Question

In following scala code:

object Timer
{
  def oncePerSecond(callback: () => Unit): Unit =
  {
    while (true)
    {
      callback()
      Thread.sleep(1000)
    }
  }

  def main(args: Array[String]): Unit =
  {
    oncePerSecond(() => 
      Console.println("Time flies... oh, you get the idea."))
  }
}

Is the anonymous function executed first when passed in as a parameter
and then again every second in the loop?

Answer 1

It’s executed as part of this:

while (true)
{
  callback()
  Thread.sleep(1000)
}

so it’ll execute every second, starting from when it’s passed in. It’s only executed in the loop. It wouldn’t be executed normally upon being passed in e.g.

def oncePerSecond(callback: () => Unit): Unit = {
   if (....) {
      callback()
   }
}

would only execute that method if a particular condition was satisfied.