Singleton

// Singleton pattern -- .NET optimized

using System; using System.Collections; namespace DoFactory.GangOfFour.Singleton.NETOptimized {       // MainApp test application    class MainApp   {           static void Main()     {       LoadBalancer b1 = LoadBalancer.GetLoadBalancer();       LoadBalancer b2 = LoadBalancer.GetLoadBalancer();       LoadBalancer b3 = LoadBalancer.GetLoadBalancer();       LoadBalancer b4 = LoadBalancer.GetLoadBalancer();        // Confirm these are the same instance        if (b1 == b2 && b2 == b3 && b3 == b4)       {         Console.WriteLine("Same instance\n");       }        // All are the same instance -- use b1 arbitrarily        // Load balance 15 requests for a server        for ( int i = 0; i < 15; i++)       {         Console.WriteLine(b1.Server);       }        // Wait for user       Console.Read();         }   }       // Singleton    sealed class LoadBalancer   {      // Static members are lazily initialized.      // .NET guarantees thread safety for static initialization      private static readonly LoadBalancer instance =        new LoadBalancer();      private ArrayList servers = new ArrayList();      private Random random = new Random();      // Note: constructor is private.      private LoadBalancer()     {        // List of available servers       servers.Add("ServerI");       servers.Add("ServerII");       servers.Add("ServerIII");       servers.Add("ServerIV");       servers.Add("ServerV");     }      public static LoadBalancer GetLoadBalancer()     {        return instance;     }           // Simple, but effective load balancer      public string Server     {        get       {          int r = random.Next(servers.Count);          return servers[r].ToString();       }     }   } }