问传递给Class的字符串显示为空

EN

class InnoString(abc: String)extends App{

  val message=abc

  override def toString(): String ={
    return message
  }



  def concat(sub : String): String={
      return  s"$sub$message"
    }
}



object checkInno extends App{
  val x = new InnoString("harshil")
  println(x)
  println(x.concat("there "))
}