How to convert a java Map to immutable Scala map via java code?

Question

I need to create a immutable Scala map with java code. I have found other things on here about this but nothing that is updated to the current version.

I've tried:

public static <A, B> Map<A, B> toScalaMap(HashMap<A, B> m) {
        return JavaConverters.mapAsScalaMapConverter(m).asScala().toMap(
                Predef.<Tuple2<A, B>>conforms()
        );
}

What's the bigger picture of what you are trying to achieve? Why do you want a Scala map in Java code? — Tyler
– Tyler, Commented Jul 11, 2017 at 19:28
I am working with the kafka AdminClient class which returns a collections.scala.immutable.Map and I want to be able to create one so I can have a mock return it in a unit test. — spillthebeans
– spillthebeans, Commented Jul 11, 2017 at 19:35

spillthebeans · Accepted Answer · 2017-07-12 13:39:31Z

5

I changed conforms to $conforms and it now runs find in both Intellij and the command line but Intellij still give a red line under JavaConverters.mapAsScalaMapConverter(m).asScala().toMap( that says cannot access scala.Predef.$less$colon$colon.

private   <A,B> scala.collection.immutable.Map<A, B> toScalaMap(Map<A, B> m) {
        return JavaConverters.mapAsScalaMapConverter(m).asScala().toMap(
                Predef.$conforms()
        );
    }

answered Jul 12, 2017 at 13:39

spillthebeans

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1 Comment

Abi Vignesh Over a year ago

Thanks a lot man. It worked ! Wondering why Intellij throws that error

Jeffrey Chung · Accepted Answer · 2017-07-11 20:38:50Z

Your code is correct. The problem is likely an issue with how you're building or running your code, or perhaps you don't have all the necessary imports. The following works with version 4.6.1 of the Scala IDE for Eclipse and Scala 2.12:

package org.soreadytohelp;

import java.util.HashMap;

import scala.Predef;
import scala.Tuple2;
import scala.collection.JavaConverters;
import scala.collection.immutable.Map;

public class MapTest {
    public static <A, B> Map<A, B> toScalaMap(HashMap<A, B> m) {
        return JavaConverters.mapAsScalaMapConverter(m).asScala().toMap(
            Predef.<Tuple2<A, B>>conforms()
        );
    }

    public static void main(String[] args) {
        HashMap<String, String> hm = new HashMap<String, String>();
        hm.put("food", "bacon");

        Map<String, String> hmAsScala = toScalaMap(hm);
        System.out.println(hmAsScala);
    }
}

Andrew Gao · Accepted Answer · 2017-07-11 21:20:59Z

0

I ran into this issue with IntelliJ, but it turned out to be just an IntelliJ compiler error and was able to run via maven just fine. Try running/building your code to see if its just a compiler error.

answered Jul 11, 2017 at 21:20

Andrew Gao

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Comments

Nicolai · Accepted Answer · 2025-01-21 19:07:23Z

0

JavaConverters are deprecated since 2.13.0
https://www.scala-lang.org/api/2.13.4/scala/collection/JavaConverters$.html

Deprecated (Since version 2.13.0) Use scala.jdk.CollectionConverters instead

Here is a solution with scala.jdk.CollectionConverters:

import scala.jdk.CollectionConverters;

...

public static <A, B> scala.collection.immutable.Map<A, B> toScalaMap(Map<A, B> theMap) {
    return scala.collection.immutable.Map.from(CollectionConverters.MapHasAsScala(theMap).asScala());
}

answered Jan 21 at 19:07

Nicolai

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