/**
 * A node with two links.  Useful for a number of data structures.
 * Note that these are not necessarily used for doubly-linked lists,
 * so the links are not required to be symmetric.  However, most
 * of the terminology used herein is biased toward doubly-linked lists.
 *
 * @author Samuel A. Rebelsky
 * @version 1.1 of April 2000
 */
public class DoublyLinkedNode
{
    // +--------+----------------------------------------
    // | Fields |
    // +--------+

    /** 
     * The next element.  Set to null when this is the
     * "last" item (e.g., the last item in a list; the
     * leaf of a tree).
     */
    protected DoublyLinkedNode next;
   
    /** 
     * The previous element.  Set to null when this is
     * the "first" item.
     */
    protected DoublyLinkedNode prev;

    /**
     * The contents of this thing.  
     */
    protected Object contents;

    // +--------------+----------------------------------
    // | Constructors |
    // +--------------+

    /**
     * Create a node that contains a particular value.
     */
    public DoublyLinkedNode(Object initialContents) {
        this.contents = initialContents;
        this.next = null;
        this.prev = null;
    } // DoublyLinkedNode(Object)

    // +------------+------------------------------------
    // | Extractors |
    // +------------+

    /**
     * Get the contents.
     */
    public Object getContents() {
        return this.contents;
    } // getContents()

    /**
     * Get the next element.  Returns null if there is no
     * next element.
     */
    public DoublyLinkedNode getNext() {
        return this.next;
    } // getNext()

    /**
     * Get the previous element.  Returns null if there is
     * no previous element.
     */
    public DoublyLinkedNode getPrev() {
        return this.prev;
    } // getPrev()

    // +-----------+-------------------------------------
    // | Modifiers |
    // +-----------+

    /**
     * Set the contents of this node.
     */
    public void setContents(Object newContents) {
       this.contents = newContents;
    } // setContents(Object)

    /**
     * Set the next element.  
     */
    public void setNext(DoublyLinkedNode newNext) {
        this.next = newNext;
    } // setNext(Object)

    /**
     * Set the previous element.  
     */
    public void setPrev(DoublyLinkedNode newPrev) {
        this.prev = newPrev;
    } // setPrev(Object)

} // class DoublyLinkedNode