Adding methods to an Objective C class interface is optional?

Question

Coming from a C++ background, one thing that confuses me about Objective C is the fact that you can add a method to a class without actually specifying it in the class interface. So I had a barrage of questions:

1. Why would someone choose to not add the method in the class interface?
2. Is it simply because of visibility?
3. Methods without a declaration in the interface are private?
4. Is declaring methods in a class interface just optional?
5. Is it different for overriding a base class' method?

Answer 1

The main difference is that C++ sets up much of its inheritance and types at compile time and Objective C does it mostly at runtime.

The only differences in putting a method in the interface (if all parameters are objects) in objective-C are that the compiler can see it at compile time and check that an object could respond to the method - if it does not then you get a warning but the compilation does succeed and the program will run and loo for the method at runtime. If the method is in the implementation of the class or a category (or some other way) then the run time will find it and call it successfully.

There are NO private methods you can call any method.