Using JRuby helps experienced Java hands and Rubyists see what's on the other side of the fence--and bring the best of Ruby to the broad universe of Java environments. With JRuby, you can: * Run your interpreted or compiled Ruby program in environments where the Java Virtual Machine is a requirement. * Treat JRuby as a "better Ruby," with faster performance for some uses and hassle-free linkage to third-party code. * Make your Java program scriptable with Ruby. * Build an app on solid libraries written in Java, Scala, Clojure, or other JVM languages. You'll learn how to call Java code from Ruby, and vice versa. You'll gain first-hand experience with dozens of JRuby's most common uses, from running web sites to building GUIs. And you'll see how it's all put together under the hood. JRuby lets you merge the best of several possible worlds, so you can create unique software using the best tools available.