You cannot change the length of a Collection (by adding or removing items) while iterating through it. You can - make a copy of the account collections, delete accounts from that copy during iteration, clear the account collection and insert all elements of the copy into the account collection *uff* - insert all accounts to delete into a toDelete collection during iteration, and then iterate over the toDelete collection and delete items from the account collection. Confused? Here's an example for the second way: public void filter(...) { | Collection<Accounts> toDelete = new ArrayList<Accounts>(); | for (Account a: accounts) | if(accounts.notAccessibleBy(user) | toDelete.add(a); | else if (accounts.accessibleBy(user) | continue; | else | toDelete.add(a); | | for (Account a: toDelete) | accounts.remove(a); | } btw: The checks you make (notAccessiblyBy, accessibleBy) seem to be a bit weird ;). It looks like you want to keep ALL accounts in the collection or delete ALL of them. Wouldn't it work like this? public void filter(...) { | if (accounts.notAccessibleBy(user)) | accounts.clear(); | } View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3960375#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...