ArrayList / for-loop

Question

My problem is simple : listeBalles is an ArrayList<Balle> and here is my code :

for (Balle b : listeBalles) {

        b.changeList(listeBalles);        
}

The matter is that the method b.changeList adds a Balle to the ArrayList listeBalles. I think that this is the matter. Here are the exceptions :

Exception in thread "main" java.util.ConcurrentModificationException

at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)

at java.util.AbstractList$Itr.next(AbstractList.java:343)

at Main.main(Main.java:31)

The line pointed is the for (Balle b : listeBalles) { line.

Thank you for your help.

See stackoverflow.com/questions/13847695/… for the remove case and how this problem is addressed — demongolem
– demongolem, Commented Apr 24, 2014 at 16:03
@demongolem add is different than remove I think. E.g. there is no support in the Iterator to add elements. — Puce
– Puce, Commented Apr 24, 2014 at 16:09
Ok, then I submit stackoverflow.com/questions/993025/… for your consideration — demongolem
– demongolem, Commented Apr 24, 2014 at 16:11

DarkAjax · Accepted Answer · 2014-04-24 16:03:56Z

1

Yes, you're right. From ArrayList's JavaDoc:

The iterators returned by this class's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException.

So basically you're not allowed to modify the List during iterating over it. What is your actual question?

edited Apr 24, 2014 at 16:03

DarkAjax

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answered Apr 24, 2014 at 16:00

Ray

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1 Comment

Danvdb Over a year ago

Thank you for the answer. But I need to do that so I used Puce's code and it worked.

Puce · Accepted Answer · 2014-04-24 16:01:28Z

0

As you cannot add elements to an ArrayList you're currently iterating over, make a copy of that list first.

E.g. try:

for (Balle b : new ArrayList(listeBalles)) {
        b.changeList(listeBalles);         
}

answered Apr 24, 2014 at 16:01

Puce

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Comments

blazy · Accepted Answer · 2014-04-24 16:01:09Z

0

The cause is that you are iterating through the List and modifying it at the same time.

answered Apr 24, 2014 at 16:01

blazy

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Andrei Nicusan · Accepted Answer · 2014-04-24 16:01:21Z

0

You cannot modify the content of a collection or array while you iterate over it in a for-each loop. What are you actually trying to do?

answered Apr 24, 2014 at 16:01

Andrei Nicusan

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