docs: update .all-contributorsrc [skip ci]

docs: add charlesfinley as a contributor

.all-contributorsrc

@@ -1038,6 +1038,24 @@
       "contributions": [
         "translation"
       ]
+    },
+    {
+      "login": "charlesfinley",
+      "name": "Matt Dolan",
+      "avatar_url": "https://avatars1.githubusercontent.com/u/6307904?v=4",
+      "profile": "https://github.com/charlesfinley",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "MananS77",
+      "name": "Manan",
+      "avatar_url": "https://avatars3.githubusercontent.com/u/21033516?v=4",
+      "profile": "https://github.com/MananS77",
+      "contributions": [
+        "review"
+      ]
     }
   ],
   "contributorsPerLine": 4,

README.md

@@ -9,7 +9,7 @@
 [![Join the chat at https://gitter.im/iluwatar/java-design-patterns](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/iluwatar/java-design-patterns?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Sonarcloud Status](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=alert_status)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns) 
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-[![All Contributors](https://img.shields.io/badge/all_contributors-114-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-116-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 # Introduction
@@ -239,6 +239,8 @@ This project is licensed under the terms of the MIT license.
   <tr>
     <td align="center"><a href="https://webpro.nl"><img src="https://avatars1.githubusercontent.com/u/456426?v=4" width="100px;" alt=""/><br /><sub><b>Lars Kappert</b></sub></a><br /><a href="#content-webpro" title="Content">🖋</a></td>
     <td align="center"><a href="https://xiaod.info"><img src="https://avatars2.githubusercontent.com/u/21277644?v=4" width="100px;" alt=""/><br /><sub><b>Mike Liu</b></sub></a><br /><a href="#translation-xiaod-dev" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/charlesfinley"><img src="https://avatars1.githubusercontent.com/u/6307904?v=4" width="100px;" alt=""/><br /><sub><b>Matt Dolan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=charlesfinley" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/MananS77"><img src="https://avatars3.githubusercontent.com/u/21033516?v=4" width="100px;" alt=""/><br /><sub><b>Manan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AMananS77" title="Reviewed Pull Requests">👀</a></td>
   </tr>
 </table>
 

abstract-document/README.md

@@ -9,21 +9,182 @@ tags:
 ---
 
 ## Intent
-Achieve flexibility of untyped languages and keep the type-safety 
+
+Use dynamic properties and achieve flexibility of untyped languages while keeping type-safety. 
+
+## Explanation
+
+The Abstract Document pattern enables handling additional, non-static properties. This pattern
+uses concept of traits to enable type safety and separate properties of different classes into
+set of interfaces.
+
+Real world example
+
+>  Consider a car that consists of multiple parts. However we don't know if the specific car really has all the parts, or just some of them. Our cars are dynamic and extremely flexible.
+
+In plain words
+
+> Abstract Document pattern allows attaching properties to objects without them knowing about it.
+
+Wikipedia says
+
+> An object-oriented structural design pattern for organizing objects in loosely typed key-value stores and exposing 
+the data using typed views. The purpose of the pattern is to achieve a high degree of flexibility between components 
+in a strongly typed language where new properties can be added to the object-tree on the fly, without losing the 
+support of type-safety. The pattern makes use of traits to separate different properties of a class into different 
+interfaces.
+
+**Programmatic Example**
+
+Let's first define the base classes `Document` and `AbstractDocument`. They basically make the object hold a property
+map and any amount of child objects.
+
+```java
+public interface Document {
+
+  Void put(String key, Object value);
+
+  Object get(String key);
+
+  <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor);
+}
+
+public abstract class AbstractDocument implements Document {
+
+  private final Map<String, Object> properties;
+
+  protected AbstractDocument(Map<String, Object> properties) {
+    Objects.requireNonNull(properties, "properties map is required");
+    this.properties = properties;
+  }
+
+  @Override
+  public Void put(String key, Object value) {
+    properties.put(key, value);
+    return null;
+  }
+
+  @Override
+  public Object get(String key) {
+    return properties.get(key);
+  }
+
+  @Override
+  public <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor) {
+    return Stream.ofNullable(get(key))
+        .filter(Objects::nonNull)
+        .map(el -> (List<Map<String, Object>>) el)
+        .findAny()
+        .stream()
+        .flatMap(Collection::stream)
+        .map(constructor);
+  }
+  ...
+}
+```
+Next we define an enum `Property` and a set of interfaces for type, price, model and parts. This allows us to create
+static looking interface to our `Car` class.
+
+```java
+public enum Property {
+
+  PARTS, TYPE, PRICE, MODEL
+}
+
+public interface HasType extends Document {
+
+  default Optional<String> getType() {
+    return Optional.ofNullable((String) get(Property.TYPE.toString()));
+  }
+}
+
+public interface HasPrice extends Document {
+
+  default Optional<Number> getPrice() {
+    return Optional.ofNullable((Number) get(Property.PRICE.toString()));
+  }
+}
+public interface HasModel extends Document {
+
+  default Optional<String> getModel() {
+    return Optional.ofNullable((String) get(Property.MODEL.toString()));
+  }
+}
+
+public interface HasParts extends Document {
+
+  default Stream<Part> getParts() {
+    return children(Property.PARTS.toString(), Part::new);
+  }
+}
+```
+
+Now we are ready to introduce the `Car`.
+
+```java
+public class Car extends AbstractDocument implements HasModel, HasPrice, HasParts {
+
+  public Car(Map<String, Object> properties) {
+    super(properties);
+  }
+}
+```
+
+And finally here's how we construct and use the `Car` in a full example.
+
+```java
+    LOGGER.info("Constructing parts and car");
+
+    var wheelProperties = Map.of(
+        Property.TYPE.toString(), "wheel",
+        Property.MODEL.toString(), "15C",
+        Property.PRICE.toString(), 100L);
+
+    var doorProperties = Map.of(
+        Property.TYPE.toString(), "door",
+        Property.MODEL.toString(), "Lambo",
+        Property.PRICE.toString(), 300L);
+
+    var carProperties = Map.of(
+        Property.MODEL.toString(), "300SL",
+        Property.PRICE.toString(), 10000L,
+        Property.PARTS.toString(), List.of(wheelProperties, doorProperties));
+
+    var car = new Car(carProperties);
+
+    LOGGER.info("Here is our car:");
+    LOGGER.info("-> model: {}", car.getModel().orElseThrow());
+    LOGGER.info("-> price: {}", car.getPrice().orElseThrow());
+    LOGGER.info("-> parts: ");
+    car.getParts().forEach(p -> LOGGER.info("\t{}/{}/{}",
+        p.getType().orElse(null),
+        p.getModel().orElse(null),
+        p.getPrice().orElse(null))
+    );
+
+    // Constructing parts and car
+    // Here is our car:
+    // model: 300SL
+    // price: 10000
+    // parts: 
+    // wheel/15C/100
+    // door/Lambo/300
+```
 
