Unresolved Reference Java

My code on linux isn’t compiling with a reference to java.io.File. On windows the code compiles and runs fine.

I’m using openjdk-1.9.0 and Intellij IDEA Ultimate latest stable build with the newest version of the kotlin plugin.
Any help would be much appreciated.

FIxed it by readding the jdk again and removing the old one. Not sure what was wrong.