The problem about Module's extend method

Now I try to overwrite a class's private class
method(ActiveRecord::Base),but it seems doesn't work,look this
scenario:

   1. module Dummy
   2. private
   3. def method_has
   4. puts "new methods has"
   5. end
   6.
   7. def method_not_has
   8. puts "method not has"
   9. end
  10. end

   1. class Sample
   2. class<<self
   3. private
   4. def method_has
   5. puts "method has"
   6. end
   7. end
   8. end
   9.
  10. Sample.extend Dummy
  11.
  12. Sample.send(:method_not_has)=>"method not has"
  13.
  14. Sample.send(:method_has)=>"method has"

but what I want is method_has return the string "new method has",How?
Why?