[wireties]

This is really just a classic C++ question. If a method or member in one class is public any other code (in the same space that has a handle/pointer to the class) can access the member or call the method. In practice it is wiser to keep everything things private and add public methods to access your private data. This way your data (or devices) controlled by the object have only carefully defined external interfaces, making your objects more "coherent".

HTH