Singleton Pattern

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Sigleton
{
    /// <summary>
    /// 单例类必须只有一个实例
    /// 单例类必须自己创建自己的唯一实例
    /// 单例类必须给所有其他对象提供这个唯一实例
    /// </summary>
    class Singleton
    {
        private static Singleton instance;

        protected Singleton()
        {}

        public static Singleton GetInstance()
        {
            if (instance == null)
            {
                instance = new Singleton();
            }
            return instance;
        }
    }
}

      为产生唯一实例，构造函数私有化，不允许外部New对象。

客户端

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Sigleton
{
    class Client1
    {
        static void Main(string[] args)
        {
            Singleton s1 = Singleton.GetInstance();
            Singleton s2 = Singleton.GetInstance();

            if (s1.Equals(s2))
            {
                Console.WriteLine("s1==s2");
            }
            else
            {
                Console.WriteLine("s1!=s2");
            }
            Console.Read();
        }
    }
}

运行代码：结果为s1==s2.


改进之后实际运用：

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace SingletonApp
{
    /// <summary>
    /// 负载均衡类类，
    /// 在负载均衡模型中，有多台服务器可供服务，任务分配随机挑选一台服务器提供服务，以确保任务均衡。
    /// </summary>
    class LoadBalancer
    {
        //字段
        private static LoadBalancer balancer;
        private ArrayList servers = new ArrayList();
        private Random random = new Random();

        //构造方法
        protected LoadBalancer()
        {
            servers.Add("serverI");
            servers.Add("serverII");
            servers.Add("serverIII");
            servers.Add("serverIV");
            servers.Add("serverV");
        }

        /// <summary>
        /// 返回类的单一实例
        /// </summary>
        /// <returns></returns>
        public static LoadBalancer GetLoadBalancer()
        {
            if (balancer == null)
            {
                Mutex mutex = new Mutex();
               
                if (balancer == null)
                {
                    balancer = new LoadBalancer();
                    mutex.Close();
                }

            }
            return balancer;
        }

        public string Server
        {
            get
            {
                int r = random.Next(servers.Count);
                return servers [r].ToString ();
            }
        }

    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SingletonApp
{
    class SingletonApp
    {
        static void Main(string[] args)
        {
            LoadBalancer b1 = LoadBalancer.GetLoadBalancer();
            LoadBalancer b2 = LoadBalancer.GetLoadBalancer();
            LoadBalancer b3 = LoadBalancer.GetLoadBalancer();
            LoadBalancer b4 = LoadBalancer.GetLoadBalancer();

            Console.WriteLine(b1.Server);
            Console.WriteLine(b2.Server);
            Console.WriteLine(b3.Server);
            Console.WriteLine(b4.Server);

            Console.ReadKey();
        }
    }
}