ArrayList.add throws ArrayIndexOutOfBoundsException [duplicate]

Question

This question already has answers here:

What are the possible problems caused by adding elements to unsynchronized ArrayList's object by multiple threads simultaneously? (4 answers)

What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it? (25 answers)

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.

Answer 1

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();
    }
}

Answer 2

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.