Translate JMonkey Tutorial to JRuby

Question

I've got all the tutorials up to beginner #5 translated and working, but I don't know Java well enough to know how to port the lines:

private ActionListener actionListener = new ActionListener() {
  public void onAction(String name, boolean keyPressed, float tpf) {
    if (name.equals("Pause") && !keyPressed) {
      isRunning = !isRunning;
    }
  }
};

private AnalogListener analogListener = new AnalogListener() {
  public void onAnalog(String name, float value, float tpf) {
    ...
  }
}

How might this work?

Answer 1

Ah, found the answer. Turns out, they were anonymous inner classes. In JRuby, you can just create a class that implements the Java interface like so:

class RBActionListener
  # This is how you implement Java interfaces from JRuby
  include com.jme3.input.controls.ActionListener

  def initialize(&on_action)
    @on_action = on_action
  end

  def onAction(*args)
    @on_action.call(*args)
  end
end

class HelloJME3
  # blah blah blah code blah blah blah

  def register_keys
    # ...
    ac = RBActionListener.new {|name, pressed, tpf @running = !@running if name == "Pause" and !pressed}
    input_manager.add_listener(ac, "Pause")
  end
end

Answer 2

As described in Calling Java from JRuby, you can use closure conversion, where blocks can be used to define a Java interface behaviour. Something like the following should work:

l = lambda { |name, pressed, tpf| running = !running if name == 'Pause' && !pressed }
input_managers.add_listener(l, ['Left', 'Right', 'Rotate'])

Answer 3

I wrapped the action listener in a method that would return an object that includes ActionListener using JRuby's :impl method

def isRunningActionListener
  return ActionListener.impl do
    |command, name, keyPressed, tpf|
      case command
        when :onAction
          if name.eql?("Pause") && !keyPressed
            isRunning = !isRunning;
          end
      end
   end
end

you could also create your own ActionListener class that includes ActionListener...

class YourActionListener
  include ActionListener
  def onAction command, name, keyPressed, tpf
    #your code here
  end
end

creating your own class might be the better option as its a lot less verbose and easier to read and understand.