Atomic Operations and multithreading

Question

Recently I was reading a tutorial, in that I came across a statement that says..

\"The Java language specification guarantees that reading or writing a variable is

Answer 1

Atomic means the operation completes without any possibility for something to happen between. eg. getAndDecrement(), on AtomicInteger, guarantees that the variable is returned AND decremented at the same time.

If it was not an atomic operation, the possibility would exist for the value to get decremented (eg. from 3 to 2), then modified by another thread (eg. changing it from 2 to 5), then returned as 5.