docs: update .all-contributorsrc [skip ci]

.all-contributorsrc

@@ -1377,24 +1377,6 @@
       "contributions": [
         "translation"
       ]
-    },
-    {
-      "login": "rohit10000",
-      "name": "Rohit Singh",
-      "avatar_url": "https://avatars.githubusercontent.com/u/20845565?v=4",
-      "profile": "https://github.com/rohit10000",
-      "contributions": [
-        "code"
-      ]
-    },
-    {
-      "login": "byoungju94",
-      "name": "byoungju94",
-      "avatar_url": "https://avatars.githubusercontent.com/u/42516378?v=4",
-      "profile": "https://github.com/byoungju94",
-      "contributions": [
-        "code"
-      ]
     }
   ],
   "contributorsPerLine": 4,

.gitignore

@@ -4,8 +4,7 @@ target
 .classpath
 .project
 *.class
-
+# Package Files #
-### Package Files ###
 *.jar
 *.war
 *.ear
@@ -14,8 +13,7 @@ target
 *.swp
 datanucleus.log
 /bin/
+/bin/
+/bin/
 *.log
 event-sourcing/Journal.json
-
-### Checkstyle ###
-.checkstyle

README.md

@@ -10,7 +10,7 @@
 [![Coverage](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=coverage)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
 [![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)
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-[![All Contributors](https://img.shields.io/badge/all_contributors-153-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-151-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 <br/>
@@ -301,10 +301,6 @@ This project is licensed under the terms of the MIT license.
     <td align="center"><a href="http://libkhadir.fr"><img src="https://avatars1.githubusercontent.com/u/45130488?v=4?s=100" width="100px;" alt=""/><br /><sub><b>KHADIR Tayeb</b></sub></a><br /><a href="#translation-tkhadir" title="Translation">🌍</a></td>
     <td align="center"><a href="https://github.com/ignite1771"><img src="https://avatars2.githubusercontent.com/u/59446563?v=4?s=100" width="100px;" alt=""/><br /><sub><b>ignite1771</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ignite1771" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/demirhalil"><img src="https://avatars1.githubusercontent.com/u/22895118?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Halil Demir</b></sub></a><br /><a href="#translation-demirhalil" title="Translation">🌍</a></td>
-    <td align="center"><a href="https://github.com/rohit10000"><img src="https://avatars.githubusercontent.com/u/20845565?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rohit Singh</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=rohit10000" title="Code">💻</a></td>
-  </tr>
-  <tr>
-    <td align="center"><a href="https://github.com/byoungju94"><img src="https://avatars.githubusercontent.com/u/42516378?v=4?s=100" width="100px;" alt=""/><br /><sub><b>byoungju94</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=byoungju94" title="Code">💻</a></td>
   </tr>
 </table>
 

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

@@ -67,7 +67,7 @@ public class DbCustomerDao implements CustomerDao {
   public Stream<Customer> getAll() throws Exception {
     try {
       var connection = getConnection();
-      var statement = connection.prepareStatement("SELECT * FROM CUSTOMERS"); // NOSONAR
+      var statement = connection.prepareStatement("SELECT * FROM CUSTOMERS");
       var resultSet = statement.executeQuery(); // NOSONAR
       return StreamSupport.stream(new Spliterators.AbstractSpliterator<Customer>(Long.MAX_VALUE,
           Spliterator.ORDERED) {

data-transfer-object-enum-impl/README.md

@@ -0,0 +1,54 @@
+---
+layout: pattern
+title: Data Transfer Object
+folder: data-transfer-object
+permalink: /patterns/data-transfer-object/
+categories: Architectural
+tags:
+ - Performance
+---
+
+## Intent
+
+Pass data with multiple attributes in one shot from client to server, to avoid multiple calls to 
+remote server. 
+
+## Explanation
+
+Real world example
+
+> We need to fetch information about customers from remote database. Instead of querying the 
+> attributes one at a time, we use DTOs to transfer all the relevant attributes in a single shot.     
+
+In plain words
+
+> Using DTO relevant information can be fetched with a single backend query. 
+
+Wikipedia says
+
+> In the field of programming a data transfer object (DTO) is an object that carries data between 
+> processes. The motivation for its use is that communication between processes is usually done 
+> resorting to remote interfaces (e.g. web services), where each call is an expensive operation. 
+> Because the majority of the cost of each call is related to the round-trip time between the client 
+> and the server, one way of reducing the number of calls is to use an object (the DTO) that 
+> aggregates the data that would have been transferred by the several calls, but that is served by 
+> one call only.
+
+## Class diagram
+
+![alt text](./etc/dto-enum-uml.png "data-transfer-object")
+
+## Applicability
+
+Use the Data Transfer Object pattern when:
+
+* The client is asking for multiple information. And the information is related.
+* When you want to boost the performance to get resources.
+* You want reduced number of remote calls.
+
+## Credits
+
+* [Design Pattern - Transfer Object Pattern](https://www.tutorialspoint.com/design_pattern/transfer_object_pattern.htm)
+* [Data Transfer Object](https://msdn.microsoft.com/en-us/library/ff649585.aspx)
+* [J2EE Design Patterns](https://www.amazon.com/gp/product/0596004273/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596004273&linkCode=as2&tag=javadesignpat-20&linkId=f27d2644fbe5026ea448791a8ad09c94)
+* [Patterns of Enterprise Application Architecture](https://www.amazon.com/gp/product/0321127420/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0321127420&linkCode=as2&tag=javadesignpat-20&linkId=014237a67c9d46f384b35e10151956bd)

