Question

What happens when a superclass has a field marked final, but a subclass overrides (hides?) this field? ‘Final’ doesn’t stop this, does it?
The specific example I’m working on is a Building class, from which different kinds of buildings inherit. The cost of each type, among other things, should be final to each subclass, but each type of building should have their own cost.

Edit: I’ve since realized that I had no idea what I was talking about above. What I really want are static variables of cost. However, if I declare these static variables in the superclass, they are static to the superclass, so Subclass1.cost, e.g., refers to the same value as Superclass.cost or Subclass2.cost. How can I make variables that are static to each subclass, without having to declare them in each class.

Answer 1

The final keyword, when applied to fields of a Java class, has nothing to do with inheritance. Instead, it indicates that outside of the constructor, that field cannot be reassigned.

Java treats name hiding and overriding separately. Overriding actually changes the observable behavior of the program at runtime by switching which function is called, while name hiding changes the program by changing the static interpretation of which field is being reference. final as applied to overriding only works for methods, because fields in Java cannot be overridden. The use of final in these different contexts is a bit confusing, unfortunately, and there is no way to prevent a field from having its name hidden in a subclass.

If you want the buildings to have different costs, one option would be to have an overridden getCost method which is overridden differently in each derived class. Alternatively, you could have a single protected or private field in the base class that stores the cost, then have each subclass set this field either directly (if this is protected) or through a base class constructor (if this field is private).

Hope this helps!