使用IEnumerable统一迭代变量类型

class Program
{static void Main(string[] args){int[] nums1 = new int[] { 1, 2, 3, 4, 5 };ArrayList nums2 = new ArrayList { 1, 2, 3, 4, 5 };Console.WriteLine(Sum(nums1));Console.WriteLine(Sum(nums2));Console.WriteLine(Avg(nums1));Console.WriteLine(Avg(nums2));}static int Sum(IEnumerable nums){int sum = 0;foreach (var n in nums){sum += (int)n;}return sum;}static double Avg(IEnumerable nums){int sum = 0;double count = 0;foreach (var n in nums){sum += (int)n;count++;}return sum/count;}}

使用接口实现松耦合：手机类为例

class Program{static void Main(string[] args){PhoneUser phoneUser = new PhoneUser(new Ericsson());phoneUser.UsePhone();}   }class PhoneUser{private IPhone _phone { get; set; }public PhoneUser(IPhone phone){_phone = phone;}public void UsePhone(){_phone.Dail();_phone.PickUp();_phone.Send();_phone.Receive();}}interface IPhone{void Dail();void PickUp();void Receive();void Send();}public class NokiaPhone : IPhone{public void Dail(){Console.WriteLine("Nokia calling...");}public void PickUp(){Console.WriteLine("Hello!This is NokiaPhone!");}public void Receive(){Console.WriteLine("Nokia message ring...");}public void Send(){Console.WriteLine("Hello");}}class Ericsson : IPhone{public void Dail(){Console.WriteLine("Ericsson calling...");}public void PickUp(){Console.WriteLine("Hello!This is Ericsson!");}public void Receive(){Console.WriteLine("Ericsson message ring...");}public void Send(){Console.WriteLine("Hello Ericsson");}}