gistfile2.txt

sebastien@greystones:/tmp$ jruby -v 
jruby 1.6.0.RC2 (ruby 1.8.7 patchlevel 330) (2011-02-25 f7688dc) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_20) [linux-amd64-java]

sebastien@greystones:/tmp$ jruby my_other_class.rb 
hello
world

my_other_class.rb

require 'java'

java_import 'MyClass'

class MyOtherClass < MyClass
  def doStuff
    super
    puts "world"
  end
end

MyOtherClass.new.doStuff

MyClass.java

public class MyClass {

  public void doStuff() {
    System.out.println("hello");
  }
}