![](/img/trans.png)
[英]Is there a standard way to convert a java.util.function,Consumer<T> into a java.util.function.Function<T, Void>
[英]Why can't I implicit convert Scala's Function1 to java.util.function.Function?
我正在嘗試創建Scala的Function1到java.util.function.Function的隱式轉換。
這是我的代碼:
object Java8ToScala extends App {
implicit def javaFuncToScalaFunc[T, R](func1: Function[T, R]): function.Function[T,R] = {
new function.Function[T, R] {
override def apply(t: T): R = func1.apply(t)
}
}
val javaFunc:function.Function[String,Int] = (s:String) => s.length
println(javaFunc.apply("foo")) // this works
private val strings = new util.ArrayList[String]()
println(strings.stream().map(javaFunc).collect(Collectors.toList())) // this doesn't work
}
編譯器消息很難理解:
[error] /xxx/Java8ToScala.scala:74: no type parameters for method map: (x$1: java.util.function.Function[_ >: String, _ <: R])java.util.stream.Stream[R] exist so that it can be applied to arguments (java.util.function.Function[String,Int])
[error] --- because ---
[error] argument expression's type is not compatible with formal parameter type;
[error] found : java.util.function.Function[String,Int]
[error] required: java.util.function.Function[_ >: String, _ <: ?R]
[error] Note: String <: Any, but Java-defined trait Function is invariant in type T.
[error] You may wish to investigate a wildcard type such as `_ <: Any`. (SLS 3.2.10)
[error] .map(javaFunc).collect(Collectors.toList()))
[error] ^
[error] /xxx/Java8ToScala.scala:74: type mismatch;
[error] found : java.util.function.Function[String,Int]
[error] required: java.util.function.Function[_ >: String, _ <: R]
[error] .map(javaFunc).collect(Collectors.toList()))
[error] ^
[error] two errors found
[error] (compile:compileIncremental) Compilation failed
[error] Total time: 7 s, completed Dec 18, 2015 10:51:15 AM
使用以下隱式轉換:
implicit def javaFuncToScalaFunc[T, R](func1: function.Function[T, R]): Function[T,R] = {
new Function[T, R] {
override def apply(t: T): R = func1.apply(t)
}
}
在您的代碼中,您有一個從Scala函數到Java函數的隱式轉換,但您應該從Java函數到Scala函數進行隱式轉換。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.