Question

I’m trying to use Scala as part of an existing Java application and now I run into an issue with dependencies injected with a setter method (no DI frameworks in this part of code). How is this handled in a Scala way?

In Scala both val and var require to be initialized when declared but I can’t do that, since the Java setters inject objects that implement a certain interface and interfaces are abstract and can not be instantiated.

class ScalaLogic {
  var service  // How to initialize?

  def setService (srv: OutputService) = {
  service = srv
}

Is there a way to initialize the var service so that I can later assign a dependency into it? It should be lexically scoped to be visible in the whole class.

Answer 1

Try using class Option. This is the moral equivalent of using null in Java. Declare the service like so:

var service: Option[MyInterface] = None

and use

service.get()

or pattern matching

service match {
    case None => ...
    case Some[MyInterface] => ...
}