src/Pure/General/file_watcher.scala

 import java.io.{File => JFile}
 import java.nio.file.FileSystems
 import java.nio.file.{WatchKey, WatchEvent, Path => JPath}
 import java.nio.file.StandardWatchEventKinds.{ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY}
 
-import scala.collection.JavaConverters
+import scala.jdk.CollectionConverters._
 
 
 class File_Watcher private[File_Watcher]  // dummy template
 {
   def register(dir: JFile): Unit = {}

             state.change_result(st =>
               {
                 val (remove, changed) =
                   st.dirs.collectFirst({ case (dir, key1) if key == key1 => dir }) match {
                     case Some(dir) =>
-                      val events =
-                        JavaConverters.collectionAsScalaIterable(
-                          key.pollEvents.asInstanceOf[java.util.List[WatchEvent[JPath]]])
+                      val events: Iterable[WatchEvent[JPath]] =
+                        key.pollEvents.asInstanceOf[java.util.List[WatchEvent[JPath]]].asScala
                       val remove = if (key.reset) None else Some(dir)
                       val changed =
                         (Set.empty[JFile] /: events.iterator) {
                           case (set, event) => set + dir.toPath.resolve(event.context).toFile
                         }