1、c# 对象

1、面向对象
封装、继承、多态
封装体现在属性方法对外界访问的限制上;

##属性：以大写开头 与java不同
c#中属性是对private字段的封装;

class User
    {
        private int oid;
        public int Oid
        {
            get {
                if (oid == 19) { return 10; }
                else { return 100; }
                 }
            set {
                if (value > 18 && value < 40)
                {
                    oid = 19;
                }
                else { oid = value; }
                 }
        }
        private string account;
        public string Account
        {
            get { return account; }
            set { account = value; }
        }
    }


public static void Main(string[] args)
        {
            User u = new User();
            u.Oid = 30;
            Console.WriteLine(u.Oid);
            Console.ReadKey(); //10
         }

简写：

 public string Account
        {
            get;
            set;
        }