Intermittent failure was due to Thread.sleep in the code. While performing unit test cases there was race condition between two threads, so it was not guaranteed to work every time. Used an interface DelayProvider for simulating delay, and while unit testing fake delay provider is used that eradicates the use of Threads in unit test cases, which is not a good practice.

Fix redundant list alloc in LotteryNumbers

README.md

@@ -8,7 +8,6 @@
 [![License MIT](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/iluwatar/java-design-patterns/master/LICENSE.md)
 [![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)
 [![Quality Gate](https://sonarcloud.io/api/project_badges/measure?project=com.iluwatar%3Ajava-design-patterns&metric=alert_status)](https://sonarcloud.io/dashboard/index/com.iluwatar%3Ajava-design-patterns)
-[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1503/badge)](https://bestpractices.coreinfrastructure.org/projects/1503)
 
 # Introduction
 

abstract-document/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>abstract-document</artifactId>
     <dependencies>

abstract-factory/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>abstract-factory</artifactId>
   <dependencies>

acyclic-visitor/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	
 	<artifactId>acyclic-visitor</artifactId>

adapter/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>adapter</artifactId>
   <dependencies>

aggregator-microservices/aggregator-service/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/information-microservice/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/inventory-microservice/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <artifactId>aggregator-microservices</artifactId>

ambassador/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>ambassador</artifactId>

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

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>api-gateway-service</artifactId>

api-gateway/image-microservice/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
 
   <modelVersion>4.0.0</modelVersion>

api-gateway/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>api-gateway</artifactId>

api-gateway/price-microservice/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
 
   <modelVersion>4.0.0</modelVersion>

async-method-invocation/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>async-method-invocation</artifactId>
   <dependencies>

balking/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
 

balking/src/main/java/com/iluwatar/balking/DelayProvider.java

@@ -0,0 +1,10 @@
+package com.iluwatar.balking;
+
+import java.util.concurrent.TimeUnit;
+
+/**
+ * An interface to simulate delay while executing some work.
+ */
+public interface DelayProvider {
+  void executeAfterDelay(long interval, TimeUnit timeUnit, Runnable task);
+}

balking/src/main/java/com/iluwatar/balking/WashingMachine.java

@@ -25,17 +25,38 @@ package com.iluwatar.balking;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.concurrent.TimeUnit;
+
 /**
  * Washing machine class
  */
 public class WashingMachine {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(WashingMachine.class);
-
+  private final DelayProvider delayProvider;
   private WashingMachineState washingMachineState;
 
+  /**
+   * Creates a new instance of WashingMachine
+   */
   public WashingMachine() {
-    washingMachineState = WashingMachineState.ENABLED;
+    this((interval, timeUnit, task) -> {
+      try {
+        Thread.sleep(timeUnit.toMillis(interval));
+      } catch (InterruptedException ie) {
+        ie.printStackTrace();
+      }
+      task.run();
+    });
+  }
+
+  /**
+   * Creates a new instance of WashingMachine using provided delayProvider. This constructor is used only for
+   * unit testing purposes.
+   */
+  public WashingMachine(DelayProvider delayProvider) {
+    this.delayProvider = delayProvider;
+    this.washingMachineState = WashingMachineState.ENABLED;
   }
 
   public WashingMachineState getWashingMachineState() {
@@ -56,12 +77,8 @@ public class WashingMachine {
       washingMachineState = WashingMachineState.WASHING;
     }
     LOGGER.info("{}: Doing the washing", Thread.currentThread().getName());
-    try {
-      Thread.sleep(50);
-    } catch (InterruptedException ie) {
-      ie.printStackTrace();
-    }
-    endOfWashing();
+
+    this.delayProvider.executeAfterDelay(50, TimeUnit.MILLISECONDS, this::endOfWashing);
   }
 
   /**

balking/src/test/java/com/iluwatar/balking/WashingMachineTest.java

@@ -22,11 +22,8 @@
  */
 package com.iluwatar.balking;
 
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -36,32 +33,39 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
  */
 public class WashingMachineTest {
 
-  private volatile WashingMachineState machineStateGlobal;
+  private FakeDelayProvider fakeDelayProvider = new FakeDelayProvider();
 
-  @Disabled
   @Test
-  public void wash() throws Exception {
-    WashingMachine washingMachine = new WashingMachine();
-    ExecutorService executorService = Executors.newFixedThreadPool(2);
-    executorService.execute(washingMachine::wash);
-    executorService.execute(() -> {
-      washingMachine.wash();
-      machineStateGlobal = washingMachine.getWashingMachineState();
-    });
-    executorService.shutdown();
-    try {
-      executorService.awaitTermination(10, TimeUnit.SECONDS);
-    } catch (InterruptedException ie) {
-      ie.printStackTrace();
-    }
+  public void wash() {
+    WashingMachine washingMachine = new WashingMachine(fakeDelayProvider);
+
+    washingMachine.wash();
+    washingMachine.wash();
+
+    WashingMachineState machineStateGlobal = washingMachine.getWashingMachineState();
+
+    fakeDelayProvider.task.run();
+
+    // washing machine remains in washing state
     assertEquals(WashingMachineState.WASHING, machineStateGlobal);
+
+    // washing machine goes back to enabled state
+    assertEquals(WashingMachineState.ENABLED, washingMachine.getWashingMachineState());
   }
 
