在这种情况下如何避免 ConcurrentModificationException？

Question

I understand that when I try to modify (add in that case) the list I got ConcurrentModificationException, but what is the best solution to fix that?

for (Map.Entry<String, Child> entry : children.entrySet() {
     childEvent.child = entry.getValue();
     if (childEvent.getDate() != null && childEvent.getDate().equals(selectedDate)) {
         if(this.selectedDayevents.isEmpty()) {
             // List                                
             this.selectedDayevents.add(childEvent);
          }
         for (CareDay selectedCareDay : this.selectedDayevents) {
             // Here I have to combine data in some cases...
         }
     }  
}

Answer 1

One simple way around this problem is to iterate over a copy of the entry set:

for (Map.Entry<String, Child> entry : new HashSet<>(children.entrySet())) {
    // same code
}

If your map is not too big and you're not doing it very often, you won't notice a difference in performance.

Answer 2

If your requirement is to enable concurrent access to the collection, then you should explore java concurrency APIs and especially ConcurrentHashMap or ConcurrentSkipListMap for your case.