Why is constructor of super class invoked when we declare the object of sub class? (Java)

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

Answer 2

Yes. A superclass must be constructed before a derived class could be constructed too, otherwise some fields that should be available in the derived class could be not initialized.

A little note: If you have to explicitly call the super class constructor and pass it some parameters:

baseClassConstructor(){     super(someParams); } 

then the super constructor must be the first method call into derived constructor. For example this won't compile:

baseClassConstructor(){      foo();       super(someParams); // compilation error }