Question

This is the code in Java language:

class A{
   A() {  print();   }
   void print() { System.out.println("A"); }
}
class B extends A{
   int i =   Math.round(3.5f);
   public static void main(String[] args){
      A a = new B();
      a.print();
   }
   void print() { System.out.println(i); }
}

It prints 0, 4.
But why does from the super class A within constructor you invoke subclass print method? I see that the print method is overridden, but in fact the ‘print’ method has been called from the superclass…
That is the drill in order to prepare for Java certification.
Best regards

Answer 1

Don’t invoke print in the constructur of A. This is where it prints 0, because the instance of B apparently isn’t fully initialized yet, and the value of B.i apparently still is 0.

The implicit constructor of B is:

public B() {
   super(); // invokes B.print!
   this.i = Math.round(3.5f);
}

As you can see, print gets executed before i is initialized. Yet, you have overridden print, the old print is never executed.