Merge branch 'master' into extension-objects

abstract-factory/README.md

@@ -27,6 +27,22 @@ Use the Abstract Factory pattern when
 * a system should be configured with one of multiple families of products
 * a family of related product objects is designed to be used together, and you need to enforce this constraint
 * you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
+* the lifetime of the dependency is conceptually shorter than the lifetime of the consumer.
+*	you need a run-time value to construct a particular dependency
+*	you want to decide which product to call from a family at runtime.
+*	you need to supply one or more parameters only known at run-time before you can resolve a dependency.
+
+## Use Cases:	
+
+*	Selecting to call the appropriate implementation of FileSystemAcmeService or DatabaseAcmeService or NetworkAcmeService at runtime.
+*	Unit test case writing becomes much easier
+
+## Consequences:
+
+*	Dependency injection in java hides the service class dependencies that can lead to runtime errors that would have been caught at compile time.
+
+
+
 
 ## Real world examples
 

data-bus/src/main/java/com/iluwatar/databus/AbstractDataType.java

@@ -1,3 +1,25 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
 /*
 The MIT License (MIT)
 

data-bus/src/main/java/com/iluwatar/databus/DataType.java

@@ -1,3 +1,25 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
 /*
 The MIT License (MIT)
 

data-bus/src/main/java/com/iluwatar/databus/Member.java

@@ -1,3 +1,25 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
 /*
 The MIT License (MIT)
 

data-bus/src/test/java/com/iluwatar/databus/DataBusTest.java

@@ -1,3 +1,25 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
 package com.iluwatar.databus;
 
 import org.junit.Before;

data-bus/src/test/java/com/iluwatar/databus/members/MessageCollectorMemberTest.java

@@ -1,3 +1,25 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
 package com.iluwatar.databus.members;
 
 import com.iluwatar.databus.data.MessageData;

data-bus/src/test/java/com/iluwatar/databus/members/StatusMemberTest.java

@@ -1,3 +1,25 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
 package com.iluwatar.databus.members;
 
 import com.iluwatar.databus.DataBus;

dependency-injection/src/main/java/com/iluwatar/dependency/injection/AdvancedSorceress.java

@@ -0,0 +1,65 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.dependency.injection;
+
+/**
+ * The MIT License
+ * Copyright (c) 2014-2017 Ilkka Seppälä
+ * <p>
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+
+/**
+ * AdvancedSorceress implements inversion of control. It depends on abstraction that can be injected
+ * through its setter.
+ */
+public class AdvancedSorceress implements Wizard {
+
+  private Tobacco tobacco;
+
+  public void setTobacco(Tobacco tobacco) {
+    this.tobacco = tobacco;
+  }
+
+  @Override
+  public void smoke() {
+    tobacco.smoke(this);
+  }
+}

dependency-injection/src/main/java/com/iluwatar/dependency/injection/App.java

@@ -1,17 +1,17 @@
 /**
  * The MIT License
  * Copyright (c) 2014-2016 Ilkka Seppälä
- *
+ * <p>
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
- *
+ * <p>
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
- *
+ * <p>
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
@@ -26,7 +26,6 @@ import com.google.inject.Guice;
 import com.google.inject.Injector;
 
 /**
- * 
  * Dependency Injection pattern deals with how objects handle their dependencies. The pattern
  * implements so called inversion of control principle. Inversion of control has two specific rules:
  * - High-level modules should not depend on low-level modules. Both should depend on abstractions.
@@ -36,21 +35,21 @@ import com.google.inject.Injector;
  * naive implementation violating the inversion of control principle. It depends directly on a
  * concrete implementation which cannot be changed.
  * <p>
- * The second wizard ({@link AdvancedWizard}) is more flexible. It does not depend on any concrete
- * implementation but abstraction. It utilizes Dependency Injection pattern allowing its
- * {@link Tobacco} dependency to be injected through its constructor. This way, handling the
- * dependency is no longer the wizard's responsibility. It is resolved outside the wizard class.
+ * The second and third wizards({@link AdvancedWizard} and {@link AdvancedSorceress}) are more flexible.
+ * They do not depend on any concrete implementation but abstraction. They utilizes Dependency Injection
+ * pattern allowing their {@link Tobacco} dependency to be injected through constructor ({@link AdvancedWizard})
+ * or setter ({@link AdvancedSorceress}). This way, handling the dependency is no longer the wizard's
+ * responsibility. It is resolved outside the wizard class.
  * <p>
- * The third example takes the pattern a step further. It uses Guice framework for Dependency
+ * The fourth example takes the pattern a step further. It uses Guice framework for Dependency
  * Injection. {@link TobaccoModule} binds a concrete implementation to abstraction. Injector is then
  * used to create {@link GuiceWizard} object with correct dependencies.
- *
  */
 public class App {
 