 ## Class diagram
+
 ![alt text](./etc/abstract-document.png "Abstract Document Traits and Domain")
 
-
 ## Applicability
+
 Use the Abstract Document Pattern when
 
-* there is a need to add new properties on the fly
+* There is a need to add new properties on the fly
-* you want a flexible way to organize domain in tree like structure
+* You want a flexible way to organize domain in tree like structure
-* you want more loosely coupled system
+* You want more loosely coupled system
-
 
 ## Credits
 
 * [Wikipedia: Abstract Document Pattern](https://en.wikipedia.org/wiki/Abstract_Document_Pattern)
 * [Martin Fowler: Dealing with properties](http://martinfowler.com/apsupp/properties.pdf)
+* [Pattern-Oriented Software Architecture Volume 4: A Pattern Language for Distributed Computing (v. 4)](https://www.amazon.com/gp/product/0470059028/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0470059028&linkId=e3aacaea7017258acf184f9f3283b492)

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasParts.java

@@ -32,7 +32,6 @@ import java.util.stream.Stream;
  */
 public interface HasParts extends Document {
 
-
   default Stream<Part> getParts() {
     return children(Property.PARTS.toString(), Part::new);
   }

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasPrice.java

@@ -32,7 +32,6 @@ import java.util.Optional;
  */
 public interface HasPrice extends Document {
 
-
   default Optional<Number> getPrice() {
     return Optional.ofNullable((Number) get(Property.PRICE.toString()));
   }

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasType.java

@@ -32,7 +32,6 @@ import java.util.Optional;
  */
 public interface HasType extends Document {
 
-
   default Optional<String> getType() {
     return Optional.ofNullable((String) get(Property.TYPE.toString()));
   }

abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java

@@ -47,7 +47,7 @@ public class AbstractDocumentTest {
     }
   }
 
-  private DocumentImplementation document = new DocumentImplementation(new HashMap<>());
+  private final DocumentImplementation document = new DocumentImplementation(new HashMap<>());
 
   @Test
   public void shouldPutAndGetValue() {

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

@@ -36,7 +36,7 @@ import org.junit.jupiter.api.Test;
  */
 public class AbstractFactoryTest {
 
-  private App app = new App();
+  private final App app = new App();
   private KingdomFactory elfFactory;
   private KingdomFactory orcFactory;
 

acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/ConfigureForDosVisitorTest.java

@@ -37,7 +37,7 @@ import uk.org.lidalia.slf4jtest.TestLoggerFactory;
  */
 public class ConfigureForDosVisitorTest {
 
-  private TestLogger logger = TestLoggerFactory.getTestLogger(ConfigureForDosVisitor.class);
+  private final TestLogger logger = TestLoggerFactory.getTestLogger(ConfigureForDosVisitor.class);
   