data-transfer-object-enum-impl/etc/data-transfer-object-enum-impl.urm.puml

@@ -0,0 +1,129 @@
+@startuml
+package com.iluwatar.datatransferenum {
+  class App {
+    - LOGGER : Logger {static}
+    + App()
+    + main(args : String[]) {static}
+  }
+  class Product {
+    - cost : Double
+    - id : Long
+    - name : String
+    - price : Double
+    - supplier : String
+    + Product()
+    + getCost() : Double
+    + getId() : Long
+    + getName() : String
+    + getPrice() : Double
+    + getSupplier() : String
+    + setCost(cost : Double) : Product
+    + setId(id : Long) : Product
+    + setName(name : String) : Product
+    + setPrice(price : Double) : Product
+    + setSupplier(supplier : String) : Product
+    + toString() : String
+  }
+  enum ProductDTO {
+    + valueOf(name : String) : ProductDTO {static}
+    + values() : ProductDTO[] {static}
+  }
+  -interface Cost {
+    + getCost() : Double {abstract}
+  }
+  -interface Id {
+    + getId() : Long {abstract}
+  }
+  -interface Name {
+    + getName() : String {abstract}
+  }
+  -interface Price {
+    + getPrice() : Double {abstract}
+  }
+  enum Request {
+    + valueOf(name : String) : Request {static}
+    + values() : Request[] {static}
+  }
+  class Create {
+    - cost : Double
+    - name : String
+    - price : Double
+    - supplier : String
+    + Create()
+    + getCost() : Double
+    + getName() : String
+    + getPrice() : Double
+    + getSupplier() : String
+    + setCost(cost : Double) : Create
+    + setName(name : String) : Create
+    + setPrice(price : Double) : Create
+    + setSupplier(supplier : String) : Create
+  }
+  enum Response {
+    + valueOf(name : String) : Response {static}
+    + values() : Response[] {static}
+  }
+  class Private {
+    - cost : Double
+    - id : Long
+    - name : String
+    - price : Double
+    + Private()
+    + getCost() : Double
+    + getId() : Long
+    + getName() : String
+    + getPrice() : Double
+    + setCost(cost : Double) : Private
+    + setId(id : Long) : Private
+    + setName(name : String) : Private
+    + setPrice(price : Double) : Private
+    + toString() : String
+  }
+  class Public {
+    - id : Long
+    - name : String
+    - price : Double
+    + Public()
+    + getId() : Long
+    + getName() : String
+    + getPrice() : Double
+    + setId(id : Long) : Public
+    + setName(name : String) : Public
+    + setPrice(price : Double) : Public
+    + toString() : String
+  }
+  -interface Supplier {
+    + getSupplier() : String {abstract}
+  }
+  class ProductResource {
+    - products : List<Product>
+    + ProductResource(products : List<Product>)
+    + getAllProductsForAdmin() : List<Private>
+    + getAllProductsForCustomer() : List<Public>
+    + getProducts() : List<Product>
+    + save(createProductDTO : Create)
+  }
+}
+Create ..+ Request
+Request ..+ ProductDTO
+Private ..+ Response
+Supplier ..+ ProductDTO
+Name ..+ ProductDTO
+ProductResource -->  "-products" Product
+Public ..+ Response
+Id ..+ ProductDTO
+Price ..+ ProductDTO
+Response ..+ ProductDTO
+Cost ..+ ProductDTO
+Create ..|> Name 
+Create ..|> Price 
+Create ..|> Cost 
+Create ..|> Supplier 
+Private ..|> Id 
+Private ..|> Name 
+Private ..|> Price 
+Private ..|> Cost 
+Public ..|> Id 
+Public ..|> Name 
+Public ..|> Price 
+@enduml

data-transfer-object-enum-impl/pom.xml

@@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2019 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xmlns: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" xmlns="http://maven.apache.org/POM/4.0.0">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.24.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>data-transfer-object-enum-impl</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <configuration>
+                            <archive>
+                                <manifest>
+                                    <mainClass>com.iluwatar.datatransferenum.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/App.java

@@ -0,0 +1,59 @@
+package com.iluwatar.datatransferenum;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Data Transfer Object pattern is a design pattern in which an data transfer object is used to
+ * serve related information together to avoid multiple call for each piece of information.
+ *
+ * <p>In this example, ({@link App}) as as product details consumer i.e. client to
+ * request for product details to server.
+ *
+ * <p>productResource ({@link ProductResource}) act as server to serve product information. And
+ * The productDto ({@link ProductDto} is data transfer object to share product information.
+ */
+public class App {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * Method as act client and request to server for details.
+   *
+   * @param args program argument.
+   */
+  public static void main(String[] args) {
+    Product tv =
+        new Product().setId(1L).setName("TV").setSupplier("Sony").setPrice(1000D).setCost(1090D);
+    Product microwave =
+        new Product().setId(2L).setName("microwave").setSupplier("Delonghi").setPrice(1000D)
+            .setCost(1090D);
+    Product refrigerator =
+        new Product().setId(3L).setName("refrigerator").setSupplier("Botsch").setPrice(1000D)
+            .setCost(1090D);
+    Product airConditioner =
+        new Product().setId(4L).setName("airConditioner").setSupplier("LG").setPrice(1000D)
+            .setCost(1090D);
+    List<Product> products =
+        new ArrayList<>(Arrays.asList(tv, microwave, refrigerator, airConditioner));
+    ProductResource productResource = new ProductResource(products);
+
+    LOGGER.info("####### List of products including sensitive data just for admins: \n {}",
+        Arrays.toString(productResource.getAllProductsForAdmin().toArray()));
+    LOGGER.info("####### List of products for customers: \n {}",
+        Arrays.toString(productResource.getAllProductsForCustomer().toArray()));
+
+    LOGGER.info("####### Going to save Sony PS5 ...");
+    ProductDto.Request.Create createProductRequestDto = new ProductDto.Request.Create()
+        .setName("PS5")
+        .setCost(1000D)
+        .setPrice(1220D)
+        .setSupplier("Sony");
+    productResource.save(createProductRequestDto);
+    LOGGER.info("####### List of products after adding PS5: {}",
+        Arrays.toString(productResource.getProducts().toArray()));
+  }
+}

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/Product.java

@@ -1,27 +1,4 @@
-/*
+package com.iluwatar.datatransferenum;
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.datatransfer.product;
 
 /**
  * {@link Product} is a entity class for product entity. This class act as entity in the demo.

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/ProductDto.java

@@ -1,27 +1,4 @@
-/*
+package com.iluwatar.datatransferenum;
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.datatransfer.product;
 
 /**
  * {@link ProductDto} is a data transfer object POJO.

