Question

I’m trying to convert a project over to scala 2.8 from 2.7 and I’ve run into some difficulty in the code that interacts with Java. Below is a slightly convoluted piece of sample code displaying the problem. Essentially I have class with a member variable of type mutable.Map[K,V] and I can’t find a way to pass that through to a method that expects a java.util.Map[K,V]. Any help would be great.

scala> import scala.collection.JavaConversions._
import scala.collection.JavaConversions._

scala> class A[K,V](m : collection.mutable.Map[K,V]) { 
     | def asJava : java.util.Map[K,V] = m
     | }

<console>:9: error: could not find implicit value for parameter ma: scala.reflect.ClassManifest[K]
       def asJava : java.util.Map[K,V] = m

Answer 1

I don’t know why you are trying to repeat the conversion from JavaConversions, but i think you can do it with adding the implicit parameter ma requested:

import scala.collection.JavaConversions._
class A[K,V](m : collection.mutable.Map[K,V]) {
 def asJava(implicit ma:ClassManifest[K]) : java.util.Map[K,V] = m
}

---

From console

scala> import scala.collection.JavaConversions._
class A[K,V](m : collection.mutable.Map[K,V]) {
 def asJava(implicit ma:ClassManifest[K]) : java.util.Map[K,V] = m
}
import scala.collection.JavaConversions._

scala>
defined class A

scala> val map=scala.collection.mutable.HashMap[Int, Int]()
map: scala.collection.mutable.HashMap[Int,Int] = Map()

scala> map += 0->1
res3: map.type = Map(0 -> 1)

scala> val a=new A(map)
a: A[Int,Int] = A@761635

scala> a.asJava
res4: java.util.Map[Int,Int] = {0=1}