How to access the private variables of a class in its subclass?

Question

This is a question I was asked in an interview: I have class A with private members and Class B extends A. I know private members of a class cannot be accessed, but the qu

Answer 1

A nested class can access to all the private members of its enclosing class—both fields and methods. Therefore, a public or protected nested class inherited by a subclass has indirect access to all of the private members of the superclass.

public class SuperClass
{
    private int a = 10;
    public void makeInner()
    {
        SubClass in = new SubClass();
        in.inner();
    }
    class SubClass
    {
        public void inner()
        {
            System.out.println("Super a is " + a);
        }
    }
    public static void main(String[] args)
    {
        SuperClass.SubClass s = new SuperClass().new SubClass();
        s.inner();
    }
}

Answer 2

Have you thought about making them protected ? Just to be sure you are aware of this option, if you are then pardon me for bringing up this trivia ;)

Answer 3

By using setter method you can use else with the help of refection you can use private member of class by setting that member say a - take a from class and set a.setAccessible(true);

Answer 4

The interviewer was either testing your knowledge of access modifiers, or your approach to changing existing classes, or both.

I would have listed them (public, private, protected, package private) with an explanation of each. Then gone on to say that class A would need to be modified to allow access to those members from class B, either by adding setters and getters, or by changing the access modifiers of the members. Or class B could use reflection. Finally, talk about the pros and cons of each approach.

Answer 5

You cannot access private members from the parent class. You have make it protected or have protected/public method that has access to them.

EDIT : It is true you can use reflection. But that is not usual and not good idea to break encapsulation.

Answer 6

You can use the setters and getters of class A. Which gives same feeling as if You are using a class A's object.