scala the language matters training

function-as-first-class-citizen.java

//-------------------------------------------//
// function as parameter java implementation //
//-------------------------------------------//

class UerFetcher  implement Callable<User>  { 
  private   String userId;
  
  @Autowired
  private  UserService  userService;
  
  publiv User call() {
      return userService.get(userId);
  }
}

List<String> userIds =  null;//  List( "1001", "1003",  "1005")
List<Future<User>> users = new ArrayList<Future<User>>() 

for(id : userIds) {
  users.add(executor.submit(new UserFetcher(id)))
}

function-as-first-class-citizen.scala

//-------------------------------------------//
// function as parameter in scala            //
//-------------------------------------------//

val userIds = List("1001", "1002", "1003",  "1004")

val userFetcher: String => Future[User] =  (id: String)  =>  future { UserService.get(id) }      

val users: List[Future[User]] = userIds.map(userFetcher)