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Rob Brew
Ranch Hand

Joined: Jun 23, 2011
Posts: 99
Hi all. Trying to manipulate an ArrayList and i get this error, what do i do?

Rob Spoor

Joined: Oct 27, 2005
Posts: 19679

When you iterate over most collections (either using an explicit Iterator or by using the for-each loop), any method call that modifies the collection will throw this exception. There are only two solutions:
1) use an explicit iterator and use the iterator's remove() method.
2) for lists only, loop using indexing. Be aware that when you delete an element, the indexing will also change. It's usually safest to loop backwards:

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I agree. Here's the link:
subject: java.util.ConcurrentModificationException