   @Test
   public void testVisitForZoom() {    

adapter/README.md

@@ -56,7 +56,7 @@ And captain expects an implementation of `RowingBoat` interface to be able to mo
 ```java
 public class Captain {
 
-  private RowingBoat rowingBoat;
+  private final RowingBoat rowingBoat;
   // default constructor and setter for rowingBoat
   public Captain(RowingBoat rowingBoat) {
     this.rowingBoat = rowingBoat;
@@ -75,7 +75,7 @@ public class FishingBoatAdapter implements RowingBoat {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(FishingBoatAdapter.class);
 
-  private FishingBoat boat;
+  private final FishingBoat boat;
 
   public FishingBoatAdapter() {
     boat = new FishingBoat();

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

@@ -29,7 +29,7 @@ package com.iluwatar.adapter;
  */
 public class FishingBoatAdapter implements RowingBoat {
 
-  private FishingBoat boat;
+  private final FishingBoat boat;
 
   public FishingBoatAdapter() {
     boat = new FishingBoat();

ambassador/src/test/java/com/iluwatar/ambassador/RemoteServiceTest.java

@@ -48,7 +48,7 @@ class RemoteServiceTest {
   }
 
   private static class StaticRandomProvider implements RandomProvider {
-    private double value;
+    private final double value;
 
     StaticRandomProvider(double value) {
       this.value = value;

arrange-act-assert/src/test/java/com/iluwatar/arrangeactassert/CashAAATest.java

@@ -60,7 +60,7 @@ public class CashAAATest {
     //Act
     cash.plus(4);
     //Assert
-    assertEquals(cash.count(), 7);
+    assertEquals(7, cash.count());
   }
 
   @Test
@@ -71,7 +71,7 @@ public class CashAAATest {
     var result = cash.minus(5);
     //Assert
     assertTrue(result);
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
   }
 
   @Test
@@ -82,7 +82,7 @@ public class CashAAATest {
     var result = cash.minus(6);
     //Assert
     assertFalse(result);
-    assertEquals(cash.count(), 1);
+    assertEquals(1, cash.count());
   }
 
   @Test
@@ -94,6 +94,6 @@ public class CashAAATest {
     var result = cash.minus(3);
     //Assert
     assertTrue(result);
-    assertEquals(cash.count(), 8);
+    assertEquals(8, cash.count());
   }
 }

arrange-act-assert/src/test/java/com/iluwatar/arrangeactassert/CashAntiAAATest.java

@@ -44,16 +44,16 @@ public class CashAntiAAATest {
     var cash = new Cash(3);
     //test plus
     cash.plus(4);
-    assertEquals(cash.count(), 7);
+    assertEquals(7, cash.count());
     //test minus
     cash = new Cash(8);
     assertTrue(cash.minus(5));
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
     assertFalse(cash.minus(6));
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
     //test update
     cash.plus(5);
     assertTrue(cash.minus(5));
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
   }
 }

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

@@ -100,7 +100,7 @@ public class ThreadAsyncExecutor implements AsyncExecutor {
     void setValue(T value) {
       this.value = value;
       this.state = COMPLETED;
-      this.callback.ifPresent(ac -> ac.onComplete(value, Optional.<Exception>empty()));
+      this.callback.ifPresent(ac -> ac.onComplete(value, Optional.empty()));
       synchronized (lock) {
         lock.notifyAll();
       }

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

@@ -28,7 +28,7 @@ package com.iluwatar.business.delegate;
  */
 public class Client {
 
-  private BusinessDelegate businessDelegate;
+  private final BusinessDelegate businessDelegate;
 
   public Client(BusinessDelegate businessDelegate) {
     this.businessDelegate = businessDelegate;

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

@@ -28,5 +28,5 @@ package com.iluwatar.business.delegate;
  */
 public enum ServiceType {
 
-  EJB, JMS;
+  EJB, JMS
 }

bytecode/src/main/java/com/iluwatar/bytecode/VirtualMachine.java

@@ -30,9 +30,9 @@ import java.util.Stack;
  */
 public class VirtualMachine {
 
-  private Stack<Integer> stack = new Stack<>();
+  private final Stack<Integer> stack = new Stack<>();
 
-  private Wizard[] wizards = new Wizard[2];
+  private final Wizard[] wizards = new Wizard[2];
 
   /**
    * Constructor.

bytecode/src/test/java/com/iluwatar/bytecode/VirtualMachineTest.java

@@ -104,7 +104,7 @@ public class VirtualMachineTest {
     bytecode[2] = LITERAL.getIntValue();
     bytecode[3] = 50;                        // health amount
     bytecode[4] = SET_HEALTH.getIntValue();
-    bytecode[5] = LITERAL.getIntValue();;
+    bytecode[5] = LITERAL.getIntValue();
     bytecode[6] = wizardNumber;
     bytecode[7] = GET_HEALTH.getIntValue();
 

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

@@ -29,7 +29,7 @@ package com.iluwatar.caching;
 public enum CachingPolicy {
   THROUGH("through"), AROUND("around"), BEHIND("behind"), ASIDE("aside");
 
-  private String policy;
+  private final String policy;
 
   CachingPolicy(String policy) {
     this.policy = policy;

chain/README.md

@@ -65,7 +65,7 @@ Then the request handler hierarchy
 ```java
 public abstract class RequestHandler {
   private static final Logger LOGGER = LoggerFactory.getLogger(RequestHandler.class);
-  private RequestHandler next;
+  private final RequestHandler next;
 
   public RequestHandler(RequestHandler next) {
     this.next = next;

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

@@ -33,7 +33,7 @@ public abstract class RequestHandler {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(RequestHandler.class);
 
-  private RequestHandler next;
+  private final RequestHandler next;
 
   public RequestHandler(RequestHandler next) {
     this.next = next;

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java

@@ -87,10 +87,7 @@ public class Car {
     } else if (!model.equals(other.model)) {
       return false;
     }
-    if (year != other.year) {
+    return year == other.year;
-      return false;
-    }
-    return true;
   }
 
   public String getMake() {

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Person.java

@@ -29,7 +29,7 @@ import java.util.List;
  * A Person class that has the list of cars that the person owns and use.
  */
 public class Person {
-  private List<Car> cars;
+  private final List<Car> cars;
 
   /**
    * Constructor to create an instance of person.

collection-pipeline/src/test/java/com/iluwatar/collectionpipeline/AppTest.java

@@ -37,7 +37,7 @@ import org.slf4j.LoggerFactory;
 public class AppTest {
   private static final Logger LOGGER = LoggerFactory.getLogger(AppTest.class);
 
