Javas HashMap&lt;K,V&gt; has no checking for concurrent modification <i>at all</i>, it&#x27;s only a check that is made during Iteration In the internal HashIterator type. It only checks that the collection wasn&#x27;t modified <i>while that iterator was iterating</i>.<p>There is nothing there to prevent the HashMap itself from corrupting completely with multiple writers, or from data racing while fetching single items on multiple threads.<p>So there is no way you can use the ConcurrentModificationException as a way of ensuring that your HashMap is actually working in a concurrent scenario, it only handles one scenario: reads, and even only reads when iterating.