A couple of days ago, one of my readers messaged me on LinkedIn about a Java interview question he has recently faced - what is the happens-before relationship in Java concurrency? What is the benefit of it, and how exactly it works? He kind of has some ideas about that its related to the Java Memory Model and provides some sort of visibility guaranteed but couldn't explain with conviction to his interviewer, particularly with a code example and was a bit disappointed. He then asked me if I can write an article about it. I said you should have read the Java concurrency in Practice book before the interview, that would have helped, but nonetheless, I liked the idea to just provide a quick overview of what is the happens-before relationship between threads in Java.