Set version number for monthly release

Fix #216 Repository vs DAO

.travis.yml

@@ -1,20 +1,18 @@
 language: java
-
 jdk:
 - oraclejdk8
 
 env:
   global:
   - GH_REF: github.com/iluwatar/java-design-patterns.git
-  - secure: "LxTDuNS/rBWIvKkaEqr79ImZAe48mCdoYCF41coxNXgNoippo4GIBArknqtv+XvdkiuRZ1yGyj6pn8GU33c/yn+krddTUkVCwTbVatbalW5jhQjDbHYym/JcxaK9ZS/3JTeGcWrBgiPqHEEDhCf26vPZsXoMSeVCEORVKTp1BSg="
+  - secure: LxTDuNS/rBWIvKkaEqr79ImZAe48mCdoYCF41coxNXgNoippo4GIBArknqtv+XvdkiuRZ1yGyj6pn8GU33c/yn+krddTUkVCwTbVatbalW5jhQjDbHYym/JcxaK9ZS/3JTeGcWrBgiPqHEEDhCf26vPZsXoMSeVCEORVKTp1BSg=
   
 before_install:
-  - "export DISPLAY=:99.0"
+- export DISPLAY=:99.0
-  - "sh -e /etc/init.d/xvfb start"
+- sh -e /etc/init.d/xvfb start
 
 after_success:
 - mvn clean test jacoco:report coveralls:report
 - bash update-ghpages.sh
 
-# Migration to container-based infrastructure  
 sudo: false

CODE_COVERAGE.md

@@ -0,0 +1,13 @@
+# Code Coverage Report generation
+
+To generate the code coverage report, execute the following command:
+> mvn clean verify
+
+This will generate code coverage report in each of the modules. In order to view the same, open the following file in your browser.
+> target/site/jacoco/index.html 
+
+Please note that the above folder is created under each of the modules. For example:
+* adapter/target/site/jacoco/index.html 
+* busniess-delegate/target/site/jacoco/index.html 
+
+

README.md

@@ -26,7 +26,13 @@ are familiar with the patterns.
 Before you dive into the material, you should be familiar with various
 [Programming/Software Design Principles](http://webpro.github.io/programming-principles/).
 
-Once you are familiar with these concepts you can start drilling down into patterns by any of the following approaches
+All designs should be as simple as possible. You should start with KISS, YAGNI,
+and Do The Simplest Thing That Could Possibly Work principles. Complexity and
+patterns should only be introduced when they are needed for practical
+extensibility.
+
+Once you are familiar with these concepts you can start drilling down into
+patterns by any of the following approaches
 
  - Using difficulty tags, `Difficulty-Beginner`, `Difficulty-Intermediate` & `Difficulty-Expert`.
  - Using pattern categories, `Creational`, `Behavioral` and others.
@@ -38,7 +44,6 @@ If you are willing to contribute to the project you will find the relevant infor
 
 # Credits
 
-* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)
 * [Effective Java (2nd Edition)](http://www.amazon.com/Effective-Java-Edition-Joshua-Bloch/dp/0321356683)
 * [Java Generics and Collections](http://www.amazon.com/Java-Generics-Collections-Maurice-Naftalin/dp/0596527756/)
 * [Let's Modify the Objects-First Approach into Design-Patterns-First](http://edu.pecinovsky.cz/papers/2006_ITiCSE_Design_Patterns_First.pdf)
@@ -48,7 +53,6 @@ If you are willing to contribute to the project you will find the relevant infor
 * [Patterns of Enterprise Application Architecture](http://www.amazon.com/Patterns-Enterprise-Application-Architecture-Martin/dp/0321127420)
 * [Spring Data](http://www.amazon.com/Spring-Data-Mark-Pollack/dp/1449323952/ref=sr_1_1)
 * [J2EE Design Patterns](http://www.amazon.com/J2EE-Design-Patterns-William-Crawford/dp/0596004273/ref=sr_1_2)
-* [Pattern Oriented Software Architecture Vol I-V](http://www.amazon.com/Pattern-Oriented-Software-Architecture-Volume-Patterns/dp/0471958697)
 
 # License
 

abstract-factory/index.md

@@ -4,9 +4,13 @@ title: Abstract Factory
 folder: abstract-factory
 permalink: /patterns/abstract-factory/
 categories: Creational
-tags: Java
+tags: 
+ - Java
+ - Gang Of Four
 ---
 
+**Also known as:** Kit
+
 **Intent:** Provide an interface for creating families of related or dependent
 objects without specifying their concrete classes.
 
@@ -22,3 +26,7 @@ objects without specifying their concrete classes.
 **Real world examples:**
 
 * [javax.xml.parsers.DocumentBuilderFactory](http://docs.oracle.com/javase/8/docs/api/javax/xml/parsers/DocumentBuilderFactory.html)
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

abstract-factory/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>abstract-factory</artifactId>
   <dependencies>

abstract-factory/src/main/java/com/iluwatar/abstractfactory/App.java

@@ -3,12 +3,18 @@ package com.iluwatar.abstractfactory;
 
 /**
  * 
- * The essence of the Abstract Factory pattern is a factory interface
+ * The Abstract Factory pattern provides a way to encapsulate a group of individual factories that
- * ({@link KingdomFactory}) and its implementations ({@link ElfKingdomFactory},
+ * have a common theme without specifying their concrete classes. In normal usage, the client
- * {@link OrcKingdomFactory}).
+ * software creates a concrete implementation of the abstract factory and then uses the generic
+ * interface of the factory to create the concrete objects that are part of the theme. The client
+ * does not know (or care) which concrete objects it gets from each of these internal factories,
+ * since it uses only the generic interfaces of their products. This pattern separates the details
+ * of implementation of a set of objects from their general usage and relies on object composition,
+ * as object creation is implemented in methods exposed in the factory interface.
  * <p>
- * The example uses both concrete implementations to create a king, a castle and
+ * The essence of the Abstract Factory pattern is a factory interface ({@link KingdomFactory}) and
- * an army.
+ * its implementations ({@link ElfKingdomFactory}, {@link OrcKingdomFactory}). The example uses both
+ * concrete implementations to create a king, a castle and an army.
  * 
  */
 public class App {
@@ -17,8 +23,10 @@ public class App {
   private Castle castle;
   private Army army;
 
+
   /**
    * Creates kingdom
+   * 
    * @param factory
    */
   public void createKingdom(final KingdomFactory factory) {
@@ -70,4 +78,33 @@ public class App {
   private void setArmy(final Army army) {
     this.army = army;
   }
+  
+
+  /**
+   * Program entry point
+   * 
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+	  
+	  App app = new App();
+	  
+	  System.out.println("Elf Kingdom");
+	  KingdomFactory elfKingdomFactory;
+	  elfKingdomFactory = app.getElfKingdomFactory();
+	  app.createKingdom(elfKingdomFactory);
+	  System.out.println(app.getArmy().getDescription());
+	  System.out.println(app.getCastle().getDescription());
+	  System.out.println(app.getKing().getDescription());
+	
+	  System.out.println("\nOrc Kingdom");
+	  KingdomFactory orcKingdomFactory;
+	  orcKingdomFactory = app.getOrcKingdomFactory();
+	  app.createKingdom(orcKingdomFactory);
+	  System.out.println(app.getArmy().getDescription());
+	  System.out.println(app.getCastle().getDescription());
+	  System.out.println(app.getKing().getDescription());
+	  
+  }
+  
 }

abstract-factory/src/main/java/com/iluwatar/abstractfactory/OrcKingdomFactory.java

@@ -18,5 +18,4 @@ public class OrcKingdomFactory implements KingdomFactory {
   public Army createArmy() {
     return new OrcArmy();
   }
-
 }

abstract-factory/src/test/java/com/iluwatar/abstractfactory/AppTest.java

@@ -1,4 +1,5 @@
 package com.iluwatar.abstractfactory;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
@@ -7,7 +8,7 @@ import org.junit.Test;
 
 public class AppTest {
 
-	private App app = new App();;
+  private App app = new App();
   private KingdomFactory elfFactory;
   private KingdomFactory orcFactory;
 

adapter/index.md

@@ -4,9 +4,13 @@ title: Adapter
 folder: adapter
 permalink: /patterns/adapter/
 categories: Structural
-tags: Java
+tags:
+ - Java
+ - Gang Of Four
 ---
 
+**Also known as:** Wrapper
+
 **Intent:** Convert the interface of a class into another interface the clients
 expect. Adapter lets classes work together that couldn't otherwise because of
 incompatible interfaces.
@@ -22,3 +26,7 @@ incompatible interfaces.
 **Real world examples:**
 
 * [java.util.Arrays#asList()](http://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#asList%28T...%29)
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

adapter/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>adapter</artifactId>
   <dependencies>
@@ -15,5 +14,10 @@
       <artifactId>junit</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 </project>

adapter/src/main/java/com/iluwatar/adapter/App.java

@@ -1,25 +1,28 @@
 package com.iluwatar.adapter;
 
 /**
+ * An adapter helps two incompatible interfaces to work together. This is the real world definition
+ * for an adapter. Interfaces may be incompatible but the inner functionality should suit the need.
+ * The Adapter design pattern allows otherwise incompatible classes to work together by converting
+ * the interface of one class into an interface expected by the clients.
  * 
- * There are two variations of the Adapter pattern: The class adapter implements
+ * <p>There are two variations of the Adapter pattern: The class adapter implements the adaptee's
- * the adaptee's interface whereas the object adapter uses composition to
+ * interface whereas the object adapter uses composition to contain the adaptee in the adapter
- * contain the adaptee in the adapter object. This example uses the object
+ * object. This example uses the object adapter approach.
- * adapter approach.
- * <p>
- * The Adapter ({@link GnomeEngineer}) converts the interface of the target class
- * ({@link GoblinGlider}) into a suitable one expected by the client
- * ({@link GnomeEngineeringManager}).
  * 
+ * <p>The Adapter ({@link GnomeEngineer}) converts the interface of the target class (
+ * {@link GoblinGlider}) into a suitable one expected by the client ({@link GnomeEngineeringManager}
+ * ).
  */
 public class App {
 
   /**
-	 * Program entry point
+   * Program entry point.
+   *
    * @param args command line args
    */
   public static void main(String[] args) {
-		Engineer manager = new GnomeEngineeringManager();
+    Engineer manager = new GnomeEngineeringManager(new GnomeEngineer());
     manager.operateDevice();
   }
 }

adapter/src/main/java/com/iluwatar/adapter/Engineer.java

@@ -8,5 +8,4 @@ package com.iluwatar.adapter;
 public interface Engineer {
 
   void operateDevice();
-
 }

adapter/src/main/java/com/iluwatar/adapter/GnomeEngineer.java

@@ -2,8 +2,8 @@ package com.iluwatar.adapter;
 
 /**
  * 
- * Adapter class. Adapts the interface of the device ({@link GoblinGlider}) into
+ * Adapter class. Adapts the interface of the device ({@link GoblinGlider}) into {@link Engineer}
- * {@link Engineer} interface expected by the client ({@link GnomeEngineeringManager}).
+ * interface expected by the client ({@link GnomeEngineeringManager}).
  * 
  */
 public class GnomeEngineer implements Engineer {
@@ -20,5 +20,4 @@ public class GnomeEngineer implements Engineer {
     glider.gainSpeed();
     glider.takeOff();
   }
-
 }

adapter/src/main/java/com/iluwatar/adapter/GnomeEngineeringManager.java

@@ -1,20 +1,26 @@
 package com.iluwatar.adapter;
 
 /**
- * 
  * GnomeEngineering manager uses {@link Engineer} to operate devices.
- * 
  */
 public class GnomeEngineeringManager implements Engineer {
 
   private Engineer engineer;
 
   public GnomeEngineeringManager() {
-		engineer = new GnomeEngineer();
+
+  }
+
+  public GnomeEngineeringManager(Engineer engineer) {
+    this.engineer = engineer;
   }
 
