docs: update .all-contributorsrc [skip ci]

docs: update README.md [skip ci]
add monitor design pattern (#1640 )
2021-10-16 17:10:43 +00:00 · 2021-10-16 17:10:42 +00:00 · 2021-10-16 20:08:53 +03:00 · 2021-10-15 20:27:23 +03:00 · 2021-10-15 20:24:49 +03:00 · 2021-10-13 13:17:48 +05:30
35 changed files with 823 additions and 964 deletions
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@ -1631,6 +1631,33 @@
      "contributions": [
        "translation"
      ]
    },
    {
      "login": "sims-keshri",
      "name": "Simran Keshri",
      "avatar_url": "https://avatars.githubusercontent.com/u/62168475?v=4",
      "profile": "https://github.com/sims-keshri",
      "contributions": [
        "code"
      ]
    },
    {
      "login": "JCarlosR",
      "name": "JCarlos",
      "avatar_url": "https://avatars.githubusercontent.com/u/3101238?v=4",
      "profile": "https://programacionymas.com",
      "contributions": [
        "translation"
      ]
    },
    {
      "login": "Dev-AliGhasemi",
      "name": "Ali Ghasemi",
      "avatar_url": "https://avatars.githubusercontent.com/u/60359433?v=4",
      "profile": "https://www.mrmoshkel.ir",
      "contributions": [
        "code"
      ]
    }
  ],
  "contributorsPerLine": 4,
--- a/README.md
+++ b/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-179-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-182-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 <br/>
@ -343,6 +343,11 @@ This project is licensed under the terms of the MIT license.
    <td align="center"><a href="https://github.com/Conhan93"><img src="https://avatars.githubusercontent.com/u/71334757?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Conny Hansson</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Conhan93" title="Documentation">📖</a></td>
    <td align="center"><a href="http://muklasr.medium.com"><img src="https://avatars.githubusercontent.com/u/43443753?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Muklas Rahmanto</b></sub></a><br /><a href="#translation-muklasr" title="Translation">🌍</a></td>
    <td align="center"><a href="https://github.com/VxDxK"><img src="https://avatars.githubusercontent.com/u/38704817?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Vadim</b></sub></a><br /><a href="#translation-VxDxK" title="Translation">🌍</a></td>
    <td align="center"><a href="https://github.com/sims-keshri"><img src="https://avatars.githubusercontent.com/u/62168475?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Simran Keshri</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=sims-keshri" title="Code">💻</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://programacionymas.com"><img src="https://avatars.githubusercontent.com/u/3101238?v=4?s=100" width="100px;" alt=""/><br /><sub><b>JCarlos</b></sub></a><br /><a href="#translation-JCarlosR" title="Translation">🌍</a></td>
    <td align="center"><a href="https://www.mrmoshkel.ir"><img src="https://avatars.githubusercontent.com/u/60359433?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ali Ghasemi</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Dev-AliGhasemi" title="Code">💻</a></td>
  </tr>
 </table>
--- a/async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/App.java
+++ b/async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/App.java
@ -59,9 +59,12 @@ import lombok.extern.slf4j.Slf4j;
@Slf4j
 public class App {
  private static final String ROCKET_LAUNCH_LOG_PATTERN = "Space rocket <%s> launched successfully";
  /**
   * Program entry point.
   */
  public static void main(String[] args) throws Exception {
    // construct a new executor that will run async tasks
    var executor = new ThreadAsyncExecutor();
@ -87,9 +90,9 @@ public class App {
    asyncResult5.await();
    // log the results of the tasks, callbacks log immediately when complete
-    log("Space rocket <" + result1 + "> launch complete");
+    log(String.format(ROCKET_LAUNCH_LOG_PATTERN, result1));
-    log("Space rocket <" + result2 + "> launch complete");
+    log(String.format(ROCKET_LAUNCH_LOG_PATTERN, result2));
-    log("Space rocket <" + result3 + "> launch complete");
+    log(String.format(ROCKET_LAUNCH_LOG_PATTERN, result3));
  }
  /**
@ -102,7 +105,7 @@ public class App {
  private static <T> Callable<T> lazyval(T value, long delayMillis) {
    return () -> {
      Thread.sleep(delayMillis);
-      log("Space rocket <" + value + "> launched successfully");
+      log(String.format(ROCKET_LAUNCH_LOG_PATTERN, value));
      return value;
    };
  }
--- a/bytecode/src/main/java/com/iluwatar/bytecode/App.java
+++ b/bytecode/src/main/java/com/iluwatar/bytecode/App.java
@ -42,6 +42,14 @@ import lombok.extern.slf4j.Slf4j;
@Slf4j
 public class App {
  private static final String LITERAL_0 = "LITERAL 0";
  private static final String HEALTH_PATTERN = "%s_HEALTH";
  private static final String GET_AGILITY = "GET_AGILITY";
  private static final String GET_WISDOM = "GET_WISDOM";
  private static final String ADD = "ADD";
  private static final String LITERAL_2 = "LITERAL 2";
  private static final String DIVIDE = "DIVIDE";
  /**
   * Main app method.
   *
@ -53,17 +61,17 @@ public class App {
        new Wizard(45, 7, 11, 0, 0),
        new Wizard(36, 18, 8, 0, 0));
-    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode("GET_HEALTH"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(String.format(HEALTH_PATTERN, "GET")));
-    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode("GET_AGILITY"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(GET_AGILITY));
-    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode("GET_WISDOM"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(GET_WISDOM));
-    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(ADD));
-    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 2"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_2));
-    vm.execute(InstructionConverterUtil.convertToByteCode("DIVIDE"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(DIVIDE));
-    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(ADD));
-    vm.execute(InstructionConverterUtil.convertToByteCode("SET_HEALTH"));
+    vm.execute(InstructionConverterUtil.convertToByteCode(String.format(HEALTH_PATTERN, "SET")));
  }
 }
--- a/caching/README.md
+++ b/caching/README.md
@ -43,29 +43,39 @@ Wikipedia says:
 **Programmatic Example**
 Let's first look at the data layer of our application. The interesting classes are `UserAccount`
-which is a simple Java object containing the user account details, and `DbManager` interface which handles
+which is a simple Java object containing the user account details, and `DbManager` which handles
-reading and writing of these objects to/from database.
+reading and writing of these objects to/from MongoDB database.
 ```java
-@Data
+@Setter
@Getter
@AllArgsConstructor
@ToString
@EqualsAndHashCode
 public class UserAccount {
  private String userId;
  private String userName;
  private String additionalInfo;
 }
-public interface DbManager {
+@Slf4j
 public final class DbManager {
-  void connect();
+  private static MongoClient mongoClient;
-  void disconnect();
+  private static MongoDatabase db;
-  
+
-  UserAccount readFromDb(String userId);
+  private DbManager() { /*...*/ }
-  UserAccount writeToDb(UserAccount userAccount);
+
-  UserAccount updateDb(UserAccount userAccount);
+  public static void createVirtualDb() { /*...*/ }
-  UserAccount upsertDb(UserAccount userAccount);
+
  public static void connect() throws ParseException { /*...*/ }
  public static UserAccount readFromDb(String userId) { /*...*/ }
  public static void writeToDb(UserAccount userAccount) { /*...*/ }
  public static void updateDb(UserAccount userAccount) { /*...*/ }
  public static void upsertDb(UserAccount userAccount) { /*...*/ }
 }
 ```
@ -161,43 +171,30 @@ strategies.
@Slf4j
 public class CacheStore {
  private static final int CAPACITY = 3;
  private static LruCache cache;
  private final DbManager dbManager;
  /* ... details omitted ... */
-  public UserAccount readThrough(final String userId) {
+  public static UserAccount readThrough(String userId) {
    if (cache.contains(userId)) {
-      LOGGER.info("# Found in Cache!");
+      LOGGER.info("# Cache Hit!");
      return cache.get(userId);
    }
-    LOGGER.info("# Not found in cache! Go to DB!!");
+    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = dbManager.readFromDb(userId);
+    UserAccount userAccount = DbManager.readFromDb(userId);
    cache.set(userId, userAccount);
    return userAccount;
  }
-  public void writeThrough(final UserAccount userAccount) {
+  public static void writeThrough(UserAccount userAccount) {
    if (cache.contains(userAccount.getUserId())) {
-      dbManager.updateDb(userAccount);
+      DbManager.updateDb(userAccount);
    } else {
-      dbManager.writeToDb(userAccount);
+      DbManager.writeToDb(userAccount);
    }
    cache.set(userAccount.getUserId(), userAccount);
  }
  public void writeAround(final UserAccount userAccount) {
    if (cache.contains(userAccount.getUserId())) {
      dbManager.updateDb(userAccount);
      // Cache data has been updated -- remove older
      cache.invalidate(userAccount.getUserId());
      // version from cache.
