Merge pull request #583 from shaiktaj/patch-1

Updated ThreadSafeLazyLoadedivoryTower

abstract-document/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
     <artifactId>abstract-document</artifactId>
     <dependencies>

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
 

abstract-factory/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>abstract-factory</artifactId>
   <dependencies>

adapter/README.md

@@ -21,6 +21,9 @@ incompatible interfaces.
 
 ![alt text](./etc/adapter.png "Adapter")
 
+## General usage of Adapter Pattern: 
++ Wrappers used to adopt 3rd parties libraries and frameworks - most of the applications using third party libraries use adapters as a middle layer between the application and the 3rd party library to decouple the application from the library. If another library has to be used only an adapter for the new library is required without having to change the application code.
+
 ## Applicability
 Use the Adapter pattern when
 
@@ -28,6 +31,19 @@ Use the Adapter pattern when
 * you want to create a reusable class that cooperates with unrelated or unforeseen classes, that is, classes that don't necessarily have compatible interfaces
 * you need to use several existing subclasses, but it's impractical to adapt their interface by subclassing every one. An object adapter can adapt the interface of its parent class.
 
+## Consequences:
+Class and object adapters have different trade-offs. A class adapter
+
+*	adapts Adaptee to Target by committing to a concrete Adaptee class. As a consequence, a class adapter won’t work when we want to adapt a class and all its subclasses.
+*	let’s Adapter override some of Adaptee’s behavior, since Adapter is a subclass of Adaptee.
+*	introduces only one object, and no additional pointer indirection is needed to get to the adaptee.
+
+An object adapter	
+
+*	let’s a single Adapter work with many Adaptees—that is, the Adaptee itself and all of its subclasses (if any). The Adapter can also add functionality to all Adaptees at once.
+*	makes it harder to override Adaptee behavior. It will require subclassing Adaptee and making Adapter refer to the subclass rather than the Adaptee itself.
+
+
 ## Real world examples
 
 * [java.util.Arrays#asList()](http://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#asList%28T...%29)

adapter/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>adapter</artifactId>
   <dependencies>

aggregator-microservices/aggregator-service/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/information-microservice/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/inventory-microservice/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <artifactId>aggregator-microservices</artifactId>

api-gateway/api-gateway-service/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>api-gateway-service</artifactId>

api-gateway/image-microservice/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
 
   <modelVersion>4.0.0</modelVersion>

api-gateway/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>api-gateway</artifactId>

api-gateway/price-microservice/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
 
   <modelVersion>4.0.0</modelVersion>

async-method-invocation/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>async-method-invocation</artifactId>
   <dependencies>

balking/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
 

bridge/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>bridge</artifactId>
   <dependencies>

builder/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>builder</artifactId>
   <dependencies>

business-delegate/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.15.0</version>
+		<version>1.17.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>business-delegate</artifactId>
 	<dependencies>

caching/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>caching</artifactId>
   <dependencies>

callback/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>callback</artifactId>
   <dependencies>

chain/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>chain</artifactId>
   <dependencies>

command/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>command</artifactId>
   <dependencies>

composite/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>composite</artifactId>
   <dependencies>

converter/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <dependencies>

cqrs/README.md

@@ -0,0 +1,29 @@
+---
+layout: pattern
+title: CQRS
+folder: cqrs
+permalink: /patterns/cqrs/
+pumlid: 7SPR4a0m3030gt00pR_RH6I8QQFouFgC_TfHb6gkd5Q7FQBx363ub4rYpoMTZKuDrYXqDX37HIuuyCPfPPTDfuuHREhGqBy0NUR0GNzAMYizMtq1
+categories: Architectural
+tags:
+ - Java
+ - Difficulty-Intermediate
+---
+
+## Intent
+CQRS Command Query Responsibility Segregation - Separate the query side from the command side.
+
+![alt text](./etc/cqrs.png "CQRS")
+
+## Applicability
+Use the CQRS pattern when
+
+* you want to scale the queries and commands independently.
+* you want to use different data models for queries and commands. Useful when dealing with complex domains.
+* you want to use architectures like event sourcing or task based UI.
+
+## Credits
+
+* [Greg Young - CQRS, Task Based UIs, Event Sourcing agh!](http://codebetter.com/gregyoung/2010/02/16/cqrs-task-based-uis-event-sourcing-agh/)
+* [Martin Fowler - CQRS](https://martinfowler.com/bliki/CQRS.html)
+* [Oliver Wolf - CQRS for Great Good](https://www.youtube.com/watch?v=Ge53swja9Dw)

cqrs/etc/cqrs.ucls

@@ -0,0 +1,115 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.0" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
+  associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
+  <interface id="1" language="java" name="com.iluwatar.cqrs.commandes.ICommandService" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/commandes/ICommandService.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="291" y="-49"/>    
+    <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="2" language="java" name="com.iluwatar.cqrs.commandes.CommandServiceImpl" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/commandes/CommandServiceImpl.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="263" width="256" x="170" y="87"/>    
+    <display autosize="false" 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="3" language="java" name="com.iluwatar.cqrs.queries.IQueryService" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/queries/IQueryService.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="182" width="248" x="176" y="428"/>    
+    <display autosize="false" 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="4" language="java" name="com.iluwatar.cqrs.queries.QueryServiceImpl" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/queries/QueryServiceImpl.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="258" width="253" x="169" y="665"/>    
+    <display autosize="false" 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="5" language="java" name="com.iluwatar.cqrs.domain.model.Book" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/domain/model/Book.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="326" width="158" x="778" y="-93"/>    
+    <display autosize="false" 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="6" language="java" name="com.iluwatar.cqrs.dto.Book" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/dto/Book.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="219" width="150" x="541" y="607"/>    
+    <display autosize="false" 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="7" language="java" name="com.iluwatar.cqrs.domain.model.Author" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/domain/model/Author.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="608" y="70"/>    
+    <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="8" language="java" name="com.iluwatar.cqrs.dto.Author" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/dto/Author.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="834" y="719"/>    
+    <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="9" language="java" name="com.iluwatar.cqrs.util.HibernateUtil" project="cqrs" 
+    file="/cqrs/src/main/java/com/iluwatar/cqrs/util/HibernateUtil.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="662" y="412"/>    
+    <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>  
+  <dependency id="10">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="9"/>  
+  </dependency>  
+  <dependency id="11">    
+    <end type="SOURCE" refId="2"/>    
+    <end type="TARGET" refId="9"/>  
+  </dependency>  
+  <realization id="12">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="3"/>  
+  </realization>  
+  <association id="13">    
+    <end type="SOURCE" refId="5" navigable="false">      
+      <attribute id="14" name="author"/>      
+      <multiplicity id="15" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="7" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <realization id="16">    
+    <end type="SOURCE" refId="2"/>    
+    <end type="TARGET" refId="1"/>  
+  </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>

