Is it safe to delete HashMap's entry when iterating over its values?

Question

Assuming I know the key, is it possible to remove it when iterating over

for (ExampleClass e : map.values()) {
    if (condition) {
        map.remove(key);
    }
}

I have found a related question (iterating over and removing from a map), but it assumes we are iterating over the key set. Does the same apply to the value set?

sometimes I wonder what would be quicker, testing to see what happens or asking at SO? — Scary Wombat, Jun 18 '14 at 07:48

score 4 · Accepted Answer · answered Jun 18 '14 at 07:47

From the HashMap javadoc:

The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException.

So you can't use map.remove(key).

From the javadoc for HashMap#values():

The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations.

So you can use Iterator#remove() to remove entries from the value set.

Is it safe to delete HashMap's entry when iterating over its values?

1 Answers1