When we remove an object by using remove() method of a

Collection or List while an Iterator thread is traversing it, we get

ConcurrentModificationException. If an Iterator detects any

structural change in Collection it can throw

ConcurrentModificationException

https://www.javatpoint.com/concurrentmodificationexception-in-java#:~:text=The%20ConcurrentModificationException%20occurs%20when%20an,thread%20is%20iterating%20over%20it.