public class Vehicle    {        public void Stop() {            Console.WriteLine("Stopped");        }        /// 
        /// 这不符合开闭原则        /// 
        ///         public void Run(string type)        {            if(type == "car")            {                Console.WriteLine("Car is running");            }            else if (type == "Truck")            {                Console.WriteLine("Truck is running");            }        }    }    public class Truck:Vehicle {        public void Run()        {            Console.WriteLine("Truck is running");        }    }    public class Car:Vehicle    {        public void Run() {            Console.WriteLine("Car is running");        }    }

public class Vehicle    {        public void Stop() {            Console.WriteLine("Stopped");        }              public virtual void Run()        {            Console.WriteLine("Vehicle is running");         }    }    public class Truck:Vehicle {        public override void Run()        {            Console.WriteLine("Truck is running");        }    }    public class Car:Vehicle    {        public override void Run()        {            Console.WriteLine("Car is running");        }    }

但是我们发现Vehicle这个类永远不会去调用run这个方法因为不符合逻辑也很模糊

abstract public class Vehicle    {        public void Stop()        {            Console.WriteLine("Stopped");        }        public abstract void Run();    }    public class Truck : Vehicle    {        public override void Run()        {            Console.WriteLine("Truck is running");        }    }    public class Car : Vehicle    {        public override void Run()        {            Console.WriteLine("Car is running");        }    }    public class RaceCar : Vehicle    {        public override void Run()        {            Console.WriteLine("RaceCar is running");        }    }

添加赛车类不会修改原本的类，之需要修改原本的类就可以了