从C#角度 单例模式 懒汉和饿汉

namespace SingleTon
{
    /// <summary>
    /// 懒汉单例、多线程安全
    /// 比较懒，在类加载时，不创建实例，因此类加载速度快，但运行时获取对象的速度慢
    /// </summary>
    public class LazySingleTon
    {
        private static LazySingleTon instance = null;
        //多线程安全
        private static object lockObject = new object();
        private LazySingleTon()
        {
            Console.WriteLine("private LazySingleTon()");
        }

        public static LazySingleTon Instance
        {
            get
            {
                //不必每次锁，提高效率
                if (instance == null)
                {
                    //多线程安全
                    lock (lockObject)
                    {
                        if (instance == null)
                        {
                            return new LazySingleTon();
                        }
                    }
                }
                return instance;
            }
        }
    }

    /// <summary>
    /// 饿汉单例
    /// 在类加载时就完成了初始化，所以类加载较慢，但获取对象的速度快
    /// </summary>
    public class EagerSingleTon
    {
        // readonly 分配的动态内存
        private static readonly EagerSingleTon instance = new EagerSingleTon();

        private EagerSingleTon()
        {
            Console.WriteLine("private EagerSingleTon()");
        }

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

    }
    class Program
    {
        static void Main(string[] args)
        {
            var lazy = LazySingleTon.Instance;
            var eager = EagerSingleTon.Instance;
        }
    }
}