单例模式的C#实现

借鉴各路大神的博客，也就不做链接了

class SingletonPattern    {        public sealed class Singleton1        {            private static readonly Singleton1 instance = new Singleton1();            static Singleton1() { }            private Singleton1() { }            public static Singleton1 Instance            {                get                {                    return instance;                }            }            //测试方法            public void Hello() { Console.WriteLine("Hello1"); }        }        public sealed class Singleton2        {            private static readonly Singleton2 instance = null;            static Singleton2()            {                instance = new Singleton2();//静态初始化，不同于Singleton1            }            private Singleton2() { }            public static Singleton2 Instance            {                get                {                    return instance;                }            }            //测试方法            public void Hello() { Console.WriteLine("Hello2"); }        }        public sealed class Singleton3        {            private static readonly Lazy<Singleton3> lazy = new Lazy<Singleton3>(() => new Singleton3());            public static Singleton3 Instance            {                get                {                    return lazy.Value;                }            }            private Singleton3() { }            //测试方法            public void Hello() { Console.WriteLine("Hello3"); }        }        /// <summary>        /// 最简单的单例，但线程不安全，对于单线程已然满足        /// </summary>        public sealed class Singleton4        {            private static Singleton4 instance = null;            private Singleton4() { }            public static Singleton4 Instance            {                get                {                    if (instance == null)                    {                        instance = new Singleton4();                    }                    return instance;                }            }            //测试方法            public void Hello() { Console.WriteLine("Hello4"); }        }        /// <summary>        /// 一重加锁，增加开销，保证线程安全        /// </summary>        public sealed class Singleton5        {            private static Singleton5 instance = null;            private static readonly object padlock = new object();            private Singleton5() { }            public static Singleton5 Instance            {                get                {                    lock (padlock)                    {                        if (instance == null)                        {                            instance = new Singleton5();                        }                        return instance;                    }                }            }            //测试方法            public void Hello() { Console.WriteLine("Hello5"); }        }        /// <summary>        /// 两重加锁，减少一重加锁的性能消耗，线程安全        /// </summary>        public sealed class Singleton6        {            private static Singleton6 instance = null;            private static readonly object padlock = new object();            private Singleton6() { }            public static Singleton6 Instance            {                get                {                    if (instance == null)                    {                        lock (padlock)                        {                            if (instance == null)                            {                                instance = new Singleton6();                            }                        }                    }                    return instance;                }            }            //测试方法            public void Hello() { Console.WriteLine("Hello6"); }        }        public sealed class Singleton7        {            private Singleton7() { }            public static Singleton7 Instance            {                get                {                    return Nested.instance;                }            }            private class Nested//通过内嵌的私有类做延时初始化            {                static Nested() { }                private Nested() { }                internal static readonly Singleton7 instance = new Singleton7();            }            //测试方法            public void Hello() { Console.WriteLine("Hello7"); }        }        public sealed class Singleton8        {            private Singleton8() { }            public static Singleton8 Instance            {                get                {                    return Nested.instance;                }            }            private class Nested            {                internal static readonly Singleton8 instance = null;                static Nested()                {                    instance = new Singleton8();//都是延时初始化，但不同于Singleton7的是静态初始化，类似Singleton1和Singleton2的区别                }                private Nested() { }            }            //测试方法            public void Hello() { Console.WriteLine("Hello8"); }        }        //对于使用Unity的朋友Singleton4够了    }