super, and the Parent That Goes First

Two situations need you to name the parent explicitly.

The first is constructors. Constructors are not inherited, so when your subclass has a constructor, it must arrange for the parent's constructor to run first. That is super(...):

class BaseTest {
    String name;
    BaseTest(String name) {
        this.name = name;
        System.out.println("1. BaseTest constructor: " + name);
    }
}
class LoginTest extends BaseTest {
    LoginTest(String name) {
        super(name);
        System.out.println("2. LoginTest constructor: " + name);
    }
}

1. BaseTest constructor: LoginTest
2. LoginTest constructor: LoginTest

Note the order, because interviewers ask about it: the parent's constructor finishes before the child's body runs. That is the only sensible order — the child may depend on fields the parent sets up, so the parent must go first. super(...) must be the very first statement in the constructor, and if you leave it out entirely, Java inserts a call to the parent's no-argument constructor for you. When the parent has no such constructor, the compiler stops you — and now you know why.

The second use is calling a parent method you have replaced. Inside an overridden method, super.setUp() runs the parent's version — which is how a subclass adds to inherited behavior rather than discarding it.

The parent going first solves a real ordering problem, but it doesn't yet let you change what a method actually does once you have it. That's the next, and more interesting, use of the parent-child relationship.