The problem about Module's extend method

Rails
1

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

  7. def method_not_has

  8.   puts "method not has"

  9. end

  10. end

  11. class Sample

  12. class<<self

  13. private

  14.   def method_has

  15.     puts "method has"

  16.   end

  17. end

  18. end

  20. Sample.extend Dummy

  22. Sample.send(:method_not_has)=>“method not has”

  24. Sample.send(:method_has)=>“method has”

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