Call a custom .jar from jruby

hello_world.rb

#javac HelloWorld.java && jar cvf HelloWorld.jar HelloWorld.class
require 'java' 
require 'HelloWorld.jar' 
import 'HelloWorld'

puts HelloWorld.new.hello 

#jruby hello_world.rb
#=> "Hello cruel world"

HelloWorld.java

public class HelloWorld {
  public String hello() { 
    return "Hello cruel world"; 
  }
}