public interface IYunSuan    {        double getResult(int num1, int num2);    }    public class jia : IYunSuan    {        public double getResult(int num1, int num2)        {            return num1 + num2;        }    }    public class jian : IYunSuan    {        public double getResult(int num1, int num2)        {            return num1 - num2;        }    }    public class cheng : IYunSuan    {        public double getResult(int num1, int num2)        {            return num1 * num2;        }    }    public class chu : IYunSuan    {        public double getResult(int num1, int num2)        {            if (num2 == 0) return 0;            return num1 / num2;        }    }        //门脸类（中间层）    public class Facade    {        IYunSuan jia1;        IYunSuan jian1;        IYunSuan cheng1;        IYunSuan chu1;        public Facade()        {            jia1 = new jia();            jian1 = new jian();            cheng1 = new cheng();            chu1 = new chu();        }        //排列内部对象的方法展示顺序        public void display1(int num1,int num2)        {            var jiaresult = jia1.getResult(num1,num2);            var jianresult = jian1.getResult(num1, num2);            var chengresult = cheng1.getResult(num1, num2);            Console.WriteLine(jiaresult);            Console.WriteLine(jianresult);            Console.WriteLine(chengresult);            Console.ReadLine();        }        public void display2(int num1, int num2)        {                        var jianresult = jian1.getResult(num1, num2);            var churesult = chu1.getResult(num1, num2);                        Console.WriteLine(jianresult);            Console.WriteLine(churesult);            Console.ReadLine();        }    }        //前端        static void Main(string[] args)        {            //前端类不需要直接和运算类打交道，符合迪米特法则（最少知识原则）、依赖倒转原则(高层不依赖低层)                        Facade f = new Facade();            f.display1(100,20);            f.display2(30,10);        }

总结：外观模式应该是我们最常用的模式之一，经典的3层架构就符合这个原则，UI层和数据层没有直接通信，而是通过业务逻辑层。UI和业务逻辑、业务逻辑和数据层 之间都在加上一个接口层（门脸接口）的话扩展性和维护性会好很多。