// package net.datastructures;
/**
 * A simple node class for a doubly-linked list.  Each DNode has a
 * reference to a stored element, a previous node, and a next node.
 * 
 * @author Roberto Tamassia
 */


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; }
}