title: Why doesn't Java ship with a CopyOnWriteMap?
body: <p>The JDK ships with <code>CopyOnWrite*</code> implementations for <code>Set</code> and <code>List</code>, but none for <code>Map</code> and I've often lamented this fact. I know there are other collections implementations out there that have them, but it would be nice if one shipped as standard. It seems like an obvious omission and I'm wondering if there was a good reason for it.  Anyone any idea why this was left out?</p>