   @Override
   public void operateDevice() {
     engineer.operateDevice();
   }
+
+  public void setEngineer(Engineer engineer) {
+    this.engineer = engineer;
+  }
 }

adapter/src/test/java/com/iluwatar/adapter/AdapterPatternTest.java

@@ -0,0 +1,68 @@
+package com.iluwatar.adapter;
+
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * An adapter helps two incompatible interfaces to work together. This is the real world definition
+ * for an adapter. Interfaces may be incompatible but the inner functionality should suit the need.
+ * The Adapter design pattern allows otherwise incompatible classes to work together by converting
+ * the interface of one class into an interface expected by the clients.
+ * 
+ * <p>There are two variations of the Adapter pattern: 
+ * The class adapter implements the adaptee's
+ * interface whereas the object adapter uses composition to contain the adaptee in the adapter
+ * object. This example uses the object adapter approach.
+ * 
+ * <p>The Adapter ({@link GnomeEngineer}) converts the interface 
+ * of the target class ({@link GoblinGlider}) into a suitable one expected by 
+ * the client ({@link GnomeEngineeringManager}
+ * ).
+ */
+public class AdapterPatternTest {
+
+  private Map<String, Object> beans;
+
+  private static final String ENGINEER_BEAN = "engineer";
+
+  private static final String MANAGER_BEAN = "manager";
+
+  /**
+   * This method runs before the test execution and sets the bean objects in the beans Map.
+   */
+  @Before
+  public void setup() {
+    beans = new HashMap<>();
+
+    GnomeEngineer gnomeEngineer = spy(new GnomeEngineer());
+    beans.put(ENGINEER_BEAN, gnomeEngineer);
+
+    GnomeEngineeringManager manager = new GnomeEngineeringManager();
+    manager.setEngineer((GnomeEngineer) beans.get(ENGINEER_BEAN));
+    beans.put(MANAGER_BEAN, manager);
+  }
+
+  /**
+   * This test asserts that when we call operateDevice() method on a manager bean, it is internally
+   * calling operateDevice method on the engineer object. The Adapter ({@link GnomeEngineer})
+   * converts the interface of the target class ( {@link GoblinGlider}) into a suitable one expected
+   * by the client ({@link GnomeEngineeringManager} ).
+   */
+  @Test
+  public void testAdapter() {
+    Engineer manager = (Engineer) beans.get(MANAGER_BEAN);
+
+    // when manager is asked to operate device
+    manager.operateDevice();
+
+    // Manager internally calls the engineer object to operateDevice
+    Engineer engineer = (Engineer) beans.get(ENGINEER_BEAN);
+    verify(engineer).operateDevice();
+  }
+}

adapter/src/test/java/com/iluwatar/adapter/AppTest.java

@@ -1,19 +0,0 @@
-package com.iluwatar.adapter;
-
-import org.junit.Test;
-
-import com.iluwatar.adapter.App;
-
-/**
- * 
- * Application test
- *
- */
-public class AppTest {
-
-	@Test
-	public void test() {
-		String[] args = {};
-		App.main(args);
-	}
-}

async-method-invocation/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>async-method-invocation</artifactId>
   <dependencies>

async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/App.java

@@ -4,23 +4,24 @@ import java.util.concurrent.Callable;
 
 /**
  * This application demonstrates the async method invocation pattern. Key parts of the pattern are
- * <code>AsyncResult</code> which is an intermediate container for an asynchronously evaluated value,
+ * <code>AsyncResult</code> which is an intermediate container for an asynchronously evaluated
- * <code>AsyncCallback</code> which can be provided to be executed on task completion and
+ * value, <code>AsyncCallback</code> which can be provided to be executed on task completion and
  * <code>AsyncExecutor</code> that manages the execution of the async tasks.
  * <p>
- * The main method shows example flow of async invocations. The main thread starts multiple tasks with
+ * The main method shows example flow of async invocations. The main thread starts multiple tasks
- * variable durations and then continues its own work. When the main thread has done it's job it collects
+ * with variable durations and then continues its own work. When the main thread has done it's job
- * the results of the async tasks. Two of the tasks are handled with callbacks, meaning the callbacks are
+ * it collects the results of the async tasks. Two of the tasks are handled with callbacks, meaning
- * executed immediately when the tasks complete.
+ * the callbacks are executed immediately when the tasks complete.
  * <p>
- * Noteworthy difference of thread usage between the async results and callbacks is that the async results
+ * Noteworthy difference of thread usage between the async results and callbacks is that the async
- * are collected in the main thread but the callbacks are executed within the worker threads. This should be
+ * results are collected in the main thread but the callbacks are executed within the worker
- * noted when working with thread pools.
+ * threads. This should be noted when working with thread pools.
  * <p>
- * Java provides its own implementations of async method invocation pattern. FutureTask, CompletableFuture
+ * Java provides its own implementations of async method invocation pattern. FutureTask,
- * and ExecutorService are the real world implementations of this pattern. But due to the nature of parallel
+ * CompletableFuture and ExecutorService are the real world implementations of this pattern. But due
- * programming, the implementations are not trivial. This example does not take all possible scenarios into
+ * to the nature of parallel programming, the implementations are not trivial. This example does not
- * account but rather provides a simple version that helps to understand the pattern.
+ * take all possible scenarios into account but rather provides a simple version that helps to
+ * understand the pattern.
  *
  * @see AsyncResult
  * @see AsyncCallback
@@ -40,8 +41,10 @@ public class App {
     AsyncResult<Integer> asyncResult1 = executor.startProcess(lazyval(10, 500));
     AsyncResult<String> asyncResult2 = executor.startProcess(lazyval("test", 300));
     AsyncResult<Long> asyncResult3 = executor.startProcess(lazyval(50L, 700));
-		AsyncResult<Integer> asyncResult4 = executor.startProcess(lazyval(20, 400), callback("Callback result 4"));
+    AsyncResult<Integer> asyncResult4 =
-		AsyncResult<String> asyncResult5 = executor.startProcess(lazyval("callback", 600), callback("Callback result 5"));
+        executor.startProcess(lazyval(20, 400), callback("Callback result 4"));
+    AsyncResult<String> asyncResult5 =
+        executor.startProcess(lazyval("callback", 600), callback("Callback result 5"));
 
     // emulate processing in the current thread while async tasks are running in their own threads
     Thread.sleep(350); // Oh boy I'm working hard here

async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/AsyncCallback.java

@@ -18,5 +18,4 @@ public interface AsyncCallback<T> {
    * @param ex empty value if execution succeeds, some exception if executions fails
    */
   void onComplete(T value, Optional<Exception> ex);
-
 }

async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/AsyncExecutor.java

@@ -38,5 +38,4 @@ public interface AsyncExecutor {
    * @throws InterruptedException if the execution is interrupted
    */
   <T> T endProcess(AsyncResult<T> asyncResult) throws ExecutionException, InterruptedException;
-
 }

async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/ThreadAsyncExecutor.java

@@ -34,7 +34,8 @@ public class ThreadAsyncExecutor implements AsyncExecutor {
   }
 
   @Override
-	public <T> T endProcess(AsyncResult<T> asyncResult) throws ExecutionException, InterruptedException {
+  public <T> T endProcess(AsyncResult<T> asyncResult) throws ExecutionException,
+      InterruptedException {
     if (asyncResult.isCompleted()) {
       return asyncResult.getValue();
     } else {
@@ -44,8 +45,8 @@ public class ThreadAsyncExecutor implements AsyncExecutor {
   }
 
   /**
-	 * Simple implementation of async result that allows completing it successfully with a value
+   * Simple implementation of async result that allows completing it successfully with a value or
-	 * or exceptionally with an exception. A really simplified version from its real life cousins
+   * exceptionally with an exception. A really simplified version from its real life cousins
    * FutureTask and CompletableFuture.
    *
    * @see java.util.concurrent.FutureTask
@@ -70,8 +71,8 @@ public class ThreadAsyncExecutor implements AsyncExecutor {
     }
 
     /**
-		 * Sets the value from successful execution and executes callback if available. Notifies
+     * Sets the value from successful execution and executes callback if available. Notifies any
-		 * any thread waiting for completion.
+     * thread waiting for completion.
      *
      * @param value value of the evaluated task
      */
@@ -85,8 +86,8 @@ public class ThreadAsyncExecutor implements AsyncExecutor {
     }
 
     /**
-		 * Sets the exception from failed execution and executes callback if available. Notifies
+     * Sets the exception from failed execution and executes callback if available. Notifies any
-		 * any thread waiting for completion.
+     * thread waiting for completion.
      *
      * @param exception exception of the failed task
      */

async-method-invocation/src/test/java/com/iluwatar/async/method/invocation/AppTest.java

@@ -14,5 +14,4 @@ public class AppTest {
     String[] args = {};
     App.main(args);
   }
-
 }

bridge/index.md

@@ -4,9 +4,13 @@ title: Bridge
 folder: bridge
 permalink: /patterns/bridge/
 categories: Structural
-tags: Java
+tags:
+ - Java
+ - Gang Of Four
 ---
 
+**Also known as:** Handle/Body
+
 **Intent:** Decouple an abstraction from its implementation so that the two can
 vary independently.
 
@@ -20,3 +24,7 @@ vary independently.
 * changes in the implementation of an abstraction should have no impact on clients; that is, their code should not have to be recompiled.
 * you have a proliferation of classes. Such a class hierarchy indicates the need for splitting an object into two parts. Rumbaugh uses the term "nested generalizations" to refer to such class hierarchies
 * you want to share an implementation among multiple objects (perhaps using reference counting), and this fact should be hidden from the client. A simple example is Coplien's String class, in which multiple objects can share the same string representation.
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

bridge/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>bridge</artifactId>
   <dependencies>

bridge/src/main/java/com/iluwatar/bridge/App.java

@@ -2,38 +2,38 @@ package com.iluwatar.bridge;
 
 /**
  * 
- * In Bridge pattern both abstraction ({@link MagicWeapon}) and implementation
+ * The Bridge pattern can also be thought of as two layers of abstraction. With Bridge, you can
- * ({@link MagicWeaponImpl}) have their own class hierarchies. The interface of the
+ * decouple an abstraction from its implementation so that the two can vary independently.
- * implementations can be changed without affecting the clients.
+ * <p>
+ * In Bridge pattern both abstraction ({@link MagicWeapon}) and implementation (
+ * {@link MagicWeaponImpl}) have their own class hierarchies. The interface of the implementations
+ * can be changed without affecting the clients.
  * 
  */
 public class App {
 
   /**
    * Program entry point
+   * 
    * @param args command line args
    */
   public static void main(String[] args) {
-		BlindingMagicWeapon blindingMagicWeapon = new BlindingMagicWeapon(
+    BlindingMagicWeapon blindingMagicWeapon = new BlindingMagicWeapon(new Excalibur());
-				new Excalibur());
     blindingMagicWeapon.wield();
     blindingMagicWeapon.blind();
     blindingMagicWeapon.swing();
     blindingMagicWeapon.unwield();
 
-		FlyingMagicWeapon flyingMagicWeapon = new FlyingMagicWeapon(
+    FlyingMagicWeapon flyingMagicWeapon = new FlyingMagicWeapon(new Mjollnir());
-				new Mjollnir());
     flyingMagicWeapon.wield();
     flyingMagicWeapon.fly();
     flyingMagicWeapon.swing();
     flyingMagicWeapon.unwield();
 
-		SoulEatingMagicWeapon soulEatingMagicWeapon = new SoulEatingMagicWeapon(
+    SoulEatingMagicWeapon soulEatingMagicWeapon = new SoulEatingMagicWeapon(new Stormbringer());
-				new Stormbringer());
     soulEatingMagicWeapon.wield();
     soulEatingMagicWeapon.swing();
     soulEatingMagicWeapon.eatSoul();
     soulEatingMagicWeapon.unwield();
-
   }
 }

bridge/src/main/java/com/iluwatar/bridge/BlindingMagicWeapon.java

@@ -34,5 +34,4 @@ public class BlindingMagicWeapon extends MagicWeapon {
   public void blind() {
     getImp().blindImp();
   }
-
 }

bridge/src/main/java/com/iluwatar/bridge/Excalibur.java

@@ -24,8 +24,6 @@ public class Excalibur extends BlindingMagicWeaponImpl {
 
   @Override
   public void blindImp() {
-		System.out
+    System.out.println("bright light streams from Excalibur blinding the enemy");
-				.println("bright light streams from Excalibur blinding the enemy");
   }
-
 }

bridge/src/main/java/com/iluwatar/bridge/MagicWeapon.java

@@ -22,5 +22,4 @@ public abstract class MagicWeapon {
   public MagicWeaponImpl getImp() {
     return imp;
   }
-
 }

bridge/src/main/java/com/iluwatar/bridge/Mjollnir.java

@@ -24,8 +24,6 @@ public class Mjollnir extends FlyingMagicWeaponImpl {
 
   @Override
   public void flyImp() {
-		System.out
+    System.out.println("Mjollnir hits the enemy in the air and returns back to the owner's hand");
-				.println("Mjollnir hits the enemy in the air and returns back to the owner's hand");
   }
-
 }

bridge/src/main/java/com/iluwatar/bridge/Stormbringer.java

@@ -26,5 +26,4 @@ public class Stormbringer extends SoulEatingMagicWeaponImpl {
   public void eatSoulImp() {
     System.out.println("Stormbringer devours the enemy's soul");
   }
-
 }

builder/index.md

@@ -4,7 +4,9 @@ title: Builder
 folder: builder
 permalink: /patterns/builder/
 categories: Creational
-tags: Java
+tags:
+ - Java
+ - Gang Of Four
 ---
 
 **Intent:** Separate the construction of a complex object from its
@@ -22,3 +24,7 @@ representations.
 
 * [java.lang.StringBuilder](http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html)
 * [Apache Camel builders](https://github.com/apache/camel/tree/0e195428ee04531be27a0b659005e3aa8d159d23/camel-core/src/main/java/org/apache/camel/builder)
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

builder/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>builder</artifactId>
   <dependencies>

builder/src/main/java/com/iluwatar/builder/App.java

@@ -4,38 +4,51 @@ import com.iluwatar. builder.Hero.HeroBuilder;
 
