Scala array to Java

Question

I have this invocation from scala class to Java

  private def initSpringActorContext: ConfigurableApplicationContext = {
    val resourceLocations = Array[String]("aopContext.xml", "akkaContext.xml")
    new GenericXmlApplicationContext(resourceLocations))
  }

And the java class expect

 public GenericXmlApplicationContext(String... resourceLocations) {
        this.load(resourceLocations);
        this.refresh();
    }

I´ve tried to cast this with import collection.JavaConverters._

But I cannot make it works with Arrays.

Any suggestion?

Cyrille Corpet · Accepted Answer · 2017-06-09 07:46:08Z

3

You do not want an Array, but a varargs.

You should do new GenericXmlApplicationContext(resourceLocations: _*)

answered Jun 9, 2017 at 7:46

Cyrille Corpet

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2 Comments

paul Over a year ago

Wow that´s magic stuff, what the hell is the scala compiler doing internally there?! Thanks a lot man!

Cyrille Corpet Over a year ago

Unlike in java, String* (scala varargs) is not the same as Array[String] in scala. Therefore, we just need to tell the compiler that we want to convert our Array to a varargs by typing it explicitly, which is done with the _* type.

vtor · Accepted Answer · 2017-06-09 08:03:09Z

2

GenericXmlApplicationContext constructor accepts varargs as an argument.

You can use : _* syntax to solve the problem.

private def initSpringActorContext: ConfigurableApplicationContext = {
    val resourceLocations = Array[String]("aopContext.xml", "akkaContext.xml")
    new GenericXmlApplicationContext(resourceLocations: _*))
  }

: in this case is a hint to scala compiler about the type of the expression you have.

_* is a type annotation; it basically says accept any value of varargs (_ for any, * for varargs)

Update: As mentioned in the comment, : _* is a fixed syntax; so above deconstruction is only for explanation purposes.

edited Jun 9, 2017 at 8:03

answered Jun 9, 2017 at 7:54

vtor

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2 Comments

Cyrille Corpet Over a year ago

Actually, _* is a fixed syntax, you cannot replace _ by String (see section 4.6.2 of Scala spec).

vtor Over a year ago

@CyrilleCorpet good point, I updated my answer to stress that. thnx

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