在C＃中声明私有静态类有什么用？

Question

Is there any use of declaring a static class as private.Here is the code below:

static class DerivedClass
{
    private static string GetVal()
    {
        return "Hello";
    }
}

Answer 1

The sample code you provided actually illustrates an internal class, not a private class. This is perfectly fine and is done all the time. It means the methods of the class are available from other classes within the same module, but not externally.

If you mean declaring private members of static classes, sure there is.

static class DerivedClass
{
    public static string GetVal()
    {
        return GetValInternal();
    }

    private static string GetValInternal()
    {
        return "Hello";
    }
}

If you mean declaring a private static nested classes (because only nested classes can be private, according to the documentation ), then you can do it, but there's probably no reason to do it.

class SomeClass
{
    private static class DerivedClass
    {
        public static string GetVal()
        {
            return "Hello";
        }
    }
}

Is equivalent to

class SomeClass
{
    private static string GetVal()
    {
        return "Hello";
    }
}

Answer 2

By default classes with no access modifiers like in your example are internal , not private . See this reference: http://msdn.microsoft.com/en-us/library/ms173121.aspx . This means that you can access this class from anywhere inside the library/project. This makes sense because it allows you to use the class internally without necessarily exposing it to the outside world.

Explicitly declaring it as private however makes sense in some rare cases only in my opinion. I have used it before for nested classes simply to group certain things together and make my code prettier/more readable. However I find that if I am creating nested classes it usually means that I need to redesign my code and pull some of it into separate files and separate classes. Rather try to stick to one class per file.