FuturesAndPromises.scala

package org.example
import scala.concurrent.{ Future, Promise, future, promise }
import scala.concurrent.ExecutionContext.Implicits.global

class FuturesAndPromises

object FuturesAndPromises {

  def main(args: Array[String]) {
    futureSample
    println
    println
    promiseSample
  }

  private def futureSample: Unit = {
    println("Future sample starts")

    // Create a future with a likely long time of completion
    val f: Future[String] = future {

      for (i ← 1 to 1000000) {}

      // You can throw an exception which will call the onComplete and onFailure callbacks
      //throw new IllegalArgumentException("Something wrong")

      // Or you can return a proper value which will call the onComplete and onSuccess callbacks 
      "Sofoklis"
    }

    registerCallbacks(f)

    println("Future loop start")
    for (i ← 1 to 10000000) {}
    println("Future Sample exit")
  }

  private def promiseSample: Unit = {
    println("Promise Sample starts")
    // Create a promise
    val p: Promise[String] = promise[String]

    // Get the associated future
    val f = p.future

    registerCallbacks(f)

    // you complete the future by 
    p success "Sofoklis"
    // or by, note that for a specific promise you can use success or failure only once 
    // p failure new IllegalArgumentException("Something went wrong")
    // you can use these methods without the fear of an exception happening
    // but if the promise is complete they have no effect the try... methods return true
    // if the 

    println(p trySuccess "Sofoklis")
    println(p tryFailure new IllegalArgumentException("Something went wrong"))

    println("Promise loop start")
    for (i ← 1 to 10000000) {}
    println("Promise sample exit")

  }

  private def registerCallbacks(f: scala.concurrent.Future[String]): Unit = {

    f onSuccess {
      case s ⇒ println("success " + s)
    }

    f onComplete {
      case s ⇒ println("complete " + s)
    }

    f onFailure {
      case ex ⇒ println("failure " + ex.getMessage)
    }
  }

}