OO: Why should constructors on abstract classes be protected, not public?

Question

C# code: Resharper suggests changing the accessibility of a public constructor in an abstract class to protected, but it does not state the rationale behind this. Can you shed some light?

Answer 1

Simply because being public makes no sense on an abstract class. An abstract class by definition cannot be created directly. It can only be created by creating an instance of a derived type. Therefore the only types that should have access to a constructor are derived types and hence protected makes much more sense that public. It more accurately describes the accessibility.

Answer 2

It is a good OO practice to do do that:

 public abstract class ExampleAbstractClass

        {

                    protected ExampleAbstractClass()

                    {

                    }

        }

You want only the inheritor classes to have access to the constructor, and the only way to do that is making the constructor protected. Keep in mind, when you add parameters to these constructors, it is a whole another discussion.

Answer 3

Similarly, static classes don't even get a default parameterless contructor...