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

You need an AtomicInteger if you need to read a variable and write a result depending on the read value. For instance, i++ reads i (e.g. 3) and writes i+1 (e.g. 4). A thread may be interrupted meanwhile, and three other threads increment i too. Now that we get back, i actually has the value 6 but our thread still writes 4, based on what it read beforehand.

AtomicInteger.getAndIncrement ensures you're not interrupted and therefore always incrementing properly. Moreover, the result is always flushed into memory, whereas a non-volatile i might not be flushed to memory. In this case other threads might not even see the changes.