Why do we need ActorSystem and ActorMaterializer?

Now, it's time to run our RunnableGraph here and find the results. We can run a RunnableGraph by calling its run function, as follows:

import akka.stream.scaladsl.{Flow, Sink, Source} 
object AkkaStreamsNumbersApp extends App{ 
  val numbersSource = Source(1 to 10) 
  val sampleSink = Sink.foreach(println) 
  val numberFlow = Flow[Int].map(num => num+1) 
  val numberRunnableGraph =
   numbersSource.via(numberFlow).to(sampleSink) 
  numberRunnableGraph.run 
} 

When we run the preceding program, we will get the following error messages:

Error:(18, 23) could not find implicit value for parameter materializer: akka.stream.Materializer 
  numberRunnableGraph.run 
 
Error:(18, 23) not enough arguments for method run: (implicit materializer: akka.stream.Materializer)akka.NotUsed. 
Unspecified value parameter materializer. 
  numberRunnableGraph...