Java example code for Getting Started

* WiP on Java version of new Hello World

Done:
- implementation for first 3 sections
- tests for first 2 sections

To do:
- formatting
- tests for section 3
- section 4 and 5
- hooking the fragments into the docs themselves

* Finish tutorial_03 conversion

* Converted tutorial 04

* Convert step 5 scala->java

* Reformat Java code (thx IntelliJ IDEA)

* Format using 2 spaces

Really it'd be neat to have something like scalariform for the Java code, too

* Make fields 'private final'

* Make message classes 'public static final'

* Use primitive long/double where possible

* sender() -> getSender()

* Static import of org.junit.Assert....

* Final actor fields

* println() the instruction to hit ENTER to quit

* Use jdocs package for quickstart, too

* Use helper methods for message handling

* Compare doubles specifying a delta

* Keep tutorial steps independent

akka-docs-new/src/test/java/jdocs/tutorial_3/DeviceTest.java

@@ -0,0 +1,94 @@
+/**
+ * Copyright (C) 2009-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package jdocs.tutorial_3;
+
+import akka.actor.ActorRef;
+import akka.actor.ActorSystem;
+import akka.testkit.javadsl.TestKit;
+
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+
+import org.scalatest.junit.JUnitSuite;
+
+import java.util.Optional;
+
+public class DeviceTest extends JUnitSuite {
+
+  static ActorSystem system;
+
+  @BeforeClass
+  public static void setup() {
+    system = ActorSystem.create();
+  }
+
+  @AfterClass
+  public static void teardown() {
+    TestKit.shutdownActorSystem(system);
+    system = null;
+  }
+
+  //#device-registration-tests
+  @Test
+  public void testReplyToRegistrationRequests() {
+    TestKit probe = new TestKit(system);
+    ActorRef deviceActor = system.actorOf(Device.props("group", "device"));
+
+    deviceActor.tell(new DeviceManager.RequestTrackDevice("group", "device"), probe.getRef());
+    probe.expectMsgClass(DeviceManager.DeviceRegistered.class);
+    assertEquals(deviceActor, probe.getLastSender());
+  }
+
+  @Test
+  public void testIgnoreWrongRegistrationRequests() {
+    TestKit probe = new TestKit(system);
+    ActorRef deviceActor = system.actorOf(Device.props("group", "device"));
+
+    deviceActor.tell(new DeviceManager.RequestTrackDevice("wrongGroup", "device"), probe.getRef());
+    probe.expectNoMsg();
+
+    deviceActor.tell(new DeviceManager.RequestTrackDevice("group", "wrongDevice"), probe.getRef());
+    probe.expectNoMsg();
+  }
+  //#device-registration-tests
+
+  //#device-read-test
+  @Test
+  public void testReplyWithEmptyReadingIfNoTemperatureIsKnown() {
+    TestKit probe = new TestKit(system);
+    ActorRef deviceActor = system.actorOf(Device.props("group", "device"));
+    deviceActor.tell(new Device.ReadTemperature(42L), probe.getRef());
+    Device.RespondTemperature response = probe.expectMsgClass(Device.RespondTemperature.class);
+    assertEquals(42L, response.requestId);
+    assertEquals(Optional.empty(), response.value);
+  }
+  //#device-read-test
+
+  //#device-write-read-test
+  @Test
+  public void testReplyWithLatestTemperatureReading() {
+    TestKit probe = new TestKit(system);
+    ActorRef deviceActor = system.actorOf(Device.props("group", "device"));
+
+    deviceActor.tell(new Device.RecordTemperature(1L, 24.0), probe.getRef());
+    assertEquals(1L, probe.expectMsgClass(Device.TemperatureRecorded.class).requestId);
+
+    deviceActor.tell(new Device.ReadTemperature(2L), probe.getRef());
+    Device.RespondTemperature response1 = probe.expectMsgClass(Device.RespondTemperature.class);
+    assertEquals(2L, response1.requestId);
+    assertEquals(Optional.of(24.0), response1.value);
+
+    deviceActor.tell(new Device.RecordTemperature(3L, 55.0), probe.getRef());
+    assertEquals(3L, probe.expectMsgClass(Device.TemperatureRecorded.class).requestId);
+
+    deviceActor.tell(new Device.ReadTemperature(4L), probe.getRef());
+    Device.RespondTemperature response2 = probe.expectMsgClass(Device.RespondTemperature.class);
+    assertEquals(4L, response2.requestId);
+    assertEquals(Optional.of(55.0), response2.value);
+  }
+  //#device-write-read-test
+
+}