We should be able to do java.lang.Thread.new { puts 'hello' } and expect to get back a thread object with the given proc as its Runnable. However it appears that the conversion of the proc to runnable gets superceded by the no-arg version of the Thread constructor, and so the converted proc is never used. It seems that when passing a block to a Java method, we should first try to find methods for which a converted closure would work, and then fall back on versions without convertible interfaces.