Why do we need Atomic* classes if wrapper classes are already immutable?

Question

I recently encountered atomic classes from java.util.concurrent.atomic package. As far as I know, immutable classes are by default thread safe by nature, so we do not need to synchronize them. Later I came to know that wrapper classes like Integer, Boolean, Character, etc are immutable by nature, so why do we need Atomic* classes like AtomicInteger or AtomicLong. Also, please explain what is AtomicReference.

Answer 1

The atomic classes are mutable, but have strong memory consistency guarantees with regard to modifications. So they serve a different purpose from the immutable wrapper classes.

The real advantage of the Atomic* classes is that they expose an atomic compare-and-swap method, which can be very useful for implementing lock-free algorithms.

Like many intermediate to advanced concurrency tools, if you can't imagine why you would need such a thing then you probably shouldn't try to use them. If you stick to immutability or explicit locking everywhere then you probably won't need atomics.