What should the accessablity of Fields in a Abstract Class be?

Question

To put it simply as an example,

public abstract class AbstractFellow {

    protected Thing buddy;
....

public class ConcreteFellow extends AbstractFellow {
            


        

Answer 1

It depends on you domain model and why you creating and abstract class. If you are defining your interface with it and want abstract class to keep some functionality it`s ok.

If you are just setting all the fields protected and then reusing them in your child classes. Well it depends, but I think a better way should be found. And it seems not very clear for your future reader to get data in the base class and all it's behavior in child classes. If you do not need base class ability to implement methods (and you do not need to store any functionality in your base class) maybe it`s a better choice to implement an interface with every of these child classes.

If you use some of base class inner fields it seems natural to me and it's ok. Just if you are using some of them in your child classes for similar things you can implement a template method and enjoy with overriding only the parts you really need to override.