如何使用Java 8从Scala 2.11收集数据流?

问题描述

我有这段代码:

import java.util.stream._
import java.util.function._

final case class AbcTest(value: String)

def funToFunction[InT, OutT](fun: InT => OutT): Function[InT, OutT] = new Function[InT, OutT] {
  override def apply(t: InT): OutT = fun(t)
}

def main(args: Array[String]): Unit = {
  Stream.of("a", "b", "c")
    .map[AbcTest](funToFunction((v: String) => AbcTest(v)))
    .collect(Collectors.toList())
}

它失败并显示以下错误消息:

And it fails with this error message:

    Error:(43, 27) type mismatch;
 found   : java.util.stream.Collector[Nothing,?0(in method main),java.util.List[Nothing]] where type ?0(in method main)
 required: java.util.stream.Collector[_ >: test.AbcTest, ?, ?]
Note: Nothing <: Any, but Java-defined trait Collector is invariant in type T.
You may wish to investigate a wildcard type such as `_ <: Any`. (SLS 3.2.10)
      .collect(Collectors.toList)

我不明白发生了什么，请帮忙.

I don't understand what's happening, please help.

推荐答案

从我所看到的以下内容来看，效果很好，请记住只是在某种类型推断方面有所帮助

Well... from what I have seen the following works absolutely fine, remember to just help a little in some type inferencing

import java.util.{stream => jStream}
import java.util.{function => jFunction}

def funToFunction[InT, OutT](fun: InT => OutT): jFunction.Function[InT, OutT] =
  new jFunction.Function[InT, OutT] {
    override def apply(t: InT): OutT = fun(t)
  }

final case class AbcTest(value: String)

val javaList =
  jStream.Stream.of("a", "b")
    .map[AbcTest](funToFunction((s: String) => AbcTest(s)))
    .collect(jStream.Collectors.toList[AbcTest])

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