Question

I want to return from a Java method a reference to a Scala object. How can I do that?

My Scala objects are like this:

trait Environment 

object LocalEnvironment extends Environment {...}
object ServerEnvironment extends Environment {...}

… and I want my Java method to be like this:

Environment getEnvironment() { return LocalEnvironment; }  // DOES NOT COMPILE

Is there a way to do this?

Answer 1

{ return LocalEnvironment$.MODULE$; }

should work.

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Edit: the reason why this works is that this is how Scala represents singleton objects. The class ObjectName$ has a field in it called MODULE$ that is populated with the single valid instance of that class. But there is also a class called ObjectName that copies all the methods as static methods. That way you can use it like Java (just call ObjectName.methodName) in most cases, and Scala gets to have a real class to pass around.

But when Java needs to pass the class around–not something normally done with a bunch of static methods, which is what object is designed to emulate in Java–you then have to know how Scala represents it internally.