public class UserData    {        List<Student> stulist = new List<Student>();  //实例化student类型的集合        public List<Student> Stulist     //设置属性读取        {            get { return stulist; }            set { stulist = value; }        }        List<Teacher> tealist = new List<Teacher>();        public List<Teacher> Tealist        {            get { return tealist; }            set { tealist = value; }        }    }

        UserData ud = new UserData();  //实例化封装后的类,调用        internal UserData Ud   //封装属性，可以不封装，但是推荐封装        {            get { return ud; }            set { ud = value; }        }