LoggableList.scala

import java.util.{ArrayList => JavaArrayList, List => JavaList}
trait LoggableList[T] extends JavaList[T] {
  abstract override def add(e: T): Boolean = {
    println("added: " + e)
    super.add(e)
  }
}
val list = new JavaArrayList[String] with LoggableList[String]
list.add("A")
list.add("B")
list.add("C")