How to decide if a method will be private, protected, internal or public?

Question

I am designing a class where some methods won't cause any harm if they are exposed as public. But they can be private as well, since they will be used only from the same class in my project.

Making them public has the following advantages:

1. Unit Testable without the need of accessors.
2. Flexibility.

Making them private has the following advantages:

1. Public documentation simplification.
2. Some unknown bugs aren't exposed.

Which are the general guidelines in this case?

Answer 1

Always make everything as private as possible.

For unit testing, I sometimes make a member internal, then use the InternalsVisibleTo attribute in the AssemblyInfo.cs to permit the unit test assembly access to the internal members.

Answer 2

Oh, please please read Ch. 06 Of Code Complete 2 by Steve McConnell, if you have access to it. That will answer your question perfectly.

In general, If the Method fits in the overall "Persona" of the class, make it public. More technically, try not to break the abstraction. I would have given an example, but I do not know the context of your work and so examples might be irrelevant.

If you do not need it, there is no need to make a Method public.

For testing, +1 to John sanders.

But I really can not explain you here as Steve has explained in CC2.

I hope its OK to post Book references on Satckoverflow? (Please comment.)