simple example of Akka STM in Java

atomic.java

new Atomic<Void>() {
  public Void atomically() {
    ref.set(refs.get() + 1);
    return null;
  }
}.execute();

jruby.rb

Class.new(Atomic) do
  def init(ref)
    @ref = ref
    self
  end
  def atomically
    @ref.set(@ref.get + 1)
  end
end.new.init(ref).execute