 /**
  * 
- * This is the Builder pattern variation as described by Joshua Bloch in
+ * The intention of the Builder pattern is to find a solution to the telescoping constructor
- * Effective Java 2nd Edition.
+ * anti-pattern. The telescoping constructor anti-pattern occurs when the increase of object
+ * constructor parameter combination leads to an exponential list of constructors. Instead of using
+ * numerous constructors, the builder pattern uses another object, a builder, that receives each
+ * initialization parameter step by step and then returns the resulting constructed object at once.
  * <p>
- * We want to build {@link Hero} objects, but its construction is complex because of the
+ * The Builder pattern has another benefit. It can be used for objects that contain flat data (html
- * many parameters needed. To aid the user we introduce {@link HeroBuilder} class.
+ * code, SQL query, X.509 certificate...), that is to say, data that can't be easily edited. This
- * {@link HeroBuilder} takes the minimum parameters to build {@link Hero} object in its
+ * type of data cannot be edited step by step and must be edited at once. The best way to construct
- * constructor. After that additional configuration for the {@link Hero} object can be
+ * such an object is to use a builder class.
- * done using the fluent {@link HeroBuilder} interface. When configuration is ready the
+ * <p>
- * build method is called to receive the final {@link Hero} object.
+ * In this example we have the Builder pattern variation as described by Joshua Bloch in Effective
+ * Java 2nd Edition.
+ * <p>
+ * We want to build {@link Hero} objects, but its construction is complex because of the many
+ * parameters needed. To aid the user we introduce {@link HeroBuilder} class. {@link HeroBuilder}
+ * takes the minimum parameters to build {@link Hero} object in its constructor. After that
+ * additional configuration for the {@link Hero} object can be done using the fluent
+ * {@link HeroBuilder} interface. When configuration is ready the build method is called to receive
+ * the final {@link Hero} object.
  * 
  */
 public class App {
 
   /**
    * Program entry point
+   * 
    * @param args command line args
    */
   public static void main(String[] args) {
 
-		Hero mage = new HeroBuilder(Profession.MAGE, "Riobard")
+    Hero mage =
-				.withHairColor(HairColor.BLACK).withWeapon(Weapon.DAGGER)
+        new HeroBuilder(Profession.MAGE, "Riobard").withHairColor(HairColor.BLACK)
-				.build();
+            .withWeapon(Weapon.DAGGER).build();
     System.out.println(mage);
 
-		Hero warrior = new HeroBuilder(Profession.WARRIOR, "Amberjill")
+    Hero warrior =
-				.withHairColor(HairColor.BLOND)
+        new HeroBuilder(Profession.WARRIOR, "Amberjill").withHairColor(HairColor.BLOND)
-				.withHairType(HairType.LONG_CURLY).withArmor(Armor.CHAIN_MAIL)
+            .withHairType(HairType.LONG_CURLY).withArmor(Armor.CHAIN_MAIL).withWeapon(Weapon.SWORD)
-				.withWeapon(Weapon.SWORD).build();
+            .build();
     System.out.println(warrior);
 
-		Hero thief = new HeroBuilder(Profession.THIEF, "Desmond")
+    Hero thief =
-				.withHairType(HairType.BALD).withWeapon(Weapon.BOW).build();
+        new HeroBuilder(Profession.THIEF, "Desmond").withHairType(HairType.BALD)
+            .withWeapon(Weapon.BOW).build();
     System.out.println(thief);
 
   }

builder/src/main/java/com/iluwatar/builder/HairType.java

@@ -7,7 +7,8 @@ package com.iluwatar.builder;
  */
 public enum HairType {
 
-	BALD("bald"), SHORT("short"), CURLY("curly"), LONG_STRAIGHT("long straight"), LONG_CURLY("long curly");
+  BALD("bald"), SHORT("short"), CURLY("curly"), LONG_STRAIGHT("long straight"), LONG_CURLY(
+      "long curly");
 
   private String title;
 

builder/src/main/java/com/iluwatar/builder/Hero.java

@@ -95,8 +95,7 @@ public class Hero {
 
     public HeroBuilder(Profession profession, String name) {
       if (profession == null || name == null) {
-				throw new IllegalArgumentException(
+        throw new IllegalArgumentException("profession and name can not be null");
-						"profession and name can not be null");
       }
       this.profession = profession;
       this.name = name;

builder/src/main/java/com/iluwatar/builder/Profession.java

@@ -13,5 +13,4 @@ public enum Profession {
   public String toString() {
     return name().toLowerCase();
   }
-
 }

builder/src/main/java/com/iluwatar/builder/Weapon.java

@@ -13,5 +13,4 @@ public enum Weapon {
   public String toString() {
     return name().toLowerCase();
   }
-
 }

business-delegate/pom.xml

@@ -6,7 +6,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.6.0</version>
+		<version>1.8.0</version>
 	</parent>
 	<artifactId>business-delegate</artifactId>
 	<dependencies>
@@ -15,5 +15,10 @@
 			<artifactId>junit</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.mockito</groupId>
+			<artifactId>mockito-core</artifactId>
+			<scope>test</scope>
+		</dependency>
 	</dependencies>
 </project>

business-delegate/src/main/java/com/iluwatar/business/delegate/App.java

@@ -1,29 +1,34 @@
 package com.iluwatar.business.delegate;
 
 /**
+ * The Business Delegate pattern adds an abstraction layer between the presentation and business
+ * tiers. By using the pattern we gain loose coupling between the tiers. The Business Delegate
+ * encapsulates knowledge about how to locate, connect to, and interact with the business objects
+ * that make up the application.
  * 
- * The Business Delegate pattern adds an abstraction layer between the presentation and business tiers.
+ * <p>Some of the services the Business Delegate uses are instantiated directly, and some can be
- * By using the pattern we gain loose coupling between the tiers. The Business Delegate encapsulates
+ * retrieved through service lookups. The Business Delegate itself may contain business logic too
- * knowledge about how to locate, connect to, and interact with the business objects that make up
+ * potentially tying together multiple service calls, exception handling, retrying etc.
- * the application.
- * <p>
- * Some of the services the Business Delegate uses are instantiated directly, and some can be retrieved
- * through service lookups. The Business Delegate itself may contain business logic too potentially tying
- * together multiple service calls, exception handling, retrying etc.
- * <p>
- * In this example the client ({@link Client}) utilizes a business delegate ({@link BusinessDelegate}) to execute a task.
- * The Business Delegate then selects the appropriate service and makes the service call.
  * 
+ * <p>In this example the client ({@link Client}) utilizes a business delegate (
+ * {@link BusinessDelegate}) to execute a task. The Business Delegate then selects the appropriate
+ * service and makes the service call.
  */
 public class App {
 
   /**
-	 * Program entry point
+   * Program entry point.
+   *
    * @param args command line args
    */
   public static void main(String[] args) {
 
     BusinessDelegate businessDelegate = new BusinessDelegate();
+    BusinessLookup businessLookup = new BusinessLookup();
+    businessLookup.setEjbService(new EjbService());
+    businessLookup.setJmsService(new JmsService());
+
+    businessDelegate.setLookupService(businessLookup);
     businessDelegate.setServiceType(ServiceType.EJB);
 
     Client client = new Client(businessDelegate);

business-delegate/src/main/java/com/iluwatar/business/delegate/BusinessDelegate.java

@@ -1,16 +1,18 @@
 package com.iluwatar.business.delegate;
 
 /**
- * 
  * BusinessDelegate separates the presentation and business tiers
- *
  */
 public class BusinessDelegate {
 
-	private BusinessLookup lookupService = new BusinessLookup();
+    private BusinessLookup lookupService;
     private BusinessService businessService;
     private ServiceType serviceType;
 
+    public void setLookupService(BusinessLookup businessLookup) {
+        this.lookupService = businessLookup;
+    }
+
     public void setServiceType(ServiceType serviceType) {
         this.serviceType = serviceType;
     }

business-delegate/src/main/java/com/iluwatar/business/delegate/BusinessLookup.java

@@ -1,17 +1,31 @@
 package com.iluwatar.business.delegate;
 
 /**
- * 
+ * Class for performing service lookups.
- * Class for performing service lookups
- *
  */
 public class BusinessLookup {
 
+  private EjbService ejbService;
+
+  private JmsService jmsService;
+
+  /**
+   * @param serviceType Type of service instance to be returned.
+   * @return Service instance.
+   */
   public BusinessService getBusinessService(ServiceType serviceType) {
     if (serviceType.equals(ServiceType.EJB)) {
-			return new EjbService();
+      return ejbService;
     } else {
-			return new JmsService();
+      return jmsService;
     }
   }
+
+  public void setJmsService(JmsService jmsService) {
+    this.jmsService = jmsService;
+  }
+
+  public void setEjbService(EjbService ejbService) {
+    this.ejbService = ejbService;
+  }
 }

business-delegate/src/test/java/com/iluwatar/business/delegate/AppTest.java

@@ -1,19 +0,0 @@
-package com.iluwatar.business.delegate;
-
-import org.junit.Test;
-
-import com.iluwatar.business.delegate.App;
-
-/**
- * 
- * Application test
- *
- */
-public class AppTest {
-	
-	@Test
-	public void test() {
-		String[] args = {};
-		App.main(args);
-	}
-}

business-delegate/src/test/java/com/iluwatar/business/delegate/BusinessDelegateTest.java

@@ -0,0 +1,78 @@
+package com.iluwatar.business.delegate;
+
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * The Business Delegate pattern adds an abstraction layer between the presentation and business
+ * tiers. By using the pattern we gain loose coupling between the tiers. The Business Delegate
+ * encapsulates knowledge about how to locate, connect to, and interact with the business objects
+ * that make up the application.
+ * 
+ * <p>Some of the services the Business Delegate uses are instantiated directly, and some can be
+ * retrieved through service lookups. The Business Delegate itself may contain business logic too
+ * potentially tying together multiple service calls, exception handling, retrying etc.
+ */
+public class BusinessDelegateTest {
+
+  private EjbService ejbService;
+
+  private JmsService jmsService;
+
+  private BusinessLookup businessLookup;
+
+  private BusinessDelegate businessDelegate;
+
+  /**
+   * This method sets up the instance variables of this test class. It is executed before the
+   * execution of every test.
+   */
+  @Before
+  public void setup() {
+    ejbService = spy(new EjbService());
+    jmsService = spy(new JmsService());
+
+    businessLookup = spy(new BusinessLookup());
+    businessLookup.setEjbService(ejbService);
+    businessLookup.setJmsService(jmsService);
+
+    businessDelegate = spy(new BusinessDelegate());
+    businessDelegate.setLookupService(businessLookup);
+  }
+
+  /**
+   * In this example the client ({@link Client}) utilizes a business delegate (
+   * {@link BusinessDelegate}) to execute a task. The Business Delegate then selects the appropriate
+   * service and makes the service call.
+   */
+  @Test
+  public void testBusinessDelegate() {
+
+    // setup a client object
+    Client client = new Client(businessDelegate);
+
+    // set the service type
+    businessDelegate.setServiceType(ServiceType.EJB);
+
+    // action
+    client.doTask();
+
+    // verifying that the businessDelegate was used by client during doTask() method.
+    verify(businessDelegate).doTask();
+    verify(ejbService).doProcessing();
+
+    // set the service type
+    businessDelegate.setServiceType(ServiceType.JMS);
+
+    // action
+    client.doTask();
+
+    // verifying that the businessDelegate was used by client during doTask() method.
+    verify(businessDelegate, times(2)).doTask();
+    verify(jmsService).doProcessing();
+  }
+}

caching/.gitignore

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

caching/etc/caching.ucls

@@ -0,0 +1,106 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
+  <class id="1" language="java" name="main.java.com.wssia.caching.App" project="CachingPatterns" 
+    file="/CachingPatterns/src/main/java/com/wssia/caching/App.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="249" y="150"/>    
+    <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="main.java.com.wssia.caching.AppManager" project="CachingPatterns" 
+    file="/CachingPatterns/src/main/java/com/wssia/caching/AppManager.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="502" y="163"/>    
+    <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="3" language="java" name="main.java.com.wssia.caching.CacheStore" project="CachingPatterns" 
+    file="/CachingPatterns/src/main/java/com/wssia/caching/CacheStore.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="537" y="436"/>    
+    <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>  
+  <enumeration id="4" language="java" name="main.java.com.wssia.caching.CachingPolicy" project="CachingPatterns" 
+    file="/CachingPatterns/src/main/java/com/wssia/caching/CachingPolicy.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="789" y="162"/>    
+    <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>  
+  </enumeration>  
+  <class id="5" language="java" name="main.java.com.wssia.caching.DBManager" project="CachingPatterns" 
+    file="/CachingPatterns/src/main/java/com/wssia/caching/DBManager.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1137" y="134"/>    
+    <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="main.java.com.wssia.caching.LRUCache" project="CachingPatterns" 
+    file="/CachingPatterns/src/main/java/com/wssia/caching/LRUCache.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="884" y="435"/>    
+    <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="7" language="java" name="main.java.com.wssia.caching.UserAccount" project="CachingPatterns" 
+    file="/CachingPatterns/src/main/java/com/wssia/caching/UserAccount.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1140" y="405"/>    
+    <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="test.java.com.wssia.caching.AppTest" project="CachingPatterns" 
+    file="/CachingPatterns/src/test/java/com/wssia/caching/AppTest.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="251" y="374"/>    
+    <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="9">    
+    <end type="SOURCE" refId="2" navigable="false">      
+      <attribute id="10" name="cachingPolicy"/>      
+      <multiplicity id="11" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="4" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="12">    
+    <end type="SOURCE" refId="8" navigable="false">      
+      <attribute id="13" name="app"/>      
+      <multiplicity id="14" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="1" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="15">    
+    <end type="SOURCE" refId="3" navigable="false">      
+      <attribute id="16" name="cache"/>      
+      <multiplicity id="17" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="6" 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>

