super keyword without extends to the super class

Question

There is a code of simple program. In constructor, super() is called without extends to the super class, I can not understand what will does this in this situat

Answer 1

There is not need to add super() because it is by default added.

It will call Object class's default constructor because in JAVA every class extends Object by default.

Answer 2

Constructor from your code works the same as:

Student(String name, int rollNum){
    this.name = name;
    this.rollNum = rollNum;
}

In your question super() is just calling constructor of Object class.

Answer 3

Every class that doesn't explicitly extend another class implicitly extends java.lang.Object. So super() simply calls the no-arg constructor of Object.

Note that this explicit call is unnecessary since the compiler would add it for you. You only need to add a super() call in a constructor when you want to invoke a superclass constructor with arguments.