.previous()
    // and tail.next will be head 
    public DoublyLinkedList() {
        // post: generates an empty list 
        head = null; 
        count = 0; 
    }
    
    public void addFirst(E value) {
        // post: value is added to beginning of list 
        if (head == null) {
            head = new Node<E>(value, null, null);
            head.setNext(head);
            head.setPrevious(head);
        }
        else {
            Node<E> newNode = new Node<E>(value, head, head.previous());
            head.previous().setNext(newNode);
            head.setPrevious(newNode);
            head = newNode;
        }
        count++; 
    }