Java Inheritance - instance variables overriding

Question

Why are Instance variables of a superclass not overidden in Inheritance ?

Answer 1

You can hide a field, but not override it.

Hiding means that a field will have a different value depending from which class it's accessed. The field in the subclass will "hide" the field in the super-class, but both exists.

That's an extremely bad practice to hide field, but works:

public class HideField {

    public static class A
    {   
        String name = "a";

        public void doIt1() { System.out.println( name ); };
        public void doIt2() { System.out.println( name ); };   
    }

    public static class B extends A
    {
        String name = "b";

        public void doIt2() { System.out.println( name ); };
    }

    public static void main(String[] args)
    {
        A a = new A();
        B b = new B();

        a.doIt1(); // print a
        b.doIt1(); // print a
        a.doIt2(); // print a
        b.doIt2(); // print b <-- B.name hides A.name
    }
}

Depending on whether the method was overriden, the field in A or B is accessed.

Never do that! That's never the solution to your problem and creates very subtle bugs related to inheritance.

Answer 2

Because inheritance is intended to modify behaviour. Behaviour is exposed through methods, and that's why they can be overridden.

Fields are not behaviour but state. You don't need to modify that, nor the private methods employed by the superclass. They are intended to allow the superclass to do it's job.