Scala Array Java Interop

Strings.java

package t;

public class Strings {
  public static String join(Object[] args) {
    if (args == null || args.length == 0) {
      return "";
    }
    StringBuilder sb = new StringBuilder();
    sb.append(args[0]);
    for (int i = 1, len = args.length; i < len; i++) {
      sb.append(",").append(args[i]);
    }
    return sb.toString();
  }

  // test
  public static void main(String[] args) {
    join(new String[] { "Hello", "world" });
  }
}

Test.scala

package t

object Test extends App {
  import Strings.join
  // val arr : Array[Any] = Array("a")
  //join(arr)
  val arr1: Array[AnyRef] = Array("a")
  join(arr1)

  //val arr2 = Array("a")
  //join(arr2)

  val arr3 = Array("a") // arr3: Array[String]
  join(arr3.asInstanceOf[Array[AnyRef]]) //

  assert(join(Array("hello", "world")) == "hello,world")
  //assert(join(Array(1, 2)) == "1,2")
  //assert(join(Array(1, 2).asInstanceOf[Array[AnyRef]]) == "1,2")

  assert(join(Array(1, 2).map(_.toString).toArray) == "1,2")
  assert(join(List[java.lang.Integer](1, 2).toArray) == "1,2")

  def test(arr: Array[Any]) = {
    //Strings.join(arr)
    Strings.join(arr.asInstanceOf[Array[AnyRef]])
  }

  println(test(Array(1, 2, 3)))
}