Can Java Subclasses Override Member Variables?

Overriding Member Variables in Java: Understanding Variable Hiding

In Java, overriding member functions is a well-known concept, but what about overriding member variables? To explore this, consider the following code:

public class A {
    public int intVal = 1;
    public void identifyClass() {
        System.out.println("I am class A");
    }
}

public class B extends A {
    public int intVal = 2;
    public void identifyClass() {
        System.out.println("I am class B");
    }
}

public class mainClass {
    public static void main(String[] args) {
        A a = new A();
        B b = new B();
        A aRef;
        aRef = a;
        System.out.println(aRef.intVal); // Output: 1
        aRef.identifyClass(); // Output: "I am class A"
        aRef = b;
        System.out.println(aRef.intVal); // Output: 1
        aRef.identifyClass(); // Output: "I am class B"
    }
}

The code aims to demonstrate the behavior of overridden member variables. However, there's a puzzle - why does aRef.intVal still return 1 after aRef is set to b, which has a intVal of 2?

The answer lies in the concept of variable hiding. When a subclass declares a variable with the same name as one in its superclass, it "hides" the superclass's variable. This means that the subclass has two variables: one from its superclass and one from its own definition.

In the code above, the intVal member variable is declared in both A and B. Therefore, when B is created, it has both intVals - one with a value of 1 inherited from A, and one with a value of 2 defined in B.

When aRef is set to a, it refers to the intVal of A. When aRef is set to b, it still refers to the intVal of A. This is because in the expression aRef.intVal, aRef resolves to the type A, and intVal is a variable of A.

To access the intVal of B, one would need to use ((B)aRef).intVal, which explicitly casts aRef to type B and allows access to B's variables.

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