单例模式

class Program
    {
        static void Main(string[] args)
        {
            //Single s1 = new Single();
            Single s1 = Single.Default();
            Console.WriteLine(s1.Num);
            s1.Num = 100;
            Single s2 = Single.Default();
            Console.WriteLine(s2.Num);

            Console.ReadKey();
        }
    }
    class Single
    {
        //阻止它被new
        //禁止在外界调用构造方法public Single()
        private Single()//单例一般采用声明一个静态构造函数
        {
            num = 10;
        }
        public static Single single;
        public static Single Default()
        {
            if (single==null)
            {
                return single = new Single();
            }
            else
            {
                return single;
            }
        }
     private int num;
        public int Num
        {
            get { return num; }
            set { num = value; }
        }
    }