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I am trying to add a object to a ArrayList and its throwing ArrayIndexOutOfBoundsException Following is the code 

private void populateInboxResultHolder(List inboxErrors){
    inboxList = new ArrayList();
    try{                
        inboxHolder = new InboxResultHolder();
        //Lots of Code
        inboxList.add(inboxHolder);
    }catch(Exception e){
        e.printStackTrace();
    }
}

And the exception is 

[3/7/12 15:41:26:715 UTC] 00000045 SystemErr     R java.lang.ArrayIndexOutOfBoundsException
[3/7/12 15:41:26:721 UTC] 00000045 SystemErr     R      at java.util.ArrayList.add(ArrayList.java:378)
[3/7/12 15:41:26:721 UTC] 00000045 SystemErr     R      at com.ml.fusion.ui.common.web.bean.inbox.InboxSearchBean.populateInboxResultHolder(InboxSearchBean.java:388)    
[3/7/12 15:41:26:721 UTC] 00000045 SystemErr     R      at com.ml.fusion.ui.common.web.bean.inbox.InboxSearchBean.searchInboxErrors(InboxSearchBean.java:197)
[3/7/12 15:41:26:721 UTC] 00000045 SystemErr     R      at com.ml.fusion.ui.common.web.bean.inbox.InboxSearchBean.viewInbox(InboxSearchBean.java:207)

But according to the signature of ArrayList.add it should not throw this exception. Please help.

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3
  • 2
    Well, since IndexOutOfBoundsException is a RuntimeException, it can be thrown without being mentionned in the method signature. Commented Mar 9, 2012 at 10:25
  • 2
    ArrayIndexOutOfBoundsException is a runtime exception, not a checked exception, so it doesn't necessarily show up in the signature of the methods that throw it. Commented Mar 9, 2012 at 10:25
  • thats right.But if you look at the add method itself there is no possibility of this exception getting thrown Commented Mar 9, 2012 at 10:29

2 Answers 2

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47

ArrayList.add() should never throw an ArrayIndexOutOfBoundsException if used "properly" so it seems that you're using your ArrayList in a way which it does not support.

It's hard to tell from just the code you've posted but my guess is that you're accessing your ArrayList from multiple threads.

ArrayList isn't synchronised and so isn't thread safe. If this is the problem you can fix it by wrapping your List using Collections.synchronizedList().

Changing your code to the following should resolve the problem:

private void populateInboxResultHolder(List inboxErrors){
    List inboxList = Collections.synchronizedList(new ArrayList());
    try{                
        inboxHolder = new InboxResultHolder();
        //Lots of Code
        inboxList.add(inboxHolder);
    }catch(Exception e){
        e.printStackTrace();
    }
}
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9 Comments

I did think in that angle.But even in that case it should not throw that exception as we are doing add and not add(index,Obj).
If you are accessing the ArrayList from multiple threads without synchronising it, it will break. What I think is happening is that two threads are trying to modify the Array which underlies the ArrayList at the same time, so it is not the correct size when one of the threads tries to add a new value.
No. If you use something outside its contract it's behaviour becomes undefined. This means you can expect it to throw any RuntimeException or corrupt your data or do anything at all. The documentation is clear that ArrayList is not supported in multiple threads so will not have any defined behaviour in that case.
It threw this Exception because it tried to add something to an Array with an index that was too big. The ArrayList stores its data in an Array and maintains the size of that Array automatically. But if you access an ArrayList from multiple threads simultaneously the Array maintaining code is not always run in the "correct order" and so you get your ArrayIndexOutOfBoundsException. Consider yourself lucky that you got an Exception and not just some corrupt or lost data. If you are accessing your ArrayList from multiple threads this is definitely the source of your problem.
No thanks. There is nothing to discuss unless you have tried using Collections.synchronisedList() and that has not fixed the problem.
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-4

The code you posted will not throw ArrayIndexOutOfBoundsException.

The exception you get is thrown in the part you omitted. Take a look at your stacktrace. Its InboxSearchBean that causes the exception. Most likely it performs a get(index) on the list with an invalid index.

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1 Comment

It's possible if you try to add from different threads.

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