[fcurts]

> but for example Java has a formal semantics.

I don't think that's really true. The Java language specification is entirely prose. The book you linked to was written by "outsider" authors and published in 1999 (!).

[chrisseaton]

That was just one example of many - there's a whole cottage industry of writing formal semantics for Java.

https://fsl.cs.illinois.edu/publications/bogdanas-rosu-2015-...

[fcurts]

None of them are official, and I bet they make major simplifications (the one you just linked to is for Java 1.4). I doubt actual language/tooling implementors benefit much from them.