Working with Arrays and Collections →hardMultiple ChoiceObjective-mapped

1Z0-829 Working with Arrays and Collections Practice Question

Which is true about CopyOnWriteArrayList?

⚠ Common exam trap

Candidates often assume 'thread-safe' collections like CopyOnWriteArrayList allow iterators to see concurrent modifications (like ConcurrentHashMap does), but CopyOnWriteArrayList iterators are snapshot-based and do not reflect modifications after creation.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Modifications are expensive as they create a new array.

CopyOnWriteArrayList is a thread-safe variant of ArrayList where all mutative operations (add, set, remove, etc.) are implemented by making a fresh copy of the underlying array. This design makes modifications expensive because each modification requires copying the entire array, but it provides safe iteration without locking. Option C correctly identifies that modifications are expensive due to the array copy.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
It is not thread-safe.
Why it's wrong here
It is thread-safe.
✗
Iterators reflect concurrent modifications.
Why it's wrong here
Iterator works on snapshot.
✓
Modifications are expensive as they create a new array.
Why this is correct
Each modification copies the underlying array.
✗
It is optimized for frequent modifications.
Why it's wrong here
Optimized for read-heavy scenarios.

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1Z0-829 Working with Arrays and Collections Practice Question

Why each option matters

Option-by-option breakdown

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