caching/index.md

@@ -0,0 +1,24 @@
+---
+layout: pattern
+title: Caching
+folder: caching
+permalink: /patterns/caching/
+categories: Other
+tags:
+ - Java
+---
+
+**Intent:** To avoid expensive re-acquisition of resources by not releasing
+the resources immediately after their use. The resources retain their identity, are kept in some
+fast-access storage, and are re-used to avoid having to acquire them again.
+
+![alt text](./etc/caching.png "Caching")
+
+**Applicability:** Use the Caching pattern(s) when
+
+* Repetitious acquisition, initialization, and release of the same resource causes unnecessary performance overhead.
+
+**Credits**
+
+* [Write-through, write-around, write-back: Cache explained](http://www.computerweekly.com/feature/Write-through-write-around-write-back-Cache-explained)
+* [Read-Through, Write-Through, Write-Behind, and Refresh-Ahead Caching](https://docs.oracle.com/cd/E15357_01/coh.360/e15723/cache_rtwtwbra.htm#COHDG5177)

caching/pom.xml

@@ -0,0 +1,51 @@
+<?xml version="1.0"?>
+<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>1.8.0</version>
+  </parent>
+  <artifactId>caching</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.mongodb</groupId>
+      <artifactId>mongodb-driver</artifactId>
+      <version>3.0.4</version>
+    </dependency>
+    <dependency>
+      <groupId>org.mongodb</groupId>
+      <artifactId>mongodb-driver-core</artifactId>
+      <version>3.0.4</version>
+    </dependency>
+    <dependency>
+      <groupId>org.mongodb</groupId>
+      <artifactId>bson</artifactId>
+      <version>3.0.4</version>
+    </dependency>
+  </dependencies>
+  <!--
+    Due to the use of MongoDB in the test of this pattern, TRAVIS and/or MAVEN might fail if the DB connection is
+    not open for the JUnit test. To avoid disrupting the compilation process, the surefire plug-in was used
+    to SKIP the running of the JUnit tests for this pattern. To ACTIVATE the running of the tests, change the
+    skipTests (below) flag to 'false' and vice-versa.
+  -->
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>2.19</version>
+        <configuration>
+          <skipTests>false</skipTests>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

caching/src/main/java/com/iluwatar/caching/App.java

@@ -0,0 +1,117 @@
+package com.iluwatar.caching;
+
+/**
+ *
+ * The Caching pattern describes how to avoid expensive re-acquisition of resources by not releasing
+ * the resources immediately after their use. The resources retain their identity, are kept in some
+ * fast-access storage, and are re-used to avoid having to acquire them again. There are three main
+ * caching strategies/techniques in this pattern; each with their own pros and cons. They are:
+ * <code>write-through</code> which writes data to the cache and DB in a single transaction,
+ * <code>write-around</code> which writes data immediately into the DB instead of the cache, and
+ * <code>write-behind</code> which writes data into the cache initially whilst the data is only
+ * written into the DB when the cache is full. The <code>read-through</code> strategy is also
+ * included in the mentioned three strategies -- returns data from the cache to the caller <b>if</b>
+ * it exists <b>else</b> queries from DB and stores it into the cache for future use. These
+ * strategies determine when the data in the cache should be written back to the backing store (i.e.
+ * Database) and help keep both data sources synchronized/up-to-date. This pattern can improve
+ * performance and also helps to maintain consistency between data held in the cache and the data in
+ * the underlying data store.
+ * <p>
+ * In this example, the user account ({@link UserAccount}) entity is used as the underlying
+ * application data. The cache itself is implemented as an internal (Java) data structure. It adopts
+ * a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The three
+ * strategies are individually tested. The testing of the cache is restricted towards saving and
+ * querying of user accounts from the underlying data store ( {@link DBManager}). The main class (
+ * {@link App} is not aware of the underlying mechanics of the application (i.e. save and query) and
+ * whether the data is coming from the cache or the DB (i.e. separation of concern). The AppManager
+ * ({@link AppManager}) handles the transaction of data to-and-from the underlying data store
+ * (depending on the preferred caching policy/strategy).
+ *
+ * <i>App --> AppManager --> CacheStore/LRUCache/CachingPolicy --> DBManager</i>
+ * </p>
+ *
+ * @see CacheStore
+ * @See LRUCache
+ * @see CachingPolicy
+ *
+ */
+public class App {
+
+  /**
+   * Program entry point
+   *
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+    AppManager.initDB(false); // VirtualDB (instead of MongoDB) was used in running the JUnit tests
+                              // and the App class to avoid Maven compilation errors. Set flag to
+                              // true to run the tests with MongoDB (provided that MongoDB is
+                              // installed and socket connection is open).
+    AppManager.initCacheCapacity(3);
+    App app = new App();
+    app.useReadAndWriteThroughStrategy();
+    app.useReadThroughAndWriteAroundStrategy();
+    app.useReadThroughAndWriteBehindStrategy();
+  }
+
+  /**
+   * Read-through and write-through
+   */
+  public void useReadAndWriteThroughStrategy() {
+    System.out.println("# CachingPolicy.THROUGH");
+    AppManager.initCachingPolicy(CachingPolicy.THROUGH);
+
+    UserAccount userAccount1 = new UserAccount("001", "John", "He is a boy.");
+
+    AppManager.save(userAccount1);
+    System.out.println(AppManager.printCacheContent());
+    userAccount1 = AppManager.find("001");
+    userAccount1 = AppManager.find("001");
+  }
+
+  /**
+   * Read-through and write-around
+   */
+  public void useReadThroughAndWriteAroundStrategy() {
+    System.out.println("# CachingPolicy.AROUND");
+    AppManager.initCachingPolicy(CachingPolicy.AROUND);
+
+    UserAccount userAccount2 = new UserAccount("002", "Jane", "She is a girl.");
+
+    AppManager.save(userAccount2);
+    System.out.println(AppManager.printCacheContent());
+    userAccount2 = AppManager.find("002");
+    System.out.println(AppManager.printCacheContent());
+    userAccount2 = AppManager.find("002");
+    userAccount2.setUserName("Jane G.");
+    AppManager.save(userAccount2);
+    System.out.println(AppManager.printCacheContent());
+    userAccount2 = AppManager.find("002");
+    System.out.println(AppManager.printCacheContent());
+    userAccount2 = AppManager.find("002");
+  }
+
+  /**
+   * Read-through and write-behind
+   */
+  public void useReadThroughAndWriteBehindStrategy() {
+    System.out.println("# CachingPolicy.BEHIND");
+    AppManager.initCachingPolicy(CachingPolicy.BEHIND);
+
+    UserAccount userAccount3 = new UserAccount("003", "Adam", "He likes food.");
+    UserAccount userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
+    UserAccount userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
+
+    AppManager.save(userAccount3);
+    AppManager.save(userAccount4);
+    AppManager.save(userAccount5);
+    System.out.println(AppManager.printCacheContent());
+    userAccount3 = AppManager.find("003");
+    System.out.println(AppManager.printCacheContent());
+    UserAccount userAccount6 = new UserAccount("006", "Yasha", "She is an only child.");
+    AppManager.save(userAccount6);
+    System.out.println(AppManager.printCacheContent());
+    userAccount4 = AppManager.find("004");
+    System.out.println(AppManager.printCacheContent());
+  }
+}

caching/src/main/java/com/iluwatar/caching/AppManager.java

@@ -0,0 +1,75 @@
+package com.iluwatar.caching;
+
+import java.text.ParseException;
+
+/**
+ *
+ * AppManager helps to bridge the gap in communication between the main class and the application's
+ * back-end. DB connection is initialized through this class. The chosen caching strategy/policy is
+ * also initialized here. Before the cache can be used, the size of the cache has to be set.
+ * Depending on the chosen caching policy, AppManager will call the appropriate function in the
+ * CacheStore class.
+ *
+ */
+public class AppManager {
+
+  private static CachingPolicy cachingPolicy;
+
+  /**
+   *
+   * Developer/Tester is able to choose whether the application should use MongoDB as its underlying
+   * data storage or a simple Java data structure to (temporarily) store the data/objects during
+   * runtime.
+   */
+  public static void initDB(boolean useMongoDB) {
+    if (useMongoDB) {
+      try {
+        DBManager.connect();
+      } catch (ParseException e) {
+        e.printStackTrace();
+      }
+    } else {
+      DBManager.createVirtualDB();
+    }
+  }
+
+  public static void initCachingPolicy(CachingPolicy policy) {
+    cachingPolicy = policy;
+    if (cachingPolicy == CachingPolicy.BEHIND) {
+      Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
+        @Override
+        public void run() {
+          CacheStore.flushCache();
+        }
+      }));
+    }
+    CacheStore.clearCache();
+  }
+
+  public static void initCacheCapacity(int capacity) {
+    CacheStore.initCapacity(capacity);
+  }
+
+  public static UserAccount find(String userID) {
+    if (cachingPolicy == CachingPolicy.THROUGH || cachingPolicy == CachingPolicy.AROUND) {
+      return CacheStore.readThrough(userID);
+    } else if (cachingPolicy == CachingPolicy.BEHIND) {
+      return CacheStore.readThroughWithWriteBackPolicy(userID);
+    }
+    return null;
+  }
+
+  public static void save(UserAccount userAccount) {
+    if (cachingPolicy == CachingPolicy.THROUGH) {
+      CacheStore.writeThrough(userAccount);
+    } else if (cachingPolicy == CachingPolicy.AROUND) {
+      CacheStore.writeAround(userAccount);
+    } else if (cachingPolicy == CachingPolicy.BEHIND) {
+      CacheStore.writeBehind(userAccount);
+    }
+  }
+
+  public static String printCacheContent() {
+    return CacheStore.print();
+  }
+}

caching/src/main/java/com/iluwatar/caching/CacheStore.java

@@ -0,0 +1,104 @@
+package com.iluwatar.caching;
+
+import java.util.ArrayList;
+
+/**
+ *
+ * The caching strategies are implemented in this class.
+ *
+ */
+public class CacheStore {
+
+  static LRUCache cache = null;
+
+  public static void initCapacity(int capacity) {
+    if (null == cache)
+      cache = new LRUCache(capacity);
+    else
+      cache.setCapacity(capacity);
+  }
+
+  public static UserAccount readThrough(String userID) {
+    if (cache.contains(userID)) {
+      System.out.println("# Cache Hit!");
+      return cache.get(userID);
+    }
+    System.out.println("# Cache Miss!");
+    UserAccount userAccount = DBManager.readFromDB(userID);
+    cache.set(userID, userAccount);
+    return userAccount;
+  }
+
+  public static void writeThrough(UserAccount userAccount) {
+    if (cache.contains(userAccount.getUserID())) {
+      DBManager.updateDB(userAccount);
+    } else {
+      DBManager.writeToDB(userAccount);
+    }
+    cache.set(userAccount.getUserID(), userAccount);
+  }
+
+  public static void writeAround(UserAccount userAccount) {
+    if (cache.contains(userAccount.getUserID())) {
+      DBManager.updateDB(userAccount);
+      cache.invalidate(userAccount.getUserID()); // Cache data has been updated -- remove older
+                                                 // version from cache.
+    } else {
+      DBManager.writeToDB(userAccount);
+    }
+  }
+
+  public static UserAccount readThroughWithWriteBackPolicy(String userID) {
+    if (cache.contains(userID)) {
+      System.out.println("# Cache Hit!");
+      return cache.get(userID);
+    }
+    System.out.println("# Cache Miss!");
+    UserAccount userAccount = DBManager.readFromDB(userID);
+    if (cache.isFull()) {
+      System.out.println("# Cache is FULL! Writing LRU data to DB...");
+      UserAccount toBeWrittenToDB = cache.getLRUData();
+      DBManager.upsertDB(toBeWrittenToDB);
+    }
+    cache.set(userID, userAccount);
+    return userAccount;
+  }
+
+  public static void writeBehind(UserAccount userAccount) {
+    if (cache.isFull() && !cache.contains(userAccount.getUserID())) {
+      System.out.println("# Cache is FULL! Writing LRU data to DB...");
+      UserAccount toBeWrittenToDB = cache.getLRUData();
+      DBManager.upsertDB(toBeWrittenToDB);
+    }
+    cache.set(userAccount.getUserID(), userAccount);
+  }
+
+  public static void clearCache() {
+    if (null != cache)
+      cache.clear();
+  }
+
+  /**
+   * Writes remaining content in the cache into the DB.
+   */
+  public static void flushCache() {
+    System.out.println("# flushCache...");
+    if (null == cache)
+      return;
+    ArrayList<UserAccount> listOfUserAccounts = cache.getCacheDataInListForm();
+    for (UserAccount userAccount : listOfUserAccounts) {
+      DBManager.upsertDB(userAccount);
+    }
+  }
+
+  public static String print() {
+    ArrayList<UserAccount> listOfUserAccounts = cache.getCacheDataInListForm();
+    StringBuilder sb = new StringBuilder();
+    sb.append("\n--CACHE CONTENT--\n");
+    for (UserAccount userAccount : listOfUserAccounts) {
+      sb.append(userAccount.toString() + "\n");
+    }
+    sb.append("----\n");
+    return sb.toString();
+  }
+}