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/ProductResource.java

@@ -1,27 +1,4 @@
-/*
+package com.iluwatar.datatransferenum;
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.datatransfer.product;
 
 import java.util.List;
 import java.util.stream.Collectors;

data-transfer-object-enum-impl/src/test/java/com/iluwatar/datatransferenum/AppTest.java

@@ -0,0 +1,44 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.datatransferenum;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+
+import org.junit.jupiter.api.Test;
+
+class AppTest {
+
+  /**
+   * Issue: Add at least one assertion to this test case.
+   * <p>
+   * Solution: Inserted assertion to check whether the execution of the main method in {@link App#main(String[])}
+   * throws an exception.
+   */
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[] {}));
+  }
+}

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

@@ -23,13 +23,7 @@
 
 package com.iluwatar.datatransfer;
 
-import com.iluwatar.datatransfer.customer.CustomerDto;
-import com.iluwatar.datatransfer.customer.CustomerResource;
-import com.iluwatar.datatransfer.product.Product;
-import com.iluwatar.datatransfer.product.ProductDto;
-import com.iluwatar.datatransfer.product.ProductResource;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -38,17 +32,11 @@ import org.slf4j.LoggerFactory;
  * The Data Transfer Object pattern is a design pattern in which an data transfer object is used to
  * serve related information together to avoid multiple call for each piece of information.
  *
- * <p>In the first example, {@link App} is a customer details consumer i.e. client to
+ * <p>In this example, ({@link App}) as as customer details consumer i.e. client to
- * request for customer details to server. {@link CustomerResource} act as server to serve customer
+ * request for customer details to server.
- * information. {@link CustomerDto} is data transfer object to share customer information.
- *
- * <p>In the second example, {@link App} is a product details consumer i.e. client to
- * request for product details to server. {@link ProductResource} acts as server to serve
- * product information. {@link ProductDto} is data transfer object to share product information.
- *
- * <p>The pattern implementation is a bit different in each of the examples. The first can be
- * thought as a traditional example and the second is an enum based implementation.
  *
+ * <p>CustomerResource ({@link CustomerResource}) act as server to serve customer information. And
+ * The CustomerDto ({@link CustomerDto} is data transfer object to share customer information.
  */
 public class App {
 
@@ -60,8 +48,6 @@ public class App {
    * @param args program argument.
    */
   public static void main(String[] args) {
-
-    // Example 1: Customer DTO
     var customerOne = new CustomerDto("1", "Kelly", "Brown");
     var customerTwo = new CustomerDto("2", "Alfonso", "Bass");
     var customers = new ArrayList<>(List.of(customerOne, customerTwo));
@@ -86,53 +72,6 @@ public class App {
     customerResource.save(customerThree);
     allCustomers = customerResource.getAllCustomers();
     printCustomerDetails(allCustomers);
-
-    // Example 2: Product DTO
-    Product tv =
-        new Product().setId(1L).setName("TV").setSupplier("Sony").setPrice(1000D).setCost(1090D);
-    Product microwave =
-        new Product()
-            .setId(2L)
-            .setName("microwave")
-            .setSupplier("Delonghi")
-            .setPrice(1000D)
-            .setCost(1090D);
-    Product refrigerator =
-        new Product()
-            .setId(3L)
-            .setName("refrigerator")
-            .setSupplier("Botsch")
-            .setPrice(1000D)
-            .setCost(1090D);
-    Product airConditioner =
-        new Product()
-            .setId(4L)
-            .setName("airConditioner")
-            .setSupplier("LG")
-            .setPrice(1000D)
-            .setCost(1090D);
-    List<Product> products =
-        new ArrayList<>(Arrays.asList(tv, microwave, refrigerator, airConditioner));
-    ProductResource productResource = new ProductResource(products);
-
-    LOGGER.info(
-        "####### List of products including sensitive data just for admins: \n {}",
-        Arrays.toString(productResource.getAllProductsForAdmin().toArray()));
-    LOGGER.info(
-        "####### List of products for customers: \n {}",
-        Arrays.toString(productResource.getAllProductsForCustomer().toArray()));
-
-    LOGGER.info("####### Going to save Sony PS5 ...");
-    ProductDto.Request.Create createProductRequestDto =
-        new ProductDto.Request.Create()
-            .setName("PS5")
-            .setCost(1000D)
-            .setPrice(1220D)
-            .setSupplier("Sony");
-    productResource.save(createProductRequestDto);
-    LOGGER.info(
-        "####### List of products after adding PS5: {}",
-        Arrays.toString(productResource.getProducts().toArray()));
   }
 
   private static void printCustomerDetails(List<CustomerDto> allCustomers) {

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

@@ -21,7 +21,7 @@
  * THE SOFTWARE.
  */
 
-package com.iluwatar.datatransfer.customer;
+package com.iluwatar.datatransfer;
 
 /**
  * {@link CustomerDto} is a data transfer object POJO. Instead of sending individual information to

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

@@ -21,7 +21,7 @@
  * THE SOFTWARE.
  */
 
-package com.iluwatar.datatransfer.customer;
+package com.iluwatar.datatransfer;
 
 import java.util.List;
 

data-transfer-object/src/test/java/com/iluwatar/datatransfer/CustomerResourceTest.java

@@ -21,16 +21,13 @@
  * THE SOFTWARE.
  */
 
-package com.iluwatar.datatransfer.customer;
+package com.iluwatar.datatransfer;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.ArrayList;
 import java.util.List;
-
-import com.iluwatar.datatransfer.customer.CustomerDto;
-import com.iluwatar.datatransfer.customer.CustomerResource;
 import org.junit.jupiter.api.Test;
 
 /**

mutex/README.md

@@ -0,0 +1,31 @@
+---
+layout: pattern
+title: Mutex
+folder: mutex
+permalink: /patterns/mutex/
+categories: Concurrency
+tags: 
+ - Decoupling
+---
+
+## Also known as
+
+* Mutual Exclusion Lock
+* Binary Semaphore
+
+## Intent
+Create a lock which only allows a single thread to access a resource at any one instant.
+
+## Class diagram
+![alt text](./etc/mutex.png "Mutex")
+
+## Applicability
+Use a Mutex when
+
+* You need to prevent two threads accessing a critical section at the same time
+* Concurrent access to a resource could lead to a race condition 
+
+## Credits
+
+* [Lock (computer science)](http://en.wikipedia.org/wiki/Lock_(computer_science))
+* [Semaphores](http://tutorials.jenkov.com/java-concurrency/semaphores.html)

mutex/etc/mutex.urm.puml

@@ -0,0 +1,27 @@
+@startuml
+package com.iluwatar.mutex {
+  class App {
+    + App()
+    + main(args : String[]) {static}
+  }
+  class Jar {
+    - beans : int
+    - lock : Lock
+    + Jar(beans : int, lock : Lock)
+    + takeBean() : boolean
+  }
+  interface Lock {
+    + acquire() {abstract}
+    + release() {abstract}
+  }
+  class Mutex {
+    - owner : Object
+    + Mutex()
+    + acquire()
+    + getOwner() : Object
+    + release()
+  }
+}
+Jar -->  "-lock" Lock
+Mutex ..|> Lock 
+@enduml

mutex/pom.xml

@@ -0,0 +1,61 @@
+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2019 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.24.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>mutex</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.mutex.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

