added new examples

Author: TofigBakhshiyev

README.md

@@ -1,2 +1,70 @@
 ## Scala Concurrent Learn
 Learn about scala futures and promises, concurrent programming
+
+#### Scala Future Basics
+
+Learn about Futures and how to print its results, Feature is used for read. [example code](src/main/scala/FuturesAndPromises/ScalaFuture.scala)
+
+#### Scala Promise
+
+Promise can be written (normally only once), Promise is used for write.
+[example code](src/main/scala/FuturesAndPromises/ScalaPromise.scala)
+
+#### Scala Concurrent example
+
+How to do calculation concurrently with Features. [example code](src/main/scala/FuturesAndPromises/ExampleConcurrent.scala)
+
+#### Scala Synchronous example
+
+How to do calculation synchronously with Features, used Await.result to wait result. [example code](src/main/scala/FuturesAndPromises/ExampleSynchronous.scala)
+
+#### Scala Parallel calculation example
+
+How to do calculation parallel with Features, used Future.sequence.
+[example code](src/main/scala/FuturesAndPromises/ExampleParallel.scala)
+
+#### Scala Parallel-2 calculation example
+
+How to do calculation parallel with Features, used Future.traverse, traverse and sequence are similar, difference is that traverse
+easily convert all the Option[Int] into just Int type.
+[example code](src/main/scala/FuturesAndPromises/ExampleParallel2.scala)
+
+#### Scala Zip two features example
+
+The Future.zip will create a new future, whose return type will be a tuple holding the return types of the two futures.
+[example code-1](src/main/scala/FuturesAndPromises/ExampleFutureZip.scala), [example dode-2](src/main/scala/FuturesAndPromises/ExampleReadingFile.scala)
+
+#### Scala FoldLeft example
+
+The foldLeft on your future operations will be run asynchronously from left to right.
+[example code](src/main/scala/FuturesAndPromises/ExampleFoldLeft.scala)
+
+#### Scala ReduceLeft example
+
+The reduceLeft is similar with foldLeft, however, reduceLeft() does not allow you to provide a default value.
+[example code](src/main/scala/FuturesAndPromises/ExampleReduceLeft.scala)
+
+#### Scala FutureThen example
+
+The andThen is used for passing partialFunction.
+[example code](src/main/scala/FuturesAndPromises/ExampleFutureThen.scala)
+
+#### Scala FirstCompletedOf callback function example
+
+The firstCompletedOf return any one of the futures which finish first.
+[example code](src/main/scala/FuturesAndPromises/ExampleFirstCompletedOf.scala)
+
+#### Scala ExecutionContext example
+
+In this example, learn how to create single threaded executionContext.
+[example code](src/main/scala/FuturesAndPromises/ExampleExecutionContext.scala)
+
+#### Scala Future recover example
+
+The recover function recovers error message.
+[example code](src/main/scala/FuturesAndPromises/ExampleFutureRecover.scala)
+
+#### More resources for concurrent and parallel programming in Scala
+- [Scala Futures for Beginners](http://allaboutscala.com/tutorials/chapter-9-beginner-tutorial-using-scala-futures/#futures-introduction)
+- [Monix](https://monix.io/)
+- [Akka Actors](https://doc.akka.io/docs/akka/current/typed/actors.html#:~:text=SayHello(%22Akka%22))%3B,running%20many%20actors%2C%20per%20JVM.)

src/main/scala/FuturesAndPromises/ExampleFutureRecover.scala

@@ -9,31 +9,33 @@ import scala.util.{Failure, Success}
  * */
 object ExampleFutureRecover {
   def main(args: Array[String]): Unit = {
-    def checkIsBig(number: Int): Future[Int] =
-      if (number > 0) Future.successful(10) else throw new IllegalStateException("number is negative")
+
+    def checkIsBig(number: Int): Future[Int] = Future {
+      if(number > 0) number
+      else throw new IllegalStateException("number is negative")
+    }
 
     checkIsBig(-1)
-      .recover{ case error: IllegalStateException if error.getMessage == "number is negative" => 0 }
+      .recover { case e: IllegalStateException if e.getMessage == "number is negative" => 0 }
       .onComplete {
-        case Success(result) =>
-          println(s"Result: $result")
-        case Failure(e) =>
-          println(s"error: ${e}")
+        case Success(donutStock)  => println(s"Results $donutStock")
+        case Failure(e)           => println(s"Error processing future operations, error = ${e.getMessage}")
       }
 
     // recoverWith,
     // Call Future.recoverWith to recover from a known exception
     checkIsBig(-1)
       .recoverWith{
         case error: IllegalStateException if error.getMessage == "number is negative" =>
-          Future.successful(0)
+          Future.successful(1)
       }
       .onComplete{
         case Success(result) =>
           println(s"Result: $result")
         case Failure(e) =>
           println(s"error: ${e}")
       }
+
     Thread.sleep(100)
   }
 }