caching/src/main/java/com/iluwatar/caching/CachingPolicy.java

@@ -0,0 +1,20 @@
+package com.iluwatar.caching;
+
+/**
+ *
+ * Enum class containing the three caching strategies implemented in the pattern.
+ *
+ */
+public enum CachingPolicy {
+  THROUGH("through"), AROUND("around"), BEHIND("behind");
+
+  private String policy;
+
+  private CachingPolicy(String policy) {
+    this.policy = policy;
+  }
+
+  public String getPolicy() {
+    return policy;
+  }
+}

caching/src/main/java/com/iluwatar/caching/DBManager.java

@@ -0,0 +1,123 @@
+package com.iluwatar.caching;
+
+import java.text.ParseException;
+import java.util.HashMap;
+
+import org.bson.Document;
+
+import com.mongodb.MongoClient;
+import com.mongodb.client.FindIterable;
+import com.mongodb.client.MongoDatabase;
+import com.mongodb.client.model.UpdateOptions;
+
+/**
+ *
+ * <p>DBManager handles the communication with the underlying data store i.e. Database. It contains the
+ * implemented methods for querying, inserting, and updating data. MongoDB was used as the database
+ * for the application.</p>
+ * 
+ * <p>Developer/Tester is able to choose whether the application should use MongoDB as its underlying
+ * data storage (connect()) or a simple Java data structure to (temporarily) store the data/objects
+ * during runtime (createVirtualDB()).</p>
+ * 
+ */
+public class DBManager {
+
+  private static MongoClient mongoClient;
+  private static MongoDatabase db;
+  private static boolean useMongoDB;
+
+  private static HashMap<String, UserAccount> virtualDB;
+
+  public static void createVirtualDB() {
+    useMongoDB = false;
+    virtualDB = new HashMap<String, UserAccount>();
+  }
+
+  public static void connect() throws ParseException {
+    useMongoDB = true;
+    mongoClient = new MongoClient();
+    db = mongoClient.getDatabase("test");
+  }
+
+  public static UserAccount readFromDB(String userID) {
+    if (!useMongoDB) {
+      if (virtualDB.containsKey(userID))
+        return virtualDB.get(userID);
+      return null;
+    }
+    if (null == db) {
+      try {
+        connect();
+      } catch (ParseException e) {
+        e.printStackTrace();
+      }
+    }
+    FindIterable<Document> iterable =
+        db.getCollection("user_accounts").find(new Document("userID", userID));
+    if (iterable == null)
+      return null;
+    Document doc = iterable.first();
+    UserAccount userAccount =
+        new UserAccount(userID, doc.getString("userName"), doc.getString("additionalInfo"));
+    return userAccount;
+  }
+
+  public static void writeToDB(UserAccount userAccount) {
+    if (!useMongoDB) {
+      virtualDB.put(userAccount.getUserID(), userAccount);
+      return;
+    }
+    if (null == db) {
+      try {
+        connect();
+      } catch (ParseException e) {
+        e.printStackTrace();
+      }
+    }
+    db.getCollection("user_accounts").insertOne(
+        new Document("userID", userAccount.getUserID()).append("userName",
+            userAccount.getUserName()).append("additionalInfo", userAccount.getAdditionalInfo()));
+  }
+
+  public static void updateDB(UserAccount userAccount) {
+    if (!useMongoDB) {
+      virtualDB.put(userAccount.getUserID(), userAccount);
+      return;
+    }
+    if (null == db) {
+      try {
+        connect();
+      } catch (ParseException e) {
+        e.printStackTrace();
+      }
+    }
+    db.getCollection("user_accounts").updateOne(
+        new Document("userID", userAccount.getUserID()),
+        new Document("$set", new Document("userName", userAccount.getUserName()).append(
+            "additionalInfo", userAccount.getAdditionalInfo())));
+  }
+
+  /**
+   *
+   * Insert data into DB if it does not exist. Else, update it.
+   */
+  public static void upsertDB(UserAccount userAccount) {
+    if (!useMongoDB) {
+      virtualDB.put(userAccount.getUserID(), userAccount);
+      return;
+    }
+    if (null == db) {
+      try {
+        connect();
+      } catch (ParseException e) {
+        e.printStackTrace();
+      }
+    }
+    db.getCollection("user_accounts").updateOne(
+        new Document("userID", userAccount.getUserID()),
+        new Document("$set", new Document("userID", userAccount.getUserID()).append("userName",
+            userAccount.getUserName()).append("additionalInfo", userAccount.getAdditionalInfo())),
+        new UpdateOptions().upsert(true));
+  }
+}

caching/src/main/java/com/iluwatar/caching/LRUCache.java

@@ -0,0 +1,146 @@
+package com.iluwatar.caching;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+
+/**
+ *
+ * Data structure/implementation of the application's cache. The data structure consists of a hash
+ * table attached with a doubly linked-list. The linked-list helps in capturing and maintaining the
+ * LRU data in the cache. When a data is queried (from the cache), added (to the cache), or updated,
+ * the data is moved to the front of the list to depict itself as the most-recently-used data. The
+ * LRU data is always at the end of the list.
+ *
+ */
+public class LRUCache {
+
+  class Node {
+    String userID;
+    UserAccount userAccount;
+    Node previous;
+    Node next;
+
+    public Node(String userID, UserAccount userAccount) {
+      this.userID = userID;
+      this.userAccount = userAccount;
+    }
+  }
+
+  int capacity;
+  HashMap<String, Node> cache = new HashMap<String, Node>();
+  Node head = null;
+  Node end = null;
+
+  public LRUCache(int capacity) {
+    this.capacity = capacity;
+  }
+
+  public UserAccount get(String userID) {
+    if (cache.containsKey(userID)) {
+      Node node = cache.get(userID);
+      remove(node);
+      setHead(node);
+      return node.userAccount;
+    }
+    return null;
+  }
+
+  /**
+   *
+   * Remove node from linked list.
+   */
+  public void remove(Node node) {
+    if (node.previous != null) {
+      node.previous.next = node.next;
+    } else {
+      head = node.next;
+    }
+    if (node.next != null) {
+      node.next.previous = node.previous;
+    } else {
+      end = node.previous;
+    }
+  }
+
+  /**
+   *
+   * Move node to the front of the list.
+   */
+  public void setHead(Node node) {
+    node.next = head;
+    node.previous = null;
+    if (head != null)
+      head.previous = node;
+    head = node;
+    if (end == null)
+      end = head;
+  }
+
+  public void set(String userID, UserAccount userAccount) {
+    if (cache.containsKey(userID)) {
+      Node old = cache.get(userID);
+      old.userAccount = userAccount;
+      remove(old);
+      setHead(old);
+    } else {
+      Node newNode = new Node(userID, userAccount);
+      if (cache.size() >= capacity) {
+        System.out.println("# Cache is FULL! Removing " + end.userID + " from cache...");
+        cache.remove(end.userID); // remove LRU data from cache.
+        remove(end);
+        setHead(newNode);
+      } else {
+        setHead(newNode);
+      }
+      cache.put(userID, newNode);
+    }
+  }
+
+  public boolean contains(String userID) {
+    return cache.containsKey(userID);
+  }
+
+  public void invalidate(String userID) {
+    System.out.println("# " + userID + " has been updated! Removing older version from cache...");
+    Node toBeRemoved = cache.get(userID);
+    remove(toBeRemoved);
+    cache.remove(userID);
+  }
+
+  public boolean isFull() {
+    return cache.size() >= capacity;
+  }
+
+  public UserAccount getLRUData() {
+    return end.userAccount;
+  }
+
+  public void clear() {
+    head = null;
+    end = null;
+    cache.clear();
+  }
+
+  /**
+   *
+   * Returns cache data in list form.
+   */
+  public ArrayList<UserAccount> getCacheDataInListForm() {
+    ArrayList<UserAccount> listOfCacheData = new ArrayList<UserAccount>();
+    Node temp = head;
+    while (temp != null) {
+      listOfCacheData.add(temp.userAccount);
+      temp = temp.next;
+    }
+    return listOfCacheData;
+  }
+
+  public void setCapacity(int newCapacity) {
+    if (capacity > newCapacity) {
+      clear(); // Behavior can be modified to accommodate for decrease in cache size. For now, we'll
+               // just clear the cache.
+    } else {
+      this.capacity = newCapacity;
+    }
+  }
+}

caching/src/main/java/com/iluwatar/caching/UserAccount.java

@@ -0,0 +1,47 @@
+package com.iluwatar.caching;
+
+/**
+ *
+ * Entity class (stored in cache and DB) used in the application.
+ *
+ */
+public class UserAccount {
+  private String userID;
+  private String userName;
+  private String additionalInfo;
+
+  public UserAccount(String userID, String userName, String additionalInfo) {
+    this.userID = userID;
+    this.userName = userName;
+    this.additionalInfo = additionalInfo;
+  }
+
+  public String getUserID() {
+    return userID;
+  }
+
+  public void setUserID(String userID) {
+    this.userID = userID;
+  }
+
+  public String getUserName() {
+    return userName;
+  }
+
+  public void setUserName(String userName) {
+    this.userName = userName;
+  }
+
+  public String getAdditionalInfo() {
+    return additionalInfo;
+  }
+
+  public void setAdditionalInfo(String additionalInfo) {
+    this.additionalInfo = additionalInfo;
+  }
+
+  @Override
+  public String toString() {
+    return userID + ", " + userName + ", " + additionalInfo;
+  }
+}

caching/src/test/java/com/iluwatar/caching/AppTest.java

@@ -0,0 +1,41 @@
+package com.iluwatar.caching;
+
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ *
+ * Application test
+ *
+ */
+public class AppTest {
+  App app;
+
+  /**
+   * Setup of application test includes: initializing DB connection and cache size/capacity.
+   */
+  @Before
+  public void setUp() {
+    AppManager.initDB(false); // VirtualDB (instead of MongoDB) was used in running the JUnit tests
+                              // to avoid Maven compilation errors. Set flag to true to run the
+                              // tests with MongoDB (provided that MongoDB is installed and socket
+                              // connection is open).
+    AppManager.initCacheCapacity(3);
+    app = new App();
+  }
+
+  @Test
+  public void testReadAndWriteThroughStrategy() {
+    app.useReadAndWriteThroughStrategy();
+  }
+
+  @Test
+  public void testReadThroughAndWriteAroundStrategy() {
+    app.useReadThroughAndWriteAroundStrategy();
+  }
+
+  @Test
+  public void testReadThroughAndWriteBehindStrategy() {
+    app.useReadThroughAndWriteBehindStrategy();
+  }
+}

callback/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>callback</artifactId>
   <dependencies>

callback/src/main/java/com/iluwatar/callback/App.java

@@ -2,8 +2,9 @@ package com.iluwatar.callback;
 
 /**
  * 
- * Callback pattern is more native for functional languages where functions are treated as first-class citizens.
+ * Callback pattern is more native for functional languages where functions are treated as
- * Prior to Java 8 callbacks can be simulated using simple (alike command) interfaces.
+ * first-class citizens. Prior to Java 8 callbacks can be simulated using simple (alike command)
+ * interfaces.
  * 
  */
 public class App {

callback/src/main/java/com/iluwatar/callback/SimpleTask.java

@@ -9,7 +9,6 @@ public class SimpleTask extends Task {
 
   @Override
   public void execute() {
-		System.out.println("Perform some important activity.");
+    System.out.println("Perform some important activity and after call the callback method.");
   }
-
 }

callback/src/test/java/com/iluwatar/callback/AppTest.java

@@ -2,18 +2,38 @@ package com.iluwatar.callback;
 
 import org.junit.Test;
 
-import com.iluwatar.callback.App;
+import static org.junit.Assert.assertEquals;
 
 /**
+ * Add a field as a counter. Every time the callback method is called increment this field. Unit
+ * test checks that the field is being incremented.
  *
- * Application test
+ * Could be done with mock objects as well where the call method call is verified.
- *
  */
 public class AppTest {
 
+  private Integer callingCount = 0;
+
   @Test
   public void test() {
-		String[] args = {};
+    Callback callback = new Callback() {
-		App.main(args);
+      @Override
+      public void call() {
+        callingCount++;
+      }
+    };
+
+    Task task = new SimpleTask();
+
+    assertEquals("Initial calling count of 0", new Integer(0), callingCount);
+
+    task.executeWith(callback);
+
+    assertEquals("Callback called once", new Integer(1), callingCount);
+
+    task.executeWith(callback);
+
+    assertEquals("Callback called twice", new Integer(2), callingCount);
+
   }
 }

chain/index.md

@@ -4,7 +4,9 @@ title: Chain of responsibility
 folder: chain
 permalink: /patterns/chain/
 categories: Behavioral
-tags: Java
+tags:
+ - Java
+ - Gang Of Four
 ---
 
 **Intent:** Avoid coupling the sender of a request to its receiver by giving
@@ -23,3 +25,7 @@ objects and pass the request along the chain until an object handles it.
 