    } else {
      dbManager.writeToDb(userAccount);
    }
  }
  public static void clearCache() {
    if (cache != null) {
      cache.clear();
@ -228,39 +225,34 @@ class.
 public final class AppManager {
  private static CachingPolicy cachingPolicy;
  private final DbManager dbManager;
  private final CacheStore cacheStore;
  private AppManager() {
  }
-  public void initDb() { /* ... */ }
+  public static void initDb(boolean useMongoDb) { /* ... */ }
  public static void initCachingPolicy(CachingPolicy policy) { /* ... */ }
  public static void initCacheCapacity(int capacity) { /* ... */ }
-  public UserAccount find(final String userId) {
+  public static UserAccount find(String userId) {
-    LOGGER.info("Trying to find {} in cache", userId);
+    if (cachingPolicy == CachingPolicy.THROUGH || cachingPolicy == CachingPolicy.AROUND) {
-    if (cachingPolicy == CachingPolicy.THROUGH
+      return CacheStore.readThrough(userId);
            || cachingPolicy == CachingPolicy.AROUND) {
      return cacheStore.readThrough(userId);
    } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      return cacheStore.readThroughWithWriteBackPolicy(userId);
+      return CacheStore.readThroughWithWriteBackPolicy(userId);
    } else if (cachingPolicy == CachingPolicy.ASIDE) {
      return findAside(userId);
    }
    return null;
  }
-  public void save(final UserAccount userAccount) {
+  public static void save(UserAccount userAccount) {
    LOGGER.info("Save record!");
    if (cachingPolicy == CachingPolicy.THROUGH) {
-      cacheStore.writeThrough(userAccount);
+      CacheStore.writeThrough(userAccount);
    } else if (cachingPolicy == CachingPolicy.AROUND) {
-      cacheStore.writeAround(userAccount);
+      CacheStore.writeAround(userAccount);
    } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      cacheStore.writeBehind(userAccount);
+      CacheStore.writeBehind(userAccount);
    } else if (cachingPolicy == CachingPolicy.ASIDE) {
      saveAside(userAccount);
    }
@ -280,35 +272,24 @@ Here is what we do in the main class of the application.
@Slf4j
 public class App {
-  public static void main(final String[] args) {
+  public static void main(String[] args) {
-    boolean isDbMongo = isDbMongo(args);
+    AppManager.initDb(false);
-    if(isDbMongo){
+    AppManager.initCacheCapacity(3);
-      LOGGER.info("Using the Mongo database engine to run the application.");
+    var app = new App();
    } else {
      LOGGER.info("Using the 'in Memory' database to run the application.");
    }
    App app = new App(isDbMongo);
    app.useReadAndWriteThroughStrategy();
    String splitLine = "==============================================";
    LOGGER.info(splitLine);
    app.useReadThroughAndWriteAroundStrategy();
    LOGGER.info(splitLine);
    app.useReadThroughAndWriteBehindStrategy();
    LOGGER.info(splitLine);
    app.useCacheAsideStategy();
    LOGGER.info(splitLine);
  }
  public void useReadAndWriteThroughStrategy() {
    LOGGER.info("# CachingPolicy.THROUGH");
-    appManager.initCachingPolicy(CachingPolicy.THROUGH);
+    AppManager.initCachingPolicy(CachingPolicy.THROUGH);
    var userAccount1 = new UserAccount("001", "John", "He is a boy.");
-
+    AppManager.save(userAccount1);
-    appManager.save(userAccount1);
+    LOGGER.info(AppManager.printCacheContent());
-    LOGGER.info(appManager.printCacheContent());
+    AppManager.find("001");
-    appManager.find("001");
+    AppManager.find("001");
    appManager.find("001");
  }
  public void useReadThroughAndWriteAroundStrategy() { /* ... */ }
@ -319,6 +300,16 @@ public class App {
 }
 ```
 Finally, here is some of the console output from the program.
 ```
 12:32:53.845 [main] INFO com.iluwatar.caching.App - # CachingPolicy.THROUGH
 12:32:53.900 [main] INFO com.iluwatar.caching.App - 
 --CACHE CONTENT--
 UserAccount(userId=001, userName=John, additionalInfo=He is a boy.)
 ----
 ```
 ## Class diagram
 ![alt text](./etc/caching.png "Caching")
--- a/caching/docker-compose.yml
+++ b/caching/docker-compose.yml
@ -1,11 +0,0 @@
 version: '3.7'
 services:
  mongodb_container:
    image: mongo:latest
    environment:
      MONGO_INITDB_ROOT_USERNAME: root
      MONGO_INITDB_ROOT_PASSWORD: rootpassword
    ports:
      - 27017:27017
    volumes:
      - ./mongo-data/:/data/db
--- a/caching/etc/caching.png
+++ b/caching/etc/caching.png
--- a/caching/pom.xml
+++ b/caching/pom.xml
@ -39,21 +39,19 @@
      <scope>test</scope>
    </dependency>
    <dependency>
-      <groupId>org.mockito</groupId>
+      <groupId>org.mongodb</groupId>
-      <artifactId>mockito-junit-jupiter</artifactId>
+      <artifactId>mongodb-driver</artifactId>
-      <version>3.12.4</version>
+      <version>3.12.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.mockito</groupId>
      <artifactId>mockito-all</artifactId>
      <version>1.10.19</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.mongodb</groupId>
-      <artifactId>mongo-java-driver</artifactId>
+      <artifactId>mongodb-driver-core</artifactId>
-      <version>3.4.1</version>
+      <version>3.0.4</version>
    </dependency>
    <dependency>
      <groupId>org.mongodb</groupId>
      <artifactId>bson</artifactId>
      <version>3.0.4</version>
    </dependency>
  </dependencies>
  <!--
--- a/caching/src/main/java/com/iluwatar/caching/App.java
+++ b/caching/src/main/java/com/iluwatar/caching/App.java
@ -1,62 +1,58 @@
 /*
 * The MIT License
 * Copyright © 2014-2021 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.caching;
 import com.iluwatar.caching.database.DbManager;
 import com.iluwatar.caching.database.DbManagerFactory;
 import lombok.extern.slf4j.Slf4j;
 /**
- * The Caching pattern describes how to avoid expensive re-acquisition of
+ * The Caching pattern describes how to avoid expensive re-acquisition of resources by not releasing
- * resources by not releasing the resources immediately after their use.
+ * the resources immediately after their use. The resources retain their identity, are kept in some
- * The resources retain their identity, are kept in some fast-access storage,
+ * fast-access storage, and are re-used to avoid having to acquire them again. There are four main
- * and are re-used to avoid having to acquire them again. There are four main
+ * caching strategies/techniques in this pattern; each with their own pros and cons. They are;
- * caching strategies/techniques in this pattern; each with their own pros and
+ * <code>write-through</code> which writes data to the cache and DB in a single transaction,
- * cons. They are <code>write-through</code> which writes data to the cache and
+ * <code>write-around</code> which writes data immediately into the DB instead of the cache,
- * DB in a single transaction, <code>write-around</code> which writes data
+ * <code>write-behind</code> which writes data into the cache initially whilst the data is only
- * immediately into the DB instead of the cache, <code>write-behind</code>
+ * written into the DB when the cache is full, and <code>cache-aside</code> which pushes the
- * which writes data into the cache initially whilst the data is only
+ * responsibility of keeping the data synchronized in both data sources to the application itself.
- * written into the DB when the cache is full, and <code>cache-aside</code>
+ * The <code>read-through</code> strategy is also included in the mentioned four strategies --
- * which pushes the responsibility of keeping the data synchronized in both
+ * returns data from the cache to the caller <b>if</b> it exists <b>else</b> queries from DB and
- * data sources to the application itself. The <code>read-through</code>
+ * stores it into the cache for future use. These strategies determine when the data in the cache
- * strategy is also included in the mentioned four strategies --
+ * should be written back to the backing store (i.e. Database) and help keep both data sources
- * returns data from the cache to the caller <b>if</b> it exists <b>else</b>
+ * synchronized/up-to-date. This pattern can improve performance and also helps to maintain
- * queries from DB and stores it into the cache for future use. These strategies
+ * consistency between data held in the cache and the data in the underlying data store.
 * determine when the data in the cache should be written back to the backing
 * store (i.e. Database) and help keep both data sources
 * synchronized/up-to-date. This pattern can improve performance and also helps
 * to maintainconsistency between data held in the cache and the data in
 * the underlying data store.
 *
- * <p>In this example, the user account ({@link UserAccount}) entity is used
+ * <p>In this example, the user account ({@link UserAccount}) entity is used as the underlying
- * as the underlying application data. The cache itself is implemented as an
+ * application data. The cache itself is implemented as an internal (Java) data structure. It adopts
- * internal (Java) data structure. It adopts a Least-Recently-Used (LRU)
+ * a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The four
- * strategy for evicting data from itself when its full. The four
+ * strategies are individually tested. The testing of the cache is restricted towards saving and
- * strategies are individually tested. The testing of the cache is restricted
+ * querying of user accounts from the underlying data store ( {@link DbManager}). The main class (
- * towards saving and querying of user accounts from the
+ * {@link App} is not aware of the underlying mechanics of the application (i.e. save and query) and
- * underlying data store( {@link DbManager}). The main class ( {@link App}
+ * whether the data is coming from the cache or the DB (i.e. separation of concern). The AppManager
- * is not aware of the underlying mechanics of the application
+ * ({@link AppManager}) handles the transaction of data to-and-from the underlying data store
- * (i.e. save and query) and whether the data is coming from the cache or the
+ * (depending on the preferred caching policy/strategy).
 * DB (i.e. separation of concern). The AppManager ({@link AppManager}) handles
 * the transaction of data to-and-from the underlying data store (depending on
 * the preferred caching policy/strategy).
 * <p>
- * <i>{@literal App --> AppManager --> CacheStore/LRUCache/CachingPolicy -->
+ * <i>{@literal App --> AppManager --> CacheStore/LRUCache/CachingPolicy --> DBManager} </i>
 * DBManager} </i>
 * </p>
 *
 * <p>
 * There are 2 ways to launch the application.
