What is difference between Fail Fast and Fail Safe

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Fail Fast	Fail Safe
Fail-Fast iterators doesn’t allow modifications of a collection while iterating over it.	Fail-Safe iterators allow modifications of a collection while iterating over it.
These iterators throw ConcurrentModificationException if a collection is modified while iterating over it.	These iterators don’t throw any exceptions if a collection is modified while iterating over it.
These iterators don’t throw any exceptions if a collection is modified while iterating over it.	They use original collection to traverse over the elements of the collection.
These iterators don’t require extra memory.	These iterators require extra memory to clone the collection
They use original collection to traverse over the elements of the collection	They use copy of the original collection to traverse over the elements of the collection