> Java developers are learning (or migrating to Scala/Groovy/Clojure)
Scala can be used instead of Java to build systems, though when a Java developer uses it for the first time to build a system, that system will need heavy refactoring to make use of Scala's functional facilities. Groovy's really intended for use with Java, not instead of it, such as gluing Java apps together, testing Java objects, scripting Grails, and 20-liners for Gradle builds. I don't know how much Clojure's used to build systems in industry, though it's certainly my language for scripting.
Scala can be used instead of Java to build systems, though when a Java developer uses it for the first time to build a system, that system will need heavy refactoring to make use of Scala's functional facilities. Groovy's really intended for use with Java, not instead of it, such as gluing Java apps together, testing Java objects, scripting Grails, and 20-liners for Gradle builds. I don't know how much Clojure's used to build systems in industry, though it's certainly my language for scripting.