Java arraylist outofbounds

Question

I know that this question has been asked a million times. And I feel like the solution will be fairly obvious to someone who hasn't been staring at it for a couple of hours. But I can't make head or tails of my out of bound exception. Here is the error:

exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 207493, Size: 207493
    at java.util.ArrayList.rangeCheck(ArrayList.java:604)
    at java.util.ArrayList.get(ArrayList.java:382)
    at affysureselect.AffySureSelect.main(AffySureSelect.java:92)
Java Result: 1

I was thinking perhaps this might be happening due to the size of the arraylist, but if that were the case I would have expected the error to be when adding, rather than the getting. Here is the code where it is dying:

    String chrompos;
    ArrayList<String> chromnum = new ArrayList<String>();
    while ((input2 = sbuff.readLine()) != null) {
        prse = input2.split("\t");
        chromnum.add(prse[0]);
        ...
        chrompos = prse[7];
     }
    int cnt = 0;
    int cnt2 = 0;
    if (chromnum.get(cnt).equals(chrompos)) { // line causing my untimely death
      end = Integer.parseInt(chromposend.get(cnt2));
      start = Integer.parseInt(chromposstart.get(cnt2));
       ...

I even tried adding:

if (cnt <= chromnum.size()) { //this line
  if (chromnum.get(cnt).equals(chrompos)) { /before the dying line

But it dies anyway, on the get, not the add. What am I missing?

System.out.println the list, and you'll see you have less elements than you think — salezica
– salezica, Commented Apr 5, 2013 at 3:48
The problem is that you're confusing 0-based indexing with 1-based indexing. If your list has 10 elements, the indexes that the elements exist at are 0-9 (when you just use ArrayList.add( Object). Your check to make sure an index exists in the ArrayList would be if (cnt < chromnum.size()). — nickb
– nickb, Commented Apr 5, 2013 at 3:50

Sudhanshu Umalkar · Accepted Answer · 2013-04-05 03:48:43Z

1

If you are incrementing cnt, make sure that it's always less that chromnum.size().

It should be-

if (cnt < chromnum.size())

answered Apr 5, 2013 at 3:48

Sudhanshu Umalkar

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1 Comment

Stephopolis Over a year ago

Oh. Duh. I knew it would be a really silly thing. Thanks so much. I will accept in 11 minutes.

user1131435 · Accepted Answer · 2013-04-05 03:49:08Z

0

Index i does not exist. You must always iterate to list.size() - 1.

answered Apr 5, 2013 at 3:49

user1131435

Comments

Rahul · Accepted Answer · 2013-04-05 03:49:30Z

0

You can't access the index i if the size of the ArrayList is also i. The maximum accessible index is i-1. Hence, the IndexOutOfBoundsException which says you're trying to access the 207493th index, even when the size of your List is also 207493.

Have a check to restrict cnt below the size of your list.

answered Apr 5, 2013 at 3:49

Rahul

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Comments

Himanshu Bhardwaj · Accepted Answer · 2013-04-05 03:50:17Z

0

Since, as per the code it looks like, that in if loop you are trying a

 chromnum.get(cnt) and cnt is initialized to 0.

So the most probable issue is that the code never entered the while-loop, juts put a SOP after the while loop and check for the arraylist size.

answered Apr 5, 2013 at 3:50

Himanshu Bhardwaj

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Comments

Hunter Zhao · Accepted Answer · 2013-04-05 03:51:40Z

0

Remove the equal sign,

if (cnt < chromnum.size()) { //this line
      if (chromnum.get(cnt).equals(chrompos)) {

Hope to help you:)

answered Apr 5, 2013 at 3:51

Hunter Zhao

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Comments

gurbieta · Accepted Answer · 2013-04-05 04:02:56Z

0

Remember that lists start with 0, so if you have a list of N items the last item will be N - 1 (because 0 is the 1st element, 1 is the 2nd and so on)

So you should write

if (cnt < chromnum.size()) {

instead of

if (cnt <= chromnum.size()) {

answered Apr 5, 2013 at 4:02

gurbieta

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Andrew Lazarus · Accepted Answer · 2013-04-05 05:34:26Z

0

1-based like Pascal: United States, English-speaking Canada.
0-based like C/Java: Quebec, (most of?) Europe.

That's the answer. The question is, How are floors indexed in an elevator.

answered Apr 5, 2013 at 5:34

Andrew Lazarus

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