-  private List<Car> cars = CarFactory.createCars();
+  private final List<Car> cars = CarFactory.createCars();
 
   @Test
   public void testGetModelsAfter2000UsingFor() {

command/README.md

@@ -36,8 +36,8 @@ public class Wizard {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Wizard.class);
 
-  private Deque<Command> undoStack = new LinkedList<>();
+  private final Deque<Command> undoStack = new LinkedList<>();
-  private Deque<Command> redoStack = new LinkedList<>();
+  private final Deque<Command> redoStack = new LinkedList<>();
 
   public Wizard() {}
 

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

@@ -30,7 +30,7 @@ public enum Size {
 
   SMALL("small"), NORMAL("normal");
 
-  private String title;
+  private final String title;
 
   Size(String title) {
     this.title = title;

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

@@ -30,7 +30,7 @@ public enum Visibility {
 
   VISIBLE("visible"), INVISIBLE("invisible");
 
-  private String title;
+  private final String title;
 
   Visibility(String title) {
     this.title = title;

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

@@ -35,8 +35,8 @@ public class Wizard {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Wizard.class);
 
-  private Deque<Command> undoStack = new LinkedList<>();
+  private final Deque<Command> undoStack = new LinkedList<>();
-  private Deque<Command> redoStack = new LinkedList<>();
+  private final Deque<Command> redoStack = new LinkedList<>();
 
   public Wizard() {
     // comment to ignore sonar issue: LEVEL critical

commander/src/main/java/com/iluwatar/commander/employeehandle/EmployeeDatabase.java

@@ -33,7 +33,7 @@ import java.util.Hashtable;
  */
 
 public class EmployeeDatabase extends Database<Order> {
-  private Hashtable<String, Order> data;
+  private final Hashtable<String, Order> data;
 
   public EmployeeDatabase() {
     this.data = new Hashtable<>();

commander/src/main/java/com/iluwatar/commander/messagingservice/MessagingDatabase.java

@@ -33,7 +33,7 @@ import java.util.Hashtable;
  */
 
 public class MessagingDatabase extends Database<MessageRequest> {
-  private Hashtable<String, MessageRequest> data;
+  private final Hashtable<String, MessageRequest> data;
 
   public MessagingDatabase() {
     this.data = new Hashtable<>();

commander/src/main/java/com/iluwatar/commander/paymentservice/PaymentDatabase.java

@@ -34,7 +34,7 @@ import java.util.Hashtable;
 
 public class PaymentDatabase extends Database<PaymentRequest> {
 
-  private Hashtable<String, PaymentRequest> data;
+  private final Hashtable<String, PaymentRequest> data;
 
   public PaymentDatabase() {
     this.data = new Hashtable<>();

commander/src/main/java/com/iluwatar/commander/queue/QueueDatabase.java

@@ -35,7 +35,7 @@ import java.util.List;
 
 public class QueueDatabase extends Database<QueueTask> {
 
-  private Queue<QueueTask> data;
+  private final Queue<QueueTask> data;
   public List<Exception> exceptionsList;
 
   public QueueDatabase(Exception... exc) {

commander/src/main/java/com/iluwatar/commander/shippingservice/ShippingDatabase.java

@@ -34,7 +34,7 @@ import java.util.Hashtable;
 
 public class ShippingDatabase extends Database<ShippingRequest> {
 
-  private Hashtable<String, ShippingRequest> data;
+  private final Hashtable<String, ShippingRequest> data;
 
   public ShippingDatabase() {
     this.data = new Hashtable<>();

