When should I use static methods in a class and what are the benefits?

Question

I have concept of static variables but what are the benefits of static methods in a class. I have worked on some projects but I did not make a method static. Whenever I need to call a method of a class, I create an object of that class and call the desired method.

Q: Static variable in a method holds it's value even when method is executed but accessible only in its containing method but what is the best definition of static method?

Q: Is calling the static method without creating object of that class is the only benefit of static method?

Q: What is the accessible range for static method?

Thanks

Answer 1

Static methods don't pass a "this" pointer to an object, so they can't reference non-static variables or methods, but may consequently be more efficient at runtime (fewer parameters and no overhead to create and destroy an object).

They can be used to group cohesive methods into a single class, or to act upon objects of their class, such as in the factory pattern.

Answer 2

Your description of a static variable is more fitting to that found in C. The concept of a static variable in Object Oriented terms is conceptually different. I'm drawing from Java experience here. Static methods and fields are useful when they conceptually don't belong to an instance of something.

Consider a Math class that contains some common values like Pi or e, and some useful functions like sin and cos. It really does not make sense to create separate instances to use this kind of functionality, thus they are better as statics:

// This makes little sense Math m = new Math(); float answer = m.sin(45);  // This would make more sense float answer = Math.sin(45); 

In OO languages (again, from a Java perspective) functions, or better known as methods, cannot have static local variables. Only classes can have static members, which as I've said, resemble little compared to the idea of static in C.