Convert java.util.ArrayList to Seq in Scala

Question

I have the following structure in Scala:

import java.util.ArrayList
val array = new ArrayList[ArrayList[String]]

// ... add values to array

Now, I need to convert it to Seq[Seq[String]], how can this be achieved?

Possible duplicate of Converting a Java collection into a Scala collection — Silvio Mayolo
– Silvio Mayolo, Commented Apr 13, 2018 at 2:56
Specifically, this answer would seem to be what you're looking for. — Silvio Mayolo
– Silvio Mayolo, Commented Apr 13, 2018 at 2:56
Thanks, but in that answer the list has one dimension, and in my question it has two. Also, it's from 2010, probably changed by now. — ps0604
– ps0604, Commented Apr 13, 2018 at 2:58

Chitral Verma · Accepted Answer · 2018-04-13 02:59:31Z

4

You can do the following,

import scala.collection.JavaConversions._
val array = new ArrayList[ArrayList[String]]
val seq: Seq[Seq[String]] = array.map(_.toSeq)
...

Let me know if this helps, Cheers.

answered Apr 13, 2018 at 2:59

Chitral Verma

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2 Comments

ps0604 Over a year ago

thanks, I had to do val seq = array.map(_.toSeq).toSeq

Chitral Verma Over a year ago

@peterSc the second .toSeq is a redundant collection conversion, so removed it. seq has a Seq type.Do mark it as accepted if it helped.

Patrick Refondini · Accepted Answer · 2018-04-13 08:19:47Z

1

A second solution using explicit conversions:

import scala.collection.JavaConverters._
import java.util.ArrayList

val array = new ArrayList[ArrayList[String]]

// Mutable, default conversion for java.util.ArrayList
val mutableSeq : Seq[Seq[String]] = array.asScala.map( _.asScala)

// Immutable, using toList on mutable conversion result
val immutableSeq : Seq[Seq[String]] = array.asScala.toList.map( _.asScala.toList)

To clarify the difference between Java JavaConverters and JavaConversions please read:

What is the difference between JavaConverters and JavaConversions in Scala?

answered Apr 13, 2018 at 8:19

Patrick Refondini

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Comments

awadhesh14 · Accepted Answer · 2021-05-14 17:57:58Z

0

The scala.collection.JavaConverters._ is depricated. The latest ways is:

import scala.collection.JavaConversions._

val a = asScalaBuffer(array)

Now you can convert a to any of the collections

to        toBuffer       toIterable   toList   toParArray   toSet      toString        toVector
toArray   toIndexedSeq   toIterator   toMap    toSeq        toStream   toTraversable

like this

val b = a.toSeq

Here is a complete tutorial

answered May 14, 2021 at 17:57

awadhesh14

898 bronze badges

3 Comments

jwvh Over a year ago

JavaConversions is not a member of package collection

awadhesh14 Over a year ago

seems like it is a member now, I checked on Scala 2.11.12

jwvh Over a year ago

2.11.12? That's far, far, from "the latest way."

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