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

It does depend on the result one needs to achieve cloning/copying/toArray(), new ArrayList(..) and the likes obtain a snapshot and does not lock the the collection. Using synchronized(collection) and iteration through ensure by the end of the iteration would be no modification, i.e. effectively locking it.

side note:(toArray() is usually preferred with some exceptions when internally it needs to create a temporary ArrayList). Also please note, anything but toArray() should be wrapped in synchronized(collection) as well, provided using Collections.synchronizedXXX.