 *  - to use "in Memory" database.
 *  - to use the MongoDb as a database
 *
 * To run the application with "in Memory" database, just launch it without parameters
 * Example: 'java -jar app.jar'
 *
 * To run the application with MongoDb you need to be installed the MongoDb
 * in your system, or to launch it in the docker container.
 * You may launch docker container from the root of current module with command:
 * 'docker-compose up'
 * Then you can start the application with parameter --mongo
 * Example: 'java -jar app.jar --mongo'
 * </p>
 *
 * @see CacheStore
@ -65,67 +61,23 @@ import lombok.extern.slf4j.Slf4j;
 */
@Slf4j
 public class App {
  /**
   * Constant parameter name to use mongoDB.
   */
  private static final String USE_MONGO_DB = "--mongo";
  /**
   * Application manager.
   */
  private final AppManager appManager;
  /**
   * Constructor of current App.
   *
   * @param isMongo boolean
   */
  public App(final boolean isMongo) {
    DbManager dbManager = DbManagerFactory.initDb(isMongo);
    appManager = new AppManager(dbManager);
    appManager.initDb();
  }
  /**
   * Program entry point.
   *
   * @param args command line args
   */
-  public static void main(final String[] args) {
+  public static void main(String[] args) {
-    // VirtualDB (instead of MongoDB) was used in running the JUnit tests
+    AppManager.initDb(false); // VirtualDB (instead of MongoDB) was used in running the JUnit tests
    // and the App class to avoid Maven compilation errors. Set flag to
    // true to run the tests with MongoDB (provided that MongoDB is
    // installed and socket connection is open).
-    boolean isDbMongo = isDbMongo(args);
+    AppManager.initCacheCapacity(3);
-    if (isDbMongo) {
+    var app = new App();
      LOGGER.info("Using the Mongo database engine to run the application.");
    } else {
      LOGGER.info("Using the 'in Memory' database to run the application.");
    }
    App app = new App(isDbMongo);
    app.useReadAndWriteThroughStrategy();
    String splitLine = "==============================================";
    LOGGER.info(splitLine);
    app.useReadThroughAndWriteAroundStrategy();
    LOGGER.info(splitLine);
    app.useReadThroughAndWriteBehindStrategy();
    LOGGER.info(splitLine);
    app.useCacheAsideStategy();
    LOGGER.info(splitLine);
  }
  /**
   * Check the input parameters. if
   *
   * @param args input params
   * @return true if there is "--mongo" parameter in arguments
   */
  private static boolean isDbMongo(final String[] args) {
    for (String arg : args) {
      if (arg.equals(USE_MONGO_DB)) {
        return true;
      }
    }
    return false;
  }
  /**
@ -133,14 +85,14 @@ public class App {
   */
  public void useReadAndWriteThroughStrategy() {
    LOGGER.info("# CachingPolicy.THROUGH");
-    appManager.initCachingPolicy(CachingPolicy.THROUGH);
+    AppManager.initCachingPolicy(CachingPolicy.THROUGH);
    var userAccount1 = new UserAccount("001", "John", "He is a boy.");
-    appManager.save(userAccount1);
+    AppManager.save(userAccount1);
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.find("001");
+    AppManager.find("001");
-    appManager.find("001");
+    AppManager.find("001");
  }
  /**
@ -148,21 +100,21 @@ public class App {
   */
  public void useReadThroughAndWriteAroundStrategy() {
    LOGGER.info("# CachingPolicy.AROUND");
-    appManager.initCachingPolicy(CachingPolicy.AROUND);
+    AppManager.initCachingPolicy(CachingPolicy.AROUND);
    var userAccount2 = new UserAccount("002", "Jane", "She is a girl.");
-    appManager.save(userAccount2);
+    AppManager.save(userAccount2);
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.find("002");
+    AppManager.find("002");
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    userAccount2 = appManager.find("002");
+    userAccount2 = AppManager.find("002");
    userAccount2.setUserName("Jane G.");
-    appManager.save(userAccount2);
+    AppManager.save(userAccount2);
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.find("002");
+    AppManager.find("002");
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.find("002");
+    AppManager.find("002");
  }
  /**
@ -170,31 +122,23 @@ public class App {
   */
  public void useReadThroughAndWriteBehindStrategy() {
    LOGGER.info("# CachingPolicy.BEHIND");
-    appManager.initCachingPolicy(CachingPolicy.BEHIND);
+    AppManager.initCachingPolicy(CachingPolicy.BEHIND);
-    var userAccount3 = new UserAccount("003",
+    var userAccount3 = new UserAccount("003", "Adam", "He likes food.");
-            "Adam",
+    var userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
-            "He likes food.");
+    var userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
    var userAccount4 = new UserAccount("004",
            "Rita",
            "She hates cats.");
    var userAccount5 = new UserAccount("005",
            "Isaac",
            "He is allergic to mustard.");
-    appManager.save(userAccount3);
+    AppManager.save(userAccount3);
-    appManager.save(userAccount4);
+    AppManager.save(userAccount4);
-    appManager.save(userAccount5);
+    AppManager.save(userAccount5);
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.find("003");
+    AppManager.find("003");
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    UserAccount userAccount6 = new UserAccount("006",
+    UserAccount userAccount6 = new UserAccount("006", "Yasha", "She is an only child.");
-            "Yasha",
+    AppManager.save(userAccount6);
-            "She is an only child.");
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.save(userAccount6);
+    AppManager.find("004");
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
    appManager.find("004");
    LOGGER.info(appManager.printCacheContent());
  }
  /**
@ -202,26 +146,20 @@ public class App {
   */
  public void useCacheAsideStategy() {
    LOGGER.info("# CachingPolicy.ASIDE");
-    appManager.initCachingPolicy(CachingPolicy.ASIDE);
+    AppManager.initCachingPolicy(CachingPolicy.ASIDE);
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    var userAccount3 = new UserAccount("003",
+    var userAccount3 = new UserAccount("003", "Adam", "He likes food.");
-            "Adam",
+    var userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
-            "He likes food.");
+    var userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
-    var userAccount4 = new UserAccount("004",
+    AppManager.save(userAccount3);
-            "Rita",
+    AppManager.save(userAccount4);
-            "She hates cats.");
+    AppManager.save(userAccount5);
    var userAccount5 = new UserAccount("005",
            "Isaac",
            "He is allergic to mustard.");
    appManager.save(userAccount3);
    appManager.save(userAccount4);
    appManager.save(userAccount5);
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.find("003");
+    AppManager.find("003");
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
-    appManager.find("004");
+    AppManager.find("004");
-    LOGGER.info(appManager.printCacheContent());
+    LOGGER.info(AppManager.printCacheContent());
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/AppManager.java
+++ b/caching/src/main/java/com/iluwatar/caching/AppManager.java
@ -23,80 +23,65 @@
 package com.iluwatar.caching;
-import com.iluwatar.caching.database.DbManager;
+import java.text.ParseException;
 import java.util.Optional;
 import lombok.extern.slf4j.Slf4j;
 /**
- * AppManager helps to bridge the gap in communication between the main class
+ * AppManager helps to bridge the gap in communication between the main class and the application's
- * and the application's back-end. DB connection is initialized through this
+ * back-end. DB connection is initialized through this class. The chosen caching strategy/policy is
- * class. The chosen  caching strategy/policy is also initialized here.
+ * also initialized here. Before the cache can be used, the size of the cache has to be set.
- * Before the cache can be used, the size of the  cache has to be set.
+ * Depending on the chosen caching policy, AppManager will call the appropriate function in the
- * Depending on the chosen caching policy, AppManager will call the
+ * CacheStore class.
 * appropriate function in the CacheStore class.
 */
@Slf4j
-public class AppManager {
+public final class AppManager {
  /**
   * Caching Policy.
   */
  private CachingPolicy cachingPolicy;
  /**
   * Database Manager.
   */
  private final DbManager dbManager;
  /**
   * Cache Store.
   */
  private final CacheStore cacheStore;
-  /**
+  private static CachingPolicy cachingPolicy;
-   * Constructor.
+
-   *
+  private AppManager() {
   * @param newDbManager database manager
   */
  public AppManager(final DbManager newDbManager) {
    this.dbManager = newDbManager;
    this.cacheStore = new CacheStore(newDbManager);
  }
  /**
-   * Developer/Tester is able to choose whether the application should use
+   * Developer/Tester is able to choose whether the application should use MongoDB as its underlying
-   * MongoDB as its underlying data storage or a simple Java data structure
+   * data storage or a simple Java data structure to (temporarily) store the data/objects during
-   * to (temporarily) store the data/objects during runtime.
+   * runtime.
   */
-  public void initDb() {
+  public static void initDb(boolean useMongoDb) {
-    dbManager.connect();
+    if (useMongoDb) {
      try {
        DbManager.connect();
      } catch (ParseException e) {
        LOGGER.error("Error connecting to MongoDB", e);
      }
    } else {
      DbManager.createVirtualDb();
    }
  }
  /**
   * Initialize caching policy.
