Not the parent and I've never read that particular book, but the premise seems rather bizarre to me, where is the excitement in implementing a slow version of Java in Java? If anyone is going to want to implement a custom interpreted language, it will likely be very different to Java, e.g. Lisp, the core of a DSL or configuration language. But it's still going to probably have functions and data types. Writing Lisp in C is exciting, one is moving up the abstraction hierarchy, building a more expressive and powerful language.

If one wants to learn specifically how Java works, then maybe a book on compilers would be better?