1  public interface IIterator
  2     {
  3         void First();
  4         void Last();
  5         bool MoveNext();
  6         object Current { get; }
  7     }
  8     /// <summary>
  9     /// 
 10     /// </summary>
 11     public class SIterator : IIterator
 12     {
 13         private CustomerList list = null;
 14         private int position = -1;
 15         public SIterator(CustomerList list)
 16         {
 17             this.list = list;
 18         }
 19         public void First()
 20         {
 21             position = 0;
 22         }
 23 
 24         public void Last()
 25         {
 26             position = list.Count - 1;
 27         }
 28 
 29         public bool MoveNext()
 30         {
 31             if (++position < list.Count)
 32             {
 33                 return true;
 34             }
 35             else
 36             { return false; }
 37         }
 38 
 39         public object Current
 40         {
 41             get
 42             {
 43                 return list[position];
 44             }
 45         }
 46     }
 47     public class RIterator : IIterator
 48     {
 49         private CustomerList list = null;
 50         private int position = 0;
 51         public RIterator(CustomerList list)
 52         {
 53             this.list = list;
 54         }
 55         public void First()
 56         {
 57             position = list.Count - 1;
 58         }
 59 
 60         public void Last()
 61         {
 62             position = 0;
 63         }
 64 
 65         public bool MoveNext()
 66         {
 67             position--;
 68             return position > 0;
 69         }
 70 
 71         public object Current
 72         {
 73             get { return list[position]; }
 74         }
 75     }
 76     public class CustomerList
 77     {
 78         private ArrayList list = null;
 79         public void Add(object value)
 80         {
 81             list.Add(value);
 82         }
 83         public void Remove(object value)
 84         {
 85             list.Remove(value);
 86         }
 87         public int Count
 88         {
 89             get
 90             {
 91                 return list.Count;
 92             }
 93         }
 94         public void Clear()
 95         {
 96             list.Clear();
 97         }
 98         public object this[int index]
 99         {
100             get
101             {
102                 if (index < 0 || index > list.Count)
103                 {
104                     throw new Exception("");
105                 }
106                 return list[index];
107             }
108 
109         }
110         public virtual IIterator CreateIterator()
111         {
112             return new SIterator(this);
113         }
114 
115     }
116     /// <summary>
117     /// 
118     /// </summary>
119     public class RList : CustomerList
120     {
121         public IIterator CreateIterator()
122         {
123             return new RIterator(this);
124         }
125     }