Scala is a functional and OO hibrid language targeting the JVM. Performance is not far from Java’s since it is a statically typed language, but you have type inference that Java doesn’t.
Scala compiles to .class files, so you can just replace your .java files with scala without greater problems because scala was designed to the JVM. This also means you can access everything in your Java code from Scala and vice-versa.
Resources
- Scala for Java programmers – A nice comparison approach between the two languages.
- Lift A RoR/Django-like framework for Scala.