| Is Modification of underlying Collection Allowed? |
NO. It throws ConcurrentModificationException if the underlying collection is structurally modified in any way except through the iterator’s own remove or add methods Note:.Fail-fast iterators throw ConcurrentModificationException on a best-effort basis and fail-fast behavior of an iterator cannot be guaranteed. |
YES. It doesn’t throw ConcurrentModificationException. |
| Whether works on Original Collection? |
YES |
NO.Iterator makes a copy of the underlying structure and iteration is done over that snapshot.So , original data structure remains structurally unchanged .Hence , no ConcurrentModificationException is thrown by the fail safe iterator. |
| Will underlying collection’s mutations are reflected after the iterator was created? |
As iterator work on the original collection, iterator will reflect additions, removals, or changes to the collection since the iterator was created. |
Drawback of using a copy of the collection rather than original collection is that the iterator will not reflect additions, removals, or changes to the collection since the iterator was created. |
| Whether add, remove and set operations are provided? |
fail-fast iterator provides remove, set, and add operations. |
Element-changing operations on iterators themselves (remove(), set(), and add()) are not supported. These methods throw UnsupportedOperationException. |
| Which Collections are Supported? |
ArrayList, Vector, HashSet,HashMap |
ConcurrrentHashMap, CopyOnWriteArrayList, CopyOnWriteArraySet |
| Memory Overhead |
NO |
YES. The clone of the underlying collection needs to be created. |
