/* ListNode.java */

package sortedlist;

/** ListNode is a class used internally by the List class.  Each
   node in a List is represented as a ListNode, with an item and 
   a reference to the next node in the list.                     */

class ListNode {
  Keyable item;
  ListNode next;

  /** Constructs a ListNode with item i and next null.
   *  @param obj will be the item in the node.
   */
  ListNode(Keyable obj) {
    item = obj;
    next = null;
  }

  /** Constructs a ListNode with item obj and next n.
    *  @param obj will be the item in the node.
    *  @param n will be the next ListNode in the list.
    */
  ListNode(Keyable obj, ListNode n) {
    item = obj;
    next = n;
  }

    
  /** Returns a reference to the node at the given position.  If 
   *  position < 1 or position > the number of nodes in the 
   *  list, returns null.  Assumes the list is acyclic.
   */
  public ListNode ptrTo (int position) {
    if (position < 1) {
      return null;
    }
    else if (position == 1) {
      return this;
    }
    else if (next == null) {
      return null;
    }
    else {
      return next.ptrTo(position-1);
    }
  }
}