Thread-safe iteration over a collection

Question

We all know when using Collections.synchronizedXXX (e.g. synchronizedSet()) we get a synchronized \"view\" of the underlying collection.

Ho

Answer 1

You've already answered your bonus question really: no, using an enhanced for loop isn't safe - because it uses an iterator.

As for which is the most appropriate approach - it really depends on how your context:

• Are writes very infrequent? If so, CopyOnWriteArrayList may be most appropriate.
• Is the collection reasonably small, and the iteration quick? (i.e. you're not doing much work in the loop) If so, synchronizing may well be fine - especially if this doesn't happen too often (i.e. you won't have much contention for the collection).
• If you're doing a lot of work and don't want to block other threads working at the same time, the hit of cloning the collection may well be acceptable.