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

@@ -0,0 +1,49 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.mutex;
+
+/**
+ * A Mutex prevents multiple threads from accessing a resource simultaneously.
+ *
+ * <p>In this example we have two thieves who are taking beans from a jar. Only one thief can take
+ * a bean at a time. This is ensured by a Mutex lock which must be acquired in order to access the
+ * jar. Each thief attempts to acquire the lock, take a bean and then release the lock. If the lock
+ * has already been acquired, the thief will be prevented from continuing (blocked) until the lock
+ * has been released. The thieves stop taking beans once there are no beans left to take.
+ */
+public class App {
+
+  /**
+   * main method.
+   */
+  public static void main(String[] args) {
+    var mutex = new Mutex();
+    var jar = new Jar(1000, mutex);
+    var peter = new Thief("Peter", jar);
+    var john = new Thief("John", jar);
+    peter.start();
+    john.start();
+  }
+
+}

mutex/src/main/java/com/iluwatar/mutex/Jar.java

@@ -0,0 +1,67 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.mutex;
+
+/**
+ * A Jar has a resource of beans which can only be accessed by a single Thief (thread) at any one
+ * time. A Mutex lock is used to prevent more than one Thief taking a bean simultaneously.
+ */
+public class Jar {
+
+  /**
+   * The lock which must be acquired to access the beans resource.
+   */
+  private final Lock lock;
+
+  /**
+   * The resource within the jar.
+   */
+  private int beans;
+
+  public Jar(int beans, Lock lock) {
+    this.beans = beans;
+    this.lock = lock;
+  }
+
+  /**
+   * Method for a thief to take a bean.
+   */
+  public boolean takeBean() {
+    var success = false;
+    try {
+      lock.acquire();
+      success = beans > 0;
+      if (success) {
+        beans = beans - 1;
+      }
+    } catch (Exception e) {
+      e.printStackTrace();
+    } finally {
+      lock.release();
+    }
+
+    return success;
+  }
+
+}

mutex/src/main/java/com/iluwatar/mutex/Lock.java

@@ -0,0 +1,35 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.mutex;
+
+/**
+ * Lock is an interface for a lock which can be acquired and released.
+ */
+public interface Lock {
+
+  void acquire() throws InterruptedException;
+
+  void release();
+
+}

mutex/src/main/java/com/iluwatar/mutex/Mutex.java

@@ -0,0 +1,67 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.mutex;
+
+/**
+ * Mutex is an implementation of a mutual exclusion lock.
+ */
+public class Mutex implements Lock {
+
+  /**
+   * The current owner of the lock.
+   */
+  private Object owner;
+
+  /**
+   * Returns the current owner of the Mutex, or null if available.
+   */
+  public Object getOwner() {
+    return owner;
+  }
+
+  /**
+   * Method called by a thread to acquire the lock. If the lock has already been acquired this will
+   * wait until the lock has been released to re-attempt the acquire.
+   */
+  @Override
+  public synchronized void acquire() throws InterruptedException {
+    while (owner != null) {
+      wait();
+    }
+
+    owner = Thread.currentThread();
+  }
+
+  /**
+   * Method called by a thread to release the lock.
+   */
+  @Override
+  public synchronized void release() {
+    if (Thread.currentThread() == owner) {
+      owner = null;
+      notify();
+    }
+  }
+
+}

mutex/src/main/java/com/iluwatar/mutex/Thief.java

@@ -21,32 +21,47 @@
  * THE SOFTWARE.
  */
 
-package com.iluwatar.strategy;
+package com.iluwatar.mutex;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-public class LambdaStrategy {
+/**
+ * Thief is a class which continually tries to acquire a jar and take a bean from it. When the jar
+ * is empty the thief stops.
+ */
+public class Thief extends Thread {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(LambdaStrategy.class);
+  private static final Logger LOGGER = LoggerFactory.getLogger(Thief.class);
 
-  public enum Strategy implements DragonSlayingStrategy {
+  /**
-    MeleeStrategy(() -> LOGGER.info(
+   * The name of the thief.
-        "With your Excalibur you severe the dragon's head!")),
+   */
-    ProjectileStrategy(() -> LOGGER.info(
+  private final String name;
-        "You shoot the dragon with the magical crossbow and it falls dead on the ground!")),
-    SpellStrategy(() -> LOGGER.info(
-        "You cast the spell of disintegration and the dragon vaporizes in a pile of dust!"));
 
-    private final DragonSlayingStrategy dragonSlayingStrategy;
+  /**
+   * The jar.
+   */
+  private final Jar jar;
 
-    Strategy(DragonSlayingStrategy dragonSlayingStrategy) {
+  public Thief(String name, Jar jar) {
-      this.dragonSlayingStrategy = dragonSlayingStrategy;
+    this.name = name;
-    }
+    this.jar = jar;
-
-    @Override
-    public void execute() {
-      dragonSlayingStrategy.execute();
-    }
   }
+
+  /**
+   * In the run method the thief repeatedly tries to take a bean until none are left.
+   */
+  @Override
+  public void run() {
+    var beans = 0;
+
+    while (jar.takeBean()) {
+      beans = beans + 1;
+      LOGGER.info("{} took a bean.", name);
+    }
+
+    LOGGER.info("{} took {} beans.", name, beans);
+  }
+
 }

