Converting a Java map into a Scala immutable map in Java code [duplicate]

Question

I have a Java class that needs to stay in Java for a variety of reasons. It is calling a method on a class implemented with a Scala trait and a Scala implementation that needs a Scala immutable map. Yes, I have seen how to use implicit and explicit code if I have the Java Map and I am doing the converting in Scala code, but I am trying to do the conversion from Java code and have seen nothing like that on Stack Overflow.

I am using Eclipse and the project has the Scala nature added to it. I tried importing scala.collection.JavaConverters, and Eclipse just gave me an error saying it couldn't find the class even though I can see the class when I open up the scala-library in the Scala Library container. I am using Scala 2.11.8

How can I write explicit code that converts the Java Map into the Scala Map in Java code?

I read through and tried to recreate that solution. Unfortunately I cannot import any of the Scala classes in my Java class, which I presume is something weird on my end. Sigh. — Keith
– Keith, Commented Jul 7, 2016 at 1:01
Sorry, but why can't you import any scala classes on your end? Even scala.collection.immutable.Map? — marcospereira
– marcospereira, Commented Jul 7, 2016 at 1:03
I wish I knew. But yeah, even scala.collection.immutable.Map will not import. — Keith
– Keith, Commented Jul 7, 2016 at 1:04
I suppose this is a problem with Eclipse. Try to reimport the project and see if it works. — marcospereira
– marcospereira, Commented Jul 7, 2016 at 1:05
No that is not a very good idea, using Scala code from Java is just horrible... the Scala compiler generates weird names that are not human-readable. Using Java from Scala is much easier because the Java compiler is way simpler and the naming rules of methods and classes much more restrictive. Simply use JavaConversions. — Dici
– Dici, Commented Jul 7, 2016 at 1:08

Abhishek Sengupta · Accepted Answer · 2020-10-30 19:00:17Z

0

Why not simply use toMap.

Something Like :

import scala.collection.JavaConverters._

// asScala creates mutable Scala Map
// toMap after asScala creates immutable Map
val scalaImmutableMap = javaMap.asScala.toMap

answered Oct 30, 2020 at 19:00

Abhishek Sengupta

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2 Comments

Amin Heydari Alashti Over a year ago

because Java map does not have the "asScala".

Abhishek Sengupta Over a year ago

@AminHeydariAlashti that's the reason import scala.collection.JavaConverters._ was used.

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