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POWhy do I need the Singleton design pattern?
 

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  1. POWhy do I need the Singleton design pattern?
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    <p>i try to learn design pattern, but it's really really hard to understand main idea of OOD. i have created my software with classic method. On the other hand i want to learn OOD. why i need singleton and others? i coded some simple program: one of them clasical(my style), the other is singleton pattern.Please teach me why do i need singleton. my method better and clear than it :)</p> <p>my style: (C#)</p> <pre><code> public partial class Singletonsuz : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { Loadbalancer balancer = new Loadbalancer(); for (int i = 0 ; i &#60; 15 ; i++) { string server = balancer.Server; Response.Write("Dispatch Request to: " + server); } } } class Loadbalancer { private List&#60;string&#62; _servers = new List&#60;string&#62;(); private Random _random = new Random(); public Loadbalancer() { _servers.Add("ServerI"); _servers.Add("ServerII"); _servers.Add("ServerIII"); _servers.Add("ServerIV"); _servers.Add("ServerV"); } public string Server { get { int r = _random.Next(_servers.Count); return _servers[r].ToString(); } } } </code></pre> <p>SINGLETON: </p> <pre><code> public partial class SingletonDP2 : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { LoadBalancer balancer = LoadBalancer.GetLoadBalancer(); for (int i = 0; i &#60; 15; i++) { string server = balancer.Server; Response.Write("Dispatch Request to: " + server ); } } class LoadBalancer { private static LoadBalancer _instance; private List&#60;string&#62; _servers = new List&#60;string&#62;(); private Random _random = new Random(); private static object syncLock = new object(); protected LoadBalancer() { _servers.Add("ServerI"); _servers.Add("ServerII"); _servers.Add("ServerIII"); _servers.Add("ServerIV"); _servers.Add("ServerV"); } public static LoadBalancer GetLoadBalancer() { if (_instance == null) { lock (syncLock) { if (_instance == null) { _instance = new LoadBalancer(); } } } return _instance; } public string Server { get { int r = _random.Next(_servers.Count); return _servers[r].ToString(); } } } } </code></pre>
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    1. COSurely, the merits/flaws of singletons have been discussed enough already... http://stackoverflow.com/questions/137975/what-is-so-bad-about-singletons http://stackoverflow.com/questions/449885/are-there-cases-where-a-singleton-is-the-best-option
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