Example for Source.fromIterator #25468 (#28582)

* add example for Source.fromIterator #25468

* scala fmt code style fix

* don't use test as a sample for docs

akka-docs/src/main/paradox/stream/operators/Source/fromIterator.md

@@ -19,6 +19,15 @@ for each materialization, which is the reason the @scala[`method`] @java[`factor
 
 If the iterator perform blocking operations, make sure to run it on a separate dispatcher.
 
+## Example
+ 
+Scala
+:   @@snip [From.scala](/akka-docs/src/test/scala/docs/stream/operators/source/From.scala) { #from-iterator }
+
+Java
+:   @@snip [From.java](/akka-docs/src/test/java/jdocs/stream/operators/source/From.java) { #from-iterator }
+
+
 ## Reactive Streams semantics
 
 @@@div { .callout }

akka-docs/src/test/java/jdocs/stream/operators/source/From.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package jdocs.stream.operators.source;
+
+import akka.actor.ActorSystem;
+import akka.stream.javadsl.Source;
+
+import java.util.Arrays;
+
+public class From {
+
+  private ActorSystem system = null;
+
+  void fromIteratorSample() {
+    // #from-iterator
+    Source.fromIterator(() -> Arrays.asList(1, 2, 3).iterator())
+        .runForeach(System.out::println, system);
+    // could print
+    // 1
+    // 2
+    // 3
+    // #from-iterator
+  }
+}

akka-docs/src/test/scala/docs/stream/operators/source/From.scala

@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.source
+
+import akka.actor.ActorSystem
+import akka.stream.scaladsl.Source
+
+object From {
+
+  implicit val system: ActorSystem = null
+
+  def fromIteratorSample(): Unit = {
+    //#from-iterator
+    Source.fromIterator(() => (1 to 3).iterator).runForeach(println)
+    // could print
+    // 1
+    // 2
+    // 3
+    //#from-iterator
+  }
+
+}