implicit conversion, override, interoperability

Question

I have the following class in Java:

public class GeneralClass {
    public Integer getInt(Double d) {
        return d.intValue();
    }
}

I would like to extend this class in scala e.g.

import scala.collection.JavaConversions._
import scala.collection.JavaConverters._

class SpecializedClass extends GeneralClass {

  override def getInt(d: Double): Int = {
    d.intValue()
  }
}

The problem is that neither scala.Double nor scala.Int are automatically converted to their respective java types.

Edit The error message is:

method getInt overrides nothing. Note: the super classes of class SpecializedClass contain the following, non final members named getInt: def getInt(d: Double): Integer

Can anybody explain that and maybe point out an elegant solution?

Answer 1

getInt in SpecializedClass does not override the method in GeneralClass. To be able to override, the function argument in SpecializedClass should be contravariant and the return type to be co-variant. Which in your case is not.

So unless you have something in getInt in SpecializedClass which takes a type T :> java.lang.Double and return type as T <: java.lang.Integer, it will not override it.

For your question, actually I dont feel the need to have such a method as Scala compiler will implicitly convert Java double to Scala Double.