使用JavaConversion在java和scala集合之间进行隐式转换
我使用一个通用函数合并了scala使用JavaConversion在java和scala集合之间进行隐式转换,java,scala,scala-collections,Java,Scala,Scala Collections,我使用一个通用函数合并了scalaMaps的scalaSet def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] = (Map[A, B]() /: (for (m <- ms; kv <- m) yield kv)) { (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
Map
s的scalaSet
def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] =
(Map[A, B]() /: (for (m <- ms; kv <- m) yield kv))
{
(a, kv) =>
a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv)
}
然而,它说存在类型不匹配
Error:(67, 11) type mismatch;
found : scala.collection.mutable.Map[A,B]
required: java.util.HashMap[A,B]
a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv)
^
JavaConversions
是否用于将util.HashMap
隐式转换为mutable.Map
?我在这里遗漏了什么?一个JavaConverter
会做你想要的吗
scala> import scala.collection.JavaConverters._
import scala.collection.JavaConverters._
scala> val x = (new java.util.HashMap[Int,Int]).asScala
x: scala.collection.mutable.Map[Int,Int] = Map()
他们说要尝试JavaConversions,因为JavaConversions是不受欢迎的
scala> import collection.JavaConverters._
import collection.JavaConverters._
scala> def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] =
| (new java.util.HashMap[A, B] /: (for (m <- ms; kv <- m) yield kv)) {
| case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
<console>:16: error: value contains is not a member of java.util.HashMap[A,B]
case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
^
<console>:16: error: java.util.HashMap[A,B] does not take parameters
case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
^
<console>:16: error: type mismatch;
found : (A, B)
required: String
case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
^
<console>:15: error: type mismatch;
found : java.util.HashMap[A,B]
required: Map[A,B]
(new java.util.HashMap[A, B] /: (for (m <- ms; kv <- m) yield kv)) {
^
scala> def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] =
| (new java.util.HashMap[A, B].asScala /: (for (m <- ms; kv <- m) yield kv)) {
| case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
<console>:15: error: type mismatch;
found : scala.collection.mutable.Map[A,B]
required: scala.collection.immutable.Map[A,B]
(new java.util.HashMap[A, B].asScala /: (for (m <- ms; kv <- m) yield kv)) {
^
scala> def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] =
| (new java.util.HashMap[A, B].asScala.toMap /: (for (m <- ms; kv <- m) yield kv)) {
| case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
mergeMaps: [A, B](ms: Set[Map[A,B]])(f: (B, B) => B)Map[A,B]
scala>import collection.JavaConverters_
导入collection.JavaConverters_
scala>defmergemaps[A,B](ms:Set[Map[A,B]])(f:(B,B)=>B):Map[A,B]=
|(new java.util.HashMap[A,B]/:(for(mf(A(kv._1),kv._2)else-kv)}
:16:错误:value contains不是java.util.HashMap[a,B]的成员
案例(a,kv)=>a+(如果(a.包含(kv.\u 1))kv.\u 1->f(a(kv.\u 1),kv.\u 2)其他kv)}
^
:16:错误:java.util.HashMap[A,B]不接受参数
案例(a,kv)=>a+(如果(a.包含(kv.\u 1))kv.\u 1->f(a(kv.\u 1),kv.\u 2)其他kv)}
^
:16:错误:类型不匹配;
发现:(A,B)
必需:字符串
案例(a,kv)=>a+(如果(a.包含(kv.\u 1))kv.\u 1->f(a(kv.\u 1),kv.\u 2)其他kv)}
^
:15:错误:类型不匹配;
找到:java.util.HashMap[A,B]
所需:地图[A,B]
(新java.util.HashMap[A,B]/:(for(mb):Map[A,B]=
|(new java.util.HashMap[A,B].asScala/:(for(mf(A(kv._1),kv._2)else-kv)}
:15:错误:类型不匹配;
找到:scala.collection.mutable.Map[A,B]
必需:scala.collection.immutable.Map[A,B]
(new java.util.HashMap[A,B].asScala/:(for(mb):Map[A,B]=
|(new java.util.HashMap[A,B].asScala.toMap/:(for(mf(A(kv._1),kv._2)else-kv)}
合并映射:[A,B](ms:Set[Map[A,B]])(f:(B,B)=>B)映射[A,B]
也许是为了说明为什么不推荐它:
scala> def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] =
| (new java.util.HashMap[A, B] /: (for (m <- ms; kv <- m) yield kv)) {
| case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
<console>:19: error: type mismatch;
found : scala.collection.mutable.Map[A,B]
required: java.util.HashMap[A,B]
case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
^
<console>:18: error: type mismatch;
found : java.util.HashMap[A,B]
required: Map[A,B]
(new java.util.HashMap[A, B] /: (for (m <- ms; kv <- m) yield kv)) {
^
scala>defmergemaps[A,B](ms:Set[Map[A,B]])(f:(B,B)=>B):Map[A,B]=
|(new java.util.HashMap[A,B]/:(for(mf(A(kv._1),kv._2)else-kv)}
:19:错误:类型不匹配;
找到:scala.collection.mutable.Map[A,B]
必需:java.util.HashMap[A,B]
案例(a,kv)=>a+(如果(a.包含(kv.\u 1))kv.\u 1->f(a(kv.\u 1),kv.\u 2)其他kv)}
^
:18:错误:类型不匹配;
找到:java.util.HashMap[A,B]
所需:地图[A,B]
(new java.util.HashMap[A,B]/:(for(mb)=for(mb)(m def mergeMaps[A,B](ms:Set[Map[A,B]])(f:(B,B)=>B):Map[A,B]={
|val ss=对于(mf(a(kv._1),kv._2)或其他kv)}
| }
已弃用?我在或上都没有发现任何提及。我的优势在于我最近参与了弃用:@jwvh我记得文档中也有一点改进,因为大多数改进都是增量的:另外,不要被新的scaladoc页面样式完全吹走。嗯,我不认为“吹走了”这是我如何描述我的反应,但我对你的见解印象深刻。谢谢分享。@jwvh先生,你能帮我吗
scala> def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] =
| (new java.util.HashMap[A, B] /: (for (m <- ms; kv <- m) yield kv)) {
| case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
<console>:19: error: type mismatch;
found : scala.collection.mutable.Map[A,B]
required: java.util.HashMap[A,B]
case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
^
<console>:18: error: type mismatch;
found : java.util.HashMap[A,B]
required: Map[A,B]
(new java.util.HashMap[A, B] /: (for (m <- ms; kv <- m) yield kv)) {
^
scala> def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B) = for (m <- ms; kv <- m) yield kv
mergeMaps: [A, B](ms: Set[Map[A,B]])(f: (B, B) => B)scala.collection.immutable.Set[(A, B)]
scala> def mergeMaps[A, B](ms: Set[Map[A, B]])(f: (B, B) => B): Map[A, B] = {
| val ss = for (m <- ms; kv <- m) yield kv
| (new java.util.HashMap[A, B] /: ss) {
| case (a, kv) => a + (if (a.contains(kv._1)) kv._1 -> f(a(kv._1), kv._2) else kv) }
| }