Groovy 1.0 and 1.1 do not support normal Java inner classes (you can have such classes only in Scripts or you can code them in Java of course).
In many cases though, you don't need them. Here is a Groovy 1.1 example which shows you how to construct a class on the fly which implements several interfaces. This would be a prime example where you would typically use an inner class in Java. In Groovy we don't have to: