Adding specific values for inherited fields

Question

I am having some trouble with inheritance (Student here). I need to be able to utilize 1 inherited private field for each subclass I make. Obviously subclasses cannot have access to inherited fields however when a new object is created that inherited private field is a part of that object. For my purposes though each subclass needs to have it's own specific value for that inherited field. My first attempt looks something like this:

Public class A {

    private int x = 0;

    public A(int n) {

        x = n;
    }

    public int useX() {

        return x;
    }
}

Public class B Extends A {
    int n = 1;

    public B() {
        super(n);
    }

    useX(); // Return 1?
}

Public class C Extends A {
    int n = 2;

    public B() {
        super(n);
    }

    useX(); // Return 2?
}

However my professors tell me that I could also be using a setter method inside of my Super class to create that new field, and from there I am confused. Can anyone help point me in the right direction?

Answer 1

An ordinary Java Bean provides public accessors and mutators (aka getters and setters) for it's fields. However, you could provide a protected setter. Something like,

public class A {
    private int x = 0;

    public int getX() { // <-- the usual name.
        return x;
    }

    protected void setX(int x) {
        this.x = x;
    }
}

Then your subclasses can invoke that setter

public class B extends A {
    public B() {
        super();
        setX(1);
    }
}

And then B.getX() (or B.useX() if you really prefer) will return 1.