cqrs/etc/cqrs.urm.puml

@@ -0,0 +1,124 @@
+@startuml
+package com.iluwatar.cqrs.util {
+  class HibernateUtil {
+    - LOGGER : Logger {static}
+    - SESSIONFACTORY : SessionFactory {static}
+    + HibernateUtil()
+    - buildSessionFactory() : SessionFactory {static}
+    + getSessionFactory() : SessionFactory {static}
+  }
+}
+package com.iluwatar.cqrs.app {
+  class App {
+    + App()
+    + main(args : String[]) {static}
+  }
+}
+package com.iluwatar.cqrs.dto {
+  class Author {
+    - email : String
+    - name : String
+    - username : String
+    + Author()
+    + Author(name : String, email : String, username : String)
+    + equals(obj : Object) : boolean
+    + getEmail() : String
+    + getName() : String
+    + getUsername() : String
+    + hashCode() : int
+    + toString() : String
+  }
+  class Book {
+    - price : double
+    - title : String
+    + Book()
+    + Book(title : String, price : double)
+    + equals(obj : Object) : boolean
+    + getPrice() : double
+    + getTitle() : String
+    + hashCode() : int
+    + toString() : String
+  }
+}
+package com.iluwatar.cqrs.commandes {
+  class CommandServiceImpl {
+    - sessionFactory : SessionFactory
+    + CommandServiceImpl()
+    + authorCreated(username : String, name : String, email : String)
+    + authorEmailUpdated(username : String, email : String)
+    + authorNameUpdated(username : String, name : String)
+    + authorUsernameUpdated(oldUsername : String, newUsername : String)
+    + bookAddedToAuthor(title : String, price : double, username : String)
+    + bookPriceUpdated(title : String, price : double)
+    + bookTitleUpdated(oldTitle : String, newTitle : String)
+    - getAuthorByUsername(username : String) : Author
+    - getBookByTitle(title : String) : Book
+  }
+  interface ICommandService {
+    + authorCreated(String, String, String) {abstract}
+    + authorEmailUpdated(String, String) {abstract}
+    + authorNameUpdated(String, String) {abstract}
+    + authorUsernameUpdated(String, String) {abstract}
+    + bookAddedToAuthor(String, double, String) {abstract}
+    + bookPriceUpdated(String, double) {abstract}
+    + bookTitleUpdated(String, String) {abstract}
+  }
+}
+package com.iluwatar.cqrs.queries {
+  interface IQueryService {
+    + getAuthorBooks(String) : List<Book> {abstract}
+    + getAuthorBooksCount(String) : BigInteger {abstract}
+    + getAuthorByUsername(String) : Author {abstract}
+    + getAuthorsCount() : BigInteger {abstract}
+    + getBook(String) : Book {abstract}
+  }
+  class QueryServiceImpl {
+    - sessionFactory : SessionFactory
+    + QueryServiceImpl()
+    + getAuthorBooks(username : String) : List<Book>
+    + getAuthorBooksCount(username : String) : BigInteger
+    + getAuthorByUsername(username : String) : Author
+    + getAuthorsCount() : BigInteger
+    + getBook(title : String) : Book
+  }
+}
+package com.iluwatar.cqrs.domain.model {
+  class Author {
+    - email : String
+    - id : long
+    - name : String
+    - username : String
+    # Author()
+    + Author(username : String, name : String, email : String)
+    + getEmail() : String
+    + getId() : long
+    + getName() : String
+    + getUsername() : String
+    + setEmail(email : String)
+    + setId(id : long)
+    + setName(name : String)
+    + setUsername(username : String)
+    + toString() : String
+  }
+  class Book {
+    - author : Author
+    - id : long
+    - price : double
+    - title : String
+    # Book()
+    + Book(title : String, price : double, author : Author)
+    + getAuthor() : Author
+    + getId() : long
+    + getPrice() : double
+    + getTitle() : String
+    + setAuthor(author : Author)
+    + setId(id : long)
+    + setPrice(price : double)
+    + setTitle(title : String)
+    + toString() : String
+  }
+}
+Book -->  "-author" Author
+CommandServiceImpl ..|> ICommandService 
+QueryServiceImpl ..|> IQueryService 
+@enduml

cqrs/pom.xml

@@ -0,0 +1,42 @@
+<?xml version="1.0"?>
+<!-- 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
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+	xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>com.iluwatar</groupId>
+		<artifactId>java-design-patterns</artifactId>
+		<version>1.17.0-SNAPSHOT</version>
+	</parent>
+	<artifactId>cqrs</artifactId>
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>com.h2database</groupId>
+			<artifactId>h2</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.hibernate</groupId>
+			<artifactId>hibernate-core</artifactId>
+		</dependency>
+	</dependencies>
+</project>

cqrs/src/main/java/com/iluwatar/cqrs/app/App.java

@@ -0,0 +1,95 @@
+/**
+ * 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.cqrs.app;
+
+import java.math.BigInteger;
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.iluwatar.cqrs.commandes.CommandServiceImpl;
+import com.iluwatar.cqrs.commandes.ICommandService;
+import com.iluwatar.cqrs.dto.Author;
+import com.iluwatar.cqrs.dto.Book;
+import com.iluwatar.cqrs.queries.IQueryService;
+import com.iluwatar.cqrs.queries.QueryServiceImpl;
+import com.iluwatar.cqrs.util.HibernateUtil;
+
+/**
+ * CQRS : Command Query Responsibility Segregation. A pattern used to separate query services from commands or writes
+ * services. The pattern is very simple but it has many consequences. For example, it can be used to tackle down a
+ * complex domain, or to use other architectures that were hard to implement with the classical way.
+ * 
+ * This implementation is an example of managing books and authors in a library. The persistence of books and authors is
+ * done according to the CQRS architecture. A command side that deals with a data model to persist(insert,update,delete)
+ * objects to a database. And a query side that uses native queries to get data from the database and return objects as
+ * DTOs (Data transfer Objects).
+ *
+ */
+public class App {
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * Program entry point
+   * 
+   * @param args
+   *          command line args
+   */
+  public static void main(String[] args) {
+    ICommandService commands = new CommandServiceImpl();
+
+    // Create Authors and Books using CommandService
+    commands.authorCreated("eEvans", "Eric Evans", "eEvans@email.com");
+    commands.authorCreated("jBloch", "Joshua Bloch", "jBloch@email.com");
+    commands.authorCreated("mFowler", "Martin Fowler", "mFowler@email.com");
+
+    commands.bookAddedToAuthor("Domain-Driven Design", 60.08, "eEvans");
+    commands.bookAddedToAuthor("Effective Java", 40.54, "jBloch");
+    commands.bookAddedToAuthor("Java Puzzlers", 39.99, "jBloch");
+    commands.bookAddedToAuthor("Java Concurrency in Practice", 29.40, "jBloch");
+    commands.bookAddedToAuthor("Patterns of Enterprise Application Architecture", 54.01, "mFowler");
+    commands.bookAddedToAuthor("Domain Specific Languages", 48.89, "mFowler");
+    commands.authorNameUpdated("eEvans", "Eric J. Evans");
+
+    IQueryService queries = new QueryServiceImpl();
+
+    // Query the database using QueryService
+    Author nullAuthor = queries.getAuthorByUsername("username");
+    Author eEvans = queries.getAuthorByUsername("eEvans");
+    BigInteger jBlochBooksCount = queries.getAuthorBooksCount("jBloch");
+    BigInteger authorsCount = queries.getAuthorsCount();
+    Book dddBook = queries.getBook("Domain-Driven Design");
+    List<Book> jBlochBooks = queries.getAuthorBooks("jBloch");
+
+    LOGGER.info("Author username : {}", nullAuthor);
+    LOGGER.info("Author eEvans : {}", eEvans);
+    LOGGER.info("jBloch number of books : {}", jBlochBooksCount);
+    LOGGER.info("Number of authors : {}", authorsCount);
+    LOGGER.info("DDD book : {}", dddBook);
+    LOGGER.info("jBloch books : {}", jBlochBooks);
+
+    HibernateUtil.getSessionFactory().close();
+  }
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/commandes/CommandServiceImpl.java

