Java multi-threading atomic reference assignment

Question

I have a cache which I implemented using a simeple HashMap. like -

HashMap cache = new HashMap();

Answer 1

You should mark the cache as volatile.

While you note that other threads may continue using a stale cache for "a long time" you should note that, without a synchronization edge, they are likely to continue using the stale cache forever. That's probably not the desired behavior.

In order of preference (mostly due to readability):

• Update the field in a synchronized method
• Use AtomicReference>
• Use volatile

See also this question.