Scala Java 错误：值过滤器不是 java.util.Map 的成员。课外作业
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Scala Java Error: value filter is not a member of java.util.Map. Works outside of class
提问by dlite922
I'm trying to refactor some Scala code in Eclipse and run into this compilation error:
我试图在 Eclipse 中重构一些 Scala 代码并遇到这个编译错误：
value filter is not a member of java.util.Map
值过滤器不是 java.util.Map 的成员
import java.io.File
import com.typesafe.config._
class ConfigLoader {
def parseFile( confFile : File) {
val conf = ConfigFactory.parseFile(confFile).root().unwrapped();
for((k,v) <- conf; (dk, dv) = (k, v.toString())) config.param += (dk -> dv);
}
(config is an object with "param" being a Map of String:String)
（config 是一个对象，其中“param”是 String:String 的 Map）
This code was pull exactly from Main() where it worked fine like so:
这段代码正是从 Main() 中提取的，它运行良好，如下所示：
object Main extends Logging {
def main(args: Array[String]) {
//code cropped for readability.
//config.param["properties"] is absolute path to a passed-in properties file.
val conf = ConfigFactory.parseFile(new java.io.File(config.param("properties"))).root().unwrapped();
for((k,v) <- conf; (dk, dv) = (k, v.toString())) config.param+=(dk -> dv);
as you can see the code is exactly the same. I've imported the same libraries. All i'm doing different in main now is instantiating ConfigLoaderand calling it like so:
如您所见，代码完全相同。我已经导入了相同的库。我现在在 main 中所做的不同是实例化ConfigLoader并像这样调用它：
cfgLoader.parseFile(config.param("properties"))
cfgLoader.parseFile(config.param("properties"))
Any ideas what's causing the error just by moving it to a class?
任何想法只是将其移动到一个类中导致错误的原因是什么？
I've googled the error and it seems to be pretty generic.
我用谷歌搜索了错误，它似乎非常通用。
采纳答案by dlite922
Turns out I was missing a tricky import after all:
事实证明，我毕竟错过了一个棘手的导入：
import collection.JavaConversions._
import collection.JavaConversions._
not to be confused with JavaConverters._which I did have.
不要与JavaConverters._我确实拥有的混淆。
Hope this helps someone else.
希望这对其他人有帮助。
回答by Juh_
The problem is that you are using a java Map which doesn't implement the monad api (map, flatMap, ...) required to use scala for-comprehension.
问题是您使用的 java Map 没有实现使用 scala for-comprehension 所需的 monad api（map、flatMap 等）。
More specifically, in your example, the compiler is complaining about missing .filtermethod. This is because you unpack each item of the map: (key, value) <- monadinstead of a direct assignment, such as entry <- monad. But even if you did use direct assignment, it would complain about missing .mapor .flatMap. See this answer to "how to make you own for-comprehension compliant scala monadfor details on the required api.
更具体地说，在您的示例中，编译器抱怨缺少.filter方法。这是因为您解压了地图的每个项目：(key, value) <- monad而不是直接赋值，例如entry <- monad. 但即使你确实使用了直接赋值，它也会抱怨缺少.map或.flatMap. 有关所需 api 的详细信息，请参阅“如何让您拥有符合理解性的 scala monad”的答案。
The simplest solution to your problem is to convert you java map into scala map using:
解决您的问题的最简单方法是使用以下方法将您的 java 地图转换为 Scala 地图：
import scala.collection.JavaConverters._
...
for((k,v) <- conf.asScala) ...
The import includes implicit that add the .asScalamethod to java map
导入包含将.asScala方法添加到 java map 的隐式
