using System;using System.Collections.Generic;using System.Text;namespace SingletonDemo{    /// 
    /// 1、普通单例    /// 
    public class SingletonA    {        private static SingletonA _instance = null;        private SingletonA() { }        public static SingletonA CreateInstance()        {            if (_instance == null)            {                _instance = new SingletonA();            }            return _instance;        }    }    /// 
    /// 2、线程安全单例    /// 
    public class SingletonB    {        private volatile static SingletonB _instance = null;        private static readonly object lockHelper = new object();        private SingletonB() { }        public static SingletonB CreateInstance()        {            if (_instance == null)            {                lock (lockHelper)                {                    if (_instance == null)                        _instance = new SingletonB();                }            }            return _instance;        }    }    /// 
    /// 3、使用.net特性的支持多线程的单件模式代码    /// 
    public sealed class SingletonC    {        private SingletonC() { }        public static readonly SingletonC Instance = new SingletonC();    }    /// 
    /// 4、使用 C# 2.0 泛型来完成单例模式的重用    /// 
    /// 
        public class SingletonProvider
    
      where T : new()    {        SingletonProvider() { }        public static T Instance        {            get { return SingletonCreator.instance; }        }        class SingletonCreator        {            static SingletonCreator() { }            internal static readonly T instance = new T();        }    }    /// 
     
    /// 4、业务类demo    /// 
    public class TestClass    {        private string _createdTimestamp;        public TestClass()        {            _createdTimestamp = DateTime.Now.ToString();        }        public void Write()        {            Console.WriteLine(_createdTimestamp);        }    }    /// 
     
    /// 4、范型单例示例    /// 
    public class demo    {        private void dosomething()        {            SingletonProvider
     
      .Instance.Write();        }    }}