>When a program contains two conflicting accesses (§17.4.1) that are not ordered by a happens-before relationship, it is said to contain a data race.

Yes, your program contains a data race, by the definition used in the JLS. The set of outcomes you may observe from a data race are specified. I'm not sure if this choice was intentional or not, but there is a guarantee that you will either print the argument or "uninitialized" and no other behavior, because String relies on final field semantics. This is would not be true in c/c++ where the equivalent code is undefined behavior and you could see any result.

In Java you can have a data race and use it productively for certain niche cases, like String.hashcode - I've also contributed some to the Guava concurrency library. This is not true in c/c++ where data races (by their definition) are undefined behavior. If you want to do the tricks you can in racy Java without UB, you have to declare your variables atomic and use relaxed memory order and possibly fences.