How to get Scala List from Java List?

Question

I have a Java API that returns a List like:

public List getByXPath(String xpathExpr)

I am using the below scala code:

Answer 1

I was looking for an answer written in Java and surprisingly couldn't find any clean solutions here. After a while I was able to figure it out so I decided to add it here in case someone else is looking for the Java implementation (I guess it also works in Scala?):

JavaConversions.asScalaBuffer(myJavaList).toList()

Answer 2

EDIT: Note that this is deprecated since 2.12.0. Use JavaConverters instead. (comment by @Yaroslav)

Since Scala 2.8 this conversion is now built into the language using:

import scala.collection.JavaConversions._

...

lst.toList.foreach{ node =>   .... }

works. asScala did not work

In 2.12.x use import scala.collection.JavaConverters._

In 2.13.x use import scala.jdk.CollectionConverters._

Answer 3

If you have to convert a Java List<ClassA> to a Scala List[ClassB], then you must do the following:

1) Add

import scala.collection.JavaConverters._

2) Use methods asScala, toList and then map

List <ClassA> javaList = ...
var scalaList[ClassB] = javaList.asScala.toList.map(x => new ClassB(x))

3) Add the following to the ClassB constructor that receives ClassA as a parameter:

case class ClassB () {
   def this (classA: ClassA) {
      this (new ClassB (classA.getAttr1, ..., classA.getAttrN))
   }
}

Answer 4

There's a handy Scala object just for this - scala.collection.JavaConverters

You can do the import and asScala afterwards as follows:

import scala.collection.JavaConverters._

val lst = node.getByXPath(xpath).asScala
lst.foreach{ node =>   .... }

This should give you Scala's Buffer representation allowing you to accomplish foreach.

Answer 5

Since scala 2.8.1 use JavaConverters._ to convert scala and Java collections using asScala and asJava methods.

import scala.collection.JavaConverters._

javalist.asScala

scalaSeq.asJava

see the Conversion relationship scala doc site

Answer 6

Shortcut to convert java list to scala list

import scala.collection.JavaConverters._

myjavaList.asScala.toList