C++设计模式编程中的迭代器模式应用解析

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;
    }
  }
}