@@ -0,0 +1,145 @@
+/**
+ * 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.cqrs.commandes;
+
+import org.hibernate.Query;
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+
+import com.iluwatar.cqrs.domain.model.Author;
+import com.iluwatar.cqrs.domain.model.Book;
+import com.iluwatar.cqrs.util.HibernateUtil;
+
+/**
+ * This class is an implementation of {@link ICommandService} interface. It uses Hibernate as an api for persistence.
+ *
+ */
+public class CommandServiceImpl implements ICommandService {
+
+  private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
+
+  private Author getAuthorByUsername(String username) {
+    Author author = null;
+    try (Session session = sessionFactory.openSession()) {
+      Query query = session.createQuery("from Author where username=:username");
+      query.setParameter("username", username);
+      author = (Author) query.uniqueResult();
+    }
+    if (author == null) {
+      HibernateUtil.getSessionFactory().close();
+      throw new NullPointerException("Author " + username + " doesn't exist!");
+    }
+    return author;
+  }
+
+  private Book getBookByTitle(String title) {
+    Book book = null;
+    try (Session session = sessionFactory.openSession()) {
+      Query query = session.createQuery("from Book where title=:title");
+      query.setParameter("title", title);
+      book = (Book) query.uniqueResult();
+    }
+    if (book == null) {
+      HibernateUtil.getSessionFactory().close();
+      throw new NullPointerException("Book " + title + " doesn't exist!");
+    }
+    return book;
+  }
+
+  @Override
+  public void authorCreated(String username, String name, String email) {
+    Author author = new Author(username, name, email);
+    try (Session session = sessionFactory.openSession()) {
+      session.beginTransaction();
+      session.save(author);
+      session.getTransaction().commit();
+    }
+  }
+
+  @Override
+  public void bookAddedToAuthor(String title, double price, String username) {
+    Author author = getAuthorByUsername(username);
+    Book book = new Book(title, price, author);
+    try (Session session = sessionFactory.openSession()) {
+      session.beginTransaction();
+      session.save(book);
+      session.getTransaction().commit();
+    }
+  }
+
+  @Override
+  public void authorNameUpdated(String username, String name) {
+    Author author = getAuthorByUsername(username);
+    author.setName(name);
+    try (Session session = sessionFactory.openSession()) {
+      session.beginTransaction();
+      session.update(author);
+      session.getTransaction().commit();
+    }
+  }
+
+  @Override
+  public void authorUsernameUpdated(String oldUsername, String newUsername) {
+    Author author = getAuthorByUsername(oldUsername);
+    author.setUsername(newUsername);
+    try (Session session = sessionFactory.openSession()) {
+      session.beginTransaction();
+      session.update(author);
+      session.getTransaction().commit();
+    }
+  }
+
+  @Override
+  public void authorEmailUpdated(String username, String email) {
+    Author author = getAuthorByUsername(username);
+    author.setEmail(email);
+    try (Session session = sessionFactory.openSession()) {
+      session.beginTransaction();
+      session.update(author);
+      session.getTransaction().commit();
+    }
+  }
+
+  @Override
+  public void bookTitleUpdated(String oldTitle, String newTitle) {
+    Book book = getBookByTitle(oldTitle);
+    book.setTitle(newTitle);
+    try (Session session = sessionFactory.openSession()) {
+      session.beginTransaction();
+      session.update(book);
+      session.getTransaction().commit();
+    }
+  }
+
+  @Override
+  public void bookPriceUpdated(String title, double price) {
+    Book book = getBookByTitle(title);
+    book.setPrice(price);
+    try (Session session = sessionFactory.openSession()) {
+      session.beginTransaction();
+      session.update(book);
+      session.getTransaction().commit();
+    }
+  }
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/commandes/ICommandService.java

@@ -0,0 +1,45 @@
+/**
+ * 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.cqrs.commandes;
+
+/**
+ * This interface represents the commands of the CQRS pattern
+ *
+ */
+public interface ICommandService {
+
+  void authorCreated(String username, String name, String email);
+
+  void bookAddedToAuthor(String title, double price, String username);
+
+  void authorNameUpdated(String username, String name);
+
+  void authorUsernameUpdated(String oldUsername, String newUsername);
+
+  void authorEmailUpdated(String username, String email);
+
+  void bookTitleUpdated(String oldTitle, String newTitle);
+
+  void bookPriceUpdated(String title, double price);
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/domain/model/Author.java

@@ -0,0 +1,100 @@
+/**
+ * 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.cqrs.domain.model;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+/**
+ * This is an Author entity. It is used by Hibernate for persistence.
+ *
+ */
+@Entity
+public class Author {
+  @Id
+  @GeneratedValue(strategy = GenerationType.IDENTITY)
+  private long id;
+  private String username;
+  private String name;
+  private String email;
+
+  /**
+   * 
+   * @param username
+   *          username of the author
+   * @param name
+   *          name of the author
+   * @param email
+   *          email of the author
+   */
+  public Author(String username, String name, String email) {
+    super();
+    this.username = username;
+    this.name = name;
+    this.email = email;
+  }
+
+  protected Author() {
+    super();
+  }
+
+  public long getId() {
+    return id;
+  }
+
+  public void setId(long id) {
+    this.id = id;
+  }
+
+  public String getUsername() {
+    return username;
+  }
+
+  public void setUsername(String username) {
+    this.username = username;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public void setName(String name) {
+    this.name = name;
+  }
+
+  public String getEmail() {
+    return email;
+  }
+
+  public void setEmail(String email) {
+    this.email = email;
+  }
+
+  @Override
+  public String toString() {
+    return "Author [name=" + name + ", email=" + email + "]";
+  }
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/domain/model/Book.java

@@ -0,0 +1,102 @@
+/**
+ * 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.cqrs.domain.model;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.ManyToOne;
+
+/**
+ * This is a Book entity. It is used by Hibernate for persistence. Many books can be written by one {@link Author}
+ *
+ */
+@Entity
+public class Book {
+  @Id
+  @GeneratedValue(strategy = GenerationType.IDENTITY)
+  private long id;
+  private String title;
+  private double price;
+  @ManyToOne
+  private Author author;
+
+  /**
+   * 
+   * @param title
+   *          title of the book
+   * @param price
+   *          price of the book
+   * @param author
+   *          author of the book
+   */
+  public Book(String title, double price, Author author) {
+    super();
+    this.title = title;
+    this.price = price;
+    this.author = author;
+  }
+
+  protected Book() {
+    super();
+  }
+
+  public long getId() {
+    return id;
+  }
+
+  public void setId(long id) {
+    this.id = id;
+  }
+
+  public String getTitle() {
+    return title;
+  }
+
+  public void setTitle(String title) {
+    this.title = title;
+  }
+
+  public double getPrice() {
+    return price;
+  }
+
+  public void setPrice(double price) {
+    this.price = price;
+  }
+
+  public Author getAuthor() {
+    return author;
+  }
+
+  public void setAuthor(Author author) {
+    this.author = author;
+  }
+
+  @Override
+  public String toString() {
+    return "Book [title=" + title + ", price=" + price + ", author=" + author + "]";
+  }
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/dto/Author.java

@@ -0,0 +1,93 @@
+/**
+ * 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.cqrs.dto;
+
+import java.util.Objects;
+
+/**
+ * 
+ * This is a DTO (Data Transfer Object) author, contains only useful information to be returned
+ *
+ */
+public class Author {
+
+  private String name;
+  private String email;
+  private String username;
+
+  /**
+   * 
+   * @param name
+   *          name of the author
+   * @param email
+   *          email of the author
+   * @param username
+   *          username of the author
+   */
+  public Author(String name, String email, String username) {
+    super();
+    this.name = name;
+    this.email = email;
+    this.username = username;
+  }
+
+  public Author() {
+    super();
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public String getEmail() {
+    return email;
+  }
+
+  public String getUsername() {
+    return username;
+  }
+
+  @Override
+  public String toString() {
+    return "AuthorDTO [name=" + name + ", email=" + email + ", username=" + username + "]";
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(username, name, email);
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) {
+      return true;
+    }
+    if (!(obj instanceof Author)) {
+      return false;
+    }
+    Author other = (Author) obj;
+    return username.equals(other.getUsername()) && email.equals(other.getEmail()) && name.equals(other.getName());
+
+  }
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/dto/Book.java

