Adding example of fold for sink #25468

akka-docs/src/main/paradox/stream/operators/Sink/fold.md

@@ -18,6 +18,16 @@ Materializes into a @scala[`Future`] @java[`CompletionStage`] that will complete
 This operator allows combining values into a result without a global mutable state by instead passing the state along
 between invocations.
 
+## Example
+
+This example reads the numbers from a source and do some calculation in the flow part and in the end uses Sink.fold and adds the incoming elements.
+
+Scala
+:   @@snip [Fold.scala](/akka-docs/src/test/scala/docs/stream/operators/sink/Fold.scala) { #fold }
+
+Java
+:   @@snip [SinkDocExamples.java](/akka-docs/src/test/java/jdocs/stream/operators/SinkDocExamples.java) { #fold }
+
 ## Reactive Streams semantics
 
 @@@div { .callout }

akka-docs/src/test/java/jdocs/stream/operators/SinkDocExamples.java

@@ -105,6 +105,15 @@ public class SinkDocExamples {
     // #lastOption-operator-example
   }
 
+  static void foldExample() {
+    // #fold
+    Source<Integer, NotUsed> source = Source.range(1, 100);
+    CompletionStage<Integer> sum =
+        source.runWith(Sink.fold(0, (res, element) -> res + element), system);
+    sum.thenAccept(System.out::println);
+    // #fold
+  }
+
   static void ignoreExample() {
     // #ignore
     Source<String, NotUsed> lines = readLinesFromFile();

akka-docs/src/test/scala/docs/stream/operators/sink/Fold.scala

@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sink
+
+import akka.actor.ActorSystem
+import akka.stream.scaladsl.{ Sink, Source }
+
+import scala.concurrent.{ ExecutionContextExecutor, Future }
+
+object Fold {
+  implicit val system: ActorSystem = ???
+  implicit val ec: ExecutionContextExecutor = system.dispatcher
+  def foldExample: Future[Unit] = {
+    //#fold
+    val source = Source(1 to 100)
+    val result: Future[Int] = source.runWith(Sink.fold(0)((acc, element) => acc + element))
+    result.map(println)
+    //5050
+    //#fold
+  }
+}