Scala中的JavaConverters和JavaConversions有什么区别？

Question

在中scala.collection，有两个非常相似的对象JavaConversions和JavaConverters。

• 这两个对象有什么区别？

• 为什么它们都存在？

• 我何时要使用一个与另一个？

Answer 1

编辑：Java Conversions有@deprecated斯卡拉2.13.0。请改用scala.jdk.CollectionConverters。JavaConversions提供了一系列隐式方法，这些方法可在Java集合和最接近的对应Scala集合之间进行转换，反之亦然。这是通过创建实现Scala接口并将调用转发到基础Java集合或Java接口并将调用转发到基础Scala集合的包装器来完成的。JavaConverters使用pimp-my-library模式将asScala方法“添加” 到Java集合和asJava方法到Scala集合，这将返回上面讨论的适当包装器。它（从2.8.1版开始）比JavaConversions（从2.8 版开始）更新，并使Scala和Java集合之间的转换变得明确。与David在回答中写的相反，我建议您养成使用的习惯，JavaConverters因为您将不太可能编写进行大量隐式转换的代码，因为您可以控制发生这种情况的唯一地方：在哪里写.asScala或.asJava。以下是JavaConverters提供的转换方法：Pimped Type&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | Conversion Method&nbsp; &nbsp;| Returned Type=================================================================================================scala.collection.Iterator&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Iteratorscala.collection.Iterator&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | asJavaEnumeration&nbsp; &nbsp;| java.util.Enumerationscala.collection.Iterable&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.lang.Iterablescala.collection.Iterable&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | asJavaCollection&nbsp; &nbsp; | java.util.Collectionscala.collection.mutable.Buffer&nbsp; &nbsp; &nbsp; &nbsp; | asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Listscala.collection.mutable.Seq&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Listscala.collection.Seq&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Listscala.collection.mutable.Set&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Setscala.collection.Set&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Setscala.collection.mutable.Map&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Mapscala.collection.Map&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asJava&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | java.util.Mapscala.collection.mutable.Map&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asJavaDictionary&nbsp; &nbsp; | java.util.Dictionaryscala.collection.mutable.ConcurrentMap | asJavaConcurrentMap | java.util.concurrent.ConcurrentMap—————————————————————————————————————————————————————————————————————————————————————————————————java.util.Iterator&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.Iteratorjava.util.Enumeration&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.Iteratorjava.lang.Iterable&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.Iterablejava.util.Collection&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.Iterablejava.util.List&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.mutable.Bufferjava.util.Set&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.mutable.Setjava.util.Map&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; | asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.mutable.Mapjava.util.concurrent.ConcurrentMap&nbsp; &nbsp; &nbsp;| asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.mutable.ConcurrentMapjava.util.Dictionary&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.mutable.Mapjava.util.Properties&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| asScala&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| scala.collection.mutable.Map[String, String]但是，要直接从Java使用转换，最好不要直接从Java调用方法JavaConversions。例如：List<String> javaList = new ArrayList<String>(Arrays.asList("a", "b", "c"));System.out.println(javaList); // [a, b, c]Buffer<String> scalaBuffer = JavaConversions.asScalaBuffer(javaList);System.out.println(scalaBuffer); // Buffer(a, b, c)List<String> javaListAgain = JavaConversions.bufferAsJavaList(scalaBuffer);System.out.println(javaList == javaListAgain); // true

Answer 2

如API中所述，JavaConversions一组隐式转换将Java集合转换为相关的scala集合。您可以将其与一起使用import collection.JavaConversions._。必要时，编译器将自动将java集合转换为正确的scala类型。JavaConverters是一组装饰器，可使用asScala或asJava方法隐式添加到要转换的集合中，以帮助将java或scala集合转换为scala或java集合。为了使用这些转换器，您需要导入：import collection.JavaConverters._您应该首选JavaConversions它，因为它通常更易于使用（无需使用asScala或asJava）。

Answer 3

在斯卡拉2.13，JavaConverters已经过时赞成scala.jdk.CollectionConverters：... scala.jdk包含对象的新程序包CollectionConverters （经典Java集合，与collection.JavaConverters2.12中类似）StreamConverters，FunctionConverters和OptionConverters...