Scala Iterator与Java Iterator的问题(一场恶梦):如何从Scala转换为Java? [英] Problems with Scala Iterator vs. Java Iterator (a casting nightmare): How to cast to Java from Scala?

问题描述

我想要完成的事情很简单: 返回包含Tuple2作为Java迭代器的列表.

What I am trying to accomplish is simple: Return the list containing a Tuple2 as a Java Iterator.

代码段为:

....public java.util.Iterator<Tuple2<Path, Text>> call(InputSplit inputSplit, java.util.Iterator<Tuple2<LongWritable, Text>> iter) throws Exception { 


    .....  java.util.List<Tuple2<Path, Text>>  elements = new java.util.ArrayList<Tuple2<Path, Text>>();
        while(iter.hasNext()){
            Tuple2<LongWritable,Text> tupled = iter.next();
            Tuple2<Path, Text> toAdd = new Tuple2<Path, Text>(file.getPath(),tupled._2);
            elements.add(toAdd);
        }
        java.util.Iterator<Tuple2<Path, Text>> it = elements.iterator();
        return it; .....}

注意:变量iter也是Java迭代器.

Note: the variable iter is also a Java Iterator.

我得到的错误是: java.lang.ClassCastException: java.util.ArrayList$Itr cannot be cast to scala.collection.Iterator

1. 我在做什么错? (我知道我正在使用Tuple2，这是针对Scala的.)
2. 如何返回具有Tuple2或Tuple2等价物的Java迭代器?

1. What am I doing wrong? (I am aware that I am using Tuple2, which is meant for Scala).
2. How do I return a Java Iterator with a Tuple2 or a Tuple2 equivalent ?

谢谢

推荐答案

您好像在进行从Java迭代器到Scala迭代器的非法转换.

Looks like you're doing an illegal cast from Java iterator to Scala iterator.

尝试使用 scala.collection.JavaConversions . 导入此隐式类时-这些转换将自动完成.

Try using scala.collection.JavaConversions. When you import this implicit class - these conversions will be done automatically.

简而言之-

import scala.collection.JavaConversions._

另一种方法是显式地进行此操作，假设javaIterator是您的Java迭代器-

Another option is to do it explicitly, assuming javaIterator is your java iterator -

import scala.collection.JavaConverters._
javaIterator.asScala

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