Are primitive datatypes thread-safe in Java

Primitive types are not thread safe. Check this tutorial.

There are three ways in which they're not safe:

• long and double aren't even guaranteed to be updated atomically (you could see half of a write from a different thread)
• The memory model doesn't guarantee that you'll see the latest updates from one thread in another thread, without extra memory barriers of some kind
• The act of incrementing a variable isn't atomic anyway

Use AtomicInteger etc for thread-safe operations.