Access a variable using parent reference type in java

Question

I have created 2 classes - Parent and Child, both like this:

Parent.java

public class Parent {
    String name = "Parent";
}

Child.java

public class Child extends Parent {
    String name = "Child";
}

The Child class is shadowing the parent class instance variable name.

I have created a main program like this:

Test.java

public class Test {

    public static void main(String[] args) {
        Parent p = new Parent();
        Child c = new Child();

        System.out.println(p.name);
        System.out.println(c.name);

        Parent pc = new Child();
        System.out.println(pc.name);
    }

}

The output of the program is this:

Parent
Child
Parent

Now I am not clear on when I try to access pc.name then I am getting output as Parent as per the above output instead of Child.

My understanding was like this, I created a reference variable pc of type Parent but it points to Child object as er my program. So during run-time time of the program, java creates an object in heap memory for the child class and since the child class is shadowing the name variable, the output of pc.name will be Child. But as per the program my understanding was not correct and this concept applies to only methods that are overriden by child class.

Can you please explain why it is different in the case of instance variable compared to methods?

Answer 1

There's no overriding for instance variables.

Your Child class has two name instance variables. The one in the Child class hides the one in the Parent class (BTW, they don't have to both be of the same type).

When you access name via a Parent reference, you get the name variable of the Parent class. When you access name via a Child reference, you get the name variable of the Child class.

Answer 2

Access to fields is always determined by the static type (that is: the type of the variable). This is in contrast to methods which are determined (a.k.a "resolved", "bound") by the runtime type of the actual object.

In other words: for field access, the compiler determines, at compilation time, is going to be accessed. In your example, you access pc.name. The compiler checks the type of the pc variable, sees that it is of type Parent and hence generates code that accesses the .name field of the Parent class.