关于OOP：静态类和单例类C#的区别

Difference between static class and singleton class c#

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Possible Duplicate:
Difference between static class and singleton pattern?

我们使用静态类进行公共操作。同样的事情也可以在singleton类中完成

这里我给两个一级是静态类，一个是单级。事实上，对于我来说，当一个人去上静态类，而当我们去上单例类的时候，事情就变得越来越难了。

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public sealed class SiteStructure
{
/// <summary>
/// This is an expensive resource we need to only store in one place.
/// </summary>
object[] _data = new object[10];

/// <summary>
/// Allocate ourselves. We have a private constructor, so no one else can.
/// </summary>
static readonly SiteStructure _instance = new SiteStructure();

/// <summary>
/// Access SiteStructure.Instance to get the singleton object.
/// Then call methods on that instance.
/// </summary>
public static SiteStructure Instance
{
get { return _instance; }
}

/// <summary>
/// This is a private constructor, meaning no outsiders have access.
/// </summary>
private SiteStructure()
{
// Initialize members, etc. here.
}
}

static public class SiteStatic
{
/// <summary>
/// The data must be a static member in this example.
/// </summary>
static object[] _data = new object[10];

/// <summary>
/// C# doesn't define when this constructor is run, but it will likely
/// be run right before it is used.
/// </summary>
static SiteStatic()
{
// Initialize all of our static members.
}
}

请解释何时需要创建静态类和何时需要单例类。谢谢