Synchronizing an object shared across threads, but not accessed concurrently

Question

Let\'s say I have a shared object with field data. Multiple threads will share a reference to this object in order to access the field. The threads never access

Answer 1

Studying the entire JLS chapter on the Java Memory Model is highly recommended – mandatory, in fact – for anyone doing concurrency in Java. Your case, specifically, is covered in JLS, 17.4.4:

"An action that starts a thread synchronizes-with the first action in the thread it starts."

This means that for your first scenario you don't need volatile. However, it would be good practice to have it anyway to be robust to future changes to the code. You should really have a good reason not to have volatile, which would be only in the case of an incredibly high read rate (millions per second at the very least).