How to build an Scala immutable map from a mutable Java map?

Question

The below class causes the compiler error :

value toMap is not a member of 
 java.util.Map[java.lang.String,java.util.List[com.recommendations.TestObject]]


class ProcessData(var distanceMap : java.util.Map[java.lang.String , java.util.List[TestObject]]) {

    def apply = {

      val m2: Map[String, Any] = distanceMap.toMap

    }

}

This line causes the error :

val m2: Map[String, Any] = distanceMap.toMap

Is the error because the value of Map distanceMap is an mutable java.util.List , hence these values need also be immutable ?

How can I build a Scala immutable map from the mutable distanceMap above ?

possible duplicate of How to convert java Map to scala Map of type LinkedHashMap[String,ArrayList[String]]? — om-nom-nom
– om-nom-nom, Commented Apr 23, 2013 at 14:41

flavian · Accepted Answer · 2013-04-24 14:14:29Z

3

import scala.collection.JavaConversions._

val m = new java.util.HashMap[String, Object]()
m.put("Foo", java.lang.Boolean.TRUE)
m.put("Bar", java.lang.Integer.valueOf(1))

val m2: Map[String, Any] = m.toMap
println(m2);

edited Apr 24, 2013 at 14:14

answered Apr 23, 2013 at 14:41

flavian

28.6k11 gold badges68 silver badges107 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

blue-sky Over a year ago

your code does not compile, java.util.Map is an interface, not a concrete class so cannot instantiate. .toMap method is not a member of java.util.Map

blue-sky Over a year ago

I'm receiving a compiler error for above code : "Multiple markers at this line - value toMap is not a member of java.util.HashMap[String,java.lang.Object] - Cannot prove that Char <:< (T, U). - Implicit conversions found: m => augmentString(m) - not enough arguments for method toMap: (implicit ev: <:<[Char,(T, U)])scala.collection.immutable.Map[T,U]. Unspecified value parameter ev."

Robert Watts · Accepted Answer · 2013-04-24 14:23:30Z

1

You are simply missing the JavaConversions import. Your code will compile with:

import scala.collection.JavaConversions._
class ProcessData(var distanceMap : java.util.Map[java.lang.String , java.util.List[TestObject]]) {
    def apply = {
      val m2: Map[String, Any] = distanceMap.toMap
    }
}

answered Apr 24, 2013 at 14:23

Robert Watts

1791 gold badge2 silver badges10 bronze badges

Collectives™ on Stack Overflow

How to build an Scala immutable map from a mutable Java map?

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related