Starting from version 2.7.2 Scala compiler supports compilation of mixed Scala/Java code base.
|Mixed Code Base Compilation Requriements|
IntelliJ IDEA Scala plugin includes settings that let you affect the mixed code base compilation.
- Press Ctrl+Alt+S to open the Settings Dialog
- Expand Compiler
- Click Scala Compiler
Select Compile Scala files first if you are using a 2.7.2 or later version to propely compile the mixed code base.
If you're using an older version, it's good to clear this option because the mixed code base is not supported anyway.