Using scala constructor to set variable defined in trait

Question

If I understand correctly, traits are the closest thing to Java interfaces and class constructors automatically set the variables.

But what if I have a class that extend

Answer 1

Bar must define the abstract var foo in Foo (would be the same for a val). This can be done in the constructor

class Bar(var foo: String) extends Foo{...}

(of course, it could be done in the body of Bar too). By default, constructor parameters will be turned to private val if need be, that is if they are used outside the initiailization code, in methods. But you can force the behavior by marking them val or var, and possibly control the visibility as in

class X(protected val s: String, private var i: Int)

Here you need a public var to implement Foo.