What are the desirable situation (real life example) to create static methods except for creating helper?

Question

I just want to understand the purpose that static method serves and what are the desirable situation where i can create static methods except some would say that static methods are used for creating helper.

Consider i have 1 website that will be used in my company only like Human resource management system like websites.

Now after Admin login in to the system admin will see the list of employees.so the method is simple which does nothing more than fetching all details of employees from employee table and will display them on the web site and this method will be define in business access layer like this in .net:

 public class EmployeeBal
    {
        public List<Employee> GetAllEmployees()
        {
                 return Select * from Employee
        }
     }

This is how i would call this method from my application.For Eg(.aspx page or mvc controller etc....)

var employeeBal= new EmployeeBal();
employeeBal.GetAllEmployees();

So my question is should i create this method as static method or non static method??

Note:This is just an example of method and this method is in my business access layer.

Consider i have 1 ecommerce website where on the home page i am displaying some list of products and on visit of that website every users can see that list of products.

so my function would be same as above define in Business acess layer:

public class ProductBal
    {
        public List<Product> DisplayProductonHomePage()
        {
                 return Select * from Products
        }
     }

So my question would be same like whether to create this method as static method or non-static method and what will happen if more than 10 users at same time simultaneously access this website then what will be the behaviour/implications of this method???

Will this method will serve the purpose of this each user if we declare this method as static??

Can anybody answer this question with briefly explaining every scenario???

Answer 1

A static method makes sense when there’s no state to maintain. What do I mean by state? Well, consider the following: You have two distinct objects, a and b, which are both of type EmployeeBal. Is there ever a case in your program where a.GetAllEmployees() and b.GetAllEmployees() would yield different results?

If not, then why do the objects a and b exist at all? The whole point of having objects is to associate some distinct state with them. If two different objects can never refer to a different state, then they fulfil no purpose.

In fact, in this situation your EmployeeBal would be exactly equivalent to System.Math, and all its methods are “helper methods” (if that’s what you want to call them). In this case, forget about static methods for a minute: your whole class should be static (static class EmployeeBal), and it should not have any constructors; because the concept of an object of type EmployeeBal simply makes no sense. In fact, in other languages EmployeeBal wouldn’t be a class at all; instead, it would be something generally called a module: a unit that logically groups code. C# has no modules, and all code must reside within classes. Classes thus fulfil a dual purpose: they group code, and they generate objects.¹

Now consider a less extreme case: EmployeeBal objects actually maintain state, and differ. Yet GetAllEmployees() will still yield the same result, regardless of which object calls the method.

In this case, EmployeeBal obviously cannot be a static class. But GetAllEmployees is still stateless, and thus doesn’t belong to objects of type EmployeeBal. And thus the method should be static.

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¹ This lack of distinction between two fundamentally distinct concepts (module and class) is actually quite annoying, and the main reason that C# behaves this way is because it was conceived to be similar to Java. It was a mistake in hindsight, but not a serious one.