This is great, but with the full two-way interop and low overhead (just add the .jar for Clojure) that functional JVM languages provide, is there really any reason to deal with the pain of doing FP in Java the language? When you don't have real closures, map/reduce/filter and other HOFs become rather tedious and inflexible.
is that what this book is about? I though it was about FP principles without any specific implementation. How do you actually do FP in Java? anonymous inner classes everywhere?
Well it covers good FP principles, but it's about Java-the-language implementations of them. So it's full of lots of code that might scare me away from FP if I were a "Java programmer".