Java Concurrency Incrementing a Value

Question

I have been reading about volatile and synchronized in Java but have been scratching my head in confusion. I am hoping someone can help me clear up

Answer 1

Volatile ensures that threads are not caching this value. Volatile ensures write / read of this value from memory is atomic but it doesn't provide locking of this variable over multi step operation.

Replace Map with ConcurrentHashMap and use atomic CAS operation.

Use : ConcurrentHashMap.putIfAbsent()