The great part about the JVM is that you can chose the language which fits the problem. If something needs the fine-grain control of Java, use Java. If anothe

The great part about the JVM is that you can chose the language which fits the problem. If something needs the fine-grain control of Java, use Java. If another part would benefit greatly from the concise and expressive Scala idioms, use Scala. Eventually it's all going to be broken down into several JARs which are passed along to the next guy, hidden by bytecode as to which JAR was written in which language.