工厂方法

abstract class LeiFeng
    {
        public abstract void Sweep();
        public abstract void Wash();
        public abstract void BuyRice();
    }

    class Undergraduate : LeiFeng
    {
        public override void Sweep()
        {
            Console.WriteLine("在校大学生，扫地");
        }

        public override void Wash()
        {
            Console.WriteLine("在校大学生，洗衣");
        }

        public override void BuyRice()
        {
            Console.WriteLine("在校大学生，买米");
        }
    }

    class Volunteer : LeiFeng
    {
        public override void Sweep()
        {
            Console.WriteLine("志愿者，扫地");
        }

        public override void Wash()
        {
            Console.WriteLine("志愿者，洗衣");
        }

        public override void BuyRice()
        {
            Console.WriteLine("志愿者，买米");
        }
    }

    interface IFactory
    {
        LeiFeng CreateLeiFeng();
    }

    class UndergraduateFactory : IFactory
    {
        public LeiFeng CreateLeiFeng()
        {
            return new Undergraduate();
        }
    }

    class VolunteerFactory : IFactory
    {
        public LeiFeng CreateLeiFeng()
        {
            return new Volunteer();
        }
    }

转自《大话设计模式》