@@ -0,0 +1,84 @@
+/**
+ * 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.cqrs.dto;
+
+import java.util.Objects;
+
+/**
+ * 
+ * This is a DTO (Data Transfer Object) book, contains only useful information to be returned
+ *
+ */
+public class Book {
+
+  private String title;
+  private double price;
+
+  /**
+   * 
+   * @param title
+   *          title of the book
+   * @param price
+   *          price of the book
+   */
+  public Book(String title, double price) {
+    super();
+    this.title = title;
+    this.price = price;
+  }
+
+  public Book() {
+    super();
+  }
+
+  public String getTitle() {
+    return title;
+  }
+
+  public double getPrice() {
+    return price;
+  }
+
+  @Override
+  public String toString() {
+    return "BookDTO [title=" + title + ", price=" + price + "]";
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(title, price);
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) {
+      return true;
+    }
+    if (!(obj instanceof Book)) {
+      return false;
+    }
+    Book book = (Book) obj;
+    return title.equals(book.getTitle()) && price == book.getPrice();
+  }
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/queries/IQueryService.java

@@ -0,0 +1,48 @@
+/**
+ * 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.cqrs.queries;
+
+import java.math.BigInteger;
+import java.util.List;
+
+import com.iluwatar.cqrs.dto.Author;
+import com.iluwatar.cqrs.dto.Book;
+
+/**
+ * 
+ * This interface represents the query methods of the CQRS pattern
+ *
+ */
+public interface IQueryService {
+
+  Author getAuthorByUsername(String username);
+
+  Book getBook(String title);
+
+  List<Book> getAuthorBooks(String username);
+
+  BigInteger getAuthorBooksCount(String username);
+
+  BigInteger getAuthorsCount();
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/queries/QueryServiceImpl.java

@@ -0,0 +1,105 @@
+/**
+ * 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.cqrs.queries;
+
+import java.math.BigInteger;
+import java.util.List;
+
+import org.hibernate.SQLQuery;
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+import org.hibernate.transform.Transformers;
+
+import com.iluwatar.cqrs.dto.Author;
+import com.iluwatar.cqrs.dto.Book;
+import com.iluwatar.cqrs.util.HibernateUtil;
+
+/**
+ * This class is an implementation of {@link IQueryService}. It uses Hibernate native queries to return DTOs from the
+ * database.
+ *
+ */
+public class QueryServiceImpl implements IQueryService {
+
+  private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
+
+  @Override
+  public Author getAuthorByUsername(String username) {
+    Author authorDTo = null;
+    try (Session session = sessionFactory.openSession()) {
+      SQLQuery sqlQuery = session
+          .createSQLQuery("SELECT a.username as \"username\", a.name as \"name\", a.email as \"email\""
+              + "FROM Author a where a.username=:username");
+      sqlQuery.setParameter("username", username);
+      authorDTo = (Author) sqlQuery.setResultTransformer(Transformers.aliasToBean(Author.class)).uniqueResult();
+    }
+    return authorDTo;
+  }
+
+  @Override
+  public Book getBook(String title) {
+    Book bookDTo = null;
+    try (Session session = sessionFactory.openSession()) {
+      SQLQuery sqlQuery = session
+          .createSQLQuery("SELECT b.title as \"title\", b.price as \"price\"" + " FROM Book b where b.title=:title");
+      sqlQuery.setParameter("title", title);
+      bookDTo = (Book) sqlQuery.setResultTransformer(Transformers.aliasToBean(Book.class)).uniqueResult();
+    }
+    return bookDTo;
+  }
+
+  @Override
+  public List<Book> getAuthorBooks(String username) {
+    List<Book> bookDTos = null;
+    try (Session session = sessionFactory.openSession()) {
+      SQLQuery sqlQuery = session.createSQLQuery("SELECT b.title as \"title\", b.price as \"price\""
+          + " FROM Author a , Book b where b.author_id = a.id and a.username=:username");
+      sqlQuery.setParameter("username", username);
+      bookDTos = sqlQuery.setResultTransformer(Transformers.aliasToBean(Book.class)).list();
+    }
+    return bookDTos;
+  }
+
+  @Override
+  public BigInteger getAuthorBooksCount(String username) {
+    BigInteger bookcount = null;
+    try (Session session = sessionFactory.openSession()) {
+      SQLQuery sqlQuery = session.createSQLQuery(
+          "SELECT count(b.title)" + " FROM  Book b, Author a where b.author_id = a.id and a.username=:username");
+      sqlQuery.setParameter("username", username);
+      bookcount = (BigInteger) sqlQuery.uniqueResult();
+    }
+    return bookcount;
+  }
+
+  @Override
+  public BigInteger getAuthorsCount() {
+    BigInteger authorcount = null;
+    try (Session session = sessionFactory.openSession()) {
+      SQLQuery sqlQuery = session.createSQLQuery("SELECT count(id) from Author");
+      authorcount = (BigInteger) sqlQuery.uniqueResult();
+    }
+    return authorcount;
+  }
+
+}

cqrs/src/main/java/com/iluwatar/cqrs/util/HibernateUtil.java

@@ -0,0 +1,58 @@
+/**
+ * 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.cqrs.util;
+
+import org.hibernate.SessionFactory;
+import org.hibernate.boot.MetadataSources;
+import org.hibernate.boot.registry.StandardServiceRegistry;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This class simply returns one instance of {@link SessionFactory} initialized when the application is started
+ *
+ */
+public class HibernateUtil {
+
+  private static final SessionFactory SESSIONFACTORY = buildSessionFactory();
+  private static final Logger LOGGER = LoggerFactory.getLogger(HibernateUtil.class);
+
+  private static SessionFactory buildSessionFactory() {
+
+    // configures settings from hibernate.cfg.xml
+    final StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure().build();
+    try {
+      return new MetadataSources(registry).buildMetadata().buildSessionFactory();
+    } catch (Exception ex) {
+      StandardServiceRegistryBuilder.destroy(registry);
+      LOGGER.error("Initial SessionFactory creation failed." + ex);
+      throw new ExceptionInInitializerError(ex);
+    }
+  }
+
+  public static SessionFactory getSessionFactory() {
+    return SESSIONFACTORY;
+  }
+
+}

cqrs/src/main/resources/hibernate.cfg.xml

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+
+    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.
+
+-->
+<!DOCTYPE hibernate-configuration SYSTEM
+"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
+
+<hibernate-configuration>
+    <session-factory>
+        <property name="dialect">org.hibernate.dialect.H2Dialect</property>
+        <property name="connection.driver_class">org.h2.Driver</property>
+        <property name="connection.url">jdbc:h2:mem:test</property>
+        <property name="connection.username">sa</property>
+        <property name="hbm2ddl.auto">create</property>
+        <mapping class="com.iluwatar.cqrs.domain.model.Author" />
+        <mapping class="com.iluwatar.cqrs.domain.model.Book" />
+    </session-factory>
+</hibernate-configuration>

cqrs/src/main/resources/logback.xml

@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    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.
+
+-->
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="info">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

