What is the difference between CopyOnWriteArraySet and a regular HashSet?

Question

CopyOnWriteArraySet is a thread-safe Set backed by a CopyOnWriteArrayList — every mutation copies the entire underlying array, so reads never block and never throw ConcurrentModificationException, but writes are expensive and it scales poorly for write-heavy or large collections. A plain HashSet is not thread-safe at all and needs external synchronization (or Collections.synchronizedSet) for concurrent access.

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CopyOnWriteArraySet is a thread-safe Set backed by a CopyOnWriteArrayList — every mutation copies the entire underlying array, so reads never block and never throw ConcurrentModificationException, but writes are expensive and it scales poorly for write-heavy or large collections. A plain HashSet is not thread-safe at all and needs external synchronization (or Collections.synchronizedSet) for concurrent access.

What is the difference between CopyOnWriteArraySet and a regular HashSet?

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