public class LinkedList<E> {

 /**
 * The root of the list keeps a reference to both the first and last
 * elements of the list.
 */
 private LinkedListNode<E> head;

 /**
 * Creates a new linked list.
 */
 public LinkedList() {
 head = new LinkedListNode<>();
 }

 /**
 * Returns the first linked list node in the list.
 *
 * @return the first element of the list.
 */
 public LinkedListNode<E> getFirst() {
 LinkedListNode<E> node = head.next;
 if (node == head) {
 return null;
 }
 return node;
 }

 /**
 * Returns the last linked list node in the list.
 *
 * @return the last element of the list.
 */
 public LinkedListNode<E> getLast() {
 LinkedListNode<E> node = head.previous;
 if (node == head) {
 return null;
 }
 return node;
 }

 /**
 * Adds a node to the beginning of the list.
 *
 * @param node the node to add to the beginning of the list.
 */
 public LinkedListNode<E> addFirst(LinkedListNode<E> node) {
 return node.insert(head.next, head);
 }

 /**
 * Adds an object to the beginning of the list by automatically creating a a
 * new node and adding it to the beginning of the list.
 *
 * @param object the object to add to the beginning of the list.
 * @return the node created to wrap the object.
 */
 public LinkedListNode<E> addFirst(E object) {
 return new LinkedListNode<>(object, head.next, head);
 }

 /**
 * Adds a node to the end of the list.
 *
 * @param node the node to add to the beginning of the list.
 */
 public LinkedListNode<E> addLast(LinkedListNode<E> node) {
 return node.insert(head, head.previous);
 }

 /**
 * Adds an object to the end of the list by automatically creating a a new node and adding it to the end of the list.
 *
 * @param object the object to add to the end of the list.
 * @return the node created to wrap the object.
 */
 public LinkedListNode<E> addLast(E object) {
 return new LinkedListNode<>(object, head, head.previous);
 }

 /**
 * Erases all elements in the list and re-initializes it.
 */
 public void clear() {
 // Remove all references in the list.
 LinkedListNode<E> node = getLast();
 while (node != null) {
 node.remove();
 node = getLast();
 }

 // Re-initialize.
 head.next = head.previous = head;
 }

 /**
 * Returns a String representation of the linked list with a comma delimited
 * list of all the elements in the list.
 *
 * @return a String representation of the LinkedList.
 */
 @Override
 public String toString() {
 LinkedListNode<E> node = head.next;
 StringBuilder buf = new StringBuilder();
 while (node != head) {
 buf.append(node.toString()).append(", ");
 node = node.next;
 }
 return buf.toString();
 }

}