When to declare methods as private

Question

I am looking for specific and exact rules to determine how a method's visibility can be declared. This is not language agnostic, it applies to the standard OOP languages.

Answer 1

A good rule to follow would be:

Members should not have more accessibility than they need.

Start with private and make them more accessible as the need arises.

Answer 2

Basically:

• Public is for when the method must be accessible by an outside class. Something like getState() would fit here.
• Private is for when the method should not be accessible by any other class, something like changeState(...). Generally this relates to the actual alteration of an object's contents - maybe you'll have a public setX(int x) that just calls the private setXInternal(int x), that way you can have extra type-checking/safety/etc. To be safe you might as well make everything private until it has to be otherwise.
• Protected is basically "public to child classes, private otherwise". Could go either way.