Scala counter not updating when Akka message is received - scala

Question

I'm trying to make a small Akka example work using the following code:
class Sender extends Actor {
#volatile var numEchoes = 0
def receive = {
case Echo => {
numEchoes += 1
println(numEchoes)
if(numEchoes < Main.NUMBER_OF_ECHOES) {
println("Heard an echo...")
}
else {
// all echoes have been received.
println("All echoes heard.")
context.system.terminate
}
}
}
}
This actor is going to receive Echo messages from several Receiver actors:
class Receiver extends Actor {
def receive = {
case Echo => sender ! Echo
}
}
However, numEchoes always prints out 1. If I was doing something wrong, I'd expect 0, but this value makes me believe something else is at play here, but I'm unable to figure out what it is.
The rest of the code is just sending this specific actor a certain number of messages (lets assume 10). I see Heard an echo... printed out 10 times, but the value of this variable does not change.

Answer 1

#wheaties was correct. The error was in the Main object, due to some late and careless copy pasting... When I was creating 1 Sender and 10 Receiver actors, this is the code I was using:
// Create the actor that will send out the messages
val sender = actorSystem.actorOf(Props[Sender], "sender")
var actorList = List[ActorRef]()
for(i <- 1 to NUMBER_OF_ECHOES) {
val receiver = actorSystem.actorOf(Props[Sender], "receiver"+i)
actorList ::= receiver
}
Of course, creating the receivers as Senders is completely wrong, so all I had to do was fix the typo and correctly spawn the actors:
// Create the actor that will send out the messages
val sender = actorSystem.actorOf(Props[Sender], "sender")
var actorList = List[ActorRef]()
for(i <- 1 to NUMBER_OF_ECHOES) {
val receiver = actorSystem.actorOf(Props[Receiver], "receiver"+i)
actorList ::= receiver
}