请各位帮我看下这个程序
昨晚编译《C#入门经典》一例题时出现了错误“Ch12Ex04.Farm <T> ”不会实现接口成员“System.Collections.Generic.IEnumerable <T> .GetEnumerator()”E:\BegVCSharp\Chapter12\Ch12Ex04\Ch12Ex04\Farm.cs
可是我在泛型类Farm中已经实现了接口IEnumerable，不知道到底错在哪里，下面是我的源代码：
Animal.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace Ch12Ex04
{
public abstract class Animal
{
protected string name;
public string Name
{
get
{
return name;
}
set
{
name = value;
}
}
//构造函数
public Animal()
{
name = "The Animal with no name. ";
}
public Animal(string newName)
{
name = newName;
}
public void Feed()
{
Console.WriteLine( "{0} has been fed. ", name);
}
//抽象方法
public abstract void MakeANoise();
}
}
--------------------------------
--------------------------------
Chicken.cs
using System;
using System.Collections.Generic;
using System.Text;

namespace Ch12Ex04
{
public class Chicken:Animal
{
public void LayEgg()
{

Console.WriteLine( "{0} has laid an egg. ", name);
}
public Chicken(string newName):base(newName)
{
}
public override void MakeANoise()
{
Console.WriteLine( "{0} says '咯咯 ' ", name);
}

}
}
--------------------------------
--------------------------------
using System;
using System.Collections.Generic;
using System.Text;

namespace Ch12Ex04
{
public class Cow:Animal
{
public void Milk()
{
Console.WriteLine( "{0} has been milked. ",name);
}
public Cow(string newName):base(newName)
{
}
public override void MakeANoise()
{
Console.WriteLine( "{0} says 'moo ' ", name);
}

}
}
=====================================================================
using System;
using System.Collections.Generic;
using System.Text;

namespace Ch12Ex04
{
public class SuperCow:Cow
{
public void Fly()
{
Console.WriteLine( "{0} is flying ", name);
}

//构造函数
public SuperCow(string newName)
: base(newName)
{
}
public override void MakeANoise()

{
Console.WriteLine( "{0} says 'I 'm super cow ", name);
}
}
}
=================================================================
报错的就是这个泛型
Farm.cs
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

namespace Ch12Ex04
{
public class Farm <T> : IEnumerable <T>
where T : Animal
{
private List <T> animals = new List <T> ();

public List <T> Animals
{
get
{
return animals;
}
}
//实现接口IEnumrable
public IEnumerable <T> GetEnumrator()
{
return animals.GetEnumerator();
}

IEnumerator IEnumerable.GetEnumerator()
{
return animals.GetEnumerator();
}
//迭代Animal类的方法
public void MakeNoises()
{
foreach (T animal in animals)
{
animal.MakeANoise();
}
}
public void FeedTheAnimals()
{
foreach (T animal in animals)
{

animal.Feed();
}
}
//迭代Cow和继承于它的类
public Farm <Cow> GetCows()
{
Farm <Cow> cowFarm = new Farm <Cow> ();
foreach (T animal in animals)
{
if (animal is Cow)
{
cowFarm.Animals.Add(animal as Cow);
}
}
return cowFarm;
}
}
}
=====================================================================
客户代码
using System;
using System.Collections.Generic;
using System.Text;

namespace Ch12Ex04
{
class Program
{
static void Main(string[] args)
{
Farm <Animal> farm = new Farm <Animal> ();
farm.Animals.Add(new Cow( "Jack "));
farm.Animals.Add(new Chicken( "John "));
farm.Animals.Add(new Chicken( "Joe "));
farm.Animals.Add(new SuperCow( "Sam "));
farm.MakeNoises();

Farm <Cow> dairyFarm = farm.GetCows();
dairyFarm.FeedTheAnimals();

foreach (Cow cow in dairyFarm)
{

if (Cow is SuperCow)
{
(cow as SuperCow).Fly();
}
}
Console.ReadKey();
}
}
}

[解决办法]
public IEnumerable <T> GetEnumrator()
{
return animals.GetEnumerator();
}

===================>

public IEnumerator <T> GetEnumrator()
{
return animals.GetEnumerator();
}