Answer
Fail-fast: Throws ConcurrentModificationException.
Fail-safe: Works on copy; allows modification.
Fail-safe: Works on copy; allows modification.
Quick Answer
Fail-fast iterators (ArrayList, HashMap) throw ConcurrentModificationException if the collection is modified during iteration (checks modCount). This is to prevent unpredictable behavior, not thread safety. Fail-safe iterators (CopyOnWriteArrayList, ConcurrentHashMap) work on a snapshot of the collection - modifications during iteration are safe but not reflected in the current iteration.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