   /**
    * Program entry point
-   * 
+   *
    * @param args command line args
    */
   public static void main(String[] args) {
@@ -60,6 +59,10 @@ public class App {
     AdvancedWizard advancedWizard = new AdvancedWizard(new SecondBreakfastTobacco());
     advancedWizard.smoke();
 
+    AdvancedSorceress advancedSorceress = new AdvancedSorceress();
+    advancedSorceress.setTobacco(new SecondBreakfastTobacco());
+    advancedSorceress.smoke();
+
     Injector injector = Guice.createInjector(new TobaccoModule());
     GuiceWizard guiceWizard = injector.getInstance(GuiceWizard.class);
     guiceWizard.smoke();

dependency-injection/src/test/java/com/iluwatar/dependency/injection/AdvancedSorceressTest.java

@@ -0,0 +1,76 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.dependency.injection;
+
+import com.iluwatar.dependency.injection.utils.InMemoryAppender;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Date: 28/04/17 - 7:40 AM
+ *
+ * @author Stanislav Kapinus
+ */
+
+public class AdvancedSorceressTest {
+
+  private InMemoryAppender appender;
+
+  @Before
+  public void setUp() {
+    appender = new InMemoryAppender(Tobacco.class);
+  }
+
+  @After
+  public void tearDown() {
+    appender.stop();
+  }
+
+  /**
+   * Test if the {@link AdvancedSorceress} smokes whatever instance of {@link Tobacco} is passed to her
+   * through the setter's parameter
+   */
+  @Test
+  public void testSmokeEveryThing() throws Exception {
+
+    final Tobacco[] tobaccos = {
+        new OldTobyTobacco(), new RivendellTobacco(), new SecondBreakfastTobacco()
+    };
+
+    for (final Tobacco tobacco : tobaccos) {
+      final AdvancedSorceress advancedSorceress = new AdvancedSorceress();
+      advancedSorceress.setTobacco(tobacco);
+      advancedSorceress.smoke();
+      // Verify if the sorceress is smoking the correct tobacco ...
+      assertEquals("AdvancedSorceress smoking " + tobacco.getClass().getSimpleName(), appender.getLastMessage());
+
+    }
+
+    // ... and nothing else is happening.
+    assertEquals(tobaccos.length, appender.getLogSize());
+
+  }
+}

event-driven-architecture/README.md

@@ -32,7 +32,7 @@ Use an Event-driven architecture when
 
 ## Credits
 
-* [Event-driven architecture - Wikipedia](http://www.computerweekly.com/feature/Write-through-write-around-write-back-Cache-explained)
+* [Event-driven architecture - Wikipedia](https://en.wikipedia.org/wiki/Event-driven_architecture)
 * [Fundamental Components of an Event-Driven Architecture](http://giocc.com/fundamental-components-of-an-event-driven-architecture.html)
 * [Real World Applications/Event Driven Applications](https://wiki.haskell.org/Real_World_Applications/Event_Driven_Applications)
 * [Event-driven architecture definition](http://searchsoa.techtarget.com/definition/event-driven-architecture)

