If I am doing something like this in a class-
private AtomicLong count = new AtomicLong(0);
count = new AtomicLong(1); // will this update is going to be visible to other threads
You're completely missing the point of
AtomicLong provides methods to manipulate it in a thread-safe manner.
Replacing your instance with a new instance bypasses all of those.
You should make all
final to prevent that.
You also need to make sure that you don't try to read the same value twice, because other threads could change it between your reads. See my blog post for more on thread-safe code.