Update: Mixed compilation is already enabled in the development branch of groovy!

Special note: The method described here works right now (September 2007). But the situtation will be changing soon. Groovy 1.1 should have a compiler that can automatically resolves all problems with mixed compilation. And it may have new ant tasks.

Idiomatic code for many languages with native lists and maps is full of them-- and the code is clearer for it. In most languages there are many uses for them but there is only one general purpose implementation. Performance and flexibility are both fixed. Groovy is different! You can use that great list and map syntax and API with any implementation.

Groovy doesn't have anonymous or inner classes. The feeling is that if your really understood the features Groovy does have you wouldn't want to write them anyway-- so they are left out. Fair enough. But how do you write toward a Java API that assumes you do have inner classes? Wouldn't it be great if Swing would accept closures instead of those ugly anonymous classes? Well (surprise) we can substitute closures for inner class in a very straight forward and easy manner.