 * [java.util.logging.Logger#log()](http://docs.oracle.com/javase/8/docs/api/java/util/logging/Logger.html#log%28java.util.logging.Level,%20java.lang.String%29)
 * [Apache Commons Chain](https://commons.apache.org/proper/commons-chain/index.html)
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

chain/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>chain</artifactId>
   <dependencies>

chain/src/main/java/com/iluwatar/chain/App.java

@@ -2,24 +2,29 @@ package com.iluwatar.chain;
 
 /**
  * 
- * Chain of Responsibility organizes request handlers ({@link RequestHandler}) into a
+ * The Chain of Responsibility pattern is a design pattern consisting of command objects and a
- * chain where each handler has a chance to act on the request on its turn. In
+ * series of processing objects. Each processing object contains logic that defines the types of
- * this example the king ({@link OrcKing}) makes requests and the military orcs
+ * command objects that it can handle; the rest are passed to the next processing object in the
- * ({@link OrcCommander}, {@link OrcOfficer}, {@link OrcSoldier}) form the handler chain.
+ * chain. A mechanism also exists for adding new processing objects to the end of this chain.
+ * <p>
+ * In this example we organize the request handlers ({@link RequestHandler}) into a chain where each
+ * handler has a chance to act on the request on its turn. Here the king ({@link OrcKing}) makes
+ * requests and the military orcs ({@link OrcCommander}, {@link OrcOfficer}, {@link OrcSoldier})
+ * form the handler chain.
  * 
  */
 public class App {
 
   /**
    * Program entry point
+   * 
    * @param args command line args
    */
   public static void main(String[] args) {
 
     OrcKing king = new OrcKing();
     king.makeRequest(new Request(RequestType.DEFEND_CASTLE, "defend castle"));
-		king.makeRequest(new Request(RequestType.TORTURE_PRISONER,
+    king.makeRequest(new Request(RequestType.TORTURE_PRISONER, "torture prisoner"));
-				"torture prisoner"));
     king.makeRequest(new Request(RequestType.COLLECT_TAX, "collect tax"));
 
   }

command/index.md

@@ -4,9 +4,13 @@ title: Command
 folder: command
 permalink: /patterns/command/
 categories: Behavioral
-tags: Java
+tags: 
+ - Java
+ - Gang Of Four
 ---
 
+**Also known as:** Action, Transaction
+
 **Intent:** Encapsulate a request as an object, thereby letting you
 parameterize clients with different requests, queue or log requests, and
 support undoable operations.
@@ -30,3 +34,7 @@ support undoable operations.
 **Real world examples:**
 
 * [java.lang.Runnable](http://docs.oracle.com/javase/8/docs/api/java/lang/Runnable.html)
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

command/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>command</artifactId>
   <dependencies>
@@ -15,5 +14,10 @@
       <artifactId>junit</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 </project>

command/src/main/java/com/iluwatar/command/App.java

@@ -2,19 +2,22 @@ package com.iluwatar.command;
 
 /**
  * 
- * In Command pattern actions are objects that can be executed and undone. 
+ * The Command pattern is a behavioral design pattern in which an object is used to encapsulate all
+ * information needed to perform an action or trigger an event at a later time. This information
+ * includes the method name, the object that owns the method and values for the method parameters.
  * <p>
- * Four terms always associated with the command pattern are command, receiver, invoker and client. A command 
+ * Four terms always associated with the command pattern are command, receiver, invoker and client.
- * object (spell) knows about the receiver (target) and invokes a method of the receiver. Values for parameters of 
+ * A command object (spell) knows about the receiver (target) and invokes a method of the receiver.
- * the receiver method are stored in the command. The receiver then does the work. An invoker object (wizard) 
+ * Values for parameters of the receiver method are stored in the command. The receiver then does
- * knows how to execute a command, and optionally does bookkeeping about the command execution. The invoker 
+ * the work. An invoker object (wizard) knows how to execute a command, and optionally does
- * does not know anything about a concrete command, it knows only about command interface. Both an invoker object 
+ * bookkeeping about the command execution. The invoker does not know anything about a concrete
- * and several command objects are held by a client object (app). The client decides which commands to execute at 
+ * command, it knows only about command interface. Both an invoker object and several command
- * which points. To execute a command, it passes the command object to the invoker object.
+ * objects are held by a client object (app). The client decides which commands to execute at which
+ * points. To execute a command, it passes the command object to the invoker object.
  * <p>
- * In other words, in this example the wizard casts spells on the goblin. The wizard keeps track of the previous
+ * In other words, in this example the wizard casts spells on the goblin. The wizard keeps track of
- * spells cast, so it is easy to undo them. In addition, the wizard keeps track of the spells undone, so they
+ * the previous spells cast, so it is easy to undo them. In addition, the wizard keeps track of the
- * can be redone.
+ * spells undone, so they can be redone.
  * 
  * 
  */
@@ -22,6 +25,7 @@ public class App {
 
   /**
    * Program entry point
+   * 
    * @param args command line args
    */
   public static void main(String[] args) {

command/src/main/java/com/iluwatar/command/Target.java

@@ -31,8 +31,8 @@ public abstract class Target {
   public abstract String toString();
 
   public void printStatus() {
-		System.out.println(String.format("%s, [size=%s] [visibility=%s]", this,
+    System.out.println(String.format("%s, [size=%s] [visibility=%s]", this, getSize(),
-				getSize(), getVisibility()));
+        getVisibility()));
     System.out.println();
   }
 }

command/src/main/java/com/iluwatar/command/Wizard.java

@@ -13,8 +13,7 @@ public class Wizard {
   private Deque<Command> undoStack = new LinkedList<>();
   private Deque<Command> redoStack = new LinkedList<>();
 
-	public Wizard() {
+  public Wizard() {}
-	}
 
   public void castSpell(Command command, Target target) {
     System.out.println(this + " casts " + command + " at " + target);

command/src/test/java/com/iluwatar/command/AppTest.java

@@ -1,19 +0,0 @@
-package com.iluwatar.command;
-
-import org.junit.Test;
-
-import com.iluwatar.command.App;
-
-/**
- * 
- * Application test
- *
- */
-public class AppTest {
-
-	@Test
-	public void test() {
-		String[] args = {};
-		App.main(args);
-	}
-}

command/src/test/java/com/iluwatar/command/CommandTest.java

@@ -0,0 +1,71 @@
+package com.iluwatar.command;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+/**
+ * The Command pattern is a behavioral design pattern in which an object is used to encapsulate all
+ * information needed to perform an action or trigger an event at a later time. This information
+ * includes the method name, the object that owns the method and values for the method parameters.
+ * 
+ * <p>Four terms always associated with the command pattern are command, receiver, invoker and 
+ * client. A command object (spell) knows about the receiver (target) and invokes a method of 
+ * the receiver.Values for parameters of the receiver method are stored in the command. The receiver
+ * then does the work. An invoker object (wizard) knows how to execute a command, and optionally 
+ * does bookkeeping about the command execution. The invoker does not know anything about a 
+ * concrete command, it knows only about command interface. Both an invoker object and several 
+ * command objects are held by a client object (app). The client decides which commands to execute
+ * at which points. To execute a command, it passes the command object to the invoker object.
+ */
+public class CommandTest {
+
+  private static final String GOBLIN = "Goblin";
+
+  /**
+   * This test verifies that when the wizard casts spells on the goblin. The wizard keeps track of
+   * the previous spells cast, so it is easy to undo them. In addition, it also verifies that the
+   * wizard keeps track of the spells undone, so they can be redone.
+   */
+  @Test
+  public void testCommand() {
+
+    Wizard wizard = new Wizard();
+    Goblin goblin = new Goblin();
+
+    wizard.castSpell(new ShrinkSpell(), goblin);
+    verifyGoblin(goblin, GOBLIN, Size.SMALL, Visibility.VISIBLE);
+
+    wizard.castSpell(new InvisibilitySpell(), goblin);
+    verifyGoblin(goblin, GOBLIN, Size.SMALL, Visibility.INVISIBLE);
+
+    wizard.undoLastSpell();
+    verifyGoblin(goblin, GOBLIN, Size.SMALL, Visibility.VISIBLE);
+
+    wizard.undoLastSpell();
+    verifyGoblin(goblin, GOBLIN, Size.NORMAL, Visibility.VISIBLE);
+
+    wizard.redoLastSpell();
+    verifyGoblin(goblin, GOBLIN, Size.SMALL, Visibility.VISIBLE);
+
+    wizard.redoLastSpell();
+    verifyGoblin(goblin, GOBLIN, Size.SMALL, Visibility.INVISIBLE);
+  }
+
+  /**
+   * This method asserts that the passed goblin object has the name as expectedName, size as
+   * expectedSize and visibility as expectedVisibility.
+   *
+   * @param goblin a goblin object whose state is to be verified against other parameters
+   * @param expectedName expectedName of the goblin
+   * @param expectedSize expected size of the goblin
+   * @param expectedVisibilty exepcted visibility of the goblin
+   */
+  private void verifyGoblin(Goblin goblin, String expectedName, Size expectedSize,
+      Visibility expectedVisibilty) {
+    assertEquals("Goblin's name must be same as expectedName", expectedName, goblin.toString());
+    assertEquals("Goblin's size must be same as expectedSize", expectedSize, goblin.getSize());
+    assertEquals("Goblin's visibility must be same as expectedVisibility", expectedVisibilty,
+        goblin.getVisibility());
+  }
+}

composite/index.md

@@ -4,7 +4,9 @@ title: Composite
 folder: composite
 permalink: /patterns/composite/
 categories: Structural
-tags: Java
+tags:
+ - Java
+ - Gang Of Four
 ---
 
 **Intent:** Compose objects into tree structures to represent part-whole
@@ -22,3 +24,7 @@ of objects uniformly.
 
 * [java.awt.Container](http://docs.oracle.com/javase/8/docs/api/java/awt/Container.html) and [java.awt.Component](http://docs.oracle.com/javase/8/docs/api/java/awt/Component.html)
 * [Apache Wicket](https://github.com/apache/wicket) component tree, see [Component](https://github.com/apache/wicket/blob/91e154702ab1ff3481ef6cbb04c6044814b7e130/wicket-core/src/main/java/org/apache/wicket/Component.java) and [MarkupContainer](https://github.com/apache/wicket/blob/b60ec64d0b50a611a9549809c9ab216f0ffa3ae3/wicket-core/src/main/java/org/apache/wicket/MarkupContainer.java)
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

composite/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>composite</artifactId>
   <dependencies>

composite/src/main/java/com/iluwatar/composite/App.java

@@ -1,16 +1,21 @@
 package com.iluwatar.composite;
 
 /**
- * 
+ * The Composite pattern is a partitioning design pattern. The Composite pattern describes that a
- * With Composite we can treat tree hierarchies of objects with uniform
+ * group of objects is to be treated in the same way as a single instance of an object. The intent
- * interface ({@link LetterComposite}). In this example we have sentences composed of
+ * of a composite is to "compose" objects into tree structures to represent part-whole hierarchies.
- * words composed of letters.
+ * Implementing the Composite pattern lets clients treat individual objects and compositions
+ * uniformly.
+ * <p>
+ * In this example we have sentences composed of words composed of letters. All of the objects can
+ * be treated through the same interface ({@link LetterComposite}).
  * 
  */
 public class App {
 
   /**
    * Program entry point
+   * 
    * @param args command line args
    */
   public static void main(String[] args) {

composite/src/main/java/com/iluwatar/composite/Letter.java

@@ -22,5 +22,4 @@ public class Letter extends LetterComposite {
   protected void printThisAfter() {
     // nop
   }
-
 }

composite/src/main/java/com/iluwatar/composite/Messenger.java

@@ -15,20 +15,19 @@ public class Messenger {
 
     List<Word> words = new ArrayList<Word>();
 
-		words.add(new Word(Arrays.asList(new Letter('W'), new Letter('h'),
+    words.add(new Word(Arrays.asList(new Letter('W'), new Letter('h'), new Letter('e'), new Letter(
-				new Letter('e'), new Letter('r'), new Letter('e'))));
+        'r'), new Letter('e'))));
-		words.add(new Word(Arrays.asList(new Letter('t'), new Letter('h'),
+    words.add(new Word(Arrays.asList(new Letter('t'), new Letter('h'), new Letter('e'), new Letter(
-				new Letter('e'), new Letter('r'), new Letter('e'))));
+        'r'), new Letter('e'))));
     words.add(new Word(Arrays.asList(new Letter('i'), new Letter('s'))));
     words.add(new Word(Arrays.asList(new Letter('a'))));
-		words.add(new Word(Arrays.asList(new Letter('w'), new Letter('h'),
+    words.add(new Word(Arrays.asList(new Letter('w'), new Letter('h'), new Letter('i'), new Letter(
-				new Letter('i'), new Letter('p'))));
+        'p'))));
-		words.add(new Word(Arrays.asList(new Letter('t'), new Letter('h'),
+    words.add(new Word(Arrays.asList(new Letter('t'), new Letter('h'), new Letter('e'), new Letter(
-				new Letter('e'), new Letter('r'), new Letter('e'))));
+        'r'), new Letter('e'))));
     words.add(new Word(Arrays.asList(new Letter('i'), new Letter('s'))));
     words.add(new Word(Arrays.asList(new Letter('a'))));
-		words.add(new Word(Arrays.asList(new Letter('w'), new Letter('a'),
+    words.add(new Word(Arrays.asList(new Letter('w'), new Letter('a'), new Letter('y'))));
-				new Letter('y'))));
 
     return new Sentence(words);
 
@@ -38,18 +37,18 @@ public class Messenger {
 
     List<Word> words = new ArrayList<Word>();
 
