ArrayIndexOutOfBoundsException:

Question

Help me to solve this error. This code is for Gutherine series.Consider the following algorithm Start with a positive number n if n is even then divide by 2 if n is odd then multiply by 3 and add 1 continue this until n becomes 1

   public class Gutherine {

    public static void main(String[] args) {
        int a[] = {8, 3,2, 1};
        int result = isGutherineSequence(a);
        System.out.println(result);
    }

    public static int isGutherineSequence(int a[]) {
        int i = 0;
        int t = 0;
        for (i = 0; i < 4; i++) {
            if (a[i] % 2 == 0) {
                if (a[i + 1] == a[i] / 2) {
                    t++;
                }
            } else if (a[i + 1] == a[i] * 3 + 1) {
                t++;
            }
        }
        if (t == 3) {
            return 1;
        } else {
            return 0;
        }
    }
    }

Eran · Answer 1 · 2015-08-15T03:58:37.727

3

Since inside your loop you access a[i+1], you should iterate i until the next to last element, so change

for (i = 0; i < 4; i++)

to

for (i = 0; i < a.length - 1; i++)

BTW, you don't need the t counter. Once you discover that the series is not a Gutherine sequence, you can return false. You also fail to check that the last element is 1. And you should return a boolean instead of 0 or 1.

Here's a suggested implementation :

public static boolean isGutherineSequence(int a[]) {
    for (int i = 0; i < a.length - 1; i++) {
        if (a[i] % 2 == 0) {
            if (a[i + 1] != a[i] / 2) {
                return false;
            }
        } else if (a[i + 1] != a[i] * 3 + 1) {
            return false;
        }
    }
    return (a[a.length - 1] == 1);
}

edited Aug 15 '15 at 03:58

answered Aug 15 '15 at 03:54

Eran

387,369
54
702
768

would only solve the problem if it's ok to not touch the rightmost array element during the run of the loop. That doesn't seem to be the case here. – La-comadreja Aug 15 '15 at 03:55
@La-comadreja The right-most array element is examined in the last iteration of the loop when you access `a[i+1]`. – Eran Aug 15 '15 at 04:01

score 1 · Answer 2 · answered Aug 15 '15 at 03:54

1

The exception is caused by your referring to

a[i + 1]

If a[i] could be any element of the array, a[i + 1] could be one to the right of the rightmost element. So your array index would be out of bounds in that case.

answered Aug 15 '15 at 03:54

La-comadreja

5,627
11
36
64

score 0 · Answer 3 · answered Aug 15 '15 at 04:11

The out-of-bounds exception results from your the indirection a[i + 1] even when i is odd. The loop in your isGutherineSequence function will let i reach 3 and the offending line

} else if (a[i + 1] == a[i] * 3 + 1) {

Will effectively try to extract a non-existent a[4].

You should either stop the loop at a previous spot or provide an alternate test for the last element.

ArrayIndexOutOfBoundsException:

3 Answers3