event-queue/README.md

@@ -0,0 +1,29 @@
+---
+layout: pattern
+title: Event Queue
+folder: event-queue
+permalink: /patterns/event-queue/
+categories: Concurrency
+tags:
+ - Java
+ - Difficulty Intermediate
+ - Queue
+---
+
+## Intent
+Event Queue is a good pattern if You have a limited accesibility resource (for example: 
+Audio or Database), but You need to handle all the requests that want to use that.
+It puts all the requests in a queue and process them asynchronously.
+Gives the resource for the event when it is the next in the queue and in same time
+removes it from the queue.
+
+![alt text](./etc/model.png "Event Queue")
+
+## Applicability
+Use the Event Queue pattern when
+
+* You have a limited accesibility resource and the asynchronous process is acceptable to reach that
+
+## Credits
+
+* [Mihaly Kuprivecz - Event Queue] (http://gameprogrammingpatterns.com/event-queue.html)

event-queue/etc/event-queue.urm.puml

@@ -0,0 +1,26 @@
+@startuml
+package com.iluwatar.event.queue {
+  class App {
+    + App()
+    + getAudioStream(filePath : String) : AudioInputStream {static}
+    + main(args : String[]) {static}
+  }
+  class Audio {
+    - MAX_PENDING : int {static}
+    - headIndex : int {static}
+    - pendingAudio : PlayMessage[] {static}
+    - tailIndex : int {static}
+    - updateThread : Thread {static}
+    + Audio()
+    + init() {static}
+    + playSound(stream : AudioInputStream, volume : float) {static}
+    + stopService() {static}
+    + update() {static}
+  }
+  class PlayMessage {
+    ~ stream : AudioInputStream
+    ~ volume : float
+    + PlayMessage()
+  }
+}
+@enduml

event-queue/etc/model.ucls

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.0" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
+  <class id="1" language="java" name="com.iluwatar.event.queue.Audio" project="event-queue" 
+    file="/event-queue/src/main/java/com/iluwatar/event/queue/Audio.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="285" y="179"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="2" language="java" name="com.iluwatar.event.queue.PlayMessage" project="event-queue" 
+    file="/event-queue/src/main/java/com/iluwatar/event/queue/PlayMessage.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="633" y="179"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <association id="3">    
+    <end type="SOURCE" refId="1" navigable="false">      
+      <attribute id="4" name="pendingAudio"/>      
+      <multiplicity id="5" minimum="0" maximum="2147483647"/>    
+    </end>    
+    <end type="TARGET" refId="2" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

event-queue/pom.xml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright (c) 2014-2016 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <artifactId>java-design-patterns</artifactId>
+    <groupId>com.iluwatar</groupId>
+    <version>1.16.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>event-queue</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

event-queue/src/main/java/com/iluwatar/event/queue/App.java

@@ -0,0 +1,59 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.event.queue;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+import javax.sound.sampled.UnsupportedAudioFileException;
+
+/**
+ * Event or message queues provide an asynchronous communications protocol, meaning that the sender
+ * and receiver of the message do not need to interact with the message queue at the same time. 
+ * Events or messages placed onto the queue are stored until the recipient retrieves them. Event 
+ * or message queues have implicit or explicit limits on the size of data that may be transmitted
+ * in a single message and the number of messages that may remain outstanding on the queue.
+ * A queue stores a series of notifications or requests in first-in, first-out order.
+ * Sending a notification enqueues the request and returns. The request processor then processes
+ * items from the queue at a later time.
+ */
+public class App {
+  /**
+   * Program entry point.
+   * 
+   * @param args command line args
+   * @throws IOException when there is a problem with the audio file loading
+   * @throws UnsupportedAudioFileException  when the loaded audio file is unsupported 
+   */
+  public static void main(String[] args) throws UnsupportedAudioFileException, IOException {
+    Audio.playSound(Audio.getAudioStream("./etc/Bass-Drum-1.wav"), -10.0f);
+    Audio.playSound(Audio.getAudioStream("./etc/Closed-Hi-Hat-1.wav"), -8.0f);
+    
+    System.out.println("Press Enter key to stop the program...");
+    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    br.read();
+    Audio.stopService();
+  }
+}

