Iterator & Removing During Iteration

Fail-fast iterators throw ConcurrentModificationException when the collection is modified during iteration; fail-safe iterators never throw CME because they work on snapshots or tolerate concurrent changes.

Iterator traverses any Collection forward-only with remove(); ListIterator extends it for Lists with backward traversal, add(), set(), and index tracking.

for-each + remove throws CME; use iterator.remove() for single removals or removeIf(predicate) for bulk removal – both keep modCount in sync.