jit

The book's code is implemented in Ruby, and the source is here, according to the author, around 6000 lines (haven't checked myself). https://github.com/jcoglan/jit If you'd really like to make a Java equivalent of any specific algorithm you can start even without a book. I guess that anybody not versed in Ruby would first have to understand a lot of Ruby details first. The author mentions other efforts relatively similar to his, in other languages, like http://gitlet.maryrosecook.com/docs/gitlet.html which is node JavaScript.