使用 Scala-2.13 在 Java 代码中将 Java 映射转换为 Scala 不可变映射

Question

我想将我的 java 映射转换为 Scala 不可变映射，我有一个示例代码可以在 Scala 2.12 中正常工作但在 Scala 2.13 中失败。

设置

untitled14\build.sbt

name := "untitled14"
version := "0.1"
scalaVersion := "2.12.13"

untitled14\project\build.properties

sbt.version = 1.4.1

untitled14\src\main\java\Main.java

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

import java.util.HashMap;
import java.util.Map;

public class Main {

    public static void main(String[] args) {

        Map<Integer, String> javaMap = new HashMap<>();
        javaMap.put(1, "java");
        javaMap.put(2, "scala");
        javaMap.put(3, "js");

        System.out.println("Java map -> " + javaMap);

        scala.collection.immutable.Map<Integer, String> scalaMap = JavaConverters
                .mapAsScalaMapConverter(javaMap)
                .asScala()
                .toMap(Predef.<Tuple2<Integer, String>>conforms());

        System.out.println("Scala map -> " + scalaMap);
    }
}

我执行的命令

sbt run

输出

Java map -> {1=java, 2=scala, 3=js}
Scala map -> Map(1 -> java, 2 -> scala, 3 -> js)

因此，您可以从上面看出代码 100% 正确运行。

现在，如果我更新 build.sbt 以使用 scala-2.13.3，将会出现编译错误。

untitled14\build.sbt

name := "untitled14"
version := "0.1"
scalaVersion := "2.13.3"

我执行的命令

sbt clean compile

输出

编译

[info] compiling 1 Java source to D:\untitled14\target\scala-2.13\classes ...
[error] D:\untitled14\src\main\java\Main.java:22:1: cannot find symbol
[error]   symbol:   method <scala.Tuple2<java.lang.Integer,java.lang.String>>conforms()
[error]   location: class scala.Predef
[error] Predef.<Tuple2<Integer, String>>conforms
[error] (Compile / compileIncremental) javac returned non-zero exit code
[error] Total time: 1 s, completed 15-Jan-2021, 6:01:18 pm

我试过使用

import scala.jdk.CollectionConverters;

import java.util.HashMap;
import java.util.Map;

public class Main {

    public static void main(String[] args) {

        Map<Integer, String> javaMap = new HashMap<>();
        javaMap.put(1, "java");
        javaMap.put(2, "scala");
        javaMap.put(3, "js");

        System.out.println("Java map -> " + javaMap);

        scala.collection.immutable.Map<Integer, String> scalaMap = CollectionConverters
                .MapHasAsScala(javaMap)
                .asScala()
                .toMap(scala.$less$colon$less.refl());

        System.out.println("Scala map -> " + scalaMap);
    }
}

但错误输出为

[info] compiling 1 Java source to D:\untitled14\target\scala-2.13\classes ...
[error] D:\untitled14\src\main\java\Main.java:20:1: cannot find symbol
[error]   symbol:   method refl()
[error]   location: class scala.$less$colon$less
[error] scala.$less$colon$less.refl
[error] (Compile / compileIncremental) javac returned non-zero exit code
[error] Total time: 1 s, completed 15-Jan-2021, 6:06:43 pm

有人可以告诉我如何正确操作吗？

注：-我用的是jvm-14, sbt-1.4.1, scala-2.13.3

Answer 1

我自己找到了解决方案，只需使用 $less$colon$less$.MODULE$.refl() 而不是 Predef.<Tuple2<Integer, String>>conforms()

import scala.$less$colon$less$;
import scala.jdk.CollectionConverters;

import java.util.HashMap;
import java.util.Map;

public class Main {

    public static void main(String[] args) {

        Map<Integer, String> javaMap = new HashMap<>();
        javaMap.put(1, "java");
        javaMap.put(2, "scala");
        javaMap.put(3, "js");

        System.out.println("Java map -> " + javaMap);

        scala.collection.immutable.Map<Integer, String> scalaMap = CollectionConverters
                .MapHasAsScala(javaMap)
                .asScala()
                .toMap($less$colon$less$.MODULE$.refl());

        System.out.println("Scala map -> " + scalaMap);
    }
}

Answer 2

您在 Scala 2.13 中有一个非常简单的解决方案：

scala.collection.immutable.Map<Integer, String> scalaMap =
        scala.collection.immutable.Map.from(scala.jdk.CollectionConverters.MapHasAsScala(javaMap).asScala());

使用 Scala-2.13 在 Java 代码中将 Java 映射转换为 Scala 不可变映射

Convert Java map into Scala immutable map in Java code with Scala-2.13

java

dictionary

scala

scala-2.13