# test.rb
class A
  class B
  end
end

# irb
> class A
> end
=> nil
> class X < A
>   autoload :B, "test"
> end
=> nil
> X::B
NameError: uninitialized constant X::B
    from org/jruby/RubyModule.java:2723:in `const_missing'
    from (irb):7:in `evaluate'
    from org/jruby/RubyKernel.java:1101:in `eval'
    from org/jruby/RubyKernel.java:1501:in `loop'
    from org/jruby/RubyKernel.java:1264:in `catch'
    from org/jruby/RubyKernel.java:1264:in `catch'
    from /Users/yuutetu/.rbenv/versions/jruby-1.7.16/bin/irb:13:in `(root)'
> X.const_get :B
=> A::B