The value of the variable is not hoisted by the Java compiler. (It's not that JVM, that only executes the byte code, what y doesn't have that kind of ambiguities.)

The semantics of Java is not undefined on multiple assignments to the same variable in an expression, so it can't hoist something if it would change the outcome.

Now, I don't actually know what the outcome is, because I don't remember whether `a += e` reads the value of `a` before or after evaluating `e`. The code is still confusing and unreadable to humans, so you shouldn't write it, but the compiler behavior is not undefined.

And if your variable is accessed from multiple threads, it may be undefined which intermediate values night be seen.