如何通过Java代码将Java Map转换为不可变的Scala地图？

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()
        );
}

Answer 1

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);
    }
}

Answer 2

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()
        );
    }

Answer 3

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.