// Textbook fragment 06.06
public class DNode<E> implements Position<E> {
  private DNode<E> prev, next;  // References to the nodes before and after
  private E element;    // Element stored in this position
  /** Constructor */
  public DNode(DNode<E> newPrev, DNode<E> newNext, E elem) {
    prev = newPrev;
    next = newNext;
    element = elem;
  }
  // Method from interface Position
  public E element() throws InvalidPositionException {
    if ((prev == null) && (next == null))
      throw new InvalidPositionException("Position is not in a list!");
    return element;
  }
  // Accessor methods
  public DNode<E> getNext() { return next; }
  public DNode<E> getPrev() { return prev; }
  // Update methods
  public void setNext(DNode<E> newNext) { next = newNext; }
  public void setPrev(DNode<E> newPrev) { prev = newPrev; }
  public void setElement(E newElement) { element = newElement; }
}