gistfile1.rb

# Unnecessary code removed

require 'java'
java_import "com.jme3.app.SimpleApplication"
java_import "com.jme3.input.controls.ActionListener"

class HelloInput < SimpleApplication

  def initKeys
    input_manager.add_listener(action_listener, ["Pause"].to_java(:string))
  end

  private
    def action_listener 
      ActionListener.new {
        def on_action(name, key_pressed, time_per_frame)
          @is_running = !@is_running if name.eql?("Pause") && !key_pressed
        end
      }
    end
end

Alternate version #2

def action_listener
  ActionListener.impl {
    def on_action(name, key_pressed, time_per_frame)
      @is_running = !@is_running if name.eql?("Pause") && !key_pressed
    end
  }
end