Differences between Fail-fast and Fail-safe iterators are as follows...

Fail-fast iterator throws ConcurrentModificationException. But Fail-safe iterator does not throw this exception.

Fail-fast iterator does not clone the original collection. Fail-safe iterator creates a copy of the original collection of objects.

A Fail-fast iterator tries to immediately throw Exception when it encounters failure. A Fail-safe Iterator works on a copy of collection instead of original collection.