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

@@ -0,0 +1,39 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.mutex;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+/**
+ * Application Test Entrypoint
+ */
+class AppTest {
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}

mutex/src/test/java/com/iluwatar/mutex/JarTest.java

@@ -0,0 +1,45 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.mutex;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import java.util.stream.IntStream;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test case for taking beans from a Jar
+ */
+public class JarTest {
+
+  @Test
+  public void testTakeBeans() {
+    var mutex = new Mutex();
+    var jar = new Jar(10, mutex);
+    IntStream.range(0, 10).mapToObj(i -> jar.takeBean()).forEach(Assertions::assertTrue);
+    assertFalse(jar.takeBean());
+  }
+
+}

mutex/src/test/java/com/iluwatar/mutex/MutexTest.java

@@ -0,0 +1,51 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.mutex;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test case for acquiring and releasing a Mutex
+ */
+public class MutexTest {
+
+  @Test
+  public void acquireReleaseTest() {
+    var mutex = new Mutex();
+    assertNull(mutex.getOwner());
+    try {
+      mutex.acquire();
+      assertEquals(mutex.getOwner(), Thread.currentThread());
+    } catch (InterruptedException e) {
+      fail(e.toString());
+    }
+    mutex.release();
+    assertNull(mutex.getOwner());
+  }
+
+}

pom.xml

@@ -141,6 +141,8 @@
         <module>module</module>
         <module>monad</module>
         <module>mute-idiom</module>
+        <module>mutex</module>
+        <module>semaphore</module>
         <module>hexagonal</module>
         <module>abstract-document</module>
         <module>aggregator-microservices</module>
@@ -197,6 +199,7 @@
         <module>filterer</module>
         <module>factory</module>
         <module>separated-interface</module>
+        <module>data-transfer-object-enum-impl</module>
         <module>special-case</module>
     </modules>
 

registry/pom.xml

@@ -1,28 +1,4 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!--
-
-    The MIT License
-    Copyright © 2014-2019 Ilkka Seppälä
-
-    Permission is hereby granted, free of charge, to any person obtaining a copy
-    of this software and associated documentation files (the "Software"), to deal
-    in the Software without restriction, including without limitation the rights
-    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-    copies of the Software, and to permit persons to whom the Software is
-    furnished to do so, subject to the following conditions:
-
-    The above copyright notice and this permission notice shall be included in
-    all copies or substantial portions of the Software.
-
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-    THE SOFTWARE.
-
--->
 <project xmlns="http://maven.apache.org/POM/4.0.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

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

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.registry;
 
 import org.slf4j.Logger;

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

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.registry;
 
 public class Customer {

registry/src/main/java/com/iluwatar/registry/CustomerRegistry.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.registry;
 
 import java.util.Map;

registry/src/test/java/com/iluwatar/registry/CustomerRegistryTest.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.registry;
 
 import org.junit.jupiter.api.BeforeAll;

semaphore/README.md

@@ -0,0 +1,33 @@
+---
+layout: pattern
+title: Semaphore
+folder: semaphore
+permalink: /patterns/semaphore/
+categories: Concurrency
+tags: 
+ - Performance
+---
+
+## Also known as
+Counting Semaphore
+
+## Intent
+Create a lock which mediates access to a pool of resources. 
+Only a limited number of threads, specified at the creation 
+of the semaphore, can access the resources at any given time.
+A semaphore which only allows one concurrent access to a resource
+is called a binary semaphore.
+
+## Class diagram
+![alt text](./etc/semaphore.png "Semaphore")
+
+## Applicability
+Use a Semaphore when 
+
+* You have a pool of resources to allocate to different threads
+* Concurrent access to a resource could lead to a race condition 
+
+## Credits
+
+* [Semaphore(programming)] (http://en.wikipedia.org/wiki/Semaphore_(programming))
+* [Semaphores] (http://tutorials.jenkov.com/java-concurrency/semaphores.html)

semaphore/etc/semaphore.urm.puml

@@ -0,0 +1,56 @@
+@startuml
+package com.iluwatar.semaphore {
+  class App {
+    + App()
+    + main(args : String[]) {static}
+  }
+  class Fruit {
+    - type : FruitType
+    + Fruit(type : FruitType)
+    + getType() : FruitType
+    + toString() : String
+  }
+  enum FruitType {
+    + APPLE {static}
+    + LEMON {static}
+    + ORANGE {static}
+    + valueOf(name : String) : FruitType {static}
+    + values() : FruitType[] {static}
+  }
+  class FruitBowl {
+    - fruit : List<Fruit>
+    + FruitBowl()
+    + countFruit() : int
+    + put(f : Fruit)
+    + take() : Fruit
+    + toString() : String
+  }
+  class FruitShop {
+    - available : boolean[]
+    - bowls : FruitBowl[]
+    - semaphore : Semaphore
+    + FruitShop()
+    + countFruit() : int
+    + returnBowl(bowl : FruitBowl)
+    + takeBowl() : FruitBowl
+  }
+  interface Lock {
+    + acquire() {abstract}
+    + release() {abstract}
+  }
+  class Semaphore {
+    - counter : int
+    - licenses : int
+    + Semaphore(licenses : int)
+    + acquire()
+    + getAvailableLicenses() : int
+    + getNumLicenses() : int
+    + release()
+  }
+}
+FruitType ..+ Fruit
+Fruit -->  "-type" FruitType
+FruitShop -->  "-semaphore" Semaphore
+FruitBowl -->  "-fruit" Fruit
+Semaphore ..|> Lock 
+@enduml

semaphore/pom.xml

@@ -0,0 +1,61 @@
+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2019 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.24.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>semaphore</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.semaphore.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

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

@@ -0,0 +1,50 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+/**
+ * A Semaphore mediates access by a group of threads to a pool of resources.
+ *
+ * <p>In this example a group of customers are taking fruit from a fruit shop. There is a bowl each
+ * of apples, oranges and lemons. Only one customer can access a bowl simultaneously. A Semaphore is
+ * used to indicate how many resources are currently available and must be acquired in order for a
+ * bowl to be given to a customer. Customers continually try to take fruit until there is no fruit
+ * left in the shop.
+ */
+public class App {
+
+  /**
+   * main method.
+   */
+  public static void main(String[] args) {
+    var shop = new FruitShop();
+    new Customer("Peter", shop).start();
+    new Customer("Paul", shop).start();
+    new Customer("Mary", shop).start();
+    new Customer("John", shop).start();
+    new Customer("Ringo", shop).start();
+    new Customer("George", shop).start();
+  }
+
+}

