Use of super keyword in Java

Question

I have doubt regarding printing of superclass constructor statement even when I have not used super() keyword in subclass.

class A
{
    int i;
    A()
    {
        System.out.println("A's constructor");
    }
}
class B extends A
{
    int i;
    B(int a , int b)
    {
        super.i=a;
        i=b;
    }
    void show()
    {
        System.out.println(super.i);
        System.out.println(i);
    }
}
class UseSuper
{
    public static void main(String[] args)
    {
        B b=new B(1,2);
        b.show();
    }
}

The output of my program is:

A's constructor

1

2

I am unable to understand why I am getting A's constructor printed on my console?

Answer 1

Check the following lines from https://docs.oracle.com/javase/tutorial/java/IandI/super.html

---

Note: If a constructor does not explicitly invoke a superclass constructor, the Java compiler automatically inserts a call to the no-argument constructor of the superclass. If the super class does not have a no-argument constructor, you will get a compile-time error. Object does have such a constructor, so if Object is the only superclass, there is no problem.

---

If a subclass constructor invokes a constructor of its superclass, either explicitly or implicitly, you might think that there will be a whole chain of constructors called, all the way back to the constructor of Object. In fact, this is the case. It is called constructor chaining, and you need to be aware of it when there is a long line of class descent.

I hope, it clears your doubts.

[Update]

Posting this update to clear OP's doubts he has mentioned in his comment below.

The following code won't compile because implicit super constructor A() has not been defined and we have also not defined it explicitly. Note that the implicit super constructor A() is automatically defined when there is no other constructor with arguments have been defined.

class A {
    int i;

    A(int x,int y){

    }
}

class B extends A {
    int i;

    B(int a, int b) {
        super.i = a;
        i = b;
    }

    void show() {
        System.out.println(super.i);
        System.out.println(i);
    }
}

public class UseSuper {
    public static void main(String[] args) {
        B b = new B(1, 2);
        b.show();
    }
}

[Another Update]

Posting this update to clear OP's another doubt which he has mentioned in his comment below.

The following code too won't compile because the super constructor A() has been declared as private preventing the child class constructor to call it.

class A {
    int i;

    private A() {
        System.out.println("A's constructor");
    }
}

class B extends A {
    int i;

    B(int a, int b) {
        super.i = a;
        i = b;
    }

    void show() {
        System.out.println(super.i);
        System.out.println(i);
    }
}

class UseSuper {
    public static void main(String[] args) {
        B b = new B(1, 2);
        b.show();
    }
}