I think this is the main advantage of Xtend. Xtend compiles to plain Java classes and uses the same typesystem as Java. This way you get excellent Java interoperability, as Xtend classes can be used seamlessly from Java and vice versa. This goes so far that I usually mix in my projects Java and Xtend code. I recently wrote a blog post about this topic, as well [1].
[1] http://sebastianbenz.de/5-Things-that-make-Xtend-a-great-Lan...