event-queue/src/main/java/com/iluwatar/event/queue/Audio.java

@@ -0,0 +1,169 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.event.queue;
+
+import java.io.File;
+import java.io.IOException;
+
+import javax.sound.sampled.AudioInputStream;
+import javax.sound.sampled.AudioSystem;
+import javax.sound.sampled.Clip;
+import javax.sound.sampled.LineUnavailableException;
+import javax.sound.sampled.UnsupportedAudioFileException;
+
+/**
+ * This class implements the Event Queue pattern.
+ * @author mkuprivecz
+ *
+ */
+public class Audio {
+
+  private static final int MAX_PENDING = 16;
+
+  private static int headIndex;
+
+  private static int tailIndex;
+
+  private static Thread updateThread = null;
+
+  private static PlayMessage[] pendingAudio = new PlayMessage[MAX_PENDING];
+
+  /**
+   * This method stops the Update Method's thread. 
+   */
+  public static synchronized void stopService() {
+    if (updateThread != null) {
+      updateThread.interrupt();
+    }
+  }
+  
+  /**
+   * This method stops the Update Method's thread. 
+   * @return boolean
+   */
+  public static synchronized boolean isServiceRunning() {
+    if (updateThread != null && updateThread.isAlive() ) {
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  /**
+   * Starts the thread for the Update Method pattern if it was not started previously.
+   * Also when the thread is is ready initializes the indexes of the queue 
+   */
+  public static void init() {
+    if (updateThread == null) {
+      updateThread = new Thread(new Runnable() {
+        public void run() {
+          while (!Thread.currentThread().isInterrupted()) {
+            Audio.update();
+          }
+        }
+      });
+    }
+    startThread();
+  }
+  
+  /**
+   * This is a synchronized thread starter
+   */
+  public static synchronized void startThread() {
+    if (!updateThread.isAlive()) {
+      updateThread.start();
+      headIndex = 0;
+      tailIndex = 0;
+    }
+  }
+
+  /**
+   * This method adds a new audio into the queue.
+   * @param stream is the AudioInputStream for the method
+   * @param volume is the level of the audio's volume 
+   */
+  public static void playSound(AudioInputStream stream, float volume) {
+    init();
+    // Walk the pending requests.
+    for (int i = headIndex; i != tailIndex; i = (i + 1) % MAX_PENDING) {
+      if (getPendingAudio()[i].getStream() == stream) {
+        // Use the larger of the two volumes.
+        getPendingAudio()[i].setVolume(Math.max(volume, getPendingAudio()[i].getVolume()));
+
+        // Don't need to enqueue.
+        return;
+      }
+    }
+    getPendingAudio()[tailIndex] = new PlayMessage(stream, volume);
+    tailIndex = (tailIndex + 1) % MAX_PENDING;
+  }
+  
+  /**
+   * This method uses the Update Method pattern.
+   * It takes the audio from the queue and plays it
+   */
+  public static void update() {
+    // If there are no pending requests, do nothing.
+    if (headIndex == tailIndex) {
+      return;
+    }
+    Clip clip = null;
+    try {
+      AudioInputStream audioStream = getPendingAudio()[headIndex].getStream();
+      headIndex++;
+      clip = AudioSystem.getClip();
+      clip.open(audioStream);
+      clip.start();
+    } catch (LineUnavailableException e) {
+      System.err.println("Error occoured while loading the audio: The line is unavailable");
+      e.printStackTrace();
+    } catch (IOException e) {
+      System.err.println("Input/Output error while loading the audio");
+      e.printStackTrace();
+    } catch (IllegalArgumentException e) {
+      System.err.println("The system doesn't support the sound: " + e.getMessage());
+    }
+  }
+
+  /**
+   * Returns the AudioInputStream of a file
+   * @param filePath is the path of the audio file
+   * @return AudioInputStream
+   * @throws UnsupportedAudioFileException when the audio file is not supported 
+   * @throws IOException when the file is not readable
+   */
+  public static AudioInputStream getAudioStream(String filePath) 
+      throws UnsupportedAudioFileException, IOException {
+    return AudioSystem.getAudioInputStream(new File(filePath).getAbsoluteFile());
+  }
+
+  /**
+   * Returns with the message array of the queue 
+   * @return PlayMessage[]
+   */
+  public static PlayMessage[] getPendingAudio() {
+    return pendingAudio;
+  }
+
+}