composite/README.md

@@ -34,7 +34,7 @@ Taking our sentence example from above. Here we have the base class and differen
 ```java
 public abstract class LetterComposite {
 
-  private List<LetterComposite> children = new ArrayList<>();
+  private final List<LetterComposite> children = new ArrayList<>();
 
   public void add(LetterComposite letter) {
     children.add(letter);
@@ -59,7 +59,7 @@ public abstract class LetterComposite {
 
 public class Letter extends LetterComposite {
 
-  private char character;
+  private final char character;
 
   public Letter(char c) {
     this.character = c;

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

@@ -28,7 +28,7 @@ package com.iluwatar.composite;
  */
 public class Letter extends LetterComposite {
 
-  private char character;
+  private final char character;
 
   public Letter(char c) {
     this.character = c;

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

@@ -31,7 +31,7 @@ import java.util.List;
  */
 public abstract class LetterComposite {
 
-  private List<LetterComposite> children = new ArrayList<>();
+  private final List<LetterComposite> children = new ArrayList<>();
 
   public void add(LetterComposite letter) {
     children.add(letter);

converter/src/main/java/com/iluwatar/converter/User.java

@@ -29,10 +29,10 @@ import java.util.Objects;
  * User class.
  */
 public class User {
-  private String firstName;
+  private final String firstName;
-  private String lastName;
+  private final String lastName;
-  private boolean isActive;
+  private final boolean isActive;
-  private String userId;
+  private final String userId;
 
   /**
    * Constructor.

converter/src/main/java/com/iluwatar/converter/UserDto.java

@@ -30,10 +30,10 @@ import java.util.Objects;
  */
 public class UserDto {
 
-  private String firstName;
+  private final String firstName;
-  private String lastName;
+  private final String lastName;
-  private boolean isActive;
+  private final boolean isActive;
-  private String email;
+  private final String email;
 
   /**
    * Constructor.

converter/src/test/java/com/iluwatar/converter/ConverterTest.java

@@ -34,7 +34,7 @@ import org.junit.jupiter.api.Test;
  */
 public class ConverterTest {
 
-  private UserConverter userConverter = new UserConverter();
+  private final UserConverter userConverter = new UserConverter();
 
   /**
    * Tests whether a converter created of opposite functions holds equality as a bijection.

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

@@ -34,7 +34,7 @@ import org.hibernate.SessionFactory;
  */
 public class CommandServiceImpl implements ICommandService {
 
-  private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
+  private final SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
 
   private Author getAuthorByUsername(String username) {
     Author author;

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

@@ -38,7 +38,7 @@ import org.hibernate.transform.Transformers;
  */
 public class QueryServiceImpl implements IQueryService {
 
-  private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
+  private final SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
 
   @Override
   public Author getAuthorByUsername(String username) {

dao/README.md

@@ -112,7 +112,7 @@ public interface CustomerDao {
 
 public class InMemoryCustomerDao implements CustomerDao {
 
-  private Map<Integer, Customer> idToCustomer = new HashMap<>();
+  private final Map<Integer, Customer> idToCustomer = new HashMap<>();
 
   @Override
   public Stream<Customer> getAll() {

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

@@ -44,7 +44,7 @@ import org.slf4j.LoggerFactory;
  */
 public class App {
   private static final String DB_URL = "jdbc:h2:~/dao";
-  private static Logger log = LoggerFactory.getLogger(App.class);
+  private static final Logger log = LoggerFactory.getLogger(App.class);
   private static final String ALL_CUSTOMERS = "customerDao.getAllCustomers(): ";
 
   /**

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

@@ -36,7 +36,7 @@ import java.util.stream.Stream;
  */
 public class InMemoryCustomerDao implements CustomerDao {
 
-  private Map<Integer, Customer> idToCustomer = new HashMap<>();
+  private final Map<Integer, Customer> idToCustomer = new HashMap<>();
 
   /**
    * An eagerly evaluated stream of customers stored in memory.

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

@@ -50,7 +50,7 @@ public class DbCustomerDaoTest {
 
   private static final String DB_URL = "jdbc:h2:~/dao";
   private DbCustomerDao dao;
-  private Customer existingCustomer = new Customer(1, "Freddy", "Krueger");
+  private final Customer existingCustomer = new Customer(1, "Freddy", "Krueger");
 
   /**
    * Creates customers schema.

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

@@ -41,7 +41,7 @@ public class MessageCollectorMember implements Member {
 
   private final String name;
 
-  private List<String> messages = new ArrayList<>();
+  private final List<String> messages = new ArrayList<>();
 
   public MessageCollectorMember(String name) {
     this.name = name;

data-mapper/src/main/java/com/iluwatar/datamapper/App.java

@@ -38,7 +38,7 @@ import org.slf4j.LoggerFactory;
  */
 public final class App {
 
-  private static Logger log = LoggerFactory.getLogger(App.class);
+  private static final Logger log = LoggerFactory.getLogger(App.class);
   private static final String STUDENT_STRING = "App.main(), student : ";
 
 

data-mapper/src/main/java/com/iluwatar/datamapper/StudentDataMapperImpl.java

@@ -33,7 +33,7 @@ import java.util.Optional;
 public final class StudentDataMapperImpl implements StudentDataMapper {
 
   /* Note: Normally this would be in the form of an actual database */
-  private List<Student> students = new ArrayList<>();
+  private final List<Student> students = new ArrayList<>();
 
   @Override
   public Optional<Student> find(int studentId) {

data-transfer-object/README.md

@@ -64,7 +64,7 @@ Customer resource class acts as the server for customer information.
 
 ```java
 public class CustomerResource {
-  private List<CustomerDto> customers;
+  private final List<CustomerDto> customers;
 
   public CustomerResource(List<CustomerDto> customers) {
     this.customers = customers;

data-transfer-object/src/main/java/com/iluwatar/datatransfer/CustomerResource.java

@@ -30,7 +30,7 @@ import java.util.List;
  * has all customer details.
  */
 public class CustomerResource {
-  private List<CustomerDto> customers;
+  private final List<CustomerDto> customers;
 
   /**
    * Initialise resource with existing customers.

decorator/README.md

@@ -70,7 +70,7 @@ public class ClubbedTroll implements Troll {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(ClubbedTroll.class);
 
-  private Troll decorated;
+  private final Troll decorated;
 
   public ClubbedTroll(Troll decorated) {
     this.decorated = decorated;

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

@@ -33,7 +33,7 @@ public class ClubbedTroll implements Troll {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(ClubbedTroll.class);
 
-  private Troll decorated;
+  private final Troll decorated;
 
   public ClubbedTroll(Troll decorated) {
     this.decorated = decorated;

decorator/src/test/java/com/iluwatar/decorator/SimpleTrollTest.java

@@ -68,7 +68,7 @@ public class SimpleTrollTest {
 
   private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
 
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();
 
     public InMemoryAppender(Class clazz) {
       ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);

delegation/src/test/java/com/iluwatar/delegation/simple/DelegateTest.java

@@ -86,7 +86,7 @@ public class DelegateTest {
    */
   private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
 