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

@@ -0,0 +1,82 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A Customer attempts to repeatedly take Fruit from the FruitShop by taking Fruit from FruitBowl
+ * instances.
+ */
+public class Customer extends Thread {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(Customer.class);
+
+  /**
+   * Name of the Customer.
+   */
+  private final String name;
+
+  /**
+   * The FruitShop he is using.
+   */
+  private final FruitShop fruitShop;
+
+  /**
+   * Their bowl of Fruit.
+   */
+  private final FruitBowl fruitBowl;
+
+  /**
+   * Customer constructor.
+   */
+  public Customer(String name, FruitShop fruitShop) {
+    this.name = name;
+    this.fruitShop = fruitShop;
+    this.fruitBowl = new FruitBowl();
+  }
+
+  /**
+   * The Customer repeatedly takes Fruit from the FruitShop until no Fruit remains.
+   */
+  public void run() {
+
+    while (fruitShop.countFruit() > 0) {
+      var bowl = fruitShop.takeBowl();
+      if (bowl != null) {
+        var fruit = bowl.take();
+        if (fruit != null) {
+          LOGGER.info("{} took an {}", name, fruit);
+          fruitBowl.put(fruit);
+          fruitShop.returnBowl(bowl);
+        }
+      }
+    }
+
+    LOGGER.info("{} took {}", name, fruitBowl);
+
+  }
+
+}

semaphore/src/main/java/com/iluwatar/semaphore/Fruit.java

@@ -0,0 +1,64 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+/**
+ * Fruit is a resource stored in a FruitBowl.
+ */
+public class Fruit {
+
+  /**
+   * Enumeration of Fruit Types.
+   */
+  public enum FruitType {
+    ORANGE, APPLE, LEMON
+  }
+
+  private final FruitType type;
+
+  public Fruit(FruitType type) {
+    this.type = type;
+  }
+
+  public FruitType getType() {
+    return type;
+  }
+
+  /**
+   * toString method.
+   */
+  public String toString() {
+    switch (type) {
+      case ORANGE:
+        return "Orange";
+      case APPLE:
+        return "Apple";
+      case LEMON:
+        return "Lemon";
+      default:
+        return "";
+    }
+  }
+
+}

semaphore/src/main/java/com/iluwatar/semaphore/FruitBowl.java

@@ -0,0 +1,92 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A FruitBowl contains Fruit.
+ */
+public class FruitBowl {
+
+  private final List<Fruit> fruit = new ArrayList<>();
+
+  /**
+   * Returns the amount of fruits left in bowl.
+   *
+   * @return The amount of Fruit left in the bowl.
+   */
+  public int countFruit() {
+    return fruit.size();
+  }
+
+  /**
+   * Put an item of Fruit into the bowl.
+   *
+   * @param f fruit
+   */
+  public void put(Fruit f) {
+    fruit.add(f);
+  }
+
+  /**
+   * Take an item of Fruit out of the bowl.
+   *
+   * @return The Fruit taken out of the bowl, or null if empty.
+   */
+  public Fruit take() {
+    if (fruit.isEmpty()) {
+      return null;
+    } else {
+      return fruit.remove(0);
+    }
+  }
+
+  /**
+   * toString method.
+   */
+  public String toString() {
+    var apples = 0;
+    var oranges = 0;
+    var lemons = 0;
+
+    for (var f : fruit) {
+      switch (f.getType()) {
+        case APPLE:
+          apples++;
+          break;
+        case ORANGE:
+          oranges++;
+          break;
+        case LEMON:
+          lemons++;
+          break;
+        default:
+      }
+    }
+
+    return apples + " Apples, " + oranges + " Oranges, and " + lemons + " Lemons";
+  }
+}

semaphore/src/main/java/com/iluwatar/semaphore/FruitShop.java

@@ -0,0 +1,120 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+/**
+ * A FruitShop contains three FruitBowl instances and controls access to them.
+ */
+public class FruitShop {
+
+  /**
+   * The FruitBowl instances stored in the class.
+   */
+  private final FruitBowl[] bowls = {
+      new FruitBowl(),
+      new FruitBowl(),
+      new FruitBowl()
+  };
+
+  /**
+   * Access flags for each of the FruitBowl instances.
+   */
+  private final boolean[] available = {
+      true,
+      true,
+      true
+  };
+
+  /**
+   * The Semaphore that controls access to the class resources.
+   */
+  private final Semaphore semaphore;
+
+  /**
+   * FruitShop constructor.
+   */
+  public FruitShop() {
+    for (var i = 0; i < 100; i++) {
+      bowls[0].put(new Fruit(Fruit.FruitType.APPLE));
+      bowls[1].put(new Fruit(Fruit.FruitType.ORANGE));
+      bowls[2].put(new Fruit(Fruit.FruitType.LEMON));
+    }
+
+    semaphore = new Semaphore(3);
+  }
+
+  /**
+   * Returns the amount of fruits left in shop.
+   *
+   * @return The amount of Fruit left in the shop.
+   */
+  public synchronized int countFruit() {
+    return bowls[0].countFruit() + bowls[1].countFruit() + bowls[2].countFruit();
+  }
+
+  /**
+   * Method called by Customer to get a FruitBowl from the shop. This method will try to acquire the
+   * Semaphore before returning the first available FruitBowl.
+   */
+  public synchronized FruitBowl takeBowl() {
+
+    FruitBowl bowl = null;
+
+    try {
+      semaphore.acquire();
+
+      if (available[0]) {
+        bowl = bowls[0];
+        available[0] = false;
+      } else if (available[1]) {
+        bowl = bowls[1];
+        available[1] = false;
+      } else if (available[2]) {
+        bowl = bowls[2];
+        available[2] = false;
+      }
+
+    } catch (InterruptedException e) {
+      e.printStackTrace();
+    } finally {
+      semaphore.release();
+    }
+    return bowl;
+  }
+
+  /**
+   * Method called by a Customer instance to return a FruitBowl to the shop. This method releases
+   * the Semaphore, making the FruitBowl available to another Customer.
+   */
+  public synchronized void returnBowl(FruitBowl bowl) {
+    if (bowl == bowls[0]) {
+      available[0] = true;
+    } else if (bowl == bowls[1]) {
+      available[1] = true;
+    } else if (bowl == bowls[2]) {
+      available[2] = true;
+    }
+  }
+
+}

semaphore/src/main/java/com/iluwatar/semaphore/Lock.java

@@ -0,0 +1,35 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+/**
+ * Lock is an interface for a lock which can be acquired and released.
+ */
+public interface Lock {
+
+  void acquire() throws InterruptedException;
+
+  void release();
+
+}