event-queue/src/main/java/com/iluwatar/event/queue/PlayMessage.java

@@ -0,0 +1,59 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.event.queue;
+
+import javax.sound.sampled.AudioInputStream;
+
+/**
+ * The Event Queue's queue will store the instances of this class.
+ * @author mkuprivecz
+ *
+ */
+public class PlayMessage {
+  
+  private AudioInputStream stream;
+  
+  private float volume;
+  
+  public PlayMessage(AudioInputStream stream, float volume) {
+    setStream(stream);
+    setVolume(volume);
+  }
+
+  public AudioInputStream getStream() {
+    return stream;
+  }
+
+  private void setStream(AudioInputStream stream) {
+    this.stream = stream;
+  }
+
+  public float getVolume() {
+    return volume;
+  }
+
+  public void setVolume(float volume) {
+    this.volume = volume;
+  }
+}

event-queue/src/test/java/com/iluwatar/event/queue/AudioTest.java

@@ -0,0 +1,77 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.event.queue;
+import static org.junit.Assert.*;
+
+import java.io.IOException;
+
+import javax.sound.sampled.UnsupportedAudioFileException;
+
+import org.junit.Test;
+
+/**
+ * Testing the Audio service of the Queue
+ * @author mkuprivecz
+ *
+ */
+public class AudioTest {
+
+  /**
+   * Test here that the playSound method works correctly
+   * @throws UnsupportedAudioFileException when the audio file is not supported 
+   * @throws IOException when the file is not readable
+   * @throws InterruptedException when the test is interrupted externally
+   */
+  @Test
+  public void testPlaySound() throws UnsupportedAudioFileException, IOException, InterruptedException {
+    Audio.playSound(Audio.getAudioStream("./etc/Bass-Drum-1.wav"), -10.0f);
+    // test that service is started
+    assertTrue(Audio.isServiceRunning());
+    // adding a small pause to be sure that the sound is ended
+    Thread.sleep(5000);
+    // test that service is finished
+    assertFalse(!Audio.isServiceRunning());
+  }
+  
+  /**
+   * Test here that the Queue
+   * @throws UnsupportedAudioFileException when the audio file is not supported 
+   * @throws IOException when the file is not readable
+   * @throws InterruptedException when the test is interrupted externally
+   */
+  @Test
+  public void testQueue() throws UnsupportedAudioFileException, IOException, InterruptedException {
+    Audio.playSound(Audio.getAudioStream("./etc/Bass-Drum-1.aif"), -10.0f);
+    Audio.playSound(Audio.getAudioStream("./etc/Bass-Drum-1.aif"), -10.0f);
+    Audio.playSound(Audio.getAudioStream("./etc/Bass-Drum-1.aif"), -10.0f);
+    assertTrue(Audio.getPendingAudio().length > 0);
+    // test that service is started
+    assertTrue(Audio.isServiceRunning());
+    // adding a small pause to be sure that the sound is ended
+    Thread.sleep(10000);
+    // test that service is finished
+    assertFalse(!Audio.isServiceRunning());
+  }
+
+}

feature-toggle/src/main/java/com/iluwatar/featuretoggle/App.java

@@ -25,6 +25,7 @@ package com.iluwatar.featuretoggle;
 
 import com.iluwatar.featuretoggle.pattern.Service;
 import com.iluwatar.featuretoggle.pattern.propertiesversion.PropertiesFeatureToggleVersion;
+import com.iluwatar.featuretoggle.pattern.tieredversion.TieredFeatureToggleVersion;
 import com.iluwatar.featuretoggle.user.User;
 import com.iluwatar.featuretoggle.user.UserGroup;
 import org.slf4j.Logger;
@@ -85,6 +86,8 @@ public class App {
     LOGGER.info(welcomeMessageturnedOff);
 