-		words.add(new Word(Arrays.asList(new Letter('M'), new Letter('u'),
+    words.add(new Word(Arrays.asList(new Letter('M'), new Letter('u'), new Letter('c'), new Letter(
-				new Letter('c'), new Letter('h'))));
+        'h'))));
-		words.add(new Word(Arrays.asList(new Letter('w'), new Letter('i'),
+    words.add(new Word(Arrays.asList(new Letter('w'), new Letter('i'), new Letter('n'), new Letter(
-				new Letter('n'), new Letter('d'))));
+        'd'))));
-		words.add(new Word(Arrays.asList(new Letter('p'), new Letter('o'),
+    words.add(new Word(Arrays.asList(new Letter('p'), new Letter('o'), new Letter('u'), new Letter(
-				new Letter('u'), new Letter('r'), new Letter('s'))));
+        'r'), new Letter('s'))));
-		words.add(new Word(Arrays.asList(new Letter('f'), new Letter('r'),
+    words.add(new Word(Arrays.asList(new Letter('f'), new Letter('r'), new Letter('o'), new Letter(
-				new Letter('o'), new Letter('m'))));
+        'm'))));
-		words.add(new Word(Arrays.asList(new Letter('y'), new Letter('o'),
+    words.add(new Word(Arrays.asList(new Letter('y'), new Letter('o'), new Letter('u'), new Letter(
-				new Letter('u'), new Letter('r'))));
+        'r'))));
-		words.add(new Word(Arrays.asList(new Letter('m'), new Letter('o'),
+    words.add(new Word(Arrays.asList(new Letter('m'), new Letter('o'), new Letter('u'), new Letter(
-				new Letter('u'), new Letter('t'), new Letter('h'))));
+        't'), new Letter('h'))));
 
     return new Sentence(words);
 

composite/src/main/java/com/iluwatar/composite/Sentence.java

@@ -24,5 +24,4 @@ public class Sentence extends LetterComposite {
   protected void printThisAfter() {
     System.out.print(".");
   }
-
 }

composite/src/main/java/com/iluwatar/composite/Word.java

@@ -24,5 +24,4 @@ public class Word extends LetterComposite {
   protected void printThisAfter() {
     // nop
   }
-
 }

dao/index.md

@@ -4,7 +4,9 @@ title: Data Access Object
 folder: dao
 permalink: /patterns/dao/
 categories: Architectural
-tags: Java
+tags:
+ - Java
+ - Difficulty-Beginner
 ---
 
 **Intent:** Object provides an abstract interface to some type of database or
@@ -16,3 +18,7 @@ other persistence mechanism.
 
 * when you want to consolidate how the data layer is accessed
 * when you want to avoid writing multiple data retrieval/persistence layers
+
+**Credits:**
+
+* [J2EE Design Patterns](http://www.amazon.com/J2EE-Design-Patterns-William-Crawford/dp/0596004273/ref=sr_1_2)

dao/pom.xml

@@ -6,14 +6,64 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-		<version>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>dao</artifactId>
+
   <dependencies>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>log4j</groupId>
+      <artifactId>log4j</artifactId>
+    </dependency>
   </dependencies>
+
+  <build>
+
+    <!-- 
+    log4j.xml file will be copied both in ${project.build.outputDirectory} 
+    and ${project.build.directory}. Thanks to Sean Patrick Floyd 
+    (http://stackoverflow.com/questions/5637532/maven-how-to-place-resource-file-together-with-jar) 
+    -->
+      
+    <resources>
+      <resource> <!-- regular processing for every resource file -->
+        <directory>src/main/resources</directory>
+      </resource>
+      <resource> <!-- processing with a different output directory for log4j.xml -->
+        <directory>src/main/resources</directory>
+        <includes>
+          <include>log4j.xml</include>
+        </includes>
+        <targetPath>..</targetPath> <!-- relative to target/classes i.e. ${project.build.directory} -->
+      </resource>
+    </resources>
+
+    <plugins>
+
+      <!-- 
+      This will exclude log4j.xml file from generated JAR 
+      -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <version>2.6</version>
+        <configuration>
+          <excludes>
+            <exclude>log4j.xml</exclude>
+          </excludes>
+          <archive>
+            <manifest>
+              <addClasspath>true</addClasspath>
+            </manifest>
+          </archive>
+        </configuration>
+      </plugin>
+
+    </plugins>
+  </build>
 </project>

dao/src/main/java/com/iluwatar/dao/App.java

@@ -3,51 +3,56 @@ package com.iluwatar.dao;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.apache.log4j.Logger;
+
 /**
  * 
- * With the DAO pattern, we can use various method calls to retrieve/add/delete/update data without directly
+ * Data Access Object (DAO) is an object that provides an abstract interface to some type of
- * interacting with the data. The below example demonstrates basic operations(CRUD): select, add, update, and delete.
+ * database or other persistence mechanism. By mapping application calls to the persistence layer,
+ * DAO provide some specific data operations without exposing details of the database. This
+ * isolation supports the Single responsibility principle. It separates what data accesses the
+ * application needs, in terms of domain-specific objects and data types (the public interface of
+ * the DAO), from how these needs can be satisfied with a specific DBMS.
+ * <p>
+ * With the DAO pattern, we can use various method calls to retrieve/add/delete/update data without
+ * directly interacting with the data. The below example demonstrates basic CRUD operations: select,
+ * add, update, and delete.
  * 
  */
 public class App {
 
+  private static Logger LOGGER = Logger.getLogger(App.class);
+
   /**
-	 * Program entry point
+   * Program entry point.
-	 * @param args command line args
+   * 
+   * @param args command line args.
    */
-	public static void main(String[] args) {
+  public static void main(final String[] args) {
-
+    final CustomerDaoImpl customerDao = new CustomerDaoImpl(generateSampleCustomers());
-		CustomerDaoImpl customerDao = new CustomerDaoImpl(generateSampleCustomers());
+    LOGGER.info("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
-
+    LOGGER.info("customerDao.getCusterById(2): " + customerDao.getCustomerById(2));
-		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
+    final Customer customer = new Customer(4, "Dan", "Danson");
-		System.out.println("customerDao.getCusterById(2): " + customerDao.getCusterById(2));
-
-		Customer customer = new Customer(4, "Dan", "Danson");
     customerDao.addCustomer(customer);
-
+    LOGGER.info("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
-		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
-
     customer.setFirstName("Daniel");
     customer.setLastName("Danielson");
     customerDao.updateCustomer(customer);
-
+    LOGGER.info("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
-		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
-
     customerDao.deleteCustomer(customer);
-
+    LOGGER.info("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
-		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
   }
 
   /**
-	 * Generate customers
+   * Generate customers.
-	 * @return list of customers
+   * 
+   * @return list of customers.
    */
   public static List<Customer> generateSampleCustomers() {
-		Customer customer1 = new Customer(1, "Adam", "Adamson");
+    final Customer customer1 = new Customer(1, "Adam", "Adamson");
-		Customer customer2 = new Customer(2, "Bob", "Bobson");
+    final Customer customer2 = new Customer(2, "Bob", "Bobson");
-		Customer customer3 = new Customer(3, "Carl", "Carlson");
+    final Customer customer3 = new Customer(3, "Carl", "Carlson");
-
+    final List<Customer> customers = new ArrayList<Customer>();
-		List<Customer> customers = new ArrayList<Customer>();
     customers.add(customer1);
     customers.add(customer2);
     customers.add(customer3);

dao/src/main/java/com/iluwatar/dao/Customer.java

@@ -11,7 +11,7 @@ public class Customer {
   private String firstName;
   private String lastName;
 
-    public Customer(int id, String firstName, String lastName) {
+  public Customer(final int id, final String firstName, final String lastName) {
     this.id = id;
     this.firstName = firstName;
     this.lastName = lastName;
@@ -21,7 +21,7 @@ public class Customer {
     return id;
   }
 
-    public void setId(int id) {
+  public void setId(final int id) {
     this.id = id;
   }
 
@@ -29,7 +29,7 @@ public class Customer {
     return firstName;
   }
 
-    public void setFirstName(String firstName) {
+  public void setFirstName(final String firstName) {
     this.firstName = firstName;
   }
 
@@ -37,34 +37,32 @@ public class Customer {
     return lastName;
   }
 
-    public void setLastName(String lastName) {
+  public void setLastName(final String lastName) {
     this.lastName = lastName;
   }
 
   @Override
   public String toString() {
-        return "Customer{" +
+    return "Customer{" + "id=" + getId() + ", firstName='" + getFirstName() + '\'' + ", lastName='"
-                "id=" + id +
+        + getLastName() + '\'' + '}';
-                ", firstName='" + firstName + '\'' +
-                ", lastName='" + lastName + '\'' +
-                '}';
   }
 
   @Override
-    public boolean equals(Object o) {
+  public boolean equals(final Object o) {
-        if (this == o) return true;
+    boolean isEqual = false;
-        if (o == null || getClass() != o.getClass()) return false;
+    if (this == o) {
-
+      isEqual = true;
-        Customer customer = (Customer) o;
+    } else if (o != null && (getClass() == o.getClass())) {
-
+      final Customer customer = (Customer) o;
-        if (id != customer.id) return false;
+      if (getId() == customer.getId())
-
+        isEqual = true;
-        return true;
+    }
+    return isEqual;
   }
 
   @Override
   public int hashCode() {
-        int result = id;
+    int result = getId();
     return result;
   }
 }

dao/src/main/java/com/iluwatar/dao/CustomerDao.java

@@ -9,9 +9,13 @@ import java.util.List;
  */
 public interface CustomerDao {
 
-    public List<Customer> getAllCustomers();
+  List<Customer> getAllCustomers();
-    public Customer getCusterById(int id);
+
-    public void addCustomer(Customer customer);
+  Customer getCustomerById(int id);
-    public void updateCustomer(Customer customer);
+
-    public void deleteCustomer(Customer customer);
+  void addCustomer(Customer customer);
+
+  void updateCustomer(Customer customer);
+
+  void deleteCustomer(Customer customer);
 }

dao/src/main/java/com/iluwatar/dao/CustomerDaoImpl.java

@@ -4,11 +4,12 @@ import java.util.List;
 
 /**
  * 
- * The data access object (DAO) is an object that provides an abstract interface to some type of database or other persistence mechanism.
+ * The data access object (DAO) is an object that provides an abstract interface to some type of
- * By mapping application calls to the persistence layer, DAO provide some specific data operations without exposing details of the database.
+ * database or other persistence mechanism. By mapping application calls to the persistence layer,
- * This isolation supports the Single responsibility principle. It separates what data accesses the application needs, in terms of
+ * DAO provide some specific data operations without exposing details of the database. This
- * domain-specific objects and data types (the public interface of the DAO), from how these needs can be satisfied with a specific DBMS,
+ * isolation supports the Single responsibility principle. It separates what data accesses the
- * database schema, etc.
+ * application needs, in terms of domain-specific objects and data types (the public interface of
+ * the DAO), from how these needs can be satisfied with a specific DBMS, database schema, etc.
  * 
  */
 public class CustomerDaoImpl implements CustomerDao {
@@ -17,7 +18,7 @@ public class CustomerDaoImpl implements CustomerDao {
   // Note: Normally this would be in the form of an actual database and not part of the Dao Impl.
   private List<Customer> customers;
 
-    public CustomerDaoImpl(List<Customer> customers) {
+  public CustomerDaoImpl(final List<Customer> customers) {
     this.customers = customers;
   }
 
@@ -27,31 +28,35 @@ public class CustomerDaoImpl implements CustomerDao {
   }
 
   @Override
-    public Customer getCusterById(int id) {
+  public Customer getCustomerById(final int id) {
-        for (int i = 0; i < customers.size(); i++) {
+    Customer customer = null;
-            if (customers.get(i).getId() == id) {
+    for (final Customer cus : getAllCustomers()) {
-                return customers.get(i);
+      if (cus.getId() == id) {
+        customer = cus;
+        break;
       }
     }
-        // No customer found
+    return customer;
-        return null;
   }
 
   @Override
-    public void addCustomer(Customer customer) {
+  public void addCustomer(final Customer customer) {
+    if (getCustomerById(customer.getId()) == null) {
       customers.add(customer);
     }
+  }
 
 
   @Override
-    public void updateCustomer(Customer customer) {
+  public void updateCustomer(final Customer customer) {
-        if (customers.contains(customer)) {
+    if (getAllCustomers().contains(customer)) {
-            customers.set(customers.indexOf(customer), customer);
+      final int index = getAllCustomers().indexOf(customer);
+      getAllCustomers().set(index, customer);
     }
   }
 
