The new features of Java 7 can be easily learned via quality blogs and other online articles. Would polyglot programming and JVM be the real strength of this book? If the answer is yeas, what % of the book is dedicated for JVM and polyglot programming?
and what other languages for JVM are covered in the book?
We like to think that the book goes further in depth with the Java 7 features than most blog posts etc. We always like to explain why language features are designed a particular way :-). That said, Polyglot probably makes up about 1/3 of the book, with Groovy, Scala and Clojure covered as well as blended into other chapters such as rapid web development and the TDD chapter.