Operator docs for Source.tick (#28225)

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

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2009-2019 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package jdocs.stream.operators.source;
+
+import akka.NotUsed;
+import akka.actor.Cancellable;
+import akka.actor.typed.ActorRef;
+import akka.actor.typed.ActorSystem;
+import akka.actor.typed.javadsl.AskPattern;
+import java.util.concurrent.CompletionStage;
+import java.time.Duration;
+
+import akka.japi.Pair;
+import akka.stream.javadsl.Flow;
+import akka.stream.javadsl.Source;
+
+public class Tick {
+
+  // not really a runnable example, these are just pretend
+  private ActorSystem<Void> system = null;
+  private ActorRef<MyActor.Command> myActor = null;
+
+  static class MyActor {
+    interface Command {}
+
+    static class Query implements Command {
+      public final ActorRef<Response> replyTo;
+
+      public Query(ActorRef<Response> replyTo) {
+        this.replyTo = replyTo;
+      }
+    }
+
+    static class Response {
+      public final String text;
+
+      public Response(String text) {
+        this.text = text;
+      }
+    }
+  }
+
+  void simple() {
+    // #simple
+    Source.tick(
+            Duration.ofSeconds(1), // delay of first tick
+            Duration.ofSeconds(1), // delay of subsequent ticks
+            "tick" // element emitted each tick
+            )
+        .runForeach(System.out::println, system);
+    // #simple
+  }
+
+  void pollSomething() {
+    // #poll-actor
+    Source<String, Cancellable> periodicActorResponse =
+        Source.tick(Duration.ofSeconds(1), Duration.ofSeconds(1), "tick")
+            .mapAsync(
+                1,
+                notUsed -> {
+                  CompletionStage<MyActor.Response> response =
+                      AskPattern.ask(
+                          myActor, MyActor.Query::new, Duration.ofSeconds(3), system.scheduler());
+                  return response;
+                })
+            .map(response -> response.text);
+    // #poll-actor
+
+    // #zip-latest
+    Flow<Integer, Pair<Integer, String>, NotUsed> zipWithLatestResponse =
+        Flow.of(Integer.class).zipLatest(periodicActorResponse);
+    // #zip-latest
+  }
+}