If I use Iterator.remove(), everything is fine. If I use ArryaList.remove(), I always receive the error java.util.ConcurrentModificationException.
Can anyone point out the reason?
Basically because that's how it's designed to work. If you delete an element from the list, the iterator doesn't know about it, and when it tries to access another element in the list, the list has changed and an error is raised. But if you remove an element through the iterator, then the itertor knows about the removal, makes the appropriate adjustment to its data structures, and continues.