fwiw, I think that FluidForce part of the example is a bad example and one we do not want anyone to use. So someone should consider a better mechanism for showing the .getInstance part of our embedding API.

This is not technically a bug because in Ruby 2.x 'def' will now return a Symbol of the method being added. Prior to Ruby 2, def would return nil. So in this example in JRuby 1.7.x we get back 'null' which is passed to getInstance which then uses self so the example works. In JRuby 9.1.x we get back :getFluidForce and then try to use the symbol to get an instance of the FluidForce interface (which of course a symbol does not implement that interface). So embedding API is working as expected but new Ruby semantics broke the example.

II will update the documentation to better illustrate what is happening (add self at bottom of fluid_force.rb) but I find this example to be a bit confusing with .getInstance.

@enebo thanks for clarifying. I will stick to container.callMethod in this case and implement the interface myself.