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();
 
     public InMemoryAppender() {
       ((Logger) LoggerFactory.getLogger("root")).addAppender(this);

dependency-injection/README.md

@@ -62,7 +62,7 @@ public interface Wizard {
 
 public class AdvancedWizard implements Wizard {
 
-  private Tobacco tobacco;
+  private final Tobacco tobacco;
 
   public AdvancedWizard(Tobacco tobacco) {
     this.tobacco = tobacco;

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

@@ -29,7 +29,7 @@ package com.iluwatar.dependency.injection;
  */
 public class AdvancedWizard implements Wizard {
 
-  private Tobacco tobacco;
+  private final Tobacco tobacco;
 
   public AdvancedWizard(Tobacco tobacco) {
     this.tobacco = tobacco;

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

@@ -31,7 +31,7 @@ import javax.inject.Inject;
  */
 public class GuiceWizard implements Wizard {
 
-  private Tobacco tobacco;
+  private final Tobacco tobacco;
 
   @Inject
   public GuiceWizard(Tobacco tobacco) {

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

@@ -29,7 +29,7 @@ package com.iluwatar.dependency.injection;
  */
 public class SimpleWizard implements Wizard {
 
-  private OldTobyTobacco tobacco = new OldTobyTobacco();
+  private final OldTobyTobacco tobacco = new OldTobyTobacco();
 
   public void smoke() {
     tobacco.smoke(this);

dependency-injection/src/test/java/com/iluwatar/dependency/injection/utils/InMemoryAppender.java

@@ -37,7 +37,7 @@ import java.util.List;
  */
 public class InMemoryAppender extends AppenderBase<ILoggingEvent> {
 
-  private List<ILoggingEvent> log = new LinkedList<>();
+  private final List<ILoggingEvent> log = new LinkedList<>();
 
   public InMemoryAppender(Class clazz) {
     ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);

dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java

@@ -34,7 +34,7 @@ import java.util.List;
 public class World {
 
   private List<String> countries;
-  private DataFetcher df;
+  private final DataFetcher df;
 
   public World() {
     this.countries = new ArrayList<String>();

double-buffer/src/main/java/com/iluwatar/doublebuffer/FrameBuffer.java

@@ -33,7 +33,7 @@ public class FrameBuffer implements Buffer {
   public static final int WIDTH = 10;
   public static final int HEIGHT = 8;
 
-  private Pixel[] pixels = new Pixel[WIDTH * HEIGHT];
+  private final Pixel[] pixels = new Pixel[WIDTH * HEIGHT];
 
   public FrameBuffer() {
     clearAll();

double-buffer/src/main/java/com/iluwatar/doublebuffer/Pixel.java

@@ -31,7 +31,7 @@ public enum Pixel {
   WHITE(0),
   BLACK(1);
 
-  private int color;
+  private final int color;
 
   Pixel(int color) {
     this.color = color;

double-buffer/src/main/java/com/iluwatar/doublebuffer/Scene.java

@@ -35,7 +35,7 @@ public class Scene {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Scene.class);
 
-  private Buffer[] frameBuffers;
+  private final Buffer[] frameBuffers;
 
   private int current;
 

double-checked-locking/src/test/java/com/iluwatar/doublechecked/locking/InventoryTest.java

@@ -109,7 +109,7 @@ public class InventoryTest {
 
 
   private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();
 
     public InMemoryAppender(Class clazz) {
       ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);

double-dispatch/src/main/java/com/iluwatar/doubledispatch/Rectangle.java

@@ -28,10 +28,10 @@ package com.iluwatar.doubledispatch;
  */
 public class Rectangle {
 
-  private int left;
+  private final int left;
-  private int top;
+  private final int top;
-  private int right;
+  private final int right;
-  private int bottom;
+  private final int bottom;
 
   /**
    * Constructor.

event-aggregator/src/main/java/com/iluwatar/event/aggregator/Event.java

@@ -31,7 +31,7 @@ public enum Event {
   STARK_SIGHTED("Stark sighted"), WARSHIPS_APPROACHING("Warships approaching"), TRAITOR_DETECTED(
       "Traitor detected");
 
-  private String description;
+  private final String description;
 
   Event(String description) {
     this.description = description;

event-aggregator/src/main/java/com/iluwatar/event/aggregator/EventEmitter.java

@@ -31,7 +31,7 @@ import java.util.List;
  */
 public abstract class EventEmitter {
 
-  private List<EventObserver> observers;
+  private final List<EventObserver> observers;
 
   public EventEmitter() {
     observers = new LinkedList<>();

event-aggregator/src/main/java/com/iluwatar/event/aggregator/Weekday.java

@@ -36,7 +36,7 @@ public enum Weekday {
   SATURDAY("Saturday"),
   SUNDAY("Sunday");
 
-  private String description;
+  private final String description;
 
   Weekday(String description) {
     this.description = description;

event-aggregator/src/test/java/com/iluwatar/event/aggregator/KingJoffreyTest.java

@@ -74,7 +74,7 @@ public class KingJoffreyTest {
   }
 
   private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();
 
     public InMemoryAppender(Class<?> clazz) {
       ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);

event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/Event.java

@@ -33,9 +33,9 @@ public class Event implements IEvent, Runnable {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Event.class);
 
