exception when trying to print an array in Java

Question

I have this very little program in Java (just started to learn this language):

package hellojava;

public class Hellojava {
    public static void main(String[] args) {
        System.out.println("Hello World");
        int[] nums = {1,2,3,4,5,6,7,8,9,10};
        int[] revs = reverse(nums);
        for (int i : revs) {
            System.out.println(revs[i]);
        }
    }

    public static int[] reverse(int[] list) {
        int[] result = new int[list.length];
        for (int i=0, j=result.length-1; i<list.length; i++, j--) {
            result[j] = list[i];
        }
        return result;
    }
}

It throws this error:

 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10 at hellojava.Hellojava.main(Hellojava.java:9).

So I pretty know what's wrong and know how to fix it, but my question is about that for loop. I thought that this enhanced for loop will work here, but it doesn't. Why's that?

Buhake Sindi · Accepted Answer · 2014-11-03 21:32:12Z

10

The problem is that the enhanced for loop gives the values of the array, not the indexes. So, 10 the value is returned, which is an invalid index.

Your loop beginning:

for (int i : revs) {

is equivalent to

for (int index = 0; index < revs.length; index++)
{
    int i = revs[index];
}

edited Nov 3, 2014 at 21:32

Buhake Sindi

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answered Nov 3, 2014 at 21:27

rgettman

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1 Comment

mentor93 Over a year ago

Damn, it's so easy! Thank you! :)

Joni · Accepted Answer · 2014-11-03 21:28:51Z

5

The enhanced for loop gives you the values in an array, not the indexes. Try

for (int i : revs) {
    System.out.println(i);
}

answered Nov 3, 2014 at 21:28

Joni

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Comments

Buhake Sindi · Accepted Answer · 2014-11-03 21:28:10Z

3

Simple:

    for (int i : revs) {
        System.out.println(i);
    }

You are using a foreach statement instead of a for indexed loop. The foreach loop iterates the array for you and assign the element of the array to i so don't consider it as an index of an array.

Here is an Oracle documentation on the For-Each Loop.

answered Nov 3, 2014 at 21:28

Buhake Sindi

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Comments

M A · Accepted Answer · 2014-11-03 21:28:22Z

3

Replace

System.out.println(revs[i]);

with

System.out.println(i);

Explanation: The variable i is the integer element and not an index.

answered Nov 3, 2014 at 21:28

M A

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