Using Scala type aliases from Java code

Question

Suppose I have type alias defined in scala as

object Foo {
  type Bar = Option[String]
}

It looks like I cannot refer to alias in Java cod

Answer 1

Type aliases are only visible to the Scala compiler, and like generic types they don't appear anywhere in the JVM class files.

If you're in Java, you're stuck using the unaliased type Option[String] since javac has no way of knowing about the type alias Bar that you declared in your Scala code. Wherever you would have used Bar just use Option[String] (which is scala.Option<String> in Java) and it should work fine.