include_package

include_once.rb

module Foo
  require 'java'
  include Java

  include_package 'javax.swing'

  class MyView < JFrame
    def initialize
      super "Casper"

      self.initUI
    end

    def initUI
      panel = JPanel.new(BorderLayout.new)
      self.getContentPane.add panel    
    end
  end
end

# fails with NameError: uninitialized constant Foo::MyView::JPanel

include_twice.rb

module Foo
  require 'java'
  include Java

  include_package 'javax.swing'

  class MyView < JFrame
    include_package 'javax.swing'

    def initialize
      super "Casper"

      self.initUI
    end

    def initUI
      panel = JPanel.new(BorderLayout.new)
      self.getContentPane.add panel    
    end
  end
end

# works