When I add a folder called "interface" in my Scala project in IntelliJ IDEA,
there is a error: "Not a valid package name".

Why is this and is this possible to change?

>Solution :

You can’t use reserved keywords.

see the list of reserved keywords:
https://docs.oracle.com/javase/specs/jls/se7/html/jls-3.html#jls-3.9