-  private int eventId;
+  private final int eventId;
-  private int eventTime;
+  private final int eventTime;
-  private boolean isSynchronous;
+  private final boolean isSynchronous;
   private Thread thread;
   private boolean isComplete = false;
   private ThreadCompleteListener eventListener;

event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/EventManager.java

@@ -43,8 +43,8 @@ public class EventManager implements ThreadCompleteListener {
   public static final int MAX_ID = MAX_RUNNING_EVENTS;
   public static final int MAX_EVENT_TIME = 1800; // in seconds / 30 minutes.
   private int currentlyRunningSyncEvent = -1;
-  private Random rand;
+  private final Random rand;
-  private Map<Integer, Event> eventPool;
+  private final Map<Integer, Event> eventPool;
 
   private static final String DOES_NOT_EXIST = " does not exist.";
 

event-driven-architecture/src/main/java/com/iluwatar/eda/event/UserCreatedEvent.java

@@ -32,7 +32,7 @@ import com.iluwatar.eda.model.User;
  */
 public class UserCreatedEvent extends AbstractEvent {
 
-  private User user;
+  private final User user;
 
   public UserCreatedEvent(User user) {
     this.user = user;

event-driven-architecture/src/main/java/com/iluwatar/eda/event/UserUpdatedEvent.java

@@ -32,7 +32,7 @@ import com.iluwatar.eda.model.User;
  */
 public class UserUpdatedEvent extends AbstractEvent {
 
-  private User user;
+  private final User user;
 
   public UserUpdatedEvent(User user) {
     this.user = user;

event-driven-architecture/src/main/java/com/iluwatar/eda/framework/EventDispatcher.java

@@ -32,7 +32,7 @@ import java.util.Map;
  */
 public class EventDispatcher {
 
-  private Map<Class<? extends Event>, Handler<? extends Event>> handlers;
+  private final Map<Class<? extends Event>, Handler<? extends Event>> handlers;
 
   public EventDispatcher() {
     handlers = new HashMap<>();

event-driven-architecture/src/main/java/com/iluwatar/eda/model/User.java

@@ -32,7 +32,7 @@ import com.iluwatar.eda.event.UserUpdatedEvent;
  */
 public class User {
 
-  private String username;
+  private final String username;
 
   public User(String username) {
     this.username = username;

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

@@ -49,7 +49,7 @@ public class Audio {
 
   private volatile Thread updateThread = null;
 
-  private PlayMessage[] pendingAudio = new PlayMessage[MAX_PENDING];
+  private final PlayMessage[] pendingAudio = new PlayMessage[MAX_PENDING];
 
   // Visible only for testing purposes
   Audio() {

extension-objects/src/main/java/concreteextensions/Commander.java

@@ -35,7 +35,7 @@ public class Commander implements CommanderExtension {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Commander.class);
 
-  private CommanderUnit unit;
+  private final CommanderUnit unit;
 
   public Commander(CommanderUnit commanderUnit) {
     this.unit = commanderUnit;

extension-objects/src/main/java/concreteextensions/Sergeant.java

@@ -35,7 +35,7 @@ public class Sergeant implements SergeantExtension {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Sergeant.class);
 
-  private SergeantUnit unit;
+  private final SergeantUnit unit;
 
   public Sergeant(SergeantUnit sergeantUnit) {
     this.unit = sergeantUnit;

extension-objects/src/main/java/concreteextensions/Soldier.java

@@ -34,7 +34,7 @@ import units.SoldierUnit;
 public class Soldier implements SoldierExtension {
   private static final Logger LOGGER = LoggerFactory.getLogger(Soldier.class);
 
-  private SoldierUnit unit;
+  private final SoldierUnit unit;
 
   public Soldier(SoldierUnit soldierUnit) {
     this.unit = soldierUnit;

facade/README.md

@@ -83,7 +83,7 @@ public abstract class DwarvenMineWorker {
 
   public abstract String name();
 
-  static enum Action {
+  enum Action {
     GO_TO_SLEEP, WAKE_UP, GO_HOME, GO_TO_MINE, WORK
   }
 }

facade/src/test/java/com/iluwatar/facade/DwarvenGoldmineFacadeTest.java

@@ -110,7 +110,7 @@ public class DwarvenGoldmineFacadeTest {
 
   private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
 
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();
 
     public InMemoryAppender() {
       ((Logger) LoggerFactory.getLogger("root")).addAppender(this);

factory-method/src/main/java/com/iluwatar/factory/method/ElfBlacksmith.java

@@ -32,7 +32,7 @@ import java.util.Map;
  */
 public class ElfBlacksmith implements Blacksmith {
 
-  private static Map<WeaponType, ElfWeapon> ELFARSENAL;
+  private static final Map<WeaponType, ElfWeapon> ELFARSENAL;
 
   static {
     ELFARSENAL = new HashMap<>(WeaponType.values().length);

factory-method/src/main/java/com/iluwatar/factory/method/ElfWeapon.java

@@ -28,7 +28,7 @@ package com.iluwatar.factory.method;
  */
 public class ElfWeapon implements Weapon {
 
-  private WeaponType weaponType;
+  private final WeaponType weaponType;
 
   public ElfWeapon(WeaponType weaponType) {
     this.weaponType = weaponType;

factory-method/src/main/java/com/iluwatar/factory/method/OrcBlacksmith.java

@@ -32,7 +32,7 @@ import java.util.Map;
  */
 public class OrcBlacksmith implements Blacksmith {
 
