实现Singleton模式(C#实现)

    ///

    /// 适用于单线程单例
    ///

class Singleton_01
    {
        //将构造函数设为私有避免重复创建
        //当instance为空时,实例化;
        private Singleton_01()
        {

        }

        private static Singleton_01 instance = null;
        public static Singleton_01 Instance
        {
            get
            {
                if (instance == null)
                    instance = new Singleton_01();
                return instance;
            }
        }
    }

///

    /// 适用于多线程单例
    /// 加上同步锁保证可以在多线程下工作,但是每次获取实例时,都需要加上同步锁,很耗时;
    ///

class Singleton_02
    {
        private Singleton_02()
        {

        }

        private static readonly object syncObj = new object();

        private static Singleton_02 instance = null;

        public static Singleton_02 Instance
        {
            get
            {
                lock(syncObj)
                {
                    if (instance == null)
                        instance = new Singleton_02();
                }

                return instance;
            }
        }
    }

    ///

    /// 适用于多线程单例
    /// 在获取实例之前提前检测是否已经被实例化,不用多次判断,加同步锁.效率更高
    ///

    class Singleton_03
    {
        private Singleton_03()
        {

        }

        private static readonly object syncObj = new object();

        private static Singleton_03 instance = null;

        public static Singleton_03 Instance
        {
            get
            {
                if (instance == null)
                {
                    lock (syncObj)
                    {
                        if (instance == null)
                            instance = new Singleton_03();
                    }
                }

                return instance;
            }
        }
    }

    ///

    /// 利用C#静态构造函数只执行一次的特性,实现单例
    ///

    class Singleton_04
    {
        private Singleton_04()
        {

        }

        private static Singleton_04 instance = new Singleton_04();

        public static Singleton_04 Instance
        {
            get
            {
                return instance;
            }
        }
    }

    ///

    /// 按需创建实例
    /// 利用C#静态类只执行一次的特性,实现单例的问题在于,只要你用到这个类,
    /// 他就会创建实例,并不是在你需要的时间创建,降低了内存的使用效率,
    /// 而我们创建一个内部类来实例化,在调用Instance时才会调用到instance,这样就避免了调用这个类时,自动实例化
    ///

class Singleton_05
    {
        Singleton_05()
        {

        }

        public static Singleton_05 Instance
        {
            get
            {
                return Nested.instance;
            }
        }

        class Nested
        {
            static Nested()
            {
            }

            internal static readonly Singleton_05 instance = new Singleton_05();
        }
    }