ArrayList / for 循环

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.

Answer 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?

Answer 2

原因是您正在遍历List并同时修改它。

Answer 3

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?

Answer 4

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

Eg try:

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