   *
   * @param policy is a {@link CachingPolicy}
   */
-  public void initCachingPolicy(final CachingPolicy policy) {
+  public static void initCachingPolicy(CachingPolicy policy) {
    cachingPolicy = policy;
    if (cachingPolicy == CachingPolicy.BEHIND) {
-      Runtime.getRuntime().addShutdownHook(new Thread(cacheStore::flushCache));
+      Runtime.getRuntime().addShutdownHook(new Thread(CacheStore::flushCache));
    }
-    cacheStore.clearCache();
+    CacheStore.clearCache();
  }
  public static void initCacheCapacity(int capacity) {
    CacheStore.initCapacity(capacity);
  }
  /**
   * Find user account.
   *
   * @param userId String
   * @return {@link UserAccount}
   */
-  public UserAccount find(final String userId) {
+  public static UserAccount find(String userId) {
-    LOGGER.info("Trying to find {} in cache", userId);
+    if (cachingPolicy == CachingPolicy.THROUGH || cachingPolicy == CachingPolicy.AROUND) {
-    if (cachingPolicy == CachingPolicy.THROUGH
+      return CacheStore.readThrough(userId);
            || cachingPolicy == CachingPolicy.AROUND) {
      return cacheStore.readThrough(userId);
    } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      return cacheStore.readThroughWithWriteBackPolicy(userId);
+      return CacheStore.readThroughWithWriteBackPolicy(userId);
    } else if (cachingPolicy == CachingPolicy.ASIDE) {
      return findAside(userId);
    }
@ -105,55 +90,41 @@ public class AppManager {
  /**
   * Save user account.
   *
   * @param userAccount {@link UserAccount}
   */
-  public void save(final UserAccount userAccount) {
+  public static void save(UserAccount userAccount) {
    LOGGER.info("Save record!");
    if (cachingPolicy == CachingPolicy.THROUGH) {
-      cacheStore.writeThrough(userAccount);
+      CacheStore.writeThrough(userAccount);
    } else if (cachingPolicy == CachingPolicy.AROUND) {
-      cacheStore.writeAround(userAccount);
+      CacheStore.writeAround(userAccount);
    } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      cacheStore.writeBehind(userAccount);
+      CacheStore.writeBehind(userAccount);
    } else if (cachingPolicy == CachingPolicy.ASIDE) {
      saveAside(userAccount);
    }
  }
-  /**
+  public static String printCacheContent() {
-   * Returns String.
+    return CacheStore.print();
   *
   * @return String
   */
  public String printCacheContent() {
    return cacheStore.print();
  }
  /**
   * Cache-Aside save user account helper.
   *
   * @param userAccount {@link UserAccount}
   */
-  private void saveAside(final UserAccount userAccount) {
+  private static void saveAside(UserAccount userAccount) {
-    dbManager.updateDb(userAccount);
+    DbManager.updateDb(userAccount);
-    cacheStore.invalidate(userAccount.getUserId());
+    CacheStore.invalidate(userAccount.getUserId());
  }
  /**
   * Cache-Aside find user account helper.
   *
   * @param userId String
   * @return {@link UserAccount}
   */
-  private UserAccount findAside(final String userId) {
+  private static UserAccount findAside(String userId) {
-    return Optional.ofNullable(cacheStore.get(userId))
+    return Optional.ofNullable(CacheStore.get(userId))
-            .or(() -> {
+        .or(() -> {
-              Optional<UserAccount> userAccount =
+          Optional<UserAccount> userAccount = Optional.ofNullable(DbManager.readFromDb(userId));
-                      Optional.ofNullable(dbManager.readFromDb(userId));
+          userAccount.ifPresent(account -> CacheStore.set(userId, account));
-              userAccount.ifPresent(account -> cacheStore.set(userId, account));
+          return userAccount;
-              return userAccount;
+        })
-            })
+        .orElse(null);
            .orElse(null);
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/CacheStore.java
+++ b/caching/src/main/java/com/iluwatar/caching/CacheStore.java
@ -23,11 +23,9 @@
 package com.iluwatar.caching;
 import com.iluwatar.caching.database.DbManager;
 import java.util.List;
 import java.util.Optional;
 import java.util.stream.Collectors;
 import lombok.extern.slf4j.Slf4j;
 /**
@ -35,34 +33,16 @@ import lombok.extern.slf4j.Slf4j;
 */
@Slf4j
 public class CacheStore {
  /**
   * Cache capacity.
   */
  private static final int CAPACITY = 3;
-  /**
+  private static LruCache cache;
   * Lru cache see {@link LruCache}.
   */
  private LruCache cache;
  /**
   * DbManager.
   */
  private final DbManager dbManager;
-  /**
+  private CacheStore() {
   * Cache Store.
   * @param dataBaseManager {@link DbManager}
   */
  public CacheStore(final DbManager dataBaseManager) {
    this.dbManager = dataBaseManager;
    initCapacity(CAPACITY);
  }
  /**
   * Init cache capacity.
   * @param capacity int
   */
-  public void initCapacity(final int capacity) {
+  public static void initCapacity(int capacity) {
    if (cache == null) {
      cache = new LruCache(capacity);
    } else {
@ -72,64 +52,57 @@ public class CacheStore {
  /**
   * Get user account using read-through cache.
   * @param userId {@link String}
   * @return {@link UserAccount}
   */
-  public UserAccount readThrough(final String userId) {
+  public static UserAccount readThrough(String userId) {
    if (cache.contains(userId)) {
-      LOGGER.info("# Found in Cache!");
+      LOGGER.info("# Cache Hit!");
      return cache.get(userId);
    }
-    LOGGER.info("# Not found in cache! Go to DB!!");
+    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = dbManager.readFromDb(userId);
+    UserAccount userAccount = DbManager.readFromDb(userId);
    cache.set(userId, userAccount);
    return userAccount;
  }
  /**
   * Get user account using write-through cache.
   * @param userAccount {@link UserAccount}
   */
-  public void writeThrough(final UserAccount userAccount) {
+  public static void writeThrough(UserAccount userAccount) {
    if (cache.contains(userAccount.getUserId())) {
-      dbManager.updateDb(userAccount);
+      DbManager.updateDb(userAccount);
    } else {
-      dbManager.writeToDb(userAccount);
+      DbManager.writeToDb(userAccount);
    }
    cache.set(userAccount.getUserId(), userAccount);
  }
  /**
   * Get user account using write-around cache.
   * @param userAccount {@link UserAccount}
   */
-  public void writeAround(final UserAccount userAccount) {
+  public static void writeAround(UserAccount userAccount) {
    if (cache.contains(userAccount.getUserId())) {
-      dbManager.updateDb(userAccount);
+      DbManager.updateDb(userAccount);
-      // Cache data has been updated -- remove older
+      cache.invalidate(userAccount.getUserId()); // Cache data has been updated -- remove older
      cache.invalidate(userAccount.getUserId());
      // version from cache.
    } else {
-      dbManager.writeToDb(userAccount);
+      DbManager.writeToDb(userAccount);
    }
  }
  /**
   * Get user account using read-through cache with write-back policy.
   * @param userId {@link String}
   * @return {@link UserAccount}
   */
-  public UserAccount readThroughWithWriteBackPolicy(final String userId) {
+  public static UserAccount readThroughWithWriteBackPolicy(String userId) {
    if (cache.contains(userId)) {
-      LOGGER.info("# Found in cache!");
+      LOGGER.info("# Cache Hit!");
      return cache.get(userId);
    }
-    LOGGER.info("# Not found in Cache!");
+    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = dbManager.readFromDb(userId);
+    UserAccount userAccount = DbManager.readFromDb(userId);
    if (cache.isFull()) {
      LOGGER.info("# Cache is FULL! Writing LRU data to DB...");
      UserAccount toBeWrittenToDb = cache.getLruData();
-      dbManager.upsertDb(toBeWrittenToDb);
+      DbManager.upsertDb(toBeWrittenToDb);
    }
    cache.set(userId, userAccount);
    return userAccount;
@ -137,13 +110,12 @@ public class CacheStore {
  /**
   * Set user account.
   * @param userAccount {@link UserAccount}
   */
-  public void writeBehind(final UserAccount userAccount) {
+  public static void writeBehind(UserAccount userAccount) {
    if (cache.isFull() && !cache.contains(userAccount.getUserId())) {
      LOGGER.info("# Cache is FULL! Writing LRU data to DB...");
      UserAccount toBeWrittenToDb = cache.getLruData();
-      dbManager.upsertDb(toBeWrittenToDb);
+      DbManager.upsertDb(toBeWrittenToDb);
    }
    cache.set(userAccount.getUserId(), userAccount);
  }
@ -151,7 +123,7 @@ public class CacheStore {
  /**
   * Clears cache.
   */
-  public void clearCache() {
+  public static void clearCache() {
    if (cache != null) {
      cache.clear();
    }
@ -160,51 +132,44 @@ public class CacheStore {
  /**
   * Writes remaining content in the cache into the DB.
   */
-  public void flushCache() {
+  public static void flushCache() {
    LOGGER.info("# flushCache...");
    Optional.ofNullable(cache)
        .map(LruCache::getCacheDataInListForm)
        .orElse(List.of())
-        .forEach(dbManager::updateDb);
+        .forEach(DbManager::updateDb);
    dbManager.disconnect();
  }
  /**
   * Print user accounts.
   * @return {@link String}
   */
-  public String print() {
+  public static String print() {
    return Optional.ofNullable(cache)
        .map(LruCache::getCacheDataInListForm)
        .orElse(List.of())
        .stream()
        .map(userAccount -> userAccount.toString() + "\n")
-        .collect(Collectors.joining("", "\n--CACHE CONTENT--\n", "----"));
+        .collect(Collectors.joining("", "\n--CACHE CONTENT--\n", "----\n"));
  }
  /**
   * Delegate to backing cache store.