   @Test
-  public void endOfWashing() throws Exception {
+  public void endOfWashing() {
     WashingMachine washingMachine = new WashingMachine();
     washingMachine.wash();
     assertEquals(WashingMachineState.ENABLED, washingMachine.getWashingMachineState());
   }
 
+  private class FakeDelayProvider implements DelayProvider {
+    private Runnable task;
+
+    @Override
+    public void executeAfterDelay(long interval, TimeUnit timeUnit, Runnable task) {
+      this.task = task;
+    }
+  }
 }

bridge/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>bridge</artifactId>
   <dependencies>

builder/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>builder</artifactId>
   <dependencies>

business-delegate/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>business-delegate</artifactId>
 	<dependencies>

caching/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>caching</artifactId>
   <dependencies>

callback/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>callback</artifactId>
   <dependencies>

chain/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>chain</artifactId>
   <dependencies>

collection-pipeline/pom.xml

@@ -27,7 +27,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>collection-pipeline</artifactId>
   <dependencies>

command/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>command</artifactId>
   <dependencies>

composite/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>composite</artifactId>
   <dependencies>

converter/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <dependencies>

cqrs/pom.xml

@@ -21,7 +21,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>cqrs</artifactId>
 	<dependencies>

dao/pom.xml

@@ -30,7 +30,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>dao</artifactId>
 

data-bus/pom.xml

@@ -33,7 +33,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>data-bus</artifactId>
     <dependencies>

data-mapper/pom.xml

@@ -28,7 +28,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>data-mapper</artifactId>
 	<dependencies>

data-transfer-object/pom.xml

@@ -28,7 +28,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>data-transfer-object</artifactId>
     <dependencies>

decorator/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>decorator</artifactId>
   <dependencies>

delegation/pom.xml

@@ -30,7 +30,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

dependency-injection/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>dependency-injection</artifactId>
   <dependencies>

dirty-flag/pom.xml

@@ -29,11 +29,11 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <groupId>com.iluwatar</groupId>
   <artifactId>dirty-flag</artifactId>
-  <version>1.20.0</version>
+  <version>1.21.0-SNAPSHOT</version>
   <name>dirty-flag</name>
   <url>http://maven.apache.org</url>
   <properties>

double-checked-locking/pom.xml

@@ -27,7 +27,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>double-checked-locking</artifactId>
   <dependencies>

double-dispatch/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>double-dispatch</artifactId>
   <dependencies>

eip-aggregator/pom.xml

@@ -26,7 +26,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
 
     <dependencies>

eip-message-channel/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>eip-message-channel</artifactId>
 	<dependencies>

eip-publish-subscribe/pom.xml

@@ -28,7 +28,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>eip-publish-subscribe</artifactId>
 	<dependencies>

eip-splitter/pom.xml

@@ -26,7 +26,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
 
     <dependencies>

eip-wire-tap/pom.xml

@@ -26,7 +26,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
 
     <dependencies>

event-aggregator/pom.xml

@@ -28,7 +28,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>event-aggregator</artifactId>
 	<dependencies>

event-asynchronous/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>event-asynchronous</artifactId>
   <dependencies>

event-driven-architecture/pom.xml

@@ -31,7 +31,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
 
     <artifactId>event-driven-architecture</artifactId>

event-queue/pom.xml

@@ -30,7 +30,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>event-queue</artifactId>
   <dependencies>

event-sourcing/pom.xml

@@ -30,7 +30,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>event-sourcing</artifactId>
   <dependencies>

execute-around/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>execute-around</artifactId>
   <dependencies>

extension-objects/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
 

facade/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>facade</artifactId>
   <dependencies>

factory-kit/pom.xml

@@ -30,7 +30,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>factory-kit</artifactId>
     <dependencies>

factory-method/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>factory-method</artifactId>
   <dependencies>

feature-toggle/pom.xml

@@ -30,7 +30,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

fluentinterface/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

flux/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>flux</artifactId>
   <dependencies>

flyweight/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>flyweight</artifactId>
   <dependencies>

front-controller/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>front-controller</artifactId>
 	<dependencies>

guarded-suspension/pom.xml

@@ -30,7 +30,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <packaging>jar</packaging>
   <artifactId>guarded-suspension</artifactId>

half-sync-half-async/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>half-sync-half-async</artifactId>
   <dependencies>

hexagonal/pom.xml

@@ -30,7 +30,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>hexagonal</artifactId>
   <dependencies>

hexagonal/src/main/java/com/iluwatar/hexagonal/domain/LotteryNumbers.java

@@ -22,13 +22,12 @@
  */
 package com.iluwatar.hexagonal.domain;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashSet;
-import java.util.List;
 import java.util.PrimitiveIterator;
 import java.util.Random;
 import java.util.Set;
+import java.util.Iterator;
 
