How can I use the volatile keyword in Java correctly?

Question

Say I have two threads and an object. One thread assigns the object:

public void assign(MyObject o) {
    myObject = o;
}

Another thread uses t

Answer 1

I am trying to understand when to use volatile and when not

You should mostly avoid using it. Use an AtomicReference instead (or another atomic class where appropriate). The memory effects are the same and the intent is much clearer.

I highly suggest reading the excellent Java Concurrency in Practice for a better understanding.