   * @param userId {@link String}
   * @return {@link UserAccount}
   */
-  public UserAccount get(final String userId) {
+  public static UserAccount get(String userId) {
    return cache.get(userId);
  }
  /**
   * Delegate to backing cache store.
   * @param userId {@link String}
   * @param userAccount {@link UserAccount}
   */
-  public void set(final String userId, final UserAccount userAccount) {
+  public static void set(String userId, UserAccount userAccount) {
    cache.set(userId, userAccount);
  }
  /**
   * Delegate to backing cache store.
   * @param userId {@link String}
   */
-  public void invalidate(final String userId) {
+  public static void invalidate(String userId) {
    cache.invalidate(userId);
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
+++ b/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
@ -32,25 +32,10 @@ import lombok.Getter;
@AllArgsConstructor
@Getter
 public enum CachingPolicy {
  /**
   * Through.
   */
  THROUGH("through"),
  /**
   * AROUND.
   */
  AROUND("around"),
  /**
   * BEHIND.
   */
  BEHIND("behind"),
  /**
   * ASIDE.
   */
  ASIDE("aside");
  /**
   * Policy value.
   */
  private final String policy;
 }
--- a/caching/src/main/java/com/iluwatar/caching/DbManager.java
+++ b/caching/src/main/java/com/iluwatar/caching/DbManager.java
@ -0,0 +1,172 @@
 /*
 * The MIT License
 * Copyright © 2014-2021 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.caching;
 import com.iluwatar.caching.constants.CachingConstants;
 import com.mongodb.MongoClient;
 import com.mongodb.client.MongoDatabase;
 import com.mongodb.client.model.UpdateOptions;
 import java.text.ParseException;
 import java.util.HashMap;
 import java.util.Map;
 import lombok.extern.slf4j.Slf4j;
 import org.bson.Document;
 /**
 * <p>DBManager handles the communication with the underlying data store i.e. Database. It contains
 * the implemented methods for querying, inserting, and updating data. MongoDB was used as the
 * database for the application.</p>
 *
 * <p>Developer/Tester is able to choose whether the application should use MongoDB as its
 * underlying data storage (connect()) or a simple Java data structure to (temporarily) store the
 * data/objects during runtime (createVirtualDB()).</p>
 */
@Slf4j
 public final class DbManager {
  private static MongoClient mongoClient;
  private static MongoDatabase db;
  private static boolean useMongoDB;
  private static Map<String, UserAccount> virtualDB;
  private static final String ERROR_MESSAGE_LOG = "Error connecting to MongoDB";
  private DbManager() {
  }
  /**
   * Create DB.
   */
  public static void createVirtualDb() {
    useMongoDB = false;
    virtualDB = new HashMap<>();
  }
  /**
   * Connect to DB.
   */
  public static void connect() throws ParseException {
    useMongoDB = true;
    mongoClient = new MongoClient();
    db = mongoClient.getDatabase("test");
  }
  /**
   * Read user account from DB.
   */
  public static UserAccount readFromDb(String userId) {
    if (!useMongoDB) {
      if (virtualDB.containsKey(userId)) {
        return virtualDB.get(userId);
      }
      return null;
    }
    if (db == null) {
      try {
        connect();
      } catch (ParseException e) {
        LOGGER.error(ERROR_MESSAGE_LOG, e);
      }
    }
    var iterable = db
        .getCollection(CachingConstants.USER_ACCOUNT)
        .find(new Document(CachingConstants.USER_ID, userId));
    if (iterable == null) {
      return null;
    }
    Document doc = iterable.first();
    String userName = doc.getString(CachingConstants.USER_NAME);
    String appInfo = doc.getString(CachingConstants.ADD_INFO);
    return new UserAccount(userId, userName, appInfo);
  }
  /**
   * Write user account to DB.
   */
  public static void writeToDb(UserAccount userAccount) {
    if (!useMongoDB) {
      virtualDB.put(userAccount.getUserId(), userAccount);
      return;
    }
    if (db == null) {
      try {
        connect();
      } catch (ParseException e) {
        LOGGER.error(ERROR_MESSAGE_LOG, e);
      }
    }
    db.getCollection(CachingConstants.USER_ACCOUNT).insertOne(
        new Document(CachingConstants.USER_ID, userAccount.getUserId())
            .append(CachingConstants.USER_NAME, userAccount.getUserName())
            .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())
    );
  }
  /**
   * Update DB.
   */
  public static void updateDb(UserAccount userAccount) {
    if (!useMongoDB) {
      virtualDB.put(userAccount.getUserId(), userAccount);
      return;
    }
    if (db == null) {
      try {
        connect();
      } catch (ParseException e) {
        LOGGER.error(ERROR_MESSAGE_LOG, e);
      }
    }
    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
        new Document(CachingConstants.USER_ID, userAccount.getUserId()),
        new Document("$set", new Document(CachingConstants.USER_NAME, userAccount.getUserName())
            .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())));
  }
  /**
   * Insert data into DB if it does not exist. Else, update it.
   */
  public static void upsertDb(UserAccount userAccount) {
    if (!useMongoDB) {
      virtualDB.put(userAccount.getUserId(), userAccount);
      return;
    }
    if (db == null) {
      try {
        connect();
      } catch (ParseException e) {
        LOGGER.error(ERROR_MESSAGE_LOG, e);
      }
    }
    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
        new Document(CachingConstants.USER_ID, userAccount.getUserId()),
        new Document("$set",
            new Document(CachingConstants.USER_ID, userAccount.getUserId())
                .append(CachingConstants.USER_NAME, userAccount.getUserName())
                .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())
        ),
        new UpdateOptions().upsert(true)
    );
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/LruCache.java
+++ b/caching/src/main/java/com/iluwatar/caching/LruCache.java
@ -29,83 +29,41 @@ import java.util.List;
 import java.util.Map;
 import lombok.extern.slf4j.Slf4j;
 /**
- * Data structure/implementation of the application's cache. The data structure
+ * Data structure/implementation of the application's cache. The data structure consists of a hash
- * consists of a hash table attached with a doubly linked-list. The linked-list
+ * table attached with a doubly linked-list. The linked-list helps in capturing and maintaining the
- * helps in capturing and maintaining the LRU data in the cache. When a data is
+ * LRU data in the cache. When a data is queried (from the cache), added (to the cache), or updated,
- * queried (from the cache), added (to the cache), or updated, the data is
+ * the data is moved to the front of the list to depict itself as the most-recently-used data. The
- * moved to the front of the list to depict itself as the most-recently-used
+ * LRU data is always at the end of the list.
 * data. The LRU data is always at the end of the list.
 */
@Slf4j
 public class LruCache {
  /**
   * Static class Node.
   */
  static class Node {
    /**
     * user id.
     */
    private final String userId;
    /**
     * User Account.
     */
    private UserAccount userAccount;
    /**
     * previous.
     */
    private Node previous;
    /**
     * next.
     */
    private Node next;
-    /**
+  static class Node {
-     * Node definition.
+    String userId;
-     *
+    UserAccount userAccount;
-     * @param id      String
+    Node previous;
-     * @param account {@link UserAccount}
+    Node next;
-     */
+
-    Node(final String id, final UserAccount account) {
+    public Node(String userId, UserAccount userAccount) {
-      this.userId = id;
+      this.userId = userId;
-      this.userAccount = account;
+      this.userAccount = userAccount;
    }
  }
-  /**
+  int capacity;
-   * Capacity of Cache.
+  Map<String, Node> cache = new HashMap<>();
-   */
+  Node head;
-  private int capacity;
+  Node end;
  /**
   * Cache {@link HashMap}.
   */
  private Map<String, Node> cache = new HashMap<>();
  /**
   * Head.
   */
  private Node head;
  /**
   * End.
   */
  private Node end;
-  /**
+  public LruCache(int capacity) {
-   * Constructor.
+    this.capacity = capacity;
   *
   * @param cap Integer.
   */
  public LruCache(final int cap) {
    this.capacity = cap;
  }
  /**
   * Get user account.
   *
   * @param userId String
   * @return {@link UserAccount}
   */
-  public UserAccount get(final String userId) {
+  public UserAccount get(String userId) {
    if (cache.containsKey(userId)) {
      var node = cache.get(userId);
      remove(node);
@ -117,10 +75,8 @@ public class LruCache {
  /**
   * Remove node from linked list.
   *
   * @param node {@link Node}
   */
-  public void remove(final Node node) {
+  public void remove(Node node) {
    if (node.previous != null) {
      node.previous.next = node.next;
    } else {
@ -135,10 +91,8 @@ public class LruCache {
  /**
   * Move node to the front of the list.
   *
   * @param node {@link Node}
   */
-  public void setHead(final Node node) {
+  public void setHead(Node node) {
    node.next = head;
    node.previous = null;
    if (head != null) {
@ -152,11 +106,8 @@ public class LruCache {
  /**
   * Set user account.
   *
   * @param userAccount {@link UserAccount}
   * @param userId      {@link String}
   */
-  public void set(final String userId, final UserAccount userAccount) {
+  public void set(String userId, UserAccount userAccount) {
    if (cache.containsKey(userId)) {
      var old = cache.get(userId);
      old.userAccount = userAccount;
@ -176,43 +127,25 @@ public class LruCache {
    }
  }
-  /**
+  public boolean contains(String userId) {
   * Check if Cache contains the userId.
