Resolve java.util.ConcurrentModificationException

Question

as the title suggests, I need to fix this exception: java.util.ConcurrentModificationException: null. Below the code that goes into error:

Map<String, List<Note>> noteByCod = notes.stream().collect(Collectors.groupingBy(Note::getCod));
noteByCod.forEach((k, v) -> v.forEach(note -> {
       if (!note.getVer() || !StringUtils.isEmpty(note.getError())) {
                noteByCod.remove(k);
       }
}));

the problem is that it is not possible to modify the collection you are iterating on, in this case how would you solve?

Even simpler noteByCod.values().removeIf(v -> v.stream().anyMatch(note -> !note.getVer() || !StringUtils.isEmpty(note.getError()))); And when you clean up your API and make a definite decision whether an error free note should return null or an empty string from getError(), you can get rid of StringUtils.isEmpty and use either getError() != null or !getError().isEmpty(). — Holger
– Holger, Commented Apr 14, 2021 at 11:01

Joachim Sauer · Accepted Answer · 2021-04-14 09:49:08Z

3

You can rewrite this to use an old-fashioned Iterator over the entry set. Iterator has a remove method that allows the last-returned object to be removed:

Map<String, List<Note>> noteByCod = ...;
Iterator<Map.Entry<String, List<Note>> it = noteByCode.entrySet().iterator();
while (it.hasNext()) {
  if (it.next().getValue().stream().anyMatch(
        note -> !note.getVer() || !StringUtils.isEmpty(note.getError()))) {
    it.remove();
  }
}));

answered Apr 14, 2021 at 9:49

Joachim Sauer

309k59 gold badges568 silver badges624 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Joop Eggen Over a year ago

The Stream way would require to collect a list of notes to remove, so this is definitely a more direct, efficient solution. If not the noteByCode is redone.

Joachim Sauer Over a year ago

@EngineerTop: removeIf is actually a nicer solution, well done. If you find a solution, you can and should post it as an answer, please don't edit your question to include it.

EngineerTop · Accepted Answer · 2021-04-14 11:19:42Z

3

Thanks, I finally solved it like this:

Map<String, List<Note>> noteByCod = notes.stream().collect(Collectors.groupingBy(Note::getCod));
noteByCod.values().removeIf(v -> v.stream().anyMatch(note -> !note.getVer() || !StringUtils.isEmpty(note.getError())));

answered Apr 14, 2021 at 11:19

EngineerTop

9310 bronze badges

1 Comment

Yassin Hajaj Over a year ago

Good job ! indeed

Collectives™ on Stack Overflow

Resolve java.util.ConcurrentModificationException

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related