如何使用scala.Float将Scala Map转换为Java Map到java.Float k/v转换

Question

我希望能够执行以下操作,但是在调用useMap时失败了.我该如何进行此转换？

scala> import scala.collection.JavaConversions._
import scala.collection.JavaConversions._

scala> import scala.collection.JavaConverters._
import scala.collection.JavaConverters._

scala> def useMap(m: java.util.Map[java.lang.Integer, java.lang.Float]) = m
useMap: (m: java.util.Map[Integer,Float])java.util.Map[Integer,Float]

scala> val v: Map[Int, Float] = Map()
v: Map[Int,Float] = Map()

scala> useMap(v)
<console>:10: error: type mismatch;
 found   : scala.collection.immutable.Map[Int,scala.Float]
 required: java.util.Map[Integer,java.lang.Float]
              useMap(v)
                     ^

它似乎适用于Map [String,String],但不适用于Map [Int,Float].

Answer 1

链接到@ pagoda_5b的解决方案有效:Scala将List [Int]转换为java.util.List [java.lang.Integer]

scala> import collection.JavaConversions._
import collection.JavaConversions._

scala> val m = mapAsJavaMap(Map(1 -> 2.1f)).asInstanceOf[java.util.Map[java.lang.Integer, java.lang.Float]]
m: java.util.Map[Integer,Float] = {1=2.1}

scala> m.get(1).getClass
res2: Class[_ <: Float] = class java.lang.Float

Answer 2

使用预定义的scala float2Float并使用JavaConverters显式执行转换.

import scala.jdk.CollectionConverters._
// Prior to Scala 2.13: import scala.collection.JavaConverters._
val scalaMap = Map(1 -> 1.0F)
val javaMap = scalaMap.map{ case (k, v) => k -> float2Float(v) }.asJava

Answer 3

隐式转换有时很难调试/理解，因此我更喜欢显式转换，如下所示：

import scala.collection.JavaConversions.mapAsJavaMap

val scalaMap = Map(1 -> 1.0F)
val javaMap = mapAsJavaMap(scalaMap)