Calling Clojure from Java

In this recipe, we will learn how to define Java classes in Clojure and call them from Java.

Getting ready

To include Java sources in a Leiningen project, we create the project.clj as follows and restart the REPL:

(defproject chapter05 "0.1.0-SNAPSHOT" 
  :description "FIXME: write description" 
  :url "http://example.com/FIXME" 
  :license {:name "Eclipse Public License" 
            :url "http://www.eclipse.org/legal/epl-v10.html"} 
  :java-source-paths ["src/java"] 
  :aot [chapter05.calling-from-java] 
  :prep-tasks [ 
               ["compile" "chapter05.calling-from-java"] 
               "javac" "compile" ] 
  :main chapter05.TestHello 
  :dependencies [[org.clojure/clojure "1.8.0"] 
                 ]) 

How to do it...

We will take a look at how we define Java classes that can be called from Java.

Defining a simple named class using gen-class

The following code is a very simple code to print string...