Just some ideas for a couple more things I have run into

jruby_extensions.rb

java_import com.foo.MyJavaClass
java_import com.foo.MyJavaInterface
java_import com.foo.TemplateClass

# Extending from generic superclass
# This is needed because a new type is created, and
# there is no way currently in JRuby to specify template classes
# because most template information is unavailable during runtime
class MyRuby < MyJavaClass(TemplateClass)
end

# Implementing a generic interface
class AnotherRuby
  include MyJavaInterface(TemplaceClass)
end

# Creating a Java Interface in Ruby
# This will allow Ruby to interface with libraries
# like Guice in use cases where it requires an interface
# instead of a class
# The idea is just treat modules as straight up interfaces and add become_java! to it.
module RubyInterface
  add_interface_annotations(com.foo.Interface => {"value" => "bar"})
  
  def foo
    puts "HI"
  end
  add_method_annotation(:foo, com.foo.FunctionInterface => {"value" => "zot"})

  become_java! false
end

# This would work by generating java bytecode which was just the interface, 
# but we would create a proxy module which contained the 
# implementation that ruby would be able to include