定义:为其他对象提供一种代理以控制对这个对象的访问

    interface IBuy
    {
        void Buy();
    }
    class agent : IBuy//代理
    {
        private IBuy m = null;
        public agent(IBuy m)
        {
            this.m = m;
        }
        public void Buy()
        {
            m.Buy();
        }
    }
    class me : IBuy//自己
    {

        public void Buy()
        {
            Console.WriteLine("我想买支笔");
        }
    }

        static void Main(string[] args)
        {
            me m = new me();
            agent a = new agent(m);
            a.Buy();
            Console.Read();
        }