Migrating Java to Scala

Question

What are the most important points to be aware of, and the workarounds, when gradually migrating an existing Java codebase to Scala? With a (potentially very long) intermediate phase where both languages are in use.

The sort of things I'm thinking about are:

• different collection hierarchies
• Java constructs that Scala can't handle well
• Scala constructs that are impractical to use in Java
• build tools
• compilation order
• immutability support in frameworks
• etc.

Answer 1

Scala doesn't like:

• inner Java classes
• static methods and variables (especially in super classes)
• raw types

Java doesn't like:

• Scala objects traits
• closures
• actors (except Scarlett Johansson and Akka Actors since they have a Java API)
• implicits, especially Manifests
• advanced type constructs (higher kinded types, structural types, abstract type vars)