semaphore/src/main/java/com/iluwatar/semaphore/Semaphore.java

@@ -0,0 +1,77 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+/**
+ * Semaphore is an implementation of a semaphore lock.
+ */
+public class Semaphore implements Lock {
+
+  private final int licenses;
+  /**
+   * The number of concurrent resource accesses which are allowed.
+   */
+  private int counter;
+
+  public Semaphore(int licenses) {
+    this.licenses = licenses;
+    this.counter = licenses;
+  }
+
+  /**
+   * Returns the number of licenses managed by the Semaphore.
+   */
+  public int getNumLicenses() {
+    return licenses;
+  }
+
+  /**
+   * Returns the number of available licenses.
+   */
+  public int getAvailableLicenses() {
+    return counter;
+  }
+
+  /**
+   * Method called by a thread to acquire the lock. If there are no resources available this will
+   * wait until the lock has been released to re-attempt the acquire.
+   */
+  public synchronized void acquire() throws InterruptedException {
+    while (counter == 0) {
+      wait();
+    }
+    counter = counter - 1;
+  }
+
+  /**
+   * Method called by a thread to release the lock.
+   */
+  public synchronized void release() {
+    if (counter < licenses) {
+      counter = counter + 1;
+      notify();
+    }
+  }
+
+}

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

@@ -0,0 +1,39 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+/**
+ * Application Test Entrypoint
+ */
+class AppTest {
+
+  @Test
+  void shouldExecuteWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}

semaphore/src/test/java/com/iluwatar/semaphore/FruitBowlTest.java

@@ -0,0 +1,55 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test taking from and putting Fruit into a FruitBowl
+ */
+public class FruitBowlTest {
+
+  @Test
+  public void fruitBowlTest() {
+    var fbowl = new FruitBowl();
+
+    assertEquals(0, fbowl.countFruit());
+
+    for (var i = 1; i <= 10; i++) {
+      fbowl.put(new Fruit(Fruit.FruitType.LEMON));
+      assertEquals(i, fbowl.countFruit());
+    }
+
+    for (var i = 9; i >= 0; i--) {
+      assertNotNull(fbowl.take());
+      assertEquals(i, fbowl.countFruit());
+    }
+
+    assertNull(fbowl.take());
+  }
+}

semaphore/src/test/java/com/iluwatar/semaphore/SemaphoreTest.java

@@ -0,0 +1,59 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.semaphore;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test case for acquiring and releasing a Semaphore
+ */
+public class SemaphoreTest {
+
+  @Test
+  public void acquireReleaseTest() {
+    var sphore = new Semaphore(3);
+
+    assertEquals(3, sphore.getAvailableLicenses());
+
+    for (var i = 2; i >= 0; i--) {
+      try {
+        sphore.acquire();
+        assertEquals(i, sphore.getAvailableLicenses());
+      } catch (InterruptedException e) {
+        fail(e.toString());
+      }
+    }
+
+    for (var i = 1; i <= 3; i++) {
+      sphore.release();
+      assertEquals(i, sphore.getAvailableLicenses());
+    }
+
+    sphore.release();
+    assertEquals(3, sphore.getAvailableLicenses());
+  }
+}

special-case/pom.xml

@@ -1,28 +1,4 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!--
-
-    The MIT License
-    Copyright © 2014-2019 Ilkka Seppälä
-
-    Permission is hereby granted, free of charge, to any person obtaining a copy
-    of this software and associated documentation files (the "Software"), to deal
-    in the Software without restriction, including without limitation the rights
-    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-    copies of the Software, and to permit persons to whom the Software is
-    furnished to do so, subject to the following conditions:
-
-    The above copyright notice and this permission notice shall be included in
-    all copies or substantial portions of the Software.
-
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-    THE SOFTWARE.
-
--->
 <project xmlns="http://maven.apache.org/POM/4.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

special-case/src/main/java/com/iluwatar/specialcase/App.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import org.slf4j.Logger;

special-case/src/main/java/com/iluwatar/specialcase/ApplicationServices.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 public interface ApplicationServices {

special-case/src/main/java/com/iluwatar/specialcase/ApplicationServicesImpl.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 public class ApplicationServicesImpl implements ApplicationServices {

special-case/src/main/java/com/iluwatar/specialcase/Db.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import java.util.HashMap;
@@ -38,13 +15,16 @@ public class Db {
    *
    * @return singleton instance of Db class
    */
-  public static synchronized Db getInstance() {
+  public static Db getInstance() {
     if (instance == null) {
-      Db newInstance = new Db();
+      synchronized (Db.class) {
-      newInstance.userName2User = new HashMap<>();
+        if (instance == null) {
-      newInstance.user2Account = new HashMap<>();
+          instance = new Db();
-      newInstance.itemName2Product = new HashMap<>();
+          instance.userName2User = new HashMap<>();
-      instance = newInstance;
+          instance.user2Account = new HashMap<>();
+          instance.itemName2Product = new HashMap<>();
+        }
+      }
     }
     return instance;
   }

special-case/src/main/java/com/iluwatar/specialcase/DomainServices.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 public interface DomainServices {

special-case/src/main/java/com/iluwatar/specialcase/DomainServicesImpl.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 public class DomainServicesImpl implements DomainServices {

special-case/src/main/java/com/iluwatar/specialcase/DownForMaintenance.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import org.slf4j.Logger;

special-case/src/main/java/com/iluwatar/specialcase/InsufficientFunds.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import org.slf4j.Logger;

special-case/src/main/java/com/iluwatar/specialcase/InvalidUser.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import org.slf4j.Logger;

special-case/src/main/java/com/iluwatar/specialcase/MaintenanceLock.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import org.slf4j.Logger;
@@ -38,9 +15,13 @@ public class MaintenanceLock {
    *
    * @return singleton instance of MaintenanceLock
    */
-  public static synchronized MaintenanceLock getInstance() {
+  public static MaintenanceLock getInstance() {
     if (instance == null) {
-      instance = new MaintenanceLock();
+      synchronized (MaintenanceLock.class) {
+        if (instance == null) {
+          instance = new MaintenanceLock();
+        }
+      }
     }
     return instance;
   }
@@ -51,6 +32,6 @@ public class MaintenanceLock {
 
