I see, it's just that I read somewhere that (and I semi-quote it) "If you need to use instanceof, it means your code is bad/needs improvement" and many agreed on what that person said. I dunno though how true it is and I don't remember if it was in game-development or general programing (as these are different in my opinion).
What do you think?
I don't think it's bad to use instanceof for this part of the code. Storing a string for the name would be perfect if it would be used as an unique Identifiant. Though,
all your paddles will be name "paddle" and all your walls will be named "wall". I think you must adjust your code with the functionnalities that you are looking for. Therefore, as you don't need 1000 different entities and you have to implement collision detection differently on each of your entity, it is a good way to do it.