Scala Akka Basics Cheat Sheet

Introduces Akka actors, actor systems and messaging with tell and ask, supervision, and the modern typed actor Behaviors API.

2 PagesAdvancedApr 8, 2026

Defining an Actor

A classic Akka actor with a message-handling receive block.

scala

import akka.actor.{Actor, ActorSystem, Props}class GreeterActor extends Actor {  def receive: Receive = {    case name: String => println(s"Hello, $name!")    case _             => println("Unknown message")  }}

Actor System & Messaging

Creating actors and sending messages with tell and ask.

scala

val system = ActorSystem("greeter-system")val greeter = system.actorOf(Props[GreeterActor](), "greeter")greeter ! "World"          // fire-and-forget (tell)// Ask pattern for a response (returns a Future)import akka.pattern.askimport akka.util.Timeoutimport scala.concurrent.duration._implicit val timeout: Timeout = Timeout(3.seconds)val future = greeter ? "World"system.terminate()

Core Akka Concepts

Key ideas behind the actor model in Akka.

ActorRef- A lightweight, location-transparent handle used to send messages to an actor; never reference the actor instance directly
Mailbox- Each actor has a queue of incoming messages processed one at a time, avoiding shared-state race conditions
Supervision- Parent actors supervise children and decide how to handle failures: Restart, Resume, Stop, or Escalate
tell (!) vs ask (?)- tell is fire-and-forget with no reply; ask returns a Future representing an eventual reply
Props- Immutable configuration object describing how to create an actor instance, passed to actorOf
context.become- Lets an actor swap its message-handling behavior at runtime for stateful protocols

Akka Typed Behaviors

The modern, type-safe actor API.

scala

import akka.actor.typed.{ActorSystem, Behavior}import akka.actor.typed.scaladsl.Behaviorsobject Greeter {  sealed trait Command  final case class Greet(name: String) extends Command  def apply(): Behavior[Command] = Behaviors.receiveMessage {    case Greet(name) =>      println(s"Hello, $name!")      Behaviors.same  }}val system: ActorSystem[Greeter.Command] = ActorSystem(Greeter(), "greeter-system")system ! Greeter.Greet("World")

Pro Tip

Never call methods directly on an actor instance or share its mutable state outside the actor — always communicate through its ActorRef with messages, or you lose Akka's single-threaded-per-actor safety guarantee.

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