cqrs/src/test/java/com/iluwatar/cqrs/IntegrationTest.java

@@ -0,0 +1,120 @@
+/**
+ * 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.cqrs;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.math.BigInteger;
+import java.util.List;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import com.iluwatar.cqrs.commandes.CommandServiceImpl;
+import com.iluwatar.cqrs.commandes.ICommandService;
+import com.iluwatar.cqrs.dto.Author;
+import com.iluwatar.cqrs.dto.Book;
+import com.iluwatar.cqrs.queries.IQueryService;
+import com.iluwatar.cqrs.queries.QueryServiceImpl;
+
+/**
+ * Integration test of IQueryService and ICommandService with h2 data
+ *
+ */
+public class IntegrationTest {
+
+  private static IQueryService queryService;
+  private static ICommandService commandService;
+
+  @BeforeClass
+  public static void initialize() {
+    commandService = new CommandServiceImpl();
+    queryService = new QueryServiceImpl();
+  }
+
+  @BeforeClass
+  public static void populateDatabase() {
+    // create first author1
+    commandService.authorCreated("username1", "name1", "email1");
+
+    // create author1 and update all its data
+    commandService.authorCreated("username2", "name2", "email2");
+    commandService.authorEmailUpdated("username2", "new_email2");
+    commandService.authorNameUpdated("username2", "new_name2");
+    commandService.authorUsernameUpdated("username2", "new_username2");
+
+    // add book1 to author1
+    commandService.bookAddedToAuthor("title1", 10, "username1");
+
+    // add book2 to author1 and update all its data
+    commandService.bookAddedToAuthor("title2", 20, "username1");
+    commandService.bookPriceUpdated("title2", 30);
+    commandService.bookTitleUpdated("title2", "new_title2");
+
+  }
+
+  @Test
+  public void testGetAuthorByUsername() {
+    Author author = queryService.getAuthorByUsername("username1");
+    assertEquals("username1", author.getUsername());
+    assertEquals("name1", author.getName());
+    assertEquals("email1", author.getEmail());
+  }
+
+  @Test
+  public void testGetUpdatedAuthorByUsername() {
+    Author author = queryService.getAuthorByUsername("new_username2");
+    Author expectedAuthor = new Author("new_name2", "new_email2", "new_username2");
+    assertEquals(expectedAuthor, author);
+
+  }
+
+  @Test
+  public void testGetBook() {
+    Book book = queryService.getBook("title1");
+    assertEquals("title1", book.getTitle());
+    assertEquals(10, book.getPrice(), 0);
+  }
+
+  @Test
+  public void testGetAuthorBooks() {
+    List<Book> books = queryService.getAuthorBooks("username1");
+    assertTrue(books.size() == 2);
+    assertTrue(books.contains(new Book("title1", 10)));
+    assertTrue(books.contains(new Book("new_title2", 30)));
+  }
+
+  @Test
+  public void testGetAuthorBooksCount() {
+    BigInteger bookCount = queryService.getAuthorBooksCount("username1");
+    assertEquals(new BigInteger("2"), bookCount);
+  }
+
+  @Test
+  public void testGetAuthorsCount() {
+    BigInteger authorCount = queryService.getAuthorsCount();
+    assertEquals(new BigInteger("2"), authorCount);
+  }
+
+}

cqrs/src/test/resources/hibernate.cfg.xml

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+
+    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.
+
+-->
+<!DOCTYPE hibernate-configuration SYSTEM
+"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
+
+<hibernate-configuration>
+    <session-factory>
+        <property name="dialect">org.hibernate.dialect.H2Dialect</property>
+        <property name="connection.driver_class">org.h2.Driver</property>
+        <property name="connection.url">jdbc:h2:mem:test</property>
+        <property name="connection.username">sa</property>
+        <property name="hbm2ddl.auto">create</property>
+        <mapping class="com.iluwatar.cqrs.domain.model.Author" />
+        <mapping class="com.iluwatar.cqrs.domain.model.Book" />
+    </session-factory>
+</hibernate-configuration>

cqrs/src/test/resources/logback.xml

@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    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.
+
+-->
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="info">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

dao/pom.xml

@@ -30,7 +30,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>dao</artifactId>
 

data-bus/.gitignore

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

data-bus/README.md

@@ -0,0 +1,33 @@
+---
+layout: pattern
+title: Data Bus
+folder: data-bus
+permalink: /patterns/data-bus/
+
+categories: Architectural
+tags:
+ - Java
+ - Difficulty-Intermediate
+---
+
+## Intent
+
+Allows send of messages/events between components of an application
+without them needing to know about each other. They only need to know
+about the type of the message/event being sent.
+
+![data bus pattern uml diagram](./etc/data-bus.urm.png "Data Bus pattern")
+
+## Applicability
+Use Data Bus pattern when
+
+* you want your components to decide themselves which messages/events they want to receive
+* you want to have many-to-many communication
+* you want your components to know nothing about each other
+
+## Related Patterns
+Data Bus is similar to
+
+* Mediator pattern with Data Bus Members deciding for themselves if they want to accept any given message
+* Observer pattern but supporting many-to-many communication
+* Publish/Subscribe pattern with the Data Bus decoupling the publisher and the subscriber

data-bus/etc/data-bus.urm.puml

@@ -0,0 +1,77 @@
+@startuml
+package com.iluwatar.databus {
+  class AbstractDataType {
+    - dataBus : DataBus
+    + AbstractDataType()
+    + getDataBus() : DataBus
+    + setDataBus(dataBus : DataBus)
+  }
+  ~class App {
+    - log : Logger {static}
+    ~ App()
+    + main(args : String[]) {static}
+  }
+  class DataBus {
+    - INSTANCE : DataBus {static}
+    - listeners : Set<Member>
+    + DataBus()
+    + getInstance() : DataBus {static}
+    + publish(event : DataType)
+    + subscribe(member : Member)
+    + unsubscribe(member : Member)
+  }
+  interface DataType {
+    + getDataBus() : DataBus {abstract}
+    + setDataBus(DataBus) {abstract}
+  }
+  interface Member {
+    + accept(DataType) {abstract}
+  }
+}
+package com.iluwatar.databus.data {
+  class MessageData {
+    - message : String
+    + MessageData(message : String)
+    + getMessage() : String
+    + of(message : String) : DataType {static}
+  }
+  class StartingData {
+    - when : LocalDateTime
+    + StartingData(when : LocalDateTime)
+    + getWhen() : LocalDateTime
+    + of(when : LocalDateTime) : DataType {static}
+  }
+  class StoppingData {
+    - when : LocalDateTime
+    + StoppingData(when : LocalDateTime)
+    + getWhen() : LocalDateTime
+    + of(when : LocalDateTime) : DataType {static}
+  }
+}
+package com.iluwatar.databus.members {
+  class CounterMember {
+    - log : Logger {static}
+    - name : String
+    + CounterMember(name : String)
+    + accept(data : DataType)
+    - handleEvent(data : MessageData)
+  }
+  class StatusMember {
+    - id : int
+    - log : Logger {static}
+    + StatusMember(id : int)
+    + accept(data : DataType)
+    - handleEvent(data : StartingData)
+    - handleEvent(data : StoppingData)
+  }
+}
+AbstractDataType -->  "-dataBus" DataBus
+DataBus -->  "-INSTANCE" DataBus
+DataBus -->  "-listeners" Member
+AbstractDataType ..|> DataType 
+MessageData --|> AbstractDataType 
+StartingData --|> AbstractDataType 
+StoppingData --|> AbstractDataType 
+CounterMember ..|> Member 
+StatusMember ..|> Member 
+@enduml

data-bus/pom.xml

@@ -0,0 +1,51 @@
+<?xml version="1.0"?>
+<!--
+
+    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 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+         xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+    <modelVersion>4.0.0</modelVersion>
+    <properties>
+        <lombok.version>1.16.14</lombok.version>
+    </properties>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.17.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>data-bus</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>

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

@@ -0,0 +1,67 @@
+/**
+ * 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)
+
+Copyright (c) 2016 Paul Campbell
+
+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;
+
+/**
+ * Base for data to send via the Data-Bus.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class AbstractDataType implements DataType {
+
+  private DataBus dataBus;
+
+  @Override
+  public DataBus getDataBus() {
+    return dataBus;
+  }
+
+  @Override
+  public void setDataBus(DataBus dataBus) {
+    this.dataBus = dataBus;
+  }
+}

