namespace Iterator_DesignPattern{  using System;  using System.Collections;  class Node   {    private string name;    public string Name     {      get       {        return name;        }    }    public Node(string s)    {      name = s;    }  }    class NodeCollection   {    private ArrayList list = new ArrayList();    private int nodeMax = 0;        // left as a student exercise - implement collection    // functions to remove and edit entries also    public void AddNode(Node n)    {      list.Add(n);       nodeMax++;          }        public Node GetNode(int i)    {      return ((Node) list[i]);    }    public int NodeMax     {            get       {        return nodeMax;      }    }  }  /*   * The iterator needs to understand how to traverse the collection    * It can do that as way it pleases - forward, reverse, depth-first,    */  abstract class Iterator   {    abstract public Node Next();      }  class ReverseIterator : Iterator  {    private NodeCollection nodeCollection;    private int currentIndex;    public ReverseIterator (NodeCollection c)    {      nodeCollection = c;            currentIndex = c.NodeMax -1; // array index starts at 0!    }    // note: as the code stands, if the collection changes,    // the iterator needs to be restarted     override public Node Next()    {      if (currentIndex == -1)        return null;      else         return(nodeCollection.GetNode(currentIndex--));    }  }    /// <summary>  ///  Summary description for Client.  /// </summary>  public class Client  {    public static int Main(string[] args)    {        NodeCollection c = new NodeCollection();      c.AddNode(new Node("first"));      c.AddNode(new Node("second"));      c.AddNode(new Node("third"));      // now use iterator to traverse this      ReverseIterator i = new ReverseIterator(c);      // the code below will work with any iterator type      Node n;      do       {        n = i.Next();        if (n != null)           Console.WriteLine("{0}", n.Name);      } while (n != null);              return 0;    }  }}