composition

gistfile1.rb

class CodeMonkey
  attr_reader :programming_language

  def initialize(language)
    @programming_language = language
  end

  def program!
    programming_language.do_your_magic!
  end
end

CodeMonkey.new( Java.new ).program!

# benefit of this over inheritance is that the relationship (protocol) between the
# two objects is obvious. With inheritance, the child can override any bits of the
# parent, and tracing any given code path tends to get a lot harder (in non trivial
# cases)