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

@@ -0,0 +1,79 @@
+/**
+ * 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.databus;
+
+import com.iluwatar.databus.data.MessageData;
+import com.iluwatar.databus.data.StartingData;
+import com.iluwatar.databus.data.StoppingData;
+import com.iluwatar.databus.members.MessageCollectorMember;
+import com.iluwatar.databus.members.StatusMember;
+
+import java.time.LocalDateTime;
+
+/**
+ * The Data Bus pattern
+ * <p>
+ * <p>{@see http://wiki.c2.com/?DataBusPattern}</p>
+ * <p>
+ * <p>The Data-Bus pattern provides a method where different parts of an application may
+ * pass messages between each other without needing to be aware of the other's existence.</p>
+ * <p>Similar to the {@code ObserverPattern}, members register themselves with the {@link DataBus}
+ * and may then receive each piece of data that is published to the Data-Bus. The member
+ * may react to any given message or not.</p>
+ * <p>It allows for Many-to-Many distribution of data, as there may be any number of
+ * publishers to a Data-Bus, and any number of members receiving the data. All members
+ * will receive the same data, the order each receives a given piece of data, is an
+ * implementation detail.</p>
+ * <p>Members may unsubscribe from the Data-Bus to stop receiving data.</p>
+ * <p>This example of the pattern implements a Synchronous Data-Bus, meaning that
+ * when data is published to the Data-Bus, the publish method will not return until
+ * all members have received the data and returned.</p>
+ * <p>The {@link DataBus} class is a Singleton.</p>
+ * <p>Members of the Data-Bus must implement the {@link Member} interface.</p>
+ * <p>Data to be published via the Data-Bus must implement the {@link DataType} interface.</p>
+ * <p>The {@code data} package contains example {@link DataType} implementations.</p>
+ * <p>The {@code members} package contains example {@link Member} implementations.</p>
+ * <p>The {@link StatusMember} demonstrates using the DataBus to publish a message
+ * to the Data-Bus when it receives a message.</p>
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+class App {
+
+  public static void main(String[] args) {
+    final DataBus bus = DataBus.getInstance();
+    bus.subscribe(new StatusMember(1));
+    bus.subscribe(new StatusMember(2));
+    final MessageCollectorMember foo = new MessageCollectorMember("Foo");
+    final MessageCollectorMember bar = new MessageCollectorMember("Bar");
+    bus.subscribe(foo);
+    bus.publish(StartingData.of(LocalDateTime.now()));
+    bus.publish(MessageData.of("Only Foo should see this"));
+    bus.subscribe(bar);
+    bus.publish(MessageData.of("Foo and Bar should see this"));
+    bus.unsubscribe(foo);
+    bus.publish(MessageData.of("Only Bar should see this"));
+    bus.publish(StoppingData.of(LocalDateTime.now()));
+  }
+}

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

@@ -0,0 +1,73 @@
+/**
+ * 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.databus;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * The Data-Bus implementation.
+ *
+ * <p>This implementation uses a Singleton.</p>
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class DataBus {
+
+  private static final DataBus INSTANCE = new DataBus();
+
+  private final Set<Member> listeners = new HashSet<>();
+
+  public static DataBus getInstance() {
+    return INSTANCE;
+  }
+
+  /**
+   * Register a member with the data-bus to start receiving events.
+   *
+   * @param member The member to register
+   */
+  public void subscribe(final Member member) {
+    this.listeners.add(member);
+  }
+
+  /**
+   * Deregister a member to stop receiving events.
+   *
+   * @param member The member to deregister
+   */
+  public void unsubscribe(final Member member) {
+    this.listeners.remove(member);
+  }
+
+  /**
+   * Publish and event to all members.
+   *
+   * @param event The event
+   */
+  public void publish(final DataType event) {
+    event.setDataBus(this);
+    listeners.forEach(listener -> listener.accept(event));
+  }
+}

data-bus/src/main/java/com/iluwatar/databus/DataType.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.
+ */
+/*
+The MIT License (MIT)
+
+Copyright (c) 2016 Paul Campbell
+
+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;
+
+/**
+ * Events are sent via the Data-Bus.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+
+public interface DataType {
+
+  /**
+   * Returns the data-bus the event is being sent on.
+   *
+   * @return The data-bus
+   */
+  DataBus getDataBus();
+
+  /**
+   * Set the data-bus the event will be sent on.
+   *
+   * @param dataBus The data-bus
+   */
+  void setDataBus(DataBus dataBus);
+}

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

@@ -0,0 +1,59 @@
+/**
+ * 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)
+
+Copyright (c) 2016 Paul Campbell
+
+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 java.util.function.Consumer;
+
+/**
+ * Members receive events from the Data-Bus.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public interface Member extends Consumer<DataType> {
+
+  void accept(DataType event);
+}

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

@@ -0,0 +1,49 @@
+/**
+ * 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.databus.data;
+
+import com.iluwatar.databus.AbstractDataType;
+import com.iluwatar.databus.DataType;
+
+/**
+ * An event raised when a string message is sent.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class MessageData extends AbstractDataType {
+
+  private final String message;
+
+  public MessageData(String message) {
+    this.message = message;
+  }
+
+  public String getMessage() {
+    return message;
+  }
+
+  public static DataType of(final String message) {
+    return new MessageData(message);
+  }
+}

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

@@ -0,0 +1,51 @@
+/**
+ * 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.databus.data;
+
+import com.iluwatar.databus.AbstractDataType;
+import com.iluwatar.databus.DataType;
+
+import java.time.LocalDateTime;
+
+/**
+ * An event raised when applications starts, containing the start time of the application.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class StartingData extends AbstractDataType {
+
+  private final LocalDateTime when;
+
+  public StartingData(LocalDateTime when) {
+    this.when = when;
+  }
+
+  public LocalDateTime getWhen() {
+    return when;
+  }
+
+  public static DataType of(final LocalDateTime when) {
+    return new StartingData(when);
+  }
+}

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

@@ -0,0 +1,51 @@
+/**
+ * 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.databus.data;
+
+import com.iluwatar.databus.AbstractDataType;
+import com.iluwatar.databus.DataType;
+
+import java.time.LocalDateTime;
+
+/**
+ * An event raised when applications stops, containing the stop time of the application.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class StoppingData extends AbstractDataType {
+
+  private final LocalDateTime when;
+
+  public StoppingData(LocalDateTime when) {
+    this.when = when;
+  }
+
+  public LocalDateTime getWhen() {
+    return when;
+  }
+
+  public static DataType of(final LocalDateTime when) {
+    return new StoppingData(when);
+  }
+}

data-bus/src/main/java/com/iluwatar/databus/members/MessageCollectorMember.java

@@ -0,0 +1,67 @@
+/**
+ * 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.databus.members;
+
+import com.iluwatar.databus.DataType;
+import com.iluwatar.databus.Member;
+import com.iluwatar.databus.data.MessageData;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.logging.Logger;
+
+/**
+ * Receiver of Data-Bus events that collects the messages from each {@link MessageData}.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class MessageCollectorMember implements Member {
+
+  private static final Logger LOGGER = Logger.getLogger(MessageCollectorMember.class.getName());
+
+  private final String name;
+
+  private List<String> messages = new ArrayList<>();
+
+  public MessageCollectorMember(String name) {
+    this.name = name;
+  }
+
+  @Override
+  public void accept(final DataType data) {
+    if (data instanceof MessageData) {
+      handleEvent((MessageData) data);
+    }
+  }
+
+  private void handleEvent(MessageData data) {
+    LOGGER.info(String.format("%s sees message %s", name, data.getMessage()));
+    messages.add(data.getMessage());
+  }
+
+  public List<String> getMessages() {
+    return Collections.unmodifiableList(messages);
+  }
+}