 /**
  *
@@ -85,11 +84,10 @@ public class LotteryNumbers {
    * @return numbers as comma separated string
    */
   public String getNumbersAsString() {
-    List<Integer> list = new ArrayList<>();
-    list.addAll(numbers);
     StringBuilder builder = new StringBuilder();
+    Iterator<Integer> iterator = numbers.iterator();
     for (int i = 0; i < NUM_NUMBERS; i++) {
-      builder.append(list.get(i));
+      builder.append(iterator.next());
       if (i < NUM_NUMBERS - 1) {
         builder.append(",");
       }

intercepting-filter/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>intercepting-filter</artifactId>
   <dependencies>

interpreter/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>interpreter</artifactId>
   <dependencies>

iterator/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>iterator</artifactId>
   <dependencies>

layers/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<groupId>com.iluwatar.layers</groupId>
 	<artifactId>layers</artifactId>

lazy-loading/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>lazy-loading</artifactId>
   <dependencies>

marker/pom.xml

@@ -24,7 +24,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
 

mediator/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>mediator</artifactId>
   <dependencies>

memento/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>memento</artifactId>
   <dependencies>

model-view-controller/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>model-view-controller</artifactId>
   <dependencies>

model-view-presenter/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>model-view-presenter</artifactId>
   <name>model-view-presenter</name>

module/pom.xml

@@ -28,7 +28,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>module</artifactId>
 	<dependencies>

monad/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>monad</artifactId>
     <dependencies>

monostate/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>monostate</artifactId>
   <dependencies>

multiton/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>multiton</artifactId>
   <dependencies>

mute-idiom/pom.xml

@@ -21,7 +21,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>mute-idiom</artifactId>
 	<dependencies>

mutex/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>mutex</artifactId>
   <dependencies>

naked-objects/dom/pom.xml

@@ -16,7 +16,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>naked-objects</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 
 	<artifactId>naked-objects-dom</artifactId>

naked-objects/fixture/pom.xml

@@ -16,7 +16,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>naked-objects</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 
 	<artifactId>naked-objects-fixture</artifactId>

naked-objects/integtests/pom.xml

@@ -16,7 +16,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>naked-objects</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 
 	<artifactId>naked-objects-integtests</artifactId>

naked-objects/pom.xml

@@ -15,7 +15,7 @@
 	<parent>
 		<artifactId>java-design-patterns</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 
 	<artifactId>naked-objects</artifactId>
@@ -350,17 +350,17 @@
 			<dependency>
 				<groupId>${project.groupId}</groupId>
 				<artifactId>naked-objects-dom</artifactId>
-				<version>1.20.0</version>
+				<version>1.21.0-SNAPSHOT</version>
 			</dependency>
 			<dependency>
 				<groupId>${project.groupId}</groupId>
 				<artifactId>naked-objects-fixture</artifactId>
-				<version>1.20.0</version>
+				<version>1.21.0-SNAPSHOT</version>
 			</dependency>
 			<dependency>
 				<groupId>${project.groupId}</groupId>
 				<artifactId>naked-objects-webapp</artifactId>
-				<version>1.20.0</version>
+				<version>1.21.0-SNAPSHOT</version>
 			</dependency>
 
 		</dependencies>

naked-objects/webapp/pom.xml

@@ -16,7 +16,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>naked-objects</artifactId>
-		<version>1.20.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 
 	<artifactId>naked-objects-webapp</artifactId>

null-object/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>null-object</artifactId>
   <dependencies>

object-mother/pom.xml

@@ -30,7 +30,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>object-mother</artifactId>
     <dependencies>

object-pool/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>object-pool</artifactId>
   <dependencies>

observer/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>observer</artifactId>
   <dependencies>

page-object/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>page-object</artifactId>
     <dependencies>

partial-response/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.20.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

poison-pill/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>poison-pill</artifactId>
   <dependencies>

pom.xml

@@ -21,7 +21,7 @@
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
     <packaging>pom</packaging>
     <inceptionYear>2014</inceptionYear>
     <properties>

private-class-data/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>private-class-data</artifactId>
   <dependencies>

producer-consumer/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>producer-consumer</artifactId>
   <dependencies>

promise/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>promise</artifactId>
   <dependencies>

property/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>property</artifactId>
   <dependencies>

prototype/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>prototype</artifactId>
   <dependencies>

proxy/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>proxy</artifactId>
   <dependencies>

queue-load-leveling/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.20.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>queue-load-leveling</artifactId>
   <dependencies>