How to use scala.collection.immutable.List in a Java code

Question

I need to write a code that compares performance of Java\'s ArrayList with Scala\'s List. I am having a hard time getting the Scala List

Answer 1

Use scala.collection.JavaConversions from inside of java.

For example to create a nested scala case class that requires a scala List in its constructor:

case class CardDrawn(player: Long, card: Int) 
case class CardSet(cards: List[CardDrawn]) 

From Java you can use asScalaBuffer(x).toList() as follows:

import scala.collection.JavaConversions;
import java.util.ArrayList;
import java.util.List;

public CardSet buildCardSet(Set widgets) { 

  List cardObjects = new ArrayList<>();

  for( Widget t : widgets ) {
    CardDrawn cd = new CardDrawn(t.player, t.card);
    cardObjects.add(cd);   
  }

  CardSet cs = new CardSet(JavaConversions.asScalaBuffer(cardObjects).toList());
  return cs;
}