   *
   * @param userId {@link String}
   * @return boolean
   */
  public boolean contains(final String userId) {
    return cache.containsKey(userId);
  }
  /**
   * Invalidate cache for user.
   *
   * @param userId {@link String}
   */
-  public void invalidate(final String userId) {
+  public void invalidate(String userId) {
    var toBeRemoved = cache.remove(userId);
    if (toBeRemoved != null) {
-      LOGGER.info("# {} has been updated! "
+      LOGGER.info("# {} has been updated! Removing older version from cache...", userId);
              + "Removing older version from cache...", userId);
      remove(toBeRemoved);
    }
  }
  /**
   * Check if the cache is full.
   * @return boolean
   */
  public boolean isFull() {
    return cache.size() >= capacity;
  }
  /**
   * Get LRU data.
   *
   * @return {@link UserAccount}
   */
  public UserAccount getLruData() {
    return end.userAccount;
  }
@ -228,8 +161,6 @@ public class LruCache {
  /**
   * Returns cache data in list form.
   *
   * @return {@link List}
   */
  public List<UserAccount> getCacheDataInListForm() {
    var listOfCacheData = new ArrayList<UserAccount>();
@ -243,14 +174,10 @@ public class LruCache {
  /**
   * Set cache capacity.
   *
   * @param newCapacity int
   */
-  public void setCapacity(final int newCapacity) {
+  public void setCapacity(int newCapacity) {
    if (capacity > newCapacity) {
-      // Behavior can be modified to accommodate
+      clear(); // Behavior can be modified to accommodate for decrease in cache size. For now, we'll
      // for decrease in cache size. For now, we'll
      clear();
      // just clear the cache.
    } else {
      this.capacity = newCapacity;
--- a/caching/src/main/java/com/iluwatar/caching/UserAccount.java
+++ b/caching/src/main/java/com/iluwatar/caching/UserAccount.java
@ -24,28 +24,19 @@
 package com.iluwatar.caching;
 import lombok.AllArgsConstructor;
-import lombok.Data;
+import lombok.Getter;
-import lombok.EqualsAndHashCode;
+import lombok.Setter;
 import lombok.ToString;
 /**
 * Entity class (stored in cache and DB) used in the application.
 */
-@Data
+@Setter
@Getter
@AllArgsConstructor
@ToString
@EqualsAndHashCode
 public class UserAccount {
  /**
   * User Id.
   */
  private String userId;
  /**
   * User Name.
   */
  private String userName;
  /**
   * Additional Info.
   */
  private String additionalInfo;
 }
--- a/caching/src/main/java/com/iluwatar/caching/constants/CachingConstants.java
+++ b/caching/src/main/java/com/iluwatar/caching/constants/CachingConstants.java
@ -26,27 +26,11 @@ package com.iluwatar.caching.constants;
 /**
 * Constant class for defining constants.
 */
-public final class CachingConstants {
+public class CachingConstants {
-  /**
+
   * User Account.
   */
  public static final String USER_ACCOUNT = "user_accounts";
  /**
   * User ID.
   */
  public static final String USER_ID = "userID";
  /**
   * User Name.
   */
  public static final String USER_NAME = "userName";
  /**
   * Additional Info.
   */
  public static final String ADD_INFO = "additionalInfo";
  /**
   * Constructor.
   */
  private CachingConstants() {
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/constants/package-info.java
+++ b/caching/src/main/java/com/iluwatar/caching/constants/package-info.java
@ -1,4 +0,0 @@
 /**
 * Constants.
 */
 package com.iluwatar.caching.constants;
--- a/caching/src/main/java/com/iluwatar/caching/database/DbManager.java
+++ b/caching/src/main/java/com/iluwatar/caching/database/DbManager.java
@ -1,52 +0,0 @@
 package com.iluwatar.caching.database;
 import com.iluwatar.caching.UserAccount;
 /**
 * <p>DBManager handles the communication with the underlying data store i.e.
 * Database. It contains the implemented methods for querying, inserting,
 * and updating data. MongoDB was used as the database for the application.</p>
 */
 public interface DbManager {
  /**
   * Connect to DB.
   */
  void connect();
  /**
   * Disconnect from DB.
   */
  void disconnect();
  /**
   * Read from DB.
   *
   * @param userId {@link String}
   * @return {@link UserAccount}
   */
  UserAccount readFromDb(String userId);
  /**
   * Write to DB.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  UserAccount writeToDb(UserAccount userAccount);
  /**
   * Update record.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  UserAccount updateDb(UserAccount userAccount);
  /**
   * Update record or Insert if not exists.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  UserAccount upsertDb(UserAccount userAccount);
 }
--- a/caching/src/main/java/com/iluwatar/caching/database/DbManagerFactory.java
+++ b/caching/src/main/java/com/iluwatar/caching/database/DbManagerFactory.java
@ -1,25 +0,0 @@
 package com.iluwatar.caching.database;
 /**
 * Creates the database connection accroding the input parameter.
 */
 public final class DbManagerFactory {
  /**
   * Private constructor.
   */
  private DbManagerFactory() {
  }
  /**
   * Init database.
   *
   * @param isMongo boolean
   * @return {@link DbManager}
   */
  public static DbManager initDb(final boolean isMongo) {
    if (isMongo) {
      return new MongoDb();
    }
    return new VirtualDb();
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/database/MongoDb.java
+++ b/caching/src/main/java/com/iluwatar/caching/database/MongoDb.java
@ -1,128 +0,0 @@
 package com.iluwatar.caching.database;
 import static com.iluwatar.caching.constants.CachingConstants.ADD_INFO;
 import static com.iluwatar.caching.constants.CachingConstants.USER_ACCOUNT;
 import static com.iluwatar.caching.constants.CachingConstants.USER_ID;
 import static com.iluwatar.caching.constants.CachingConstants.USER_NAME;
 import com.iluwatar.caching.UserAccount;
 import com.iluwatar.caching.constants.CachingConstants;
 import com.mongodb.MongoClient;
 import com.mongodb.MongoClientOptions;
 import com.mongodb.MongoCredential;
 import com.mongodb.ServerAddress;
 import com.mongodb.client.MongoDatabase;
 import com.mongodb.client.model.UpdateOptions;
 import java.util.List;
 import lombok.extern.slf4j.Slf4j;
 import org.bson.Document;
 /**
 * Implementation of DatabaseManager.
 * implements base methods to work with MongoDb.
 */
@Slf4j
 public class MongoDb implements DbManager {
  private static final String DATABASE_NAME = "admin";
  private static final String MONGO_USER = "root";
  private static final String MONGO_PASSWORD = "rootpassword";
  private MongoClient client;
  private MongoDatabase db;
  /**
   * Connect to Db. Check th connection
   */
  @Override
  public void connect() {
    MongoCredential mongoCredential = MongoCredential.createCredential(MONGO_USER,
                    DATABASE_NAME,
                    MONGO_PASSWORD.toCharArray());
    MongoClientOptions options = MongoClientOptions.builder().build();
    client = new MongoClient(new ServerAddress(), List.of(mongoCredential), options);
    db = client.getDatabase(DATABASE_NAME);
  }
  @Override
  public void disconnect() {
    client.close();
  }
  /**
   * Read data from DB.
   *
   * @param userId {@link String}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount readFromDb(final String userId) {
    var iterable = db
            .getCollection(CachingConstants.USER_ACCOUNT)
            .find(new Document(USER_ID, userId));
    if (iterable.first() == null) {
      return null;
    }
    Document doc = iterable.first();
    if (doc != null) {
      String userName = doc.getString(USER_NAME);
      String appInfo = doc.getString(ADD_INFO);
      return new UserAccount(userId, userName, appInfo);
    } else {
      return null;
    }
  }
  /**
   * Write data to DB.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount writeToDb(final UserAccount userAccount) {
    db.getCollection(USER_ACCOUNT).insertOne(
            new Document(USER_ID, userAccount.getUserId())
                    .append(USER_NAME, userAccount.getUserName())
                    .append(ADD_INFO, userAccount.getAdditionalInfo())
    );
    return userAccount;
  }
  /**
   * Update DB.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount updateDb(final UserAccount userAccount) {
    Document id = new Document(USER_ID, userAccount.getUserId());
    Document dataSet = new Document(USER_NAME, userAccount.getUserName())
            .append(ADD_INFO, userAccount.getAdditionalInfo());
    db.getCollection(CachingConstants.USER_ACCOUNT)
            .updateOne(id, new Document("$set", dataSet));
    return userAccount;
  }
  /**
   * Update data if exists.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount upsertDb(final UserAccount userAccount) {
    String userId = userAccount.getUserId();
    String userName = userAccount.getUserName();
    String additionalInfo = userAccount.getAdditionalInfo();
    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
            new Document(USER_ID, userId),
            new Document("$set",
                    new Document(USER_ID, userId)
                            .append(USER_NAME, userName)
                            .append(ADD_INFO, additionalInfo)
            ),
            new UpdateOptions().upsert(true)
    );
    return userAccount;
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/database/VirtualDb.java
+++ b/caching/src/main/java/com/iluwatar/caching/database/VirtualDb.java
@ -1,78 +0,0 @@
 package com.iluwatar.caching.database;
 import com.iluwatar.caching.UserAccount;
 import java.util.HashMap;
 import java.util.Map;
 /**
 * Implementation of DatabaseManager.