   @Override
-    public void deleteCustomer(Customer customer) {
+  public void deleteCustomer(final Customer customer) {
-        customers.remove(customer);
+    getAllCustomers().remove(customer);
   }
 }

dao/src/main/resources/log4j.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
+<log4j:configuration debug="true"
+	xmlns:log4j='http://jakarta.apache.org/log4j/'>
+
+	<appender name="console" class="org.apache.log4j.ConsoleAppender">
+		<layout class="org.apache.log4j.PatternLayout">
+			<param name="ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
+		</layout>
+	</appender>
+
+	<root>
+		<level value="INFO" />
+		<appender-ref ref="console" />
+	</root>
+
+</log4j:configuration>

dao/src/test/java/com/iluwatar/dao/AppTest.java

@@ -1,19 +0,0 @@
-package com.iluwatar.dao;
-
-import org.junit.Test;
-
-import com.iluwatar.dao.App;
-
-/**
- * 
- * Application test
- *
- */
-public class AppTest {
-
-	@Test
-	public void test() {
-		String[] args = {};
-		App.main(args);
-	}
-}

dao/src/test/java/com/iluwatar/dao/CustomerDaoImplTest.java

@@ -0,0 +1,99 @@
+package com.iluwatar.dao;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class CustomerDaoImplTest {
+
+  private CustomerDaoImpl impl;
+  private List<Customer> customers;
+  private static final Customer CUSTOMER = new Customer(1, "Freddy", "Krueger");
+
+  @Before
+  public void setUp() {
+    customers = new ArrayList<Customer>();
+    customers.add(CUSTOMER);
+    impl = new CustomerDaoImpl(customers);
+  }
+
+  @Test
+  public void deleteExistingCustomer() {
+    assertEquals(1, impl.getAllCustomers().size());
+    impl.deleteCustomer(CUSTOMER);
+    assertTrue(impl.getAllCustomers().isEmpty());
+  }
+
+  @Test
+  public void deleteNonExistingCustomer() {
+    final Customer nonExistingCustomer = new Customer(2, "Robert", "Englund");
+    impl.deleteCustomer(nonExistingCustomer);
+    assertEquals(1, impl.getAllCustomers().size());
+  }
+
+  @Test
+  public void updateExistingCustomer() {
+    final String newFirstname = "Bernard";
+    final String newLastname = "Montgomery";
+    final Customer customer = new Customer(CUSTOMER.getId(), newFirstname, newLastname);
+    impl.updateCustomer(customer);
+    final Customer cust = impl.getCustomerById(CUSTOMER.getId());
+    assertEquals(newFirstname, cust.getFirstName());
+    assertEquals(newLastname, cust.getLastName());
+  }
+
+  @Test
+  public void updateNonExistingCustomer() {
+    final int nonExistingId = getNonExistingCustomerId();
+    final String newFirstname = "Douglas";
+    final String newLastname = "MacArthur";
+    final Customer customer = new Customer(nonExistingId, newFirstname, newLastname);
+    impl.updateCustomer(customer);
+    assertNull(impl.getCustomerById(nonExistingId));
+    final Customer existingCustomer = impl.getCustomerById(CUSTOMER.getId());
+    assertEquals(CUSTOMER.getFirstName(), existingCustomer.getFirstName());
+    assertEquals(CUSTOMER.getLastName(), existingCustomer.getLastName());
+  }
+
+  @Test
+  public void addCustomer() {
+    final Customer newCustomer = new Customer(3, "George", "Patton");
+    impl.addCustomer(newCustomer);
+    assertEquals(2, impl.getAllCustomers().size());
+  }
+
+  @Test
+  public void addAlreadyAddedCustomer() {
+    final Customer newCustomer = new Customer(3, "George", "Patton");
+    impl.addCustomer(newCustomer);
+    assertEquals(2, impl.getAllCustomers().size());
+    impl.addCustomer(newCustomer);
+    assertEquals(2, impl.getAllCustomers().size());
+  }
+
+  @Test
+  public void getExistinCustomerById() {
+    assertEquals(CUSTOMER, impl.getCustomerById(CUSTOMER.getId()));
+  }
+
+  @Test
+  public void getNonExistinCustomerById() {
+    final int nonExistingId = getNonExistingCustomerId();
+    assertNull(impl.getCustomerById(nonExistingId));
+  }
+
+  /**
+   * An arbitrary number which does not correspond to an active Customer id.
+   * 
+   * @return an int of a customer id which doesn't exist
+   */
+  private int getNonExistingCustomerId() {
+    return 999;
+  }
+}

dao/src/test/java/com/iluwatar/dao/CustomerTest.java

@@ -0,0 +1,74 @@
+package com.iluwatar.dao;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class CustomerTest {
+
+  private Customer customer;
+  private static final int ID = 1;
+  private static final String FIRSTNAME = "Winston";
+  private static final String LASTNAME = "Churchill";
+
+  @Before
+  public void setUp() {
+    customer = new Customer(ID, FIRSTNAME, LASTNAME);
+  }
+
+  @Test
+  public void getAndSetId() {
+    final int newId = 2;
+    customer.setId(newId);
+    assertEquals(newId, customer.getId());
+  }
+
+  @Test
+  public void getAndSetFirstname() {
+    final String newFirstname = "Bill";
+    customer.setFirstName(newFirstname);
+    assertEquals(newFirstname, customer.getFirstName());
+  }
+
+  @Test
+  public void getAndSetLastname() {
+    final String newLastname = "Clinton";
+    customer.setLastName(newLastname);
+    assertEquals(newLastname, customer.getLastName());
+  }
+
+  @Test
+  public void notEqualWithDifferentId() {
+    final int newId = 2;
+    final Customer otherCustomer = new Customer(newId, FIRSTNAME, LASTNAME);
+    assertNotEquals(customer, otherCustomer);
+    assertNotEquals(customer.hashCode(), otherCustomer.hashCode());
+  }
+
+  @Test
+  public void equalsWithSameObjectValues() {
+    final Customer otherCustomer = new Customer(ID, FIRSTNAME, LASTNAME);
+    assertEquals(customer, otherCustomer);
+    assertEquals(customer.hashCode(), otherCustomer.hashCode());
+  }
+
+  @Test
+  public void equalsWithSameObjects() {
+    assertEquals(customer, customer);
+    assertEquals(customer.hashCode(), customer.hashCode());
+  }
+
+  @Test
+  public void testToString() {
+    final StringBuffer buffer = new StringBuffer();
+    buffer.append("Customer{id=");
+    buffer.append("" + customer.getId());
+    buffer.append(", firstName='");
+    buffer.append(customer.getFirstName());
+    buffer.append("\', lastName='");
+    buffer.append(customer.getLastName() + "\'}");
+    assertEquals(buffer.toString(), customer.toString());
+  }
+}

decorator/index.md

@@ -4,9 +4,13 @@ title: Decorator
 folder: decorator
 permalink: /patterns/decorator/
 categories: Structural
-tags: Java
+tags:
+ - Java
+ - Gang Of Four
 ---
 
+**Also known as:** Wrapper
+
 **Intent:** Attach additional responsibilities to an object dynamically.
 Decorators provide a flexible alternative to subclassing for extending
 functionality.
@@ -18,3 +22,7 @@ functionality.
 * to add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects
 * for responsibilities that can be withdrawn
 * when extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for subclassing
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

decorator/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>decorator</artifactId>
   <dependencies>

decorator/src/main/java/com/iluwatar/decorator/App.java

@@ -2,18 +2,21 @@ package com.iluwatar.decorator;
 
 /**
  * 
- * Decorator pattern is a more flexible alternative to subclassing. The decorator
+ * The Decorator pattern is a more flexible alternative to subclassing. The Decorator class
- * class implements the same interface as the target and uses composition to
+ * implements the same interface as the target and uses composition to "decorate" calls to the
- * "decorate" calls to the target.
+ * target. Using the Decorator pattern it is possible to change the behavior of the class during
+ * runtime.
  * <p>
- * Using decorator pattern it is possible to change class behavior during
+ * In this example we show how the simple {@link Troll} first attacks and then flees the battle.
- * runtime, as the example shows.
+ * Then we decorate the {@link Troll} with a {@link SmartTroll} and perform the attack again. You
+ * can see how the behavior changes after the decoration.
  * 
  */
 public class App {
 
   /**
    * Program entry point
+   * 
    * @param args command line args
    */
   public static void main(String[] args) {
@@ -23,11 +26,13 @@ public class App {
     Hostile troll = new Troll();
     troll.attack();
     troll.fleeBattle();
+    System.out.printf("Simple troll power %d.\n", troll.getAttackPower());
 
     // change the behavior of the simple troll by adding a decorator
     System.out.println("\nA smart looking troll surprises you.");
     Hostile smart = new SmartTroll(troll);
     smart.attack();
     smart.fleeBattle();
+    System.out.printf("Smart troll power %d.\n", smart.getAttackPower());
   }
 }

decorator/src/main/java/com/iluwatar/decorator/Hostile.java

@@ -9,6 +9,8 @@ public interface Hostile {
 
   void attack();
 
+  int getAttackPower();
+
   void fleeBattle();
 
 }

decorator/src/main/java/com/iluwatar/decorator/SmartTroll.java

@@ -1,10 +1,9 @@
 package com.iluwatar.decorator;
 
 /**
- * SmartTroll is a decorator for {@link Hostile} objects.
+ * SmartTroll is a decorator for {@link Hostile} objects. The calls to the {@link Hostile} interface
- * The calls to the {@link Hostile} interface are intercepted
+ * are intercepted and decorated. Finally the calls are delegated to the decorated {@link Hostile}
- * and decorated. Finally the calls are delegated
+ * object.
- * to the decorated {@link Hostile} object.
  *
  */
 public class SmartTroll implements Hostile {
@@ -21,10 +20,15 @@ public class SmartTroll implements Hostile {
     decorated.attack();
   }
 
+  @Override
+  public int getAttackPower() {
+    // decorated troll power + 20 because it is smart
+    return decorated.getAttackPower() + 20;
+  }
+
   @Override
   public void fleeBattle() {
     System.out.println("The troll calls for help!");
     decorated.fleeBattle();
   }
-
 }

decorator/src/main/java/com/iluwatar/decorator/Troll.java

@@ -11,8 +11,12 @@ public class Troll implements Hostile {
     System.out.println("The troll swings at you with a club!");
   }
 
+  @Override
+  public int getAttackPower() {
+    return 10;
+  }
+
   public void fleeBattle() {
     System.out.println("The troll shrieks in horror and runs away!");
   }
-
 }

dependency-injection/pom.xml

@@ -1,12 +1,11 @@
 <?xml version="1.0"?>
-<project
+<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"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-	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>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>dependency-injection</artifactId>
   <dependencies>

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

@@ -2,9 +2,8 @@ package com.iluwatar.dependency.injection;
 
 /**
  * 
- * AdvancedWizard implements inversion of control.
+ * AdvancedWizard implements inversion of control. It depends on abstraction that can be injected
- * It depends on abstraction that can be injected through
+ * through its constructor.
- * its constructor.
  *
  */
 public class AdvancedWizard implements Wizard {

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

@@ -10,24 +10,25 @@ import com.google.inject.Injector;
  * - High-level modules should not depend on low-level modules. Both should depend on abstractions.
  * - Abstractions should not depend on details. Details should depend on abstractions.
  * <p>
- *  In this example we show you three different wizards. The first one ({@link SimpleWizard}) is a naive 
+ * In this example we show you three different wizards. The first one ({@link SimpleWizard}) is a
- *  implementation violating the inversion of control principle. It depends directly on a concrete
+ * naive implementation violating the inversion of control principle. It depends directly on a
- *  implementation which cannot be changed.
+ * concrete implementation which cannot be changed.
  * <p>
- *  The second wizard ({@link AdvancedWizard}) is more flexible. It does not depend on any concrete implementation 
+ * The second wizard ({@link AdvancedWizard}) is more flexible. It does not depend on any concrete
- *  but abstraction. It utilizes Dependency Injection pattern allowing its {@link Tobacco} dependency to be
+ * implementation but abstraction. It utilizes Dependency Injection pattern allowing its
- *  injected through its constructor. This way, handling the dependency is no longer the wizard's
+ * {@link Tobacco} dependency to be injected through its constructor. This way, handling the
- *  responsibility. It is resolved outside the wizard class.
+ * 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 Injection.
+ * The third example takes the pattern a step further. It uses Guice framework for Dependency
- *  {@link TobaccoModule} binds a concrete implementation to abstraction. Injector is then used to create
+ * Injection. {@link TobaccoModule} binds a concrete implementation to abstraction. Injector is then
- *  {@link GuiceWizard} object with correct dependencies.
+ * 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) {

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

@@ -4,9 +4,8 @@ import javax.inject.Inject;
 
 /**
  * 
- * GuiceWizard implements inversion of control.
+ * GuiceWizard implements inversion of control. Its dependencies are injected through its
- * Its dependencies are injected through its constructor
+ * constructor by Guice framework.
- * by Guice framework.
  *
  */
 public class GuiceWizard implements Wizard {

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

@@ -2,8 +2,8 @@ package com.iluwatar.dependency.injection;
 
 /**
  * 
- * Naive Wizard implementation violating the inversion of control principle.
+ * Naive Wizard implementation violating the inversion of control principle. It should depend on
- * It should depend on abstraction instead.
+ * abstraction instead.
  *
  */
 public class SimpleWizard implements Wizard {

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

@@ -8,6 +8,7 @@ package com.iluwatar.dependency.injection;
 public abstract class Tobacco {
 
   public void smoke(Wizard wizard) {
-		System.out.println(String.format("%s smoking %s", wizard.getClass().getSimpleName(), this.getClass().getSimpleName()));
+    System.out.println(String.format("%s smoking %s", wizard.getClass().getSimpleName(), this
+        .getClass().getSimpleName()));
   }
 }

double-checked-locking/pom.xml

@@ -1,10 +1,9 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+<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">
-	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>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-		<version>1.6.0</version>
+    <version>1.8.0</version>
   </parent>
   <artifactId>double-checked-locking</artifactId>
   <dependencies>