-  private static Map<WeaponType, OrcWeapon> ORCARSENAL;
+  private static final Map<WeaponType, OrcWeapon> ORCARSENAL;
 
   static {
     ORCARSENAL = new HashMap<>(WeaponType.values().length);

factory-method/src/main/java/com/iluwatar/factory/method/OrcWeapon.java

@@ -28,7 +28,7 @@ package com.iluwatar.factory.method;
  */
 public class OrcWeapon implements Weapon {
 
-  private WeaponType weaponType;
+  private final WeaponType weaponType;
 
   public OrcWeapon(WeaponType weaponType) {
     this.weaponType = weaponType;

factory-method/src/main/java/com/iluwatar/factory/method/WeaponType.java

@@ -30,7 +30,7 @@ public enum WeaponType {
 
   SHORT_SWORD("short sword"), SPEAR("spear"), AXE("axe"), UNDEFINED("");
 
-  private String title;
+  private final String title;
 
   WeaponType(String title) {
     this.title = title;

feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/propertiesversion/PropertiesFeatureToggleVersion.java

@@ -42,7 +42,7 @@ import java.util.Properties;
  */
 public class PropertiesFeatureToggleVersion implements Service {
 
-  private boolean isEnhanced;
+  private final boolean isEnhanced;
 
   /**
    * Creates an instance of {@link PropertiesFeatureToggleVersion} using the passed {@link

feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/User.java

@@ -29,7 +29,7 @@ package com.iluwatar.featuretoggle.user;
  */
 public class User {
 
-  private String name;
+  private final String name;
 
   /**
    * Default Constructor setting the username.

feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/UserGroup.java

@@ -35,8 +35,8 @@ import java.util.List;
  */
 public class UserGroup {
 
-  private static List<User> freeGroup = new ArrayList<>();
+  private static final List<User> freeGroup = new ArrayList<>();
-  private static List<User> paidGroup = new ArrayList<>();
+  private static final List<User> paidGroup = new ArrayList<>();
 
 
   /**

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

@@ -94,7 +94,7 @@ public class App {
         .filter(positives())
         .first(4)
         .last(2)
-        .map(number -> "String[" + valueOf(number) + "]")
+        .map(number -> "String[" + number + "]")
         .asList();
     prettyPrint("The lazy list contains the last two of the first four positive numbers "
         + "mapped to Strings: ", lastTwoOfFirstFourStringMapped);

fluentinterface/src/main/java/com/iluwatar/fluentinterface/fluentiterable/lazy/LazyFluentIterable.java

@@ -198,7 +198,7 @@ public class LazyFluentIterable<E> implements FluentIterable<E> {
       @Override
       public Iterator<T> iterator() {
         return new DecoratingIterator<T>(null) {
-          Iterator<E> oldTypeIterator = iterable.iterator();
+          final Iterator<E> oldTypeIterator = iterable.iterator();
 
           @Override
           public T computeNext() {

flux/src/main/java/com/iluwatar/flux/action/Action.java

@@ -28,7 +28,7 @@ package com.iluwatar.flux.action;
  */
 public abstract class Action {
 
-  private ActionType type;
+  private final ActionType type;
 
   public Action(ActionType type) {
     this.type = type;

flux/src/main/java/com/iluwatar/flux/action/ActionType.java

@@ -28,6 +28,6 @@ package com.iluwatar.flux.action;
  */
 public enum ActionType {
 
-  MENU_ITEM_SELECTED, CONTENT_CHANGED;
+  MENU_ITEM_SELECTED, CONTENT_CHANGED
 
 }

flux/src/main/java/com/iluwatar/flux/action/Content.java

@@ -31,7 +31,7 @@ public enum Content {
   PRODUCTS("Products - This page lists the company's products."), COMPANY(
       "Company - This page displays information about the company.");
 
-  private String title;
+  private final String title;
 
   Content(String title) {
     this.title = title;

flux/src/main/java/com/iluwatar/flux/action/ContentAction.java

@@ -28,7 +28,7 @@ package com.iluwatar.flux.action;
  */
 public class ContentAction extends Action {
 
-  private Content content;
+  private final Content content;
 
   public ContentAction(Content content) {
     super(ActionType.CONTENT_CHANGED);

flux/src/main/java/com/iluwatar/flux/action/MenuAction.java

@@ -29,7 +29,7 @@ package com.iluwatar.flux.action;
  */
 public class MenuAction extends Action {
 
-  private MenuItem menuItem;
+  private final MenuItem menuItem;
 
   public MenuAction(MenuItem menuItem) {
     super(ActionType.MENU_ITEM_SELECTED);

flux/src/main/java/com/iluwatar/flux/action/MenuItem.java

@@ -30,7 +30,7 @@ public enum MenuItem {
 
   HOME("Home"), PRODUCTS("Products"), COMPANY("Company");
 
-  private String title;
+  private final String title;
 
   MenuItem(String title) {
     this.title = title;

flux/src/main/java/com/iluwatar/flux/dispatcher/Dispatcher.java

@@ -39,7 +39,7 @@ public final class Dispatcher {
 
   private static Dispatcher instance = new Dispatcher();
 
-  private List<Store> stores = new LinkedList<>();
+  private final List<Store> stores = new LinkedList<>();
 
   private Dispatcher() {
   }

flux/src/main/java/com/iluwatar/flux/store/Store.java

@@ -33,7 +33,7 @@ import java.util.List;
  */
 public abstract class Store {
 
-  private List<View> views = new LinkedList<>();
+  private final List<View> views = new LinkedList<>();
 
   public abstract void onAction(Action action);