Double number returns stackoverflow

Question

The highest number that double can represent is extremely high, I thought. Though following code throws an exception. It's actually my full code.

public class Summe {
public static void main(String[] args) {
    System.out.println(summe(20000));
  }

public static double summe(double s) {
    return s == 0 ? s : s + summe(s-1); 
  }
}

Thanks for the answers so far. My question is: How can I make my code work?

Range of double has nothing to do with it. You recurrently call `summe` 20k times overflowing stack. Also... What is you actual question? — luk32, Oct 18 '14 at 22:50
How many times do you think `summe` is being called before it returns? — Oliver Charlesworth, Oct 18 '14 at 22:50
I think summe gets called around 20000 times. Where is the limit of a stack ? — Quatsch, Oct 18 '14 at 23:22

score 5 · Answer 1 · answered Oct 18 '14 at 22:51

5

The problem here isn't the size of number a double can hold - the problem is the size of the stack. Here, you have 20K nested call to summe, which is way too much for the stack to handle, and hence, it overflows. If s were an int instead of a double, you'd have the exact same problem.

answered Oct 18 '14 at 22:51

Mureinik

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And the fact that he's using exact comparison on floating-point doesn't help the base case. – chrylis -cautiouslyoptimistic- Oct 18 '14 at 22:51
@chrylis: The base case is absolutely fine. 20000 - 1 (etc.) will be calculated without any loss of precision. – Oliver Charlesworth Oct 18 '14 at 22:52
1

@chrylis Good point, even though in this case it coincidentally works. – biziclop Oct 18 '14 at 22:52
As a note, on my machine the stack falls over after 6279 calls. – chrylis -cautiouslyoptimistic- Oct 18 '14 at 22:54
My stack overflows at 5300. 5299 still works fine. Thats weird – Quatsch Oct 18 '14 at 23:24

score 0 · Answer 2 · edited May 23 '17 at 12:29

0

You made too many recursive call to summe.

You should read this question carefully to get a full explanation : What is a StackOverflowError?

edited May 23 '17 at 12:29

Community

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answered Oct 18 '14 at 22:54

ToYonos

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Double number returns stackoverflow

2 Answers2