如何使用 scala.Float 到 java.Float k/v 转换将 Scala Map 转换为 Java Map
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How can I convert Scala Map to Java Map with scala.Float to java.Float k/v conversion
提问by rvange
I would like to be able to perform the following, but it fails in the call to useMap. How can I perform this conversion?
我希望能够执行以下操作，但在调用 useMap 时失败。如何执行此转换？
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)
^
It seems to work with Map[String, String], but not Map[Int, Float].
它似乎适用于 Map[String, String]，但不适用于 Map[Int, Float]。
采纳答案by cyber4ron
Use scala predefined float2Floatand use CollectionConverters to perform conversion explicitly.
使用 scala 预定义float2Float并使用 CollectionConverters 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
回答by rvange
The solution linked to by @pagoda_5b works: Scala convert List[Int] to a java.util.List[java.lang.Integer]
@pagoda_5b 链接的解决方案有效：Scala convert List[Int] to a 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
回答by Shrey
Implicit conversions are sometimes hard to debug/understand and therefore I prefer explicit conversions as follows:
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)
回答by senia
scala> v.asJava
<console>:16: error: type mismatch;
found : java.util.Map[Int,scala.Float]
required: java.util.Map[Integer,java.lang.Float]
The type of vis Map[scala.Int, scala.Float], not Map[java.lang.Integer, java.lang.Float].
的类型v是Map[scala.Int, scala.Float]，不是Map[java.lang.Integer, java.lang.Float]。
You could try this:
你可以试试这个：
import java.lang.{Float => JFloat}
useMap(v.map{ case (k, v) => (k: Integer) -> (v: JFloat)})
