CODEWITHSUNDEEP
javascalaimplicit-conversionscala-java-interop
matt
matt

Reputation: 4734

Implicit conversion of java.util.List to scala List does not occur

I have very basic problem with scala.collection.JavaConversions. I would expect that following code would work but implicit conversion from java.util.List[String] to scala List[String] does not happen. Why?

import collection.JavaConversions._
import java.util
class Test {
  def getStrings() : List[String] = {
    val results : java.util.List[String] = new java.util.ArrayList[String]()
    results
  }
}

I get following message from compi

type mismatch;
 found   : java.util.List[String]
 required: scala.collection.immutable.List[String]
    results
    ^

Upvotes: 11

Views: 9232

Answers (2)

pannu
pannu

Reputation: 538

All you need to do is to import this:

import scala.collection.JavaConversions._

Upvotes: 14

Jatin
Jatin

Reputation: 31724

Convert it to:

def getStrings() : Seq[String] = {
    val results : java.util.List[String] = new java.util.ArrayList[String]()
    results
  }

This is because, the implicit function for the conversion is defined as:

implicit def asScalaBuffer[A](l: java.util.List[A]): mutable.Buffer[A]

It returns a mutable.Buffer and not scala.collection.immutable.List. Hence the error. So alternative is to use a Seq instead of List or convert it to a immutable.List as below:

def getStrings() : List[String] = {
    val results = new java.util.ArrayList[String]()     
    results.toList
}

Upvotes: 24

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