List Concurrent Modification Exception

Question

The following codes throws the java.util.ConcurrentModificationException
public static void main(String[] args) {
        List<Integer> list1 = new LinkedList<Integer>();
        ListIterator head = list1.listIterator();
        list1.add(1);
        while(head.hasNext()) {
            System.out.println(head.next());
    }But if I put list1.add(1) before
   ListIterator head = list1.listIterator();, then it runs fine.
I've googled the exception and get the idea that it is caused by 2 threads accessing the list. Where are the 2 threads?
Edited by: pinkyDeveloper on Feb 17, 2009 3:00 PM

Answer 1

nothing to do with threads and everything to do with changing the list after getting the iterator and then iterating with the iterator. Don't do this unless you change the list through the iterator. You might want to read the API on LinkedList which states:
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.
Edited by: Encephalopathic on Feb 17, 2009 3:13 PM