   public void setLock(boolean lock) {
     this.lock = lock;
-    LOGGER.info("Maintenance lock is set to: ", lock);
+    LOGGER.info("Maintenance lock is set to: " + lock);
   }
 }

special-case/src/main/java/com/iluwatar/specialcase/MoneyTransaction.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 public class MoneyTransaction {

special-case/src/main/java/com/iluwatar/specialcase/OutOfStock.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import org.slf4j.Logger;

special-case/src/main/java/com/iluwatar/specialcase/ReceiptDto.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import org.slf4j.Logger;

special-case/src/main/java/com/iluwatar/specialcase/ReceiptViewModel.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 public interface ReceiptViewModel {

special-case/src/test/java/com/iluwatar/specialcase/AppTest.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;

special-case/src/test/java/com/iluwatar/specialcase/SpecialCasesTest.java

@@ -1,26 +1,3 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
 package com.iluwatar.specialcase;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;

strategy/README.md

@@ -122,51 +122,6 @@ Program output:
     You cast the spell of disintegration and the dragon vaporizes in a pile of dust!    
 ```
 
-What's more, the new feature Lambda Expressions in Java 8 provides another approach for the implementation:
-
-```java
-public class LambdaStrategy {
-
-  private static final Logger LOGGER = LoggerFactory.getLogger(LambdaStrategy.class);
-
-  public enum Strategy implements DragonSlayingStrategy {
-    MeleeStrategy(() -> LOGGER.info(
-        "With your Excalibur you severe the dragon's head!")),
-    ProjectileStrategy(() -> LOGGER.info(
-        "You shoot the dragon with the magical crossbow and it falls dead on the ground!")),
-    SpellStrategy(() -> LOGGER.info(
-        "You cast the spell of disintegration and the dragon vaporizes in a pile of dust!"));
-
-    private final DragonSlayingStrategy dragonSlayingStrategy;
-
-    Strategy(DragonSlayingStrategy dragonSlayingStrategy) {
-      this.dragonSlayingStrategy = dragonSlayingStrategy;
-    }
-
-    @Override
-    public void execute() {
-      dragonSlayingStrategy.execute();
-    }
-  }
-}
-```
-
-And here's the dragonslayer in action.
-
-```java
-    LOGGER.info("Green dragon spotted ahead!");
-    dragonSlayer.changeStrategy(LambdaStrategy.Strategy.MeleeStrategy);
-    dragonSlayer.goToBattle();
-    LOGGER.info("Red dragon emerges.");
-    dragonSlayer.changeStrategy(LambdaStrategy.Strategy.ProjectileStrategy);
-    dragonSlayer.goToBattle();
-    LOGGER.info("Black dragon lands before you.");
-    dragonSlayer.changeStrategy(LambdaStrategy.Strategy.SpellStrategy);
-    dragonSlayer.goToBattle();
-```
-
-Program output is the same as above one.
-
 ## Class diagram
 
 ![alt text](./etc/strategy_urm.png "Strategy")

strategy/etc/strategy.urm.puml

@@ -14,19 +14,6 @@ package com.iluwatar.strategy {
   interface DragonSlayingStrategy {
     + execute() {abstract}
   }
-  class LambdaStrategy {
-    - LOGGER : Logger {static}
-    + LambdaStrategy()
-  }
-  enum Strategy {
-    + MeleeStrategy {static}
-    + ProjectileStrategy {static}
-    + SpellStrategy {static}
-    - dragonSlayingStrategy : DragonSlayingStrategy
-    + execute()
-    + valueOf(name : String) : Strategy {static}
-    + values() : Strategy[] {static}
-  }
   class MeleeStrategy {
     - LOGGER : Logger {static}
     + MeleeStrategy()
@@ -43,10 +30,7 @@ package com.iluwatar.strategy {
     + execute()
   }
 }
-Strategy ..+ LambdaStrategy
-Strategy -->  "-dragonSlayingStrategy" DragonSlayingStrategy
 DragonSlayer -->  "-strategy" DragonSlayingStrategy
-Strategy ..|> DragonSlayingStrategy 
 MeleeStrategy ..|> DragonSlayingStrategy 
 ProjectileStrategy ..|> DragonSlayingStrategy 
 SpellStrategy ..|> DragonSlayingStrategy 

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

@@ -60,7 +60,7 @@ public class App {
     dragonSlayer.changeStrategy(new SpellStrategy());
     dragonSlayer.goToBattle();
 
-    // Java 8 functional implementation Strategy pattern
+    // Java 8 Strategy pattern
     LOGGER.info("Green dragon spotted ahead!");
     dragonSlayer = new DragonSlayer(
         () -> LOGGER.info("With your Excalibur you severe the dragon's head!"));
@@ -73,16 +73,5 @@ public class App {
     dragonSlayer.changeStrategy(() -> LOGGER.info(
         "You cast the spell of disintegration and the dragon vaporizes in a pile of dust!"));
     dragonSlayer.goToBattle();
-
-    // Java 8 lambda implementation with enum Strategy pattern
-    LOGGER.info("Green dragon spotted ahead!");
-    dragonSlayer.changeStrategy(LambdaStrategy.Strategy.MeleeStrategy);
-    dragonSlayer.goToBattle();
-    LOGGER.info("Red dragon emerges.");
-    dragonSlayer.changeStrategy(LambdaStrategy.Strategy.ProjectileStrategy);
-    dragonSlayer.goToBattle();
-    LOGGER.info("Black dragon lands before you.");
-    dragonSlayer.changeStrategy(LambdaStrategy.Strategy.SpellStrategy);
-    dragonSlayer.goToBattle();
   }
 }

transaction-script/src/main/java/com/iluwatar/transactionscript/HotelDaoImpl.java

@@ -49,7 +49,7 @@ public class HotelDaoImpl implements HotelDao {
   public Stream<Room> getAll() throws Exception {
     try {
       var connection = getConnection();
-      var statement = connection.prepareStatement("SELECT * FROM ROOMS"); // NOSONAR
+      var statement = connection.prepareStatement("SELECT * FROM ROOMS");
       var resultSet = statement.executeQuery(); // NOSONAR
       return StreamSupport.stream(new Spliterators.AbstractSpliterator<Room>(Long.MAX_VALUE,
           Spliterator.ORDERED) {