What you need for this book
One piece of software required for this book is the Java Development Kit (JDK), which you can obtain from http://www.oracle.com/technetwork/java/javase/downloads/index.html. JDK is necessary to run and develop on the Java platform.
The other major piece of software that you'll need is Leiningen 2, which you can download and install from http://leiningen.org/. Leiningen 2 is a tool used to manage Clojure projects and their dependencies. It has become the de facto standard project tool in the Clojure community.
Throughout this book, we'll use a number of other Clojure and Java libraries, including Clojure itself. Leiningen will take care of downloading these for us as we need them.
You'll also need a text editor or Integrated Development Environment (IDE). If you already have a text editor of your choice, you can probably use it. See http://clojure.org/getting_started for tips and plugins for using your particular favorite environment. If you don't have a preference, I'd suggest that you take a look at using Eclipse with Counterclockwise. There are instructions to this set up at https://code.google.com/p/counterclockwise/.
That is all that's required. However, at various places throughout the book, some recipes will access other software. The recipes in Chapter 8, Working with Mathematica and R, that are related to Mathematica will require Mathematica, obviously, and those that are related to R will require that. However, these programs won't be used in the rest of the book, and whether you're interested in those recipes might depend on whether you already have this software.