Java Index Array Out of Bounds Exception

Question

This loop is strange.

I ran this in Java, it gives an Index out of bounds exception. I can't find an int l declaration anywhere in the source code and i can't figure out what it is and found out that it is legal for it to be declared this way.

But the deal here is, i don't understand what this piece of code is doing. For any size of resultSIList, it gives an ArrayIndexOutOfBoundsException.

for (int i = offset, l = Math.min(i + maxItemsInOnePage, totalSIs); i < l; i++){
    resultSIList.get(i);
}

EDIT: Thanks all.

Here is a runnable code i am using to try to understand this entire loop. Yes it is a horrible piece of junk.

public class IndexOutOfBoundsTest {
    public static void main(String args[]){
        int offset = 50;

        int maxItemsInOnePage = 50;

        int totalSIs = 50;

        final int buildThis = 15;

        List resultSIList = new ArrayList();

        // build list
        for(int zz = 0; zz < buildThis; zz ++){
            resultSIList.add("Hi " + zz);
        }

        try{
            for (int i = offset,
                    d = Math.min(i + maxItemsInOnePage, totalSIs);
                    i < d; i++){

               System.out.println(resultSIList.get(i));
           }
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

I've got one word for you: debugger. Step through and see how the behavior fails to match your assumptions. — duffymo
– duffymo, Commented Mar 28, 2012 at 9:23
That piece is looping i from offset to Math.min(offset + maxItemsInOnePage, totalSIs)-1. (The initialization is horribly written, but that's what it does as far as I understand.) But how could anyone here know what those variables are? What's resultSIList, etc.? You must post the whole relevant code, otherwise no one can help you. — Joonas Pulakka
– Joonas Pulakka, Commented Mar 28, 2012 at 9:26
Also one should not use "l" as a variable name. it looks like 1 and I and makes reading code very difficult. — mdakin
– mdakin, Commented Mar 28, 2012 at 9:28

jordeu · Accepted Answer · 2012-03-28 09:44:40Z

2

This code loops 'resulSIList' from 'offset' position to the minimum of 'offset + maxItemsInOnePage' and 'totalSIs'.

If offset > 0 and totalSIs = resultSIList.size() I think that it won't give you a out of bounds exception.

In your example you have an offset of 50 and the list size it's only 15. You have to check that your offset is less than the list size.

edited Mar 28, 2012 at 9:44

answered Mar 28, 2012 at 9:26

jordeu

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Comments

Andreas Dolk · Accepted Answer · 2012-03-28 09:46:06Z

1

It works as expected if and only if totalSIs is equal to or less then the size of the resultSIList. Double check that value. Here's a working example with some random values:

List<Integer> resultSIList = Arrays.asList(1,2,3,4,5,6,7,8);
int totalSIs = resultSIList.size();
int maxItemsInOnePage = 2;
int offset = 1;

for (int i = offset, l = Math.min(i + maxItemsInOnePage, totalSIs); i < l; i++){
  resultSIList.get(i);
}

From you added code I see, that totalSIs is bigger (=50) then the list size (=15).

You could add

 totalSIs = resultsSIList.size();

right behind the for loop for a quick fix.

edited Mar 28, 2012 at 9:46

answered Mar 28, 2012 at 9:32

Andreas Dolk

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2 Comments

HJW Over a year ago

Hi Andreas, i think you are right about this. Have you any idea if this is something like a code mistake, or it really is trying to do something?

Andreas Dolk Over a year ago

It may be doing something reasonable in its context - which I do not know. The code you've shown is a quite complicated way to throw an AIOOBE ;)

Tom · Accepted Answer · 2012-03-28 09:27:17Z

1

to get some more info you could run it with some logging added:

System.out.println("offset: " + offset);
System.out.println("maxItemsInOnePage: " + maxItemsInOnePage);
System.out.println("totalSIs: " + totalSIs);
System.out.println("resultSIList.size(): " + resultSIList.size());
for (int i = offset, l = Math.min(i + maxItemsInOnePage, totalSIs); i < l; i++){
    System.out.println("i: " + i);
    resultSIList.get(i);
}

running this should shed some light on your problem; the last i that gets printed was out of bound and by analyzing the four first printouts, you should find your problem.

answered Mar 28, 2012 at 9:27

Tom

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Comments

adarshr · Accepted Answer · 2012-03-28 09:23:20Z

0

Check if offset is less than the size of your list.

answered Mar 28, 2012 at 9:23

adarshr

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1 Comment

Alexander Pavlov Over a year ago

If offset is greater or equal (presumably, totalSIs), then the for body will not run (due to i < l).

stefan bachert · Accepted Answer · 2012-03-28 09:30:32Z

0

You should always check whether your index i is less the size

for (int i = offset, l = Math.min(i + maxItemsInOnePage, totalSIs);
      i < l && i < resultSIList.size ();
      i++){
  resultSIList.get(i);
}

answered Mar 28, 2012 at 9:30

stefan bachert

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