data-bus/src/main/java/com/iluwatar/databus/members/StatusMember.java

@@ -0,0 +1,82 @@
+/**
+ * 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.databus.members;
+
+import com.iluwatar.databus.DataType;
+import com.iluwatar.databus.Member;
+import com.iluwatar.databus.data.MessageData;
+import com.iluwatar.databus.data.StartingData;
+import com.iluwatar.databus.data.StoppingData;
+
+import java.time.LocalDateTime;
+import java.util.logging.Logger;
+
+/**
+ * Receiver of Data-Bus events.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class StatusMember implements Member {
+
+  private static final Logger LOGGER = Logger.getLogger(StatusMember.class.getName());
+
+  private final int id;
+
+  private LocalDateTime started;
+
+  private LocalDateTime stopped;
+
+  public StatusMember(int id) {
+    this.id = id;
+  }
+
+  @Override
+  public void accept(final DataType data) {
+    if (data instanceof StartingData) {
+      handleEvent((StartingData) data);
+    } else if (data instanceof StoppingData) {
+      handleEvent((StoppingData) data);
+    }
+  }
+
+  private void handleEvent(StartingData data) {
+    started = data.getWhen();
+    LOGGER.info(String.format("Receiver #%d sees application started at %s", id, started));
+  }
+
+  private void handleEvent(StoppingData data) {
+    stopped = data.getWhen();
+    LOGGER.info(String.format("Receiver #%d sees application stopping at %s", id, stopped));
+    LOGGER.info(String.format("Receiver #%d sending goodbye message", id));
+    data.getDataBus().publish(MessageData.of(String.format("Goodbye cruel world from #%d!", id)));
+  }
+
+  public LocalDateTime getStarted() {
+    return started;
+  }
+
+  public LocalDateTime getStopped() {
+    return stopped;
+  }
+}

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

@@ -0,0 +1,74 @@
+/**
+ * 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;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import static org.mockito.BDDMockito.then;
+import static org.mockito.Mockito.never;
+
+/**
+ * Tests for {@link DataBus}.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class DataBusTest {
+
+  @Mock
+  private Member member;
+
+  @Mock
+  private DataType event;
+
+  @Before
+  public void setUp() {
+    MockitoAnnotations.initMocks(this);
+  }
+
+  @Test
+  public void publishedEventIsReceivedBySubscribedMember() {
+    //given
+    final DataBus dataBus = DataBus.getInstance();
+    dataBus.subscribe(member);
+    //when
+    dataBus.publish(event);
+    //then
+    then(member).should().accept(event);
+  }
+
+  @Test
+  public void publishedEventIsNotReceivedByMemberAfterUnsubscribing() {
+    //given
+    final DataBus dataBus = DataBus.getInstance();
+    dataBus.subscribe(member);
+    dataBus.unsubscribe(member);
+    //when
+    dataBus.publish(event);
+    //then
+    then(member).should(never()).accept(event);
+  }
+
+}

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

@@ -0,0 +1,62 @@
+/**
+ * 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;
+import com.iluwatar.databus.data.StartingData;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.time.LocalDateTime;
+
+/**
+ * Tests for {@link MessageCollectorMember}.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class MessageCollectorMemberTest {
+
+  @Test
+  public void collectMessageFromMessageData() {
+    //given
+    final String message = "message";
+    final MessageData messageData = new MessageData(message);
+    final MessageCollectorMember collector = new MessageCollectorMember("collector");
+    //when
+    collector.accept(messageData);
+    //then
+    Assert.assertTrue(collector.getMessages().contains(message));
+  }
+
+  @Test
+  public void collectIgnoresMessageFromOtherDataTypes() {
+    //given
+    final StartingData startingData = new StartingData(LocalDateTime.now());
+    final MessageCollectorMember collector = new MessageCollectorMember("collector");
+    //when
+    collector.accept(startingData);
+    //then
+    Assert.assertEquals(0, collector.getMessages().size());
+  }
+
+}

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

@@ -0,0 +1,79 @@
+/**
+ * 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;
+import com.iluwatar.databus.data.MessageData;
+import com.iluwatar.databus.data.StartingData;
+import com.iluwatar.databus.data.StoppingData;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.time.LocalDateTime;
+import java.time.Month;
+
+/**
+ * Tests for {@link StatusMember}.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public class StatusMemberTest {
+
+  @Test
+  public void statusRecordsTheStartTime() {
+    //given
+    final LocalDateTime startTime = LocalDateTime.of(2017, Month.APRIL, 1, 19, 9);
+    final StartingData startingData = new StartingData(startTime);
+    final StatusMember statusMember = new StatusMember(1);
+    //when
+    statusMember.accept(startingData);
+    //then
+    Assert.assertEquals(startTime, statusMember.getStarted());
+  }
+
+  @Test
+  public void statusRecordsTheStopTime() {
+    //given
+    final LocalDateTime stop = LocalDateTime.of(2017, Month.APRIL, 1, 19, 12);
+    final StoppingData stoppingData = new StoppingData(stop);
+    stoppingData.setDataBus(DataBus.getInstance());
+    final StatusMember statusMember = new StatusMember(1);
+    //when
+    statusMember.accept(stoppingData);
+    //then
+    Assert.assertEquals(stop, statusMember.getStopped());
+  }
+
+  @Test
+  public void statusIgnoresMessageData() {
+    //given
+    final MessageData messageData = new MessageData("message");
+    final StatusMember statusMember = new StatusMember(1);
+    //when
+    statusMember.accept(messageData);
+    //then
+    Assert.assertNull(statusMember.getStarted());
+    Assert.assertNull(statusMember.getStopped());
+  }
+
+}

data-mapper/pom.xml

@@ -28,7 +28,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.15.0</version>
+		<version>1.17.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>data-mapper</artifactId>
 	<dependencies>

decorator/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>decorator</artifactId>
   <dependencies>

delegation/pom.xml

@@ -30,7 +30,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

dependency-injection/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>dependency-injection</artifactId>
   <dependencies>

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());
+
+  }
+}

double-checked-locking/pom.xml

@@ -27,7 +27,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>double-checked-locking</artifactId>
   <dependencies>

double-dispatch/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>double-dispatch</artifactId>
   <dependencies>

event-aggregator/pom.xml

@@ -28,7 +28,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.15.0</version>
+		<version>1.17.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>event-aggregator</artifactId>
 	<dependencies>

event-asynchronous/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>event-asynchronous</artifactId>
   <dependencies>

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-driven-architecture/pom.xml

@@ -31,7 +31,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.15.0</version>
+        <version>1.17.0-SNAPSHOT</version>
     </parent>
 
     <artifactId>event-driven-architecture</artifactId>

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 Sepp<70>l<EFBFBD>
+
+    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>1.17.0-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());
+  }
+
+}

execute-around/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.15.0</version>
+    <version>1.17.0-SNAPSHOT</version>
   </parent>
   <artifactId>execute-around</artifactId>
   <dependencies>

extension-objects/README.md

@@ -0,0 +1,28 @@
+---
+layout: pattern
+title: Extension objects
+folder: extension-objects
+permalink: /patterns/extension-objects/
+categories: Behavioral
+tags:
+ - Java
+ - Difficulty-Intermediate
+---
+
+## Intent
+Anticipate that an object’s interface needs to be extended in the future. Additional
+interfaces are defined by extension objects.
+
+![Extension_objects](./etc/extension_obj.png "Extension objects")
+
+## Applicability
+Use the Extension Objects pattern when:
+
+* you need to support the addition of new or unforeseen interfaces to existing classes and you don't want to impact clients that don't need this new interface. Extension Objects lets you keep related operations together by defining them in a separate class
+* a class representing a key abstraction plays different roles for different clients. The number of roles the class can play should be open-ended. There is a need to preserve the key abstraction itself. For example, a customer object is still a customer object even if different subsystems view it differently.
+* a class should be extensible with new behavior without subclassing from it.
+
+## Real world examples
+
+* [OpenDoc](https://en.wikipedia.org/wiki/OpenDoc)
+* [Object Linking and Embedding](https://en.wikipedia.org/wiki/Object_Linking_and_Embedding)

