一、单例模式

①单例模式的定义：是用来保证这个类在运行期间只会被创建一个实例，并提供一个访问它的全局访问点。

②单例模式的作用：保证一个类只有一个访问实例，节省系统资源。

③单例模式的特点：私有构造方法；私有成员变量；公有获取实例方法。

二、单例模式实现

①懒汉式单例

using System;
using System.Collections.Generic;
using System.Text;namespace SingleModel
{//懒汉式单例模式public class Single{//私有构造private Single() { }//单例public static Single GetInstance(){return SingleHolder._Instance;}//内部类private static class SingleHolder{internal static readonly Single _Instance = new Single();}}//Class_end
}

②饿汉式单例

using System;
using System.Collections.Generic;
using System.Text;namespace SingleModel
{//饿汉式单例模式public class Single2{private static readonly Single2 _Instance = new Single2();private Single2() { }public static Single2 GeInstance(){return _Instance;}}//Class_end
}

③懒汉式单例

using System;
using System.Collections.Generic;
using System.Text;namespace SingleModel
{//懒汉式单例public class Single3{//定义一个保存实例的静态变量private static Single3 _Instance;//定义一个保证线程同步标识private static readonly object _Synchronized = new object();private Single3() { }public static Single3 GeInstance(){if (_Instance==null){lock (_Synchronized){//双重锁定if (_Instance==null){_Instance = new Single3();}}}return _Instance;}}//Class_end
}

④实现控制实例数目单例

using System;
using System.Collections.Generic;
using System.Text;namespace SingleModel
{//实现控制实例数目public class SingleExtand{//私有构造private SingleExtand() { }//定义一个缺省的key值前缀 private static string _DefaultPreKey = "Cache";//记录当前实例public static int _SingleNum = 1;//定义实例的最大数目private static int _MaxSingleNum = 3;//定义一个保证线程同步的标识private static readonly object _Synchronized = new object();//缓存实例的容器private static Dictionary<String, SingleExtand> _SinleDic = new Dictionary<string, SingleExtand>();//本类实例public static SingleExtand GetInstance(){string key = _DefaultPreKey + _SingleNum;SingleExtand sinleExtand = null;if (_SinleDic.ContainsKey(key)){sinleExtand = _SinleDic[key];}if (sinleExtand==null){lock (_Synchronized){if (sinleExtand == null){sinleExtand = new SingleExtand();_SinleDic.Add(key, sinleExtand);}} }_SingleNum++;if (_SingleNum>_MaxSingleNum){_SingleNum = 1;}return sinleExtand;}}//Class_end
}

三、单例测试

using System;namespace SingleModel
{class Program{static void Main(string[] args){Console.WriteLine("（线程安全）单例模式");Console.WriteLine("饿汉式单例1");Single single1 = Single.GetInstance();Single single2 = Single.GetInstance();Single single3 = Single.GetInstance();Console.WriteLine("single1:" + single1.GetHashCode());Console.WriteLine("single2:" + single2.GetHashCode());Console.WriteLine("single3:" + single3.GetHashCode());Console.WriteLine("\n");Console.WriteLine("懒汉式单例2");Single2 single21 = Single2.GeInstance();Single2 single22 = Single2.GeInstance();Single2 single23 = Single2.GeInstance();Console.WriteLine("single21:" + single21.GetHashCode());Console.WriteLine("single22:" + single22.GetHashCode());Console.WriteLine("single23:" + single23.GetHashCode());Console.WriteLine("\n");Console.WriteLine("懒汉式单例3");Single3 single31 = Single3.GeInstance();Single3 single32 = Single3.GeInstance();Single3 single33 = Single3.GeInstance();Console.WriteLine("single31:" + single31.GetHashCode());Console.WriteLine("single32:" + single32.GetHashCode());Console.WriteLine("single33:" + single33.GetHashCode());Console.WriteLine("\n");Console.WriteLine("控制实例数目的单例");SingleExtand singleExtand1 = SingleExtand.GetInstance();SingleExtand singleExtand2 = SingleExtand.GetInstance();SingleExtand singleExtand3 = SingleExtand.GetInstance();SingleExtand singleExtand4 = SingleExtand.GetInstance();SingleExtand singleExtand5 = SingleExtand.GetInstance();SingleExtand singleExtand6 = SingleExtand.GetInstance();Console.WriteLine("singleExtand1:" + singleExtand1.GetHashCode());Console.WriteLine("singleExtand2:" + singleExtand2.GetHashCode());Console.WriteLine("singleExtand3:" + singleExtand3.GetHashCode());Console.WriteLine("singleExtand4:" + singleExtand4.GetHashCode());Console.WriteLine("singleExtand5:" + singleExtand5.GetHashCode());Console.WriteLine("singleExtand6:" + singleExtand6.GetHashCode());Console.WriteLine("\n");Console.ReadLine();}}
}

运行结果如下：

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C#中线程安全的单例模式

一、单例模式

二、单例模式实现

三、单例测试

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