     // --------------------------------------------
+    
+    Service service2 = new TieredFeatureToggleVersion();
 
     final User paidUser = new User("Jamie Coder");
     final User freeUser = new User("Alan Defect");
@@ -92,8 +95,8 @@ public class App {
     UserGroup.addUserToPaidGroup(paidUser);
     UserGroup.addUserToFreeGroup(freeUser);
 
-    final String welcomeMessagePaidUser = service.getWelcomeMessage(paidUser);
-    final String welcomeMessageFreeUser = service.getWelcomeMessage(freeUser);
+    final String welcomeMessagePaidUser = service2.getWelcomeMessage(paidUser);
+    final String welcomeMessageFreeUser = service2.getWelcomeMessage(freeUser);
     LOGGER.info(welcomeMessageFreeUser);
     LOGGER.info(welcomeMessagePaidUser);
   }

marker/.gitignore

@@ -0,0 +1 @@
+/target/

marker/README.md

@@ -0,0 +1,30 @@
+---
+layout: pattern
+title: Marker Interface
+folder: marker
+permalink: /patterns/marker/
+categories: Design
+tags:
+ - Java
+ - Difficulty-Beginner
+---
+
+## Intent
+Using empty interfaces as markers to distinguish special treated objects.
+
+![alt text](./etc/MarkerDiagram.png "Marker Interface")
+
+## Applicability
+Use the Marker Interface pattern when
+
+* you want to identify the special objects from normal objects (to treat them differently)
+* you want to mark that some object is available for certain sort of operations
+
+## Real world examples
+
+* [javase.8.docs.api.java.io.Serializable](https://docs.oracle.com/javase/8/docs/api/java/io/Serializable.html)
+* [javase.8.docs.api.java.lang.Cloneable](https://docs.oracle.com/javase/8/docs/api/java/lang/Cloneable.html)
+
+## Credits
+
+* [Effective Java 2nd Edition by Joshua Bloch](https://www.amazon.com/Effective-Java-2nd-Joshua-Bloch/dp/0321356683)

marker/etc/MarkerDiagram.ucls

@@ -0,0 +1,41 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.0" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
+  <class id="1" language="java" name="Guard" project="marker" file="/marker/src/main/java/Guard.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="416" y="348"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <interface id="2" language="java" name="Permission" project="marker" file="/marker/src/main/java/Permission.java" 
+    binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="261" y="175"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <class id="3" language="java" name="Thief" project="marker" file="/marker/src/main/java/Thief.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="236" y="355"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <realization id="4">    
+    <end type="SOURCE" refId="1"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

marker/etc/marker.urm.puml

@@ -0,0 +1,2 @@
+@startuml
+@enduml

marker/pom.xml

@@ -0,0 +1,41 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+    The MIT License
+    Copyright (c) 2014-2016 Ilkka Seppälä
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <parent>
+    <artifactId>java-design-patterns</artifactId>
+    <groupId>com.iluwatar</groupId>
+    <version>1.16.0-SNAPSHOT</version>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+
+  <artifactId>marker</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+
+</project>

marker/src/main/java/App.java

@@ -0,0 +1,70 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Created by Alexis on 28-Apr-17.
+ * With Marker interface idea is to make empty interface and extend it.
+ * Basically it is just to identify the special objects from normal objects.
+ * Like in case of serialization , objects that need to be serialized must implement serializable interface
+ * (it is empty interface) and down the line writeObject() method must be checking
+ * if it is a instance of serializable or not.
+ * <p>
+ * Marker interface vs annotation
+ * Marker interfaces and marker annotations both have their uses,
+ * neither of them is obsolete or always better then the other one.
+ * If you want to define a type that does not have any new methods associated with it,
+ * a marker interface is the way to go.
+ * If you want to mark program elements other than classes and interfaces,
+ * to allow for the possibility of adding more information to the marker in the future,
+ * or to fit the marker into a framework that already makes heavy use of annotation types,
+ * then a marker annotation is the correct choice
+ */
+public class App {
+
+  /**
+   * Program entry point
+   *
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+
+    final Logger logger = LoggerFactory.getLogger(App.class);
+    Guard guard = new Guard();
+    Thief thief = new Thief();
+
+    if (guard instanceof Permission) {
+      guard.enter();
+    } else {
+      logger.info("You have no permission to enter, please leave this area");
+    }
+
+    if (thief instanceof Permission) {
+      thief.steal();
+    } else {
+      thief.doNothing();
+    }
+  }
+}
+

