Scala Array[String] to Java Collection[String]

Question

I have a Scala array of strings:

val names:Array[String] = something.map(...)

I need to call an Android(java) method that accepts a Collection

public void addAll (Collection<? extends T> collection)

How do I covert the Array to a Collection?

Community · Accepted Answer · 2017-05-23 12:25:42Z

21

Java approach:

java.util.Arrays.asList(names: _*)

Scala approach:

import collection.JavaConversions._

val namesColl: java.util.Collection[String] = names.toSeq

In the latter approach names array is first converted to Seq[String] and then an implicit conversion located in JavaConversions figures out that Java collection is needed so it applies necessary transformation trasparently. Don't worry, it is constant in time.

edited May 23, 2017 at 12:25

CommunityBot

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answered Jan 11, 2012 at 15:05

Tomasz Nurkiewicz

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7 Comments

Steve Over a year ago

Thanks, but what do you mean by "Java approach"?

Tomasz Nurkiewicz Over a year ago

@Steve: I added the "Scala approach" as well :-).

Steve Over a year ago

Perfect, thank you for the explanation. Any reason why you would choose one over the other?

Tomasz Nurkiewicz Over a year ago

@DanielC.Sobral: As far as I can tell Arrays.asList creates one wrapper while toSeq and implicit conversion - two. In both cases there is no copying of an array, hence constant time complexity. So the difference is minimal, but I agree.

lqbweb Over a year ago

Please, can you explain what is the logic behind the " _* ", it works but I don't understand. When you type "name:" I guess that you are operating over names, with a sort of dynamic collection, and then you return it, right? What is exactly "names: _*" returning? if Java Arrays are the same as Scala arrays why doen't work directly?

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RubberDuck · Accepted Answer · 2018-05-09 14:34:37Z

4

JavaConversions is now deprecated. You should use JavaConverters instead.

import collection.JavaConverters.asJavaCollection
val collection = asJavaCollection(Array("some value"))

answered May 9, 2018 at 14:34

RubberDuck

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