引用类型

/**//// <summary>
    /// Class1 的摘要说明。
    /// </summary>
    class Class1
    {
        /**//// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main(string[] args)
        {
            Class2 c21 = new Class2();
            Class2 c22 = c21;
            c21.UserName = "this is a name";
            Console.WriteLine("c21.UserName:"+c21.UserName);
            Console.WriteLine("c22.UserName:"+c22.UserName);

            c22.UserName = "this is a changed name";

            Console.WriteLine("c21.UserName:"+c21.UserName);
            Console.WriteLine("c22.UserName:"+c22.UserName);
            
            int a = 100;
            Console.WriteLine(Class2.GetSquare(a));
            
            Console.ReadLine();

            //结果：
//            c21.UserName:this is a name 
//            c22.UserName:this is a name
//            c21.UserName:this is a changed name
//            c22.UserName:this is a changed name
//            10000

        }
    }

    public class Class2
    {
        private string userName;
        public string UserName
        {
            get{return userName;}
            set{userName=value;}
        }

        public static int GetSquare(int parm)
        {
            return parm*parm;
        }
        public static string GetString(string str)
        {
            return str+str;
        }
    }