How to use Array in JCommander in Scala - scala

Question

I want to use JCommander to parse args.
I wrote some code:
import com.beust.jcommander.{JCommander, Parameter}
import scala.collection.mutable.ArrayBuffer
object Config {
#Parameter(names = Array("--categories"), required = true)
var categories = new ArrayBuffer[String]
}
object Main {
def main(args: Array[String]): Unit = {
val cfg = Config
JCommander
.newBuilder()
.addObject(cfg)
.build()
.parse(args.toArray: _*)
println(cfg.categories)
}
}
Howewer it fails with
com.beust.jcommander.ParameterException: Could not invoke null
Reason: Can not set static scala.collection.mutable.ArrayBuffer field InterestRulesConfig$.categories to java.lang.String
What am i doing wrong?

Answer 1

JCommander uses knowledge about types in Java to map values to parameters. But Java doesn't have a type scala.collection.mutable.ArrayBuffer. It has a type java.util.List. If you want to use JCommander you have to stick to Java's build-in types.
If you want to use Scala's types use one of Scala's libraries that handle in in more idiomatic manner: scopt or decline.

Answer 2

Working example
import java.util
import com.beust.jcommander.{JCommander, Parameter}
import scala.jdk.CollectionConverters._
object Config {
#Parameter(names = Array("--categories"), required = true)
var categories: java.util.List[Integer] = new util.ArrayList[Integer]()
}
object Hello {
def main(args: Array[String]): Unit = {
val cfg = Config
JCommander
.newBuilder()
.addObject(cfg)
.build()
.parse(args.toArray: _*)
println(cfg.categories)
println(cfg.categories.getClass())
val a = cfg.categories.asScala
for (x <- a) {
println(x.toInt)
println(x.toInt.getClass())
}
}
}