 * implements base methods to work with hashMap as database.
 */
 public class VirtualDb implements DbManager {
  /**
   * Virtual DataBase.
   */
  private Map<String, UserAccount> db;
  /**
   * Creates new HashMap.
   */
  @Override
  public void connect() {
    db = new HashMap<>();
  }
  @Override
  public void disconnect() {
    db = null;
  }
  /**
   * Read from Db.
   *
   * @param userId {@link String}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount readFromDb(final String userId) {
    if (db.containsKey(userId)) {
      return db.get(userId);
    }
    return null;
  }
  /**
   * Write to DB.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount writeToDb(final UserAccount userAccount) {
    db.put(userAccount.getUserId(), userAccount);
    return userAccount;
  }
  /**
   * Update reecord in DB.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount updateDb(final UserAccount userAccount) {
    return writeToDb(userAccount);
  }
  /**
   * Update.
   *
   * @param userAccount {@link UserAccount}
   * @return {@link UserAccount}
   */
  @Override
  public UserAccount upsertDb(final UserAccount userAccount) {
    return updateDb(userAccount);
  }
 }
--- a/caching/src/main/java/com/iluwatar/caching/database/package-info.java
+++ b/caching/src/main/java/com/iluwatar/caching/database/package-info.java
@ -1,4 +0,0 @@
 /**
 * Database classes.
 */
 package com.iluwatar.caching.database;
--- a/caching/src/main/java/com/iluwatar/caching/package-info.java
+++ b/caching/src/main/java/com/iluwatar/caching/package-info.java
@ -1,20 +0,0 @@
 /**
 * The MIT License
 * Copyright © 2014-2021 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.caching;
--- a/caching/src/test/java/com/iluwatar/caching/AppTest.java
+++ b/caching/src/test/java/com/iluwatar/caching/AppTest.java
@ -25,21 +25,25 @@ package com.iluwatar.caching;
 import org.junit.jupiter.api.Test;
 import java.io.IOException;
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 /**
 * Tests that Caching example runs without errors.
 */
 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}
   * throws an exception.
   */
  @Test
  void shouldExecuteApplicationWithoutException() {
    assertDoesNotThrow(() -> App.main(new String[]{}));
  }
 }
--- a/caching/src/test/java/com/iluwatar/caching/CachingTest.java
+++ b/caching/src/test/java/com/iluwatar/caching/CachingTest.java
@ -23,11 +23,11 @@
 package com.iluwatar.caching;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 /**
 * Application test
 */
@ -43,30 +43,32 @@ class CachingTest {
    // to avoid Maven compilation errors. Set flag to true to run the
    // tests with MongoDB (provided that MongoDB is installed and socket
    // connection is open).
-    app = new App(false);
+    AppManager.initDb(false);
    AppManager.initCacheCapacity(3);
    app = new App();
  }
  @Test
  void testReadAndWriteThroughStrategy() {
-    assertNotNull(app);
+	assertNotNull(app);
    app.useReadAndWriteThroughStrategy();
  }
  @Test
  void testReadThroughAndWriteAroundStrategy() {
-    assertNotNull(app);
+	assertNotNull(app);
    app.useReadThroughAndWriteAroundStrategy();
  }
  @Test
  void testReadThroughAndWriteBehindStrategy() {
-    assertNotNull(app);
+	assertNotNull(app);
    app.useReadThroughAndWriteBehindStrategy();
  }
  @Test
  void testCacheAsideStrategy() {
-    assertNotNull(app);
+	assertNotNull(app);
    app.useCacheAsideStategy();
  }
 }
--- a/caching/src/test/java/com/iluwatar/caching/database/MongoDbTest.java
+++ b/caching/src/test/java/com/iluwatar/caching/database/MongoDbTest.java
@ -1,84 +0,0 @@
 package com.iluwatar.caching.database;
 import com.iluwatar.caching.UserAccount;
 import com.iluwatar.caching.constants.CachingConstants;
 import com.mongodb.client.FindIterable;
 import com.mongodb.client.MongoCollection;
 import com.mongodb.client.MongoDatabase;
 import org.bson.Document;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.mockito.Mock;
 import org.mockito.internal.util.reflection.Whitebox;
 import static com.iluwatar.caching.constants.CachingConstants.ADD_INFO;
 import static com.iluwatar.caching.constants.CachingConstants.USER_ID;
 import static com.iluwatar.caching.constants.CachingConstants.USER_NAME;
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.*;
 class MongoDbTest {
  private static final String ID = "123";
  private static final String NAME = "Some user";
  private static final String ADDITIONAL_INFO = "Some app Info";
  @Mock
  MongoDatabase db;
  private MongoDb mongoDb = new MongoDb();
  private UserAccount userAccount;
  @BeforeEach
  void init() {
    db = mock(MongoDatabase.class);
    Whitebox.setInternalState(mongoDb, "db", db);
    userAccount = new UserAccount(ID, NAME, ADDITIONAL_INFO);
  }
  @Test
  void connect() {
    assertDoesNotThrow(() -> mongoDb.connect());
  }
  @Test
  void readFromDb() {
    Document document = new Document(USER_ID, ID)
            .append(USER_NAME, NAME)
            .append(ADD_INFO, ADDITIONAL_INFO);
    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
    FindIterable<Document> findIterable = mock(FindIterable.class);
    when(mongoCollection.find(any(Document.class))).thenReturn(findIterable);
    when(findIterable.first()).thenReturn(document);
    assertEquals(mongoDb.readFromDb(ID),userAccount);
  }
  @Test
  void writeToDb() {
    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
    doNothing().when(mongoCollection).insertOne(any(Document.class));
    assertDoesNotThrow(()-> {mongoDb.writeToDb(userAccount);});
  }
  @Test
  void updateDb() {
    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
    assertDoesNotThrow(()-> {mongoDb.updateDb(userAccount);});
  }
  @Test
  void upsertDb() {
    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
    assertDoesNotThrow(()-> {mongoDb.upsertDb(userAccount);});
  }
 }
--- a/factory/src/main/java/com/iluwatar/factory/App.java
+++ b/factory/src/main/java/com/iluwatar/factory/App.java
@ -26,9 +26,9 @@ package com.iluwatar.factory;
 import lombok.extern.slf4j.Slf4j;
 /**
- * Factory is an object for creating other objects, it providing Providing a static method to 
+ * Factory is an object for creating other objects. It provides a static method to 
 * create and return objects of varying classes, in order to hide the implementation logic 
- * and makes client code focus on usage rather then objects initialization and management.
+ * and makes client code focus on usage rather than objects initialization and management.
 *
 * <p>In this example an alchemist manufactures coins. CoinFactory is the factory class and it
 * provides a static method to create different types of coins.
--- a/localization/es/README.md
+++ b/localization/es/README.md
@ -34,13 +34,13 @@ Todos los diseños deben ser lo más simples posible. Deberías comenzar con los
 Una vez que esté familiarizado con estos conceptos, puedes comenzar a profundizar con los
 [patrones de diseño disponibles](https://java-design-patterns.com/patterns/) por cualquiera de los siguientes enfoques
- - Buscar un patrón específico por su nombre. ¿No puedes encontrar uno? Informe un nuevo patrón [aquí](https://github.com/iluwatar/java-design-patterns/issues).
+ - Buscar un patrón específico por su nombre. ¿No puedes encontrar uno? Informa de un nuevo patrón [aquí](https://github.com/iluwatar/java-design-patterns/issues).
 - Usando etiquetas como `Performance`, `Gang of Four` ó `Data access`.
 - Usando categorías de patrones, `Creational`, `Behavioral` y otras.
-Esperamos que las soluciones orientadas a objetos presentadas en este sitio le resulten útiles en sus arquitecturas y se divierta aprendiéndolas tanto como nosotros desarrollándolas.
+Esperamos que las soluciones orientadas a objetos presentadas en este sitio te resulten útiles en sus arquitecturas y se divierta aprendiéndolas tanto como nosotros desarrollándolas.
-# Como contribuir
+# Cómo contribuir
 Si estás dispuesto a contribuir al proyecto encontrarás la información relevante en nuestra [wiki del desarrollador](https://github.com/iluwatar/java-design-patterns/wiki). Te ayudaremos y responderemos tus preguntas en la [sala de chat de Gitter](https://gitter.im/iluwatar/java-design-patterns).
--- a/monitor/README.md
+++ b/monitor/README.md
@ -0,0 +1,71 @@
 ---
 layout: pattern
 title: Monitor
 folder: monitor
 permalink: /patterns/monitor/
 categories: Concurrency
 language: en
 tags:
 - Performance
 ---
 ## Intent
 Monitor pattern is used to create thread-safe objects and prevent conflicts between threads in concurrent applications.
 ## Explanation
 In plain words
 > Monitor pattern is used to enforce single-threaded access to data. Only one thread at a time is allowed to execute code within the monitor object.
 Wikipedia says
 > In concurrent programming (also known as parallel programming), a monitor is a synchronization construct that allows threads to have both mutual exclusion and the ability to wait (block) for a certain condition to become false. Monitors also have a mechanism for signaling other threads that their condition has been met.
 **Programmatic Examples**
 Consider there is a bank that transfers money from an account to another account with transfer method . it is `synchronized` mean just one thread can access to this method because if many threads access to it and transfer money from an account to another account in same time balance changed !   
