require 'java'

class SwingBuilder
  def initialize
    @me = nil
  end

  def method_missing(sym, *args, &block)
    if sym.to_s == "layout"
      cls = eval("java.awt.#{args[0].to_s.split('_').collect do |s|; s.capitalize; end.join}Layout")
      return @me.layout = cls.new
    end

    if @me.respond_to? sym
      @me.send(sym, *args, &block)
    else
      cls = eval("javax.swing.J#{sym.to_s.split('_').collect do |s|; s.capitalize; end.join}")
      if block
        @oldme = @me
        if @oldme
          @oldme.add(@me = cls.new(*args))
        else
          @me = cls.new(*args)
        end
        @top ||= @me
        self.instance_eval(&block)
        @me = @oldme
      else
        @me.add(cls.new(*args))
      end

      @top
    end
  end
end

sw = SwingBuilder.new

frame = sw.frame("My Frame") {
  layout :flow
  button("A Button")
  text_field("A Text Field")
  set_size 500, 500
  always_on_top = true
}

frame.show