Question

Consider this code:

class Test {
    Test() {
        System.out.println("In constructor of Superclass");
    }

    int adds(int n1, int n2) {
        return(n1+n2);
    }

    void print(int sum) {
        System.out.println("the sums are " + sum);
    }
}


class Test1 extends Test {
    Test1(int n1, int n2) {
        System.out.println("In constructor of Subclass");
        int sum = this.adds(n1,n2);
        this.print(sum);
    }

    public static void main(String[] args) {
        Test1 a=new Test1(13,12);
        Test c=new Test1(15,14);
    }
}

If we have a constructor in super class, it will be invoked by every object that we construct for the child class (ex. Object a for class Test1 calls Test1(int n1, int n2) and as well as its parent Test()).

Why does this happen?

The output of this program is:

In constructor of Superclass

In constructor of Subclass

the sums are 25

In constructor of Superclass

In constructor of Subclass

the sums are 29

Answer 1

Because it will ensure that when a constructor is invoked, it can rely on all the fields in its superclass being initialised.

see 3.4.4 in here