松 紧 耦合, 依赖注入(DI)

class Program
    {
        static void Main(string[] args)
        {
            var engine = new Engine();
            var car = new Car(engine);
            car.Run(3);
            Console.WriteLine(car.Speed);
        }
    }

public class Engine
    {
        public int RPM { get; private set; }
        public void work(int gas)
        {
            this.RPM = 1000 * gas;
        }
    }

class Car
    {
        private Engine _engine;
        public Car(Engine engine)
        {
            this._engine = engine;
        }
        public int Speed { get; private set; }

        public void Run(int gas)
        {
            _engine.work(gas);
            this.Speed = _engine.RPM / 100;
        }
    }

interface IPhone
    {
        void Dail();
        void PickUp();
        void Send();
        void Receive();
    }

class ApplePhone:IPhone
    {
        public void Dail() { Console.WriteLine("Buy?"); }
        public void PickUp() { Console.WriteLine("Buy??"); }
        public void Send() { Console.WriteLine("Buy???"); }
        public void Receive() { Console.WriteLine("Buy????"); }
    }

class XiaoMiPhone:IPhone
    {
        public void Dail() { Console.WriteLine("Are U Ok?"); }
        public void PickUp() { Console.WriteLine("Hello?"); }
        public void Send() { Console.WriteLine("Think You!"); }
        public void Receive() { Console.WriteLine("Think You Very Much!"); }
    }

class User
    {
        private IPhone _phone;
        public User(IPhone phone)
        {
            this._phone = phone;
        }
        public void UsePhone()
        {
            _phone.Dail();
            _phone.Dail();
            _phone.Dail();
        }

    }

 static void Main(string[] args)
        {
            var user = new User(new ApplePhone());
            var user2 = new User(new XiaoMiPhone());
            user.UsePhone();
            user2.UsePhone();
       }