ConcurrentModificationException when iterating over map

Question

I am getting ConcurrentModificationException when iterating over a content of a map

    for (String sourceKey : sMap.getContent().keySet()) {

        List<String> sourceValues = sMap.getValues(sourceKey);
        List<String> targetValues = tMap.getValues(sourceKey);

        if (areMultiple(sourceValues)) {
        ....
    }

sMap.getContent() returns Map<String, List<String>> , of which i am getting keys only.

Note that no modification of map's content is done. I am only iterating here.

What am i doing wrong here? How can i correct the situation when exception is thrown?

Answer 1

This will occur if the underlying collection that is being iterated over is modified by anything other than the Iterator itself.

Try using a ConcurrentHashMap instead of a plain HashMap