[deanCommie]

I know C# and Java, but not Scala.

That is NOT at all clear for me. Why is: (new Foo).fiz = "fuz" // valid?

fiz is Final! Why would you be allowed to re-assign a final variable on an instance??

[bilalq]

Final does not mean immutable, but non-overridable through inheritance. The val keyword is what makes things immutable.