设计模式一(单例模式)

    class Singleton
    {
        private static Singleton _instance = null;
        private static readonly object SynObject = new object();

        // 定义私有构造函数，使外界不能创建该类实例
        private Singleton()
        {
        }

        public static Singleton Instance
        {
            get
            {
                if (_instance == null)
                {
                    lock (SynObject)
                    {
                        if (_instance == null)
                        {
                            _instance = new Singleton();
                        }
                    }
                }

                return _instance;
            }
        }
    }