marker/src/main/java/Guard.java

@@ -0,0 +1,37 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Class defining Guard
+ */
+public class Guard implements Permission {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(Guard.class);
+
+  protected static void enter() {
+
+    LOGGER.info("You can enter");
+  }
+}

marker/src/main/java/Permission.java

@@ -0,0 +1,28 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+/**
+ * Interface without any methods
+ * Marker interface is based on that assumption
+ */
+public interface Permission {
+}

marker/src/main/java/Thief.java

@@ -0,0 +1,40 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Class defining Thief
+ */
+public class Thief {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(Thief.class);
+
+  protected static void steal() {
+    LOGGER.info("Steal valuable items");
+  }
+
+  protected static void doNothing() {
+    LOGGER.info("Pretend nothing happened and just leave");
+  }
+}

marker/src/test/java/AppTest.java

@@ -0,0 +1,35 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+import org.junit.Test;
+
+/**
+ * Application test
+ */
+public class AppTest {
+
+  @Test
+  public void test() {
+    String[] args = {};
+    App.main(args);
+  }
+}

marker/src/test/java/GuardTest.java

@@ -0,0 +1,38 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+import org.junit.Test;
+
+import static org.hamcrest.CoreMatchers.instanceOf;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Guard test
+ */
+public class GuardTest {
+
+  @Test
+  public void testGuard() {
+    Guard guard = new Guard();
+    assertThat(guard, instanceOf(Permission.class));
+  }
+}

marker/src/test/java/ThiefTest.java

@@ -0,0 +1,36 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+
+/**
+ * Thief test
+ */
+public class ThiefTest {
+  @Test
+  public void testThief() {
+    Thief thief = new Thief();
+    assertFalse(thief instanceof Permission);
+  }
+}

pom.xml

@@ -122,7 +122,7 @@
         <module>factory-kit</module>
         <module>feature-toggle</module>
         <module>value-object</module>
-		    <module>module</module>
+        <module>module</module>
         <module>monad</module>
         <module>mute-idiom</module>
         <module>mutex</module>
@@ -133,6 +133,7 @@
         <module>promise</module>
         <module>page-object</module>
         <module>event-asynchronous</module>
+        <module>event-queue</module>
         <module>queue-load-leveling</module>
         <module>object-mother</module>
         <module>data-bus</module>
@@ -140,6 +141,8 @@
         <module>guarded-suspension</module>
         <module>balking</module>
         <module>extension-objects</module>
+        <module>marker</module>
+
     </modules>
 
     <dependencyManagement>
@@ -303,23 +306,23 @@
                                     </action>
                                 </pluginExecution>
                                 <pluginExecution>
-                                	<pluginExecutionFilter>
-                                		<groupId>
-                                			com.github.markusmo3.urm
-                                		</groupId>
-                                		<artifactId>
-                                			urm-maven-plugin
-                                		</artifactId>
-                                		<versionRange>
-                                			[1.4.1,)
-                                		</versionRange>
-                                		<goals>
-                                			<goal>map</goal>
-                                		</goals>
-                                	</pluginExecutionFilter>
-                                	<action>
-                                		<ignore/>
-                                	</action>
+                                    <pluginExecutionFilter>
+                                        <groupId>
+                                            com.github.markusmo3.urm
+                                        </groupId>
+                                        <artifactId>
+                                            urm-maven-plugin
+                                        </artifactId>
+                                        <versionRange>
+                                            [1.4.1,)
+                                        </versionRange>
+                                        <goals>
+                                            <goal>map</goal>
+                                        </goals>
+                                    </pluginExecutionFilter>
+                                    <action>
+                                        <ignore/>
+                                    </action>
                                 </pluginExecution>
                             </pluginExecutions>
                         </lifecycleMappingMetadata>