Recursive function throws java.lang.StackOverflowError

Question

I get the error java.lang.StackOverflowError when I try to run my code:

public class calc {
    public static void main(String[] args){
double zahl = 847362;
System.out.println( wannawoerk(zahl) );

}


public static double wannawoerk(double zahl){
    if (zahl == 1)
        return 1;
    else
        return wannawoerk(zahl - 1) + zahl;
} }

Is there any workaround for this problem? I have to use a recursive function without for, while, etc.

Why `double`? The problem here is either A) The stack can't go 847,361 frames deep (think about it, that's a lot), or B) IEEE-754 double-precision binary floating point fun and games. I suspect (A), but... — T.J. Crowder, Oct 17 '16 at 12:55
"Thrown when a stack overflow occurs because an application recurses too deeply." — eldo, Oct 17 '16 at 13:00

Bathsheba · Answer 1 · 2016-10-17T14:00:04.027

9

Repeated subtraction of 1 from zahl will eventually give you 1. (Floating point subtraction by an integer on integers in this range is exact: you'd only get oddities above the 53rd power of 2).

Your problem is that your JVM is probably not going to allow you that many recursive calls.

A stack depth approaching one million is really not going to end well!

edited Oct 17 '16 at 14:00

answered Oct 17 '16 at 12:55

Bathsheba

231,907
34
361
483

For mentioning that integers up to 2^^54 are represented without error. +1 64-bit float has a 53-bit mantissa as the top bit is always 1 for normalised number only the bottom 52 bits need to be stored. 2^^54 is the last ok integer as it's a power of two but 2^^54+1 can't be represented. – Peter Lawrey Oct 17 '16 at 13:23
Hum. We'll meet in the middle. I think the first number that can't be represented is 2^^53 + 1 – Bathsheba Oct 17 '16 at 14:00

Jiri Tousek · Accepted Answer · 2016-10-17T13:53:19.037

1

If you're required to use recursion, you could increase memory available for stack: java -Xss256m YourClass - sets stack to 256MB max.

In real world, you'd most probably use a while loop for this. Or, in this case, compute it right away (you don't need recursion for the thing you are computing), but I guess that's not the point.

edited Oct 17 '16 at 13:53

answered Oct 17 '16 at 13:03

Jiri Tousek

12,211
5
29
43

@Bathsheba You're right. I didn't bother to verify it as IMO it is secondary and not to the point of question. But I see having wrong formula in the answer is not a good idea and could mislead someone, so I removed it. – Jiri Tousek Oct 17 '16 at 13:54
Thanks for the answer, Jiri. – Hans Müller Oct 17 '16 at 18:32

score 1 · Answer 3 · answered Oct 17 '16 at 13:20

1

The stack is not unlimited and Java doesn't have tail call optimisation. The simplest solution is to have the method

return zahl * (zahl + 1) / 2;

Ideally you wouldn't use double instead you would write

public static long sumUpTo(int n) {
    return n * (n + 1L) / 2;
}

To make any sane optimisation you need a more realistic method.

answered Oct 17 '16 at 13:20

Peter Lawrey

525,659
79
751
1,130

1

Upvoted. 1) for the tail call snippet and, 2) for taking the time to write out the closed form solution. – Bathsheba Oct 17 '16 at 13:21
But there is no recursion. – Hans Müller Oct 17 '16 at 18:22
@HansMüller indeed. Recursion is rarely a good idea in Java esp when the level of recursion is order N of an input. Order log N is okay such as for balanced binary trees. – Peter Lawrey Oct 18 '16 at 03:55

score 0 · Answer 4 · edited May 23 '17 at 10:34

0

This example of yours is very also illustrated in this comment! along with a few other very detailed explanations of this issue, why it happens and how to handle it.

edited May 23 '17 at 10:34

Community

1
1

answered Oct 17 '16 at 13:32

Simon Jensen

488
1
3
19

1

I did consider it, but since the general question and explanation was different and only one of the answers provided in the link was similar I wasn't too sure about it. So simply not to ruin anything, I would leave that decision to someone more competent in that matter than myself – Simon Jensen Oct 17 '16 at 13:39

Recursive function throws java.lang.StackOverflowError

4 Answers4