Looping through Collection and getting ConcurrentModificationException

Question

I'm trying to loop through a collection to delete some objects referenced by that collection but keep coming up against a ConcurrentModificationException.
BwView view = svci.getViewsHandler().find("Lists");
              Collection<BwSubscription> subarr = new TreeSet<BwSubscription>();
              subarr = svci.getSubscriptionsHandler().getAll();  
              if (subarr == null) {
                   logger.info("Its not working");
              for (BwSubscription sub: subarr) {
                   logger.info("Removing subs " + sub);
                   svci.beginTransaction();
                   svci.getSubscriptionsHandler().delete(sub);
                   logger.info("Deleting calendars :" + sub);
                   svci.endTransaction();
             The loop is allowing me to delete the first entry but then fails with the exception.
I have tried with a generic loop but this doesn't initialise the sub entity so the loop fails and is ignored leading to problems later in the code.
BwView view = svci.getViewsHandler().find("Lists");
              BwSubscription[] subarr = (BwSubscription[])view.getSubscriptions().toArray(new BwSubscription []{});
              if (subarr == null) {
                   logger.info("Its not working");
              for (int i=subarr.length - 1; i>=0; i--) {
                   sub = subarr;
               logger.info("Removing subs " + sub);
               svci.beginTransaction();
               svci.getSubscriptionsHandler().delete(sub);
               logger.info("Deleting calendars :" + sub);
               svci.endTransaction();
Sub is either not initialised or gets initialised as 0 causing an ArrayIndexOutofBoundsException. I'd be grateful for some advice on getting the code to loop correctly.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

Answer 1

While iterating over a collection (using its iterator), a ConcurrentModificationException will be thrown if the collection is modified, except if it is modified using the iterator itself.. The enhanched for-loop you're using is iterating over the collection by implicitly using an Iterator. To do what you want, make the Iterator explicit (change the enhanced for-loop to a while loop) and then use iterator.remove().