关键字集合和IDictionary  public abstract class Animal    {        protected string name;         public string Name        {            get            {                return name;            }            set            {                name = value;            }        }         public Animal()        {            name = "The animal with no name";        }         public Animal(string newName)        {            name = newName;        }         public void Feed()        {            Console.WriteLine("{0} has been fed.", name);        }    } _____________________________________________________________________________________________________     public class Cow : Animal    {        public void Milk()        {            Console.WriteLine("{0} has been milked.", name);        }         public Cow(string newName)            : base(newName)        {        }    } _____________________________________________________________________________________________________     public class Chicken : Animal    {        public void LayEgg()        {            Console.WriteLine("{0} has laid an egg.", name);        }         public Chicken(string newName) : base(newName)        {        }    } _____________________________________________________________________________________________________     public class Animals : DictionaryBase    {        public void Add(string newID, Animal newAnimal)        {            Dictionary.Add(newID, newAnimal);        }         public void Remove(string animalID)        {            Dictionary.Remove(animalID);        }         public Animals()        {        }         public Animal this[string animalID]        {            get            {                return (Animal)Dictionary[animalID];            }            set            {                Dictionary[animalID] = value;            }        }    } _____________________________________________________________________________________________________     public class Program    {        static void Main(string[] args)        {            Animals animalCollection = new Animals();            Animal cow = new Cow("a");            Animal chicken = new Chicken("b");            animalCollection.Add("a", cow);            animalCollection.Add("b", chicken);            foreach (DictionaryEntry myEntry in animalCollection)            {                Console.WriteLine("New {0} object added to custon collection," +                    "Name = {1}", myEntry.Value.ToString(), ((Animal)myEntry.Value).Name);            }            Console.ReadKey();        }    }

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