Possible Duplicate:
When to Use Static Classes in C#
why anyone would write a static class. we can declare a static method in any class and just call that method without creating class instance. so please tell me in what type of situation a person would create a static class and also tell me what are the main differences between static class and normal class.
thanks
A static class cannot be instantiated. It's main uses are to make it clear that the class has no instance methods and to prevent people from accidentally trying to "new" the class.
A static class cannot contain any constructors, only a static constructor that is called first time one of its members is accessed.
That is basically the difference. Performance wise we also get another for free by the compiler since it can check to make sure that no instance members are accidentally added. The compiler will guarantee that instances of this class cannot be created.
Static classes are also sealed and therefore cannot be inherited.
http://msdn.microsoft.com/en-us/library/79b3xss3(v=VS.100).aspx
A static class is basically the same as a non-static class, but there is one difference: a static class cannot be instantiated. In other words, you cannot use the new keyword to create a variable of the class type.
Another valid point is that Extension Methods has to be declared in a static class
http://en.wikipedia.org/wiki/Extension_method
The new language feature of extension methods in C# 3.0, however, makes the latter code possible. This approach requires a static class and a static method.
Generally I would advise you not to write static classes.
There are cases where you want them though
Extension methods have to live on static classes. This is the best reason to have a static class.
If you do have a bunch of static methods that don't make sense as extension methods and don't fit into your object model then there might be room for a collection of static methods. This is particularly the case when you cannot redesign your app.
Sometimes this happens because you are dealing with some 3rd party stuff that you cannot change. Then if you end up with a class with only static methods on it - you should make it static since anyone creating an instance is clearly not understanding what you have done.
Having said all of that for the most part my advices is avoid static methods, classes and data. I am not saying never use them - just try not to.
In static class all method all static. we can not declare normal method in static class.
differences between static class and normal class.
We can not create object of static class, when we use method of static class just use classname.MethodName but in normal class we have to first create object of class then we can access method of normal class.
static class ex.
Class1.functionname();
normal class ex.
Class1 cs = new class1();
cs.functionname();
functionname should not be private.
The difference is that you can't instantiate a static class. So you'd make a class static if you don't want it ever being instantiated. This is useful in cases when you're dealing with threading issues, and you want all threads to be guaranteed to use the same instance of your class.
A more philosophical scenario is when you have a class that doesn't need to be instantiated, such as (for example) you're building a database application and you create one class to do all the database access stuff. It's basically just a collection of methods. Then making the class static simply becomes a step to make your design more consistent.
