java - Why is super class constructor always called

I have the following 2 classes

public class classA {

    classA() {
        System.out.println("A");
    }
}

class classB extends classA {
    classB() {
        System.out.println("B");
    }
}

and then running

classA c = new classB();

or

classB c = new classB(); 

always gives

A
B

Why is this happening? At first glance, in either scenario, I would assume that only the classB constructor would be called and thus the only output would be

B

but this is clearly wrong.