return statement

[Jim Colwood]

Hi all,

any idea why this would return "Sum = 15" and not "Sum = 1"?

  class Calculator{

  public static void main(String[] args){

    Calculator calc = new Calculator();
    System.out.println("Sum = " + calc.calculate(5));

  }

  public int calculate(int n){
    if(n == 1){
      return n;
    } else {
      return (calculate(n-1) + n);
    }
  }
}  

couldn't find a similar thread with my brief search in the forum.
Thanks.

[W. Joe Smith]

I was wrong, so I deleted this post. Don't want false information floating out there confusing everyone! See below post for correct answer.

[Ruben Soto]

Calculate calls itself recursively, so:
Calculate(5) = Calculate(4) + 5
= Calculate(3) + 4 + 5
= Calculate(2) + 3 + 4 + 5
= Calculate(1) + 2 + 3 + 4 + 5
= 1 + 2 + 3 + 4 + 5
= 15

[Devaka Cooray]

Good question. Please QuoteYourSources.

[Jim Colwood]

Thanks for your replies guys.

Yes Joe, I had my doubts about your reply. so I added couple of lines in the code to see what's going on at runtime.

  class Calculator{

  public static void main(String[] args){
    Calculator calc = new Calculator();
    System.out.println("Sum = " + calc.calculate(5));
  }

  public int calculate(int n){
    if(n == 1){
      System.out.println("n = " + n + "; FIRST return 

reached.");
      return n;
    } else {
      System.out.println("n = " + n + "; SECOND return 

reached.");
      return (calculate(n-1) + n);
    }

  }
}  

Ruban, your calculation is right. but the real question i have is, even if the FIRST return statement returns the int, why is the returned value 15?

I had a question with similar logic in a Java test offered to me by a recruiter.
Thanks again.

[Henry Wong]

Ruban, your calculation is right. but the real question i have is, even if the FIRST return statement returns the int, why is the returned value 15?

The FIRST return statement did return an int, but not to the main() method -- it returned it back to the calculate() method, which called it. If the main() method had triggered the FIRST return statement, then it would have printed 1.

Henry

[Jim Colwood]

Duh! it seems simple after you explained it, but it's easy to miss it.

Thanks a lot Henry.