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https://issues.apache.org/jira/browse/COLLECTIONS-663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16239363#comment-16239363
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Bruno P. Kinoshita commented on COLLECTIONS-663:
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I believe the Javadocs from asMap from MultiValuedMap indicate it works for as
a view for a state in the collection. If you have to alter the map or the
values collection, I'd try first using the mapIterator() method from the
MultiValuedMap. It returns a custom iterator.
The following altered code works for me:
{code:java}
public void testAlteringCollection() {
MultiValuedMap<Integer, Integer> multiMap = new
HashSetValuedHashMap<>();
multiMap.put(1, 10);
multiMap.put(2, 20);
Iterator<Integer> it = multiMap.mapIterator();
for (Iterator<Integer> iterator = multiMap.mapIterator();
iterator.hasNext();) {
Integer i = iterator.next();
iterator.remove(); // only the innerCollection is altered
}
}
{code}
Does it help? Bruno
> Unexpected ConcurrentModificationException when altering Collection of a
> MultiValuedMap
> ---------------------------------------------------------------------------------------
>
> Key: COLLECTIONS-663
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-663
> Project: Commons Collections
> Issue Type: Bug
> Reporter: Christophe Schmaltz
> Priority: Trivial
>
> Testcase:
> {code} @Test
> public void test() {
> MultiValuedMap<Integer, Integer> multiMap = new
> HashSetValuedHashMap<>();
> multiMap.put(1, 10);
> multiMap.put(2, 20);
> for (Collection<Integer> innerCollection :
> multiMap.asMap().values()) {
> for (Iterator<Integer> iterator =
> innerCollection.iterator(); iterator.hasNext();) {
> Integer i = iterator.next();
> iterator.remove(); // only the innerCollection
> is altered
> }
> // innerCollection.add(6); // adding stuff back should
> also work...
> }
> }{code}
> This test unexpectedly throws a ConcurrentModificationException.
> The issue is that when calling {{iterator.remove()}} the
> {{AbstractMultiValuedMap.ValuesIterator}} detects that the Collection is
> empty and calls {{AbstractMultiValuedMap.this.remove(key);}}.
> It may be better if the iterator of the inner collection had a reference on
> the iterator if the outer map and called {{containerIterator.remove()}}
> instead.
> *Note:* this solution would again present issues if the user tries to add new
> elements in this now empty collection (which was removed from the parent).
> In the current state, it is quite unclear why an exception is thrown, without
> debugging the code.
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