extension-objects/etc/extension-objects.urm.puml

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

extension-objects/etc/extension_obj.ucls

@@ -0,0 +1,180 @@
+<?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="concreteextensions.Soldier" project="extension-objects" 
+    file="/extension-objects/src/main/java/concreteextensions/Soldier.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="483" y="339"/>    
+    <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="units.Unit" project="extension-objects" 
+    file="/extension-objects/src/main/java/units/Unit.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="192" y="115"/>    
+    <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="3" language="java" name="abstractextensions.SoldierExtension" project="extension-objects" 
+    file="/extension-objects/src/main/java/abstractextensions/SoldierExtension.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="510" y="229"/>    
+    <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>  
+  <interface id="4" language="java" name="abstractextensions.UnitExtension" project="extension-objects" 
+    file="/extension-objects/src/main/java/abstractextensions/UnitExtension.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="510" y="116"/>    
+    <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="5" language="java" name="units.SoldierUnit" project="extension-objects" 
+    file="/extension-objects/src/main/java/units/SoldierUnit.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="157" 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>  
+  <class id="6" language="java" name="concreteextensions.Sergeant" project="extension-objects" 
+    file="/extension-objects/src/main/java/concreteextensions/Sergeant.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="650" y="375"/>    
+    <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="7" language="java" name="abstractextensions.SergeantExtension" project="extension-objects" 
+    file="/extension-objects/src/main/java/abstractextensions/SergeantExtension.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="672" y="230"/>    
+    <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="8" language="java" name="units.SergeantUnit" project="extension-objects" 
+    file="/extension-objects/src/main/java/units/SergeantUnit.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="315" y="460"/>    
+    <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="9" language="java" name="units.CommanderUnit" project="extension-objects" 
+    file="/extension-objects/src/main/java/units/CommanderUnit.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="99" width="210" x="429" y="476"/>    
+    <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="10" language="java" name="concreteextensions.Commander" project="extension-objects" 
+    file="/extension-objects/src/main/java/concreteextensions/Commander.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="823" y="477"/>    
+    <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="11" language="java" name="abstractextensions.CommanderExtension" project="extension-objects" 
+    file="/extension-objects/src/main/java/abstractextensions/CommanderExtension.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="827" y="217"/>    
+    <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>  
+  <realization id="12">    
+    <end type="SOURCE" refId="1"/>    
+    <end type="TARGET" refId="3"/>  
+  </realization>  
+  <realization id="13">    
+    <end type="SOURCE" refId="10"/>    
+    <end type="TARGET" refId="11"/>  
+  </realization>  
+  <generalization id="14">    
+    <end type="SOURCE" refId="9"/>    
+    <end type="TARGET" refId="2"/>  
+  </generalization>  
+  <association id="15">    
+    <end type="SOURCE" refId="1" navigable="false">      
+      <attribute id="16" name="unit"/>      
+      <multiplicity id="17" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="5" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="18">    
+    <end type="SOURCE" refId="10" navigable="false">      
+      <attribute id="19" name="unit"/>      
+      <multiplicity id="20" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="9" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="21">    
+    <end type="SOURCE" refId="2" navigable="false">      
+      <attribute id="22" name="unitExtension"/>      
+      <multiplicity id="23" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="4" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <realization id="24">    
+    <end type="SOURCE" refId="6"/>    
+    <end type="TARGET" refId="7"/>  
+  </realization>  
+  <generalization id="25">    
+    <end type="SOURCE" refId="3"/>    
+    <end type="TARGET" refId="4"/>  
+  </generalization>  
+  <generalization id="26">    
+    <end type="SOURCE" refId="5"/>    
+    <end type="TARGET" refId="2"/>  
+  </generalization>  
+  <generalization id="27">    
+    <end type="SOURCE" refId="7"/>    
+    <end type="TARGET" refId="4"/>  
+  </generalization>  
+  <generalization id="28">    
+    <end type="SOURCE" refId="8"/>    
+    <end type="TARGET" refId="2"/>  
+  </generalization>  
+  <association id="29">    
+    <end type="SOURCE" refId="6" navigable="false">      
+      <attribute id="30" name="unit"/>      
+      <multiplicity id="31" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="8" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <generalization id="32">    
+    <end type="SOURCE" refId="11"/>    
+    <end type="TARGET" refId="4"/>  
+  </generalization>  
+  <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>

extension-objects/pom.xml

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    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.
+
+-->
+<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>1.17.0-SNAPSHOT</version>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+
+  <artifactId>extension-objects</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+</project>

extension-objects/src/main/java/App.java

@@ -0,0 +1,84 @@
+/**
+ * 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 abstractextensions.CommanderExtension;
+import abstractextensions.SergeantExtension;
+import abstractextensions.SoldierExtension;
+import units.CommanderUnit;
+import units.SergeantUnit;
+import units.SoldierUnit;
+import units.Unit;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Anticipate that an object’s interface needs to be extended in the future.
+ * Additional interfaces are defined by extension objects.
+ */
+public class App {
+
+  /**
+   * Program entry point
+   *
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+
+    //Create 3 different units
+    Unit soldierUnit = new SoldierUnit("SoldierUnit1");
+    Unit sergeantUnit = new SergeantUnit("SergeantUnit1");
+    Unit commanderUnit = new CommanderUnit("CommanderUnit1");
+
+    //check for each unit to have an extension
+    checkExtensionsForUnit(soldierUnit);
+    checkExtensionsForUnit(sergeantUnit);
+    checkExtensionsForUnit(commanderUnit);
+
+  }
+
+  private static void checkExtensionsForUnit(Unit unit) {
+    final Logger logger = LoggerFactory.getLogger(App.class);
+
+    SoldierExtension soldierExtension = (SoldierExtension) unit.getUnitExtension("SoldierExtension");
+    SergeantExtension sergeantExtension = (SergeantExtension) unit.getUnitExtension("SergeantExtension");
+    CommanderExtension commanderExtension = (CommanderExtension) unit.getUnitExtension("CommanderExtension");
+
+    //if unit have extension call the method
+    if (soldierExtension != null) {
+      soldierExtension.soldierReady();
+    } else {
+      logger.info(unit.getName() + " without SoldierExtension");
+    }
+
+    if (sergeantExtension != null) {
+      sergeantExtension.sergeantReady();
+    } else {
+      logger.info(unit.getName() + " without SergeantExtension");
+    }
+
+    if (commanderExtension != null) {
+      commanderExtension.commanderReady();
+    } else {
+      logger.info(unit.getName() + " without CommanderExtension");
+    }
+  }
+}

extension-objects/src/main/java/abstractextensions/CommanderExtension.java

@@ -0,0 +1,31 @@
+/**
+ * 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 abstractextensions;
+
+/**
+ * Interface with their method
+ */
+public interface CommanderExtension extends UnitExtension {
+
+  void commanderReady();
+}

extension-objects/src/main/java/abstractextensions/SergeantExtension.java

@@ -0,0 +1,31 @@
+/**
+ * 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 abstractextensions;
+
+/**
+ * Interface with their method
+ */
+public interface SergeantExtension extends UnitExtension {
+
+  void sergeantReady();
+}

extension-objects/src/main/java/abstractextensions/SoldierExtension.java

@@ -0,0 +1,30 @@
+/**
+ * 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 abstractextensions;
+
+/**
+ * Interface with their method
+ */
+public interface SoldierExtension extends UnitExtension {
+  void soldierReady();
+}

extension-objects/src/main/java/abstractextensions/UnitExtension.java

@@ -0,0 +1,29 @@
+/**
+ * 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 abstractextensions;
+
+/**
+ * Other Extensions will extend this interface
+ */
+public interface UnitExtension {
+}