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/DeviceGroup.java

@@ -0,0 +1,119 @@
+/**
+ * Copyright (C) 2009-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package jdocs.tutorial_3;
+
+import java.util.Set;
+import java.util.Map;
+import java.util.HashMap;
+
+import akka.actor.AbstractActor;
+import akka.actor.ActorRef;
+import akka.actor.Props;
+import akka.actor.Terminated;
+import akka.event.Logging;
+import akka.event.LoggingAdapter;
+
+import jdocs.tutorial_3.Device;
+import jdocs.tutorial_3.DeviceManager;
+
+//#device-group-full
+public class DeviceGroup extends AbstractActor {
+  private final LoggingAdapter log = Logging.getLogger(getContext().getSystem(), this);
+
+  final String groupId;
+
+  public DeviceGroup(String groupId) {
+    this.groupId = groupId;
+  }
+
+  //#device-group-register
+  public static Props props(String groupId) {
+    return Props.create(DeviceGroup.class, groupId);
+  }
+  //#device-group-register
+
+  public static final class RequestDeviceList {
+    final long requestId;
+
+    public RequestDeviceList(long requestId) {
+      this.requestId = requestId;
+    }
+  }
+
+  public static final class ReplyDeviceList {
+    final long requestId;
+    final Set<String> ids;
+
+    public ReplyDeviceList(long requestId, Set<String> ids) {
+      this.requestId = requestId;
+      this.ids = ids;
+    }
+  }
+  //#device-group-register
+//#device-group-register
+//#device-group-register
+//#device-group-remove
+
+  final Map<String, ActorRef> deviceIdToActor = new HashMap<>();
+  //#device-group-register
+  final Map<ActorRef, String> actorToDeviceId = new HashMap<>();
+  //#device-group-register
+
+  @Override
+  public void preStart() {
+    log.info("DeviceGroup {} started", groupId);
+  }
+
+  @Override
+  public void postStop() {
+    log.info("DeviceGroup {} stopped", groupId);
+  }
+
+  private void onTrackDevice(DeviceManager.RequestTrackDevice trackMsg) {
+    if (this.groupId.equals(trackMsg.groupId)) {
+      ActorRef deviceActor = deviceIdToActor.get(trackMsg.deviceId);
+      if (deviceActor != null) {
+        deviceActor.forward(trackMsg, getContext());
+      } else {
+        log.info("Creating device actor for {}", trackMsg.deviceId);
+        deviceActor = getContext().actorOf(Device.props(groupId, trackMsg.deviceId), "device-" + trackMsg.deviceId);
+        //#device-group-register
+        getContext().watch(deviceActor);
+        actorToDeviceId.put(deviceActor, trackMsg.deviceId);
+        //#device-group-register
+        deviceIdToActor.put(trackMsg.deviceId, deviceActor);
+        deviceActor.forward(trackMsg, getContext());
+      }
+    } else {
+      log.warning(
+              "Ignoring TrackDevice request for {}. This actor is responsible for {}.",
+              groupId, this.groupId
+      );
+    }
+  }
+
+  private void onDeviceList(RequestDeviceList r) {
+    getSender().tell(new ReplyDeviceList(r.requestId, deviceIdToActor.keySet()), getSelf());
+  }
+
+  private void onTerminated(Terminated t) {
+    ActorRef deviceActor = t.getActor();
+    String deviceId = actorToDeviceId.get(deviceActor);
+    log.info("Device actor for {} has been terminated", deviceId);
+    actorToDeviceId.remove(deviceActor);
+    deviceIdToActor.remove(deviceId);
+  }
+
+  @Override
+  public Receive createReceive() {
+    return receiveBuilder()
+            .match(DeviceManager.RequestTrackDevice.class, this::onTrackDevice)
+            .match(RequestDeviceList.class, this::onDeviceList)
+            .match(Terminated.class, this::onTerminated)
+            .build();
+  }
+}
+//#device-group-remove
+//#device-group-register
+//#device-group-full