What features of Scala cannot be translated to Java?

Question

The Scala compiler compiles direct to Java byte code (or .NET CIL). Some of the features of Scala could be re-done in Java straightforwardly (e.g. simple for comprehensions, classes, translating anonymous/inner functionc etc). What are the features that cannot be translated that way?

That is presumably mostly of academic interest. More usefully, perhaps, what are the key features or idioms of Scala that YOU use that cannot be easily represented in Java?

Are there any the other way about? Things that can be done straightforwardly in Java that have no straightforward equivalent in Scala? Idioms in Java that don't translate?

Answer 1

Traits are one thing that does not have an equivalent. Traits are Interfaces with code in them. You can copy the code to all classes that have a trait mixed in, but that is not the same thing.

Also I believe scala type system is more complete. While it will eventually map to the JVM types (actually suffer erasure). You can express some things in the Scala type system that may not be possible in Java (like variances).