module InvokableHash
   def as(java_ifc)
     # Each method will create a key in the hash which points to a block
     # which is called 
     java_ifc.impl {|name, *args| self[name].call(*args)}
   end
end

class Hash
   include InvokableHash
end

impl = {
 :i => 10,
 :hasNext => proc { impl[:i] > 0 },
 :next => proc { impl[:i] -= 1 }
}

iter = impl.as java.util.Iterator
while (iter.hasNext)
   puts iter.next
end

http://blog.headius.com/2007/12/groovy-in-ruby-implement-interface-with.html

Groovy has the as keyword which enables the implementation of a Java interface by using the as keyword, its quite easy to mimic this in JRuby.

Groovy Map as Interface method in JRuby

ruby, groovy

Ruby