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Chen edited comment on COLLECTIONS-663 at 11/5/19 1:52 AM: ----------------------------------------------------------- Hi,[~chris333] MapIterator.setValue() really is not supported, there is a not elegant code to implement your problem what I understand. {code:java} public void testWhatINeedToWork() { ListValuedMap<Integer, Integer> multiMap = new ArrayListValuedHashMap<>(); multiMap.put(1, 10); multiMap.put(1, 20); multiMap.put(2, 10); System.out.println(multiMap); for(Collection<Integer> col: multiMap.asMap().values()){ if(col instanceof List){ List<Integer> list = (List<Integer>) col; for(ListIterator it = list.listIterator(); it.hasNext(); ){ Integer value = (Integer) it.next(); if(value % 2== 0){ it.set(value*2); } } } } System.out.println(multiMap); } {code} was (Author: guoping1): Hi,[~chris333] MapIterator.setValue() really is not supported, there is a not elegant code to implement your problem what I understand. {code:java} //代码占位符 public void testWhatINeedToWork() { ListValuedMap<Integer, Integer> multiMap = new ArrayListValuedHashMap<>(); multiMap.put(1, 10); multiMap.put(1, 20); multiMap.put(2, 10); System.out.println(multiMap); for(Collection<Integer> col: multiMap.asMap().values()){ if(col instanceof List){ List<Integer> list = (List<Integer>) col; for(ListIterator it = list.listIterator(); it.hasNext(); ){ Integer value = (Integer) it.next(); if(value % 2== 0){ it.set(value*2); } } } } System.out.println(multiMap); } {code} > 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 > Assignee: Bruno P. Kinoshita > 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. -- This message was sent by Atlassian Jira (v8.3.4#803005)