 ```
 class Bank {
     private int[] accounts;
     Logger logger;
     public Bank(int accountNum, int baseAmount, Logger logger) {
         this.logger = logger;
         accounts = new int[accountNum];
         Arrays.fill(accounts, baseAmount);
     }
     public synchronized void transfer(int accountA, int accountB, int amount) {
         if (accounts[accountA] >= amount) {
             accounts[accountB] += amount;
             accounts[accountA] -= amount;
             logger.info("Transferred from account :" + accountA + " to account :" + accountB + " , amount :" + amount + " . balance :" + getBalance());
         }
     }
 ```
 getBalance always return total amount and the total amount should be same after each transfers 
 ```
     private synchronized int getBalance() {
         int balance = 0;
         for (int account : accounts) {
             balance += account;
         }
         return balance;
     }
 }
 ```
 ## Class diagram
 ![alt text](./etc/monitor.urm.png "Monitor class diagram")
 ## Applicability
 Use the Monitor pattern when
 * we have a shared resource and there is critical section .
 * you want to create thread-safe objects .
 * you want to achieve mutual exclusion in high level programming language .
--- a/monitor/etc/monitor.urm.png
+++ b/monitor/etc/monitor.urm.png
--- a/monitor/etc/monitor.urm.puml
+++ b/monitor/etc/monitor.urm.puml
@ -0,0 +1,12 @@
@startuml
 Main - Bank : use
 class Main{
    + main(args : String[]) : void
 }
 class Bank{
    - accounts : int[]
    + Bank (accountNum : int , baseAccount : int)
    + transfer(accountA : int , accountB : int , amount : int) : void {synchronized}
    - getBalance() : void {synchronized}
 }
@enduml
--- a/monitor/pom.xml
+++ b/monitor/pom.xml
@ -0,0 +1,59 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
    The MIT License
    Copyright © 2014-2021 Ilkka Seppälä
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
 -->
 <project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <artifactId>java-design-patterns</artifactId>
        <groupId>com.iluwatar</groupId>
        <version>1.24.0-SNAPSHOT</version>
    </parent>
    <artifactId>monitor</artifactId>
    <dependencies>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <!-- Maven assembly plugin is invoked with default setting which we have
                in parent pom and specifying the class having main method -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-assembly-plugin</artifactId>
                <executions>
                    <execution>
                        <configuration>
                            <archive>
                                <manifest>
                                    <mainClass>com.iluwatar.abstractdocument.Main</mainClass>
                                </manifest>
                            </archive>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
 </project>
--- a/monitor/src/main/java/com/iluwatar/monitor/Bank.java
+++ b/monitor/src/main/java/com/iluwatar/monitor/Bank.java
@ -0,0 +1,37 @@
 package com.iluwatar.monitor;
 import java.util.Arrays;
 import java.util.logging.Logger;
 // Bank class implements the Monitor pattern
 public class Bank {
    private int[] accounts;
    Logger logger;
    public Bank(int accountNum, int baseAmount, Logger logger) {
        this.logger = logger;
        accounts = new int[accountNum];
        Arrays.fill(accounts, baseAmount);
    }
    public synchronized void transfer(int accountA, int accountB, int amount) {
        if (accounts[accountA] >= amount) {
            accounts[accountB] += amount;
            accounts[accountA] -= amount;
            logger.info("Transferred from account :" + accountA + " to account :" + accountB + " , amount :" + amount + " . balance :" + getBalance());
        }
    }
    public synchronized int getBalance() {
        int balance = 0;
        for (int account : accounts) {
            balance += account;
        }
        return balance;
    }
    public int[] getAccounts() {
        return accounts;
    }
 }
--- a/monitor/src/main/java/com/iluwatar/monitor/Main.java
+++ b/monitor/src/main/java/com/iluwatar/monitor/Main.java
@ -0,0 +1,60 @@
 /*
 * The MIT License
 * Copyright © 2014-2021 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.monitor;
 import java.util.*;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.logging.Logger;
 /**
 * <p>The Monitor pattern is used in concurrent algorithms to achieve mutual exclusion.</p>
 *
 * <p>Bank is a simple class that transfers money from an account to another account using
 * {@link Bank#transfer}. It can also return the balance of the bank account stored in the bank.</p>
 *
 * <p>Main class uses ThreadPool to run threads that do transactions on the bank accounts.</p>
 */
 public class Main {
    public static void main(String[] args) {
        Logger logger = Logger.getLogger("monitor");
        var bank = new Bank(4, 1000, logger);
        Runnable runnable = () -> {
            try {
                Thread.sleep((long) (Math.random() * 1000));
                Random random = new Random();
                for (int i = 0; i < 1000000; i++)
                    bank.transfer(random.nextInt(4), random.nextInt(4), (int) (Math.random() * 1000));
            } catch (InterruptedException e) {
                logger.info(e.getMessage());
            }
        };
        ExecutorService executorService = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 5; i++) {
            executorService.execute(runnable);
        }
    }
 }
--- a/monitor/src/main/test/java/com/iluwater/java/BankTest.java
+++ b/monitor/src/main/test/java/com/iluwater/java/BankTest.java
@ -0,0 +1,55 @@
 package com.iluwater.java;
 import com.iluwatar.monitor.Bank;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.*;
 import static org.junit.jupiter.api.Assumptions.*;
 import java.util.logging.Logger;
 public class BankTest {
    private static Bank bank;
    private static final int ACCOUNT_NUM = 4;
    private static final int BASE_AMOUNT = 1000;
    private static final Logger LOGGER = Logger.getLogger("monitor");
    @BeforeAll
    public static void Setup() {
        bank = new Bank(ACCOUNT_NUM, BASE_AMOUNT, LOGGER);
    }
    @Test
    public void GetAccountHaveNotBeNull() {
        assertNotNull(bank.getAccounts());
    }
    @Test
    public void LengthOfAccountsHaveToEqualsToAccountNumConstant() {
        assumeTrue(bank.getAccounts() != null);
        assertEquals(ACCOUNT_NUM, bank.getAccounts().length);
    }
    @Test
    public void TransferMethodHaveToTransferAmountFromAnAccountToOtherAccount() {
        bank.transfer(0, 1, 1000);
        int accounts[] = bank.getAccounts();
        assertEquals(0, accounts[0]);
        assertEquals(2000, 2000);
    }
    @Test
    public void BalanceHaveToBeOK() {
        assertEquals(4000, bank.getBalance());
    }
    @AfterAll
    public static void TearDown() {
        bank = null;
    }
 }
Author	SHA1	Message	Date
allcontributors[bot]	45eda74a7a	docs: update .all-contributorsrc [skip ci]	2021-10-16 17:10:43 +00:00
allcontributors[bot]	a643270c09	docs: update README.md [skip ci]	2021-10-16 17:10:42 +00:00
Ali Ghasemi	c2786e5dc4	add monitor design pattern (#1640 ) * add monitor design pattern . * add extra line and change compiler version to 11 in pom.xml. * encapsulate getBalance method . * update puml file . * export uml as png . * duplicate codes eliminated . * update tag * change the format of pom.xml * using logger to print * change AtomicRefrence to type inference var * explanations added ! * Update monitor/README.md Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> * Update monitor/README.md Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> * Update monitor/src/main/java/com/iluwatar/monitor/Main.java Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> * Update monitor/src/main/java/com/iluwatar/monitor/Main.java Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> * Update monitor/src/main/java/com/iluwatar/monitor/Main.java Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> * Update monitor/src/main/java/com/iluwatar/monitor/Main.java Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> * e.printStackTrace have changed to logger to prints standard output (STD OUT) . * add programmatic example . * Delete mvnw * mvnw.cmd deleted . * added mvnw from master * AddUnitTest * Add language to readme.md Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com> Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> Co-authored-by: Subhrodip Mohanta <subhromo@cisco.com> Co-authored-by: Subhrodip Mohanta <contact@subho.xyz>	2021-10-16 20:08:53 +03:00
allcontributors[bot]	a1f3c6fe20	docs: add JCarlosR as a contributor for translation (#1857 ) * docs: update README.md [skip ci] * docs: update .all-contributorsrc [skip ci] Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>	2021-10-15 20:27:23 +03:00
JCarlos	0ad44ced24	docs: Fix typos spanish readme and factory (#1834 ) * Fix typos for Spanish README * Fix typos in the factory example	2021-10-15 20:24:49 +03:00
allcontributors[bot]	4c5c0fd63e	docs: add sims-keshri as a contributor for code (#1853 ) * docs: update README.md [skip ci] * docs: update .all-contributorsrc [skip ci] Co-authored-by: Subhrodip Mohanta <hello@subho.xyz> Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>	2021-10-13 13:17:48 +05:30
Simran Keshri	5a644f1092	refactoring: Critical Sonar Issues (#1833 ) * Resolve Sonar Code Smell: Define a constant instead of duplicating this literal 'Space rocket <' 4 times. * Resolve Sonar Critical Code Smell: Define a constant instead of duplicating this literal 'Error connecting to MongoDB' 4 times. * Fix checkstyle violation. * Resolve Sonar Critical Code Smell: Define a constant instead of duplicating this literal 'LITERAL 0' 4 times. Co-authored-by: Subhrodip Mohanta <hello@subho.xyz>	2021-10-13 13:15:22 +05:30
Ilkka Seppälä	cab9048e06	docs: fixes for yaml frontmatter (#1851 ) Co-authored-by: Subhrodip Mohanta <hello@subho.xyz>	2021-10-13 12:59:55 +05:30