How does Scala's mutable Map update [map(key) = newValue] syntax work?

Question

I\'m working through Cay Horstmann\'s Scala for the Impatient book where I came across this way of updating a mutable map.

scala> val scores = scala.coll         


        

Answer 1

Can you try this: => to update list of Map

import java.util.concurrent.ConcurrentHashMap
import scala.collection.JavaConverters._
import scala.collection.concurrent

val map: concurrent.Map[String, List[String]] = new ConcurrentHashMap[String, List[String]].asScala

def updateMap(key: String, map: concurrent.Map[String, List[String]], value: String): Unit = {
map.get(key) match {
case Some(list: List[String]) => {
val new_list = value :: list
map.put(key, new_list)
}
case None => map += (key -> List(value))
}
}