When Apache Groovy was first released, it offered closures and dynamic typing on the JVM ecosystem, but nowadays Java has lambdas and inferred typing, so Groovy doesn't really have much fundamentally different to offer anymore. And since version 2.x, Groovy is also "trying to compete on Java's home turf" because it has static-typing annotations, but Kotlin and Scala are probably better choices if you want static typing on the JVM because it was baked into them from the get-go instead of being bolted on as in Groovy 2.x.

Groovy is a truly dynamic language (with all the pros and cons that come with that). So you can put it into contexts such as interactive scripting where Java will always be suboptimal and solve problems Java doesn't even want to solve. On the other hand, every single good idea that Scala comes up with will eventually be co-opted by Java, because there is no reason for that not to happen. It is just a matter of time.

When higher kinded types come to Java, please ring me up!

Touche - yes, I agree that Java is probably never going to attempt to introduce that!