subclass needs access to private attribute of abst

问题:

I have an abstract java class that implements a couple of its methods, but not others. In the methods it implements it uses a private attribute variable. The variable used also needs to be used in a subclass.

As I see it my options are:

• Declare the private variable in both the subclass and the super class
• defer the implementation of the methods currently implemented in the abstract class to the subclasses

Are there other options? Which of these makes more sense and why?

回答1:

The question is how you want to maintain your state: If it is of no concern, where the value is stored, you can just add a private member "on top" of the other and use that instead of the one in the superclass. If you want to have some methods from your superclass and some methods from your subclass to access the same state, you need to change visibility:

You could declare the variable as protected, making it accessible in the subclass, or implement accessor methods, or even make it public.

回答2:

Hopefully the abstract class has been designed such that you shouldn't need access to the private fields. As to which of your two methods to use, that depends entirely on what the abstract class and your subclass are and what they're supposed to be doing.

If you only need read access to this variable and the superclass methods don't modify it, you can just add another (completely separate) private field of the same name/type to your subclass. If you're attempting to modify the behaviour of the superclass methods by changing the field, you're going to have to override the methods instead.