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)
^
它似乎适用于MapString、String,但不适用于MapInt、Float。
发布于 2015-12-23 02:06:35
使用scala预定义的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
发布于 2013-05-17 20:17:08
由@pagoda_5b works链接的解决方案: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
发布于 2018-10-26 08:59:39
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)
https://stackoverflow.com/questions/16583265
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